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Superior collicular projection to intralaminar thalamus in rat
Brain Research, 378 (1986) 223-233 Elsevier
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Superior Collicular Projection to Intralaminar Thalamus in Rat DWAYNE S.G. YAMASAKI1, GEORGE M. KRAUTHAMER 1and ROBERT W. RHOADES 1'2 Department of Anatomy, University of Medicine and Dentistry of New Jersey, 1Rutgers Medical School and 2School of Osteopathic Medicine, Piscataway, NJ 08854 ( U. S. A.) (Accepted November 26th, 1985) Key words: superior colliculus - - rat - - intralaminar thalamus - - projection neuron - - patch - - double labeling - - autoradiography
The superior collicular (SC) cells which project to the intralaminar thalamus (IT; nuclei centralis lateralis, CL; paracentralis, PC; parafascicularis, Pf) in the rat were identified by means of retrograde transport of wheatgerm agglutinin conjugated horseradish peroxidase (WGA-HRP). SC-IT cells were located throughout the mediolateral and rostrocaudal exents of the tectum ipsilateral to the thalamic injection. In this SC, they had a primarily bilaminar distribution in the lower one-half of the stratum griseum intermediale (SGI) and upper portion of the stratum griseum profundum (SGP). In these laminae, SC-IT cells were arranged in clusters or patches similar to those which have been described for many inputs to the deep SC laminae. A small number of SC-IT cells were also observed in the deep laminae of the tectum contralateral to the thalamic injection. Double labelling experiments using True Blue (TB) and Diamidino Yellow (DY) demonstrated that < 1% of the contralaterally projecting SC-IT cells also innervated ipsilateral IT. Anterograde tracing with [3H]leucine demonstrated further that SC projected heavily to CL, PC and Pf. This projection also extended into the medial portion of the posterior thalamus (PO).
INTRODUCTION It is now well established that most of the inputs to the deep layers ( S G I , stratum album i n t e r m e d i u m S A I , SGP and stratum album p r o f u n d u m - - S A P ) of the m a m m a l i a n SC are a r r a y e d in a discontinuous or patch-like fashion (see H u e r t a and Harting 32 and I1ling and Graybie133 for recent reviews). This organization had led to the suggestion that the deep SC laminae may be organized as a series of processing modules in which subsets of tectal afferents converge upon specific subpopulations of SC neurons, and further, that the outputs of the deep layers may be coupled to these patches of afferent input 31. T h e r e is some evidence that SC p r o j e c t i o n neurons in the deep laminae have discontinuous distributions. Several years ago, Castiglioni et al. 9 n o t e d that tectospinal neurons in m o n k e y were clustered and W e b e r et al. 63 r e p o r t e d similar d a t a for the cat. M o r e recently, H u e r t a et al. 3a d e m o n s t r a t e d that the SC neurons projecting to the trigeminal brainstem complex
(probably to the trigeminal m o t o r nucleus, see Graham 19) in cat were also distributed discontinuously and further that they were located within or immediately adjacent to the patches of input to the SC from these same brainstem nuclei. It is not yet clear whether all of the efferent projections from the deep SC laminae arise from neurons a r r a y e d in a m o d u l a r fashion. F o r example, Henke124 m a d e no m e n t i o n of clustering of the SC cells which were labelled after injection of H R P into the paralemniscal zone of the lateral tegmental area in cat. E d w a r d s and H e n k e l is also observed (see their Fig. 8) that the tectal neurons projecting to the s u p r a o c u l o m o t o r central gray were distributed fairly continuously in the rostral portion of the colliculus. Most recently, M a y and Hall 43 have shown that the SC neurons which send axons into the p r e d o r s a l bundle of the grey squirrel were distributed quite evenly through the SGI. Interestingly, the nigrotectal p r o j e c t i o n in this species also has a continuous distribution in this lamina 43. This is quite different from o t h e r m a m m a l s in which the ni-
Correspondence: D.S.G. Yamasaki, Rutgers Medica! School, Department of Anatomy, University of Medicine and Dentistry of New Jersey, Piscataway, NJ 08854 (U. S.A.) .... 0006-8993/86/$03.50 © 1986 Elsevier Science Publishers B.V. (Biomedical Division)
224 grotectal pathway has a patchy termination in the SC (see Rhoades et al. 54, for data and a review). Even less is known regarding the distributions of deep layer SC cells whose axons ascend to innervate thalamic targets. Huerta and Harting 3° have reported (in abstract form) that the SC neurons labelled after injections into a number of diencephalic nuclei in cat are arranged in clumps or clusters. Comans and Snow 13, on the other hand, observed that SC-Pf neurons in the same species formed fairly continuous mediolaterally oriented bands in the intermediate and deep laminae. As a portion of a larger project concerned with connections between the SC and IT in rat, we have made relatively large W G A - H R P deposits into IT and observed tha labelled neurons in the ipsilateral SC had a distinctly patch-like organization. In addition, we have used anterograde tracing methods to delineate the terminal distribution of the SC projection to IT. A preliminary report describing a portion of these data has been presented 65.
viewed with dark-field optics. Reconstrucffons were accomplished with the aid of a drawing tube.
Double labelling experiments
MATERIALS AND METHODS
Because our retrograde tracing study demonstrated S C - I T cells both ipsilateral and contralateral to the injection site (see Results) we carried out additional double labelling experiments to determine whether individual SC cells projected to IT on both sides of the diencephalon. Six additional rats were prepared in the manner described above and the left IT was injected with 350-550 nl of TB 7. F o u r d a y s later the animal was reanesthetized and the right IT was injected with DY 36. These injections were made according to the method of Fish and Rhoades 16. After an additional 36 h, the animal was perfused with physiological saline followed by 4% phosphate-buffered paraformaldehyde. A block of tissue containing both the diencephalon and midbrain was cut at 50 ,urn on a freezing microtome, plated on unsubbed slides, coverslipped using mineral oil and examined with a Nikon Biophot microscope equipped with episcopic fluorescence optics.
Retrograde tracing with WGA-HRP
Anterograde tracing with FH]leucine
Sprague-Dawley rats (n = 17) were anesthetized with chloral hydrate (a 3.5% solution in normal saline; 1 ml/100 g) and placed in a stereotaxic headholder. The skull overlying IT was drilled away and a pipette (50 tzm tip) filled with W G A - H R P (Sigma, 4% in saline) was lowered into CL and Pf (anterior 3.6-3.8, lateral 1.3 and 4.5-5.0 mm ventral to the cortical surface; modified from Albe-Fessard et al.2). When the pipette was in position, W G A - H R P was ejected by electrophoresis using 3 ¢tA (DC) for 1 min. After survival times which ranged between 18 and 48 h, rats were perfused according to the method of Rosene and Mesulam 55. Brains were immediately removed, blocked and sectioned in the transverse plane at a thickness of 50 ktm. Tissue was processed according to the protocol of Mesulam 45 for the demonstration of H R P reaction product. Following the histochemical reaction, alternate sections from all brains were counterstained with thionin according to the method of Adams 1. While counterstaining was necessary to define the thalamic nuclei included in the injection site, SC laminae were most readily apparent when the tissue was simply
Six rats were anesthetized as described above and injected with 0.01 ktl of [3H]leucine (spec. act. 110 Ci/mM, final concentration 67/zCi//d) using pressure. After 5-7 days, they were perfused with physiological saline followed by 10% phosphate-buffered formalin. Following saturation with buffered sucrose, blocks containing the diencephalon and midbrain were sectioned at 50 y m and processed for autoradiography using the method of Cowan et al. 12. After exposure for 4 - 6 wks, autoradiograms were developed with D-19, fixed, counterstained with thionin, dehydrated, cleared and coverslipped. Sections were analyzed using both bright- and dark-field optics. RESULTS
WGA-HRP experiments The injections which provided the data reported here typically included CL, Pf and, in some cases, the lateral portion of the mediodorsal nucleus (MD). Since injections restricted to the lateral portion of MD label only a few neurons medially within SC 62, its inclusion in our W G A - H R P deposits is unlikely to
225
Fig. 1. A: low-power dark-field photomicrograph at SC which demonstrates the patch-like distribution of WGA-HRP labelled SC-IT neurons. Note the bilaminar arrangement of labelled cells within lower SGI and upper SGP. In each panel (A-D), medial is toward the right. SO, stratum opticum; refer to text for remaining abbreviations. B: dark-field photomicrograph of the WGA-HRP injection site. The deposit was located within the rostral portion of nucleus PF and included the caudal region of CL. FR, Habenulo-interpeduncular tract (retroflex bundle of Meynert); Hb, Habenula. C and D: higher power dark-field photomicrographs of labelled SC-IT neurons. The majority of cells are multipolar in shape, others are vertically oriented fusiform neurons. Note that the cell clusters tend to form radially registered bands between the two laminae.
have influenced the results we report here. The center of one injection is illustrated in Fig. lB. Our deposits labelled n u m e r o u s cells in the deep laminae of the ipsilateral SC and a few scattered neurons in these layers on the contralateral side. In the SC ipsilateral to the thalamic injection, labelled cells were located primarily in the lower one-half of the SGI and the upper portion of the SGP (Figs. 1A, C and 2). A smaller n u m b e r of labelled n e u r o n s were also visible in the SAI, lower SGP, and SAP. The average somal diameter for 100 n e u r o n s measured in the SGI was 11.0/~m (S.D. = 3.5), that for the same n u m b e r of cells measured in the SAI was 14.0/~m (S.D. = 4.2) and that for 100 labelled n e u r o n s measured in the SGP was 1 4 . 7 ~ m (S.D. -- 3.9). We also
measured 100 labelled n e u r o n s in the SAP and here the average somal diameter was 14.6/~m (S.D. = 3.9). The largest labelled n e u r o n s we observed had average somal diameters of 2 0 - 2 3 / z m and these were located in the SAI and SGP. The largest cell measured in the SGI had a somal diameter of 18/~m. Labelled n e u r o n s in all laminae tended to have either fusiform or, more often, multipolar morphology. As is evident from Figs. 1A, C and 2, the labelled cells in the lower SGI and upper SGP were arrayed in patches. F u r t h e r m o r e , the clusters in these two layers appeared to be in register radially (Fig. 1C). These patches of labelled n e u r o n s ranged b e t w e e n 80 and 220/~m in their mediolateral extent and the intervening gaps varied between 80 and 100/~m. In gener-
226
1051
0
15
SGS SO SGI SAI
130C
150
170 J'C?y~
2.0mm
~
75
~'-? 180 190
Fig. 2. Serial reconstruction of the SC shown in Fig. 1. Each dot represents one WGA-HRP labelled SC-IT neuron. The numbers represent distances in microns from the most rostral section shown at the upper left.
al, the patches of labelled cells tended to be broader in the lateral portion of the tectum (see, for example, section 95 in the reconstruction in Fig. 2). While the serial reconstruction in Fig. 2 gives the impression that the patches of labelled neurons were continuous over considerable distances along the rostrocaudal axis of the SC (note the lateral-most cluster in sections 55-95 and 130-150), the labelled cells did not form long longitudinally oriented bands similar to those that have been reported for several tectal afferent pathways 21,54. For purposes of comparison, we also labelled the superficial layer tectal cells which projected to another thalamic nucleus, the dorsal lateral geniculate, in two rats. In the region of the SC which corresponded topographically with the injection site (Fig. 3A, B),
the labelled cells formed a continuous band in the lower portion of the stratum griseum superficiale (SGS). This result is consistent with the findings that have been reported by others 4°,57 and it suggests strongly that the discontinuous distribution of S C - I T projection neurons was not an artifact of the procedures that we employed to label these cells.
Double labelling experiments The results of the double labelling experiments indicated that virtually all of the contralaterally projecting S C - I T cells did not have an additional axon branch which innervated ipsilateral IT. Both the TB and D Y injections (Fig. 4A) labelled numerous SC neurons, and as was the case in the W G A - H R P experiments, cells labelled with a given tracer were visi-
227
Fig. 3. A: low-power dark-field photomicrograph of SC neurons labelled from a W G A - H R P deposit placed within the dorsal lateral geniculate (shown in C). The majority of labelled cells are located in the ventral one-half of SGS, and are arranged in a continuous mediolateral band. B: higher power dark-field photomicrograph of the area delineated by the 3 lines in A.
228
Fig. 4. A: D Y (on the left) and TB (on the right) injection sites in IT of one rat. The dashed line denotes the borders of the section. B: a cluster of labelled cells in the lower SGI of the right SC. With the 355 n m filter, n u m e r o u s TB labelled n e u r o n s are readily visible. The arrows point to cells which were labelled with both TB and DY. B': the same field photographed with a 410 n m filter. T h e TB labelling is much dimmer, but D Y labelled nuclei fluoresce m u c h more brightly. The arrow point to the cells denoted in the same way in B. C: a higher power photomicrograph which further illustrates the labelling obtained with the fluorecent tracers. The thin solid arrows point to TB labelling and the open arrows denote DY. The cell on the upper right is double labelled. C': the same section taken with a 410 n m filter; only the D Y labelling is visible. The calibration for A is 1 ram, that for B and B' is 1 0 0 ~ m and that for C and C' is 50~tm.
229
1
Fig. 5. Bright- and dark-field photomicrographs from a rat which received two [JH]leucine deposits. A: the injection site included the lateral two-thirds and much of the anteroposterior extent of SC. B, C and D: dark-field photomicrographs of labelled SC-IT fibers at caudal Pf (A 3.0), rostral Pf (A 3.3) and CL (A 4.4) respectively, from the deposit shown in A. Note that labelled SC-IT fibers project to all of the IT nuclei, as well as to the adjacent PO. E, F and G: bright-field photomicrographs of adjacent sections to those shown in B, C and D, respectively.
230 ble in the rostromedial portion of the deep laminae contralateral to the injection site. While cells labelled with either TB or DY were numerous in this region (Fig. 4B, B'), double labelled S C - I T neurons (Fig. 4B, C) were extremely rare and accounted for < 1% of neurons which projected from a given SC to the contralateral IT.
Anterograde tracing experiments with [3H]leucine The autoradiographic experiments demonstrated that S C - I T fibers terminated throughout the rostrocaudal extent of IT. They showed (Fig. 5) that SC projected heavily to Pf, CL and the adjacent, medial portion of PO. Rostrally, weaker labelling was also observed in PC and the central medial nucleus (CM). As should be evident from Fig. 5B, C, the labelling in Pf was much denser and more extensive lateral to the fasciculus retroflexus (FR) than medial to that fiber bundle. This was the case regardless of the location of the SC injection site. S C - I T axons travelled to the diencephalon via two pathways, a dorsal route through the pretectum and a ventral route via the zona incerta (Fig. 5B). DISCUSSION The S C - I T pathway has been described in a number of species including the macaque 4'522'49'56, squirrel monkey 17, cat 3'8'13'18'19'41'47'56'58'62, opossum 6'42'52, tree shrew 23, rabbit 29 and rat ll'4s. In general, the organization of this projection is quite similar in these different animals. Tectofugal fibers course through the pretectal region to enter either nucleus centrum medianum, Pf or both, and continue into the more rostral intralaminar nuclei which include the central medial nucleus (CM), CL, and PC. While SC has been shown to project to MD in macaque 5'22, cat 19'47 and rabbit 29, our autoradiograms provided no evidence for such a proiection in rat. Chevalier and Deniau 11 also make no mention of SC terminals in MD. Our data also indicated a second, more ventral projection which ran into the zona incerta and then turned dorsally to enter IT. This has also been described in previous reports on the rat 11, cat 8 and rabbit 29. The cells of origin of the S C - I T pathway have been reported to be small 18'22, medium-sized 44 or me-
dium to large-sized multipolar cells 62 located in the intermediate and deep collicular layers. Two recent reports in cat have also noted the existence of S C - I T neurons in the SGS and SO 18'35. We noted that the S C - I T pathway has a weak, crossed component, and this has also been shown in the cat 3A3'18'35'47, monkey 22'49'56, rat 11'65 and rabbit 29. The results of our retrograde tracing experiments were consistent with the generalization that deep layer tectal efferent neurons which project to a given target may be arrayed in a discontinuous fashion. This result was obtained when either W G A - H R P , TB or DY was used as a tracer. Our finding thus agrees with those which have been provided for other SC outputs by Harting and his associates 3°-32'63. Our data show further that these patches of output ~neurons may 'cut across' laminae since the cluster of labelled cells which we observed were comprised primarly of neurons in the lower portion of the SGI and upper part of the SGP. The data we have provided do not, however, provide any evidence that the arrangement of these cells corresponds closely with that for any subset of tectal afferents. In fact, recordings from antidromically activated S C - I T neurons in this species 64 suggest the possibility that they may receive input from a number of sources. Many of these cells have somatosensory receptive fields which encompass much of the body surface, and complex response properties 53 which also suggest multiple afferent inputs. Electrophysiological results have indicated further that IT may not be the only target of at least some of the cells which we labelled. Yamasaki et al. 64 and Chevalier and Deniau 11 have both reported that some S C - I T neurons were also antidromically activated from the spi'nal cord and the latter authors also noted that a number of these neurons also sent axon collaterals to the contralateral SC. The intra-axonal injection experiments of Grantyn and Grantyn 2° also indicate that a given SC cell in cat may innervate a number of brainstem nuclei. Thus, while a large body of anatomical data are consistent with a modular organization of SC afferents and efferents, it is also clear that a given tectal cell may receive input from many different sources and send axon collaterals to multiple targets. The organization of the S C - I T pathway may have important implications for the relationship between SC and the basal ganglia in the organization of motor
231 output. The S C - I T p a t h w a y terminates in the same region of the thalamus which in turn projects to the striatum in the rat 25,34,46,50,59-61 and it m a y provide a link in a pathway by which modification of tectal output by the basal ganglia is signalled back to the striatum 39. T h e r e is now considerable evidence that the responses of SC neurons can be p r o f o u n d l y suppressed by stimulation of the substantia nigra, pars reticulata 1°'14 and that the activity of SC cells involved in eye m o v e m e n t s is negatively c o r r e l a t e d with that of nigral neurons 26-28. Of considerable importance in the present context is the fact that Chevalier et al. 1° have shown that tectospinal neurons are among those whose responses are suppressed by nigral stimulation. O u r own etectrophysiological and anatomical experiments 64,65 and the single unit recording studies of Chevalier and D e n i a u 11 have d e m o n s t r a t e d that at least some tectospinal neurons also project to IT, the S C - I T - s t r i a t u m p a t h w a y could thus provide a copy of descending tectofugal output to the striatum. While existing anatomical data clearly support the possibility of such a ' l o o p ' (at least at the level of the light microscope) it is not clear w h e t h e r the f e e d b a c k
REFERENCES 1 Adams, J.C., Stabilizing and rapid thionin staining of TMBbased HRP reaction product, Neurosci. Lett., 17 (1980) 7-9. 2 Albe-Fessard, D., Stutinsky, F. and Libouban, S., Atlas St~reotaxique du Diencdphalie du Rat Blanc, Centre National de la Recherche Scientifique, Paris, 1971. 3 Altman, J. and Carpenter, M.B., Fiber projections of the superior colliculus in the cat, J. Comp. Neurol., 116 (1961) 157-177. 4 Benevento, L.A. and Rezak, M., Further observations in the projections of the layers of the superior colliculus in the rhesus monkey with autoradiographic tracings methods, Soc. Neurosci. Abstr., 3 (1977) 553. 5 Benevento, L.A. and Fallon, J.H., The ascending projections of the superior colliculus in the rhesus monkey (Macaca mulatta), J. Comp. Neurol., 160 (1975) 339-362. 6 Benevento, L.A. and Ebner, F.F., Pretectal, tectal, retinal and cortical projections to thalamic nuclei of the opossum in stereotaxic coordinates, Brain Research, 18 (1970) 171-175. 7 Bentivoglio, M., Kuypers, H.G.J.M., Catsman-Berrevoets, C.E. and Dann, O., Fluorescent retrograde neuronal labeling in rat by means of substances binding specifically to adenine-thymine rich DNA, Neurosci. Lett., 12 (1979) 235-240. 8 Bucher, V.M. and Burgi, S.M., Some observations on the
would be positive or negative. A s n o t e d above, there is considerable evidence that substantia nigra, pars reticulata activation inhibits SC cells. A n u m b e r of studies have also d e m o n s t r a t e d that excitation in the striatum (or caudate nucleus) inhibits nigral neurons 51'66. S o m e w h a t less is k n o w n regarding the influence of IT upon striatal neurons. Kitai and his associates 37,38 have, however, d e m o n s t r a t e d that electrical stimulation of the medial thalamus in cat produces monosynaptic EPSPs in caudate neurons. Currently, there is no information regarding the effects of SC stimulation u p o n IT neurons. Thus, suggestions regarding the 'net effect' of this potential f e e d b a c k loop upon SC cells must await further electrophysiological experimentation. ACKNOWLEDGEMENTS S u p p o r t e d in part by E Y 04170, D E 06528, BNS 8500142 and the U M D N J F o u n d a t i o n ( R . W . R . ) . Thanks to Dr. G o r d o n M a c d o n a l d for assistance in obtaining the animals used in these e x p e r i m e n t s and to A n n M a r i e Szczepanik and D i a n e W o e r n e r for excellent technical assistance.
fiber connections of the di- and mesencephalon in the cat, J. Comp. Neurol., 93 (1950) 139-172. 9 Castiglioni, A.J., Gallway, M.C. and Coulter, J.D., Spinal projections from midbrain in monkey, J. Comp. Neurol., 178 (1978) 329-346. 10 Chevalier, G., Vacher, S., Deniau, J.M. and Desban, M., Disinhibition as a basic process in the expression of striatal functions. I. The striato-nigral influence on tecto-spinal/tecto-diencephalic neurons, Brain Research, 334 (1985) 215-226. 11 Chevalier, G. and Deniau, J.M., Spatio-temporal organization of a tecto-spinal/tecto-diencephalic neuronal system, Neuroscience, 12 (1984) 427-439. 12 Cowan, W.M., Gottlieb, D.I., Hendrickson, A.E., Price, J.L. and Woolsey, T.A., The autoradiographic demonstration of axonal connections in the central nervous system, Brain Research, 37 (1972) 21-51. 13 Cowmans, P.E. and Snow, P.J., Ascending projections to nucleus parafascicularis in the cat, Brain Research, 230 (1981) 337-341. 14 Deniau, J.M. and Chevalier, G., Disinhibition as a basic process in the expression of striatal functions. II. The striatonigral influence on thalamocortical cells of the ventromedial thalamic nucleus, Brain Research, 334 (1985) 227-233. 15 Edwards, S.B. and Henkel, C.K., Superior colliculus connections with the extraocular motor nuclei in the cat, J. Comp. Neurol., 179 (1978) 451-468. 16 Fish, S.E. and Rhoades, R.W., A method for making very
232 small, quantifiable micropipette injections of axonal tracer substances, J. Neurosci. Meth., 4 (1981) 291-297. 17 Frankfurter, A. and Harting, J.K., Diencephalic projections of the superior colliculus in the squirrel monkey, Soc. Neurosci. Abstr., 2 (1976) 1112. 18 Graham, J. and Berman, N., Origins of the pretectal and tectal projections to the central lateral nucleus in the cat, Neurosci. Lett., 26 (1981) 209-214. 19 Graham, J., An autoradiographic study of the efferent connections of the superior colliculus in the cat, J. Comp. Neurol., 173 (1977) 629-654. 20 Grantyn, A. and Grantyn, R., Axonal patterns and sites of termination of cat superior colliculus neurons projecting in the tecto-bulbo-spinal tract, Exp. Brain Res., 46 (1982) 243-256. 21 Graybiel, A.M., A satellite system of the superior colliculus: the parabigeminal nucleus and its projections to the superficial collicular layers, Brain Research, 145 (1978) 365-374. 22 Hatting, J.K., Huerta, M.F., Frankfurter, A.K., Strominger, N.L. and Royce, G.J., Ascending pathways from the monkey superior colliculus: an autoradiographic analysis, J. Comp. Neurol., 192 (1980) 853-882. 23 Harting, J.K., Hall, W.C., Diamond, L.T. and Martin, G.F., Anterograde degeneration study of the superior coUiculus in Tupaia glis: evidence for a subdivision between superficial and deep layers, J. Comp. Neurol., 148 (1973) 361-386. 24 Henkel, C.K., Afferent sources of a lateral midbrain tegmental zone associated with the pinnae in the cat as mapped by retrograde transport of horseradish peroxidase, J. Comp. Neurol., 203 (1981) 213-226. 25 Hiddema, F. and Droogleever Fortuyn, J., The projection of the intermediary nuclear system of the thalamus and of the parataenial and the paraventricular nucleus in the rat, Psychiatr. Neurol. Neurochir., 63 (1960) 8-6. 26 Hikosaka, O. and Wurtz, R.H., Modification of saccadic eye movements by GABA-related substances. I. Effect of muscimol and bicuculline in monkey superior colliculus, J. Neurophysiol., 53 (1985) 266-291. 27 Hikosaka, O. and Wurtz, R.H., Modification of saccadic eye movements by GABA-related substances. II. Effects of muscimol in monkey substantia nigra pars reticulata, J. Neurophysiol., 53 (1985) 292-308. 28 Hikosaka, O. and Wurtz, R.H., Visual and oculomotor functions of monkey substantia nigra pars reticulata. IV. Relation of substantia nigra to superior colliculus, J. Neurophysiol., 49 (1983) 1285-1301. 29 Holstege, G. and Collewijn, H., The efferent connections of the nucleus of the optic tract and the superior colliculus in the rabbit,, J. Comp. Neurol., 209 (1982) 139-175. 30 Huerta, M.F. and Harting, J.K., Cells of origin of tectofugal pathways, a horseradish peroxidase analysis, Soc. Neurosci. Abstr., 7 (1982) 462. 31 Huerta, M.F., Frankfurter, A.J. and Hatting, J.K., The trigeminocollicular projection in the cat: patch-like endings within the intermediate gray, Brain Research, 211 (1981) 1-13. 32 Huerta, M.F. and Harting, J.K., The mammalian superior colliculus: studies of its morphology and connections. In H. Vanegas (Ed.), Comparative Neurology of the Optic Tecturn, Plenum, New York, NY, 1984, pp. 687-773. 33 Illing, R.-B. and Graybiel, A.M., Convergence of afferents from frontal cortex and substantia nigra onto acetylcholin-
esterase-rich patches of the cat's superior collictl/us, N'euroscience, 14 (1985) 455-482. 34 Jones, E.G. and Leavitt, R.Y., Retrograde axonal transport and the demonstration of non-specific projections to the cerebral cortex and striatum from thalamic intralaminar nuclei in the rat, cat and monkey, J. Comp. Neurol., 154 (1974) 349-378. 35 Kaufman, E.F.S. and Rosenquist, A.C., Afferent connections of the thalamic intralaminar nuclei in the cat, Brain Research, 335 (1985) 281-296. 36 Keizer, K., Kuypers, H.G.J.M., Huisman, A.M. and Dann, O., Diamidino yellow dihydrochloride (DY-2HC1); a new fluorescent retrograde neuronal tracer, which migrates only very slowly out of the cell, Exp. Brain Res., 51 (1983) 179-191. 37 Kitai, S.T., Kocsis, J.D., Preston, R.J. and Sugimori, M., Monosynaptic inputs to caudate neurons identified by intracellular injection of horseradish peroxidase, Brain Research, 109 (1976) 601-606. 38 Kocsis, J.D., Sugimori, M. and Kitai, S.T., Convergence of excitatory synaptic inputs to caudate spiny neurons, Brain Research, 124 (1977) 403-413. 39 Krauthamer, G.M., Sensory functions of the neostriatum. In I. Divac and R. Oberg (Eds.), The Neostriatum, Pergamon, Oxford, 1979. 40 Mackay-Sim, A., Sefton, A.J. and Martin, P.R., Subcortical projections to lateral geniculate and thalamic reticular nuclei in the hooded rat, J. Comp. Neurol., 213 (1983) 24-35. 41 Marburg, O. and Warner, F.J., The pathways of the tectum (anterior colliculus) of the midbrain in cats, J. Nerv. Ment. Dis., 106 (1947) 415-446. 42 Martin, G.F., Efferent tectal pathways of the opossum (Didelphis virginiana), J. Comp. Neurol., 135 (1969) 209-224. 43 May, P.J. and Hall, W.C., Relationships between the nigrotectal pathway and the cells of origin of the predorsal bundle, J. Comp. Neurol., 226 (1984) 357-376. 44 McGuinness, C.M. and Krauthamer, G.M., The afferent projections to the centrum medianum of the cat as demonstrated by retrograde transport of horseradish peroxidase, Brain Research, 184 (1980) 255-269. 45 Mesulam, M.-M., Tetramethyl benzidine for horseradish peroxidase neurohistochemistry: a non-carcinogenic blue reaction-product with superior sensitivity for visualizing neuronal afferents and efferents, J. Histochem. Cytochem., 26 (1978) 106-117. 46 Nauta, H.J., Pritz, M.B. and Lasek, R.J., Afferents to the rat caudoputamen studied with horseradish peroxidase. An evaluation of a retrograde neuroanatomical research method, Brain Research, 67 (1974) 219-238. 47 Niimi, K., Miki, M. and Kawamura, S., Ascending projections of the superior colliculus in the cat, Okajimas Fol. Anat. Jap., 47 (1970) 269-287. 48 Papez, J.W. and Freeman, G.L., Superior colliculi and their fiber connections in the rat, J. Comp. Neurol., 51 (1930) 409-439. 49 Partlow, G.D., Colonnier, M. and Szabo, J., Thalamic projections of the superior colliculus in the rhesus monkey, Macaca mulatta. A light and electron microscopic study, J. Comp. Neurol., 171 (1977) 285-318. 50 Powell, T.P.S. and Cowan, W.M., The connexions of the midline and intra-laminar nuclei of the thalamus of the rat, J. Anat. (London), 88 (1954) 307-319. 51 Racagni, G., Bruno, F., Cattabeni, F., Maggi, A., DiGiu-
233
52
53
54
55
56
57
58
59
lio, A.M~; Parenti, M. and Groppetti, A., Functional interaction between rat substantia nigra and striatum: GABA and dopamine interrelation, Brain Research, 134 (1977) 353-358. Rafols, J.A. and Matzke, H.A., Efferent projections of the superior colliculus in the opossum, J. Comp. Neurol., 138 (1970) 147-160. Rhoades, R.W., Mooney, R.D. and Jacquin, M.F., Complex somatosensory receptive fields of cells in the deep laminae of the hamster's superior colliculus, J. Neurosci., 3 (1983) 1342-1354. Rhoades, R.W., Kuo, D.C., Polcer, J.D., Fish, S.E. and Voneida, T.J., Indirect visual cortical input to the deep layers of the hamster's superior colliculus via the basal ganglia, J. Comp. Neurol., 208 (1982) 239-254. Rosene, D.L. and Mesulam, M.-M., Fixation variables in horseradish peroxidase neurohistochemistry. I. The effects of fixation time and perfusion procedures upon enzyme activity, J. Histochem. Cytochem., 26 (1978) 28-39. Royce, G.J., Strominger, N.L. and Harting, J.K., Projections of the superior colliculus to the intralaminar thalamic nuclei in the cat and rhesus monkey, Soc. Neurosci. Abstr., 2 (1976) 1090. Sugita, S., Otani, K., Tokunaga, A. and Terasawa, K., Laminar origin of the tecto-thalamic projections in the albino rat, Neurosci. Lett., 43 (1983) 143-147. Tasiro, S., Experimental-anatomische Untersuching l~lber die efferenten Bahnen aus den vier Hiigeln der Katze, Z. Mikorsk.-Anat. Forsch., 47 (1940) 1-32. Van Der Kooy, D. and Carter, D.A., The organization of
the efferent projections and striatal afferents of the entopeduncular nucleus and adjacent areas in the rat, Brain Research, 211 (1981) 15-36. 60 Van Der Kooy, D., The organization of the thalamic, nigral and raphe cells projecting to the medial vs lateral caudateputamen in rat. A fluorescent retrograde double labeling study, Brain Research, 169 (1979) 381-387. 61 Veening, J.G., Cornelissen, F.M. and Lieven, P.A.J.M., The topical organization of the afferents to the caudatoputamen of the rat. A horseradish peroxidase study, Neuroscience, 5 (1980) 1253-1268. 62 Velayos, J.L. and Reinoso-Suarez, F., Topographic organization of the brainstem afferents to the mediodorsal thalamic nucleus, J. Comp. Neurol., 206 (1982) 17-27. 63 Weber, J.T., Martin, G.F., Behan, M., Huertz, M.F. and Harting, J.K., The precise origin of the tectospinal pathway in three common laboratory animals: a study using the horseradish peroxidase method, Neurosci. Lett., 11 (1979) 121-127. 64 Yamasaki, D.S., Krauthamer, G.M. and Rhoades, R.W., Response properties of tectal neurons which project to the parafascicular thalamic nucleus in the rat, Anat. Rec., 211 (1985) 219A. 65 Yamasaki, D.S. and Krauthamer, G.M., Fiber terminals of the superior collicular projection into the parafascicular complex in the rat, Soc. Neurosci. Abstr., 9 (1983) 1215. 66 Yoshida, M. and Precht, W., Monosynaptic inhibition of neurons of the substantia nigra by caudatonigral fibers, Brain Research, 32 (1971) 225-228.
223
BRE 11854
Superior Collicular Projection to Intralaminar Thalamus in Rat DWAYNE S.G. YAMASAKI1, GEORGE M. KRAUTHAMER 1and ROBERT W. RHOADES 1'2 Department of Anatomy, University of Medicine and Dentistry of New Jersey, 1Rutgers Medical School and 2School of Osteopathic Medicine, Piscataway, NJ 08854 ( U. S. A.) (Accepted November 26th, 1985) Key words: superior colliculus - - rat - - intralaminar thalamus - - projection neuron - - patch - - double labeling - - autoradiography
The superior collicular (SC) cells which project to the intralaminar thalamus (IT; nuclei centralis lateralis, CL; paracentralis, PC; parafascicularis, Pf) in the rat were identified by means of retrograde transport of wheatgerm agglutinin conjugated horseradish peroxidase (WGA-HRP). SC-IT cells were located throughout the mediolateral and rostrocaudal exents of the tectum ipsilateral to the thalamic injection. In this SC, they had a primarily bilaminar distribution in the lower one-half of the stratum griseum intermediale (SGI) and upper portion of the stratum griseum profundum (SGP). In these laminae, SC-IT cells were arranged in clusters or patches similar to those which have been described for many inputs to the deep SC laminae. A small number of SC-IT cells were also observed in the deep laminae of the tectum contralateral to the thalamic injection. Double labelling experiments using True Blue (TB) and Diamidino Yellow (DY) demonstrated that < 1% of the contralaterally projecting SC-IT cells also innervated ipsilateral IT. Anterograde tracing with [3H]leucine demonstrated further that SC projected heavily to CL, PC and Pf. This projection also extended into the medial portion of the posterior thalamus (PO).
INTRODUCTION It is now well established that most of the inputs to the deep layers ( S G I , stratum album i n t e r m e d i u m S A I , SGP and stratum album p r o f u n d u m - - S A P ) of the m a m m a l i a n SC are a r r a y e d in a discontinuous or patch-like fashion (see H u e r t a and Harting 32 and I1ling and Graybie133 for recent reviews). This organization had led to the suggestion that the deep SC laminae may be organized as a series of processing modules in which subsets of tectal afferents converge upon specific subpopulations of SC neurons, and further, that the outputs of the deep layers may be coupled to these patches of afferent input 31. T h e r e is some evidence that SC p r o j e c t i o n neurons in the deep laminae have discontinuous distributions. Several years ago, Castiglioni et al. 9 n o t e d that tectospinal neurons in m o n k e y were clustered and W e b e r et al. 63 r e p o r t e d similar d a t a for the cat. M o r e recently, H u e r t a et al. 3a d e m o n s t r a t e d that the SC neurons projecting to the trigeminal brainstem complex
(probably to the trigeminal m o t o r nucleus, see Graham 19) in cat were also distributed discontinuously and further that they were located within or immediately adjacent to the patches of input to the SC from these same brainstem nuclei. It is not yet clear whether all of the efferent projections from the deep SC laminae arise from neurons a r r a y e d in a m o d u l a r fashion. F o r example, Henke124 m a d e no m e n t i o n of clustering of the SC cells which were labelled after injection of H R P into the paralemniscal zone of the lateral tegmental area in cat. E d w a r d s and H e n k e l is also observed (see their Fig. 8) that the tectal neurons projecting to the s u p r a o c u l o m o t o r central gray were distributed fairly continuously in the rostral portion of the colliculus. Most recently, M a y and Hall 43 have shown that the SC neurons which send axons into the p r e d o r s a l bundle of the grey squirrel were distributed quite evenly through the SGI. Interestingly, the nigrotectal p r o j e c t i o n in this species also has a continuous distribution in this lamina 43. This is quite different from o t h e r m a m m a l s in which the ni-
Correspondence: D.S.G. Yamasaki, Rutgers Medica! School, Department of Anatomy, University of Medicine and Dentistry of New Jersey, Piscataway, NJ 08854 (U. S.A.) .... 0006-8993/86/$03.50 © 1986 Elsevier Science Publishers B.V. (Biomedical Division)
224 grotectal pathway has a patchy termination in the SC (see Rhoades et al. 54, for data and a review). Even less is known regarding the distributions of deep layer SC cells whose axons ascend to innervate thalamic targets. Huerta and Harting 3° have reported (in abstract form) that the SC neurons labelled after injections into a number of diencephalic nuclei in cat are arranged in clumps or clusters. Comans and Snow 13, on the other hand, observed that SC-Pf neurons in the same species formed fairly continuous mediolaterally oriented bands in the intermediate and deep laminae. As a portion of a larger project concerned with connections between the SC and IT in rat, we have made relatively large W G A - H R P deposits into IT and observed tha labelled neurons in the ipsilateral SC had a distinctly patch-like organization. In addition, we have used anterograde tracing methods to delineate the terminal distribution of the SC projection to IT. A preliminary report describing a portion of these data has been presented 65.
viewed with dark-field optics. Reconstrucffons were accomplished with the aid of a drawing tube.
Double labelling experiments
MATERIALS AND METHODS
Because our retrograde tracing study demonstrated S C - I T cells both ipsilateral and contralateral to the injection site (see Results) we carried out additional double labelling experiments to determine whether individual SC cells projected to IT on both sides of the diencephalon. Six additional rats were prepared in the manner described above and the left IT was injected with 350-550 nl of TB 7. F o u r d a y s later the animal was reanesthetized and the right IT was injected with DY 36. These injections were made according to the method of Fish and Rhoades 16. After an additional 36 h, the animal was perfused with physiological saline followed by 4% phosphate-buffered paraformaldehyde. A block of tissue containing both the diencephalon and midbrain was cut at 50 ,urn on a freezing microtome, plated on unsubbed slides, coverslipped using mineral oil and examined with a Nikon Biophot microscope equipped with episcopic fluorescence optics.
Retrograde tracing with WGA-HRP
Anterograde tracing with FH]leucine
Sprague-Dawley rats (n = 17) were anesthetized with chloral hydrate (a 3.5% solution in normal saline; 1 ml/100 g) and placed in a stereotaxic headholder. The skull overlying IT was drilled away and a pipette (50 tzm tip) filled with W G A - H R P (Sigma, 4% in saline) was lowered into CL and Pf (anterior 3.6-3.8, lateral 1.3 and 4.5-5.0 mm ventral to the cortical surface; modified from Albe-Fessard et al.2). When the pipette was in position, W G A - H R P was ejected by electrophoresis using 3 ¢tA (DC) for 1 min. After survival times which ranged between 18 and 48 h, rats were perfused according to the method of Rosene and Mesulam 55. Brains were immediately removed, blocked and sectioned in the transverse plane at a thickness of 50 ktm. Tissue was processed according to the protocol of Mesulam 45 for the demonstration of H R P reaction product. Following the histochemical reaction, alternate sections from all brains were counterstained with thionin according to the method of Adams 1. While counterstaining was necessary to define the thalamic nuclei included in the injection site, SC laminae were most readily apparent when the tissue was simply
Six rats were anesthetized as described above and injected with 0.01 ktl of [3H]leucine (spec. act. 110 Ci/mM, final concentration 67/zCi//d) using pressure. After 5-7 days, they were perfused with physiological saline followed by 10% phosphate-buffered formalin. Following saturation with buffered sucrose, blocks containing the diencephalon and midbrain were sectioned at 50 y m and processed for autoradiography using the method of Cowan et al. 12. After exposure for 4 - 6 wks, autoradiograms were developed with D-19, fixed, counterstained with thionin, dehydrated, cleared and coverslipped. Sections were analyzed using both bright- and dark-field optics. RESULTS
WGA-HRP experiments The injections which provided the data reported here typically included CL, Pf and, in some cases, the lateral portion of the mediodorsal nucleus (MD). Since injections restricted to the lateral portion of MD label only a few neurons medially within SC 62, its inclusion in our W G A - H R P deposits is unlikely to
225
Fig. 1. A: low-power dark-field photomicrograph at SC which demonstrates the patch-like distribution of WGA-HRP labelled SC-IT neurons. Note the bilaminar arrangement of labelled cells within lower SGI and upper SGP. In each panel (A-D), medial is toward the right. SO, stratum opticum; refer to text for remaining abbreviations. B: dark-field photomicrograph of the WGA-HRP injection site. The deposit was located within the rostral portion of nucleus PF and included the caudal region of CL. FR, Habenulo-interpeduncular tract (retroflex bundle of Meynert); Hb, Habenula. C and D: higher power dark-field photomicrographs of labelled SC-IT neurons. The majority of cells are multipolar in shape, others are vertically oriented fusiform neurons. Note that the cell clusters tend to form radially registered bands between the two laminae.
have influenced the results we report here. The center of one injection is illustrated in Fig. lB. Our deposits labelled n u m e r o u s cells in the deep laminae of the ipsilateral SC and a few scattered neurons in these layers on the contralateral side. In the SC ipsilateral to the thalamic injection, labelled cells were located primarily in the lower one-half of the SGI and the upper portion of the SGP (Figs. 1A, C and 2). A smaller n u m b e r of labelled n e u r o n s were also visible in the SAI, lower SGP, and SAP. The average somal diameter for 100 n e u r o n s measured in the SGI was 11.0/~m (S.D. = 3.5), that for the same n u m b e r of cells measured in the SAI was 14.0/~m (S.D. = 4.2) and that for 100 labelled n e u r o n s measured in the SGP was 1 4 . 7 ~ m (S.D. -- 3.9). We also
measured 100 labelled n e u r o n s in the SAP and here the average somal diameter was 14.6/~m (S.D. = 3.9). The largest labelled n e u r o n s we observed had average somal diameters of 2 0 - 2 3 / z m and these were located in the SAI and SGP. The largest cell measured in the SGI had a somal diameter of 18/~m. Labelled n e u r o n s in all laminae tended to have either fusiform or, more often, multipolar morphology. As is evident from Figs. 1A, C and 2, the labelled cells in the lower SGI and upper SGP were arrayed in patches. F u r t h e r m o r e , the clusters in these two layers appeared to be in register radially (Fig. 1C). These patches of labelled n e u r o n s ranged b e t w e e n 80 and 220/~m in their mediolateral extent and the intervening gaps varied between 80 and 100/~m. In gener-
226
1051
0
15
SGS SO SGI SAI
130C
150
170 J'C?y~
2.0mm
~
75
~'-? 180 190
Fig. 2. Serial reconstruction of the SC shown in Fig. 1. Each dot represents one WGA-HRP labelled SC-IT neuron. The numbers represent distances in microns from the most rostral section shown at the upper left.
al, the patches of labelled cells tended to be broader in the lateral portion of the tectum (see, for example, section 95 in the reconstruction in Fig. 2). While the serial reconstruction in Fig. 2 gives the impression that the patches of labelled neurons were continuous over considerable distances along the rostrocaudal axis of the SC (note the lateral-most cluster in sections 55-95 and 130-150), the labelled cells did not form long longitudinally oriented bands similar to those that have been reported for several tectal afferent pathways 21,54. For purposes of comparison, we also labelled the superficial layer tectal cells which projected to another thalamic nucleus, the dorsal lateral geniculate, in two rats. In the region of the SC which corresponded topographically with the injection site (Fig. 3A, B),
the labelled cells formed a continuous band in the lower portion of the stratum griseum superficiale (SGS). This result is consistent with the findings that have been reported by others 4°,57 and it suggests strongly that the discontinuous distribution of S C - I T projection neurons was not an artifact of the procedures that we employed to label these cells.
Double labelling experiments The results of the double labelling experiments indicated that virtually all of the contralaterally projecting S C - I T cells did not have an additional axon branch which innervated ipsilateral IT. Both the TB and D Y injections (Fig. 4A) labelled numerous SC neurons, and as was the case in the W G A - H R P experiments, cells labelled with a given tracer were visi-
227
Fig. 3. A: low-power dark-field photomicrograph of SC neurons labelled from a W G A - H R P deposit placed within the dorsal lateral geniculate (shown in C). The majority of labelled cells are located in the ventral one-half of SGS, and are arranged in a continuous mediolateral band. B: higher power dark-field photomicrograph of the area delineated by the 3 lines in A.
228
Fig. 4. A: D Y (on the left) and TB (on the right) injection sites in IT of one rat. The dashed line denotes the borders of the section. B: a cluster of labelled cells in the lower SGI of the right SC. With the 355 n m filter, n u m e r o u s TB labelled n e u r o n s are readily visible. The arrows point to cells which were labelled with both TB and DY. B': the same field photographed with a 410 n m filter. T h e TB labelling is much dimmer, but D Y labelled nuclei fluoresce m u c h more brightly. The arrow point to the cells denoted in the same way in B. C: a higher power photomicrograph which further illustrates the labelling obtained with the fluorecent tracers. The thin solid arrows point to TB labelling and the open arrows denote DY. The cell on the upper right is double labelled. C': the same section taken with a 410 n m filter; only the D Y labelling is visible. The calibration for A is 1 ram, that for B and B' is 1 0 0 ~ m and that for C and C' is 50~tm.
229
1
Fig. 5. Bright- and dark-field photomicrographs from a rat which received two [JH]leucine deposits. A: the injection site included the lateral two-thirds and much of the anteroposterior extent of SC. B, C and D: dark-field photomicrographs of labelled SC-IT fibers at caudal Pf (A 3.0), rostral Pf (A 3.3) and CL (A 4.4) respectively, from the deposit shown in A. Note that labelled SC-IT fibers project to all of the IT nuclei, as well as to the adjacent PO. E, F and G: bright-field photomicrographs of adjacent sections to those shown in B, C and D, respectively.
230 ble in the rostromedial portion of the deep laminae contralateral to the injection site. While cells labelled with either TB or DY were numerous in this region (Fig. 4B, B'), double labelled S C - I T neurons (Fig. 4B, C) were extremely rare and accounted for < 1% of neurons which projected from a given SC to the contralateral IT.
Anterograde tracing experiments with [3H]leucine The autoradiographic experiments demonstrated that S C - I T fibers terminated throughout the rostrocaudal extent of IT. They showed (Fig. 5) that SC projected heavily to Pf, CL and the adjacent, medial portion of PO. Rostrally, weaker labelling was also observed in PC and the central medial nucleus (CM). As should be evident from Fig. 5B, C, the labelling in Pf was much denser and more extensive lateral to the fasciculus retroflexus (FR) than medial to that fiber bundle. This was the case regardless of the location of the SC injection site. S C - I T axons travelled to the diencephalon via two pathways, a dorsal route through the pretectum and a ventral route via the zona incerta (Fig. 5B). DISCUSSION The S C - I T pathway has been described in a number of species including the macaque 4'522'49'56, squirrel monkey 17, cat 3'8'13'18'19'41'47'56'58'62, opossum 6'42'52, tree shrew 23, rabbit 29 and rat ll'4s. In general, the organization of this projection is quite similar in these different animals. Tectofugal fibers course through the pretectal region to enter either nucleus centrum medianum, Pf or both, and continue into the more rostral intralaminar nuclei which include the central medial nucleus (CM), CL, and PC. While SC has been shown to project to MD in macaque 5'22, cat 19'47 and rabbit 29, our autoradiograms provided no evidence for such a proiection in rat. Chevalier and Deniau 11 also make no mention of SC terminals in MD. Our data also indicated a second, more ventral projection which ran into the zona incerta and then turned dorsally to enter IT. This has also been described in previous reports on the rat 11, cat 8 and rabbit 29. The cells of origin of the S C - I T pathway have been reported to be small 18'22, medium-sized 44 or me-
dium to large-sized multipolar cells 62 located in the intermediate and deep collicular layers. Two recent reports in cat have also noted the existence of S C - I T neurons in the SGS and SO 18'35. We noted that the S C - I T pathway has a weak, crossed component, and this has also been shown in the cat 3A3'18'35'47, monkey 22'49'56, rat 11'65 and rabbit 29. The results of our retrograde tracing experiments were consistent with the generalization that deep layer tectal efferent neurons which project to a given target may be arrayed in a discontinuous fashion. This result was obtained when either W G A - H R P , TB or DY was used as a tracer. Our finding thus agrees with those which have been provided for other SC outputs by Harting and his associates 3°-32'63. Our data show further that these patches of output ~neurons may 'cut across' laminae since the cluster of labelled cells which we observed were comprised primarly of neurons in the lower portion of the SGI and upper part of the SGP. The data we have provided do not, however, provide any evidence that the arrangement of these cells corresponds closely with that for any subset of tectal afferents. In fact, recordings from antidromically activated S C - I T neurons in this species 64 suggest the possibility that they may receive input from a number of sources. Many of these cells have somatosensory receptive fields which encompass much of the body surface, and complex response properties 53 which also suggest multiple afferent inputs. Electrophysiological results have indicated further that IT may not be the only target of at least some of the cells which we labelled. Yamasaki et al. 64 and Chevalier and Deniau 11 have both reported that some S C - I T neurons were also antidromically activated from the spi'nal cord and the latter authors also noted that a number of these neurons also sent axon collaterals to the contralateral SC. The intra-axonal injection experiments of Grantyn and Grantyn 2° also indicate that a given SC cell in cat may innervate a number of brainstem nuclei. Thus, while a large body of anatomical data are consistent with a modular organization of SC afferents and efferents, it is also clear that a given tectal cell may receive input from many different sources and send axon collaterals to multiple targets. The organization of the S C - I T pathway may have important implications for the relationship between SC and the basal ganglia in the organization of motor
231 output. The S C - I T p a t h w a y terminates in the same region of the thalamus which in turn projects to the striatum in the rat 25,34,46,50,59-61 and it m a y provide a link in a pathway by which modification of tectal output by the basal ganglia is signalled back to the striatum 39. T h e r e is now considerable evidence that the responses of SC neurons can be p r o f o u n d l y suppressed by stimulation of the substantia nigra, pars reticulata 1°'14 and that the activity of SC cells involved in eye m o v e m e n t s is negatively c o r r e l a t e d with that of nigral neurons 26-28. Of considerable importance in the present context is the fact that Chevalier et al. 1° have shown that tectospinal neurons are among those whose responses are suppressed by nigral stimulation. O u r own etectrophysiological and anatomical experiments 64,65 and the single unit recording studies of Chevalier and D e n i a u 11 have d e m o n s t r a t e d that at least some tectospinal neurons also project to IT, the S C - I T - s t r i a t u m p a t h w a y could thus provide a copy of descending tectofugal output to the striatum. While existing anatomical data clearly support the possibility of such a ' l o o p ' (at least at the level of the light microscope) it is not clear w h e t h e r the f e e d b a c k
REFERENCES 1 Adams, J.C., Stabilizing and rapid thionin staining of TMBbased HRP reaction product, Neurosci. Lett., 17 (1980) 7-9. 2 Albe-Fessard, D., Stutinsky, F. and Libouban, S., Atlas St~reotaxique du Diencdphalie du Rat Blanc, Centre National de la Recherche Scientifique, Paris, 1971. 3 Altman, J. and Carpenter, M.B., Fiber projections of the superior colliculus in the cat, J. Comp. Neurol., 116 (1961) 157-177. 4 Benevento, L.A. and Rezak, M., Further observations in the projections of the layers of the superior colliculus in the rhesus monkey with autoradiographic tracings methods, Soc. Neurosci. Abstr., 3 (1977) 553. 5 Benevento, L.A. and Fallon, J.H., The ascending projections of the superior colliculus in the rhesus monkey (Macaca mulatta), J. Comp. Neurol., 160 (1975) 339-362. 6 Benevento, L.A. and Ebner, F.F., Pretectal, tectal, retinal and cortical projections to thalamic nuclei of the opossum in stereotaxic coordinates, Brain Research, 18 (1970) 171-175. 7 Bentivoglio, M., Kuypers, H.G.J.M., Catsman-Berrevoets, C.E. and Dann, O., Fluorescent retrograde neuronal labeling in rat by means of substances binding specifically to adenine-thymine rich DNA, Neurosci. Lett., 12 (1979) 235-240. 8 Bucher, V.M. and Burgi, S.M., Some observations on the
would be positive or negative. A s n o t e d above, there is considerable evidence that substantia nigra, pars reticulata activation inhibits SC cells. A n u m b e r of studies have also d e m o n s t r a t e d that excitation in the striatum (or caudate nucleus) inhibits nigral neurons 51'66. S o m e w h a t less is k n o w n regarding the influence of IT upon striatal neurons. Kitai and his associates 37,38 have, however, d e m o n s t r a t e d that electrical stimulation of the medial thalamus in cat produces monosynaptic EPSPs in caudate neurons. Currently, there is no information regarding the effects of SC stimulation u p o n IT neurons. Thus, suggestions regarding the 'net effect' of this potential f e e d b a c k loop upon SC cells must await further electrophysiological experimentation. ACKNOWLEDGEMENTS S u p p o r t e d in part by E Y 04170, D E 06528, BNS 8500142 and the U M D N J F o u n d a t i o n ( R . W . R . ) . Thanks to Dr. G o r d o n M a c d o n a l d for assistance in obtaining the animals used in these e x p e r i m e n t s and to A n n M a r i e Szczepanik and D i a n e W o e r n e r for excellent technical assistance.
fiber connections of the di- and mesencephalon in the cat, J. Comp. Neurol., 93 (1950) 139-172. 9 Castiglioni, A.J., Gallway, M.C. and Coulter, J.D., Spinal projections from midbrain in monkey, J. Comp. Neurol., 178 (1978) 329-346. 10 Chevalier, G., Vacher, S., Deniau, J.M. and Desban, M., Disinhibition as a basic process in the expression of striatal functions. I. The striato-nigral influence on tecto-spinal/tecto-diencephalic neurons, Brain Research, 334 (1985) 215-226. 11 Chevalier, G. and Deniau, J.M., Spatio-temporal organization of a tecto-spinal/tecto-diencephalic neuronal system, Neuroscience, 12 (1984) 427-439. 12 Cowan, W.M., Gottlieb, D.I., Hendrickson, A.E., Price, J.L. and Woolsey, T.A., The autoradiographic demonstration of axonal connections in the central nervous system, Brain Research, 37 (1972) 21-51. 13 Cowmans, P.E. and Snow, P.J., Ascending projections to nucleus parafascicularis in the cat, Brain Research, 230 (1981) 337-341. 14 Deniau, J.M. and Chevalier, G., Disinhibition as a basic process in the expression of striatal functions. II. The striatonigral influence on thalamocortical cells of the ventromedial thalamic nucleus, Brain Research, 334 (1985) 227-233. 15 Edwards, S.B. and Henkel, C.K., Superior colliculus connections with the extraocular motor nuclei in the cat, J. Comp. Neurol., 179 (1978) 451-468. 16 Fish, S.E. and Rhoades, R.W., A method for making very
232 small, quantifiable micropipette injections of axonal tracer substances, J. Neurosci. Meth., 4 (1981) 291-297. 17 Frankfurter, A. and Harting, J.K., Diencephalic projections of the superior colliculus in the squirrel monkey, Soc. Neurosci. Abstr., 2 (1976) 1112. 18 Graham, J. and Berman, N., Origins of the pretectal and tectal projections to the central lateral nucleus in the cat, Neurosci. Lett., 26 (1981) 209-214. 19 Graham, J., An autoradiographic study of the efferent connections of the superior colliculus in the cat, J. Comp. Neurol., 173 (1977) 629-654. 20 Grantyn, A. and Grantyn, R., Axonal patterns and sites of termination of cat superior colliculus neurons projecting in the tecto-bulbo-spinal tract, Exp. Brain Res., 46 (1982) 243-256. 21 Graybiel, A.M., A satellite system of the superior colliculus: the parabigeminal nucleus and its projections to the superficial collicular layers, Brain Research, 145 (1978) 365-374. 22 Hatting, J.K., Huerta, M.F., Frankfurter, A.K., Strominger, N.L. and Royce, G.J., Ascending pathways from the monkey superior colliculus: an autoradiographic analysis, J. Comp. Neurol., 192 (1980) 853-882. 23 Harting, J.K., Hall, W.C., Diamond, L.T. and Martin, G.F., Anterograde degeneration study of the superior coUiculus in Tupaia glis: evidence for a subdivision between superficial and deep layers, J. Comp. Neurol., 148 (1973) 361-386. 24 Henkel, C.K., Afferent sources of a lateral midbrain tegmental zone associated with the pinnae in the cat as mapped by retrograde transport of horseradish peroxidase, J. Comp. Neurol., 203 (1981) 213-226. 25 Hiddema, F. and Droogleever Fortuyn, J., The projection of the intermediary nuclear system of the thalamus and of the parataenial and the paraventricular nucleus in the rat, Psychiatr. Neurol. Neurochir., 63 (1960) 8-6. 26 Hikosaka, O. and Wurtz, R.H., Modification of saccadic eye movements by GABA-related substances. I. Effect of muscimol and bicuculline in monkey superior colliculus, J. Neurophysiol., 53 (1985) 266-291. 27 Hikosaka, O. and Wurtz, R.H., Modification of saccadic eye movements by GABA-related substances. II. Effects of muscimol in monkey substantia nigra pars reticulata, J. Neurophysiol., 53 (1985) 292-308. 28 Hikosaka, O. and Wurtz, R.H., Visual and oculomotor functions of monkey substantia nigra pars reticulata. IV. Relation of substantia nigra to superior colliculus, J. Neurophysiol., 49 (1983) 1285-1301. 29 Holstege, G. and Collewijn, H., The efferent connections of the nucleus of the optic tract and the superior colliculus in the rabbit,, J. Comp. Neurol., 209 (1982) 139-175. 30 Huerta, M.F. and Harting, J.K., Cells of origin of tectofugal pathways, a horseradish peroxidase analysis, Soc. Neurosci. Abstr., 7 (1982) 462. 31 Huerta, M.F., Frankfurter, A.J. and Hatting, J.K., The trigeminocollicular projection in the cat: patch-like endings within the intermediate gray, Brain Research, 211 (1981) 1-13. 32 Huerta, M.F. and Harting, J.K., The mammalian superior colliculus: studies of its morphology and connections. In H. Vanegas (Ed.), Comparative Neurology of the Optic Tecturn, Plenum, New York, NY, 1984, pp. 687-773. 33 Illing, R.-B. and Graybiel, A.M., Convergence of afferents from frontal cortex and substantia nigra onto acetylcholin-
esterase-rich patches of the cat's superior collictl/us, N'euroscience, 14 (1985) 455-482. 34 Jones, E.G. and Leavitt, R.Y., Retrograde axonal transport and the demonstration of non-specific projections to the cerebral cortex and striatum from thalamic intralaminar nuclei in the rat, cat and monkey, J. Comp. Neurol., 154 (1974) 349-378. 35 Kaufman, E.F.S. and Rosenquist, A.C., Afferent connections of the thalamic intralaminar nuclei in the cat, Brain Research, 335 (1985) 281-296. 36 Keizer, K., Kuypers, H.G.J.M., Huisman, A.M. and Dann, O., Diamidino yellow dihydrochloride (DY-2HC1); a new fluorescent retrograde neuronal tracer, which migrates only very slowly out of the cell, Exp. Brain Res., 51 (1983) 179-191. 37 Kitai, S.T., Kocsis, J.D., Preston, R.J. and Sugimori, M., Monosynaptic inputs to caudate neurons identified by intracellular injection of horseradish peroxidase, Brain Research, 109 (1976) 601-606. 38 Kocsis, J.D., Sugimori, M. and Kitai, S.T., Convergence of excitatory synaptic inputs to caudate spiny neurons, Brain Research, 124 (1977) 403-413. 39 Krauthamer, G.M., Sensory functions of the neostriatum. In I. Divac and R. Oberg (Eds.), The Neostriatum, Pergamon, Oxford, 1979. 40 Mackay-Sim, A., Sefton, A.J. and Martin, P.R., Subcortical projections to lateral geniculate and thalamic reticular nuclei in the hooded rat, J. Comp. Neurol., 213 (1983) 24-35. 41 Marburg, O. and Warner, F.J., The pathways of the tectum (anterior colliculus) of the midbrain in cats, J. Nerv. Ment. Dis., 106 (1947) 415-446. 42 Martin, G.F., Efferent tectal pathways of the opossum (Didelphis virginiana), J. Comp. Neurol., 135 (1969) 209-224. 43 May, P.J. and Hall, W.C., Relationships between the nigrotectal pathway and the cells of origin of the predorsal bundle, J. Comp. Neurol., 226 (1984) 357-376. 44 McGuinness, C.M. and Krauthamer, G.M., The afferent projections to the centrum medianum of the cat as demonstrated by retrograde transport of horseradish peroxidase, Brain Research, 184 (1980) 255-269. 45 Mesulam, M.-M., Tetramethyl benzidine for horseradish peroxidase neurohistochemistry: a non-carcinogenic blue reaction-product with superior sensitivity for visualizing neuronal afferents and efferents, J. Histochem. Cytochem., 26 (1978) 106-117. 46 Nauta, H.J., Pritz, M.B. and Lasek, R.J., Afferents to the rat caudoputamen studied with horseradish peroxidase. An evaluation of a retrograde neuroanatomical research method, Brain Research, 67 (1974) 219-238. 47 Niimi, K., Miki, M. and Kawamura, S., Ascending projections of the superior colliculus in the cat, Okajimas Fol. Anat. Jap., 47 (1970) 269-287. 48 Papez, J.W. and Freeman, G.L., Superior colliculi and their fiber connections in the rat, J. Comp. Neurol., 51 (1930) 409-439. 49 Partlow, G.D., Colonnier, M. and Szabo, J., Thalamic projections of the superior colliculus in the rhesus monkey, Macaca mulatta. A light and electron microscopic study, J. Comp. Neurol., 171 (1977) 285-318. 50 Powell, T.P.S. and Cowan, W.M., The connexions of the midline and intra-laminar nuclei of the thalamus of the rat, J. Anat. (London), 88 (1954) 307-319. 51 Racagni, G., Bruno, F., Cattabeni, F., Maggi, A., DiGiu-
233
52
53
54
55
56
57
58
59
lio, A.M~; Parenti, M. and Groppetti, A., Functional interaction between rat substantia nigra and striatum: GABA and dopamine interrelation, Brain Research, 134 (1977) 353-358. Rafols, J.A. and Matzke, H.A., Efferent projections of the superior colliculus in the opossum, J. Comp. Neurol., 138 (1970) 147-160. Rhoades, R.W., Mooney, R.D. and Jacquin, M.F., Complex somatosensory receptive fields of cells in the deep laminae of the hamster's superior colliculus, J. Neurosci., 3 (1983) 1342-1354. Rhoades, R.W., Kuo, D.C., Polcer, J.D., Fish, S.E. and Voneida, T.J., Indirect visual cortical input to the deep layers of the hamster's superior colliculus via the basal ganglia, J. Comp. Neurol., 208 (1982) 239-254. Rosene, D.L. and Mesulam, M.-M., Fixation variables in horseradish peroxidase neurohistochemistry. I. The effects of fixation time and perfusion procedures upon enzyme activity, J. Histochem. Cytochem., 26 (1978) 28-39. Royce, G.J., Strominger, N.L. and Harting, J.K., Projections of the superior colliculus to the intralaminar thalamic nuclei in the cat and rhesus monkey, Soc. Neurosci. Abstr., 2 (1976) 1090. Sugita, S., Otani, K., Tokunaga, A. and Terasawa, K., Laminar origin of the tecto-thalamic projections in the albino rat, Neurosci. Lett., 43 (1983) 143-147. Tasiro, S., Experimental-anatomische Untersuching l~lber die efferenten Bahnen aus den vier Hiigeln der Katze, Z. Mikorsk.-Anat. Forsch., 47 (1940) 1-32. Van Der Kooy, D. and Carter, D.A., The organization of
the efferent projections and striatal afferents of the entopeduncular nucleus and adjacent areas in the rat, Brain Research, 211 (1981) 15-36. 60 Van Der Kooy, D., The organization of the thalamic, nigral and raphe cells projecting to the medial vs lateral caudateputamen in rat. A fluorescent retrograde double labeling study, Brain Research, 169 (1979) 381-387. 61 Veening, J.G., Cornelissen, F.M. and Lieven, P.A.J.M., The topical organization of the afferents to the caudatoputamen of the rat. A horseradish peroxidase study, Neuroscience, 5 (1980) 1253-1268. 62 Velayos, J.L. and Reinoso-Suarez, F., Topographic organization of the brainstem afferents to the mediodorsal thalamic nucleus, J. Comp. Neurol., 206 (1982) 17-27. 63 Weber, J.T., Martin, G.F., Behan, M., Huertz, M.F. and Harting, J.K., The precise origin of the tectospinal pathway in three common laboratory animals: a study using the horseradish peroxidase method, Neurosci. Lett., 11 (1979) 121-127. 64 Yamasaki, D.S., Krauthamer, G.M. and Rhoades, R.W., Response properties of tectal neurons which project to the parafascicular thalamic nucleus in the rat, Anat. Rec., 211 (1985) 219A. 65 Yamasaki, D.S. and Krauthamer, G.M., Fiber terminals of the superior collicular projection into the parafascicular complex in the rat, Soc. Neurosci. Abstr., 9 (1983) 1215. 66 Yoshida, M. and Precht, W., Monosynaptic inhibition of neurons of the substantia nigra by caudatonigral fibers, Brain Research, 32 (1971) 225-228.