- Email: [email protected]
Anatomical study of neural projections to the superior colliculus of the big brown bat,Eptesicus fuscus
Brain Research, 416 (1987) 375-380
375
Elsevier BRE 22391
Anatomical study of neural projections to the superior colliculus of the big brown bat, Eptesicus fuscus Shangqing Zhang 1, Xinde Sun a and Philip H.-S. Jen 2 1Department of Biology, East China Normal University, Shanghai (People's Republic of China) and 2Division of Biological Sciences, The University of Missouri, Columbia, MO (U.S.A.) (Accepted 28 April 1987)
Key words: Superior colliculus, Auditory input; Horseradish peroxidase; Bat
Auditory inputs to the intermediate and deep layers of the superior colliculus of the bat, Eptesicus fuscus, were studied by iontophoretic injection of horseradish peroxidase (HRP) into the superior colliculus. HRP was injected into the recording sites of superior collicular neurons that responded to acoustic stimuli (4 ms duration, 0.5 ms rise-decay times). The results showed that the superior colliculus received its auditory projections mainly from the inferior colliculus bilaterally, but with ipsilateral projections prevailing. A few projections came from the dorsal nucleus of the lateral lemniscus. HRP-labeled neurons were also found in 11 other brain structures.
The superior colliculus (SC) of a vertebrate is a multimodal center which integrates auditory, visual and somatic inputs 1'2'6'8'9'12'13'26. It is involved in an animal's orienting li15.25.27,33.34.
responses
to
sensory
stimu-
The visual centers of insectivorous bats are generally poorly developed but the SC is an exception 3. The SC consists of a narrow band of superficial layers receiving direct retinal inputs and wide bands of intermediate and deep layers 7. Recent studies indicate that SC neurons of bats respond to ultrasonic signals 16"22'24'28'31. In order to study the neural inputs of these SC neurons, we injected H R P iontophoretically into the recording sites after studying their auditory response properties. We report here that the SC of the bat receives auditory inputs mainly from the inferior colliculus (IC) bilaterally. Studies were conducted in 10 Eptesicus fuscus (body weight 20-25 g). The procedures to record SC neurons responding to acoustic stimuli have been described previously 16'24. Briefly, under Nembutal anesthesia (45-50 mg/kg body weight), the flat head of a 1.8-cm nail was mounted onto the exposed skull of a bat. After fixing the bat's head by locking the shank
of the nail with a set screw, an HRP-filled glass electrode (tip diameter 8 - 1 0 / z m , impedance 2 - 4 mQ) was inserted into the exposed SC to record extracellularly neurons which respond to acoustic stimuli (4 ms duration, 0.5 ms rise-decay times). The stimulus was delivered from a condenser loudspeaker placed 14 cm in front of the bat. After studying the basic auditory properties of the recorded neuron, H R P solution was iontophoretically injected into the recording site (500-700 nA, 40-60 min), The electrode was then withdrawn. Between 24 and 28 h later, the bat was sacrificed with an overdose of Nembutal and perfused transcardially with 120 ml 0.9% saline followed by 100 ml fixative (2% paraformaldehyde, 1.25% glutaraidehyde in 0.1 M phosphate buffer pH 7.4). The brain was removed and kept in fixative for 8-10 hours at 4 °C before it was thoroughly rinsed in phosphate buffer (0.1 M pH 7.4) containing 10% sucrose. Frozen sections (50/xm) were cut along the frontal plane of the brain. After several brief washes in 0.1 M phosphate buffer, all sections were incubated in TMB and TMB + H20219. Sections were mounted, dried (some were counterstained with Neutral red) and covered-slipped with permount before they were
Correspondence: P.H.-S. Jen, Division of Biological Sciences, The University of Missouri-Columbia, MO, U.S.A. 0006-8993/87/$03.50 © 1987 Elsevier Science Publishers B.V. (Biomedical Division)
376
A
B
D
Fig. 1. Brain sections drawn from 4 bats in which HRP was injected into the superior colliculus. Each HRP injection site is shown by a filled black area and each labeled neuron is shown by a black dot. In A, the two branches of labelled fibers as demonstrated in Fig. 3Ab are also drawn. HRP was injected into the left superior colliculus in 3 bats (A, B, D) and into the right superior colliculus in one bat (C). CG, central gray; HY, hypothalamus; IC, inferior colliculus: MG. medial geniculate body: ND. dentate nucleus: NF. fastigial nucleus; NI, interpeduncular nucleus; NLL, nucleus of the lateral lemniscus: NP. pontine nucleus: NV. vestibular nucleus: P. pons: RF. reticular formation; SC, superior colticulus: SN. substantia nigra; VC. visual cortex; ZI. zona incerta.
377 examined in light- and dark-field. Labeled neurons and fibers were photographed. One bat without H R P injection was treated with TMB as a control for endogenous peroxidase activity. No such labeling was observed in areas showing labeled neurons in experimental bats. Because the auditory physiological properties of the SC neurons have been described previously 16'24'2s, this report will only describe our anatomical findings. The iontophoretic injection of HRP generally generated an injection site which varied from 150 to 250 ~tm in diameter. All injection sites were located in the central to medial portion of the SC. Each injection site was characterized by very dark staining and granulated tissue. The area surrounding the injection site contained more homogeneously stained neurons and fibers. Fig. 1 shows brainstem sections drawn from 4 bats in which H R P was injected into one SC of each bat. It is clear that the injection site was either in the superficial and intermediate layers (Fig. 1A,B) or in the intermediate and deep layers (Fig. 1C,D) of the SC. Careful microscopic examination of these sections showed that HRP-labeled neurons were found in 13 different cortical and subcortical brain structures (Fig. 2). However, we did not find labeled neurons in any nucleus of the somatosensory system. We also noted that labeled neurons in the visual cortex could only be found when the H R P was injected into the superficial layer. A representative HRP injection site, HRP-labeled fibers and neurons found in different brain structures are shown in Fig. 3. Each H R P injection site generally received two branches of fiber tracts. One branch (Figs. 1A,3Ab) arises ventrolaterally and terminates in the injection site. This branch mainly contains fibers of neurons in the ipsilateral central nucleus of inferior colliculus (ICC), nucleus of the lateral lemniscus (NLL), zona incerta, substantia nigra and pontine nucleus. The other branch arises from the contralateral side and crosses over through the central gray before terminating in the injection site. it contains fibers originating contralaterally in the corresponding nuclei. In every brain we examined, we found that the IC always contained the most numerous labeled neurons. These neurons were generally found in the ventromedial portion of the ICC (vmlCC). Within the vmlCC, labeled neurons in the rostral portion were
st~"
nucle.~
I fasti~lal aentate I
Fig. 2. A summary of neural inputs to the superior colliculus of bats based upon the HRP study.
generally located medialdorsally and those in the caudal portion were located lateroventrally. They were either triangular, multipolar neurons with radially extending dendrites (Fig. 3Bin-o) or spindleshaped bipolar neurons (Fig. 3Bp). Their somata generally ranged from 15 to 25 ym. Only a few labeled neurons were found in the ventral portion of the external nucleus of the IC. Labeled neurons were also found in another auditory nucleus, the NLL. They were most often found in the dorsal NLL. These neurons were oval (Fig. 3Bh) or spindledshaped with soma diameter of 20 urn. Labeled neurons found in other brain structures were either triangular (Fig. 3Ba,d,e,i,j,k), oval (Fig. 3Bb,f,g), spherical (Fig. 3Bc) or elongated (Fig. 3BI). Their somata ranged from 10 to 35 urn. Some of these neurons were multipolar and had rather elaborate extending dendrites (Fig. 3Bd,f,i). Sources of cortical and subcortical projections to the SC have been investigated in various animals, including cats 11"14'18"20,23,32, rats 4,1°, guinea pig 32, tree shrews s, hamsters 3°, rabbits 29, monkeys 2j and owls fT. All these studies reported that the SC receives auditory projections from the IC, although the degree of IC projection varies across species. Our data suggest that the SC of the bat primarily receives its auditory inputs from the IC, but it also receives some projections from the dorsal NLL. This finding supports our previous electrophysiological demonstration that the basic auditory response properties of acoustically evoked SC neurons are very similar to those of IC
S ~
~
~
B
~,~ii~i~~. ~~'~ 0 i~
J
YAm
g
h
~9~
~
•
~.~
T~
i~~
J J
4
k
rn
379
n
o
'
P
50 Fig. 3. Photomicrographs showing an HRP injection site inside the SC(Aa), labeled fibers (Ab) projecting to the injection site and labeled neurons in different brain structures (Ba-p). Labeled cells are found in medial vestibular nucleus (Ba), cerebellar fastigial nucleus (Bb), cerebellar dentate nucleus (Bc), lateral pontine nucleus (Bd), visual cortex (Be), contralateral superior colliculus (Bf), interpeduncular nucleus (Bg), dorsal nucleus of lateral lemniscus (Bh), reticular formation (Bi), central gray (Bj), substantia nigra (Bk), zona incerta (BI), and inferior colliculus (Bm-p).
neurons of the same bat ~6"24"2s. Our data also suggest
jection exist. In this regard, it is rather surprising that
that the upper layer of the SC receives visual inputs not only directly from the retina 7, but also from the visual cortex (Fig. 3Be). Although we only focally injected the H R P into the recording site, labeled neu-
we did not find labeled neurons in any nucleus of the somatosensory system of the bat. It remains to be de-
rons could also be found in brain structures other than the ICC and NLL (Fig. 2). This result suggests that afferent fibers from non-auditory structures also project to the H R P injection site. With the exception of projections from the somatosensory system, our list of non-auditory structures containing labeled neurons is comparable to that of other studies 4' ~0.1E.,~o, although species differences in degree of pro-
1 Allon, N. and Wollberg, Z., Responses of cells in the superior colliculus of the squirrel monkey to auditory stimuli, Brain Research, 159 (1978) 321-330. 2 Atkinson, W.H., Click-evoked response at the superior colliculusof the cat, Exp. Neurol., 62 (1978) 501-509. 3 Baron, G., Signification eco-ethologique du developpement allometrique des deux systemes visuels chez les chiropteres, Revue Can. Biol., 36 (1977) 1-16. 4 Carey, C.L. and Webster, D.B., Ascending and descending projections of the inferior colliculus in the kangaroo rat (Dipodomys merriami), Brain, Behav. and Evol., 4 (1971) 401-412. 5 Casseday, J.H., Jones, D.R. and Diamond, I.T., Projections from cortex to tectum in the tree shrew, Tupaia glis, J. Comp. Neurol., 185 (1979) 253-292. 6 Chalupa, L.M. and Rhoades, R.W., Responses of visual, somatosensory and auditory neurons in the golden hamster's superior colliculus, J. Physiol. (London), 270 (1977) 595-626. 7 Crowle, P.K., Experimental Investigation of Retinofugal
termined if our finding is simply due to injection bias or species-specific difference. Future experiments involving other sensory stimuli and even smaller injection sites should be able to provide answers to this question. This study is partially supported by a grant from the National Institutes of Health ( D H H S 1 RO1 NS 20527). We thank Dr. G. Summers' for comments on the early version of this paper.
Connections to the Diencephalon and Midbrain of Chiroptera, Ph.D. Thesis, Indiana University, Bloomington, 1974. 8 Drager, U.C. and Hubel, D.H., Responses to visual stimulation and relationship between visual, auditory and somatosensory inputs in mouse superior colliculus, J. Neurophysiol., 38 (1975) 690-713. 9 Drager, U.C. and Hubel, D.H., Topography of visual and somatosensory projections to mouse superior colliculus, J. Neurophysiol., 39 (1976) 91-101. 10 Druga, R. and Syka, J., Projections from auditory structures to the superior colliculus in the rat, Neurosci. Lett., 45 (1984) 247-252. 11 Edwards, S.B., Ginsberg, C.L., Henkin, C.K. and Stein, B.E., Sources of subcortical projections to the superior colliculus in the cat, J. Comp. Neurol., 184 (1979) 309-330. 12 Finlay, B.L., Schneps, S.E., Wilson, K.G. and Schneider, G.E., Topography of visual and somatosensory projections to the superior colliculus of the golden hamster, Brain Research, 142 (1978) 223-235. 13 Gordon, B., Receptive fields in deep layers of cat superior
380 colliculus, J. Neurophysiol., 36 (1973) 157-178. 14 Grofova, I., Ottersen, O.P. and Rinvik, E., Mesencephalic and diencephalic afferents to the superior colliculus and aqueductal gray substance demonstrated by retrograde axonal transport of horseradish peroxidase in the cat, Brain Research, 146 (1978) 205-220. 15 Harris, L.R., The superior colticulus and movements of the head and eyes in cats, J. Physiol. (London), 300 (19801 367-391. 16 Jen, P.H.-S., Sun, X.D., Kamada, T., Zhang, S.Q. and Shimozawa, T., Auditory response properties and spatial response areas of superior collicular neurons of the FM bat, Eptesicus fuscus, J. Comp. Physiol., 154 (1984) 407-413. 17 Knudsen, E.I. and Knudsen, P.F., Space-mapped auditory projections from the inferior colliculus to the optic tectum in the owl, J. Comp. Neurol., 218 (1983) 187-196. 18 Kudo, M., Projections of the nuclei of the lateral lemniscus in the cat: an autoradiographic study, Brain Research, 22t (19811 57-69. 19 Mesulam, M.M., Tracing Neural Connections with Horseradish Peroxidase, Wiley, New York, 1982. 20 Moore, R.Y. and Goldberg, J.M., Ascending projections of the inferior colliculus in the cat, J. Comp. Neurol., 121 (1963) 109-136. 21 Moore, R.Y. and Goldberg, J.M., Projections of the inferior colliculus in the monkey, Exp. Neurol., 14 (1966) 429-438. 22 Poussin, C. and Schlegel, P., Directional sensitivity of auditory neurons in the superior colliculus of the bat, Eptesicus fuscus using free field sound stimulation, J. Comp. Physiol., 154 (1984) 253-261. 23 PoweU, E.W. and Hatton, J.B., Projections of the inferior colliculus in the cat, J. Comp. Neurol., 136 (1969) 183-192. 24 Shimozawa, T., Sun, X.D. and Jen, P.H.-S., Auditory
25
26
27
28
29
30
31
32
33
34
space representation in the supeno~ colliculus oi the i~lg brown bat. Eptesicus fuscus. Bra~ Re~'.. ~;ll ~1~84~ 289-296. Sprague, J.M. and Meikle. T.tt.. Jr.. l'he role ot the ,~uperior colliculus in visually guided behaviour_ E.~p Neurol. 11 (1965~ 115-146 Stem B.E. and Arigbede M.O. t',mmodal and mu[nmodal response properties of neurons m the cat's superior coiliculus. Exp. Neurol.. 36 (19721 1711- '~96 Stein B.E.. Goldberg, S.J. and Clamann. H.P.. The control of eye movement by the superior collicu[us in the alert cat. Brain Research. 118 I'1976) 469-4"7'4 Sun. X.D. Jen. P.H.-S. and Kamada. f . Neurons r a t h e superior colliculus of echo-locating bats respond to ultrasonic signals. Brain Res.. 275 ( 1983~ 14~- 152 Tarlov. E.C. and Moore. R.Y.. The ~ccto-thalam~c connections in the brain of the rabbit r ( o m p Neurol 126 119731 403-422 Van Buskirk. R.L.. Subcorticat auditory and somatosensorv afferents to hamster superior eolliculus, Brain Res. Bull. 111(19831 583-587. Wong, D.. Spatial tuning ol aud~tor'~ neurons m the superior colliculus of the echo-locating bat. Mvotis luc(fugus. ttearing Research 16 ~19841 261-270 Woolard. H.H. and Harpman. J.A.. ihe connections of the inferior colliculus and of the dorsal nucleus of the lateral lemniscus. J. Anat.. 74 (19401 441-458. Wurtz. R.H. and Albano. J.E.. Vi,,uomotor functions Ol the primate superior colliculus Ann Rev. Neurosci. 3 198(1/ 189-226 Wurtz R H . and Goldberg, M.E.. Superior cotticulus celt responses related to eye movement,, ~n awake monkeys_ Science. 171 19711 82-84.
375
Elsevier BRE 22391
Anatomical study of neural projections to the superior colliculus of the big brown bat, Eptesicus fuscus Shangqing Zhang 1, Xinde Sun a and Philip H.-S. Jen 2 1Department of Biology, East China Normal University, Shanghai (People's Republic of China) and 2Division of Biological Sciences, The University of Missouri, Columbia, MO (U.S.A.) (Accepted 28 April 1987)
Key words: Superior colliculus, Auditory input; Horseradish peroxidase; Bat
Auditory inputs to the intermediate and deep layers of the superior colliculus of the bat, Eptesicus fuscus, were studied by iontophoretic injection of horseradish peroxidase (HRP) into the superior colliculus. HRP was injected into the recording sites of superior collicular neurons that responded to acoustic stimuli (4 ms duration, 0.5 ms rise-decay times). The results showed that the superior colliculus received its auditory projections mainly from the inferior colliculus bilaterally, but with ipsilateral projections prevailing. A few projections came from the dorsal nucleus of the lateral lemniscus. HRP-labeled neurons were also found in 11 other brain structures.
The superior colliculus (SC) of a vertebrate is a multimodal center which integrates auditory, visual and somatic inputs 1'2'6'8'9'12'13'26. It is involved in an animal's orienting li15.25.27,33.34.
responses
to
sensory
stimu-
The visual centers of insectivorous bats are generally poorly developed but the SC is an exception 3. The SC consists of a narrow band of superficial layers receiving direct retinal inputs and wide bands of intermediate and deep layers 7. Recent studies indicate that SC neurons of bats respond to ultrasonic signals 16"22'24'28'31. In order to study the neural inputs of these SC neurons, we injected H R P iontophoretically into the recording sites after studying their auditory response properties. We report here that the SC of the bat receives auditory inputs mainly from the inferior colliculus (IC) bilaterally. Studies were conducted in 10 Eptesicus fuscus (body weight 20-25 g). The procedures to record SC neurons responding to acoustic stimuli have been described previously 16'24. Briefly, under Nembutal anesthesia (45-50 mg/kg body weight), the flat head of a 1.8-cm nail was mounted onto the exposed skull of a bat. After fixing the bat's head by locking the shank
of the nail with a set screw, an HRP-filled glass electrode (tip diameter 8 - 1 0 / z m , impedance 2 - 4 mQ) was inserted into the exposed SC to record extracellularly neurons which respond to acoustic stimuli (4 ms duration, 0.5 ms rise-decay times). The stimulus was delivered from a condenser loudspeaker placed 14 cm in front of the bat. After studying the basic auditory properties of the recorded neuron, H R P solution was iontophoretically injected into the recording site (500-700 nA, 40-60 min), The electrode was then withdrawn. Between 24 and 28 h later, the bat was sacrificed with an overdose of Nembutal and perfused transcardially with 120 ml 0.9% saline followed by 100 ml fixative (2% paraformaldehyde, 1.25% glutaraidehyde in 0.1 M phosphate buffer pH 7.4). The brain was removed and kept in fixative for 8-10 hours at 4 °C before it was thoroughly rinsed in phosphate buffer (0.1 M pH 7.4) containing 10% sucrose. Frozen sections (50/xm) were cut along the frontal plane of the brain. After several brief washes in 0.1 M phosphate buffer, all sections were incubated in TMB and TMB + H20219. Sections were mounted, dried (some were counterstained with Neutral red) and covered-slipped with permount before they were
Correspondence: P.H.-S. Jen, Division of Biological Sciences, The University of Missouri-Columbia, MO, U.S.A. 0006-8993/87/$03.50 © 1987 Elsevier Science Publishers B.V. (Biomedical Division)
376
A
B
D
Fig. 1. Brain sections drawn from 4 bats in which HRP was injected into the superior colliculus. Each HRP injection site is shown by a filled black area and each labeled neuron is shown by a black dot. In A, the two branches of labelled fibers as demonstrated in Fig. 3Ab are also drawn. HRP was injected into the left superior colliculus in 3 bats (A, B, D) and into the right superior colliculus in one bat (C). CG, central gray; HY, hypothalamus; IC, inferior colliculus: MG. medial geniculate body: ND. dentate nucleus: NF. fastigial nucleus; NI, interpeduncular nucleus; NLL, nucleus of the lateral lemniscus: NP. pontine nucleus: NV. vestibular nucleus: P. pons: RF. reticular formation; SC, superior colticulus: SN. substantia nigra; VC. visual cortex; ZI. zona incerta.
377 examined in light- and dark-field. Labeled neurons and fibers were photographed. One bat without H R P injection was treated with TMB as a control for endogenous peroxidase activity. No such labeling was observed in areas showing labeled neurons in experimental bats. Because the auditory physiological properties of the SC neurons have been described previously 16'24'2s, this report will only describe our anatomical findings. The iontophoretic injection of HRP generally generated an injection site which varied from 150 to 250 ~tm in diameter. All injection sites were located in the central to medial portion of the SC. Each injection site was characterized by very dark staining and granulated tissue. The area surrounding the injection site contained more homogeneously stained neurons and fibers. Fig. 1 shows brainstem sections drawn from 4 bats in which H R P was injected into one SC of each bat. It is clear that the injection site was either in the superficial and intermediate layers (Fig. 1A,B) or in the intermediate and deep layers (Fig. 1C,D) of the SC. Careful microscopic examination of these sections showed that HRP-labeled neurons were found in 13 different cortical and subcortical brain structures (Fig. 2). However, we did not find labeled neurons in any nucleus of the somatosensory system. We also noted that labeled neurons in the visual cortex could only be found when the H R P was injected into the superficial layer. A representative HRP injection site, HRP-labeled fibers and neurons found in different brain structures are shown in Fig. 3. Each H R P injection site generally received two branches of fiber tracts. One branch (Figs. 1A,3Ab) arises ventrolaterally and terminates in the injection site. This branch mainly contains fibers of neurons in the ipsilateral central nucleus of inferior colliculus (ICC), nucleus of the lateral lemniscus (NLL), zona incerta, substantia nigra and pontine nucleus. The other branch arises from the contralateral side and crosses over through the central gray before terminating in the injection site. it contains fibers originating contralaterally in the corresponding nuclei. In every brain we examined, we found that the IC always contained the most numerous labeled neurons. These neurons were generally found in the ventromedial portion of the ICC (vmlCC). Within the vmlCC, labeled neurons in the rostral portion were
st~"
nucle.~
I fasti~lal aentate I
Fig. 2. A summary of neural inputs to the superior colliculus of bats based upon the HRP study.
generally located medialdorsally and those in the caudal portion were located lateroventrally. They were either triangular, multipolar neurons with radially extending dendrites (Fig. 3Bin-o) or spindleshaped bipolar neurons (Fig. 3Bp). Their somata generally ranged from 15 to 25 ym. Only a few labeled neurons were found in the ventral portion of the external nucleus of the IC. Labeled neurons were also found in another auditory nucleus, the NLL. They were most often found in the dorsal NLL. These neurons were oval (Fig. 3Bh) or spindledshaped with soma diameter of 20 urn. Labeled neurons found in other brain structures were either triangular (Fig. 3Ba,d,e,i,j,k), oval (Fig. 3Bb,f,g), spherical (Fig. 3Bc) or elongated (Fig. 3BI). Their somata ranged from 10 to 35 urn. Some of these neurons were multipolar and had rather elaborate extending dendrites (Fig. 3Bd,f,i). Sources of cortical and subcortical projections to the SC have been investigated in various animals, including cats 11"14'18"20,23,32, rats 4,1°, guinea pig 32, tree shrews s, hamsters 3°, rabbits 29, monkeys 2j and owls fT. All these studies reported that the SC receives auditory projections from the IC, although the degree of IC projection varies across species. Our data suggest that the SC of the bat primarily receives its auditory inputs from the IC, but it also receives some projections from the dorsal NLL. This finding supports our previous electrophysiological demonstration that the basic auditory response properties of acoustically evoked SC neurons are very similar to those of IC
S ~
~
~
B
~,~ii~i~~. ~~'~ 0 i~
J
YAm
g
h
~9~
~
•
~.~
T~
i~~
J J
4
k
rn
379
n
o
'
P
50 Fig. 3. Photomicrographs showing an HRP injection site inside the SC(Aa), labeled fibers (Ab) projecting to the injection site and labeled neurons in different brain structures (Ba-p). Labeled cells are found in medial vestibular nucleus (Ba), cerebellar fastigial nucleus (Bb), cerebellar dentate nucleus (Bc), lateral pontine nucleus (Bd), visual cortex (Be), contralateral superior colliculus (Bf), interpeduncular nucleus (Bg), dorsal nucleus of lateral lemniscus (Bh), reticular formation (Bi), central gray (Bj), substantia nigra (Bk), zona incerta (BI), and inferior colliculus (Bm-p).
neurons of the same bat ~6"24"2s. Our data also suggest
jection exist. In this regard, it is rather surprising that
that the upper layer of the SC receives visual inputs not only directly from the retina 7, but also from the visual cortex (Fig. 3Be). Although we only focally injected the H R P into the recording site, labeled neu-
we did not find labeled neurons in any nucleus of the somatosensory system of the bat. It remains to be de-
rons could also be found in brain structures other than the ICC and NLL (Fig. 2). This result suggests that afferent fibers from non-auditory structures also project to the H R P injection site. With the exception of projections from the somatosensory system, our list of non-auditory structures containing labeled neurons is comparable to that of other studies 4' ~0.1E.,~o, although species differences in degree of pro-
1 Allon, N. and Wollberg, Z., Responses of cells in the superior colliculus of the squirrel monkey to auditory stimuli, Brain Research, 159 (1978) 321-330. 2 Atkinson, W.H., Click-evoked response at the superior colliculusof the cat, Exp. Neurol., 62 (1978) 501-509. 3 Baron, G., Signification eco-ethologique du developpement allometrique des deux systemes visuels chez les chiropteres, Revue Can. Biol., 36 (1977) 1-16. 4 Carey, C.L. and Webster, D.B., Ascending and descending projections of the inferior colliculus in the kangaroo rat (Dipodomys merriami), Brain, Behav. and Evol., 4 (1971) 401-412. 5 Casseday, J.H., Jones, D.R. and Diamond, I.T., Projections from cortex to tectum in the tree shrew, Tupaia glis, J. Comp. Neurol., 185 (1979) 253-292. 6 Chalupa, L.M. and Rhoades, R.W., Responses of visual, somatosensory and auditory neurons in the golden hamster's superior colliculus, J. Physiol. (London), 270 (1977) 595-626. 7 Crowle, P.K., Experimental Investigation of Retinofugal
termined if our finding is simply due to injection bias or species-specific difference. Future experiments involving other sensory stimuli and even smaller injection sites should be able to provide answers to this question. This study is partially supported by a grant from the National Institutes of Health ( D H H S 1 RO1 NS 20527). We thank Dr. G. Summers' for comments on the early version of this paper.
Connections to the Diencephalon and Midbrain of Chiroptera, Ph.D. Thesis, Indiana University, Bloomington, 1974. 8 Drager, U.C. and Hubel, D.H., Responses to visual stimulation and relationship between visual, auditory and somatosensory inputs in mouse superior colliculus, J. Neurophysiol., 38 (1975) 690-713. 9 Drager, U.C. and Hubel, D.H., Topography of visual and somatosensory projections to mouse superior colliculus, J. Neurophysiol., 39 (1976) 91-101. 10 Druga, R. and Syka, J., Projections from auditory structures to the superior colliculus in the rat, Neurosci. Lett., 45 (1984) 247-252. 11 Edwards, S.B., Ginsberg, C.L., Henkin, C.K. and Stein, B.E., Sources of subcortical projections to the superior colliculus in the cat, J. Comp. Neurol., 184 (1979) 309-330. 12 Finlay, B.L., Schneps, S.E., Wilson, K.G. and Schneider, G.E., Topography of visual and somatosensory projections to the superior colliculus of the golden hamster, Brain Research, 142 (1978) 223-235. 13 Gordon, B., Receptive fields in deep layers of cat superior
380 colliculus, J. Neurophysiol., 36 (1973) 157-178. 14 Grofova, I., Ottersen, O.P. and Rinvik, E., Mesencephalic and diencephalic afferents to the superior colliculus and aqueductal gray substance demonstrated by retrograde axonal transport of horseradish peroxidase in the cat, Brain Research, 146 (1978) 205-220. 15 Harris, L.R., The superior colticulus and movements of the head and eyes in cats, J. Physiol. (London), 300 (19801 367-391. 16 Jen, P.H.-S., Sun, X.D., Kamada, T., Zhang, S.Q. and Shimozawa, T., Auditory response properties and spatial response areas of superior collicular neurons of the FM bat, Eptesicus fuscus, J. Comp. Physiol., 154 (1984) 407-413. 17 Knudsen, E.I. and Knudsen, P.F., Space-mapped auditory projections from the inferior colliculus to the optic tectum in the owl, J. Comp. Neurol., 218 (1983) 187-196. 18 Kudo, M., Projections of the nuclei of the lateral lemniscus in the cat: an autoradiographic study, Brain Research, 22t (19811 57-69. 19 Mesulam, M.M., Tracing Neural Connections with Horseradish Peroxidase, Wiley, New York, 1982. 20 Moore, R.Y. and Goldberg, J.M., Ascending projections of the inferior colliculus in the cat, J. Comp. Neurol., 121 (1963) 109-136. 21 Moore, R.Y. and Goldberg, J.M., Projections of the inferior colliculus in the monkey, Exp. Neurol., 14 (1966) 429-438. 22 Poussin, C. and Schlegel, P., Directional sensitivity of auditory neurons in the superior colliculus of the bat, Eptesicus fuscus using free field sound stimulation, J. Comp. Physiol., 154 (1984) 253-261. 23 PoweU, E.W. and Hatton, J.B., Projections of the inferior colliculus in the cat, J. Comp. Neurol., 136 (1969) 183-192. 24 Shimozawa, T., Sun, X.D. and Jen, P.H.-S., Auditory
25
26
27
28
29
30
31
32
33
34
space representation in the supeno~ colliculus oi the i~lg brown bat. Eptesicus fuscus. Bra~ Re~'.. ~;ll ~1~84~ 289-296. Sprague, J.M. and Meikle. T.tt.. Jr.. l'he role ot the ,~uperior colliculus in visually guided behaviour_ E.~p Neurol. 11 (1965~ 115-146 Stem B.E. and Arigbede M.O. t',mmodal and mu[nmodal response properties of neurons m the cat's superior coiliculus. Exp. Neurol.. 36 (19721 1711- '~96 Stein B.E.. Goldberg, S.J. and Clamann. H.P.. The control of eye movement by the superior collicu[us in the alert cat. Brain Research. 118 I'1976) 469-4"7'4 Sun. X.D. Jen. P.H.-S. and Kamada. f . Neurons r a t h e superior colliculus of echo-locating bats respond to ultrasonic signals. Brain Res.. 275 ( 1983~ 14~- 152 Tarlov. E.C. and Moore. R.Y.. The ~ccto-thalam~c connections in the brain of the rabbit r ( o m p Neurol 126 119731 403-422 Van Buskirk. R.L.. Subcorticat auditory and somatosensorv afferents to hamster superior eolliculus, Brain Res. Bull. 111(19831 583-587. Wong, D.. Spatial tuning ol aud~tor'~ neurons m the superior colliculus of the echo-locating bat. Mvotis luc(fugus. ttearing Research 16 ~19841 261-270 Woolard. H.H. and Harpman. J.A.. ihe connections of the inferior colliculus and of the dorsal nucleus of the lateral lemniscus. J. Anat.. 74 (19401 441-458. Wurtz. R.H. and Albano. J.E.. Vi,,uomotor functions Ol the primate superior colliculus Ann Rev. Neurosci. 3 198(1/ 189-226 Wurtz R H . and Goldberg, M.E.. Superior cotticulus celt responses related to eye movement,, ~n awake monkeys_ Science. 171 19711 82-84.