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Bilateral changes in soma size of geniculate relay cells and corticogeniculate cells after neonatal monocular enucleation in rats
Brain Research, 301 (1984) 13-23
13
Elsevier BRE 10004
Bilateral Changes in Soma Size of Geniculate Relay Cells and Corticogeniculate Cells •After Neonatal Monocular Enucleation in Rats YUTAKA FUKUDA and CHIE-FANG HSIAO
Department of Neurophysiology, Institute of Higher Nervous Activity, Osaka University Medical School, Kita-ku, Osaka (Japan) (Accepted October 4th, 1983)
Key words: bilateral changes - - soma size - - geniculate relay cell - - corticogeniculate cell - - rat - - monocular enucleation
Soma areas of relay cells of the lateral geniculate nucleus and of corticogeniculate cells of normal rats (n = 4) were compared with those of neonatally unilaterally eye-enucleated adult rats (n = 13). These cells were labeled by retrogradely transported HRP. Monocular enucleation was performed on postnatal days 1 (PND 1) (n = 4), 3 (PND 3) (n = 5) and 6 (PND 6) (n = 4). The results are summarized as follows. (1) In PND 1 rats soma areas of relay cells were 12-16% smaller than those of normal rats, but only for the geniculate nucleus ipsilateral to the remaining eye. In PND 3 and 6 rats the areal shrinkage of relay cells was 27-39% of the normal control for both hemispheres, though it was less marked in the hemisphere contralateral to the remaining eye. (2) The corticogeniculate cells were distributed in layers V and VI in eye-enucleated rats as well as in normal rats. Soma areas of both layer V and VI cells increased in PND 1 rats for both hemispheres by about 15-47% of the normal control. In PND 3 rats increase in soma size tended to occur for layer VI cells, although the data varied from animal to animal• In summary, it was established that unilateral eye-enucleation in rats at birth induced soma size changes of the geniculate relay cells and of the corticogeniculate cells in the non-deafferented as well as in the deafferented hemisphere. Possible mechanisms for the bilateral changes in soma area of central visual cells after neonatal monocular enucleation are discussed. INTRODUCTION Studying retinogeniculate projections in neonatally unilaterally eye-enucleated rats, we reached the conclusion that after m o n o c u l a r enucleation some retinal ganglion cells of the remaining eye change their projection from the contralateral to the ipsilat-
relay cells and corticogeniculate cells labeled by means of a retrograde axonal flow of HRp3,13,20,22,30,32. The results show that unilateral eye-enucleation at an appropriate stage of the neonatal period caused characteristic soma
size changes in both hemi-
eral hemisphere u. In parallel with this, we have re-
spheres, a decrease in L G d relay cells and an increase in corticogeniculate cells.
cently shown that in these rats the total fiber count of the optic tract decreased on the side contralateral to
MATERIALS AND METHODS
the remaining eye, while it increased on the ipsilateral side 33. These findings led us to test whether or not neurons of the dorsal lateral geniculate nucleus (LGd) and of the visual cortex would also be involved in plastic changes following neonatal unilateral eye enucleation. In recent studies cell somas of various central visual nuclei have been reported to be modified after functional deafferentation or eye-enucleation 2,930~2°.35. Thus, the present experiment was designed to detect possible changes in soma size of L G d
A total of 17 adult albino rats (Wistar strain) of either sex, weighing 350--400 g, 3-5 months old, were used. Except for 4, all other rats u n d e r w e n t the monocular enucleation operation at postnatal days 1 (PND 1), 3 (PND 3) or 6 (PND 6). In the first series of experiments (Experiment I) an H R P injection was made into the primary visual cortex (area 17) contralateral ( C O N T R A ) or ipsilateral (IPSI) to the remaining eye; in the second series (Experiment II) it
Correspondence: Y. Fukuda, Department of Neurophysiology, Institute of Higher Nervous Activity, Osaka University Medical School, Nakanoshima 4-3-57, Kita-ku, Osaka, Japan. 0006-8993/84/$03.00© 1984 Elsevier Science Publishers B.V.
14 was made into the LGd of either side. In the following the laterality of the LGd and the visual cortex of unilaterally eye-enucleated rats is specified with reference to the remaining eye, i.e. the abbreviations IPSI and C O N T R A refer to ipsi- and contralateral to the remaining eye, respectively. The animals used and the laterality of the H R P injection site are listed in Tables I and II for Experiments I and II, respectively. (Note that the animals which received H R P injections into both sites are listed in both tables.) In either series of experiments two normal intact rats were similarly treated to provide the control data. The H R P injections were performed in the following way. Under Nembutal anesthesia (50 mg/kg, i.p.) the animals were placed in a stereotaxic head-holder. A solution of H R P (Sigma type VI, 40% in saline or Tris-HC1 buffer, pH 7.6) was ejected through micropipettes by applying currents of 5-10/~A in pulses of 7 s on, 7 s off for 20-25 min. The position of the electrode tip was checked in every experiment by monitoring physiological responses to single flash stimuli through the electrode. The coordinates for the LGd injection was 3.5 mm lateral from the midline and about 4.5 mm below the cortical surface as in the companion paper 11. For the visual cortical injection the electrode was placed in the center of area 17, 3 mm lateral to lambda 5,12,19. Except for H R P 27, 3 shots were made in each injection site, about 100 ~um apart rostro-caudally. The total volume of H R P solution ejected was about 0.3,ul. In H R P 27, many shots were made for the special purpose referred to in Resuits. After a survival period of 48 h, all H R P injected animals were deeply anesthetized with ether and perfused intracardially with Karnovsky's 17 fixative. Brains were removed and stored in the same fixative overnight at 4 °C and then rinsed for 48 h at 4 °C in 30% sucrose phosphate buffer. Frontal sections were made at 60/~m on a freezing microtome, reacted with D A B (3,3'-diaminobenzidine) and counterstained with 0.1% cresylviolet as described in the companion paperll. Preparations were scanned microscopically under bright- or dark-field illumination. For the areal measurements, each of the labeled cells was outlined by a drawing tube attached to a microscope with a final magnification of 840x, and the outline drawings were processed by a semiautomatic image analyzing system, AMS (Leiz). Tissue shrinkages were not cor-
rected for in the measurements of cell soma area. RESULTS
Experiment 1: geniculocortical projection Injection sites and labeled cells. As shown in Fig. 1A, the center of the H R P injection site was stained dark brown, being surrounded b y a light halo 34. It is apparent here that the area of the H R P injection was restricted within layers I-VI and did not expand into the white matter. The extent of the injection site varied from animal to animal as shown diagrammatically in Fig. 2. The dark brown areas and the surrounding halos are represented by the black and shaded areas, respectively. Except for the most medial shot in H R P 27 and two shots in H R P 43, the center of the injection was always within the gray matter. In each diagram the medial and lateral borders of area 17 are indicated. Except for H R P 42 and 7 where the injection sites extended medially into area 18a 19, the focus of the injection was localized within area 17. In no case did the injection extend into area 18, lateral to area 1712,19. Thus with a few exceptions the labeled cells in the LGd are assumed to be relay cells projecting to area 17. Sample photomicrographs of HRP-labeled cells in LGd are presented in Fig. 1B and D. Cell B was located in the dorsolateral border of the nucleus next to the optic tract fibers running from the lower right to the upper left in this photograph and characterized by two vertically oriented dendrites. In a more central part of the nucleus the labeled cells appeared like cell D. Usually two or three dendrites emanated from a tri- or quadrangular soma s-l~. Soma areas of relay cells. The distributions of the soma area of HRP-labeled relay cell in the LGd of normal rats were compared with those of neonatally enucleated rats (Table I, Fig. 3). In Fig. 3 are shown typical histograms of the cell soma area for two normal ( H R P 8 and 27), two PND 1 ( H R P 22 and 21), two PND 3 ( H R P 24 and 7) and two PND 6 ( H R P 25 and 26) rats. Inset figures in each histogram show distributions of labeled cells within the LGd. In H R P 27 (Fig. 3B) of diffusely distributed labeled cells only those situated within the central area of the nucleus (the area excepted from blackening) were subject to soma area measurements. In this case we intended to label as many relay cells as possible by making many
15
A
Fig. 1. Photomicrographs of injection site, retrogradely labeled geniculate relay cells and corticogeniculate cells. A: injection site was localized within IPSI area 17 of neonatally enucleated rat (HRP 21). Note that two dense focuses of H R P injection with a surrounding halo were restricted within the gray matter. The superior colliculus below the HRP-injected cortex was somewhat shrunken, indicating that this side is contralateral to the enucleated eye. Horizontal bar, 1 mm. Preparations underwent reactions with D A B and were counterstained with 0.1% cresylviolet. B and D: labeled geniculate relay cells. C and F: labeled corticogeniculate cells in layer V of area 17. E and G: labeled corticogeniculate cells in layer VI of area 17. Horizontal bar in B-F, 20 ~m.
16
HRP 9?
HRP
22
21
4?
46
94
?
95
26
49
43
Fig. 2. Schematic drawings of extent of H R P injections in all subjects of Experiment I (see Table I). Dense focuses of H R P granulations are represented by black and the surrounding halo by shading. In every drawing the medial and lateral borders of area 17 are indicated. Except for H R P 27 and 43, injections were localized within the gray matter, not extending into the white matter. In H R P 7 and 42 the injection extended into area 18.
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18 TABLE
I
Soma areas of HRP-labeled relay cells in the LGd Experimental condition
Animal No.
Mean soma area ± S.D. #~m21
(n)
% Change from normal and significance level
Normal Normal PND 1 Contra Contra Ipsi Ipsi PND 3 Contra lpsi PND 6 Contra Contra Ipsi Ipsi
HRP 8 HRP 27
159 ± 49 167 ± 29
(239) (1701
HRP 22 HRP47 HRP 21 HRP46
164 +_55 173 _+48 138 _+36 144 + 38
(2(19) (132) (132) (99)
+ 11.9 + 6.3 --15.5 --11.7
n.s. P < I).(12 P < 0.1101 P < 0.001
HRP 24 HRP 7
115 _+23 99 ± 31
(235) (93)
--29.5 --39.4
P < 0.1101 P < (1.001
HRP 25 HRP 42 HRP 26 HRP 43
118 ± 25 120 + 25 102 _+31 1117+ 29
(193) (166) (166) (146)
--27.7 --26.5 --37.4 --34.2
P P P P
< < < <
0.01)l 0.001 0.001 0.(1111
shots within area 17 (see Fig. 2). In all other cases the injection was limited to a small cortical area and hence labeled relay cells were localized in a relatively small region. It is worth noting that in the IPSI hemisphere of PND 1 rats and in both hemispheres of PND 3 and 6 rats, the labeled relay cells are more densely packed within a narrow region than in normal rats or in the C O N T R A hemisphere of the PND 1 rat (compare Fig. 3 D - H with Fig. 3 A - C ) . This
gradely labeled relay cells only those located in the
may just reflect an immature development of dendrites and a consequent shrinkage of the nucleus itself. It is also worth noting that even though the IPSI
the C O N T R A LGd did not significantly differ from that in the normal control, while the mean soma area on the IPSI side was 12-16% less than that in the nor-
LGd had shrunken, each part of it sent a projection to the visual cortex, keeping the same topographic relation as seen in normal rats. This appears to parallel several reports on congenital anophthalmic mice in which a clear topographical projection from the LGd to the visual cortex is preserved 7,~. In PND 1 rats the soma areas of relay cells are slightly smaller than in normal rats, but only for the deafferented or IPSI LGd (Fig. 3 A - D ) . However, in PND 3 and 6 rats this was seen in bilateral LGds (Fig. 3 E - H ) . The mean soma areas obtained from normal and unilaterally eye-enucleated rats are summarized in Table I. The soma size of relay cells may differ according to the locations within the nucleus 6,8.18.37. To minimize a possible bias in the normal control data due to this, many injections were made in one normal rat (HRP 27) into area 17. and of retro-
mal control. In PND 3 and 6 rats, the 1PSI and CONT R A cells were 34-39% and 27-30% smaller in soma area than those in the normal rats, respectively. Thus, the soma area of the geniculate relay cells are consistently smaller on the IPSI side than on the C O N T R A side. A n o t h e r important finding is that when eye enucleation was done at PND 1 the decrease in soma size of the relay cell was relatively mild on the IPSI side, while it showed no significant changes on the C O N T R A side. Especially of interest was the finding that in the rats enucleated at PND 3 and 6 the decrease in soma size also occurred for the C O N T R A (non-deafferented) side.
central part of the LGd were selected for soma area measurements so as to supplement the control data in H R P 8, in which labeled cells were localized in the mid-dorsal LGd. In Table I, the mean of the soma areas in H R P 8 and 27 was taken as the normal control and percent changes from this are listed in the rightmost column, together with the significance level. In PND 1 rats, the mean soma area of relay cells in
E x p e r i m e n t II: corticogeniculate projection Injection sites and labeled cells. Sample photographs of the HRP injection sites are shown in
19 Fig. 1A of the companion paper 11. As is the case with the injection into the visual cortex, the center appeared as a dark brown area surrounded by a light halo. In Fig. 4 the exent of the injection in each rat is shown by the black and shaded areas, representing the brown-colored area and the surrounding halo, respectively. In H R P 10,16,22,24,23 and 14 the injection sites were restricted to the L G d , but in H R P 47, 15, 21 and 46 there were slight invasions of the injection into the ventral part. Although there was a possibility of involvement of the corticogeniculate cells which project to the ventral part of the geniculate nucleus, their contribution to the data could be assumed minimum. Sample photomicrographs of HRP-labeled cells in area 17 are shown in Fig. 1C, E, F and G. Cell F was in layer V whereas all others were in layer VI. Cell F is a typical pyramidal cell characterized by a long apical dendrite and several basal dendrites. Such clearly identified pyramidal cells were not u n c o m m o n among the labeled cells in layer V21,31. Like cells C, E and G, labeled cells in layer VI varied in soma shape:
HRP
10
21
16
f
46
circular, ovoid or triangular. However, they had structures suggestive of apical dendrites, so that they were judged to correspond to the small pyramidal cells identified in Golgi stainings 4.14.27.36. Cell C was in the upper part of layer VI, cell E in the intermediate one and cell G in the bottom. It was a general impression in layer VI that superficially located cells were slightly larger than those located deeply, as reported previously36. Soma areas of corticogeniculate cells. The distribution histograms of the soma area were compared between normal and unilaterally eye-enucleated rats of PND 1 (Fig. 5). The labeled cells in the upper half of layer VI (Via) and in its lower half (VIb) were treated separately. Fig. 5 clearly shows that soma areas of the corticogeniculate cells in layers V, Via and VIb are distributed in a larger range for P N D 1 rats than for normal ones. The enlargement of the soma area appears to be greater for layer VI cells than for layer V cells. An important finding here was that the enlargement of cell soma occurred in the C O N T R A as well as in the IPSI side. All the numerical data of the
22
47
15
14
Fig. 4. Schematic drawings of the extent of HRP injection within LGd and ventral geniculate nucleus in all subjects of Experiment II (see Table II). For each case the most heavily reacted section was selected for the drawing. Conventions are the same as in Fig. 2. Except for HRP 47 and 21, dense focuses of HRP injection were confined to the LGd.
20
CONTRA
PND 1
A
0
IP51
D
Layer V
TOO
200
300
B
0
100
200
300
E
Layer Vl
I
100
200
I
I
300
C
0
100
200
I
300
F
Lo.yer Vlb
I
% -- &O
--20
I
0
100
200
SOMA AREA (urn 2)
I
300
I
0
100
200
I
--0
300
SOMA AREA (j.im 2)
Fig. 5. Soma area histograms of corticogeniculate cells in area 17 for normal (white columns) and neonatally one-eye-enucleated rats, PND 1 (hatched columns). A, B and C: corticogeniculate cells of the side C O N T R A to the remaining eye (HRP 21). D, E and F: corticogeniculate cells of the side IPSI to the remaining eye (HRP 22). Note that on both sides cells in layer V, Via and Vlb are all significantly larger in neonatal enucleates than in normal rats. Mean soma area is indicated by open or closed triangles on the abscissa.
21 TABLE II Soma areas of HRP-labeled cortico-geniculate cells in layers V, Via and Vlb Experimental condition
Animal no.
Mean soma area _+S.D. (~m 2) (n) V
Normal Normal PND1 Contra Contra Ipsi Ipsi PND 3 Contra Contra Ipsi Ipsi
Via
Vlb
HRP 10 HRP 16
148+36 (217) 144_+25 (243)
87+ 17 (66) 80___12 (101)
HRP 21 HRP 46 HRP 22 HRP 47
176_+40 (149) 173+33 (112) 180+40 (126) 174_+34 (89)
121_+20 ( 4 0 ) 119_+16 (50) 114+23 (29) 101 +18 (39)
HRP 24 HRP 23 HRP 15 HRP 14
147-+27 (212) 134_+24 (108) 135+27 (256) 145_+29 (164)
98+22 (95) 91+17 (31) 82_+14 (34) 86-+16 (40)
soma area for P N D 1 and P N D 3 rats are summarized in Table II. The mean values of the data from the two normal rats ( H R P 10 and 16) were taken as controls. The percentage changes from the normal controls are shown in the rightmost column for each class of cells of P N D 1 and 3 rats. In P N D 1 rats, the enlargement of the cell soma in the C O N T R A side was attained to a similar degree to that seen in the IPSI side. A n o t h e r interesting point would be that layer VI cells were m o r e m a r k e d l y enlarged than layer V cells. A l t h o u g h changes in the soma area in P N D 3 rats varied from e x p e r i m e n t to e x p e r i m e n t , there was a consistent tendency that an e n l a r g e m e n t of soma area, if any, occurred preferentially in layer VI cells than in layer V cells ( H R P 15 is excepted from this rule). DISCUSSION The present study has shown that after neonatal monocular enucleation in rats plastic changes in soma size occur for the geniculate relay cells as well as for the corticogeniculate cells. With respect to the relay ceils, reduction in soma size occurred only for the IPSI L G d in P N D 1 rats and for both sides in P N D 3 and 6 rats. By contrast, a consistent increase in soma area was o b s e r v e d bilaterally for corticogeniculate cells in P N D 1 rats. In the following we will discuss two findings in turn. S o m a size o f geniculate relay cells
It is generally shown that cell growth in the central
% change from normal V
Via
Vlb
+ 20.4 + 18.5 + 23.4 + 19.5
+ 45.6 + 43.0 + 36.5 +21.6
+ 46.7 + 37.8 + 42.4 + 15,8
+ 0.7 --8.1 --7.7 --0.5
+ 17.0 + 9.5 --1.9 + 3.0
+ 11,0 + 2.0 --5.4 + 23.7
70+ 14 (120) 69+12 (59) 101_+22(89) 95+ 18 (86) 99_+23 (28) 80_+20 (38) 77_+17 (183) 71+10 (73) 65_+11 (76) 86+ 15 (45)
nervous system is maintained in part by the presence of synaptic inputs. Therefore, the decrease in soma size of geniculate relay cells contralateral to the enucleated eye, namely IPSI to the remaining eye, could be assumed as a result of retardation or arrest of cell growth due to deafferentation of the retinal projections. According to Karlsson 16, synaptogenesis in the rat L G d begins to develop a r o u n d P N D 3 and gradually increase towards P N D 15. Thus, in the neonatal period only a small n u m b e r of retinal axons m a k e synaptic contacts and hence, most of the relay cells are free from synaptic invasions. Correspondingly, dendritic expansions are still primitive at this stage and gradually increase towards P N D 16-1825,2s. Therefore, relay cells when deafferented at this stage naturally went into retardation in later developments. The question arises, however, why the decrease in soma area was more m o d e r a t e for P N D 1 rats than for P N D 3 and 6 rats. This could be explained if we recall the fact that when a unilateral eye-enucleation was p e r f o r m e d at P N D 1 the remaining retina reveals an ability to p r o d u c e a b e r r a n t IPSI projections, which ability gradually diminishes as postnatal days pass. Therefore, in rats unilaterally enucleated at P N D 1 the a b e r r a n t IPSI projection of the remaining eye can provide synaptic inputs to maintain cell growth in the deafferented or IPS1 L G d . A n o t h e r interesting finding was that the decrease in soma area also occurred for the relay cells in nondeafferented or C O N T R A L G d . This appears to be in parallel with the finding by H e a d o n et al. 9 for the
22 monkey LGd that after monocular closure at a late
There remains a question as to why the enlarge-
juvenile stage shrinkage in soma area occurred for
ment in soma size occurs for corticogeniculate cells in bilateral visual cortices. It seems likely that enlarge-
relay cells in both deprived and non-deprived laminae. They interpreted the soma size changes in the non-deprived lamina as a result of some interactions between cells in the neighboring laminae. However,
ment of IPS1 cells are related to their possible arborization of axonal terminals in the L G d so as to compensate for a reduction of retinal afferents on that
in the present study on the rat LGd, cell shrinkages in
side. On the other hand, a significant enlargement in
the deafferented and non-deafferented sites oc-
soma area found for C O N T R A cells could not be explained in the same way, since in the C O N T R A LGd
curred in different hemispheres, so that it is unrealistic to conceive of such interactions between relay cells in the two LGds. There must be more basic sys-
retinal afferents were less affected and soma sizes of
tematic control of cell growth in the two sides of the
balance the relay cell growth in the two LGds.
finding relevant to this issue was reported by Rhoades and Dellacroce2~, after neonatal monocular enucleation in hamsters the distribution of cells giving rise to callosal axons was expanded only for the
S o m a size o f c o r t i c o g e n i c u l a t e cells
C O N T R A visual cortex, and correspondingly the expansion of the distribution of callosal axon terminals
LGd. For example, some humoral factors may suppress the cell growth in non-deafferented site so as to
A significant increase in soma area was observed only for PND 1 rats and the increase was moderate or not apparent in PND 3 rats. This is quite contrary to the soma size changes of the geniculate relay cells. In the latter case, reduction in soma size was more conspicuous in PND 3 and 6 rats than in PND 1 rats. Such an asynchronous change in soma size for the LGd relay cells and corticogeniculate cells would suggest that the development of corticogeniculate cells in layer V and VI progress in a m a n n e r relatively independent of the growth of LGd relay cells in unilaterally eye-enucleated rats. This implication is consistent with recent studies which proved that in normal rats pyramidal cells in layers V and VI develop earlier than pyramidal and non-pyramidal cells in layer IV where most of the geniculocortical projections termi-
relay cells were in the normal range. A n interesting
was noticed only in the IPSI visual cortex. In our preliminary experiments the same was found true for rats unilaterally eye-enucleated on PND 1 (Yamanishi-Mitani and Fukuda, in preparation): the cortical cells projecting to the callosum showed larger soma area on the C O N T R A side, with expanded terminal arborizations on the IPSI side. If these callosally projecting cells with large somas in layers V and VI also send axons to the LGd by axonal bifurcation, they may be labeled with H R P injected into the CONT R A LGd. This can be tested by using a double-labeling method in future. On the other hand, it is also possible that some general trophic factors may function to balance the growth of corticogeniculate cells in two hemispheres.
natel,l~.24,26.
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5 Fukuda, Y. and Sugitani, M., Cortical projections of two types of principal cells of the rat lateral geniculate body, Brain Research, 67 (1974) 157-161. 6 Fukuda, Y., Sumitomo, 1., Sugitani, M. and lwama, K.. Distribution of fast and slow principal cells in the rat dorsal lateral geniculate nucleus. In M. Ito et al. (Eds.). Integrative Control Functions o f the Brain. Vol. IlL Kodansba, Tokyo/Elsevier, Amsterdam, 1980, pp. 72-78. 7 Godement, P., Saillour, P. and Imbert, M., Thalamic afferents to the visual cortex in congenitally anopthalmic mice, Neurosci. Lett.. 13 (1979)271-278. 8 Grossman, A., Lieberman, A. R. and Webster, K. E., A Golgi study of the rat dorsal lateral geniculate nucleus, J. comp. Neurol., 150 (1973) 441-466, 9 Headon, M. P., Sloper, J. J., Hiorns, R. W. and Powell, T.
23 P. S., Cell size changes in undeprived laminae of monkey lateral geniculate nucleus after monocular closure, Nature (Lond,), 281 (1979) 572-574. 10 Heumann, D. and Rabinowicz, Th., Postnatal development of the dorsal lateral geniculate nucleus in the normal and enucleated albino mouse, Exp. Brain Res., 38 (1980) 75-85. 11 Hsiao, C.-F. and Fukuda, Y., Plastic changes in the distribution and soma size of retinal ganglion cells after neonatal monocular enucleation in rats, Brain Research, 301 (1984) 1-12. 12 Hughes, H. C., Anatomical and neurobehavioral investigations concerning the thalamo-cortical organization of the rat's visual system, J. comp. Neurol., 175 (1977) 311-336. 13 Jacobson, S. and Trojanowski, J. Q., Corticothalamic neurons and thalamocortical terminal fields. An investigation in rat using horseradish peroxidase and autoradiography, Brain Research, 85 (1975) 385--401. 14 Juraska, J. M. and Fifkova, E., A Golgi study of the early postnatal development of the visual cortex of the hooded rat, J. comp. Neurol., 183 (1979) 247-256. 15 Kaiserman-Abramof, I. R., Graybiel, A. M. and Nauta, W. J. H., The thalamic projection to cortical area 17 in a congenitally anophthalmic mouse strain, Neurosciences, 5 (1980) 41-52. 16 Karlsson, U., Observations on the postnatal development of neuronal structures in the lateral geniculate nucleus of the rat by electron microscopy, J. Ultrastructure Res., 17 (1967) 158-175. 17 Karnovsky, M. J., A formaldehyde-glutaraldehyde fixative of high osmolarity for use in electronmicroscopy, J. Cell Biol., 27 (1965) 137A. 18 Kriebel, R. M., Neurons of the dorsal larteral geniculate nucleus of the albino rat, J. comp. Neurol., 159 (1975) 45-68. 19 Krieg, W. S,, Connections of the cerebral cortex. I. The albino rat. A topography of the cortical areas, J. comp. Neurol., 84 (1946) 221-275. 20 LeVay, S. and Ferster, D., Relay cell classes in the lateral geniculate nucleus of the cat and the effects of visual deprivation, J. comp. Neurol., 172 (1977) 563-584. 21 LeVere, T. E., The primary visual system of the rat: a primer of its anatomy, Physiol. Psychol., 6 (1978) 142-169. 22 Lund, J. S., Lund, R. D., Hendrikson, A. E., Bunt, A. H. and Fuchs, A. F.. The origin of efferent pathways from the primary visual cortex, area 17, of the macaque monkey as shown by retrograde transport of horseradish peroxidase, J. comp. NeuroL, 164 (1975) 287-304. 23 Lund, R. D., Cunningham, T. J. and Lund, J. S., Modified optic projections after unilateral eye removal in young rats, Brain Behav. Evol.. 8 (1973) 51-72.
24 Lund, R. D. and Mustari, M. J., Development of the geniculocortical pathway in rats, J. comp. Neurol., 173 (1977) 289-306. 25 Parnavelas, J. F., Bradford, R., Mounty, E. J. and Lieberman, A. R., Postnatal growth of neuronal perikarya in the dorsal lateral geniculate nucleus of the rat, Neurosci. Lett., 5 (1977) 33-37. 26 Parnavelas, J. G. and Lieberman, A. R.. An ultrastructural study of the maturation of neuronal somata in the visual cortex of the rat, Anat. EmbryoL, 157 (1979) 311-328. 27 Parnavelas. J. G., Lieberman, A. R. and Webster, K. E., Organization of neurons in the visual cortex, area 17, of the rat, J. Anat., 124 (1977) 305-322. 28 Parnavelas, J. G., Mounty, E. J.. Bradford, R. and Lieberman, A. R., The postnatal development of neurons in the dorsal lateral geniculate nucleus of the rat: a Golgi study, J. comp. NeuroL, 171 (1977) 481-500. 29 Rhoades, R. and Dellacroce, D. D., Neonatal enucleation induces an asymmetric pattern of visual callosal connections in hamsters, Brain Research, 202 (1980) 189-195. 30 Schober, W., Luth, H.-J. and Gruschka, H., Die Herkunft afferenter Axone im striaren Kortex der Albinoratte: Eine Studie mit Meerrettich-peroxidase, Z. mikrosk.-anat. Forsch., 90 (1976) 399-415. 31 Schober, W. and Winkelmann, E., Die geniculo-kortikale Projektion bei Albinoratten, J. Hirnforsch., 18 (1977) 1-20.
32 Sefton, J. A., Mackay-Sim, A., Baur, L. and Cottee, L. J., Cortical projections to visual centres in the rat: an HRP study. Brain Research, 215 (1981) 1-13. 33 Shirokawa, T., Fukuda, Y. and Sugimoto, T., Bilateral reorganization of rat optic tracts following enucleation of one eye at birth, Exp. Brain Res., 51 (1983) 172-178. 34 Venegas, H., Hollfinder, H. and Distel, H., Early stages of uptake and transport of horseradish-peroxidase by cortical structures, and its use for the study of local neurons and their processes, J. comp. NeuroL, 177 (1978) 193-212. 35 Vital-Durand, F,, Garey, L. J. and Blakemore, C., Monocular and binocular deprivation in the monkey: morphological effects and reversibility, Brain Research, 158 (1978) 45-64. 36 Werner, L., Hedlich, A., Winkelmann, E. und Brauer, K., Versuch einer Identifizierung von Nervenzellen des visuellen Kortex der Ratte nach Nissl- und Golgie-Kopschdarstellung, Z. Hirnforsch., 20 (1979) 121-139. 37 Werner, L. und Kruger, G.. Kwalitative und kwantitative Untersuchungen am Corpus geniculatum laterale (Cgl) der Laborratte. III. Differenzierung von Projektions und Interneuronen im Nissl-Prfiparat und deren Topographie, Z. mikrosk.-anat. Forsch., 87 (1973)701-729.
13
Elsevier BRE 10004
Bilateral Changes in Soma Size of Geniculate Relay Cells and Corticogeniculate Cells •After Neonatal Monocular Enucleation in Rats YUTAKA FUKUDA and CHIE-FANG HSIAO
Department of Neurophysiology, Institute of Higher Nervous Activity, Osaka University Medical School, Kita-ku, Osaka (Japan) (Accepted October 4th, 1983)
Key words: bilateral changes - - soma size - - geniculate relay cell - - corticogeniculate cell - - rat - - monocular enucleation
Soma areas of relay cells of the lateral geniculate nucleus and of corticogeniculate cells of normal rats (n = 4) were compared with those of neonatally unilaterally eye-enucleated adult rats (n = 13). These cells were labeled by retrogradely transported HRP. Monocular enucleation was performed on postnatal days 1 (PND 1) (n = 4), 3 (PND 3) (n = 5) and 6 (PND 6) (n = 4). The results are summarized as follows. (1) In PND 1 rats soma areas of relay cells were 12-16% smaller than those of normal rats, but only for the geniculate nucleus ipsilateral to the remaining eye. In PND 3 and 6 rats the areal shrinkage of relay cells was 27-39% of the normal control for both hemispheres, though it was less marked in the hemisphere contralateral to the remaining eye. (2) The corticogeniculate cells were distributed in layers V and VI in eye-enucleated rats as well as in normal rats. Soma areas of both layer V and VI cells increased in PND 1 rats for both hemispheres by about 15-47% of the normal control. In PND 3 rats increase in soma size tended to occur for layer VI cells, although the data varied from animal to animal• In summary, it was established that unilateral eye-enucleation in rats at birth induced soma size changes of the geniculate relay cells and of the corticogeniculate cells in the non-deafferented as well as in the deafferented hemisphere. Possible mechanisms for the bilateral changes in soma area of central visual cells after neonatal monocular enucleation are discussed. INTRODUCTION Studying retinogeniculate projections in neonatally unilaterally eye-enucleated rats, we reached the conclusion that after m o n o c u l a r enucleation some retinal ganglion cells of the remaining eye change their projection from the contralateral to the ipsilat-
relay cells and corticogeniculate cells labeled by means of a retrograde axonal flow of HRp3,13,20,22,30,32. The results show that unilateral eye-enucleation at an appropriate stage of the neonatal period caused characteristic soma
size changes in both hemi-
eral hemisphere u. In parallel with this, we have re-
spheres, a decrease in L G d relay cells and an increase in corticogeniculate cells.
cently shown that in these rats the total fiber count of the optic tract decreased on the side contralateral to
MATERIALS AND METHODS
the remaining eye, while it increased on the ipsilateral side 33. These findings led us to test whether or not neurons of the dorsal lateral geniculate nucleus (LGd) and of the visual cortex would also be involved in plastic changes following neonatal unilateral eye enucleation. In recent studies cell somas of various central visual nuclei have been reported to be modified after functional deafferentation or eye-enucleation 2,930~2°.35. Thus, the present experiment was designed to detect possible changes in soma size of L G d
A total of 17 adult albino rats (Wistar strain) of either sex, weighing 350--400 g, 3-5 months old, were used. Except for 4, all other rats u n d e r w e n t the monocular enucleation operation at postnatal days 1 (PND 1), 3 (PND 3) or 6 (PND 6). In the first series of experiments (Experiment I) an H R P injection was made into the primary visual cortex (area 17) contralateral ( C O N T R A ) or ipsilateral (IPSI) to the remaining eye; in the second series (Experiment II) it
Correspondence: Y. Fukuda, Department of Neurophysiology, Institute of Higher Nervous Activity, Osaka University Medical School, Nakanoshima 4-3-57, Kita-ku, Osaka, Japan. 0006-8993/84/$03.00© 1984 Elsevier Science Publishers B.V.
14 was made into the LGd of either side. In the following the laterality of the LGd and the visual cortex of unilaterally eye-enucleated rats is specified with reference to the remaining eye, i.e. the abbreviations IPSI and C O N T R A refer to ipsi- and contralateral to the remaining eye, respectively. The animals used and the laterality of the H R P injection site are listed in Tables I and II for Experiments I and II, respectively. (Note that the animals which received H R P injections into both sites are listed in both tables.) In either series of experiments two normal intact rats were similarly treated to provide the control data. The H R P injections were performed in the following way. Under Nembutal anesthesia (50 mg/kg, i.p.) the animals were placed in a stereotaxic head-holder. A solution of H R P (Sigma type VI, 40% in saline or Tris-HC1 buffer, pH 7.6) was ejected through micropipettes by applying currents of 5-10/~A in pulses of 7 s on, 7 s off for 20-25 min. The position of the electrode tip was checked in every experiment by monitoring physiological responses to single flash stimuli through the electrode. The coordinates for the LGd injection was 3.5 mm lateral from the midline and about 4.5 mm below the cortical surface as in the companion paper 11. For the visual cortical injection the electrode was placed in the center of area 17, 3 mm lateral to lambda 5,12,19. Except for H R P 27, 3 shots were made in each injection site, about 100 ~um apart rostro-caudally. The total volume of H R P solution ejected was about 0.3,ul. In H R P 27, many shots were made for the special purpose referred to in Resuits. After a survival period of 48 h, all H R P injected animals were deeply anesthetized with ether and perfused intracardially with Karnovsky's 17 fixative. Brains were removed and stored in the same fixative overnight at 4 °C and then rinsed for 48 h at 4 °C in 30% sucrose phosphate buffer. Frontal sections were made at 60/~m on a freezing microtome, reacted with D A B (3,3'-diaminobenzidine) and counterstained with 0.1% cresylviolet as described in the companion paperll. Preparations were scanned microscopically under bright- or dark-field illumination. For the areal measurements, each of the labeled cells was outlined by a drawing tube attached to a microscope with a final magnification of 840x, and the outline drawings were processed by a semiautomatic image analyzing system, AMS (Leiz). Tissue shrinkages were not cor-
rected for in the measurements of cell soma area. RESULTS
Experiment 1: geniculocortical projection Injection sites and labeled cells. As shown in Fig. 1A, the center of the H R P injection site was stained dark brown, being surrounded b y a light halo 34. It is apparent here that the area of the H R P injection was restricted within layers I-VI and did not expand into the white matter. The extent of the injection site varied from animal to animal as shown diagrammatically in Fig. 2. The dark brown areas and the surrounding halos are represented by the black and shaded areas, respectively. Except for the most medial shot in H R P 27 and two shots in H R P 43, the center of the injection was always within the gray matter. In each diagram the medial and lateral borders of area 17 are indicated. Except for H R P 42 and 7 where the injection sites extended medially into area 18a 19, the focus of the injection was localized within area 17. In no case did the injection extend into area 18, lateral to area 1712,19. Thus with a few exceptions the labeled cells in the LGd are assumed to be relay cells projecting to area 17. Sample photomicrographs of HRP-labeled cells in LGd are presented in Fig. 1B and D. Cell B was located in the dorsolateral border of the nucleus next to the optic tract fibers running from the lower right to the upper left in this photograph and characterized by two vertically oriented dendrites. In a more central part of the nucleus the labeled cells appeared like cell D. Usually two or three dendrites emanated from a tri- or quadrangular soma s-l~. Soma areas of relay cells. The distributions of the soma area of HRP-labeled relay cell in the LGd of normal rats were compared with those of neonatally enucleated rats (Table I, Fig. 3). In Fig. 3 are shown typical histograms of the cell soma area for two normal ( H R P 8 and 27), two PND 1 ( H R P 22 and 21), two PND 3 ( H R P 24 and 7) and two PND 6 ( H R P 25 and 26) rats. Inset figures in each histogram show distributions of labeled cells within the LGd. In H R P 27 (Fig. 3B) of diffusely distributed labeled cells only those situated within the central area of the nucleus (the area excepted from blackening) were subject to soma area measurements. In this case we intended to label as many relay cells as possible by making many
15
A
Fig. 1. Photomicrographs of injection site, retrogradely labeled geniculate relay cells and corticogeniculate cells. A: injection site was localized within IPSI area 17 of neonatally enucleated rat (HRP 21). Note that two dense focuses of H R P injection with a surrounding halo were restricted within the gray matter. The superior colliculus below the HRP-injected cortex was somewhat shrunken, indicating that this side is contralateral to the enucleated eye. Horizontal bar, 1 mm. Preparations underwent reactions with D A B and were counterstained with 0.1% cresylviolet. B and D: labeled geniculate relay cells. C and F: labeled corticogeniculate cells in layer V of area 17. E and G: labeled corticogeniculate cells in layer VI of area 17. Horizontal bar in B-F, 20 ~m.
16
HRP 9?
HRP
22
21
4?
46
94
?
95
26
49
43
Fig. 2. Schematic drawings of extent of H R P injections in all subjects of Experiment I (see Table I). Dense focuses of H R P granulations are represented by black and the surrounding halo by shading. In every drawing the medial and lateral borders of area 17 are indicated. Except for H R P 27 and 43, injections were localized within the gray matter, not extending into the white matter. In H R P 7 and 42 the injection extended into area 18.
17
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18 TABLE
I
Soma areas of HRP-labeled relay cells in the LGd Experimental condition
Animal No.
Mean soma area ± S.D. #~m21
(n)
% Change from normal and significance level
Normal Normal PND 1 Contra Contra Ipsi Ipsi PND 3 Contra lpsi PND 6 Contra Contra Ipsi Ipsi
HRP 8 HRP 27
159 ± 49 167 ± 29
(239) (1701
HRP 22 HRP47 HRP 21 HRP46
164 +_55 173 _+48 138 _+36 144 + 38
(2(19) (132) (132) (99)
+ 11.9 + 6.3 --15.5 --11.7
n.s. P < I).(12 P < 0.1101 P < 0.001
HRP 24 HRP 7
115 _+23 99 ± 31
(235) (93)
--29.5 --39.4
P < 0.1101 P < (1.001
HRP 25 HRP 42 HRP 26 HRP 43
118 ± 25 120 + 25 102 _+31 1117+ 29
(193) (166) (166) (146)
--27.7 --26.5 --37.4 --34.2
P P P P
< < < <
0.01)l 0.001 0.001 0.(1111
shots within area 17 (see Fig. 2). In all other cases the injection was limited to a small cortical area and hence labeled relay cells were localized in a relatively small region. It is worth noting that in the IPSI hemisphere of PND 1 rats and in both hemispheres of PND 3 and 6 rats, the labeled relay cells are more densely packed within a narrow region than in normal rats or in the C O N T R A hemisphere of the PND 1 rat (compare Fig. 3 D - H with Fig. 3 A - C ) . This
gradely labeled relay cells only those located in the
may just reflect an immature development of dendrites and a consequent shrinkage of the nucleus itself. It is also worth noting that even though the IPSI
the C O N T R A LGd did not significantly differ from that in the normal control, while the mean soma area on the IPSI side was 12-16% less than that in the nor-
LGd had shrunken, each part of it sent a projection to the visual cortex, keeping the same topographic relation as seen in normal rats. This appears to parallel several reports on congenital anophthalmic mice in which a clear topographical projection from the LGd to the visual cortex is preserved 7,~. In PND 1 rats the soma areas of relay cells are slightly smaller than in normal rats, but only for the deafferented or IPSI LGd (Fig. 3 A - D ) . However, in PND 3 and 6 rats this was seen in bilateral LGds (Fig. 3 E - H ) . The mean soma areas obtained from normal and unilaterally eye-enucleated rats are summarized in Table I. The soma size of relay cells may differ according to the locations within the nucleus 6,8.18.37. To minimize a possible bias in the normal control data due to this, many injections were made in one normal rat (HRP 27) into area 17. and of retro-
mal control. In PND 3 and 6 rats, the 1PSI and CONT R A cells were 34-39% and 27-30% smaller in soma area than those in the normal rats, respectively. Thus, the soma area of the geniculate relay cells are consistently smaller on the IPSI side than on the C O N T R A side. A n o t h e r important finding is that when eye enucleation was done at PND 1 the decrease in soma size of the relay cell was relatively mild on the IPSI side, while it showed no significant changes on the C O N T R A side. Especially of interest was the finding that in the rats enucleated at PND 3 and 6 the decrease in soma size also occurred for the C O N T R A (non-deafferented) side.
central part of the LGd were selected for soma area measurements so as to supplement the control data in H R P 8, in which labeled cells were localized in the mid-dorsal LGd. In Table I, the mean of the soma areas in H R P 8 and 27 was taken as the normal control and percent changes from this are listed in the rightmost column, together with the significance level. In PND 1 rats, the mean soma area of relay cells in
E x p e r i m e n t II: corticogeniculate projection Injection sites and labeled cells. Sample photographs of the HRP injection sites are shown in
19 Fig. 1A of the companion paper 11. As is the case with the injection into the visual cortex, the center appeared as a dark brown area surrounded by a light halo. In Fig. 4 the exent of the injection in each rat is shown by the black and shaded areas, representing the brown-colored area and the surrounding halo, respectively. In H R P 10,16,22,24,23 and 14 the injection sites were restricted to the L G d , but in H R P 47, 15, 21 and 46 there were slight invasions of the injection into the ventral part. Although there was a possibility of involvement of the corticogeniculate cells which project to the ventral part of the geniculate nucleus, their contribution to the data could be assumed minimum. Sample photomicrographs of HRP-labeled cells in area 17 are shown in Fig. 1C, E, F and G. Cell F was in layer V whereas all others were in layer VI. Cell F is a typical pyramidal cell characterized by a long apical dendrite and several basal dendrites. Such clearly identified pyramidal cells were not u n c o m m o n among the labeled cells in layer V21,31. Like cells C, E and G, labeled cells in layer VI varied in soma shape:
HRP
10
21
16
f
46
circular, ovoid or triangular. However, they had structures suggestive of apical dendrites, so that they were judged to correspond to the small pyramidal cells identified in Golgi stainings 4.14.27.36. Cell C was in the upper part of layer VI, cell E in the intermediate one and cell G in the bottom. It was a general impression in layer VI that superficially located cells were slightly larger than those located deeply, as reported previously36. Soma areas of corticogeniculate cells. The distribution histograms of the soma area were compared between normal and unilaterally eye-enucleated rats of PND 1 (Fig. 5). The labeled cells in the upper half of layer VI (Via) and in its lower half (VIb) were treated separately. Fig. 5 clearly shows that soma areas of the corticogeniculate cells in layers V, Via and VIb are distributed in a larger range for P N D 1 rats than for normal ones. The enlargement of the soma area appears to be greater for layer VI cells than for layer V cells. An important finding here was that the enlargement of cell soma occurred in the C O N T R A as well as in the IPSI side. All the numerical data of the
22
47
15
14
Fig. 4. Schematic drawings of the extent of HRP injection within LGd and ventral geniculate nucleus in all subjects of Experiment II (see Table II). For each case the most heavily reacted section was selected for the drawing. Conventions are the same as in Fig. 2. Except for HRP 47 and 21, dense focuses of HRP injection were confined to the LGd.
20
CONTRA
PND 1
A
0
IP51
D
Layer V
TOO
200
300
B
0
100
200
300
E
Layer Vl
I
100
200
I
I
300
C
0
100
200
I
300
F
Lo.yer Vlb
I
% -- &O
--20
I
0
100
200
SOMA AREA (urn 2)
I
300
I
0
100
200
I
--0
300
SOMA AREA (j.im 2)
Fig. 5. Soma area histograms of corticogeniculate cells in area 17 for normal (white columns) and neonatally one-eye-enucleated rats, PND 1 (hatched columns). A, B and C: corticogeniculate cells of the side C O N T R A to the remaining eye (HRP 21). D, E and F: corticogeniculate cells of the side IPSI to the remaining eye (HRP 22). Note that on both sides cells in layer V, Via and Vlb are all significantly larger in neonatal enucleates than in normal rats. Mean soma area is indicated by open or closed triangles on the abscissa.
21 TABLE II Soma areas of HRP-labeled cortico-geniculate cells in layers V, Via and Vlb Experimental condition
Animal no.
Mean soma area _+S.D. (~m 2) (n) V
Normal Normal PND1 Contra Contra Ipsi Ipsi PND 3 Contra Contra Ipsi Ipsi
Via
Vlb
HRP 10 HRP 16
148+36 (217) 144_+25 (243)
87+ 17 (66) 80___12 (101)
HRP 21 HRP 46 HRP 22 HRP 47
176_+40 (149) 173+33 (112) 180+40 (126) 174_+34 (89)
121_+20 ( 4 0 ) 119_+16 (50) 114+23 (29) 101 +18 (39)
HRP 24 HRP 23 HRP 15 HRP 14
147-+27 (212) 134_+24 (108) 135+27 (256) 145_+29 (164)
98+22 (95) 91+17 (31) 82_+14 (34) 86-+16 (40)
soma area for P N D 1 and P N D 3 rats are summarized in Table II. The mean values of the data from the two normal rats ( H R P 10 and 16) were taken as controls. The percentage changes from the normal controls are shown in the rightmost column for each class of cells of P N D 1 and 3 rats. In P N D 1 rats, the enlargement of the cell soma in the C O N T R A side was attained to a similar degree to that seen in the IPSI side. A n o t h e r interesting point would be that layer VI cells were m o r e m a r k e d l y enlarged than layer V cells. A l t h o u g h changes in the soma area in P N D 3 rats varied from e x p e r i m e n t to e x p e r i m e n t , there was a consistent tendency that an e n l a r g e m e n t of soma area, if any, occurred preferentially in layer VI cells than in layer V cells ( H R P 15 is excepted from this rule). DISCUSSION The present study has shown that after neonatal monocular enucleation in rats plastic changes in soma size occur for the geniculate relay cells as well as for the corticogeniculate cells. With respect to the relay ceils, reduction in soma size occurred only for the IPSI L G d in P N D 1 rats and for both sides in P N D 3 and 6 rats. By contrast, a consistent increase in soma area was o b s e r v e d bilaterally for corticogeniculate cells in P N D 1 rats. In the following we will discuss two findings in turn. S o m a size o f geniculate relay cells
It is generally shown that cell growth in the central
% change from normal V
Via
Vlb
+ 20.4 + 18.5 + 23.4 + 19.5
+ 45.6 + 43.0 + 36.5 +21.6
+ 46.7 + 37.8 + 42.4 + 15,8
+ 0.7 --8.1 --7.7 --0.5
+ 17.0 + 9.5 --1.9 + 3.0
+ 11,0 + 2.0 --5.4 + 23.7
70+ 14 (120) 69+12 (59) 101_+22(89) 95+ 18 (86) 99_+23 (28) 80_+20 (38) 77_+17 (183) 71+10 (73) 65_+11 (76) 86+ 15 (45)
nervous system is maintained in part by the presence of synaptic inputs. Therefore, the decrease in soma size of geniculate relay cells contralateral to the enucleated eye, namely IPSI to the remaining eye, could be assumed as a result of retardation or arrest of cell growth due to deafferentation of the retinal projections. According to Karlsson 16, synaptogenesis in the rat L G d begins to develop a r o u n d P N D 3 and gradually increase towards P N D 15. Thus, in the neonatal period only a small n u m b e r of retinal axons m a k e synaptic contacts and hence, most of the relay cells are free from synaptic invasions. Correspondingly, dendritic expansions are still primitive at this stage and gradually increase towards P N D 16-1825,2s. Therefore, relay cells when deafferented at this stage naturally went into retardation in later developments. The question arises, however, why the decrease in soma area was more m o d e r a t e for P N D 1 rats than for P N D 3 and 6 rats. This could be explained if we recall the fact that when a unilateral eye-enucleation was p e r f o r m e d at P N D 1 the remaining retina reveals an ability to p r o d u c e a b e r r a n t IPSI projections, which ability gradually diminishes as postnatal days pass. Therefore, in rats unilaterally enucleated at P N D 1 the a b e r r a n t IPSI projection of the remaining eye can provide synaptic inputs to maintain cell growth in the deafferented or IPS1 L G d . A n o t h e r interesting finding was that the decrease in soma area also occurred for the relay cells in nondeafferented or C O N T R A L G d . This appears to be in parallel with the finding by H e a d o n et al. 9 for the
22 monkey LGd that after monocular closure at a late
There remains a question as to why the enlarge-
juvenile stage shrinkage in soma area occurred for
ment in soma size occurs for corticogeniculate cells in bilateral visual cortices. It seems likely that enlarge-
relay cells in both deprived and non-deprived laminae. They interpreted the soma size changes in the non-deprived lamina as a result of some interactions between cells in the neighboring laminae. However,
ment of IPS1 cells are related to their possible arborization of axonal terminals in the L G d so as to compensate for a reduction of retinal afferents on that
in the present study on the rat LGd, cell shrinkages in
side. On the other hand, a significant enlargement in
the deafferented and non-deafferented sites oc-
soma area found for C O N T R A cells could not be explained in the same way, since in the C O N T R A LGd
curred in different hemispheres, so that it is unrealistic to conceive of such interactions between relay cells in the two LGds. There must be more basic sys-
retinal afferents were less affected and soma sizes of
tematic control of cell growth in the two sides of the
balance the relay cell growth in the two LGds.
finding relevant to this issue was reported by Rhoades and Dellacroce2~, after neonatal monocular enucleation in hamsters the distribution of cells giving rise to callosal axons was expanded only for the
S o m a size o f c o r t i c o g e n i c u l a t e cells
C O N T R A visual cortex, and correspondingly the expansion of the distribution of callosal axon terminals
LGd. For example, some humoral factors may suppress the cell growth in non-deafferented site so as to
A significant increase in soma area was observed only for PND 1 rats and the increase was moderate or not apparent in PND 3 rats. This is quite contrary to the soma size changes of the geniculate relay cells. In the latter case, reduction in soma size was more conspicuous in PND 3 and 6 rats than in PND 1 rats. Such an asynchronous change in soma size for the LGd relay cells and corticogeniculate cells would suggest that the development of corticogeniculate cells in layer V and VI progress in a m a n n e r relatively independent of the growth of LGd relay cells in unilaterally eye-enucleated rats. This implication is consistent with recent studies which proved that in normal rats pyramidal cells in layers V and VI develop earlier than pyramidal and non-pyramidal cells in layer IV where most of the geniculocortical projections termi-
relay cells were in the normal range. A n interesting
was noticed only in the IPSI visual cortex. In our preliminary experiments the same was found true for rats unilaterally eye-enucleated on PND 1 (Yamanishi-Mitani and Fukuda, in preparation): the cortical cells projecting to the callosum showed larger soma area on the C O N T R A side, with expanded terminal arborizations on the IPSI side. If these callosally projecting cells with large somas in layers V and VI also send axons to the LGd by axonal bifurcation, they may be labeled with H R P injected into the CONT R A LGd. This can be tested by using a double-labeling method in future. On the other hand, it is also possible that some general trophic factors may function to balance the growth of corticogeniculate cells in two hemispheres.
natel,l~.24,26.
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