456
Brain Research, 92 (1975) 456~-61 © Elsewer Scientific Pubhshmg Company, Amsterdam - Printed m The Netherlands
Certain connections of the visual cortex of the monkey shown by the use of horseradish peroxidase
D. A. WINFIELD, K. C GATTER ANDT. P. S. POWELL Department of Human Anatomy, South Parks Road, OxJord OXI 3QX (Great Br:tam)
(Accepted Aprd 1st, 19751
The use of the enzyme horseradish peroxldase (HRP) for determining the cells of origin of fibre pathways in the CNS has already proved to be a valuable new technique 13. In a study of the connections of the visual cortex of the rhesus monkey with this method, marked differences in the abdity to trace the different connections have become apparent and these observations agree closely with those made in the same functional area of another primate brain 2°. The experiments have, however, provided evidence for extrageniculate thalamocortIcal projections to the visual cortex. In 7 monkeys HRP was injected into the cortex of area 17, the perJstriate area or the boundary region between them. H R P (Sigma VI) was made up in concentrations of 20 or 30 % and injected with a 1 #1 Hamilton syringe electrically driven. The visual cortex of one hemisphere was exposed under sterile conditions. In each brain 6-10 injections were made and they were separated from each other by approximately 2 mm; 0.2/zl of enzyme was injected at each site over a period of 20 mln and the needle was left in situ for a further 10 min before withdrawal. The animals were allowed to survive for periods of 2-5 days and were then perfused with buffered saline and a mixture of 3~,', paraformaldehyde and 1°,, glutaraldehyde. The brains were removed a few hours later and immersed in the same fixative for periods of up to 24 h. Blocks were cut of the occipital lobes of both hemispheres, and of the entire anteroposterlor extent of the d~encephalon and basal ganglia. They were immersed in 30 ~,, buffered sucrose until they had completely sunk. Frozen sections were cut at 40/~m and several 1.20 series were taken and processed according to the method of Graham and Karnovsky 8 with dlamlnobenzldine and hydrogen peroxide. Some series were lightly counterstamed with cresyl violet while others were left unstained for dark-field examination. In 2 brains the enzyme was found to be restricted to area 17 on the dorsolateral surface of the hemisphere; in one brain it was in the cortex of area 17 close to the boundary with area 18 and in 4 It involved the external edge of area 17 together wlth that of area 18 in the posterior wall of the lunate sulcus. The sites of injection were easily recogmzed by the characteristic brown staining reaction (Fig. 2) and the in-
457
aU, Flg. 1. The site of injections of HRP into the visual cortex and the distribution of the labelled cells (solid black) m experiment 231, in the basal nucleus (B), in the lateral geniculate nucleus (LG) and in the inferior and lateral parts of the pulvinar (Pi, PI) respectively. Medial nucleus (M), ventrolateral nucleus (VL), ventral posterior nucleus (VP), putamen (Put), habenular nuclei (H), lateroposterJor nucleus (LP), suprageniculate nucleus (SG), medial genlculate nucleus (MG), oral and medial part3 of the pulvinar (Po and Pm), superior colliculus (SC).
dlvidual injections had usually become one confluent area extending through the depth of the cortex. At the injection sites and their margins numerous neurones were seen to be filled homogeneously with brown reaction product, whereas up to a few millimetres away fewer neurones distributed throughout the depth of the cortex were seen, with the enzyme clearly localized in the form of granules within the cell cytoplasm. The extent and distribution of these granule-containing cells agree closely with the horizontal extent of intrinsic fibre connections determined by other techniques 6. In the cortex and underlying white matter numerous lightly stained fibres were seen. In the lateral geniculate nucleus of all brains there has been a well defined band of labelled cells throughout all laminae in the caudal third of its anteroposterior extent (Figs. 1, 3 and 4). Within the affected area almost all of the neurones contained numerous small brown granules distributed throughout their cytoplasm (Fig. 7), and under dark-field illumination the granules glowed brightly. Away from the area of maximum labelling the number of labelled cells rapidly becomes smaller and the concentrations of granules within them diminishes. The site of the affected band in the lateral geniculate varies in its medio-lateral position m different experiments, depending upon the site of injection, and the distribution is in close agreement with what is already known of the organization of the geniculo-cortical projection 17. Thus after an injection, at approximately the middle of the exposed lateral surface of area 17, the band of labelled cells occupies the middle of the medio-lateral extent of the lateral
i
Oo
459 geniculate nucleus. As the injection site is moved towards the superomedial part of the lunate sulcus the labelled band of cells comes to occupy progressively more medial portions of the laminae of the lateral geniculate nucleus. The intensity of the labelling in the cells did not appear to vary within the range of survival period used within the experiments. In 4 of the experiments labelled cells were also found in the pulvinar. In each of these 4 experiments the enzyme had either been injected or had diffused into varying extents of that part of the peristriate cortex adjoining area 17 and occupying the posterior wall of the lunate sulcus (Fig. 2). In the sections of the thalamus containing the most caudal parts of the lateral geniculate nucleus labelled cells were also found in the neighbouring inferior part of the pulvinar (Fig. 1). More caudally the band of labelled neurones in the inferior part of the pulvinar became continuous with a similarly labelled group of cells in the more dorsally situated pars lateralis. The appearance of the cells was similar to those in the lateral geniculate nucleus and within the affected region the majority of cells again appeared to take up the enzyme (Fig. 6). In two of the brains there were well defined groups of cells in both the inferior and lateral parts of the pulvinar, but in the other two unequivocal labelling was seen only in the inferior part. The extent of involvement of the pulvinar could be correlated with the degree to which penstriate cortex was injected in an antero-postenor direction, and it usually took the form of a narrow band which was continuous, anteriorly and medially, with that in the geniculate and caudally it became progressively more dorsally situated. In the caudal part of the basal nucleus 1°, which is situated inferior to most of the antero-posterior extent of the globus pallidus, but more posteriorly sweeps dorsally to lie between the globus pallidus and putamen, there are several cells which have taken up H R P enzyme in the form of granules (Fig. 1). The cells are large and contain numerous granules like those in the thalamic nuclei (Fig. 5). The cortex at the boundary of areas 17 and 18 and the rest of the peristriate cortex of the side opposite to that of the injection was examined for the presence of labelled cells of origin of commissural fibres. In two brains only were cells found with unequivocal brown granules of reaction product. These were found in the experiments in which most of the cortex of the posterior wall of the lunate sulcus had been filled with HRP. The occipital lobe of the normal side had been cut sagittally and the labelled cells formed restricted groups: in the deep part of layer III close to the fundus of the lunate sulcus, in a site known to receive commissural fibres 21, and at the boundary of
F~g. 2. Site of injection of HRP into the cortex of area 18 and the boundary of 17-18 in a saglttal section of the brain in experiment 231. This section and those of the succeeding photographs have been lightly counterstained with cresyl violet. × 12. Fig. 3. Coronal section of the lateral geniculate nucleus of the same brain to show the band of labelled cells m the medial parts of all 6 laminae. × 25. Fig. 4. The band of labelled cells in the 6 laminae of the lateral geniculate nucleus at higher magnification. Note that the medial margin of the nucleus is to the left in this figure, in contrast to that in Fig. 3. × 100. Fig. 5. Two labelled cells m the basal nucleus. × 750. Fig. 6. Three labelled cells from the inferior pulvlnar. × 1200. Fig. 7. Labelled cells in the magnocellular layer of the lateral geniculate nucleus. × 900.
460 areas 17 and 18, including the large cells in layer 111, characteristic of this junctional region and for which there is evidence for their being the origin of commissural fibres 7,20. The finding of undoubted granules of reaction product m cells m the lateral geniculate nucleus, after injection of H R P into the vzsual cortex, is not surprising and the presence of such cells in a band through all cell laminae and the distribution within the gemculate correlated well with the site of rejection and what is known of the orgamzatlon of the gemculo-calcarlne projection. The amount of reaction product in individual cells, however, was more than we have seen m any other sate and examination of the sections under high magnification indicated that a very high proportion of the neurones within the affected zone contained granules, an observation which is confirmed in a parallel EM study 19. The intense labelhng of cells m the lateral geniculate nucleus stands m contrast to the difficulty in labelhng the cells of origin of the commissural fibres from the opposite hemisphere. Our expeNence has been similar to that of Wong-Riley e° working m the sqmrrel monkey, for although she found some cells labelled at the boundary between areas 17 and 18, she emphasized the weakness of the staining. Some of the possible reasons for the differences In uptake and transport of the enzyme have already been discussed 11,15. The presence of labelled cells m the inferior and lateral parts of the pulvinar 12 m 4 brains ~s of interest m view of the recent statement lo that 'other inputs to area 18 in the monkey, for example from thalamus outside the geniculate, are at present conjectural'. The precise projection of these cells has not been established m these experiments, but no labelled cells were found m the pulvinar in which the injection site was limited to area 17 and the number of labelled cells in the pulwnar increased progressively w~th the extent of peristrmte cortex injected. It should be emphasized that the absence of labelled cells in the pulvinar after injection of area 17 only cannot be interpreted as excluding a projection from the pulwnar to strmte cortex. The d~strlbution of labelled cells m the pulvinar is very szmilar to that of the retrograde cell degeneration after a lesion of the penstriate cortex in a site overlapping those of our mject~ons t4. The site of the labelled cells fits closely the posihon that one would have expected on the bas~s of the retinotopic orgamzation at the 17/18 boundary and m the inferior pulvinar of the owl-monkey 1. These parts of the pulvinar have been shown to receive fibres2,9, TM from the visual cortex and there is ewdence for a projection to them from the retina 3. Further, after a large lesion in the pulvmar fibre degeneration has been found in the per~strmte cortex a. The significance of the labelling in the caudal part of the basal nucleus is uncertain, but a projection from this nucleus to extensive areas of the neocortex has been shown by Divac 5, Kievit and Kuypers 12 and other unpublished experiments in this laboratory. This work was supported by grants from the Science Research Councd and the Wellcome Trust.
461 1 ALLMAN, J. M., KAAS, J. H., LANE, R. H., AND MEIZEN, F. M., A representation of the visual field in the inferior nucleus of the pulvinar in the owl monkey (Aotus trivtrgatus), Brain Research, 40 (1972) 291-302. 2 CAMPOS-ORTEGA,J. A., AND HAYHOW, W. R., On the organization o f t b e visual cortical projection to the pulvinar in Macaca mulatta, Brain Behav. Evolut., 6 (1972) 394-423. 3 CAMPOS-ORTEGA,J. A., HAYHOW, W. R., AND CLOVER, P. F. DEV., A note on the problem of retinal projections to the inferior pulvinar nucleus of primates, Brain Behav. Evolut., 3 (1970) 368-414. 4 CRAGG, B. G., AND AXNSWORTH, A., The topography of the afferent projections in the clrcumstriate visual cortex of the monkey studied by the Nauta method, Vision Res., 9 (1969) 733-747. 5 DtVAC, I., Magnocellular nuclei of the basal forebraln project to neocortex, brain stem and olfactory bulb. Review of some functional correlates, Brain Research, 93 (1975) 385-398. 6 FISKEN, R . A . , GAREY, L.J., AND POWELL, T. P. S., Patterns of degeneration after intrinsic lesions of the visual cortex (area 17) of the monkey, Brain Research, 53 (1973) 208-213. 7 GLICKSTEIN, M., AND WHITTERIDGE, D., Degeneration of layer III pyramidal cells in area 18 following destruction of callosal input, Anat. Rec., 178 (1974) 362-363. 8 GRAHAM,R. C., AND KARNOVSKY, M. J., The early stages of absorption of injected horseradish peroxidase in the proximal tubules of mouse kidney: ultrastructural cytochemistry by a new technique, J. Htstochem. Cytochem., 14 (1966) 291-302. 9 HOLL.~NDER, H., Projections from the striate cortex to the diencephalon in the squirrel monkey (Saimirt sciurus). A hght microscopic radioautographic study following lntracortical injection of H'~-leucine, J. comp. Neurol., 155 (1974) 425440. 10 HUBEL, O. H., AND WIESEL, T. N., Sequence regularity and geometry of orientation columns in the monkey striate cortex, J. comp. Neurol., 158 (1974) 267-294. 11 JONES, E. G., Possible determinants of the degree of retrograde neuronal labeling with horseradish peroxidase, Brain Research, 85 (1975) 249-253. 12 KIEVIT, J., AND KUYPERS, H. G. J. M., Subcortical afferents to the frontal lobe in the rhesus monkey studied by means of retrograde horseradish peroxidase transport, Brain Research, 85 (1975) 261-266. 13 LAVAIL, J . H . , WINSTON, K . R . , AND TISH, A., A method based on retrograde lntra-axonal transport of protein for identification of cell bodies of origin of axons terminating in the CNS, Brain Research, 58 (1973) 470-477. 14 LEGROS CLARK, W. E., AND NORTHFIELD, D. W. C., The cortical projection of the pulvinar in the macaque monkey, Brain, 60 (1937) 126-142. 15 NAUTA, H. J. W., 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. 16 OLSZEWSKY,J., The Thalamus of the Macaca mulatta, Karger, New York, 1952. 17 POLIAK, S., The Main Afferent Fiber Systems of the Cerebral Cortex in Primates, University of California Press, Beikeley, Calif., 1932. 18 SPATZ, W. B., AND ERDMANN, G., Strlate cortex prolections to the lateral genlculate and other thalamic nuclei: a study using degeneration and autoradlographic tracing methods in the marmoset callithrix, Brain Research, 82 (1974) 91-108. 19 WINFIELD,D. A., GATTER, K. C., AND POWELL, T. P. S., An electron microscopic study of retrograde and orthograde transport of horseradish peroxidase to the lateral geniculate nucleus of the monkey, Brain Research, 92 (1975) 462-467. 20 WONG-RILEY, M. T. T., Demonstration of gentculocortlcal and callosal projection neurons in the squirrel monkey by means of retrograde axonal transport of horseradish peroxidase, Brain Research, 79 0974) 267-272. 21 ZEKI, S. M., Interbemlspberic connections of prestriate cortex in monkey, Brain Research, 19 (1970) 63-75.
Brain Research, 92 (1975) 456~-61 © Elsewer Scientific Pubhshmg Company, Amsterdam - Printed m The Netherlands
Certain connections of the visual cortex of the monkey shown by the use of horseradish peroxidase
D. A. WINFIELD, K. C GATTER ANDT. P. S. POWELL Department of Human Anatomy, South Parks Road, OxJord OXI 3QX (Great Br:tam)
(Accepted Aprd 1st, 19751
The use of the enzyme horseradish peroxldase (HRP) for determining the cells of origin of fibre pathways in the CNS has already proved to be a valuable new technique 13. In a study of the connections of the visual cortex of the rhesus monkey with this method, marked differences in the abdity to trace the different connections have become apparent and these observations agree closely with those made in the same functional area of another primate brain 2°. The experiments have, however, provided evidence for extrageniculate thalamocortIcal projections to the visual cortex. In 7 monkeys HRP was injected into the cortex of area 17, the perJstriate area or the boundary region between them. H R P (Sigma VI) was made up in concentrations of 20 or 30 % and injected with a 1 #1 Hamilton syringe electrically driven. The visual cortex of one hemisphere was exposed under sterile conditions. In each brain 6-10 injections were made and they were separated from each other by approximately 2 mm; 0.2/zl of enzyme was injected at each site over a period of 20 mln and the needle was left in situ for a further 10 min before withdrawal. The animals were allowed to survive for periods of 2-5 days and were then perfused with buffered saline and a mixture of 3~,', paraformaldehyde and 1°,, glutaraldehyde. The brains were removed a few hours later and immersed in the same fixative for periods of up to 24 h. Blocks were cut of the occipital lobes of both hemispheres, and of the entire anteroposterlor extent of the d~encephalon and basal ganglia. They were immersed in 30 ~,, buffered sucrose until they had completely sunk. Frozen sections were cut at 40/~m and several 1.20 series were taken and processed according to the method of Graham and Karnovsky 8 with dlamlnobenzldine and hydrogen peroxide. Some series were lightly counterstamed with cresyl violet while others were left unstained for dark-field examination. In 2 brains the enzyme was found to be restricted to area 17 on the dorsolateral surface of the hemisphere; in one brain it was in the cortex of area 17 close to the boundary with area 18 and in 4 It involved the external edge of area 17 together wlth that of area 18 in the posterior wall of the lunate sulcus. The sites of injection were easily recogmzed by the characteristic brown staining reaction (Fig. 2) and the in-
457
aU, Flg. 1. The site of injections of HRP into the visual cortex and the distribution of the labelled cells (solid black) m experiment 231, in the basal nucleus (B), in the lateral geniculate nucleus (LG) and in the inferior and lateral parts of the pulvinar (Pi, PI) respectively. Medial nucleus (M), ventrolateral nucleus (VL), ventral posterior nucleus (VP), putamen (Put), habenular nuclei (H), lateroposterJor nucleus (LP), suprageniculate nucleus (SG), medial genlculate nucleus (MG), oral and medial part3 of the pulvinar (Po and Pm), superior colliculus (SC).
dlvidual injections had usually become one confluent area extending through the depth of the cortex. At the injection sites and their margins numerous neurones were seen to be filled homogeneously with brown reaction product, whereas up to a few millimetres away fewer neurones distributed throughout the depth of the cortex were seen, with the enzyme clearly localized in the form of granules within the cell cytoplasm. The extent and distribution of these granule-containing cells agree closely with the horizontal extent of intrinsic fibre connections determined by other techniques 6. In the cortex and underlying white matter numerous lightly stained fibres were seen. In the lateral geniculate nucleus of all brains there has been a well defined band of labelled cells throughout all laminae in the caudal third of its anteroposterior extent (Figs. 1, 3 and 4). Within the affected area almost all of the neurones contained numerous small brown granules distributed throughout their cytoplasm (Fig. 7), and under dark-field illumination the granules glowed brightly. Away from the area of maximum labelling the number of labelled cells rapidly becomes smaller and the concentrations of granules within them diminishes. The site of the affected band in the lateral geniculate varies in its medio-lateral position m different experiments, depending upon the site of injection, and the distribution is in close agreement with what is already known of the organization of the geniculo-cortical projection 17. Thus after an injection, at approximately the middle of the exposed lateral surface of area 17, the band of labelled cells occupies the middle of the medio-lateral extent of the lateral
i
Oo
459 geniculate nucleus. As the injection site is moved towards the superomedial part of the lunate sulcus the labelled band of cells comes to occupy progressively more medial portions of the laminae of the lateral geniculate nucleus. The intensity of the labelling in the cells did not appear to vary within the range of survival period used within the experiments. In 4 of the experiments labelled cells were also found in the pulvinar. In each of these 4 experiments the enzyme had either been injected or had diffused into varying extents of that part of the peristriate cortex adjoining area 17 and occupying the posterior wall of the lunate sulcus (Fig. 2). In the sections of the thalamus containing the most caudal parts of the lateral geniculate nucleus labelled cells were also found in the neighbouring inferior part of the pulvinar (Fig. 1). More caudally the band of labelled neurones in the inferior part of the pulvinar became continuous with a similarly labelled group of cells in the more dorsally situated pars lateralis. The appearance of the cells was similar to those in the lateral geniculate nucleus and within the affected region the majority of cells again appeared to take up the enzyme (Fig. 6). In two of the brains there were well defined groups of cells in both the inferior and lateral parts of the pulvinar, but in the other two unequivocal labelling was seen only in the inferior part. The extent of involvement of the pulvinar could be correlated with the degree to which penstriate cortex was injected in an antero-postenor direction, and it usually took the form of a narrow band which was continuous, anteriorly and medially, with that in the geniculate and caudally it became progressively more dorsally situated. In the caudal part of the basal nucleus 1°, which is situated inferior to most of the antero-posterior extent of the globus pallidus, but more posteriorly sweeps dorsally to lie between the globus pallidus and putamen, there are several cells which have taken up H R P enzyme in the form of granules (Fig. 1). The cells are large and contain numerous granules like those in the thalamic nuclei (Fig. 5). The cortex at the boundary of areas 17 and 18 and the rest of the peristriate cortex of the side opposite to that of the injection was examined for the presence of labelled cells of origin of commissural fibres. In two brains only were cells found with unequivocal brown granules of reaction product. These were found in the experiments in which most of the cortex of the posterior wall of the lunate sulcus had been filled with HRP. The occipital lobe of the normal side had been cut sagittally and the labelled cells formed restricted groups: in the deep part of layer III close to the fundus of the lunate sulcus, in a site known to receive commissural fibres 21, and at the boundary of
F~g. 2. Site of injection of HRP into the cortex of area 18 and the boundary of 17-18 in a saglttal section of the brain in experiment 231. This section and those of the succeeding photographs have been lightly counterstained with cresyl violet. × 12. Fig. 3. Coronal section of the lateral geniculate nucleus of the same brain to show the band of labelled cells m the medial parts of all 6 laminae. × 25. Fig. 4. The band of labelled cells in the 6 laminae of the lateral geniculate nucleus at higher magnification. Note that the medial margin of the nucleus is to the left in this figure, in contrast to that in Fig. 3. × 100. Fig. 5. Two labelled cells m the basal nucleus. × 750. Fig. 6. Three labelled cells from the inferior pulvlnar. × 1200. Fig. 7. Labelled cells in the magnocellular layer of the lateral geniculate nucleus. × 900.
460 areas 17 and 18, including the large cells in layer 111, characteristic of this junctional region and for which there is evidence for their being the origin of commissural fibres 7,20. The finding of undoubted granules of reaction product m cells m the lateral geniculate nucleus, after injection of H R P into the vzsual cortex, is not surprising and the presence of such cells in a band through all cell laminae and the distribution within the gemculate correlated well with the site of rejection and what is known of the orgamzatlon of the gemculo-calcarlne projection. The amount of reaction product in individual cells, however, was more than we have seen m any other sate and examination of the sections under high magnification indicated that a very high proportion of the neurones within the affected zone contained granules, an observation which is confirmed in a parallel EM study 19. The intense labelhng of cells m the lateral geniculate nucleus stands m contrast to the difficulty in labelhng the cells of origin of the commissural fibres from the opposite hemisphere. Our expeNence has been similar to that of Wong-Riley e° working m the sqmrrel monkey, for although she found some cells labelled at the boundary between areas 17 and 18, she emphasized the weakness of the staining. Some of the possible reasons for the differences In uptake and transport of the enzyme have already been discussed 11,15. The presence of labelled cells m the inferior and lateral parts of the pulvinar 12 m 4 brains ~s of interest m view of the recent statement lo that 'other inputs to area 18 in the monkey, for example from thalamus outside the geniculate, are at present conjectural'. The precise projection of these cells has not been established m these experiments, but no labelled cells were found m the pulvinar in which the injection site was limited to area 17 and the number of labelled cells in the pulwnar increased progressively w~th the extent of peristrmte cortex injected. It should be emphasized that the absence of labelled cells in the pulvinar after injection of area 17 only cannot be interpreted as excluding a projection from the pulwnar to strmte cortex. The d~strlbution of labelled cells m the pulvinar is very szmilar to that of the retrograde cell degeneration after a lesion of the penstriate cortex in a site overlapping those of our mject~ons t4. The site of the labelled cells fits closely the posihon that one would have expected on the bas~s of the retinotopic orgamzation at the 17/18 boundary and m the inferior pulvinar of the owl-monkey 1. These parts of the pulvinar have been shown to receive fibres2,9, TM from the visual cortex and there is ewdence for a projection to them from the retina 3. Further, after a large lesion in the pulvmar fibre degeneration has been found in the per~strmte cortex a. The significance of the labelling in the caudal part of the basal nucleus is uncertain, but a projection from this nucleus to extensive areas of the neocortex has been shown by Divac 5, Kievit and Kuypers 12 and other unpublished experiments in this laboratory. This work was supported by grants from the Science Research Councd and the Wellcome Trust.
461 1 ALLMAN, J. M., KAAS, J. H., LANE, R. H., AND MEIZEN, F. M., A representation of the visual field in the inferior nucleus of the pulvinar in the owl monkey (Aotus trivtrgatus), Brain Research, 40 (1972) 291-302. 2 CAMPOS-ORTEGA,J. A., AND HAYHOW, W. R., On the organization o f t b e visual cortical projection to the pulvinar in Macaca mulatta, Brain Behav. Evolut., 6 (1972) 394-423. 3 CAMPOS-ORTEGA,J. A., HAYHOW, W. R., AND CLOVER, P. F. DEV., A note on the problem of retinal projections to the inferior pulvinar nucleus of primates, Brain Behav. Evolut., 3 (1970) 368-414. 4 CRAGG, B. G., AND AXNSWORTH, A., The topography of the afferent projections in the clrcumstriate visual cortex of the monkey studied by the Nauta method, Vision Res., 9 (1969) 733-747. 5 DtVAC, I., Magnocellular nuclei of the basal forebraln project to neocortex, brain stem and olfactory bulb. Review of some functional correlates, Brain Research, 93 (1975) 385-398. 6 FISKEN, R . A . , GAREY, L.J., AND POWELL, T. P. S., Patterns of degeneration after intrinsic lesions of the visual cortex (area 17) of the monkey, Brain Research, 53 (1973) 208-213. 7 GLICKSTEIN, M., AND WHITTERIDGE, D., Degeneration of layer III pyramidal cells in area 18 following destruction of callosal input, Anat. Rec., 178 (1974) 362-363. 8 GRAHAM,R. C., AND KARNOVSKY, M. J., The early stages of absorption of injected horseradish peroxidase in the proximal tubules of mouse kidney: ultrastructural cytochemistry by a new technique, J. Htstochem. Cytochem., 14 (1966) 291-302. 9 HOLL.~NDER, H., Projections from the striate cortex to the diencephalon in the squirrel monkey (Saimirt sciurus). A hght microscopic radioautographic study following lntracortical injection of H'~-leucine, J. comp. Neurol., 155 (1974) 425440. 10 HUBEL, O. H., AND WIESEL, T. N., Sequence regularity and geometry of orientation columns in the monkey striate cortex, J. comp. Neurol., 158 (1974) 267-294. 11 JONES, E. G., Possible determinants of the degree of retrograde neuronal labeling with horseradish peroxidase, Brain Research, 85 (1975) 249-253. 12 KIEVIT, J., AND KUYPERS, H. G. J. M., Subcortical afferents to the frontal lobe in the rhesus monkey studied by means of retrograde horseradish peroxidase transport, Brain Research, 85 (1975) 261-266. 13 LAVAIL, J . H . , WINSTON, K . R . , AND TISH, A., A method based on retrograde lntra-axonal transport of protein for identification of cell bodies of origin of axons terminating in the CNS, Brain Research, 58 (1973) 470-477. 14 LEGROS CLARK, W. E., AND NORTHFIELD, D. W. C., The cortical projection of the pulvinar in the macaque monkey, Brain, 60 (1937) 126-142. 15 NAUTA, H. J. W., 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. 16 OLSZEWSKY,J., The Thalamus of the Macaca mulatta, Karger, New York, 1952. 17 POLIAK, S., The Main Afferent Fiber Systems of the Cerebral Cortex in Primates, University of California Press, Beikeley, Calif., 1932. 18 SPATZ, W. B., AND ERDMANN, G., Strlate cortex prolections to the lateral genlculate and other thalamic nuclei: a study using degeneration and autoradlographic tracing methods in the marmoset callithrix, Brain Research, 82 (1974) 91-108. 19 WINFIELD,D. A., GATTER, K. C., AND POWELL, T. P. S., An electron microscopic study of retrograde and orthograde transport of horseradish peroxidase to the lateral geniculate nucleus of the monkey, Brain Research, 92 (1975) 462-467. 20 WONG-RILEY, M. T. T., Demonstration of gentculocortlcal and callosal projection neurons in the squirrel monkey by means of retrograde axonal transport of horseradish peroxidase, Brain Research, 79 0974) 267-272. 21 ZEKI, S. M., Interbemlspberic connections of prestriate cortex in monkey, Brain Research, 19 (1970) 63-75.
