Loss of Y-cells in the lateral geniculate nucleus of monocularly deprived tree shrews.

In tree shrews (Tupaia glis) reared with one eye closed, Y-cells were almost entirely absent in the binocular segment of the lateral geniculate laminae receiving input from the deprived eye. Y-cells were found in the monocular segment of these laminae, and in the binocular segment of the laminae with input from the normal eye. X-cells were present in both the deprived and normal laminae and appeared unaffected by the deprivation. A number of abnormal cells were also found, and these were located primarily in the binocular segment where Y-cells were absent.

Superior colliculus of the tree shrew: a structural and functional subdivision into superficial and deep layers.

Superficial lesions of the superior colliculus produced deficits in form discrimination, while deeper lesions produced, in addition, an inability to track objects. These two syndromes were related to an anatomical subdivision: Superficial lesions resulted in anterograde degeneration in the visual thalamus, whereas lesions confined to the deeper layers produced degeneration in the nonvisual thalamus and in brainstem motor areas.

A third parallel visual pathway to primate area V1.

Recent studies of the primate visual system have focused on the proposal that the perception of form and motion are processed by two parallel pathways that originate from separate populations of cells in the retina. Earlier proposals for parallel processing of visual signals identified a third pathway that could be traced from the retina to the visual cortex. This third pathway was assumed to be unimportant. A growing body of evidence suggests that this pathway to cortex is distinct anatomically, physiologically and neurochemically, and is well represented in primates. These findings raise new and interesting questions not only about the role of this pathway, but also about the intracortical integration of afferent parallel signals.

ITCH modulates SIRT6 and SREBP2 to influence lipid metabolism and atherosclerosis in ApoE null mice.

Atherosclerosis is a chronic inflammatory disease characterized by the infiltration of pro-inflammatory macrophages into a lipid-laden plaque. ITCH is an E3 ubiquitin ligase that has been shown to polarize macrophages to an anti-inflammatory phenotype. We therefore investigated the effect of ITCH deficiency on the development of atherosclerosis. ApoE-/-ITCH-/- mice fed a western diet for 12 weeks showed increased circulating M2 macrophages together with a reduction in plaque formation. Bone marrow transplantation recreated the haemopoietic phenotype of increased circulating M2 macrophages but failed to affect plaque development. Intriguingly, the loss of ITCH lead to a reduction in circulating cholesterol levels through interference with nuclear SREBP2 clearance. This resulted in increased LDL reuptake through upregulation of LDL receptor expression. Furthermore, ApoE-/-ITCH-/- mice exhibit reduced hepatic steatosis, increased mitochondrial oxidative capacity and an increased reliance on fatty acids as energy source. We found that ITCH ubiquitinates SIRT6, leading to its breakdown, and thus promoting hepatic lipid infiltration through reduced fatty acid oxidation. The E3 Ubiquitin Ligase ITCH modulates lipid metabolism impacting on atherosclerosis progression independently from effects on myeloid cells polarization through control of SIRT6 and SREBP2 ubiquitination. Thus, modulation of ITCH may provide a target for the treatment of hypercholesterolemia and hyperlipidemia.

Direct W-like geniculate projections to the cytochrome oxidase (CO) blobs in primate visual cortex: axon morphology.

The primate lateral geniculate nucleus (LGN) is composed of large, medium, and small cells located, respectively, in magnocellular (M), parvocellular (P), and specialized layers (intercalated and S-layers in simians, koniocellular (K) layers in prosimians). Several studies have examined the physiology and connections of M and P LGN cells and have concluded that they provide separate contributions to visual perception via separate pathways. Less is known about the structure and contributions of the small LGN cells. This study examined the distribution and structure of K LGN cell axons in the cortex of the prosimian, Galago crassicaudatus. Wheat germ agglutinin conjugated to horseradish peroxidase, or Phaseonlus vulgaris leucoaglutinin, was injected into the LGN K layers to demonstrate the overall axon projection pattern and the details of individual axons, respectively. Location of axons within striate cortex was specified relative to boundaries determined by Nissl or cytochrome oxidase (CO) stains on the same or adjacent sections. Our results show that K LGN axons end as single complex arbors within one CO blob zone in layer III; they never terminate in interblob zones. These axons also emit a collateral in layer I that arborizes more broadly and spans both CO blob and interblob zones. These data, together with data on K cell physiology and intralaminar cortical connections, suggest that the LGN small cell pathway could modulate the activity of the other two pathways in striate cortex and contribute directly to visual perception.

Development of acetylcholinesterase activity in the lateral geniculate nucleus.

The pattern of acetylcholinesterase activity in the tree shrew (Tupaia belangeri) lateral geniculate nucleus (LGN) undergoes a number of striking changes during postnatal development. The adult tree shrew LGN is made up of six cellular layers divided by relatively cell-free interlaminar zones. At birth, however, the nucleus appears unlaminated when processed with conventional Nissl-staining techniques. The cellular lamination appears during the first postnatal week. The eyes open much later, typically at the end of the third week after birth. In the adult tree shrew, acetylcholinesterase (AChE) activity is found throughout the nucleus (both within and between the six cellular layers). In most sections examined, reaction product is slightly more intense in the lateral cell layers (4, 5, and 6). This is in sharp contrast to the pattern at birth (postnatal day zero, or P0). The detectable AChE activity at this age is apparently found in inchoate layers 1-2 and 4-5. Within these pairs, areas innervated by the ipsilateral eye (i.e., incipient layers 1 and 5) appear to contain more reaction product. From P0 to P4, the density of AChE activity increases in layers 1-2 and 4-5 and becomes detectable in the barely evident layers 3 and (usually) 6 at this age. By the middle of the second postnatal week, after laminae are clearly apparent with a Nissl stain, AChE activity has increased and is mainly associated with each cellular layer in the nucleus. During the third week after birth this pattern undergoes a radical shift. The most intense AChE activity is now in the interlaminar zones. Finally, as the adult pattern emerges, AChE activity increases in the cellular layers and all areas of the nucleus exhibit relatively high levels of AChE activity. Superimposed on this changing laminar pattern of AChE activity are changes related to the retinotopic map within the nucleus. Portions of the LGN representing central vision develop their characteristic pattern of activity several days ahead of the regions representing more peripheral visual field locations. AChE activity is also found transiently in the optic tract near the LGN during the first 3 postnatal weeks. Two (possibly three) groups of AChE-carrying fibers can be traced from the optic chiasm to their apparent sites of termination (or origin) in the parabigeminal nucleus, ventral lateral geniculate nucleus, and dorsal LGN. The activity present in the optic tract disappears shortly after eye opening.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of calcium-binding proteins within the parallel visual pathways of a primate (Galago crassicaudatus).

Bush babies possess three distinct parallel pathways to striate cortex (V1 or area 17). The calcium-binding proteins parvalbumin (PV) and calbindin (CB) typically show complementary regional distributions in the brain, often associated with specific aspects of functionally related groups of cells. We asked whether PV+ and CB+ immunoreactivity differentiate central visual parallel pathways in this species. Results show that PV and CB cell and neuropil staining is strongly complementary in the lateral geniculate nucleus (LGN) and is associated with separate parallel pathways. CB+ immunoreactivity is dense, but cytochrome oxidase (CO) staining is light in the paired koniocellular layers. PV+ and CO+ immunoreactivity is most dense in the parvocellular and magnocellular layers. Combined analyses of cell size, retrograde labeling, and double labeling have confirmed that all PV+ and CB+ LGN cells are geniculocortical relay cells; none was found to be gamma-aminobutyric acid (GABA)ergic. In V1, dense PV+ neuropil closely matches the expression of CO in layer 4 and in the blobs of layer 3. CB+ staining is most dense in layers 2 and 3A and is not strongly expressed within the CO interblobs. Finally, PV and CB are not found in related parallel pathway components in the LGN and V1 (e.g., in V1, CO blobs exhibit dense PV+ neuropil, yet they are targets of the small K geniculocortical relay cells that are CB+ in the LGN). Our findings support the view that three functionally distinct visual pathways project to V1 from the LGN. However, the differences in the patterns of localization of PV and CB in the LGN and in V1 suggest that these proteins may be utilized in different ways in these two visual areas.

A light microscopic and electron microscopic study of the superficial layers of the superior colliculus of the tree shrew (Tupaia glis).

Histochemical, Golgi, and electron microscopic methods were used to study the superficial layers of the superior colliculus of the tree shrew. Following horseradish peroxidase injections in the dorsal lateral ceniculate nucleus (LGd) and the pulvinar (Pul), retrogradely labeled somata were found in the upper two-thirds and the lower third of the stratum griseum superficiale (SGS), respectively, as has been described by Albano et al. ('79). In tissue prepared with Golgi methods, somata, similar in locatin and shape to those projecting to the LGd, had narrow, vertically oriented dendritic arbors, which were confined to the upper two-thirds of th SGS. Cells located in the lower third of the SGS had larger somata, similar to those projecting to the Pul, and wider dendritic arbors, which were confirmed to the lower two-thirds of the SGS. Electron microscopic comparison of the number of degenerating terminals following enucleation and striate cortex lesion indicated that within the SGS terminals from the retina overwhelmingly outnumbered those from the cortex. In both types of material, degenerating terminals were observed throughtout the SGS. However, the majority of te degenerating striate terminals were found in the lower SGS. Thus, cells that project to the LGd and those that project to the Pul differ not only with respect to location, size, and dendritic morphology, but also with respect to the proportion of retinal and straite afferents which terminate in the region of their dendritic trees.

Morphological effects of monocular deprivation and recovery on the dorsal lateral geniculate nucleus in galago.

The effects of monocular lid-suture deprivation on development were evaluated by measurement of cell sizes in the lateral geniculate nuclei of six deprived and three normally reared galagos. In all animals autoradiographic demonstration of the retino-thalamic projections from one eye was used to define the lamination and distinguish the monocular from the binocular segment of the nucleus. Our results indicate that monocular deprivation significantly affects cell growth in both the binocular and monocular geniculate segments, with the greater change occurring in the binocular segment, suggesting that both visual experience and binocular competitive interactions influence geniculate cell growth in these primates. In animals forced to use their deprived eye for 2 months or more by reverse suturing, disparity of cell sizes is reduced in the monocular segment, while differences in binocular segment cell sizes are maintained. Our results also show that monocular deprivation with or without later reverse suture has an unequal influence on different geniculate layers, such that cells in laminae 4 and 5 are not as severely affected as the remaining layers. This differential influence could relate either to the unique pattern of projection of these layers to cortex or to functional differences between layers.

Synaptic and neurochemical characterization of parallel pathways to the cytochrome oxidase blobs of primate visual cortex.

The primary visual cortex (V1) of primates is unique in that it is both the recipient of visual signals, arriving via parallel pathways (magnocellular [M], parvocellular [P], and koniocellular [K]) from the thalamus, and the source of several output streams to higher order visual areas. Within this scheme, output compartments of V1, such as the cytochrome oxidase (CO) rich blobs in cortical layer III, synthesize new output pathways appropriate for the next steps in visual analysis. Our chief aim in this study was to examine and compare the synaptic arrangements and neurochemistry of elements involving direct lateral geniculate nucleus (LGN) input from the K pathway with those involving indirect LGN input from the M and P pathways arriving from cortical layer IV. Geniculocortical K axons were labeled via iontophoretic injections of wheat germ agglutinin-horseradish peroxidase into the LGN and intracortical layer IV axons (indirect P and M pathways to the CO-blobs) were labeled by iontophoretic injections of Phaseolus vulgaris leucoagglutinin into layer IV. The neurochemical content of both pre- and postsynaptic profiles was identified by postembedding immunocytochemistry for gamma-amino butyric acid (GABA) and glutamate. Sizes of pre- and postsynaptic elements were quantified by using an image analysis system, BioQuant IV. Our chief finding is that K LGN axons and layer IV axons (indirect input from M and P pathways) exhibit different synaptic relationships to CO blob cells. Specifically, our results show that within the CO blobs: 1) all K cell axons contain glutamate, and the vast majority of layer IV axons contain glutamate with only 5% containing GABA; 2) K axons terminate mainly on dendritic spines of glutamatergic cells, while layer IV axons terminate mainly on dendritic shafts of glutamatergic cells; 3) K axons have larger boutons and contact larger postsynaptic dendrites, which suggests that they synapse closer to the cell body within the CO blobs than do layer IV axons. Taken together, these results suggest that each input pathway to the CO blobs uses a different strategy to contribute to the processing of visual information within these compartments.

Relationships between cytochrome oxidase (CO) blobs in primate primary visual cortex (V1) and the distribution of neurons projecting to the middle temporal area (MT).

The cytochrome oxidase (CO) blobs and interblobs in layer 3B of primate visual cortex have different sets of corticocortical connections. Cortical layers below layer 3B also project corticocortically, but the relationship of efferent projections from the deeper layers to the overlying blob/interblob architecture is less clear. We studied the tangential organization of neurons projecting from primary visual cortex (V1) to the middle temporal visual area (MT) and their relationship to the CO blobs. MT-projecting neurons in two primate species, bush babies and owl monkeys, were retrogradely labeled, then charted in tangential sections, and compared to the positions of the overlying CO blobs. In both primate species, MT-projecting neurons in layer 3C were unevenly distributed in the tangential plane, with dense patches of labeled cells that were aligned with the CO blobs. A novel two-dimensional spatial correlation method was used to show the colocalization of MT-projecting cells with the overlying blobs. Chi-square analyses performed with the cortical surface equally divided into compartments of blob, interblob, and blob/interblob borders showed that blob columns tended to have about 1.5 times more MT-projecting cells (P < 0.0001) than interblob columns. Similar analyses were applied to published data on V1 cells projecting to area MT in macaque monkey (Shipp and Zeki [1989] Euro J Neurosci 1:310-332). Again, the results showed a significant correlation between the cell distribution and CO blobs. Taken together, these results suggest that layer 3C is not uniform but is made up of a mosaic of cells that project to area MT and cells that project to some other location. These findings also indicate that the mosaic organization of layer 3C is related in some unique way to the overlying CO architecture.

Development of the lateral geniculate nucleus: interactions between retinal afferent, cytoarchitectonic, and glial cell process lamination in ferrets and tree shrews.

We have studied the relationship of retinal afferents, glial cell processes, and neuronal cytoarchitectonics in the lateral geniculate nucleus (LGN) of two species: tree shrews (Tupaia belangeri) and ferrets (Mustela putoris). Both species are relatively immature at birth, allowing the development of these features to be studied in the perinatal period. Retinal afferents, visualized by intraocular injection of a wheat germ agglutinin/horseradish peroxidase conjugate (WGA-HRP), are apparently the first elements of the developing LGN to exhibit a characteristic layered pattern in tree shrews and ferrets. Some radial glia still remain in the LGN of both species as the retinal afferents are in the process of segregating. Glial cell processes were visualized immunohistochemically with antibodies to glial fibrillary acidic protein (GFAP) or vimentin. In both the ferret and tree shrew, layering of glial cell processes is first seen as the overlap of retinal terminal fields diminishes. In the tree shrew LGN, these bands of dense glial cell staining are seen in apparent future cellular layers, whereas in the ferret, glial cell banding appears in interlaminar zones. If one or both eyes are removed at birth in tree shrews (before LGN cell layers are formed), the glial cell pattern seen 1 week later is in accord with the distribution of surviving nerve cells. The glial processes do not appear to invade regions left by degenerating retinal terminals or dying LGN cells. Several days after the appearance of layered glial cell processes (in the tree shrew) or at about the same time as glial layering (in the ferret), the first interlaminar spaces develop between neuronal cells, marking the beginning of cytoarchitectonic lamination, with its distinctive alternating cell-rich and cell-poor zones. Over the next several weeks, LGN neurons in both species continue to segregate into characteristic layers until the final, adult pattern of neuronal lamination is evident; as this process is completed, glial cell lamination disappears. These observations suggest that glial cells may be involved in establishing the neuronal layers that characterize the mature LGN of many species.

Organization of cytochrome oxidase staining in the visual cortex of nocturnal primates (Galago crassicaudatus and Galago senegalensis): I. Adult patterns.

The distribution and differential staining patterns of cytochrome oxidase (CO) activity in visual cortical areas have provided useful anatomical markers for the modular organization of area 17 (striate cortex) and area 18 in primates. In macaque and squirrel monkeys, previous studies have shown that the majority of cells that lie in areas of high CO activity are color selective, are nonoriented, and project to adjacent zones of high CO activity in area 17 and to stripes of high CO activity in area 18. By contrast, most cells in zones with weak CO activity in area 17 have relatively narrow orientation tuning and are not color selective (Livingstone and Hubel: J. Neurosci. 4:309-356, 2830-2835, '84; 7:3371-3377, '87). The periodic organization of CO activity in area 17, the "blobs," and the stripe-like organization in area 18 thus seem to define visual cortical processing modules and/or channels in primates. We have investigated the organization of CO activity in areas 17 and 18 in two species of nocturnal prosimian primates [Galago crassicaudatus (GCC) and Galago senegalensis (GSS)] in order to evaluate CO staining patterns in primates that have been reported to possess almost exclusively rod retinae and no color vision. In area 17 of both species, our results show that, as in diurnal and nocturnal simian primates, the darkest CO staining occurs in layers III and IV, with clear periodicity in layer III (i.e., CO blobs) and homogeneous staining in layer IV beta, the cortical recipient sublayer of the geniculate parvocellular layers. In GCC, individual blobs in layer III appear to be larger and less frequent than has been reported for the macaque monkey. Unlike simian primates, both galago species exhibit clear CO periodicities within layer IV alpha, the cortical recipient sublayer of the magnocellular geniculate layers. In addition, faint CO periodicities are apparent in layer VI and scattered large darkly CO stained pyramidal cells are visible throughout layer V. Quantitative analysis suggests that CO periodicities are more frequent in GSS than in GCC, suggesting that there may be evolutionary pressure to maintain the same number of CO modules within the smaller striate cortex of the lesser galago, although this is not the trend found across distantly related species. CO activity in area 18 is less well-developed than reported in other primates. In fact, we could not reliably identify discontinuities in CO staining in area 18 of GSS.(ABSTRACT TRUNCATED AT 400 WORDS)

Ocular dominance columns and retinal projections in New World spider monkeys (Ateles ater).

Retinal projections and the degree of ocular segregation in the striate cortex were examined by transneuronal autoradiography following unilateral intraocular injections of 3H-proline in a New World primate, the spider monkey (Ateles ater). The results show that, within the lateral geniculate nucleus (LGN), retinal fibers terminate in six principal layers and within the interlaminar spaces adjacent to the magnocellular layers, as well as the S layers ventral to the magnocellular layers. Projections to the superior colliculus, both ipsilateral and contralateral to the injected eye, were patchy and restricted to the superficial gray layer. Our main result shows that, in the striate cortex, LGN projections terminate in well-defined ocular dominance columns in layer IV. Labelled columns were most clearly delimited in layer IVb, where they averaged 373 + 42 micron in width in both the ipsilateral and contralateral hemispheres, slightly smaller than those reported originally from electrophysiological studies of striate cortex in spider monkeys (Hubel and Wiesel, '68). Unlabelled intercolumns were significantly narrower than labelled columns, which suggests that there may be overlap between input from the two eyes between columns. Quantitative measures showed above-background label also in cortical layers IIIb, V, and VI. Our results support the idea that among primates, ocular dominance columns are not limited to Old World species. At the same time, it is apparent that spider monkeys are exceptional among New World primates in having sharply delimited columns. The functional significance of the variation in the degree of ocular segregation in the cortex and its relation to primate evolution are discussed.

Neuronal classes and their relation to functional and laminar organization of the lateral geniculate nucleus: a Golgi study of the prosimian primate, Galago crassicaudatus.

The neuronal organization of the lateral geniculate nucleus of the prosimian primate, Galago crassicaudatus, was studied in Golgi-Kopsch-impregnated material. On the basis of cytoarchitecture, electrophysiology, and connections the nucleus is divisible into three pairs of layers--one magnocellular, one parvocellular, and one koniocellular--each part of a separate retinogeniculate and geniculostriate pathway (Itoh et al., '82; Norton and Casagrande, '82). In Macaca and Saimiri, which have equally distinct geniculate subdivisions, it has been reported that, outside of cell size, no one morphological attribute differentiates magnocellular from parvocellular neurons (Campo-Ortega et al., '68; Wong-Riley, '72; Saini and Garey, '81; Wilson and Hendrickson, '81). Results presented here are not inconsistent with this conclusion. However, when the results are analyzed from the standpoint of the collective traits that distinguish the cell groups that make up the layers, clear morphological differences are evident. Using this approach we find the following differences between presumed projection neurons and interneurons in each pair of layers. The projection neurons of the magnocellular layers, as a group, exhibit large cell bodies with radially arranged dendrites which often extend beyond laminar borders. The magnocellular interneurons are larger than their counterparts in the other layers and, like the magnocellular projection neurons, exhibit radially arranged dendrites. The former, however, also share characteristics in common with other interneurons such as relatively small somata, few proximal dendrites, and complex distal dendritic appendages. In contrast, the projection neurons and interneurons of the parvocellular layers have smaller somata and more restricted dendritic spreads than their counterparts in the magnocellular layers. Dendritic arbors of parvocellular neurons are typically oriented perpendicular to laminar borders and remain confined to their layer of origin. The koniocellular neurons represent a more diverse population but collectively are distinct in that the dendrites of almost all neurons in these layers run parallel to the layers. The fact that presumed interneurons and projection neurons in a single layer share a number of related dendritic features suggests that both groups together are responsible for the structural and, hence, functional architecture of a layer.(ABSTRACT TRUNCATED AT 400 WORDS)

Intrinsic connections of layer III of striate cortex in squirrel monkey and bush baby: correlations with patterns of cytochrome oxidase.

This study used biocytin and horseradish peroxidase (HRP) to examine the intrinsic connections of the cytochrome oxidase (CO) rich blob and CO poor nonblob zones within layer III of striate cortex in two primate species, nocturnal prosimian bush babies (Galago crassicaudatus) and diurnal simian squirrel monkeys (Saimiri sciureus). Our main objective was to determine whether separate classes of lateral geniculate nucleus (LGN) cells projected to separate superficial layer zones or layers in either species. There were three significant findings. First, we confirm that layer III consists of three sublayers, IIIA, IIIB, and IIIC in both species. Layer IIIA receives input from layers IIIB, IIIC, and V, with little or no input from LGN recipient layers IV and VI. Layer IIIB receives its input from nearly every cortical layer. Layer IIIC, receives input principally from layers IV alpha [which receives its input from magnocellular (M) LGN cells] and from layers V and VI. Taken together with other findings on the extrinsic connections of these layers, our data suggest that IIIA and IIIC provide output to separate hierarchies of visual areas and IIIB acts as a set of interneurons. Second, we find that, as in macaque monkeys, cells in both IV beta and IV alpha of bush babies and squirrel monkeys project to layer IIIB, converging within the blobs. These results suggest that information from all LGN cell classes [parvocellular (P), M, and the Koniocellular (K) or their equivalents] may be integrated within the blobs. Thus, blobs in all of these primates may perform a function that transcends visual niche differences. Third, our data show a species specific difference in the connections of the IIIB nonblobs; nonblobs receive indirect input via IV alpha from the LGN M pathway in bush babies but receive indirect input via IV beta from the LGN parvocellular (P) pathway in squirrel monkeys. These findings indicate that the role of nonblob zones within striate cortex differs from that of blob zones and takes into account visual niche differences.

Does the visual system of the flying fox resemble that of primates? The distribution of calcium-binding proteins in the primary visual pathway of Pteropus poliocephalus.

It has been proposed that flying foxes and echolocating bats evolved independently from early mammalian ancestors in such a way that flying foxes form one of the suborders most closely related to primates. A major piece of evidence offered in support of a flying fox-primate link is the highly developed visual system of flying foxes, which is theorized to be primate-like in several different ways. Because the calcium-binding proteins parvalbumin (PV) and calbindin (CB) show distinct and consistent distributions in the primate visual system, the distribution of these same proteins was examined in the flying fox (Pteropus poliocephalus) visual system. Standard immunocytochemical techniques reveal that PV labeling within the lateral geniculate nucleus (LGN) of the flying fox is sparse, with clearly labeled cells located only within layer 1, adjacent to the optic tract. CB labeling in the LGN is profuse, with cells labeled in all layers throughout the nucleus. Double labeling reveals that all PV+ cells also contain CB, and that these cells are among the largest in the LGN. In primary visual cortex (V1) PV and CB label different classes of non-pyramidal neurons. PV+ cells are found in all cortical layers, although labeled cells are found only rarely in layer I. CB+ cells are found primarily in layers II and III. The density of PV+ neuropil correlates with the density of cytochrome oxidase staining; however, no CO+ or PV+ or CB+ patches or blobs are found in V1. These results show that the distribution of calcium-binding proteins in the flying fox LGN is unlike that found in primates, in which antibodies for PV and CB label specific separate populations of relay cells that exist in different layers. Indeed, the pattern of calcium-binding protein distribution in the flying fox LGN is different from that reported in any other terrestrial mammal. Within V1 no PV+ patches, CO blobs, or patchy distribution of CB+ neuropil that might reveal interblobs characteristic of primate V1 are found; however, PV and CB are found in separate populations of non-pyramidal neurons. The types of V1 cells labeled with antibodies to PV and CB in all mammals examined including the flying fox suggest that the similarities in the cellular distribution of these proteins in cortex reflect the fact that this feature is common to all mammals.

Differential effects of monocular deprivation seen in different layers of the lateral geniculate nucleus.

Recent investigations have suggested that the morphological effects of monocular deprivation can be explained by a developmental competitive interaction between the pathways from the two eyes. This study presents evidence in the tree shrew for binocular competition and for an unequal effect of such competition on the different layers of the lateral geniculate nucleus. The effects of monocular deprivation were evaluated by comparing cell size changes in the binocular and monocular segments of the lateral geniculate nucleus in three tree shrews raised with one eye sutured. In two of these animals the open eye was injected with 3H proline in order to identify accurately geniculate layers innervated by the non-deprived eye. Cell sizes in three normal animals and one monocularly enucleated animal were measured for comparison. The results show the following main effects: First, that monocular deprivation significantly changes cell size in the binocular but not the monocular segment of the geniculate nucleus. Comparisons with cell size in normal animals indicates that non-deprived cells may grow in response to deprivation. Second, that cell size in geniculate lamina 3 is not affected by monocular deprivation, suggesting that cells in this layer are morphologically or functionally secluded from competitive interactions affecting the other layers. Finally, that monocular enucleation in the adult tree shrew affects all parts of the geniculate nucleus including layer 3 and the monocular segment, demonstrating that these parts of the geniculate nucleus are responsive to lack of retinal innervation.

Cortical connections of area 17 in tree shrews.

In order to better understand the organization of extrastriate cortex in tree shrews, injections in area 17 of wheat germ agglutinin or tritiated proline were used to reveal an intrinsic pattern of connections, ipsilateral connections with area 18 and two other subdivisions of cortex, and callosal connections with areas 17 and 18 of the opposite cerebral hemisphere. Areal patterns of connections were best seen in sections cut parallel to the surface of flattened cortex. Within area 17, periodic foci of labeled terminations and cells extended from and surrounded injection sites as described by Rockland et al. ('82). Single injections produced multiple foci of labeled terminations and cells in area 18. The foci tended to fuse into short bands that sometimes crossed the width of area 18. Double injections produced more foci, and multiple injections tended to produce more continuous regions of label. An overall retinotopic pattern was evident with rostral area 17 connected to rostral area 18 and caudal area 17 connected to caudal area 18. Terminations extended through layers II-VI, with some increase in density in layer IV. Cells in area 18 projecting back to area 17 were in layers III and V. The injections also allowed identification of previously undefined subdivisions of visual cortex in temporal cortex immediately adjoining area 18. Dense reciprocal connections were observed in a 13 mm2 oval of cortex on the lateral border of the middle section of area 18 that we define as the temporal dorsal area, TD. Connections indicate a crude topographic organization with lower field represented rostrally and upper field caudally. Inputs were most dense in the middle cortical layers, and labeled cells were supragranular, and less frequently, infragranular. A 10-mm2 oval of cortex near the posterior edge of the hemisphere, the temporal posterior area (TP), contained labeled cells after area 17 injections, but terminal labeling was only obvious in the dorsal part. Single injections sometimes produced quite separate dorsal and ventral zones of label in TP, suggesting a small separate dorsal division. A crude retinotopic order appears to exist within ventral TP, with the lower field most ventral. Labeled cells were largely supragranular. A fourth zone of ipsilateral connections was in posterior limbic cortex bordering area 17 on the ventromedial surface of the cerebral hemisphere. The callosal connections were reciprocal and included regions 1 mm wide on either side of the area 17 and area 18 border. Callosal connections were rougly homotopic. Callosal terminations included superficial layers, and projecting cells were both supragranular and infragranular.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of monocular deprivation on the morphology of retinogeniculate axon arbors in a primate.

Previous studies of the monocularly deprived (lid-sutured) primate (Galago crassicaudatus) have shown that magnocellular (M) and parvocellular (P) lateral geniculate nucleus (LGN) cells that receive input from the deprived eye are smaller than counterparts that receive input from the nondeprived eye; deprived koniocellular (K) cells show wide variability in size, but they do not differ from their nondeprived counterparts (Casagrande and Joseph, '80). Although deprivation results in cell-size changes, the physiological properties of deprived LGN cells do not change from normal (that is, P cells have normal X-like properties, M cells have normal Y-like properties, and K cells have normal W-like properties). Because of these findings, we were interested in determining how the morphology of retinogeniculate axon arbors is affected by deprivation. To this end, 104 horseradish-peroxidase-filled retinogeniculate arbors from galagos deprived from birth to maturity were completely reconstructed within the binocular segment of the LGN. These arbors were qualitatively and quantitatively compared with 56 arbors reconstructed from normal galagos as part of another study (Lachica and Casagrande, '88). Our main findings are as follows. Deprived M and P arbors are affected by deprivation in the same general manner: compared with normal arbors, they are altered in shape (rather than being round or columnar, respectively, both groups have terminals that are elongated parallel to laminar borders); they are smaller in area, and they have fewer boutons but innervate the LGN with a greater density of boutons. K arbors are affected by deprivation in the same manner, but less severely. Finally, our results show that nondeprived arbors are also affected by eyelid suture. Specifically, all nondeprived arbor groups are smaller in area than normal and possess more boutons/mm3. We interpret these changes in the morphology of deprived retinogeniculate axons to suggest that abnormal competitive interactions begin by affecting primarily immature LGN cells and their axons and that the retinogeniculate axons presynaptic to these cells experience secondary degenerative effects. Our results also show that similar manipulations of visual experience can result in changes that are not necessarily comparable across species such as cats and primates.