The effects of monocular enucleation on visual topography in area 17 in the rabbit

Summary The effects of neonatal monocular enucleation on the topographic representation of the ipsilateral visual field in the visual cortex of the rabbit were investigated, using electrophysiological recordings of multi-unit activity in area 17. Topography of receptive fields was determined in normal adult rabbits, adult rabbits monocularly enucleated on the day of birth and adult rabbits monocularly enucleated as adults. In normal rabbits and in adult enucleates, the projection from the ipsilateral eye is represented by a strip of cortex extending approximately 2 mm from the 17/18 border. In neonatal enucleates, the width of the area of cortex in which the projection from the ipsilateral eye is represented was approximately twice as large as normal. Visual topography was normal in the superior-inferior axis but was distorted in the nasotemporal axis. Our data suggest that the abnormal topography observed in the visual cortex of neonatally enucleated rabbits may play a major role in shaping the abnormal visual callosal projections observed in these animals. In addition, our data indicate that, following neonatal monocular enucleation, developmental abnormalities in the topography of geniculocortical projections can occur independently of any alteration in the retinogeniculate projection patterns.     

发育中大鼠视觉与听觉皮质胼胝体联系的轴突形态学研究

用顺行示踪剂 BDA标记研究了发育中大鼠视觉与听觉皮质胼胝体轴突的形态学。 BDA应用于出生后第 4d的视觉皮质后 ,整个视觉皮质包括 17区内侧部 、 层已可见一些标记的胼胝体轴突。第 5～ 8d时 ,许多标记的胼胝体轴突已到达皮质浅层 ( ～ 层 )。第 13 d时 ,17区内侧部又不见胼胝体轴突 ,表明早期此区的胼胝体轴突为暂时性的 ;17/ 18界区则含大量胼胝体轴突 ,并在 层和 / 、 、 层分别形成致密的和稀疏的终末丛。第 17d时 ,致密的终末丛可见于上述各层 ,与成年的分布模式类似。 BDA应用于听觉皮质后 ,标记的胼胝体轴突见于对侧听觉和视觉皮质 (即同源性和异源性胼胝体轴突 )。第 13～ 2 8d期间 ,虽然同源性胼胝体轴突的形态逐渐变化 ,但它们显示类似的明显的柱状构筑。第 13～ 2 4d,一定数量的异源性胼胝体轴突可见于整个视觉皮质包括 17区内侧部。但至第 2 8d,这些轴突大多被排除 ,并且此时的轴突标记模式已类似成年。提示 ,视觉皮质大多数异源性胼胝体轴突是暂时性的     

Callosal projections between areas 17 in the adult tree shrew (Tupaia belangeri)

Summary In the primary visual cortex (area 17) of the tree shrew (Tupaia belangeri) neurons projecting to the contralateral area 17 via the corpus callosum were identified by horseradish peroxidase histochemistry (HRP, WGA-HRP). The distribution of homotopic and heterotopic connections was studied. We found that a narrow stripe of area 17 close to the dorsal area 17/18 border — which corresponds to the visual field along the vertical meridian — is connected via homotopic callosal projections. The adjacent dorsal part of area 17, which largely corresponds to the binocular visual field, is connected via homotopic as well as heterotopic projections. Heterotopic projections originate in the cortical stripe along the area 17/18 border and their contralateral targets are displaced medially. Callosal neurons are located mostly in supragranular but also occur in infragranular layers. The supragranular neurons in general are pyramidal cells. In addition to these findings, we confirmed earlier reports on ipsilateral projections of the primary visual area to the dLGN, the claustrum, area 18 and other visual areas.The authors wish to dedicate this paper to Prof. W. Lierse in honour of his 60th birthday     

Postnatal development of biotinylated dextran amine-labeled corpus callosum axons projecting from the visual and auditory cortices to the visual cortex of the rat

The distribution and morphology of developing corpus callosum (CC) axons in rat visual cortex was studied by unilateral application of the in vivo anterograde tracer biotinylated dextran amine (BDA) to the visual or auditory cortex of newborns through adults. Changes in the distribution and morphology of CC axons during development were observed. Following BDA placement only in visual cortex, nearly all CC projections were to visual cortex (homotopic CC projections). At postnatal day (PND) 5-8, labeled CC axons were found throughout the contralateral visual cortex, including area 17; these CC axons could be followed from the white matter to layer I. By PND 13, few CC axons were found in medial area 17, indicating the existence of transitory CC axons in area 17 at younger ages. Morphological changes were investigated at the area 17/18a border and showed that CC axon collaterals were not formed until PND 8, and terminal arbors were not visible until PND 13; by PND 17, the adult CC-axon terminal pattern was present. At all ages, only a few heterotopic CC projections from visual to auditory cortex were found in the gray matter, although many labeled CC axons extended laterally into the white matter underlying the auditory cortex. Following BDA placement only in auditory cortex, CC projections to both auditory (homotopic CC projections) and visual (heterotopic CC projections) cortex were observed. At all ages, the homotopic CC projections were present throughout the auditory cortex, but were not distributed homogeneously; densely labeled CC axons showed a distinct columnar organization. The heterotopic CC projections were present in all visual cortical areas, including medial area 17, in significant numbers until PND 24, but were mostly eliminated by PND 28, at which time a labeling pattern similar to the adult was found. Thus, most of the heterotopic CC projections were transitory. The present study confirms the existence of transitory CC axons projecting through all layers of the visual cortex, as revealed by DiI, and extends the DiI results by showing that these transitory CC axons arise from both homotopic and heterotopic origins. Furthermore, different sources of transitory CC axons have different timetables for elimination.     

Functional consequences of modification of callosal connections by perinatal enucleation in rat visual cortex

The effects of neonatal monocular enucleation (right eye) on the callosal connections in the rat visual cortex were studied by physiological and morphological methods. Evoked activity was recorded in the left hemisphere, i.e. contralaterally to the enucleated eye. After enucleation, trans-callosally evoked responses were recorded in a widened stripe of the lateral visual cortex. Compared with the controls, the responsive area was expanded laterally and medially, i.e. into the lateral part of the primary visual area and within the secondary visual cortex (lateral part). Within about 0.5 mm of the expansion, the responses did not differ from those recorded in areas with "normal" callosal connections. Morphological evidence is presented suggesting that this expansion of evoked responses with high amplitudes and short latencies corresponds to an extension of callosal connections with a high density of axon terminals in layers two and three. Further medially within the primary visual cortex, callosally evoked responses with low amplitudes and longer latencies were recorded. The main types of unit responses and characteristic interactions between visually and callosally evoked responses are shown and discussed. These results suggest that following neonatal enucleation (1) the callosal connections expand and form functional synapses in the lateral part of the visual cortex, (2) these connections can activate cortical neurons either directly or by mediation of associational connections between the lateral secondary and primary visual cortex areas and (3) callosal connections can interact with visually evoked potentials and unit responses.     

Electrophysiological properties and input-output organization of callosal neurons in cat association cortex

Intracellular recordings from association cortical areas 5 and 7 were performed in cats under barbiturate or ketamine-xylazine anesthesia to investigate the activities of different classes of neurons involved in callosal pathways, which were electrophysiologically characterized by depolarizing current steps. Excitatory postsynaptic potentials (EPSPs), inhibitory postsynaptic potentials (IPSPs), and/or antidromic responses were elicited by stimulating homotopic sites in the contralateral cortical areas. Differential features of EPSPs related to latencies, amplitudes, and slopes were detected in closely located (50 microm or less) neurons recorded in succession along the same electrode track. In contrast to synchronous thalamocortical volleys that excited most neurons within a cortical column, stimuli applied to homotopic sites in the contralateral cortex activated neurons at restricted cortical depths. Median latencies of callosally evoked EPSPs were 1.5 to 4 ms in various cortical cell-classes. Fast-rhythmic-bursting neurons displayed EPSPs whose amplitudes were threefold larger, and latencies two- or threefold shorter, than those found in the three other cellular classes. Converging callosal and thalamic inputs were recorded in the same cortical neuron. EPSPs or IPSPs were elicited by stimulating foci spaced by <1 mm in the contralateral cortex. In the overwhelming majority of neurons, latencies of antidromic responses were between 1.2 and 3.1 ms; however, some callosal neurons had much longer latencies, 相似文献   

Elaborate organization of visual cortex in the hamster

We have studied the organization of visual cortex in the hamster by analyzing and correlating the distributions of callosal and striate-extrastriate connections. Our results show that, in lateral extrastriate cortex, callosal connections form an elaborate pattern which delineates at least 3 regions poor in callosal connections. These regions receive projections from striate cortex which are distributed into multiple separate fields. Two additional striate-projection fields were observed in medial extrastriate cortex, and another field was often observed near the posterolateral border of primary somatosensory cortex. All striate recipient fields are reciprocally connected with striate cortex. The patterns of callosal and striate-extrastriate connections in the hamster are similar, although not identical, to the corresponding patterns in rats and mice. Our results provide evidence that the organization of visual cortex in the hamster is highly elaborate, and suggest that extrastriate cortex is subdivided into multiple visual areas.     

大鼠运动皮层来自胼胝体的同位和异位神经元

实验的目的是用HRP逆行追踪法研究投射至大鼠运动皮层的胼胝体神经元的形态和分布,将HRP注射到大鼠一侧运动皮层后,对侧运动皮层中逆行标记的胼胝体神经元为中等大小的锥体细胞,分布于II／III,V和VI层,其中,V,VI层的细胞较为宽,大;计算机辅助三维重构的图象显示了注射部位和标记部位有很好的对应投射关系。此外,还首次观察到对侧眶回（外侧和腹外侧）向运动皮层的投射。这些位于眶回深层的胼胝体神经元较小而扁,且这种异位起源有投射区域的特异性。仅投向Frl的前端（触须和鼻缘的代表区）,而不向Fr3(爪,唇和舌的代表区）。这些同位和异位胼胝体起源提示了在大鼠的运动功能和其发达的嗅觉之间可能的内在联系。     

Reciprocal heterotopic callosal connections between the two striate areas in Tupaia

Summary WGA-HRP injections were placed into area 17 close to the border with area 18 of Tupaia belangeri in order to study the callosal connections of the striate area in this animal. Most callosal neurons were found in the striate cortex (57.6–86.9%), some in the extrastriate area 18 (10.6–28.1%), and a few in even more temporal regions (2.5–14.3%). Concerning only the area 17, reciprocal homotopic connections could be observed as a strip along the area 17/18 border. Additionally, heterotopic callosal connections could be seen in regions representing the binocular visual field, especially the lower part. The area 17 cells were mostly located in the supragranular layers II and III (94.1–97.2%). But neurons could also be found in the infragranular layers, especially layer VI (2.6–5.2%) and in layer IV (0.2–1.1%). Homotopic projections were mostly seen in layers IIIc and V. The majority of the supragranular and infragranular neurons are pyramidal cells. However, a newly defined subpopulation of neurons, most probably stellate cells, were discovered forming a band in sublayer IIIc, very close to the layer III/IV border.     

Visually triggered K-complexes: a study in New Zealand rabbits

K-complexes are the EEG elements recorded during the state of developing sleep and during slow wave sleep. They are the only EEG components which can be elicited by sensory stimulation during sleep. The peculiarity of New Zealand rabbits to sleep with their eyes open allows the use of visual stimuli to elicit K-complexes. Experiments were performed with three rabbits. For visual stimulation, an elongated screen illuminated by LED flashes was attached to an implant on the animal’s skull. The screen covered 20–120° of the visual field of one eye, and moved with the head during animal motion. One-millisecond flashes (15-s interval) were used during daytime in an illuminated room. Flashes elicited evoked responses, which, during the first stages of sleep, were often accompanied by K-complexes. The induced K-complexes were recorded from electrodes located both above visual and somatosensory areas. Evoked responses to visual stimuli were also recorded from both pairs of electrodes, although they were generated exclusively in the visual cortex. Correlation analysis showed that visual evoked responses and K-complexes induced by this stimulation were generated in visual cortex, and passively spread to the electrodes above the somatosensory area. Investigation of the latencies of induced K-complexes revealed two time windows when these complexes could be seen. Within each window there was no correlation between latency and amplitude of K-complexes. There was also no correlation between amplitudes of the visual evoked responses and K-complexes elicited by these responses. We propose that visual stimulation in light sleep temporarily opens a gate for some independent external signals, which evoke activation of the visual cortex, reflected in K-complexes.     

Relation of callosal and striate-extrastriate cortical connections in the rat: Morphological definition of extrastriate visual areas

Summary The main purpose of this study was to correlate the tangential distributions of visual callosal and striate-extrastriate connections in the rat. Cells of origin and terminations of the visual callosal pathway of one hemisphere were labeled by the anterograde and retrograde transport of horseradish peroxidase (HRP) after multiple injections of this enzyme in the contralateral hemisphere, while ipsilateral striate-extrastriate projection fields were revealed by using the autoradiographic method following single injections of 3H-proline in striate cortex. A remarkable complementarity in the distribution of both cortico-cortical pathways was revealed by superimposing in a camera lucida the patterns of callosal and striate-extrastriate projections from consecutive tangential sections processed for HRP and autoradiography, respectively. Projections from striate cortex are distributed into multiple extrastriate fields which are partially or totally surrounded by cortical strips containing dense and overlapping accumulations of labeled callosal cells and terminations. In addition to projections to the following striate recipient areas described in previous reports: posterior (P), posterolateral (PL), lateromedial (LM), laterolateral (LL), anterolateral (AL) and anteromedial (AM); projections to laterointermediate (LI), laterolateral anterior (LLa), anterior (A), medial (M) and pararhinal (PR) areas were defined in the present study. Striate-extrastriate projection fields occupy only a portion of the acallosal islands that contain them, and the location of the fields within these islands correlates with the retinotopic location of the isotope injection in striate cortex. When compared to previous physiological and anatomical maps of extrastriate visual areas in the rat, the present results indicate that the distribution of callosal connections correlates with the borders of extrastriate visual areas, and that the projection from striate cortex into these areas is retinotopically organized. Surprisingly, a direct projection from striate cortex to the head representation region in somatosensory cortex was labeled, a finding that challenges the view that primary sensory areas do not connect directly.Supported by NIH grants EY 02877 to V.M.M. and HD 3352 to the Waisman Center     

Binocular responses of cortical cells and the callosal projection in the albino rat

Four hundred and fifteen cells were recorded in the binocular segment of the visual cortex in the albino rat. Cells encountered were mainly dominated by the contralateral eye. The percentage of binocularly-driven cells increased as the electrode was moved towards the border between areas 17 and 18a. Ninety percent of the cells studied in the region of the border could be driven by electrical stimulation applied at the corresponding site in the opposite hemisphere. Within area 17, however, there were only about 30% of such cells. Through the combined use of electrical stimulation and reversible cortical cooling, two types of contributions by callosal fibres were revealed. One is that the callosal fibres constitute the only inputs from the ipsilateral eye to a cell. The other is that the callosal input provides ipsilateral reinforcement to a binocular cell. These results are compatible with neuroanatomical findings and show that binocularity of visual cortical cells in this animal depends, to a great degree, on the function of callosal fibres.     

Callosal connections of suprasylvian visual areas in the cat

After horseradish peroxidase injections in cat's lateral suprasylvian visual area and in areas 17 and 18, labeled callosal neurons are found within the various subdivisions of the lateral suprasylvian area, mostly in regions where the area centralis and vertical meridian are represented. The homotopic callosal projections from lateral suprasylvian area to lateral suprasylvian area originate almost exclusively from layer III. The heterotopic callosal projections from the lateral suprasylvian area to areas 17 and 18 originate mainly from layer VI but also from layer III. Callosal neurons in the lateral suprasylvian area are pyramidal cells (layers III and VI), fusiform and triangular cells (layer VI).The distribution of callosal neurons in the lateral suprasylvian area is similar to that previously found in areas 17 and 18 in the sense that in all these areas callosal neurons are preferentially located near the vertical meridian representation within two radially separated laminae. However, the preponderance of layer VI neurons in the projection from the lateral suprasylvian area to contralateral areas 17 and 18 is different from what was observed in other callosal connections. Since layer VI usually gives rise to corticothalamic projections it is possible that similar feed-back mechanisms may modulate the information sent to the lateral suprasylvian area from the thalamus and the primary visual areas.     

Functional organization of the cortical 17/18 border region in the cat

The representation of the visual field in the 17/18 border region of the cat's visual cortex, and the layout of orientation and ocular dominance columns, were studied by making many closely spaced electrode penetrations into the superficial layers of the flattened dorsal region of the marginal gyrus and recording response properties at each location. The 17/18 border region was defined by measuring the change in the horizontal component of receptive field position within the gyrus: as the position of the recording electrode moved from medial to lateral, the receptive fields moved towards the vertical midline, indicating that the electrode was in area 17; as penetrations were made in increasingly lateral positions, the trend reversed, and receptive field positions moved away from the midline, indicating that the electrode was in area 18. The receptive fields of cells close to the border straddled, or lay within 2 degrees-3 degrees on either side of the vertical midline. In addition, patches of cortex were sometimes encountered in which cells had receptive field centers located up to 7 degrees in the ipsilateral visual field. Experiments in which maps were made in the left and right hemispheres of a single animal showed that these patches had a complementary distribution in the two hemispheres. Cells within the patches behaved as though driven by Y-cell inputs: they usually had large receptive fields and responded to rapidly-moving stimuli. They were broadly tuned for orientation and strongly dominated by the contralateral eye. Fourier spectral analysis of orientation selectivity maps showed that iso-orientation bands had an average spacing of 1.14 +/- 0.1 mm and tended to be elongated in a direction orthogonal to the 17/18 border. Individual bands crossed the border without obvious interruption, although singularities (points of discontinuity in the layout of orientations) were more frequently observed in the border region than in adjacent areas. Two dominant periodicities could be measured in the maps of ocular dominance, one at around 0.8 +/- 0.2 mm and a second at 2.0 +/- 0.3 mm. No constant direction of elongation was noted. These are close to the periods present within areas 17 and 18 respectively.     

Primary visual cortex projections to extrastriate cortices in enucleated and anophthalmic mice

In the mouse, visual extrastriate areas are located within distinct acallosal zones. It has been proposed that the striate–extrastriate and callosal projections are interdependent. In visually deprived mice, the normal patterns of callosal and striate–extrastriate projections are disrupted. It remains unknown whether visual deprivation affects the topography of V1-extrastriate projections and their relationship with callosal projections. Two anterograde tracers were injected in V1 and multiple retrograde tracer injections were performed in the contralateral hemisphere of intact and enucleated C57BL/6 mice and in ZRDCT/An mice to determine the effects of prenatal and postnatal afferent sensory activity on the topography of V1-extrastriate and callosal projections. Greater topographic anomalies were found in striate–extrastriate projections of anophthalmic than enucleated mice. In enucleated mice, the relationship between striate–extrastriate projections and callosal zones was highly variable. In anophthalmic mice, there was also a greater overlap between these projections. These results suggest that the prenatal afferent sensory activity regulates some aspects of the distribution of V1-extrastriate and callosal projections, in addition to the development of a normal topographic representation in extrastriate areas.     

Olivocerebellar projection to the cardiovascular zone of rabbit cerebellum.

Climbing fiber responses were evoked in the medial vermal cortex of lobule VIIa by stimulation of the contralateral medial accessory olive (MAO) in anesthetized, paralyzed rabbits. Effective stimulating sites were localized in a small medial part of the caudal MAO, at 0.4-1.6 mm rostral from the caudal pole of the MAO (total length of the MAO, 4.2 mm). Stimulation of this MAO area induced depression in renal sympathetic nerve activity and this depressant response disappeared after ablation of lobule VIIa. Following injections of horseradish peroxidase into the small areas of lobule VIb, VIc, VIIa or VIIb, retrogradely labeled cells were found in corresponding small particular regions of the MAO: lobule VIb to the most caudal part, lobule VIc to the next caudal, lobule VIIa to the most rostral within the caudal MAO, and lobule VIIb further rostrally to the intermediate MAO. There was a clear disparity between the medial halves of lobules VI and VII projected from the medial MAO and the lateral halves from the lateral MAO. These results show that climbing fiber projections to lobules VI and VII are topographically organized, and that the medial region of lobule VIIa, related to cardiovascular function, receives climbing fibers from a localized small medial region of the caudal MAO.     

Functional organization of the cortical 17/18 border region in the cat

Summary The representation of the visual field in the 17/18 border region of the cat's visual cortex, and the layout of orientation and ocular dominance columns, were studied by making many closely spaced electrode penetrations into the superficial layers of the flattened dorsal region of the marginal gyrus and recording response properties at each location. The 17/18 border region was defined by measuring the change in the horizontal component of receptive field position within the gyrus: as the position of the recording electrode moved from medial to lateral, the receptive fields moved towards the vertical midline, indicating that the electrode was in area 17; as penetrations were made in increasingly lateral positions, the trend reversed, and receptive field positions moved away from the midline, indicating that the electrode was in area 18. The receptive fields of cells close to the border straddled, or lay within 2°–3° on either side of the vertical midline. In addition, patches of cortex were sometimes encountered in which cells had receptive field centers located up to 7° in the ipsilateral visual field. Experiments in which maps were made in the left and right hemispheres of a single animal showed that these patches had a complementary distribution in the two hemispheres. Cells within the patches behaved as though driven by Y-cell inputs: they usually had large receptive fields and responded to rapidly-moving stimuli. They were broadly tuned for orientation and strongly dominated by the contralateral eye. Fourier spectral analysis of orientation selectivity maps showed that iso-orientation bands had an average spacing of 1.14 ± 0.1 mm and tended to be elongated in a direction orthogonal to the 17/18 border. Individual bands crossed the border without obvious interruption, although singularities (points of discontinuity in the layout of orientations) were more frequently observed in the border region than in adjacent areas. Two dominant periodicities could be measured in the maps of ocular dominance, one at around 0.8 ± 0.2 mm and a second at 2.0 ± 0.3 mm. No constant direction of elongation was noted. These are close to the periods present within areas 17 and 18 respectively.     

Neonatal superior collicular lesions alter visual callosal development in hamster

Summary Visual callosal connections were examined using autoradiographic (ARG) and horse-radish peroxidase (HRP) techniques in normal adult hamsters, and in adults subjected to ablation of the superficial tectal laminae at birth. Additional ARG and HRP experiments were carried out in hamsters 1–27 days of age in order to describe the normal development of this pathway. Neonatal collicular lesions, which deprived visual cortical neurons of a major terminal zone in the midbrain, substantially altered the visual callosal pathway. In the lesioned animals, the numbers of supragranular callosal cells in the 17–18a border region and lamina VI callosal neurons in medial area 17 were significantly greater than normal. The ARG experiments demonstrated additional clearcut abnormalities in the visual callosal pathway of the lesioned hamsters. First, the mediolateral extent of the supragranular callosal zone around the 17–18a border was increased. Secondly, dense label was visible over lower layer V and lamina VI throughout area 17. Finally, labelling in lamina I could also be observed across the entire mediolateral extent of area 17.Experiments in the developing hamsters suggested that some of the abnormalities observed in the lesioned animals may have resulted from the maintenance of normally transient developmental states. During the first postnatal week, both callosal cells and anterograde labelling were evenly distributed throughout the dorsal posterior neocortex, but only in the subplate region. During the second postnatal week, supragranular callosal cells were also labelled in both medial and lateral area 17, but from their first appearance, they were always most numerous in the 17–18a border region. At the same time callosal axons invaded the supragranular laminae, but only near the 17–18a border. By the end of the second postnatal week, the visual callosal pathway was very similar to that in the adult.     

A comparison of visual callosal organization in normal,bilaterally enucleated and congenitally anophthalmic mice

Summary Visual callosal connections were examined using the horseradish peroxidase (HRP) technique in normal, neonatal and adult C57BL mice, and in adults of this strain which were bilaterally enucleated within 12 h of birth. In addition, callosal connections were also delineated in two strains of congenitally anophthalmic mice, ZRDCTan and or^J. Material from 129/J mice served as controls for the latter strain. In normal adults anterograde labelling and HRP labelled cells were visible primarily at the borders of area 17. In the 17–18a border region, labelled neurons were located primarily in layers II–III and V. In the medial striate cortex, a small number of labelled cells were present, primarily in lamina VI. Anterograde HRP labelling in the normal adults was also located primarily at the borders of area 17. At the 17–18a border, it was very heavy in layers V and VI, somewhat lighter in layer IV, and fairly dense in layers II–III and the lower half of lamina I. Labelling indicative of anterograde HRP transport was also visible in lowermost lamina V and layer VI across the entire mediolateral extent of area 17. In normals injected with HRP on postnatal day 2 and perfused 24 h later, callosal neurons were distributed throughout the dorsal posterior neocortex, primarily in layers V and VI. Only a very few labelled cells were visible in the supragranular laminae. In adult mice blinded at birth, the zone of callosal cells and terminals extended much further into area 17 than in normals, but aside from the anterograde labelling in layer VI and lowermost lamina V, the medial one-third of the striate cortex was still for the most part devoid of callosal cells and fibers. The laminar distributions of the labelled cells and anterograde transport in the blinded animals were the same as in the normal mice. In both strains of anophthalmic mice the pattern of callosal connections was unlike that in either the normals or neonatal enucleates. In the caudal visual cortex, callosal cells and anterograde transport indicative of terminal labelling were visible primarily in the 17–18a border area. Rostrally, however, they were both distributed in multiple (two-three) patches within area 17. Serial reconstructions demonstrated that these patches tended to be aligned in stripes which ran parallel to the 17–18a border. One of these was always located at the 17–18a border, and here the laminar distribution of labelled cells and anterograde labelling was the same as in the normals. In the more medial patches, however, labelled cells and anterograde labelling were confined almost completely to layers II and III. The distribution of callosal cells in neonatal ZRDCT-an mice was not appreciably different from that in C57BL mice of the same age.     

The size of the zone of origin of callosal afferents projecting to the primary visual cortex contralateral to the remaining eye in rats monocularly enucleated at different postnatal ages

Summary The cortical zone from which callosal afferents projecting to the primary visual cortex (area Oc1) originate was studied in monocularly enucleated and normal rats. The extent of this cortical strip was determined by retrograde labeling with HRP and by measurement of its width in coronal sections. Albino rats were monocularly enucleated from the 23rd ontogenetic day to the 120th and iontophoretical injections into Oc1 contralateral to the remaining eye were done more than one year after enucleation. The width of the labeled strip of perikarya in the hemisphere ipsilateral to the remaining eye was largest in neonatally enucleated rats (about 1.1 mm) and declined with increasing age at which enucleation was performed. Additionally, the perikarya of callosal afferents in the hemisphere ipsilateral to the remaining eye in rats enucleated as young adults (90th and 120th ontogenetic day) were labeled in significantly wider strips (about 0.6 mm) than in unoperated control rats (about 0.4 mm).