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Brains of adult monkeys with chronic lesions of dorsal columns of spinal cord at cervical levels undergo large-scale reorganization. Reorganization results in expansion of intact chin inputs, which reactivate neurons in the deafferented hand representation in the primary somatosensory cortex (area 3b), ventroposterior nucleus of the thalamus and cuneate nucleus of the brainstem. A likely contributing mechanism for this large-scale plasticity is sprouting of axons across the hand-face border. Here we determined whether such sprouting takes place in area 3b. We first determined the extent of intrinsic corticocortical connectivity between the hand and the face representations in normal area 3b. Small amounts of neuroanatomical tracers were injected in these representations close to the electrophysiologically determined hand-face border. Locations of the labeled neurons were mapped with respect to the detailed electrophysiological somatotopic maps and histologically determined hand-face...

Brains of adult monkeys with chronic lesions of dorsal columns of spinal cord at cervical levels undergo large-scale reorganization. Reorganization results in expansion of intact chin inputs, which reactivate neurons in the deafferented hand representation in the primary somatosensory cortex (area 3b), ventroposterior nucleus of the thalamus and cuneate nucleus of the brainstem. A likely contributing mechanism for this large-scale plasticity is sprouting of axons across the hand–face border. Here we determined whether such sprouting takes place in area 3b. We first determined the extent of intrinsic corticocortical connectivity between the hand and the face representations in normal area 3b. Small amounts of neuroanatomical tracers were injected in these representations close to the electrophysiologically determined hand–face border. Locations of the labeled neurons were mapped with respect to the detailed electrophysiological somatotopic maps and histologically determined hand–face border revealed in sections of the flattened cortex stained for myelin. Results show that intracortical projections across the hand–face border are few. In monkeys with chronic unilateral lesions of the dorsal columns and expanded chin representation, connections across the hand–face border were not different compared with normal monkeys. Thalamocortical connections from the hand and face representations in the ventroposterior nucleus to area 3b also remained unaltered after injury. The results show that sprouting of intrinsic connections in area 3b or the thalamocortical inputs does not contribute to large-scale cortical plasticity.

The cytoarchitectonic subdivisions and neuronal classes of the visual wulst were studied by cresyl violet, Golgi Colonnier and rapid Golgi technique. The wulst has been categorized into four laminae viz. the most superficial hyperpallium apicale (HA), intermediate interstitial nucleus of the hyperpallium apicale (IHA), hyperpallium intercalatum (HI), and innermost laminae hyperpallium densocellulare (HD). The wulst neurons have been classified into four main cell types: projection neurons having spinous dendrites and axon projecting widely within the same or different regions; local circuit neurons with aspinous dendrites and local axon arborization; stellate neurons being small with thin sparsely spinous dendrites and small sized granule cells with local axon arborization. The projection neurons are further sub classified into pyramidal (moderately spinous and sparsely spinous) and multipolar neurons (highly spinous, moderately spinous and sparsely spinous). Moderately spinous pyramidal neurons are present in the HA whereas sparsely spinous pyramidal neurons are present in the HD. The highly and moderately spinous multipolar neurons are encountered in the HA, HI and HD whereas moderately and sparsely spinous multipolar neurons are found in the IHA and HD respectively. The granule cells are of two types; spinous and aspinous, restricted only in the IHA. Local circuit neurons are present in all laminae except IHA. Stellate neurons are sparsely spinous found in all the four laminae. The dendrites have spines with small stalk and a knob like head. The morphology of dendritic spines (stalk length and head diameter) varies in different neurons and regions. The present findings have been compared with data reported in the wulst of other birds and also with the neuronal morphology of reptilian dorsal cortex and mammalian visual cortex.

Neurons in the hippocampal complex (dorsomedial forebrain) were described and located following Golgi impregnation. Five fields were recognized in the hippocampal complex: medial and lateral hippocampus, parahippocampal area, central field of the parahippocampal area and crescent field. In the medial hippocampus three layers have been observed: suprapyramidal towards the pial surface, pyramidal at the central and infrapyramidal adjacent to the ventricle. Neurons of the hippocampal complex were classified in to two main cell groups: predominant projection neurons with spinous dendrites and local circuit neurons. Projection neurons were further sub classified into three main types: pyramidal, pyramidal like, and multipolar neurons. In addition to these neurons, monotufted and bitufted neurons were also observed in the medial and lateral hippocampus with low frequency. The pyramidal neurons were dominant neuronal types in the pyramidal layer-II of the medial hippocampus, mixed with pyramidal like and multipolar neurons. Pyramidal and pyramidal-like neurons were found restricted in the pyramidal layer II of the medial hippocampus while the multipolar neurons were uniformly distributed in all subfields of the hippocampal complex. In the lateral hippocampus irregular shaped radial glial cells were present near the ventricular wall and projecting their dendrites towards the pia. Second group of local circuit neurons with local arborization of their projections were present in the medial hippocampus and in parahippocampal area.

The present study, based on neurohistological techniques (Nissl-staining, Golgi-impregnation), focuses on the cytoarchitecture of the corticoid complex in the strawberry finch, Estrilda amandava. This complex in birds occupies the dorsolateral surface of the telencephalic pallium and remains subdivided into an intermediate corticoid area (CI) and a dorsolateral corticoid area (CDL). The CDL in the strawberry finch is a thin superficial part of the caudal pallium adjoining the medially situated hippocampal formation, whereas the CI is demarcated between the CDL and the parahippocampal area of telencephalon. Neurons of the corticoid complex are classified into three main cell groups: predominant projection neurons, local circuit neurons and stellate neurons. The spinous projection neurons send out distant projecting axons that typically extend several varicose collaterals. Most of these collaterals lie parallel to the ventricle. These neurons are subclassified into pyramidal neurons (localized only in the CI) and multipolar neurons (present in both the CI and CDL). The CDL also possesses small and medium-sized horizontal cells, which are bitufted or multipolar with smooth, moderately branching dendrites. The aspinous local circuit neurons extend short axons that ramify locally. Stellate neurons have sparse spinous dendrites and locally arborizing axons. The corticoid complex of birds corresponds to the lateral cerebral cortex of lizards and to the entorhinal cortex of mammals on the basis of neuronal morphology and bidirectional connections between adjacent areas.

The cyto-architecture and morphology of the neuronal types of the dorsomedial cortex of the lizard, Hemidactylus flaviviridis has been studied with the help of Cresyl violet staining and Golgi impregnation method. The dorsomedial cerebral cortex displayed three neuronal layers. Layer-I contains only few neuronal somas and also the dendrites ascending from the subjacent layers. Layer-II is characterized by two to three cell thick densely packed neuronal somas. Layer-III contains loosely packed neuronal somas and the dendrites and axon descending from layer-I and II. Below the layer-III an ependymal layer is observed just above the ventricle. Six classes of neurons were distinguished in the cellular layer of dorsomedial cortex of Hemidactylus flaviviridis: bitufted neurons, pyramidal neurons, inverted pyramidal neurons, bipyramidal neurons, multipolar neurons, and candelabra-like monotufted neurons. The pyramidal cells were large showing more or less single type present in the cellular layer. The multipolar neurons have mostly intracortical dendritic branching and connections. Bipyramidal neurons showed pyramidal appearance of their soma and send dendritic branches towards the superficial plexiform layer and deep plexiform layer. The candelabra-like monotufted neurons have very high dendritic branching. The comparison of the neuronal types of dorsomedial cortex of reptiles with the parahippocampal area of birds and CA3 region of mammalian hippocampus suggests possibility of their homology.

The present book work tried to classify various types of neurons in the telencephalon of strawberry finch, Estrilda amandava. This study shows the various types of neurons, their morphological characteristics (Soma diameter, spine density, dendritic field, axonal length) and projections in the several fields of forebrain and deduced homology of various regions with reptilian and mammalian cerebral cortex. The findings show that the medial arm of the V-shaped layer of hippocampus corresponds to Ammon’s horn and the parahippocampus to the subiculum of mammals. The hippocampal complex of birds is comparable to the reptilian dorsomedial cortex. The corticoid complex of birds is homologous with reptilian lateral cortex and mammalian entorhinal cortex. The visual wulst of birds is homologous with reptilian dorsal cortex and mammalian visual cortex. The present study of neuronal classes of several regions has given important base for the further studies as Estrilda amandava seems to be a suitable avian model for studying the experimental tracing, immunocytochemistry, electrophysiology, lesion and regeneration experiments to identify the path & complexity of neuronal regeneration.