Gy. Somogyi

Numerical estimation of γ-aminobutyric acid (GABA)-containing neurons in three thalamic nuclei of the cat: Direct GABA immunocytochemistry

The percentage of neurons that are immunoreactive for the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA) was determined within: (1) the lateral geniculate nucleus (LGN), (2) the ventrobasal complex (VB) and (3) the antero-ventral nucleus (AV) of the thalamus in the cat. An antiserum to GABA was used to stain GABA-containing perikarya in 1.0 micrometer thick Araldite-embedded sections. Immunostained somata in all three nuclei were invariably smaller than the immuno-negative nerve cells. 27% of all neurons in the LGN, 33% in the VB and 25% in the AV were immunoreactive for GABA.

Neuronal and synaptic arrangement in the lateralis posterior-pulvinar complex of the thalamus in the cat

Abstract Golgi and electron microscope studies on the cats LP-pulvinar formation of the thalamus reveal the presence of two characteristically different cell populations: principal (or relay) cells and Golgi type II interneurons. These two cell types show little if any difference, both at the light and electron microscope level, from the characteristics of the similar cell types and the ultrastructural arrangement found in the sensory relay nuclei. Characteristic synaptic glomeruli (or encapsulated zones) are found in abundance in the LP-pulvianr complex. Four different types of terminal profiles containing synaptic vesicles can be identified in these glomeruli:RL = large axonal terminals with spheroid vesicles;RL = small axonal terminals with similar vesicles (relatively rare in the glomeruli and abundant in the general extraglomerular neuropil);F 1 = probably axonal profiles with flattened vesicles (present both in the glomeruli and in the general neuropil); andF 2 = profiles interpreted as of dendritic nature and belonging to Golgi type II interneurons. The numbers, percentages of different types of terminal profiles and of various combinations of interprofile contacts have been determined.

Ultrastructure of the anterior ventral and anterior medial nuclei of the cat thalamus.

SummaryElectron microscopical studies of the thalamic AV-AM nuclei substantiated the presence of two main types of neurons, i.e. principal (or relay) cells and Golgi type II interneurons. Characteristic synaptic islands are found in abundance in the AV-AM. Four different types of synaptic terminals have been identified in these islands: RL-boutons = large axonal terminals with round synaptic vesicles; RS-boutons = small axonal terminals with round synaptic vesicles; F1-boutons = small axonal profiles containing flattened synaptic vesicles, and F2-profiles interpreted as presynaptic dendrite appendages, bearing pleomorphic vesicles, both belonging to the Golgi type II interneurons. — The synaptic relations were studied in normal preparations and after lesions in the mamillary body, limbic cortex and hippocampus. The specific afferents (RL-boutons) — originating from the medial mamillary nucleus — are presynaptic to both relay cell dendrites and “presynaptic” dendrite profiles of Golgi type II interneurons, which in turn are presynaptic to the same relay dendrites (synaptic triads). RS-boutons originate mainly from limbic cortex and hippocampus.

Golgi study on cat hippocampal formation

SummaryThe Golgi architecture of the Fascia dentata and hippocampus is described in the cat. The main cell types are like those found in other species. The initial collaterals of granule cell axons were demonstrated and are commented on. The interneurons proved to be of several types and subtypes not observed in lower species. The intrinsic fibers and few of the afferents — both in the dentate fascia and in the hippocampus — are discussed.

Some comparative quantitative data on the different (Relay and associative) thalamic nuclei in the cat

SummaryThe ultrastructure of the ventrobasal complex (VB) of the cat thalamus was investigated in order to compare the data with those obtained in other thalamic nuclei. New data are described regarding the identification of Golgi II type neurons and several forms of axo-somatic synapses. By means of a quantitative analysis the number of different profiles, distribution of interprofile contacts, synaptic densities and degree of synaptic input of the two main cell-types were defined. The quantitative data obtained in the VB complex were compared with values for the lateral geniculate body (CGL), nucleus anterior ventralis (AV-non-sensory relay thalamic nucleus) and nucleus lateralis posterior-pulvinar complex (LP-PU-associative thalamic nucleus).The quantitative data reveal that:1.The occurrence of RL terminals is equal in the two relay nuclei (VB and AV) and three-fold higher than in the LP-PU.2.The percentage ratio of specific terminals (RL) in the total surface area in the relay nuclei is three-fold higher than in the LP-PU.3.The RL→D synapses are twice as numerous in the relay nuclei as in the associative nucleus.4.The density of synaptic RS profiles in VB is half of that found in LP-Pu.5.In the thalamic relay nuclei the number of synaptic contacts on Golgi II type neurons is one-third of the synaptic supply of relay neurons; in the LP-Pu the amount of synaptic contacts on Golgi II type neuron approaches the synaptic supply of projective neurons.

Limbic projections to the cat thalamus

Retrograde axonal transport of horseradish peroxidase was used to identify the afferent projection systems of the anterior thalamic nuclei in the cat. The results indicate that fibres projecting to the three anterior nuclei of the thalamus arise from the hippocampal region, septum and cingulate cortex unilaterally and from the hypothalamus (mamillary nuclei) both bilaterally and unilaterally. The cells of the medial mamillary nuclei send their axons to the ipsilateral AV and AM nuclei whereas the lateral mamillary nucleus projects bilaterally to the AD nuclei.

Electron microscopic study of terminal degeneration in the anterodorsal thalamic nucleus of the cat.

SummaryThe ultrastructure and synaptic organization of the anterodorsal nucleus (AD) of the thalamus were investigated under normal and experimental conditions. The large glomeruli are composed of an extensive central dendrite, probably arising from a projecting neuron, and of various terminal boutons. Besides the typical small bouton (RS) filled with round vesicles, two specializations of the large bouton (RL) containing round vesicles are found. The larger one (RL1) is characterized by a looser arrangement of synaptic vesicles and many mitochondria; it undergoes dark degeneration following unilateral lesions of the mamillary body in both AD. The intermediate type (RL2) is distinguished by a denser arrangement of vesicles; it undergoes dark degeneration following lesions of the midline nuclei of the thalamus. The two types of terminal boutons (F1 and F2) which contain flattened or pleomorphic vesicles do not degenerate following lesions of the mamillary body and midline nuclei; they belong to Golgi type II interneurons.

Types of thalamo-cortical relay neurons in the anteroventral nucleus of the cat

SummaryNeurons displaying a thalamo-cortical projection were marked by means of the retrograde transport of horseradish peroxidase (HRP), and the labeled elements were compared with neurons impregnated by the Golgi technique. Injections of HRP into the posterior area of the limbic cortex resulted in its uptake by various anterior thalamic nuclei, especially the anteroventral nucleus. HRP-positive cells are characterized by their position, dendritic orientation, and the shape and size of their somata. On the basis of the combined HRP- and Golgi-analysis three different types of thalamo-cortical relay neurons can be distinguished.

Quantitative histological study on the thalamic ventro-basal complex of the cat

SummaryA quantitative analysis was carried out on the thalamic ventrobasal (VB) complex of the cat. The following numerical and metrical parameters of the neuronal elements (cells and fibers) were determined:1.Volume of nucleus: 27.38 mm32.Total number of neurons: 243,0003.Total number of fibers of medial lemniscus: 26,0004.Volume of arborization space of one lemniscal fiber: 2.26×106 μm3. Numerical data of relay neurons and lemniscal fibers and their relations as basic factors in the estimation of the degree of divergence and convergence of lemniscal input were calculated and compared. It was found that the probable degree of convergence is four-fold (1–4) and of divergence 27-fold (1–27) with regard to the relationship of fibers and cells in the VB. The quantitative data obtained in the VB and our considerations on convergence and divergence were compared with analogous values obtained for the lateral geniculate body LGB. The differences between the two sensory relay nuclei reflect differences in their modes of impulse transmission.

A combined horseradish peroxidase and Golgi study on the afferent connections of the ventrobasal complex of the thalamus in the cat

SummaryAfferent connections to the ventrobasal complex (VB) of the thalamus were studied by means of retrograde transport of horseradish peroxidase (HRP) and by the Golgi-method. After HRP-injection into the VB, peroxidase-positive cells were observed contralaterally in the dorsal column nuclei (DCN), in the trigeminal nuclei and in the lateral cervical nucleus (LCN), and ipsilaterally in the somatosensory I (SI) and II (SII) cortical areas. Labeled cells of different shape and size were compared with neurons impregnated by the Golgi-technique. On the basis of HRP-labeling it is concluded that cells projecting to the VB are different in size and shape even within one region and that they correspond to the relay or efferent neurons observed in the Golgimaterial.