T. Tömböl

A comparative Golgi study of chicken (Gallus domesticus) and homing pigeon (Columba livia) hippocampus

Neurons and fibres in the chick and homing pigeon hippocampus were described following Golgi impregnation. Two principal classes of neurons were distinguished: projection neurons with distant projecting axons and spiny dendrites, and local circuit neurons. In the homing pigeon and chicken hippocampus there are three types of projection neurons: pyramidal, pyramidal-like and multipolar. The pyramidal and pyramidal-like neurons are only found in the central ’pyramidal’ layer of the hippocampus whereas multipolar neurons are present in the suprapyramidal, pyramidal and infrapyramidal layers. The axon of projection neurons typically emits several varicose collaterals from the initial section. Most of these collaterals extend along the infrapyramidal layer of the hippocampus, while others ascend to the pyramidal and suprapyramidal layers where they branch. The number of impregnated axon collaterals was higher in the homing pigeon than in the chick hippocampus. A variety of multiangular/ovoid local circuit neurons ranging from small to large size are found in the homing pigeon and chick hippocampus. Their axons develop local arborisation of varicose branches, the extent of which varies with the type of local circuit neurons. The density of GABA immunopositive local circuit neurons was found to be greater in the homing pigeon than in the chick. The profuse arborisation of projection neuron axon collaterals and the higher density of GABA-immunopositive local circuit neurons in the homing pigeon hippocampus may underlie the differences in hippocampal function between the homing pigeon and chick, and this complex local connectivity may contribute to the ability of spatial orientation and memory.

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.

GABA-immunohistological observations, at the electron-microscopical level, of the neurons of isthmic nuclei in chicken, Gallus domesticus

Abstract Following a demonstration of Golgi-impregnated neurons and their terminal axon arborization in the optic tectum, the neurons of the nucleus parvocellularis and magnocellularis isthmi were studied by means of postembedded electron-microscopical (EM) γ-aminobutyric acid (GABA)-immunogold staining. In the parvocellular nucleus, none of the neuronal cell bodies or dendrites displayed GABA-like immunoreactivity in EM preparations stained by postembedded GABA-immunogold. However, numerous GABA-like immunoreactive and also unlabeled terminals established synapses with GABA-negative neurons. GABA-like immunoreactive terminals were usually found at the dendritic origin. Around the dendritic profiles, isolated synapses of both GABA-like immunoreactive and immunonegative terminals established glomerulus-like structures enclosed by glial processes. All giant and large neurons of the magnocellular nucleus of the isthmi displayed GABA-like immunoreactivity. Their cell surface was completely covered by GABA-like immunoreactive and unlabeled terminals that established synapses with the neurons. These neurons are thought to send axon collaterals to the parvocellular nucleus; their axons enter the tectum opticum. The morphological characteristics of neurons of both isthmic nuclei are like those of interneurons, because of their numerous axosomatic synapses with both asymmetrical and symmetrical features. These neurons are not located among their target neurons and exert their modulatory effect on optic transmission in the optic tectum at a distance.

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.

The ramification and connections of retinal fibres in layer 7 of the domestic chick optic tectum: a Golgi impregnation, anterograde tracer and GABA-immunogold study

Layer 7 is one of the retinorecipient layers of the avian optic tectum. However, little information is available about the neuronal organization of this layer and its implications for visual function. Golgi impregnation was used to investigate the retinal input to and the neuronal architecture of layer 7 of the chick optic tectum, which forms a narrow band between the two cell‐dense layers 6 and 8. Anterograde tracers were also used to investigate the afferent and efferent connections of layer 7, in both the light and the electron microscope, together with GABA immunogold labelling. Three types of radial neuron were defined according to the origin and course of their axons. The perikarya of these neurons were situated in tectal layers 10–11. The principal dendrites of these radial neurons ascended to the tectal surface and gave rise to dendritic side‐branches in layer 7. These dendritic side‐branches received asymmetric synapses from the terminations of retinal fibre arborisations. Type 2 radial neurons, whose axons arose from the deep pole of the perikaryon or occasionally from a basal dendrite, were shown to project to the nucleus isthmi pars magnocellularis, which has previously been demonstrated to be GABAergic and to project to glomerulus‐like complexes in tectal layers 4–5. In these layers, the dendritic branches of layer 13 neurons that project to the nucleus rotundus have previously been shown to receive retinal fibre input. Therefore, the retinal input to layer 7 may be able to modulate the transmission of information to the visual thalamus, by way of a feedback loop to layers 4–5 of the tectum involving the nucleus isthmi pars magnocellularis.

A golgi and a combined Golgi/GABA immunogold study of local circuit neurons in the homing pigeon hippocampus.

Three types of local circuit neurons have recently been reported in the homing pigeon hippocampus. The principal type appears to be constituted by the medium-sized angular or ovoid local circuit neurons that occur in all layers of the hippocampus. The current Golgi study has revealed that these neurons can be classified according to their axonal arborisation extension: (1) in all directions, (2) principally medio-laterally, or (3) dorso-ventrally. The local circuit neurons with dorso-ventral axon arborisation are present only in the subpyramidal layer. Serial sections of a Golgi-impregnated medium-sized, multiangular local circuit neuron in the pyramidal layer and a small, ovoid neuron in the suprapyramidal layer were investigated in the electron microscope. Some of these sections were processed for GABA immunogold cytochemistry. The soma and large dendrites of both neurons displayed GABA immunogold labelling. On the soma of medium-sized local circuit neuron there were numerous terminals; on the soma of the small one relatively fewer terminals were observed. The terminals contained round and/or flat synaptic vesicles. The long axonal branches of the neurons exhibited varicosities containing flattened or pleomorphic vesicles. Axo-dendritic, axo-somatic and a few axo-axonic synapses were observed. The large dense axon arborisation field of medium-sized local circuit neurons is properly situated to modulate intrinsic hippocampal activity and that of the small local circuit neurons is well situated to modulate the hippocampal input in the suprapyramidal layer.

Golgi and electron-microscopic golgi-GABA immunostaining study of the avian optic tectum.

The neuronal structures and their possible connections in the optic tectum of chicks were studied by using Golgi impregnation, in light microscopy, and Golgi-GABA immunogold staining in electron microscopy. The terminals of the optic fibers displayed different patterns and orientation in various laminae of the avian optic tectum. The shape of the branching and the terminals of the optic fibers conformed to the postsynaptic neuronal structures. In Golgi preparations, the terminals in tectal layers 4 and 5 seemed to be located rather densely, and they contact, among other things, the ‘dendritic terminal sections’ of large ganglion cells of layer 13 of the tectum. This connection could be responsible for direct optic transmission via ganglion cells to the nucleus rotundus. Additionally, the contacts established by optic terminals in these layers with the tectal neurons arranged with their dendrites parallel to the surface of the tectum, could provide the structural basis for an inhibitory system. The terminals of isthmic nuclei were found in this optic lamina, too. The optic terminals in layer 7 contacted the dendritic side branches of some radial tectal neurons.

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.

Ultrastructural Changes of the Neuromuscular Junction in Reperfusion Injury

Ischemia followed by reperfusion of skeletal muscle frequently takes place in trauma surgery. Anoxia followed by reoxygenation leads to reperfusion injury, which damages the involved tissues. However, no information is available about how the neuromuscular junction is affected by ischemia-reperfusion. Tourniquet ischemia of the left hind limb was applied in the anesthetized rat for 2 h. Reperfusion lasted for 2 and 24 h and for 1, 2 and 4 weeks. The extensor digitorum longus and the soleus muscles from both legs were prepared for electron-microscopic analyses. Morphological changes of the neuromuscular junction were investigated. In all cases only the nerve endings (terminals) were affected. The postsynaptic structures were not affected. Changes can be grouped in two categories: degeneration and recovery. Degeneration consisted of the loss of synaptic vesicles, disruption of the presynaptic membrane, degeneration of the mitochondria and the development of vacuoles. It was most severe at 24 h and was still present at 4 weeks of reperfusion. Recovery started at 1 week of reperfusion and lasted at least for 4 weeks. It consisted of the slow reappearance of synaptic vesicles and mitochondria, and restoration of the presynaptic membrane with active zones. Ultrastructure of the skeletal muscle fibers did not show pathological changes. The recovery of the structures may be regulated by the Schwann cells and also by the postsynaptic membrane which is not affected by 2 h of ischemia followed by reperfusion.

Neuronal cell types in the thalamic intralaminar central lateral nucleus of the cat

SummaryThe existence of Golgi type II neurons was verified in the anterior intralaminar central lateral (CL) nucleus of the cat thalamus, and its projection cell types were identified, by means of Golgi impregnation. CL principal neurons were found to display a large- or medium-sized cell body and a radiate dendritic pattern. Their primary dendrites were limited in number, and had a rather long course; they were poorly ramified. The axons of principal neurons were impregnated only occasionally and for a short distance. Projection neurons of the ‘bushy’ or tufted type, described in the main thalamic sensory nuclei, were not identified in the CL in the present study. Typical Golgi type II neurons were found throughout CL. They were mainly small-sized, and displayed a rich dendritic arborization characterized by dendritic appendages. The axons of Golgi type II neurons were seen to give rise to extensive local arborizations. The present findings indicate that in the cat CL, principal cells are mainly represented by radiate neurons. Typical local circuit neurons also are evident in CL, suggesting that the activity of anterior intralaminar structures is regulated by intrinsic mechanisms similar to those operating in the main thalamic relay nuclei.