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The principal afferent fibres of the avian optic tectum are the optic fibres of retinal origin. They terminate on the contralateral side, in the external layers (2-7) of the optic tectum (called optic layers) turning into these layers from the external surface. The terminal branchings of the optic fibres develop four densely innervated areas in layers 2, 3, 4-5 and 7. Their terminals are large and of various appearance in the different areas. In the middle third of the optic layer (in layers 4-5), thin dendritic terminal sections of tectal ganglion cells (according to Ramòn y Cajal) of layer 13 terminate into bunches. Phaseolus vulgaris lectin immunotracer corroborates these dendritic endings (further: dendritic terminals) of tectal ganglion cells. The direct connections between these dendritic terminals and the supposed optic fibres were studied under electron microscope and it was found that the large terminals of optic fibres containing round synaptic vesicles establish asymmetrical synapses with several dendritic profiles, among them Phaseolus lectin labelled dendritic terminals of ganglion cells. This result morphologically supports the former physiological observation of a direct synaptic transmission between optic fibres and ganglion cells of layer 13. In addition, on the dendritic terminals of ganglion cells, symmetrical synapses established by GABA-positive terminals were found. The optic terminals, the GABA-immunopositive terminals and the dendritic terminals of ganglion cells form complex synaptic units surrounded with glial sheath, and thus they establish glomerulus-like synaptic units. The size of the dendritic tree and the branching pattern of the dendrites of ganglion cells point to divergence and convergence in visual transmission.

The brains of kittens prenatally exposed to ethanol were studied by the rapid-Golgi method at PN1 and PN9 days. The sizes of the alcohol damaged brains were different. Delayed gyrification was observed on the brain surface. The neurons in subcortical (thalamic) centres and cortical areas developed later than in normal animals. Between days PN1 and PN9 rapid changes occurred in the development of the structural elements of brains of prenatally alcohol exposed kittens.

In the Golgi preparation of visual Wulst of chicken four types of projection neurons were found: type 1a, 1b, 1c, and 1d neurons, which are distinguished on the basis of their dendritic ramification pattern and especially on the density of the dendritic spines. Type 1a has large dendritic tree with moderately dense spiny dendrites. Type 1b has very dense spiny dendrites. Type 1c is a small neuron with moderately dense spiny dendrites. Type 1d is a star-pyramid-like neuron with a short, bifurcating apical dendrite. The final dendritic pattern and spine density of projection neurons was found to develop at the end of the first month. In the Wulst short axon cells (interneurons-INs) of different types occur: large, medium-sized and small INs can be observed. Their axon-arborizations are significantly different from each other. Some of them are GABA-immuno-positive neurons, which are very probably inhibitory interneurons. Stellate-like neurons also occur in IHA and HIS. These neurons have sparsely spiny dendrites and locally arborizing axons.

The Golgi method more than hundred years old can reveal new results also in the current research of CNS. The study provides examples for using the Golgi method and demonstrates the types of neurons, the various types of interneurons, characterizes the stellate cells in layer IV of the cortex. The Golgi method is applicable for the observation of maturation process and also for demonstrating different pathological alterations of neurons in the CNS.

The ultrastructure of interneurons was studied in the cat and it was found to differ from that of the pyramidal and granule cells. The size, shape and topographic situation of the cell body of interneurons were the criteria for approaching their identification with the cells found in Golgi material. Some interneuron dendrites are also described. The varicose and spindle-shaped dendritic profiles belonging to interneurons are different in size. In Golgi material the interneurons have beaded (varicose) or spindle-shaped dendrites. The arrangement of synaptic terminals on the interneuron dendritic surface seems to be their characteristic feature.

The ultrastructure of mossy fibre terminals, granule cells, and pyramidal neurons was studied in cat material. The average of the mossy terminals and the density of the synaptic vesicles were analysed. The large mossy terminals establish mainly axo-spiny synapses on the apical dendrites of pyramidal neurons in the CA3 area, but some axo-dendritic synapses were also observed. Mossy fibre endings were found in the subgranular layer, and also on the dendrites of interneurons.

The Golgi architecture of the nucleus caudatus in rabbit, cat, monkey and human material was analysed. The brains were prepared by Golgi--Kopsch impregnation. The fairly divergent types of neurons practically belong to two main groups: projective or efferent neurons and local- or interneurons. The efferent neurons -- as it has been confirmed by experimental studies -- establish far contacts with various regions of the brain. According to the Golgi picture, their axon emits several collaterals, which produce local connections. The interneurons have only locally arborizing axon. The are mainly responsible for intrinsic connections of the nucleus. In both main groups of caudate neurons, several types and subtypes were observed. The number of the types and subtypes of the neurons show an increasing tendency in the phylogenetic series.

Special orientations of dendritic trees of projective (relay) neurons were observed in the thalamic nuclei; and it was found to be different in the various nuclei. It can be explained by the size, course, site of the fibre bundles which enter and/or transgress the nuclei. The orientation of dendritic tree and the size of the branching area of dendrites (specific active dendritic space) were analysed by computer. The quantitative data of neuronal elements in some thalamic nuclei gave the opportunity to consider the possible degree of divergence and convergence of sensory fibres regarding their connections with the projective neurons.

The rhesus monkey's visual cortex was studied on Golgi material. The terminal arborization of the geniculate fibres and non-specific vertical fibres have been analysed. The interneurons (intrinsic neurons) of the area described in detail and classified on the basis of their axonal and dendrite arborizations. The stellate neurons in layer IV are discussed.

This paper describes the neurons in different cortical areas and traces their postnatal changes. Rapid Golgi and Golgi--Kopsch impregnation were carried out in 1-day-old and 9-day-old kittens. The maturation of the pyramidal neurons can be observed mainly on their basal dendritic orientation and on development of the dendritic spines. The differentiation of the interneurons (non-pyramidal) also proceeds on the first postnatal days. These, though slightly less mature than the associated pyramidal neurons, are identifiable already on the first postnatal day. It is concluded that there are significant differences in the maturation of the neurons in the various cortical areas.