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The authors have described a new method of coloration on anatomic slices of the central nervous system realised on formolated subjects. They have presented their first results on their experiences carried out on the different levels of the brain, and this simple method of proceeding shows how interesting it could be for all practicians of Neurosciences and for the teaching of Neuroanatomy.

The nucleus tractus solitarii (NTS) has long been considered as the first central relay for gustatory and visceral afferent informations only. However, data obtained during the past ten years, with neuroanatomical, biochemical and electrophysiological techniques, clearly demonstrate that the NTS is a structure with a high degree of complexity, which plays, at the medullary level, a key role in several integrative processes. The NTS, located in the dorsomedial medulla, is a structure of small size containing a limited number of neurons scattered in a more or less dense fibrillar plexus. The distribution and the organization of both the cells and the fibrillar network are not homogeneous within the nucleus and the NTS has been divided cytoarchitectonically into various subnuclei, which are partly correlated with the areas of projection of peripheral afferent endings. At the ultrastructural level, the NTS shows several complex synaptic arrangements in form of glomeruli. These arrangements provide morphological substrates for complex mechanisms of intercellular communication within the NTS. The NTS is not only the site of vagal and glossopharyngeal afferent projections, it receives also endings from facial and trigeminal nerves as well as from some renal afferents. Gustatory and somatic afferents from the oropharyngeal region project with a crude somatotopy within the rostral part of the NTS and visceral afferents from cardiovascular, digestive, respiratory and renal systems terminate viscero-topically within its caudal part. Moreover the NTS is extensively connected with several central structures. It projects directly to multiple brain regions by means of short connections to bulbo-ponto-mesencephalic structures (parabrachial nucleus, motor nuclei of several cranial nerves, ventro-lateral reticular formation, raphe nuclei...) and long connections to the spinal cord and diencephalic and telencephalic structures, in particular the hypothalamus and some limbic structures. The NTS is also the recipient of several central afferent inputs. It is worth to note that most of the structures that receive a direct projection from the NTS project back to the nucleus. Direct projections from the cerebral cortex to the NTS have also been identified. These extensive connections indicate that the NTS is a key structure for autonomic and neuroendocrine functions as well as for integration of somatic and autonomic responses in certain behaviors. The NTS contains a great diversity of neuroactive substances. Indeed, most of the substances identified within the central nervous system have also been detected in the NTS and may act, at this level, as classical transmitters and/or neuromodulators.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Frequently there is an opposition between olfactory and visual senses. Fresh water fishes are generally macrosomatic and microptic, marine fishes (especially coral reef fishes) are microsmatic and macroptic while piscivorous pelagic fishes are macrosmatic and macroptic. 2. The importance of the cerebellum is a function of both the fish's activity level and its body size. 3. There is a marked opposition between the diencephalon and the medulla oblongata and a greater one between the non-olfactory-telencephalon (NOT) and the medulla oblongata (MA). Although it is not possible to give an accurate evolutionary significance, the ratio of NOT/MA is low in primitive teleostean fishes and high in more derived species (Acanthuridae and Tetraodontiformes).

Lesions affecting the neocortex have been carried out in 16 cats. Wallerian degeneration projects to the vegetative effector nuclei (nucleus of the vagus nerve and the nuclei intermedio-lateralis and intermedio-medialis of the spinal cord). The methods of silver impregnation used were those of Nauta, Fink-Heimer and Velayos-Ullán. Corticofugal fibers which show an intercalary formation, such as the nuclei reticularis parvocellularis, lateralis and dorsalis, and the nucleus of the solitary tract, are more numerous. There are also direct fibers for the intermediate zone (intermedio-lateralis and intermedio-medialis nuclei) of the thoracic and sacral spinal cord.

The quantitative study of the brain of Amia, Lepisosteus and Polypterus leads to results which are compared to those previously got on the Sturgeon and three species of Tleosts (the Rainbow Trout, the Carp and the Ballan wrasse). The volumetric analysis has been applied at first to the whole brain (encephalization indices) and later to the main subdivision of the brain: telencephalon, diencepahlon... (relation indices and relative volumes). Some result are discussed in regard to the various opinions expressed about the phylogenetic affinities of the studied species. According to the brain organisation, the Bichir (Polyterus) seems to be at a relatively high level of evolution, and no relationship can be expected with the Chondrosteans. Amia and Lepisosteus show a common general brain pattern, but some peculiarities allow to consider Amia as more primitive than Lepisosteus--although the osteological characteristics and the scale structure lead to put together the first one and the Teleosts.

The brain of the Pond-loach (Misgurnus fossilis) is very closely related to that of Cyprinidae. In the Medulla oblongata, the facial lobe-in relation with the skin taste buds, especially on the barbels-is bigger than the vagal lobes-which are related with the mouth taste buds. The intraspecific relations between brainweight and bodyweight or various body lengths show a real sexual dimorphism (brain dimegaly). The interspecific brain-bodyweight relationship shows an allometric coefficient of 0.505 in males and 0.485 in females, very close to that of the Rainbow trout. The encephalization index (63) is very close to that of the Tench, and a little lower than that of the Cyprinidae as a whole.