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The molecular characterization of glial lineage cells in two urodele species, Ambystoma mexicanum and Triturus carnifex, has been investigated immunocytochemically with antibodies directed against intermediate filament proteins, glial fibrillary acidic protein (GFAP) and vimentin. Ambystoma astroglia shows clear GFAP-immunopositivity and vimentin-immunonegativity. The condition in Triturus is quite the opposite, showing only a strong vimentin immuno-reaction. In these urodele brain the astroglia is represented by radial glial cells with their somata lining cerebral ventricles (tanycytes). Each of them originates a thick process which radially crosses the periventricular gray matter and branches within the neuropil. These glial fibers originate endfeet on the subpial surface and on blood vessel wall. Only in the spinal cord cell bodies of immunopositive radial glia are displaced from the ependyma of the central canal which is almost immunonegative except the tanycytes forming the dorsal and ventral septum. No mammalian-like astrocytes appear neither in brain nor in spinal cord. The interspecific difference in the intermediate filament protein expression in radial glial cells could suggest that as regards this character Triturus retains a more immature condition than Ambystoma.

Ambystoma and Xenopus were used to investigate olfactory terminations in the forebrain by exploiting the selective binding of soybean agglutinin to primary olfactory projections. Lectin binding and tridimensional reconstruction provided new information on the distribution of olfactory glomeruli and on regional and interspecific differences. Ambystoma showed an uniform labelling of all olfactory terminations, which were localized in the rostro-lateral forebrain without obvious segregation of different terminal fields, except at dorsal levels. On the contrary, the binding pattern of Xenopus confirmed the existence of three sets of primary olfactory neurons characterized by clear differences in lectin binding. Selective soybean agglutinin binding and a detailed tridimensional reconstruction provided evidence for the existence of a set of neuronal projections, described for the first time, which terminate in a discrete bilateral region of the forebrain localized below the main olfactory bulb. The presence of three different sets of primary olfactory neurons, the experimental potentials and the possible functional significance of SBA binding sites are discussed.

The uptake of 6-H3 thymidine in the optic tectum and the forebrain of the newt following injury to one of the two nervous areas, shows a marked proliferative response in the telencephalon in the presence of a lesion on the right optic tectum, and a poor response of the optic tectum after a lesion on the right telencephalic lobe. A similar proliferative response is also obtained when the specimens received only the cold shock. In both experimental conditions maximum uptake is obtained after 7 days. It is assumed that the matrix cells of the forebrain and the undifferentiated cells of the optic tectum respond differently to the regeneration factor released by the nervous tissue following a lesion or a cold shock.

We have investigated the ultrastructural and histochemical (AChE and BuChE) features of intracerebral vessels in newt. The blood vessels of the newt brain are paired and end in a closed loop. The two limbs, each of them has delineate the lumen by one endothelial cell, are enclosed within a single basement membrane and are separated from each other by a thin intercapillary wall. The brain capillaries are un-fenestrated and the overlapping endothelial cells were connected by clefts. Ependymal astrocytes extensively ensheath the surface of brain capillaries, but the sheats are incomplete. Pericytes and mast cells are frequently sandwiched in the endothelial basal lamina. Microglial cells are also present adjacent to cerebral vessels. The newt cerebral capillaries are characterized by high levels of AChE. This enzyme is localized in the basal membrane and in extracellular spaces between the overlapping endothelial cells. The vascular walls are instead deprived of BuChE activity. The non-nervous role of cholinesterases is discussed.

The histochemical distribution of acetylcholinesterase (AChE) activity in the brain and spinal cord of Rana esculenta, has been studied. Moreover the levels of choline acetyl-transferase (ChAT) and of AChE, have been determined biochemically in different regions of the central nervous system. The results obtained from combining the histochemical and biochemical analyses allowed us to obtain more significant information on the localization of cholinergic neurons and the projection areas of the cholinergic terminals.

The ultrastructure of myelinated fibres in the ventro-medial area of medulla oblongata of metamorphosing Bufo bufo was studied. In the first stages of metamorphosis the fibres show normal distribution of the axonal organelles, while in the myelin sheaths the lamellae appear detached from one another with an irregular period and absence of the intra-period line. In the middle and final stages of metamorphosis there are myelin sheaths like those described above, but there are others with compact lamellae, regular period and intraperiod line always visible. Moreover, it is possible to observe myelin sheaths with intermediate characteristics. In that period of metamorphosis many myelinized axons may show degenerative pictures, more or less evident. However, these always precede possible degenerative aspects of the myelin sheath. The different morphological characteristics of the sheaths can be interpreted as different maturation stages of the myelin sheath, from embryonal to definitive-conditions. It is less easy to interpret the significance of the numerous degenerating nervous fibres observed in the cone sidered area of medulla oblongata. On the basis of the bibliographic data and preceding studies, the Authors think that degeneration of the fibres is not necessarily linked to cellular degeneration, but to a quiescent condition in which many nervous cells of the Amphibian's CNS would settle during metamorphosis while waiting for replacement of the target organs.

The retrograde transport of HRP after periocular space injection was investigated in mesencephalon and medulla oblongata of newt brain. In the tegmentum the neurons of oculomotor and troclear nucleus are filled. In the optic tectum some filled cells of mesencephalic trigeminal nucleus were, for the first time, described. This suggest that these neurons are deputated to proprioceptive innervation of the extrinsic ocular muscles. In the medulla oblongata the labelled neurons were located in the ganglion of Gasser and in the sensitive column of the trigeminal area. Other labelled neurons were found in the abducent nucleus and in the visceromotor column of the facial nerve. The authors discuss the analogy between the trigeminal labelled neurons of the medulla oblongata with supratrigeminal nucleus of the mammals.

We have investigated the structure and the cholinesterase features of the brain capillaries in two adult Amphibians (Rana esculenta and Bufo bufo). We found that brain capillaries are un-fenestrated and the endothelial cell edges are joined by tight junctions. The brain capillaries in both species are characterized by high levels of AChE. This enzyme is only localized in the basal membrane, whereas we have found the reaction product neither in the endoplasmatic reticulum nor in the Golgi apparatus. On the contrary the brain capillaries are deprived of BuChE. Only in one experiment traces of reaction product were found. The significance of this datum and the non-nervous role of cholinesterase is discussed.