Glycine immunoreactivity in the brainstem auditory and vestibular nuclei of the guinea pig.

An immunohistochemical study was performed on the brainstem of the guinea pig, using a specific antibody against glycine. Glycine-like immunoreactivity was observed in stellate and multipolar neurons in the cochlear nucleus, in the medial and lateral nuclei of the trapezoid body and in the ventromedial periolivary cell group. No immunoreactive neurons were found in the vestibular nuclei. Positive fibre tracts were observed mainly in dorsal acoustic stria and lateral lemniscus. The results are consistent with electrophysiological and anatomical data from the literature concerning the response pattern in the fusiform layer of the dorsal cochlear nucleus and the phenomenon of binaural inhibition in the superior olivary complex.

GABA immunoreactivity in the primary nuclei of the auditory central nervous system.

Structures containing gamma-amino butyric acid (GABA) were investigated in the guinea pig cochlear nuclei and superior olivary complexes by means of an immunohistochemical procedure using an antibody directed against GABA. Immunoreactivity was observed in cell bodies of the superficial layers of the ventral and dorsal cochlear nuclei, in lateral superior olive, in some neurons of the medial superior olive, in lateral preolivary nuclei and in the lateral nucleus of the trapezoid body. Fibers and profiles exhibiting GABA immunoreactivity were found in almost all regions of the lower auditory pathways. The abundance of GABA in these regions indicates an important role of this inhibitory amino-acid in the auditory brainstem.

Evolution of Xenopus endodermal cells cultured on different extracellular matrix components. Identification of primordial germ cells.

Plated on untreated glass substrate, Xenopus endodermal cells are unable to undergo any morphological or cytological differentiation. Culture on artificial substrates prepared with components of the extracellular matrix, the endodermal cell behavior is entirely different. To identify the primordial germ cells (PGC), we use three coated substrate types: fibronectin, collagen and collagen plus fibronectin. These substrates allow us to distinguish three cell types shortly after explantation. Using fibronectin-coated substrate, most of the cells, after attachment and spreading, form cellular islets which tend to fuse, leading to the formation of a polyhedric cell monolayer. Such fusing is notably reduced on composite substrate (Coll + FN) or on collagen substrate only. Thus it is possible to distinguish the special morphological features exhibited by the rest of the cells. Some of them retain the aspect of endodermal gastrula cells in vitro. Others, elongated or spindle-shaped, possess the characteristics of PGC. Nevertheless, the identification and sampling of the presumed germ cells is easier on COLL + FN-coated substrate. The morphological and cytological characteristics of the elongated cells are similar to those observed during PGC migration through the endodermal mass. According to these results, there is little doubt that these elongated cells are primordial germ cells.

[Development of the adenylate cyclase activity of the embryonic chorda-mesoderm and endoderm during the migration of primordial germ cells in Xenopus laevis (anuran amphibian)]. / Evolution de l'activité adénylate cyclasique du cordomésoderme et de l'endoderme embryonnaires pendant la migration des cellules germinales primordiales chez Xenopus laevis (amphibien anoure).

In the embryo of Xenopus laevis, adenylate cyclase activity is higher in the chorda-mesoderm than in the endoderm. The peak of activity in the chorda-mesoderm is observed at the beginning of the migration of the primordial germ cells (PGC). There could be a correlation between the adenylate cyclase activity of the chorda-mesoderm and the intraendodermic migration of the PGC.