Calretinin expression in specific neuronal systems in the brain of an advanced teleost, the grey mullet (Chelon labrosus).

The distribution of calretinin (CR) in the brain of an "advanced" teleost, the grey mullet, was studied by using immunoblotting and immunocytochemical techniques. In immunoblots of protein extracts of rat and mullet brains, the CR antibody stained a single band of about 29 kDa. CR immunoreactivity was observed in specific neuronal populations of all brain regions. The primary olfactory system, the optic nerve fibers, and some sensory fibers of other cranial nerves exhibited strong CR immunoreactivity. In the forebrain, the CR-immunoreactive (CR-ir) populations were scarce in the telencephalon and hypophysiotrofic hypothalamus, but numerous in many specialized nuclei of the diencephalon (preglomerulosus complex, nucleus glomerulosus, anterior glomerular nucleus, nucleus diffusus) and pretectum (parvocellular and magnocellular superficial pretectal nuclei, central pretectal nucleus), which are related to sensory systems. The two main forebrain bundles, medial and lateral, contained numerous CR-ir fibers. The midbrain sensory centers (optic tectum and torus semicircularis) exhibited numerous CR-ir cells and fibers. Likewise, the secondary gustatory nucleus of the isthmus is one of the nuclei exhibiting more intense CR immunoreactivity. Characteristically, the efferent cerebellar system (eurydendroid cells and brachium conjunctivum) and some afferent cerebellar fibers were CR-ir. In the medulla oblongata, a number of reticular cells, the inferior olive, and the magnocellular octaval nucleus exhibited CR immunoreactivity. CR-ir motoneurons were also observed in the spinal cord and in the oculomotor nucleus. Together with results obtained in other vertebrates, present results suggest that neural systems using calretinin to maintain intracellular calcium concentration have been rather well conserved during vertebrate evolution.

Expression of thymosin beta4 messenger RNA in normal and kainate-treated rat forebrain.

Thymosin beta4 is a major actin-sequestering peptide widely distributed in mammalian tissues, including the nervous system. In the present study, we analyse the expression of thymosin beta4 in normal and kainate-treated rat forebrain. In untreated animals, thymosin beta4 messenger RNA is mainly expressed in neurons of the hippocampal formation, neocortex and amygdaloid complex, as well as in oligodendrocytes. Other high-expressing areas are the tanycytic ependyma of the infundibulum, the substantia nigra pars compacta, and the supraoptic and premammillary nuclei. In rats treated with kainate, an excitotoxin that induces synaptic activation in the CA1-CA3 pyramidal neurons of the hippocampus, the levels of thymosin beta4 were clearly increased in the hippocampus and neocortex during the first 2-3 h after injection. In the long term, kainate causes neuronal degeneration in the CA1-CA3 regions of the hippocampus and functionally related structures, provoking a depletion of thymosin beta4 messenger RNA in these areas; however, the levels of this transcript are restored two weeks after kainate injection. Moreover, we have found that, in these degenerating zones, gliosis is accompanied by an elevation of the levels of thymosin beta4 messenger RNA, particularly in the CA1-CA3 region of the hippocampus, the lateral geniculate nucleus and the mammillothalamic tract. The present results demonstrate the existence of relatively high levels of thymosin beta4 messenger RNA in several areas of the rat forebrain, indicating that this peptide plays an important role in the regulation of actin polymerization in these regions of the brain. Moreover, the elevation of this messenger RNA after kainate treatment suggests a function of thymosin beta4 in the production and remodelling of neuronal processes. Finally, our findings provide evidence for a participation of this actin-sequestering molecule in the reactivity of certain types of glial cell that follows kainate lesions.

Fine structure of the medullary lateral line area of Chelon labrosus (order perciformes), a nonelectroreceptive teleost.

The ultrastructure and synaptic organization of the nucleus medialis and cerebellar crest of the teleost Chelon labrosus have been investigated. The nucleus medialis receives projections from the anterior and posterior lateral line nerves. This nucleus consists of oval neurons and large crest cells ("Purkinje-like" cells) whose apical dendrites branch in the overlying molecular layer, the cerebellar crest. In the dorsal region of the nucleus medialis, the perikarya and smooth primary dendrites of the crest cells are interspersed among myelinated fibers and nerve boutons. The ventral layer of the nucleus medialis contains crest cell perikarya and dendrites as well as oval neurons. The cerebellar crest lacks neuronal bodies, but the apical dendrites of crest cells receive synapses from unmyelinated and myelinated fibers. In the cerebellar crest, two types of terminals are presynaptic to the crest cell dendrites: boutons with spherical vesicles that form asymmetric synapses with dendritic spines and boutons containing pleomorphic vesicles that form symmetric synapses directly on the dendritic shaft. Most axon terminals found on the somata and primary dendrites of crest cells in the nucleus medialis have pleomorphic vesicles and form symmetric contacts, though asymmetric synapses with spherical vesicles and mixed synapses can be observed; these mixed synapses exhibit gap junctions and contain spherical vesicles. Unlike crest cells, the oval neuron perikarya receive three types of contacts (symmetric, asymmetric, and mixed). The origins and functions of these different bouton types in the nucleus medialis are discussed.

An immunocytochemical and ultrastructural study of a specialized glial region of the medulla oblongata of the adult and juvenile grey mullet.

Electron microscopy together with glial fibrillary acidic protein (GFAP) and vimentin immunocytochemistry reveals the presence of a specialized glial region in the octavolateral area of the medulla oblongata of adult and juvenile grey mullets, Chelon labrosus. Glial cells, which can he characterized as ependymal and subependymal cells, originate in the walls of the lateral recess of the fourth ventricle. They contain numerous gliofilaments and are connected through frequent gap junctions. Electron microscopy also reveals the lack of nerve cell parikarya and processes in this region. Immunocytochemistry reveals that the glial cells are strongly GFAP-positive in both adults and juveniles, whereas vimentin is only detected in this region in juveniles. The meninges associated with this glial region contains connective fibres, formed of very thick collagen fibres, that arc metachromatic and PAS-positive under light microscopy. These findings strongly support a structural role for this medullary specialization. Differences between adults and juveniles in the distribution of GFAP- and vimentin-immunoreactive structures in other regions of the medulla oblongata are also reported.

Light- and electron microscopic study of oligodendrocytes in the lateral line area of the medulla in Chelon labrosus (Teleostei).

The oligodendrocytes of the medullary lateral line area of the teleost Chelon labrosus were studied with light and electron microscopy. Oligodendrocytes are sharply differentiated from neurons or other class of glia cells from their ultrastructural characteristics. The three subtypes of oligodendrocytes (light, medium and dark) that have been recognized are not homogeneously distributed but have preferential locations related to the size of nearby myelinated fibres. No perineuronal oligodendrocytes are present in this medullary center. Oligodendrocytes show a variety of dense bodies, sometimes of bizarre shapes, in addition to characteristic mitochondria and endoplasmic reticulum. Three types of intercellular junctions were observed in these cells: gap junctions, tight junctions and puncta adhaerentia. Gap junctions and puncta adhaerentia link oligodendrocyte somata and astrocytic processes. Tight junctions were observed both between oligodendrocytes and between oligodendrocytes and astrocytic processes. The significance of these results is discussed in relation to the maturation and function of oligodendrocytes and the characteristics of fish brains.

Central projections of the vagus nerve in Chelon labrosus Risso (Teleostei, O. Perciformes).

The primary projections of the vagus nerve and its nuclei in a perciform teleost, Chelon labrosus, are described after application of hoseradish peroxidase (HRP) labeling and Nissl and silver staining methods. The vagus nerve has three peripheral roots, rostral, medial and caudal, which are formed from viscerosensory and visceromotor rootlets. In addition to viscerosensory and visceromotor rootlets, the caudal root has a cutaneous root and a 'descending' root. Dorsally in the caudal root, a fiber bundle enters the medulla from the retroocular and opercular skin region; this bundle joins the descending trigeminal root and courses with it rostrally and caudally. Fibers from another rootlet, which enters dorsolaterally, course caudally towards the spinal cord. This rootlet has not been described in other fishes. The vagal viscerosensory nucleus, where most of the viscerosensory fibers terminate, forms a column in which two types of neurons can be distinguished. The most caudal part of the nucleus is continuous with the commissural nucleus, into which vagal nerve projections also enter. No vagal projections were found in the area postrema. In the visceromotor column, two types of neurons are seen lateroventral to the IV ventricle.

Action of actinomycin D on glycosidase levels in the small intestine of hamsters.

Actinomycin D affects a number of functions of the epithelial cells of the small intestine. Maltase, saccharase and lactase levels in the small intestine of hamsters treated with various dosages of actinomycin D over various periods of time, differed from those observed in control animals: administration of 0.25 micrograms/g body weight, gave rise to a statistically significant increase in the maltase and saccharase levels measured after 4 h and a statistically significant reduction in the lactase levels measured after 8 h; administration of 1.5 micrograms/g body weight reduced the activity of all three enzymes at all times post-administration, the decrease being statistically significant for maltase after 2 and 8 h.

Primary nerve projections and primary nuclei of the octaval nerve in the teleost Chelon labrosus. An HRP study.

The medullary nuclei and the primary projections of the octaval nerve have been studied in the Teleost Chelon labrosus, using argentic impregnations, NISSL stains and anterograde marking with peroxidase. The octaval nerve enters the medulla in two separate branches, the anterior and posterior. In its intramedullary traject it originates ascendent and descendent bundles. Its fibres end principally in the ventral part of the octavo-lateral area, with practically no overlapping with the terminals of the lateral line nerves. Three neuronal groups appear in this zone: the magnocellular vestibular nucleus, the tangential nucleus and the descending octaval nucleus. The magnocellular nucleus, formed by large neurons, receives thick fibres from the anterior branch of the octaval nerve. The tangential nucleus can be subdivided into three parts: Dorsal, intermediate and ventral depending upon its afferents and efferents. The dorsal part receives fibres from the posterior root of the octaval nerve. Fibres from the anterior branch end in the intermediate and ventral parts. The descending octaval nucleus, formed by polymorphous neurons, receives descending fibres from the octaval nerve branches. These fibres form a peculiar neuropil. A few fibres from both branches end in the medial nucleus of the octavolateral area. No primary projections of the octaval nerve have been found to the cerebellar crests.