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Neurons are born in the ventricular walls of the vertebrate central nervous system. From there, the young neurons migrate to their final destinations, where differentiation occurs. Neuronal migration has been described during the ontogeny of the avian and mammalian brain. Whereas in mammals most neurogenesis occurs during early development, in the adult avian forebrain wide-spread neurogenesis continues to occur. How do neurons born in adulthood reach their final destination? We report here that small elongated cells, born in the ventricular zone adjacent to the lateral ventricle, differentiate into mature neurons 20-40 days later, after migrating over distances of up to 5 mm. Migration rates are highest (28 micron h-1) when young neurons migrate through regions which are rich in radial glia. The adult vertebrate brain offers unique opportunities for studying factors that regulate neuronal migration, pathfinding and differentiation.

When embryonic central nervous system neurons are seeded at low densities with Eagle's basal medium supplemented with the serum substitute N1, glucose, and glutamine, neuronal survival for even 24 h requires the additional supply of exogenous pyruvate--and so does the survival of many peripheral nervous system neurons. Pyruvate can be replaced by alpha-ketoglutarate or oxaloacetate, but not by Krebs cycle substrates that are not keto acids. Most other alpha-keto acids tested (though not beta- or gamma-keto acids) also mimic pyruvate. The apparent equivalence to pyruvate of all these compounds includes identical ED50 values (300 microM for embryonic avian fore-brain neurons, 30-40 microM for rat hippocampal neurons), and also identical susceptibilities to the pyruvate-sparing effects of other low-molecular-weight agents present in Dulbecco's modified Eagle's medium or in astroglia conditioned medium. The substitute alpha-keto acids, however--unlike pyruvate, alpha-ketoglutarate, or oxaloacetate--support cell survival only in the presence of alpha-amino acids that transaminate to alpha-ketoglutarate, oxaloacetate, or pyruvate. The alpha-keto acids, therefore, operate as acceptors of amino groups from appropriate donors to generate Krebs cycle-relevant substrates. Consistent with this view, [14C]glutamate did not generate appreciable 14CO2 unless accompanied by a suitable alpha-keto acid.(ABSTRACT TRUNCATED AT 250 WORDS)

A method for studies of organic solvent effects on the development of neurones and astrocytes is described. Chick embryos in ovo were exposed to a low concentration of carbon tetrachloride vapours. After the exposure, primary cultures of neurones and astrocytes were prepared from the brain hemispheres of the embryos. Toxic effects of the solvent were analyzed in the cultures during the course of cellular differentiation as changes in cell growth and morphology, respiratory activity, and biochemical properties characteristic of each cell type. The development of neurones from embryos exposed from day 5 to day 8 to 25 p.p.m. of carbon tetrachloride was not affected by the exposure. On the other hand, growth rate and respiratory activity of astrocytes from embryos exposed from day 11 to day 14 to 25 p.p.m. of CCl4 were affected by the exposure, whereas no morphological changes or changes in the cyclic AMP levels could be observed. Consequently, low concentrations of carbon tetrachloride seem to affect the development of astrocytes rather than that of neurones in our experimental system.

One of the dogmas of neurobiology has it that when nerve cells in the vertebrate brain die, they are not replaced by new ones. The author finds to the contrary. He has shown that when the adult canary needs to learn new songs, it does grow some new neurons. The finding could eventually lead to the discovery of ways to repair lesions in the human brain.

The ontogenesis of the synaptic function was investigated in the central noradrenaline (NA), dopamine (DA), serotonin (5-HT), acetylcholine (ACh) and GABA nervous systems of developing rats. Monoamines histochemically first appeared on days 12 to 14 in the fetal brain and may exert a trophic action on target neurons as a "differentiation signal". The presynaptic functions such as the high affinity uptake and depolarization-induced, Ca2+-dependent release of L-[3H]DA, and [2H]DA, and [3H]DA, and [3H]5-HT were observed in synaptosomes and slices from the fetus (18 days of gestation) and brain of newborn rats. Monoamine-stimulated activity of adenylate cyclase and specific binding of ligands in NA(alpha 1, alpha 2, beta 1, beta 2), DA, 5-HT, ACh (muscarinic and nicotinic) and GABA receptors indicated dynamic changes through postnatal development. Behavioral findings suggest when neurotransmitter receptors become sensitive and reach functional maturity (NA and DA, already at birth; 5-HT and muscarinic ACh, 15 to 20 days; GABA, 12 to 13 days (mouse)). In addition, differences in behavioral responsiveness to drugs were observed in rats at various developing stages, probably due to the interaction between plural neuronal systems. Finally, the brain undergoing rapid differentiation seems to be most sensitive to hormones and centrally acting drugs. Thus, permanent alteration in central functions may occur when some classes of drugs, dose-dependently, are administrated to animals at the perinatal stage.