The effect of culture conditions, serum supplementation or chemically defined medium and the influence of thyroid hormone were studied on the development of the Na2+,K2+-adenosine triphosphatase (Na+,K+-ATPase) and on the intracellular content of K+ and Na+ ions in cultures which either were greatly enriched in a neuronal cell type, the cerebellar granule cells, or contained a mixed population of cells (brain reaggregates). Foetal rat brain reaggregates displayed lower Na+,K+-ATPase activity when cultured in chemically defined medium than in the presence of serum. Supplementation of the serum-free medium with thyroid hormone resulted in a rise in the Na+,K+-ATPase activity and [+H]ouabain binding to levels similar to those found in the cultures grown in the serum-containing medium. Thyroid hormone had no significant effect on the Mg2+-ATPase activity and on the intracellular content of Na+ and K+ ions. In the granule cell-enriched cerebellar surface cultures the Na+,K+-ATPase activity was lower when the cells were grown in chemically defined medium compared with the serum-containing medium, and the intracellular Na+ to K+ ratio was higher. Thyroid hormone had no effect on the Na+,K+-ATPase activity, [3H]ouabain binding or Mg2+-ATPase activity. The hormone also failed to influence ATPase activities in cerebellar astrocytes maintained in chemically defined medium. Although thyroid hormone had no effect on the Na+,K+-ATPase activity of cultured cerebellar granule cells, treatment with the hormone resulted in a decrease in the ratio of intracellular Na+ to K+ ion content. The effect of the hormone on the Na+,K+-pump activity in live cells was therefore tested by estimating ouabain-sensitive 86Rb uptake. This was regulated as in other cell types, by the rate of Na+ entry: the Na+-ionophore monensin trebled the rate of 86Rb uptake, which was also increased (+30–100%) by 10% foetal calf serum, the maximal response being obtained by about 20 min exposure to serum. The effect was completely blocked by the Na+/H+ exchange inhibitor amiloride. The factor(s) in the serum responsible for the regulation of the Na+,K+-pump were, however, not the thyroid hormones, which failed to affect 86Rb uptake.

The development of the gamma-aminobutyrate (GABA)-ergic system in the human cerebral cortex and cerebellum was studied in post mortem specimens, by estimating the activity of glutamate decarboxylase (GAD) and the binding capacity for muscimol as markers of GABA-ergic nerve terminals and GABA receptors respectively. The age periods studied were as follows (number of specimens in parentheses): fetal period, 17--24 and 28 weeks, gestational age (GA) (15); perinatal period, 26--42 weeks GA (9); postnatal period, 43--56 and 74 weeks GA (11); adult life, 26, 47, 57--73 years (9). Total protein and DNA were estimated in all specimens. Differences between the cerebral cortex and the cerebellum in the ontogenesis of the GABA-ergic system were revealed. In the cerebral cortex, GAD-specific activity increased progressively during development, but at term had only reached approximately 20% of the adult value, and the trend in the postnatal specimens indicated that the adult level is not reached until some time after 60 weeks GA. The concentration of muscimol binding sites, on the other hand, rose more rapidly than GAD activity with age in the cerebral cortex, attaining adult values by 60 weeks GA and being already at term approximately 45% of the mean adult figure. In the cerebellum, the relative development of pre- and postsynaptic markers was the reverse of that in the cerebral cortex: GAD specific activity had reached the adult value by 60 weeks GA and approximately 40% of this adult level was attained at term, while the muscimol binding site concentration was only about 10% of the adult value at term and was still increasing at 60 weeks GA. The affinity of the receptor for [3H]-muscimol did not change during development, and was the same in cerebral cortex and cerebellum.

The development of the gamma-aminobutyrate (GABA)-ergic system in the human cerebral cortex and cerebellum was studied in post mortem specimens, by estimating the activity of glutamate decarboxylase (GAD) and the binding capacity for muscimol as markers of GABA-ergic nerve terminals and GABA receptors respectively. The age periods studied were as follows (number of specimens in parentheses): fetal period, 17--24 and 28 weeks, gestational age (GA) (15); perinatal period, 26--42 weeks GA (9); postnatal period, 43--56 and 74 weeks GA (11); adult life, 26, 47, 57--73 years (9). Total protein and DNA were estimated in all specimens. Differences between the cerebral cortex and the cerebellum in the ontogenesis of the GABA-ergic system were revealed. In the cerebral cortex, GAD-specific activity increased progressively during development, but at term had only reached approximately 20% of the adult value, and the trend in the postnatal specimens indicated that the adult level is not reached until some time after 60 weeks GA. The concentration of muscimol binding sites, on the other hand, rose more rapidly than GAD activity with age in the cerebral cortex, attaining adult values by 60 weeks GA and being already at term approximately 45% of the mean adult figure. In the cerebellum, the relative development of pre- and postsynaptic markers was the reverse of that in the cerebral cortex: GAD specific activity had reached the adult value by 60 weeks GA and approximately 40% of this adult level was attained at term, while the muscimol binding site concentration was only about 10% of the adult value at term and was still increasing at 60 weeks GA. The affinity of the receptor for [3H]-muscimol did not change during development, and was the same in cerebral cortex and cerebellum.

The effect of undernutrition on the activity of glutamate decarboxylase (GAD) and choline acetyltransferase (ChAc) (markers for the GABA-ergic and the cholinergic transmitter system, respectively) was studied in various parts of the rat brain at the age of 10, 15 and 21 days, and at day 54 following 33 days of rehabilitation. The brain regions investigated were the olfactory bulbs, cerebellum, pons-medulla, hypothalamus, colliculi, cerebral cortex hippocampus and the residual brain. Undernutrition resulted in a marked retardation of the developmental rise of the activities of both enzymes, expressed in terms of either total brain part or unit weight or protein. The effect diminished with age even during the period of nutritional deprivation. In most brain regions the enzyme activities were restored to normal after rehabilitation. In the cerebral cortex the total activity of both enzymes was persistently reduced, although the concentration of GAD exceeded the control levels. A negative correlation was manifested between the activities of GAD and ChAc in the different brain parts (except the cerebellum) during development. The correlation became significant by day 21 in the controls, but only after postweaning rehabilitation of the undernourished rats. The results showed therefore that undernutrition caused a reversible retardation in the development of these two transmitter enzymes, and they suggested that even the balance of the GABA-ergic and cholinergic systems throughout the brain can be restored to normal by rehabilitation.

The effect of undernutrition on the rate of protein synthesis and the development of metabolic compartmentation of glutamate in the brain was investigated by using [U -14 C] leucine as precursor. In the brain of normal rats the incorporation rate of [14C] leucine into protein was at a maximum during the 3rd week after birth, but in the undernourished animal this rate was markedly lower. The biochemical maturation of the brain, followed in terms of the age-dependent increase in the glutamine/glutamate specific radioactivity ratio, was severly retarded in the undernourished animals, mainly as a result of a marked depression in the conversion of leucine carbon into glutamine. However these biochemical effects of undernutrition were reversible: on rehabilitation from Day 21-35 the rate of conversion of leucine carbon, both into proteins and glutamate and glutamine, was restored to normal.