Prenatal and postnatal ontogenesis of neurotransmitter-synthetizing enzymes and [ 125I]tetanus toxin binding capacity in the mouse hypothalamus

Abstract

In order to estimate the early neuronal maturation in the hypothalamus, we followed the development of 3 neurotransmitter-synthetizing enzymes (TH, GAD, ChAT) and a neuronal cell surface marker (tetanus toxin) in the hypothalamus as compared to cerebral hemispheres. This showed that TH, ChAT and GAD activities were present in both structures on the fourteenth fetal day. Yet, before birth, whereas GAD and ChAT activities remained low and followed a similar development in the 2 structures, TH activity was important and higher in hypothalamus than in brain hemispheres. After birth the activities of the 3 enzymes increased rapidly between day 5 and day 20, but their evolution in the hypothalamus always preceded that in the cerebral hemispheres. Tetanus toxin binding capacity was present on the thirteenth fetal day in the 2 structures, but during fetal life in the hypothalamus, the level of toxin binding was always higher than in the cerebral hemispheres. After birth, the toxin binding increased between day 2 and day 10 and reached adult level at the same time in both structures, around day 15. We conclude that neuronal maturation proceeds earlier in the hypothalamus than in brain hemispheres, and that the differentiation of a neuronal surface marker appears concomitantly with that of specific intraneuronal enzymes.