Embryonic development of four different subsets of cholinergic neurons in rat cervical spinal cord.

The developmental stage at which a neuron becomes committed to a neurotransmitter phenotype is an important time in its ontogenetic history. The present study examines when choline acetyltransferase (ChAT) is first detected within each of four different subsets of cholinergic neurons previously identified in the cervical enlargement of the spinal cord: namely, motor neurons, partition cells, central canal cluster cells, and dorsal horn neurons. By examining the temporal sequence of embryonic development of these cholinergic neurons, we can infer the relationships between ChAT expression and other important developmental events. ChAT was first detected reliably on embryonic day 13 (E13) by both biochemical and immunocytochemical methods, and it was localized predominantly within motor neurons. A second group of primitive-appearing ChAT-positive cells was detected adjacent to the ventricular zone on E14. These neurons seemed to disperse laterally into the intermediate zone by E15, and, on the basis of their location, were tentatively identified as partition cells. A third group of primitive ChAT-immunoreactive cells was detected on E16, both within and around the ventral half of the ventricular zone. By E17, some members of this "U"-shaped group appeared to have dispersed dorsally and laterally, probably giving rise to dorsal horn neurons as well as dorsal central canal cluster cells. Other members of this group remained near the ventral ventricular zone, most likely differentiating into ventral central canal cluster cells. Combined findings from the present study and a previous investigation of neurogenesis (Phelps et al.: J. Comp. Neurol. 273:459-472, '88), suggest that premitotic precursor cells have not yet acquired the cholinergic phenotype because ChAT is not detectable until after the onset of neuronal generation for each of the respective subsets of cholinergic neurons. However, ChAT is expressed in primitive bipolar neurons located within or adjacent to the germinal epithelium. Transitional stages of embryonic development suggest that these primitive ChAT-positive cells migrate to different locations within the intermediate zone to differentiate into the various subsets of mature cholinergic neurons. Therefore, it seems likely that spinal cholinergic neurons are committed to the cholinergic phenotype at pre- or early migratory stages of their development. Our results also hint that the subsets of cholinergic cells may follow different migration routes. For example, presumptive partition cells may use radial glial processes for guidance, whereas dorsal horn neurons may migrate along nerve fibers of the commissural pathway. Cell-cell interactions along such diverse migratory pathways could play a role in determining the different morphological, and presumably functional, phenotypes expressed by spinal cholinergic neurons.

The effect of acute ethanol administration on GABA receptor binding in cerebellum and hypothalamus.

The effect of the intraperitoneal administration of ethanol on [3H]GABA binding and glutamic acid decarboxylase (GAD) in cerebellum and hypothalamus was investigated. Acute ethanol administration produced an increase in the binding capacity of the high affinity GABA binding sites and a decrease in the binding capacity of low affinity sites. A decrease in the binding capacity of the high affinity GABA binding sites and an increase in the binding capacity of the low affinity sites were observed in the hypothalamus. No apparent changes were detected in the binding affinities for the two types of GABA receptor sites in both brain areas following ethanol treatment. Ethanol enhanced GAD activity in the cerebellum and reduced GAD activity in the hypothalamus. Changes in GABA binding may be involved in some of the neuropharmacological effects of ethanol.

Effect of a powerful antagonist of LH-RH on testicular function in prepubertal male rats.

The effects of N-Ac-D-p-F-Phe1,D-p-Cl-Phe2,D-Trp3,6,D-Ala10-LH-RH, a new antagonistic analog of LH-RH, were tested on the testicular function and serum FSH and LH levels in immature male rats. Prolonged administration of this analog to prepubertal male rats resulted in lower testicular and seminal vesicle weights as compared with control rats treated with the vehicle only. Spermatogenesis was markedly delayed in rats injected with the analog. Serum FSH and LH levels were significantly lower in the analog-treated rats as compared to the controls. These data show that LH-RH antagonists may be useful for inhibition of spermatogenesis.

Prolonged treatment with gamma-aminobutyric acid (GABA)-mimetic substances in prepubertal male rats.

The effect of chronic treatment with a gamma-aminobutyric acid (GABA)-mimetic compound, progabide, and an inhibitor of GABA-transaminase, gamma-acetylenic GABA (GAG), was tested in prepubertal male rats. The effect of gamma-butyrolactone (GBL), given orally, was also tested. The rats treated with progabide did not show any difference in body, testicular, or seminal vesicle weights or serum prolactin levels, as compared with control rats. Treatment with GAG, at both dose levels used, did not significantly affect body weight. Testicular weight was significantly lower in the group of rats treated with the low dosage of GAG (5 mg/kg), and serum prolactin was significantly lower in the rats treated with the high dosage of GAG (20 mg/kg) as compared with control rats. In the first experiment performed with GBL, the rats given this compound had significantly lower body and testicular weights as compared with control rats. In the second experiment, GBL-treated rats had body weights similar to those of control rats, but testicular weights were significantly decreased. Prolonged treatment with GABA mimetics may affect the hypothalamic-pituitary-testicular axis.