The effects of the tricyclic antidepressant amitriptyline on the rat hypothalamic-pituitary-adrenocortical (HPA) system were studied. The time-course experiments showed that amitriptyline, given via the drinking water (4.5 mg/kg.day), produces significant decreases (P < 0.05) in adrenal weight after 5 (-20%) and 7 weeks (-21%) of treatment. Hippocampal mineralocorticoid receptor (MR) levels were down-regulated at days 3 (-27%) and 7 (-20%), and transiently up-regulated at 2 (+40%), 5 (+74%), and 7 (+18%) weeks of treatment. Hippocampal glucocorticoid receptor (GR) levels were slightly down-regulated at days 3 (-8%) and 7 (-17%), transiently up-regulated by 26% at 5 weeks, and indistinguishable from controls after 7 weeks of treatment. MR levels were unchanged in the hypothalamus and neocortex, whereas hypothalamic GR concentrations were elevated and neocortical receptor levels were not altered. Dose-response experiments showed significant decreases in adrenal weight when rats were treated with 4.5 (-14%), 8.8 (-16%) and 14.5 (-13%) mg/kg.day antidepressant, but this applied only for the 4.5- (-14%) and 8.8- (-12%) mg/kg.day doses when the ratio of adrenal weight to body weight was considered. The dose-response relationship regarding hippocampal GR content displayed an inverted U-shaped curve, whereas this was less marked for MR levels. A dose of 4.5 mg/kg.day appeared to be optimal for the rise in MR as well as GR. Concerning the neuroendocrine implications of chronic antidepressant treatment, amitriptyline (5 weeks, 4.5 mg/kg.day) produced significant decreases in basal (ACTH, -47%; corticosterone, -31%) as well as stress (30 min novel environment)-induced plasma ACTH (-38%) and corticosterone (-57%) levels. Previous experiments have forwarded a role of limbic MR in the tonic control of basal HPA activity. Based on the present data, we hypothesize that during amitriptyline treatment a rise in limbic MR may be the initial phenomenon in a successively adjusting HPA system, as evidenced by the decreasing plasma hormone concentrations, declining adrenal size, and up-regulation of GR in particular brain regions.
To address the possibility that stem cell factor (SCF) is a paracrine regulator of germ cell development in the adult rat testis, stage-specific distribution of SCF messenger RNA (mRNA) was investigated with Northern blot and in situ hybridization analyses. The highest levels of SCF mRNA were found in stages II-VI of the rat seminiferous epithelial cycle, whereas the lowest levels were in stages VII-VIII. Intermediate levels of SCF mRNA were detected in stages IX-XIV-I of the cycle. The expression of the SCF gene was found to be developmentally regulated, and the expression pattern followed the process of Sertoli cell proliferation and differentiation during postnatal life. The effect of mouse recombinant SCF on spermatogonial DNA synthesis was studied using an in vitro tissue culture system for stage-defined seminiferous tubules. A significant increase in DNA synthesis in spermatogonia could be detected when tubule segments from stage XII were cultured in the presence of 100 ng/ml SCF for 48 h (P < 0.05) and 72 h (P < 0.01). This observation was further confirmed with autoradiographic analyses; almost a 100-fold increase in thymidine incorporation in the SCF-treated (100 ng/ml) tubule segments was observed compared with that in untreated samples. The results of the present study suggest that SCF is a Sertoli cell-produced paracrine regulator and acts as a survival factor for spermatogonia in the adult rat seminiferous epithelium in a stage-specific manner.
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