Luteinizing hormone beta (LHβ) and follicle stimulating hormone beta (FSHβ) subunits and their mRNAs were studied in the ram pars tuberalis following different seasonal (winter vs summer) and experimental (intact vs castrated animals) conditions. Hormone-containing cells were identified by immunohistochemistry, and mRNAs for LHβ and FSHβ by in situ hybridization using homologous double-stranded35S-cDNAs. The labelling was quantified by image analysis. Immunohistochemical staining showed that cells containing LHβ and FSHβ were localized mainly in the ventral part of the pars tuberalis but that, in the summer, additional LHβ-containing cells were present in the dorsal part in intact rams. On the other hand, LHβ-mRNA labelling was found in the whole pars tuberalis in wethers but only in the ventral part in intact rams. The magnitude of LHβ-mRNA labelling was significantly greater in summer than in winter rams, and in castrated than in intact animals (P<0.001). However, the number of labelled cells was found to be the greatest in the winter (P<0.001) and was not affected by castration. FSHβ-mRNA expression was similar to that of LHβ-mRNA except that the level and extent were considerably lower. Thus, our results show an increase in the magnitude of gonadotropin β subunit-mRNA in the summer and following castration; this increase appears to involve the entire par
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