Seasonal variations in pituitary thyrotropes of the hibernating bat Myotis lucifugus lucifugus: an immunohistochemical study.

Pituitary thyrotropes were identified throughout the year in the hibernating bat Myotis lucifugus lucifugus by means of light microscopic immunohistochemistry. These cells occupied a small proportion of the volume of the pars distalis (mean = 1.36% in males; mean = 1.52% in females) and exhibited a limited distribution pattern that was characteristic of all animals examined. Cells that were immunoreactive with an antiserum directed against the beta subunit of thyroid-stimulating hormone were most numerous in the median rostral and ventral regions; they were scarce or absent in the dorsal portion of the gland and in the extreme lateral wings. No significant seasonal variations were observed in this cell population in females. In males, however, immunoreactive thyrotropes occupied a significantly larger proportion of the pars distalis in June (following arousal from hibernation than at other times of year. No evidence of involution was observed in these anterior pituitary cells in either males or females during hibernation.