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

Abstract

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.

Immunohistochemical and Morphometric Study of Pituitary Pars Distalis Thyrotrophs of Male Viscacha (Lagostomus maximus maximus): Seasonal Variations and Effect of Melatonin and Castration

“…Seasonal variations studies of the thyrotroph cells number and cellular activity carried out in woodchuck ( Marmota monax ) have shown that these parameters vary according to the thyroid gland activity and the animal physiological activities (Frink et al, 1980). A higher proportion of these cells in June after hibernation and a lower proportion in December during mating were observed in bat (Anthony and Gustafson, 1984). This finding suggests that the increase of thyrotrophs frequency in spring coincides with a metabolic activity increase and also with early stages of the spermatogenesis.…”

“…The localization and morphology of PD TSH cells were studied in species such as monkey (Girord and Trouillas, 1980), bat (Anthony and Gustafson, 1984; Mikami et al, 1988), rat (Kum et al, 2006), toad (Miranda et al, 1996), and bullfrog (Tanaka et al, 1990), and the results show a similar distribution pattern in different species. It is interesting to point out that the TSH cells are generally restricted to the PD anterior and medial zones, and they are rarely observed in the dorsal region next to pars intermedia (PI).…”

“…Quantitative studies have shown that the thyrotrophs generally constitute a small proportion of the PD cells, 4–6% (Childs et al, 1983) and 2.09% (Dada et al, 1984) in rat, 1.36% in bat (Anthony and Gustafson, 1984), 0.43% in mouse (Messier, 1965), 5% in voles (Clarke and Forsyth, 1964), and 1% in black‐tailed deer (West and Nordan, 1976). In viscacha, the values observed were between 2.39% and 1.16% (summer–early autumn and winter, respectively), showing a similar proportion to that reported for other species.…”

“…Several studies on different species such as bullfrog (Tanaka et al, 1990), rat (Kum et al, 2006), dog (el‐Etreby and el‐Bab, 1978), bat (Mikami et al, 1988), and monkey (Girod and Trouillas, 1980) have described the morphological characteristics and localization of the TSH cells in the pituitary pars distalis (PD). Some investigations on woodchuck (Frink et al, 1980), bat (Anthony and Gustafson, 1984), and rat (Yoshimura et al, 1982; Kum et al, 2006) have reported variations in the cells activity, number, and ultrastructure in relation to the reproductive season. Other authors have investigated the relation between the pineal gland and the HPT axis.…”

Endocrine Control of the Reproductive Activity in Hibernating Bats

“…Most findings on the function of hormoneproducing cells have been made using immunohistochemistry with heterologous antisera as follows. During the arousal period, thyrotrophs show the increased activity (Anthony and Gustafson, 1984b). Annual changes in corticotrophs are related to the so-called fat cycle in tropical vespertilionid bats (Singh and Krishna, 1996b).…”