Testicular Recrudescence in the Male Black Bear (Ursus americanus): Changes in Testicular Luteinizing Hormone-, Follicle-Stimulating Hormone-, and Prolactin-Receptor Ribonucleic Acid Abundance and Dependency on Prolactin

Abstract

Testicular recrudescence in male black bears (Ursus americanus) is initiated in January and completed in May. The goals of this study in the black bear were to determine 1) if testicular abundance of LH-receptor (LHr), FSH-receptor (FSHr), and prolactin-receptor (PRLr) mRNA changes during recrudescence; 2) if these changes in mRNA abundance are associated with changes in serum LH, PRL, and testosterone (T) concentrations; and 3) if the spring increase in serum PRL concentrations is required for testicular recrudescence. Serum was obtained monthly from nine male bears for 2 yr, except in July and August. To suppress endogenous PRL, four bears were treated with Parlodel LAR, 50 mg per 70 kg body weight, monthly from January through May, whereas five bears served as controls. Testicular biopsies were obtained in January, March, and May and analyzed for LHr, FSHr, and PRLr mRNA abundance using reverse transcriptase-competitive polymerase chain reaction. The LHr and PRLr mRNA abundance was low in January, increased in March, and remained high in May, whereas the FSHr mRNA abundance remained constant. Serum concentrations of PRL and T increased in March, coincident with the increase in testicular LHr and PRLr mRNA abundance. Suppression of serum PRL concentrations during testicular recrudescence 1) prevented the increase in testicular LHr and PRLr mRNA abundance observed among control bears in March, 2) lowered serum T concentrations in March and April, and 3) resulted in reduced testis size in May. We conclude that testicular LHr and PRLr mRNA are seasonally regulated, and that PRL has a role in testicular recrudescence in the black bear.

Seasonal influence on fecal immunoreactive testosterone concentrations of male Formosan black bears (Ursus thibetanus formosanus)

“…Records in 2002 and 2005 from the Shou Shan Zoo in Kaohsiung showed that mating behavior was observed between June and September. An increase in photoperiod may cause luteinizing hormone receptor and prolactin receptor to increase, possibly related to an increase in the response between luteinizing hormone and the testes, which in turn stimulates the production of testosterone (Tsubota et al 1999;Komatsu et al 1997;Howell-Skalla et al 2000;Howell-Skalla et al 2002). Furthermore, the belief that breeding seasons are longer and earlier in subtropical zones has been verified by this study.…”

Absence of seasonal changes in FSHR gene expression in the cat cumulus–oocyte complex in vivo and in vitro

“…Contrary to our hypothesis and previous studies in seasonal male species (black bear, Howell-Skalla et al 2000;bat, Hayashi et al 2002;sheep, Sanford et al 2002), expression of these isoforms did not differ between reproductively active and inactive stages in the female cat. Therefore, this observation suggested that Tr-FSHR did not have a regulatory function in seasonal FSH sensitivity in the latter species.…”

“…Seasonally mediated variation in FSHR expression (mRNA or protein) has only been demonstrated in males of a few species (black bear, Howell-Skalla et al 2000;bat, Hayashi et al 2002; sheep, Sanford et al 2002) where reductions are directly correlated with spermatogenic declines. Therefore, this relationship is interesting to examine, especially given knowledge that a decrease in FSHR density has the potential of altering the response of rat granulosa cells to FSH from being stimulatory to antagonistic (Donadeu & Ascoli 2005).…”

Visualization of gene expression of prolactin-receptor (PRL-R) by in situ hybridization in reproductive organs of Typhlonectes compressicauda, a gymnophionan amphibian

“…In all species studied, PRL acts by binding to a specific membrane receptor (PRL-R) (Clarke et al 1997;Jabbour et al 1998;Ohkubo et al 1998;Howell-Skalla et al 2000;Sandra et al 2000;Higashimoto et al 2001). Two main forms of PRL-R transcript have been identified (BoleFeysot et al 1998), one of which is specific for a short form of receptor (Boutin et al 1988), while the other is specific for a long form whose molecule possesses a cytoplasmic tail (Boutin et al 1988;Shirota et al 1990).…”