Prolactin Secretion in Female Siberian Hamsters following Hypothalamic Deafferentation Role of Photoperiod and Dopamine

Abstract

The role of the hypothalamic paraventricular nucleus (PVN) region in the control of seasonal prolactin (PRL) responses was investigated in female Siberian hamsters via disruption of PVN afferent connections from the region of the suprachiasmatic nucleus (SCN). Adult female hamsters received sham surgery or horizontal knife cuts placed ventral to the PVN so as to sever dorsally projecting fibers from the SCN and were either immediately transferred to a short-day photoperiod [10 h light: 14 h dark (10L: 14D); experiment (exp.) 1A] or returned to the long-day photoperiod (16L:8D; exp. 1B and 2). Serial blood samples were analyzed for determination of circulating PRL and follicle-stimulating hormone (FSH; exp. 1 A) levels at various time points after surgery. In exp. 1 A, sham-operated animals showed a steady decline in circulating levels of both PRL and FSH during exposure to 10L. Animals with knife cuts that passed through the extent of the SCN were prevented from showing declines in PRL and FSH during exposure to 10L. Animals with knife cuts located ventral to or through the PVN but dorsal to the SCN maintained high FSH levels during short-day exposure but showed a decline in PRL. Similarly, animals with knife cuts in exp. IB and 2 showed a decline in circulating PRL despite continued exposure to a stimulatory photoperiod. In exp. 2, the efficacy of a dopaminergic agonist (CB154) and an antagonist (pimozide) in altering circulating PRL under the 16L photoperiod was evaluated. CB154 induced declines in PRL in knife-cut but not sham-operated animals, whereas administration of pimozide elevated circulating PRL in both groups. These results suggest that disruption of afferent input to the PVN region may result in reductions in circulating PRL independently of the photoperiodic regulation of this hormone, and via mechanisms other than increased dopaminergic tone, i.e., possibly through disruption of a hypothalamic PRL-stimulating system.

Evidence for an endogenous per1 ‐ and ICER ‐independent seasonal timer in the hamster pituitary gland

“…Pharmacological experiments using the same in vivo model have clearly shown that seasonal changes in prolactin secretion occur independent of hypothalamic dopamine or noradrenaline secretion (29,30). Studies of seasonal rodents have only implied a partial role for hypothalamic signaling in seasonal prolactin regulation (31,32) and suggest that some neuronal control of prolactin secretion occurs independent of photoperiod (33). It has therefore been hypothesized that hypothalamic factors primarily regulate prolactin homeostasis via feedback loops, whereas tuberalin acts within these loops to drive seasonal prolactin secretion and thereby regulate the 'set point' of prolactin homeostasis throughout the seasonal cycle (30).…”

The effect of photoperiod and melatonin on plasma prolactin concentrations in female guanaco (Lama guanicoe) in captivity

“…Some effects of photoperiod on prolactin release occur independently of the pineal melatonin signal. In this case, the hypothalamic regulation of prolactin is predominantly via an inhibitory dopaminergic input (Badura & Goldman, 1994).…”

Analysis of Mitotic Activity of Fetal Tissues by Continuous Administration of (2-14C)Thymidine into Maternal Abdominal Aorta in Hamsters.

“…The morning when spermatozoa in the vaginal smear were detected was defined as day 1 of pregnancy. On day 12 of pregnancy, the pregnant Accepted for publication: May 8, 1996 Correspondence: A. Narita F and teratological fields [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], because their length of pregnancy is short, estrus can be easily detected by vaginal mucus, regular 4-day estrous cycles continue until 20 months of age [8], and their fetuses have high sensitivity to exogenous teratogens [1-4, 6, 7, 9, 10].…”