Expression of Daily Torpor in the Djungarian Hamster <i>(Phodopus sungorus) </i>Is Correlated with the Testosterone-Driven Vasopressin Content in the Lateral Septum

Abstract

In the Djungarian hamster (Phodopus sungorus), torpor bouts appear after exposure to short photoperiods (SP) for 11 weeks. Castration accelerates the occurrence of daily torpor when performed between the 1st week before and the 4th week after transfer to SP. In animals castrated 8 weeks before transfer to SP, daily torpor was observed nearly at the same time as in the control group. Vasopressin-immunoreactivity (VP-ir) in the lateral septum (LS) of the Djungarian hamster was examined. Dense VP-ir was seen in sexually active and in sexually inactive hamsters implanted with testosterone (T) capsules. No VP-ir could be detected in sexually inactive animals. Thus, the presence of VP-ir in the LS depends on circulating T levels. In control animals exposed to SP, complete disappearance of VP-ir in the LS was observed after 8 weeks. Castration on the day of transfer to SP reduced this period to 6 weeks. In these animals, the early occurrence of daily torpor is related to the quick disappearance of VP-ir in the LS. When castrated animals were maintained under long photo-periods the disappearance of VP-ir was not complete. However, VP-ir disappeared completely after transfer to SP. The results suggest that the SP message acts on daily torpor indirectly via testicular regression but also ‘directly’ via VP septal innervation.

Differential response patterns of kisspeptin and RFamide‐related peptide to photoperiod and sex steroid feedback in the Djungarian hamster (Phodopus sungorus)

“…To study the effects of photoperiod in the presence of testosterone, we implanted castrated animals at the time of castration with SILASTIC (Dow Corning Corp., Midland, MI, USA) tube capsules filled with testosterone (Sigma, St Quentin Fallavier, France) as reported previously . LP and SP adapted hamsters were implanted during castration surgery.…”

“…19,20 To study the effects of photoperiod in the presence of testosterone, we implanted castrated animals at the time of castration with SILASTIC (Dow Corning Corp., Midland, MI, USA) tube capsules filled with testosterone (Sigma, St Quentin Fallavier, France) as reported previously. 21 LP and SP adapted hamsters were implanted during castration surgery. The capsules (length 7.5 mm, inner diameter 1.57 mm and outer diameter 2.4 mm) were implanted s.c. under 3% isofl urane anaesthesia and delivered an LP testosterone level corresponding to the peak of the circadian testosterone rhythm in P. sungorus.…”

“…The capsules (length 7.5 mm, inner diameter 1.57 mm and outer diameter 2.4 mm) were implanted s.c. under 3% isofl urane anaesthesia and delivered an LP testosterone level corresponding to the peak of the circadian testosterone rhythm in P. sungorus. 14,[20][21][22] Again, these animals were analysed after 4 weeks of testosterone treatment (LPCT and SPCT groups).…”

Generation of the Melatonin Endocrine Message in Mammals: A Review of the Complex Regulation of Melatonin Synthesis by Norepinephrine, Peptides, and Other Pineal Transmitters

“…VPergic innervation displays gender and seasonal variations, and is dependent on sex hormone concentrations in some brain areas, such that the increase in VP is correlated to an increase in testosterone concentration (see De Vries et al, 1984Hermes et al, 1990;Pévet et al, 1987, for review). Therefore, VP 364 SIMONNEAUX AND RIBELAYGA is involved in the regulation of some seasonal functions such as hibernation (Hermes et al, 1989) and daily torpor (Ouarour et al, 1995). OT and VP are also involved in the transmission of circadian information within the photoneuroendocrine system.…”

Effects of 5-HT Denervation of the Suprachiasmatic Nuclei or Lesions of the Median Raphe Nucleus on Daily Torpor in the Djungarian Hamster, <i>Phodopus sungorus</i>

“…Although hibernation is distinguishable from daily torpor, the two processes represent changes in the set point for body temperature (Tb), which thus implies some common mech anisms. In the European hamster (Cricetus cricetus), for example, a testosterone-dependent vasopressin neurotransmitter system has been shown to be involved in the expression of hibernation [6] and this system is also involved in daily torpor regulation in the Djungarian hamster [7]. Vasopressin, how ever, is not the only neurotransmitter in volved in the regulation of these seasonal functions.…”