Effects of Photoperiod and Ambient Temperature on the Gonadotropin-Releasing Hormone Neuronal System in the Gray Hamster, <i>Tscherskia triton</i>

Abstract

In seasonal breeders like the hamster, gonadal function depends on the photoperiod. The present study examined the effects of different photoperiods and ambient temperatures on the gonadotropin-releasing hormone (GnRH) neuronal system in male gray hamsters, Tscherskia triton. Hamsters were kept from birth under a long-day (LD: 16 h light and 8 h dark) photoperiod and at 23°C until the experiment began. The animals were then kept for 30 days under different photoperiods and ambient temperatures. After autopsy, immunocytochemical and semiquantitative reverse transcription-polymerase chain reaction analyses were performed on the hamster forebrain. Exposure to a short-day (SD: 8 h light and 16 h dark) photoperiod at 23°C induced a functional decline in the GnRH neuronal system (increased neuron number and immunoreactivity, and reduced cell size). LD with low ambient temperature (7°C) did not influence the GnRH neuronal system. In contrast, SD with low ambient temperature enhanced the SD-induced functional decline in GnRH neurons. Changes in immunoreactivity of GnRH fibers in the median eminence, their release site, were also similar to those in neuronal perikarya. Significant differences in GnRH gene expression were detected in the SD only group and the SD with low ambient temperature group. However, no differences were detected between the two groups. These findings suggest that low ambient temperature enhanced the SD-induced decline in GnRH release from nerve terminals, but was not a crucial factor in the synthesis of this decapeptide.

Trans‐seasonal activation of the neuroendocrine reproductive axis: Low‐temperature winter dormancy modulates gonadotropin‐releasing hormone neurons in garter snakes

“…Other environmental cues, such as temperature and resource availability, can be used to supplement photoperiod information to fine‐tune responses to the environment. In gray hamsters ( Tscherskia triton ), for example, the combination of a short photoperiod together with low ambient temperature enhanced the inhibitory effects of short days on GnRH release (Kawamoto et al, 2000). In some animals, however, supplementary cues play a much greater role than photoperiod in regulating seasonal rhythms; in ectotherms that undergo prolonged periods of winter dormancy underground, for example, environmental temperature is the dominant cue regulating seasonal rhythms.…”

Photoperiod-Independent Hypothalamic Regulation of Luteinizing Hormone Secretion in a Free-Living Sonoran Desert Bird, the Rufous-Winged Sparrow <i>(Aimophila carpalis)</i>

“…However, it could also indicate increased storage of GnRH. Enlarged GnRH cells are commonly observed during breeding or when GnRH production is believed to be high in birds [Foster et al, 1987;Goldsmith et al, 1989;Hahn and Ball, 1995;Parry et al, 1997;Cho et al, 1998;Deviche et al, 2000;MacDougall-Shackleton et al, 2001;Moore et al, 2006], mammals [Kawamoto et al, 2000], and fish [Davis and Fernald, 1990;Francis et al, 1992;White and Fernald, 1993]. Ultrastructural studies of neurons in mammals show increased endoplasmic reticulum and number of granulated vesicles associated with increased cell body size [King et al, 1974;Tsuruo et al, 1984;Rance et al, 1990] which is consistent with increased peptide production.…”

“…Ultrastructural studies of neurons in mammals show increased endoplasmic reticulum and number of granulated vesicles associated with increased cell body size [King et al, 1974;Tsuruo et al, 1984;Rance et al, 1990] which is consistent with increased peptide production. Further, proGnRH mRNA (also referred to as GnRH mRNA) is higher in animals with larger GnRH-ir cell bodies [Kawamoto et al, 2000;White et al, 2002].…”

Basic properties and annual changes of follicle‐stimulating hormone receptors in the testis of horseshoe bats, Rhinolophus ferrumequinum

“…Serum T was measured by radioimmunoassay using the dextran-charcoal method (ICN Biomedical Inc., Costa Mesa, CA ) as reported previously (Kawamoto et al, 2000b). Assay of T was performed with 100 to 400 µl of serum sample per tube and extracted with 2 ml of diethyl ether per 100 µl of serum.…”