Photoperiodic Regulation of Histamine H3 Receptor and VGF Messenger Ribonucleic Acid in the Arcuate Nucleus of the Siberian Hamster

Abstract

To survive winter the Siberian hamster has evolved profound physiological and behavioral adaptations, including a moult to winter pelage, regression of the reproductive axis, onset of daily torpor and increased capacity for thermogenesis. However, one of the most striking adaptations is the catabolism of intraabdominal and sc fat reserves contributing to the loss of up to 40% of body weight. These physiological and behavioral adaptations are photoperiodically driven, yet neither the site(s) in the brain nor the molecular mechanism(s) involved in the regulation of these profound adaptations is known. Here we report a dynamic regulation of gene expression in a dorsal region of the medial posterior area of the arcuate nucleus (dmpARC) of the Siberian and Syrian hamster brain in response to altered photoperiod. We show mRNA for the histamine H3 receptor is down-regulated and VGF is up-regulated in the dmpARC in hamsters switched from long- to short-day photoperiod. These data provide further evidence to support the view that the dmpARC is a major site to relay photoperiodic changes and as a site for the long-term regulation of seasonal physiology and behavior.

The Histaminergic Signaling System Exerts a Neuroprotective Role against Neurodegenerative-Induced Processes in the Hamster

“…Moreover, the high expression levels of H 1 R following the blockade of H 3 Rs plus the recent detection of the elevated transcription pattern of another major cellular stress factor, i.e., heat shock proteins (unpublished data) in the amygdala, supply convincing evidence that this limbic region and the increased expression of H 1 R, together with low H 3 R mRNA levels in another hibernating species (Barrett et al, 2005), may turn out to be key protective components for the different brain regions of patients with neurodegenerative disorders.…”

“…On the other hand, high expression levels of H 3 R, especially in amygdalar areas as well as the cortex layers of the hamster treated with 3-NP, appear to be consistent with species-specific responses as shown by an up-regulation of this subtype in striatum of stressed rats (Ito et al, 1999) as compared with a down-regulation in diencephalic areas of other pathological states such as status epilepticus in the rat (Jin et al, 2005). Moreover, even environmental-related stressful conditions tend to play a determinant role on the transcriptional activity of this subtype as confirmed by the varying photoperiodic effects accounting for a down-regulating trend of H 3 R mRNA levels in the same brain region of another species, the Siberian hamster (Barrett et al, 2005).…”

Role of VGF-Derived Peptides in the Control of Food Intake, Body Weight and Reproduction

“…Under the control of photoperiod this species naturally becomes obese in the summer, but then enters a catabolic state in which it becomes hypophagic during winter and catabolises abdominal fat reserves such that it loses up to a third of its total body weight [29,30,31]. Barrett et al [32] found that VGF mRNA expression is dramatically regulated in relation to this body weight cycle, with significantly higher hypothalamic expression in the winter catabolic state as compared to the summer anabolic state (fig. 2) [32].…”

“…Barrett et al [32] found that VGF mRNA expression is dramatically regulated in relation to this body weight cycle, with significantly higher hypothalamic expression in the winter catabolic state as compared to the summer anabolic state (fig. 2) [32]. This upregulation is restricted to the dorsomedial posterior arcuate nucleus (dmpArc), a region of the hamster hypothalamus where a number of other genes related to retinoic acid, histaminergic and serotoninergic signaling have also been documented to change in relation to season [32,33,34].…”

“…2) [32]. This upregulation is restricted to the dorsomedial posterior arcuate nucleus (dmpArc), a region of the hamster hypothalamus where a number of other genes related to retinoic acid, histaminergic and serotoninergic signaling have also been documented to change in relation to season [32,33,34]. The increased abundance of VGF mRNA in the winter weight-loss state is consistent with the view expressed by Bartolomucci et al [15] that VGF-derived peptides exert a catabolic function.…”