Meeting Abstract
Siberian hamsters (Phodopus sungorus) exhibit robust seasonal rhythms in immune function and stress responsiveness. The environmental cue driving these seasonal adjustments is photoperiod, which is encoded endogenously by the duration of rhythmic pineal melatonin (Mel) secretion. The central neuroendocrine targets mediating Mel-dependent regulation of stress responsiveness and immune function remain unspecified. There are multiple neural Mel targets in Siberian hamsters, including the suprachiasmatic nucleus (SCN), the nucleus reuniens (NRe), and the paraventricular nucleus of the thalamus (PVt). The PVt is of particular interest with regard to stress and immunity as it has been implicated in the neural regulation of the stress response. To address the role of the PVt in seasonal alterations of these measures, male Siberian hamsters underwent PVt ablation or sham ablation. Animals from each group were then exposed to either short- or long-day light cycles. On Week 5 post-ablation, blood samples were collected and used to perform a white blood cell (WBC) count and differential, and a bactericidal capacity assay. On Week 7, animals were exposed to a restraint stress test, during which blood samples were collected and used to perform a WBC count and differential, and a cortisol EIA. Results indicate that the PVt is necessary for the expression of the short-day bactericidal phenotype. PVt status also impacted WBC differential. In addition, these results will be considered in the context of ongoing hormone assays for circulating cortisol. These findings implicate the PVt in mediating seasonal regulation of immunity and stress responsiveness.
