Food scarcity under long photoperiod suppresses Tshβ expression in the pars tuberalis
To test at what level of the signaling cascade metabolic cues act to modify PNES output signals, we measured gene expression levels in the posterior and anterior hypothalamus. Because the posterior hypothalamic block did not contain the pars distalis, Tshβ expression can be exclusively attributed to the pars tuberalis. Tshβ expression was significantly reduced (50% reduction) in male voles at high workloads (Fig. 2A,C; Table S4). In males, this effect is stronger in common voles than in Tundra voles (Fig. 2A,C, Table S4). In females, this effect was only observed in Common voles at 10°C (Fig. 2B,D; Table S4). Temperature did not affect Tshβ expression, but a significant reduction was found only in female common voles at 10°C (Fig. 2A-D; Table S4). Overall, Tshβ and gonadal weight show a positive relationship (Fig. 3A-D), indicating that Tshβ is involved in suppressing gonadal development when food is scarce.
After translation, TSHβ and αGSU locally dimerize to form active TSH, which can bind to its receptor (TSHr) located in the tanycytes around the third ventricle of the brain. Workload did not affect Tshrexpression in both sexes of both species (Fig. 2A-D, Table S4). Although common vole females show slightly elevated Tshr expression at 10°C, general Tshr levels were lower in Common voles than in Tundra voles (Fig. 2A-D, Table S4).
Although TSH generally leads to increased Dio2 levels, workload induced changes in Tshβ are not reflected in Dio2expression (Fig. 2A-D), suggesting that modifying factors other than TSH can affect posterior hypothalamic Dio2 expression.
Kiss1 expressing neurons are located in the ARC nucleus in the posterior hypothalamus and are involved in metabolic regulation and food intake. For this reason, it was unexpected that workload and temperature did not affect Kiss1 expression in the posterior hypothalamus (Fig. 2A-D, Table S4).
The DMH and VMH of the posterior hypothalamus are nuclei that are involved in the regulation of feeding behavior and both these areas are capable of expressing Rfrp3 . Although overall Rfrp3expression was higher at 21°C, no effects of workload on Rfrp3expression were observed (Fig. 2A-D, Table S4).