Expression of TRPM8 in sheep reproductive tissues and brain areas important for the expression of reproductive behavior

Abstract

The Transient Receptor Potential Melastatin 8 (TRPM8) channel is a temperature-sensitive, calcium permeable ion channel and purported testosterone receptor. To determine how the hormone environment influences the expression of TRPM8 in gonadal tissue and areas of the brain important for reproduction, tissue from western white-faced cross-bred ewes, rams, and gonadectomized males (wethers; n = 6 per group) approximately 6 mo of age were collected. TRPM8 mRNA expression was greater (P = 0.01) in prostate of rams than wethers. Testes had greater (P = 0.004) expression of TRPM8 mRNA than the ovary. Differences in protein expression was similar with the testes having greater (P = 0.007) TRPM8 protein than the ovary. Protein expression did not differ (P = 0.6) in the prostate due to presence (ram) or absence (wether) of the testes. In the brain, TRPM8 varied in the amygdala with rams tending (P = 0.07) to express more mRNA which was reflected in greater (P = 0.04) number of neurons staining positive for TRPM8 in the central amygdala. Differences among ewes and wethers were not detected. This pattern was not observed (P ≥ 0.16) in the hypothalamus or olfactory bulb. To determine if TRPM8 was associated with the expression of ram sexual behavior, brains from rams categorized as high (n = 4) or low (n = 3) sexual activity were collected and blocked. Presence of TRPM8 channels was verified in the amygdala and hypothalamus of rams but was absent in the ventral tegmental area. Numbers of neurons staining positive for TRPM8 did not differ by expression of sexual behavior (P ≥ 0.2) in any area quantified. While expression of TRPM8 is more robust in tissues from intact males, expression of the channel does not appear to be important in the expression of sexual behavior.