Castration effects on the expression of kisspeptin and RFRP-3 and their co-expression with ERα in the ram hypothalamus.

The mechanism by which testicular hormones exert a negative feedback action is unclear, as GnRH neurons do not contain receptors for androgen or oestrogen. The RF-amides; Kisspeptin and RF-amide related peptide-3 (RFRP-3) could be potential neuronal pathways. In ewes, 93% of arcuate kisspeptin cells co-express ERα (1), with hypothalamic RFRP-3 cells expressing ERα range between 20% in mice (2) and 40% in Syrian hamsters (3). This study aimed to identify if castration influenced the expression of ERα in kisspeptin and RFRP-3 neurons in the ram. Dual label immunohistochemistry for the co-expression of the RF-amides with ERα was used to compare the percentage of RF-amide cells containing ERα in the hypothalamus of paired (n=4) intact merino rams and long term wethers and in rams castrated 4 weeks previous or sham castrated rams, with ewe tissue (luteal phase) included for comparison (n=4/group). Ninety percent of kisspeptin cells in the caudal arcuate nucleus in wethers (long and short term) and ewes labelled with ERα. Rams by comparison, expressed very few kisspeptin cells, and therefore did not express ERα. Less than 1% of RFRP-3 neurons co-expressed ERα in the merino sheep regardless of group. By contrast, RFRP-3 fibres were in great abundance in intact rams. This suggests that kisspeptin abundance and its co-expression with ERα is influenced by feedback of testicular hormones. The lack of co-expression of RFRP-3 and ERα in the ram suggests that oestrogen negative feedback is unlikely to involve RFRP-3 neurons. (1) FRANCESCHINI, I., LOMET, D., CATEAU, M., DELSOL, G., TILLET, Y. & CARATY, A. 2006. Kisspeptin immunoreactive cells of the ovine preoptic area and arcuate nucleus co-express estrogen receptor alpha. Neuroscience Letters, 401, 225-230. (2) MOLNAR, C. S., KALLO, I., LIPOSITS, Z. & HRABOVSZKY, E. 2011. Estradiol down-regulates RF-amide-related peptide (RFRP) expression in the mouse hypothalamus. Endocrinology, 152, 1684-90. (3) KRIEGSFELD, L. J., MEI, D. F., BENTLEY, G. E., UBUKA, T., MASON, A. O., INOUE, K., UKENA, K., TSUTSUI, K. & SILVER, R. 2006. Identification and characterization of a gonadotropin-inhibitory system in the brains of mammals. Proc Natl Acad Sci U S A, 103, 2410-5