Characterizing the relationship between gonadotropin releasing hormone (GnRH), kisspeptin, and RFamide related peptide 3 (RFRP-3) neurons in the equine hypothalamus across the estrous cycle and in the anovulatory seasons.

The study explores the relationship between Gonadotropin Releasing Hormone (GnRH), kisspeptin, and RFamide related peptide 3 (RFRP-3) neurons in horses, and their influence on the estrous cycle and non-breeding periods.

Methodology

• The hypothalamus of horses were collected during different periods: non-breeding season, mid-transition, and throughout the breeding season.
• The researchers used fluorescent immunohistochemistry to label the neuropeptides of interest, such as GnRH, kisspeptin, and RFRP-3.
• They then studied the number, location, and interactions of these neuropeptides in the hypothalamus.

Findings

• The study found that GnRH cells were primarily located in the Arcuate Nucleus (ARC).
• Kisspeptin cells were mainly found in the ARC, with a few cells located dorsal to the ARC and around the third ventricle (3V).
• The average number of kisspeptin cells varied amongst animals and showed no clear pattern relative to season or stage of the estrous cycle.
• However, they did observe a seasonal difference in the ARC population of kisspeptin cells.
• RFRP-3 cells were found in lesser quantities than others and were observed in the ARC, Ventromedial Hypothalamus (VMH), and Dorsomedial Hypothalamus (DMH).
• The average number of RFRP-3 cells seemed higher in pre-ovulatory animals in comparison to other stages.

Interactions between Neurons

• The results showed that the degree of interaction between GnRH and kisspeptin did not change significantly with season or stage of the estrous cycle.
• Similarly, the degree of interactions between kisspeptin and RFRP-3 fibers did not change noticeably with season or stage of the estrous cycle.
• This finding suggested the possible presence of a very short loop feedback mechanism between the three peptides.

Conclusions

• The observed changes in the RFRP-3 neurons suggest a possible role in the regulation of reproduction in horses.
• However, the study concludes that it is unlikely for RFRP-3 to serve as a gonadotropin inhibitory factor because of the small numbers observed and the constant interactions with kisspeptin regardless of the season or stage in the estrous cycle.