Distribution of Kisspeptin and the Kisspeptin Receptor in the Canine Hypothalamus

Abstract

Abstract Kisspeptin is a protein that plays an important role in the hypothalamic-pituitary-gonadal axis. The major populations of kisspeptin neurons in the hypothalamus are found in the arcuate nucleus and the preoptic area in different mammalian species. Kisspeptin is known to regulate the release of GnRH from GnRH neurons in the hypothalamus and in this way regulates the release of luteinising hormone and follicle stimulating hormone by the pituitary gland as well. Luteinising hormone and follicle stimulating hormone are important hormones for normal gonadal development and function. Hence, the kisspeptin signalling system is an interesting target to therapeutically modulate the reproductive cycle in the bitch, for example non-surgical oestrus prevention or induction of ovulation. We studied the distribution and localisation of kisspeptin and the kisspeptin receptor in the canine hypothalamus by performing immunohistochemical analysis of hypothalamic tissue sections. Previous research shows that the kisspeptin receptor is expressed on GnRH neurons, to confirm this we will also perform an immunohistochemical study using an antibody raised against GnRH. We found one population of kisspeptin receptor immunopositive neurons in the hypothalamus of the dog. These neurons were present in the ventromedial portion of the hypothalamic tissue on both sides of the third ventricle, we consider this area to be the arcuate nucleus. Kisspeptin immunopositive neurons were also present in the arcuate nucleus and also more dorsal in the ventromedial nucleus and the dorsomedial nucleus. Unfortunately, we did not find GnRH immunopositive cells in the canine hypothalamus. It is known from studies in other mammalian species that there are two major populations of kisspeptin and kisspeptin receptor expressing neurons: the arcuate nucleus and the preoptic area. In this study we only found one population of neurons expressing the kisspeptin receptor and kisspeptin, possibly because the POA was lost during dissection of the hypothalamus from the brain, or because kisspeptin and the kisspeptin receptor were downregulated in these areas because the bitch used in our study was in anoestrus. More research is necessary to demonstrate the localisation of GnRH neurons in the canine hypothalamus by using immunohistochemistry and eventually a double immunohistochemistry protocol should be performed to find out if the kisspeptin receptor is indeed present on GnRH neurons in the dog as well.