Kisspeptin (encoded by the Kiss1 gene) and neurokinin B (NKB; encoded by the Tac2 gene) are critical regulators of the female reproductive axis. Inactivating mutations to NKB and its receptor, NK3R or to Kiss1 and its receptor Kiss1R lead to infertility in both humans and mice. There are two major populations of Kiss1 neurons located in the arcuate nucleus (ARC) and anteroventral periventricular nucleus (AVPV) that directly contact gonadotrophin-releasing hormone (GnRH) neurons and control the negative and positive feedback of sex steroids necessary for reproductive function. In the ARC, Kiss1 neurons co-express both NKB, which stimulates kisspeptin release, and dynorphin A, which inhibits kisspeptin release, in a population of neurons called KNDy neurons. The medial amygdala (MeA), which is involved in emotion and pheromone processing, also contains a population of Kiss1 and NK3R expressing neurons; however, the functional role in the central control of reproduction of these neuron populations in the MeA remains ill-defined. Preliminary experiments from our lab found that injection of senktide, a specific agonist of NK3R, into the area of the MeA where the NK3R neurons are located induces LH release in mice.
In Specific Aim 1, a combination of transgenic Kiss1 mice and adeno- associated virus (AAV) injections targeted specifically to Kiss1 neurons in the MeA will be used to manipulate Kiss1 neuron function to determine their role in luteinizing hormone (LH) secretion (which closely mirrors pulses of GnRH), fertility and reproductive behavior.
In Specific Aim 2, neurons expressing NK3R in the MeA will be specifically ablated using the ribosomal inactivating toxin saporin conjugated to an agonist for NK3R to determine the role of these MeA neurons in reproductive function. The MeA is a highly interconnected brain region that sends afferent projections to and receives efferent projections from multiple brain areas involved in the regulation of reproduction but the neuronal projections between Kiss1 and Tac2 expressing neurons in this region are unknown. Additionally, while Tac2 is expressed in many brain areas, including the centromedial amygdala (CeM) and the ARC, the source of NKB acting in the MeA through NK3R remains to be identified.
In Specific Aim 3, a combination of anterograde and retrograde AAV injections in either Kiss1-Cre or Tac2-Cre transgenic mice will map the neural projections between the MeA and regions that regulate the release of Kisspeptin and GnRH, and regions involved in reproductive behavior and pheromone processing. These results will begin to define the role of MeA Kiss1 and NK3R expressing neurons in the regulation of reproductive function compared to populations of these neurons in other brain regions. Understanding the role of the MeA in the integration of emotions and bonding with reproduction is critical to understanding sexual behavior in many species, including humans, and could aid in the development of new approaches to treat central reproductive disorders.
Mutations to the genes that encode for kisspeptin or neurokinin B (NKB) result in infertility in humans and mice and while the contribution of these neuropeptides to reproductive function has been studied in multiple brain regions, their role in the medial amygdala, a key integrating center for neuroendocrine and social cues, has not been fully characterized. This proposal will examine the contribution of kisspeptin and NKB in the medial amygdala to female reproductive function in mice, as well as the neuroanatomical connections between these medial amygdala neurons and other brain regions involved in the control of neuroendocrine function and fertility. This work will increase our understanding of how kisspeptin and NKB act in the brain and may contribute to the development of new therapies to potentially target and treat infertility resulting from neuroendocrine disruptions.
