Characterisation of the role of amygdala kisspeptin neurons in the male and female house mouse

: chemosensory, neuroendocrine and physiological mechanisms

Abstract

The medial amygdala (MeA) is a critical centre in the limbic brain that responds to olfactory cues and alters reproductive physiology. However, the underlying neuronal circuits regulating these functions remain poorly defined. My studies aimed to test whether MeA kisspeptin (MeA^Kiss) neurons in mice are sensitive to sexually relevant olfactory stimuli and transmit signals to alter reproductive physiology. Anterograde viral tracing revealed 11% GnRH neurons receiving MeA^Kiss appositions in female mice similar to 15% previously reported in male mice. Using transgenic mice, I demonstrate that MeA^Kiss neurons are sensitive to pheromones in both males and females. However, their response is sexually dimorphic with males exhibiting increased c-Fos activity in MeA^Kiss neurons and female exhibiting suppressed c-Fos after exposure to opposite-sex urine. The activation of MeA^Kiss neurons in male mice was concomitant with a pheromone-induced LH rise while females lacked a LH response to pheromones. Next, I employed DREADDs (designer receptors exclusively activated by designer drugs) to determine whether specific modulation of MeA^Kiss neurons impacts circulating LH levels. In the absence of an olfactory stimulus, DREADD activation of MeA^Kiss neurons in male mice induced a >15-fold rise in LH indicating that MeA^Kiss neurons were directly involved in regulating the pheromone-induced LH response in males. Since GnRH/LH secretion can be modulated by GABA and glutamate signalling, I analysed MeA^Kiss neurons in male mice for their capacity to elaborate these neurotransmitters. Multiplex ISH labelling for GABA and glutamate markers revealed 71% MeA^Kiss neurons as GABAergic and 29% as glutamatergic with approximately 6% co expressing markers for both neurotransmitters. Contrary to the results obtained with male mice, neither acute nor chronic DREADD activation of MeA^Kiss neurons in female mice altered LH levels. In fact, my additional experiments ablating MeA^Kiss neurons using a cutting-edge genetic strategy did not alter ovarian cyclicity or reproductive hormone levels suggesting that MeA^Kiss neurons are not involved in regulating the female reproductive axis. Overall my results reveal important sex differences in the function of MeA^Kiss neurons in regulating reproductive endocrine physiology.

Date of Award	28 Jun 2019
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Javier Tello (Supervisor)