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Hypothalamic gonadotropin-releasing hormone (GnRH) controls the reproductive axis via promotion of adenohypophyseal luteinizng hormone (LH) and follicle-stimulating hormone (FSH) production. These gonadotropins mediate the production of sexual steroid hormones in the gonads, which play a critical role in the regulation of GnRH production through feedback mechanisms. Estradiol (E2) secreted in the ovaries achieves this via interneurons expressing the neuropeptide kisspeptin (KP). Pathologic functioning of KP-GnRH signalling can cause the disruption of pubertal and reproductive events. KP neuron populations are also present in the median amygdala and the lateral septum (LS), albeit in lower numbers. The role and functions of extrahypothalamic KP cells are, as of now, poorly understood. The goal of my research was to shed light on the ontogeny, sexual dimorfism and E2-mediated control of the lateral septal KP neuronpopulation in a transgenic mouse model. KP cells are first present in the LS at the age of 26-27 days old. The number of cells tagged by the fluorescent marker ZsGreen grew continuously throughout development, until reaching 120-150 in adulthood. Male mice showed a lower number of cells in most age categories as compared to females. I was able to induce KP expression in 20-day old female mice by 4-day-long E2 treatment. This observation supported our idea of KP expression being induced by rising E2 levels during maturation. For this reason, we are planning to examine the effects of E2 on gene expression of LS KP cells via new generation RNA-Seq experiments.