The reproductive system is critically dependent upon pulsatile hormone release, which is driven by a small population of gonadotropin-releasing hormone (GnRH) neurons located in the hypothalamus. In particular, the secretion of luteinizing hormone from the anterior pituitary, is essential for reproduction and tightly patterned and controlled by the secretion of GnRH. Until recently, the scattered distribution of the GnRH cell bodies limited the investigation of the cellular events that lead to pulsatile secretion of LH. Therefore, the numbers of GnRH neurons involved in a pulse, their location, and patterns of electrical firing had never been determined. Using cutting edge optogenetic technology, we generated a mouse model in which the GnRH neurons that control gonadotropin secretion could selectively be activated in living animals using blue light delivered to the hypothalamus using optical fibres. Previously we have characterized the profile of pulsatile secretion of LH in ovariectomized conscious mice using a fast blood sampling collection and here aimed to replicate these LH pulses in vivo. Using a range of different frequencies and durations of optogenetic stimulation, we have been able to define that 10 Hz stimulation for 2 min was sufficient to generate a pulse-like increment of LH release. The same result was found for optical activation of GnRH projections in the median eminence. Under these conditions, the dynamics of optogenetically-evoked LH pulses paralleled to that of endogenous LH pulses suggesting that the minimal parameters of GnRH neuron activation we found were likely to closely ressemble the dynamics occurring in vivo. This first insight into how GnRH neurons generate a pulse of LH in vivo provides critical information for understanding and manipulating the genesis of gonadotropin pulsatility in reproductive biology.