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Electrical synapses connect a network of gonadotropin releasing hormone neurons in a cichlid fish

Significance The hypothalamus controls reproductive development and function via a small peptide, gonadotropin releasing hormone (GnRH1), delivered to the pituitary. To be effective, GnRH1 must be released in a pulsatile manner, but it is not known how this is achieved. We recorded from pairs of genetically labeled GnRH1 neurons in the brains of reproductively active fish and show that these cells are strongly and uniformly interconnected by electrical synapses that can be reversibly blocked. These electrical synapses likely contribute to the pulsatile firing of GnRH1 neurons, producing the coordinated output needed for reproduction, the most important act of any organism. Initiating and regulating vertebrate reproduction requires pulsatile release of gonadotropin-releasing hormone (GnRH1) from the hypothalamus. Coordinated GnRH1 release, not simply elevated absolute levels, effects the release of pituitary gonadotropins that drive steroid production in the gonads. However, the mechanisms underlying synchronization of GnRH1 neurons are unknown. Control of synchronicity by gap junctions between GnRH1 neurons has been proposed but not previously found. We recorded simultaneously from pairs of transgenically labeled GnRH1 neurons in adult male Astatotilapia burtoni cichlid fish. We report that GnRH1 neurons are strongly and uniformly interconnected by electrical synapses that can drive spiking in connected cells and can be reversibly blocked by meclofenamic acid. Our results suggest that electrical synapses could promote coordinated spike firing in a cellular assemblage of GnRH1 neurons to produce the pulsatile output necessary for activation of the pituitary and reproduction.