GREENWOOD, AK; FERNALD, RD; Stanford University: Electrical Properties of Gonadotropin-Releasing Hormone Neurons as a Funtion of Reproductive Status

Reproductive capacity is plastic throughout the life of vertebrates on a daily, monthly and yearly basis. In the African cichlid fish Haplochromis burtoni, reproductive ability and the Hypothalamic-Pituitary-Gonadal (HPG) axis are controlled by the social environment. Adult H. burtoni males exist in one of two reproductive states, and can switch between these states depending on the social environment. The HPG axis is upregulated in territorial (T) males which have larger gonads, increased levels of circulating androgens and increased production of gonadotropin-releasing hormone (GnRH) when compared to nonterritorial (NT) males. These differences in reproductive capacity are controlled by the amount of GnRH released by neurons in the preoptic area (POA). Accordingly, we asked whether electrical activity of POA GnRH neurons differs as a function of reproductive status. Using whole-cell current clamp we recorded from GnRH neurons in slices of T and NT brains. We found no differences between T and NT GnRH neurons in basic electrical properties such as resting membrane potential, input resistance, membrane time constant, action potential size and duration, evoked spiking frequency, and spontaneous activity. We concluded that any differences between T and NT GnRH neurons are likely at the synaptic level and are examining which neurotransmitters influence these cells. Bath-applied dopamine was found to reversibly inhibit GnRH neurons. This inhibition was not diminished by tetrodotoxin, suggesting that dopamine acts directly on GnRH cells. Future work will consider whether dopamine differentially regulates GnRH neuron activity in territorial and nonterritorial males.