Activity-dependent modulation of gonadotrophin-releasing hormone neurone activity by acute oestradiol

Oestradiol (E₂) exerts potent feedback actions upon gonadotrophin-releasing hormone (GnRH) neurones and part of this feedback action may occur through the rapid action of E₂. Using a transgenic GnRH-Pericam mouse line that allows real-time intracellular calcium concentrations ([Ca²⁺](i)) to be monitored in adult GnRH neurones in a brain slice preparation, we examined the acute effects of 100 pM-100 nM E₂ on [Ca²⁺](i) transients in spontaneously active GnRH neurones. Approximately 30% of GnRH neurones exhibit spontaneous [Ca²⁺](i) transients at a frequency greater than two transients/15 min in adult female mice. In these cells, treatment with an incremental 1, 10, 100 nM E₂ protocol or 100 pM E₂ alone resulted in the suppression or complete cessation of [Ca²⁺](i) transients in 15 of 18 (83%) GnRH neurones. This effect was mimicked by E₂ bound to albumin, suggesting a membrane site of action, and was maintained in oestrogen receptor β knockout mice, indicating that this receptor is not essential for the rapid suppression of [Ca²⁺](i) transients. These findings contrast with those GnRH neurones exhibiting very few or no [Ca²⁺](i) transients (< 2 transients/15 min) that exhibit the opposite response of being activated by acute E₂. A series of dual calcium-cell-attached electrical recordings showed that [Ca²⁺](i) transients were associated with GnRH neurone burst firing and that E₂ suppression or activation of [Ca²⁺](i) transients was mirrored by a depression or initiation of burst firing. Taken together, these studies demonstrate that the acute actions of E₂ on GnRH neurones are critically dependent upon their pattern of burst firing.