Immunocytochemical Evidence for Oestrogen Receptors within GABA Neurones Located in the Perinuclear Zone of the Supraoptic Nucleus and GABAA Receptor β2/β3 Subunits on Supraoptic Oxytocin Neurones

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Abstract
The mechanisms by which oestrogen modulates the biosynthetic and secretory activity of magnocellular oxytocin neurones are poorly understood. Using an antibody directed against the oestrogen receptor (ER), the distribution of ER-immunoreactive (-IR) cells in relation to the supraoptic nucleus (SON) was examined. Although no ER-IR cells were detected within the SON, a small population of immunoreactive cells separate from those in the preoptic area was identified in the perinuclear zone of the SON. Double-labelling experiments with an antibody specific for glutamic acid decarboxylase (GAD), the neuronal enzyme producing gamma aminobutyric acid (GABA), revealed that approximately 60% of perinuclear zone ER-IR cells contained GAD. A further set of immunocytochemistry experiments using an antibody raised against the beta 2 and beta 3 sub-units of the GABAA receptor revealed immunoreactivity in the SON. Double-labelling experiments demonstrated that both oxytocin-IR and non-oxytocin-IR neurones in the SON were immunoreactive for beta 2 and/or beta 3 sub-units of the GABAA receptor. These studies have identified ERs within a GABAergic neural population in the perinuclear zone of the SON and shown that magnocellular oxytocin neurones in the SON possess GABAA receptors comprised of beta 2 and/or beta 3 sub-units. In conjunction with previous evidence that the perinuclear zone GABA neurones are an important source of GABA terminals in the SON, these results provide a morphological basis for the hypothesis that perinuclear zone GABA neurones may be part of a steroid-sensitive neural circuitry transmitting oestrogen input to oxytocin neurones in the SON.