Developmental regulation of a local positive autocontrol of supraoptic neurons

Mature oxytocin (OT) and vasopressin (AVP) magnocellular neurons of the hyp othalamic supraoptic nuclei (SON) autocontrol their electrical activity via somatodendritic release of their respective peptides. Because OT and AVP a re synthesized early in development and could play an important role in the maturation of these neurons, we checked whether the peptides are released within the SON and act on their secreting neurons during 3 weeks of postnat al development. We used patch-clamp recordings from SON neurons in rat hypo thalamic horizontal slices to show that the spontaneous electrical activity of immature SON neurons is blocked by OT or AVP receptor antagonists, demo nstrating a basal somatodendritic release of the peptides. Application of O T or AVP depolarizes SON neurons and stimulates activity typical of the cor responding mature neurons. This effect is directly on SON neurons because i t is recorded in dissociated neurons. Radioimmunoassays from isolated SON w ere used to show that each peptide facilitates its own release at a somatod endritic level, exhibiting a self-sustaining positive feedback loop. This a utocontrol is not uniform during development because the proportion of neur ons depolarized by the peptides, the amplitude of the depolarization, and t he propensity of the peptides to facilitate their own release are maximal d uring the second postnatal week and decrease thereafter. These data are con sistent with a role of autocontrol in the maturation of SON neurons because it is maximal during the delimited period of postnatal development that co rresponds to the period of major synapse formation.