Histaminergic control of oxytocin release in the paraventricular nucleus during lactation in rats

The central neurotransmitters regulating both systemic and central release of oxytocin (OT) during lactation are not completely defined. Although cent ral histaminergic systems have been implicated in systemic release of OT, t he role of this neurotransmitter in suckling-induced intranuclear OT secret ion has not been investigated. Therefore, microdialysis of the paraventricu lar nucleus (PVN) was used to determine if suckling stimulates histamine re lease within the PVN and if nursing-induced intranuclear OT release is redu ced by local blockade of either H1 or H2 histamine receptors. Female Holtzm an rats were implanted wit microdialysis probes adjacent to the PVN on lact ation days 8-12. The next day, the pups and dam were separated for 4 h, reu nited, and again separated. Histamine concentrations in dialysates were mea sured before, during, and following suckling. In separate animals, a simila r separation/reunion paradigm was used, but the dialysate OT concentration was measured during PVN perfusion with vehicle or an H1 or H2 receptor anta gonist. Suckling increased dialysate concentrations of both histamine and O T in the PVN. Furthermore, local pharmacological blockade of either H1 or H 2 receptors prevented the increase in OT release in the PVN during suckling . These data demonstrate that activation of histamine receptors in the PVN is necessary for intranuclear release of OT induced by suckling and extend previous findings demonstrating a similar relationship between central hist amine and systemic release of OT. (C) 2001 Academic Press.