Chapter 7: Pregnancy and opioid interactions with the anterior peri-third ventricular input to magnocellular oxytocin neurones

Abstract

Publisher Summary Structures in the lamina terminalis are major sources of input to the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei, and both magnocellular oxytocin and vasopressin neurones receive inputs from these sources. Electrophysiological, lesioning and retrograde and anterograde transport studies have shown that the sub-fornical organ (SFO) projects both directly and indirectly, via the nucleus medianus (median preoptic nucleus), to the PVN and SON. Similarly, there are both direct and indirect projections from the organum vasculosum of the lamina terminalis (OVLT). Acute lesion of the region anterior and ventral to the third ventricle (AV3V region), involving the nucleus medianus, silences supraoptic neurones, indicating that this region provides a tonic drive producing the continuous pattern of firing activity of oxytocin neurones. In the rat, magnocellular oxytocin neurones are osmoresponsive, and the oxytocin secreted as a result probably has a natriuretic role, acting in concert with vasopressin. An acute AV3V lesion renders oxytocin neurones incompetent to respond to an acute hyperosmotic stimulus, and an infusion of the angiotensin II antagonist saralasin into a lateral cerebral ventricle achieves the same result, as well as silencing their basal activity.