Cardiovascular regulation of vasopressin neurons in the supraoptic nucleus

This paper reviews the regulation of hypothalamic vasopressin and oxytocin neurosecretory cells in the neural response to plasma volume expansion. Man y questions remain unanswered regarding how an increase in volume affects n eurohypophysial hormone secretion, what receptors are important in mediatin g this response, and which neural pathways are responsible for conveying th e signal from those receptors to the hypothalamus. Plasma volume expansion activates regions of the central nervous system associated with inhibition of vasopressin release, oxytocin secretion, and inhibition of sympathetic n erve activity. Cardiac receptors, not arterial baroreceptors, are primarily responsible for activation of the regions associated with regulation of va sopressin secretion and sympathetic outflow. Other stimuli that as yet are undefined account for activation of oxytocin-secreting neurons. Electrophys iology experiments have measured the inhibition of vasopressin-secreting ma gnocellular neurons in the supraoptic nucleus by select stimulation of card iac receptors in the caval-atrial junction. Further experiments suggest tha t the perinuclear zone, a population of neurons surrounding the supraoptic nucleus, is a necessary part of the pathway by which caval-atrial stretch d ecreases the excitability of vasopressin neurons. The perinuclear zone is a lso a necessary synapse for arterial baroreceptor-mediated inhibition of va sopressin neurons. This suggests that the neural pathways that inhibit vaso pressin release in response to an increase in blood pressure and an increas e in blood volume may overlap at the perinuclear zone of the supraoptic nuc leus. Finally, the integration of various neural pathways activated by mult iple receptors to ultimately determine the activity of magnocellular neuron s and vasopressin secretion is discussed. (C) 2001 Academic Press.