Lesion of the perinuclear zone attenuates cardiac sensitivity of vasopressinergic supraoptic neurons.

Discrete stretch of the caval-atrial junction decreases the activity of vasopressin-secreting neurons in the supraoptic nucleus (SON). The perinuclear zone (PNZ) of the SON is necessary for inhibition of vasopressin neurons following an increase in blood pressure. To determine whether the PNZ is necessary for cardiopulmonary regulation of vasopressin neurons, male rats received three unilateral injections of the excitotoxin ibotenic acid (n = 9) or phosphate-buffered saline vehicle (n = 10) into the PNZ. Extracellular activity of antidromically identified phasic vasopressin neurons in the ipsilateral SON was recorded. Of the 26 neurons recorded from vehicle-injected rats 26 were inhibited by an increase in blood pressure and 22 of those neurons were sensitive to caval-atrial distension. Of the neurons recorded from PNZ-lesion rats, only 12 of 29 were inhibited by an increase in blood pressure (P < 0.05), and only 11 neurons were sensitive to caval-atrial stretch (P < 0.05). Functional lesion of the PNZ significantly attenuates both arterial and cardiopulmonary baroreceptor-mediated inhibition of supraoptic vasopressin neurons, suggesting that the PNZ is a necessary component of both pathways.