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

Discrete stretch of the caval-atrial junction decreases the activity of vas opressin-secreting neurons in the supraoptic nucleus (SON). The perinuclear zone (PNZ) of the SON is necessary for inhibition of vasopressin neurons f ollowing an increase in blood pressure. To determine whether the PNZ is nec essary for cardiopulmonary regulation of vasopressin neurons, male rats rec eived three unilateral injections of the excitotoxin ibotenic acid (n = 9) or phosphate-buffered saline vehicle (n = 10) into the PNZ. Extracellular a ctivity of antidromically identified phasic vasopressin neurons in the ipsi lateral 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 neu rons were sensitive to caval-atrial distension. Of the neurons recorded fro m PNZ-lesion rats, only 12 of 29 were inhibited by an increase in blood pre ssure (P < 0.05), and only 11 neurons were sensitive to caval-atrial stretc h (P < 0.05). Functional lesion of the PNZ significantly attenuates both ar terial and cardiopulmonary baroreceptor-mediated inhibition of supraoptic v asopressin neurons, suggesting that the PNZ is a necessary component of bot h pathways.