Abstract
I investigated the effects of hemorrhage, retransfusion of the shed blood and an in-tracarotid infusion of hypertonic solution on the unit activity of antidromically identified neurohypophysial neurosecretory neurons recorded from the rat supraoptic area.
Hemorrhage which reduced the arterial systolic pressure to 50% of the prehemorrhage pressure caused a significant increase in firing rate in 14 of the 21 units examined. Retrans-fusion of the shed blood inhibited 8 of the 19 units tested.
An increase in firing rate was observed following the osmotic stimuli in 5 of the 16 units examined, while these units did not respond to an infusion of Locke's solution.
Four of the 5 units that showed an excitation following a hyperosmolal stimulus were examined successfully for both hemorrhage and retransfusion of the shed blood. Two of the 4 units exhibited an excitation after hemorrhage and an inhibition following the retrans-fusion. Another one responded to the bleeding with an excitation and the remaining one unit did not respond to either treatment. These results clearly indicate that presynaptic pathways mediating neural information on the body fluid osmolarity and on circulating blood volume and/or arterial blood pressure converge on each of some paticular supraoptic neuro-secretory neurons.
