CONTROL OF ACTIVITY OF NEURONS IN THE SUPRAOPTIC NUCLEUS

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Abstract
Single unit activities were recorded from the supraoptic nucleus of nearby regions by microelectrodes in chloralose anesthetized cats or cats decerebrated under ether. Only those neurons found to respond to intracarotid injections of hypertonic saline were studied. Stimulation of the cingulate gyrus or somatic afferents of the leg nerves evoked a much higher rate of firing in these "osmosensitive neurons." Stimulation of the motor cortex and prefrontal areas likewise excited these neurons but less effectively. These excitations were frequently succeeded by brief periods of inhibition, but in more than half the cells studied only excitation occurred. Stimulation of the posterior lobe of the cerebellum had a predominantly inhibitory action of these "osmosensitive neurons." Only a few units were excited by cerebellar stimuli. Acetylcholine given intra-arterially augmented the rate of discharge in these neurons. Epinephrine had, if any effect, an inhibitory action. Changes in arterial pressure did not correlate with responses observed. Hypertonic glucose injections likewise caused a positive reaction in the "osmosensitive neurons." Isotonic glucose caused only a brief small augmentation in rate of cell firing.