Abstract
It has been known that the urine volume decreases during muscular exercise but the mechanism of this change has not been well known. Since an increase in the plasma antidiuretic hormone level in exercise has been reported, it is necessary to study the activity of SON neurons during exercise. We examined reactions of neurosecretory neurons in the supraoptic nucleus (SON) to activation of muscle afferents by electrical and chemical stimulation in anesthetized and hemispherectomized cats. While group I fibers from muscle spindle receptors did not influence SON neural activities, group III and IV gastrocnemius muscle nerves activated by electrical stimulation excited SON neurons after a latency of 80－100 msec. This excitation was followed by a long lasting inhibition. Injections of chemicals into the arteries to the gastrocnemius muscle excited SON neurons. We concluded that activation of the muscle afferents either by electrical or chemical stimulations, increased the activity of the SON neurons suggesting that small-fiber afferents from the muscle played an important role in increasing the plama ADH level during exercise.
