SYMPATHETIC ENHANCEMENT OF PERIPHERAL SENSORY INPUT IN THE FROG

Abstract

Novel stimuli, such as sudden sounds, movements, or changes in illumination give rise to bursts of sympathetic efferent activity in peripheral nerves of Rana clamitans and R. pipiens; these efferent bursts in turn elicit barrages of peripheral afferent (apparently mechanoreceptive) activity. A transient enhancement of positivity of the outer skin surface accompanies the enhanced cutaneous sensory inflow. In intact frogs the correlated sympathetic, peripheral afferent, and electrodermal activities always precede by several seconds the onset of "voluntary" motor activity. Iterative light-off stimuli are especially effective in repeatedly eliciting the electrodermal responses in R. clamitans; the responses may continue to occur periodically for several seconds following cessation of the light-off stimuli, suggesting that a type of "expectancy" might be developed in frogs of this species. Ongoing peripheral tactile and gustatory responses are facilitated by electrical stimulation of the sympathetic trunk. Slow waves of electrical activity in the medulla oblongata follow stimulation of the sympathetic trunk, provided that some cranial nerves remain intact from the brain to the periphery. It is possible that this positive peripheral feedback of sensory input via somatic-visceral reflexes is involved in general behavioral arousal.