Impulse activity of medulla oblongata in rats in response to stimulation of taste receptors and visceral chemoreceptors.

We have recorded extracellularly the impulse activity of the rat medulla oblongata during stimulation of taste receptors of the tongue and visceral chemoreceptors with solutions of hydrochloric acid and sodium chloride. We have detected in the caudal region of the nucleus of the solitary tract, neurons that react to the chemical stimulation of either one or both the receptive zones mentioned. The response reactions of the isolated groups of units (taste, viscerochemical, and convergent neurons) are tonic and are characterized by a high level of impulse activity. We have established that the neurons of each of the groups isolated are capable of discriminating between salt and acid solutions. Using the example of sodium chloride solutions we have shown that an increase in the number of viscerochemical neurons which inhibit their own background activity on increase in the concentration of any substance in the intestine is an important index of the satiation of an animal and can serve as a starting link in the mechanism of food rejection.