Carbachol triggering of desynchronized sleep phenomena: enhancement via small volume infusions.

Two physical factors affecting the behavioral effects of drugs microinjected into the pontine tegmentum have been studied. Reducing the volume of vehicle produced a dramatic enhancement of the capacity of the long-acting cholinergic agent carbachol to induce desynchronized (D) sleep-like behavior (Dcarb). Enhancement of Dcarb was also achieved by substitute passive diffusion for active pumping of a given volume of carbachol solution. Controlling these two physical factors makes Dcarb a compelling experimental model for the study of D sleep mechanisms. The results also give support to the concept of a localized population of cholinoceptive neurons in the pontine reticular formation whose activation is a key step in the generation of physiological D.