Two inbred rat sublines that differ in spontaneous yawning behavior also differ in their responses to cholinergic and dopaminergic drugs.

This work compares the sensitivities of high-yawning (HY) and low-yawning (LY) sublines of Sprague-Dawley rats to dopaminergic and cholinergic yawning-inducing drugs. HY animals are significantly more sensitive to apomorphine and (-)3PPP than LY animals. Physostigmine is a less effective yawning-inducer in HY than in LY rats. With pilocarpine no differences were detected between both sublines in regard to its yawning-inducing activity. Since yawning behavior is subject to dopaminergic (inhibitory) and cholinergic (excitatory) influences, it is suggested that the genetic differences between these sublines affect the dopaminergic pathways that normally regulate yawning frequency.