Initiation and inhibition of the release croak of Rana pipiens.

A release croak is emitted by unreceptive female frogs when they are clasped by males; receptive females are silence. This report investigates the sources of stimuli which initiate and inhibit the release croak of Rana pipiens. Experiment 1 demonstrates that manual clasping of the trunk rather than the legs elicits the croak. Experiment 2 shows that denervation of the skin of the trunk prevents the release call in response to manual stimulation. Experiment 3 confirms that artificial distension of the body with fluid inhibits the release croak in response to manual stimulation. Experiment 4 shows that artifically-distended females, who are not in the normal endocrinological state that accompanies mating, are silent and receptive in response to clasping by sexually-active male frogs. The first two experiments imply that stimulation of the skin of the trunk initiates the release croak; Experiments 3 and 4 suggest that an internal afferent source inhibits the release croak and might mediate an important aspect of receptivity in female frogs.