Role of superior colliculus serotonin in the grooming behaviour of cats

Abstract

The present study provides evidence that a serotonergic system in the superior colliculus is involved in the regulation of grooming behaviour. Significant decreases in tryptophan hydroxylase activity and serotonin content were found in the superior colliculi of cats with pontile lesions and frontal neocortical lesions, which display a dissociation of appetitive and consummatory grooming behaviours. Neither tryptophan hydroxylase activity nor serotonin content were significantly changed in thyroidectomized cats, which display the same abnormal grooming behaviour. 5-Hydroxytryptophan administration or monoamine oxidase inhibition plus tryptophan administration abolished the abnormal grooming behaviour in each of the three groups of cats, suggesting that the change in a serotonergic system is a critical aspect of the abnormal behaviour in cats with pontile lesions and frontal neocortical lesions, and that a serotonergic system may also be involved in the genesis of the abnormal grooming behaviour in thyroidectomized cats. Functional inactivation of the serotonergic system by lysergic acid diethylamide administration or by serotonin receptor blockade did not induce the abnormal grooming behaviour in normal cats, indicating that other factors are involved in the genesis of the abnormal behaviour. Previous studies indicated that glucocorticoids are the other critical factor. Thus, a serotonergic system in the superior colliculi, operating at some level of glucocorticoid function, is involved in the integration of appetitive and consummatory grooming behaviours. These data provide the first demonstration of the biological mechanisms underlying the integration of the appetitive (learned) and consummatory (unlearned) components of instinctive behaviour.