Serotonin, the superior colliculus, and grooming behavior in cats with neocortical lesions

Previous studies of cats with pontile lesions indicate that a serotonergic deficit exists in the superior colliculi and that this deficit is involved in the genesis of an abnormal grooming behavior. Cats with frontal neocortical lesions exhibit the same serotonergic deficit and the same abnormal grooming behavior. The present study established that the serotonergic deficit is involved in the mediation of the abnormal grooming behavior in cats with frontal neocortical lesions. Microinjections of 5-hydroxytryptophan (5-HTP) and 5-hydroxytryptamine (5-HT) into the superior colliculi abolished or signigicantly reduced the abnormal behavior in cats with frontal neocortical lesions, whereas no effects of 5-HTP were observed after injections into the cerebrospinal fluid above the superior colliculi, into the tegmentum beneath the superior colliculi, or into the medial dorsal nucleus rostral to the superior colliculi. Other substances (tryptophan, noradrenaline, and gamma-amino-butyric acid) had no effect on the abnormal behavior when injected into the superior colliculi. Further evidence implicating a serotonergic deficit in the mediation of the abnormal behavior was obtained by systemic injections: The abnormal behavior was abolished with 5-HTP in cats with frontal neocortical lesions and in adrenalectomized cats that were previously treated with p-chlorophenylalanine.. The present study also demonstrated that the abnormal grooming behavior is induced by frontal neocortical lesions and not by more caudal lesions of the neocortex. The anatomical relations between the frontal neocortex and the superior colliculus and the role of these structures in grooming behavior are discussed.