Distinct grooming patterns induced by intracerebroventricular injection of CRH, TRH and LHRH in male rats

This paper reports the effects on grooming, related behaviors and levels of anxiety induced by the hypophysiotropic peptides corticotropin-releasing hormone (CRH, 1 microgram, 0.2 nmol, icv), thyrotropin-releasing hormone (TRH, 100 micrograms, 275 nmol, icv) and luteinizing hormone-releasing hormone (LHRH, 1.5 micrograms, 1.3 nmol, icv) administered into the lateral ventricle of the brain (icv) of adult male rats of a Holtzman-derived colony (N = 15, each group). CRH induced an increase in total grooming scores, whereas LHRH, TRH and vehicle had no effect. CRH strongly increased face and head grooming and induced head shakes. The time spent in rearing and gnawing was significantly decreased. In the plus-maze, CRH reduced the time of exploration in the open arm. TRH increased face grooming and induced body shakes. LHRH had no effect on grooming or rearing behavior. No body or head shakes were observed after LHRH administration. Scoring of individual grooming elements demonstrated differences in action of the three peptides. Although both CRH and TRH increased face grooming, only CRH induced head grooming. Furthermore, CRH induced predominantly head shakes while TRH increased body shake activity. In contrast, CRH was anxiogenic and TRH appeared to induce stereotyped behavior. From the characterization of grooming elements and related responses, we conclude that each hypophysiotropic peptide induces a specific behavioral pattern.