THYROTROPIN-RELEASING-HORMONE INJECTED INTO THE NUCLEUS-ACCUMBENS-SEPTI SELECTIVELY INCREASES FACE GROOMING IN RATS

The effect of unilateral injection of peptides into the nucleus accumb ens septi (NAS) on subcategories of grooming behavior was studied in m ale rats. The peptides used were: thyrotropin releasing hormone (TRH), luteinizing hormone releasing hormone (LHRH) and corticotropin releas ing hormone (CRH). Male rats (Holtzman strain, 240-270 g body weight) injected with progressive doses of TRH (100, 200 and 400 ng) at 5-day intervals were compared with the control state (injection of artificia l cerebrospinal fluid, CSF). A selective increase in face grooming was observed with the 100 ng (49.78 +/- 6.11, N = 18) and 200 ng (50.29 /- 7.72, N = 17) doses of TRH (P<0.05 vs CSF injection, 26.94 +/- 3.64 , N = 18). Face grooming increased further with the 400 fig dose (55.1 9 +/- 8.26, N = 16, P<0.01), but a dose-response curve could not be ob tained at the dose range used. Rank scratching, head, body and genital grooming were not altered by the TRH injection, but the rearing behav ior was inhibited (10.33 +/- 1.56; N = 18; 10.76 +/- 1.77, N = 17; 12 +/- 2.06, N = 16) (P<0.05 for all doses vs controls, 20.61 +/- 2.81, N = 18). The rats that received LHRH (75 ng, N = 16) and CRH (100 ng, N = 14) did not show behavioral changes when compared with their contro l states. The results show that injection of TRH into the NAS, but not the injection of LHRH or CRH, selectively increases face grooming wit hout affecting other subcategories of grooming at the doses used, and appears to link this peptide with the neural substrate of stereotyped behavior.