Thyrotropin releasing hormone injected into the nucleus accumbens septi selectively increases face grooming in rats

ABSTRACT

The effect of unilateral injection of peptides into the nucleus accumbens septi (NAS) on subcategories of grooming behavior was studied in male rats. The peptides used were thyrotropin releasing hormone (TRH), luteinizing hormone releasing hormone (LHRH) and corticotropin releasing 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 artificial 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 ng dose (55.19 + 8.26, N = 16, P<0.01), but a dose-response curve could not be obtained at the dose range used. Flank scratching, head, body and genital grooming were not altered by the TRH injection, but the rearing behavior 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 control states. The results show that injection on TRH into the NAS, but not the injection of LHRH or CRH, selectively increases face grooming without affecting other subcategories of grooming at the doses used, and appears to link this peptide with the neural substrate of stereotyped behavior.