Prazosin blocks the glutamatergic effects of N-methyl-D-aspartic acid on lordosis behavior and luteinizing hormone secretion in the estrogen-primed female rat

We have observed that intracerebroventricular (icv) injection of selective N-methyl-D-aspartic acid (NMDA)-type glutamatergic receptor antagonists inhibits lordosis in ovariectomized (OVX), estrogen-primed rats receiving progesterone or luteinizing hormone-releasing hormone (LHRH). When NMDA was injected into OVX estrogen-primed rats, it induced a significant increase in lordosis. The interaction between LHRH and glutamate was previously explored by us and another groups. The noradrenergic systems have a functional role in the regulation of LHRH release. The purpose of the present study was to explore the interaction between glutamatergic and noradrenergic transmission. The action of prazosin, an alpha1- and alpha2b-noradrenergic antagonist, was studied here by injecting it icv (1.75 and 3.5 µg/6 µL) prior to NMDA administration (1 µg/2 µL) in OVX estrogen-primed Sprague-Dawley rats (240-270 g). Rats manually restrained were injected over a period of 2 min, and tested 1.5 h later. The enhancing effect induced by NMDA on the lordosis/mount ratio at high doses (67.06 ± 3.28, N = 28) when compared to saline controls (6 and 2 µL, 16.59 ± 3.20, N = 27) was abolished by prazosin administration (17.04 ± 5.52, N = 17, and 9.33 ± 3.21, N = 20, P < 0.001 for both doses). Plasma LH levels decreased significantly only with the higher dose of prazosin (1.99 ± 0.24 ng/mL, N = 18, compared to saline-NMDA effect, 5.96 ± 2.01 ng/mL, N = 13, P < 0.05). Behavioral effects seem to be more sensitive to the alpha-blockade than hormonal effects. These findings strongly suggest that the facilitatory effects of NMDA on both lordosis and LH secretion in this model are mediated by alpha-noradrenergic transmission.

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 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.

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 mug, 0.2 nmol, icv), thyrotropin-releasing hormone (TRH, 100 mug, 275 nmol, icv) and luteinizing hormone-releasing hormone (LHRH, 1.5 mug, 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.