Prazosin blocks the glutamatergic effects of N-methyl-D-aspartic acid on lordosis behavior and luteinizing hormone secretion in the estrogen-primed female rat
Landa, A.I.; Cabrera, R.J.; Gargiulo, P.A.
We have observed that intracerebroventricular (iicv/i) 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 span style=font-family: Symbol;a/span1- and span style=font-family: Symbol;a/span2b-noradrenergic antagonist, was studied here by injecting it iicv /i(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 lt; 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 lt; 0.05). Behavioral effects seem to be more sensitive to the span style=font-family: Symbol;a/span-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 span style=font-family: Symbol;a/span-noradrenergic transmission.
Keywords: Sexual behavior; Glutamate; Luteinizing hormone; Noradrenergic transmission; Prazosin; N-methyl-D-aspartic acid.