Neuroscience Letters, I26 ( 199I) 9497 &j 1991 Elsevier Scientific Publishers Ireland Ltd. 0304-3940/91/S 03.50 ADONIS0304394091002323
94
NSL 07750
Excitatory amino acid modulation of lordosis in the rat M.M. McCarthy’, G.H. Curran’ and H.H. Feder’*2 ‘Institute qf Animal Behavior and”Department ofBiologicalSciences, Rutgers University, Newark,
NJ 07012 (U.S.A.)
(Received 23 August 1991; Revised version received 3 December 1991; Accepted 6 February 1991) Ke.vwords:
NMDA; AP-5; Hypothalamus; Preoptic area
Microinfusion of the excitatory ammo acid agonist N-methyl-p-aspartate (NMDA) into the mediobasal hypothalamus (MBH) significantly reduced lordosis in estrogen plus progesterone-treated female rats at 10 min post-infusion with recovery to pretest values by 30 min (P< .05; Wilcoxon). Microinfusion of the specific NMDA antagonist o,t.2-amino-5-phosphonopentoic acid (AP-5) into the same sites was without effect on lordosis responding of fully receptive females. There was also a significant increase in the number of females vocalizing to mounts by males after infusion of NMDA but not after infusion of AP-5 into the MBH. When NMDA was infused into the preoptic area (POA) there was no effect on lordosis responding of full receptive females, but AP-5 infusion resulted in a significant inhibition of lordosis at 10 min post-infusion. There was no difference between groups in percentage of females vocalizing after drug infusion into the POA. These results suggest that increased excitatory amino acid activity in the MBH and decreased excitatory amino acid activity in the POA inhibits lordosis behavior.
The sexually receptive posture of the female rat, lordosis, is steroid-dependent and is correlated with increased neuronal activity in the ventromedial hypothalamus (VMH) and reduced when there is increased neuronal activity in the preoptic area (POA) [see ref. 17 for review]. Several ‘classical’ neurotransmitters and neuropeptides have been implicated in the control of lordosis behavior [6] but only recently has a role for amino acid transmitters in the regulation of female receptivity become apparent. The inhibitory amino acid transmitter y-aminobutyric acid (GABA) has a dual effect on lordosis responding. GABA agonists administered into the mediobasal hypothalamus (MBH) and the midbrain central gray (MCG) facilitate lordosis, but increased GABAergic acitvity in the POA inhibits this behavioral response [I 3, 141. The excitatory amino acid transmitter glutamate has been reported to markedly and transiently inhibit lordosis when infused into the MBH of receptive female rats [lo] suggesting that excitation of certain medial hypothalamic neurons inhibits the lordosis reflex. The existence of lordosis facilitating and suppressing neuronal systems in the forebrain which act independently of the VMH have also been reported [ 191. We report here that the specific excitatory amino acid receptor agonist, N-methyl-DCorrespondence: M.M. McCarthy, Rockefeller University, 1230 York Avenue. New York, NY 10021. U.S.A.
aspartate (NMDA), and its selective antagonist, D,L-2amino-5phosphonopentoic acid (AP-S), affect lordosis differentially when infused into the MBH and POA of sexually receptive female rats. Modulation of nociception is also an important aspect of reproduction [ 171 and excitatory amino acid neurotransmission may be important to this modulation since infusion of NMDA into the MBH significantly increased the number of females vocalizing when mounted by the male at 10 min postinfusion. Vocalizations can be considered an indicator of nociceptive thresholds [5, 181. Adult female Sprague-Dawley rats (Charles River, Kingston, NY) weighing 25&350 g were housed individually in suspended wire mesh cages on a reversed light cycle (lights off from 10.00 to 20.00 h). Temperature was maintained at approximately 22°C and Purina Lab Chow and water were available ad libitum. Females were bilaterally ovariectomized and cannulated by stereotaxic placement with double-barrel 23-gauge guide cannulae under Ketamine anesthesia (20-25 mg i.p.; Bristol Labs, Syracuse, NY, plus 0.5 mg Xlazine; Mobay Corp., Shawnee, KA). Injection cannulae were 28 gauge and cut to 0.5 mm longer than the guide cannulae (Plastic One, Roanoke VA). Approximately 2 weeks after surgery, females were injected S.C. with estradiol benzoate (EB, 1Opg; 48 h prior to testing) and progesterone (P, 1 mg; 4 h prior to testing) dissolved in sesame oil and given in a 0.1 ml volume. At the time of testing (beginning at
95
MBH
q
NMDA
n
A?-5
n
SALINE
PRETEST (MINUTES POST-INJECTION) Fig. 1.Change in lordosis quotient (LQ) after infusion of NMDA, AP-5 or saline into the MBH of EB + P-treated female rats. There was a significant decrease in LQ at 10 min post-infusion in NMDA-infused rats as compared to pre-test levels (PcO.05; Wilcoxon). Infusion of AP-5 and saline into the MBH did not affect subsequent lordosis responding.
13.00 h, 3 h after lights out) females were placed in a Plexiglas arena (45 cm diameter) with one or two stud males for at least 10 mounts to establish a pretest lordosis quotient (LQ=number of lordosis/number of mounts x 100). Microinfusion of drugs into brain began within 1 h of pretesting and postinfusion testing was performed at lo,30 and 60 min. Cannulae were aimed either at the MBH (AP= - 3.0 mm; depth=9.5 mm) or the POA (AP= -0.5 mm; depth= 8.5 mm). At the completion of the experiment, the brains of representative animals of each group were histologically processed and cannulae placement in the POA and MBH verified. All observations were done under a 25 W red light. Steroids and drugs were obtained from Sigma (St. Louis MO). Experiment 1: Influence of NMDA and AP-5 infused into the MBH on lordosis. After pretesting, females with an LQ of 60% or greater were bilaterally infused with either NMDA (20 ng/0.25 pl/cannula, pH = 7.2, n = 7), AP-5 (50 ng/0.25 #annula, pH = 8.0; n = 11) or saline (n = 3) into the MBH over a 30 s period using two 1 ~1 Hamilton syringes under light Metofane anesthesia (Pitman-Moore, Washington Crossing, NJ). Post-injection tests consisted of measuring the lordosis response of the female to 10 mounts. Vocalizations by the female in response to mounting by the male were noted as ‘yes’ or ‘no’ with a ‘yes’ response being given if the female vocalized to at least 3 of 10 mounts. All behavioral tests were separated by two weeks and drug treatments were random. There was no apparent effect of order of drug treatment or testing on subsequent lordosis responding. Experiment 2: Influence of NMDA and AP-5 infused into the POA on lordosis. An additional group of
females was bilaterally infused with NMDA (n = 7), AP5(n = 8) or saline (n = 4) into the POA and behaviorally tested in the same manner as above. Results Expt. 1: Microinfusion of 20 ng of NMDA into the MBH resulted in a significant decrease in LQ at 10 min post-infusion as compared to the pretest (P < .05; Wilcoxon) with full recovery to pretest levels by 30 and 60 min. Microinfusion of AP-5 or saline into the MBH was without effect on LQ at any time post-infusion (Fig. 1). There was a significant increase in the number of NMDA-treated females that vocalized when mounted by males during the 10 min post-infusion test in compar-
TABLE I PERCENTAGE OF FEMALES EXHIBITING FREQUENT VOCALIZATIONS WHEN MOUNTED BY MALES DURING POST-INFUSION TESTS Time post-infusion (min) IO
30
60
85.7%* (6/7) 36.4% (4/l 1)
42.6% (3/7) 36.4% (4/l 1)
14.3%(l/7) 12.5%(l/8)
MBH
NMDA AP-5 Saline
0% (O/3)
0% (O/3)
33.4% (2/6) 37.5% (3/8) 25.0% (l/4)
16.7% (l/6) 37.5% (3/8)
0% (O/3)
POA
NMDA AP-5 Saline
0% (O/4)
16.7%(l/6) 12.5%(l/S) 0% (O/4)
*P < 0.05; Cochrans Q-test, Q = 9 between pretest, 10 and 30 min postinfusion.
96
POA
%l NMDA
n AP-5 n SALINE
1
PRETEST (MINUTESPOST-IKIECTION) Fig. 2. Change decrease
in lordosis
quotient
(LQ) after infusion
in LQ at IO min post-infusion
into the POA did not affect subsequent
of NMDA,
in AP-5 infused lordosis
AP-5 or saline into the POA of EB+P-treated
rats as compared
to pre-test
levels (PcO.05;
female rats. There was a significant
Wilcoxon).
Infusion
of NMDA
and saline
responding.
ison to the pretest and 30 min post-infusion test (Cochran’s Q-test; Q = 9, P < .05). There was no difference in the number of AP-5-treated females vocalizing when mounted by the male (Table I). 1 Results Expt. 2: Microinfusion of 50 ng AP-5 into the POA significantly reduced LQ at 10 min post-infusion with full recovery to pretest levels by 30 and 60 min (P-C .05, Wilcoxon). A 10 ng dose of AP-5 was without effect on lordosis responding (n = 3) and a 100 ng dose did not further increase the magnitude of the effect in the POA (n = 3). Both NMDA and saline were without effect on lordosis responding when infused into the POA (Fig. 2). Furthermore, there was no effect of NMDA on vocalizations when infused into the POA as there was in the MBH. Treatment with AP-5 also did not significantly increase vocalizations at any time post-infusion (Table I). We report here that excitatory amino acids exert a dual effect on lordosis behavior. Microinfusion of NMDA into the MBH transiently decreases lordosis responding whereas the selective antagonist AP-5 is without effect on fully receptive females. However, when infused into the POA, AP-5 decreases lordosis and NMDA is without effect on fully receptive females. In addition, modulation of nociception, as determined by vocalizations in response to mounting, also seems to be influenced by excitatory amino acids in the MBH since infusion of NMDA into this site significantly increased the number of females vocalizing in response to mounting by males. In addition to effects on reproductive behavior, excitatory amino acids have been implicated in the control of
gonadotropin secretion and pain processing. For example, administration of excitatory amino acids has been reported to elevate serum LH levels acutely in male [1, 7, 161and female rats [12]. The induction by excitatory amino acids of LH release has been attributed to their direct action on LHRH secretion in the hypothalamus rather than to an effect on the pituitary [3]. Both the NMDA [ 1, 12, 15, 161and non-NMDA receptor type [7] appear to be involved. In ovariectomized rats treated with estrogen in order to induce an LH surge, both NMDA and non-NMDA antagonists administered intraventricularly block the LH surge without affecting FSH or prolactin levels [12] indicating a role for endogenous excitatory amino acids in regulating LH release. In male rats it has been shown that microinjection of NMDA into the medial POA but not into the arcuate or ventromedial nuclei, increases LH secretion [15]. It has been suggested that activation of NMDA receptors in rostra1 brain regions, such as the POA, and of non-NMDA receptors in more caudal areas (i.e. arcuate nucleus) mediate LHRH secretion and thereby LH release [12]. In the current study, the action of AP-5, a selective NMDA antagonist, in depressing lordosis when infused into the POA, may be a result of inhibition of LHRH-secreting neurons of the POA. Microinfusion of LHRH into the POA rapidly facilitates lordosis behavior in rats [8] and it can be speculated that inhibition of LHRH-secreting POA neurons by blockade of excitatory afferents transiently suppresses the behavioral response. Excitatory amino acids have also been implicated as neurotransmitters involved in the regulation of nocicep-
97
tion. Microinfusion of NMDA into the midbrain central gray (MCG) produces a potent analgesia [9] and the NMDA antagonist, MK-801, blocks morphine and stress-induced analgesia in male mice [l 11.Administration of NMDA intrathecally at the spinal cord has the opposite effect, producing a hyperalgesia accomplanied by vocalizations and scratching [18]. In the current experiments, NMDA infused into the MBH resulted in an increase in vocalizations in response to mounting by males, indicating an increased sensitivity of drug-treated females to somatosensory stimuli. It has been suggested that in order for a female rat to be highly receptive she must also be partially analgesic so that high intensity stimulation from the male is not perceived as noxious [ 171. The decrease in sexual receptivity after NMDA injection into the MBH may be due to a partial loss of this analgesia, so that the female now attempts to avoid being mounted by the male. Descending input from the medial hypothalamus has been found to modulate the response to noxious input at the level of the spinal cord [4] and there is an excitatory amino acid projection from the VMH to the MCG in the rat [2]. Thus, the possibility exists, but has not been established, that excitatory amino acid transmission in the MBH regulates nociception. In conclusion, the current results establish that excitatory amino acid transmission affects sexual receptivity in a dual fashion. Lordosis is reduced when excitatory amino acid transmission increases in the MBH and decreases in POA. GABAergic drugs also exert a dual effect on lordosis, with a very similar time course, but in the case of GABA transmission lordosis is reduced when GABA activity decreases in MBH and increases in POA [13]. It is possible that these effects are related, i.e., GABA may block excitatory amino acid transmission and thereby facilitate lordosis responding. Whether the involvement of excitatory amino acids in the control of sexual behavior is exclusive to the NMDA receptor or includes non-NMDA receptors is unknown at this time. This is publication No. 517 of the Institute of Animal Behavior and No. 89 of the Department of Biological Sciences and was supported by Grant NIH HD 04467 and Busch Bequest Funds to H.H.F. 1 Arslan, M., Phol, CR. and Plant, T.M., or.-2-amino-5-phosphonopentanoic acid, a specific N-methyl-D-aspartic acid receptor antagnoist, suppresses pulsatile LH release in the rat, Neuroendocrinology, 47(1988)465468. 2 Beart, P.M., Nicolopoulos, LX, West, D.C. and Headley, P.M. An excitatory amino acid projection from ventromedial hypothalamus to periaqueductal gray in the rat: autoradiographic and electrophysiological evidence, Neurosci. Lett., 85(1988)205-211.
3 Bourguignon, J.-P., Gerard, A. and Franchimont, P., Direct activation of gondadotropin-releasing hormone secretion through different receptors to neuroexcitatory amino acids, Neuroendocrinology, 49(1989)4022408. 4 Carstens, E., Hypothalamic inhibition of rat dorsal horn neuronal responses to noxious skin heating, Pain, 25(1986)95-107. 5 Crowley, W.R., Jacobs, R., Volpe, J., Rodriguez-Sierra, J.F. and Komisaruk, B.R., Analgesic effect of vaginal stimulation in rats: Modulation be graded stimulus intensity and hormones, Physiol. Behav., 16 (1976) 483488. 6 Crowley, W.R, O’Connor, L.H. and Feder, H.H. Neurotransmitters and social behavior. In J. Balthazart (Ed.), Molecular and Cellular Basis of Social Behavior in Vertebrates, Springer, New York, 1988, pp. 162-128. 7 Donoso, A.O., Lopez, F.J. and Negro-Vilar, A., Glutamate receptors of the non-N-methyl-D-aspartic acid type mediate the increase in luteinizing hormone-releasing hormone release by excitatory amino acids in vitro, Endocrinology, 126 (1990) 414420. 8 Dudley, C.A. and Moss, R.L. Facilitation of lordosis in female rats by CNS site specific infusions of an LH-RH fragment, Ac-LH-RH(5510), Brain Res., 441 (1988) 161-167. 9 Jacquet, Y.F., The NMDA receptor: central role in pain inhibition in rat periaqueductal gray, Eur. J. Pharmacol., 154 (1988) 271-276. 10 Kow, L.-M., Harlan, R., Shivers, B.D. and Pfaff, D.W., Inhibition of lordosis reflex in rats by intrahypothalamic infusion of neural excitatory agents: evidence that the hypothalamus contains separate inhibitory and facilitatory elements, Brain Res., 341 (1985) 26 34. 11 Lipa, S.M. and Kavaliers, M., Sex differences in the inhibitory effects of the NMDA antagonist, MK-801, on morphine and stressinduced analgesia, Brain Res., 24 (1990) 6277630. 12 Lopez, F.J., Donoso, A.O. and Negro-Vilar, A., Endogenous excitatory amino acid neurotransmission regulates the estradiolinduced surge in ovariectomized rats, Endocrinology, 126 (1990) 1771-1773. 13 McCarthy, M.M., Malik, K.F. and Feder, H.H., GABAergic neurotransmission in the medial hypothalamus facilitates lordosis but has the opposite effect in the preoptic area/anterior hypothalamus, Brain Res., 507 (1990) 40-44. 14 McCarthy, M.M., Pfaff, D.W. and Schwartz-Giblin, S., GABA in the midbrain central gray facilitates lordosis, Sot. Neurosci. Abstr., (1990) 380.3. 15 Ondo, J.G., Wheeler, D.D. and Dom, R.M., Hypothalamic site of action for N-methyl-D-aspartate (NMDA) on LH secretion, Life Sci., 43(1988)2283-2286. 16 Price, M.T., Olney, J.W. and Cicero, T.J., Acute elevations of serum luteinizing hormone induced by kainic acid, N-methyl aspartic acid or homocysteic acid, Neuroendocrinology, 26(1978)352-358. Pfaff, D.W. and Schwartz-Giblin, S., Cellular mechanisms of female reproductive behavior. In E. Knobil and J. Neil1 et al. (Eds.), The Physiology of Reproduction, Raven, New York, 1988, pp. 1487-1569. Rargorodsky, G. and Urea, G., Intrathecal N-methyl-D-aspartate (NMDA) activates both nociceptive and antinociceptive systems, Brain Res., 422 (1987) 158-162. Yamanouchi, K. and Arai, Y., Forebrain and lower brainstem participation in facilitatory and inhibitory regulation of the display of lordosis in female rats, Physiol. Behav., 30(1983)155159.
94
NSL 07750
Excitatory amino acid modulation of lordosis in the rat M.M. McCarthy’, G.H. Curran’ and H.H. Feder’*2 ‘Institute qf Animal Behavior and”Department ofBiologicalSciences, Rutgers University, Newark,
NJ 07012 (U.S.A.)
(Received 23 August 1991; Revised version received 3 December 1991; Accepted 6 February 1991) Ke.vwords:
NMDA; AP-5; Hypothalamus; Preoptic area
Microinfusion of the excitatory ammo acid agonist N-methyl-p-aspartate (NMDA) into the mediobasal hypothalamus (MBH) significantly reduced lordosis in estrogen plus progesterone-treated female rats at 10 min post-infusion with recovery to pretest values by 30 min (P< .05; Wilcoxon). Microinfusion of the specific NMDA antagonist o,t.2-amino-5-phosphonopentoic acid (AP-5) into the same sites was without effect on lordosis responding of fully receptive females. There was also a significant increase in the number of females vocalizing to mounts by males after infusion of NMDA but not after infusion of AP-5 into the MBH. When NMDA was infused into the preoptic area (POA) there was no effect on lordosis responding of full receptive females, but AP-5 infusion resulted in a significant inhibition of lordosis at 10 min post-infusion. There was no difference between groups in percentage of females vocalizing after drug infusion into the POA. These results suggest that increased excitatory amino acid activity in the MBH and decreased excitatory amino acid activity in the POA inhibits lordosis behavior.
The sexually receptive posture of the female rat, lordosis, is steroid-dependent and is correlated with increased neuronal activity in the ventromedial hypothalamus (VMH) and reduced when there is increased neuronal activity in the preoptic area (POA) [see ref. 17 for review]. Several ‘classical’ neurotransmitters and neuropeptides have been implicated in the control of lordosis behavior [6] but only recently has a role for amino acid transmitters in the regulation of female receptivity become apparent. The inhibitory amino acid transmitter y-aminobutyric acid (GABA) has a dual effect on lordosis responding. GABA agonists administered into the mediobasal hypothalamus (MBH) and the midbrain central gray (MCG) facilitate lordosis, but increased GABAergic acitvity in the POA inhibits this behavioral response [I 3, 141. The excitatory amino acid transmitter glutamate has been reported to markedly and transiently inhibit lordosis when infused into the MBH of receptive female rats [lo] suggesting that excitation of certain medial hypothalamic neurons inhibits the lordosis reflex. The existence of lordosis facilitating and suppressing neuronal systems in the forebrain which act independently of the VMH have also been reported [ 191. We report here that the specific excitatory amino acid receptor agonist, N-methyl-DCorrespondence: M.M. McCarthy, Rockefeller University, 1230 York Avenue. New York, NY 10021. U.S.A.
aspartate (NMDA), and its selective antagonist, D,L-2amino-5phosphonopentoic acid (AP-S), affect lordosis differentially when infused into the MBH and POA of sexually receptive female rats. Modulation of nociception is also an important aspect of reproduction [ 171 and excitatory amino acid neurotransmission may be important to this modulation since infusion of NMDA into the MBH significantly increased the number of females vocalizing when mounted by the male at 10 min postinfusion. Vocalizations can be considered an indicator of nociceptive thresholds [5, 181. Adult female Sprague-Dawley rats (Charles River, Kingston, NY) weighing 25&350 g were housed individually in suspended wire mesh cages on a reversed light cycle (lights off from 10.00 to 20.00 h). Temperature was maintained at approximately 22°C and Purina Lab Chow and water were available ad libitum. Females were bilaterally ovariectomized and cannulated by stereotaxic placement with double-barrel 23-gauge guide cannulae under Ketamine anesthesia (20-25 mg i.p.; Bristol Labs, Syracuse, NY, plus 0.5 mg Xlazine; Mobay Corp., Shawnee, KA). Injection cannulae were 28 gauge and cut to 0.5 mm longer than the guide cannulae (Plastic One, Roanoke VA). Approximately 2 weeks after surgery, females were injected S.C. with estradiol benzoate (EB, 1Opg; 48 h prior to testing) and progesterone (P, 1 mg; 4 h prior to testing) dissolved in sesame oil and given in a 0.1 ml volume. At the time of testing (beginning at
95
MBH
q
NMDA
n
A?-5
n
SALINE
PRETEST (MINUTES POST-INJECTION) Fig. 1.Change in lordosis quotient (LQ) after infusion of NMDA, AP-5 or saline into the MBH of EB + P-treated female rats. There was a significant decrease in LQ at 10 min post-infusion in NMDA-infused rats as compared to pre-test levels (PcO.05; Wilcoxon). Infusion of AP-5 and saline into the MBH did not affect subsequent lordosis responding.
13.00 h, 3 h after lights out) females were placed in a Plexiglas arena (45 cm diameter) with one or two stud males for at least 10 mounts to establish a pretest lordosis quotient (LQ=number of lordosis/number of mounts x 100). Microinfusion of drugs into brain began within 1 h of pretesting and postinfusion testing was performed at lo,30 and 60 min. Cannulae were aimed either at the MBH (AP= - 3.0 mm; depth=9.5 mm) or the POA (AP= -0.5 mm; depth= 8.5 mm). At the completion of the experiment, the brains of representative animals of each group were histologically processed and cannulae placement in the POA and MBH verified. All observations were done under a 25 W red light. Steroids and drugs were obtained from Sigma (St. Louis MO). Experiment 1: Influence of NMDA and AP-5 infused into the MBH on lordosis. After pretesting, females with an LQ of 60% or greater were bilaterally infused with either NMDA (20 ng/0.25 pl/cannula, pH = 7.2, n = 7), AP-5 (50 ng/0.25 #annula, pH = 8.0; n = 11) or saline (n = 3) into the MBH over a 30 s period using two 1 ~1 Hamilton syringes under light Metofane anesthesia (Pitman-Moore, Washington Crossing, NJ). Post-injection tests consisted of measuring the lordosis response of the female to 10 mounts. Vocalizations by the female in response to mounting by the male were noted as ‘yes’ or ‘no’ with a ‘yes’ response being given if the female vocalized to at least 3 of 10 mounts. All behavioral tests were separated by two weeks and drug treatments were random. There was no apparent effect of order of drug treatment or testing on subsequent lordosis responding. Experiment 2: Influence of NMDA and AP-5 infused into the POA on lordosis. An additional group of
females was bilaterally infused with NMDA (n = 7), AP5(n = 8) or saline (n = 4) into the POA and behaviorally tested in the same manner as above. Results Expt. 1: Microinfusion of 20 ng of NMDA into the MBH resulted in a significant decrease in LQ at 10 min post-infusion as compared to the pretest (P < .05; Wilcoxon) with full recovery to pretest levels by 30 and 60 min. Microinfusion of AP-5 or saline into the MBH was without effect on LQ at any time post-infusion (Fig. 1). There was a significant increase in the number of NMDA-treated females that vocalized when mounted by males during the 10 min post-infusion test in compar-
TABLE I PERCENTAGE OF FEMALES EXHIBITING FREQUENT VOCALIZATIONS WHEN MOUNTED BY MALES DURING POST-INFUSION TESTS Time post-infusion (min) IO
30
60
85.7%* (6/7) 36.4% (4/l 1)
42.6% (3/7) 36.4% (4/l 1)
14.3%(l/7) 12.5%(l/8)
MBH
NMDA AP-5 Saline
0% (O/3)
0% (O/3)
33.4% (2/6) 37.5% (3/8) 25.0% (l/4)
16.7% (l/6) 37.5% (3/8)
0% (O/3)
POA
NMDA AP-5 Saline
0% (O/4)
16.7%(l/6) 12.5%(l/S) 0% (O/4)
*P < 0.05; Cochrans Q-test, Q = 9 between pretest, 10 and 30 min postinfusion.
96
POA
%l NMDA
n AP-5 n SALINE
1
PRETEST (MINUTESPOST-IKIECTION) Fig. 2. Change decrease
in lordosis
quotient
(LQ) after infusion
in LQ at IO min post-infusion
into the POA did not affect subsequent
of NMDA,
in AP-5 infused lordosis
AP-5 or saline into the POA of EB+P-treated
rats as compared
to pre-test
levels (PcO.05;
female rats. There was a significant
Wilcoxon).
Infusion
of NMDA
and saline
responding.
ison to the pretest and 30 min post-infusion test (Cochran’s Q-test; Q = 9, P < .05). There was no difference in the number of AP-5-treated females vocalizing when mounted by the male (Table I). 1 Results Expt. 2: Microinfusion of 50 ng AP-5 into the POA significantly reduced LQ at 10 min post-infusion with full recovery to pretest levels by 30 and 60 min (P-C .05, Wilcoxon). A 10 ng dose of AP-5 was without effect on lordosis responding (n = 3) and a 100 ng dose did not further increase the magnitude of the effect in the POA (n = 3). Both NMDA and saline were without effect on lordosis responding when infused into the POA (Fig. 2). Furthermore, there was no effect of NMDA on vocalizations when infused into the POA as there was in the MBH. Treatment with AP-5 also did not significantly increase vocalizations at any time post-infusion (Table I). We report here that excitatory amino acids exert a dual effect on lordosis behavior. Microinfusion of NMDA into the MBH transiently decreases lordosis responding whereas the selective antagonist AP-5 is without effect on fully receptive females. However, when infused into the POA, AP-5 decreases lordosis and NMDA is without effect on fully receptive females. In addition, modulation of nociception, as determined by vocalizations in response to mounting, also seems to be influenced by excitatory amino acids in the MBH since infusion of NMDA into this site significantly increased the number of females vocalizing in response to mounting by males. In addition to effects on reproductive behavior, excitatory amino acids have been implicated in the control of
gonadotropin secretion and pain processing. For example, administration of excitatory amino acids has been reported to elevate serum LH levels acutely in male [1, 7, 161and female rats [12]. The induction by excitatory amino acids of LH release has been attributed to their direct action on LHRH secretion in the hypothalamus rather than to an effect on the pituitary [3]. Both the NMDA [ 1, 12, 15, 161and non-NMDA receptor type [7] appear to be involved. In ovariectomized rats treated with estrogen in order to induce an LH surge, both NMDA and non-NMDA antagonists administered intraventricularly block the LH surge without affecting FSH or prolactin levels [12] indicating a role for endogenous excitatory amino acids in regulating LH release. In male rats it has been shown that microinjection of NMDA into the medial POA but not into the arcuate or ventromedial nuclei, increases LH secretion [15]. It has been suggested that activation of NMDA receptors in rostra1 brain regions, such as the POA, and of non-NMDA receptors in more caudal areas (i.e. arcuate nucleus) mediate LHRH secretion and thereby LH release [12]. In the current study, the action of AP-5, a selective NMDA antagonist, in depressing lordosis when infused into the POA, may be a result of inhibition of LHRH-secreting neurons of the POA. Microinfusion of LHRH into the POA rapidly facilitates lordosis behavior in rats [8] and it can be speculated that inhibition of LHRH-secreting POA neurons by blockade of excitatory afferents transiently suppresses the behavioral response. Excitatory amino acids have also been implicated as neurotransmitters involved in the regulation of nocicep-
97
tion. Microinfusion of NMDA into the midbrain central gray (MCG) produces a potent analgesia [9] and the NMDA antagonist, MK-801, blocks morphine and stress-induced analgesia in male mice [l 11.Administration of NMDA intrathecally at the spinal cord has the opposite effect, producing a hyperalgesia accomplanied by vocalizations and scratching [18]. In the current experiments, NMDA infused into the MBH resulted in an increase in vocalizations in response to mounting by males, indicating an increased sensitivity of drug-treated females to somatosensory stimuli. It has been suggested that in order for a female rat to be highly receptive she must also be partially analgesic so that high intensity stimulation from the male is not perceived as noxious [ 171. The decrease in sexual receptivity after NMDA injection into the MBH may be due to a partial loss of this analgesia, so that the female now attempts to avoid being mounted by the male. Descending input from the medial hypothalamus has been found to modulate the response to noxious input at the level of the spinal cord [4] and there is an excitatory amino acid projection from the VMH to the MCG in the rat [2]. Thus, the possibility exists, but has not been established, that excitatory amino acid transmission in the MBH regulates nociception. In conclusion, the current results establish that excitatory amino acid transmission affects sexual receptivity in a dual fashion. Lordosis is reduced when excitatory amino acid transmission increases in the MBH and decreases in POA. GABAergic drugs also exert a dual effect on lordosis, with a very similar time course, but in the case of GABA transmission lordosis is reduced when GABA activity decreases in MBH and increases in POA [13]. It is possible that these effects are related, i.e., GABA may block excitatory amino acid transmission and thereby facilitate lordosis responding. Whether the involvement of excitatory amino acids in the control of sexual behavior is exclusive to the NMDA receptor or includes non-NMDA receptors is unknown at this time. This is publication No. 517 of the Institute of Animal Behavior and No. 89 of the Department of Biological Sciences and was supported by Grant NIH HD 04467 and Busch Bequest Funds to H.H.F. 1 Arslan, M., Phol, CR. and Plant, T.M., or.-2-amino-5-phosphonopentanoic acid, a specific N-methyl-D-aspartic acid receptor antagnoist, suppresses pulsatile LH release in the rat, Neuroendocrinology, 47(1988)465468. 2 Beart, P.M., Nicolopoulos, LX, West, D.C. and Headley, P.M. An excitatory amino acid projection from ventromedial hypothalamus to periaqueductal gray in the rat: autoradiographic and electrophysiological evidence, Neurosci. Lett., 85(1988)205-211.
3 Bourguignon, J.-P., Gerard, A. and Franchimont, P., Direct activation of gondadotropin-releasing hormone secretion through different receptors to neuroexcitatory amino acids, Neuroendocrinology, 49(1989)4022408. 4 Carstens, E., Hypothalamic inhibition of rat dorsal horn neuronal responses to noxious skin heating, Pain, 25(1986)95-107. 5 Crowley, W.R., Jacobs, R., Volpe, J., Rodriguez-Sierra, J.F. and Komisaruk, B.R., Analgesic effect of vaginal stimulation in rats: Modulation be graded stimulus intensity and hormones, Physiol. Behav., 16 (1976) 483488. 6 Crowley, W.R, O’Connor, L.H. and Feder, H.H. Neurotransmitters and social behavior. In J. Balthazart (Ed.), Molecular and Cellular Basis of Social Behavior in Vertebrates, Springer, New York, 1988, pp. 162-128. 7 Donoso, A.O., Lopez, F.J. and Negro-Vilar, A., Glutamate receptors of the non-N-methyl-D-aspartic acid type mediate the increase in luteinizing hormone-releasing hormone release by excitatory amino acids in vitro, Endocrinology, 126 (1990) 414420. 8 Dudley, C.A. and Moss, R.L. Facilitation of lordosis in female rats by CNS site specific infusions of an LH-RH fragment, Ac-LH-RH(5510), Brain Res., 441 (1988) 161-167. 9 Jacquet, Y.F., The NMDA receptor: central role in pain inhibition in rat periaqueductal gray, Eur. J. Pharmacol., 154 (1988) 271-276. 10 Kow, L.-M., Harlan, R., Shivers, B.D. and Pfaff, D.W., Inhibition of lordosis reflex in rats by intrahypothalamic infusion of neural excitatory agents: evidence that the hypothalamus contains separate inhibitory and facilitatory elements, Brain Res., 341 (1985) 26 34. 11 Lipa, S.M. and Kavaliers, M., Sex differences in the inhibitory effects of the NMDA antagonist, MK-801, on morphine and stressinduced analgesia, Brain Res., 24 (1990) 6277630. 12 Lopez, F.J., Donoso, A.O. and Negro-Vilar, A., Endogenous excitatory amino acid neurotransmission regulates the estradiolinduced surge in ovariectomized rats, Endocrinology, 126 (1990) 1771-1773. 13 McCarthy, M.M., Malik, K.F. and Feder, H.H., GABAergic neurotransmission in the medial hypothalamus facilitates lordosis but has the opposite effect in the preoptic area/anterior hypothalamus, Brain Res., 507 (1990) 40-44. 14 McCarthy, M.M., Pfaff, D.W. and Schwartz-Giblin, S., GABA in the midbrain central gray facilitates lordosis, Sot. Neurosci. Abstr., (1990) 380.3. 15 Ondo, J.G., Wheeler, D.D. and Dom, R.M., Hypothalamic site of action for N-methyl-D-aspartate (NMDA) on LH secretion, Life Sci., 43(1988)2283-2286. 16 Price, M.T., Olney, J.W. and Cicero, T.J., Acute elevations of serum luteinizing hormone induced by kainic acid, N-methyl aspartic acid or homocysteic acid, Neuroendocrinology, 26(1978)352-358. Pfaff, D.W. and Schwartz-Giblin, S., Cellular mechanisms of female reproductive behavior. In E. Knobil and J. Neil1 et al. (Eds.), The Physiology of Reproduction, Raven, New York, 1988, pp. 1487-1569. Rargorodsky, G. and Urea, G., Intrathecal N-methyl-D-aspartate (NMDA) activates both nociceptive and antinociceptive systems, Brain Res., 422 (1987) 158-162. Yamanouchi, K. and Arai, Y., Forebrain and lower brainstem participation in facilitatory and inhibitory regulation of the display of lordosis in female rats, Physiol. Behav., 30(1983)155159.
