138
Brain Research, 568 (1991) 138-146 © 1991 Elsevier Soence Publishers B.V. All rights reserved 0006-8993/91/$03.50
BRES 17286
Effects of non-competitive N M D A receptor antagonists on reproductive and motor behaviors in female rats Amos Fleischmann, Patricia A. Vincent and Anne M. Etgen Departments of Psychtatry and Neuroscience, Albert Emstein College of Medwme, Bronx, NY 10461 (U S.A.) (Accepted 6 August 1991) Key words: N-Methyl-D-aspartate; MK-801; Dextrorphan; Reproductive behavior; Motor behavior; Female rat
MK-801 and dextrorphan, selective non-competmve antagonists at N-methyl-t)-aspartate (NMDA) receptors, were used to evaluate the effect of NMDA receptor blockade on sexual and motor behaviors in female rats. Ovanectormzed rats were treated with estradiol benzoate (EB) for 48 or 72 h followed by progesterone (P) 3.5-4 h before testing the animals for sexual receptivity. After testing for estrous responsiveness, the effect of NMDA antagonists on several motor behaviors was also assessed. Lordosis frequency and intensity were inhibited in animals that received 0.5 mg/kg MK-801 30 rain before EB; the same dose of MK-801 was relatively ineffective when adrmnistered 24 h after EB. In neither case did MK-801-treated females differ from controls when motor behaviors were assessed after mating tests. When 30 mg/kg dextrorphan, a short-acting NMDA antagonist, was administered 15 min before P, sexual behavior was not blocked. However, both 0.05 mg/kg MK-801 and 30 mg/kg dextrorphan suppressed ongoing female sexual behavior within 30 min m animals made receptive with EB and P. These deficits in sexual behavior were associated with changes in motor performance MK-801 (0.1 mg/kg) and dextrorphan (30 mg/kg) abolished movement m the vertical dimension (e.g. jumping and rearing). By contrast, the drugs increased movement m the longitudinal (locomotion) and lateral (circling) dimensions. At 0.2 mg/kg, MK-801 blocked movement in both the vertical and longitudinal dimensions; however, It failed to block circling. Only at 0.4 mg/kg did MK-801 inhibit lateral movements and righting reflexes. It is likely that the acute inhibition of sexual behavior by NMDA antagonists is related to changes m sensorimotor processmg and/or motor performance. INTRODUCTION Activation of N-methyl-D-aspartate ( N M D A ) receptors has been shown to induce release of luteinizing hormone ( L H ) from the pituitary and g o n a d o t r o p i n releasing h o r m o n e ( G n R H ) from the hypothalamus 2'1°'22'3°. N M D A receptors can also m o d u l a t e estradiol (E2), progesterone (P) and corticosteroid-induced release of L H and follicle-stimulating h o r m o n e 3'19. In addition, N M D A receptors are involved in the control of various m o t o r behaviors 14-16'26. F e m a l e reproductive behavior in rats is coordinated temporally with the preovulatory L H surge, and it consists of a variety of m o r e or less complex motor behaviors. Therefore, it is reasonable to suggest that N M D A receptors might also be involved in the regulation of female reproductive behavior. Reproductive behavior in female rats includes both proceptive (hopping, darting and e a r wiggling) and receptive (lordosis) components. Priming of the rat brain by the ovarian steroid h o r m o n e s (E2 and P) facilitates the display of reproductive behavior in response to app r o p r i a t e sensory stimulation from a mounting male 23. Thus, N M D A receptors m a y be involved in the priming
actions of steroids on brain regions that regulate female sexual behavior and/or with the sensorimotor integration required for the p r o p e r execution of receptive and/or proceptive behaviors. Such an involvement m a y be confirmed if sexual behavior is inhibited by administration of antagonists with selectivity for the N M D A r e c e p t o r either prior to steroid administration or after the onset of h o r m o n e - d e p e n d e n t estrous responsiveness. The development of non-competitive, specific antagonists for the N M D A r e c e p t o r which are capable of crossing the b l o o d - b r a i n barrier enables investigators to block N M D A receptors using systemic drug administration 18' 24. Therefore, this study utilized two non-competitive N M D A antagonists, MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine hydrogen maleate] and d e x t r o r p h a n [(+)-3-hydroxy-N-methylmorphinan], to examine the influence of N M D A receptors on female reproductive behaviors as well as potential m o t o r effects associated with these drugs. MATERIALS AND METHODS Ammals and materials Adult female Sprague-Dawley rats (175-200 g) were purchased
Correspondence: A.M. Etgen, Department of Psychiatry, Albert Einstein College of Medicine, 1300 Morns Park Avenue, Bronx, NY 10461, U.S.A
139 from Taconic Farm (Germantown, NY). Ammals were housed in groups of 4 in plastac cages with food and water available ad libiturn. A 14-10 h, reverse light-dark cycle was maintamed with lights off at 12.00 h. Rats were ovariohysterectomized (OVX) bilaterally under Metofane anesthesia (Pitman-Moore, Inc., Atlanta, GA). Behavior testing was initiated 1 week after OVX and was conducted during the dark phase of the light cycle. In most experiments animals were injected subcutaneously (s.c.) with 2/~g of estradiol benzoate (EB) followed 44 h later by 500/~g of P (Steraloids, Inc., Wilton, NH) and were tested for sexual and motor behaviors 3.5-4 li after the P injection. In some experiments (see Results), animals received 2/~g of EB 24 and 48 h before P. Dextrorphan was donated graciously by Hoffman-La Roche, Ltd. (Nutley, NJ). MK-801 was purchased from Research Biochemicals, Inc. (Natick, MA).
inversion which results in all 4 paws resting on the surface was defined as righting reflex time.
Statistical analysis of data Data were analyzed using analysis of variance followed by posthoe tests for specific between-group comparisons (Scheffe or t-tests) or by Student's t-tests when only two groups were compared. In experiments where individual animals were tested more than once, appropriate repeated measures statistical designs were employed. Differences were considered significant if P < 0.05. For non-parametric data, Mann-Whitney U-tests or Wilcoxon signed-rank tests were used.
RESULTS
Tests for reproductive behavior Experienced stimulus males were placed in 20-gallon glass arenas and allowed to adapt for 20-30 rain. Females were then placed in the arenas until they received 10 mounts with pelvic thrusting from the male. A lordosis quotient (LQ = number of lordosis/ number of mounts x 100) was derived as a measure of behavioral receptivity. The quality of each lordosis was also rated on a scale of 0-3 to yield a lordosis score (LS)ll: 0, no lordosis; 1, shallow lordosis; 2, definite dorsiflexion of the spine; 3, exaggerated lordosis. The presence or absence of proceptive behaviors (darting and ear wiggling) was also recorded. The number of times a male touched a female with his snout (male-female contacts) and the number of times a female touched a male with her snout (femalemale contacts) during the lordosis testing were recorded as a measure of social contact.
Expt. 1. Effect o f MK-801 on E B priming of female sexual behavior
Tests for motor behavior
i m e n t e r was b l i n d to t h e a n i m a l s ' d r u g t r e a t m e n t . D e x -
Some or all of the following motor behavior tests were administered to female rats approximately 15 rain after the conclusion of tests for reproductive behavior. The order in which the individual tests were administered was randomized. Rearing. The number of times an animal reared during a 60-s testing session was recorded. Rearing was defined as elevation of the rat's forebody so that the animal stands only on its lund legs. Rearing is considered as a measure of movement in the vertical dimension. Jumping. The rat was held upside down by its tail so that its legs and paws could touch a wall. Jumping away from the wall (vertically to the wall and body axis and parallel to the floor) was measured. Jumping served as a measure of the ability to initiate movement vertically to the body axis. The animal's lateral body movement (attempt of the ammal to revert to an upward positaon) was also noted. The test was terminated after 60 s if the animal did not jump and the time to jump considered as 60 s. Falling. The animals were placed on a small (2 x 5 m.) elevated platform 55 in. above the floor. The time spent by an animal on the platform until it fell to a soft surface was recorded. The test was terminated after 60 s if the animal did not fall off of the platform. The tame spent on the surface served as a measure of the ability of vertical cliff to inlubit longitudinal movement. Locomotion. Simultaneously with the measurement of rearing, locomotaon was also assessed. Each animal was placed in the huddle of horizontal corridor (24 × 12 in.) divided into 72 equal squares and was permitted to move freely. The number of squares entered by the animal during a 60-s test session was recorded. Locomotion is performed almost completely m the longitudinal direction and thus served as a measurement for longitudinal movement. C~rcling. An animal was placed in the middle of a round testing chamber that had a surface radius of 10 in. The number of 360 ° rotations made by the animal in a 60-s test session was recorded. Circling served as a measure of movement lateral to the body axis. Righting reflex. The rat was placed in the center of the testing chamber in the supine position (back resting against the floor of horizontal surface) at the beginning of the tnal. Time required for
t r o r p h a n was n o t u s e d in t h e s e e x p e r i m e n t s b e c a u s e of
To e v a l u a t e t h e effect o f N M D A r e c e p t o r b l o c k a d e o n E B p r i m i n g , O V X f e m a l e s (n = 10) w e r e i n j e c t e d with 2 / z g o f E B 48 h b e f o r e b e h a v i o r testing; 0.5 m g / k g M K 801 o r saline vehicle was a d m i n i s t e r e d s.c. 30 m i n p r i o r to E B . This p r o c e d u r e was r e p e a t e d 1 w e e k l a t e r e x c e p t t h a t rats w h i c h r e c e i v e d M K - 8 0 1 t h e f a s t w e e k r e c e i v e d saline v e h i c l e t h e s e c o n d w e e k , and vice versa. In t h e s e and s u b s e q u e n t e x p e r i m e n t s o n E B p r i m i n g , t h e e x p e r -
its short d u r a t i o n o f action. L o r d o s i s b e h a v i o r , m e a s u r e d by b o t h L Q a n d LS, was i n h i b i t e d m a r k e d l y by M K - 8 0 1 (Fig. 1 A ) . A l t h o u g h p r o c e p t i v e b e h a v i o r s w e r e d i s p l a y e d by 10/10 animals w h e n t h e y r e c e i v e d saline, 0/10 animals w e r e p r o c e p t i v e w h e n t h e y r e c e i v e d M K - 8 0 1 p r i o r to E B . M o t o r b e h a v i o r s such as l o c o m o t i o n , r e a r i n g , falling a n d righting reflexes w e r e n o t a f f e c t e d by t h e M K 801 p r e t r e a t m e n t (Table I). W e n e x t d e t e r m i n e d w h e t h e r M K - 8 0 1 h a d long-lasting s u p p r e s s i v e effects o n t h e m o t o r e x e c u t i o n o f r e p r o d u c t i v e b e h a v i o r s r a t h e r t h a n i n t e r f e r i n g specifically w i t h the E B p r i m i n g . A n i m a l s w e r e t r e a t e d with 0.5 m g / k g M K - 8 0 1 (n = 8) o r saline v e h i c l e (n = 8) 24 h after 2/~g o f E B . R e p r o d u c t i v e and m o t o r b e h a v i o r s w e r e t e s t e d 48 h l a t e r (72 h a f t e r E B i n j e c t i o n ) , b e t w e e n 3.5 and 4 h after 500/~g o f P. L o r d o s i s f r e q u e n c y (i.e. L Q ) was n o t a f f e c t e d w h e n MK-801 was a d m i n i s t e r e d 24 h after E B (Fig. 1B). T h e quality of lordosis (i.e. LS) was r e d u c e d slightly but significantly by this M K - 8 0 1 p r e t r e a t m e n t . Proceptive behaviors (data not shown), locomotion, rearing, falling and righting reflexes w e r e n o t a f f e c t e d significantly by t h e d r u g (Table I).
Expt. 2. Effect o f dextrorphan on P facilitation of estrous behavior To e v a l u a t e the effects o f N M D A
receptor blockade
140
A
E~ 100
3
100
75 2
2
(./)
50
!,
25
0
0
CONTROL
MK-801
tO
.j
50
V-
Z u_.l 1-
o9
-J
0
0
CONTROL
MK-801
Fig. 1. MK-801 effects on estrogen priming of lordosts. OVX female rats were injected with 2 •g of EB 48 h (A) or 72 h (B) prior to behavioral testing and with 500/~g of P 3.5-4 h pnor to testing (A,B). MK-801 (0.5 mg/kg) or saline (control) was applied 30 min before (A) or 24 h after (B) EB. Solid bars represent lordosis scores, and striped bars represent lordosis quotients. The values are means - S.E.M. (n = 10 in A ; n = 8 in B ) . *Significantly less than control, P < 0.05, t-test.
on P-facilitated mating behavior, saline (n = 5) or 30 mg/kg of the short-acting antagonist d e x t r o r p h a n (n = 5) was administered 15 min before an injection of 500 /~g of P. MK-801 was not used in this experiment because its half-life in brain and plasma is approximately 2 h 29, and it continues to influence m o t o r behaviors for m o r e than 4 h after administration (Fleischmann, unpublished observations). These O V X females were p r i m e d with 2 /~g of E B for 48 h before P. Sexual behavior was tested 3 . 5 - 4 h after P. There were no differences between the animals which received d e x t r o r p h a n prior to P injection and the vehicle control group. The m e a n L Q (--- S . E . M . ) for the control and for the drug-treated animals was 90 --- 7.7 and 92 --- 3.7, respectively ( P < 0.82, unpaired t-test). The mean LS ( - S . E . M . ) for the control and for the drug-treated group was 1.4 --- 0.88 and 1.6 +- 0.14, respectively ( P > 0.41, t-test).
TABLE I Motor behavtors in rats exposed for 48 h to MK-801 OVX female rats were injected wtth 2/tg of EB 48 or 72 h prior to behaxaoral testing and with 500/~g of P 3.5-4 h prior to testmg MK-801 (0.5 mg/kg) or saline was injected 30 min before or 24 h after EB. The values presented are means -+ S.E.M Treatment
Rearing (no./min)
Falhng (s)
Locomotion Righting (dtvzston/mm) (s)
Salinea MK-801a
8.4 --- 1.1 7.8 - 2.3
54.4 +-- 5 6 56 8 +-- 3.2
54.1 --- 8.1 49.9 --- 9.6
Brain Research, 568 (1991) 138-146 © 1991 Elsevier Soence Publishers B.V. All rights reserved 0006-8993/91/$03.50
BRES 17286
Effects of non-competitive N M D A receptor antagonists on reproductive and motor behaviors in female rats Amos Fleischmann, Patricia A. Vincent and Anne M. Etgen Departments of Psychtatry and Neuroscience, Albert Emstein College of Medwme, Bronx, NY 10461 (U S.A.) (Accepted 6 August 1991) Key words: N-Methyl-D-aspartate; MK-801; Dextrorphan; Reproductive behavior; Motor behavior; Female rat
MK-801 and dextrorphan, selective non-competmve antagonists at N-methyl-t)-aspartate (NMDA) receptors, were used to evaluate the effect of NMDA receptor blockade on sexual and motor behaviors in female rats. Ovanectormzed rats were treated with estradiol benzoate (EB) for 48 or 72 h followed by progesterone (P) 3.5-4 h before testing the animals for sexual receptivity. After testing for estrous responsiveness, the effect of NMDA antagonists on several motor behaviors was also assessed. Lordosis frequency and intensity were inhibited in animals that received 0.5 mg/kg MK-801 30 rain before EB; the same dose of MK-801 was relatively ineffective when adrmnistered 24 h after EB. In neither case did MK-801-treated females differ from controls when motor behaviors were assessed after mating tests. When 30 mg/kg dextrorphan, a short-acting NMDA antagonist, was administered 15 min before P, sexual behavior was not blocked. However, both 0.05 mg/kg MK-801 and 30 mg/kg dextrorphan suppressed ongoing female sexual behavior within 30 min m animals made receptive with EB and P. These deficits in sexual behavior were associated with changes in motor performance MK-801 (0.1 mg/kg) and dextrorphan (30 mg/kg) abolished movement m the vertical dimension (e.g. jumping and rearing). By contrast, the drugs increased movement m the longitudinal (locomotion) and lateral (circling) dimensions. At 0.2 mg/kg, MK-801 blocked movement in both the vertical and longitudinal dimensions; however, It failed to block circling. Only at 0.4 mg/kg did MK-801 inhibit lateral movements and righting reflexes. It is likely that the acute inhibition of sexual behavior by NMDA antagonists is related to changes m sensorimotor processmg and/or motor performance. INTRODUCTION Activation of N-methyl-D-aspartate ( N M D A ) receptors has been shown to induce release of luteinizing hormone ( L H ) from the pituitary and g o n a d o t r o p i n releasing h o r m o n e ( G n R H ) from the hypothalamus 2'1°'22'3°. N M D A receptors can also m o d u l a t e estradiol (E2), progesterone (P) and corticosteroid-induced release of L H and follicle-stimulating h o r m o n e 3'19. In addition, N M D A receptors are involved in the control of various m o t o r behaviors 14-16'26. F e m a l e reproductive behavior in rats is coordinated temporally with the preovulatory L H surge, and it consists of a variety of m o r e or less complex motor behaviors. Therefore, it is reasonable to suggest that N M D A receptors might also be involved in the regulation of female reproductive behavior. Reproductive behavior in female rats includes both proceptive (hopping, darting and e a r wiggling) and receptive (lordosis) components. Priming of the rat brain by the ovarian steroid h o r m o n e s (E2 and P) facilitates the display of reproductive behavior in response to app r o p r i a t e sensory stimulation from a mounting male 23. Thus, N M D A receptors m a y be involved in the priming
actions of steroids on brain regions that regulate female sexual behavior and/or with the sensorimotor integration required for the p r o p e r execution of receptive and/or proceptive behaviors. Such an involvement m a y be confirmed if sexual behavior is inhibited by administration of antagonists with selectivity for the N M D A r e c e p t o r either prior to steroid administration or after the onset of h o r m o n e - d e p e n d e n t estrous responsiveness. The development of non-competitive, specific antagonists for the N M D A r e c e p t o r which are capable of crossing the b l o o d - b r a i n barrier enables investigators to block N M D A receptors using systemic drug administration 18' 24. Therefore, this study utilized two non-competitive N M D A antagonists, MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine hydrogen maleate] and d e x t r o r p h a n [(+)-3-hydroxy-N-methylmorphinan], to examine the influence of N M D A receptors on female reproductive behaviors as well as potential m o t o r effects associated with these drugs. MATERIALS AND METHODS Ammals and materials Adult female Sprague-Dawley rats (175-200 g) were purchased
Correspondence: A.M. Etgen, Department of Psychiatry, Albert Einstein College of Medicine, 1300 Morns Park Avenue, Bronx, NY 10461, U.S.A
139 from Taconic Farm (Germantown, NY). Ammals were housed in groups of 4 in plastac cages with food and water available ad libiturn. A 14-10 h, reverse light-dark cycle was maintamed with lights off at 12.00 h. Rats were ovariohysterectomized (OVX) bilaterally under Metofane anesthesia (Pitman-Moore, Inc., Atlanta, GA). Behavior testing was initiated 1 week after OVX and was conducted during the dark phase of the light cycle. In most experiments animals were injected subcutaneously (s.c.) with 2/~g of estradiol benzoate (EB) followed 44 h later by 500/~g of P (Steraloids, Inc., Wilton, NH) and were tested for sexual and motor behaviors 3.5-4 li after the P injection. In some experiments (see Results), animals received 2/~g of EB 24 and 48 h before P. Dextrorphan was donated graciously by Hoffman-La Roche, Ltd. (Nutley, NJ). MK-801 was purchased from Research Biochemicals, Inc. (Natick, MA).
inversion which results in all 4 paws resting on the surface was defined as righting reflex time.
Statistical analysis of data Data were analyzed using analysis of variance followed by posthoe tests for specific between-group comparisons (Scheffe or t-tests) or by Student's t-tests when only two groups were compared. In experiments where individual animals were tested more than once, appropriate repeated measures statistical designs were employed. Differences were considered significant if P < 0.05. For non-parametric data, Mann-Whitney U-tests or Wilcoxon signed-rank tests were used.
RESULTS
Tests for reproductive behavior Experienced stimulus males were placed in 20-gallon glass arenas and allowed to adapt for 20-30 rain. Females were then placed in the arenas until they received 10 mounts with pelvic thrusting from the male. A lordosis quotient (LQ = number of lordosis/ number of mounts x 100) was derived as a measure of behavioral receptivity. The quality of each lordosis was also rated on a scale of 0-3 to yield a lordosis score (LS)ll: 0, no lordosis; 1, shallow lordosis; 2, definite dorsiflexion of the spine; 3, exaggerated lordosis. The presence or absence of proceptive behaviors (darting and ear wiggling) was also recorded. The number of times a male touched a female with his snout (male-female contacts) and the number of times a female touched a male with her snout (femalemale contacts) during the lordosis testing were recorded as a measure of social contact.
Expt. 1. Effect o f MK-801 on E B priming of female sexual behavior
Tests for motor behavior
i m e n t e r was b l i n d to t h e a n i m a l s ' d r u g t r e a t m e n t . D e x -
Some or all of the following motor behavior tests were administered to female rats approximately 15 rain after the conclusion of tests for reproductive behavior. The order in which the individual tests were administered was randomized. Rearing. The number of times an animal reared during a 60-s testing session was recorded. Rearing was defined as elevation of the rat's forebody so that the animal stands only on its lund legs. Rearing is considered as a measure of movement in the vertical dimension. Jumping. The rat was held upside down by its tail so that its legs and paws could touch a wall. Jumping away from the wall (vertically to the wall and body axis and parallel to the floor) was measured. Jumping served as a measure of the ability to initiate movement vertically to the body axis. The animal's lateral body movement (attempt of the ammal to revert to an upward positaon) was also noted. The test was terminated after 60 s if the animal did not jump and the time to jump considered as 60 s. Falling. The animals were placed on a small (2 x 5 m.) elevated platform 55 in. above the floor. The time spent by an animal on the platform until it fell to a soft surface was recorded. The test was terminated after 60 s if the animal did not fall off of the platform. The tame spent on the surface served as a measure of the ability of vertical cliff to inlubit longitudinal movement. Locomotion. Simultaneously with the measurement of rearing, locomotaon was also assessed. Each animal was placed in the huddle of horizontal corridor (24 × 12 in.) divided into 72 equal squares and was permitted to move freely. The number of squares entered by the animal during a 60-s test session was recorded. Locomotion is performed almost completely m the longitudinal direction and thus served as a measurement for longitudinal movement. C~rcling. An animal was placed in the middle of a round testing chamber that had a surface radius of 10 in. The number of 360 ° rotations made by the animal in a 60-s test session was recorded. Circling served as a measure of movement lateral to the body axis. Righting reflex. The rat was placed in the center of the testing chamber in the supine position (back resting against the floor of horizontal surface) at the beginning of the tnal. Time required for
t r o r p h a n was n o t u s e d in t h e s e e x p e r i m e n t s b e c a u s e of
To e v a l u a t e t h e effect o f N M D A r e c e p t o r b l o c k a d e o n E B p r i m i n g , O V X f e m a l e s (n = 10) w e r e i n j e c t e d with 2 / z g o f E B 48 h b e f o r e b e h a v i o r testing; 0.5 m g / k g M K 801 o r saline vehicle was a d m i n i s t e r e d s.c. 30 m i n p r i o r to E B . This p r o c e d u r e was r e p e a t e d 1 w e e k l a t e r e x c e p t t h a t rats w h i c h r e c e i v e d M K - 8 0 1 t h e f a s t w e e k r e c e i v e d saline v e h i c l e t h e s e c o n d w e e k , and vice versa. In t h e s e and s u b s e q u e n t e x p e r i m e n t s o n E B p r i m i n g , t h e e x p e r -
its short d u r a t i o n o f action. L o r d o s i s b e h a v i o r , m e a s u r e d by b o t h L Q a n d LS, was i n h i b i t e d m a r k e d l y by M K - 8 0 1 (Fig. 1 A ) . A l t h o u g h p r o c e p t i v e b e h a v i o r s w e r e d i s p l a y e d by 10/10 animals w h e n t h e y r e c e i v e d saline, 0/10 animals w e r e p r o c e p t i v e w h e n t h e y r e c e i v e d M K - 8 0 1 p r i o r to E B . M o t o r b e h a v i o r s such as l o c o m o t i o n , r e a r i n g , falling a n d righting reflexes w e r e n o t a f f e c t e d by t h e M K 801 p r e t r e a t m e n t (Table I). W e n e x t d e t e r m i n e d w h e t h e r M K - 8 0 1 h a d long-lasting s u p p r e s s i v e effects o n t h e m o t o r e x e c u t i o n o f r e p r o d u c t i v e b e h a v i o r s r a t h e r t h a n i n t e r f e r i n g specifically w i t h the E B p r i m i n g . A n i m a l s w e r e t r e a t e d with 0.5 m g / k g M K - 8 0 1 (n = 8) o r saline v e h i c l e (n = 8) 24 h after 2/~g o f E B . R e p r o d u c t i v e and m o t o r b e h a v i o r s w e r e t e s t e d 48 h l a t e r (72 h a f t e r E B i n j e c t i o n ) , b e t w e e n 3.5 and 4 h after 500/~g o f P. L o r d o s i s f r e q u e n c y (i.e. L Q ) was n o t a f f e c t e d w h e n MK-801 was a d m i n i s t e r e d 24 h after E B (Fig. 1B). T h e quality of lordosis (i.e. LS) was r e d u c e d slightly but significantly by this M K - 8 0 1 p r e t r e a t m e n t . Proceptive behaviors (data not shown), locomotion, rearing, falling and righting reflexes w e r e n o t a f f e c t e d significantly by t h e d r u g (Table I).
Expt. 2. Effect o f dextrorphan on P facilitation of estrous behavior To e v a l u a t e the effects o f N M D A
receptor blockade
140
A
E~ 100
3
100
75 2
2
(./)
50
!,
25
0
0
CONTROL
MK-801
tO
.j
50
V-
Z u_.l 1-
o9
-J
0
0
CONTROL
MK-801
Fig. 1. MK-801 effects on estrogen priming of lordosts. OVX female rats were injected with 2 •g of EB 48 h (A) or 72 h (B) prior to behavioral testing and with 500/~g of P 3.5-4 h pnor to testing (A,B). MK-801 (0.5 mg/kg) or saline (control) was applied 30 min before (A) or 24 h after (B) EB. Solid bars represent lordosis scores, and striped bars represent lordosis quotients. The values are means - S.E.M. (n = 10 in A ; n = 8 in B ) . *Significantly less than control, P < 0.05, t-test.
on P-facilitated mating behavior, saline (n = 5) or 30 mg/kg of the short-acting antagonist d e x t r o r p h a n (n = 5) was administered 15 min before an injection of 500 /~g of P. MK-801 was not used in this experiment because its half-life in brain and plasma is approximately 2 h 29, and it continues to influence m o t o r behaviors for m o r e than 4 h after administration (Fleischmann, unpublished observations). These O V X females were p r i m e d with 2 /~g of E B for 48 h before P. Sexual behavior was tested 3 . 5 - 4 h after P. There were no differences between the animals which received d e x t r o r p h a n prior to P injection and the vehicle control group. The m e a n L Q (--- S . E . M . ) for the control and for the drug-treated animals was 90 --- 7.7 and 92 --- 3.7, respectively ( P < 0.82, unpaired t-test). The mean LS ( - S . E . M . ) for the control and for the drug-treated group was 1.4 --- 0.88 and 1.6 +- 0.14, respectively ( P > 0.41, t-test).
TABLE I Motor behavtors in rats exposed for 48 h to MK-801 OVX female rats were injected wtth 2/tg of EB 48 or 72 h prior to behaxaoral testing and with 500/~g of P 3.5-4 h prior to testmg MK-801 (0.5 mg/kg) or saline was injected 30 min before or 24 h after EB. The values presented are means -+ S.E.M Treatment
Rearing (no./min)
Falhng (s)
Locomotion Righting (dtvzston/mm) (s)
Salinea MK-801a
8.4 --- 1.1 7.8 - 2.3
54.4 +-- 5 6 56 8 +-- 3.2
54.1 --- 8.1 49.9 --- 9.6
