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Effects of medial preoptic lesions on male mouse ultrasonic vocalizations and copulatory behavior
Brahl Research Bulletin, Vol. 6, pp. 109-112. Printed in the U.S.A.
Effects of Medial Preoptic Lesions on Male Mouse Ultrasonic Vocalizations and Copulatory Behavior N. JAY BEAN
Department of Psychology, Vassal" College, Poughkeepsie, N Y 12601 ANTONIO
A. NUNEZ
Department of Psychology, Michigan State University, East Lansing, MI 44824 AND ROBERT CONNER
Department of Psychology, Bowling Green State University, Bowling, Green, OH 43402 R e c e i v e d 22 M a y 1980 BEAN, N. J., A. A. NUNEZ AND R. CONNER. Effects o f medial preoptic lesions on male mouse ultrasonic vocalizations and copulatory behavior. BRAIN RES. BULL. 6(2) 109-112, 1981.--In male mice, lesions in the medial preoptic area (MPA) reduced the proportion of animals showing mounting behavior but failed to abolish ano-genital exploration of the female. The lesions did not affect the amount of 70 kHz ultrasound elicited by intact females or by soiled bedding obtained
from female-occupied cages. These results suggest that early components of male sexual behavior are mediated by neural systems outside the MPA. Medial preoptic lesions
Male sexual behavior
Courtship
B I L A T E R A L lesions of the medial-preoptic area (MPA) result in severe impairment or complete abolishment of copulatory behavior in males of several mammalian species including mice [5], rats [2, 6, 9], guinea pigs [13], cats [8], dogs [7] and monkeys [18]. It has been suggested that the precise role played by the MPA in male copulatory behavior is one of mediating the initiation of the copulatory sequence [I, 2, 19]. Thus in some situations, animals with MPA lesions may approach and investigate a receptive female but fail to display the complete pattern of male copulatory behavior [7]. Based upon these observations, it becomes of interest to further investigate the effects of MPA lesions on the early components of male sexual behavior. Male mice of several strains [12] emit 70 kHz-ultrasonic vocalizations as part of their courtship behavior [21]. These vocalizations are elicited by adult female mice or by chemical stimuli present in female urine [12,20]. Male vocalizations occur early in a male-female encounter and in most cases accompany or precede ano-genitai contact with the female. Consistent with observations on other components of male sexual behavior, castration reduces male ultrasonic vocalizations and testos-
Ultrasounds
Male mice
Vocalizations
terone treatment restores the behavior to precastration levels [3,11]. In the present experiment, we investigated the effects of MPA lesions on courtship vocalizations and other components of male mouse sexual behavior. METHOD
Animals Sexually naive male Swiss-Webster (SW) mice, 90-120 days of age on the first behavioral test, were used as subjects. Ten adult C57BL/6J (C57) females served as stimuli for the vocalization tests and 20 adult SW females were used as stimuli for the sex-behavior test. All mice were obtained from the animal colony at Bowling Green State University, Bowling Green, Ohio. The C57 females were used in the ultrasound tests because these females rarely vocalize and seem to elicit more ultrasounding from the SW males. The SW females were ovariectomized 3-4 weeks before testing and were made receptive with injections of estradiol benzoate and progesterone [4]. The SW females were used for the sex-behavior tests because preliminary evidence
1Supported in part by Postdoctoral Fellowship NS 05854-01 from NINCDS to A. A. N. A preliminary report of this research was presented at the Eastern Conference on Reproductive Behavior annual meeting in New Orleans, June 7, 1979. We are grateful to Janet Gray for helpful comments on the manuscript.
C o p y r i g h t © 1981 A N K H O
I n t e r n a t i o n a l Inc.--0361-9230/81/020109-04500.90/0
ll0 suggested that these females were more responsive to the hormone regimen. Therefore, these females were better stimuli for the sex-behavior tests. The males were individually housed in plastic cages (29x 18x 13 cm) with sawdust on the floor and the females were housed 3-6 to a cage. The estrous cycle of the C57 females was not monitored. All animals had free access to food (Purina rodent chow) and water. A 12:12 light-dark cycle of illumination was maintained in the animal colony and behavioral testing was conducted during the last 3-hr of the light period in a room illuminated by dim red light.
Apparatus A Holgate Ultrasonic receiver (model MK V) set to a center frequency of 70 kHz was used to detect ultrasounds. The Holgate receiver transforms ultrasounds into audible sounds as described elsewhere [20,21]. The Holgate microphone was placed about 25 cm above the test cage (29× 18x 13 cm). Vocalization tests involving female stimuli as well as sex-behavior tests were conducted in the males' home cages. Tests using bedding as stimuli were conducted in plastic cages that had been cleaned and rinsed with alcohol. erocedllre Before surgery, the males were given two 3-min vocalization tests, 48-hr apart, to assess their responsive to a C57 female. In all tests, the 3-min test period was preceded by a l-min habituation period. If an ultrasound was emitted during this habituation period, a 2-min interval without an ultrasound was allowed to elapse prior to the beginning of a 3-min test session. The amount of ultrasound emitted during the test was quantified by dividing the 3-min test into thirty-six 5-sec scoring blocks. The test began when the stimulus female was introduced into the test cage. After the pre-surgical vocalization test, the males were divided into a MPA-lesion group and a sham-lesion group. Under ether anesthesia, animals in the MPA-lesion group received a single, mid-line electrolytic lesion (2 mA for 15 sec) aimed at the MPA. The electrode used was a No. 1 stainless steel insect pin insulated except for 0.5 mm at the tip. The stereotaxic coordinates were: I mm anterior to bregma and 5-ram ventral from the dura, with the incisor bar 4-mm above the ear bars. The electrode was lowered along the midline after retracting the midsaggital sinus. Approximately 60% of the operated animals (n= 16) recovered from surgery. Sham-lesion animals (n=8) endured all surgical procedures except that no current was passed through the electrode. Two weeks after surgery, all males received two 3-min vocalization tests, 48 hr apart with C57 females as stimuli. Two weeks later, the males were given 2 additional vocalization tests. In these tests, soiled bedding from cages housing the C57 females and clean bedding were used as stimuli. Each bedding test was separated by 48 hr and the two conditions were administered in a counterbalanced order within each group. After the l-min habituation period, 15-g of either clean or soiled bedding were placed in the test cage with the male. Ultrasounds were monitored for 3-min as described above. One week after the bedding tests, each male received a si.ngle 30-min test of sex behavior with a receptive SW female. After a 10-min habituation period in the testing room, the female was introduced into the test cage. Laten-
BEAN, N U N E Z AND CONNER cies to begin ano-genital exploration and to mount were recorded along with the number of mounts and mounts with thrusts. If the male failed to show mounting behavior during the$irst 10-rain, the female was replaced. At the conclusion of testing, body weights were measured (nearest 0. i g) and the males were sacrificed by decapitation. Both testes were removed, cleaned, and weighed (nearest 0.001 g). The brains were removed and fixed in 10% Formalin; frozen coronal sections (50 tz) were stained with cresyl violet for histological evaluation. Reconstructions of the lesions were made by one of the authors without knowledge of the behavioral data for the individual animals. The Wilcoxon signed-ranks test was used for all within group comparisons. Differences between groups were evaluated using the Mann-Whitney U test and the Fisher exact probability test [16]. Differences were considered statistically significant when p<0.05 (two-tailed tests).
RESULTS
Histology Based entirely upon the histological evaluation of the brains, without knowledge of the behavioral data, a readily discernable large and a small lesion group (n=8 in each group) were formed (Fig. I). The animals' brains that were placed in the large lesion group evidenced damage to the anterior hypothalamus, suprachiasmatic nuclei and the periventricular area in addition to bilateral damage to the MPA. The small lesion group evidenced damage that was restricted to the periventricular MPA. In all cases, the third ventricle was enlarged.
Ultrasonic Vocalization The analysis of the vocalization data from the tests with the stimulus female indicated no significant differences between the pre- and the post-lesion tests for each group or between groups during the pre- or the post-lesion test sessions. Therefore, the lesions did not affect the ultrasonic vocalizations of the males when tested with a female. The tests with bedding as a stimulus also failed to show significant differences across groups. For all groups, though, the amount of ultrasound monitored during the tests with soiled bedding was significantly greater than that monitored during tests with clean bedding (p<0.05~ (Figs. 2 and 3).
Sex Behavior Table 1 summarizes the effects of MPA damage on sex behavior. Large lesions significantly reduced the proportion of animals showing mounting behavior in comparison with both the sham and the small-lesion groups 09<0.05). Small MPA lesions did not reduce the proportion of animals showing mounting behavior and the latencies to the first mount for these animals were similar to those recorded for shams. However, the small lesions did significantly reduce the proportion of animals showing mounts with thrusts (.o<0.05). No intromissions were observed in the test session. All males engaged in ano-genital exploration of the female during the sex-behavior test. However, the latency to initiate this behavior was significantly greater for shams when compared with the lesion groups (p's<0.05). No significant differences in final body weights or testicular weights were found across groups (Table 1).
BRAIN LESIONS AND COURTSHIP BEHAVIOR
!11 [--]
40.t/)
"O t-
Sham Lesion Small MPA Lesion Large MPA Lesion
5 a0u) 0
_o 20m d ~lOU.I co +& iX
Pre-lesion
Post-lesion
FIG. 2. Mean (-+SEM) number of 5-sec blocks with ultrasounds on the tests before surgery (Pre-lesion) an on the post-surgical tests (Post-lesion) with intact females as stimuli.
1
40"13 tO tO t~
5
[
I Sham Lesion Small MPA Lesion Large MPA Lesion
30-
t(/)
FIG. 1. Tracing of sections through a representative large MPA lesion (top) and a representative small MPA lesions (bottom). The solid area represents the extent of the damage. The atlas of Montemurro and Dukelow [I0] was used to evaluate the brain sections. Ms: medial septal area; mpa: medial-preoptic area; lpa: lateralpreoptic areas; dbb: diagonal band of Broca; mfb: medial forebrain bundle; aha: anterior hypothalamus.
m
20-
6 tO
10UJ CO
+2
iX
Clean litter DISCUSSION
Different phases of male sexual behavior may be mediated by neuroanatomically distinct systems. For example, male rats with lesions in the MPA show deficits in the initiation of copulatory behavior (i.e., long latencies to the first mount and intromission), however, if intromission is achieved, males with MPA lesions can perform in a fashion comparable to intact males [1]. The present findings suggest that the MPA is similarly involved in the initiation of male mouse mounting behavior, thus confirming earlier reports [5,14]. On the other hand, an intact MPA is not necessary for the display of other components of male mouse sexual behavior that preceded mounting. In this experiment, lesions that virtually abolished mounting did not affect courtship vocalizations. Furthermore, animals with MPA damage showed normal ano-genitai exploration of the female with shorter latencies than controls. A similar observation has been reported for male dogs [7] suggesting that MPA damage may facilitate this aspect of male sexual behavior.
Soiled litter
FIG. 3. Mean (_+SEM) number of 5-sec blocks with ultrasounds in tests with clean or soiled bedding. For each group, the differences between the two conditions .were statistically significant.
Additionally, the ability to discriminate between clean and soiled bedding was not disrupted by the lesions. Experiments with rats [19] have shown that knife cuts lateral to the MPA disrupt male sexual behavior without affecting the males' preference for the odor of a receptive over a nonreceptive female. Thus, the MPA does not seem to mediate the early components of sexual arousal in mice and other mammalian species [7,19]. As suggested by others [19], the MPA seems to play a role in the transition from sexual arousal (i.e., investigation of the females; ultrasounds) to other components of the normal copulatory pattern of the species (i.e., mounting).
112
BEAN, NUNEZ
AND CONNER
TABLE 1 EFFECTS OF MEDIAL PREOPTIC (MPA) LESIONS ON SEXUAL BEHAVIOR, BODY WEIGHT AND TESTICULAR WEIGHT Measure
Surgical Group Sham Lesion
Ano-genital Exploration Proportion Responding Latency (min)* Mounting Behavior Proportion Responding Latency (min)* Proportion Showing Mounts with Thrusts Body Weights (g)* Testicular Weights (mg)*
Small MPA Lesion
8/8 6.8 - 1.5
8/8 2.1 _ 0.2"t
Large MPA Lesion
8/8 2.6 _ 0.5"1"
6/8 17.3 -_+ 3.8
6/8 18.3 _+ 4.5
1/85 29.4
6/8
1/8~:
0/8~t
47.0 _ 4.2 281 - 30
41.8 --- 0.2 280 -+ 10
45.0 _+ 4.7 284 -+ 60
*Mean _+ SEM. tSignificantly different from the Sham-Lesion group (Mann-Whitney U test, p<0.05; two tailed test). +Significantly different from the Sham-Lesion group (Fisher test p<0.05; twotailed test).
A l t e r n a t i v e l y , the o b s e r v e d deficits in m o u n t i n g b e h a v i o r could be a s c r i b e d to a r e d u c t i o n in circulating a n d r o g e n s induced by M P A damage. P r e v i o u s work has s h o w n t h a t , after c a s t r a t i o n , early c o m p o n e n t s o f male sexual b e h a v i o r can b e m a i n t a i n e d with d o s e s of t e s t o s t e r o n e that are not effective in m a i n t a i n i n g m o u n t i n g b e h a v i o r [17]. H o w e v e r ,
o t h e r i n v e s t i g a t o r s [ 15] h a v e found no e v i d e n c e o f a d e c r e a s e in t e s t o s t e r o n e levels in mice following M P A lesions a n d in the p r e s e n t e x p e r i m e n t , M P A d a m a g e did not affect testicular weight o r b o d y weight, suggesting t h a t the b e h a v i o r a l deficits seen a f t e r the lesions were p r o b a b l y i n d e p e n d e n t o f c h a n g e s in the p i t u i t a r y - g o n a d a l axis.
REFERENCES 1. Caggiula, A. R., S. M. Antelman and M. J. Zigmond. Disruption of copulation in male rats after hypothalamic lesions: A behavioral, anatomical and neurochemical analysis. Brain Res. 59: 273-287, 1973. 2. Chen, J. J. and D. K. Bliss. Effects of sequential preoptic and mammillary lesions on male rat sexual behavior. J. comp. physiol. Psychol. 87: 814--847, 1974. 3. Dizinno, G. and G. Whitney. Androgen influence on male mouse ultrasounds during courtship. Hormones Behav. 8: 188-192, 1977. 4. Edwards, D. A. Induction of estrous in female mice: Extrogenprogesterone interactions. Hormones Behav. 1: 299-304, 1970. 5. Edwards, D. A., C. Pastin, K. Thomason and M. Shivers. Brain damage and sexual behavior. Paper presented at the Eastern Conference on Reproductive Behavior, 1978, Madison, Wis• consin. 6. Giantonio, G. W., N. L. Lund and A. A. Gerall. Effects of diencephalic and rhinencephalic lesions on the male rat's sexual behavior. J. comp. physiol. Psychol. 73: 38--46, 1970. 7. Hart, B. L. Medial preoptic-anterior hypothalamic area and socio-sexual behavior of male dogs: A comparative neuropsychological analysis. J. comp. physiol. Psychol. 86: 328-349, 1974. 8. Hart, B. L., C. M. Haugen and D. M. Peterson. Effects of medial preoptic-anterior hypothalamic lesions on mating behavior of male cats. Brain Res. 54: 177-191, 1973. 9. Heimer, L. and K. Larsson. Impairment of mating behavior in male rats following lesions in the preoptic-anterior hypothalamic continuum. Brain Res. 3: 248-263, 1967. 10. "Montemurro, D. G. and R. H. Dukelow. A Stereotaxic Atlas o f the Diencephalon and Related Structures o f the Mouse. Mount Kisco, New York: Futura, 1972.
I 1. Nunez, A. A., J. Nyby and G. Whitney. The effect of testosterone, estradiol and dihydrotestosterone on male mouse (Mils musculus) ultrasonic vocalizations. Hormones Behav. 11: 264-272, 1978. 12. Nyby, J. and G. Whitney. Ultrasonic communication of adult myomorph rodents. Neurosci. Biobehav. Rev. 2: 1-14, 1978. 13. Phoenix, C. H. Hypothalamic regulation of sexual behavior in male guinea pigs. J. comp. physiol. Psychol. 54: 72-77, 1962. 14. Quadagno, D. M., S. M. Albelda, T. E. McGill and L. G. Kaplan. Intracranial cyclohexamide: Effects on male mouse sexual behavior and plasma testosterone.'Pharmac. Biochem. Behav. 4: 185-189, 1976. 15. Shivers, M. and D. A. Edwards. Hypothalamic destruction and mouse aggression. Physiol. Psychol. 6: 485--487, 1978. 16. Siegel, S. Nonparametric Statistics for the Behavioral Sciences. New York: McGraw-Hill, 1956. 17. Singer, J. J. Anogenital explorations and testosterone proprionate induced sexual arousal in rats. Behav. Biol. 7: 743747, 1972. 18. Slimp, J. C., B. L. Hart and R. W. Goy. Heterosexual, autosexual and social behavior of adult male rhesus monkeys with medial preoptic-anterior hypothalamic lesions. Brain Res. 142: 105-122, 1978. 19. Szechtman, H., A. R. Caggiula and D. Wulkan. Preoptic knife cuts and sexual behavior in male rats. Brain Res. 150: 569-595, 1978. 20. Whitney, G., M. Alpern, G. Dizinno and G. Horowitz. Female odors evoke ultrasounds from male mice. Anita. Learn. Behav. 2: 13-18, 1974. 21. Whitney, G., J. R. Coble, M. D. Stockton and E. F. Tilson. Ultrasonic emissions: Do they facilitate courtship of mice? J. comp. physiol. Psychol. 84: 445--452, 1973.
Effects of Medial Preoptic Lesions on Male Mouse Ultrasonic Vocalizations and Copulatory Behavior N. JAY BEAN
Department of Psychology, Vassal" College, Poughkeepsie, N Y 12601 ANTONIO
A. NUNEZ
Department of Psychology, Michigan State University, East Lansing, MI 44824 AND ROBERT CONNER
Department of Psychology, Bowling Green State University, Bowling, Green, OH 43402 R e c e i v e d 22 M a y 1980 BEAN, N. J., A. A. NUNEZ AND R. CONNER. Effects o f medial preoptic lesions on male mouse ultrasonic vocalizations and copulatory behavior. BRAIN RES. BULL. 6(2) 109-112, 1981.--In male mice, lesions in the medial preoptic area (MPA) reduced the proportion of animals showing mounting behavior but failed to abolish ano-genital exploration of the female. The lesions did not affect the amount of 70 kHz ultrasound elicited by intact females or by soiled bedding obtained
from female-occupied cages. These results suggest that early components of male sexual behavior are mediated by neural systems outside the MPA. Medial preoptic lesions
Male sexual behavior
Courtship
B I L A T E R A L lesions of the medial-preoptic area (MPA) result in severe impairment or complete abolishment of copulatory behavior in males of several mammalian species including mice [5], rats [2, 6, 9], guinea pigs [13], cats [8], dogs [7] and monkeys [18]. It has been suggested that the precise role played by the MPA in male copulatory behavior is one of mediating the initiation of the copulatory sequence [I, 2, 19]. Thus in some situations, animals with MPA lesions may approach and investigate a receptive female but fail to display the complete pattern of male copulatory behavior [7]. Based upon these observations, it becomes of interest to further investigate the effects of MPA lesions on the early components of male sexual behavior. Male mice of several strains [12] emit 70 kHz-ultrasonic vocalizations as part of their courtship behavior [21]. These vocalizations are elicited by adult female mice or by chemical stimuli present in female urine [12,20]. Male vocalizations occur early in a male-female encounter and in most cases accompany or precede ano-genitai contact with the female. Consistent with observations on other components of male sexual behavior, castration reduces male ultrasonic vocalizations and testos-
Ultrasounds
Male mice
Vocalizations
terone treatment restores the behavior to precastration levels [3,11]. In the present experiment, we investigated the effects of MPA lesions on courtship vocalizations and other components of male mouse sexual behavior. METHOD
Animals Sexually naive male Swiss-Webster (SW) mice, 90-120 days of age on the first behavioral test, were used as subjects. Ten adult C57BL/6J (C57) females served as stimuli for the vocalization tests and 20 adult SW females were used as stimuli for the sex-behavior test. All mice were obtained from the animal colony at Bowling Green State University, Bowling Green, Ohio. The C57 females were used in the ultrasound tests because these females rarely vocalize and seem to elicit more ultrasounding from the SW males. The SW females were ovariectomized 3-4 weeks before testing and were made receptive with injections of estradiol benzoate and progesterone [4]. The SW females were used for the sex-behavior tests because preliminary evidence
1Supported in part by Postdoctoral Fellowship NS 05854-01 from NINCDS to A. A. N. A preliminary report of this research was presented at the Eastern Conference on Reproductive Behavior annual meeting in New Orleans, June 7, 1979. We are grateful to Janet Gray for helpful comments on the manuscript.
C o p y r i g h t © 1981 A N K H O
I n t e r n a t i o n a l Inc.--0361-9230/81/020109-04500.90/0
ll0 suggested that these females were more responsive to the hormone regimen. Therefore, these females were better stimuli for the sex-behavior tests. The males were individually housed in plastic cages (29x 18x 13 cm) with sawdust on the floor and the females were housed 3-6 to a cage. The estrous cycle of the C57 females was not monitored. All animals had free access to food (Purina rodent chow) and water. A 12:12 light-dark cycle of illumination was maintained in the animal colony and behavioral testing was conducted during the last 3-hr of the light period in a room illuminated by dim red light.
Apparatus A Holgate Ultrasonic receiver (model MK V) set to a center frequency of 70 kHz was used to detect ultrasounds. The Holgate receiver transforms ultrasounds into audible sounds as described elsewhere [20,21]. The Holgate microphone was placed about 25 cm above the test cage (29× 18x 13 cm). Vocalization tests involving female stimuli as well as sex-behavior tests were conducted in the males' home cages. Tests using bedding as stimuli were conducted in plastic cages that had been cleaned and rinsed with alcohol. erocedllre Before surgery, the males were given two 3-min vocalization tests, 48-hr apart, to assess their responsive to a C57 female. In all tests, the 3-min test period was preceded by a l-min habituation period. If an ultrasound was emitted during this habituation period, a 2-min interval without an ultrasound was allowed to elapse prior to the beginning of a 3-min test session. The amount of ultrasound emitted during the test was quantified by dividing the 3-min test into thirty-six 5-sec scoring blocks. The test began when the stimulus female was introduced into the test cage. After the pre-surgical vocalization test, the males were divided into a MPA-lesion group and a sham-lesion group. Under ether anesthesia, animals in the MPA-lesion group received a single, mid-line electrolytic lesion (2 mA for 15 sec) aimed at the MPA. The electrode used was a No. 1 stainless steel insect pin insulated except for 0.5 mm at the tip. The stereotaxic coordinates were: I mm anterior to bregma and 5-ram ventral from the dura, with the incisor bar 4-mm above the ear bars. The electrode was lowered along the midline after retracting the midsaggital sinus. Approximately 60% of the operated animals (n= 16) recovered from surgery. Sham-lesion animals (n=8) endured all surgical procedures except that no current was passed through the electrode. Two weeks after surgery, all males received two 3-min vocalization tests, 48 hr apart with C57 females as stimuli. Two weeks later, the males were given 2 additional vocalization tests. In these tests, soiled bedding from cages housing the C57 females and clean bedding were used as stimuli. Each bedding test was separated by 48 hr and the two conditions were administered in a counterbalanced order within each group. After the l-min habituation period, 15-g of either clean or soiled bedding were placed in the test cage with the male. Ultrasounds were monitored for 3-min as described above. One week after the bedding tests, each male received a si.ngle 30-min test of sex behavior with a receptive SW female. After a 10-min habituation period in the testing room, the female was introduced into the test cage. Laten-
BEAN, N U N E Z AND CONNER cies to begin ano-genital exploration and to mount were recorded along with the number of mounts and mounts with thrusts. If the male failed to show mounting behavior during the$irst 10-rain, the female was replaced. At the conclusion of testing, body weights were measured (nearest 0. i g) and the males were sacrificed by decapitation. Both testes were removed, cleaned, and weighed (nearest 0.001 g). The brains were removed and fixed in 10% Formalin; frozen coronal sections (50 tz) were stained with cresyl violet for histological evaluation. Reconstructions of the lesions were made by one of the authors without knowledge of the behavioral data for the individual animals. The Wilcoxon signed-ranks test was used for all within group comparisons. Differences between groups were evaluated using the Mann-Whitney U test and the Fisher exact probability test [16]. Differences were considered statistically significant when p<0.05 (two-tailed tests).
RESULTS
Histology Based entirely upon the histological evaluation of the brains, without knowledge of the behavioral data, a readily discernable large and a small lesion group (n=8 in each group) were formed (Fig. I). The animals' brains that were placed in the large lesion group evidenced damage to the anterior hypothalamus, suprachiasmatic nuclei and the periventricular area in addition to bilateral damage to the MPA. The small lesion group evidenced damage that was restricted to the periventricular MPA. In all cases, the third ventricle was enlarged.
Ultrasonic Vocalization The analysis of the vocalization data from the tests with the stimulus female indicated no significant differences between the pre- and the post-lesion tests for each group or between groups during the pre- or the post-lesion test sessions. Therefore, the lesions did not affect the ultrasonic vocalizations of the males when tested with a female. The tests with bedding as a stimulus also failed to show significant differences across groups. For all groups, though, the amount of ultrasound monitored during the tests with soiled bedding was significantly greater than that monitored during tests with clean bedding (p<0.05~ (Figs. 2 and 3).
Sex Behavior Table 1 summarizes the effects of MPA damage on sex behavior. Large lesions significantly reduced the proportion of animals showing mounting behavior in comparison with both the sham and the small-lesion groups 09<0.05). Small MPA lesions did not reduce the proportion of animals showing mounting behavior and the latencies to the first mount for these animals were similar to those recorded for shams. However, the small lesions did significantly reduce the proportion of animals showing mounts with thrusts (.o<0.05). No intromissions were observed in the test session. All males engaged in ano-genital exploration of the female during the sex-behavior test. However, the latency to initiate this behavior was significantly greater for shams when compared with the lesion groups (p's<0.05). No significant differences in final body weights or testicular weights were found across groups (Table 1).
BRAIN LESIONS AND COURTSHIP BEHAVIOR
!11 [--]
40.t/)
"O t-
Sham Lesion Small MPA Lesion Large MPA Lesion
5 a0u) 0
_o 20m d ~lOU.I co +& iX
Pre-lesion
Post-lesion
FIG. 2. Mean (-+SEM) number of 5-sec blocks with ultrasounds on the tests before surgery (Pre-lesion) an on the post-surgical tests (Post-lesion) with intact females as stimuli.
1
40"13 tO tO t~
5
[
I Sham Lesion Small MPA Lesion Large MPA Lesion
30-
t(/)
FIG. 1. Tracing of sections through a representative large MPA lesion (top) and a representative small MPA lesions (bottom). The solid area represents the extent of the damage. The atlas of Montemurro and Dukelow [I0] was used to evaluate the brain sections. Ms: medial septal area; mpa: medial-preoptic area; lpa: lateralpreoptic areas; dbb: diagonal band of Broca; mfb: medial forebrain bundle; aha: anterior hypothalamus.
m
20-
6 tO
10UJ CO
+2
iX
Clean litter DISCUSSION
Different phases of male sexual behavior may be mediated by neuroanatomically distinct systems. For example, male rats with lesions in the MPA show deficits in the initiation of copulatory behavior (i.e., long latencies to the first mount and intromission), however, if intromission is achieved, males with MPA lesions can perform in a fashion comparable to intact males [1]. The present findings suggest that the MPA is similarly involved in the initiation of male mouse mounting behavior, thus confirming earlier reports [5,14]. On the other hand, an intact MPA is not necessary for the display of other components of male mouse sexual behavior that preceded mounting. In this experiment, lesions that virtually abolished mounting did not affect courtship vocalizations. Furthermore, animals with MPA damage showed normal ano-genitai exploration of the female with shorter latencies than controls. A similar observation has been reported for male dogs [7] suggesting that MPA damage may facilitate this aspect of male sexual behavior.
Soiled litter
FIG. 3. Mean (_+SEM) number of 5-sec blocks with ultrasounds in tests with clean or soiled bedding. For each group, the differences between the two conditions .were statistically significant.
Additionally, the ability to discriminate between clean and soiled bedding was not disrupted by the lesions. Experiments with rats [19] have shown that knife cuts lateral to the MPA disrupt male sexual behavior without affecting the males' preference for the odor of a receptive over a nonreceptive female. Thus, the MPA does not seem to mediate the early components of sexual arousal in mice and other mammalian species [7,19]. As suggested by others [19], the MPA seems to play a role in the transition from sexual arousal (i.e., investigation of the females; ultrasounds) to other components of the normal copulatory pattern of the species (i.e., mounting).
112
BEAN, NUNEZ
AND CONNER
TABLE 1 EFFECTS OF MEDIAL PREOPTIC (MPA) LESIONS ON SEXUAL BEHAVIOR, BODY WEIGHT AND TESTICULAR WEIGHT Measure
Surgical Group Sham Lesion
Ano-genital Exploration Proportion Responding Latency (min)* Mounting Behavior Proportion Responding Latency (min)* Proportion Showing Mounts with Thrusts Body Weights (g)* Testicular Weights (mg)*
Small MPA Lesion
8/8 6.8 - 1.5
8/8 2.1 _ 0.2"t
Large MPA Lesion
8/8 2.6 _ 0.5"1"
6/8 17.3 -_+ 3.8
6/8 18.3 _+ 4.5
1/85 29.4
6/8
1/8~:
0/8~t
47.0 _ 4.2 281 - 30
41.8 --- 0.2 280 -+ 10
45.0 _+ 4.7 284 -+ 60
*Mean _+ SEM. tSignificantly different from the Sham-Lesion group (Mann-Whitney U test, p<0.05; two tailed test). +Significantly different from the Sham-Lesion group (Fisher test p<0.05; twotailed test).
A l t e r n a t i v e l y , the o b s e r v e d deficits in m o u n t i n g b e h a v i o r could be a s c r i b e d to a r e d u c t i o n in circulating a n d r o g e n s induced by M P A damage. P r e v i o u s work has s h o w n t h a t , after c a s t r a t i o n , early c o m p o n e n t s o f male sexual b e h a v i o r can b e m a i n t a i n e d with d o s e s of t e s t o s t e r o n e that are not effective in m a i n t a i n i n g m o u n t i n g b e h a v i o r [17]. H o w e v e r ,
o t h e r i n v e s t i g a t o r s [ 15] h a v e found no e v i d e n c e o f a d e c r e a s e in t e s t o s t e r o n e levels in mice following M P A lesions a n d in the p r e s e n t e x p e r i m e n t , M P A d a m a g e did not affect testicular weight o r b o d y weight, suggesting t h a t the b e h a v i o r a l deficits seen a f t e r the lesions were p r o b a b l y i n d e p e n d e n t o f c h a n g e s in the p i t u i t a r y - g o n a d a l axis.
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