Possible Role of Cingulate Cortex in Regulating Sexual Behavior in Male Rats: Effects of Lesions and Cuts

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1 Endocrinol Japon 1992, 39 (3), Possible Role of Cingulate Cortex in Regulating Sexual Behavior in Male Rats: Effects of Lesions and Cuts KOREHITO YAMANOUCHI AND YASUMASARAI* Neuroendocrinology, Department of Basic Human Sciences, School of Human Sciences, Waseda University, Saitama 359 and *Department of Anatomy, Juntendo University School of Medicine, Tokyo 113, Japan Abstract. The role of the cingulate cortex in regulating male sexual behavior was studied in testosterone propionate-treated castrated male rats. Males with lesions in the anterior part of the cingulate cortex showed lower levels of mount, intromission and ejaculation activities than shamoperated control males and males with lesions in the posterior part of the cingulate cortex or the frontal cortex. In male rats in which lateral connections of the anterior cingulate cortex were bilaterally interrupted by sagittal cuts, the sexual activity was much lower than in the control rats, being comparable to that of the anterior cingulate cortex lesion group, but transection of the anterior connections by a transverse cut made in the anterior part of the anterior cingulate had no effect. These results suggest that the anterior cingulate cortex and its lateral connections are critical in regulating male sexual behavior in male rats. Key words: Cingulate cortex, Male sexual behavior, Male rat, Lesion, Androgen. (Endocrinol Japon 39: , 1992) THE PREOPTIC area-anterior hypothalamus continuum (POA-AH) is generally accepted to be a critical neural component to exert an androgendependent facilitatory influence on regulation of masculine sexual behavior, because destruction of the POA-AH diminished androgen-induced sexual behavior [1-4]. Conversely electrical stimulation [5] or direct implantation of crystalline testosterone propionate in the POA-AH [6, 7] facilitated sexual behavior in male rats. As well as the POA-AH, neural substrates located at a higher level, such as in limbic and neocortical structures have also been thought to play an important role in regulating male sexual behavior [8-10]. Lesions in the septum [4], the corticomedial amygdaloid area [11, 12] or the olfactory bulb [13, 14] and ablation of the vomeronasal organ [15] caused Received: January 14, 1992 Accepted: March 27, 1992 Correspondence to: Dr. Yasumasa ARAI, Department of Anatomy, Juntendo University School of Medicine, Hongo, Bunkyo-ku, Tokyo 113, Japan. marked impairment of male copulatory behavior. Furthermore, removal of a very large cortical area in male rats has also been shown to impair mating performance [16]. Larsson [17, 18] suggested that the frontal and dorsolateral cortex are concerned with the regulation of sexual behavior in the male rat. In the present series of experiments, to clarify the role of the medial cortex in regulating sexual behavior, several types of lesions and cuts were made in the cingulate cortex and male copulatory behavior was examined in androgen-treated castrated male rats. Materials and Methods Sexually inexperienced adult male Wistar rats ( g) were maintained under a controlled photoperiod (14:10 h, light: dark) and temperature (24-24 Ž). The male rats were castrated and received bilateral lesions or surgical cuts in the

2 230 YAMANOUCHI et al. Fig. 1. Photographs of the brain with lesions in the anterior cingulate cortex (AC(:XL) (A), posterior cingulate cortex (PCCXL) (B) and frontal cortex (FCXL) (C). A Fig. 2. Schematic representation of the sagittal cut (SC) and transverse cut (TC) in the frontal section at the level of the septum (A), at the dorsal surface (B) and in the sagittal section (C). Abbreviations: AC, anterior commissure; CC, corpus callosum; OC, optic chiasma; SPT, septum. cingulate cortex or the frontal cortex under ether anesthesia. The medial part of the frontal bone (anterior to the bregma) was opened with a dental drill and the medial surface of the cortex corresponding to the anterior cingulate cortex was sucked out bilaterally with an aspirator in 16 castrated males (ACCXL) (see Fig. 1). The medial surface of the brain posterior to the bregma corresponding to the posterior cingulate cortex was sucked out in 9 males (PCCXL). The frontal cortex was lesioned bilaterally (FCXL) in 9 males. In 8 castrated males, the medial part of the frontal bone was opened without suction of the cortex as a sham operated control (Sham). In order to interrupt the lateral connections of the anterior cingulate cortex, bilateral sagittal cuts (SC) were performed by lowering a 4 mm long razor blade to just above the corpus callosum at a level anterior to the bregma and 0.5 mm lateral to the midline in 11 male rats (see Fig. 2). In 10 males, a transverse cut (TC) was made with a 3 mm wide razor blade at a point 1 mm anterior to the bregma in order to cut the anterior connections of the anterior CCX. Four weeks after the operation, all males were injected with 500 Đg testosterone propionate (TP, dissolved in 0.1 ml sesame oil) daily for 21 days. Observation of male sexual behavior was carried out on day 11 and day 21 following the initiation of daily injections of TP. Each experimental male rat was adapted to an observation cage (40 cm h, 60 cm w, 50 cm d) for 4-5 min. Then a receptive female, which was castrated and primed with 2 Đg estradiol benzoate daily for 3-4 days and 0.5 mg progesterone on the day of the test, was placed with an experimental male. The observation of

3 CINGULATE CORTEX AND MALE SEXUAL BEHAVIOR 231 masculine sexual behavior was continued for 30 min. The receptive female was changed to another about min after the start in order to diminish the influence of affinity between the experimental male and the female. The following standard measures of male sexual behavior were recorded: frequency (number) of mounts (MF) and intromissions (IF) in 30 min or during periods from the start to the first ejaculation, the MF and IF being calculated every 5 min, and the frequency of ejaculation (EF) in 30 min.; latency (sec) of mounts (ML), intromissions (IL) and ejaculations (EL) (times from start to first occurrence of each behavior in 30 min). After the end of the behavioral test, the precise localization of the lesion or the cut was determined histologically in each brain. The mean frequencies of behavior (MF, IF and EF) were analyzed by Student's t-test or the Cochran Cox method. ML, IL and EL were analyzed by U-test. For comparison of the incidence of behavior among groups, with Yates' correction was used. Results Behavioral results are shown in Fig. 3 and Table 1. Effect of lesions: In the first test (11 days after initiation of TP injection), most of the Sham males showed mounts and intromissions and the mean MF and IF were 5.2 }1.5 and 3.2 }1.1, respectively. The sexual activities in FCXL and PCCXL males were comparable to those of Sham males. In contrast, the mean MFs and IFs in the ACCXL groups were significantly lower than those in the Sham group (MF: P<0.005, IF: P<0.01). Most animals in all groups did not show an ejaculatory pattern (see Table 1). In the second test on day 21, all Sham males mounted and achieved intromission. The mean MF and IF in this group increased to 7.1 }1.5 and 4.0 }0.9, respectively. The same levels of incidences and frequencies of mounting and intromission as in the Sham group were observed in the PCCXL and FCXL groups (see Fig. 3 and Table 1), but the mean MF (2.9 }0.8) and IF (1.1 }0.03) in the ACCXL group were very low compared to the Sham group (P<0.05 and P<0.005, respectively). Ejaculation was observed in 5 of 8 Sham males, but Fig. 3. Mean frequencies of mounting (MF) (black column) and intromission (IF) (white column) in each group. All male rats were treated with 500,ƒÊg testosterone propionate (TP) daily for 21 days. Behavioral tests were carried out at day 11 and 21 following initiation of daily TP treatments. The bars on the top of the black column and below the top of the white column are the SE of the mean MF and IF, respectively. ACCXL, anterior cingulate cortex lesions; PCCXL, posterior cingulate cortex lesions; FCXL, frontal cortex lesions; SC, sagittal cuts in the anterior cingulate level; TC, transverse cut in the anterior cingulate level. *, P<0.05 vs. sham (t-test).

4 232 YAMANOUCHI et al. Table 1. Effects of the cingulate cortex lesions or cuts on male sexual activities All male rats were treated with 500 Đg testosterone propionate daily for 21 days. The behavioral tests were carried out at day 11 (1st test) and 21 (2nd test). ML (mount latency), IL (intromission latency) and EL (ejaculation latency) are median values. EF, ejaculation frequency; ACCXL, anterior cingulate cortex lesion; PCCXL, posterior cingulate cortex lesion; FCXL, frontal cortex lesion; SC, sagittal cut; TC, transverse cut (see text). *, P<0.05; **, P<0.01 vs. sham (ę2-test); ***, P<0.05 vs. sham (t-test). in only 1 of 16 males with ACCXL (P<0.02, vs. Sham). The mean EF (0.6 }0.1) of the Sham group was higher than that (0.1 }0.1) of the ACCXL group (P<0.05). The start of intromission in ACCXL males was greatly delayed compared to Sham males, median values for IL being greater than those of the Sham group (P<0.005). Effect of cuts: In the first test, TC males showed the same levels of male sexual activity as Sham males (see Fig. 3 and Table 1). In contrast, the mean MF and IF in the SC group were much lower than those of the Sham group (P<0.005). In the second test, the mean MF and IF of the TC group increased to 4.2 }1.4 and 1.8 }0.6, respectively. SC males as well as ACCXL males still showed low sexual activity. Only 4 of 11 SC males mounted (P<0.05 vs. Sham) and the mean MF was 1.0 }0.6 (P<0.001 vs. Sham). An intromission pattern was seen in only one SC male (P<0.01 vs. Sham). This SC male with intromission achieved ejaculation. In spite of low sexual activity, ACCXL and SC males showed significant sexual interest in estrous females. They actively approached the estrous female and sniffed her body and genital area. Some of them had a strange mounting pattern. They began to pursue a female, but ran through her back without showing a characteristic pattern of mounting behavior. Photographs of the brain with lesions were shown in Fig. 1. Histological examinations indicated that ACCXLs were localized in bilateral medial corteces including the anterior cingulate cortex and the medial part of the frontal isocortical region (Fr2, see reference [19]) from the level of the genu corpus callosum to the level of the septum. In all ACCXL males except 3, lesions were located just above the corpus callosum. In the 3 ACCXL males, the corpus callosum was partially damaged, but the septum remained intact. PCCXL was located in the medial cortex (the posterior cingulate or the retrosplenial cortex and posterior part of the Fr2) between the level of posterior part of the septum and the level of the anterior end of the hippocampus. In this group, the hippocampus and the corpus callosum were partially damaged. Small lesions were found in the septal area in 4 PCCXL males. The ACCXL area and the area of PCCXL occasionally overlapped at the level of the posterior part of the septum. The FCXL was located

5 CINGULATE CORTEX AND MALE SEXUAL BEHAVIOR laterally to the ACCXL area, corresponding to a part of the primary motor cortex and Fr 2 [19]. The lesions in the FCXL group were placed in the frontal cortex from the level of the genu of the corpus callosum to the level of the septum. In most FCXL-animals, however, lesions did not invade the corpus callosum. The SC were located from the level of the genu of the corpus callosum to the level of the septum (Fig. 2). The cut in SC males extended ventrally to the dorsal part of the corpus callosum. In the TC group, the cut also extended to the dorsal part of the corpus callosum in the anterior cingulate cortex. The cingulum bundle seems to be transected by TC. In a number of TC and SC rats, the surface of the cortex was partially damaged. Discussion In the present series of experiments, the ACCXL significantly suppressed the frequency of mounts, intromissions and ejaculations and delayed the onset of the behavior in male rats, but the PCCXL and the FCXL failed to do it. These results indicate that the anterior cingulate cortex plays a critical role in regulating male sexual behavior in male rats. Larsson [17] showed in his early decorticating work that removal of the wide medial cortical area, partially including our ACCXL area, had no effect on male sexual activity in sexually experienced non-castrated male rats. Rather he found that the lesions in the frontal cortex or the temporal cortex tended to eliminate male copulatory behavior [17, 18]. These results do not seem to be consistent with the present results. The discrepancy can be interpreted to be partly due to differences in sexual experience and/or hormonal conditions in the experimental male rats. It has been reported that sexually experienced male rats might suffer less impairment of mating performance than sexually inexperienced males following medial cortical lesions As well as ACCXL, the SC in the anterior cingulate cortex suppressed male sexual activity. This seems to indicate the importance of the lateral connections of the anterior cingulate cortex in sexual behavior regulation. The anterior cingulate cortex has been reported to have extensive fiber connections not only with other cortical areas but also subcortical structures limbic, thalamic, hypothalamic and mesencephalic areas [19]. Domesick [20] suggested that cingulate output fibers leave these ventrolaterally and the cingulum bundle conveys the inputs from subcortical structures. If that is the case, suppression of male sexual behavior by the SC in the present study could be attributed to the result of the interruption of the outputs to the limbic and hypothalamic structures and/or that of association fibers connected to other cortical areas. On the other hand, the inputs of the anterior cingulate cortex from the subcortical structures do not contribute to the regulation of male sexual behavior, because the TC which transects the cingulum bundle had no effect. ACCXL and SC males repeatedly pursed and courted females, but failed to complete the mating behavior in this experiment. A similar phenomenon has been found in male rats with septal lesions [4]. There is evidence suggesting that lesions in the cingulate cortex lead to disruption of the orderly sequencing of behavior. A good example has been reported in maternal behavior in rat mothers with cingulate cortex lesions. They failed to complete the behavioral sequence of maternal behavior in a normal fashion [21]. In ACCXL and SC males, it is possible that the mechanisms which integrate sensory and various sexual responses into an effective behavioral sequence were affected by the lesions or the cuts, but sexual motivation was not impaired. It is not yet known whether the function of the cingulate cortex is dependent on androgen. There is a report that neurons containing androgen receptor exist in the cingulate cortex [22]. Further studies are needed to clarify these points. Acknowledgments This study was supported by grants-in-aids from the Ministry of Education, Science and Culture of Japan.

6 YAMANOUCHI et al. References 1. Larsson K, Heimer L (1964) Mating behaviour of male rats after lesions in the preoptic area. Nature 202: Heimer L, Larsson K (1967) Impairment of mating behavior in male rats following lesions in the preoptic anterior hypothalamic continuum. Brain Res 3: Christensen LW, Nance DM, Gorski RA (1977) Effects of hypothalamic and preoptic lesions on reproductive behavior in male rats. Brain Res Bull 2: Kondo Y, Shinoda A, Yamanouchi K, Arai Y (1990) Role of septum and preoptic area in regulating masculine and feminine sexual behavior in male rats. Horm Behav 24: Malsbury CW (1971) Facilitation of male rat copulatory behavior by electrical stimulation of the medial preoptic area. Physiol Behav 7: Davidson JM (1966) Activation of the male rats sexual behavior by intracerebral implantation of androgen. Endocrinology 79: Christensen LW, Clemens LG (1974) Intrahypothalamic implants of testosterone or estradiol and resumption of masculine sexual behavior in long-term castrated male rats. Endocrinology 95: Malsbury CW, Pfaff DW (1974) Neural and hormonal determinants of mating behavior in adult male rats. A review. In: Dicara LV (ed) Limbic and Autonomic Nervous Systems Research. Plenum, New York: Larsson K (1979) Features of the neuroendocrine regulation of masculine sexual behavior. In: Beyer C (ed) Comprehensive Endocrinology-Endocrine Control of Sexual Behavior. Raven Press, New York: Hart BJ, Leedy MG (1985) Neurological bases of male sexual behavior. In: Addler N, Pfaff DW, Goy RW (eds) Handbook of Behavioral Neurobiology Vol 7- Reproduction. Plenum Press, New York: Harris VS, Sachs BD (1975) Copulatory behavior in male rats following amygdaloid lesions. Brain Res 86: Kondo Y (1992) Lesions of the medial amygdala produce severe impairment of copulatory behavior in sexually inexperienced male rats. Physiol Behav 51: Heimer L, Larsson K (1967) Mating behavior of male rats after olfactory bulb lesions Physiol Behav 2: Murphy MR, Schneider GE (1970) Olfactory bulb removal eliminates mating behavior in the male golden hamster. Science 167: Saito TR, Moltz H (1986) Copulatory behavior of sexually naive and sexually experienced male rats following removal of the vomeronasal organ. Physiol Behav 37: Beach FA (1940) Effects of cortical lesions upon the copulatory behavior of male rats. J Comp Psychol 29: Larsson K (1962) Mating behavior in male rats after cerebral cortex ablation-i Effects of lesions in the dorsolateral and the median cortex. J Exp Zool 151: Larsson K (1964) Mating behavior in male rats after cerebral cortex ablation-ii Effects of lesions in the frontal lobes compared to lesions in the posterior half of the hemispheres. J Exp Zool 155: Zilles K, Wree A (1985) Cortex: Areal and laminar structure. In: Paxinos G (ed) The Rat Nervous System, Vol 1, Forebrain and midbrain. Academic Press, Sydney: Domesick VB (1969) Projections from the cingulate cortex in the rat. Brain Res 12: Slotnick BM (1967) Disturbances of maternal behavior in the rat following lesions of the cingulate cortex. Behaviour 29: Sar M, Stumpf WE (1974) Distribution of androgen-concentrating neurons in rat brain. In: Stumpf WE, Grant LD (eds) Anatomical Neuroendocrinology. Karger, Basel,