Endocrinol. Japon. 1983 30, (1) 29-33

Occurrence of Lordosis-like Posture in Male and Mice Given Manual Stimulation During the Early Period of Anesthesia

NOBORUTAKASUGI, MASAMITANAKA* AND HIDEO KATO

Department of Biology, Yokohama City University, Seto 22-2, Kanazawa-ku, Yokohama 236

Abstract

Normal estrous or diestrous female, ovariectomized female and plus progestin-primed, ovariectomized female mice of the ICR/JCL strain adopted a lordosis- like posture (LLP) in response to manual stimulation of the dorsal rump when they stood at the initiation of barbiturate anesthesia. Normal and castrated male mice also adopted a LLP following manual stimulation at the commencement of barbiturate anesthesia. In contrast, approximately 60% of anesthetized female mice at day 14 of gestation showed LLP without any tactile stimulation. In these pregnant mice, manual stimulation never brought about any change in the LLP incidence at the initiation of barbiturate anesthesia.

Lordosis, the most characteristic posture although incidence of the posture increases in female sexual behavior, is induced in slightly following treatment of castrated laboratory during the periovulatory males with estrogen or estrogen plus proges- period either by mounting of the males tin (Davidson, 1969; Ward, 1974; Yama- (Lisk, 1962) or by manual stimulation of nouchi and Arai, 1976). the dorsal rump (Beach, 1966; Pfaff and On the other hand, Gorski (1971) and Sakuma, 1979a). The lordosis posture con- Arai et al. (1978) have demonstrated that sists of head elevation, rump elevation, the estrogen-progestin treatment induces downward back-arching and bending a high incidence of lordosis in adult male (for review, see Arai et al., 1978). Ovari- rats whose testes were removed within a ectomy abolishes the occurrence of lordosis few days after birth. Female rats treated in sexually mature female rats. Treatment neonatally with androgen, however, hardly with estrogen or estrogen plus progestin display any lordosis as adults. It has been results in the resumption of lordosis in considered, therefore, that both endogenous ovariectomized rats (Beach, 1967). Lordosis and exogenous androgen suppresses the has therefore been considered a - development of female sexual behavior in sensitive reflexive response to tactile stimu- the of neonatal rats, and activates lation (Komisaruk, 1974). Normal male the programming of male sexual behavior. rats exhibit lordosis only on rare occasions, In the present study, the lordosis-like pos- ture was found in male and female mice Received September 30, 1982. at the initiation of barbiturate anesthesia, *Present address: Department of Pharmacology, the results being reported herein. St. Marianna University School of Medicine, Miya- mae-Ku, Kawasaki 213, Japan. Endocrinol. Japon. 30 TAKASUGI et al. February 1983

by stroking the back at the initiation of barbiturate anesthesia. The LLP-assuming

Materials and Methods mice (LLP mice) elevated their heads at an angle of 30•‹ to 120•‹, and lifted their rumps

Two-month-old, male and female mice of the slightly. Of the female LLP mice, 27% ICR/JCL strain were purchased from Clea Japan Inc., were estrous and the remaining diestrous. Tokyo. The mice, ranging from 25-30g in body Six of 28 ovariectomized, anesthetized mice weight, were kept in our laboratory vivarium for about one month at a temperature of 23-25•Ž under also adopted the LLP in response to manual a LD 12h:12h schedule. They were given food stimulation (Table 1, Fig. 1). In both pellets (Clea's CA-1) and tap water ad libitum. groups, however, the were unable Gonadectomy was performed at ca. 2 months of to maintain the LLP for more than 10 age, and used for experiments one month later. Sodium pentobarbital (K & K Lab., Plainview, minutes from the start of the posture. New York), 500mg, was dissolved in 100ml aqueous solution containing 20% propylene glycol and 10% LLP under barbiturate anesthesia in ovariec- ethanol. Mice were anesthetized by intraperitoneal tomized mice receiving injections of estrogen injection of the barbiturate in a dose of 40mg/kg body weight. When the barbiturate-injected mice and progestin became incapable of showing the righting reflex in Eight ovariectomized female mice given response to tail pinching, it was decided that the 3 daily injections of 0.4ƒÊg EB and a single animals started to fall into anesthesia. In all anes- thetized mice, except for one of two groups of injection of 0.1mg P successively were

pregnant mice, the experimenter stroked the dorsal mounted by sexually experienced males. rump with his finger starting within 30seconds after Seven of them (87.5%) displayed typical the initiation of anesthesia. Female mice were lordosis, indicating that the dose of EB and mated by the males, and the day when a vaginal P was enough to induce lordosis. plug was found in the female was regarded as day 0 of gestation. The females at day 14 of gestation Fifty-seven ovariectomized mice which were used for experiments. Three daily s. c. injec- received similar injections of EB and P tions of 0.4ƒÊg benzoate (EB, Sigma Co., were anesthetized with the barbiturate 6h St. Louis)/0.2ml sesame oil and a single s.c. injection of 0.1mg progesterone (P, Sigma Co.)/0.2ml oil on after P injection, and 23 of them showed the following day were given to ovariectomized mice. LLP in respone to manual stimulation. The hormone-primed mice were anesthetized with There was no statistically significant diffe- the barbiturate 6h after P injection. rence in LLP incidence between ovariecto- Vaginal smears were observed daily in all normal and ovariectomized females. In mice adopting the mized, anesthetized mice and those treated lordosis-like posture, the angle of elevation of the with EB and P (Table 1). The hormone- head was measured. It was impossible to measure treated mice never showed LLP over 8 the angle of elevation of the rump since the rump was slightly lifted. The lordosis-like posture, con- minutes. sisting of rump elevation, downward arching of the back and head elevation at an angle of more than LLP in normal and castrated male mice 30•‹, was determined as a positive response. Duration under barbiturate anesthesia of the posture was also measured with a stopwatch. Twenty-eight of 54 normal male mice anesthetized with the barbiturate displayed LLP following manual stimulation (Fig. 2). Results In 4 of 14 castrated male mice, LLP was induced by manual stimulation under bar- Lordosis-like posture (LLP) in normal female, biturate anesthesia (Table 1). The duration and ovariectomized mice under barbiturate time of LLP was 10-120seconds in both anesthesia groups of the males. Twenty-two of 53 normal female mice adopted a LLP in response to stimulation Vol.30, No.1 LORDOSIS-LIKE POSTURE IN ANESTHETIZED MICE 31

Fig. 1. An ovariectomized female mouse adopting a lordosis-like posture (LLP) at the initiation of barbiturate anesthesia.

Fig. 2. A normal male mouse exhibiting LLP under bar- biturate anesthesia.

Table 1. Occurrence of lordosis-like posture (LLP) in mice given manual stimulation (MS) at the initiation of barbiturate anesthesia.

*E: Estrus , D: Diestrus; **EB: Estradiol benzoate, P: Progesterone; Incidence of LLP (ƒÔ2 test): a vs b 0.01

LLP in pregnant mice under barbiturate stage. It is likely, therefore, that LLP anesthesia found in the present investigation is iden- Seventeen mice at day 14 of gestation tical to the lordosis posture in female were anesthetized with the barbiturate. sexual behavior. Ten of them displayed LLP without any An electroencephalographic study by tactile stimulation. In another group of 14 Margherita et al. (1965) indicated that in mice at the same gestation day, the dorsal rats, a characteristic activation pattern rump was stroked by the experimenter at appears in the ventromedial the initiation of anesthesia. Eight of the (VMH) and basolateral amygdala (BLA) in pregnant, anesthetized mice exhibited LLP a particular light stage of barbiturate anes- when given manual stimulation (Table 1). thesia. Accordingly, it seems probable There is no significant difference in LLP that VMH and/or BLA is related to the incidence between the anesthetized pregnant occurrence of LLP in mice at the initiation mice and those given the tactile stimulation. of barbiturate anesthesia. Yamanouchi and Arai (1975) demonstrated that castrated male rats receiving injections of estrogen Discussion and progestin display lordosis when dorsal afferent to the preoptic and an- Normal estrous female and ovariecto- terior hypothalamic areas were surgically mized, estrogen- or estrogen plus progestin- interrupted. A further study revealed that primed female rats and guinea pigs display the anterolateral fibers connected with the lordosis in response to mounting of the medial basal hypothalamus may function males or to manual stimulation (Beach, in facilitating lordosis in estrogen plus 1966; Pfaff and Sakuma, 1979a). In con- progestin-primed rats (Yamanouchi and trast, normal male, normal diestrous female, Arai, 1979). Pfaff and Sakuma (1979a, and gonadectomized rats of both b) also reported that electrical stimulation hardly adopted the lordosis posture at all of the ventromedial nucleus (VMN) facili- (Gorski, 1971; Arai et al., 1978). The present tates lordosis triggered either by male study, however, revealed that the lordosis- mounting or by manual stimulation in like posture (LLP) is induced by manual ovariectomized, estrogen plus progestin- stimulation in male and female mice of primed rats, and that electrolytic lesions of the ICR/JCL strain despite the presence the VMN induce a gradual decline in the or absence of their gonads as well as in the reflex. According to Beach's studies (1943, diestrous state when the animals stood at 1944), injury to the brain cortices resulted the initiation of barbiturate anesthesia. in the facilitation of lordosis in female Administration of estrogen and progestin rats, suggesting the presence of a cortical did not alter LLP incidence in ovariecto- inhibitory system. In view of these fin- mized, anesthetized females given manual dings, it is reasonable to conclude that the stimulation. These findings suggest that LLP reflex found in the present study is LLP is a hormone-independent phenomenon. triggered by tactile stimulation when the The LLP-assuming mice (LLP mice) lifted barbiturate suppresses the inhibitory system, the rump slightly, though the head eleva- and simultaneously activates the stimulative tion and the back depression were suffi- system regardless of the presence or absence ciently provoked. Such slight elevation of of . the rump in LLP mice may be due to the In the present investigation, it is of weakened extensor stretch of limbs paralyzed interest that LLP occurred in mice at day by the barbiturate at a relatively early 14 of gestation without any tactile stimu- Vol.30, No.1 LORDOSIS-LIKE POSTURE IN ANESTHETIZED MICE 33 lation when the animals stood at the ini- of reflexive mechanism involved in copulatory behavior. Physiol. Rev., 47, 289-316. tiation of barbiturate anesthesia. However, Davidson, J. M. (1969). Effects of estrogen on the manual stimulation never resulted in any sexual behavior of male rats. Endocrinology 84, change in LLP incidence in the anesthe- 1365-1372. tized, pregnant mice. These findings seem Gorski, R. A. (1971). Gonadal hormones and the perinatal development of neuroendccrine function. to indicate that at the initiation of bar- In Frontiers in Neuroendocrinology, (Eds. Martini, biturate anesthesia, the stimulative system L. and W. F. Ganong), Oxford Univ. Press, New of the brain is aroused for a longer period York, pp.237-290. than the inhibitory system in the presence Komisaruk, B. R. (1974). Neural and hormonal interactions in the reproductive behavior of female of hormones during gestation, and is acti- rats. In Reproductive Behavior (Eds., Montagna, vated by some stimuli of the distended W. and W. A. Sadler) Plenum Publ. Co., New uteri or abdomen. On the other hand, the York, pp.97-129. Lisk, R. D. (1962). Diencephalic placement of possibility cannot be excluded that in mouse estradiol and sexual receptivity in the female rat. brain, responsiveness of the behavior-indu- Am. J. Physiol. 203, 493-496. cing system to sexual input is greatly Margherita, G., D. Albritton, R. MacInnes, R. altered by hormones during gestation. Hayward, and R. Gorski (1965). Electroencephalo- graphic changes in ventromedial hypothalamus and amygdala induced by vaginal and other peri- pheral stimuli. Exp. Neurol., 13, 96-108. 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