Male copulatory behavior and female maternal behavior in neonatally bulbectomized rats

Olfactory bulbs were destroyed in six-day-old male and female rats, and anosmia was confirmed in adulthood. Bulbectomized males initiated apparently normal sexual activity at the same age as did control animals. As virgins, bulbectomized females did not injure foster young; when allowed to mate and deliver young, they displayed apparently normal maternal behavior. It was concluded that neonatal olfactory bulbectomy does not preclude the development of essentially normal copulatory behavior in the male rat and maternal behavior in the female rat.     

Initiation of mating behavior in developing male rats following peripheral electric shock

When shocked on the flanks in the presence of estrous females, juvenile male rats displayed their first series of intromissions and ejaculation at a significantly younger age than non-shocked males or males shocked 24 hr before sex tests. A premature release of testosterone was not responsible for the phenomenon, as judged by genital organ weights and blood testosterone determinations made 24 hr following the initial ejaculation. Males induced to copulate with shock at early ages continued to display intromissions and ejaculation on subsequent tests without further peripheral electrical stimulation. However, in prepuberally castrated male rats, peripheral shock in conjunction with injections of a high dose of testosterone propionate (TP) was less successful than TP alone in facilitating the initial intromission. The results are discussed in terms of a three-part hypothesis concerning the initial activation of adult sexual behavior in the male rat.     

Rostral midbrain lesions and copulatory behavior in male rats

Discrete electrolytic lesions were placed in the mesencephalic dorsal noradrenergic (DNE) bundle of 22 male Sprague-Dawley rats, and sham operations were performed on 14 control animals. Eight components of copulatory behavior were compared in 2 preoperative and 2 postoperative heterosexual mating tests. A significant postlesion decrease in the postejaculatory interval (PEI), number of intromissions, number of incomplete mounts and the ejaculation latency from the first intromission (ELI) occurred. Norepinephrine levels were significantly reduced in the hippocampus, amygdala and hypothalamus, but not in the preoptic area. The only statistically significant correlations between NE concentrations and behavior in the lesioned animals were negative (hippocampal NE with PEI and ELI). The results support the hypothesis that rostral midbrain lesions disinhibit some components of male rodent copulatory behavior, but suggest that a system or systems other than the DNE bundle may be responsible for this disinhibition.     

Masculine sexual behavior: Pacing and ejaculatory patterns in female rats induced by electrical shock

The purpose of this experiment was to compare the responsiveness of male and female rats to peripheral electrical shock. Gonadectomized males and females were treated with androgen as adults and then tested for male copulatory behavior under shock and non-shock conditions. There was no significant difference in the periodicity of male copulatory behavior due to sex. The delivery of shock at 30 sec intervals paced the behavior and increased the rate of copulation. Peripheral electrical shock did not affect the number of intromissions per mount bout; however it did increase the number of intromissions per minute exhibited by both sexes. An unexpected finding during the course of testing was the display of the ejaculatory pattern by 3 of the 8 females tested. These results lend additional support to the hypothesis that the factors underlying masculine copulatory behavior in the female are very similar, if not identical, to those present in the male.     

From dud to stud: copulatory behavior elicited through conditioned arousal in sexually inactive male rats

Sexually inactive male rats were conditioned to associate tones with electric shock to the flanks. In subsequent tests, when only tones were presented in the presence of an estrous female, these males began to copulate, pacing their behavior to the tone presentations. Only one animal tested for sexual behavior without the tones mated. It is suggested that the momentary augmentation of nonspecific arousal can lead to the initiation and subsequent pacing of mating responses in noncopulators.     

Dihydrotestosterone stimulates mounting behavior but not lordosis in female rats

The ability of androgens to stimulate masculine sexual behavior is thought to depend on the aromatization of such androgens to estrogens. In this scheme, reduced androgens such as dihydrotestosterone (DHT) which cannot be aromatized, are thought to exert major peripheral but little or no central nervous system influences on the display of masculine sexual behavior. Further, an early report that DHT can induce lordosis, an estrogen (E) dependent behavior, led to a notion that DHT may effect behavior through metabolic intermediates such as 5α-androstane-3β, 17β-diol (ADIOL) which then binds to estrogen receptors eliciting the E-dependent lordotic response. The present study reexamined and compared the relative effectiveness of a range of DHT dosages in stimulating a characteristic masculine (mounting) and feminine (lordosis) sexual behavior. Adult ovariectomized rats were randomly assigned to either 250 μg or 1 mg daily injections of DHT or DHTP. Other animals received OIL injections or crystalline DHT delivered by two different lengths (20 mm or 40 mm) of Silastic capsules. Animals were tested once weekly (for 5 weeks) for mounting behavior (20 minute test). Then animals were tested thrice (once weekly) for lordosis 4 hrs after the addition of 500 μg Progesterone (P). Finally, all females were tested for lordotic potential to respond to 10 μg EB plus P. 1 mg DHT or DHTP dosages and the 40 mm-Silastic condition significantly increased mounting behavior over that of lower dosages and OIL controls. A significant correlation existed between mounting frequency and circulating level of serum DHT. Treatment with DHTP was not different than DHT in eliciting mounting behavior. Lordosis was not enhanced by any treatment with DHT or DHTP over that of controls, although all females were capable of lordotically responding to EB. These data demonstrate that DHT can induce mounting behavior, but not lordosis, suggesting that whatever action DHT has may not occur via estrogen or estrogen receptors. A role for androgen and androgen receptors upon mounting behavior is discussed.     

Elicitation of ejaculation and penile reflexes in spinal male rats by peripheral electric shock

Mild electrical shock, applied bilaterally to the skin of the flank of spinal male rats occasionally evokes an ejaculatory complex consisting of seminal expulsion followed by penile erections and flips. The ejaculatory reaction appears to be inhibited by penile stimulation. The inhibitory effect of penile stimulation on ejaculation may represent a spinal mechanism responsible for the obligatory copulatory intromissions which precede ejaculation. The function of penile erections and flips, may be to pack and seal seminal plugs into the vaginocervical junction.     

Influence of female copulatory behavior on the induction of pseudopregnancy in the female rat.

Female regulation of inter-intromission intervals and the successful induction of pseudopregnancy were investigated. Three groups of intact female rats received 5, 10 or 15 intromissions, respectively, in a two-compartment escape-re-entry mating arena in the presence of three sexually vigorous males. Three additional groups of intact females received 5, 10 or 15 intromissions in the same arena but were not allowed access to the escape platform and thus were not allowed to pace their sexual contacts. Five intromissions were sufficient to induce pseudopregnancy in a majority of females allowed to pace their sexual contacts, as compared with females in the no-escape condition. With increasing numbers of intromissions (10 and 15 intromissions) pseudopregnancy was seen in a majority of females in both the escape and no-escape conditions. Inter-intromission intervals were extended for all escape groups. The results demonstrate that female regulation of the temporal receipt of intromissions contributes a complementary behavioral component to the mating sequence which can potentiate the stimulation of intromissions by the male.     

Characterization of copulatory behavior in female mice: evidence for paced mating

In this study we characterized female mouse sexual behavior using a pacing paradigm similar to that used to evaluate sexual behavior in female rats. A pacing chamber was designed for use with mice and we compared the sexual behavior of female mice that were tested in both pacing and nonpacing paradigms and under different hormone conditions. We found that, like rats, female mice do pace their copulatory behavior by altering the temporal sequence of copulatory events. Female mice take longer to return to the male after an ejaculation, compared to either a mount or intromission. However, it is still unclear if female-paced mating serves the same functions as it does in female rats. More work is needed to confirm that paced mating induces hormonal changes needed for pregnancy as is the case in rats.     

Tail pinch induces sexual behavior in olfactory bulbectomized male rats

Adult male Long-Evans rats were subjected to bilateral olfactory bulbectomy, sham surgery or no treatment. Of 34 bulbectomized rats, 24 failed to ejaculate on either of 2 tests with a primed ovariectomized female. All control animals exhibited normal sexual behavior, and 10 bulbectomized animals ejaculated at least once during the 2 tests. Later histological examination revealed a relationship between size of lesion and extent of behavioral deficits. After a third test, 16 nonejaculatory animals were subjected to a tail pinch (TP) procedure, immediately followed by a fourth test. The remaining 8 nonejaculatory animals were tested similarly, but without tail pinch. Ten of the 16 tail pinch animals showed complete sexual behavior on the first test, while 2 additional animals began to copulate after a second TP procedure 4 days later. Only 1 of the 8 animals not receiving TP ejaculated on these tests. Thus, TP applied shortly before sexual behavior tests can induce copulation in some males whose behavior had been disrupted by olfactory bulbectomy.     

Age differences in copulatory behavior and serum 17β-estradiol in female rhesus monkeys

Young, sexually mature female rhesus monkeys housed in outdoor groups have been found to exhibit significantly longer mating periods associated with first conception compared with the duration of the annual mating period exhibited by older, multiparous females. An analysis of the sexual behavior and corresponding serum concentrations of 17β-estradiol (E2) and progesterone (P) in two age groups of rhesus females revealed that young females copulated on significantly more days prior to the E2, ovulatory peak than did older females. Serum concentrations of E2 were significantly higher from ?30 to Day ?10 prior to the E2 peak (Day 0) in young females. Estradiol concentrations were similar for both age groups during the remaining follicular and periovulatory period. No age differences in serum P were observed between the two groups. Serum E2 levels associated with the onset of mating were similar in the two age groups with levels rising from 73.5±4.0 pg/ml prior to mating to 97.2±4.6 pg/ml. Thus the hormonal profile associated with the onset of mating is similar for both age groups, and the earlier occurrence of mating behavior prior to ovulation in young females is accounted for by an earlier rise in serum E2.     

Maternal behavior in male rats: Critical times for the suppressive action of androgens

To determine whether the first day of life is the only period during infancy when removal of the testes permanently alters maternal behavior in rats, male Sprague-Dawley rats were castrated on either Day 1, 5, 10, 25 or 70 of life and were tested as adults for maternal behavior following testosterone replacement. Males castrated on Day 1, 5 or 10 responded significantly sooner to pups and spent longer times exhibiting maternal behavior than did males castrated on Day 25 or later. However removal of the testes on the first day of life was maximally effective. Treatment with testosterone neither inhibited nor facilitated maternal behavior. Thus there is no one critical period in infancy for differentiation of the neural substrate for maternal behavior, although removal of androgen at birth is maximally effective for the onset of maternal behavior in the adult.     

Effects of chronic activity wheel running and imipramine on masculine copulatory behavior after olfactory bulbectomy

We examined the effects of chronic activity wheel running and imipramine administration on appetitive behavior after olfactory bulbectomy (OBX). Male Long-Evans rats were randomly assigned to the following conditions using a 2 x 2 x 2 design: (1) bilateral OBX or sham surgery, (2) voluntary activity wheel running or sedentary home cage, and (3) daily imipramine or saline injections. After 21 days of treatment, animals underwent behavioral testing for copulatory activity and sucrose preference. Bulbectomized animals exhibited decrements in copulatory performance and reductions in sucrose intake compared to sham animals. Within the bulbectomized groups, imipramine-treated rats either did not copulate or had reduced ejaculation frequencies. However, activity wheel running attenuated the copulatory deficits induced by OBX. The findings encourage studies of physical activity and male sexual dysfunction among depressed men being treated by pharmacotherapy.     

Testosterone induced mounting behavior in adult female rats born in litters of different female to male ratios

Female rats can show mounting behavior towards isosexual or heterosexual conspecifics. The present experiments were designed to study whether the prenatal presence of male fetuses would affect display of this mounting behavior in adulthood. Therefore mounting behavior, after gonadectomy and during continuous treatment with testosterone propionate (TP) was studied in female rats which were born in litters without male siblings (“all female” litters) and in litters with a variable number of male siblings. Litter composition at birth did not affect display of adult mounting behavior during protracted tests (a total of 6 tests during 8 weeks of treatment with TP). The data indicate that TP induced mounting behavior in adulthood occurs independent of the prenatal presence of male fetuses. If mounting behavior in adulthood has to be “organized” by prenatally present androgen (the current way of thinking), then the present data indicate that female rat fetuses provide themselves with these hormones. It would then seem inappropriate to judge adult mounting behavior as a sign of “masculinization” of the rat brain.     

Redirected oral behavior in rats induced by tail-pinch and electrical stimulation of the tail

Two seemingly non-specific stimuli, tail-pinch and electrical stimulation of the tail (EST), produce different responses to food in rats: tail-pinch induces eating whereas EST elicits licking of food pellets. However, even if administered several months earlier, prior tail-pinch changes the response to pellets during EST from licking to eating. If their tail is within reach, naive rats lick it rather than food pellets. However, they rarely pursue the tail after their initial attempts to reach it are prevented; instead, they eat or lick food. In fact, if they have prior tail-pinch experience, they first eat during EST even with the tail in sight and reach. Thus the response to tail stimulation is directed specifically at the tail and is redirected towards food when the tail is not available. Different oral responses during tail-pinch and EST suggest that the two stimuli induce different sensations; however, the redirected response is modifiable by learning.     

Long-term kindling of the basolateral amygdala impairs copulatory behavior in male rats

This experiment examined the consequences of long-term kindling of the basolateral amygdala on male sexual behavior and the frequency of both spontaneous wet dog shakes (WDS) and those induced by the 5-HT_2A receptor agonist DOI. Results demonstrated that following 60 stimulations of the left basolateral amygdala over a 4-week period, male Long–Evans rats exhibited decrements in every aspect of sexual behavior. Specifically, latencies to mount, intromit and ejaculate were all prolonged following long-term kindling, and ejaculation frequencies were significantly reduced. Furthermore, spontaneous peri-copulatory WDS were increased in kindled rats, suggesting a possible role of the 5-HT_2A receptor. However, countering this suggestion, there were no differences between sham and kindled rats on WDS induced by the 5-HT_2A receptor agonist DOI. These results suggest that kindled rats may exhibit elevated levels of endogenous serotonin during exposure to a female rat, which would attenuate copulatory behavior, while concurrently increasing WDS expression.     

Induction of female sexual behavior by GTP in ovariectomized estrogen primed rats

The effect of both intrahypothalamic and systemic administration of guanosine triphosphate (GTP) on lordosis behavior was studied in ovariectomized and ovariectomized-adrenalectomized, estrogen-primed rats (estradiol benzoate, 4 μg). This estrogen dose per se induced only weak or no lordosis behavior. Injection of GTP into the medial hypothalamic area (100 μg in 2.5 μl) elicited lordosis behavior with relatively short latency in 6 out of 7 rats. Systemic administration of GTP in a dose range of 0.8 mg to 5.0 mg to ovariectomized estrogen-primed rats, stimulated intense lordosis behavior in all subjects. Weak lordosis responses were displayed within the first 12 hr after GTP injection, but at 48 hr all rats were highly estrous. Lordosis behavior remained for up to eight days, its duration being related to the dose of GTP administered. GTP (2 mg) induced lordosis behavior in ovariectomized, adrenalectomized estrogen-primed rats, thus excluding the participation of adrenal steroids in this effect. The results are interpreted in terms of the stimulation of adenyl cyclase-cAMP systems by GTP.     

Estradiol treatment and precopulatory behavior in ovariectomized female rats

Female rats of Wistar strain were injected SC, starting at Day 5 after ovariectomy, with estradiol dipropionate (ED) at weekly intervals. Forty-eight hours after each injection they were subjected to standardized mating tests. A 6 μg ED dose showed to be insufficient to maintain estrous behavior. Both precopulatory and lordosis behavior disappeared in the course of eight weeks. On the other hand, the behavioral effectiveness of 10 and 30 μg ED increased with the number of injected doses. Under these circumstances, estradiol proved to be sufficient to induce not only full copulatory readiness but also all the degree of precopulatory behavior of pattern (Presenting, Hopping ending in Presenting, and Darting ending in Presenting). Although there are large individual differences in behavioral effectiveness of ED, the estradiol thresholds for inducing Presenting, Hopping, and Darting were found to increase in the given order. However, prolonged (up to Week 12) treatment with 30 μg ED resulted in the disappearance all estrous behaviors. This decline of estradiol effectiveness was reversed by increasing the estradiol dose to 100 μg.     

Effects of stimulus female on sexual behavior of male rats given olfactory tubercle and corticomedial amygdaloid lesions

Lesions of the olfactory tubercle (OT) or corticomedial amygdala (CMA) damaging projections from the main or accessory olfactory bulbs, respectively, were made in male rats. When paired with ovariectomized females treated with estradiol benzoate (EB) and progesterone (Experiment 1) sexual behavior of lesioned males did not differ from sham and unoperated controls. During Experiment 2 males were paired with females chronically treated with EB only. Lesions of the OT did not affect mating while CMA lesions produced lengthened ejaculatory latencies (EL), longer mean interintromission intervals and more intromissions per ejaculation. Lesions of the CMA produced EL which were either within a normal range or noticeably extended with ejaculatory deficits becoming more exaggerated through three ejaculatory series. Low levels of soliciting by EB treated females seemed to precipitate ejaculatory deficits.     

Sexual behavior in aged, noncycling female rats

Sexual behavior of 19 month old, noncycling, female rats was evaluated for a period of 8 days. The sexual behavior of 11 aged females revealing constant vaginal cornification (CVC) for 30 days prior to, and during the observation period was variable. Eight of the CVC females showed consistently high lordosis quotients (LQ), whereas 3 showed no lordosis. A significant negative correlation was found between food intake and LQ over the 8 day period. In 8 other aged females, the vaginal smear was characterized by a mixture of both leucocytes and cornified cells, each day, for a period of 30 days prior to, and during the observation period. Lordosis behavior was absent in all females revealing this mixed type (MX) smear when they were tested. At random times after the test period, 3 CVC and 2 MX females showed a vaginal cycle. As the vaginal cycle was observed each female was again tested for sexual behavior. All 5 females were highly receptive when placed with the male during the evening of vaginal proestrus, but not at other times. It is concluded that despite disruptions of regular ovarian cyclicity, aged female rats are still capable of showing a lordosis response.