Sexually inexperienced male Wistar rats (strain WI in our colony) known to very infrequently display spontaneous lordosis behavior (Schaeffer et al., 1990b) were used. A first group was tested four times at 5-day intervals for lordosis with vigorous stimulus males (heterotypic sexual behavior), immediately following testing for masculine sexual activity with highly receptive females (homotypic sexual behavior). A small number of animals displayed lordosis during the first test, but more and more animals displayed this behavior from the first to the fourth test. There was no relationship between the degree of masculine sexual activity—intromission without ejaculation or ejaculation—and the occurrence of lordosis behavior. A second group was tested only once for both masculine sexual activity and lordosis behavior as above and afterwards three times at 5-day intervals for lordosis behavior in the absence of any previous testing for masculine sexual activity. A few animals displayed lordosis during their first test. As compared to the first group, the animals which had not displayed lordosis in the first test never showed lordosis responses in the following tests. It is concluded that both homotypic and heterotypic sexual interactions are required for the display of lordosis behavior in the strain of Wistar rats used in this study.

Etude au comportement de lordose chez des rats mâles sexuellement inexperimentes ou apres une experience copulatoire avec des femelles. Cette etude s'interesse aux correlations existant entre le comportement de lordose et les concentrations sanguines de progesterone, œstradiol-17β et testosterone

The aim of this study was to investigate the olfactory mechanisms regulating the display of lordosis behavior in intact Wistar male rats bred in our colony. Gonadally intact males show a low capacity to respond by lordosis to male mounts and were insensitive to manipulations of the olfactory system (exposure to the odor of male urine or accessory bulb removal (AOBR)) which have been previously shown to facilitate the display of lordosis behavior in orchidectomized animals primed with ovarian hormones. Treatment with either estradiol benzoate (EB) or EB and progesterone (P) consecutively did not render these gonadally intact animals sensitive to the effects of AOBR. By contrast exposure to male urine was capable of facilitating the display of lordosis behavior in intact male rats given EB + P consecutively. These results are discussed in the light of previous findings showing that (1) two inhibitory structures, the accessory olfactory bulb and the septal and preoptic areas, are involved in the control of lordosis behavior in the male rat; (2) the effects of olfactory cues on the display of lordosis behavior are dependent on the action of both EB and P in orchidectomized animals.

The effects of androgen treatment (TP) from postnatal day 20 (P20) onwards on the accessory olfactory bulbs' (AOB) development were studied in rats orchidectomized at birth (PO) or on P20. TP failed to restore impaired AOB development in the rats castrated at PO but completely restored AOB development in those castrated at P20. Androgen secretion during both the perinatal and prepubescent periods appeared to be critical for male AOB development.

The aim of this study was to investigate the mechanisms involved in the inhibitory action of progesterone on estrogen-induced facilitatory effects of estradiol benzoate on lordosis behavior in the male rat. Intact adult male rats were given 1) 25 μg estradiol benzoate (EB) and 100 μg progesterone (P) at an interval of 42 hr. EB injected animals served as controls 2) EB followed by 3 doses of 400 μg dexamethasone (DEXA) and P as above. EB + DEXA injected animals served as controls. Testing for lordosis behavior was performed by 50±hr after EB injection. A significant decrease in the number of the males displaying lordosis in response to the mounts of stimulus males resulted from P injection following EB treatment as compared to EB controls. DEXA treatment significantly reduced the number of EB animals showing lordosis responses but completely prevented the inhibitory effects of exogenous P to occur. Blood P values appeared to be significantly lower in EB + DEXA males than in their EB counterparts. The results provide evidence that endogenous P is involved in the display of lordosis behavior by EB-treated intact males. They mainly suggest that the effects of exogenous P on estrogen-induced lordosis behavior in the intact male rat result from sequential inhibitory mechanisms involving exposure of the animals to the successive action of endogenous and exogenous P.

The aim of this investigation was 1) to compare the development of AOB in male and female rats before birth, early after birth, and at later stages of sexual immaturity and maturity 2) to examine the effects of early and delayed castration after birth on AOB development in the male rat. A significant increase of the surface area of AOB was observed in both sexes from birth until postnatal day 7, but AOB was found to be larger in males than in females. From the end of the first postnatal week AOB stopped growing until day 40 in both males and females. After this time AOB resumed its development until day 60 in males, while no changes occurred in females over the same period. Castration of males at birth or six hours later impaired development of AOB. Castration of males on postnatal days 20 or 30 also impaired AOB development until day 60. The results strongly suggest that the development of AOB in the male rat is dependent on the two well known "perinatal" and "adult" phases of the endocrine activity of the testes.

Rats were orchidectomized (ORCH) as adults and given successive doses of 0.5 microgram or 1.0 microgram of oestradiol benzoate (EB) combined or not with dexamethasone (DEXA) at the end of oestrogen treatment; successive doses of olive oil. They were presented to stimulus males on the day of the last EB injection and decapitated immediately after the behavioural test. Animals given EB or olive oil only served as controls. There was a significant rise in blood progesterone concentration in animals given 0.5 and 1.0 microgram EB as compared with oil-treated animals. A higher blood progesterone concentration was observed at the end of the behavioural session in oil-treated and 0.5 microgram EB-treated ORCH rats than in their isolated counterparts, an effect which appeared not to dependent on lordosis responses to mounting attempts of the males. DEXA completely suppressed the rise in blood progesterone concentration in oestrogenized ORCH rats presented to stimulus males. Presentation of ORCH rats to stimulus males was then concluded to constitute a stressful condition capable of inducing adrenocortical progesterone secretion in ORCH animals.

Orchidectomized rats were given estrogen and progesterone and tested for feminine behavior in the presence of a mounting male after accessory olfactory bulb removal (AOBR). Complete AOBR caused a rise in the number of estrogen-progesterone-treated male rats responding by lordosis behavior to male mounts as compared to controls and sham-operated animals. By contrast, LQ scores did not appear to differ in these three groups of animals. The results are discussed in terms of involvement of the main and the accessory olfactory systems in the regulation of feminine behavior in the male rat.

Male rats castrated as adults were given successive doses of estradiol benzoate (EB) combined or not with dexamethasone (DEXA) at the end of estrogen treatment. Two experiments were done to determine if progesterone (P) of adrenocortical origin was involved in the display of lordosis behavior under these experimental circumstances. There was a significant rise in blood P concentration in animals given 0.5 and 1.0 μg EB when compared with oil-control injected animals an effect which was completely suppressed by DEXA treatment. An increase in the proportion of estrogen treated animals displaying lordosis responses to male mounts was found with increasing doses of EB and paralleled the effects of EB on P adrenocortical secretion. However the number of feminized animals given 1 μ g EB + DEXA was reduced to the level corresponding to the effects of 0.5 μg EB on lordosis behavior. These data show that the secretion of P by the adrenals is involved in the expression of lordosis behavior in castrated male rats primed with repeated doses of estrogen.

This study was designed to evaluate in the male rat the hormonal requirements for the facilitation of feminine behavior by the odor of male urine. Wistar rats from the WI and WII strains in our colony were orchidectomized (ORCH) as adults. A first group was given a single dose of 75 μg estradiol benzoate (EB) and tested for lordosis behavior 48 hr later. Exposure to the odor of male urine by 9±1 hr before the behavioral session did not increase the number of animals showing lordosis behavior as compared to non exposed controls. A second group of WI rats was given 0.5 μg EB every day for 4 or 8 days. A similar number of animals displayed lordosis behavior irrespective of whether they were exposed to the odor of urine before testing. A third group of WI rats was injected with 75 μg EB and 1 mg progesterone (P) 39 hr apart. Exposure to the odor of urine during estrogen treatment remained ineffective but significantly increased the number of animals showing lordosis behavior when performed at the time of P injection. A last group of WII rats was given 25 μg EB and 100 μg or 150 μg P 39 hr apart. Although uncapable as such to facilitate lordosis behavior the dose of 100 μg P rendered the animals responsive to the odor of urine. It was concluded that (1) the perception by feminized males of olfactory signals from the male was dependent on P; (2) an interaction between hormonal and sensory mechanisms was involved in the facilitation of lordosis behavior in the male rat.

The aim of this work was to study the influence of the hormonal milieu on the facilitory effects of olfactory stimuli originating from female urine on lordosis behavior in orchidectomized (ORCH) feminized rats. Urine from ovariectomized (OVX) rats was shown to increase the proportion of ORCH rats displaying lordosis behavior, an effect which was enhanced if the OVX rats had been given progesterone. Treatment of OVX rats with estradiol benzoate did not affect the pheromonal activity of their urine. Dexamethasone treatment of OVX rats completely suppressed the facilitory effects of their urine on the feminine behavior in males. A higher proportion of feminized rats displayed lordosis following exposure to urine collected from pseudopregnant rats than did their unexposed counterparts. Dexamethasone treatment of pseudopregnant rats did not abolish this effect. These results suggest that the adrenal cortex is capable, in the absence of the ovaries, of manufacturing some pheromonal substance which stimulates feminine behavior in the male rat. The nature of this substance remains unknown. Furthermore progesterone itself is involved in the emission of olfactory signals which control feminine behavior in the male rat.

The mechanism of hypercalcitoninemia associated with aging was investigated in male rats. To mimic some of the hormonal changes with aging, orchidectomized (Orch) and hyperprolactinemic rats were used to mimic the physiological status of aging. Orch and haloperidol-induced hyperprolactinemic rats aged 3, 8, and 17 months were infused with CaCl2 and then bled from a jugular catheter following the CaCl2 challenge. Rat thyroid gland was incubated with Locke's medium at 37°C for 30 minutes. Compared with 8- and 3-month-old rats, 17-month-old rats exhibited the lowest levels of plasma testosterone and the highest levels of plasma prolactin (PRL) and calcitonin (CT). The release of CT in the thyroid glands in vitro was highest in 17-month-old rats. Orchidectomy decreased rat plasma CT and thyroid CT release in vitro. Hyperprolactinemic rats had higher levels of plasma PRL and CT compared with control animals. The release of thyroid Ct in vitro was greater in hyperprolactinemic rats. These results suggest that the hypersecretion of CT in 17-month-old rats may be due in part to hyperprolactinemia.

Feminine behavior in the male rat can be enhanced by exposing ORCH animals primed with estradiol benzoate and progesterone to the odor of urine collected from intact male adult congeners [20]. The present study provides evidence that this pheromonal effect is androgen dependent. A higher proportion of ORCH feminized rats displayed lordosis behavior following exposure to the odor of urine for either intact male rats or from ORCH rats supplemented with testosterone propionate than did ORCH feminized rats exposed to the odor of urine originating from non injected ORCH males.

The aim of this study was to determine if the display of lordosis behavior in the male rat could be influenced by the olfactory environment. Unexperienced adult male rats were orchidectomized (ORCH). They were primed with 75 μg estradiol benzoate and 1 mg progesterone was injected at an interval of 39 hr following long-term (LT = 3 weeks) or short-term (SHT = 8 hr 30 min) exposure to the odor of male or female urine. For 10 min they were placed in the presence of a “stimulus” male of proven sexual vigor 9 hr 30 min ± 1 hr after progesterone injection. Both LT and SHT exposure to the odor of male urine caused a significant increase in the number of ORCH rats which showed lordosis response to male mounts compared to either the ORCH rats exposed to the odor of female urine or to the controls. Following complete olfactory bulb removal (COBR), no difference was observed in the occurrence of lordosis behavior between the ORCH rats whether or not exposed to the odor of urine. For the ORCH-COBR rats exposed to male urine the proportion of animals responding to mounts did not differ from that of their nonbulbectomized counterparts. In comparing the effects of COBR vs anterior olfactory bulb removal (AOBR) lordosis behavior occurred more frequently in COBR than in AOBR-ORCH rats. The lordosis quotient (LQ) was not affected by exposure to the odor of male urine in the nonbulbectomized ORCH rats. In contrast, it appeared to be higher in both COBR and AOBR animals than in their nonbulbectomized counterparts. The olfactory bulbs were then concluded to inhibit the display of lordosis behavior in the male rat. It was also thought that the olfactory stimuli originating from male urine were capable of releasing the hypothalamic structures involved in the control of lordosis behavior of the male rat from an olfactory inhibitory influence.