Cl. Aron

Studies on feminine sexual behavior in the male rat: Influence of olfactory stimuli

Abstract 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.

Effects of ventromedial nucleus lesions on the display of lordosis behavior in the male rat. Interactions with facilitory effects of male urine.

Previous observations showed that exposure to the odor of male urine prior to mating could enhance the display of lordosis behavior in male rats feminized with ovarian hormones. This study was performed to determine in feminized male rats whether the control of lordosis behavior by the olfactory system was mediated by the ventromedial nucleus (VMN) of the hypothalamus. Male rats were orchidectomized (ORCH) as adults and primed with 25 micrograms estradiol benzoate (EB) and 150 micrograms progesterone (P) 40 hr apart. Lordosis behavior was tested 9 +/- 1 hr after P injection. VMN lesions were shown to completely suppress the display of lordosis behavior as compared to sham VMN operated and dorsomedial nucleus (DMN) lesioned animals. Exposure of feminized rats to the odor of male urine by 9 +/- 1 hr before mating significantly increased the proportion of ORCH rats that displayed lordosis behavior in response to male mounts. This effect was abolished by VMN lesions but was maintained in the sham VMN operated and DMN lesioned animals. These results were discussed in the light of the present knowledge on the neuroendocrine and olfactory structures which mediate lordosis behavior in the male rat.

Stress related effects in the control of sexual receptivity and in the secretion of progesterone by the adrenals in cyclic female rats

Abstract The present study examined the acute effects of ether anaesthesia and/or blood removal by heart puncture on progesterone blood concentration at different times of proestrus and on subsequent estrous mating behavior during the night following proestrus in sham adrenalectomized and adrenalectomized 4-day cyclic female rats. A statistically significant increase in blood progesterone concentration was observed on proestrus at 09:00, 13:30 and 15:30, a very short time after heart puncture under a 3 min ether anaesthesia in sham adrenalectomized rats as compared to their adrenalectomized counterparts. Following this blood removal procedure at the preceding times a greater number of sham adrenalectomized female rats displayed mating behavior (17/20) than their adrenalectomized counterparts (11/23). It is suggested that adrenocortical related effects of ether anaesthesia and/or surgical manipulations may be involved in the display of estrous sexual receptivity in the rat.

Endogenous progesterone and lordosis behavior in male rats given estrogen alone

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 microgram 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 microgram EB + DEXA was reduced to the level corresponding to the effects of 0.5 microgram 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.

Hormonal control of the perception of the olfactory signals which facilitate lordosis behavior in the male rat

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 micrograms 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 micrograms EB every day for 4 to 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 micrograms 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 micrograms EB and 100 micrograms or 150 micrograms P 39 hr apart. Although uncapable as such to facilitate lordosis behavior the dose of 100 micrograms 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.

Facilitory effects of male urine on feminine behavior in the male rat: Androgen-dependency

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.

Role played by serotonin in the control of estrous receptivity, ovarian activity and ovulation in the cyclic female rat

Abstract The effects of parachlorophenylalanine (pCPA) on ovulation and on estrous sexual receptivity have been investigated in gonadally intact four-day cyclic female rats. (1) When injected at 1800 hr on diestrus II, pCPA was shown to inhibit both ovulation and estrous sexual receptivity, an effect which was prevented by 5-hydroxytryptophan (5HTP). (2) The inhibitory effects of pCPA were overcome by 10 μg estradiol benzoate (EB) when injected on the morning of diestrus II at 1000 hr. No changes in the timing of either LH release or ovulation resulted from EB injection. (3) Blood estradiol 17β (E2) concentration did not appear to be modified at 2400 hr during the night from diestrus II to proestrus following pCPA injection. (4) A significant decrease in E2 was noted on proestrus at 0800 hr in pCPA-treated females but this effect was not prevented by 5HTP. (5) While no changes in blood progesterone (P) concentration occurred from 0900 hr until 1300 hr on proestrus, a specific decrease in blood P concentration was observed on proestrus at 1530 hr after pCPA treatment on diestrus II at 1800 hr.

Does corpus luteum function autonomously during estrous cycle in the rat? A possible involvement of LH and prolactin

This study examined the of LH and prolactin in the control of corpus luteum function during 4-day cycles in the rat. Bromocriptine (BRC) treatment was performed on proestrus or/and estrus morning that means before or after the preovulatory release of LH. This caused complete blood prolactin depression from the time of injection until diestrus 1 afternoon. This decrease in blood prolactin concentration was associated with a rise in the tonic level of LH secretion in those females which received BRC as soon as on proestrus. We first observed that injection on the morning of proestrus of doses of BRC capable of blunting prolactin secretion on proestrus afternoon did not significantly impair the preovulatory release of LH and did not prevent ovulation occurring during the following night. The life span of the corpora lutea edified from ovarian follicles rupturing before or under BRC administration did not exceed that of those formed under physiological circumstances since 4-day cycles culminating in ovulation constantly took place in all the treated animals whatever the time of BRC injection. To determine the pattern of luteal activity in the absence of prolactin secretion, we measured blood progesterone concentration from estrus until late diestrus in female rats injected with BRC on proestrus and/or estrus at 1100 h. The initiation of the function of corpus luteum on estrus and the achievement of its full activity on diestrus 1 did not appear to be affected by BRC. By contrast the level of blood progesterone declined more rapidly on the morning of diestrus 2 in BRC-treated than in control females. The capacity for autonomous progesterone secretion by corpus luteum of the cycle was discussed in the light of previous and present observations.

Progesterone secretion by luteinized unruptured follicles in mature female rats

The ability of luteinized unruptured follicles (LUF) to display luteal activity was investigated in mature female rats. Previous findings in our laboratory showed that increasing doses of LH, when injected on late diestrus in 4-day cyclic rats, were capable of inducing the formation of either LUF or postovulatory corpora lutea (POCL) in a dose dependent manner. Four-day cyclers were injected on diestrus 2 at 4.30 p.m. (day 0) with 2.7 micrograms or 5.4 micrograms/100 g of an ovine LH preparation (x 2.94 NIH LH S3) and were killed at different times during the three successive days following injection. Natural 4-day cyclers were killed at corresponding times following spontaneous LH release on proestrus afternoon (day 0). Both LUF and POCL were observed in LH-treated females. LUF appeared more numerous in females given 2.7 micrograms LH than in both natural cyclers and in females injected with 5.4 micrograms LH. On day 1 during the rising phase of luteal activity serum progesterone (P) level did not differ in the three groups despite the high number of LUF in females given 2.7 micrograms LH. On day 2 at 11 a.m. lower P values were observed in both groups of LH-treated females than in natural cyclers, this corresponding to a greater proportion of LUF in the former than in the latter. On day 2, at 5 p.m. by the time of full activity of POCL in natural cyclers, P did not differ in the three groups irrespective of the relative number of ruptured or unruptured follicles. On day 3, P sharply declined in LH-treated and natural cyclers. These results suggest that LUF are capable of secreting P during a period corresponding to the duration of corpus luteums life span in cyclic female rats.

How different procedures of blood removal affect blood progesterone concentration in the cyclic female rat

The effects of different procedures of blood removal on blood progesterone level were studied in female rats throughout the diestrous period of estrous cycle. Unoperated, sham operated, adrenalectomized and ovariectomized females were used. The complete manipulation comprising ether anaesthesia and blood collection lasted 3-4 min. Blood removal in itself did not exceed one minute. Blood progesterone levels appeared to be higher in unoperated, sham operated and ovariectomized females bled by heart puncture or from the abdominal vena cava under ether anaesthesia than in their decapitated counterparts bled without ether anaesthesia. Adrenalectomy prevented this effect from occurring. No difference in blood progesterone concentration was noted between anaesthetized and unanesthetized decapitated unoperated females. It was concluded that some procedures of blood removal under ether anaesthesia might cause a stress-related rise in blood progesterone concentration and that ether anaesthesia was not involved.