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In the ewe, the mediobasal hypothalamus (MBH) is the primary central site for estradiol to generate the preovulatory GnRH/LH surges and sexual behavior. This area contains numerous neurons expressing the estradiol receptor alpha, distributed in the ventromedial nucleus (VMN) and the infundibular nucleus (IN). A large proportion of these neurons express somatostatin, making this neuropeptide a potential candidate for transmission of the estradiol signal to the GnRH neurons located in the preoptic area. We tested this hypothesis using ovariectomized ewes that had been subjected to an artificial estrous cycle. In the first experiment, 22 h after progesterone removal, ewes received estradiol (treated ewes) or empty implants (control ewes) for 4 h and then were killed. Using in situ hybridization, we showed that this short estradiol treatment increased the somatostatin mRNA amount by about 50% in the VMN and 42% in the IN. In the second experiment, preovulatory estradiol signal was replaced by somatostatin intracerebroventricular (ICV) administration. This treatment abolished LH pulsatility and dramatically decreased the mean basal level of LH secretion while it did not affect the mean plasma GH concentration. We demonstrated that an increase in somatostatin mRNA occurs at the time of the negative feedback effect of estradiol on LH secretion during the early stage of the GnRH surge induction. As ICV somatostatin administration inhibits the pulsatile LH secretion by acting on the central nervous system, we suggest that somatostatin synthesized in the MBH could be involved in the estradiol negative feedback before the onset of the preovulatory surge.

In sheep, the mediobasal hypothalamus (MBH) has been shown to be the primary central site of estradiol (E2) action that induces both the preovulatory surge and sexual behaviour. However, the nature of the neurotransmitters or neuromodulators synthesized in the MBH during E2 stimulation remains to be clearly defined. After the cloning of the ovine cDNA sequences and using in situ hybridization, hypothalamic proopiomelanocortin (POMC), and preproneuropeptide Y (preproNPY) mRNA expression was studied in ovariectomized ewes that received a sequential treatment of progesterone and E2. As we showed that an exposition to E2 only for 4h well in advance on the LH surge onset is sufficient to induce the preovulatory surge and estrous behaviour, mRNA expression was evaluated in ewes treated with 6x30-mm E2 implants (experimental group) or with empty implants (control group) and slaughtered 4h after the start of the E2 treatment. Our results demonstrate that this short E2 treatment significantly decreased both the mean number of silver grains per POMC-containing cell (35%) and the mean number of POMC-cells (38%) in the ovine infundibular nucleus, whereas the treatment had no effect on preproNPY mRNA expression. These observations suggest that a reduction of POMC gene transcription could participate to the early neural mechanism of E2 feedback.

Dopamine has been implicated in the control of sexual behaviour, but its role seems quite complex and controversial. The aim of the present experiments was to investigate the effects of dopamine (DA) acting on D2 receptors in the mediobasal hypothalamus (MBH) on sexual behaviour in female sheep. To achieve this, the D2 agonist, quinpirole, was administered bilaterally via microdialysis probes into the MBH of ovariectomized ewes either before or after oestradiol (E2) administration. Quinpirole (100 ng/ml) infused for 6 h just before E2 hastened the onset of oestrus behaviour and the luteinizing hormone surge, whereas the same treatment given 6-12 h or 18-21 h after E2 decreased the intensity of sexual receptivity without affecting LH or prolactin secretion. We then tested the hypothesis that E2 stimulates the onset of oestrus partly by decreasing DA activation of D2 receptors. In this case the D2 antagonists pimozide or spiperone (100 ng/ml) were infused into the MBH via microdialysis probes for 11 h in the absence of E2 administration. A significant number of ewes showed induction of receptivity with both antagonists, although its intensity was significantly lower than that induced by E2. These treatments generally did not significantly alter extracellular concentrations of monoamines or aminoacids although quinpirole modulated the ability of sexual interactions to increase noradrenaline release. These experiments show that DA acts via D2 receptors in the MBH to control female sexual behaviour in a biphasic manner: the onset of sexual motivation and receptivity requiring an initial increase in activation followed by a decrease. This dual action could explain some of the controversies concerning DA action on sexual behaviour.

Although a neural site of action for estradiol in inducing a LH surge via a surge of GnRH is now well established in sheep, the precise target(s) for estrogen within the brain is unknown. To address this issue, two experiments were conducted during the breeding season using an artificial model of the follicular phase. In the first experiment, bilateral 17beta-estradiol microimplants were positioned in either the medial preoptic area (MPOA) or the mediobasal hypothalamus (MBH), and LH secretion was monitored. An initial negative feedback inhibition of LH secretion was observed in ewes that had estradiol microimplants located in the MPOA (6 of 6 ewes) or caudal MBH in the vicinity of the arcuate nucleus (4 of 4). In contrast, a normal LH surge was only found in animals bearing estradiol microimplants in the MBH (5 of 10). Detailed analysis of estradiol microimplant location with respect to the estrogen receptor-alpha-immunoreactive cells of the hypothalamus revealed that 4 of the 5 ewes exhibiting a LH surge had microimplants located bilaterally within or adjacent to the area of estrogen receptor-expressing cells of the ventromedial nucleus. Two of these ewes exhibited a LH surge without showing any form of estrogen negative feedback. In the second experiment, we used the technique of hypophyseal portal blood collection to monitor GnRH secretion directly at the time of the LH surge induced by estradiol delivered either centrally or peripherally. Central estradiol implants induced the GnRH surge. The duration and mean plasma concentration of GnRH during the surge were not different between animals given peripheral or central MBH estradiol implants. Cholesterol-filled MBH microimplants did not evoke a GnRH surge. We conclude that the ventromedial nucleus is the primary site of action for estradiol in stimulating the preovulatory GnRH surge of the ewe, whereas the MPOA and possibly the caudal MBH are sites at which estrogen can act to inhibit LH secretion. These data provide evidence for the sites within the ovine hypothalamus responsible for mediating the bimodal influence of estradiol on GnRH secretion and suggest that different, and possibly independent, neuronal cell populations are responsible for the negative and positive feedback actions of estradiol.

During behavioural oestrus female sheep, like females of many species, become both attracted to and sexually receptive towards males, whereas at other times they will avoid them. The mediobasal hypothalamus is the main site for the feedback action of sex steroids to induce sexual behaviour in the sheep and in previous studies we have shown that noradrenaline and serotonin are released in this region during sexual interactions with males. The current study investigated whether such changes are specific to interactions with males and if visual or olfactory cues or somatosensory stimulation during mating are critical. In vivo microdialysis sampling was carried out in the mediobasal hypothalamus of ovariectomized ewes submitted to artificial oestrous cycles. Release of monoamines and amino acid transmitters was first measured in animals during and after oestrus when they were exposed to interactions with either males or females or presentation of food. Noradrenaline concentrations only increased significantly when the females were in oestrus and interacted with males irrespective of whether intromissions were permitted. Females were then exposed to visual (faces) or odour (a home pen) cues from males or to the males themselves. Slide images of male faces increased concentrations of amines, glutamate and GABA during early oestrus, when females spent most time looking at them. During late oestrus noradrenaline, glutamate and GABA concentrations also increased in response to the male faces but no transmitter changes were seen during the luteal phase or at any time where the females were exposed to female faces, or inverted male faces. Exposure to male odour produced a lower increase in noradrenaline concentrations when females were in early oestrus but marked increases 20 and 30 min after exposure to male odours in late oestrus. No other transmitters were affected. Exposure to a male and mating with him when females were in early or late oestrus produced increased noradrenaline concentrations similar to those seen with face stimuli alone although other neurotransmitters were unaffected. These results show that noradrenaline, and to a lesser extent dopamine, serotonin, glutamate and GABA release in the mediobasal hypothalamus, can be modulated specifically in the oestrous female by sensory information coming from the male during oestrus. The differential effects of male cues during early and late oestrus suggest their involvement in (i) proceptive or anticipatory sexual responses shown by the female to male cues, and (ii) receptive sexual responses, and suggest that the mediobasal hypothalamus plays a key role in the integration of hormonal action on sexual motivation and processing of sensory information during oestrus.

In female sheep, progesterone blocks the induction by oestradiol of both sexual behaviour and the pre-ovulatory surges of gonadotrophin releasing hormone (GnRH) and luteinising hormone (LH). However, the central sites of action of progesterone remain poorly defined, so we attempted to locate them by implanting progesterone intracerebrally in ovariectomised ewes treated with exogenous steroids to induce oestrous behaviour and the LH surge. Single bilateral implants or a double bilateral implants filled with progesterone or cholesterol were placed in the ventromedial hypothalamus (VMH) or the preoptic area (POA). Control ewes were not implanted. To determine the inhibitory capacity of the central progesterone implants, ewes received an injection (i.m.) of 8 micrograms or 16 micrograms of oestradiol. The single bilateral implants of progesterone failed to block oestrous behaviour and the LH surge induced by 8 micrograms of oestradiol. Double bilateral progesterone implants in the VMH blocked the sexual behaviour (P < 0.05) and the LH surge (P < 0.05), but implants in the POA blocked only sexual receptivity (P < 0.05). No changes were observed after central implantation of cholesterol. Our results support the hypothesis that progesterone acts centrally in the VMH and the POA to inhibit the induction of LH surge and sexual behaviour by oestradiol.

The preovulatory surge of LH, or positive feedback response to oestradiol, is related to the steroid's direct stimulating action on the pituitary gland, but we have demonstrated that, in sheep, the central nervous system plays an essential role in its action: a preovulatory GnRH surge. Since GnRH neurons appear to contain few, if any receptors for oestradiol the question is raised: Where in the central nervous system does oestradiol act to stimulate GnRH secretion? A series of experiments were conducted with a combination of techniques for sampling pituitary portal blood and stereotaxic brain micro-implantations of oestradiol. Castrated Ile-de-France breed ewes were treated during the pseudo follicular phase of successive artificial cycles, receiving either peripheral oestradiol implants or brain implants containing oestradiol or cholesterol. Administration of oestradiol implants into the ventromedial region of the hypothalamus induced a preovulatory GnRH surge in 5 out of 10 animals. The interval between estradiol and the GnRH surge was comparable with that observed in animals treated with a peripheral implant although the amplitude of the surge was smaller. No GnRH surges were observed in animals treated with cholesterol. Finally, there was an inverse correlation between the response intensity (amplitude of the GnRH/LH surges) and the distance separating implants from cells in the region carrying oestradiol receptors. These results show that the mediobasal hypothalamus is a site of action for the oestradiol-induced preovulatory GnRH surge in the ewe. Immunohistochemical tests should identify the nature of the cells forming the relay for the steroid action.

Recent studies have demonstrated that an important component of the positive feedback response to oestradiol in mammals is an action within the central nervous system to induce a large surge in the secretion of gonadotrophin-releasing hormone (GnRH). This oestradiol-induced neuroendocrine signal for ovulation has been best characterized in ewes. The GnRH surge is high in amplitude; the amount secreted increases on average more than 40 times above the pre-surge baseline value. The initial increment in GnRH secretion precedes or coincides with the onset of the LH surge. The GnRH surge is of extended duration, lasting far longer than the preovulatory LH surge. A molecular variant of GnRH, which is less active biologically than native GnRH, is co-secreted at the time of the surge, but termination of the LH surge cannot be accounted for by a change in biological activity of the secreted GnRH. Generation of the GnRH surge appears to follow a characteristic progressive change in the pattern of GnRH in portal blood. High concentrations of oestradiol initially stimulate the secretion of GnRH between pulses; this is followed by augmentation of both pulsatile and interpulse GnRH release producing the rising limb of the surge. Finally, recent experiments have indicated that the local application of oestradiol to the ventromedial nucleus of the hypothalamus is sufficient to stimulate the GnRH surge, suggesting a key rol for this hypothalamic area in the generation of this neuroendocrine signal for ovulation.

Dose-response relationships have been suggested for the role of estradiol (E2) in the induction of both the LH surge and estrous behavior in the ewe. However, it is not always clear whether it is the amount of E2 or the length of time that E2 is present that is important. Furthermore, in previous studies, the intensity of sexual behavior has rarely been studied quantitatively. Our aims in this work were to analyze in more detail the effects of two injected doses of estradiol benzoate (25 or 50 micrograms) for the induction of both the LH surge and estrous behavior (experiment I) and to dissociate the roles of quantity and duration of presence of E2 as administered by implants (experiment II). Increasing the dose of E2 in both experiment I and experiment II decreased the latency to onset of both the LH surge and the receptivity. The duration of E2 presence marginally affected the latency of both responses and the duration of the LH surge. By contrast, the duration of receptivity depended largely on the duration of E2 presence (experiment II: r = 0.569, P < 0.01). This result explains the dose-duration effect mentioned previously in the literature and found in experiment I. The maximum response increased with dose in both experiment I and experiment II for receptivity and only in experiment I for the LH surge. We conclude that, at estrus, E2 acts in a similar fashion to induce receptive behavior and the LH surge but controls the maximum levels and the duration of these endocrine and behavioral responses differently.

When estrous behavior is induced in ovariectomized ewes by subjecting them to progestagen priming followed by a dose of estrogen large enough to guarantee estrus in all animals, an abnormally long period of estrus in induced, suggesting that the regime of steroid replacement needs modification. Using quantitative tests for proceptivity and receptivity, we studied the patterns of sexual behavior of intact ewes and then attempted to reproduce them in the same animals after they had been ovariectomized. We used various combinations of exogenous estrogen, androgen, and progestagen and compared the behavioral responses with an endocrine response, the preovulatory surge of luteinizing hormone (LH). In intact ewes, sexual behavior and the LH surge were closely synchronized and their characteristics differed slightly between the middle and the end of the breeding season. Proceptive behavior was not greatly affected by the frequency of tests, but the duration of receptivity was significantly reduced by frequent testing. In ovariectomized ewes, we found that: (a) progesterone priming is essential for normal patterns of receptive and proceptive behavior, and for synchronizing the behavioral and endocrine responses to estrogen; (b) androgens do not play a major role in the control of either receptive or proceptive behavior; and (c) the inclusion of a low dose of estrogen with the progestagen in the 'priming' regime improves the responses to estradiol-17 beta. Under these conditions, the timing, intensity and duration of the behavior are very close to those observed in the same ewes when they were intact and cycling spontaneously.

Most of the literature suggests that in sheep as in rodents nervous structures involved in female sexual behaviour are not necessarily identical to those involved in the LH surge. In rodents, oestradiol triggers female sexual behaviour by acting on a restricted area of the mediobasal hypothalamus whereas the concomitant induction of the preovulatory LH surge is at least partially under the control of more anterior structures. The central sites of oestradiol action, however, remained poorly defined in sheep. To provide this definition, 37 ovariectomized ewes were stereotaxically implanted unilaterally or bilaterally with a guide cannula in preoptic area (POA), anterior, mediobasal, lateral, or posterior hypothalamus (AH, MBH, LHT, PH). Experiments were made during the breeding season (Br) and the anoestrous period (An: unilat only) and females were primed with a peripheral treatment of progesterone and a dose of 17 beta-oestradiol subthreshold for both the LH surge and sexual behaviour. Intracranial implants (i.d. = 0.45 mm) of crystalline E2 were lowered 16 h after progesterone removal and left in the brain for 48 h. Whereas POA implants never had any significant effects on either the behaviour or the LH surge, all MBH implants caused receptivity (11 bilat, 5 unilat Br and 5 unilat An). Bilateral MBH implants also induced proceptivity in 9 of 11 ewes and increased the LH levels in 7 of them. These proportions do not differ significantly from those observed after a 25 microgram peripheral injection of E2. Unilateral MBH implants had no significant effect on proceptivity and LH increase but oestrous behaviour was induced by some implants placed laterally to the MBH (25 recept and 3/5 procept).(ABSTRACT TRUNCATED AT 250 WORDS)

Ovariectomized adult Ewes daily treated with I/M injections of testosterone propionate (10 mg/day) or oestradiol benzoate (200 microgram/day) show male-like sexual behaviour and simultaneously a permanent female receptivity. Additional daily treatment with 100 mg of progresterone results in a rapid decrease in male sexual responses both when Ewes are treated with testosterone and with oestradiol. No effect is observed on the female receptivity. Cyproterone acetate (100 mg/day) given to Ewes in addition to daily injection of testosterone propionate (10 mg/day) has effects similar to those of progesterone. These results show that progesterone has antiandrogen and antioestrogen properties and that this hormone administered at high doses is able to inhibit male activity.

All motor patterns of male sexual behaviour can be observed in young lambs from the first days of the life. They considerably increase on weeks 2 to 5 when they decrease dramatically and remain stable up to over 6 months of age. This evolution has no direct relation with that of the physiological events. The adult female has a complete bisexual potentiality. The development of the sexual behaviour during ontogeny appears as a continuous process rather than to be limited to the period of puberty or sexual differentiation.

The effects of treating captive talapoin monkeys acutely (twice daily for 7 days) with naltrexone hydrochloride (0.25 mg 0.5 mg and 1 mg/kg intramuscular injections twice daily), naloxone hydrochloride (0.5 mg/kg IM twice daily) and sulpiride (1.5 mg/kg IM twice daily) was studied in social pairs and singly caged animals. The behaviour of social pairs and endocrine changes in all treated monkeys were monitored before, during and after withdrawal of the course of drug treatment. Naltrexone and naloxone, but not sulpiride, significant increased grooming and grooming invitations while aggressive behaviour, self grooming, scratching and general locomotor activity were unaffected. There was an overall increase in LH, testosterone and cortisol in plasma samples taken 60 mins after opiate receptor blockade. Prolactin was unchanged but increased dramatically in animals treated with sulpiride. No significant endocrine changes were observed to precede the increased grooming behaviour which opiate receptor blockade induced. The behavioural changes reported for this primate support the view that positive affect arising from social bonds may be mediated by cerebral endorphin containing systems.

The re-introduction of rams after a period of separation was used to stimulate LH secretion and induce ovulation in seasonally anovulatory ewes maintained under natural photoperiod. In 2 experiments, the rams were introduced in the morning or the evening to test for diurnal variations in responsiveness to the treatment. In the first experiment, with Romanov ewes, the ram-induced increase in tonic LH secretion was significantly earlier in the ewes treated (N = 6) at 07:30 h (mean +/- s.e.m. delay to first pulse: 20 +/- 6 min) than in those (N = 5) treated at 19:30 h (66 +/- 15 min; P = 0.006). The pulse interval after the ram effect was significantly shorter in ewes that subsequently ovulated (120 +/- 10 min) than in ewes that did not ovulate (288 +/- 108 min; P = 0.043). There was a significant decline in pulse amplitude from 6.7 +/- 1.2 to 3.4 +/- 0.6 ng/ml (both groups combined) after the introduction of rams (P = 0.040). Of the 11 ewes, 7 subsequently ovulated and a preovulatory LH surge was observed in 6 of these 30-36 h after ram introduction. In the second experiment, with seasonally anoestrous Préalpes-du-Sud ewes, the effect of the timing of the introduction of rams on the periovulatory events was tested. The delay to the onsets of oestrus and the LH surge was not affected, but the ovulation rate was higher after ram introduction in the morning (1.42) than in the evening (1.14). In the 12-h period before the introduction of the rams in the first experiment, there was a difference between the groups in the secretion of LH, but the existence of diurnal rhythms in the concentrations of LH or FSH were not confirmed in a later study in which 7 ewes were sampled every 20 min for 36 h. In contrast, there was a distinct diurnal variation in the secretion of prolactin, with the highest values being recorded at night and the lowest around midday (P = 0.025). The rise and fall in prolactin values did not appear to coincide with dawn or dusk.(ABSTRACT TRUNCATED AT 400 WORDS)

Ovariectomized Ewes, treated daily with 100 micrograms of oestradiol benzoate (OB) show simultaneously female and male sexual behaviour. Male sexual behaviour is never seen in intact females. When given simultaneous with OB, progesterone prevents the action of the oestrogen. When given before the start of oestrogen treatment, progesterone also inhibits the effects of OB on male sexual behaviour for several weeks. By contrast, progesterone pretreatment has both inhibitory and facilitatory effect on the induction of female sexual behaviour. At first, it delays the appearance of female behaviour but then increases the response to oestrogen. These results suggest that progesterone could be involved in the dissociation between male and female behaviour normally seen in Sheep.

The effects of sophrology and epidural analgesia on early relationship between the mother and her child were studied on a simple of 190 deliveries. The mothers were observed during and just after delivery. Mothers who had been separated from their child before the end of the observation were excluded from the study. The patients had the choice between epidural analgesia or prenatal care with sophrology. Participation to prenatal courses has statistically a positive effect on the relation between the mother and her child (p less than 0.01). Instead, epidural analgesia and posture have very limited effect on this factor. However, a trend to more interaction is found in multipari and patients who didn't choose epidural analgesia.

Adult ovariectomized ewes, daily injected with testosterone propionate (2 to 22 mg), showed male-like sexual behaviour, never seen in untreated females, but very similar to that in normal rams. After a few days of latency (3 days minimum), this behaviour gradually appeared and increased in frequency until a plateau was reached. The time-course in which the plateau was reached depended on the androgen dose and on previous experience with male sexual behaviour. Some male-like behaviour might have persisted after the end of the treatment. The results have been discussed in terms of possible mechanisms of action on the central nervous system.