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ABSTRACT: For a better understanding of the mechanisms that lead to the preovulatory GnRH/LH surge and estrus behavior, the minimum estradiol (E) requirements (dose and duration) to induce each of these events were determined and compared between two breeds of ewes having either single (Ile de France) or multiple (Romanov) ovulations. The ewes were initially studied during a natural estrus cycle, and were then ovariectomized and run through successive artificial estrus cycles. For these artificial cycles the duration and amplitude of the follucular phase E increase were manipulated by E implants. Under all conditions, the onset of estrus behavior was similar in the two breeds, although its duration was longer in Romanov ewes. While a moderate E signal (6 cm for 12 h) induced an LH surge in 10/10 Ile de France ewes, a larger E signal (12 cm for 12 h) was minimally effective in Romanov ewes (4/10). Additional studies revealed that a small E signal (3 cm for 6 h) induced full estrus behavior in all Romanov ewes but was completely ineffective in Ile de France animals (0/10). Higher doses and mostly longer durations of the E signal (12 cm for 24 h) were required to induce a surge in all the Romanov ewes. These results demonstrate a clear difference in the E requirement for the induction of estrus behavior and the LH surge between breeds of ewes that have different ovulation rates. These data provide compelling evidence that, in one breed, the neuronal systems that regulate both events require different estrogen signals.
Biology of Reproduction 05/2007; 76(4):673-80. · 4.01 Impact Factor
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ABSTRACT: Exposure of anestrous ewes to a ram or its odor results in the activation of the luteinizing hormone (LH) secretion leading to reinstatement of cyclicity in most females. Sexual experience and learning have been suggested as important factors to explain the variability of the female responses. In experiment 1, we compared the behavioral and endocrine responses of four groups of anestrous females that differed in age (young or adult) and previous exposure to males [naive (no exposure) or experienced (courtship behavior for young and numerous mating for adults)]. Age did not seem to affect the LH response to males or their odor. In contrast, sexual experience was a critical factor: the proportion of females exhibiting an LH response to male odor was significantly higher in experienced than in naive ewes. Sexual experience affected the response to male odor, but did not have an effect on responses to the male himself. A second experiment investigated whether the LH response to male odor could result from an associative learning process. Accordingly, we tested the effectiveness of a conditioned stimulus (lavender odor) previously associated with the male, in inducing the endocrine response. The results indicate that the odor of lavender activated LH secretion only in ewes that have been previously exposed to scented males. This demonstrates that ewes are able to learn the association between a neutral odor and their sexual partner.
Chemical Senses 10/2004; 29(7):555-63. · 2.60 Impact Factor
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ABSTRACT: Our aim was to study the role of the olfactory amygdala (medial and cortical nuclei) and the ventromedial nucleus of the hypothalamus (VMN) in the ability of the male odour or live males to induce a release of luteinizing hormone in anoestrus ewes. To achieve this, we temporarily blocked the activity of these structures by localized retrodialysis administration of the anaesthetic lidocaine. The effect of ram odour on the secretion of luteinizing hormone was completely blocked by inactivation of the cortical nucleus of the amygdala. In contrast, inactivation of part of the accessory olfactory system (the medial nucleus of the amygdala or the VMN) had no effect. In the presence of the male, lidocaine never impaired the endocrine response of the ewes. These results show that modulation of reproduction by the sexual partner even through pheromonal cues does not occur via the direct circuit of the accessory system. On the contrary, the cortical nucleus of the amygdala is absolutely necessary for the treatment of and/or the response to the male olfactory signal but this structure can be bypassed when other sensory cues are available.
European Journal of Neuroscience 04/2004; 19(6):1581-90. · 3.63 Impact Factor
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ABSTRACT: We assessed the role of learning in the expression of female sexual behavior and evaluated the relative importance of age versus experience. Two studies were conducted with ovariectomized ewes submitted to steroid treatment that mimicked an estrus cycle. We compared behavioral (experiments 1 and 2), neurochemical (experiment 1), and endocrine (experiment 2) responses of sexually naive young and adult ewes versus sexually experienced adults when exposed to males. In a third study, we compared their performance in an instrumental learning test and the extent to which it was affected by stress. These experiments showed that proceptivity is affected both by age and sexual experience. In experiment 1 only experienced adults were proceptive and displayed an increase in hypothalamic norepinephrine. By the second estrus cycle (experiment 2) naive adults performed similarly to experienced adults but proceptive behavior was still inferior in young ewes. Receptivity was also different between groups but affected more by age than by sexual experience. All ewes mated during the first interaction with a male, although males' latency to ejaculation was shorter with experienced females than naive adults or naive young. Young ewes found food as readily as adults in experiment 3 but were more affected by stress. Together, these experiments show that both experience and age influence sexual activity and that sensitivity to stress may also be involved. This may contribute to the deficient reproductive performance that is often observed in young female mammals.
Hormones and Behavior 04/2004; 45(3):190-200. · 3.87 Impact Factor
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ABSTRACT: Preovulatory GnRH secretion in ewes, measured in portal blood and cerebrospinal fluid, starts at the time of the LH surge, approximately 4 h after the onset of estrous behavior, and lasts as long as receptivity (36-48 h), which is much longer than the LH surge. This study tested the hypothesis that the extended GnRH secretion is involved in the maintenance of receptive behavior, prolonging the initial triggering effect of E2. Ovariectomized ewes were subjected to artificial estrous cycles and infused intracerebroventricularly either with a water soluble GnRH antagonist (Teverelix, Exp 1 and 2) or GnRH (Exp 3 and 4) after preovulatory E2 challenges of various intensity. The GnRH antagonist infused for 20 h (0.5 mg/ml, flow rate 3 microl/min) following a treatment with 2 x 30-mm E2 implants for 24 h (Exp 1) significantly reduced receptivity 36-48 h post E2 compared with vehicle infusion. By contrast, when the GnRH antagonist was infused with E2 implants still present (Exp 2: E2 for 48 h, GnRH antagonist given 24-44 h after E2 insertion, n = 14) receptivity was not affected. Administration of GnRH (0.5 mg/ml, flow rate 3 microl/min) when receptivity began to decline (Exp 3: 30-48 h after a 6-h 2 x 30-mm E2 implants n = 12) resulted in significantly higher receptivity scores at 48 and 52 h post E2 in GnRH treated animals compared with vehicle treated. GnRH infusion of ewes under subthreshold E2 treatment (Exp 4: GnRH 6-24 h after implantation of 1 x 30-mm E2 for 3 h, n = 12 in a cross-over design) significantly increased their receptivity compared with vehicle administration at 18 and 24 h post E2 insertion, but receptivity remained lower than when induced by high doses of E2. Our results demonstrate for the first time that GnRH is involved in the control of receptivity in a ruminant species and suggest that in the cycling ewe the sustained preovulatory GnRH secretion plays a physiological role in extending the duration of estrous behavior. They also indicate that it is possible to dissociate a direct effect of E2 on estrous behavior from its effect via stimulation of GnRH secretion.
Endocrinology 02/2002; 143(1):139-45. · 4.46 Impact Factor
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ABSTRACT: In sheep, melatonin secretion occurs rapidly after the onset of darkness, but the interval fluctuates according to different authors. The aim of this study was to determine this interval in sheep subjected to a long or a short photoperiod. Blood samples were taken at the right jugular vein every 100 s for 1 hr after the onset of darkness. The experiment was repeated on three consecutive days either in long (LD 16:8) or in short photoperiod (LD 8:16) on the same animals. Melatonin secretion was found to begin within 11 min under long photoperiod and 20 min under short period. It can be concluded that the onset of melatonin secretion depends on the duration of the photoperiod.
Journal of Pineal Research 09/1999; 27(1):1-8. · 5.79 Impact Factor
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ABSTRACT: In mammals, the photoperiodic information, received by the retina, is transmitted to the pineal gland. In both organs, melatonin is produced and functions as a neurohormone giving temporal information to the organism. A four-step enzymatic pathway, involving in particular the tryptophan hydroxylase (TPOH), the rate-limiting enzyme in serotonin synthesis, and the serotonin N-acetyltransferase (NAT) that converts serotonin to N-acetylserotonin, allows the synthesis of melatonin. Many studies on melatonin synthesis modulation have focused on the enzyme NAT, but the regulation of TPOH is less well understood. We report here a quantitative study, using a reverse transcription polymerase chain reaction (RT-PCR) analysis, of the nycthemeral expression of TPOH and NAT mRNAs in the ovine retina and pineal gland. In both organs, we show a nocturnal increase in mRNA levels of the two enzymes. suggesting a role of transcriptional mechanisms in the regulation of melatonin synthesis. However, the amplitude of the observed increase in TPOH and NAT mRNAs expression can not entirely explain the 7-fold nocturnal increase in the plasma melatonin level. Our results suggest that, in the sheep, post-transcriptional mechanisms might also be involved in the day/night modulation of melatonin production.
Journal of Pineal Research 06/1999; 26(4):193-203. · 5.79 Impact Factor
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Advances in experimental medicine and biology 02/1999; 460:133-5. · 1.09 Impact Factor
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ABSTRACT: Previous data have demonstrated that a single 1-hr light pulse at night affects the secretion of melatonin in the ram if it was given at the appropriate time. This paper reports the effect on melatonin secretion of a 1-hr light pulse given at two different times at night to two groups of rams kept in constant darkness the day following light application. It appears that the animals were able to remember the light pulse if it was given 12 hr but not 9 hr after the lights were turned off. This memory could possibly be stored in the suprachiasmatic nucleus as reported recently in the rat.
Journal of Pineal Research 12/1996; 21(4):218-24. · 5.79 Impact Factor
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ABSTRACT: Previous data have demonstrated that a single 1-hr light pulse at night affects the secretion of melatonin in the ram if it was given at the appropriate time. This paper reports the effect on melatonin secretion of a 1 -hr light pulse given at two different times at night to two groups of rams kept in constant darkness the day following light application. It appears that the animals were able to remember the light pulse if it was given 12 hr but not 9 hr after the lights were turned off. This memory could possibly be stored in the suprachiasmatic nucleus as reported recently in the rat.
Journal of Pineal Research 10/1996; 21(4):218 - 224. · 5.79 Impact Factor
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ABSTRACT: This paper describes the development of a new technique to measure melatonin contents in the pineal gland of moving sheep: the microdialysis. A dialysis probe was used to collect extracellular fluid in the sheep pineal gland, but also to inject directly into it different drugs such as isoproterenol at a very low concentration. The probe was implanted the day before the beginning of the experiment in order to obtain low levels of melatonin. This technique makes it possible to measure melatonin in the dialysate and plasma of rams submitted to 8L:16D. No melatonin either in the dialysate or in the plasma was found during the light phase. Shortly after lighting off, the melatonin concentration increased in the dialysate and plasma and remained stable during the dark phase. Melatonin concentrations began to decrease before lighting on and no detectable levels were found during the following light phase. The secretion of melatonin is, at least, under adrenergic regulation. Local infusion of isoproterenol (90 microliters at 10(-6) M), an agonist of beta adrenergic receptor, through the probe, increased melatonin levels during 2 h, even when infusions were repeated 3 times. This demonstrates the presence of beta adrenergic receptors. The technique presented in this paper could be of considerable interest for studying sheep pineal gland and its main secretion, melatonin, for example during diurnal rhythms or for studying its regulation.
Journal of Neuroendocrinology 06/1996; 8(5):387-94. · 3.14 Impact Factor
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ABSTRACT: In the pineal organ of the pike (Esox lucius, teleost), the rhythmic production of melatonin by the photoreceptor cells is governed by a population of endogenous circadian oscillators, synchronized and entrained by the light/dark (L/D) cycle. Production of melatonin is inhibited by light and highly increased in the dark. In the present study, isolated and superfused pike pineals were exposed to a 24-hour temperature cycle of high (10 degrees C) or low (4 degrees C) amplitude, either under L/D, or under constant darkness. Under L/D, photoperiod is the dominant entraining stimulus for the melatonin secretion rhythm. It was high during the dark phase and low during the light phase, either under cold light/warm dark or under warm light/cold dark conditions. Under a warm light/cold dark cycle, the amplitude of the melatonin rhythm was reduced. In pineals cultured at 10 degrees C, a 20 degrees C temperature pulse potentiated or reduced the night-induced rise in melatonin production when applied, during the dark or during the preceding light phase, respectively. Under constant darkness, high- or low-amplitude temperature cycles could synchronize the rhythmic production of melatonin, which peaked with the high temperature. However, the shape of the oscillation could appear modified under warm subjective-L/cold subjective-D, depending on the experimental conditions. Finally, the rhythmic release of melatonin synchronized by a temperature cycle under constant darkness was no longer observed after removal of the external zeitgeber. The present study provides direct evidence that the pineal acts as a photothermotransducer.
Neuroendocrinology 12/1994; 60(5):535-43. · 2.38 Impact Factor
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ABSTRACT: The present study describes the patterns of melatonin production in the mule (Equus asinus x Equus caballus). Blood was sampled hourly for 24 h from eight mule mares in spring and fall. The data obtained show the presence of a circadian rhythm of production of melatonin, with highest values during the dark phase both in spring and fall. In fall the nightly rise of melatonin production begins earlier in the dark phase and reaches higher quantitative levels than in spring. The morning decline of melatonin production is similar in the two seasons. Maximal levels of nightly melatonin production in the mule are about 10 x higher than those described in the horse. The results reported here indicate the persistence of brain structures able to receive and transduce environmental signals in the mule, a genetically sterile mammalian hybrid.
Journal of Pineal Research 05/1991; 10(3):130-5. · 5.79 Impact Factor
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ABSTRACT: The objective of this study was to investigate the entrainment of melatonin rhythms in rams using symmetrical light-dark cycles of different period length. Five groups of six Ile de France rams were kept in 12L:12D for 7 weeks and then (i) 12L:12D, (ii) 11L:11D, (iii) 10L:10D, (iv) 13L:13D and (v) 14L:14D for a further 3 weeks. Environmental factors other than the light dark cycle were not controlled. The onset and offset of the plasma melatonin rhythm in DD after 3 weeks of the respective light treatments was assessed for 48 hr, immediately after transferring to DD. The duration of secretion in DD was positively related to the length of the previous dark phase. The phase of the melatonin rhythm with respect to the anticipated dark phase suggested entrainment with no change in phase-relationship to the zeitgeber by 12L:12D and 13L:13D. Entrainment with a phase-delay or a phase-advance was apparent after 11L:11D and 14L:14D, but the individual rhythms were not all synchronized with respect to each other after 10L:10D. Activity recordings for 2-3-week periods during 12L:12D, 10L:10D and 14L:14D all showed a major 24-hr component at all times, with activity during the light phase in 12L:12D. It appears that melatonin may be readily desynchronized from overt activity-rest cycles in sheep. The upper and lower entrainment limits are probably greater than 28 hr and close to 20 hr cycles, respectively.
Chronobiology International 02/1989; 6(4):329-39. · 4.03 Impact Factor
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ABSTRACT: Dopamine has been implicated in the control of sexual behavior, 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 behavior 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 (100ng/ml) infused for 6h just before E2 hastened the onset of oestrus behavior and the luteinizing hormone surge, whereas the same treatment given 6 to 12h or 18 to 21h 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 (100ng/ml) were infused into the MBH via microdialysis probes for 11h in the absence of E2 adminsitration. 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 of 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
