Hair from sexually active bucks strongly activates olfactory sensory inputs but fails to trigger early first ovulation in prepubescent does

Early exposure of does to sexually active bucks triggers early puberty onset correlating with neuroendocrine changes. However, the sensory pathways that are stimulated by the male are still unknown. Here, we assessed whether responses to olfactory stimuli are modulated by social experience (exposure to males or not) and/or endocrine status (prepubescent or pubescent). We used a calcium imaging approach on goat sensory cells from the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). For both cell types, we observed robust responses to active male hair in females under three physiological conditions: prepubescent females isolated from males (ISOL PrePub), pubescent females exposed to males (INT Pub) and isolated females (ISOL Pub). Response analysis showed overall greater proportion of responses to buck hair in ISOL PrePub. We hypothesized that females would be more responsive to active buck hair during the prepubertal period, with numerous responses perhaps originating from immature neurons. We also observed a greater proportion of mature olfactory neurons in the MOE and VNO of INT Pub females suggesting that male exposure can induce plastic changes on olfactory cell function and organization. To determine whether stimulation by male odor can advance puberty, we exposed prepubescent does to active buck hair (ODOR). In both ODOR and females isolated from males (ISOL) groups, puberty was reached one month after females exposed to intact bucks (INT), suggesting that olfactory stimulation is not sufficient to trigger puberty.

Maintenance of permanent sexual activity throughout the year in seasonal bucks using short photoperiodic cycles in open barns

Seasonality of reproductive activity in rams and bucks is the major constraint in temperate and subtropical zones. Rapid alternation between 1 month of short days and 1 month of long days (LD) over three years in lightproof buildings eliminates this seasonality. We examined if this would also work in open barns, using only supplementary light. Over two years, one group of bucks (n = 7) was subjected to alternate 1 month of LD and 1 month of permanent light (LD-LL) and another group (n = 7) to alternate 1 month of LD and 1 month of natural light (LD-NL). A simultaneous control group, used for both experiments (CG1, n = 6; CG2, n = 6), remained under natural photoperiod. BW, testis weight (TW), plasma testosterone (T) and cortisol (C) were evaluated in all bucks. CG1 and CG2 bucks showed identical dramatic seasonal variations in BW (stable or decreasing in summer), TW (from 85 ± 12 g in February to 127 ± 7 g in July) and T (from 2.7 ± 1.2 ng/mL in January-April to 24.3 ± 3.2 ng/mL in June-October). By contrast, BW of LD-LL and LD-NL bucks increased regularly during the experiment. From 5 and 9 months after the experiment onset, LD-LL and LD-NL bucks, respectively, maintained constant TW of 115 ± 5 g until the experiment end. After the first 3 months <5 ng/mL, T of LD-LL bucks remained constant (5-10 ng/mL) until the experiment end. By contrast, T of LD-NL bucks showed four periods of low (<5 ng/mL) and two periods of high concentrations (18.1 ± 2.6 and 11.9 ± 3.4 ng/mL). Plasma C remained low (5-8 ng/mL) and did not change with group or light treatment. These results show for the first time in any seasonal photoperiodic species that it is possible to maintain the sexual activity of males all year round in open buildings using alternating periods of LD and LL. By contrast, return to NL instead of LL every other month does not prevent seasonality in T concentration. These results raise interesting questions about the photoperiodic control of neuroendocrine regulation of seasonal sexual activity and suggest that these treatments can be used to manage males in open barns in farms and in artificial insemination centres. (Spanish and French versions of the full text are available as Supplementary Materials S1 and S2).

Male-induced early puberty correlates with the maturation of arcuate nucleus kisspeptin neurons in does

In goats, early exposure of spring-born females to sexually active bucks induces an early puberty onset assessed by the first ovulation. This effect is found when females are continuously exposed well before the male breeding season starting in September. The first aim of this study was to evaluate whether a shortened exposure of females to males could also lead to early puberty. We assessed the onset of puberty in Alpine does isolated from bucks (ISOL), exposed to wethers (CAS), exposed to intact bucks from the end of June (INT1), or mid-August (INT2). Intact bucks became sexually active in mid-September. At the beginning of October, 100% of INT1 and 90% of INT2 exposed does ovulated, in contrast to the ISOL (0%) and CAS (20%) groups. This demonstrated that contact with males that become sexually active is the main factor prompting precocious puberty in females. Furthermore, a reduced male exposure during a short window before the breeding season is sufficient to induce this phenomenon. The second aim was to investigate the neuroendocrine changes induced by male exposure. We found a significant increase in kisspeptin immunoreactivity (fiber density and number of cell bodies) in the caudal part of the arcuate nucleus of INT1 and INT2 exposed females. Thus, our results suggest that sensory stimuli from sexually active bucks (e.g., chemosignals) may trigger an early maturation of the ARC kisspeptin neuronal network leading to gonadotropin-releasing hormone secretion and first ovulation.

Population density does not affect seasonal regulation of reproductive physiology in male water voles

Most small rodent species display cyclic fluctuations in their population density. The mechanisms behind these cyclical variations are not yet clearly understood. Density-dependent effects on reproductive function could affect these population variations. The fossorial water vole ecotype, Arvicola terrestris, exhibits multi-year cyclical dynamics with outbreak peaks. Here, we monitored different water vole populations over 3 years, in spring and autumn, to evaluate whether population density is related to male reproductive physiology. Our results show an effect of season and inter-annual factors on testis mass, plasmatic testosterone level, and androgen-dependent seminal vesicle mass. By contrast, population density does not affect any of these parameters, suggesting a lack of modulation of population dynamics by population density.

Sexually active male goats stimulate the endocrine and sexual activities of other males in seasonal sexual rest through the "buck-to-buck effect"

Male goats rendered sexually active by exposure to a photoperiodic treatment are more efficient than untreated goats in stimulating LH secretion and ovulation in seasonally anestrous goats. This phenomenon is called the "male effect." Here, we determined whether sexually active bucks are able to stimulate the endocrine and sexual activities of other bucks in seasonal sexual rest through the phenomenon that we called the "buck-to-buck effect." We used bucks rendered sexually active (SA) during sexual rest by exposure to 2.5 mo of artificial long days (16 h of light per d) and untreated, sexually inactive (SI) bucks. In Experiment 1, we determined the short-term (21 d) LH and testosterone responses of sexually inactive bucks joined with a SA or SI buck. In Experiment 2, we determined the long-term (60 d) testosterone and sexual behavior responses of sexually inactive bucks joined with 2 SA or SI bucks. In Experiment 3, we determined the efficacy of bucks initially exposed to the buck-to-buck effect, the SABB bucks, to thereafter induce a "classical" male effect in seasonally anestrous goats. In Experiments 1 and 2, there was an interaction between time and groups in LH and testosterone plasma concentrations (P < 0.01). In Experiment 1, plasma LH concentrations were greater in bucks joined with a SA buck than in those joined with an SI buck (P < 0.05). In Experiments 1 and 2, testosterone concentrations were greater in bucks joined with SA bucks than in those joined with SI bucks (P < 0.05). In addition, in Experiment 2, the sexually inactive bucks joined with SA bucks displayed more nudging than those joined with SI bucks (P < 0.001). In Experiment 3, kidding rates did not differ between females joined with SA (34 of 40: 85%) or SABB bucks (32 of 40: 80%; P > 0.05). We concluded that the endocrine and sexual activities of bucks during sexual rest can be stimulated by SA bucks. In addition, SABB bucks are able to stimulate the reproductive activity of seasonally anestrous goats.

Photoperiod is involved in the regulation of seasonal breeding in male water voles (Arvicola terrestris)

Mammals living at temperate latitudes typically display annual cyclicity in their reproductive activity: births are synchronized when environmental conditions are most favorable. In a majority of these species, day length is the main proximate factor used to anticipate seasonal changes and to adapt physiology. The brain integrates this photoperiodic signal through key hypothalamic structures, which regulate the reproductive axis. In this context, our study aimed to characterize regulations that occur along the hypothalamo-pituitary-gonadal (HPG) axis in male fossorial water voles (Arvicola terrestris, also known as Arvicola amphibius) throughout the year and to further probe the implication of photoperiod in these seasonal regulations. Our monthly field monitoring showed dramatic seasonal changes in the morphology and activity of reproductive organs, as well as in the androgen-dependent lateral scent glands. Moreover, our data uncovered seasonal variations at the hypothalamic level. During the breeding season, kisspeptin expression in the arcuate nucleus (ARC) decreases, while RFRP3 expression in the dorsomedial hypothalamic nucleus (DMH) increases. Our follow-up laboratory study revealed activation of the reproductive axis and confirmed a decrease in kisspeptin expression in males exposed to a long photoperiod (summer condition) compared with those maintained under a short photoperiod (winter condition) that retain all features reminiscent of sexual inhibition. Altogether, our study characterizes neuroendocrine and anatomical markers of seasonal reproductive rhythmicity in male water voles and further suggests that these seasonal changes are strongly impacted by photoperiod.

Field study reveals morphological and neuroendocrine correlates of seasonal breeding in female water voles, Arvicola terrestris

Seasonally breeding mammals display timely physiological switches between reproductive activity and sexual rest, which ensure synchronisation of births at the most favourable time of the year. These switches correlate with seasonal changes along the hypothalamo-pituitary-gonadal axis, but they are primarily orchestrated at the hypothalamic level through environmental control of KISS1-dependent GnRH release. Our field study shows that births of fossorial water voles, Arvicola terrestris, are concentrated between March and October, which indicates the existence of an annual reproductive cycle in this species. Monthly field monitoring for over a year further reveals dramatic seasonal changes in the morphology of the ovary, uterus and lateral scent glands, which correlate with the reproductive status. Finally, we demonstrate seasonal variation in kisspeptin expression within the hypothalamic arcuate nucleus. Altogether, this study demonstrates a marked rhythm of seasonal breeding in the water vole and we speculate that this is governed by seasonal changes in photoperiod.

Review: Managing sheep and goats for sustainable high yield production

This review discusses the most relevant aspects of nutritional, reproductive and health management, the three pillars of flock efficiency, production and sustainability regarding the intensification of production in sheep and goats. In small ruminants, reproductive management is dependent on seasonality, which in turn depends on breed and latitude. Nutrition represents the major cost for flocks and greatly affects their health, the quality of their products and their environmental impact. High-yielding sheep and goats have very high requirements and dietary intake, requiring nutrient-dense diets and sophisticated nutritional management that should always consider the strong interrelationships among nutrition, immunity, health, reproduction, housing and farm management. The reproductive pattern is to a great extent assisted by out-of-season breeding, facilitating genetic improvement schemes, and more recently by advanced reproductive technologies. Heath management aims to control or eradicate economic and zoonotic diseases, ensuring animal health and welfare, food safety and low ecosystem and environmental impacts in relation to chemical residues and pathogen circulation. In highly producing systems, nutrition, genetic and hazard factors assume a complex interrelationship. Genomic and management improvement research and technological innovation are the keys to sustain sheep and goat production in the future.

Nutritional supplementation improves the sexual response of bucks exposed to long days in semi-extensive management and their ability to stimulate reproduction in goats

In confined management systems, well-nourished bucks rendered sexually active by exposure to long days are efficient in fertilizing out-of-season goats. However, underfeeding is common in semi-extensive management systems and may reduce the reproductive efficiency of bucks. The objective of the present study was to determine whether nutritional supplementation improved the sexual activity of bucks submitted to long days in semi-extensive management systems and their ability to stimulate the reproduction of goats in semi-extensive or confined conditions. In experiment 1, three groups of bucks were placed in different flocks and grazed daily with females for 7 h. Each day after grazing, males were separated from females and moved into open pens. One group did not receive any treatment (control group; n = 6). Two other groups were submitted to artificially long days from 15 November to 15 January. From 16 January, one group did not receive nutritional supplementation (long-day group; n = 5), whereas bucks from the other group each received 600 g of a commercial concentrate (long-day+supplementation group; n = 5). The fourth group was kept in confined conditions, exposed to long days and fed alfalfa hay (long-day confined group; n = 6). On 26 March, anovulatory goats from other flocks were assigned to four groups (n = 27 each) and confined separately in open pens. Three bucks of each group were housed with the females. Pregnancy rates were greater in the goats housed with the long-day group than those housed with the control group (P < 0.01). However, pregnancy rates did not differ between the long-day confined group (89%) and long-day+supplementation group (70%; P = 0.09), but these rates were greater than those from the long-day (37%) and control groups (0%; P < 0.05). In experiment 2, two groups of males (n = 3 each) were incorporated into two flocks under semi-extensive management and grazed daily with females for 7 h. One group of males did not receive any treatment (control group). The other group was submitted to long days and nutritional supplementation as in experiment 1 (long-day+supplementation group). Males remained with females during the whole study. The pregnancy rate was greater in the goats joined by males of the long-day+supplementation group (78%) than in those from the control group (0%; P < 0.001). We conclude that long days and nutritional supplementation improve the ability of bucks kept in semi-extensive management to stimulate reproduction of out-of-season goats in confined or semi-extensive management systems.

Is it time to reconsider the relative weight of sociosexual relationships compared with photoperiod in the control of reproduction of small ruminant females?

In goats and sheep from the temperate and subtropical latitudes, the breeding season lasts from early autumn to late winter, whereas the anestrous season lasts from late winter to late summer. In prepubertal or postpartum females, the duration of the quiescent period depends mainly on the season of parturition and of nursing duration. In both situations, the ovulatory activity starts only during the breeding season. Photoperiod has been generally considered as a major regulator of all these periods of reproductive activity/inactivity in female sheep and goats (ie puberty, seasonal anestrus, postpartum anestrus). In particular, regarding seasonal anestrus, the sociosexual interactions between males and females have been considered to have only a modulatory role, limited to few weeks preceding the onset or after the offset of the breeding season. Nonetheless, we recently showed that the use of sexually active males plays a crucial role to trigger ovulatory and estrous activities during the anestrous season and also in prepubertal and postpartum females. In fact, in females exposed to sexually active males, puberty is strikingly advanced in comparison with females exposed to sexually inactive castrated males or to isolated females (6 mo vs 7.5 mo). Most females (>85%) exposed during the anestrous season to sexually active males ovulated, whereas a low proportion of them ovulated when in contact with sexually inactive males (<10%). Interestingly, the presence of these sexually active males allows females to ovulate all the year round and prevents the seasonal decrease of LH plasma concentrations in ovariectomized females treated with an estradiol implant. Finally, the presence of sexually active males triggers ovulation in postpartum anestrous females nursing their offspring. All these findings show that sexually active males can play an important role to reduce anestrous periods. We need, therefore, to reconsider the relative weight of sociosexual relationships, compared with photoperiod, in the management of reproduction of goat does and ewes.

Light-induced sexually active rams provoke LH preovulatory surges and enhances LH concentrations in ewes after progestagen treatment

The effect of the introduction of sexually active rams in spring on LH secretion in ewes after progestagen treatment has been studied. Two rams were induced into a sexually active state by exposure to 2 months of long days (16 h of light/d) from 1 January (SAR), and another 2 rams were exposed to the natural photoperiod, so that they were not sexually activated in spring (control; C). At the end of the long-day period, rams were returned to natural photoperiod conditions. Fifteen ewes synchronized in estrus by intravaginal sponges were assigned to three groups at sponge withdrawal (hour 0): SAR (n = 5), exposed to SAR rams; C (n = 5), exposed to C rams, and ISO (n = 5), kept isolated from rams. Twenty-four hours after pessary removal (hour 0), rams were introduced into the SAR and C groups. Three SAR ewes presented preovulatory LH surges; the proportion was significantly (P < 0.05) higher in this group (3/5) than in the others (C: 0/5, ISO: 0/5). SAR introduction induced a more marked (P < 0.05) increase in mean LH plasma concentrations (before rams: 1.34 ± 0.19; after rams: 6.94 ± 2.66 ng/ml) than C (before: 0.96 ± 0.29; after: 3.60 ± 1.44) or ISO (before: 1.26 ± 0.42; after: 2.14 ± 1.36) groups, and significantly (P < 0.05) higher plasma LH levels after ram introduction. In conclusion, only light-treated sexually activated rams induced LH preovulatory surges in ewes in the seasonal anestrus, when ewes are synchronized with progestagen treatment in the absence of eCG.

Male effect using photostimulated bucks and nutritional supplementation advance puberty in goats under semi-extensive management

Well-nourished spring-born female goats reach puberty in the autumn of the same year. Contrastingly, undernourished spring-born females reach puberty in the autumn of the following year. Therefore, in this study, we reared female goats (undernourished) under semi-extensive management and determined whether the introduction of photostimulated, sexually active males, advances puberty in these females, and whether nutritional supplementation increases the proportion of kidding females. Goats were born on March 30 and weaned at 2 months of age. Then, they grazed natural vegetation from 10:00 to 18:00 each day. Starting in December, two groups did not receive feed supplementation after grazing, whereas two other groups received 600 g daily supplements of a commercial concentrate. In April, one non-supplemented (n = 10) and other supplemented groups (n = 11) were moved indoors and kept in separate pens, where they were joined with sexually active bucks (n = 1 per group). Males were rotated daily between groups for 7 days. Other non-supplemented (n = 8) and supplemented groups (n = 11) were not joined with males. Most of the female goats under study reached puberty (70-100%). However, in supplemented and non-supplemented groups joined with males, puberty commenced much earlier (April) than in those non-exposed to males (September) (P < 0.001). The proportion of pregnant goats did not differ between groups joined with males (P > 0.05), but the proportion of goats that kidded was higher in supplemented (7/11) than in non-supplemented goats (2/10) (P < 0.05). In conclusion, in spring-born goats, the male effect using sexually active males advanced puberty, and nutritional supplementation increased the proportion of kidding goats in females reared under semi-extensive management.

In vivo magnetic resonance imaging reveals the effect of gonadal hormones on morphological and functional brain sexual dimorphisms in adult sheep

Sex differences in the brain and behavior are produced by the perinatal action of testosterone, which is converted into estradiol by the enzyme aromatase in the brain. Although magnetic resonance imaging (MRI) has been widely used in humans to study these differences, the use of animal models, where hormonal status can be properly manipulated, is necessary to explore the mechanisms involved. We used sheep, a recognized model in the field of neuroendocrinology, to assess brain morphological and functional sex differences and their regulation by adult gonadal hormones. To this end, we performed voxel-based morphometry and a resting-state functional MRI approach to assess sex differences in gonadally intact animals. We demonstrated significant sex differences in gray matter concentration (GMC) at the level of the gonadotropic axis, i.e., not only within the hypothalamus and pituitary but also within the hippocampus and the amygdala of intact animals. We then performed the same analysis one month after gonadectomy and found that some of these differences were reduced, especially in the hypothalamus and amygdala. By contrast, we found few differences in the organization of the functional connectome between males and females either before or after gonadectomy. As a whole, our study identifies brain regions that are sexually dimorphic in the sheep brain at the resolution of the MRI and highlights the role of gonadal hormones in the maintenance of these differences.

Continuous presence of females in estrus does not prevent seasonal inhibition of LH and androgen concentrations in bucks

In male goats, being in permanent visual contact with females in estrus does not prevent seasonal variation in certain endocrine hormone levels and sexual activities. In this study, we tested whether continuous and full contact with females in estrus prevented seasonal endocrinological variation in bucks. In 1 experiment (Exp. 1), we verified that the sudden introduction of goats in estrus increased the plasma concentrations of androgen in bucks during the nonbreeding season under our experimental conditions. In another experiment (Exp. 2), we tested the ability of estrous goats to prevent seasonal inhibition of LH and androgen secretions in bucks kept in permanent and full contact with them. In Exp. 1, 3 groups of bucks (n = 5 in each group) were isolated from females from the months of July to January. On January 27, one group continued being isolated from females; a second group was exposed to ovariectomized, untreated goats; and a third group was exposed to ovariectomized goats with induced estrus. Plasma androgen concentrations were determined every 2 h from 8 h before to 8 h after the introduction of females. The introduction of estrus-induced goats significantly increased androgen concentrations, which were higher than in the isolated bucks, as well as in those exposed to untreated goats (P < 0.05). In Exp. 2 (n = 5 per group), one group of bucks was isolated from females from October to July, whereas two other groups remained in contact with ovariectomized goats, either untreated or regularly induced to estrus. In the three groups of bucks, plasma concentrations of LH were determined once during the months of October, February, March, and June, whereas androgen concentrations were determined weekly from October to July. The mean plasma LH and androgen concentrations were low and did not differ among the groups of bucks during the normal seasonal period of sexual inactivity (P > 0.05). We conclude that full contact and sexual interactions with estrus-induced goats failed to stop the seasonality of LH and androgen plasma concentrations of bucks, although bucks could respond to the introduction of females by acute increases in plasma LH and androgen.

Highly precocious activation of reproductive function in autumn-born goats (Capra hircus) by exposure to sexually active bucks

Goats are seasonal breeders with the main cue controlling the timing of breeding season being photoperiod. Hence, the season of birth impacts puberty onset: spring-born goats reach puberty in autumn, at 7 mo of age, whereas autumn-born goats reach puberty at 1 yr during the next reproductive season. The aim of this study was to determine whether exposure of autumn-born young females to sexually active males could counteract the delay in puberty onset observed in autumn-born goats. Females exposed to sexually active males (n = 8) reached puberty earlier than isolated females (n = 8), with exposed females ovulating at a mean age of 3.5 mo. To our knowledge, such precocious puberty onset obtained through social stimulation has never been described in the literature. Moreover, those exposed females exhibited estrus behavior for most ovulations. Our results indicate that in goats born out of season, exposure to sexually active bucks is a really efficient approach to induce early puberty, suggesting that social interactions could have a crucial impact on the regulation of pubertal transition.

Light-induced sexually active rams prevent the seasonal inhibition of luteinizing-hormone in ovariectomized estradiol-implanted ewes

The effect of the continuous presence of sexually active Rasa Aragonesa rams on the plasma luteinizing-hormone (LH) concentrations of ewes was studied from November to May. Light-treated rams were rendered sexually active (SA rams) by exposure to 2 months of artificially long days (16 h light/8 h dark) in one of two groups from either 1 November (SAR1, n = 3) or 1 December (SAR2, n = 3). Rams (n = 6) in a Control group were kept under the natural photoperiod. Thirty ewes were ovariectomized in September and implanted with a subcutaneous implant (l = 15 mm) that contained estradiol-17β. One group of ewes (SAR; n = 10) was housed with control rams from 1 October to 15 February before being housed with SAR1 rams from 16 February to 31 March, and with SAR2 rams from 1 April to 31 May. A second group of ewes (C; n = 10) remained with control rams throughout the experiment, and a third group was kept isolated from rams throughout the experiment (ISO; n = 10). Blood samples were collected weekly from November to May, and plasma LH concentrations were measured. In the breeding season (November-February), plasma LH concentrations of ewes did not differ significantly between groups (SAR: 2.00 ± 0.34; C: 1.88 ± 0.16; ISO: 1.67 ± 0.51 ng/ml). From March to May (seasonal anestrus), however, LH plasma concentrations decreased in the C and ISO groups (1.30 ± 0.20 and 0.48 ± 0.04 ng/ml, respectively), but remained at the same level as in the breeding season in the SAR group (2.30 ± 0.17 ng/ml; P < 0.001). Significant differences (P < 0.01) between groups were observed from March onwards: LH concentrations were highest in SAR ewes (P < 0.001) and lowest in the ISO ewes. In conclusion, the continuous presence of sexually active rams prevented the seasonal decrease in plasma LH concentrations, probably by preventing the seasonal negative feedback of estradiol on LH secretion.

Progesterone doses of 5, 3 or 1 mg do not prevent short ovulatory cycles in goats exposed to photo-stimulated bucks

The aim of this study was to determine whether lower doses than 25 mg of progesterone reduce the frequency of short ovulatory cycles in seasonal anestrous goats exposed to sexually active bucks. Females from the control group were given an im dose of 2 mL olive oil (n = 9). Females from the experimental groups were given an im dose of 1 mg (n = 15), 3 mg (n = 16), 5 mg (n = 15) or 25 mg (n = 16) of progesterone diluted in 2 mL olive oil, 48 h prior exposition to bucks (n = 1 per group). Males were daily switched among groups, and they remained with goats during 21 days. The proportion of goats that ovulated was high (≥87%), and was not different among groups (P > 0.05). In contrast, the proportion of goats that displayed short ovulatory cycles differed among groups (P < 0.05). Indeed, the proportion of goats displaying short ovulatory cycles was lower in those treated with 25 mg (12%) than in those from the control (78%), 1 mg (85%), 3 mg (50%), or 5 mg (71%) groups (P < 0.05), but there were no differences among these last four groups (P > 0.05). Finally, the percentage of kidding females (≥40%) and the number of kids born per female (≥1.4) did not differ among groups (P > 0.05). In conclusion, an im dose of 25 mg of progesterone was more effective than 5, 3 or 1 mg to avoid the short ovulatory cycles in seasonal anestrous goats exposed to the male effect.

Sexually active bucks are a critical social cue that activates the gonadotrope axis and early puberty onset in does

In rodents, early exposure to adult male is well known to induce an early puberty in females (Vandenbergh effect). This phenomenon has been less studied in other mammals. In goats, despite our extensive knowledge about the "male-effect" phenomenon in adults (i.e. ovulation induced by the introduction of the male during the anestrous), there are few data on the consequences of an early exposure of females to males. Here, we evaluated the puberty onset of young alpine goats when raised since weaning with intact bucks (INT), with castrated bucks (CAS) or isolated from bucks (ISOL). The INT group had the first ovulation 1.5 month before the two other groups. Despite the earlier puberty the INT group of females had normal and regular ovarian cycles. Morphological study of the genital tract showed that at 6 months, uterus of INT goats was 40% heavier than CAS and ISOL goats. Moreover, INT females had a myometrium significantly thicker and INT was the only group having corpora lutea. In our study, INT females were pubescent in the month following the entry of bucks into the breeding season, suggesting that only sexually active bucks provide the signal responsible for puberty acceleration. By removing direct contact with the bucks, we showed that somatosensory interactions were dispensable for an early puberty induction. Finally, no difference in the GnRH network (fiber density and number of synaptic appositions) can be detected between pubescent and non-pubescent females, suggesting that the male stimulations triggering puberty onset act probably on upstream neuronal networks, potentially on kisspeptin neurons.

Sexually active bucks counterbalance the seasonal negative feedback of estradiol on LH in ovariectomized goats

We showed previously that the permanent presence of bucks rendered sexually active by photoperiodic treatments, thereafter called photostimulated bucks, prevents the occurrence of seasonal anovulation; also, the introduction of these sexually active bucks induces ovulations during seasonal anestrus. Here, we studied the response of ovariectomized goats bearing 12-mm subcutaneous implants filled or not with estradiol to sexually active males to determine (1) whether the permanent presence of such bucks prevents the decrease of LH despite the presence of a negative feedback by estradiol mimicking that of seasonal anestrus (experiment 1) and (2) whether the introduction of photostimulated bucks increases the plasma LH concentrations in spite of this negative feedback (experiment 2). In experiment 1, one group of goats remained in contact with sexually active bucks, whereas the other group remained in contact with control bucks. Plasma LH concentrations were high and did not differ with time or between groups of females from November to February (P > 0.05), when both types of bucks were sexually active. Afterward, in goats in contact with control and sexually inactive bucks, LH concentrations decreased from March (P ≤ 0.01) and remained low until May, whereas LH levels remained high from March to May in goats in contact with the photostimulated bucks (P > 0.05). In experiment 2, 2 groups of females bearing empty subcutaneous implants, and 2 groups of goats bearing subcutaneous implants filled with estradiol, were exposed to control or photostimulated bucks. Plasma LH concentrations did not increase in goats bearing empty implants, when exposed to control or photostimulated bucks (from 2.01 ± 0.26 to 1.98 ± 0.31 ng/mL, and from 2.45 ± 0.29 to 2.42 ± 0.21 ng/mL respectively; P > 0.05). In contrast, plasma LH concentrations increased from 0.97 ± 0.41 to 2.80 ± 0.62 ng/mL in goats exposed to the photostimulated bucks and bearing estradiol implants (P < 0.05). Thus, the permanent presence of sexually active bucks prevented the decrease of plasma LH concentration in OVX + E2 goats during the seasonal anestrus, and the introduction of the photostimulated bucks increased the plasma LH concentrations in OVX + E2 goats during the seasonal anestrus. Therefore, we conclude that in both cases, the photostimulated bucks are able to reduce or counterbalance the seasonal negative feedback of estradiol on LH secretion.

Exposure to Photoperiod-Melatonin-Induced, Sexually-Activated Rams after Weaning Advances the Resumption of Sexual Activity in Post-Partum Mediterranean Ewes Lambing in January

This study was aimed to determine whether the presence of sexually stimulated rams by photoperiodic and melatonin treatments can advance the resumption of post-partum sexual activity in Mediterranean ewes lambing in January and weaned at the end of the breeding season at 41°N, in March. Rams were exposed to two months of long days (16 h light/day) and given three melatonin implants at the end of the long days (sexually-activated rams; SAR). Control rams (CR) were exposed to the natural photoperiod. Thirty-six ewes weaned on 25 February were assigned to one of two groups. From 1 March to 30 June, one group was housed with four SAR males (SAR-treated; n = 18), and the other group (CR-treated; n = 18) was housed with four unstimulated rams. Ovulation was assessed once per week based on plasma progesterone concentrations. Estrus was monitored daily by marks left on ewes by rams' harnesses. SAR-treated ewes had a shorter (p < 0.01) weaning-first estrus interval than CR-treated ewes (61 ± 17 days vs. 102 ± 47 days; mean date of first estrus after weaning on April 26 and June 6, respectively). The proportion of the ewes ovulating in April or May was higher (p < 0.05) in the SAR-treated group than in the CR-treated group. SAR-treated ewes resumed estrous activity sooner than CR-treated ewes such that, in April, May, and June, the proportion of females that exhibited estrus was higher (p < 0.01) in the SAR-treated group (72%, 89%, and 100%, respectively) than in the CR-treated group (17%, 44%, and 61%, respectively). In conclusion, the introduction at weaning of sexually activated rams advanced the resumption of estrous activity in ewes in spring. The practical implications of this work could be important in ewes adapted for intensive production and accelerated lambing systems.

Maintaining bucks over 35 days after a male effect improves pregnancy rate in goats

The ovulation can be induced by the introduction of a male among a group of anovulatory goats, a phenomenon called the ‘male effect’. The objective of this study was to determine whether maintaining bucks over 35 days after the initial introduction of males, improves pregnancy rate in goats. We used sexually active bucks, which were joined (n = 2 each) with three groups of goats (n = 30 each): (i) males remained with females for 15 days (Control group); (ii) males remained with females for 35 days (same buck group); (iii) males were removed at Day 23 and replaced by other males, which were not familiar to the females and which remained with females until Day 35 (new buck group). Percentage of goats ovulating did not differ among groups at Day 19 (≥87%; P = 0.12). Pregnancy rates at Day 35 did not differ between groups (≥70%; P = 0.90). At Day 55, pregnancy rates were similar in the same and new buck groups (96%; P = 1.0), but were higher than that of the Control group (73%; P < 0.05). Therefore, maintaining bucks over 35 days after the onset of the male effect improved pregnancy rate more than 20 points compared with females that remained with the same bucks for 15 days only.

A high level of male sexual activity is necessary for the activation of the medial preoptic area and the arcuate nucleus during the 'male effect' in anestrous goats

In small ungulates such as sheep or goats, the introduction of a male among a group of anovulatory females during the anestrus season leads to the reactivation of the gonadotrope axis and ovulation, a phenomenon known as the 'male effect'. In goats, our previous studies have demonstrated the importance of male sexual activity for an efficient reactivation of the gonadotrope axis assessed through ovulation and blood LH pulsatility. In the present experiment, we assessed whether the level of male sexual activity would also induce differential activation of two brain regions of key importance for the reactivation of GnRH activity, namely the medial preoptic area and the hypothalamic arcuate nucleus. In both structures, we observed a differential activation of Fos in females, depending on the level of buck sexual activity. Indeed, goats unexposed to males showed low levels of expression of Fos while those exposed to sexually inactive bucks showed an intermediate level of Fos expression. Finally, the highest level of Fos expression was found in females exposed to sexually active males. However, and contrary to our initial hypothesis, we were not able to find any specific activation of kisspeptin cells in the arcuate nucleus following the introduction of highly sexually active males. As a whole, these results demonstrate that the level of male sexual activity is a key factor to stimulate brain regions involved in the control of the gonadotrope axis in the context of the male effect in goats.

Computation of a high-resolution MRI 3D stereotaxic atlas of the sheep brain

The sheep model was first used in the fields of animal reproduction and veterinary sciences and then was utilized in fundamental and preclinical studies. For more than a decade, magnetic resonance (MR) studies performed on this model have been increasingly reported, especially in the field of neuroscience. To contribute to MR translational neuroscience research, a brain template and an atlas are necessary. We have recently generated the first complete T1-weighted (T1W) and T2W MR population average images (or templates) of in vivo sheep brains. In this study, we 1) defined a 3D stereotaxic coordinate system for previously established in vivo population average templates; 2) used deformation fields obtained during optimized nonlinear registrations to compute nonlinear tissues or prior probability maps (nlTPMs) of cerebrospinal fluid (CSF), gray matter (GM), and white matter (WM) tissues; 3) delineated 25 external and 28 internal sheep brain structures by segmenting both templates and nlTPMs; and 4) annotated and labeled these structures using an existing histological atlas. We built a quality high-resolution 3D atlas of average in vivo sheep brains linked to a reference stereotaxic space. The atlas and nlTPMs, associated with previously computed T1W and T2W in vivo sheep brain templates and nlTPMs, provide a complete set of imaging space that are able to be imported into other imaging software programs and could be used as standardized tools for neuroimaging studies or other neuroscience methods, such as image registration, image segmentation, identification of brain structures, implementation of recording devices, or neuronavigation. J. Comp. Neurol. 525:676-692, 2017. © 2016 Wiley Periodicals, Inc.

Comparison of the effects of mesquite pod and Leucaena extracts with phytoestrogens on the reproductive physiology and sexual behavior in the male rat

Mesquite (Prosopis sp.) and Leucaena leucocephala are widespread legumes, widely used to feed several livestock species and as food source for human populations in several countries. Both mesquite and Leucaena contain several phytoestrogens which might have potential estrogenic effects. Thus, the aim of this study was to evaluate the effects of mesquite pod and Leucaena extracts on several aspects of behavior and reproductive physiology of the male rat. The effects of the extracts were compared with those of estradiol (E2) and of two isoflavones: daidzein (DAI) and genistein (GEN). The following treatments were given to groups of intact male rats: vehicle; mesquite pod extract; Leucaena extract; E2; DAI; GEN. The results indicate that mesquite pod and Leucaena extracts disrupt male sexual behavior in a similar way to DAI and GEN, but less than E2. The main disruptor of sexual behavior was E2, however after 40 and 50days of administration, both extracts and phytoestrogens disrupted sexual behavior in a similar way to E2. The extracts also increased testicular germ cell apoptosis, decreased sperm quality, testicular weight, and testosterone levels, as phytoestrogens did, although these effects were less than those caused by estradiol. The number of seminiferous tubules with TUNEL-positive germ cells increased in extracts treated groups in a similar way to phytoestrogens groups, and E2 caused the greatest effect. The number of TUNEL-positive cells per tubule increased only in Leucaena extract and E2 groups, but not in mesquite- and phytoestrogens-treated groups. Spermatocytes and round spermatids were the TUNEL-positive cells observed in all experimental groups. This effect was associated with smaller testicular weights without atrophy in experimental groups compared with control. Testicular atrophy was only observed in estradiol-treated males. Testosterone decreased in males of all experimental groups, compared with control, this androgen was undetectable in E2 treated males. These results suggest that mesquite pod and Leucaena extracts cause effects similar to those of phytoestrogens in male rat reproduction, these effects were lower than those caused by E2.

Sexually active bucks are efficient to stimulate female ovulatory activity during the anestrous season also under temperate latitudes

Goats are seasonal breeders and photoperiod is the main cue controlling the onset and offset of the breeding season. Nevertheless introducing a sexually active buck in a group of females during anestrous can stimulate their reproductive function and induce ovulation. This "male-effect" is very efficient under subtropical latitudes, when using sexually active males previously stimulated by a photoperiodic treatment. However, there is less evidence of its feasibility under temperate latitudes where the more important variation in day length could be responsible for a stronger inhibition of female sexual activity. The aim of this study was therefore to determine whether intense sexual activity can be induced in alpine bucks during the non-breeding season by a long-day treatment under temperate latitude and if these males could be used to produce an efficient male-effect. Bucks (n=21) were divided in two groups, one submitted to a photoperiodic treatment from November 1st to January 15th and then switched to natural photoperiod, while the other group remained entirely under the natural photoperiod. The ones submitted to this light treatment exhibit higher testicular volume and testosterone level 6 weeks after the end of the treatment. At the end of March, bucks were used to stimulate anestrous does (n=41) continuously for 15 days. We showed that (a) light treatment was efficient to induce an increase of sexual activity in bucks and (b) that the introduction of stimulated bucks among females induced a significantly higher proportion of ovulation in anestrous does than control bucks (86% vs 5%). Our results indicate that under temperate latitudes induction of ovulation in females during the anestrous season is feasible using bucks treated with long-days during winter.

Sexually active males prevent the display of seasonal anestrus in female goats

A well-defined season of sexual rest controlled by photoperiod is observed in female sheep and goats during spring and summer, delineating their "anestrous season"; bucks also decrease sexual activity at about the same time. Nutrition and/or socio-sexual stimuli play only secondary roles. However, the presence of sexually active males can reduce the length of seasonal anestrus. Whether it can also completely suppress anestrus has not been investigated. Here we tested this in goats in 3 experiments, using bucks rendered sexually active out of season by exposure to long days. The continuous presence of these males prevented goats to display seasonal anestrus: 12/14 females cycled the year round, vs. 0/13 and 0/11 for females with un-treated bucks or without bucks (experiment 1). When active bucks were removed, females immediately entered anestrus (7/7 stopped ovulating vs. 1/7 if maintained with active bucks; experiment 2). Finally, 7/7 anestrous does with bucks in sexual rest since 1.5months commenced cycling rapidly during mid-anestrous, when these bucks became sexually active following a treatment with artificial long days, vs. 0/7 with un-treated bucks or no bucks (experiment 3). The presence/withdrawal of active bucks had a highly significant effect in the three experiments (P≤0.002). Therefore, the presence of a mating opportunity can completely override the photoperiodic inhibition of reproduction of females throughout the anestrous season. Results suggest that we must re-evaluate the relative contributions of photoperiod vs. other external cues in controlling seasonal reproduction, thus offering new non-pharmaceutical ways for controlling out-of-season reproduction in small ruminants.

Importance of intense male sexual behavior for inducing the preovulatory LH surge and ovulation in seasonally anovulatory female goats

The present study was carried out to determine whether the presence of photostimulated sedated male goats could stimulate the LH preovulatory surge and ovulation in seasonal anestrous goats. Sexually experienced male goats were treated with artificial long days (16 hours light per day) from 1 November to 15 January to stimulate their sexual activity in March and April, corresponding to the natural sexual rest. A female group of goats (n=20) was exposed to non-sedated males who displayed an intense sexual behavior and provided strong odor (non-sedated group). Another female group of goats (n=20) was exposed to the photo-stimulated male goats, but these males were sedated with Xylazine 2% to prevent the expression of sexual behavior (sedated group). The sedated males also provided a strong odor. Females of both groups had full physical and visual contact with non-sedated or sedated males. In both groups, the males remained with females during 4 days. The LH preovulatory surge of 10 female goats per group was measured by determination of LH plasma concentrations in samples taken every 3 hours. In addition, in all goats, (n=20 by group), ovulation was determined by measuring plasma concentrations of progesterone. The proportion of female goats showing a preovulatory LH surge was higher in goats exposed to non-sedated (10/10) than in those exposed to sedated bucks (0/10; P<0.0001). Similarly, most of does in contact with non-sedated males ovulated (19/20), but none of those in contact with sedated males did so (0/20; P<0.0001). We conclude that the expression of an intense sexual behavior by male goats is necessary to induce LH preovulatory surge and ovulation in seasonally anovulatory goats.

Reducing exposure to long days from 75 to 30 days of extra-light treatment does not decrease the capacity of male goats to stimulate ovulatory activity in seasonally anovulatory females

The response of male goats exposed to different durations of long days (LD) during an extra-light treatment in autumn-winter, and their ability to induce ovulations in seasonally anovulatory goats were investigated in 2 experiments. In experiment 1, control males were exposed to natural photoperiod (n = 5), whereas 4 additional groups (n = 5/group) were exposed to 16 h of light per d during 75, 45, 30, or 15 d of LD. In the 4 groups, photoperiodic treatments ended on January 15th. Plasma concentrations of testosterone were determined in blood samples obtained once a week from October 15th to May 30th. The rise of testosterone levels occurred earlier in males from the 75-LD and 45-LD groups than in those from the 30-LD, 15-LD, and control groups (P < 0.05). In addition, the time during which levels of testosterone remained >5 ng/mL was longer in males from the 75-LD and 45-LD than in those from the 30-LD and 15-LD groups (P < 0.05). In experiment 2, a group of anovulatory goats (n = 13) was isolated from males, while 3 additional groups were put in contact during 15 d with males previously exposed to 75, 45, or 30 days of LD (n = 25, 27, and 26 females/group, respectively and n = 3 males per group). The proportion of goats that ovulated was higher in the 3 groups in contact with the photo-stimulated males (range: 88%-92%) than in the group isolated from them (0%; P < 0.05). The proportion of pregnant females did not differ between the 3 groups of does in contact with photo-stimulated males (range: 78%-92%; P > 0.05). We conclude that, in our experimental conditions, a photoperiodic treatment as short as 30 d of LD during autumn-winter, stimulated testosterone secretion of bucks during their period of sexual rest and rendered them able to induce ovulations in seasonal anestrous goats and to obtain pregnancies in these females.

Two or 24 h of daily contact with sexually active males results in different profiles of LH secretion that both lead to ovulation in anestrous goats

Two experiments were conducted to (a) determine whether sexually active males are able to stimulate the sexual activity of anestrous female goats when duration of contact is reduced to an intermittent contact shorter than 4 daily hours and (b) compare the pattern of secretion of LH when anestrous goats are exposed either permanently or intermittently to males. In the first experiment, 4 groups of anovulatory goats were exposed to sexually active males for 24, 4, 2, or 1 h/d during 15 consecutive days, whereas control females remained isolated. More than 89% of females in the groups exposed to the sexually active bucks ovulated, whereas only 5% did so in the control group (P < 0.001). However, the proportion of females ovulating before day 4 was greater in the 2-, 4-, or 24-h contact groups than in the control, whereas it did not differ between the control group and the 1-h contact group (P = 0.02, <0.001, <0.001 and 0.23, respectively). In the second experiment, 3 groups of anovulatory goats were exposed permanently (24 h/d) or intermittently (2 h/d) to bucks during 5 d or remained isolated. We found that pulsatility of luteinizing hormone (LH) increased in the intermittent and permanent contact groups after males were introduced to females (P = 0.05); this pulsatility of LH remained elevated in the permanent-contact group, whereas it decreased in the intermittent-contact group, once the male was removed (P = 0.32 and 0.05, respectively). We conclude that 1 or 2 daily hours of contact with sexually active males is sufficient to stimulate ovulatory activity in anovulatory goats; however, ovulation is obtained through a different pattern of secretion of LH.

Looking for the bird Kiss: evolutionary scenario in sauropsids

Background

The neuropeptide Kiss and its receptor KissR are key-actors in the brain control of reproduction in mammals, where they are responsible for the stimulation of the activity of GnRH neurones. Investigation in other vertebrates revealed up to 3 Kiss and 4 KissR paralogs, originating from the two rounds of whole genome duplication in early vertebrates. In contrast, the absence of Kiss and KissR has been suggested in birds, as no homologs of these genes could be found in current genomic databases. This study aims at addressing the question of the existence, from an evolutionary perspective, of the Kisspeptin system in birds. It provides the first large-scale investigation of the Kisspeptin system in the sauropsid lineage, including ophidian, chelonian, crocodilian, and avian lineages.

Results

Sauropsid Kiss and KissR genes were predicted from multiple genome and transcriptome databases by TBLASTN. Phylogenetic and syntenic analyses were performed to classify predicted sauropsid Kiss and KissR genes and to re-construct the evolutionary scenarios of both gene families across the sauropsid radiation.

Genome search, phylogenetic and synteny analyses, demonstrated the presence of two Kiss genes (Kiss1 and Kiss2 types) and of two KissR genes (KissR1 and KissR4 types) in the sauropsid lineage. These four genes, also present in the mammalian lineage, would have been inherited from their common amniote ancestor. In contrast, synteny analyses supported that the other Kiss and KissR paralogs are missing in sauropsids as in mammals, indicating their absence in the amniote lineage. Among sauropsids, in the avian lineage, we demonstrated the existence of a Kiss2-like gene in three bird genomes. The divergence of these avian Kiss2-like sequences from those of other vertebrates, as well as their absence in the genomes of some other birds, revealed the processes of Kiss2 gene degeneration and loss in the avian lineage.

Conclusion

These findings contribute to trace back the evolutionary history of the Kisspeptin system in amniotes and sauropsids, and provide the first molecular evidence of the existence and fate of a Kiss gene in birds.

Decrease in the seasonality of sexual behavior and sperm production in bucks by exposure to short photoperiodic cycles

Bucks show seasonal variation in their body weight and sexual activity. Three groups of six Alpine and Saanen bucks were used over two consecutive years to investigate if rapid alternations between long and short days could abolish this seasonal variation. The control group was kept under natural annual daylength, while the experimental groups were exposed to alternations of either 1 month of 16L:8D and 1 month of 8L:16D (2-month treatment) or to 2 months of 16L:8D and 2 months of 8L:16D (4-month treatment). In the control group, body weight, sexual behavior, testicular weight and sperm production showed important seasonal variations: body weight decreased between September and January by about 7 kg; refusal to ejaculate went up to 25% in August; testicular weight varied from 103 +/- 2 g (March) to 149 +/- 7 g (October). In contrast, seasonal variations of these parameters decreased in the two experimental groups. In the 2-month treatment group, testicular weight increased from 134 +/- 7 (March) to 148 +/- 8 g (October); while in the 4-month treatment group it increased from 123 +/- 10 to 138 +/- 12 g, respectively; in the same period, the two experimental groups of bucks produced a larger total number of spermatozoa per ejaculate (6.3 +/- 0.3 x 10(9); 2-month treatment and 7.2 +/- 0.3; 4-month treatment) than in the control group (4.2 +/- 0.4). We conclude that rapid alternations between long and short days decreased seasonality in the sexual activity of bucks.

Mesquite pod extract modifies the reproductive physiology and behavior of the female rat

Phytoestrogens are non steroidal compounds that can bind to estrogen receptors, mimicking some effects of estradiol (E(2)). These compounds are widespread among legumes, which are used as pasture, and their importance in animal agriculture has increased. Mesquite (Prosopis sp) is a widespread legume, widely used to feed several livestock species in Mexico. The main product of mesquite is the pod, which is considered high quality food. As a legume, it could be assumed that mesquite contains some amounts of phytoestrogens which might induce potential estrogenic effects. However, to our knowledge, there are no reports regarding the possible estrogenic activity of this legume either in livestock or in animal models such as the rat. Therefore, in this study, we evaluated the potential estrogenic effects of mesquite pod extract on several aspects of behavior and reproductive physiology of the female rat. The effects of the extract were compared with those of E(2) and two isoflavones: daidzein (DAI) and genistein (GEN). The following treatments were given to groups of intact and ovariectomized (OVX) female rats: vehicle; mesquite pod extract; E(2); GEN; DAI. Compared to vehicle groups, mesquite pod extract, DAI, GEN, and E(2) increased uterine weight and induced growth in vaginal and uterine epithelia. In intact rats, mesquite pod extract, GEN and DAI altered estrous cyclicity, decreased lordotic quotient and intensity of lordosis. In OVX rats, mesquite pod extract, DAI and GEN induced vaginal estrus, increased vaginal epithelium height, and induced lordosis, although its intensity was reduced, compared with intact rats in estrus and E2-treated rats. These results suggest that mesquite pod extract could have estrogenic activity. However, the presence of phytoestrogens in this legume remains to be confirmed.

Functional characterization of polymorphic variants for ovine MT1 melatonin receptors: possible implication for seasonal reproduction in sheep

In seasonal breeding species, the gene encoding for the melatonin MT(1) receptor (oMT(1)) is highly polymorphic and numerous data have reported the existence of an association between an allele of the receptor and a marked expression of the seasonality of reproduction in ewes. This allele called "m" (previously named "-" allele) carries a mutation leading to the absence of a MnlI restriction site as opposed to the "M" allele (previously named "+" allele) carrying the MnlI restriction site (previously "+" allele). This allows the determination of the three genotypes "M/M" (+/+), "M/m" (+/-) and "m/m" (-/-). This mutation is conservative and could therefore not be causal. However, it is associated with another mutation introducing the change of a valine to an isoleucine in the fifth transmembrane domain of the receptor. Homozygous "M/M" and "m/m" animals consequently express structurally different receptors respectively named oMT(1) Val(220) and oMT(1) Ile(220). The objective of this study was to test whether these polymorphic variants are functionally different. To achieve this goal, we characterized the binding properties and the transduction pathways associated with both variants of the receptors. Using a pharmacological approach, no variation in binding parameters between the two receptors when transiently expressed in COS-7. In stably transfected HEK293 cells, significant differences were detected in the inhibition of cAMP production whereas receptors internalization processes were not different. In conclusion, the possibility that subtle alterations induced by the non conservative mutation in "m/m" animals might modify the perception of the melatoninergic signal is discussed in the context of melatonin action.