The relationship between sexual and aggressive behaviour, and pituitary and testicular activity during the seasonal sexual cycle of rams, and the influence of photoperiod

Six adult Soay rams were housed under artificial lighting conditions with alternating 16-week periods of long (16 h light: 8 h darkness) and short days (8L:16D) During long days the rams were reproductively quiescent: the abrupt change from long to short days induced a specific succession of responses in the reproductive system. Plasma LH and FSH levels began to increase after 2-4 weeks, followed almost immediately by a rise in plasma testosterone levels accompanied by growth of the testes. Testicular activity continued to increase during short days and the greatly elevated androgen levels apparent after 5-10 weeks caused changes in the peripheral target organs, including growth of the epididymides, development of the sexual flush on the exposed ventral skin and heightened genital sensitivity. High testosterone levels were also associated with an increase in aggressive (scored by a mechanical device) and sexual (incidence of Flehmen) behavior which was at peak about 1 month after the start of the peak androgen levels. The change to long days was associated with a decrease in plasma gonadotrophin levels within 2 weeks followed by a progressive decline in all reproductive parameters measured. Implantation of a low dose of testosterone (200 mg) during the period of reproductive quiescence induced the development of the sexual flush and an increase in genital tactile sensitivity, although behaviour was not significantly affected. The annual changes in reproductive physiology and behaviour of 12 Soay rams living under natural lighting conditions were recorded for comparison with the experimental situation. The nadir of the sexual cycle was in the spring and early summer, and the sequence of events culminating in the mating season in the autumn was similar to that induced experimentally.     

Partial abolition of seasonal variations of testicular weight in rams by decreasing the photoperiod

Under moderate latitudes all breeds of rams undergo seasonal variations in testicular weight with a maximum during summer under decreasing daylength ([1]-[4]). Similarly, in rams submitted to a 6-month artificial light regime [5] or to an alternation of long (16L:8D) and short (8L:16D) days [6] an increase in testicular weight occurred following a decrease in daylength and vice versa. However this effect is transitory, a phenomenon which can be referred as photorefractoriness. In the present study the influence of the period of the light cycle on variation in testicular weight in the ram was investigated. 4 groups of 6 adults Ile-de-France rams were submitted to artificial light cycles where the daylength varied between 8-16 hrs. and the period (T) was 6, 4, 3, or 2 months respectively (Groups T6, T4, T3, and T2). Testicular volume was measured fortnightly using an orchidometer, Variations in testicular volume were submitted to harmonic regression analysis following the model y(t)=mu + a sin(2(pi t/tau) + phi). Cyclic changes in testicular volume were seen with each light cycle, at least in groups T6, T4, and T3 (Fig.). Analysis (Table) showed that: (1) the coefficient of determination R2 was high in the groups (2) mean testicular volume has increased from 258 to 294 cm3 when the period of the light cycle decreased from 6 to 2 months; (3) conversely, the amplitude decreased from 66.5 to 26.5 cm3 as the period decreased; (4) maximal testicular volumes (mean plus amplitude) were similar in all groups (range: T4, 312,5-T6,324 cm3) while minima (mean less amplitude) differed significantly (P<0.000,1) between groups (range: T6 and T4 about 190, T2 267.5 cm3) and (50 th computed periods of testicular volumes cycles were almost identical to the imposed light cycles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of photoperiod and protein diet on growth hormone secretion in rams

Studies of sheep were undertaken to determine the effects of photoperiod and protein diet on growth hormone (GH) secretion. Rams were subjected to either a control (RI) or an inverted (R2) 6-month (semestral) light regime. In both light regimes day lengths varied gradually between 8 and 16 hr. Within each light regime group of animals, the rams received either a low (L) or a high (H) protein diet containing the same level of energy. Plasma GH profiles consisting of 13 hourly samples were determined at regular intervals corresponding to known day lengths. Analysis of variance indicated that there was a significant effect of day length (P less than 0.01) and protein diet (P less than 0.05) on GH secretion, the two light regimes R1 and R2 were equivalent with respect to GH secretion, and there were no interactions among the three experimental factors. Although mean GH secretion was consistently higher in L groups than in H groups, there was a similar trend in all the animals of increasing GH secretion as day length increased. GH secretion was maximum when the day length reached 13 hr 20 min in increasing photoperiods in L groups (15.6 +/- 1.6 ng X h X ml-1) and 16 hr in H groups (13.0 +/- 1.2 ng X h X ml-1). From these results we conclude that both an increasing day length and a deficiency in protein diet stimulate GH secretion in rams but the GH response to these two factors may involve different regulatory processes and may have different functions.     

Seasonal variation in testicular volume and sexual behavior of Chios and Serres rams

The seasonality of testicular volume and sexual behavior in two Greek breeds of sheep, Chios and Serres, was studied using 10 mature rams of each breed. The rams were kept out of breeding during 2 consecutive years. Live weight was recorded at monthly intervals. Testicular volume was measured at 2-week intervals using an orchidometer. Sexual behavior was recorded at 4-week intervals by exposing rams to oestradiol-treated ovariectomized ewes. The total number of mounts and matings, and the reaction time to first mount and mating were recorded. Chios rams were heavier than Serres rams (87.4 +/- 2.0 kg versus 76.4 +/- 1.9 kg, respectively). All traits varied significantly with month but only testicular volume exhibited a clear seasonal trend in both breeds, with a maximum volume in July-August and a minimum in February-April. Number of mounts showed clear seasonal trend in the Chios breed, with maximum in November. Number of mounts was significantly correlated with length of daylight (-0.18 and -0.21 for Chios and Serres, respectively; P < 0.01) and relative humidity (0.14 and 0.17 for Chios and Serres, respectively; P < 0.05). Testicular volume was positively correlated with air temperature (0.28; P < 0.01) and relative humidity (-0.23; P < 0.01) in the Serres breed only. Results of this study suggest that the testicular volume and number of mounts exhibit seasonal variation in the Chios and Serres rams.     

Early photoperiod history and short-day responsiveness in Siberian hamsters

Siberian hamsters exhibit seasonal, photoperiod influenced cycles of reproductive activity, body size, pelage characteristics, and thermoregulatory behavior. Laboratory populations generally exhibit inter-individual variability in expression of photoperiod responsiveness, with a subset of individuals that fail to show the species typical responses to short photoperiod. This variability is partly explained by a genetic component, as it has been possible to increase the number of short-day nonresponders by artificial selection. Responsiveness to short photoperiod is also substantially influenced by photoperiod history in this species; hamsters that have been raised under long (16L) or very long (18L) day lengths are less likely to exhibit winter-type responses to short days as compared to hamsters raised under an intermediate (14L) day length. In the present experiment, we examined effects of age and early photoperiod history in a strain of Siberian hamsters that had been selected for short-day nonresponsiveness. Hamsters transferred into short photoperiod on the day of birth were uniform in exhibiting winter-type responses. However, hamsters raised until 25 days of age in either continuous illumination or in 16L exhibited variation in responsiveness when subsequently moved into short photoperiod. We conclude that virtually all hamsters of the short-day nonresponsive strain are born responsive to short days. Subsequent development of resistance to potential short day effects is dependent on age and/or photoperiod history.     

Induction of flowering by cytokinins in a short-day plant, Lemna paucicostata

Lemna paucicostata, normally a short-day plant, can be inducedto flower under long-day conditions by providing a cytokininin a medium containing a high level of ferric citrate (5 x 10^–4M).Interestingly, when a cytokinin and EDDHA are present togetherin the medium, flowering is induced even at low levels of iron(10^–5 and 5 x 10^–5M ferric citrate). However, inthe absence of a cytokinin, flowering takes place only undershort days. (Received September 30, 1968; )     

Induction of flowering by seasonal changes in photoperiod

In many plants, major developmental transitions such as the initiation of flowering are synchronized to the changing seasons. Day length provides one of the environmental cues used to achieve this. We describe the molecular mechanisms that measure day length and control flowering in Arabidopsis. Also, we compare these mechanisms with those that control flowering time in rice. This comparison suggests that components of the Arabidopsis regulatory network are conserved in other species, but that their regulation can be altered to generate different phenotypic responses.     

Induction of flowering in Lemna paucicostata,a short-day plant,by chelating agents and iron

Summary Lemna paucicostata is a short-day plant which normally flowers only in a medium supplemented with EDTA or EDDHA. On a molar basis EDDHA is more effective for induction of flowering. The chelating agent can be replaced by high concentrations of ferric citrate in the medium. Simultaneous supply of both EDDHA and a high level of ferric citrate results in flowering even under long days.     

Flower formation in vitro in a quantitative short-day tobacco: interrelation between photoperiod and infructescence development

The flowering response of thin layers excised from branch internodes of Nicotiana tabacum cv. Maryland Catterton (quantitative short-day plant for induction) was studied under three photoperiodic treatments. The explants were excised from inflorescences bearing flowers only, flowers and green fruits, or from infructescences with green fruits only. The aim of the study was to investigate the post-inductive photoperiodic effects on in vitro flower bud formation in a quantitative short-day tobacco and the relation with infructescence development. Short days quantitatively enhanced the flower bud regeneration capacities of explants in all stages of development, both as number of explants induced to produce flowers and as mean number of flowers per explant. There was no significant difference in flower bud formation on explants of the first two stages, which produced much more flowers than those of the third stage. Observations in planta showed that, during the 20 days separating the second stage from the first stage, there was no significant difference in the number of floral buds and flowers present on the inflorescence; however, the branch internodes lengthened, as did the floral buds and flowers. During the 10 days leading to the third stage, the number of capsules did not change significantly, but a high rate of floral abscission occurred. The present results show that in Nicotiana tabacum cv. Maryland Catterton short day quantitatively controls not only the inductive step of the flowering process, but also affects the capacity to regenerate flower buds during the late post-inductive phases. The responsiveness to the photoperiodic signal decreases only when the plant exhibits only fruits.     

Effect of undegradable protein supply on testicular size, spermiogram parameters and sexual behavior of mature Assaf rams

Eighteen mature Assaf rams were used to study the effect of undegradable protein (UDP) supply on testicular size, sperm production and quality, testosterone secretion and reproductive behavior. Animals were allocated to three groups of six animals each and fed during 10 weeks with different diets which were designed to supply approximately 0.5MJ of metabolisable energy (ME)/kg LBW(0.75) and 9g of effective rumen degradable protein (ERDP)/MJ of fermentable ME to all animals and to induce differences in rumen UDP intake (0.97, 1.72 and 3.08g of UDP/kg LBW(0.75) for LP, MP and HP diets, respectively). Neither plasma testosterone concentration nor reproductive behavior parameters (number of services, number of mounts without ejaculation and reaction time to first mount) were affected (P > 0.05) by protein intake. Nevertheless, there were significant (P < 0.05) differences between diets in both testicular size and sperm production. Scrotal circumference was lower in LP compared to MP and HP groups, no significant differences being observed between these latter two groups at any time. In relation to sperm production, the lowest and the highest values were always observed in LP and HP groups, respectively. MP group showed intermediate values, significantly different from those of LP and HP groups on Week 5 and only from those of LP group on Week 9. The present results provide a better understanding of the effect of protein nutrition and suggest that UDP should be supplied to Assaf rams during the mating season to improve their reproductive performance.     

Sperm output and hormone concentrations in Finn and Dorset rams exposed to long- and short-day lighting

Seasonal changes in photoperiod have a substantial effect on sexual behavior and reproduction in rams. Little information is available on sperm output from high libido versus average libido rams subjected to intensive semen collection while being exposed to controlled short versus long photoperiods. Six Finn and six Dorset rams were compared in a reversal design, which allowed rams of both breeds to be exposed to 8 h versus 16 h of light. During each of two 84-d periods rams were subjected twice to an initial depletion of epididymal sperm reserves by collecting up to 26 ejaculates of semen in 3 d, followed by up to 10 ejaculates per day, 1, 3, 5, and 7 d after the initial depletion. A total of 2673 semen samples were collected. Nearly twice as many ejaculates (63.6% of the total) were obtained from Finn rams as from Dorset rams during both the initial and subsequent 3-d sperm depletion periods. This difference in libido was associated with obtaining 33.6 +/- 3.1 x 10(9) sperm from Finn rams versus 10.0 +/- 2.2 x 10(9) sperm from Dorset rams during the initial depletion period (P<0.05). Changes in photoperiod did not affect sperm output (P>0.05) in Finn rams, but may have affected Dorset rams. With 16 h of light, prolactin was significantly (P<0.05) increased in both breeds, particularly in Finn rams. Testosterone in both breeds followed an endogenous rhythm, not affected by the change in controlled photoperiods.     

The neurobiology of sexual partner preferences in rams

The question of what causes a male animal to seek out and choose a female as opposed to another male mating partner is unresolved and remains an issue of considerable debate. The most developed biologic theory is the perinatal organizational hypothesis, which states that perinatal hormone exposure mediates sexual differentiation of the brain. Numerous animal experiments have assessed the contribution of perinatal testosterone and/or estradiol exposure to the development of a male-typical mate preference, but almost all have used hormonally manipulated animals. In contrast, variations in sexual partner preferences occur spontaneously in domestic rams, with as many as 8% of the population exhibiting a preference for same-sex mating partners (male-oriented rams). Thus, the domestic ram is an excellent experimental model to study possible links between fetal neuroendocrine programming of neural mechanisms and adult sexual partner preferences. In this review, we present an overview of sexual differentiation in relation to sexual partner preferences. We then summarize results that test the relevance of the organizational hypothesis to expression of same-sex sexual partner preferences in rams. Finally, we demonstrate that the sexual differentiation of brain and behavior in sheep does not depend critically on aromatization of testosterone to estradiol.     

The response of rams and ewes of three breeds to artificial photoperiod

Rams and ewes of the Romney Marsh (N = 6), Dorset Horn (N = 8) and Australian Merino (N = 8) breeds were subjected to 4 successive periods of alternating 6 h light/18 h dark ('short' days) and 18 h light/6 h dark ('long' days) preceded by 16 weeks of 12 h light/12 h dark. The initial period was of 32 weeks (16 weeks 'short' days; 16 weeks 'long' days) and the next 3 were of 24 weeks (12 weeks 'short' days; 12 weeks 'long' days). Rams of all breeds showed a cyclic pattern of growth and regression of testes associated with plasma testosterone concentration, influenced by the change in light regimen 15-19 weeks previously. Sexual behaviour was also cyclic but lagged by some 6-7 weeks. The changes were greatest in the Romneys and least in the Merinos in which a higher degree of sexual activity was evident even when the testes were regressed (P less than 0.001). This was the major breed difference. All ewes of the Romney and Dorset breeds showed marked seasonality related to the imposed light regimen, whereas only 1 of the 4 Merinos did so. The mean peak of ovarian activity in the former 2 breeds coincided with that of maximum sexual activity of rams housed with them; that is, some 6 weeks after maximum scrotal volume. The rams and ewes were subjected to serial blood sampling episodes for plasma LH and testosterone and tested for plasma LH release following GnRH administration. There was little variation between breeds in LH concentration. Testosterone concentration varied greatly in the ram, highest levels associated with the developed phase of the testes and with maximum LH pulse frequency. The LH response to GnRH changed with respect to the state of the gonads. Maximal responses were observed in the developing phase of testicular growth although this variation was greater in the Romney and Dorsets than in the Merinos (P less than 0.001). In the ewes, maximal responses were seen in the follicular phase (P less than 0.001), with no difference between the luteal and acyclic phases. There were no breed differences. Plasma pooled from the serial blood sampling episodes was assayed for prolactin.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of photoperiod and temperature on testicular function in amphibians

Most amphibians present an annual testicular cycle characterized by a quiescent period (late autumn-winter) and a spermatogenic period (spring and summer). At the end of the period of spermatogenesis undifferentiated interstitial cells transform into steroid-secreting Leydig cells which regress in spring at the beginning of the new spermatogenetic cycle. The testicular cycle is controlled by the pituitary gonadotropin levels which are high in autumn and winter, low in spring and increase temporarily in the middle of summer. Photoperiod and temperature seem to be the most important external factors involved in the regulation of this cycle in many amphibian species since the colder the geographic area, the longer the quiescent period and the shorter the spermatogenic period. This suggests the occurrence of a potentially continuous cycle in these species, in contrast with that which occurs in other species having an endogenous rhythm of testicular function which is much less sensitive to environmental factors. Although the specific response to temperature can vary widely between species, the most frequent observation in amphibians with a potentially continuous cycle is that exposure to mild temperatures (15-20 degrees C, according to the spring temperatures of the different geographic areas) stimulates spermatogenesis even during the period of testicular quiescence. If this mild temperature is combined with a long photoperiod, complete spermatogenesis is attained. Experiments performed during the period of germ-cell proliferation (development from spermatogonia to round spermatids) indicated that low temperatures (below 11 degrees C) as well as short photoperiods (less than 8 h of light) hinder germ-cell proliferation. Moderately high temperatures (about 30 degrees C) do not impair this proliferation. In the newt Triturus marmoratus, it has been shown that an excessively long photoperiod (over 16 h) has the same effect as a short photoperiod. In this species eyes are not required for the testicular photoperiodic response. Photoperiod appears to have no effect on spermiogenesis (differentiation of round spermatids into spermatozoa), because once round spermatids are formed, spermiogenesis will occur even in total darkness. Mild temperatures seem to be necessary for spermiogenesis as well as for androgen biosynthesis because neither process will take place at extreme temperatures. Results on the effect of photoperiod in steroidogenesis differ between species.     

Effects of partial destruction of the suprachiasmatic nuclei on two circadian parameters: wheel-running activity and short-day induced testicular regression

Summary Many circadian rhythms in mammals are regulated by the suprachiasmatic nuclei located in the anterior hypothalamus. The suprachiasmatic nuclei are a heterogeneous population of neurons loosely segregated into regions. In an effort to determine if a regional specificity of control of different circadian rhythms exists within the SCN, the effect of small electrolytic lesions of the suprachiasmatic nuclei was examined on two parameters which are known to depend on the circadian system for their normal expression: wheel-running activity and short-day induced testicular regression. While some SCN lesions altered both the circadian rhythm of locomotor activity and the normal temporal pattern of gonadal regression on short-days, other partial lesions of the suprachiasmatic nuclei were found to effect one parameter without effecting the other. Detailed histological analysis of the neural damage sustained by the suprachiasmatic nuclei did not indicate an obvious regional specificity of function within the nuclei. However, the results do suggest that functionally specific neural pathways emerging from the suprachiasmatic nuclei carry circadian information to independent neural circuits responsible for locomotor activity and neuroendocrine-gonadal function.Abbreviations SCN suprachiasmatic nucleus - SCG superior cervical ganglion - NAT N-acetyltransferase - LD light/dark cycle - DD constant darkness - circadian period - phase angle of entrainment - HRP horseradish peroxidase - SEM standard error of the mean - vPVN hypothalamic paraventricular nucleus - DMH hypothalamic dorsomedial nucleus - PVT thalamic paraventricular nucleus - IMLN intermediolateral nucleus     

Effect of breed and age on sexual behaviour of rams

The objective of this study was to highlight the problems that arise during the reproduction between thin-tailed rams and fat-tailed ewes. At the same time, particular emphasis laid on the influence of sheep breed, sheep age, time after ram introduction and day of the ewe estrus cycle on ram and ewe sexual behaviour. Rams were subjected to sexual performance tests by being individually exposed to 12 ewes for 3 h daily, 19 consecutive days. The 16 rams of the experiment were separated according to their age (9 and 21 months old) and breed (Chios and Karagouniki), and the 96 ewes of Chios fat-tailed breed, were divided by age (9 and 21 months old). The main characteristics of courtship behaviour, like sniffing, nudging, flehmen response and following were recorded and studied in detail. Mature Chios rams, which were the only one with previous experience of Chios ewes, exhibited higher rates of sexual interest per ewe than the other rams (P < 0.05). On the other hand, rams sniffed and nudged more young than mature ewes (P < 0.05), probably due to the fact that young ewes did not express intense symptoms of estrus. Young rams exhibited substandard sexual interest towards mature ewes, when they first came in contact with them (P < 0.05). In general, Karagouniki thin-tailed rams exhibited reduced rates of mating behaviour when they courted with Chios fat-tailed ewes in comparison with Chios rams (P < 0.05). Moreover, as the time after ram introduction passed, the frequency and duration of sexual behaviour components decreased (P < 0.001). Finally, the effect of the day of the experiment was only significant in the case of sniffing, which increased during the first 2 days and then declined and stabilized (P < 0.01). As it was demonstrated, ram age and ram breed played a fundamental role in the exhibition of sexual interest elements.     

Induction of flowering in Lemna gibba G3 under short-day conditions

In the presence of the chelating agent EDDHA, long-day duckweedLemna gibba G3 was induced to flower under a short-day scheduleof 9 hr of light and 15 hr of darkness in a 24-hr cycle. Weconcluded that EDDHA creates effects very similar to those ofsalicylic acid. When EDDHA or salicylic acid was added to thenutrient medium in combination with BA, flowering was inducedeven under conditions of 8 hr of light and 16 hr of darkness.Under a photoperiod of 9 hr, BA markedly enhanced the effectof EDDHA as well as salicylic acid. On the other hand, BA alonewas ineffective as far as flowering was concerned. By quantitativeinteractions, BA seems to complement the modifying effect ofEDDHA or salicylic acid on flowering in this duckweed strain. (Received June 25, 1976; )