Stress inhibits seasonal and FSH-induced ovarian recrudescence in the lizard,Mabuya carinata

The opioid peptide leucine enkephalin modulates hypothalamic-hypophysial axis in the cichlid fish Oreochromis mossambicus

In vertebrates, opioid peptides are thought to be involved in the regulation of reproduction; however, the significance of enkephalins in testicular function remains unclear. We examined the influence of δ-opioid receptor agonist leucine enkephalin (L-ENK) on the hypophysial-testicular axis of the cichlid fish Oreochromis mossambicus. Treatment with a low dose of L-ENK (60 µg) caused a significant increase in the numbers of primary and secondary spermatocytes and early and late spermatids, concomitant with intense immunolabelling of testicular androgen receptors, but did not significantly alter serum luteinizing hormone (LH) and 11-ketotestosterone (11-KT) levels compared to those of controls. Nevertheless, treatment with a high dose of L-ENK (200 µg) caused a significant reduction in the numbers of secondary spermatocytes as well as late spermatids associated with marginal immunolabelling of androgen receptors and significantly lower concentrations of serum 11-KT and LH compared to controls. In addition, the serum cortisol level was not affected in low-dose L-ENK-treated fish, but its level was significantly increased in the high-dose L-ENK-treated group. Together, these findings indicate that a low dose of L-ENK stimulates the germ cells at the meiosis stage and promotes further stages of spermatogenesis, whereas a high concentration of L-ENK inhibits spermatogenesis at the advanced stages. This effect appears to be mediated through the suppression of testicular steroidogenesis and the reduction of LH release in the pituitary gland of tilapia. The findings also suggest that elevated L-ENK levels in teleosts may exert their inhibitory influence on the hypophysial-testicular axis via glucocorticoids.

The influence of the opioid pentapeptide methionine-enkephalin on seasonal and FSH-induced ovarian recrudescence in the gecko Hemidactylus frenatus

Although methionine-enkephalin (M-ENK) is implicated in the regulation of reproductive functions in vertebrates, its function in reptiles is little understood. This study aims to elucidate the role of M-ENK on seasonal and follicle stimulating hormone (FSH)-induced ovarian recrudescence in the gecko Hemidactylus frenatus. In the first experiment, administration of 5 µg M-ENK did not affect germinal bed activity or follicular developmental stages I, II, and III (previtellogenic) and IV (vitellogenic), but there were no stage V (vitellogenic) follicles in the ovary. However, there was a significant decrease in the mean numbers of oogonia and primary oocytes in the germinal bed associated with the complete absence of stage IV and V follicles in 25 µg M-ENK-treated lizards in contrast to experimental controls. Furthermore, there was a significant decrease in gonadotropin-releasing hormone - immunoreactive (GnRH-ir) content in the median eminence (ME) and pars distalis (PD) of the pituitary gland and sparse labelling of hypothalamic GnRH-ir neurons in 25 µg M-ENK-treated lizards. In the second experiment, treatment with FSH during the regression phase of the ovarian cycle resulted in the appearance of stage IV and V follicles, in contrast to their absence in the initial controls and treatment controls. However, treatment with 25 µg M-ENK + FSH did not result in the appearance of these follicles, indicating the inhibitory effect of M-ENK on FSH-induced ovarian recrudescence. These findings suggest that M-ENK inhibits the germinal bed and vitellogenic follicular growth in a dose-dependent manner, possibly mediated through the suppression of GnRH release in the ME and PD. In addition, M-ENK may also act at the level of the ovary in the gecko.

The opioid peptide leucine-enkephalin disrupts seasonal and gonadotropin-induced ovarian recrudescence in the gecko Hemidactylus frenatus

The enkephalins are known to regulate many physiological functions, including reproduction in vertebrates. However, the role of leucine-enkephalin (L-ENK) in the ovarian recrudescence activity of reptiles is not known. In the present study, we studied the influence of L-ENK on seasonal and FSH-induced ovarian recrudescence during the breeding and non-breeding phases of the cycle in the tropical and subtropical gecko Hemidactylus frenatus. In the first experiment, treatment with 5 and 25 μg L-ENK resulted in a dose-dependent inhibitory effect on the hypothalamic gonadotropin-releasing hormone (GnRH) neurons and ovary, as indicated by a significantly decreased percent area of GnRH-immunoreactive (GnRH-ir) fibres in the median eminence and pars distalis of the pituitary gland, concomitant with complete absence of stage V (late vitellogenic) follicles in the ovary compared to those of experimental controls. In the second experiment, administration of FSH to lizards in the regression phase stimulated the recruitment of stage IV and V (vitellogenic) follicles in contrast to their absence in initial controls or treatment controls. However, similar treatment of FSH in combination with 25 μg L-ENK did not result in the development of stage IV or V follicles. Together, these results suggest for the first time that treatment with 5 and 25 μg L-ENK exerts a dose-dependent inhibitory effect on the hypothalamic GnRH release into the median eminence and pituitary gland, leading to the blockade of ovarian recrudescence. These results also suggest a possible direct inhibitory effect of L-ENK at the level of the ovary in the gecko.

Corticosterone mediated mate choice affects female mating reluctance and reproductive success

The study of stress-related hormones as mediators of sexual selection has traditionally focused on the effect of glucocorticoids on male quality and competing ability. However, environmental stressors are expected to affect both males and females, and the strength of sexual selection might be affected by changes in female mating decisions, a hypothesis that has rarely been tested. Here, we investigated whether female common lizard (Zootoca vivipara) mating behaviour and mating preferences are affected by different levels of administered corticosterone and conditioned by the familiarity of their partners, which is known to influence Z. vivipara social behaviour. To this end, two females, one corticosterone-treated and one control female, were simultaneously presented with an unfamiliar male and the following day with either a familiar or an unfamiliar male. Females treated with corticosterone (Cort) were more aggressive towards males and mated less. Furthermore, copulation probability in Cort females, but not in control females, increased with body size. On the second day, Cort females only mated with familiar partners. In contrast, male behaviour towards females was not affected by treatment and only bigger males successfully copulated with Cort females. This shows that corticosterone directly affected female mating behaviour and mating preferences, while male mating behaviour was unaffected by the female's level of corticosterone. Environmental and social stressors may affect reproductive strategies of females, the strength of sexual selection, and sexual conflict through their effects on female glucocorticoid levels, potentially in a wide range of species.

Prenatal stress from trawl capture affects mothers and neonates: a case study using the southern fiddler ray (Trygonorrhina dumerilii)

Assessing fishing effects on chondrichthyan populations has predominantly focused on quantifying mortality rates. Consequently, sub-lethal effects of capture stress on the reproductive capacity of chondrichthyans are largely unknown. We investigated the reproductive consequences of capture on pregnant southern fiddler rays (Trygonorrhina dumerilii) collected from Swan Bay, Australia, in response to laboratory-simulated trawl capture (8 h) followed immediately by air exposure (30 min). Immediately prior to, and for up to 28 days post trawling, all females were measured for body mass (BM), sex steroid concentrations (17-β estradiol, progesterone, testosterone) and granulocyte to lymphocyte (G:L) ratio. At parturition, neonates were measured for total length (TL), BM and G:L ratio. Trawling reduced maternal BM and elevated the G:L ratio for up to 28 days. Trawling did not significantly affect any sex steroid concentrations relative to controls. Neonates from trawled mothers were significantly lower in BM and TL than control animals, and had an elevated G:L ratio. Our results show that capture of pregnant T. dumerilii can influence their reproductive potential and affect the fitness of neonates. We suggest other viviparous species are likely to be similarly affected. Sub-lethal effects of capture, particularly on reproduction, require further study to improve fisheries management and conservation of chondrichthyans.

Study of spermatogenesis fetal testis exposed noise stress during and after natal period in rat

Noise stress is dangerous natural contaminant that produces harmful physiological, psychological and morphological outcomes to the body. So this study was conducted in order to investigate the effects of noise stress on the parenchyma of testis. Healthy mature females rats (n = 20) were mated with the mature male rats and then randomly allocated equally either to experimental or control groups. Experimental group has given daily noise stress up to birth their child. In the second step, the child's pregnant rats of experimental group were distributed to three subgroups as follow: group I (without exposure to noise stress), group II (exposure to noise for 8 weeks) and group III (exposure to noise for 14 weeks) for morphometric analysis of their child's testicles by sacrificing of them at weeks 14. In general, the testes of non-exposed group were grown larger than ones in the noise exposed groups. Moreover, the testes of the experimental group 1 were larger than the other experimental groups. Indeed, the rate of atrophic seminiferous tubules and jumbled appearance of the interstitial space were more observed in the noise stress exposed group than non-exposed ones. In addition, seminiferous tubules analysis revealed that the characteristics of interstitial space cells and epithelial germinative cells of the seminiferous tubules in the control group were better than the noise exposed groups. It seems that the noise stress has negative influences on the fertility of male based on enhancing of the apoptotic process induced by pathogenesis stress and suppressing the kinetics spermatogenesis.

Cloacal Gland and Gonadal Photoresponsiveness in Male Japanese Quail Selected for Divergent Plasma Corticosterone Response to Brief Restraint

Corticosterone is linked to testicular depression, and in Coturnix, a relatively photorefractory species, day length and androgen dependency in cloacal gland development and foam production are evident. Furthermore, male quail selected for reduced (low stress, LS) rather than exaggerated (high stress, HS) plasma corticosterone stress response show more photo-induced reproductive development, greater resistance to reproductive declines induced by exposure to very short days, and a quicker recovery to a higher reproductive level upon return to long days. To determine whether a milder reduction in day length would also influence stress line reproductive photoresponsiveness, and perhaps photorefractoriness, males grown on 16 h of light were given 13 h of light for 4 wk followed by a return to long days for 12 wk. Cloacal gland measurements were made following the initial stimulatory photoperiod and weekly thereafter during the 2 light treatments. Plasma testosterone was determined initially, after 4 wk of light reduction, and at the end of the study, along with BW, testes weight (TWT), and TWT relative to BW. Cloacal gland volume (CVOL) was greater in LS than HS males grown on long days. Whereas exposure to 13 h of light reduced CVOL in both lines, line differences (LS > HS) persisted during the first 3 wk of light reduction. Moreover, by 2 wk of rephotostimulation, and weekly thereafter, line differences (LS > HS) in CVOL reemerged. Cloacal gland foam production and the proportion of individuals that produced cloacal gland foam responses reflected changes in CVOL. The BW did not differ by line, yet LS males had a higher TWT and TWT relative to BW than HS ones. All individuals, however, exhibited relative photorefractory responses. Whereas none of the LS males completely resisted reproductive regression induced by a 3 h light reduction, LS males showed other reproductive benefits upon mild photocastration and subsequent rephotostimulation (e.g., greater resistance to CVOL and cloacal gland foam production losses during a mild light crash and quicker restoration to full reproductive potential upon relighting).

Influence of stress on gonadotrophin induced testicular recrudescence in the lizard Mabuya Carinata

Administration (ip) of FSH (10 IU/0.1 ml distilled water (dw)/lizard/alternate days/30 days) to adult male lizards, Mabuya carinata, during the early recrudescence phase of the reproductive cycle caused activation of spermatogenic and steroidogenic activity of the testis, as shown by a significant increase in mean number of spermatogonia, primary spermatocytes and spermatids, and serum levels of testosterone, as compared to initial controls. In addition, there were abundant spermatozoa in the lumen of the seminiferous tubules. Interestingly, administration of a similar dosage of FSH to lizards exposed to stressors (handling, chasing, and noise randomly applied, five times a day for 30 days) resulted in a significant increase in mean number of spermatogonia and primary spermatocytes over initial control values, whereas the number of secondary spermatocytes and spermatids and serum levels of testosterone did not significantly differ from those of initial controls, and were significantly lower than FSH treated normal lizards. Further, spermatozoa were infrequently found in the seminiferous tubules of these lizards. Treatment controls (receiving 0.1 ml dw/lizard/alternate days for 30 days) did not show significant variation in mean number of spermatogonia, spermatocytes and spermatids, and serum levels of testosterone from initial controls. Another group of lizards was exposed to stressors and did not receive FSH. These lizards showed a significant decrease in mean number of secondary spermatocytes compared to treatment controls and all other parameters did not significantly differ from those of both control groups. The results reveal that gonadotrophin-induced spermatogonial proliferation occurs under stressful conditions, whereas progress of spermatogenesis beyond primary spermatocyte stage is impaired due to inhibition (under stress) of gonadotrophin induced steroidogenic activity in M. carinata.

Cloacal Gland and Testes Development in Male Japanese Quail Selected for Divergent Adrenocortical Responsiveness

The time course of sexual development in male quail from lines selected for either a reduced (low stress, LS) or an exaggerated (high stress, HS) plasma corticosterone response to brief restraint was determined. Sexual development was assessed by examination of cloacal gland area (CAREA) and volume (CVOL), proportion of individuals that produced cloacal gland foam, and the intensity of cloacal gland foam production (CFP) at 4, 5, 6, 8, 10, 14, and 16 wk of age. These intervals encompass ages during which growing, photostimulated quail would be expected to evolve from being totally prepubescent to well into adulthood. Testes weight (TW) and the proportion of individuals that had achieved a combined TW of 500 mg (PI500) were also measured at 6 and 16 wk of age. Mean CAREA and CVOL were similar in LS and HS quail at 4 wk of age. Beginning at 5 wk of age and thereafter, CAREA was greater (P < 0.05) in LS than in HS quail. Similarly, beginning at 6 wk of age and thereafter, CVOL was greater (P < 0.05) in LS than in HS quail. More LS than HS birds also expressed foam at 4 (P < 0.05), 5 (P = 0.15), and 6 wk (P < 0.05) of age. From 8 wk on, all birds were in foam production. CFP results mimicked those found for CAREA and CVOL in that LS quail tended toward higher CFP values than HS quail at all intervals of measurement. TW were higher (P < 0.02) in LS than HS quail when data from the 2 ages at which testes were harvested were combined. At 6 wk of age, the LS and HS birds showed a PI500 line difference (P < 0.08) of 1.0 and 0.91, respectively; by 16 wk, all birds exhibited a maximum PI500. The results suggest that 1) selection for reduced adrenocortical responsiveness in Coturnix is accompanied by an accelerated onset of puberty in males, and 2) enhanced reproductive development in LS males remains extant throughout early to middle-age adulthood.

Photoperiod-Induced Changes in Cloacal Gland Physiology and Testes Weight in Male Japanese Quail Selected for Divergent Adrenocortical Responsiveness

In quail, activation of the hypothalamic-pituitary-adrenal axis has been linked to depression in the hypothalamic-pituitary-testicular axis, and cloacal gland development and foam production are known to be androgen dependent. Therefore, photoperiod manipulations that induce gonadal growth (long day) and involution (short day) were used to examine changes in cloacal gland physiology in male quail from lines selected for a reduced (low stress, LS) or exaggerated (high stress, HS) plasma corticosterone response to brief restraint. Line differences in cloacal gland area (CAREA) and volume (CVOL), the proportion of individuals that produced cloacal gland foam (PICF), and the intensity of cloacal gland foam production (CFP) were initially assessed in adult males maintained on stimulatory, long photoperiods of 14L:10D. Thereafter, these variables were re-examined weekly in the same males during their subsequent exposure to 3 wk of short days (6L:18D) followed by return to long d for 3 more wk. Line differences in testes weight relative to body weight (RTW) were also measured at the end of the study. CAREA and CVOL were markedly greater in LS than HS males grown under long days. As expected, these indices of cloacal gland size were greatly reduced upon exposure to short days in both lines. However, line differences (LS > HS) in CAREA and CVOL were maintained during the first 2 wk of exposure to short days. Line differences in the depressed cloacal gland size measures were no longer evident by the third week on short days as well as after the first week of relighting wherein there were no further depressions in gland size of either line. However, by the end of 2 wk of rephotostimulation and thereafter, marked line differences (LS > HS) in CAREA and CVOL re-emerged. Photoperiod-induced line effects on CFP generally mimicked those of CAREA and CVOL. The PICF was marginally different (P < 0.07) between the lines (LS > HS) only after 1 wk of light reduction. After 3 wk of rephotostimulation, RTW was nearly 25% greater in LS quail. The results suggest that selection for reduced adrenocortical responsiveness in Coturnix has resulted in certain reproductive advantages in middle-aged, adult males maintained on stimulatory photoperiods as well as in such adults subjected to photocastration and subsequent rephotostimulation.

Beta-endorphin disrupts seasonal and FSH-induced ovarian recrudescence in the lizard Mabuya carinata

Administration (ip) of an opioid peptide, beta-endorphin (beta-EP) (0.1, 0.5, or 1 microg beta-EP/day/lizard for 30 days) during seasonal recrudescence phase of the ovarian cycle inhibited ovarian recrudescence as shown by the absence of vitellogenic follicles in the ovary in contrast to their presence in treatment controls in the lizard Mabuya carinata. In the germinal bed, treatment of 0.1 microg beta-EP did not affect primordial follicles, whereas their mean number was significantly lower in lizards treated with 0.5 or 1 microg beta-EP compared to those of treatment controls. There was also suppression of oviductal development as shown by a significantly lower relative weight of the oviduct and regressed oviductal glands in lizards treated with all the dosages of beta-EP compared to treatment controls. In another experiment, administration of FSH (10 IU FSH/alternate day/lizard for 30 days) during the regression phase of the ovarian cycle induced development of vitellogenic follicles, whereas the treatment controls showed only previtellogenic follicles. In addition, there was a significant increase in the ovarian and oviductal weights compared to initial and treatment controls. However, simultaneous administration of similar dosage of FSH and beta-EP (0.5 microg/day/lizard) did not induce ovarian recrudescence as shown by the absence of vitellogenic follicles in the ovary and significantly lower weight of the ovary and the oviduct and the mean number of oogonia, oocytes, and primordial follicles compared to those of FSH-treated lizards. The results indicate that beta-EP inhibits seasonal as well as FSH-induced ovarian recrudescence. Inhibitory effect of beta-EP on follicular development despite FSH administration implies its effect at the ovarian level in M. carinata. While adversely affecting the ovarian follicular development, beta-EP did not affect the adrenal gland as there was no significant variation in the mean nuclear diameter of the adrenocortical cells of treatment controls and beta-EP-treated lizards. Furthermore, administration of beta-EP caused a significant decrease in the mean number of islands of white pulp of the spleen indicating its adverse effect on immunity.