Changes in mating behavior, erectile function, and nitric oxide levels in penile corpora cavernosa in streptozotocin-diabetic rats.
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This study assessed whether the in vivo production of nitric oxide (NO) in the penis is impaired in experimental diabetes and whether this phenomenon can be explained by abnormal levels of NO synthase isoenzymes and/or plasma androgens. Adult male Sprague-Dawley rats were injected with streptozotocin (STZ) (40 mg/kg, i.p.) or vehicle. One half of the STZ-treated animals received daily insulin replacement. Twelve weeks later, the animals were tested for mating behavior and erectile reflexes. They were then anesthetized with urethane (1 g/kg), and the NO levels in their corpora cavernosa were monitored electrochemically with porphyrin microsensors before and after electrostimulation of the cavernous nerve. The intracavernous pressure (ICP) was measured simultaneously. The diabetic animals had substantial impairment in the mating and erectile reflexes tests, decreased basal and stimulated NO levels in the corpora, and a reduced ICP response to cavernous nerve stimulation. Insulin replacement fully reversed the effects of diabetes on the mating reflexes, the basal NO signals, and the ICP responses to electrical field stimulation and partially restored the stimulated NO release. Neither diabetes nor diabetes with insulin treatment had significant effects on serum testosterone levels or NOS isoform (nNOS, eNOS, and iNOS) protein content in penile homogenates, indicating that the changes found in erectile function were independent of such variables. These results also suggest that the diabetes-induced reduction in corporeal NO levels could be mainly due to the lack of some essential cofactors for NOS activity rather than to changes in the amount of enzyme proteins. (+info)
Polyandry produces sexy sons at the cost of daughters in red flour beetles.
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Female mating with multiple males within a single fertile period is a common phenomenon in the animal kingdom. Female insects are particularly promiscuous. It is not clear why females mate with multiple partners despite several potential costs, such as expenditure of time and energy, reduced lifespan, risk of predation and contracting sexually transmitted diseases. Female red flour beetles (Tribolium castaneum) obtain sufficient sperm from a single insemination to retain fertility for several months. Nonetheless they copulate repeatedly within minutes with different males despite no direct fitness benefits from this behaviour. One hypothesis is that females mate with multiple partners to provide indirect benefits via enhanced offspring fitness. To test this hypothesis, we compared the relative fitness of F(1) offspring from females mated with single males and multiple males (2, 4, 8, or 16 partners), under the condition of relatively high intraspecific competition. We found that a female mating with 16 males enhanced the relative fitness of F(1) males (in two out of three trials) but reduced F(1) females' fitness (in two independent trials) in comparison with singly mated females. We also determined whether several important fitness correlates were affected by polyandry. We found that F(1) males from mothers with 16 partners inseminated more females than F(1) males from mothers with a single partner. The viability of the eggs sired or produced by F(1) males and females from highly polyandrous mothers was also increased under conditions of low intra-specific competition. Thus, the effects of polyandry on F(1) offspring fitness depend on environmental conditions. Our results demonstrated a fitness trade-off between male and female offspring from polyandrous mothers in a competitive environment. The mechanisms and biological significance of this unique phenomenon are discussed. (+info)
Effects of pyrethroid insecticide ICON (lambda cyhalothrin) on reproductive competence of male rats.
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AIM: To assess the effect of ICON (trade name of lambda-cyhalothrin) on sexual competence and fertility of male rats. METHODS: Male rats were gavaged daily for 7 consecutive days with different doses of ICON (63 mg/kg and 100 mg/kg) or vehicle (distilled water). Their sexual behaviour and fertility were evaluated at different time points during treatment and post-treatment using receptive females. RESULTS: Treatment had no effect on fertility, but sexual competence was seriously impaired: libido (assessed in terms of pre-coital sexual behaviour, and numbers of mounting, intromission and ejaculation), sexual arousability/motivation (in terms of latencies for mounting, intromission and ejaculation), sexual vigour (judged by frequencies of mounting and intromission or copulatory efficiency). In addition, ICON suppressed intromission ratio, indicating erectile dysfunction. These effects on sexual function had a rapid onset and was reversible. ICON-induced sexual dysfunction was mediated by multiple mechanisms, mainly toxicity, stress, sedation and possibly via GABA and dopaminergic systems. CONCLUSION: Exposure to ICON may cause sexual dysfunction in male rats. (+info)
Pre- and post-insemination episodes of sexual selection in the fowl, Gallus g. domesticus.
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Although much attention has been recently directed to sexual selection arising after insemination from sexual promiscuity, little is known about the mechanisms determining reproductive success after insemination, and the way these mechanisms interact with each other and with selective mechanisms occurring before insemination: mate choice and mate acquisition. Here, we briefly review the findings of an on-going study investigating the mechanisms generating variation in reproductive success at both a pre- and a post-insemination stage in the domestic fowl. Female preference consistently favours socially dominant males before and after insemination. However, although social status mediates the number of sperm that a male inseminates into a female, dominant males may inseminate sperm of lower fertilising quality than their subordinates. We argue that mitochondrial genes may contribute to determine sperm quality, and speculate that the maternal control of mitochondrial genes may prevent sexual selection from operating on males, thus explaining both the lack of a positive correlation between social dominance and sperm quality and the maintenance of variation in male quality in the fowl. (+info)
The parvocellular vasotocin system of Japanese quail: a developmental and adult model for the study of influences of gonadal hormones on sexually differentiated and behaviorally relevant neural circuits.
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Vasotocin (VT; the antidiuretic hormone of birds) is synthesized by diencephalic magnocellular neurons projecting to the neurohypophysis. A sexually dimorphic system of VT-immunoreactive (ir) parvocellular elements has been described within the male medial preoptic nucleus (POM) and the nucleus of the stria terminalis, pars medialis (BSTm). VT-ir fibers are present in many diencephalic and extradiencephalic locations, and quantitative morphometric analyses demonstrated their sexually dimorphic distribution in regions involved in the control of different aspects of reproduction. Moreover, systemic or intracerebroventricular injections of VT markedly inhibit the expression of some aspects of male sexual behavior. In adult animals, circulating levels of testosterone (T) have a profound influence on the VT immunoreactivity within BSTm, POM, and lateral septum. Castration markedly decreases the immunoreaction, whereas T-replacement therapy restores a situation similar to the intact birds. We observed no changes in gonadectomized females treated with T. These changes parallel similar changes in male copulatory behavior (not present in castrated male quail, fully expressed in castrated, T-treated males). The restoration by T of the VT immunoreactivity in castrated male quail could be fully mimicked by a treatment with estradiol (E(2)), suggesting that the aromatization of T into E(2) may play a key limiting role in both the activation of male sexual behavior and the induction of VT synthesis. This dimorphism has an organizational nature: administration of E(2) to quail embryos (a treatment that abolishes male sexual behavior) results in a dramatic decrease of the VT immunoreactivity in sexually dimorphic regions. Conversely, the inhibition of E(2) synthesis during embryonic life (a treatment that stimulates the expression of male copulatory behavior in treated females exposed in adulthood to T) results in a malelike distribution of VT immunoreactivity. The VT parvocellular system of the Japanese quail can therefore be considered an accurate marker of the sexual differentiation of brain circuits mediating copulatory behavior and could be a very sensitive indicator of the activity of estrogenlike substances on neural circuits. (+info)
Male phenotype predicts insemination success in guppies.
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Theory predicts that mate choice can lead to an increase in female fecundity if the secondary sexual traits used by females to assess male quality covary with the number of sperm transferred during copulation. Where females mate multiply, such a relationship between male attractiveness and ejaculate size may, additionally (or alternatively), serve to augment the effect of indirect selection by biasing paternity in favour of preferred males. In either case, a positive correlation between male attractiveness and the size of ejaculates delivered at copulation is predicted. To date, some of the most convincing (indirect) evidence for this prediction comes from the guppy, a species of fish exhibiting a resource-free mating system in which attractive males tend to have larger sperm reserves. We show that, during solicited copulations, male guppies with preferred phenotypes actually transfer more sperm to females than their less-ornamented counterparts, irrespective of the size of their initial sperm stores. Our results also reveal that, during coercive copulations, the relationship between ejaculate size and the male's phenotype breaks down. This latter result, in conjunction with our finding that mating speed--a factor under the female's control-is a significant predictor of ejaculate size, leads us to speculate that females may exert at least partial control over the number of sperm inseminated during cooperative matings. (+info)
Copulation corrupts immunity: a mechanism for a cost of mating in insects.
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There are well documented costs of mating in insects but little evidence for underlying mechanisms. Here, we provide experimental evidence for a hormone-based mechanism that reduces immunity as a result of mating. We examined the mealworm beetle Tenebrio molitor and show that (i) mating reduces a major humoral immune effector-system (phenoloxidase) in both sexes, and (ii) that this down-regulation is mediated by juvenile hormone. Because both juvenile hormone and phenoloxidase have highly conserved functions across all insects, the identified mechanism is similarly likely to be highly conserved. The positive physiological function of mating-induced juvenile hormone secretion is gamete and accessory gland production: we propose that its negative effects on immune function are the consequence of physiological antagonism. Therefore, we have identified a physiological tradeoff between mating and immunity. Our results suggest that increasing mating success can result in increasing periods of immune suppression, which in turn implies that reproductively successful individuals may be more vulnerable to infection by, and the negative fitness effects of, pathogens. (+info)
Participation of 5-HT(1B) receptors in the inhibitory actions of serotonin on masculine sexual behaviour of mice: pharmacological analysis in 5-HT(1B) receptor knockout mice.
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1 The role of the 5-Hydroxytryptamine(1B) (5-HT(1B)) receptor subtype in masculine sexual behaviour in mice was analysed in both 5-HT(1B) receptor knockout (KO(1B)) and wild-type (WT) animals. 2 Comparison of male copulatory behaviour of WT and KO(1B) strains revealed that KO(1B) mice become interested earlier in sexual behaviour, but require more stimulation to achieve ejaculation than its corresponding WT strain. 3 The pharmacological manipulation of male sexual activity in the WT strain showed that the serotonin precursor 5-Hydroxytryptophan (5-HTP), the 5-HT(1B) agonist (1-(m-trifluoromethylphenyl) piperazine (TFMPP) and the 5-Hydroxytryptamine(1A) (5-HT(1A)) receptor agonist 8-hydroxy-2-di-n-propylamino-tetralin (8-OH-DPAT) all inhibited male copulatory behaviour in mice. 4 In KO(1B) mice, TFMPP lacked an effect, 5-HTP exerted a mild inhibitory effect while 8-OH-DPAT provoked only a tendency towards a reduction in the percentage of animals that achieved ejaculation. In general, KO(1B) mice were less sensitive to the inhibitory actions of 5-HTP and 8-OH-DPAT than the WT strain. 5 Based on these results, we can suggest that serotonin plays a general inhibitory role in the sexual behaviour of male mice and that both 5-HT(1B) and 5-HT(1A) receptor subtypes participate in the inhibitory actions of this neurotransmitter. 6 The absence of the 5-HT(1B) receptor subtype affected both components of mouse masculine sexual behaviour, motivation and execution, further confirming the involvement of this receptor subtype in the control of this behaviour. In addition, the diminished sensitivity to serotonergic stimulation exhibited by KO(1B) mice suggests the occurrence of compensatory changes as a consequence of the absence of the 5-HT(1B) receptor subtype. (+info)