Abstract
BackgroundOpioid receptors and endogenous opioid peptides act not only in the control of nociceptive pathways, indeed several reports demonstrate the effects of opiates on sperm cell motility and morphology suggesting the importance of these receptors in the modulation of reproduction in mammals. In this study we investigated the expression of delta opioid receptors on equine spermatozoa by western blot/indirect immunofluorescence and its relationship with sperm cell physiology.MethodsWe analyzed viability, motility, capacitation, acrosome reaction and mitochondrial activity in the presence of naltrindole and DPDPE by means of a computer assisted sperm analyzer and a fluorescent confocal microscope. The evaluation of viability, capacitation and acrosome reaction was carried out by the double CTC/Hoechst staining, whereas mitochondrial activity was assessed by means of MitoTracker Orange dye.ResultsWe showed that in equine sperm cells, delta opioid receptor is expressed as a doublet of 65 and 50 kDa molecular mass and is localized in the mid piece of tail; we also demonstrated that naltrindole, a delta opioid receptor antagonist, could be utilized in modulating several physiological parameters of the equine spermatozoon in a dose-dependent way. We also found that low concentrations of the antagonist increase sperm motility whereas high concentrations show the opposite effect. Moreover low concentrations hamper capacitation, acrosome reaction and viability even if the percentage of cells with active mitochondria seems to be increased; the opposite effect is exerted at high concentrations. We have also observed that the delta opioid receptor agonist DPDPE is scarcely involved in affecting the same parameters at the employed concentrations.ConclusionsThe results described in this paper add new important details in the comprehension of the mammalian sperm physiology and suggest new insights for improving reproduction and for optimizing equine breeding.
Highlights
Opioid receptors and endogenous opioid peptides act in the control of nociceptive pathways, several reports demonstrate the effects of opiates on sperm cell motility and morphology suggesting the importance of these receptors in the modulation of reproduction in mammals
Adaptation, which is a consequence of a prolonged exposure to opiates, can cause the internalization of the receptor via a classic endocytic pathway occurring in a ligand specific manner that is independent of ligand ability to stimulate G-protein signalling explaining the differences in the efficacy and abuse potential of various opiates [22]
We have analyzed the effects of DOR activation in the presence of specific agonist/antagonist compounds contributing to deepen the knowledge of the equine sperm cell physiology
Summary
Opioid receptors and endogenous opioid peptides act in the control of nociceptive pathways, several reports demonstrate the effects of opiates on sperm cell motility and morphology suggesting the importance of these receptors in the modulation of reproduction in mammals. Endogenous opioids act as neurotransmitters in both central and peripheral nervous system [1]. They were found in several other districts such as adrenal medulla, pancreatic islets, pituitary, intes-. Several reports demonstrate the effects of opiate compounds on sperm cell motility [14,15,16] and morphology [17] suggesting the importance of these receptors in the modulation of reproduction in mammals. Adaptation, which is a consequence of a prolonged exposure to opiates, can cause the internalization of the receptor via a classic endocytic pathway occurring in a ligand specific manner that is independent of ligand ability to stimulate G-protein signalling explaining the differences in the efficacy and abuse potential of various opiates [22]
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