Presence and Function of Dopamine Transporter (DAT) in Stallion Sperm: Dopamine Modulates Sperm Motility and Acrosomal Integrity

Abstract

Dopamine is a catecholamine with multiple physiological functions, playing a key role in nervous system; however its participation in reproductive processes and sperm physiology is controversial. High dopamine concentrations have been reported in different portions of the feminine and masculine reproductive tract, although the role fulfilled by this catecholamine in reproductive physiology is as yet unknown. We have previously shown that dopamine type 2 receptor is functional in boar sperm, suggesting that dopamine acts as a physiological modulator of sperm viability, capacitation and motility. In the present study, using immunodetection methods, we revealed the presence of several proteins important for the dopamine uptake and signalling in mammalian sperm, specifically monoamine transporters as dopamine (DAT), serotonin (SERT) and norepinephrine (NET) transporters in equine sperm. We also demonstrated for the first time in equine sperm a functional dopamine transporter using 4-[4-(Dimethylamino)styryl]-N-methylpyridinium iodide (ASP+), as substrate. In addition, we also showed that dopamine (1 mM) treatment in vitro, does not affect sperm viability but decreases total and progressive sperm motility. This effect is reversed by blocking the dopamine transporter with the selective inhibitor vanoxerine (GBR12909) and non-selective inhibitors of dopamine reuptake such as nomifensine and bupropion. The effect of dopamine in sperm physiology was evaluated and we demonstrated that acrosome integrity and thyrosine phosphorylation in equine sperm is significantly reduced at high concentrations of this catecholamine. In summary, our results revealed the presence of monoamine transporter DAT, NET and SERT in equine sperm, and that the dopamine uptake by DAT can regulate sperm function, specifically acrosomal integrity and sperm motility.

Effect of Pergolide Therapy on Semen Parameters in a Stallion With Pituitary Pars Intermedia Dysfunction

“…Many mammalian (including equine) spermatozoids have also been shown to exhibit D2 receptors which are sensitive to dopamine and dopamine agonists [18][19]. According to different studies in human and equine semen, dopamine agonists have a negative influence on semen motility [18][19]. We cannot confirm such an effect in the single case we have documented.…”

“…A further explanation for the observed decrease of ejaculate volumes could be a direct influence of pergolide on the D2-receptor of the central or peripheral nervous system influencing the ejaculatory process [11]. Many mammalian (including equine) spermatozoids have also been shown to exhibit D2 receptors which are sensitive to dopamine and dopamine agonists [18][19]. According to different studies in human and equine semen, dopamine agonists have a negative influence on semen motility [18][19].…”

Survey on basal blood plasma catecholamine concentrations in Martina Franca donkey (Equus asinus)

“…However, donkeys employed in onotherapy are handled immediately after weaning. Dopamine is also involved in many biological processes in mammals, involved in cognition, emotions [25,26], control and coordination of motor activity and in brain reward systems [27]. Catecholamines also play a role in the body's adjustment to mental stress [22].…”

“…This may explain the higher plasma adrenaline concentrations in younger animals, considering that adrenaline plays a predominant role in the phases preceding exercise, whereas it seems that noradrenaline has a predominant role in sustaining physical activity [24]. Dopamine is also involved in many biological processes in mammals, involved in cognition, emotions [25,26], control and coordination of motor activity and in brain reward systems [27]. There is a lack of information on dopamine in equids.…”

Physiology and Metabolic Anomalies of Dopamine in Horses: A Review

“…In stallions, Urra et al [33] documented that DA acts as a physiological modulator of viability, capacitation and sperm motility. Indeed, the acrosome integrity and thyrosine phosphorylation is significantly reduced at high concentrations of this catecholamine in equine sperm.…”