Melatonin Has a Beneficial Effect on Stallion Sperm Quality in Cool Condition

Calcium affects stallion spermatozoa parameters in different incubation temperatures

This study was aimed to determine the effect of CaCl2 on the motility and viability of stallion spermatozoa during different incubation temperatures. Experimental samples were prepared by diluting the ejaculates (n = 10) from three uniformly housed and fed breeding stallions with six different concentrations of CaCl2 (A: 0.1125, B: 0.225, C: 0.45, D: 0.938, E: 1.25, and F: 1.875 mg/mL). The control samples (CON) were prepared by diluting ejaculate only with physiological solution. Samples were divided into two aliquots for analyses at different storage temperatures (5 °C and 37 °C). The motility parameters were analysed by Computer Assisted Semen Analysis system at several time intervals (0, 1, 2 and 3 h) and the viability was assessed using a mitochondrial toxicity test (MTT) realized at the end of incubation at both temperatures. Addition of CaCl2 to stallion semen showed significant effect on motility parameters, especially in the highest concentrations at 5 °C. Significant objectionable effect of CaCl2 on both total and progressive motility was observed at temperature 37 °C compared to control sample. However, results of velocity curved line in samples C, D and F at time 1 h and also at time 2 h in sample F showed significant positive effect of CaCl2. Sperm viability in experimental samples did not show a significant difference compared to the control at either 5 °C or 37 °C. The results of this study did not confirm essential effect of calcium on reproductive parameters of stallion. To conclude, our study demonstrated that the effect of CaCl2 on stallion sperm motility differs in a dose-dependent manner; however, the overall impact on motility parameters does not seem to be beneficial.

A combination of biomarkers for predicting stallion sperm fertility

Equine breeding would benefit greatly from reliable biomarkers of stallion or ejaculate fertility. The aim of the study was to investigate how several in vitro sperm characteristics correlate with fertility after artificial insemination, to explore the potential to build a fertility prediction model for stallions. Cooled insemination doses (3-5 per stallion) were obtained from various studs. Sperm membrane integrity, acrosome integrity, chromatin integrity, mitochondrial membrane potential, and reactive oxygen species production were evaluated by flow cytometry 24-30 h after semen collection, and sperm motility was assessed by computer aided sperm analysis. Calcein violet was used to differentiate viable spermatozoa. Per season pregnancy rates for these stallions were available the following year. Positive correlations were found between pregnancy rate and straightness (r = 0.43, p ≤ 0.001), as well as pregnancy rate and the proportion of living hydrogen peroxide positive spermatozoa (r = 0.32, p ≤ 0.05). There were negative correlations between pregnancy rate and amplitude of lateral head displacement (r = -0.26, p ≤ 0.05), and between pregnancy rate and the mean fluorescence of dead superoxide positive spermatozoa (r = -0.46, p < 0.001). Principal component analysis indicated that motility, membrane integrity, DNA fragmentation, and reactive oxygen species production were associated with pregnancy rate. Therefore, a combination of these factors could be used as a biomarker of fertility when assessing ejaculates. However, data from more individuals would be required to construct a model for fertility prediction.

Improving chilled and frozen buck sperm characteristics by adding melatonin and L-carnitine to the preservation medium

This study evaluated the effects of melatonin (MLT) and L-carnitine supplementation on sperm quality and antioxidant capacity during chilled and cryopreservation. Twenty-four ejaculates were collected from six Damascus bucks, 4 ejaculates each, from mid-September to mid-October 2022. The pooled semen from each collecting session was divided into 5 equal aliquots after being diluted (1:10) with Tris-citric acid egg yolk extender. The first aliquot served as a control (treatment-free). MLT was added to the second and third aliquots at low and high doses (LD: 4 and HD: 8 μL/mL) (v/v), respectively, while L-carnitine (LC) was added to the fourth and fifth aliquots at the same aforementioned doses. The aliquots were stored at 4°C for 48 h to assess sperm physical and morphological characteristics, alongside lipids peroxidase (LP) production and glutathione peroxidase (GPX) activity. The optimum doses of MLT and LC that showed potential for maintaining sperm characteristics throughout the chilled storage period were further investigated for protecting the spermatozoa after exposure to cryopreservation stress compared to the control. The results showed higher sperm motility (%) in the MLT-HD group, higher (p ≤ .05) sperm viability (%) in the MLT-LD, and both aliquots of LC at T24 hours of chilled preservation. Normal sperm (%) was higher (p ≤ .05) in both LC-LD and MLT-LD groups than other groups, while sperm acrosome integrity (%) was higher (p ≤ .05) in the LC-LD group. Morphological abnormalities (%) were improved (p ≤ .05) in all treated aliquots compared with control. The mean value of GPX activity was higher (p ≤ .05) in both MLT groups, while the concentration of LP increased (p ≤ .05) in the LC-HD or control groups. Furthermore, supplementing buck sperm medium with 4 μL/mL of MLT or LC improved (p < .05) the sperm characteristics and decreased (p < .05) DNA fragmentation index after thawing.

Effect of Melatonin and Caffeine Supplementation to Freezing Medium on Cryosurvival of Peruvian Paso Horse Sperm Using a Two-Step Accelerating Cooling Rate

This research examined the antioxidant and cryoprotective effects of melatonin (ME) and caffeine (CAF) supplementation in freezing medium on the cryosurvival of Peruvian Paso horse sperm using a two-step accelerating cooling rate. Twenty ejaculates from four adult and fertile stallions were recovered, initially diluted with INRA-96®, and finally frozen with INRA-Freeze® with either no supplementation (as control), 1 μM ME, or 2 mM CAF using a two-ramp freezing system content inside a cryogenic-box and liquid nitrogen vapors. The sperm kinematic parameters and integrity of the plasma and acrosomal membranes of fresh semen and cryopreserved samples were evaluated using the CASA system (SCA-Evolution® 2018) and PI/fluorescein isothiocyanate-conjugated peanut (Arachis hypogaea) agglutinin double fluorescent test, respectively. The oxidative stress of post-thaw sperm samples was also assessed using the CellRox Deep Red fluorescence test. The results showed that curvilinear velocity and average-path velocity were greater (p < 0.05) after freezing with CAF than the control group. In addition, there were significance differences (p < 0.01) between stallions (1-4) in post-thaw kinematic parameters regardless of ME or CAF addition. Both ME and CAF improved (p < 0.05) the proportion of sperm with intact plasma membranes and intact acrosomes. Nevertheless, neither CAF nor ME improved the oxidative stress after the cryopreservation process.

Effect of Different Concentrations of Melatonin on Ram Epididymal Spermatozoa Recovered Post-mortem under Oxidative Stress Conditions and Storage at 4 °C

The current study examines the protective effects of different melatonin concentrations on fresh ram epididymis spermatozoa after post-mortem recovery under normal and oxidative stress conditions and during liquid preservation (4^o C) at different times (24, 48, and 72h). The testes were obtained from a local slaughterhouse during the breeding season. Spermatozoa were isolated from cauda epididymidis. In experiment 1, the effects of adding different concentrations of melatonin (0, 15, 60, and 240 μg/mL) under normal and oxidative stress conditions were evaluated. Fifty μM of hydrogen peroxide was used to induce oxidative stress. Also, in experiment 2, the spermatozoa samples were chilled to 4^o C and stored for 72 h. Sperm total motility, viability, membrane, DNA integrity, and morphological abnormality were evaluated at 0, 24, 48, and 72 h after cooling storage. In experiment 1, melatonin treatment preserved viability increased TAC and SOD activities, and reduced MDA levels compared to control. Also, melatonin reduced the harmful effects of H2O2 under induced oxidative stress. In experiment 2, Melatonin at concentrations of 15 and 60 g/mL greatly increased sperm viability after 3 days of cold storage. Furthermore, it could have a significant protective effect on the motility of cooled sperm. Melatonin supplementation preserved higher sperm membrane integrity at concentrations of 15 and 60μg/mL, DNA integrity at a concentration of 15μg/mL, and abnormality at a concentration of 60μg/mL after 3 days of storage. The results suggest that melatonin can be used to reduce the adverse effects of induced oxidative stress in spermatozoa. Furthermore, ram epididymal spermatozoa could be stored at 4 °C for 72 h when treated with melatonin.

Shielding effect of melatonin improves seminal quality and oxidative stress indices during chilled storage of ram semen

Supplementation of antioxidant to semen extender maintains seminal quality by reducing oxidative stress during preservation time period. The main aim of this study was to investigate the effect of different concentrations of melatonin supplementation on liquid storage of Magra ram semen. This study was performed on adult Magra ram (n = 8), and seminal ejaculates (48) were collected and evaluated for various macroscopic and microscopic seminal quality parameters for further processing. After preliminary evaluation, ejaculates of each collection session were mixed and divided into four equal aliquots. All the aliquots were diluted (1:10) with Tris-citric fructose egg yolk extender contained sans melatonin served as control, whereas the other three aliquots were supplemented with 0.5, 1 and 2 mM MLT which were grouped as MLT0.5, MLT1 and MLT2, respectively. Thereafter, the samples were stored at 4 ºC for 72 h, and various seminal parameters (individual sperm progressive motility, viability, abnormalities, plasma membrane functionality) along with oxidative stress parameters (total antioxidant capacity (TAC), malondialdehyde (MDA)) were evaluated at 0, 24, 48 and 72 h of preservation. The results indicated that the mean percent values for progressive sperm motility, viability, plasma membrane functionality and TAC were significantly higher (p < 0.05) in treated groups with the highest values in MLT1 group. Significantly lower (p < 0.05) percentage of total sperm abnormalities and MDA level was observed in treatment groups compared to control group. The results report that supplementation of 1 mM melatonin efficiently maintains the seminal quality and ameliorates oxidative stress during preservation at 4 ºC to 72 h.

Supplementation of melatonin to cooling and freezing extenders improves canine spermatozoa quality measures

Background

Sperm freezing and cold storage are the two most common assisted reproductive technologies in the canine breeding industry. The freeze-thawing process causes significant detrimental changes in both sperm cell structure and function. Previous research has confirmed that excessive accumulation of un-scavenged free radicals (oxidative stress) plays an important role in the cryopreservation-induced damage to sperm cells. Also, the gradual accumulation of the free radicals during cold storage leads to a decline in the sperm quality markers. Melatonin is an endogenous neurohormone synthesized from tryptophan amino acid by pineal glands. Besides its several well-known physiologic roles, melatonin has a significant antioxidant potential through direct free radical scavenging properties. Therefore, the current study was designed to evaluate the potential in vitro protective properties of melatonin (0.5, 1, and 2 mM) on canine sperm cells after freezing or during long-term cold storage (9 days, 5 °C) on most important sperm in vitro fertility markers.

Results

Melatonin at 0.5, 1- or 2-mM concentrations could preserve significantly higher sperm total motility after 4 days of cold storage. However, only the 1- and 2 mM melatonin concentrations could result in better TM and PM values after 7 days of cold storage. Furthermore, melatonin supplementation could preserve higher sperm viability and acrosome integrity after 7 days of storage. Also, it could have significant protective effects on the cooled sperm DNA integrity. In the freezing section of the current research, melatonin at either 1- or 2-mM concentrations could not improve the sperm post-thaw TM and PM, whereas they improved sperm DNA integrity. Also, the post-thaw plasma membrane functional integrity and sperm velocity parameters were not affected by the treatment. Although DMSO (Dimethyl Sulfoxide) as the melatonin solvent could reduce the level of sperm lipid peroxidation and even improve the post-thaw sperm DNA integrity compared to the negative control, it reduced the post-thaw sperm progressive motility. However, the negative effects were reversed by concurrent melatonin supplementation at 1- and 2-mM concentrations.

Conclusion

The addition of 1- or 2-mM melatonin to the canine sperm freezing and cooling media could improve sperm motility, viability, acrosome, and DNA integrity.

Sperm characteristics, peroxidation lipid and antioxidant enzyme activity changes in milt of Brycon orbignyanus cryopreserved with melatonin in different freezing curves

The objective of this study was to evaluate extender supplemented with melatonin and freezing curves on the antioxidant enzyme activity, peroxidation lipid and sperm characteristics of cryopreserved Brycon orbignyanus milt. Males (n = 16) and females (n = 5) were hormonally induced with two doses (0.5 mg and 5.0 mg kg^-1) of carp pituitary extract, and their gametes were collected by light abdominal massage. The fresh milt was diluted at a ratio of 1:4 (milt:extender) in the following solutions: (Control) 10% methyl glycol (MG) + 5% Beltsville thawing solution; (M1) Control + 1 mM melatonin; and (M2) Control + 2 mM melatonin. The freezing curves were C1 (automated freezer) and C2 (dry shipper for 24 h). After each curve was recorded, the straws were transferred to a liquid nitrogen container until the analyses were performed. The samples were thawed in a water bath (60 °C, 8 s) and evaluated using the Sperm Class Analyzer software for the parameters total motility, progressive motility, curvilinear velocity, straight line velocity, mean displacement velocity, straightness, and linearity. The following were also measured: motility time, vitality, morphology, oxidative stress (lipid peroxidation, activity of catalase and superoxide dismutase, quantification of nitric oxide), and fertilization and hatching rates. The data were analyzed within R by one-way analysis of variance and Tukey's test for comparison of means (p < 0.05). A significant difference (p < 0.05) was observed between the solutions in vitality, morphology, motility, and fertilization rate, the solutions with melatonin having the best values. Total motility, progressive motility, and motility time were significantly different. Among oxidative stress markers, only lipid peroxidation and superoxide dismutase activity showed an effect of the curve × solution interaction (p < 0.05), the solutions with melatonin yielding the lowest values. The fertilization and hatching rates were also higher under the melatonin treatments, regardless of the curve. Melatonin 2 mM and slow curve are indicated for the cryopreservation of fish species sperm as it led to the slowest detrimental spermatozoa effects and better fertilization and hatching rates.

Role of Antioxidants in Cooled Liquid Storage of Mammal Spermatozoa

Cooled preservation of semen is usually associated with artificial insemination and genetic improvement programs in livestock species. Several studies have reported an increase in reactive oxidative species and a decrease in antioxidant substances and sperm quality parameters during long-term semen storage at refrigerated temperatures. The supplementation of antioxidants in extenders before refrigeration could reduce this detrimental effect. Various antioxidants have been tested, both enzymatic, such as superoxide dismutase and catalase, and non-enzymatic, such as reduced glutathione, vitamins E and C and melatonin. However, the problem of oxidative stress in semen storage has not been fully resolved. The effects of antioxidants for semen-cooled storage have not been reviewed in depth. Therefore, the objective of the present study was to review the efficiency of the supplementation of antioxidants in the extender during cooled storage of semen in livestock species.

Melatonin can improve viability and functional integrity of cooled and frozen/thawed rabbit spermatozoa

Melatonin is known to protect sperm against freezing-inflicted damage in different domestic species. The aim of the study was to evaluate the effect of supplementation of semen extender with melatonin on the quality and DNA integrity of cooled and frozen/thawed rabbit spermatozoa. We also investigated whether the addition of melatonin to the semen extender could improve the fertility of rabbit does artificially inseminated with frozen/thawed semen. Semen samples collected from eight rabbit bucks were pooled and then diluted in INRA-82 supplemented either with (0.5, 1.0 or 1.5 mM) or without (0.0 mM) melatonin. Diluted semen was cooled at 5°C for 24 hr. For cryopreservation and based on the first experiment's best result, semen samples were diluted in INRA-82 in the presence or absence of 1.0 mM melatonin and then frozen in 0.25 ml straws. Following cooling or thawing, sperm quality and DNA integrity were evaluated. Furthermore, the fertility of frozen/thawed semen was investigated after artificial insemination. Supplementation of semen extender with 1.0 mM melatonin improved (p < .05) motility, viability, membrane and acrosome integrities in cooled semen compared with other groups. Sperm quality and DNA integrity were higher (p < .05) in frozen/thawed semen diluted in 1.0 mM melatonin-supplemented extender than in the control group. Conception and birth rates were higher in does inseminated with 1.0 mM melatonin treated semen compared with the controls. In conclusion, supplementation of semen extender with 1.0 mM melatonin improved the quality of cooled and frozen/thawed rabbit spermatozoa. Melatonin can preserve DNA integrity and enhance the fertility of frozen/thawed rabbit spermatozoa.

The Relationship of Mitochondrial Membrane Potential, Reactive Oxygen Species, Adenosine Triphosphate Content, Sperm Plasma Membrane Integrity, and Kinematic Properties in Warmblood Stallions

Equine sperm possesses a unique physiology because its energy supply is mostly dependent on oxidative phosphorylation of mitochondria as an aerobic source of adenosine triphosphate (ATP) generation. The present study was, therefore, conducted to investigate the relationship between sperm kinematic and functional variables in stallions. Semen samples were collected from five warmblood stallions (three ejaculates from each stallion), diluted with INRA96 and transferred to the laboratory. Next, sperm motility, mitochondrial membrane potential (MMP), production of superoxide anion (as a reactive oxygen species; ROS), ATP content, and plasma membrane integrity were assessed. Motion and functional characteristics differed among investigated stallions (P < .05). In addition, it was revealed MMP was positively correlated with the level of ROS and ATP content and progressive motility (P < .05). The level of ROS was positively correlated with ATP content and negatively correlated with plasma membrane integrity and straightness (P < .05). Adenosine triphosphate content was positively correlated with progressive motility, curvilinear velocity, average path velocity, and beat cross frequency and reversely correlated with plasma membrane integrity and straightness (P < .05). Plasma membrane integrity was positively correlated with straight line velocity, linearity, and straightness and negatively correlated with curvilinear velocity (P < .01). In conclusion, the present study substantiated that kinematic and functional characteristics varied among various warmblood stallions. Furthermore, the present study implicated although higher mitochondrial activity increases ATP synthesis, it leads to elevated superoxide anion production, which could culminate in disintegration of the sperm plasma membrane, thereby altering motion characteristics and swimming pattern of sperm.

Effect of melatonin supplementation to a cytoprotective medium on post-thawed Brycon orbignyanus sperm quality preserved during different freezing times

The aim of the present study is to verify the viability of frozen B. orbignyanus sperm cells after freezing with dilution media containing different concentrations of the melatonin and after different freezing times. Semen from 15 males was collected and pooled as five pools from three random animals. Oocytes (100) from three females were separately used for fertilization. There were three treatments: (C) Control Medium: 90% of extender Beltsville thawing solution (5% concentration) + 10% methylglycol (MG); (M1) Control Medium + 1 mM melatonin; and (M2) Control Medium + 2 mM melatonin. Sperm samples were diluted in media at a final proportion of 1:4 [125 μl sperm (25% V/V) + 337.5 μl BTS (65% V/V) + 37.5 μl MG (10% V/V)]. Melatonin was added at final solution. Three Dry shipper freezing times were used: T1 (15 min), T2 (12 h) and T3 (24 h). The samples were transferred, stored in a cryobank and thawed in a water bath at 60 °C for 5 s and evaluated concerning viability, morphology and fertilization rate. B. orbignyanus semen frozen in M2 presented the highest fertilization rate (8.40 ± 2.54%). The highest vitality (85.2 ± 2.8%), motility (64.63 ± 8.3%), motility duration (84.22 ± 11.4 s) and progressive motility (17.01 ± 1.2%) rates were maintained for M2. The highest number of altered cells was observed in C (57.4 ± 5.9%). Melatonin at 2 mmol L^-1 associated with the cryoprotectant methylglycol in cryopreservation could be used to improve a cryobank for endangered Brycon orbignyanus populations.

Effects of cashew gum and nanoparticles on cooled stallion semen

BACKGROUND

Cryopreservation of stallion spermatozoa tends to cause plasma membrane damage due to the low ratio of cholesterol to phospholipids. Gums have been suggested as an alternative cryoprotectant to glycerol for stallion spermatozoa. Therefore, the present experiment was designed to verify whether the effect of addition of cashew gum (CG), or nanoparticles (NP) containing CG, to the extender before cooling on sperm quality in stallion semen. Ejaculates from 6 stallions were extended and split between six treatment groups (control, a-tocopherol [TOC], CG1, CG0.5, NP1 and NP0.5), stored in cryotubes at 4 °C.

RESULTS

Aliquots were analysed by computer-assisted sperm motility analysis on the day of collection, and after 24 h and 48 h of cold storage. After 48 h, the total motility with NP1 (78.53 + 6.31%) was similar to control 85.79 + 6.31% at 0 h. The same pattern was observed for progressive motility. Membrane integrity assessed by flow cytometer was similar between control, TOC and G1 at all storage times. The DNA fragmentation in the control group increased at all time points, whereas chromatin integrity was maintained after 24 h in TOC and NP0.5 compared to 0 h. There was no increase in the proportion of live spermatozoa producing hydrogen peroxide, but there was a tendency for an increased proportion of spermatozoa in the live superoxide category in CG1 after 24 h cooled storage.

CONCLUSIONS

The addition of CG or CG-derived NP to extender for stallion semen was not harmful to the sperm cells.

Effect of melatonin on bovine sperm characteristics and ultrastructure changes following cryopreservation

The production of reactive oxygen species (ROS) during cryopreservation of semen alters the sperm motion and mobility characteristics, resulting in poor or failure of conception rate after artificial insemination (AI). Melatonin an antioxidant is able to modulate the effect of ROS and prevents spermatozoa by reducing the oxidative stress during freezing process. Eight ejaculates from eight healthy HF bulls diluted with Tris egg yolk glycerol extender were divided into five equal aliquots. The Computer Assisted Semen Analyser (CASA) results showed no significant difference between the control-post- thaw samples and melatonin-treated samples; however, the velocity of spermatozoa with regard to the VAP, VSL showed highest increase in the 0.25 mM MLT-treated semen followed by 0.1 mM MLT treated semen except for VCL where velocity increased with increase in the concentration of melatonin. The vigour of spermatozoa regard to BCF, STR and LIN recorded highest increase in the 0.25 mM MLT treated semen followed by 0.1 mM MLT-treated semen except for the ALH where vigour increased with increase in the concentration of melatonin. The electron micrography images illustrated that the addition of 0.1 mM melatonin protected the plasma membrane and acrosome region and maintained the ultrastructure integrity of the cryopreserved spermatozoa when compared to control group, whereas the electron micrography of spermatozoa treated with 0.2 and 0.25 mM melatonin illustrated highest damage to the plasma and acrosome membrane. Thus concluding that inclusion of melatonin to sperm extender can improve the post-thaw quality of cryopreserved bull spermatozoa.

Cryoprotective effect of melatonin supplementation on post-thawed rooster sperm quality

Reactive oxygen species (ROS) and free radicals are one of the major detrimental factors that can negatively affect the quality of sperm during cryopreservation. Melatonin is an effective antioxidant and free radical scavenger in various cells. In this study, therefore, the aim was to evaluate the post-thawed quality of spermatozoa after cryopreservation of rooster semen in freezing extender supplemented with melatonin. Semen samples from seven Green-legged Partridge roosters were pooled and diluted with EK extender supplemented with 10^-3, 10^-6, or 10^-9 M melatonin (control sample was prepared without supplementation with melatonin), and the pooled sample was subjected to cryopreservation. Post-thawed sperm motility was determined using the IVOS system, whereas plasma membrane status, acrosome integrity, mitochondrial activity, lipid peroxidation, chromatin status, and apoptotic-like changes were determined using fluorochromes and flow cytometry. Results, indicate post-thaw motile sperm cell count was greater (P < 0.05) in the frozen samples supplemented with melatonin (10^-3 and 10^-6 M) than the control sample. Although no significant differences were observed in post-thawed acrosomal integrity, plasma membrane integrity and mitochondrial activity were greater (P < 0.05) in samples frozen with melatonin (10^-3 and 10^-6 M) than that of the control sample. In addition, with supplementation of melatonin there was a decrease (P < 0.05) in the amount of lipid peroxidation, DNA fragmentation, and apoptotic-like changes after thawing. These results indicate there is a positive effect of melatonin supplementation in rooster semen freezing extenders on post-thaw sperm quality.

Melatonin supplementation improves the intactness of plasma membrane and acrosomal membrane of cryopreserved spermatozoa in Hariana bull

Supplementation of MT @ 2 mM was more beneficial in cryopreservation of Hariana bull spermatozoa as evidenced from post-thawed sperm membrane integrity and acrosomal intactness. Melatonin can be recommended to be used @ 2 mM concentration into the semen extender to increase the post thaw sperm functional attributes in Hariana bull.

Effect of addition of melatonin on liquid storage of ram semen at 4°C

Adding a certain amount of antioxidants to semen extender has been shown to improve semen quality. The aim of present study was to elucidate whether the supplementation of melatonin to the Tris-based extender (CTR) could enhance the quality of ram spermatozoa during storage at 4°C. Ram semen samples were collected and diluted with CTR extender containing different concentrations (0, 0.05 (M 0.05), 0.1 (M 0.1), 0.2 (M 0.2) or 0.4 (M 0.4) mM) of melatonin. Sperm routine indicators, mitochondrial activity, total antioxidant capacity (T-AOC) and malondialdehyde (MDA) content were analysed in control and melatonin treatment groups. The higher per cent of motility, plasma membrane integrity, mitochondrial activity and T-AOC activity was observed in M 0.05, M 0.1 and M 0.2 groups compared to control group at 5 days of storage (p < 0.05), while lower percentage of MDA content was observed among these groups (p < 0.05). In addition, there were no significant differences in acrosome integrity among the control and M 0.05, M 0.1 and M 0.2 groups during the experiment. The above results show that the addition of 0.05, 0.1, 0.2 mM of melatonin is beneficial to the preservation of ram semen during liquid storage at 4°C mainly through antioxidative stress.

Neuronal signaling repertoire in the mammalian sperm functionality

The common embryonic origin has been a recurrent explanation to understand the presence of "neural receptors" in sperm. However, this designation has conditioned a bias marked by the classical neurotransmission model, dismissing the possibility that neurotransmitters can play specific roles in the sperm function by themselves. For instance, the launching of acrosome reaction, a fundamental sperm function, includes several steps that recall the process of presynaptic secretion. Unlike of postsynaptic neuron, whose activation is mediated by molecular interaction between neurotransmitter and postsynaptic receptors, the oocyte activation is not mediated by receptors, but by cytosolic translocation of sperm phospholipase (PLCζ). Thus, the sperm has a cellular design to access and activate the oocyte and restore the ploidy of the species by an "allogenic pronuclear fusion." At subcellular level, the events controlling sperm function, particularly the capacitation process, are activated by chemical signals that trigger ion fluxes, sterol oxidation, synthesis of cyclic adenosine monophosphate, protein kinase A activation, tyrosine phosphorylations and calcium signaling, which correspond to second messengers similar to those associated with exocytosis and growth cone guidance in neurons. Classically, the sperm function associated with neural signals has been analyzed as a unidimensional approach (single ligand-receptor effect). However, the in vivo sperm are exposed to multidimensional signaling context, for example, the GABAergic, monoaminergic, purinergic, cholinergic, and melatoninergic, to name a few. The aim of this review is to present an overview of sperm functionality associated with "neuronal signaling" and possible cellular and molecular mechanisms involved in their regulation.