Gamma-aminobutyric acid (GABA) A and B receptors mediate the stimulatory effects of GABA on the human sperm acrosome reaction: interaction with progesterone

Acute exposure to isoflurane impairs sperm parameters in mice

Isoflurane, an inhalational anesthetic from the halogenated group, has been increasingly used in the medical and scientific fields. Due to its characteristics, it is capable of inducing anesthesia quickly and quietly; however, the adverse effects resulting from its use have not yet been fully elucidated, especially with regard to reproductive aspects. Considering its common use in research laboratories, whether for performing surgical procedures or for prior exposure to euthanasia, knowledge about its interference in sperm parameters of experimental models characterizes an important study goal. The aim of the present study was to determine the interference of acute exposure to isoflurane on the sperm quality of mice, both immediately previous to euthanasia and in later evaluation, twenty days after a single anesthetic exposure. Our results demonstrate that acute anesthetic exposure reduces sperm motility and is responsible for the formation of damaged sperm cells that are prone to apoptosis, which may affect the outcome of reproductive experiments even 20 days after exposure.

Clinical use of progesterone in human sperm preparation media for increasing IVF success

RESEARCH QUESTION

Can the addition of progesterone and neurotensin, molecular agents found in the female reproductive tract, after sperm washing increase the fertilization potential of human spermatozoa?

DESIGN

(i) Cohort study of 24 men. Spermatozoa selected by swim-up were incubated in either progesterone or neurotensin (0.1-100 µM) for 1-4 h, and hyperactive motility and binding to hyaluronan (0.1-100 µM) were assessed. The effect of progesterone 10 µM on sperm function was assessed in a blinded manner, including: hyperactive motility, binding to hyaluronan, tyrosine phosphorylation, acrosome reaction and oxidative DNA damage. (i) Embryo safety testing [one-cell mouse embryo assay (MEA), endotoxin and sterility counts (n = 3)] in preclinical embryo models of IVF (murine and porcine, n = 7 each model) and a small preliminary human study (n = 4) of couples undergoing standard IVF with oocytes inseminated with spermatozoa ± 10 µM progesterone.

RESULTS

Progesterone 10 µM increased sperm binding to hyaluronan, hyperactive motility and tyrosine phosphorylation (all P < 0.05). Neurotensin had no effect (P > 0.05). Progesterone 10 µM in human embryo culture media passed embryo safety testing (MEA, endotoxin concentration and sterility plate count). In preclinical models of IVF, the exposure of spermatozoa to progesterone 10 µM and oocytes to progesterone 1 µM was not detrimental, and increased the fertilization rate in mice and the blastocyst cell number in mice and pigs (all P ≤ 0.03). In humans, every transferred blastocyst that had been produced from spermatozoa exposed to progesterone resulted in a live birth.

CONCLUSION

The addition of progesterone to sperm preparation media shows promise as an adjunct to current methods for increasing fertilization potential. Randomized controlled trials are required to determine the clinical utility of progesterone for improving IVF outcomes.

Gamma-aminobutyric acid (GABA) can affect physiological processes in preimplantation embryos via GABAA and GABAB receptors

Purpose

Several widely used substances (e.g., some therapeutics or food supplements) can act on gamma-aminobutyric acid (GABA) receptors, and we investigated whether the activation of these receptors could affect the preimplantation embryo.

Methods

Transcripts of all GABA receptor subunits and selected proteins were examined using quantitative RT-PCR and immunohistochemistry. To analyze the effects of receptor activation, in vitro culture of mouse preimplantation embryos with natural and synthetic GABA receptor ligands was used.

Results

We detected nine GABA receptor transcripts in mouse blastocysts and 14 GABA receptor transcripts in ovulated oocytes. The results of this study indicate that ionotropic GABA_A receptors can be formed from α5, β3, and γ3 (or δ, π) subunits, GABA_A-ρ receptors can be formed from ρ2 subunits and metabotropic GABA receptors can be formed from GABA_B1b and GABA_B2 subunits in mouse blastocysts. Supplementing the culture medium with GABA at concentrations of 2-10 mM or with specific GABA_A and GABA_B receptor agonists (at concentrations of 10-100 μM) significantly increased the proportion of dead cells in blastocysts. The GABA-induced effects were prevented by pretreatment of embryos with GABA_A and GABA_B receptor antagonists.

Conclusion

The results of this study indicate that GABA and synthetic GABA receptor ligands can negatively affect preimplantation embryos via GABA_A and GABA_B receptors.

Differential protein expression of GABA A receptor alpha 1 subunit and calbindin in rat spermatozoa associated with proteomic analysis in testis following methamphetamine administration

Methamphetamine (METH) can induce spermatogenesis impairment, testicular apoptosis, and abnormal sperm quality. It also promotes changes in the expression of receptors for sex hormones and neurotransmitters, including GABA receptors in the testis. Proteomic assessment focusing on proteins involved in the calcium signalling pathway in the testis can facilitate diagnostic factors contributing to testicular and sperm functions, especially those related to spermatogenesis and fertilisation. In this study, we proposed to determine the localisation and differential expression of GABA A receptor alpha 1 subunit (GABA A-α1) in the spermatozoa of METH-administered rats. The differential proteomic profile of the testis was also observed by focusing on proteins in the KEGG pathways belonging to the calcium signalling pathway. There were 212 differentially expressed proteins in the rat testis, based on the cut-off value of 1.2-fold change. Most of those proteins, 13 proteins, were classified in the calcium signalling pathway, including 4 down-regulated and 9 up-regulated proteins. An immunolocalisation study of the GABA A-α1 receptor and calbindin revealed their localisation in the equatorial segment of the head in the rat spermatozoa. The expression of calbindin is also found in the middle piece of sperm. An increase in GABA A-α1 receptor in rat spermatozoa was correlated with an increase in abnormal sperm motility and morphology after methamphetamine exposure. Moreover, calbindin expression in sperm decreased in METH-administered rats. All our findings demonstrate that METH influences intracellular calcium homeostasis by acting through the calcium signalling pathway-associated proteins. Moreover, it might disrupt ion homeostasis in sperm through the GABA A-α1 receptor and calbindin, triggering a change in intracellular calcium and chloride ions. These changes may cause abnormalities in spermatogenesis, testicular apoptosis, and sperm quality impairment.

High mRNA expression of GABA receptors in human sperm with oligoasthenoteratozoospermia and teratozoospermia and its association with sperm parameters and intracytoplasmic sperm injection outcomes

Objective

This study investigated the mRNA expression of gamma-aminobutyric acid (GABA) receptors in the sperm of oligoasthenoteratozoospermic (OAT) and teratozoospermic (TER) men compared to normozoospermic (NOR) men, as well as the relationships between GABA receptor expression and sperm parameters, fertilization rate, and embryo quality.

Methods

The mRNA expression of GABA A-α1 and GABA B-R2 receptors in sperm was examined using reverse transcription–polymerase chain reaction in three groups of patients: NOR (n=32), OAT (n=22), and TER (n=45). The fertilization rate and embryo quality were assessed in 35 patients undergoing intracytoplasmic sperm injection (ICSI; 10 NOR, 10 OAT, and 15 TER men).

Results

OAT men had significantly higher mRNA expression of GABA A-α1 and GABA B-R2 receptors in sperm than NOR men; however, the difference between TER and NOR men was not significant. High levels of these receptors were significantly correlated with low sperm concentration, motility, and morphology, as well as the rate of good-quality embryos (GQEs) at the cleavage stage after ICSI. Patients whose female partners had a >50% GQE rate at the cleavage stage had significantly lower levels of GABA A-α1 receptor expression than those whose partners had a ≤50% GQE rate.

Conclusion

Our findings indicate that mRNA levels of GABA receptors in human sperm are correlated with poor sperm quality and associated with embryo development after ICSI treatment. The GABA A-α1 receptor in sperm has a stronger relationship with embryo quality at the cleavage stage than the GABA B-R2 receptor.

Environment and Male Fertility: Effects of Benzo-α-Pyrene and Resveratrol on Human Sperm Function In Vitro

Lifestyle, cigarette smoking and environmental pollution have a negative impact on male fertility. Therefore, the aim of this study was to evaluate the in-vitro effects of benzo-α-pyrene (BaP) and aryl hydrocarbon receptor (AHR) agonists on motility and bio-functional sperm parameters. We further assessed whether resveratrol (RES), an AHR antagonist and antioxidant molecule, had any protective effect. To accomplish this, 30 normozoospermic, healthy, non-smoker men not exposed to BaP were enrolled. Spermatozoa of 15 men were incubated with increasing concentrations of BaP to evaluate its effect and to establish its dose response. Then, spermatozoa of the 15 other men were incubated with BaP (15 µM/mL), chosen according to the dose-response and/or RES to evaluate its antagonistic effects. The effects of both substances were evaluated after 3 h of incubation on total and progressive sperm motility and on the following bio-functional sperm parameters evaluated by flow cytometry: Degree of chromatin compactness, viability, phosphatidylserine externalization (PS), late apoptosis, mitochondrial membrane potential (MMP), DNA fragmentation, degree of lipoperoxidation (LP), and concentrations of mitochondrial superoxide anion. Benzo-α-pyrene decreased total and progressive sperm motility, impaired chromatin compactness, and increased sperm lipoperoxidation and mitochondrial superoxide anion levels. All these effects were statistically significant at the lowest concentration tested (15 µM/mL) and they were confirmed at the concentration of 45 µM/mL. In turn, RES was able to counteract the detrimental effects of BaP on sperm motility, abnormal chromatin compactness, lipid peroxidation, and mitochondrial superoxide. This study showed that BaP alters sperm motility and bio-functional sperm parameters and that RES exerts a protective effect on BaP-induced sperm damage.

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.

Psychotropics and Male Reproduction

Psychotropic drugs, including antidepressants, antipsychotics, and anticonvulsants, all have negative effects on sexual function and semen quality. These adverse events vary among men and are less pronounced for some medications, allowing their effects to be managed to some extent. Use of specific serotonin reuptake inhibitors (SSRIs) is prevalent in men of reproductive age; and application to treat premature ejaculation increases the number of young men on SSRI therapy. Oxidative damage to sperm can result from prolonged residence in the male reproductive tract. The increase in ejaculatory latency seen with SSRIs likely underlies some of their negative effects on semen quality, including higher sperm DNA fragmentation, seen in all SSRIs evaluated thus far. These medications increase prolactin (PRL) levels in some men, and this is often credited with inhibitory effects on male reproduction; however, testosterone levels are generally normal, reducing the likelihood of direct HPG axis inhibition by PRL. The tricyclic antidepressants have also been shown to increase PRL levels in some studies but not in others. The exception is the tricyclic antidepressant clomipramine, which profoundly increases PRL levels and may depress semen quality. Other antidepressants modulating synaptic levels of serotonin, norepinephrine, and/or dopamine may have toxicity similar to SSRIs, but most have not been evaluated. In limited studies, norepinephrine-dopamine reuptake inhibitors (NDRIs) and serotonin agonist/reuptake inhibitors (SARIs) have had minimal effects on PRL levels and on sexual side effects. Antipsychotic medications increase PRL, decrease testosterone, and increase sexual side effects, including ejaculatory dysfunction. The greatest evidence is for chlorpromazine, haloperidol, reserpine, risperidone, and thioridazine, with less effects seen with aripiprazole and clozapine. Remarkably few studies have looked at antipsychotic effects on semen quality, and this is an important knowledge gap in reproductive pharmacology. Lithium increases PRL and LH levels and decreases testosterone although this is informed by few studies. The anticonvulsants, many used for other indications, generally decrease free or bioavailable testosterone with variable effects on the other reproductive hormones. Valproate, carbamazepine, oxcarbazepine, and levetiracetam decrease semen quality; other anticonvulsants have not been investigated for this adverse reaction. Studies are required evaluating endpoints of pregnancy and offspring health for psychotropic medications.

Different transcriptional levels of GABAA receptor subunits in mouse cumulus cells around oocytes at different mature stage

γ-Aminobutyric acid (GABA) is a principal inhibitory neurotransmitter in the central nervous system (CNS) of vertebrates. However, GABA and its receptor are found not only in peripheral neuronal tissue but also in many peripheral nonneuronal tissues, and thought to have multiple physiological functions. The bidirectional communication between oocytes and cumulus cells (CCs) plays a significant role in oocyte maturation and metabolism. In our previously study, the expression level of α5 subunit in CCs isolated from oocytes of patients with polycystic ovary syndrome had been found to be associated with oocyte nuclear maturity. In this study, we investigated the transcriptional levels of GABA_A receptor subunits in germinal vesicle (GV) and metaphase II (MII) mouse CCs, and explored the role of GABA-A receptor subunits during ovarian follicular development and oocyte maturation. We found that GABA_A receptor subunits exhibited differential transcriptional levels in CCs at different oocyte nuclear maturity stages. It suggested an involvement of GABA-A receptor subunits related to oocyte maturation and certain functions.

Carbonic anhydrases and their functional differences in human and mouse sperm physiology

Fertilization is a key reproductive event in which sperm and egg fuse to generate a new individual. Proper regulation of certain parameters (such as intracellular pH) is crucial for this process. Carbonic anhydrases (CAs) are among the molecular entities that control intracellular pH dynamics in most cells. Unfortunately, little is known about the function of CAs in mammalian sperm physiology. For this reason, we re-explored the expression of CAI, II, IV and XIII in human and mouse sperm. We also measured the level of CA activity, determined by mass spectrometry, and found that it is similar in non-capacitated and capacitated mouse sperm. Importantly, we found that CAII activity accounts for half of the total CA activity in capacitated mouse sperm. Using the general CA inhibitor ethoxyzolamide, we studied how CAs participate in fundamental sperm physiological processes such as motility and acrosome reaction in both species. We found that capacitated human sperm depend strongly on CA activity to support normal motility, while capacitated mouse sperm do not. Finally, we found that CA inhibition increases the acrosome reaction in capacitated human sperm, but not in capacitated mouse sperm.

Bull sperm acrosome reaction induced by gamma-aminobutyric acid (GABA) is mediated by GABAergic receptors type A

The effect of gamma-aminobutyric acid (GABA) on the bull sperm acrosome reaction was evaluated, and the interaction of progesterone, a physiologic inducer of the acrosome reaction, with the GABA receptor was explored. The acrosome reaction was stimulated by GABA in a dose-dependent manner. This effect was inhibited completely by bicuculline, a GABA A receptor antagonist, but GABA B and C receptor antagonists had no effect. Accordingly, muscimol, a GABA A receptor agonist, stimulated the acrosome reaction to the same extent as GABA, whereas baclofen (GABA B receptor agonist) and CACA (GABA C receptor agonist), had no effect. Preincubation with progesterone followed by the addition of GABA resulted in a significant increase in the percentage of acrosome reacted spermatozoa compared with progesterone or GABA alone. Taking into account that this increase was less than a simple addition of effects, it might be suggested that GABA and progesterone act through the same receptor and/or use the same mechanism of action. To test this hypothesis, the abilities of GABA and progesterone to induce acrosome reaction were tested in the presence of bicuculline, which suppressed both stimulatory effects. Given that the GABA A receptor is linked to the Cl(-) channel, we tested whether picrotoxin, a blocker of this channel, could modulate the effects of progesterone or GABA. Cl(-) channel blocker picrotoxin dramatically reduced the GABA and progesterone-initiated AR.

IN CONCLUSION

GABA and progesterone stimulate the acrosome reaction in bull spermatozoa acting through a classical GABA A receptor. The mechanism of action requires the functional integrity of the Ca(2+) Cl(-) channel.

Expression of GAT1 in male reproductive system and its effects on reproduction in mice

The present study was carried out to identify GABA (gamma-aminobutyric acid) transport protein I (GAT1) in male reproductive organs and to study the effect of GAT1 overexpression on the male reproductive system in GAT1 transgenic mice (TG). Expression and location of GAT1 in testes, epididymis, and sperm of wild-type (WT) mice were identified by immunohistochemistry and western-blot. Histological changes of testes, epididymis, and sperm of transgenic mice overexpressing GAT1 were detected by immunofluorenscent staining and haematoxylin and eosin (HE) staining. GAT1 expression was detected in the testes, epididymis, and sperm of non-transgenic mice. Vacuolization and deformity of spermatogenic cells were observed in the transgenic mice, but the epididymis was unremarkable. Immunofluorenscent staining showed that the number of diastrophic and decapitated sperm increased significantly in transgenic mice to 46.9% from 7.3% in nontransgenic mice. These results suggest that abnormal expression of GAT1 could result in spermiogenesis function injury, sperm paramorphia and dysgenesis.

Delineation of downstream signalling components during acrosome reaction mediated by heat solubilized human zona pellucida

BACKGROUND

Human egg is enveloped by a glycoproteinaceous matrix, zona pellucida (ZP), responsible for binding of the human spermatozoa to the egg and induction of acrosomal exocytosis in the spermatozoon bound to ZP. In the present manuscript, attempts have been made to delineate the downstream signalling components employed by human ZP to induce acrosome reaction.

METHODS

Heat-solubilized human ZP (SIZP) was used to study the induction of acrosome reaction in capacitated human spermatozoa using tetramethylrhodamine isothiocyanate conjugated Pisum sativum agglutinin (TRITC-PSA) in absence or presence of various pharmacological inhibitors. In addition, intracellular calcium ([Ca2+]i) levels in sperm using Fluo-3 acetoxymethyl ester as fluorescent probe were also estimated in response to SIZP.

RESULTS

SIZP induces acrosomal exocytosis in capacitated human sperm in a dose dependent manner accompanied by an increase in [Ca2+]i. Human SIZP mediated induction of acrosome reaction depends on extracellular Ca2+ and involves activation of Gi protein-coupled receptor, tyrosine kinase, protein kinases A & C and phosphoinositide 3 (PI3)- kinase. In addition, T-type voltage operated calcium channels and GABA-A receptor associated chloride (Cl-) channels play an important role in SIZP mediated induction of acrosome reaction.

CONCLUSIONS

Results described in the present study provide a comprehensive account of the various downstream signalling components associated with human ZP mediated acrosome reaction.

Localisation and function of voltage-dependent anion channels (VDAC) in bovine spermatozoa

Sperm motility, regulation of cell volume, sperm capacitation, acrosome reaction and tight binding of spermatozoa to the zona pellucida are crucial events in the process of fertilisation. Voltage-dependent anion channels (VDAC) are highly conserved pore-forming proteins implicated in apoptosis, metabolite transport between mitochondria and cytosol, energy metabolism, and cell volume regulation in somatic cells. Several studies have demonstrated the presence of VDAC in cell compartments other than mitochondria. In previous studies using immunofluorescence, we were able to localise VDAC2 and VDAC3 in outer dense fibres of the bovine sperm flagellum. Furthermore, we described the presence of VDAC2 in the head of bovine sperm. In the present study, we confirm the localisation of VDAC2 in the acrosomal region of bovine spermatozoa using immunoelectron microscopy. After incubation with anti-VDAC antibodies raised against each VDAC isoform, bovine spermatozoa showed an increased loss of the acrosomal cap, noticeable changes in the surface of the head, coiled tails and an increased cell volume. The incubation of bovine spermatozoa with anti-VDAC antibodies might lead to alteration of the intracellular ion concentration that causes changes in the cell volume, followed by destabilization of the cytoskeleton and, finally, to loss of the acrosomal cap.

Effects of tumour necrosis factor-alpha on human sperm motility and apoptosis

The aim of this study was to evaluate the effects of tumour necrosis factor-alpha (TNF-alpha) on sperm motility, mitochondrial membrane potential (DeltaPsi), phosphatidylserine (PS) externalization, sperm chromatin packaging quality, and DNA fragmentation. Motile spermatozoa, obtained from 10 normozoospermic men, were incubated with increasing concentrations of TNF-alpha and analyzed 1, 3, 6, and 24 h after incubation by flow cytometry. TNF-alpha decreased total motility 24 h after incubation at 10 ng/mL and progressive motility 3 h after incubation. Accordingly, TNF-alpha reduced sperm DeltaPsi in a concentration- and time-dependent manner. TNF-alpha increased the percentage of spermatozoa with PS externalization from the concentration of 1 ng/mL 1 h after incubation. TNF-alpha produced sperm chromatin and DNA damage in a concentration- and time-dependent manner. In conclusion, these findings may explain the reduction of fertility, secondary to upregulated production of TNF-alpha, in men with urogenital infections.

The peripheral GABAergic system as a target in endocrine disorders

In addition to its well-recognized function as a cerebral inhibitory transmitter, less well established is the role of GABA in peripheral nervous and endocrine systems. We summarize current evidence that GABA serves as a neurotransmitter or neuromodulator in the autonomic nervous system and as a hormone or trophic factor in non-neuronal peripheral tissue as well. GABA is widely distributed in endocrine tissues including the pituitary, pancreas, adrenal glands, uterus, ovaries, placenta and testis. Moreover, GABA is involved in the pathophysiology of endocrine disorders such as diabetes mellitus, diseases of adrenal glands and reproductive tracts. Current literature indicates that the peripheral GABA system in the autonomic nervous system, endocrine and immune systems is as yet nearly an unexplored target for diagnosis and drug treatment.

The sperm, a neuron with a tail: 'neuronal' receptors in mammalian sperm

A number of plasma membrane receptor types originally thought to be specific to neurons have been found in other somatic cells. More surprisingly, the mammalian sperm and neuron appear to share many of these 'neuronal' receptors. The morphology, chromosome number, genomic activity, and functions of those two cell types are as unlike as any two cells in the body, but they both achieve their highly disparate goals with the aid of a number of the same receptors. Exocytosis in neurons and sperm is essential to the functions of these cells and is strongly influenced by similar receptors. 'Neuronal' receptor types in sperm may also play a role in the control of sperm motility (a function of course not shared by neurons). This review will consider the evidence for the presence of sperm plasma membrane 'neuronal' receptors and for their significance to mammalian sperm function. The persuasiveness of the evidence varies depending on the receptor being considered, but there is strong experimental support for the presence and importance of a number of 'neuronal' receptors in sperm.

Human follicular fluid stimulates the sperm acrosome reaction by interacting with the γ-aminobutyric acid receptors

OBJECTIVE

To evaluate whether gamma-aminobutyric acid receptors are involved in human sperm acrosome reaction induced by the follicular fluid (FF).

DESIGN

Random selection of normal sperm samples.

SETTING

Normal men in an university clinic of andrology.

PATIENT(S)

Men with normal sperm analysis parameters.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Acrosome reaction on motile spermatozoa.

RESULT(S)

Follicular fluid stimulated the acrosome reaction dose-dependently. The effect of a maximally effective concentration of FF (30%, vol/vol) was significantly suppressed by bicuculline, a GABAA receptor antagonist, and saclofen, a GABAB receptor antagonist, added concomitantly. Each of the two antagonists used alone was devoid of effect. Because the GABAA receptor is linked to the chloride channel, we tested whether picrotoxin, a blocker of this channel, could modulate the effects of the FF. Picrotoxin alone did not have any effect on the acrosome reaction induced by the FF, whereas it had a significant suppressive effect if coincubated with saclofen. The acrosome reaction induced by the FF was also inhibited by picrotoxin plus verapamil, a calcium channel blocker, whereas verapamil alone had no significant effect. This suggested that both chloride and calcium ions mediated the acrosome reaction induced by the FF.

CONCLUSION(S)

The simultaneous blockade of GABAA and GABAB receptors suppressed the acrosome reaction induced by the FF. This finding suggested that GABA receptors play a physiologic role in sperm activation and shed further light on the mechanism of FF action on human sperm acrosome reaction.

Proteins of multiple classes may participate in nongenomic steroid actions

Responses to steroids initiated from non-nuclear receptors impinge on a wide variety of cellular responses and utilize nearly all known signal transduction webs. While the mechanisms by which steroid receptors localize in the membrane are still unclear, it is apparent that this alternative localization allows steroid receptors to participate in a wide range of complex functions influencing cell proliferation, death, and differentiation. The central debate still remains the identity of the protein class or classes that mediate membrane-initiated (nongenomic) responses. The data thus far have supported several possibilities, including: nuclear steroid receptor-like forms in non-nuclear locations; other known (nonsteroid) membrane receptors or channels with additional steroid-binding sites; enzymes; transporters; receptors for serum steroid-binding proteins; unique and previously undescribed proteins; or chimeras of typical steroid receptor domains with other unique or known protein domains. Categorizing membrane steroid receptor proteins based exclusively on the actions of antagonists and agonists, without considering cell context and protein partnering issues, may mislead us into predicting more receptor subtypes than really exist. However, the plethora of signaling and functional outcomes may indicate the participation of more than one kind of steroid-binding protein. Resolving such unanswered questions will require future investigative focus on this alternative arm of steroid action, which is likely to yield as many therapeutic opportunities as have nuclear steroid mechanisms.

Impaired reproduction in transgenic mice overexpressing γ-aminobutyric acid transporter I (GAT1)

It is well documented that g-aminobutyric acid (GABA) system existed in reproductive organs. Recent researches showed that GABAA and GABAB receptors were present in testis and sperm, and might mediate the acrosome reaction induced by GABA and progesterone. GABA transporter I (GAT1) also existed in testis and sperm, but its physiological function was unknown. In the present study, we used GAT1 overexpressing mice to explore GAT1 function in male reproductive system. We found that the expression level of GAT1 continuously increased in wild-type mouse testis from 1 month to 2 months after birth. GAT1 overexpression in mouse affected testis development, which embodied reduced testis mass and slowed spermatogenesis in transgenic mice. Moreover, transgenic mice showed increase of the percentage of broken sperm. The further study revealed that the reproductive capacity was impaired in GAT1 overexpressing mice. In addition, testosterone level was significantly low in transgenic mice compared with that in wild-type mice. Our findings provided the first evidence that abnormal expression of GAT1 could result in dysgenesis, and indicated that GAT1 might be therapeutically targeted for contraception or dysgenesis treatment.

Encoding of progesterone stimulus intensity by intracellular [Ca2+] ([Ca2+]i) in human spermatozoa

Progesterone induces a biphasic Ca(2+) influx and consequent acrosome reaction in human spermatozoa. We have used two procedures to vary the stimulus (dosage and prior receptor desensitization) to investigate the encoding of stimulus strength by intracellular [Ca(2+)] ([Ca(2+)](i)). Acrosome reaction and amplitude (but not kinetics) of the transient [Ca(2+)](i) response (population measurement) showed sigmoidal dose sensitivity over the range 0.3 nM-3 microM, saturating at approximately 300 nM (ED(50) approximately 30 nM). The amplitude of the sustained response saturated at 3 microM. Single-cell imaging showed that the amplitudes of both transient and sustained [Ca(2+)](i) responses were highly dose-dependent, but that their frequency of occurrence and kinetics were largely dose-independent. Fluorimetric measurements confirmed that progesterone-induced [Ca(2+)](i) influx was subject to desensitization, with second and subsequent applications of 3 microM progesterone being ineffective. However, sequential additions of 3 nM, 30 nM and 3 microM progesterone generated transient [Ca(2+)](i) responses at each concentration, the amplitude and duration of the response to 3 microM progesterone being reduced compared with non-pretreated cells. Single-cell imaging revealed that pretreatment had no effect on the proportion of responsive cells, but single-cell responses, similarly to population responses, were smaller and markedly reduced in duration, consistent with an effect of desensitization on a late component of the [Ca(2+)](i) transient. We conclude that the strength of the progesterone stimulus, when varied by dosage or by desensitization, is encoded by an analogue [Ca(2+)](i) signal. Dose dependency of the acrosome reaction is therefore determined not by the number of progesterone-responsive cells but by variation in the probability of exocytosis in a 'constant' responsive population.

Evidence for a GABAergic system in rodent and human testis: local GABA production and GABA receptors

The major neurotransmitter of the central nervous system, gamma-aminobutyric acid (GABA), exerts its actions through GABA(A), GABA(B) and GABA(C) receptors. GABA and GABA receptors are, however, also present in several non-neural tissues, including the endocrine organs pituitary, pancreas and testis. In the case of the rat testis, GABA appears to be linked to the regulation of steroid synthesis by Leydig cells via GABA(A) receptors, but neither testicular sources of GABA, nor the precise nature of testicular GABA receptors are fully known. We examined these points in rat, mouse, hamster and human testicular samples. RT-PCR followed by sequencing showed that the GABA-synthesizing enzymes glutamate decarboxylase (GAD) 65 and/or GAD67, as well as the vesicular GABA transporter vesicular inhibitory amino acid transporter (VIAAT/VGAT) are expressed. Testicular GAD in the rat was shown to be functionally active by using a GAD assay, and Western blot analysis confirmed the presence of GAD65 and GAD67. Interstitial cells, most of which are Leydig cells according to their location and morphological characteristics, showed positive immunoreaction for GAD and VIAAT/VGAT proteins. In addition, several GABA(A) receptor subunits (alpha1-3, beta1-3, gamma1-3), as well as GABA(B) receptor subunits R1 and R2, were detected by RT-PCR. Western blot analysis confirmed the results for GABA(A) receptor subunits beta2/3 in the rat, and immunohistochemistry identified interstitial Leydig cells to possess immunoreactive GABA(A) receptor subunits beta2/3 and alpha1. The presence of GABA(A) receptor subunit alpha1 mRNA in interstitial cells of the rat testis was further shown after laser microdissection followed by RT-PCR analysis. In summary, these results describe molecular details of the components of an intratesticular GABAergic system expressed in the endocrine compartment of rodent and human testes. While the physiological significance of this peripheral neuroendocrine system conserved throughout species remains to be elucidated, its mere presence in humans suggests the possibility that clinically used drugs might be able to interfere with testicular function.

The human sperm head: a key for successful fertilization

In order to examine the predictive value of determining the sperm head shape, the acrosomal size, the presence of acrosomal vacuoles, and the challenged acrosome reaction (AR) on the outcome of a standard in vitro fertilization (IVF) program, a prospective study was conducted that included 75 couples undergoing IVF treatment. An assessment of sperm morphology was performed using the Hobson Sperm Tracker (Hobson Tracker Limited, Sheffield, United Kingdom). The assessment of the AR was performed before and after adding pooled undiluted human follicular fluid (FF). The outcome measure was an IVF rate of inseminated oocytes. A positive correlation was found between the fertilization rate (FR%) and the proportion of the sperm with a normal (oval) head shape (P <.001), the sperm exhibiting acrosomal vacuoles (P <.003), the sperm with a normal acrosomal size (40%-70% of total head area, P <.025), and the sperm undergoing AR after adding FF (P <.001). Multiple logistic regression analysis revealed that by incorporating the above 4 parameters, the sensitivity of prediction of IVF FR% values was 79%, and the specificity was 93%, with a positive predictive value of 96%. This study shows that the multiparametric assessment of the sperm head is useful in predicting the FR% values of a standard IVF treatment. The automated analysis used in this study is shown to maintain a level of precision and accuracy acceptable for application in a routine semen analysis situation.

Membrane-initiated events account for progesterone's ability to regulate intracellular free calcium levels and inhibit rat granulosa cell mitosis

It has been proposed that the antimitogenic action of progesterone (P(4)) is mediated through a membrane receptor that has GABA(A) receptor-like characteristics. To test this hypothesis, studies were designed to compare the antimitogenic effects of P(4) with its gamma amino butyric acid(A) (GABA(A)) receptor-activating metabolite, 5alpha-pregnane-3alpha-21-diol-20-one (5alpha3alpha). These studies revealed that P(4) was more effective than 5alpha3alpha in blocking mitogen-dependent mitosis of both small granulosa cells (GCs) and spontaneously immortalized granulosa cells (SIGCs). Ligand binding studies illustrated that P(4) bound to SIGCs with an apparent dissociation constant (K(d)) of 0.32 +/- 0.09 microM, whereas 5alpha3alpha bound with an apparent K(d) of 40 +/- 19 microM. Further, the GABA(A) antagonist, bicuculline, did not attenuate P(4)'s antimitotic action in SIGCs. Finally, reverse transcriptase-polymerase chain reaction (RT-PCR) studies demonstrated that none of the 6 known alpha chains of the GABA(A) receptors to which bicuculline binds were detected in SIGCs. Taken together, these studies suggest that P(4) does not mediate its action via a GABA(A)-like receptor. Additional studies revealed that P(4) regulated intracellular free calcium levels ([Ca(2+)](i)) as part of its antimitotic action. Specifically, P(4) maintained a basal [Ca(2+)](i) level that was slightly lower than normal. Increasing extracellular calcium not only increased basal [Ca(2+)](i) but also attenuated P(4)'s antimitogenic effect. P(4)'s actions appeared to be initiated at the membrane, since horseradish peroxidase conjugated-P(4) (HP-P(4)), which is cell impermeable, was as effective in blocking mitosis as P(4). Progesterone receptor (PR) mRNA was not detected in SIGCs by RT-PCR analysis, which is consistent with the findings in GCs. However, a 60-kDa protein was detected within crude membrane fractions of both GCs and SIGCs using an antibody directed against the ligand binding domain of the PR (C-262). This antibody was also used in immunocytochemical studies to detect a protein that was associated with the plasma membrane of SIGCs. It is proposed that this 60-kDa protein mediates P(4)'s membrane-initiated actions.

Inhibitory action of halothane on rat masculine sexual behavior and sperm motility

Adult male rats were exposed to inhale halothane in the following regime: 15 ppm/4 h/5 days/week/9 weeks. Sexual behavior observations and sperm motility test were made before halothane exposure (0 days) and at 15, 30, 45 and 60 days of exposure. Fifteen days after halothane exposure, this anesthetic inhibited the proportion of animals displaying ejaculation. In those animals ejaculating, halothane produced an inhibition of masculine sexual behavior reflected as an increase in the intromission latency, number of mounts and postejaculatory interval. At 30 days after exposure, only an increase in the intromission latency was observed. At 45 and 60 days, the inhibitory effect of halothane on sexual behavior disappeared. Similarly, at 15 and 30 days, but not at 45 or 60 days of halothane exposure, a reduced sperm motility was observed. Such transient effects of halothane suggest the development of tolerance to the inhibitory actions of this anesthetic on sexual behavior and sperm motility. These halothane effects are in line with an inhibition of masculine sexual behavior after stimulation of the GABAergic system.

Identification of gamma1 subunit of GABA(A) receptor in rat testis

The isoform type of gamma subunits of GABA(A) receptor is a molecular determinant of its pharmacological characteristics. At present, the existence of GABA(A) receptor in mammalian sperm is still a controversy. By using degenerate primers designed according to highly conserved region in all three gamma (gamma1, gamma2 and gamma3) subunits cloned in rat brain, we performed reverse transcription polymerase chain reaction (RT-PCR) to examine the expression pattern of gamma subunits of GABA(A) receptor in rat testis. Only one 370 bp fragment was obtained from RT-PCR in rat testis and sequencing results showed that it represented gamma1 subunit, but not gamma2 or gamma3 subunit. Using the cloned fragment as probe, a 3.8 kb transcript which in size as same as gamma1 subunit in rat brain was detected in rat testis mRNA by performing Northern blot assay. Furthermore, results of in situ hybridization assay confirmed that gamma1 subunit was expressed in round spermatids and spermatozoa, maybe also in secondary spermatocyte. These evidences proved that gamma1 subunit of GABA(A) receptor is exclusively expressed in rat testis and this feature may be the structural basis of the specific function of GABA(A) receptors in sperm acrosome reaction.

Identification of GABA(B) receptor in rat testis and sperm

gamma-Aminobutyric acid (GABA) can mimic and potentiate the action of progesterone in initiating the acrosome reaction (AR) of mammalian sperm, indicating that sperm contain receptors for GABA. This contention was validated by identifying the receptor (R) subtype, GABA(A)R, in mammalian sperm. In the present study a second subtype, GABA(B)R, was identified in rat testis and sperm. Total RNAs of rat testis and sperm were prepared and used as template to synthesize the respective cDNAs by the RT-PCR method. Two splice variants of the cDNA coding GABA(B)R1 (GABA(B)R1a and GABA(B)R1c) and GABA(B)R2 were identified. Extracts of rat testis, spermatogenic cells and sperm contained two proteins with estimated molecular sizes of 130 and 100 kDa, corresponding to GABA(B)R1a and GABA(B)R1c/lb, respectively, determined by Western blot using polyclonal anti-GABA(B)R1 antibody. By an indirect immunofluorescence technique, GABA(B)R1 was located on the head of rat sperm. The present finding is the first direct demonstration that mammalian sperm contain GABA(B)R.