1 By use of the whole-cell configuration of the patch-clamp technique, membrane currents induced by cyclopiazonic acid (CPA; an inhibitor of the sarcoplasmic reticulum (SR) calcium-ATPase) were investigated in single smooth muscle cells freshly dispersed from the mouse anococcygeus. Voltagedependent calcium currents were blocked with extracellular nifedipine and caesium and tetraethylammonium chloride were used to block voltage-dependent potassium currents. 2 At a holding potential of -40 mV, CPA (10 tiM) activated an inward current that consisted of two distinct components. The first was an initial transient current with an amplitude of 19.6 + 1.9 pA while the second was sustained and had an amplitude of 3.5 + 0.3 pA. 3 The current-voltage (I-V) relationship for the transient current showed marked outward rectification. The current had a reversal potential of 9.1 + 1.1 mV which was shifted to 29.0 + 4.2 mV when the extracellular chloride concentration was lowered from 148.4 to 58.4 mM. The sustained current had a near-linear I-V relationship and a reversal potential of 31.0+2.7 mV. Removal of extracellular calcium had no effect on the transient current, but shifted the reversal potential of the sustained current to 18.2+ 5.7 mV. 3 The initial transient current was abolished in cells bathed in extracellular solutions containing the chloride channel blockers, 4,4' diisothiocyanato-stilbene-2,2'-disulphonic acid (DIDS; 1 mM) or anthracene-9-carboxylic acid (A-9-C; 1 mM), and was absent in cells containing the calcium buffers EGTA (1 to 5 mM) or BAPTA (10 mM). The second sustained current was unaffected by either the chloride channel blockers or the intracellular calcium buffers. 4 Treatment of the cells with caffeine (10 mM) produced similar inward currents to those produced by CPA. In the presence of caffeine, CPA (10 gM) induced no further inward current. 5 In organ bath studies, CPA (10 gM)-induced contractions of the mouse anococcygeus were inhibited by cadmium and nickel (both 50-400 uM) and the general calcium entry blocker, SKF 96365 (10 gM); lanthanum and gadolinium had no effect at concentrations up to 400 gM. The pharmacology of the CPA-induced non-selective cation current mirrored that of the CPA-induced whole muscle contraction being reversed by cadmium (100 tM) and SKF 96365 (10 uM), but unaffected by lanthanum (400 gM).The initial chloride conductance was unaffected by cadmium, SKF 96365 or lanthanum. 6 It is concluded that CPA activates a transient calcium-dependent chloride current as a consequence of calcium release from intracellular stores; this current would result in depolarization and opening of voltage-operated calcium channels, which mediate the nifedipine-sensitive component of muscle contraction. In addition, as a result of emptying the SR, CPA activates a non-selective cation conductance which may underlie the nifedipine-insensitive calcium entry process utilised during sustained contraction.

Dopamine and oxytocin have established roles in the central regulation of penile erection in rats; however, the neural circuitries involved in a specific erectile context and the interaction between dopamine and oxytocin mechanisms remain to be elucidated. The medial preoptic area (MPOA), supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus may serve as candidate sites because they contain oxytocin cells, receive dopaminergic inputs and have been implicated in mediating masculine sexual behavior. Double immunofluorescence revealed that substantial numbers of oxytocin cells in the MPOA, SON and PVN possess dopamine D(2), D(3) and D(4) receptors. In anaesthetized rats, using intracavernous pressure as a physiological indicator of erection, blockade of lumbosacral oxytocin receptors (UK, 427843) reduced erectile responses to a nonselective dopamine agonist (apomorphine), suggesting that dopamine recruits a paraventriculospinal oxytocin pathway. In conscious males in the absence of a female, penile erection elicited by a D(2)/D(3) (Quinelorane) but not D(4) (PD168077) agonist was associated with activation of medial parvocellular PVN oxytocin cells. In another experiment where males were given full access to a receptive female, a D(4) (L-745870) but not D(2) or D(3) antagonist (L-741626; nafadotride) inhibited penile erection (intromission), and this was correlated with SON magnocellular oxytocin neuron activation. Together, the data suggest dopamine's effects on hypothalamic oxytocin cells during penile erection are context-specific. Dopamine may act via different parvocellular and magnocellular oxytocin subpopulations to elicit erectile responses, depending upon whether intromission is performed. This study demonstrates the potential existence of interaction between central dopamine and oxytocin pathways during penile erection, with the SON and PVN serving as integrative sites.

Fertilization is well correlated with sperm concentration, rate of forward motility, and percentage of live, uncapacitated ejaculated spermatozoa, which is regulated in part by cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Phosphodiesterases (PDEs) hydrolyze cyclic nucleotides to their corresponding monophosphates, thereby counterbalancing the activities of cAMP and cGMP, and PDE11 is highly expressed in the testis, prostate, and developing spermatozoa. However, a physiological role of PDE11 is not known. We generated PDE11 knockout (PDE11 À/À ) mice to investigate the role of PDE11 in spermatozoa physiology. Ejaculated sperm from PDE11 À/À mice displayed reduced sperm concentration, rate of forward progression, and percentage of live spermatozoa. Pre-ejaculated sperm from PDE11 À/À mice displayed increased premature/spontaneous capacitance. These data are consistent with human data and suggest a role for PDE11 in spermatogenesis and fertilization potential. This is the first phenotype described for the PDE11 À/À mouse and the first report of a physiological role for PDE11.

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Background and purpose: Oxytocin is believed to be involved in ejaculation by increasing sperm number and contracting ejaculatory tissues. However, oxytocin may mediate these effects via oxytocin or vasopressin (AVP) receptors. The aim of this study was to determine the effect of oxytocin and AVP on peripheral tissues involved in ejaculation and to identify the receptor subtype(s) involved. Experimental approach: Standard tissue bath techniques were used to measure isometric tension from tissues involved in ejaculation and erection. Key results: Oxytocin and AVP failed to elicit a tonic contractile response in rat and rabbit testes, vas deferens, epididymis, seminal vesicles and prostate. In contrast, oxytocin and AVP elicited large tonic contractions in erectile (corpus spongiosum and corpus cavernosum) and ejaculatory (prostatic urethra, bladder neck and ejaculatory duct) tissues in a concentrationdependent manner. Conclusions and implications:The contractile effect of oxytocin on rat and rabbit ejaculatory and erectile tissues is mediated via V 1A receptors. Endothelin-1-induced contractions are not due to endogenous oxytocin or AVP release. V 1A receptor antagonists may have a therapeutic role in both erectile dysfunction and premature ejaculation.