Effect of chronic clonidine treatment on transmitter release from sympathetic varicosities of the guinea-pig vas deferens.
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ABSTRACT:
SUBMITTER: Knight D
PROVIDER: S-EPMC1573076 | biostudies-other | 2001 Dec
REPOSITORIES: biostudies-other
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Project description:1. The effect of chronic morphine treatment (CMT) on sympathetic innervation of the mouse vas deferens and on alpha(2)-adrenoceptor mediated autoinhibition has been examined using intracellular recording of excitatory junction potentials (EJPs) and histochemistry. 2. In chronically saline treated (CST) preparations, morphine (1 microM) and the alpha(2)-adrenoceptor agonist (clonidine, 1 microM) decreased the mean amplitude of EJPs evoked with 0.03 Hz stimulation by 81+/-8% (n=16) and 92+/-6% (n=7) respectively. In CMT preparations, morphine (1 microM) and clonidine (1 microM) decreased mean EJP amplitude by 68+/-8% (n=7) and 79+/-8% (n=7) respectively. 3. When stimulating the sympathetic axons at 0.03 Hz, the mean EJP amplitude recorded from smooth muscles acutely withdrawn from CMT was four times greater than for CST smooth muscles (40.7+/-3.8 mV, n=7 compared with 9.9+/-0.3 mV, n=7). 4. Part of the increase in mean EJP amplitude following CMT was produced by a 31% increase in the density of sympathetic axons and varicosities innervating the smooth muscle. 5. Results from the present study indicate that the effectiveness of alpha(2)-adrenoceptor mediated autoinhibition is only slightly reduced in CMT preparations. Most of the cross tolerance which develops between morphine, clonidine and alpha(2)-adrenoceptor mediated autoinhibition occurs as a consequence of increased efficacy of neuromuscular transmission which is produced by an increase in the probability of transmitter release and an increase in the density of sympathetic innervation.
| S-EPMC1572583 | biostudies-other
Project description:Prejunctional nicotinic acetylcholine receptors (nAChRs) amplify postganglionic sympathetic neurotransmission, and there are indications that intraterminal Ca(2+) stores might be involved. However, the mechanisms by which nAChR activation stimulates neurotransmitter release at such junctions is unknown. Rapid local delivery (picospritzing) of the nAChR agonist epibatidine was combined with intracellular sharp microelectrode recording to monitor spontaneous and field-stimulation-evoked neurotransmitter release from sympathetic nerve terminals in the mouse isolated vas deferens. Locally applied epibatidine (1 µM) produced 'epibatidine-induced depolarisations' (EIDs) that were similar in shape to spontaneous excitatory junction potentials (SEJPs) and were abolished by nonselective nAChR antagonists and the purinergic desensitizing agonist ?,?-methylene ATP. The amplitude distribution of EIDs was only slightly shifted towards lower amplitudes by the selective ?7 nAChR antagonists ?-bungarotoxin and methyllcaconitine, the voltage-gated Na(+) channel blocker tetrodotoxin or by blocking voltage-gated Ca(2+) channels with Cd(2+). Lowering the extracellular Ca(2+) concentration reduced the frequency of EIDs by 69%, but more surprisingly, the Ca(2+)-induced Ca(2+) release blocker ryanodine greatly decreased the amplitude (by 41%) and the frequency of EIDs by 36%. Ryanodine had no effect on electrically-evoked neurotransmitter release, paired-pulse facilitation, SEJP frequency, SEJP amplitude or SEJP amplitude distribution. These results show that activation of non-?7 nAChRs on sympathetic postganglionic nerve terminals induces high-amplitude junctional potentials that are argued to represent multipacketed neurotransmitter release synchronized by intraterminal Ca(2+)-induced Ca(2+) release, triggered by Ca(2+) influx directly through the nAChR. This nAChR-induced neurotransmitter release can be targeted pharmacologically without affecting spontaneous or electrically-evoked neurotransmitter release.
| S-EPMC3245264 | biostudies-literature
Project description:Horizontal cells are lateral interneurons that participate in visual processing in the outer retina but the cellular mechanisms underlying transmitter release from these cells are not fully understood. In non-mammalian horizontal cells, GABA release has been shown to occur by a non-vesicular mechanism. However, recent evidence in mammalian horizontal cells favors a vesicular mechanism as they lack plasmalemmal GABA transporters and some soluble NSF attachment protein receptor (SNARE) core proteins have been identified in rodent horizontal cells. Moreover, immunoreactivity for GABA and the molecular machinery to synthesize GABA have been found in guinea pig horizontal cells, suggesting that if components of the SNARE complex are expressed they could contribute to the vesicular release of GABA. In this study we investigated whether these vesicular and synaptic proteins are expressed by guinea pig horizontal cells using immunohistochemistry with well-characterized antibodies to evaluate their cellular distribution. Components of synaptic vesicles including vesicular GABA transporter, synapsin I and synaptic vesicle protein 2A were localized to horizontal cell processes and endings, along with the SNARE core complex proteins, syntaxin-1a, syntaxin-4 and synaptosomal-associated protein 25 (SNAP-25). Complexin I/II, a cytosolic protein that stabilizes the activated SNARE fusion core, strongly immunostained horizontal cell soma and processes. In addition, the vesicular Ca(2+)-sensor, synaptotagmin-2, which is essential for Ca(2+)-mediated vesicular release, was also localized to horizontal cell processes and somata. These morphological findings from guinea pig horizontal cells suggest that mammalian horizontal cells have the capacity to utilize a regulated Ca(2+)-dependent vesicular pathway to release neurotransmitter, and that this mechanism may be shared among many mammalian species.
| S-EPMC3743676 | biostudies-literature
Project description:Nicotinic agonists increase sympathetic field-stimulus-evoked contraction of the rodent vas deferens, presumably by increasing evoked neurotransmitter release. This presumption was tested in two species.The effect of the nicotinic acetylcholine receptor (nAChR) agonist epibatidine on neurotransmitter release in mouse and guinea pig isolated vas deferens was investigated using contraction studies and conventional intracellular recording techniques.In 12 of 14 mouse vasa deferentia, slow bath application of epibatidine (100 nM) had no significant effect on excitatory junction potential (EJP) amplitude and spontaneous EJP (SEJP) frequency. However, rapid application of epibatidine to the mouse vas deferens caused an increase in SEJP frequency (by 530%), with no effect on EJP amplitude. Despite the absence of an effect on EJPs, electrically-evoked contractions of the mouse vas deferens were significantly increased in the presence of epibatidine (by 50%). A transient contraction was reliably induced by a higher epibatidine concentration (1 microM). This contraction was significantly reduced in the presence of prazosin, tetrodotoxin, or alpha,beta-methyleneATP. Epibatidine did not induce a contraction in the presence of a combination of prazosin, alpha,beta-methyleneATP and cyclopentolate. In guinea pig vasa deferentia, bath-applied epibatidine potentiated EJP amplitude in a biphasic pattern, lasting for at least 30 minutes.The nAChR-mediated augmentation of neurogenic contraction is indeed prejunctional, but in the mouse arises from an increase in spontaneous neurotransmitter release that primes smooth muscle for subsequent contraction, while in the guinea pig there is a direct augmentation of evoked neurotransmitter (ATP) release.
| S-EPMC2013884 | biostudies-other
Project description:1. The effects of the main component of the Tityus serrulatus scorpion venom, toxin TsTX-I, were studied on the contractility and release of neurotransmitters in the rat vas deferens. Since TsTX-I is known to act on sodium channels, we used veratridine, another sodium channel agent, for comparison. 2. Toxin TsTX-I induced concentration-dependent contractions with an EC(50) value of 47.8+/-0.1 nM and a maximum effect of 84.4+/-10.4% of that for BaCl(2). 3. Contractions by TsTX-I were abolished by denervation or tetrodotoxin (0.1 microM), showing that the toxin effects depend on the integrity of sympathetic nerve terminals. 4. To check for the presence of a noradrenergic component, experiments were conducted after removal of adrenergic stores in nerve terminals by reserpinization (10 mg kg(-1), 24 h prior to experiments) or blockade of alpha(1) adrenoceptors by prazosin (30 microM), showing that these procedures did not modify the response to TsTX-I, and therefore that adrenoceptors were not involved in contractions. 5. To check for the presence of a purinergic component, experiments were carried out after blockade of P(2X) receptors by suramin (0.1 mM) or desensitization by alpha,beta-methylene-ATP (30 microM). These agents greatly abolished the contractile response to TsTX-I (about 83% by desensitization and 96% by suramin), showing the involvement of purinergic receptors. 6. The release of noradrenaline and purinergic agents (ATP, ADP, AMP and adenosine) was detected by HPLC. Together, the total release of purines in the presence of TsTX-I was about 42 times higher than in the control group. In contrast, TsTX-I did not modify the overflow of noradrenaline, showing that the release was selective for purines. 7. The release of purinergic agents was reduced by the N-type calcium channel blocker omega-conotoxin GVIA (1 microM) and by the P/Q-type blocker omega-conotoxin MVIIC (1 microM), showing that the effects of TsTX-I are calcium-dependent. 8. The results show that TsTX-I produced a selective release of purines from postganglionic sympathetic nerves in the rat vas deferens.
| S-EPMC1576030 | biostudies-other
Project description:Congenital absence of the vas deferens (CAVD) may have various clinical presentations depending on whether it is bilateral (CBAVD) or unilateral (CUAVD), complete or partial, and associated or not with other abnormalities of the male urogenital tract. CBAVD is usually discovered in adult men either during the systematic assessment of cystic fibrosis or other CFTR-related conditions, or during the exploration of isolated infertility with obstructive azoospermia. The prevalence of CAVDs in men is reported to be approximately 0.1%. However, this figure is probably underestimated, because unilateral forms of CAVD in asymptomatic fertile men are not usually diagnosed. The diagnosis of CAVDs is based on clinical, ultrasound, and sperm examinations. The majority of subjects with CAVD carry at least one cystic fibrosis-causing mutation that warrants CFTR testing and in case of a positive result, genetic counseling prior to conception. Approximately 2% of the cases of CAVD are hemizygous for a loss-of-function mutation in the ADGRG2 gene that may cause a familial form of X-linked infertility. However, despite this recent finding, 10-20% of CBAVDs and 60-70% of CUAVDs remain without a genetic diagnosis. An important proportion of these unexplained CAVDs coexist with a solitary kidney suggesting an early organogenesis disorder (Wolffian duct), unlike CAVDs related to CFTR or ADGRG2 mutations, which might be the result of progressive degeneration that begins later in fetal life and probably continues after birth. How the dysfunction of CFTR, ADGRG2, or other genes such as SLC29A3 leads to this involution is the subject of various pathophysiological hypotheses that are discussed in this review.
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Project description:BACKGROUND AND PURPOSE: In the present study, a rodent model was used to investigate whether the alpha(2A)-adrenoceptor (alpha(2A)) represents the presynaptic autoinhibitory receptor regulating sympathetic transmitter release in the kidney. Moreover, the potential role of alpha(2A) as a heteroceptor regulating adenosine triphosphate (ATP) release was tested. EXPERIMENTAL APPROACH: Kidneys from wild-type (WT) and alpha(2A)-knockout (KO) mice were isolated and perfused. Renal nerves were stimulated with platinum-electrodes. Endogenously released noradrenaline (NA) was measured by HPLC. The perfusion pressure was monitored continuously. KEY RESULTS: Renal nerve stimulation (RNS) induced a frequency (1,2,5,7.5,10,15 Hz)-dependent release of NA in WT mice (994+/-373, 2355+/-541, 6375+/-950, 11626+/-1818, 19138+/-2001 pg NA g(-1) kidney (means+/-s.e.m.)). There was a 2.7-fold (5 Hz) increase of NA release in alpha(2A)-KO mice. In WT animals alpha-adrenoceptor blockade by phentolamine increased RNS-induced NA release in a concentration-dependent manner up to 350% of control. No facilitation by phentolamine was observed in alpha(2A)-KO mice. Pressor responses to 1 Hz and 2 Hz were resistant to alpha(1)-adrenoceptor blockade (0.03 microM prazosin) but abolished by P(2) receptor blockade (5 microM PPADS). Blockade of alpha(2)-adrenoceptors (1 microM rauwolscine) increased these purinergic pressor responses to 296+/-112% (1 Hz) in WT but not in alpha(2A)-KO mice. Exogenous ATP (100 microM) increased basal but not RNS-induced NA release. CONCLUSIONS AND IMPLICATIONS: alpha(2A)-Adrenoceptor-activation inhibits NA and ATP release from renal sympathetic nerves. Pressor responses to RNS at higher stimulation frequencies (>2 Hz) are mediated by NA. At lower frequencies neuronally released ATP seems to be the predominant transmitter mediating renovascular resistance.
| S-EPMC2013843 | biostudies-other
Project description:This study utilizes morphological and mechanistic endpoints to characterize the onset of bilateral atresia of the vas deferens in a recently derived cystic fibrosis (CF) rat model. Embryonic reproductive structures, including Wolffian (mesonephric) duct, Mullerian (paramesonephric) duct, mesonephric tubules, and gonad, were shown to mature normally through late embryogenesis, with involution of the vas deferens and/or epididymis typically occurring between birth and postnatal day 4 (P4), although timing and degree of atresia varied. No evidence of mucus obstruction, which is associated with pathology in other CF-affected tissues, was observed at any embryological or postnatal time point. Reduced epididymal coiling was noted post-partum and appeared to coincide with, or predate, loss of more distal vas deferens structure. Remarkably, α smooth muscle actin expression in cells surrounding duct epithelia was markedly diminished in CF animals by P2.5 when compared to wild type counterparts, indicating reduced muscle development. RNA-seq and immunohistochemical analysis of affected tissues showed disruption of developmental signaling by Wnt and related pathways. The findings have relevance to vas deferens loss in humans with CF, where timing of ductular damage is not well characterized and underlying mechanisms are not understood. If vas deferens atresia in humans begins in late gestation and continues through early postnatal life, emerging modulator therapies given perinatally might preserve and enhance integrity of the reproductive tract, which is otherwise absent or deficient in 97% of males with cystic fibrosis.
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Project description:Following testicular spermatogenesis, mammalian sperm continue to mature in a long epithelial tube known as the epididymis, which plays key roles in remodeling sperm protein, lipid, and RNA composition. To understand the roles for the epididymis in reproductive biology, we generated a single-cell atlas of the murine epididymis and vas deferens. We recovered key epithelial cell types including principal cells, clear cells, and basal cells, along with associated support cells that include fibroblasts, smooth muscle, macrophages and other immune cells. Moreover, our data illuminate extensive regional specialization of principal cell populations across the length of the epididymis. In addition to region-specific specialization of principal cells, we find evidence for functionally specialized subpopulations of stromal cells, and, most notably, two distinct populations of clear cells. Our dataset extends on existing knowledge of epididymal biology, and provides a wealth of information on potential regulatory and signaling factors that bear future investigation.
| S-EPMC7426093 | biostudies-literature
Project description:Simultaneous electrophysiology and confocal microscopy were used to investigate purinergic neurotransmission at single smooth muscle cells (SMCs) in mouse isolated vas deferens, and to explore the relationship between two high-resolution P2X-receptor-mediated measures of per pulse ATP release: transient peaks in the first time derivative of the rising phase of excitatory junction potentials (EJPs) recorded in single SMCs ('discrete events'; DEs) and neuroeffector Ca(2+) transients (NCTs) in the impaled SMCs. This study shows that discrete events represent neurotransmitter release onto the impaled cell. First, the median amplitude of the first derivative of the EJP was larger when there was a coincident NCT in the impaled cell, compared with instances when no coincident NCT occurred. Second, the time-to-peak amplitude of the first derivative was shorter if there was a coincident NCT in the impaled cell, compared with when no coincident NCT was observed within the field. Surprisingly, first derivative amplitude increased with the distance (of the corresponding NCT) from the microelectrode. The microelectrode did not locally inhibit the functional quantal size as there was no effect of distance on the normalized NCT amplitude. When the significant effect of distance (between the microelectrode and NCTs) on the first derivative amplitude was removed, there was no correlation between the unstandardized residual (of distance vs. first derivative amplitude) and NCT amplitude. The absence of a correlation between DE and NCT amplitudes suggests that the NCT amplitude is a poor measure of quantal size. The usefulness of NCTs hence lies primarily in locating neurotransmitter release and measuring changes in local release probability.
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