RESUMO

We have demonstrated that the activation of P2X3 receptor on peripheral afferent neurons is critical to development of inflammatory hyperalgesia in peripheral tissue, although pharmacological administration of prostaglandin E(2) or sympathomimetic amines is enough to sensitize primary afferent neurons by acting directly in neuronal receptors. Therefore, to clarify this ambiguity this study verifies whether P2X3 receptor activation on primary afferent neurons enables the sensitization induced by prostaglandin E(2) or sympathomimetic amine. Initially, this study confirmed that co-administration of A317491 (60 µg/paw), a selective P2X3 receptor antagonist, or pre-treatment with dexamethasone (1 mg/mL/kg) prevents the mechanical hyperalgesia induced by carrageenan (300 µg/paw) in the rat's hind paw. Sub-threshold doses of PGE(2) (4 ng/paw) or dopamine (0.4 µg/paw), that do not induce hyperalgesia by themselves, when injected just following αßmeATP or carrageenan in rats treated with dexamethasone induced hyperalgesia, which is prevented by A317491 or treatment with periganglionar (DRG-L5) injections of ODN-antisense, against P2X3 receptor. Furthermore, because PKCɛ translocation induces an increase of neuronal susceptibility to inflammatory mediators, this study demonstrates that αßmeATP in peripheral tissue increases the expression of PKCɛ in cell membranes of DRG-L5, and in contrast, the administration of PKCɛ translocation inhibitor (1 µg/paw) in peripheral tissue 45 min before αßmeATP, prevented the hyperalgesia induced by sub-threshold dose of PGE(2) (4 ng/paw). In conclusion, this study suggests that neuronal P2X3 receptor activation and the consequent PKCɛ translocation increase the susceptibility of nociceptor to inflammatory mediators allowing the development of inflammatory hyperalgesia.

Assuntos

RESUMO

The bed nucleus of the stria terminalis pars ventralis (vBNST) receives dense noradrenergic terminals and contains the highest concentration of noradrenaline (NA) in the brain. We used autoradiography following retrograde axonal transport of [(3)H]-NA to identify selectively whether noradrenergic neurons innervating the vBNST originate in the medulla oblongata and/or the locus coeruleus. In combination with this technique, non-isotopic in situ hybridization for the NMDA-NR1 receptor subunit mRNA was used to examine, on the same brain sections, its expression in noradrenergic neurons that innervate the vBNST. The results showed that 60 +/- 6% and 35 +/- 7% of the total number of radiolabeled cells detected after injection of [(3)H]-NA in the vBNST were located in brainstems A1 and A2 noradrenergic cell groups, respectively. In addition, 18.5 +/- 4.2% of radiolabeled cells in A1 and 15.7 +/- 5% in A2 also expressed the mRNA for the NMDA-NR1 receptor subunit. In contrast, only 4 +/- 3% of the radiolabeled cells were present in the locus coeruleus, and none of these cells was positive to NMDA-NR1 receptor subunit mRNA. The present results provide evidence that BNST noradrenergic fibers and terminals originate predominantly from A1 and A2 noradrenergic cell groups, and that a significant number of these noradrenergic neurons also express the mRNA for the NMDA-NR1 receptor subunit. The observation that brainstem noradrenergic neurons innervating the vBNST express NMDA receptor mRNA gives anatomical support to the regulation of NA release by NMDA presynaptic receptors.

Assuntos

RESUMO

In rat atria isolated with their cardioaccelerans nerves and labeled with [3H]norepinephrine, exposure to 1 x 10(-7) mol/L angiotensin II (Ang II) and 1 x 10(-7) mol/L Ang-(1-7) increased the release of radioactivity elicited by nerve stimulation (0.5-millisecond-long square-wave pulses at 2 Hz during 2 minutes) by 90% and 60%, respectively. The facilitatory effect on noradrenergic neurotransmission caused by both peptides was stereospecifically prevented by N omega-nitro-L-arginine methyl ester (1 x 10(-4) mol/L), an inhibitor of nitric oxide synthase that catalyzes the conversion of L-arginine to nitric oxide, as well as by 1 x 10(-5) mol/L methylene blue, a substance that inhibits the guanylate cyclase considered as the final target of nitric oxide action. On the other hand, the precursor of nitric oxide synthesis. L-arginine (1 x 10(-3) mol/L), reversed the prevention produced by N omega-nitro-L-arginine methyl ester on the increased release of norepinephrine caused by Ang II and Ang-(1-7). The present results suggest that nitric oxide could be involved in the neuromodulatory function elicited by both Ang II and Ang-(1-7) in rat atria. The physiological role of this observation is still under study.

Assuntos

RESUMO

To determine whether the release of tritiated noradrenaline (NA) from the sympathetic nerve terminals of the rat vas deferens is an accurate reflection of the release of endogenous NA, we compared the electrically-evoked release of tritiated and endogenous NA from the prostatic sections of the vasa deferentia of male rats. We found that while the release of tritiated NA was completely dependent on the presence of calcium, the release of endogenous NA was not. The overflow of both, tritiated and endogenous NA, was virtually unaffected by blockade of the neuronal uptake mechanism by desipramine. In contrast, blockade of the extraneuronal uptake greatly increased the overflow of endogenous NA, while having no effect on the overflow of tritiated NA. Tritiated NA release, on the other hand, was sensitive to prejunctional regulation, while the release of endogenous NA was not. Increases in stimulus train duration induced a significant increase in the release of endogenous NA, but not in that of tritiated NA. In contrast, the later responded to lower stimulus train frequencies and reached a plateau at lower frequency values as compared to the endogenous NA release. Our results indicate the existence of marked differences between the release of tritiated and endogenous NA. We conclude that: 1) the assumption that tritiated NA release provides a good marker for endogenous NA release in the rat was deferens seems unwarranted; 2) the use of endogenous NA to study the release process in the vas deferens requires a re-examination of the experimental conditions used, in order to minimize possible artifacts that may obscure the study of neuronal release; 3) the choice between measuring the release of tritiated or endogenous NA must be evaluated for each tissue in particular, taking into account its cytoarchitecture, as well as the experimental conditions used.

Assuntos

RESUMO

To determine whether the release of tritiated noradrenaline (NA) from the sympathetic nerve terminals of the rat vas deferens is an accurate reflection of the release of endogenous NA, we compared the electrically-evoked release of tritiated and endogenous NA from the prostatic sections of the vasa deferentia of male rats. We found that while the release of tritiated NA was completely dependent on the presence of calcium, the release of endogenous NA was not. The overflow of both, tritiated and endogenous NA, was virtually unaffected by blockade of the neuronal uptake mechanism by desipramine. In contrast, blockade of the extraneuronal uptake greatly increased the overflow of endogenous NA, while having no effect on the overflow of tritiated NA. Tritiated NA release, on the other hand, was sensitive to prejunctional regulation, while the release of endogenous NA was not. Increases in stimulus train duration induced a significant increase in the release of endogenous NA, but not in that of tritiated NA. In contrast, the later responded to lower stimulus train frequencies and reached a plateau at lower frequency values as compared to the endogenous NA release. Our results indicate the existence of marked differences between the release of tritiated and endogenous NA. We conclude that: 1) the assumption that tritiated NA release provides a good marker for endogenous NA release in the rat was deferens seems unwarranted; 2) the use of endogenous NA to study the release process in the vas deferens requires a re-examination of the experimental conditions used, in order to minimize possible artifacts that may obscure the study of neuronal release; 3) the choice between measuring the release of tritiated or endogenous NA must be evaluated for each tissue in particular, taking into account its cytoarchitecture, as well as the experimental conditions used

Assuntos

Assuntos