Trypsin enhances sympathetic neuron-dependent plasma extravasation in the rat knee joint

Perfusion of 6-hydroxydopamine through the rat knee joint causes an increase in plasma extravasation by activation of sympathetic neuron terminals. Similarly, the increase in plasma extravasation in the rat knee joint produced by the inflammatory mediator bradykinin is dependent on the sympathetic post-ganglion neuron. There is evidence that both 6-hydroxydopamine and bradykinin release a number of mediators, some of which appear to enhance plasma extravasation and some which inhibit it. We attempted to determine the nature of inhibitory factor(s) by co-infusing trypsin (which rapidly cleaves peptides) with 6-hydroxydopamine. We observed a marked enhancement of 6-hydroxydopamine-induced plasma extravasation by trypsin. This effect appeared to be specific to neurogenic plasma extravasation since trypsin alone had little effect on plasma extravasation and trypsin did not affect non-neurogenic plasma extravasation (that produced by platelet activating factor). Taken together, the data suggests that 6-hydroxydopamine not only releases mediators from the sympathetic neuron that produce plasma extravasation, but also an inhibitor(s) of plasma extravasation that is peptide in nature.

Further substantiation of a significant role for the sympathetic nervous system in inflammation

This study provides significant new evidence substantiating a role of the postganglionic sympathetic neuron in plasma extravasation in the knee-joint of the rat. Increased plasma extravasation produced by the potent inflammatory mediator bradykinin was mimicked by 6-hydroxydopamine, a selective stimulator of sympathetic fibers. Various treatments (chemical sympathectomy, co-perfusion with the local anesthetic lidocaine, or co-perfusion with depolarizing concentrations of potassium) similarly modulated plasma extravasation induced by both bradykinin and 6-hydroxydopamine, but not that produced by platelet activating factor. We also showed that bradykinin is able to release norepinephrine in the knee-joint, indicating action on the sympathetic postganglionic neuron. In summary, these experiments provide substantial additional evidence supporting a significant contribution of the sympathetic post-ganglionic neuron terminal to inflammatory plasma extravasation.

Peripheral and central contributions to the persistent expression of spinal cord fos-like immunoreactivity produced by sciatic nerve transection in the rat

Previous studies have demonstrated that noxious stimuli, intense enough to produce tissue injury, evoke a transient expression of the Fos protein product of the c-fos proto-oncogene in neurons, in regions of the spinal cord that contribute to the transmission of nociceptive messages in the rat. Since there is evidence that increases in fos-like immunoreactivity reflect increases in neuronal activity, it has thus been possible to identify populations of neurons that are activated in response to tissue injury. In this study we used immunocytochemical localization of fos-like immunoreactive (FLI) neurons to map the patterns of neuronal activity in the spinal cord at different times after peripheral nerve injury in the rat. Sciatic nerve transection induced a persistent (at least 1 month) elevation in the number of FLI neurons, predominantly in laminae 1, 2, 5, 6 and 7 of the ipsilateral lumbar enlargement of the spinal cord. In the L5 segment, the expression of fos-like immunoreactivity in the superficial dorsal horn (laminae 1 and 2) fluctuated, with peaks of Fos expression at 2 h, 2 days and 2 weeks after nerve transection. Furthermore, by 2 weeks after nerve injury, the distribution of labelled neurons in the superficial laminae of the dorsal horn shifted, with the most densely labelled cells now located in the central portion of the superficial dorsal horn. In contrast, the pattern of labelled neurons in laminae 5, 6 and 7 was relatively constant over the 4-week study period. Local anesthetic block of the sciatic nerve significantly decreased the number of FLI neurons when it was administered at either 2 days or 2 weeks post nerve injury. At 2 days, injection of the local anesthetic subcutaneously in the dorsum of neck, to control for a systemic action, also reduced expression of FLI in laminae 1 and 2; at 2 weeks, the systemic injection of the local anesthetic reduced expression of FLI throughout the gray matter of the spinal cord. These results demonstrate that peripheral nerve injury, in contrast to tissue injury, induces a prolonged increase in Fos expression in neurons predominantly in those regions of the spinal cord that are associated with the transmission of nociceptive messages. This pattern of fos-like immunoreactivity is probably the result of persistent neuronal activity in the spinal cord. The increased 'activity' in the spinal cord appears to be maintained both by abnormal activity in the injured peripheral nerve as well as by reorganization of circuits within the spinal cord secondary to the nerve injury.

Effects of injury discharge on the persistent expression of spinal cord fos-like immunoreactivity produced by sciatic nerve transection in the rat

We recently reported that peripheral nerve injury produced by sciatic nerve transection induces a persistent increase in the expression of the immunoreactive Fos protein product of the c-fos proto-oncogene, an indicator of neuronal activity, in the lumbar spinal cord of the rat and that local anesthetic blockade of the peripheral neuroma attenuates this long-term expression of Fos. In addition to the sustained activity of the injured afferents, the nerve transection itself results, acutely, in a massive injury-induced neural discharge. In this study we evaluated the effect of blocking this massive injury discharge on the persistence of Fos expression. Just prior to nerve transection we applied the short-acting local anesthetic, lidocaine, to the sciatic nerve. Control injections were made subcutaneously on the dorsum of the neck. We report that injection of the local anesthetic, by either route, significantly reduced the number of fos-like immunoreactive neurons at 2 days after nerve transection. The effect was only observed on neurons in the superficial dorsal horn. These results indicate that along with sustained activity of injured afferents and of reorganization of central circuits after injury, the initial brief discharge at the time of nerve injury contributes to a prolonged increase in the activity of spinal cord neurons.

Mechanical hyperalgesia in streptozotocin-diabetic rats is not sympathetically maintained

It has been suggested that the mechanism underlying the pain that occurs in patients with diabetic neuropathy may be similar to that mediating sympathetically maintained pain (SMP), such as occurs in patients with reflex sympathetic dystrophy. To evaluate this suggestion we have examined a model of diabetes mellitus, the streptozotocin-diabetic (STZ-D) rat, for features characteristic of SMP. We demonstrate that the decrease in nociceptive threshold observed in the STZ-D rat is not attenuated by chemical sympathectomy nor exacerbated by intradermal injection of norepinephrine (NE). In addition, the NE content is markedly decreased in the skin of the STZ-D rat. These results suggest that altered nociceptive thresholds associated with diabetic neuropathy are not sympathetically maintained.

Temporal factors in the enhancement of morphine analgesia by desipramine

Administration of desipramine, the tricyclic noradrenergic agent, for 7 days pre-operatively, had been found to potentiate postoperative morphine analgesia. In this study we investigated the necessary timing of administration of desipramine in its action to potentiate morphine analgesia. We report that the administration of desipramine for only 3 days, starting 7 days before surgery, also potentiated postoperative morphine analgesia and that the analgesia observed was not different from that in patients receiving a full 7 days of desipramine pre-operatively. The potentiation of morphine analgesia observed was most evident as a prolongation of the analgesic response. Patients who also received desipramine for only 3 days, but starting 3 days pre-operatively had an analgesic response to postoperative morphine that was the same as that in patients receiving placebo. The ability of the administration of desipramine early in the pre-operative week to interact with postoperative morphine and the lack of response when desipramine was given late in the week does not have an explanation at present. However, it may reflect the known latency in humans to the onset of the central effects of tricyclic antidepressants (TCAs).

Peptides and the primary afferent nociceptor

An expanding knowledge of neuropeptides and their function has led to a profound change in our view of how the PAN contributes to pain. In addition to their expected direct action on postsynaptic cells in the dorsal horn, neuropeptides can modify transmitter release from nearby terminals of other PANs and/or diffuse to act on dorsal horn neurons at a considerable distance from their site of release (Fig. 2). Contrary to early expectations and despite the evidence that several neuropeptides excite central nociceptive neurons, there is no clear correspondence between neuropeptide content and physiologically defined classes of small-diameter primary afferents. There is, however, a tendency for populations of afferents innervating different organs to differ consistently in their peptide content. In fact, the peptide content of primary afferents is, in part, determined by specific factors in the tissues that they innervate. Furthermore, peptide content can change dramatically in response to certain prolonged stimuli or nerve damage. The lack of correspondence of peptide content and physiological response pattern, the plasticity of peptide content, its tissue specificity, and the possibility for action at a distance from the site of their release from central PAN terminals strongly suggest that PAN peptides have functions that are fundamentally different from those of the short-range actions of amino acid neurotransmitters that are also found in the PAN. Finally, nowhere is the plasticity of function of the PAN more evident than at its peripheral terminals. Long-term changes are produced in these terminals by a host of peptides that derive from a variety of cell types. The complexity of this transduction process is augmented by the activity-induced release of peripherally active neuropeptides from the PAN itself. In addition to the variety of fundamental neurobiological issues that recent studies of PANs have raised, they have also generated a great deal of clinical interest, in view of the role of the PAN in inflammation and its accessibility for study and for therapeutic intervention.

Comparison of intradermal and subcutaneous hyperalgesic effects of inflammatory mediators in the rat

In recent studies, the superfusion of the corium side of the skin with inflammatory mediators failed to produce sensitization of nociceptors to mechanical stimuli. We have studied the effects of intradermal (i.d.) and subcutaneous (s.c.) injections of prostaglandin E2 (PGE2) and bradykinin (BK) in a behavioral model of hyperalgesia. PGE2 or BK was injected into the rat hind-paw, and paw-withdrawal thresholds in response to noxious mechanical stimulation before and after the drug were compared. Subcutaneous injection of PGE2 (1-1000 ng), a hyperalgesic inflammatory mediator, did not significantly alter paw-withdrawal thresholds, under the same conditions in which i.d. injections dose-dependently lowered paw-withdrawal thresholds. Similarly, BK (1-1000 ng), another hyperalgesic mediator, given s.c. failed to significantly alter paw-withdrawal thresholds while i.d. injections dose-dependently lowered paw-withdrawal thresholds. The prostaglandin E-type, EP1 receptor antagonist SC19220 (750 ng), given s.c. prior to PGE2 (i.d.) did not significantly change PGE2-induced hyperalgesia. However, SC19220 significantly attenuated PGE2 hyperalgesia when both were injected i.d. Also, s.c. administration of the mu-opioid antagonist, DAMGO, before PGE2 did not inhibit PGE2-induced hyperalgesia as opposed to i.d. injection. These results suggest that the inability of s.c. injection of PGE2 or BK to reach its receptor site on the terminals of primary afferent nociceptors may be responsible for the ineffectiveness of these hyperalgesic mediators to sensitize cutaneous nociceptors to mechanical stimuli in the rat and underscore the importance of the site of application and site of action of hyperalgesic agents in the study of hyperalgesic mechanisms.

Antinociception produced by receptor selective opioids. Modulation of supraspinal antinociceptive effects by spinal opioids

This study evaluated the antinociceptive effects produced when different combinations of supraspinal mu- and delta-opioid agonists were co-administered with spinal mu-, delta-, and kappa-opioid agonists. Using the Randall-Selitto paw-withdrawal test, in the rat, changes in nociceptive thresholds were measured following co-administration of sequentially increasing i.c.v. doses of either DAMGO or DPDPE with a low-antinociceptive dose of intrathecal DAMGO, DPDPE, or U50,488H. Antinociceptive synergy (i.e. a more than additive antinociceptive effect) was demonstrated with all of the combinations tested except for supraspinal DPDPE co-administered with spinal DAMGO. The results of this study provide support for the suggestion that supraspinal and spinal antinociceptive mechanisms share, in part, common neural circuits. Marked differences in the overall magnitude of the antinociceptive effects produced by the various combinations of opioid agonists were demonstrated through a secondary analysis of the data. When sequentially increasing i.c.v. doses of DAMGO were administered, significantly larger increases in nociceptive thresholds were observed with co-administration of intrathecal injections of low antinociceptive doses of either DAMGO or U50,488H compared to DPDPE. In contrast, when DPDPE was administered supraspinally, the largest increases in nociceptive thresholds were demonstrated with co-administration of DPDPE at the spinal site. The results of the secondary analysis provide support for the hypothesis that descending antinociceptive control systems activated by supraspinal administration of selective mu- and delta-opioid agonists interact, differently, with spinal mu-, delta-, and kappa-opioidergic mechanisms.

Chronically administered nicotine attenuates bradykinin-induced plasma extravasation and aggravates arthritis-induced joint injury in the rat

We recently showed that acute administration of nicotine in the rat decreases bradykinin-induced plasma extravasation and that adrenal medullary-derived epinephrine, acting at a beta 2-adrenergic receptor, mediates the nicotine effect. Since agents which decrease bradykinin-induced plasma extravasation have been associated with increased joint injury in a rat model of chronic inflammation (experimental arthritis induced by subcutaneous injection of Mycobacterium butyricum) we examined the effect of chronic nicotine on both plasma extravasation and the severity of joint injury. In normal rats, bradykinin-induced plasma extravasation was decreased after nicotine administered both by repeated injection (10(-2) mg/kg, s.c., once per h for 4 h) and by continuous long-term infusion (subcutaneous mini-osmotic pump; 1.5 x 10(-3) mg/kg per h for 30 days). Nicotine-induced inhibition of bradykinin-induced plasma extravasation did not show tachyphylaxis. In rats with arthritis, chronic administration of nicotine also produced a decrease in bradykinin-induced plasma extravasation. This effect of chronic nicotine in the arthritic rats was antagonized by co-administration of hexamethonium (a nicotinic receptor antagonist), by surgical removal of the adrenal medulla, or by co-administration of ICI-118,551 (a beta 2-adrenoceptor antagonist). Chronic administration of nicotine decreased the latency to the onset of arthritis and, in a dose-dependent manner, led to an increase in the radiographic joint injury score.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurogenic and non-neurogenic mechanisms of plasma extravasation in the rat

We describe two distinct mechanisms for the enhancement of plasma extravasation in the knee joint of the rat. One is activated by bradykinin and is neurogenic; the other is activated by platelet-activating factor and is non-neurogenic. Bradykinin-induced synovial plasma extravasation is known to be dependent on the sympathetic postganglionic neuron terminal, and to involve prostaglandins, ATP, adenosine A2 receptor action, and the attraction and activation of neutrophils. In this study we found that bradykinin-induced plasma extravasation also involves endothelium-derived relaxing factor; specifically we found that bradykinin-induced plasma extravasation was antagonized stereospecifically by the inhibitor of endothelium-derived relaxing factor synthesis, NG-monomethyl-L-arginine. Perfused alone, platelet-activating factor produced an increase in synovial plasma extravasation which was markedly reduced by the platelet-activating factor receptor antagonists BN 52021 and WEB 2086 (these antagonists did not affect bradykinin-induced plasma extravasation). Platelet-activating factor-induced plasma extravasation was not affected by NG-monomethyl-L-arginine, indomethacin (a prostaglandin synthesis inhibitor), phenol 3-(5H-thiozolo[2,3b]quinazolin) (an A2 receptor adenosine antagonist), dextran sulfate (an inhibitor of leukocyte rolling), hydroxyurea (a depletor of leukocytes), chronic sympathectomy or the depletion of unmyelinated afferent fibers. Of note, the magnitude of platelet-activating factor-induced plasma extravasation was increased by co-perfusion with prostaglandin E2 and attenuated by co-perfusion with L-arginine; that is, two of the mediators involved in neurogenic bradykinin-induced plasma extravasation exerted an influence on non-neurogenic plasma extravasation. Separate mechanisms for bradykinin and platelet-activating factor plasma extravasation were further demonstrated in the streptozotocin-treated diabetic rat, in which there is a peripheral neuropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanical hyperalgesia in streptozotocin-diabetic rats

Recent evidence strongly suggests that the hyperalgesia induced by agents acting directly on the primary afferent is mediated by stimulatory G-proteins and the cAMP second messenger system. In this study, we used the Randall-Selitto paw-pressure device to study hyperalgesia that develops in the streptozotocin-diabetic rat. Subcutaneous injection of streptozotocin in male Sprague-Dawley rats induced hyperglycemia and glucosuria detectable within 24 h of injection. A decrease in mechanical nociceptive threshold in the hindpaw was detected after one week. Intradermal injection of indomethacin, a cyclooxygenase inhibitor, had no significant effect on nociceptive threshold; and prostaglandin E2, which produces hyperalgesia by a direct action on the primary afferent, decreased nociceptive threshold similarly in streptozotocin-diabetic and control rats. Guanosine 5'-O-(2-thiodiphosphate), which blocks stimulatory G-proteins, attenuated the prostaglandin E2-hyperalgesia in both streptozotocin-diabetic and control rats, but had no effect on baseline nociceptive threshold in either group. Intradermal injection of either 2',5'-dideoxyadenosine, an inhibitor of adenylate cyclase, or phosphodiesterase, which degrades cAMP, increased mechanical nociceptive threshold in streptozotocin-diabetic rats whilst not affecting mechanical nociceptive threshold in the control rats. Intradermal injection of 8-bromo cAMP, a membrane-permeable analog of cAMP, produced hyperalgesia of significantly greater magnitude in the streptozotocin-diabetic rats than the control rats. Intradermal injection of N6-cyclopentyl adenosine, an A1-type adenosine agonist, which can activate an inhibitory G-protein and decrease cAMP production, also increased nociceptive thresholds in streptozotocin-diabetic rats. This effect was blocked by pertussis toxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal medullary modulation of the inhibition of bradykinin-induced plasma extravasation by intrathecal nicotine

In the present experiments, we studied the effect of i.t. nicotine on synovial bradykinin-induced plasma extravasation (BK-PE), assessed by measurement of extravasation of Evan's blue dye into the rat knee joint. We report that in normal rats, i.t. nicotine dose-dependently inhibited BK-PE; the dose required was 100 times greater than the effective s.c. dose. In adrenal medullectomized rats, i.t. nicotine inhibited BK-PE at doses 10(6) times smaller than in rats with intact adrenal medullae. A similar leftward shift in the i.t. nicotine dose-response curve was seen in normal rats after blocking peripheral nicotinic receptors by hexamethonium or after bilateral denervation of the adrenal medulla. Intra-articular infusion of the knee joint in normal rats with knee joint perfusate collected from donor rats that had received i.t. nicotine decreased BK-PE significantly. Denervation of the sciatic nerves in the donor rat did not affect this action of i.t. nicotine. Perfusate collected from adrenal medullectomized donor rats that had received i.t. nicotine resulted in a greater decrease of BK-PE compared to the decrease produced by perfusate from normal donor rats that received i.t. nicotine. Intra-articular pretreatment of recipient rats with different receptor antagonists [phentolamine (alpha adrenoceptors), ICI-118,551 (beta 2 adrenoceptors), methysergide (serotoninergic S1/2 receptors) or naloxone (opioid receptors)] did not affect the BK-PE response produced by this perfusate. Nicotine, when administered i.t., can inhibit synovial BK-PE, but this effect is expressed only at high doses in the presence of an intact adrenal medulla.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of bradykinin-induced plasma extravasation in the rat knee joint by sympathetic co-transmitters

We describe the contribution of various sympathetic post-ganglionic neuron mediators to bradykinin-induced plasma extravasation in the knee joint of the rat. Co-perfusion of the sympathetic post-ganglionic neuron mediators, norepinephrine or neuropeptide Y with bradykinin resulted in diminished plasma extravasation. In contrast, the putative sympathetic post-ganglionic neuron mediators of bradykinin-induced plasma extravasation, namely prostaglandin E2, ATP, the selective adenosine A2-receptor agonist, CGS21680 or the endothelium-derived relaxing factor (as its precursor L-arginine) all greatly enhanced bradykinin-induced plasma extravasation, but produced little or no increase in plasma extravasation administered alone. The data show that sympathetic post-ganglionic neuron-derived mediators may either inhibit or enhance plasma extravasation induced by bradykinin, and we hypothesize that differential release of mediators from the sympathetic post-ganglionic neuron terminal, in response to varying stimuli, regulates local plasma extravasation during inflammation.

Increased responsiveness of sensory neurons in the saphenous nerve of the streptozotocin-diabetic rat

1. This study examined sensory neurons in the saphenous nerve of rats treated with streptozotocin to induce diabetes (STZ-D). Several physiological properties of sensory neurons were not significantly different in STZ-D compared with control (CON) rats, including percentage and rate of spontaneous activity seen in the whole nerve and mechanical and thermal thresholds of individual C-fibers. 2. The response of STZ-D and CON C-fibers to a sustained (1 min) mechanical stimulus of threshold force was similar. However, during the 5 min immediately after removal of this stimulus, there was a much greater afterdischarge in STZ-D rats (STZ-D: n = 35; 14.6 +/- 5.1 action potentials/5 min, mean +/- SE; CON: n = 34; 3.9 +/- 0.7 action potentials/5 min). The number of action potentials during a sustained (1 min) suprathreshold mechanical (445 g) stimulus was also significantly greater in the C-fibers from STZ-D rats (STZ-D: n = 44; 149.7 +/- 18.4 action potentials; CON: n = 45; 84.7 +/- 12.2 action potentials). The afterdischarge during the 5 min immediately after removal of the sustained suprathreshold stimulus was also greater in C-fibers from STZ-D rats (STZ-D: 38.7 +/- 13.1 action potentials/5 min; CON: 9.3 +/- 2.3 action potentials/5 min). 3. There was a significant difference between C-fibers from STZ-D and CON rats with respect to the distribution among certain sensory classes.(ABSTRACT TRUNCATED AT 250 WORDS)

Antinociception produced by receptor selective opioids: modulation of spinal antinociceptive effects by supraspinal opioids

The effect of intracerebroventricular administration of low-antinociceptive doses of selective mu- (DAMGO) or delta- (DPDPE) opioid agonists on the dose-dependent antinociceptive effects produced by intrathecal administration of sequentially increasing doses of selective mu-, delta-, or kappa-(U50,488H) opioid agonists was evaluated, in the rat, using the Randall-Selitto paw-withdrawal test. When DPDPE or U50,488H was administered intrathecally, the low doses of both intracerebroventricular DAMGO and intracerebroventricular DPDPE markedly enhanced the antinociceptive effects of both intrathecal opioids. In contrast, when DAMGO was administered intrathecally, both intracerebroventricular DAMGO and intracerebroventricular DPDPE, administered in low doses, markedly antagonized the antinociceptive effects of the intrathecal opioid. In addition, the intracerebroventricular administration of a low-antinociceptive dose of a second mu-opioid agonist, morphiceptin, antagonized the antinociceptive effects of intrathecal morphiceptin. The antagonism of the antinociceptive effects observed with spinal administration of DAMGO is dose-dependent, with the effect observed only at low doses. Furthermore, the antagonism cannot be explained by a reduction in motor deficits produced by intrathecal administration of DAMGO, because there were no differences in motor deficits, measured with an accelerating Rotarod treadmill, between intrathecal DAMGO administered as a single agent or as part of a combination regimen. The differences in antinociceptive effects obtained with the various supraspinal and spinal combinations are discussed in terms of the interactions that may occur between brainstem and spinal opioid receptor sites.

Inhibition of spinal opioid analgesia by supraspinal administration of selective opioid antagonists

The effect of intracerebroventricular administration of a selective mu- (CTOP) or delta- (ICI 174,864) opioid receptor antagonist on the antinociceptive effects produced by intrathecal administration of selective mu- (DAMGO), delta- (DPDPE) and kappa- (U50-488H) opioid receptor agonists was evaluated using the Randall-Selitto paw-withdrawal test, in the rat. While the intracerebroventricular administration of CTOP or ICI 174,864, alone, had no effect on nociceptive thresholds, intracerebroventricular administration of CTOP and ICI 174,864 produced marked antagonism of the antinociceptive effects of intrathecal DAMGO. The antinociceptive effects of intrathecal administration of DPDPE or U50,488H were not antagonized by intracerebroventricular administration of CTOP or ICI 174,864. These data suggest that, in the rat, along with the established descending antinociceptive pathways, there is an ascending antinociceptive control mechanism projecting from the spinal cord to the brainstem. The ascending antinociceptive control involves mu- and delta-opioid agonism at supraspinal sites and appears to be mediated selectively by mu-, but not by delta- or kappa-opioid agonism at the spinal level.

Sensory neuropeptide interactions in the production of plasma extravasation in the rat

We used an experimental model of neurogenic inflammation to study the contribution of the primary afferent peptides substance P, calcitonin gene-related peptide, galanin and somatostatin to plasma extravasation in rat synovium. Perfusion of the C-fiber excitotoxin, capsaicin (1.6 mM), through the knee joint of the pentobarbital anesthetized rat, increased plasma extravasation transiently (< 30 min). Perfusion of substance P (1 microM) or calcitonin gene-related peptide (100 nM), two primary afferent neuropeptides that are released by acute capsaicin administration, had no significant effect on plasma extravasation. Co-perfusion of these two neuropeptides, however, evoked an increase in plasma extravasation that was greater than that produced by capsaicin remaining above 250% of the baseline level by the end of the perfusion period (55 min). Capsaicin co-perfused with either galanin (100 nM) or somatostatin (1 microM) failed to increase plasma extravasation. Neither galanin nor somatostatin significantly affected increase in plasma extravasation induced by co-perfusion of substance P plus calcitonin gene-related peptide. Therefore, we suggest that galanin and somatostatin inhibit, presynaptically, the release of substance P and calcitonin gene-related peptide from primary afferent terminals. The interactions among these four neuropeptides provide a novel mechanism for the regulation of primary afferent neurogenic inflammation.

Sympathoadrenal contribution to nicotinic and muscarinic modulation of bradykinin-induced plasma extravasation in the knee joint of the rat

Previous results from this laboratory demonstrated that plasma extravasation produced by intra-articular infusion of bradykinin in the rat is mediated by an action on the sympathetic terminals in the knee joint and that adrenal medullary epinephrine regulates the plasma extravasation provoked by bradykinin. Because the release of epinephrine is under cholinergic control, we have now evaluated the effect of nicotinic and muscarinic cholinergic agonists on bradykinin-induced plasma extravasation in the knee joint of the rat. We report that s.c. administration of nicotine and carbachol attenuated plasma extravasation induced by bradykinin; this attenuation was significantly antagonized by systemic injection of hexamethonium and atropine, respectively. The nicotine and carbachol effects were also significantly attenuated after removal of the adrenal medulla. These results indicate that both nicotine and carbachol can inhibit bradykinin-induced plasma extravasation and that this inhibition is mediated, at least in part, through activation of nicotinic and muscarinic receptors in the adrenal medulla. Finally, local perfusion of the knee joint with hexamethonium did not affect the inhibition of bradykinin-induced plasma extravasation produced by systemic nicotine. Intra-articular perfusion of atropine potentiated the inhibition of bradykinin-induced plasma extravasation by systemic carbachol, indicating that muscarinic receptors in the synovium also contribute to plasma extravasation. The inhibitory action of nicotine on plasma extravasation may contribute, in part, to the reported increased severity of arthritis in individuals who smoke.

Delta- and kappa-opioid agonists inhibit plasma extravasation induced by bradykinin in the knee joint of the rat

We used an experimental model of neurogenic inflammation, plasma extravasation induced by bradykinin or capsaicin, to study the effect of receptor-selective opioid agonists on plasma extravasation. Plasma extravasation was induced in the knee joint of the rat by continuous perfusion of either bradykinin (160 ng/ml), an inflammatory mediator produced at sites of tissue injury, that produces plasma extravasation significantly dependent on the sympathetic postganglionic neuron, or capsaicin (5 mg/ml), a C-fiber excitotoxin, that induces plasma extravasation that is dependent on both primary afferents and sympathetic post-ganglionic neurons. When selective delta-((d-Pen2,5)-enkephalin) or kappa-(trans-3,4-dichloro-N-methyl-N[2-(- pyrolidinyl)cyclohexyl]benzeneacetamide; U50,488H) opioid agonists were perfused with bradykinin, plasma extravasation was significantly attenuated. Co-perfusion of the non-selective opioid antagonist naloxone (1 microM), reversed this opioid-induced inhibition of bradykinin-induced plasma extravasation. In contrast, co-perfusion of a selective mu-opioid agonist (Tyr-d-Ala-Gly-NMe-Phe-Gly-ol) did not reduce bradykinin-induced plasma extravasation. Tyr-d-Ala-Gly-NMe-Phe-Gly-ol was, however, able to completely inhibit the plasma extravasation produced by capsaicin. These results suggest that delta- and kappa-, but not mu-selective opioids inhibit bradykinin-stimulated plasma extravasation, while a mu-selective opioid inhibits primary afferent-dependent plasma extravasation. Therefore, inhibition of neurogenic plasma extravasation by receptor-selective opioids may depend on the relative contribution to plasma extravasation of unmyelinated afferent and sympathetic postganglionic neuron terminals. Our findings can also explain, in part, the variation in anti-inflammatory effects of receptor-selective opioids reported in different inflammatory conditions.

Enhancement of pentazocine analgesia by clonidine

Opiate-adrenergic interactions were investigated by studying the effect of the selective alpha 2-adrenergic agonist, clonidine, on the analgesia produced by intravenous placebo and by the predominantly kappa-opiate agonist, pentazocine, in patients with dental postoperative pain. Clonidine did not affect the pain level when administered with intravenous placebo. When administered with pentazocine, clonidine caused a statistically significant increase in pentazocine analgesia. Comparison is made to other opiate-adrenergic interactions and possible mechanisms are discussed.

Norepinephrine-induced increase in sympathetic neuron-derived prostaglandins is independent of neuronal release mechanisms

The contribution of exocytosis to norepinephrine-stimulated prostaglandin release from sympathetic postganglionic neurons was evaluated in homogenates of adult rat superior cervical ganglia. Incubation of ganglion homogenates with norepinephrine (1 mM) for 30 min caused an increased release of prostaglandin E2 and prostaglandin I2 (measured as the stable metabolite, 6-keto-PGF1a). Neither tetrodotoxin (10 mM), K+ (120 mM), nor EDTA in Ca(2+)-free buffer affected prostaglandin generation under basal and norepinephrine-stimulated conditions. These results suggest that the increase in prostaglandin production by sympathetic neurons after norepinephrine administration is not through the release of previously synthesized intracellular stores. Instead, the increase in prostaglandins in response to norepinephrine appears to be explained by de novo synthesis.