Inhibition of carrageenin-induced pedal oedema in rats by immobilisation stress

Behavioral and Biochemical Effects of Mukia madrespatana Following Single Immobilization Stress on Rats

BACKGROUND AND OBJECTIVES

Elevated oxidative stress has been shown to play an important role in the diagnosis and prognosis of stress and memory-related complications. Mukia madrespatana (M. madrespatana) has been reported to have various biological and antioxidant properties. We intended to evaluate the effect of M. madrespatana peel on single immobilization stress-induced behavioral deficits and memory changes in rats. Materials and Methods: M. madrespatana peel (2000 mg/kg/day, orally) was administered to control and immobilize stressed animals for 4 weeks. Anxiolytic, antidepressant, and memory-enhancing effects of M. madrespatana were observed in both unstressed and stressed animals. Results: Lipid peroxidation was decreased while antioxidant enzymes were increased in both unstressed and stressed animals. Acetylcholine level was increased while acetylcholinesterase activity was decreased in both M. madrespatana treated unstressed and stressed rats. There was also an improvement in memory function. Serotonin neurotransmission was also regulated in M. madrespatana treated rats following immobilization stress with anxiolytic and anti-depressive effects. Conclusion: Based on the current study, it is suggested that M. madrespatana has strong antioxidant properties and may be beneficial as dietary supplementation in stress and memory-related conditions.

Antidepressant and antistress activity of GC-MS characterized lipophilic extracts ofGinkgo bilobaleaves

Lipophilic extracts of Ginkgo biloba L. leaves were tested for their possible role on rodent models of depression and stress. Lipophilic extracts of Ginkgo leaves (LEG) at (50 and 100 mg/kg, p.o.) exhibited dose dependent, significant antidepressant activity in the behavioral despair test and learned helplessness rodent model of depression. The activities were comparable to that of imipramine (15 mg/kg) and EGb 761 (50 mg/kg). In the cold immobilization stress induced gastric ulcer model of stress, only the LEG showed a significant reduction in the ulcer index. GC-MS characterization of this bioactive extract was found to be rich in a group of 6-alkyl salicylates (6-AS), along with a fatty alcohol, fatty acids and cardanols. The n-heptadecenyl salicylate represented 60% of the 6-AS. Notable was the absence of dihydroxy alkylphenols which are linked to allergic reactions similar to the urushiols present in poison ivy. In commercial products of Ginkgo, these dihydroxy phenols as well as the favorable 6-AS are removed during enrichment of flavonol glycosides and terpenic lactones. The current findings suggest that intact carboxylic acid groups containing 6-AS are the bioactive components of the lipophilic extract of Ginkgo leaves with antidepressant and antistress activities.

Non-opioid-dependent anti-inflammatory effects of low frequency electroacupuncture

Low frequency electroacupuncture, which is commonly used in pain relief, is known to induce opioid-mediated analgesia. This study examined the contribution of the opioid system in mediating the anti-inflammatory effects of low frequency EA in a standard model of acute inflammation, the carrageenan-induced edema model. Carrageenan was injected in the hind paw of anesthetized rats and low frequency electroacupuncture was applied to acupoints equivalent to Zusanli (St 36) and Sanyinjiao (Sp 6) in humans just prior to the induction of inflammation in the ipsilateral leg. Induction of Fos protein, reflecting neuronal activation, was investigated in the spinal cord with immunohistochemistry. It was found that electroacupuncture strongly inhibited the carrageenan-induced edema by over 60%, and suppressed the associated Fos expression in the superficial laminae (I-II) of the ipsilateral dorsal horn by 50%. Neither the anti-edematous effect nor the suppression of Fos expression in the superficial spinal laminae was affected by intraperitoneal injection of the opioid antagonist naloxone. These results demonstrate that low frequency electroacupuncture is capable of inhibiting peripheral inflammation and the associated central neuronal activity via a non-opioid-dependent mechanism.

Repeated, but not acute, stress suppresses inflammatory plasma extravasation

Clinical findings suggest that inflammatory disease symptoms are aggravated by ongoing, repeated stress, but not by acute stress. We hypothesized that, compared with single acute stressors, chronic repeated stress may engage different physiological mechanisms that exert qualitatively different effects on the inflammatory response. Because inhibition of plasma extravasation, a critical component of the inflammatory response, has been associated with increased disease severity in experimental arthritis, we tested for a potential repeated stress-induced inhibition of plasma extravasation. Repeated, but not single, exposures to restraint stress produced a profound inhibition of bradykinin-induced synovial plasma extravasation in the rat. Experiments examining the mechanism of inhibition showed that the effect of repeated stress was blocked by adrenalectomy, but not by adrenal medullae denervation, suggesting that the adrenal cortex mediates this effect. Consistent with known effects of stress and with mediation by the adrenal cortex, restraint stress evoked repeated transient elevations of plasma corticosterone levels. This elevated corticosterone was necessary and sufficient to produce inhibition of plasma extravasation because the stress-induced inhibition was blocked by preventing corticosterone synthesis and, conversely, induction of repeated transient elevations in plasma corticosterone levels mimicked the effects of repeated stress. These data suggest that repetition of a mild stressor can induce changes in the physiological state of the animal that enable a previously innocuous stressor to inhibit the inflammatory response. These findings provide a potential explanation for the clinical association between repeated stress and aggravation of inflammatory disease symptoms and provide a model for study of the biological mechanisms underlying the stress-induced aggravation of chronic inflammatory diseases.

Effect of centrally administered enkephalins on carrageenin-induced paw oedema in rats

Intracerebroventricularly (icv) administered met-enkephalin, leu-enkephalin, and morphine induced dose-related attenuation of carrageenin-induced acute paw oedema in rats. Naloxone (10 micrograms, icv) antagonized the anti-inflammatory effects of the enkephalins (20 micrograms) and morphine (20 micrograms), but itself induced an anti-inflammatory effect at a higher dose (50 micrograms, icv). The anti-inflammatory effects of the enkephalins, morphine, and the higher dose of naloxone were significantly inhibited by metyrapone, an inhibitor of endogenous corticoid synthesis. The icv-administered doses of the enkephalins and morphine induced insignificant inflammation-attenuating effects when administered i.p. Results suggest that the anti-inflammatory effects of the enkephalins and morphine are exerted through central opiate receptors. Furthermore, the inflammation-attenuating effects of these drugs and the higher dose of naloxone appear to be dependent upon endogenous corticoids, suggesting that activation of the hypothalamo-pituitary-adrenocortical axis may be involved.

Central muscarinic receptor subtypes and carrageenin-induced paw oedema in rats

In an earlier report from this laboratory, it was demonstrated that the central cholinergic system exerted a modulatory pro-inflammatory effect on carrageenin-induced paw inflammation in rats. In this study, the role of the central muscarinic receptors in cholinergic modulation of peripheral inflammation was investigated by using several M1 and M2 receptor agonists and antagonists. The M1 receptor agonists aceclidine and arecholine and the nonspecific muscarinic receptor agonist oxotremorine augmented carrageenin oedema, an effect attenuated by the M1 receptor antagonist scopolamine. Physostigmine behaved like a M1 receptor agonist at all dose levels. However, the other M2 receptor agonist, carbachol, produced a dose-dependent dual effect, with lower doses attenuating the oedema and higher doses augmenting the inflammation. While the former action appeared to be due to M2 receptor stimulation, because it was blocked by AF-DX 116--a M2 receptor antagonist, the latter action appeared to be induced by M1 receptor stimulation, because it was inhibited by scopolamine. The pro-inflammatory effect of the M2 receptor antagonists AF-DX 116 and gallamine appeared to be induced by enhanced neuronal release of acetylcholine, because the effects were not evident following pretreatment with hemicholinium, which attenuates synthesis of the amine. Muscarinic receptor binding studies with (3H)-QNB indicated that the corpus striatum has substantially higher population of M1 receptors compared with the cerebellum. In the corpus striatum, (3H)-QNB binding indicated initial up-regulation followed by down-regulation of M1 receptors during peak inflammation, which appeared to persist even after a decrease in the inflammation. In contrast, the M1 receptors in the cerebellum appeared to be down-regulated very transiently during the early phase of the inflammation. While these receptor alterations may be due to the inflammation, it is equally possible that they represent changes induced by the stress of pain and inflammation induced by carrageenin.

Temporal study of carrageenan-induced PMN migration in mice

The time course of polymorphonuclear neutrophil (PMN) migration in an experimental inflammatory granuloma induced by carrageenan in the mice was studied at 6 different times of the day. Compared to saline, the number of PMN increased as soon as 240 min and reached high level at 480 min when migration was induced by carrageenan. The data showed circadian variations in the time course of cell migration. After 240 and 360 minutes of migration, the number of PMN was highest in the cell trap implanted at 09.00 whereas minimum values were obtained at 01.00. After 480 minutes of implantation, the PMN migration was maximal when the carrageenan experiment was performed at 05.00 and minimum values were obtained at 13.00. Thus, a significant rhythm was demonstrated in the time course of PMN migration.

Effect of centrally administered prostaglandin D2 and some prostaglandin synthesis inhibitors on carrageenan-induced paw oedema in rats

The putative modulatory role of central prostaglandins (PGs) on peripheral inflammation has been explored by investigating the effects of intracerebroventricularly (i.c.v.) administered PGD2, the major rodent brain PG, hydrocortisone, a phospholipase A2 inhibitor, and the cyclo-oxygenase inhibitors, paracetamol and mefenamic acid, on carrageenan-induced paw inflammation in rats. PGD2 produced a dose-related inflammation-augmenting effect, whereas hydrocortisone and the PG synthesis inhibitors, paracetamol and mefenamic acid, induced attenuation of the peripheral oedema. These findings confirm an earlier report from this laboratory which had indicated that central PGs may modulate peripheral inflammation and that conventional anti-inflammatory agents exert at least part of their effect by inhibiting central PG synthesis.

Brain monoamines during carrageenan-induced acute paw inflammation in rats

Paw inflammation was induced in rats by sub-plantar administration of carrageenan. Significant inflammatory oedema was observed 1 h later and the peak effect was noted between 3-4 h. The oedema was markedly reduced after 12-24 h. Steady state levels of whole brain and hypothalamic monoamines were estimated spectrofluorometrically during the course of the carrageenan-induced paw inflammation. In addition, the rate of accumulation of the brain 5-hydroxytryptamine (5-HT) and noradrenaline (NA) was assessed in clorgyline-pretreated rats during the inflammation. The whole brain and hypothalamic concentrations of 5-HT and NA were augmented during the early phase of the inflammation, but fell below control values when peak inflammation was achieved. Thereafter, the monoamine levels tended to normalize by 24 h when the inflammation had virtually subsided. On the contrary, whole brain and hypothalamic dopamine levels remained largely unaffected. The rate of accumulation of brain 5-HT and NA were enhanced during carrageenan inflammation, indicating that the turnover of these monoamines is augmented during the inflammatory process. The results suggest that acute peripheral inflammation may significantly affect central 5-HT and noradrenergic activity in rats.

Intracerebroventricularly administered bradykinin augments carrageenan-induced paw oedema in rats

Intracerebroventricular (i.c.v.) administered bradykinin (2.5 and 5.0 micrograms/rat) was found to augment carrageenan-induced acute paw oedema throughout the 4 h post-carrageenan observation period. The effect was statistically significant with the higher dose. The pro-inflammatory effect of i.c.v. bradykinin was antagonized following pretreatment with hemicholinium and atropine ethoiodide administered i.c.v., drugs that reduce central cholinergic activity. Similarly, central administration of drugs that inhibit the synthesis of eicosanoids, hydrocortisone, diclofenac and paracetamol, also attenuated the pro-inflammatory effect of bradykinin. The findings indicate that the inflammation-promoting effect of centrally administered bradykinin involves the central prostaglandin and cholinergic neurotransmitter systems.