Antinociception Induced by Moringa Stenopetela (Baker f.) Cufod. Leaves Extract and Possible Mechanisms of Action

Moringa stenopetala (Baker f.) Cufod., is an endemic species growing in the south of Ethiopia. M. stenopetala is often consumed as food and used in traditional medicine and it has also been traditionally used for relieving of pain in Ethiopia. This study aimed to investigate the antinociceptive effect and mechanisms of action of M. stenopetala leaves methanol extract in mice. The per-oral doses of 50, 100, and 200 mg/kg of M. stenopetala extract were tested for antinociceptive action by using hot-plate, tail-immersion, and writhing tests. The possible mechanisms of in the antinociceptive action were investigated by pre-treatment with 5 mg/kg naloxone (non-selective opioid antagonist), 1 mg/kg ketanserin (5-HT2A/2C receptor antagonist), and 1 mg/kg yohimbine (α2 adrenoceptor antagonist). The methanol extract of M. stenopetala showed antinociceptive effect in all tests. The significant involvement of 5-HT2A/2C receptors and α2 adrenoceptors in antinociception induced by M. stenopetala extract in the hot-plate and tail-immersion tests, as well as significant contribution of opioid receptors and α2 adrenoceptors in writhing test, were identified. In conclusion, these findings demonstrate that the methanol extract of M. stenopetala has potential in pain management. Thisstudywillcontributetonewtherapeuticapproachesandprovideguidancefornewdrug development studies.

Potentiation of capsaicin-induced neurogenic inflammation by 5-HT7 receptors in the rat hind paw: Involvement of calcitonin gen-related peptide.

A decrease in the activation threshold of primary sensory neurons to transient receptor potential V1 (TRPV1) stimulation by serotonin 5-HT7 receptors has been reported but no confirmation if this might translate into facilitation of neurogenic inflammation has been provided. We analysed the modulation of capsaicin (CAP)-induced neurogenic inflammation in the rat hind paw by the selective 5-HT7 receptor agonist, LP-44, and the involvement of calcitonin gen-related peptide (CGRP) in this effect. Animals received intra-plantar injections (30 µL) of vehicle, CAP (0.05%, 0.1% and 0.2%), LP-44 (7.5 and 15 nmol) and the combination of LP-44 + CAP; then, the time course of the inflammatory responses was measured. The effect of the 5-HT7 receptor antagonist, SB-269970 (3 mg/kg, s.c.), on responses produced by LP-44 alone and combined with CAP was tested. As expected, CAP produced concentration- and time-dependent inflammatory responses in the hind paw. Interestingly, LP-44 by itself also produced inflammation in a concentration- and time-dependent manner, and magnified CAP-induced responses. Systemic pre-treatment with SB-269970 significantly blunted LP-44 (15 nmol)-induced inflammation as well as magnified inflammatory responses produced by the combination of LP-44 (7.5 and 15 nmol) + CAP (0.1%) thus confirming the involvement of 5-HT7 receptors. Finally, the non-peptide CGRP receptor antagonist, BIBN4096 (3 mg/kg, s.c.), strongly inhibited the potentiated inflammatory responses induced by LP-44 (7.5 and 15 nmol) + CAP (0.1%) thus substantiating their neurogenic nature. Thus, sensitization of CAP-sensitive primary sensory neurons by 5-HT7 receptors may result in facilitation of neurogenic inflammation involving CGRP in the rat hind paw.

Serotonin 5-HT6 receptor blockade reverses the age-related deficits of recognition memory and working memory in mice.

Studies have shown that the blockade of 5-HT6 receptors (5-HT6R) can improve memory processes and reverse age-related spatial episodic like memory deficits. Since normal aging in the human is associated with a decline in episodic and working memory, we assessed the effect of the 5-HT6R blockade (SB-271046) on recognition memory (object recognition task) (a component of episodic like memory) in parallel to working memory (spontaneous alternation task in the T-maze) performances in young, adult, aged and senescent mice. Deficits in consolidation of non spatial recognition memory that were observed in 17- and 21-month-old mice were found to be reversed by 5-HT6R blockade. Deficits in working memory performances were only apparent as late as at 25 months of age; again, these deficits were reversed by 5-HT6R blockade. This study revealed in the mouse that, as in humans, working memory is more lately altered than recognition memory during aging and that such memory deficits could be counteracted by the use of 5-HT6R antagonists.

Differences in the dynamics of serotonin reuptake transporter occupancy may explain superior clinical efficacy of escitalopram versus citalopram.

Escitalopram the S-enantiomer of the racemate citalopram, is clinically more effective than citalopram in the treatment of major depressive disorder. However, the precise mechanism by which escitalopram achieves superiority over citalopram is yet to be determined. It has been hypothesized that the therapeutically inactive R-enantiomer competes with the serotonin-enhancing S-enantiomer at a low-affinity allosteric site on serotonin reuptake transporters (SERTs), and reduces the effectiveness of the S-enantiomer at the primary, high-affinity serotonin-binding site. This study summarizes the results of two recent single-photon emission computerized tomography studies measuring SERT occupancy in citalopram-treated and escitalopram-treated healthy volunteers, after a single dose and multiple doses (i.e. under steady-state conditions). The single-dose study showed no attenuating effect of R-citalopram. After multiple dosing, however, SERT occupancy was significantly reduced in the presence of R-citalopram. Under steady-state conditions, R-enantiomer concentrations were greater than for the S-enantiomer because of slower clearance of R-citalopram. A pooled analysis suggests that build-up of the R-enantiomer after repeated citalopram dosing may lead to increased inhibition of S-enantiomer occupancy of SERT. This review adds to the growing body of evidence regarding differences in the dynamics of SERT occupancy, that is, molecular mechanisms underlying the often-observed superior clinical efficacy of escitalopram compared with citalopram in major depressive disorder.

Some studies on the 5-hydroxytryptamine receptors in the isolated rat uterus.

Selective 5-hydroxytryptamine (5-HT) receptor antagonists were employed to further characterize the receptor subtypes mediating the contractile actions of 5-HT on the isolated uterine preparations of the rat. Increasing concentrations (10(-8)-10(-6) M) of the 5-HT receptor antagonist methysergide produced rightward shifts of the concentration-response curves of the 5-HT-induced contractions (pA2=8.05, slope of A-S plot=1.12 n=7) ketanserin a 5-HT2A receptor antagonist (10(-8)-10(-6) M) competitively antagonized the actions of 5-HT on the preparation (pA2=8.81; slope=1.04; n=7). Both LY53857 (10(-8)-10(-6) M) and ICI169369 (10(-8)-10(-6) M) which are known 5-HT2 receptor blockers also produced concentration-dependent shifts of the curves LY53857 yielded a pA2 of 8.9 (slope=0.82; n=7) while the pA2 for ICI169369 on the preparation was 7.9 (slope=1.29; n=7). ICS205930 a potent 5-HT3 blocker (10(-12)-10(-9) M) also produced concentration-dependent shifts of the curves (pA2=11.3; slope=0.94; n=7). The presence of 5-HT1 receptors could not be established. However both 5-HT2 and 5-HT3 receptors seem to be present on the rat uterine preparation.

Is nitric oxide involved in 5-HT3 receptor-mediated neurogenic relaxation of guinea pig proximal colon?

The relaxations mediated by the activation of 5-HT receptors in the guinea pig proximal colon were investigated. Longitudinal strips were cut from the colon segment and placed into the bath. In the presence of atropine (0.2 microM), the relaxations were evoked by adding increasing concentrations of 5-HT (1-100 microM). Noncumulative concentration-response curves were established in the absence and presence of either 5-HT or nitric oxide synthase (NOS) antagonists. Selective 5-HT3 antagonists tropisetron (10 and 100 nM) and ondansetron (1 microM) inhibited the relaxations and shifted the concentration-response curves to the right. Similar effects were observed in the presence of the NOS inhibitor N(G)-nitro-L-arginine (3.2, 10, 32 microM) and partly reversed with L-arginine (100, 320 microM). N(G)-nitro-D-arginine, serving as a negative control, was ineffective. The relaxations were further inhibited in the presence of the soluble guanylate cyclase blocker methylene blue (10 microM) or NO scavenger hemoglobin (32 microM). These results suggest that the 5-HT3 receptor plays a role in neurogenic relaxations of guinea pig proximal colon, which are at least partly mediated via release of NO from nerve endings.

Dose ranging phase I study of the serotonin antagonist GR38032F for prevention of cisplatin-induced nausea and vomiting.

GR38032F is a specific 5-HT3 (serotonin) receptor antagonist with antiemetic activity in animal and early human studies. We performed a dose-ranging phase I study of GR38032F in 43 evaluable patients receiving cisplatin 60 120 mg/m2 for the first time (38 of these patients were chemotherapy-naive). Intravenous GR38032F was administered over a dose range from 0.01 to 0.48 mg/kg given three times at four-hour intervals beginning one half hour before cisplatin, and patients were observed for 24 hours. An additional five patients were treated with 0.18 mg/kg given three times at six-hour intervals. Excellent antiemetic efficacy was noted, with 44% of patients experiencing no vomiting and 26% no nausea. Major protection from vomiting (less than or equal to 2 episodes) and from nausea (less than or equal to 2 hours) was experienced by 81% and 44%, respectively. Mild to moderate headache (40%), lightheadedness (21%), and elevated transaminase (19%) were the most common adverse events reported. One patient experienced an apparent hypersensitivity reaction that responded to conventional medications. No extrapyramidal reactions or akathisia were seen. GR38032F was effective through most of the dose range. However, efficacy decreased at the 0.01 mg/kg level and number and intensity of adverse events increased at the 0.48 mg/kg level. Analysis of those patients receiving high-dose cisplatin (100 to 120 mg/m2) revealed a positive association of GR38032F dose and antiemetic activity (Fisher's exact test, two-sided; P less than .05). The 5-HT3 receptor antagonists may provide antiemetic efficacy similar to high-dose metoclopramide without antidopaminergic toxicity. The maximum recommended dose on this schedule of GR38032F is 0.36 mg/kg.