Pharmacological characterization of lysophosphatidic acid‐induced pain with clinically relevant neuropathic pain drugs

Lysophosphatidic acid (LPA), an initiator of neuropathic pain, causes allodynia. However, few studies have evaluated the pharmacological profile of LPA‐induced pain. In this study, a LPA‐induced pain model was developed and pharmacologically characterized with clinically relevant drugs used for neuropathic pain, including antiepileptics, non‐steroidal anti‐inflammatory agents, analgesics, local anaesthetics/antiarrhythmics and antidepressants. Gabapentin (1–30 mg/kg, p.o.) significantly reversed LPA‐induced allodynia, but neither indomethacin (30 mg/kg, p.o.) nor morphine (0.3–3 mg/kg, s.c.) did, which indicates that LPA‐induced pain consists mostly of neuropathic rather than inflammatory pain. Both pregabalin (0.3–10 mg/kg, p.o.) and ω‐CgTX MVIIA (0.01–0.03 μg/mouse, i.t.) completely reversed LPA‐induced allodynia in a dose‐dependent manner. Lidocaine (1–30 mg/kg, s.c.), mexiletine (1–30 mg/kg, p.o.) and carbamazepine (10–100 mg/kg, p.o.) significantly ameliorated LPA‐induced allodynia dose dependently. Milnacipran (30 mg/kg, i.p.) produced no significant analgesic effect in LPA‐induced allodynia. In LPA‐injected mice, expression of the α2δ1 subunit of the voltage‐gated calcium channel (VGCC) was increased in the dorsal root ganglion (DRG) and spinal dorsal horn. Furthermore, the VGCC current was potentiated in both the DRG from LPA‐injected mice and LPA (1 μM)‐treated DRG from saline‐injected mice, and the potentiated VGCC current was amended by treatment with gabapentin (100 μM). The LPA‐induced pain model described here mimics aspects of the neuropathic pain state, including the sensitization of VGCC, and may be useful for the early assessment of drug candidates to treat neuropathic pain.     

Antidepressant‐like effect of bis‐eugenol in the mice forced swimming test: evidence for the involvement of the monoaminergic system

Dehydrodieugenol, known as bis‐eugenol, is a eugenol ortho dimer, and both compounds were able to exhibit anti‐inflammatory and antioxidant activities in previous studies. Furthermore, eugenol showed antidepressant‐like effect; however, the biological actions of bis‐eugenol on experimental models for screening antidepressant activity are still unknown. The present study investigated a possible antidepressant‐like activity of bis‐eugenol in the forced swimming test (FST) and tail suspension test (TST) in mice and the involvement in the monoaminergic system in this effect. In addition, a neurochemical analysis on brain monoamines of mice acutely treated with bis‐eugenol was also conducted. Bis‐eugenol decreased the immobility time in the FST and TST without accompanying changes in ambulation in the open field test at 10 mg/kg, i.p.. Nevertheless, it induced ambulation at 25 and 50 mg/kg doses. The anti‐immobility effect of bis‐eugenol (10 and 50 mg/kg, i.p.) was prevented by pretreatment of mice with p‐chlorophenylalanine (PCPA, 100 mg/kg, i.p., an inhibitor of serotonin synthesis, for four consecutive days), yohimbine (1 mg/kg, i.p., an α2‐adrenoceptor antagonist), SCH23390 (15 μg/kg, s.c., a dopamine D1 receptor antagonist) and sulpiride (50 mg/kg, i.p., a dopamine D2 receptor antagonist). Monoamines analysis using high‐performance liquid chromatograph revealed significant increase in the 5‐HT, NE and DA levels in brain striatum. The present study indicates that bis‐eugenol possesses antidepressant‐like activity in FST and TST by altering dopaminergic, serotonergic and noradrenergic systems function.     

Eugenol reduces acute pain in mice by modulating the glutamatergic and tumor necrosis factor alpha (TNF‐α) pathways

Eugenol is utilized together with zinc oxide in odontological clinical for the cementation of temporary prostheses and the temporary restoration of teeth and cavities. This work explored the antinociceptive effects of the eugenol in different models of acute pain in mice and investigated its possible modulation of the inhibitory (opioid) and excitatory (glutamatergic and pro‐inflammatory cytokines) pathways of nociceptive signaling. The administration of eugenol (3–300 mg/kg, p.o., 60 min or i.p., 30 min) inhibited 82 ± 10% and 90 ± 6% of the acetic acid‐induced nociception, with ID₅₀ values of 51.3 and 50.2 mg/kg, respectively. In the glutamate test, eugenol (0.3–100 mg/kg, i.p.) reduced the response behavior by 62 ± 5% with an ID₅₀ of 5.6 mg/kg. In addition, the antinociceptive effect of eugenol (10 mg/kg, i.p.) in the glutamate test was prevented by the i.p. treatment for mice with naloxone. The pretreatment of mice with eugenol (10 mg/kg, i.p.) was able to inhibit the nociception induced by the intrathecal (i.t.) injection of glutamate (37 ± 9%), kainic (acid kainite) (41 ± 12%), α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) (55 ± 5%), and substance P (SP) (39 ± 8%). Furthermore, eugenol (10 mg/kg, i.p.) also inhibited biting induced by tumor necrosis factor alpha (TNF‐α, 65 ± 8%). These results extend our current knowledge of eugenol and confirm that it promotes significant antinociception against different mouse models of acute pain. The mechanism of action appears to involve the modulation of the opioid system and glutamatergic receptors (i.e., kainate and AMPA), and the inhibition of TNF‐α. Thus, eugenol could represent an important compound in the treatment for acute pain.     

Involvement of monoaminergic system in the antidepressant‐like effect of riparin I from Aniba riparia (Nees) Mez (Lauraceae) in mice

In past studies conducted by our group, riparin I (rip I) isolated from the green fruit of Aniba riparia presented antianxiety effects in mice, while its analogs rip II and III showed anxiolytic and antidepressant‐like actions. This time around, we investigated a possible antidepressant activity of rip I using the forced swimming test (FST) and tail suspension test (TST) as predictive tests for antidepressant activity in rodents. In addition, the involvement of the monoaminergic system in this effect was also assessed. rip I was acutely administered by intraperitoneal (i.p.) and oral (p.o) routes to male mice at doses of 25 and 50 mg/kg. Results showed that rip I at both tested doses and administration routes produced a significant decrease in immobility time in FST and TST. The pretreatment of mice with prazosin (1 mg/kg, i.p., an α₁‐adrenoceptor antagonist), yohimbine (1 mg/kg, i.p., an α₂‐adrenoceptor antagonist), SCH23390 (15 μg/kg, i.p., a dopamine D1 receptor antagonist), sulpiride (50 mg/kg, i.p., a dopamine D2 receptor antagonist), p‐chlorophenylalanine (100 mg/kg, an inhibitor of serotonin synthesis) or ritanserin (4 mg/kg, a serotonin 5‐HT2_a/2_c receptor antagonist) blocked the anti‐immobility effects elicited by rip I (50 mg/kg, p.o.) in the FST. Taken together, results indicate that rip I produces significant antidepressant‐like activity in the FST and TST, and this effect seems to be dependent on its interaction with noradrenergic, dopaminergic and serotonergic systems.     

Memantine delayed N‐methyl‐D‐aspartate ‐induced convulsions in neonatal rats

Memantine (1‐amino‐3,5‐dimethyladamantane) is a moderate‐affinity uncompetitive antagonist of N‐methyl‐d‐aspartate (NMDA) receptors. In this study, we have explored the effect of memantine against N‐methyl‐d‐aspartate (NMDA)‐induced seizures in neonatal rats. Here, we evaluated various behavioral seizure abnormalities in neonatal rats (Sprague–Dawley; postnatal day 9) after an intraperitoneal administration of NMDA. Further, we explored whether an acute administration of memantine could protect these neonates against different phases of convulsions induced by NMDA. In a separate study, we have compared the effect of levetiracetam in the same animal model. Exogenous administration of NMDA (30 mg/kg., i.p.) in neonatal rats resulted in arrest of activity, emprosthotonos curvature (trunk is bent forward by the entire muscles), myoclonic jerks, and forelimb/hindlimb clonus. The clonus phase in neonates was followed by loss of righting reflex and continuous seizures (for more than 5 min) suggesting status epilepticus, tonic extension, and death. Pretreatment of memantine hydrochloride (10–30 mg/kg., i.p.) dose‐dependently delayed the onset of different phases of convulsions induced by NMDA. Memantine at the highest dose was found to be ataxic in rat neonates, while lower doses were free of any observed behavioral signs of toxicity. Levetiracetam (25 mg/kg., i.p.) when administered 30 min before the NMDA challenge blocked only the jerk phase and did not affect other phases of NMDA‐induced convulsions. These data indicated that memantine and other safer uncompetitive NMDA receptor antagonists may be protective in the management of neonatal seizures.     

Antidepressant‐like activity of gallic acid in mice subjected to unpredictable chronic mild stress

This study was designed to evaluate antidepressant‐like activity of gallic acid in Swiss young male albino mice subjected to unpredictable chronic mild stress and to explore the possible underlying mechanisms for this activity. Gallic acid (5, 10, 20 mg/kg, i.p.) and fluoxetine (10 mg/kg, i.p.) per se were administered daily to unstressed mice and other groups of mice subjected to unpredictable mild stress, 30 min after the injection for 21 successive days. The antidepressant‐like activity was evaluated using forced swim test (FST) and sucrose preference test. Stress significantly increased immobility period of mice in FST. Gallic acid (10 and 20 mg/kg, i.p.) and fluoxetine significantly decreased immobility period of unstressed and stressed mice in FST and prevented the stress‐induced decrease in sucrose preference, indicating significant antidepressant‐like activity. There was no significant effect on locomotor activity of the mice by the drugs. Gallic acid (10 and 20 mg/kg, i.p.) significantly decreased Monoamine oxidase‐A (MAO‐A) activity, malondialdehyde levels, and catalase activity in unstressed mice; and significantly prevented the stress‐induced decrease in reduced glutathione and catalase activity; and also significantly prevented stress‐induced increase in MAO‐A activity, malondialdehyde levels, plasma nitrite, and corticosterone levels. Thus, gallic acid showed antidepressant‐like activity in unstressed and stressed mice probably due to its antioxidant activity and through inhibition of MAO‐A activity and decrease in plasma nitrite levels. In addition, gallic acid also showed antidepressant‐like activity in stressed mice probably through decrease in plasma corticosterone levels.     

Sumatriptan reduces severity of status epilepticus induced by lithium–pilocarpine through nitrergic transmission and 5‐HT1B/D receptors in rats: A pharmacological‐based evidence

Status epilepticus (SE) is a life‐threatening neurologic disorder that can be as both cause and consequence of neuroinflammation. In addition to previous reports on anti‐inflammatory property of the anti‐migraine medication sumatriptan, we have recently shown its anticonvulsive effects on pentylenetetrazole‐induced seizure in mice. In the present study, we investigated further (i) the effects of sumatriptan in the lithium–pilocarpine SE model in rats, and (ii) the possible involvement of nitric oxide (NO), 5‐hydroxytryptamin 1B/1D (5‐HT_1B/1D) receptor, and inflammatory pathways in such effects of sumatriptan. Status epilepticus was induced by lithium chloride (127 mg/kg, i.p) and pilocarpine (60 mg/kg, i.p.) in Wistar rats. While SE induction increased SE scores and mortality rate, sumatriptan (0.001‐1 mg/kg, i.p.) improved it (P < 0.001). Administration of the selective 5‐HT_1B/1D antagonist GR‐127935 (0.01 mg/kg, i.p.) reversed the anticonvulsive effects of sumatriptan (0.01 mg/kg, i.p.). Although both tumor necrosis factor‐α (TNF‐α) and NO levels were markedly elevated in the rats' brain tissues post‐SE induction, pre‐treatment with sumatriptan significantly reduced both TNF‐α (P < 0.05) and NO (P < 0.001) levels. Combined GR‐127935 and sumatriptan treatment inhibited these anti‐inflammatory effects of sumatriptan, whereas combined non‐specific NOS (L‐NAME) or selective neuronal NOS (7‐nitroindazole) inhibitors and sumatriptan further reduced NO levels. In conclusion, sumatriptan exerted a protective effect against the clinical manifestations and mortality rate of SE in rats which is possibly through targeting 5‐HT_1B/1D receptors, neuroinflammation, and nitrergic transmission.     

The anti-hyperalgesic effects of carbamazepine and oxcarbazepine are attenuated by treatment with adenosine receptor antagonists

The antinociceptive effects of carbamazepine and oxcarbazepine, and the influence of caffeine, were examined in a paw pressure test in rats. Carbamazepine (10-40 mg/kg; intraperitoneal, i.p.) and oxcarbazepine (40-160 mg/kg; i.p.) caused a significant dose-dependent reduction of the paw inflammatory hyperalgesia induced by concanavalin A (Con A), intraplantarly (i.p1.). A comparable pattern of antinociceptive effect of carbamazepine and oxcarbazepine was observed; the only difference is their potency, in that carbamazepine was about three times more potent than oxcarbazepine. Caffeine (5-20mg/kg; i.p.), a non-selective adenosine receptor antagonist, significantly depressed the antinociceptive effects of carbamazepine and oxcarbazepine, in a dose- and time-dependent manner. Also, a significant depression of the antinociceptive effects of carbamazepine and oxcarbazepine was observed by pretreatment with 1,3-dipropyl-8-cyclopentylxantine (DPCPX, 0.4 and 0.8 mg/kg; i.p.), an adenosine A(1) receptor antagonist. These findings indicate that, in a paw inflammatory hyperalgesia in rats, the antinociceptive effects of both drugs are, at least partially, mediated by adenosine A(1) receptors. In conclusion, the present study suggests the potential clinical importance of carbamazepine and oxcarbazepine in the treatment of inflammatory pain. In addition, caffeine consumption could possibly depress the analgesic effects of both anticonvulsive drugs.     

Pretreatment with melatonin protects against cyclophosphamide‐induced oxidative stress and renal damage in mice

Cyclophosphamide (CP) is widely used in treatment of different cancers. Nephrotoxicity is one of the dose‐limiting side effects of CP. This study was carried out to investigate the effect of melatonin (MEL) on CP‐induced nephrotoxicity in mice. In this study, 50 Swiss albino mice (20–25 g) were randomly divided into five groups. Mice were pretreated with MEL intraperitoneally (i.p) in doses of 5, 10 and 20 mg/kg for five consecutive days, and CP (200 mg/kg, i.p) was administrated on the 5th day 1 h after the last dose of MEL. Then on day 6, blood samples were collected to determine serum creatinine (Cr) and blood urea nitrogen (BUN) levels. The kidneys were used for histological examination, biochemical assays and real‐time PCR studies. Malondialdehyde (MDA), glutathione (GSH), protein carbonyl (PC), nitric oxide (NO) level, catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and myeloperoxidase (MPO) activity were assessed in renal tissue. In addition, the expression of SOD2 and PGx1 was measured using real‐time PCR method in renal tissue. Results showed that CP administration significantly increases Cr, BUN, MDA, PC, NO level and MPO activity. It also decreases renal GSH level, SOD, GPx and CAT activity. Pretreatment with MEL (especially 20 mg/kg, i.p.) for 5 days prevented these changes; however, it did not affect the SOD activity. Our results revealed that MEL might be useful for prevention of the nephrotoxicity induced by CP through ameliorative effects on biochemical indices and oxidative stress parameters.     

Neuropharmacological effects of lipoic acid and ubiquinone on δ‐aminolevulinic dehydratase,Na+, K+‐ATPase,and Mg2+‐ATPase activities in rat hippocampus after pilocarpine‐induced seizures

In this study, we investigated the effects of lipoic acid (LA) in the hippocampus oxidative stress caused by pilocarpine‐induced seizures in adult rats. Wistar rats were treated with 0.9% saline (i.p., control group), LA (10 mg/kg, i.p., LA group), ubiquinone [20 mg/kg, i.p., ubiquinone (UQ) group], pilocarpine (400 mg/kg, i.p., P400 group), and the association of LA (10 mg/kg, i.p.) plus pilocarpine (400 mg/kg, i.p.) or UQ (20 mg/kg, i.p.) plus pilocarpine (400 mg/kg, i.p.), 30 min before of administration of P400 (LA plus P400 group and UQ plus P400 group, respectively). After the treatments, all groups were observed for 1 h. The enzyme activities (δ‐aminolevulinic dehydratase (δ‐ALA‐D), Mg²⁺‐ATPase, and Na⁺, K⁺‐ATPase) were measured using spectrophotometric methods, and the results compared to values obtained from saline and pilocarpine‐treated animals. Protective effects of LA and UQ were also evaluated on the same parameters. We reported here for the first time that Na⁺, K⁺‐ATPase and δ‐ALA‐D activities inhibition and Mg²⁺‐ATPase stimulation in the pilocarpine model are probably attributed to the oxidative stress caused by seizures in the rat hippocampus. The addition of the antioxidants LA and UQ may reverses the previously mentioned Na⁺, K⁺‐ATPase and δ‐ALA‐D inhibitions and Mg²⁺‐ATPase stimulation. Conclusions: The oxidative stress plays an important signaling role in pilocarpine‐induced seizures, and antioxidant drugs might be considered as therapeutical tools in this pathology.     

Antidepressant‐like effect of riparin II from Aniba riparia in mice: evidence for the involvement of the monoaminergic system

In a previous study conducted by our group, riparin II (ripII) isolated from the green fruit of Aniba riparia presented antianxiety effects in mice. This study investigates a possible antidepressant activity of rip II using two predictive tests for antidepressant activity in rodents: the forced swimming test (FST) and tail suspension test (TST). Additionally, the mechanisms involved in the antidepressant‐like effect in mice were also assessed. Rip II was acute administered by intraperitoneal (i.p.) and oral (p.o) routes to male mice at doses of 25 and 50 mg/kg. Results showed that ripII at both tested doses and administration routes produced a significant decrease of immobility time in FST and TST. The pretreatment of mice with prazosin (1 mg/kg, i.p., an α1‐adrenoceptor antagonist), SCH23390 (15 μg/kg, i.p., a dopamine D1 receptor antagonist), sulpiride (50 mg/kg, i.p., a dopamine D2 receptor antagonist), p‐chlorophenylalanine (100 mg/kg, an inhibitor of serotonin synthesis), or NAN‐190 (0.5 mg/kg, a serotonin 5‐HT1A receptor antagonist) completely blocked the anti‐immobility effects elicited by riparin II (50 mg/kg, p.o.) in the FST. This study indicates that riparin II produces significant antidepressant‐like activity in the forced swimming and TSTs, and this effect seems to be dependent on its interaction with noradrenergic, dopaminergic, and serotonergic systems.     

Dual effect of cAMP agonist on ameliorative function of PKA inhibitor in morphine‐dependent mice

The present study shows interactive effects of bucladesine (db‐cAMP) as a cyclic adenosine monophosphate (cAMP) agonist and H‐89 as a protein kinase A (PKA) inhibitor on naloxone‐induced withdrawal signs in morphine‐dependent mice. Animals were treated subcutaneously with morphine thrice daily with doses progressively increased from 50 to 125 mg/kg. A last dose of morphine (50 mg/kg) was administered on the 4th day. Several withdrawal signs were precipitated by intraperitoneal (i.p.) administration of naloxone (5 mg/kg). Different doses of bucladesine (50, 100, 200 nm /mouse) and H‐89 (0.05, 0.5, 1, 5 mg/kg) were administered (i.p.) 60 min before naloxone injection. In combination groups, bucladesine was injected 15 min before H‐89 injection. Single administration of H‐89 (0.5, 1, 5 mg/kg) and bucladesine (50, 100 nm /mouse) significantly attenuated prominent behavioral signs of morphine withdrawal. Lower doses of bucladesine (50, 100 nm /mouse) in combination with H‐89 (0.05 mg/kg) increased the inhibitory effects of H‐89 on withdrawal signs while in high dose (200 nm /mouse) decreased the ameliorative function of H‐89 (0.05 mg/kg) in morphine‐dependent animals. It is concluded that H‐89 and bucladesine could affect morphine withdrawal syndrome via possible interaction with cyclic nucleotide messengering systems, protein kinase A signaling pathways, and modified related neurotransmitters.     

Amlodipine,an L‐type calcium channel blocker,protects against chlorpromazine‐induced neurobehavioural deficits in mice

This study investigated the modulatory and chemopreventive benefit of amlodipine (AML), a dihydropyridine calcium channel antagonist, against neurobehavioural abnormalities (NAs) associated with chlorpromazine (CPZ) toxicity in mice. Adult mice were divided into five groups of six animals/group. Group 1 (control) was administered saline (10 mL/kg i.p.). Group 2 received CPZ (2 mg/kg i.p.). Groups 3 and 4 received bromocriptine (BMC, 2.5 mg/kg s.c.) and AML (1 mg/kg s.c.), respectively, while group 5 received their combination. Groups 3–5 later received CPZ 30 min after initial treatments. Animals were subjected to neurobehavioural tests and euthanized 18 h later. CPZ‐induced NAs were characterized by significant increase (P < 0.001) in cataleptic behaviour and lowered (P < 0.05) spontaneous activity reaction time in mice. There were also significant (P < 0.001) increases in malondialdehyde levels and decreased locomotion plus learning and memory parameters (P < 0.05–0.001). AML pretreatment alone did not alleviate CPZ‐induced motor deficits in the mice. While pretreatment with BMC alone attenuated CPZ‐associated catalepsy, its combination with AML further protected mice against NAs. Furthermore, BMC pretreatment did not affect CPZ‐induced increase in malondialdehyde level, but AML or BMC+AML significantly (P < 0.05) decreased malondialdehyde in the CPZ‐treated rats. Reduced glutathione levels and activities of superoxide dismutase and catalase remained elevated in all treatment groups. In conclusion, data from this study suggest possible chemopreventive benefit of AML alone or in combination with BMC against CPZ‐associated neurobehavioural deficits. The ameliorative effect of AML may be related to its antioxidant and/or calcium channel blocking property.     

Dissociation of rewarding,anti‐aversive and anti‐nociceptive effects of different classes of anti‐nociceptives in the rat

It was previously shown that morphine more potently reduces the affective as compared to the sensory component of nociception, and this effect is independent of morphine's rewarding properties. Here we investigated whether this finding can be generalized to other classes of anti‐nociceptive drugs. The effect of oxycodone (0–10 mg/kg, i.p.), tramadol (0–10 mg/kg, i.p.), ibuprofen (0–300 mg/kg, i.p.) and pregabalin (0–31.6 mg/kg, i.p.) on negative affect and mechanical hypersensitivity accompanying carrageenan‐induced (0.5% intraplantar) inflammatory nociception was assessed using conditioned place aversion (CPA) and Randall Selitto paw pressure test, respectively. The rewarding effect of these drugs was assessed using conditioned place preference (CPP). All four anti‐nociceptive drugs dose‐dependently reduced carrageenan‐induced CPA and mechanical hypersensitivity. Furthermore all drugs induced CPP, except for ibuprofen. Similar to morphine, oxycodone and tramadol showed a large dissociation of anti‐aversive versus anti‐nociceptive potency, i.e. 10 times more potent against the affective versus the sensory component of nociception. Oxycodone and tramadol were 30 and 10 times more potent to produce CPP in animals under normal versus painful conditions. Ibuprofen and pregabalin also showed a dissociation of anti‐aversive and anti‐nociceptive potency, but less pronounced (i.e. three times more potent against the affective component). However, pregabalin showed no dissociation between rewarding potency under normal versus painful conditions. Taken together, these data suggest that the dissociation of rewarding potency in animals under normal versus painful conditions is limited to drugs with an opioid mechanism of action, while the dissociation of anti‐aversive and anti‐nociceptive potency applies to anti‐nociceptive drugs with different mechanisms of action.     

Effect of glatiramer acetate on short‐term memory impairment induced by lipopolysaccharide in male mice

Glatiramer acetate (GA) demonstrates neuroprotective, neurogenesis, and anti‐inflammatory properties. This study examines the probable protective effect of acute GA on lipopolysaccharide (LPS)‐induced memory impairment in male mice and further explores which routes of administration [subcutaneous (s.c.) or intracerebroventricular (i.c.v.)] exert optimum effect. Memory performance was evaluated in two‐trial recognition Y‐maze and passive‐avoidance tasks evaluating special recognition memory and fear memory, respectively. Memory impairment was induced by LPS [100 μg/kg, intraperitoneally (i.p.)], 4 h before training. In Y‐maze, GA (10, 2.5, 0.625, 0.153, and 0.03 mg/kg, s.c.; 250 μg/mouse; i.c.v.) was administered 10 min following LPS, and special memory was assayed in Y‐maze apparatus. In passive avoidance, LPS (100, 250 μg/kg; i.p.) was injected 4 h before receiving foot shock, and GA (10, 2.5; s.c.) or (250 μg/mouse; i.c.v.) was administered 4 h before the shock. Following 24 h, the fear memory was evaluated. Memory impaired significantly following LPS (100, 250 μg/kg; i.p.) in Y‐maze and passive‐avoidance tasks, P < 0.001 and P < 0.05, respectively. The data revealed that GA (250 μg/mouse, i.c.v.) and GA (10, 2.5 mg/kg; s.c.) in Y‐maze reversed memory impairment (LPS 100 μg/kg, i.p.) (P < 0.01). In passive‐avoidance task, GA (2.5, 10 mg/kg; s.c.) reversed LPS‐induced impairment and the mice showed significantly longer latency times during the retention trial (P < 0.01). GA improved memory impairment both centrally and systemically. It improved spatial recognition memory increasing the average time in the novel arm and improved fear memory increasing latency time. GA administration improved memory impairment profoundly through both systemic and central routs.     

Pain attenuating actions of vincristinet-preconditioning in chemotherapeutic agent-induced neuropathic pain: key involvement of T-type calcium channels

Preconditioning is a well-documented strategy that induces hepatic protection, renal protection, cardioprotection, and neuroprotection but its mechanism still remains to be elucidated. Hence, the present study investigated the protective mechanism underlying pain attenuating effects of vincristine-preconditioning in chemotherapeutic agent-induced neuropathic pain. Neuropathic pain was induced by administration of vincristine (50 µg/kg, i.p.) for 10 days in rats. Vincristine-preconditioning was induced by administration of vincristine (2, 5, and 10 µg/kg, i.p) for 5 days before administration of pain-inducing dose of vincristine (50 µg/kg, i.p.). Vincristine-preconditioning (10 µg/kg, i.p) for 5 days significantly reduced vincristine (50 µg/kg, i.p.) induced pain-related behaviors including paw cold allodynia, mechanical hyperalgesia, and heat hyperalgesia. However, vincristine (2 and 5 µg/kg, i.p) did not significantly ameliorate the vincristine (50 µg/kg, i.p.) induced neuropathic pain in rats. Furthermore, to explore the involvement of calcium channels in pain attenuating mechanism of vincristine-preconditioning, T-type calcium channel blocker, ethosuximide (100 and 200 mg/kg, i.p.) and L-type calcium channel blocker, amlodipine (5 and 10 mg/kg, i.p.) were used. Pretreatment with T-type calcium channel blocker, ethosuximide significantly abolished vincristine-preconditioning-induced protective effect. However, pretreatment with L-type calcium channel blocker, amlodipine did not alter vincristine-preconditioning-induced pain-related behaviors. This indicates that vincristine-preconditioning has protective effect on pain-related parameters due to opening of calcium channels, particularly T-type calcium channels that lead to entry of small magnitude of intracellular calcium through these channels and prevent the deleterious effects of high-dose vincristine.     

Evidence for the involvement of the serotonergic, noradrenergic, and dopaminergic systems in the antidepressant-like action of riparin III obtained from Aniba riparia (Nees) Mez (Lauraceae) in mice

Previous work has shown that intraperitoneal administration of riparin III (ripIII) reduces immobility time in the forced swimming test (FST), which suggests potential antidepressant activity. As the mechanism of action is not completely understood, this study is aimed at investigating the antidepressant‐like action of ripIII. Following intraperitoneal administration of ripIII at doses of 25 and 50 mg/kg, there were decreases in the immobility time in the FST and tail suspension test without accompanying changes in ambulation (data not shown). The pretreatment of mice with sulpiride (50 mg/kg, i.p.), prazosin (1 mg/kg, i.p.), yohimbine (1 mg/kg, i.p.), and p‐chlorophenylalanine (PCPA, 100 mg/kg, i.p. for, four consecutive days) significantly prevented the anti‐immobility effect of ripIII in the FST. On the other hand, the anti‐immobility effect of ripIII (50 mg/kg, v.o.) was not altered by pretreatment of mice with SCH23390 (15 μg/kg, i.p.) Furthermore, ripIII potentiated the sleeping latency and sleeping time of the pentobarbital‐induced sleeping time test and also potentiated apomorphine (16 mg/kg, i.p.)‐induced hypothermia in mice. In conclusion, the present study provides evidence that the antidepressant‐like effect of ripIII is dependent on its interaction with the serotonergic, noradrenergic (α₁‐ and α₂‐ receptors), and dopaminergic (dopamine D₂ receptors) systems.     

Elucidation of molecular mechanism involved in neuroprotective effect of Coenzyme Q10 in alcohol‐induced neuropathic pain

The aim of the present investigation was to evaluate the effect of Coenzyme Q10 and its combination with vitamin E in alcohol‐induced chronic neuropathic pain. Male Wistar rats were orally treated with alcohol (10 g/kg, 35% v/v, b.i.d.) for 10 weeks. Coenzyme Q10 (25, 50, and 100 mg/kg) and vitamin E (100 mg/kg) were coadministered orally for 1 h after ethanol administration for 10 weeks. Various nerve functions, biochemical, and molecular parameters were assessed. Chronic administration of ethanol for 10 weeks resulted significant development of neuropathic pain. Treatment with Coenzyme Q10 (50 and 100 mg/kg) for 10 weeks showed significant and dose dependently increased in level of nociceptive threshold, endogenous antioxidant, and Na,K‐ATPase enzyme. Coenzyme Q10 (50 and 100 mg/kg) significantly restored the levels of motor nerve conduction velocity and sensory nerve conduction velocity. It also showed significant decrease in levels of endogenous calcium, oxidative–nitrosative stress, TNF‐α, IL‐1β, and IL‐4 level. Alteration in protein expression of polymerase gamma (pol γ) was significantly restored the Coenzyme Q10 treatment. The important finding of the study is that, Coenzyme Q10 (100 mg/kg) and α‐tocopherol (100 mg/kg) combination‐treated rats showed more significant prevention of behavioral, biochemical, and molecular neurotoxic effect of alcohol administration than Coenzyme Q10 or α‐tocopherol alone treated group. It is evident from the finding of present investigation that plethora of mechanism including inhibition of oxido‐nitrosative stress, release of pro‐inflammatory cytokine, modulation of endogenous biomarker, and protection of pol γ protein expression simultaneously orchestrate to exhibits neuroprotective effect of Coenzyme Q10, vitamin E and their combination.     

Participation of central imidazoline binding sites in antinociceptive effect of ethanol and nicotine in rats

Despite synergistic morbidity and mortality, concomitant consumption of alcohol and tobacco is increasing, and their antinociceptive effect has been linked with co‐abuse. Present study was designed to investigate the role of imidazoline binding sites in the antinociceptive effect of nicotine, ethanol, and their combination. Separate group of male Sprague–Dawley rats (200–250 g) were treated with different doses of alcohol (0.50–2 g/kg, i.p.) or nicotine (0.25–1 mg/kg, i.p.), and their combination evaluated in tail flick test. Influence of endogenous imidazoline binding site ligands, agonist, and antagonists were determined by their prior treatment with effective or subeffective doses of either ethanol or nicotine. Ethanol, nicotine, or their subeffective dose combination exhibited significant antinociceptive effects in dose‐dependent manner. Antinociceptive effect of ethanol and nicotine was significantly augmented by intracerebroventricular (i.c.v.) administration of endogenous imidazoline receptor ligands, harmane (25 μg/rat, i.c.v.) and agmatine (10 μg/rat, i.c.v.), as well as imidazoline I₁/α₂ adrenergic receptor agonist, clonidine (2 μg/rat, i.c.v.), I₁ agonist moxonidine (25 μg/rat, i.c.v.), and imidazoline I₂ agonist, 2‐BFI (10 μg/rat, i.c.v.). Conversely, antinociception elicited by ethanol or nicotine or their subeffective dose combination was antagonized by pretreatment with imidazoline I₁ antagonist, efaroxan (10 μg/rat, i.c.v.), and I₂ antagonist, idazoxan (4 μg/rat, i.c.v.), at their per se ineffective doses. These findings project imidazoline binding ligands as important therapeutic molecules for central antinociceptive activity as well as may reduce the co‐abuse potential of alcohol and nicotine.     

N‐methyl‐d‐aspartate receptor‐mediated modulations of the anti‐allodynic effects of 5‐HT1B/1D receptor stimulation in a rat model of trigeminal neuropathic pain

Previous studies showed that triptans and other 5‐HT_1B/1D‐receptor agonists attenuate hyper‐responsiveness to mechanical stimulation of the face in a rat model of trigeminal neuropathic pain, probably by activating 5‐HT_1B/1D‐receptors on primary afferent nociceptive fibers. We now tested whether blockade of post‐synaptic receptors for the excitatory amino acid glutamate released by these fibers would increase this action. We thus evaluated whether (±)1‐hydroxy‐3‐aminopyrrolidine‐2‐one (HA‐966), an antagonist at the glycine/d ‐serine site of N‐methyl‐d ‐aspartate (NMDA)‐receptors, would potentiate the anti‐allodynic action of dihydroergotamine and zolmitriptan in rats with chronic constriction injury to the infraorbital nerve (CCI‐ION). Complementary studies were performed with other NMDA‐receptor ligands and in rats with chronic constriction injury to the sciatic nerve (CCI‐SN) for comparison. Injury was produced by loose ligatures of the nerves. Responsiveness to mechanical stimulation (vibrissae or hindpaw territories) with von Frey filaments was used to evaluate allodynia 2 weeks after nerve ligature. Rats received NMDA‐receptor ligands or saline 20 min before dihydroergotamine (25–100μg/kg, i.v.) or zolmitriptan (25–100μg/kg, s.c.). HA‐966 (2.5 mg/kg, s.c.), inactive on its own, enhanced the anti‐allodynic effects of dihydroergotamine (eightfold increase) and zolmitriptan (threefold increase) in CCI‐ION rats, but these drugs exerted no effects in allodynic CCI‐SN rats. NMDA‐receptor blockade by memantine (5 mg/kg, i.p.) also enhanced, whereas activation at glycine/NMDA site by d ‐cycloserine (3 mg/kg, i.p.) reduced the anti‐allodynic properties of zolmitriptan in CCI‐ION rats. Combined administration of NMDA‐receptor antagonist and 5‐HT_1B/1D‐receptor agonist may be a promising approach for alleviating trigeminal neuropathic pain.