Enhanced central histaminergic transmission attenuates compulsive-like behavior in mice.

Present investigation demonstrated the effect of central histaminergic transmission on the compulsive-like marble burying and spontaneous alteration behavior (SAB) in mice. Result demonstrates that on enhancement of endogenous histaminergic transmission in mice achieved by central (i.c.v.) administration of histamine or central histamine neuronal releaser, H3 receptor antagonist or on intraperitoneal (i.p.) administration of histamine precursor, l-histidine significantly attenuated the number of marble buried in marble burying behavior (MBB) test as well as obliterated the persistent behavior induced by 5-HT1A receptor agonist, 8-OH-DPAT in T-Maze test. Furthermore, central injection of histamine H1 receptor agonist, FMPH or H2 receptors agonist, amthamine also attenuated the MBB in mice. On the other hand, prior i.c.v administration of H1 but not H2 receptor antagonist attenuated the effects exhibited in MBB test on mice by all the above agents capable of enhancing the endogenous central histaminergic transmission. Thus, the results of the present investigation delineate the attenuating effect of central histaminergic transmission predominantly via H1 receptor on compulsive-like behavior in mice.

Role of histamine H1 receptor in caffeine induced locomotor sensitization.

The present study elucidated the role of histamine H1 receptor in the caffeine induced locomotor sensitization. Intermittent administration of caffeine (15 mg/kg, i.p.) on alternate days (induction phase) i.e. 1st, 3rd, 5th, 7th, 9th, 11th and 13th resulted in the development of locomotor sensitization. In addition, challenge with sub-stimulant dose of caffeine (10 mg/kg, i.p.) directly on 17th day to induction group animals resulted in expression to locomotor sensitization to caffeine. I.c.v. injection of histaminergic agents concomitantly with caffeine during induction phase i.e. histamine H1 receptor agonist, FMPH (6.5 µg/mouse) significantly potentiated while H1 receptor antagonist, cetirizine (0.1 µg/mouse) attenuated the locomotor sensitization induced by caffeine (15 mg/kg, i.p.). In addition, challenge with caffeine (10 mg/kg, i.p.) on the expression day (17th) to the induction group mice on FMPH + caffeine treatment showed enhanced, while those on cetirizine + caffeine treatment exhibited lesser expression to locomotor sensitization. Therefore, a possible contributory role of the central histaminergic system via H1 receptor stimulation or up-regulation in the caffeine-induced locomotor sensitizing effect is proposed.

Ethanol induced antidepressant-like effect in the mouse forced swimming test: modulation by serotonergic system.

AIM: The present investigation explored the modulatory role of serotonergic transmission in the acute ethanol-induced effects on immobility time in the mouse forced swim test (FST). METHODS AND RESULTS: Acute i.p. administration of ethanol (20% w/v, 2 or 2.5 g/kg, i.p.) decreased the immobility time in FST of mice, indicating its antidepressant-like effect while lower doses of ethanol (1, 1.5 g/kg, i.p.) were devoid of any effect in the FST. The mice pre-treated with a sub-effective dose of 5-HT2A agonist, DOI (10 µg/mouse, i.c.v.) or 5-HT1A receptor antagonist, WAY 100635 (0.1 µg/mouse, i.c.v.) but not with the 5-HT2A/2C antagonist, ketanserin (1.5 µg/mouse, i.c.v.) exhibited a synergistic reduction in the immobility time induced by sub-effective dose of ethanol (1.5 g/kg, i.p.). On the other hand, ethanol (2.5 g/kg, i.p.) failed to decrease the immobility time in mice, pre-treated with 5-HT1A agonist, 8-OH-DPAT (0.1 µg/mouse, i.c.v.) or ketanserin (1.5 µg/mouse, i.c.v.). In addition, pre-treatment with a 5-HT neuronal synthesis inhibitor, p-CPA (300 mg/kg, i.p. × 3 days) attenuated the anti-immobility effect ethanol (2.5 g/kg, i.p.) in mouse FST. CONCLUSIONS: Thus, the results of the present study points towards the essentiality of the central 5-HT transmission at the synapse for the ethanol-induced antidepressant-like effect in the FST wherein the regulatory role of the 5-HT1A receptor or contributory role of the 5-HT2A/2C receptor-mediated mechanism is proposed in the anti-immobility effect of acute ethanol in mouse FST.

Central histaminergic transmission modulates the ethanol induced anxiolysis in mice.

Intrigued by the report demonstrating an increase in brain histamine levels by ethanol administration and central histamine transmission to affect the anxiety related behaviors, the present study examined the permissive role of central histaminergic transmission in the acute anxiolytic-like effect of the ethanol on elevated plus maze (EPM) in mice. Results demonstrated that prior administration of the agents that are known to enhance the brain histamine transmission, i.e. low dose of histamine (0.1µg/mouse, i.c.v.) or histamine precursor, l-histidine (500, 1000mg/kg, i.p.) or low dose of histamine releasing agent (H3 receptor inverse agonist), thioperamide (2µg/mouse) attenuated the acute anitanxiety-like effect of ethanol (2g/kg, i.p, 8% w/v) in mice on EPM. However, pre-treatment with the H1 receptor antagonist, cetirizine (0.1µg/mouse, i.c.v.) or H2 receptor antagonist, ranitidine (50µg/mouse, i.c.v.) failed to affect the attenuating effect of low dose of histamine on ethanol induced anxiolysis. On the other hand, only H1 receptor antagonist, cetirizine (0.1µg/mouse, i.c.v.) was able to partially reverse the attenuation of ethanol induced anxiolysis by l-histidine (1000mg/kg, i.p.). Surprisingly, in mice pre-treated with the higher dose of histamine (50µg/mouse, i.c.v.) or thioperamide (10µg/mouse, i.c.v.), the ethanol (2g/kg, i.p.) induced antianxiety-like effect was further enhanced on EPM. Furthermore, this potentiating effect of high dose of histamine on the ethanol (2g/kg, i.p.) was exacerbated on pre-treatment with the H1 receptor antagonist, cetirizine, while H2 receptor antagonist, ranitidine completely reversed this action of high dose of histamine on ethanol. Supportive to these results, i.c.v. pre-treatment with H1 receptor agonist, FMPH (2, 6.5µg/mouse, i.c.v.) attenuated while H2 receptor agonist, amthamine (0.1, 0.5µg/mouse, i.c.v.) enhanced the ethanol induced anxiolysis in mice. Thus, it is reasonable to contemplate that central histaminergic transmission functions to negatively modulate the acute ethanol-induced anxiolysis probably via stimulation of postsynaptic H1 receptor and histamine might contribute to the anxiolytic action of ethanol via H2 receptor activation.

Contribution of the central histaminergic transmission in the cataleptic and neuroleptic effects of haloperidol.

The antipsychotic properties of haloperidol are primarily attributed to its ability to block dopamine D2 receptors. Histaminergic transmission modulates some of the behavioral effects of haloperidol. Hence, the present study investigated the contribution of central histaminergic transmission in the cataleptic and neuroleptic effect of haloperidol respectively, using bar test and conditioned avoidance response (CAR) in a two-way shuttle box. The studies revealed that haloperidol (0.50 or 1 mg/kg, i.p.) exhibited cataleptic behavior and inhibited conditioned avoidance response (CAR) in the doses 0.25 or 0.50 mg in rats. The rats, pretreated centrally (i.c.v.) with histamine precursor, L-histidine (1, 2.5 µg) or histamine neuronal inducer (H3 receptor antagonist), thioperamide (20, 50 µg/rat), showed an enhanced cataleptic effect with sub-maximal dose of haloperidol (0.5 mg/kg, i.p.). Similarly, the neuroleptic effect of haloperidol (0.25 mg/kg, i.p.) in CAR was also potentiated in the rats pretreated with L-histidine (2.5 µg) or thioperamide (50 µg/rat). Further, the cataleptic effect of haloperidol (1 mg/kg, i.p.) was attenuated in rats pretreated with the H1 receptor antagonist, chlorpheniramine (60, 80 µg/rat, i.c.v.) or H2 receptor antagonist, ranitidine (60 µg/rat, i.c.v.). However, the neuroleptic effect of haloperidol (0.5 mg/kg, i.p.) was completely reversed by pretreatment with ranitidine (60 µg/rat, i.c.v.), and partially attenuated by chlorpheniramine (80 µg/rat, i.c.v.). These findings suggest the possible involvement of histaminergic transmission in the cataleptic and neuroleptic effects of haloperidol probably via H1 or H2 receptor stimulation.

Bronchorelaxant, mast cell stabilizing, anti-inflammatory and antioxidant activity of Randia dumetorum (Retz.) Lamk. extracts.

Randia dumetorum (RD) fruits in different form have been ethnopharmacologically reported to possess antiasthmatic property. Therefore, present study was undertaken to evaluate two different extracts of RD i.e., ethyl acetate (RD-EA) and methanol (RD-ME) for bronchorelaxant, anti-inflammatory, mast cell stabilizing and antioxidant effect along with safety margin, according to OECD guidelines for toxicity. RD-ME and RD-EA (1 mg/mL) exhibited 68.75 and 57.39% inhibition of contraction against acetylcholine, while against histamine induced contraction, inhibition observed was 100 and 78.13%, respectively. Moreover, extracts attenuated the experimentally induced inflammation at 200 mg/kg with % inhibition of 41.62 by RD-ME and 30.36 by RD-EA in carrageenan model, while in egg albumin model RD-ME and RD-EA exhibited % inhibition of 48.31 and 33.75, respectively. In addition, RD-ME and RD-EA at 100 microg/mL demonstrated significant decrease in histamine release of 08.31 and 16.71 in C-48/80 induced mast cell degradation. RD extracts also exhibited antioxidant activity in DPPH, reducing power and metal chelation method, along with safe margin for oral administration as observed in acute toxicity evaluation.

Endocannabinoid analogues exacerbate marble-burying behavior in mice via TRPV1 receptor.

Activation of cannabinoid CB(1) receptor is shown to inhibit marble-burying behavior (MBB), a behavioral model for assessing obsessive-compulsive disorder (OCD). Anandamide, an endogenous agonist at CB(1) receptor also activates the transient receptor potential vanilloid type 1 (TRPV1) channels but at a higher concentration. Furthermore, anandamide-mediated TRPV1 effects are opposite to that of the CB(1) receptor. Therefore, the present study was carried out to investigate the influence of low and high doses of anandamide on MBB in CB(1) and TRPV1 antagonist pre-treated mice. The results revealed that i.c.v. administration of lower doses of anandamide (1-10 µg/mouse) or its analogues (AM404 or URB597; 1-5 µg/mouse) inhibited MBB indicating the anticompulsive activity. Conversely, at higher doses (40 or 20 µg/mouse) these compounds increased MBB similar to capsaicin (TRPV1 agonist, 100 µg/mouse) exhibiting a pro-compulsive effect. Pretreatment with AM251 (CB(1) antagonist, 1 µg/mouse) antagonized the anticompulsive effect of these compounds, while their pro-compulsive effect at higher doses was attenuated by inactive dose of capsazepine (TRPV1 antagonist, 10 µg/mouse). However, capsazepine per se at a higher dose (100 µg/mouse) inhibited MBB. When given daily for 14 days, the anticompulsive effect of anandamide and its analogues gradually disappeared, whereas capsazepine either alone or with URB597 produced consistent inhibition of MBB comparable to fluoxetine. Thus, the study indicates the biphasic influence of anandamide on MBB, and chronic administration of capsazepine either alone or with URB597 might be an effective tool in the treatment of OCD.

Involvement of endocannabinoids in antidepressant and anti-compulsive effect of fluoxetine in mice.

Endocannabinoid analogues exhibit antidepressant and anti-compulsive like effects similar to that of serotonin selective reuptake inhibitors (SSRIs) indicating a parallelism between the effects of serotonin and endocannabinoids. Therefore, the present study was designed to investigate the role of endocannabinoids in the antidepressant and anti-compulsive like effect of fluoxetine using mice model of forced swim test (FST) and marble-burying behavior (MBB). The results revealed that intracerebroventricular injections of endocannabinoid analogues, anandamide, a CB(1) agonist (AEA: 1-20 µg/mouse); AM404, an anandamide transport inhibitor (0.1-10 µg/mouse); and URB597, a fatty acid amide hydrolase inhibitor (0.05-10 µg/mouse) produced antidepressant-like effect dose-dependently, whereas influenced the MBB in a biphasic manner (produced a U-shaped dose-response curve). Fluoxetine (2.5-20 mg/kg, i.p.) dose dependently decreased the immobility time as well as burying behavior. Co-administration of sub-effective dose of fluoxetine (2.5 mg/kg, i.p.) potentiated the effect of sub-effective dose of AEA (0.5 µg/mouse, i.c.v.), AM404 (0.05 µg/mouse, i.c.v) or URB597 (0.01 µg/mouse, i.c.v) in both the paradigms. Interestingly, pretreatment with AM251, a CB(1) antagonist, blocked the effect of fluoxetine in FST and MBB at a dose (1 µg/mouse, i.c.v) that per se had no effect on either parameter. Similar effects were obtained with endocannabinoid analogues in AM251 pretreated mice. However, AM251 increased the burying behavior in MBB at a highest dose tested (5 µg/mouse). None of the treatments had any influence on locomotor activity. Thus, the study indicates an interaction between endocannabinoid and serotonergic system in regulation of depressive and compulsive-like behavior.

Endocannabinoids mediate anxiolytic-like effect of acetaminophen via CB1 receptors.

Acetaminophen (Paracetamol), a most commonly used antipyretic/analgesic agent, is metabolized to AM404 (N-arachidonoylphenolamine) that inhibits uptake and degradation of anandamide which is reported to mediate the analgesic action of acetaminophen via CB1 receptor. AM404 and anandamide are also reported to produce anxiolytic-like behavior. In view of the implication of endocannabinoids in the effect of acetaminophen, we contemplated that acetaminophen may have anxiolytic-like effect. Therefore, this possibility was tested by observing the effects of various doses of acetaminophen in mice on anxiety-related indices of Vogel conflict test and social interaction test. The results from both the tests indicated that acetaminophen (50, 100, or 200 mg/kg, i.p.) or anandamide (10 or 20 microg/mouse, i.c.v.) dose dependently elicited anxiolytic-like effect, that was comparable to diazepam (2 mg/kg, i.p.). Moreover, co-administration of sub-effective dose of acetaminophen (25 mg/kg, i.p.) and anandamide (5 microg/mouse, i.c.v) produced similar anxiolytic effect. Further, pre-treatment with AM251 (a CB1 receptor antagonist; 1 mg/kg, i.p.) antagonized the effects of acetaminophen and anandamide with no per se effect at 1 mg/kg dose, while anxiogenic effect was evident at a higher dose (5 mg/kg, i.p.). None of the treatment/s was found to induce any antinociceptive or locomotor impairment effects. In conclusion, the findings suggested that acetaminophen (50, 100, or 200 mg/kg, i.p.) exhibited dose dependent anxiolytic effect in mice and probably involved endocannabinoid-mediated mechanism in its effect.

The 5-HT3 receptor antagonist, ondansetron, blocks the development and expression of ethanol-induced locomotor sensitization in mice.

Manipulation of the serotonergic system has been shown to alter ethanol sensitization. Ondansetron is a 5-HT3 receptor antagonist, reported to attenuate cocaine and methamphetamine-induced behavioral sensitization, but no reports are available on its role in ethanol-induced behavioral sensitization. Therefore, an attempt has been made to assess this issue by using an earlier used animal model of ethanol-induced locomotor sensitization. Results indicated that ondansetron (0.25-1.0 mg/kg, subcutaneously) given before the challenge dose of ethanol (2.4 g/kg, intraperitoneally) injection, significantly and dose dependently attenuated the expression of sensitization. In addition, ondansetron (1.0 mg/kg, subcutaneously) given before ethanol injection on days 1, 4, 7, and 10 significantly blocked the development (days 1, 4, 7, and 10), and expression (day 15) of sensitization to the locomotor stimulant effect of ethanol injection. Ondansetron had no effect per se on locomotor activity and did not affect blood ethanol levels. Therefore, the results raise the possibility that ondansetron blocked the development and expression of ethanol-induced locomotor sensitization by acting on 5-HT3 receptors.

Effects of central administration of gonadotropin-releasing hormone agonists and antagonist on elevated plus-maze and social interaction behavior in rats.

The correlation between neuronal mechanism of anxiety and neuroanatomic expression/neuromodulatory role of gonadotropin-releasing hormone (GnRH), points to a role of GnRH in the modulation of anxiety. Therefore, we investigated the influence of GnRH agonists and antagonist on the anxiety-like behavior of rats in the elevated plus-maze and social interaction tests. GnRH agonists, leuprolide [100 or 200 ng/rat, intracerebroventricularly (i.c.v.)] or 6-D-tryptophan luteinizing hormone-releasing hormone (400 ng/rat, i.c.v.), significantly increased percentage of open arms entries, time spent in open arms, and time spent in social interaction. The observed anxiolytic effect of these agents was comparable with diazepam (0.5-1.0 mg/kg, intraperitoneally). Treatment with a GnRH antagonist [pGlu-D-Phe-Trp-Ser-Tyr-D-Ala-Leu-Arg-Pro-Gly-NH2, (100 ng/rat, i.c.v.)], significantly reduced percentage of open arm indices and decreased time spent in social interaction, indicating an anxiogenic-like effect. Further, castrated rats exhibited anxiogenic-like behavior in these tests, which was significantly attenuated by leuprolide (200 ng/rat, i.c.v.) or 6-D-tryptophan luteinizing hormone-releasing hormone (400 ng/rat, i.c.v.), indicating the noninvolvement of peripheral sex hormone in their anxiolytic-like effect, at least in castrated rats. In conclusion, this study indicated a putative role of GnRH in the control of anxiety, and further adds to the importance of investigating the possible role of the hypothalamus-pituitary-gonadal axis in regulating the anxiety-related disorders arising out of hypothalamus-pituitary-adrenal axis dysregulation.

Evaluation of GABAergic neuroactive steroid 3alpha-hydroxy-5alpha-pregnane-20-one as a neurobiological substrate for the anti-anxiety effect of ethanol in rats.

RATIONALE: Acute systemic ethanol administration is known to elevate plasma and cerebral levels of neuroactive steroid 3alpha-hydroxy-5alpha-pregnane-20-one (3alpha, 5alpha-THP; allopregnanolone) to a concentration sufficient to potentiate GABA(A) receptors. We have earlier demonstrated that 3alpha, 5alpha-THP mediates the antidepressant-like effect of ethanol in Porsolt forced swim test. OBJECTIVE: The aim of the present study is to explain the relationship between endogenous GABAergic neurosteroids and anxiolytic effect of ethanol in Sprague-Dawley rats. METHOD: The mediation of 3alpha, 5alpha-THP in the anti-anxiety effect of ethanol was assessed by pharmacological interactions of ethanol with various endogenous neurosteroidal modulators and using simulated physiological conditions of altered neurosteroid content in elevated plus maze (EPM) test. RESULTS: Pretreatment of 3alpha, 5alpha-THP (0.5-2.5 mug/rat, i.c.v.) or neurosteroidogenic agents such as 3alpha, 5alpha-THP precursor progesterone (5 or 10 mg/kg, i.p.), 11-beta hydroxylase inhibitor metyrapone (50 or 100 mg/kg, i.p.) or the GABA(A) receptor agonist muscimol (25 ng/rat, i.c.v.) significantly potentiated the anti-anxiety effect of ethanol (1 g/kg, i.p.). On the other hand, the GABAergic antagonistic neurosteroid dehydroepiandrosterone sulphate (DHEAS) (1 mg/kg, i.p.), the GABA(A) receptor blocker bicuculline (1 mg/kg, i.p.), the 5alpha-reductase inhibitor finasteride (50 x 2 mg/kg, s.c.) or the mitochondrial diazepam binding inhibitory receptor antagonist PK11195 (1 mg/kg, i.p.) reduced ethanol-induced preference of time spent and number of entries into open arms. Anti-anxiety effect of ethanol was abolished in adrenalectomized (ADX) rats as compared to sham-operated control. This ADX-induced blockade was restored by prior systemic injection of progesterone, signifying the contribution of peripheral steroidogenesis in ethanol anxiolysis. Socially isolated animals known to exhibit decreased brain 3alpha, 5alpha-THP and GABA(A) receptor functions displayed reduced sensitivity to the effects of ethanol and 3alpha, 5alpha-THP in EPM test. CONCLUSIONS: Our results demonstrated the contributory role of neuroactive steroid 3alpha, 5alpha-THP in the anti-anxiety effect of ethanol. It is speculated that ethanol-induced modulation of endogenous GABAergic neurosteroids, especially 3alpha, 5alpha-THP, might be crucial pertinent to the etiology of 'trait' anxiety (tension reduction) and ethanol abuse.