Modulation of the anticonvulsant effect of swim stress by agmatine.

Agmatine is an endogenous l-arginine metabolite with neuroprotective effects in the stress-response system. It exerts anticonvulsant effects against several seizure paradigms. Swim stress induces an anticonvulsant effect by activation of endogenous antiseizure mechanisms. In this study, we investigated the interaction of agmatine with the anticonvulsant effect of swim stress in mice on pentylenetetrazole (PTZ)-induced seizure threshold. Then we studied the involvement of nitric oxide (NO) pathway and endogenous opioid system in that interaction. Swim stress induced an anticonvulsant effect on PTZ seizures which was opioid-independent in shorter than 1-min swim durations and opioid-dependent with longer swims, as it was completely reversed by pretreatment with naltrexone (NTX) (10mg/kg), an opioid receptor antagonist. Agmatine significantly enhanced the anticonvulsant effect of opioid-independent shorter swim stress, in which a combination of subthreshold swim stress duration (45s) and subeffective dose of agmatine (1mg/kg) revealed a significantly higher seizure threshold compared with either one. This effect was significantly reversed by NO synthase inhibitor NG-nitro-l-arginine (L-NAME (Nω-Nitro-L-arginine methyl ester), 5mg/kg), suggesting an NO-dependent mechanism, and was unaffected by NTX (10mg/kg), proving little role for endogenous opioids in the interaction. Our data suggest that pretreatment of animals with agmatine acts additively with short swim stress to exert anticonvulsant responses, possibly by mediating NO pathway.

A COX/5-LOX Inhibitor Licofelone Revealed Anticonvulsant Properties Through iNOS Diminution in Mice.

Licofelone is a COX/5-LOX inhibitor, which recently was approved as an effective treatment for osteoarthritis. Beside its analgesic and anti-inflammatory effects, some reports show neuro-protective properties for this agent in central nervous system. Several lines of evidence declare the involvement of COX or LOX isoenzymes in epileptic disorders. To set the foundation for future research into the neurobiology of licofelone as a potential therapeutic agent, we studied the effect of licofelone in an animal model of epilepsy. Although different neurotransmitters and neuro-modulators like nitric oxide were introduced as suggested targets of licofelone, the underlying mechanisms of central effects of this drug are not still fully understood. We have utilized pentylenetetrazole-induced clonic seizure model to investigate the behavioral consequences of licofelone administration and its possible mechanisms in seizure susceptibility. Licofelone revealed anticonvulsant properties at the dose of 10 mg/kg (i.p) or higher in mice. Pre-treatment with NO (nitric oxide) donor, L-arginine, reversed this anticonvulsant effects dose dependently. L-NAME, as a non-selective nitric oxide synthase (NOS) inhibitor, potentiated the anticonvulsant effects of licofelone. A neuronal NOS inhibitor, 7-NI did not affect seizure threshold alone or in combination with licofelone. Using non-effective doses of selective inhibitors of inducible NOS, aminoguanidine or 1400W, significantly increased the seizure threshold when were accompanied by licofelone in low doses. These data support the involvement of NO as an important role player in the central neuro-protective properties of licofelone. Furthermore, it implies that down regulation of iNOS seems crucial for anticonvulsant properties of this COX/5-LOX inhibitor in seizure susceptibility.

Nitric oxide mediates the anticonvulsant effects of thalidomide on pentylenetetrazole-induced clonic seizures in mice.

Thalidomide is an old glutamic acid derivative which was initially used as a sedative medication but withdrawn from the market due to the high incidence of teratogenicity. Recently, it has reemerged because of its potential for counteracting number of diseases, including neurodegenerative disorders. Other than the antiemetic and hypnotic aspects, thalidomide exerts some anticonvulsant properties in experimental settings. However, the underlying mechanisms of thalidomide actions are not fully realized yet. Some investigations revealed that thalidomide could elicit immunomodulatory or neuromodulatory properties by affecting different targets, including cytokines (such as TNF α), neurotransmitters, and nitric oxide (NO). In this regard, we used a model of clonic seizure induced by pentylenetetrazole (PTZ) in male NMRI mice to investigate whether the anticonvulsant effect of thalidomide is affected through modulation of the l-arginine-nitric oxide pathway or not. Injection of a single effective dose of thalidomide (10 mg/kg, i.p. or higher) significantly increased the seizure threshold (P<0.05). On the one hand, pretreatment with low and per se noneffective dose of l-arginine [NO precursor] (10, 30 and 60 mg/kg) prevented the anticonvulsant effect of thalidomide. On the other hand, NOS inhibitors [l-NAME and 7-NI] augmented the anticonvulsant effect of a subeffective dose of thalidomide (1 and 5 mg/kg, i.p.) at relatively low doses. Meanwhile, several doses of aminoguanidine [an inducible NOS inhibitor] (20, 50 and 100 mg/kg) failed to alter the anticonvulsant effect of thalidomide significantly. In summary, our findings demonstrated that the l-arginine-nitric oxide pathway can be involved in the anticonvulsant properties of thalidomide, and the role of constitutive nNOS is prominent in the reported neuroprotective feature.

Tropisetron attenuates amyloid-beta-induced inflammatory and apoptotic responses in rats.

BACKGROUND: Alzheimer's disease (AD) is a neurodegenerative disorder featured by deposition of beta-amyloid (Aß) plaques in the hippocampus and associated cortices and progressive cognitive decline. Tropisetron, a selective 5-HT3 receptor antagonist, is conventionally used to counteract chemotherapy-induced emesis. Recent investigations describe antiphlogistic properties for tropisetron. It has been shown that tropisetron protects against rat embolic stroke. We investigated protective properties of tropisetron in a beta-amyloid (Aß) rat model of AD and possible involvement of 5-HT3 receptors. MATERIAL AND METHODS: Aß (1-42) was injected into the hippocampus of male rats. Animals were treated intracerebroventricularly with tropisetron, mCPBG (selective 5-HT3 receptor agonist) or mCPBG plus tropisetron on days 1, 3, 5 and 7. Seven days following Aß administration, inflammatory markers (TNF-α, COX-2, iNOS and NF-κB), apoptotic markers (caspase 3 cytochrome c release) and calcineurin phosphatase activity were assessed in hippocampus. RESULTS: Seven days following Aß inoculation, control animals displayed dramatic increase in TNF-α, COX-2, iNOS, NF-κB, active caspase 3, cytochrome c release and calcineurin phosphatase activity in the hippocampus. Tropisetron significantly diminished the elevated levels of these markers and reversed the cognitive deficit. Interestingly, tropisetron was also found to be a potent inhibitor of calcineurin phosphatase activity. The selective 5-HT3 receptor agonist mCPBG, when co-administered with tropisetron, completely reversed the procognitive and anti-apoptotic properties of tropisetron while it could only partially counteract the anti-inflammatory effects. mCPBG alone significantly aggravated Aß-induced injury. CONCLUSION: Our findings indicate that tropisetron protects against Aß-induced neurotoxicity in vivo through both 5-HT3 receptor-dependent and independent pathways.

The role of 5-HT(3) receptors in the additive anticonvulsant effects of citalopram and morphine on pentylenetetrazole-induced clonic seizures in mice.

Citalopram, a selective serotonin reuptake inhibitor (SSRI), is frequently used in the treatment of major depressive disorders. In addition to its antidepressant features, citalopram shows some anticonvulsive properties at lower doses, whereas higher doses, ingested in cases of suicide, have been associated with seizures. Moreover, some reports support the enhancing effect of morphine on different responses of SSRIs such as analgesic and anticonvulsant properties. Although the exact mechanisms of these additive effects are not yet fully understood, 5-HT(3) receptor has recently been shown to play an important role in the central effects of SSRIs and morphine. In this regard, we used a model of clonic seizures induced by pentylenetetrazole (PTZ) in male NMRI mice to investigate whether morphine and citalopram exhibit additive anticonvulsant effects and, if so, whether this effect is mediated through modulation of 5-HT(3) receptors. In our study, citalopram at lower doses (0.5 and 1 mg/kg, ip) significantly increased the seizure threshold (P<0.01) and at a higher dose (50 mg/kg) had proconvulsive effects. Moreover, morphine at low and noneffective doses had additive effects on the anticonvulsive properties of citalopram. This additive effect was prevented by pretreatment with low and noneffective doses of tropisetron (a 5-HT(3) receptor antagonist) and augmented by 1-(m-chlorophenyl)-biguanide (mCPBG, a 5-HT(3) receptor agonist). Moreover, low doses of morphine (0.1 and 0.5 mg/kg) alone or in combination with potent doses of 5-HT(3) receptor agonist or antagonist could not alter the proconvulsive properties of citalopram at higher dose (50 mg/kg), ruling out the contribution of 5-HT(3) to this effect. In summary, our findings demonstrate that 5-HT(3) receptor mediates the additive anticonvulsant properties of morphine and low-dose citalopram. This could constitute a new approach to augmenting the efficacy and curtailing the adverse effects of citalopram.

Agmatine enhances the anticonvulsant effect of lithium chloride on pentylenetetrazole-induced seizures in mice: Involvement of L-arginine/nitric oxide pathway.

After nearly 60years, lithium is still the mainstay in the treatment of mood disorders. In addition to its antimanic and antidepressant effects, lithium also has anticonvulsant properties. Similar to lithium, agmatine plays a protective role in the central nervous system against seizures and has been reported to enhance the effect of different antiepileptic agents. Moreover, both agmatine and lithium have modulatory effects on the L-arginine/nitric oxide pathway. This study was designed to investigate: (1) whether agmatine and lithium exert a synergistic effect against clonic seizures induced by pentylenetetrazole and (2) whether or not this synergistic effect is mediated through inhibition of the L-arginine/nitric oxide pathway. In our study, acute administration of a single potent dose of lithium chloride (30mg/kg ip) increased seizure threshold, whereas pretreatment with a low and independently noneffective dose of agmatine (3mg/kg) potentiated a subeffective dose of lithium (10mg/kg). N(G)-L-arginine methyl ester (L-NAME, nonspecific nitric oxide synthase inhibitor) at 1 and 5mg/kg and 7-nitroindazole (7-NI, preferential neuronal nitric oxide synthase inhibitor) at 15 and 30mg/kg augmented the anticonvulsant effect of the noneffective combination of lithium (10mg/kg ip) and agmatine (1mg/kg), whereas several doses (20 and 40mg/kg) of aminoguanidine (inducible nitric oxide synthase inhibitor) failed to alter the seizure threshold of the same combination. Furthermore, pretreatment with independently noneffective doses (30 and 60mg/kg) of L-arginine (substrate for nitric oxide synthase) inhibited the potentiating effect of agmatine (3mg/kg) on lithium (10mg/kg). Our findings demonstrate that agmatine and lithium chloride have synergistic anticonvulsant properties that may be mediated through the L-arginine/nitric oxide pathway. In addition, the role of constitutive nitric oxide synthase versus inducible nitric oxide synthase is prominent in this phenomenon.

A randomized, double-blind, parallel pharmacokinetic study comparing the trastuzumab biosimilar candidate, AryoTrust®, and reference trastuzumab in healthy subjects.

BACKGROUND: AryoTrust® (AryoGen Pharmed Co., Iran) is a biosimilar candidate for the EU-sourced reference trastuzumab, Herceptin®. This study was designed to evaluate the bioequivalence between AryoTrust® and Herceptin®. RESEARCH DESIGN AND METHODS: In this double-blind, parallel study, 60 healthy male subjects were randomized 1:1 to receive a single dose of AryoTrust® or Herceptin® (6 mg/kg) as intravenous infusion. The primary endpoint of the study was the area under the concentration versus time to infinity (AUC0-inf), and the main secondary endpoints were maximum measured concentration (Cmax), area under the concentration versus time from zero to the last quantifiable concentration time (AUC0-last), immunogenicity, and safety. RESULTS: Sixty subjects were enrolled in the study and baseline demographics were similar between the two groups. The two groups demonstrated similar pharmacokinetic parameters and the 90% confidence interval (CI) for primary and secondary endpoints were within the bioequivalence acceptance range (80.00%-125.00%). No serious adverse event or immunogenicity was reported, and all of the adverse events reported were mild and similar between the two treatment groups. CONCLUSION: AryoTrust® was well tolerated, had a similar safety profile to reference trastuzumab, and its pharmacokinetic bioequivalence was confirmed. TRIAL REGISTRATION: The trial is registered at Indian Trials Registry (CTRI/2019/03/018218).

Oxytocin is involved in the proconvulsant effects of Sildenafil: Possible role of CREB.

Sildenafil is a phosphodiesterase type 5 inhibitor mainly used for male erectile dysfunction. One of rare yet serious adverse effects of Sildenafil is its potential to decrease seizure threshold. Ample evidence suggests that Sildenafil exerts central effects through induction of Oxytocin (OT) secretion and CREB phosphorylation. The aim of the present study is to evaluate potential roles of OT and CREB in the proconvulsant effects of Sildenafil. The Pentylenetetrazole-induced seizure was used as a standard convulsion model in this study. OT release and pCREB expression were evaluated in the hippocampus of mice using ELISA and western blot assays, respectively. Our results showed that Sildenafil at the dose of 10mgkg(-1) or higher, significantly decreased seizure threshold. Pretreatment with a non-effective dose of OT, potentiated while OT receptor antagonist, Atosiban, reversed fully the proconvulsant effects of Sildenafil (5mgkg(-1)). At biochemical inspection, Sildenafil markedly increased CREB which was attenuated by coadministration of Atosiban. The present study shows for the first time that OT release and the subsequent CREB phosphorylation are involved in the proconvulsant effects of acute Sildenafil treatment in an experimental model of seizure.

Zinc Chloride and Lead Acetate-Induced Passive Avoidance Memory Retention Deficits Reversed by Nicotine and Bucladesine in Mice.

It is very important to investigate the neurotoxic effects of metals on learning and memory processes. In this study, we tried to investigate the effects and time course properties of oral administration of zinc chloride (25, 50, and 75 mg/kg, for 2 weeks), lead acetate (250, 750, 1,500, and 2,500 ppm for 4, 6 and 8 weeks), and their possible mechanisms on a model of memory function. For this matter, we examined the intra-peritoneal injections of nicotine (0.25, 0.5, 1, and 1.5 mg/kg) and bucladesine (50, 100, 300, and 600 nM/mouse) for 4 days alone and in combination with mentioned metals in the step-through passive avoidance task. Control animals received saline, drinking water, saline, and DMSO (dimethyl sulfoxide)/deionized water (1:9), respectively. At the end of each part of studies, animals were trained for 1 day in step-through task. The avoidance memory retention alterations were evaluated 24 and 48 h later in singular and combinational studies. Zinc chloride (75 mg/kg) oral gavage for 2 weeks decreased latency times compared to control animals. Also, lead acetate (750 ppm oral administrations for 8 weeks) caused significant lead blood levels and induced avoidance memory retention impairments. Four-days intra-peritoneal injection of nicotine (1 mg/kg) increased latency time compared to control animals. Finally, findings of this research showed that treatment with intra-peritoneal injections of nicotine (1 mg/kg) and/or bucladesine (600 nM/mouse) reversed zinc chloride- and lead acetate-induced avoidance memory retention impairments. Taken together, these results showed the probable role of cholinergic system and protein kinase A pathways in zinc chloride- and lead acetate-induced avoidance memory alterations.

How sodium arsenite improve amyloid ß-induced memory deficit?

Evidence has shown that arsenic exposure, besides its toxic effects results in impairment of learning and memory, but its molecular mechanisms are not fully understood. In the present study, we examined sodium arsenite (1, 5, 10, 100nM) effects on contextual and tone memory of male rats in Pavlovian fear conditioning paradigm alone and in co-administration with ß-amyloid. We detected changes in the level of caspase-3, nuclear factor kappa-B (NF-κB), cAMP response element-binding (CREB), heme oxygenase-1 and NF-E2-related factor-2 (Nrf2) by Western blot. Sodium arsenite in high doses induced significant memory impairment 9 and 16days after infusion. By contrast, low doses of sodium arsenite attenuate memory deficit in Aß injected rats after 16days. Our data revealed that treatment with high concentration of sodium arsenite increased caspase-3 cleavage and NF-κB level, 9days after injection. Whereas, low doses of sodium arsenite cause Nrf2 and HO-1 activation and increased CREB phosphorylation in the hippocampus. These findings suggest the concentration dependent effects of sodium arsenite on contextual and tone memory. Moreover, it seems that the neuroprotective effects of ultra-low concentrations of sodium arsenite on Aß-induced memory impairment is mediated via an increase Nrf2, HO-1 and CREB phosphorylation levels and decrease caspase-3 and NF-κB amount.

Involvement of PPAR receptors in the anticonvulsant effects of a cannabinoid agonist, WIN 55,212-2.

Cannabinoid and PPAR receptors show well established interactions in a set of physiological effects. Regarding the seizure-modulating properties of both classes of receptors, the present study aimed to evaluate the roles of the PPAR-gamma, PPAR-alpha and CB1 receptors on the anticonvulsant effects of WIN 55,212-2 (WIN, a non selective cannabinoid agonist). The clonic seizure thresholds after intravenous administration of pentylenetetrazole (PTZ) were assessed in mice weighing 23-30 g. WIN increased the seizure threshold dose dependently. Pretreatment with pioglitazone, as a PPARγ agonist, potentiated the anticonvulsant effects of WIN, while PPARγ antagonist inhibited these anticonvulsant effects partially. On the other hand PPARα antagonist reduced the anticonvulsant effects of WIN significantly. Finally the combination of CB1 antagonist and PPARα antagonist could completely block the anticonvulsant properties of WIN. Taken together, these results show for the first time that a functional interaction exists between cannabinoid and PPAR receptors in the modulation of seizure susceptibility.

Hypoxia/ischemia a key player in early post stroke seizures: modulation by opioidergic and nitrergic systems.

Stroke is a leading cause of death, disability, and socioeconomic loss worldwide. All attempts at pharmacological reduction of the complications of stroke (e.g. post-stroke seizure, and brain׳s vulnerability to hypoxic/ischemic injury) have failed. Endogenous opioids and nitric oxide (NO) overproduction has been documented in brain hypoxia/ischemia (H/I), which can exert pro-convulsive effects. In this study, we aimed to examine the possible involvement of opioidergic and nitrergic pathways in the pathogenesis of post-stroke seizure. H/I was induced by right common carotid ligation and sham-operated mice served as controls. We demonstrated that right common carotid ligation decreases the threshold for clonic seizures induced by pentylenetetrazole (PTZ), a GABA antagonist. Furthermore, pro-convulsive effect of H/I following right common carotid ligation was blocked by naltrexone (NTX) (3mg/kg), NG-Nitro-l-arginine methyl ester (l-NAME) (10mg/kg), and aminoguanidine (AG) (100mg/kg) administration (P<0.001). Interestingly, co-administration of non-effective doses of NTX and l-NAME (1 and 0.5mg/kg, respectively) reverses epileptogenesis of H/I (P<0.001). In the same way, co-administration of non-effective doses of NTX and AG (1 and 5mg/kg, respectively), reverses epileptogenesis of H/I (P<0.001). Indeed, the histological studies performed on mice exposed to H/I confirmed our previous data. These findings suggest hyper-susceptibility to PTZ induced seizure following H/I is mediated by interaction of opioidergic, and iNOS/NO pathways. Therefore, our results identify new pharmacological targets and provide the rationale for a novel strategy to promote recovery after stroke and possibly other brain injuries.

Protective effects of lithium chloride on seizure susceptibility: Involvement of α2-adrenoceptor.

For more than 60years, lithium has been the mainstay in the treatment of mental disorders as a mood stabilizer. In addition to the antimanic and antidepressant responses, lithium also shows some anticonvulsant properties. In spite of the ascertained neuroprotective effects of this alkali metal, the underlying mechanisms through which lithium regulates behavior are still poorly understood. Among different targets, some authors suggest neuromodulatory effects of lithium are the consequences of interaction of this agent with the brain neurotransmitters including adrenergic system. In order to study the involvement of α2-adrenergic system in anticonvulsant effect of lithium, we used a model of clonic seizure induced by pentylenetetrazole (PTZ) in male NMRI mice. Injection of a single effective dose of lithium chloride (30mg/kg, i.p.) significantly increased the seizure threshold (p<0.01). The anticonvulsant effect of an effective dose of lithium was prevented by pre-treatment with low and per se non-effective dose of clonidine [α2-adrenoceptor agonist] (0.05, 0.1 and 0.25mg/kg). On the other hand, yohimbine [α2-adrenoceptor antagonist] augmented the anticonvulsant effect of sub-effective dose of lithium (10mg/kgi.p.) at relatively low doses (0.1, 0.5, 1 and 2.5mg/kg). Moreover, UK14304 [a potent and selective α2-adrenoceptor agonist] (0.05 and 0.1mg/kg) and RX821008 [a potent and selective α2D-adrenoceptor antagonist] (0.05, 0.1 and 0.25mg/kg) repeated the same results confirming that these modulatory effects are conducted specifically through the α2D-adrenoceptors. In summary, our findings demonstrated that α2-adrenoceptor pathway could be involved in the anticonvulsant properties of lithium chloride in the model of chemically induced clonic seizure.

Paradoxical role of PKA inhibitor on amyloidß-induced memory deficit.

In spite of characterizing the role of protein kinase A (PKA) in activating biochemical mechanisms, few studies have investigated the effects of PKA inhibitors on memory functions. In the present study, we used Pavlovian fear conditioning paradigm to evaluate memory alterations caused by two doses of H89 (as a conditional inhibitor of PKA) alone and in combination with amyloid-ß (Aß) in rats. Moreover, we used the Western blotting method to investigate the alterations in markers of transcription, oxidative stress, inflammation, and apoptosis pathways involved in memory impairment. Stereotaxic surgery was done to inject Aß (30 ng/side) directly into the hippocampal CA1 area bilaterally and H89 (5 or 10 µM) intracerebroventricular unilaterally. One series of rats were trained 7 days after injections, then contextual and tone tests were conducted on days 8 and 9, respectively. Second series of rats were trained 14 days after the injections and tests were carried out on days 15 and 16. Our behavioral results showed that H89 (5 µM) not only has no destructive effect on memory, but also attenuates memory deficit caused by Aß in combination groups. In contrast, H89 (10µM) has a reversible destructive effect on memory. Our molecular findings indicated that low dose of H89 increases CREB phosphorylation, Nrf2 and HO-1 which results in survival resistance to the stress. On the contrary, H89 with higher concentration leads to substantial increase of NF-κB and caspase-3 levels, which impair memory functions. In conclusion, our data suggest that H89 as a PKA inhibitor influences memory process through a dose and time dependent manner.

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.

A cAMP analog reverses contextual and tone memory deficits induced by a PKA inhibitor in Pavlovian fear conditioning.

Despite extensive investigations, molecular mechanisms underlying the formation of fear memory are not completely understood. We have previously investigated the role of protein kinase AII (PKAII) in spatial acquisition and memory retention using Morris water maze. In the current study, we have further analyzed the role of PKA in memory consolidation using a fear conditioning response model. Experiments were performed using intrahippocampal infusions of dibutyryl cyclic AMP (bucladesine), a cell permeable analog of cAMP and H89, as a selective PKAII inhibitor, in male rats. The animals were trained for one session which included 4 consecutive trials of tone-shock pairing on the training day. Fear to the context and tone was evaluated by measuring freezing behavior 24h and 48h after training respectively. Bilateral infusion of 100 and 300µM/side of bucladesine immediately after training increased freezing percentage in rats, which indicated an improvement in memory consolidation. Administration of 10µM/side (but not 5µM/side) of H-89 impaired contextual and cued fear conditioning significantly compared to the control animals. Moreover, administration of bucladesine (100 and 300µM/side), 5min after H-89 infusion (10µM/side) reversed the impairment of contextual and auditory-cued fear conditioning in rats and freezing percentage increased to those of control animals. Altogether, these results indicate that PKA inhibitor-induced memory deficit was attenuated by a cAMP analog and that the cAMP/PKA signaling pathway has an important role for memory consolidation in fear conditioning response model.

Role of nitric oxide in additive anticonvulsant effects of agmatine and morphine.

The anticonvulsant effects of agmatine, an endogenous polyamine and a metabolite of l-arginine, have been shown in various experimental seizure models. Agmatine also potentiates the anti-seizure activity of morphine. The present study aimed to investigate a possible involvement of nitric oxide (NO) pathway in the protection by agmatine and morphine co-administration against pentylenetetrazole (PTZ) -induced seizure in male mice. To this end, the thresholds for the clonic seizures induced by the intravenous administration of PTZ, a GABA antagonist, were assessed. Intraperitoneal administration of morphine at lower dose (1mg/kg) increased the seizure threshold. Also intraperitoneal administration of agmatine (5 and 10mg/kg) increased the seizure threshold significantly. Combination of subeffective doses of morphine and agmatine led to potent anticonvulsant effects. Non-effective doses of morphine (0.1 and 0.5mg/kg) were able to induce anticonvulsant effects in mice pretreated with agmatine (3mg/kg). Concomitant administration of either the non-selective nitric oxide synthase (NOS) inhibitor L-NAME (1, 5mg/kg, i.p.) or the selective NOS inhibitor 7-NI (15, 30mg/kg, i.p.), with an ineffective combination of morphine (0.1mg/kg) plus agmatine (1mg/kg) produced significant anticonvulsant impacts. Moreover, the NO precursor, l-arginine (30, 60mg/kg, i.p.), inhibited the anticonvulsant action of agmatine (3mg/kg) plus morphine (0.5mg/kg) co-administration. Our results indicate that pretreatment of animals with agmatine enhances the anticonvulsant effects of morphine via a mechanism which may involve the NO pathway.

The role of nitric oxide in the PKA inhibitor induced spatial memory deficits in rat: involvement of choline acetyltransferase.

Several lines of evidence show that cAMP-PKA signaling pathway plays critical role in memory functions and suggest nitric oxide as an important modulator in learning and memory. In this study, we assessed the effects of intra-hippocampal infusion of H-89, a selective PKAII inhibitor, and 1400 W, a selective inducible nitric oxide synthase (iNOS) inhibitor, on spatial memory in rats. By using the Morris water maze, spatial memory retention parameters were examined 48 h after the infusions through measuring escape latency, traveled distance, and swimming speed. The rats receiving intra-hippocampal infusions of 1400 W (100 µM/side) showed a significant reduction (*P<0.05) in escape latency and traveled distance in comparison with the control saline group. In contrast, a significant increase (**P<0.01) in escape latency and traveled distance was observed after infusion of 10 µM H-89. Moreover, among combination groups, co-administration of 1400 W (400 µM/side) with 10 µM/side of H-89 caused a significant reduction (*P<0.05) in escape latency and traveled distance in comparison with the H-89 group. Also, we evaluated the molecular effects of 1400 W on the expression of choline acetyltransferase (ChAT), a cholinergic marker, in the CA1 region of the hippocampus and medial septal area (MSA). Immunohistochemical analysis of post-training bilateral intra-hippocampal infusion of 1400 W revealed a significant increase in ChAT immunoreactivity levels in both the CA1 and the MSA regions. Overall, the results suggest that 1400 W has protective effect against H89-induced spatial memory impairment. Moreover, the observed memory improvements caused by 1400 W infusions, might be due to interaction of iNOS with the cholinergic system.

5-HT(3) receptor mediates the dose-dependent effects of citalopram on pentylenetetrazole-induced clonic seizure in mice: involvement of nitric oxide.

Citalopram is a selective serotonin reuptake inhibitor (SSRI), widely used in the treatment of depressive disorders. It has been shown that citalopram affects seizure susceptibility. Although the exact mechanism of these effects are not yet fully understood, recent data suggest that 5HT(3) receptors and nitric oxide (NO) might participate in the central effects of SSRIs. In this study in a mouse model of clonic seizure induced by pentylenetetrazole we investigated whether 5-HT(3) receptors are involved in the effects of citalopram on seizure threshold. In our experiments, citalopram at lower doses (0.5 and 1mg/kg, i.p) significantly increased the seizure threshold and at higher doses (≥25mg/kg) showed proconvulsive effects. Moreover, mCPBG (a 5-HT(3) receptor agonist) at low and non-effective doses augmented while non-effective doses of tropisetron prevented the anticonvulsive properties of citalopram. On the other hand, Low doses of nitric oxide synthase inhibitors l-NAME and 7-NI alone or in combination with lower doses of 5-HT(3) receptor agonist enhanced the anticonvulsive property of citalopram, while l-arginine (NO precursor) alone or in combination with tropisetron blocked the protective effect of citalopram. In summary, our findings demonstrate that 5-HT(3) receptor mediates the anticonvulsant properties of low doses of citalopram, whereas it seems that the proconvulsive effect is mostly mediated through the NO pathway and can be totally blocked by NOS inhibitors. This could propose a new approach toward finding the mechanism of citalopram activity, curtailing the adverse effects of citalopram and perhaps managing the convulsions as a vicious consequence of citalopram overdose.