5-HT1A receptors in the dorsal hippocampus mediate the anxiogenic effect induced by the stimulation of 5-HT neurons in the median raphe nucleus

We evaluated the involvement of dorsal hippocampus (DH) 5-HT1A receptors in the mediation of the behavioral effects caused by the pharmacological manipulation of 5-HT neurons in the median raphe nucleus (MRN). To this end, we used the rat elevated T-maze test of anxiety. The results showed that intra-DH injection of the 5-HT1A/7 agonist 8-OH-DPAT facilitated inhibitory avoidance, an anxiogenic effect, without affecting escape. Microinjection of the 5-HT1A antagonist WAY-100635 was ineffective. In the elevated T-maze, inhibitory avoidance and escape have been related to generalized anxiety and panic disorders, respectively. Intra-MRN administration of the excitatory aminoacid kainic acid, which non-selectively stimulates 5-HT neurons in this brain area facilitated inhibitory avoidance and impaired escape performance, but also affected locomotion. Intra-MRN injection of WAY-100635, which has a disinhibitory effect on the activity of 5-HT neurons in this midbrain area, only facilitated inhibitory avoidance. Preadministration of WAY-100635 into the DH blocked the behavioral effect of intra-MRN injection of WAY-100635, but not of kainic acid. These results indicate that DH 5-HT1A receptors mediate the anxiogenic effect induced by the selective stimulation of 5-HT neurons in the MRN. (c) 2007 Elsevier B.V. and ECNP. All rights reserved.

Quercetin does not alter lipopolysaccharide-induced fever in rats

Fever is considered an important component of the acute phase response of the body in defence against invading organisms such as bacteria. Quercetin, an important representative of the flavonoid class, has been extensively studied as an anti-inflammatory agent. In the present study, we investigated the effect of quercetin, administered orally (5, 25 and 50 mg kg(-1)) or intraperitoneally (50 mg kg(-1)), on the febrile response induced by either intraperitoneally (50 mu g kg(-1)) or intravenously (5 mu g kg(-1)) injected lipopolysaccharide (LPS from Escherichia coli) in rats. In contrast with the well known anti-inflammatory activity of quercetin, the results demonstrate that quercetin, at the doses used, did not alter the fever induced by LPS, regardless of the route of administration.

Effects of reversible inactivation of the dorsal hippocampus on the behavioral and cardiovascular responses to an aversive conditioned context

In rats, conditioned fear to context causes freezing immobility and cardiovascular changes. The dorsal hippocampus (DH) has a critical role in several memory processes, including conditioning fear to contextual information. To explore a possible involvement of the DH in contextual fear conditioning-evoked cardiovascular (mean arterial pressure and heart rate increases) and behavioral (freezing) responses, DH synaptic transmission was temporarily inhibited by bilateral microinjections of 500 nl of the nonselective synapse blocker, cobalt chloride (COCl2, 1 mmol/l), at different periods of the experimental procedure. During re-exposure to the foot shock chamber in which conditioning had taken place, bilateral DH inhibition 10 min before the conditioning session had no effect on either behavioral or cardiovascular responses. Bilateral DH inhibition immediately after the conditioning session (110 min) decreased both behavioral and cardiovascular responses during the context test. Finally, 48 h after the conditioning session, bilateral DH inhibition 10 min before re-exposure to the foot shock chamber significantly reduced cardiovascular responses but not freezing responses. These results suggest that contextual fear conditioning acquisition does not depend on the DH. This structure, however, is crucial for the consolidation of contextual fear. Moreover, although the DH appears to be less important for the behavioral (freezing) changes induced by re-exposure to the aversive conditioned context, it may play an important role on the cardiovascular responses generated by this model.

Cannabidiol inhibits the hyperphagia induced by cannabinoid-1 or serotonin-1A receptor agonists

Delta 9-THC is a component of Cannabis sativa that increases food intake in animals and humans, an effect prevented by selective CB1 receptor antagonists. Cannabidiol (CBD) is another constituent of this plant that promotes several opposite neuropharmacological effects compared to Delta 9-THC. CBD mechanisms of action are still not clear, but under specific experimental conditions it can antagonize the effects of cannabinoid agonists, block the reuptake of anandamide and act as an agonist of 5-HT1A receptors. Since both the cannabinoid and serotoninergic systems have been implicated in food intake control, the aim of the present work was to investigate the effects caused by CBD on hyperphagia induced by agonists of CB1 or 5-HT1A receptors. Fed or fasted Wistar rats received intraperitoneal (i.p.) injections of CBD (1, 10 and 20 mg/kg) and food intake was measured 30 min later for 1 h. Moreover, additional fed or fasted groups received, after pretreatment with CBD (20 mg/kg) or vehicle, i.p. administration of vehicle, a CBI receptor agonist WIN55,212-2 (2 mg/kg) or a 5-HT1A receptor agonist 8-OH-DPAT (1 mg/kg) and were submitted to the food intake test for 1 h. CBD by itself did not change food intake in fed or fasted rats. However, it prevented the hyperphagic effects induced by WIN55,212-2 or 8-OH-DPAT. These results show that CBD can interfere with food intake changes induced by a CB1 or 5-HT1A receptor agonist, suggesting that its role as a possible food intake regulator should be further investigate. (C) 2011 Elsevier Inc. All rights reserved.

Role of complement C5a in mechanical inflammatory hypernociceptio: potential use of C5a receptor antagonists to control inflammatory pain

particularly neutrophil chemoattraction. Herein, the role of C5a in the genesis of inflammatory hypernociception was investigated in rats and mice using the specific C5a receptor antagonist PMX53 (AcF-[OP(D-Cha)WR]). Experimental approach: Mechanical hypernociception was evaluated with a modification of the Randall-Selitto test in rats and electronic pressure meter paw test in mice. Cytokines were measured by ELISA and neutrophil migration was determined by myeloperoxidase activity. Key results: Local pretreatment of rats with PMX53 (60-180 mg per paw) inhibited zymosan-, carrageenan-, lipopolysaccharide (LPS)- and antigen-induced hypernociception. These effects were associated with C5a receptor blockade since PMX53 also inhibited the hypernociception induced by zymosan- activated serum and C5a but not by the direct-acting hypernociceptive mediators, prostaglandin E-2 and dopamine. Underlying the C5a hypernociceptive mechanisms, PMX53 did not alter the cytokine release induced by inflammatory stimuli. However, PMX53 inhibited cytokine-induced hypernociception. PMX53 also inhibited the recruitment of neutrophils induced by zymosan but not by carrageenan or LPS, indicating an involvement of neutrophils in the hypernociceptive effect of C5a. Furthermore, the C5a-induced hypernociception was reduced in neutrophil-depleted rats. Extending these findings in rats, blocking C5a receptors also reduced zymosan- induced joint hypernociception in mice. Conclusions and implications: These results suggest that C5a is an important inflammatory hypernociceptive mediator, acting by a mechanism independent of hypernociceptive cytokine release, but dependent on the presence of neutrophils. Therefore, we suggest that inhibiting the action of C5a has therapeutic potential in the control of inflammatory pain.

Blockade of the chemokine receptor CXCR2 ameliorates adjuvant-induced arthritis in rats

Background and purpose: Chemokine receptors CXCR1 and CXCR2 may mediate influx of neutrophils in models of acute and chronic inflammation. The potential benefits of oral administration of a CXCR1/2 inhibitor, DF 2162, in adjuvant-induced polyarthritis (AIA) were investigated. Experimental approach: A model of AIA in rats was used to compare the therapeutic effects of the treatment with DF2162, anti-TNF or anti-CINC-1 antibodies on joint inflammation and local production of cytokines and chemokines. Key results: DF2162 prevented chemotaxis of rat and human neutrophils induced by chemokines acting on CXCR1/2. DF2162 was orally bioavailable and metabolized to two major metabolites. Only metabolite 1 retained CXCR1/2 blocking activity. Treatment with DF2162 ( 15 mg kg(-1), twice daily) or metabolite 1, but not metabolite 2, starting on day 10 after arthritis induction diminished histological score, the increase in paw volume, neutrophil influx and local production of TNF, IL-1 beta, CCL2 and CCL5. The effects of DF2162 were similar to those of anti-TNF, and more effective than those of anti-CINC-1, antibodies. DF2162 prevented disease progression even when started 13 days after arthritis induction. Conclusions and implications: DF 2162, a novel orally-active non-competitive allosteric inhibitor of CXCR1 and CXCR2, significantly ameliorates AIA in rats, an effect quantitatively and qualitatively similar to those of anti-TNF antibody treatment. These findings highlight the contribution of CXCR2 in the pathophysiology of AIA and suggest that blockade of CXCR1/2 may be a valid therapeutic target for further studies aiming at the development of new drugs for treatment of rheumatoid arthritis.

Dose-dependent beneficial hemodynamic effects of BAY 41-2272 in a canine model of acute pulmonary thromboembolism

The current therapy of acute pulmonary embolism is focused on removing the mechanical obstruction of the pulmonary vessels. However, accumulating evidence suggests that pulmonary vasoconstriction drives many of the hemodynamic changes found in this condition. We examined the effects of stimulation of soluble guanylate cyclase with BAY 41-2272 (5-Cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine) in an anesthetized dog model of acute pulmonary embolism. Hemodynamic and arterial blood gas evaluations were performed in non-embolized dogs treated with vehicle (N = 5), and in embolized dogs (intravenous injections of microspheres) that received BAY 41-2272 intravenously in doses of 0.03, 0.1, 0.3, and 1 mg/kg/h or vehicle (1 ml/kg/h of 1.13% ethanol in saline, volume/volume). Plasma cGMP and thiobarbituric acid reactive substances concentrations were determined using a commercial enzyme immunoassay and a fluorometric method, respectively. The infusion of BAY 41-2272 resulted in a decrease in pulmonary artery pressure by similar to 29%, and in pulmonary vascular resistance by similar to 46% of the respective increases induced by lung embolization (both P<0.05). While the higher doses of BAY 41-2272 produced no additional effects on the pulmonary circulation, they caused significant arterial hypotension and reduction in systemic vascular resistance (both P<0.05). Although BAY 41-2272 increased cGMP concentrations (P<0.05), it did not affect the hypoxemia and the increased oxidative stress caused by lung embolization. These results suggest that stimulation of soluble guanylate cyclase with low (but not high) doses of BAY 41-2272 produces selective pulmonary vasodilation during acute pulmonary embolism. The dose-dependent systemic effects produced by BAY 41-2272, however, may limit its usefulness in larger doses. (C) 2007 Elsevier B.V. All rights reserved.

Cardiovascular effects of L-glutamate injected in the medial prefrontal cortex of spontaneously hypertensive rats

We have previously reported that L-glutamate (L-glu) injected into the ventral portion of medial prefrontal cortex (vMPFC) of unanesthetized normotensive Wistar rats elicited cardiovascular responses. In the present study we investigated whether the spontaneously hypertensive rat (SHR) exhibit abnormal cardiovascular responses after L-glu microinjection in the vMPFC. Microinjections of L-glu (3, 9, 27, 81 or 150 nmol/200 nl) caused long-lasting dose-related depressor and bradycardiac responses in unanesthetized SHR (n = 6, each dose). Pressor and tachycardiac responses were evoked after the injection of 81 nmol of L-glu in the vMPFC of normotensive Wistar rats (n=6). Systemic pretreatment with the betal-adrenoceptor antagonist atenolol (1.5 mg/kg, i.v.) had no effect on L-glu cardiovascular responses evoked in the SHR (n=5). However, the treatment with the muscarinic antagonist homatropine methyl bromide (I mg/kg, i.v.) blocked the bradycardiac response to L-glu, without significant effects on depressor response evoked by L-glu in the SHR (n = 5). These results indicate that the bradycardiac response to the injection of L-glu injection in the vMPFC is due to activation of the parasympathetic system and not to inhibition of the cardiac sympathetic input. In conclusion, results indicate opposite cardiovascular responses when L-glu was microinjected in the vMPFC of unanesthetized SHR or normotensive. The bradycardiac response observed in the SHR was due to parasympathetic activation and was not affected by pharmacological blockade of the cardiac sympathetic output. (C) 2007 Elsevier B.V. All rights reserved.

Involvement of dorsal raphe nucleus and dorsal periaqueductal gray 5-HT receptors in the modulation of mouse defensive behaviors

Previous findings point to the involvement of the dorsal raphe nucleus (DRN) and dorsal periaqueductal gray (dPAG) serotonergic receptors in the mediation of defensive responses that are associated with specific subtypes of anxiety disorders. These studies have mostly been conducted with rats tested in the elevated T-maze, an experimental model of anxiety that was developed to allow the measurement, in the same animal, of two behaviors mentioned: inhibitory avoidance and one-way escape. Such behavioral responses have been respectively related to generalized anxiety disorder (GAD) and panic disorder (PD). In order to assess the generality of these findings, in the current study we investigated the effects of the injection of 5-HT-related drugs into the DRN and dPAG of another rodent species, mouse, on the mouse defense test battery (MDTB), a test of a range of defensive behaviors to an unconditioned threat, a predator. Male CD-1 mice were tested in the MDTB after intra-DRN administration of the 5-HT(1A) receptor antagonist WAY-100635 or after intra-dPAG injection of two serotonergic agonists, the 5-HT1A receptor agonist 8-OH-DPAT and the 5-HT(2A/2C) receptor agonist DOI. Intra-DRN injection of WAY-100635 did not change behavioral responses of mice confronted with a rat in the MDTB. In the dPAG, both 8-OH-DPAT and DOI consistently impaired mouse escape behavior assessed in the MDTB. Intra-dPAG infusion of 8-OH-DPAT also decreased measures of mouse risk assessment in the rat exposure test. In conclusion, the current findings are in partial agreement with previous results obtained with rats tested in the elevated T-maze. Although there is a high level of similarity between the behavioral effects obtained in rats (elevated T-maze) and mice (MDTB and RET) with the infusion of 5-HT agonists into the dPAG, the same is not true regarding the effects of blockade of DRN 5-HT(1A) receptors in these rodent species. These data suggest that there may be differences between mice and rats regarding the involvement of the DRN in the mediation of defensive behaviors. (C) 2010 Elsevier B.V. and ECNP. All rights reserved.

Both alpha 1 and alpha 2-adrenoceptors mediate the cardiovascular responses to noradrenaline microinjected into the bed nucleus of the stria terminal of rats

Background and purpose: We have previously shown that noradrenaline microinjected into the bed nucleus of stria terminalis (BST) elicited pressor and bradycardiac responses in unanaesthetized rats. In the present study, we investigated the subtype of adrenoceptors that mediates the cardiovascular response to noradrenaline microinjection into the BST. Experimental approach: Cardiovascular responses following noradrenaline microinjection into the BST of male Wistar rats were studied before and after BST pretreatment with different doses of the selective alpha(1)-adrenoceptor antagonist WB4101, the alpha(2)-adrenoceptor antagonist RX821002, the combination of WB4101 and RX821002, the non-selective beta-adrenoceptor antagonist propranolol, the selective beta(1)-adrenoceptor antagonist CGP20712 or the selective beta(2)-adrenoceptor antagonist ICI118,551. Key results: Noradrenaline microinjected into the BST of unanaesthetized rats caused pressor and bradycardiac responses. Pretreatment of the BST with different doses of either WB4101 or RX821002 only partially reduced the response to noradrenaline. However, the response to noradrenaline was blocked when WB4101 and RX821002 were combined. Pretreatment with this combination also shifted the resulting dose-effect curve to the left, clearly showing a potentiating effect of this antagonist combination. Pretreatment with different doses of either propranolol or CGP20712 increased the cardiovascular responses to noradrenaline microinjected into the BST. Pretreatment with ICI118,551 did not affect cardiovascular responses to noradrenaline. Conclusion and implications: The present results indicate that alpha(1) and alpha(2)-adrenoceptors mediate the cardiovascular responses to noradrenaline microinjected into the BST. In addition, they point to an inhibitory role played by the activation of local beta(1)-adrenoceptors in the cardiovascular response to noradrenaline microinjected into the BST.

Aripiprazole, an atypical antipsychotic prevents the motor hyperactivity induced by psychotomimetics, and psyphostimulants in mice

Aripiprazole is an atypical antipsychotic that acts as a partial agonist at the dopamine D-2 receptor. It has been mainly investigated in dopamine-based models of schizophrenia, while its effects on glutamate-based paradigms have remained to be further characterized. Due to its unique mechanism of action, aripiprazole has also been considered as a replacement medication for psychostimulant abuse. Thus, in the present study we tested the hypothesis that aripiprazole would prevent the motor hyperactivity induced by psychostimulant and psychotomimetic drugs that act either by dopaminergic or glutamatergic mechanisms. Male Swiss mice received injections of aripiprazole (0.1-1 mg/kg) followed by drugs that enhance the dopamine-mediated neurotransmission, amphetamine (3 mg/kg) or cocaine (5 mg/kg), or by glutamate NMDA-receptor antagonists, ketamine (60 mg/kg) or MK-801 (0.4 mg/kg). Independent groups also received aripiprazole (0.1-1 mg/kg) or haloperidol (0.5 mg/kg) and were tested for catalepsy. All doses of aripiprazole were effective in preventing the motor stimulant effects of amphetamine and cocaine. Moreover, the higher dose also prevented the effects of ketamine and MK-801. The present study reports the effects of aripiprazole in dopaminergic and glutamatergic models predictive of antipsychotic activity, suggesting that both may be useful for screening novel partial agonists with antipsychotic activity. It also shows that aripiprazole may prevent the acute effects of psychostimulant drugs without significant motor impairment. C) 2007 Elsevier B.V. All rights reserved.

Nitric oxide-mediated anxiolytic-like and antidepressant-like effects in animal models of anxiety and depression

The effects of microinjection of the nitric oxide (NO) precursor L-arginine (L-Arg), the NO synthase (NOS) inhibitors N-methyl-L-arginine (L-NAME) and 7-nitroindazole (7-NI), and the cyclic guanosine 3`,5`-monophosphate (cGMP) analog 8-Br-cGMP into the dorsal raphe nucleus (DRN) were assessed in rats using the elevated plus maze (EPM) and the forced swim test (FST). L-Arg (100 and 200 nmol) produced an anxiolytic-like effect in the EPM. 8-Br-cGMP (25 and 50 nmol) dose-dependently increased locomotor activity. In the FST, antidepressant-like effects were produced by L-Arg (50 and 100 nmol) and 8-Br-cGMP (12.5 and 25 nmol). Dual effects were observed with NOS inhibitors L-NAME and 7-NI in both the EPM and FST. While low doses of L-NAME (25 nmol) or 7-NI (1 nmol) induced a selective increase in EPM open arm exploration and a decrease in immobility time in the FST, high doses (L-NAME 400 nmol, 7-NI 10 nmol) decreased locomotor activity. These results show that interference with NO-mediated neurotransmission in the DRN induced significant and complex motor and emotional effects. Further studies are needed to elucidate the mechanisms involved in these effects. (C) 2007 Elsevier Inc. All rights reserved.

15d-prostaglandin J(2) inhibits inflammatory hypernociception: Involvement of peripheral opioid receptor

The 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) is an endogenous ligand of peroxisome proliferator-activated receptors gamma (PPAR-gamma) and is now recognized as a potent anti-inflammatory mediator. However, information regarding the influence of 15d-PGJ(2) on inflammatory pain is still unknown. In this study, we evaluated the effect of 15d-PGJ(2) upon inflammatory hypernociception and the mechanisms involved in this effect. We observed that intraplantar administration of 15d-PGJ(2) (30-300 ng/paw) inhibits the mechanical hypernociception induced by both carrageenan (100 mu g/paw) and the directly acting hypernociceptive mediator, prostaglandin E-2 (PGE(2)). Moreover, 15d-PGJ(2) [100 ng/temporomandibular joint (TMJ)] inhibits formalininduced TMJ hypernociception. On the other hand, the direct administration of 15d-PGJ(2) into the dorsal root ganglion was ineffective in blocking PGE(2)- induced hypernociception. In addition, the 15d-PGJ(2) antinociceptive effect was enhanced by the increase of macrophage population in paw tissue due to local injection of thioglycollate, suggesting the involvement of these cells on the 15d-PGJ(2)-antinociceptive effect. Moreover, the antinociceptive effect of 15d-PGJ(2) was also blocked by naloxone and by the PPAR-gamma antagonist 2-chloro-5-nitro-N-phenylbenzamide (GW9662), suggesting the involvement of peripheral opioids and PPAR-gamma receptor in the process. Similar to opioids, the 15d-PGJ(2) antinociceptive action depends on the nitric oxide/cGMP/protein kinase G (PKG)/K-ATP(+) channel pathway because it was prevented by the pretreatment with the inhibitors of nitric-oxide synthase (N-G-monomethyl-L-arginine acetate), guanylate cyclase] 1H-(1,2,4)-oxadiazolo(4,2-alpha) quinoxalin-1- one[, PKG [indolo[2,3-a]pyrrolo[3,4-c]carbazole aglycone (KT5823)], or with the ATP-sensitive potassium channel blocker glibenclamide. Taken together, these results demonstrate for the first time that 15d-PGJ(2) inhibits inflammatory hypernociception via PPAR-gamma activation. This effect seems to be dependent on endogenous opioids and local macrophages.

Effects of intracisternal administration of cannabidiol on the cardiovascular and behavioral responses to acute restraint stress

Systemic administration of cannabidiol (CBD), a non-psychotomimetic compound from Cannabis sativa, attenuates the cardiovascular and behavioral responses to restraint stress. Although the brain structures related to CBD effects are not entirely known, they could involve brainstem structures responsible for cardiovascular control. Therefore, to investigate this possibility the present study verified the effects of CBD (15.30 and 60 nmol) injected into the cisterna magna on the autonomic and behavioral changes induced by acute restraint stress. During exposure to restraint stress (1 h) there was a significant increase in mean arterial pressure (MAP) and heart rate (HR). Also, 24 h later the animals showed a decreased percentage of entries onto the open arms of the elevated plus-maze. These effects were attenuated by CBD (30 nmol). The drug had no effect on MAP and HR baseline values. These results indicate that intracisternal administration of CBD can attenuate autonomic responses to stress. However, since CBD decreased the anxiogenic consequences of restraint stress, it is possible that the drug is also acting on forebrain structures. (C) 2011 Elsevier Inc. All rights reserved.

Antihypertensive effects exerted by enalapril in mild to moderate hypertension are not associated with changes in the circulating levels of nitric oxide-related markers

The antihypertensive effects of angiotensin-converting enzyme inhibitors (ACEi) are explained, at least in part, by enhanced bradykinin-dependent nitric oxide (NO) formation and decreased angiotensin II-induced oxidative stress and vasoconstriction. We examined for the first time whether treatment with enalapril increases the plasma levels of markers of NO formation and decreases oxidative stress in mild to moderate hypertensive patients. Eighteen untreated hypertensive patients were treated with enalapril 10 mg/day (n = 10) or 20 mg/day (n = 8) for 60 days. Eighteen normotensive healthy controls were followed for the same period. Venous blood samples were collected at baseline and after 30/60 days of treatment with enalapril. Plasma NOx (nitrites + nitrates) concentrations were determined by using the Griess reaction. Plasma nitrite and whole blood nitrite concentrations were determined by using an ozone-based chemiluminescence assay. Plasma thiobarbituric acid-reactive species (TBARS) and 8-isoprostane concentrations were determined by a fluorimetric method and by ELISA, respectively. Treatment with enalapril decreased blood pressure in hypertensive patients. However, we found no significant changes in plasma NOx, nitrite, whole blood nitrite, and in the levels of markers of oxidative stress in both normotensive controls and hypertensive patients treated with enalapril. Our data show that enalapril 10-20 mg/day does not affect the concentrations of relevant markers of NO formation or markers of oxidative stress in mild to moderately hypertensive subjects, despite satisfactory blood pressure control. Our findings do not rule out the possibility that ACEi may produce such effects in more severely hypertensive patients treated with higher doses of ACEi.