Strain-dependent effects of diazepam and the 5-HT2B/2C receptor antagonist SB 206553 in spontaneously hypertensive and Lewis rats tested in the elevated plus-maze

Investigating the effect of hydro-alcoholic extract of Salix aegyptiaca on anxiety in male rat

Background:

Anxiety disorders are frequently common neuropsychiatric disorders. Herbal medicines are widespread and used universal as a treatment compound for anxiety. The present study investigated the effects of hydro-alcoholic extract of Salix aegyptiaca blossom on rat behavior in the elevated plus-maze (EPM) and compared results with the effects of diazepam, as a positive control drug.

Materials and Methods:

Seventy adult male Wistar rats were divided into seven groups (N = 10). Animals received S. aegyptiaca extract (25, 50, 100 mg/kg) or Diazepam (0.3, 0.6, or 1.2 mg/kg) intraperitoneally and the control group was given the vehicle (10 ml/kg) 30 min before submitting into plus-maze test. The number of entries into the open and closed arms, the percentage of entries into the open arms of the EPM, and the time spent in the open arms were recorded.

Results:

The results revealed significant increases in percentage of entries into the open arms (P < 0.01) and in the time spent in the open arms (P < 0.01) after administration of diazepam (0.3, 0.6) and S. aegyptiaca (50, 100 mg/kg) in compare with control group. S. aegyptiaca extract has no effects on the total distance covered by animals and number of closed arms entries, whereas diazepam decreased these parameters. The locomotor activity was not significantly changed by S. aegyptiaca.

Conclusion:

Single-session administration of optimum doses of total extract of S. aegyptiaca has anxiolytic effects in rat similar to the low dose of diazepam. More research is needed for better understanding of anxiolytic properties and neurobiological mechanisms of action and probable interactions of S. aegyptiaca extract with neurotransmitters.

New therapeutic opportunities for 5-HT2C receptor ligands in neuropsychiatric disorders

The 5-HT2C receptor (R) displays a widespread distribution in the CNS and is involved in the action of 5-HT in all brain areas. Knowledge of its functional role in the CNS pathophysiology has been impaired for many years due to the lack of drugs capable of discriminating among 5-HT2R subtypes, and to a lesser extent to the 5-HT1B, 5-HT5, 5-HT6 and 5-HT7Rs. The situation has changed since the mid-90s due to the increased availability of new and selective synthesized compounds, the creation of 5-HT2C knock out mice, and the progress made in molecular biology. Many pharmacological classes of drugs including antipsychotics, antidepressants and anxiolytics display affinities toward 5-HT2CRs and new 5-HT2C ligands have been developed for various neuropsychiatric disorders. The 5-HT2CR is presumed to mediate tonic/constitutive and phasic controls on the activity of different central neurobiological networks. Preclinical data illustrate this complexity to a point that pharmaceutical companies developed either agonists or antagonists for the same disease. In order to better comprehend this complexity, this review will briefly describe the molecular pharmacology of 5-HT2CRs, as well as their cellular impacts in general, before addressing its central distribution in the mammalian brain. Thereafter, we review the preclinical efficacy of 5-HT2C ligands in numerous behavioral tests modeling human diseases, highlighting the multiple and competing actions of the 5-HT2CRs in neurobiological networks and monoaminergic systems. Notably, we will focus this evidence in the context of the physiopathology of psychiatric and neurological disorders including Parkinson's disease, levodopa-induced dyskinesia, and epilepsy.

Presynaptic CB(1) cannabinoid receptors control frontocortical serotonin and glutamate release--species differences

Both the serotonergic and endocannabinoid systems modulate frontocortical glutamate release; thus they are well positioned to participate in the pathogenesis of psychiatric disorders. With the help of fluorescent and confocal microscopy, we localized the CB(1) cannabinoid receptor (CB(1)R) in VGLUT1- and 2- (i.e. glutamatergic) and serotonin transporter- (i.e. serotonergic) -positive fibers and nerve terminals in the mouse and rat frontal cortex. CB(1)R activation by the synthetic agonists, WIN55212-2 (1 μM) and R-methanandamide (1 μM) inhibited the simultaneously measured evoked Ca(2+)-dependent release of [(14)C]glutamate and [(3)H]serotonin from frontocortical nerve terminals of Wistar rats, in a fashion sensitive to the CB(1)R antagonists, O-2050 (1 μM) and LY320135 (5 μM). CB(1)R agonists also inhibited the evoked release of [(14)C]glutamate in C57BL/6J mice in a reversible fashion upon washout. Interestingly, the evoked release of [(14)C]glutamate and [(3)H]serotonin was significantly greater in the CB(1)R knockout CD-1 mice. Furthermore, CB(1)R binding experiments revealed similar frontocortical CB(1)R density in the rat and the CD-1 mouse. Still, the evoked release of [(3)H]serotonin was modulated by neither CB(1)R agonists nor antagonists in wild-type CD-1 or C57BL/6J mice. Altogether, this is the first study to demonstrate functional presynaptic CB(1)Rs in frontocortical glutamatergic and serotonergic terminals, revealing species differences.

Chronic aortic denervation decreases anxiety and impairs social memory in rats

AIMS

The present study investigates anxiety-like behaviour and social cognitive performance in rats with chronic aortic denervation.

MAIN METHODS

The aortic depressor nerve was bilaterally transected in Wistar rats, causing an almost complete disruption of baroreceptors. Bilateral aortic denervated (bAD), sham-operated (SHAM), and intact (CTRL) rats performed an elevated plus-maze test and an olfactory social memory test, one and three months after operation. Blood pressure and heart rate were monitored in all animals.

KEY FINDINGS

Systolic blood pressure, blood pressure lability and heart rate were elevated in bAD rats compared to SHAM and CTRL rats. In the elevated plus-maze test, bAD rats spent clearly more time in investigating open arms and performed more open arm entries than SHAM and CTRL rats during both testing sessions. The olfactory social memory test revealed that acquisition time during first contact with a juvenile rat did not differ between the groups of rats. The recognition time spent by SHAM and CTRL group of rats was distinctly decreased in comparison to the acquisition time, an indication of social memory. bAD rats investigated the juvenile rat during the second contact to a similar extent than during the first contact, both one and three months after denervation.

SIGNIFICANCE

These results suggest that bilateral aortic denervation induces chronic neurogenic hypertension and elevated blood pressure lability, decreases anxiety-like behaviour and deteriorates social memory in rats while acquiring of social information is not affected.

Two inbred rat strains contrasting for anxiety-related behaviors show similar levels of defensive responses to cat odor

Rodents are known to display fear-related responses when exposed to the odor of natural predators, such as cats, even when they are totally naïve to these stimuli. Based on that, a behavioral test in which rats are exposed to cat odor has been developed and proposed to model some forms of anxiety. The objective of the present study was thus to compare the LEW (Lewis) and SHR (spontaneously hypertensive rats) inbred rat strains, which display genetic differences in other classical models of anxiety, in the cat odor test. As expected, cat odor produced an increase in fear-related behaviors. However, no clear differences were found between the two strains tested. These results suggest that the type of stress experienced by LEW and SHR strains exposed to cat odor is different from that elicited by exposure to classical models of anxiety such as the elevated plus-maze, black/white box and open-field tests.

Lewis rats are more sensitive than Fischer rats to successive negative contrast, but less sensitive to the anxiolytic and appetite-stimulating effects of chlordiazepoxide

Lewis rats show greater anticipatory contrast effects than Fischer 344 rats. Specifically, relative to Fischer rats, Lewis rats exhibit greater avoidance of a saccharin cue when it predicts the future availability of a preferred sucrose reward [Grigson, P.S., Freet, C.S. The suppressive effects of sucrose and cocaine, but not lithium chloride, are greater in Lewis than in Fischer rats: evidence for the reward comparison hypothesis. Behav Neurosci 2000;114:353-363.]. Experiment 1 was designed to determine whether Lewis rats also would demonstrate greater contrast in another paradigm, successive negative contrast (SNC). The results demonstrated a tendency for greater SNC in Lewis rats and then slower recovery from the unexpected loss of reward relative to the Fischer rats. Pretreatment with the anxiolytic agent, chlordiazepoxide (CDP), effectively eliminated contrast in the Fischer rats, but served to prolong recovery from contrast in the Lewis rats. Finally, the results of Experiment 2 demonstrated that Fischer rats, but not Lewis rats, increase consumption of a 0.1 M sucrose solution following pretreatment with CDP. Together, the results show that, while both Lewis and Fischer rats demonstrate SNC, the effect is more sustained in the Lewis rats and these rats are insensitive to both the anxiolytic and the appetite-stimulating effects of CDP.

Serotonin (1A) receptor involvement in acute 3,4-methylenedioxymethamphetamine (MDMA) facilitation of social interaction in the rat

The current study assessed whether various co-administered serotonin (5-HT) receptor antagonists could prevent some of the acute behavioral effects of 3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") in rats. In the social interaction test, MDMA (5 mg/kg) significantly increased the duration of total social interaction between two conspecifics meeting for the first time. Microanalysis showed that MDMA increased adjacent lying and approach behaviours while reducing anogenital sniffing. MDMA (5 mg/kg) also caused elements of the serotonin syndrome including low body posture and piloerection. In the emergence test, MDMA significantly increased hide time and emergence latency indicating increased anxiety-like behavior. Pretreatment with the 5HT 1A receptor antagonist, WAY 100635 (1 mg/kg), prevented MDMA-induced increases in social interaction and markers of the serotonin syndrome while the 5-HT 1B receptor antagonist GR 55562 (1 mg/kg) and 5-HT 2A receptor antagonist ketanserin (1 mg/kg) were ineffective. The 5-HT 2B/2C receptor antagonist, SB 206553 (2 mg/kg), prevented MDMA-induced prosocial effects but caused pronounced thigmotaxis (hyperactivity at the periphery of the testing chamber). The anxiogenic effect of MDMA on the emergence test was not prevented by pretreatment with any of the 5-HT receptor antagonists tested. These results indicate that prosocial effect of MDMA may involve 5-HT 1A and possibly 5-HT 2B/2C receptors. In contrast, MDMA-induced generalised anxiety, as measured by the emergence test, seems unlikely to involve the 5-HT 1A, 5-HT 1B or 5-HT 2A, 5-HT 2B or 5-HT 2C receptors.

Effects of ethanol on locomotor and anxiety-like behaviors and the acquisition of ethanol intake in Lewis and spontaneously hypertensive rats

The purpose of the present study was to investigate whether Lewis (LEW) and spontaneously hypertensive rats (SHR), characterized in numerous behavioral tests as strains with high-anxiety and low-anxiety, respectively, could differ in their sensitivity to the effects of ethanol in the elevated plus maze (EPM) and the open field (OF), two classical models of anxiety/emotionality, as well as in the acquisition of ethanol drinking behavior. It was also of interest to examine the relationship between sweet and bitter fluids preference and ethanol intake. SHR and LEW rats were given saline or ethanol injections (0.6 or 1.2 g/kg, ip.) and tested in the EPM and OF. Subsequently the same animals were given continuous free choice between water and ethanol solution (2-8%). Additional groups of animals were exposed to a free-choice regimen between saccharin (0.002-0.09%) or quinine (0.0001-0.0015%) and water. The low dose of ethanol (0.6 g/kg) induced anxiolytic-like effects and intensive locomotor activation mainly in SHR rats tested in the OF arena. Overall, LEW counterparts were unaffected in OF test. In oral self-administration paradigm, SHR rats consumed significantly more ethanol than LEW rats. Concerning other solutions, SHR rats consumed large amounts of saccharin compared with LEW rats. These data indicate that the SHR preference for ethanol intake may be positively related to their differential sensitivity to the anxiolytic/stimulant effects of ethanol and to the sensitivity of this strain for saccharin reinforcement. In addition, these findings provide evidence that the SHR strain may represent a useful genetic and pharmacological tool to investigate ethanol drinking traits.

Genetic differences in the elevated plus-maze persist after first exposure of inbred rats to the test apparatus

The elevated plus-maze (EPM) is an anxiety model thought to assess different types of emotional states depending on whether or not the animals have been previously exposed to the test apparatus. Accordingly, benzodiazepine-treated rodents generally differ from controls in the first but not in the second EPM trial. Inbred Lewis and SHR rats of both sexes (N=10) were submitted twice (test and retest) to the EPM with a 24 h interval between trials. Overall strain differences (Lewis<SHR) were observed in both males and females concerning anxiety-related measures (time spent and percent of entries in the open arms) regardless of previous maze experience. Moreover, prior exposure to the test apparatus produced an overall decrease in the approach towards the open arms in both strains and sexes. The fact that genetic differences did not diminish or disappear in the second trial, suggests that test and retest in the EPM are likely to share some common emotional components and that differences between naïve LEW and SHR rats are not similar to those observed between control and benzodiazepine-treated animals.

Discriminative stimulus effects of m-chlorophenylpiperazine as a model of the role of serotonin receptors in anxiety

Serotonin is known to play a role in anxiety. The roles of serotonin reuptake and 5-HT1A receptors have been well characterized, but the contribution of other serotonin receptor subtypes is not as clear. 1-(3-Chlorophenyl)-piperazine (mCPP), which binds non-selectively to a wide range of serotonin receptors, has often been used to produce anxiety in humans and in animal models. Because functional assays indicate that mCPP is significantly more potent at 5-HT2C receptors, it may serve as a tool to investigate the contribution of 5-HT2C receptors to anxiety. This paper reviews the results of behavioral tests using mCPP, including the drug discrimination assay, to model anxiety. Although the discriminative stimulus effects of mCPP do not seem to be a useful screen for general anxiolytics, they do seem to be useful for characterization of the contribution of 5-HT1B and 5-HT2C receptors to the mediation of anxiety-like behaviors.

Differential anxiolytic effect of enalapril and losartan in normotensive and renal hypertensive rats

The effect of angiotensin-converting enzyme (ACE) inhibitor enalapril (EPL) (2 and 4 mg/kg), angiotensin (AT) II receptor antagonist losartan (LRN) (5 and 10 mg/kg), and anxiolytic drug diazepam (DZP) (0.5 mg/kg) on anxiety parameters were evaluated in experimentally induced renal hypertensive rats (RHR). Renal hypertension was induced in Wistar strain male albino rats weighing 200-250 g by following the method of Goldblatt. The animals having systolic blood pressure more than 180-210 mm Hg were subjected to open-field exploratory behaviour, elevated plus maze behaviour, and social interaction tests of anxiety. The RHR showed hyperactivity in open-field behaviour and anxiogenicity in elevated plus maze and social interaction tests. Losartan (5 and 10 mg/kg) and DZP (0.5 mg/kg) significantly attenuated the hyperactivity and anxiogenic behaviour in experimentally induced hypertensive rats and induced anxiolysis in normotensive rats (NTR). Enalapril reversed the hypertension-induced alteration only at higher dose (4 mg/kg) and failed to show any effect in NTR. It can be concluded that renin angiotensin aldosterone system (RAAS) has a significant role on behaviour, and LRN has shown better effect in reversing the hyperactivity and anxiogenicity in the experimentally induced hypertensive rats, indicating a possible role of AT receptor in the mediation of anxiolysis.

Wistar-Kyoto rats are sensitive to the hypolocomotor and anxiogenic effects of mCPP

Wistar-Kyoto (WKY) rats, but not spontaneously hypertensive rats (SHRs), are insensitive to the acute hypolocomotor and anxiogenic effects of the selective serotonin reuptake inhibitors (SSRIs), fluoxetine and citalopram, in elevated plus-maze tests. Several observations suggest that these strain-dependent effects involve postsynaptic serotonin (5-HT) receptors. In keeping with the recent finding that citalopram-elicited anxiety in Sprague-Dawley rats, as measured in the social interaction test, involves 5-HT(2C) receptor stimulation, we tested the hypothesis that this receptor is prone to subsensitivity in WKY rats, compared to SHRs. Thus, we first examined the acute behavioural effects of the 5-HT(2B/2C) receptor agonist, mCPP, in SHRs and WKY rats exposed to an elevated plus-maze; in addition, because WKY rats display anxiety and hypolocomotion, compared to SHRs, we next used the 5-HT(2B/2C) receptor antagonist, SB-206553, to test whether 5-HT(2C) receptors are tonically active in WKY rats. The results confirmed that WKY rats and SHRs differ in locomotor activity and anxiety-related behaviours, and showed that pretreatment with mCPP decreased locomotion in both strains. In contrast, the strains differed with respect to mCPP-elicited anxiety, as WKY rats were sensitive to the lowest dose of mCPP, while only the highest dose increased anxiety in SHRs. Finally, elevated plus-maze behaviours of SHRs and WKY rats were found to be insensitive to SB-206553 pretreatment. This study therefore suggests that 5-HT(2C) receptors (at least those which mediate mCPP-induced hypolocomotion and anxiety) are neither desensitized nor tonically active in WKY rats.