Clonidine potentiates the effects of 5-HT1A, 5-HT1B and 5-HT2A/2C antagonists and 8-OH-DPAT in the mouse forced swimming test

Are Noradrenergic Transmission Reducing Drugs Antidepressants?

Major depressive disorder (MDD) remains a significant public health problem worldwide, and revised treatment strategies are therefore urgently needed, including the creation of novel antidepressant compounds or using existing molecular entities in new ways. Etiologic theories of MDD from decades ago have suggested that synaptic deficiencies of monoaminergic neurotransmitters play a causative role in this neuropsychiatric disorder, and that boosting monoamines with drugs such as SSRIs, SNRIs, TCAs, and MAOIs has antidepressant effects and in some individuals can even induce hypomania or mania. While other factors, such as various intracellular molecular pathways and hippocampal neurogenesis, undoubtedly also play a role in MDD, monoaminergic boosting drugs nonetheless have clearly demonstrated antidepressant properties. There is also, however, a body of studies in the preclinical literature suggesting that monoaminergic transmission reducing drugs, including noradrenergic ones, also have antidepressant-like behavioral properties in rodents. Given that there is increasing evidence that the monoamines have u-shaped or Janus-faced dose-response properties, in which a mid-range value is "optimal" in a variety of behavioral and physiological processes, it is plausible that either too much or too little synaptic norepinephrine in key circuits may exacerbate MDD in some individuals. Here we briefly review rodent depression-related behavioral data, focusing on the forced swim test, from three major classes of noradrenergic transmission reducing drugs (alpha2 agonists, beta blockers, alpha1 antagonists), and find much support for the hypothesis that they have antidepressant-like properties. Whether these drugs are antidepressants in human subjects remains to be determined.

Synergistic Action of Sodium Selenite with some Antidepressants and Diazepam in Mice

BACKGROUND

The antidepressant and anxiolytic effects of selenium (Se) have been proven in many studies. This work was aimed at confirming these activities of its inorganic form-sodium selenite-and examining the possible synergy of action with antidepressants and diazepam.

METHODS

The antidepressant- and anxiolytic-like activity of Se was assessed using forced swim tests (FSTs) and elevated plus-maze test (EPMs). Spontaneous locomotor activity was measured using photoresistor actimeters. The experiments were conducted on male Albino Swiss mice.

RESULTS

Sodium selenite (0.5 mg/kg) reduced the immobility time in the FSTs and extended time spent in the open arms of EPMs without affecting locomotor activity The combined administration of Se at an ineffective dose (0.25 mg/kg) together with imipramine (15 mg/kg), fluoxetine (5 mg/kg), tianeptine (10 mg/kg), but not with reboxetine (2.5 mg/kg), resulted in a reduction of immobility time in FSTs, and with a threshold dose of diazepam (0.25 mg/kg) led to the prolongation of time spent in the open arms of the EPM. Moreover, the antidepressant-like effect of Se (0.5 mg/kg) was significantly reduced by pretreatment with p-chlorophenylalanine (100 mg/kg).

CONCLUSIONS

The results may indicate the participation of serotonergic transmission to antidepressant action of Se and GABA-ergic transmission to its anxiolytic effects.

Antidepressant-like activity of venlafaxine and clonidine in mice exposed to single prolonged stress - A model of post-traumatic stress disorder. Pharmacodynamic and molecular docking studies

BACKGROUND

Post-traumatic stress disorder (PTSD) is a growing issue worldwide characterized by stress and anxiety in response to re-experiencing traumatic events which strongly impair patient's quality of life and social functions. Available antidepressant and anxiolytic drugs are not efficacious in the majority of treated individuals. This necessitates a significant medical demand to develop novel therapeutic strategies for PTSD.

EXPERIMENTAL APPROACH

Animal model of PTSD was induced using a mouse single prolonged stress protocol (mSPS). To assess the activity of venlafaxine and clonidine, the forced swim test (FST) was used repeatedly 24h, 3days, 8days, 15days and 25days after mSPS. To get insight into a possible mechanism of anti-PTSD action, molecular docking procedure was utilized for the most active drug. This in silico part comprised molecular docking of enantiomers of venlafaxine to human transporters for serotonin (hSERT), norepinephrine (hNET) and dopamine (hDAT).

KEY RESULTS

In mSPS-subjected mice FST revealed the effectiveness of venlafaxine, however in non SPS-subjected mice both venlafaxine and clonidine were active. Molecular docking studies indicated that the affinity of venlafaxine to monoamine transporters is growing in the following rank order: hDAT<hNET<hSERT. Both venlafaxine enantiomers present different selectivity and binding mode.

CONCLUSION AND IMPLICATIONS

Venlafaxine but not clonidine was effective in an animal model of PTSD. Its mechanism of action, i.e., SERT, NET and DAT inhibition indicates potential drug targets for PTSD treatment. We expect that these results will contribute to a broader application of VLX in PTSD patients.

Investigation of allyphenyline efficacy in the treatment of alcohol withdrawal symptoms

We have recently demonstrated that allyphenyline, behaving as α2C-adrenoceptor/serotonin 5-HT1A receptor agonist and α2A-adrenoceptor antagonist, in mice enhanced morphine analgesia, attenuated morphine withdrawal symptoms, showed significant antidepressant-like activity and was devoid of sedative side effects. Opioid and alcohol withdrawal shares several common neurobiological and molecular mechanisms. Therefore, in this study we expanded our analysis of the pharmacological properties of allyphenyline by investigating its ability to prevent the expression of somatic withdrawal signs, anxiety-like behavior and hyperlocomotion associated with chronic ethanol intoxication. Rats were subjected to induction of ethanol dependence via repeated daily intragastric ethanol (20%) administration for 4 consecutive days. Twelve hours after the last alcohol administration, somatic alcohol withdrawal signs were scored. Results revealed a significant expression of physical withdrawal signs that were not affected by intraperitoneal (i.p.) administration of allyphenyline at the doses of 0.05, 0.275 and 0.5 mg/kg. In contrast, allyphenyline (0.05 and 0.275 mg/kg i.p.) significantly reduced hyperanxiety-like behavior observed 6 days after alcohol intoxication as measured using the defensive burying test. Allyphenyline also reduced open field hyperlocomotor activity associated with alcohol withdrawal. Notably, the anxiolytic effect of the compound, as well as the already reported antidepressant action, was observed at very low doses, suggesting the involvement of its α2C-adrenoceptor/serotonin 5-HT1A receptor agonism. Therefore, the present investigation suggests that allyphenyline might represent an interesting pharmacological tool to investigate the potential of compounds exhibiting α2C-adrenoceptor/serotonin 5-HT1A receptor agonism and α2A-adrenoceptor antagonism in the treatment of hyperanxiety and hyperlocomotion occurring during alcohol withdrawal in dependent subjects.

Head movement: a novel serotonin-sensitive behavioral endpoint for tail suspension test analysis

The tail suspension test (TST) as an antidepressant and depression-related behavior screen, has many advantages over the forced swim test (FST) in terms of procedural simplicity and consistent SSRI response. However, the FST has traditionally offered more specific neuromodulatory information by differentiating between serotonin (5-HT) and norepinephrine sensitive behavior categories. Head movement is a newly characterized behavior endpoint in the FST and TST with a selective 5-HT sensitivity. In this investigation, we show that the baseline and drug response profile of head movement previously found in the 129S6 strain of mice (Lockridge et al., 2010) is reproducible in the C57 strain. Head movement is inversely correlated to FST swimming and elevated in the TST by SSRI administration. The use of a weighted bin sample analysis method differentiates TST behaviors into fluoxetine-responsive head movement and desipramine-responsive struggling. The use of 5-HT subtype receptor agonists, after depleting endogenous 5-HT with pCPA, shows the head movement suppressing effect of 5-HT2A and 5-HT2C postsynaptic receptor activation. 5-HT1A and 5-HT1B agonists were ineffective. We propose that a head movement focused analysis can add sensitive and reliable 5-HT detection capability to mouse TST testing with minimal effort but significant reward.

Involvement of serotonin receptor subtypes in the antidepressant-like effect of beta receptor agonist Amibegron (SR 58611A): an experimental study

New therapeutic strategies against depression, with less side effects and thus greater efficacy in larger proportion of depressed patients, are needed. Amibegron (SR58611A) is the first selective β3 adrenergic agent that has been shown to possess a profile of antidepressant activity in rodents. To investigate the involvement of serotonin receptors in the effects of amibegron, we used the serotonin 5HT1A receptor antagonist WAY-100635 (WAY) or serotonin 5HT2A-2C receptor antagonist ketanserin or serotonin 5HT3 receptor antagonist ondansetron in mice forced swimming test (FST). The locomotor activity was evaluated by measuring the total distance moved in the apparatus and the speed of the animals in the open field test. Imipramine (30mg/kg) significantly reduced immobility time compared to vehicle-treated group while amibegron (5 and 10mg/kg) dose dependently reduced immobility time in the FST. WAY(0.1mg/kg), ondansetron (1mg/kg), ketanserin(5mg/kg) had no effect on immobility time in naive mice while all of the drugs partially and significantly reversed amibegron (10mg/kg) induced decreasement in the immobility time in FST. None of the drugs alter locomotor activity in the open field test. The antidepressant-like effect of amibegron in the FST seems to be mediated by an interaction with serotonin 5-HT1A, serotonin 5-HT2A-2C and serotonin 5-HT3 receptors.

Low Doses of Allyphenyline and Cyclomethyline, Effective against Morphine Dependence, Elicit an Antidepressant-like Effect

This study demonstrated that cyclomethyline (2) and the corresponding enantiomers (R)-(-)-2 and (S)-(+)-2, displaying α2C-adrenoreceptor (AR) agonism/α2A-AR antagonism, similarly to allyphenyline (1) and its enantiomers, significantly decreased the naloxone-precipitated withdrawal symptoms in mice at very low doses. It also highlighted that such positive effects on morphine dependence can even be improved by additional serotoninergic 5-HT1A receptor (5-HT1A-R) activation. Indeed, 1 or the single (S)-(+)-1, 2, or both its enantiomers, all behaving as α2C-AR agonists/α2A-AR antagonists/5-HT1A-R agonists, alone and at the same low dose, improved morphine withdrawal syndrome and exerted a potent antidepressant-like effect. Therefore, considering the elevated comorbidity between opiate abuse and depressed mood and the benefit of these multifunctional compounds to both disorders, it is possible that they prove more efficacious and less toxic than a cocktail of drugs in managing opioid addiction.

Repeated exposure to chlorpyrifos alters the performance of adolescent male rats in animal models of depression and anxiety

Chlorpyrifos (CPF) is a broad spectrum, highly effective organophosphorus (OP) pesticide that has been largely used worldwide. Over the past decades, numerous studies have assessed the potential neurotoxic effects of either acute or chronic exposure to CPF on developing brain. Despite being an acetylcholinersterase inhibitor, the effects of CPF are not only confined to cholinergic system, but are involved in a wide variety of neurotransmitter systems, especially the serotonin (5-HT) system, which leads to long-lasting changes in 5-HT-related emotional behaviors. In our present study, 4-week-old adolescent male Sprague-Dawley rats were repeatedly exposed to CPF at daily doses of 10, 20, 40, 80, and 160 mg/kg/day (s.c., 7 days), and then subjected to a battery of emotional behavioral tests that related to serotonergic function in order to determine CPF effects in adolescent rats. Results in behavioral tests demonstrated CPF significantly increased the entries to and time spent in the open arms in the elevated plus-maze test at the dose of 40-160 mg/kg, the number of shocks in the Vogel's conflict test at the dose of 20-160 mg/kg, and significantly decreased the latency to feed in the novelty-suppressed feeding test in both dose range. Interestingly, in the forced swimming test, at the dose of 10mg/kg, CPF significantly increased the immobility time, whereas it significantly decreased the immobility time at the dose of 160 mg/kg. Our data suggest that repeated exposure to CPF elicits alterations of the emotional behaviors related to serotonergic nervous system in adolescent male rats. However, the underlying mechanism needs further investigations.

α2-Adrenergic agonists antagonise the anxiolytic-like effect of antidepressants in the four-plate test in mice

Selective serotonin reuptake inhibitors (SSRIs) and serotonin/noradrenaline reuptake inhibitors (SNRIs) has been reported to be efficient in anxiety disorders. Some animal models have demonstrated an anxiolytic-like effect following acute administration, however, it is not yet known how noradrenergic receptors are implicated in the therapeutic effects of antidepressants (ADs) in anxiety. The effects of two alpha(2)-adrenoceptor agonists (clonidine, guanabenz) on anxiolytic-like effect of two SSRIs (paroxetine and citalopram) and two SNRIs (venlafaxine and milnacipran) were evaluated in the four-plate test (FPT) in mice. Paroxetine (4 mg/kg), citalopram (8 mg/kg), venlafaxine (8 mg/kg), and milnacipran (8 mg/kg) administered intraperitoneally (i.p.) increased the number of punishments accepted by mice in the FPT. Clonidine (0.0039-0.5 mg/kg) and guanabenz (0.03-0.5mg/kg) had no effect on the number of punishments accepted by mice. Clonidine (0.03 and 0.06 mg/kg) and guanabenz (0.125 and 0.5 mg/kg) (i.p. -45 min) reversed the anti-punishment effect of paroxetine, citalopram, venlafaxine and milnacipran (i.p. -30 min). But if the antidepressants are administered 45 min before the test and alpha(2)-adrenoceptor agonists 30 min before the test, alpha(2)-adrenoceptor agonists failed to alter the anti-punishment effect of antidepressants. The results of this present study indicate that alpha(2)-adrenoceptor agonists antagonise the anxiolytic-like effect of antidepressants in mice when they are administered 15 min before the administration of antidepressant suggesting a close inter-regulation between noradrenergic and serotoninergic system in the mechanism of SSRIs and SNRIs in anxiety-like behaviour.

Evidence for serotonin receptor subtypes involvement in agmatine antidepressant like-effect in the mouse forced swimming test

This study investigated the involvement of 5-HT(1) and 5-HT(2) receptors in the antidepressant-like effect of agmatine in the mouse forced swimming test (FST). Pretreatment with p-chlorophenylalanine methyl ester (PCPA; 100 mg/kg, intraperitoneally (i.p.), an inhibitor of serotonin synthesis, for 4 consecutive days), methysergide (5 mg/kg, i.p., a serotonin (5-HT) antagonist), pindolol (32 mg/kg, i.p., a 5-HT(1A/1B) receptor/beta-adrenoceptor antagonist), N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridynyl)cyclohexanecarboxamide (WAY 100635; 0.3 mg/kg, subcutaneously (s.c.), a selective 5-HT(1A) receptor antagonist), 1-(2-methoxyphenyl)-4[-(2-phthalimido)butyl]piperazine) (NAN-190; 0.5 mg/kg, i.p., a 5-HT(1A) receptor antagonist), 1-(2-(1-pyrrolyl)-phenoxy)-3-isopropylamino-2-propanol (isamoltane; 2.5 mg/kg, i.p., a 5-HT(1B) receptor antagonist), cyproheptadine (3 mg/kg, i.p., a 5-HT(2) antagonist) or ketanserin (5 mg/kg, i.p., a 5-HT(2A/2C) receptor antagonist), but not with propranolol (2 mg/kg, i.p., a beta-adrenoceptor antagonist), prevented the effect of agmatine (10 mg/kg, i.p.) in the FST. A subeffective dose of agmatine (0.001 mg/kg, i.p.) produced a synergistic antidepressant-like effect with pindolol (32 mg/kg), NAN-190 (0.5 mg/kg, i.p.), WAY 100635 (0.03 mg/kg, s.c.), (+)-8-hydroxy-2-(di-n-propylamino)tetralin HBr (8-OH-DPAT; 0.01 mg/kg, i.p., a 5-HT(1A) receptor agonist), R(-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI; 1 mg/kg, i.p., a preferential 5-HT(2A) receptor agonist), or fluoxetine (10 mg/kg, i.p., a selective serotonin reuptake inhibitor, SSRI) but not with isamoltane (2.5 mg/kg, i.p.), ritanserin (4 mg/kg, i.p., a 5-HT(2A/2C) receptor antagonist) or ketanserin (5 mg/kg, i.p.). Taken together, the results firstly demonstrate that agmatine antidepressant-like effects in the FST seem to be mediated, at least in part, by an interaction with 5-HT(1A/1B) and 5-HT(2) receptors.

In the rat forced swimming test, chronic but not subacute administration of dual 5-HT/NA antidepressant treatments may produce greater effects than selective drugs

The rat forced swimming test (FST) distinguishes selective serotonin (5-HT) and selective noradrenaline (NA) reuptake-inhibitors, which respectively increase swimming and climbing behaviours. However, NA-system-mediated inhibition of 5-HT-induced swimming prevents dual 5-HT/NA reuptake-inhibition to produce concurrently climbing with swimming. Since adaptative neurochemical processes occur in the treatment of depression, we examined the influence of long-term antidepressant treatment on these interactions.

METHODS

(1) Selective [fluoxetine: 10 mg/kg; desipramine: 10 mg/kg] and non-selective [milnacipran: 40 mg/kg; mirtazapine: 20 mg/kg] antidepressants were administered subacutely (3inj) and chronically (17inj) over 16 days. (2) A subacute fluoxetine-desipramine combination (10-10 mg/kg) was administered in rats that were pre-treated with chronic-desipramine (10 mg/kg per day, 14 days). (3) NA-system-mediated interactions were further examined by combining the alpha(2)-receptor agonist clonidine (5, 10, 20, 200 microg/kg) with 10 mg/kg fluoxetine.

RESULTS

(1) Long-term treatment with either fluoxetine or desipramine does not modify the behavioural response produced by their subacute administration. (2) In contrast, whereas subacute-milnacipran increases climbing solely, chronic-milnacipran produces greater anti-immobility effects and increases both climbing and swimming behaviours. Similarly, the fluoxetine-desipramine combination produces climbing solely, but increases both climbing and swimming behaviours in animals pre-treated with chronic-desipramine. Chronic but not subacute-mirtazapine increases swimming behaviour. (3) clonidine dose-dependently antagonizes fluoxetine-induced anti-immobility effects and swimming behaviour.

CONCLUSIONS

Chronic enhancement of NA-transmission alters NA-system-mediated inhibition of 5-HT-induced behaviour in the FST, which may involve alpha(2)-receptors.

Role of 5-HT1A receptors in the mediation of acute citalopram effects: a 8-OH-DPAT challenge study

(1) The study was aimed to investigate the effects of the minimal effective doses of acute citalopram (5 mg/kg), (+/-)-8-hydroxydipropylaminotetralin HBr (8-OH-DPAT; 0.1 mg/kg), and their combined treatment on the rat open field and forced swimming behaviour and post-mortem monoamine content. (2) The animals were prospectively divided into the vehicle- and para-chlorophenylalanine (p-CPA)-pretreated (350 mg/kg) groups. (3) Acute citalopram (5 mg/kg), 8-OH-DPAT (0.1 mg/kg), or their combined treatment had no major effect on the rat open field and forced swimming behaviour. (4) The post-mortem catecholamine content in four brain regions studied was unchanged in all treatment groups. (5) The combined 8-OH-DPAT (0.1 mg/kg) and citalopram (5 mg/kg) treatment partially reversed the p-CPA-induced decrease of serotonin (5-HT) and 5-hydroxy-indolacetic acid (5-HIAA) content. (6) The present experiments demonstrate that the 5-HT1A receptors mediate some of the selective serotonin reuptake inhibitor (SSRI)-induced biochemical phenomena.

Paroxetine: a review

Paroxetine is a potent and selective serotonin reuptake inhibitor (SSRI) with currently approved indications for the treatment of depression, obsessive-compulsive disorder, panic disorder and social phobia. It is also used in the treatment of generalized anxiety disorder, post traumatic stress disorder, premenstrual dysphoric disorder and chronic headache. Paroxetine, a phenylpiperidine derivative, is the most potent inhibitor of the reuptake of serotonin (5-hydroxytryptamine, 5-HT) of all the currently available antidepressants including the class of SSRIs. It is a very weak inhibitor of norepinephrine (NE) uptake but it is still more potent at this site than the other SSRIs. The selectivity of paroxetine, i.e., the ratio of inhibition of uptake of norepinephrine to serotonin (NE/5-HT) is amongst the highest of the SSRIs. Paroxetine has little affinity for catecholaminergic, dopaminergic or histaminergic systems and by comparison with tricyclic antidepressants (TCAs) has, therefore, a reduced propensity to cause central and autonomic side effects. Paroxetine exhibits some affinity for the muscarinic cholinergic receptor but much less than the TCAs. In addition, the adaptive changes of somatodendritic (5-HT(1A)) and terminal (5-HT(1B/1D)) autoreceptors observed with paroxetine are different to those observed with TCAs; it also inhibits nitric oxide synthase. It is both a substrate and an inhibitor of cytochrome isoenzyme P450 2D6. Paroxetine is well absorbed orally and undergoes extensive first pass metabolism that is partially saturable. Its metabolites are pharmacologically inactive in vivo. Steady state levels are achieved after 4-14 days and an elimination half-life of 21 h is consistent with once-daily dosing. There is wide inter-individual variation in the pharmacokinetics of paroxetine in adults as well as in the young and the elderly with higher plasma concentrations and slower elimination noted in the latter. Elimination is also reduced in severe renal and hepatic impairment. Serious adverse events are, however, extremely rare even in overdose. In summary, paroxetine is well tolerated and effective in the treatment of both depressive and anxiety disorders across the age range.

The antidepressant activity of inositol in the forced swim test involves 5-HT(2) receptors

The effect of inositol as an antidepressant was previously demonstrated in both animal models of depression-like behavior and in clinical trials. Unlike most antidepressant drugs, inositol does not have a clear target in the synapse and was not demonstrated to alter monoamine levels in the brain. The present study attempted to draw a psychopharmacological profile of inositol's behavioral effects by exploring the interactions between the drug and specific receptor agonists and antagonists in the forced swim test. Rats received inositol treatment (or control) in combination with the serotonergic metabolism inhibitor PCPA or with the noradrenergic neurotoxin DSP-4. Results indicated that PCPA but not DSP-4 abolished the ability of inositol to cause a reduction in immobility time in the forced swim test. In mice, the specific 5-HT(2A)/5-HT(2C) antagonist ritanserin, but not the 5-HT(1A)/5-HT(1B)/beta adrenergic antagonist pindolol, abolished inositol's effect in the forced swim test. The 5-HT(2A)/5-HT(2C) agonist DOI and the 5-HT(1A) agonist 8-OH-DPAT did not have any significant effects on inositol's activity. The present data indicates that the antidepressant effect of inositol may involve 5-HT(2) receptors. It is thus possible that the effects of reuptake antidepressant drugs and the effects of inositol may have a common final pathway.