Snjezana Lelas

Anti-conflict effects of benzodiazepines in rhesus monkeys: relationship with therapeutic doses in humans and role of GABAA receptors

Rationale and ObjectivesConflict procedures are used to study mechanisms underlying the anxiolytic effects of benzodiazepines (BZs). We established a conflict procedure with rhesus monkeys in order to examine the role of GABAA receptors in the anxiolytic-like effects of BZs.MethodsFour rhesus monkeys responded under a two-component multiple schedule in which responding was maintained under a fixed-ratio schedule of food delivery in the absence (non-suppressed responding) and presence (suppressed responding) of response-contingent electric shock.ResultsConventional BZs (alprazolam, flunitrazepam, clonazepam, nitrazepam, lorazepam, bromazepam, diazepam, flurazepam, clorazepate, chlordiazepoxide) engendered increases in the average rates of suppressed responding at low to intermediate doses and decreased the average rates of non-suppressed responding at higher doses. Positive correlations were observed when the therapeutic potencies of BZs in humans were compared with potencies to increase the rates of suppressed responding (R2=0.83) or decrease the rates of non-suppressed responding (R2=0.60). The 5-HT1A agonist buspirone increased the rates of suppressed responding, although the effects were modest, whereas the opioid morphine lacked anti-conflict effects. The BZ antagonist flumazenil also modestly increased the rates of suppressed responding. A relatively low dose of flumazenil enhanced, while a high dose blocked, alprazolam’s anti-conflict effects. Compounds selective for α1 subunit-containing GABAA receptors (zolpidem, zaleplon, CL218,872) engendered relatively weak increases in the rates of suppressed responding.ConclusionsA rhesus monkey conflict procedure was established with predictive validity for therapeutic doses in people and provided evidence that anxiolytic-like effects of BZs can occur with relatively low intrinsic efficacy at GABAA receptors and are reduced by α1GABAA receptor selectivity.

Effects of CRF1 receptor antagonists and benzodiazepines in the Morris water maze and delayed non-matching to position tests

RationaleBenzodiazepines continue to be widely used for the treatment of anxiety, but it is well known that benzodiazepines have undesirable side effects, including sedation, ataxia, cognitive deficits and the risk of addiction and abuse. CRF1 receptor antagonists are being developed as potential novel anxiolytics, but while CRF1 receptor antagonists seem to have a better side-effect profile than benzodiazepines with respect to sedation and ataxia, the effects of CRF1 receptor antagonists on cognitive function have not been well characterized. It is somewhat surprising that the potential cognitive effects of CRF1 receptor antagonists have not been more fully characterized since there is some evidence to suggest that these compounds may impair cognitive function.ObjectiveThe Morris water maze and the delayed non-matching to position test are sensitive tests of a range of cognitive functions, including spatial learning, attention and short-term memory, so the objective of the present experiments was to assess the effects of benzodiazepines and CRF1 receptor antagonists in these tests.ResultsThe benzodiazepines chlordiazepoxide and alprazolam disrupted performance in the Morris water maze and delayed non-matching to position at doses close to their therapeutic, anxiolytic doses. In contrast, the CRF1 receptor antagonists DMP-904 and DMP-696 produced little or no impairment in the Morris water maze or delayed non-matching to position test even at doses 10-fold higher than were necessary to produce anxiolytic effects.ConclusionsThe results of the present experiments suggest that, with respect to their effects on cognitive functions, CRF1 receptor antagonists seem to have a wider therapeutic index than benzodiazepines.

Comparison of zolpidem and midazolam self-administration under progressive-ratio schedules: consumer demand and labor supply analyses.

Progressive ratio (PR) schedules of intravenous drug self-administration are useful for establishing the relationships between reinforcing effectiveness and pharmacological actions of abused drugs. The authors compared the reinforcing effects of 2 short-duration benzodiazepine-type drugs differing in their receptor selectivity: zolpidem (selective for gamma aminobutyric acid Type A [GABA(A)] receptors containing alpha1 subunits) and midazolam (nonselective). Reinforcing effectiveness was evaluated using a PR schedule of intravenous drug injection in rhesus monkeys in which the response requirement increased across the experimental session and the initial response requirement (IRR) was varied. Analyses based on consumer demand and labor supply models of behavioral economics revealed that the relative reinforcing effectiveness of zolpidem was greater than that of midazolam. For consumer demand analyses, the degree of difference between zolpidem and midazolam depended on whether price was calculated on the basis of different IRRs or different doses of drug. According to labor supply analysis, the reinforcing effects of midazolam were influenced by the economic concept referred to as a price effect to a greater degree than those of zolpidem. These findings suggest that a compound with selectivity for GABA(A) receptors containing alpha1 subunits has greater reinforcing effectiveness than a nonselective compound with similar pharmacokinetics, albeit under a limited range of conditions (high response costs). Differences in price effects may play a key role in determining the relative reinforcing effectiveness of selective versus nonselective benzodiazepine agonists.

Discovery of disubstituted piperidines and homopiperidines as potent dual NK1 receptor antagonists-serotonin reuptake transporter inhibitors for the treatment of depression.

This report describes the synthesis, structure-activity relationships and activity of piperidine, homopiperidine, and azocane derivatives combining NK1 receptor (NK1R) antagonism and serotonin reuptake transporter (SERT) inhibition. Our studies culminated in the discovery of piperidine 2 and homopiperidine 8 as potent dual NK1R antagonists-SERT inhibitors. Compound 2 demonstrated significant activity in the gerbil forced swimming test, suggesting that dual NK1R antagonists-SERT inhibitors may be useful in treating depression disorders.

NK1 receptor antagonism lowers occupancy requirement for antidepressant-like effects of SSRIs in the Gerbil forced swim test

The known interactions between the serotonergic and neurokinin systems suggest that serotonin reuptake inhibitor (SSRIs) efficacy may be improved by neurokinin-1 receptor (NK1R) antagonism. In the current studies combination of a subeffective dose of an SSRI (0.3 mg/kg fluoxetine or 0.03 mg/kg citalopram) with a subeffective dose of an NK1R antagonist (0.3 mg/kg aprepitant or 1 mg/kg CP-122,721) produced efficacy in the gerbil forced swim test (FST). Serotonin transporter (SERT) occupancy produced by 1 mg/kg fluoxetine (lowest efficacious dose) was 52 ± 5% and was reduced to 29 ± 4% at 0.3 mg/kg, a dose that was efficacious in combination with 0.3 mg/kg aprepitant or 1 mg/kg CP-122,721; the corresponding NK1R occupancies were 79 ± 4% and 61 ± 4% for aprepitant and CP-122,721, respectively. For citalopram, SERT occupancy at the lowest efficacious dose (0.1 mg/kg) was 50 ± 4% and was reduced to 20 ± 5% at 0.03 mg/kg, a dose that was efficacious when combined with aprepitant (0.3 mg/kg). Aprepitant (10 mg/kg) augmented the serotonin elevation produced by fluoxetine (1 or 10 mg/kg) in the gerbil prefrontal cortex; i.e. NK1R antagonism can modulate serotonin responses. A novel orally-available dual-acting NK1R antagonist/SERT inhibitor BMS-795176 is described; gerbil Ki = 1.4 and 1 nM at NK1R and SERT, respectively. BMS-795176 was efficacious in the gerbil FST; efficacy was observed with 35 ± 3% SERT occupancy and 73 ± 3% NK1R occupancy. The interaction between NK1R antagonism and SERT inhibition to lower the SERT occupancy required for antidepressant-like efficacy suggests that BMS-795176 has the potential to improve efficacy with a reduction in SSRI-associated side effects.

Design, optimization, and in vivo evaluation of a series of pyridine derivatives with dual NK1 antagonism and SERT inhibition for the treatment of depression.

A series of substituted pyridines, ether linked to a phenylpiperidine core were optimized for dual NK(1)/SERT affinity. Optimization based on NK(1)/SERT binding affinities, and minimization of off-target ion channel activity lead to the discovery of compound 44. In vivo evaluation of 44 in the gerbil forced swim test (a depression model), and ex-vivo NK(1)/SERT receptor occupancy data support the potential of a dual acting compound for the treatment of depression.

Monoamine reuptake site occupancy of sibutramine: Relationship to antidepressant-like and thermogenic effects in rats

Sibutramine was formerly marketed as an anti-obesity agent. The current study investigated the relationships between monoamine reuptake site occupancy for sibutramine and both its antidepressant-like efficacy and thermogenic effects. Sibutramines effects on locomotor activity (LMA) and food intake were also evaluated. Sibutramine occupied monoamine reuptake binding sites with the rank order of potency of NET>SERT>DAT; at 10mg/kg, po, occupancy was 95% NET, 81% SERT and 73% DAT. Sibutramine produced antidepressant-like behavior in the forced swim test; at the lowest effective dose (3mg/kg, po) occupancy was 61%, 90% and 23% at SERT, NET and DAT sites, respectively. Sibutramine also increased body core temperature in a dose- and time-dependent manner; at the lowest effective dose (30mg/kg) SERT, NET and DAT occupancies were respectively 78%, 86% and 59%. A significant decrease in food consumption was observed at 3 and 10mg/kg, po. LMA was increased at ≥10mg/kg, sc. The relationship between efficacy in the FST and occupancy was also determined for citalopram, fluoxetine and reboxetine. Similarly, the relationship between thermogenesis and target occupancy for several single or double/triple reuptake inhibitors was measured and showed that >40-50% DAT binding was required for thermogenesis. Thermogenesis was blocked by the D1 antagonist SCH39166 (3mg/kg, sc). Our findings indicate that the antidepressant-like effect of sibutramine may result from additive or synergistic actions on the three reuptake binding targets. At higher doses, sibutramine produces thermogenesis; DAT inhibition and activation of dopamine D1 receptors are required for this effect.

Discovery of a cyclopentylamine as an orally active dual NK1 receptor antagonist-serotonin reuptake transporter inhibitor.

Cyclopentylamine 4 was identified as a potent dual NK1R antagonist-SERT inhibitor. This compound demonstrated significant oral activity in the gerbil forced swimming test, suggesting that dual NK1R antagonists-SERT inhibitors may be useful in treating depression disorders.