Sharon Cheetham

[3H]paroxetine binding in rat frontal cortex strongly correlates with [3H]5-HT uptake: effect of administration of various antidepressant treatments.

Paroxetine is a selective and potent inhibitor of 5-hydroxytryptamine (5-HT) uptake into serotonergic neurones. [3H]Paroxetine binding to rat frontal cortex was of high affinity with a high percentage of specific binding. The binding data of both competition and saturation studies fitted a single site binding model. [3H]Paroxetine binding was potently inhibited by the selective 5-HT uptake inhibitors. In addition, a very good correlation was demonstrated between the ability of twenty-three compounds to inhibit [3H]paroxetine binding to rat frontal cortical membranes and [3H]5-HT uptake into rat frontal cortical synaptosomes. These data support the view that [3H]paroxetine binds to a single site which corresponds to the 5-HT uptake site. Using this ligand, the effects of repeated administration of antidepressant drugs with a wide range of pharmacological actions and electroconvulsive shock on 5-HT reuptake sites were examined. [3H]Paroxetine binding parameters (Kd and Bmax) were unaltered by all treatments. It would, therefore, appear that antidepressant therapy does not produce adaptive changes in 5-HT uptake sites.

[3H]Nisoxetine—A radioligand for noradrenaline reuptake sites: Correlation with inhibition of [3H]noradrenaline uptake and effect of DSP-4 lesioning and antidepressant treatments

Nisoxetine is a potent and selective inhibitor of noradrenaline uptake into noradrenergic neurones. [3H]Nisoxetine binding to rat frontal cortical membranes was of high affinity. The binding data of both competition and saturation studies fitted a single site binding model. [3H]Nisoxetine binding was potently inhibited by the selective noradrenaline uptake inhibitors desipramine and protriptyline. In addition, a very good correlation was obtained between the ability of 25 monoamine reuptake inhibitors and related compounds both to inhibit [3H]nisoxetine binding and to inhibit [3H]noradrenaline uptake in rat frontal cortex. DSP-4 (10-100 mg/kg, i.p.) dose-dependently depleted cortical noradrenaline concentrations (51-100%), with no significant effects on 5-HT and dopamine. These depletions, which were used as a marker of loss of noradrenergic nerve terminals, were associated with a dose-dependent decrease in the number of [3H]nisoxetine binding sites (20-97%) with no change in binding affinity. Furthermore, a good correlation was obtained between cortical noradrenaline concentrations and the number of [3H]nisoxetine binding sites. These data support the view that [3H]nisoxetine binds to a single population of homogeneous sites associated with the noradrenaline transporter complex. Using this ligand, the effects of repeated administration of both antidepressant drugs with a range of pharmacological actions and of electroconvulsive shock on noradrenaline reuptake sites were examined. The number and affinity of [3H]nisoxetine binding sites were unaltered by all treatments. It is unlikely, therefore, that antidepressant therapy would produce adaptive changes in noradrenaline uptake sites.

A comparison of the effects on central 5-HT function of sibutramine hydrochloride and other weight-modifying agents

1 Effects on 5‐HT function of sibutramine and its active metabolites, BTS 54 354 and BTS 54 505, were compared with fluoxetine, (+)‐fenfluramine and (+)‐amphetamine. 2 In vitro sibutramine weakly inhibited [3H]‐5‐HT uptake into brain synaptosomes. BTS 54 354, BTS 54 505 and fluoxetine were powerful [3H]‐5‐HT uptake inhibitors, whereas (+)‐fenfluramine and (+)‐amphetamine were very much weaker. Conversely, whilst sibutramine, its metabolites and fluoxetine did not release [3H]‐5‐HT from brain slices at 10−5M, (+)‐fenfluramine and (+)‐amphetamine concentration‐dependently increased [3H]‐5‐HT release. 3 Sibutramine and fluoxetine had no effect on 5‐hydroxytryptophan (5‐HTP) accumulation in either frontal cortex or hypothalamus at doses <10 mg kg−1. In contrast, (+)‐amphetamine (3 mg kg−1) reduced 5‐HTP in hypothalamus, whilst (+)‐fenfluramine (1 mg kg−1) decreased 5‐HTP in both regions. 4 Sibutramine (10 mg kg−1 i.p.) and fluoxetine (10 mg kg−1 i.p.) produced slow, prolonged increases of extracellular 5‐HT in the anterior hypothalamus. In contrast, (+)‐fenfluramine (3 mg kg−1 i.p.) and (+)‐amphetamine (4 mg kg−1 i.p.) induced rapid, short‐lasting increases in extracellular 5‐HT. 5 Only (+)‐fenfluramine (10 mg kg−1) altered 5‐HT2A receptors in rat frontal cortex when given for 14 days, producing a 61% reduction in receptor number and a 18% decrease in radioligand affinity. 6 These results show that sibutramine powerfully enhances central 5‐HT function via its secondary and primary amine metabolites; this effect, like that of fluoxetine, is almost certainly mediated through 5‐HT uptake inhibition. By contrast, (+)‐fenfluramine enhances 5‐HT function predominantly by increasing 5‐HT release. (+)‐Amphetamine, though weaker than (+)‐fenfluramine, also enhances 5‐HT function by release.

Reduced dopamine turnover in the basal ganglia of depressed suicides

We have measured the concentrations of dopamine, and the dopamine metabolites homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC), in five brain regions from suicide victims with a firm retrospective diagnosis of depression, and matched controls. The suicides were divided into those free of antidepressant drugs and those in whom prescription of antidepressant drugs was clearly documented. DOPAC concentrations were significantly lower in caudate, putamen and nucleus accumbens of antidepressant-free suicides compared to controls. In antidepressant-treated suicides, lower concentrations of DOPAC were observed in the basal ganglia, reaching statistical significance in caudate. Lower DOPAC concentrations were largely restricted to those suicides who died by non-violent methods. There were no significant differences in dopamine and HVA concentrations in either suicide group compared to controls, although there was a trend for HVA concentrations to be lower in suicides. This study provides evidence for reduced dopamine turnover, as judged from reduced DOPAC levels, in depressed suicides, although we cannot exclude the possibility that this may be due to ingestion of toxic agents.

Dopamine D1 and D2 receptor binding sites in brain samples from depressed suicides and controls

Dopamine D1 and D2 receptors were measured (by saturation binding of [3H]SCH23390 and [3H]raclopride) in caudate, putamen and nucleus accumbens, obtained at post-mortem from suicide victims with a firm retrospective diagnosis of depression, and matched controls. There were no differences in the number or affinity of D1 or D2 receptors between suicides who had been free of antidepressants for at least three months prior to death, and controls. Increased numbers and decreased affinity of D2 receptors were however found in each brain region of antidepressant-treated suicides. We argue that these increases are related to concurrent treatment with neuroleptics rather than a direct effect of antidepressants. Increased numbers of D1 receptors in antidepressant-treated suicides were seen only in nucleus accumbens. This increase could not be clearly attributed to neuroleptics and may be related to antidepressant treatment.

Dopamine, but not norepinephrine or serotonin, reuptake inhibition reverses motor deficits in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated primates

Monoamine reuptake inhibitors that do not discriminate between the transporters for dopamine (DA), norepinephrine (NE), or 5-hydroxytryptamine (5-HT, serotonin) can reverse locomotor deficits and motor disability in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets. DA reuptake inhibition is presumed to be primarily responsible, but the role played by inhibition of NE and 5-HT reuptake is unknown. We now evaluate the efficacy of a range of monoamine reuptake inhibitors either alone or in combination in MPTP-treated common marmosets to determine the actions required for effective antiparkinsonian activity. Monoamine reuptake inhibitors not discriminating between the DA, NE, and 5-HT transporters [1-[1-(3,4-dichlororphenyl)cyclobutyl]-2-(3-diaminethylaminopropylthio)ethanone monocitrate (BTS 74 398) and nomifensine] reversed locomotor deficits and motor disability in MPTP-treated marmosets but bupropion was without effect. The selective DA reuptake inhibitor 1-(2-(bis-(4-fluorophenyl)-methoxy)ethyl)-4-(3-phenylpropyl) piperazine) dihydrochloride (GBR 12909) also reversed these motor deficits. The relative efficacy of the compounds (BTS 74 398 > GBR 12909 > nomifensine ≫ bupropion) paralleled their potency in inhibiting DA uptake in vitro and in vivo. In contrast, the selective NE reuptake inhibitor nisoxetine and the 5-HT reuptake inhibitor sertraline administered alone failed to improve motor function and tended to worsen the deficits. Coadministration of nisoxetine attenuated the improvement in motor deficits produced by GBR 12909. Coadministration of sertraline also abolished the reversal of motor deficits produced by GBR 12909. Coadministration of both sertraline and nisoxetine similarly abolished the improvement of motor deficits produced by GBR 12909. Molecules possessing potent DA reuptake inhibitory activity may be useful in the treatment of the motor symptoms of Parkinsons disease. In contrast, there seems to be no role for NE or 5-HT reuptake inhibitors, and they may impair antiparkinsonian activity mediated through dopaminergic mechanisms.

Prokineticin 2 Is a Hypothalamic Neuropeptide That Potently Inhibits Food Intake

OBJECTIVE Prokineticin 2 (PK2) is a hypothalamic neuropeptide expressed in central nervous system areas known to be involved in food intake. We therefore hypothesized that PK2 plays a role in energy homeostasis. RESEARCH DESIGN AND METHODS We investigated the effect of nutritional status on hypothalamic PK2 expression and effects of PK2 on the regulation of food intake by intracerebroventricular (ICV) injection of PK2 and anti-PK2 antibody. Subsequently, we investigated the potential mechanism of action by determining sites of neuronal activation after ICV injection of PK2, the hypothalamic site of action of PK2, and interaction between PK2 and other hypothalamic neuropeptides regulating energy homeostasis. To investigate PK2s potential as a therapeutic target, we investigated the effect of chronic administration in lean and obese mice. RESULTS Hypothalamic PK2 expression was reduced by fasting. ICV administration of PK2 to rats potently inhibited food intake, whereas anti-PK2 antibody increased food intake, suggesting that PK2 is an anorectic neuropeptide. ICV administration of PK2 increased c-fos expression in proopiomelanocortin neurons of the arcuate nucleus (ARC) of the hypothalamus. In keeping with this, PK2 administration into the ARC reduced food intake and PK2 increased the release of α-melanocyte–stimulating hormone (α-MSH) from ex vivo hypothalamic explants. In addition, ICV coadministration of the α-MSH antagonist agouti-related peptide blocked the anorexigenic effects of PK2. Chronic peripheral administration of PK2 reduced food and body weight in lean and obese mice. CONCLUSIONS This is the first report showing that PK2 has a role in appetite regulation and its anorectic effect is mediated partly via the melanocortin system.

Dopamine reuptake inhibition and failure to evoke dyskinesia in MPTP-treated primates.

Nonspecific monoamine reuptake inhibitors reverse motor abnormalities in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated marmosets without evoking established dyskinesia. However, it is not known whether dopamine reuptake inhibition alone explains these actions or whether noradrenaline and/or serotonin reuptake blockade also contributes. L-DOPA (12.5 mg/kg, p.o.) rapidly reversed the baseline locomotor deficits and motor disabilities, but evoked dyskinesia (especially limb chorea) in MPTP-treated common marmosets primed to exhibit involuntary movements. In contrast, the selective dopamine reuptake inhibitor 1-(2-(bis-(4-fluorophenyl)-methoxy)ethyl)-4-(3-phenylpropyl) piperazine dihydrochloride (GBR 12909) reversed motor deficits in a dose-dependent manner but, unlike L-DOPA, did not evoke established dyskinesia in these animals. Therefore, inhibition of dopamine reuptake does not evoke established dyskinesia in MPTP-treated primates.

Combination of the sodium-glucose cotransporter-2 inhibitor empagliflozin with orlistat or sibutramine further improves the body-weight reduction and glucose homeostasis of obese rats fed a cafeteria diet.

The present study assessed the potential of the sodium glucose-linked transporter (SGLT)-2 inhibitor empagliflozin to decrease body weight when administered alone or in combination with the clinically effective weight-loss agents orlistat and sibutramine in obese rats fed a cafeteria diet. Female Wistar rats were exposed to a cafeteria diet to induce obesity. Empagliflozin was dosed once daily (10, 30, and 60 mg/kg) for 28 days. Combination studies were subsequently performed using a submaximal empagliflozin dose (10 mg/kg) with either sibutramine or orlistat. Body weight, food, and water intake were recorded daily. The effect of drug treatment on glucose tolerance, relevant plasma parameters, and carcass composition was determined. Empagliflozin dose-dependently reduced body weight, plasma leptin, and body fat though increased urinary glucose excretion. The combination of empagliflozin and orlistat significantly reduced body weight compared to animals treated with either drug alone, and significantly improved glucose tolerance, plasma insulin, and leptin compared to vehicle-treated controls. The effect of sibutramine to improve glycemic control in an oral glucose-tolerance test was also significantly increased, with empagliflozin and combination treatment leading to a reduction in carcass fat greater than that observed with either drug alone. These data demonstrate that empagliflozin reduces body weight in cafeteria-fed obese rats. In combination studies, empagliflozin further improved the body-weight or body-fat loss of animals in comparison to orlistat or sibutramine alone. Such studies may indicate improved strategies for the treatment of obese patients with prediabetes or type 2 diabetes.

Dopamine D2 receptors: A potential pharmacological target for nomifensine and tranylcypromine but not other antidepressant treatments

Treatment for 1 or 14 days by IP injection with the antidepressants, amitriptyline (10 mg/kg), bupropion (30 mg/kg), desipramine (10 mg/kg), GBR 12909 (10 mg/kg), sibutramine HCl (3 mg/kg), mianserin (5 mg/kg), and zimeldine (10 mg/kg), did not affect the number or affinity of dopamine D2 receptors determined by [3H]raclopride binding to rat striatal membranes. Similarly, neither did a single, nor repeated (five times over 10 days), electroconvulsive shock, given under halothane anaesthesia, have any effect on [3H]raclopride binding parameters. By contrast, the noradrenaline and dopamine reuptake inhibitor, nomifensine (5 mg/kg), and the monoamine oxidase inhibitor, tranylcypromine (5 mg/kg), decreased the number of dopamine D2 receptors by 12% and 11%, respectively, when given for 14 days. Administration of the D2 receptor antagonist, haloperidol (1 mg/kg), for 14 days increased the number of [3H]raclopride binding sites by 17%. Thus, the data demonstrate that although nomifensine and tranylcypromine decrease D2 receptor number after 14 days administration, this adaptive change is not observed with other antidepressant treatments. However, the findings do not preclude a contribution of altered dopamine D2 receptor function to the efficacy of those drugs with potent effects on dopaminergic neuronal function.