Preclinical Assessment of the Abuse Potential of Purified Botanical Cannabidiol: Self-Administration, Drug Discrimination, and Physical Dependence.

Cannabidiol (CBD) is a constituent of the cannabis plant with a diverse array of pharmacological activities as well as potential therapeutic uses. An oral formulation of CBD (Epidiolex in the US; Epidyolex in Europe) is approved for treating seizures associated with rare and severe forms of epilepsy. These studies, which supported the approval of the medication, investigated abuse-related effects of CBD in rats and nonhuman primates (NHPs) using drug self-administration, drug discrimination, and physical dependence procedures and characterized its pharmacokinetics. In NHPs (n = 5) that self-administered midazolam (0.01 or 0.032 mg/kg/infusion), CBD (0.1-3.2 mg/kg/infusion) failed to maintain responding above vehicle levels. CBD maintained very modest levels of self-administration in rats (n = 7-8) that self-administered heroin (0.015 mg/kg/infusion) and did not increase drug-lever responding, up to a dose of 150 mg/kg (by mouth), in rats (n = 6) trained to discriminate 0.5 mg/kg (i.p.) midazolam. In juvenile (5-6 weeks old) and adult (10-11 weeks old) male and female rats, discontinuation of chronic treatment (twice daily for 20 days) with an oral formulation of CBD (20 or 100 mg/kg, by mouth) did not reliably produce signs of withdrawal. Pharmacokinetic studies confirmed that the dosing regimens used in these studies resulted in therapeutically relevant plasma levels. Taken together, the lack of reliable self-administration, the failure to increase drug-lever responding in rats trained to discriminate midazolam, and the absence of withdrawal signs upon discontinuation of chronic treatment indicate that CBD has very low abuse potential and is unlikely to produce physical dependence. SIGNIFICANCE STATEMENT: Legalization of cannabis across the United States and elsewhere has led to intense investigation into the safety and therapeutic potential of cannabis and its constituent materials, including cannabidiol (CBD). Results of these preclinical abuse potential studies on CBD indicate no rewarding properties, physical dependence potential, or similarity to a benzodiazepine. Together with data from in vitro pharmacology and human abuse potential studies, the abuse potential of Epidiolex in humans is likely to be negligible.

A review of late-stage CNS drug candidates for the treatment of obesity.

Obesity is an important causative factor in morbidity, disability and premature death. Increasing levels of obesity will impose enormous health, financial and social burdens on worldwide society unless effective interventions are implemented. For many obese individuals, diet and behavioural modification need to be supplemented by pharmacotherapy. Preclinical research has revealed a greater understanding of the complex nature of the hypothalamic regulation of food intake and has generated a wide range of new molecular targets for the development of drug candidates for obesity treatment. As shown by the clinical results that have been obtained with this next generation of therapies, some approaches, for example, fixed-dose drug combinations, have already demonstrated an ability to deliver levels of efficacy that are not achievable with the current antiobesity drug therapies. The regulatory and marketing landscape for development, registration and commercialisation of novel centrally acting drugs for treatment of obesity and related metabolic disorders has changed substantially in recent years. Now a much greater emphasis is placed on tolerability and safety, as well as efficacy. In this review we briefly describe the therapeutic approaches to tackle obesity that are in late-stage clinical development. We then discuss drugs in late-stage development for the treatment of obesity and also future directions.

Experimental strategies to discover and develop the next generation of psychedelics and entactogens as medicines.

Research on classical psychedelics (psilocybin, LSD and DMT) and entactogen, MDMA, has produced a renaissance in the search for more effective drugs to treat psychiatric, neurological and various peripheral disorders. Psychedelics and entactogens act though interaction with 5-HT2A and other serotonergic receptors and/or monoamine reuptake transporters. 5-HT, which serves as a neurotransmitter and hormone, is ubiquitously distributed in the brain and peripheral organs, tissues and cells where it has vasoconstrictor, pro-inflammatory and pro-nociceptive actions. Serotonergic psychedelics and entactogens have known safety and toxicity risks. For these drugs, the risks been extensively researched and empirically assessed through human experience. However, novel drug-candidates require thorough non-clinical testing not only to predict clinical efficacy, but also to address the risks they pose during clinical development and later after approval as prescription medicines. We have defined the challenges researchers will encounter when developing novel serotonergic psychedelics and entactogens. We describe screening techniques to predict clinical efficacy and address the safety/toxicity risks emerging from our knowledge of the existing drugs: 1) An early-stage, non-clinical screening cascade to pharmacologically characterise novel drug-candidates. 2) Models to detect hallucinogenic activity. 3) Models to differentiate hallucinogens from entactogens. 4) Non-clinical preclinical lead optimisation technology (PLOT) screening to select drug-candidates. 5) Modified animal models to evaluate the abuse and dependence risks of novel psychedelics in Safety Pharmacology testing. Our intention has been to design non-clinical screening strategies that will reset the balance between benefits and harms to deliver more effective and safer novel psychedelics for clinical use. This article is part of the Special Issue on 'National Institutes of Health Psilocybin Research Speaker Series'.

Psychedelics: Threshold of a Therapeutic Revolution.

This Special Issue of Neuropharmacology on psychedelics provides a timely and comprehensive update on progress following the previous Neuropharmacology Special Issue "Psychedelics: New Doors, Altered Perceptions". Remarkable advances have been made in basic and clinical research on psychedelics in the five years since 2018. It is partly based on the seminar series focused on psilocybin organized by the National Institutes of Health (NIH), USA from April to June 2021, the "NIH Psilocybin Research Speaker Series". Participants were world leading experts, including scientists, medical practitioners, clinical psychologists and oncologists, and attendees from additional disciplines of patient advocacy, law, government science policy and regulatory policy. To provide a global perspective, their contributions are complemented with reviews by some of the world's most eminent scientists in the field. The US Food and Drug Administration (FDA) has granted two breakthrough therapy designations for psilocybin in treatment resistant depression (TRD) in 2018 and major depressive disorder (MDD) in 2019, as well as for MDMA for the treatment of post-traumatic stress disorder (PTSD) in 2017. Clinical trials are in progress to assess the therapeutic value of psilocybin in MDD and TRD, and in other indications such as cancer-related anxiety and depression, anorexia, PTSD, substance use disorders and various types of chronic pain. The contributors' insights should assist basic and applied science for transition of psychedelics from bench to potential mainstream therapies. The implications are global, because FDA approval of these new medicines will increase international interest and efforts.

Selective 5-HT6 receptor ligands: progress in the development of a novel pharmacological approach to the treatment of obesity and related metabolic disorders.

The increasing global prevalence of obesity unequivocally demonstrates that neither behavioural (diet and exercise) nor pharmacological approaches to this health problem are working. In this area of high unmet clinical need, the 5-HT6 receptor has generated enormous interest amongst academic and pharmaceutical industry scientists as a molecular target for the development of a new generation of safe and more effective anti-obesity drugs. In this review, we have described the major developments that have occurred in the fields of the medicinal chemistry and pharmacology of 5-HT6 ligands, with particular emphasis on their potential application as novel anti-obesity drugs. The last 5 years have witnessed an increasing understanding of the 5-HT6 receptor and its structural requirements that has produced an explosion in the number and diversity of novel, highly selective 5-HT6 receptor agonists, partial agonists and antagonists that have been designed and synthesized. In animal models, 5-HT6 receptor ligands of all functional types have been shown to decrease food intake when given acutely and chronically, to evoke profound and sustained weight-loss in obese animals, and concomitantly to improve a number of cardio-metabolic risk factors. Comparator studies in obese animal models, which are highly predictive of clinical outcomes, indicate that 5-HT6 ligands may have the potential to be more efficacious in the treatment of obesity than the current generation of anti-obesity drugs.

New perspectives from microdialysis studies in freely-moving, spontaneously hypertensive rats on the pharmacology of drugs for the treatment of ADHD.

Attention deficit hyperactivity disorder (ADHD) is a common childhood psychiatric condition that is effectively treated by catecholaminergic drugs with a variety of different mechanisms and the SH rat is frequently used as a model of this disorder. In vivo microdialysis in freely-moving rats has been employed extensively to provide a better understanding of the pharmacodynamics of drugs at their sites of action. In this review, these three topics are brought together to explore the contribution of in vivo microdialysis studies in spontaneously hypertensive (SH) rats to our understanding of the neurochemical deficits in this rat strain and the actions of ADHD drugs on catecholaminergic function in the prefrontocortex (PFC), striatum and nucleus accumbens. What is revealed is that basal efflux of norepinephrine in the PFC is attenuated, whilst striatal and mesolimbic dopaminergic neurotransmission is hyperfunctional; the latter observation fits closely with the hyperactive phenotype of the SH rat. Furthermore, experiments performed with the enantiomers of amphetamine and threo-methylphenidate demonstrate that pharmacodynamic effects of drugs reported from experiments in outbred rat strains, e.g. Sprague-Dawleys, do not necessarily translate to the SH rat. When the findings are compared with the clinical efficacy of drugs used in treating ADHD, they indicate that the most efficacious drugs powerfully increase both norepinephrinergic and dopaminergic neurotransmission.

Phenylephrine-induced activity in mice as a model of central alpha 1-adrenoceptor function. Effects of acute and repeated administration of antidepressant drugs and electroconvulsive shock.

Intracerebroventricular injection of the alpha 1-agonists phenylephrine (10-100 micrograms) or methoxamine (10-50 micrograms) produced a dose-dependent increase in locomotor activity and behavioural excitation in mice. The syndrome induced by phenylephrine was inhibited by prazosin but not yohimbine, RX 781094 or propranolol. Methoxamine-induced responses were, however, also reduced by yohimbine. Activity induced by phenylephrine was not affected by metergoline or pirenperone but was reduced by haloperidol and spiroperidol. This latter effect, however, may have been due to inhibition of alpha 1-adrenoceptors and/or dopamine receptors. Pretreatment with alpha-methyl-p-tyrosine or FLA-63 reduced responses to phenylephrine by respectively inhibiting either the locomotor activity or the other behavioural components of the syndrome. This suggests that some residual noradrenergic and possibly also dopaminergic function may be necessary for the behavioural expression of the effects of phenylephrine. The activity was inhibited by mianserin and amitriptyline but not by desmethylimipramine. When these antidepressant drugs were given twice daily for 14 days, mianserin alone affected the activity induced by phenylephrine, tested either 12 or 60 hr after the final injection. This behaviour was also not altered 24 hr after the mice had received an electroconvulsive shock under halothane anaesthesia, once daily for 10 days. In conclusion, the data suggest that the behavioural syndrome induced by phenylephrine probably provides a specific and quantifiable assessment of central alpha 1-adrenoceptor function and that in general this is unaltered following repeated administration of antidepressant drugs or electroconvulsive shock.

Repeated administration of triiodothyronine (T3) to rats enhances nigrostriatal and mesolimbic dopaminergic behavioural responses.

A once daily injection to rats of triiodothyronine (T3; 100 micrograms/kg s.c.) for 10 days enhanced the locomotor responses of rats pretreated with tranylcypromine (5 mg/kg) to an injection into the nucleus accumbens of dopamine (5 micrograms bilaterally), when tested 24 hr after the last T3 administration. This treatment did not, however, alter the control responses of tranylcypromine-pretreated rats to injection of saline (1 microliter bilaterally). Injection of T3 for 10 days enhanced the circling responses of unilateral nigrostriatal-lesioned rats to apomorphine (0.5 mg/kg) but not to methamphetamine (0.5 mg/kg). The probable explanation for the latter result was the finding that repeated T3 administration lowered basal striatal dopamine concentrations. The treatment also produced a trend towards reduced dopamine concentrations in the n. accumbens, although the difference did not reach statistical significance. These data suggest that repeated T3 injection causes an increased post-synaptic function of both the nigrostriatal and mesolimbic dopamine systems in rat brain.

The effects of acute and repeated administration of T3 to mice on 5-HT1 and 5-HT2 function in the brain and its influence on the actions of repeated electroconvulsive shock.

The effects of the administration of L-triiodothyronine (T3) On the function of 5-HT in the CNS and its influence on the actions of electroconvulsive shock have been examined in mice. A single injection of T3 (100 micrograms/kg) had no effect 24 hr later on either 5-HT1A-mediated hypothermia, induced by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.5 mg/kg) or the 5-HT1B-mediated locomotor response to 5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl) 1-H-indole (RU 24969; 50 ng i.c.v.). This treatment increased 5-HT2-induced head-twitches, produced by 5-methoxy-N,N'-dimethyltryptamine (5-MeODMT; 2 mg/kg), but did not alter 5-HT2 receptors in the frontal cortex, suggesting that this potentiation was mediated indirectly through a modulatory neurotransmitter. One injection of T3 had no effect on the concentration of 5-HT in the forebrain or mid/hindbrain, but increased 5-HIAA in the latter region. Daily injections of T3 for 10 days attenuated the responses to both 8-OH-DPAT and RU 24969. Furthermore, 5-MeODMT-induced head-twitches returned to control values and this was accompanied by a 10% decrease in 5-HT2 receptors in the cortex. Repeated administration of T3 increased levels of 5-HT in mid/hindbrain and concentrations of 5-HIAA both here and in forebrain. Hence, treatment with T3 attenuated the function of 5-HT1A and 5-HT1B receptors, but increased 5-HT2-mediated responses, although the time-courses for these effects were different. Triiodothyronine also enhanced the synthesis and turnover of 5-HT in the brain of the mouse. Repeated electroconvulsive shock (90 V, 1 sec) decreased the hypothermia induced by 8-OH-DPAT. However, 5-MeODMT-induced head-twitches were enhanced by acute and repeated electroconvulsive shock. Administration of T3 together with electroconvulsive shock did not alter the effects of electroconvulsive shock on 5-HT1A-mediated hypothermia, but markedly potentiated its actions on 5-HT2-mediated responses. These findings provide possible pharmacological evidence for the suggested antidepressant effects of T3 and the potentiation of antidepressant therapy by this thyroid hormone.

Hypophysectomy does not prevent the enhanced monoamine-mediated behavioural responses following repeated electroconvulsive shocks.

Groups of hypophysectomised rats were given either an electroconvulsive shock (ECS; 125V, 1 sec) once daily for 10 days or a sham-shock. Twenty-four hours after the final treatment both groups were tested for their responses to the dopamine agonist, apomorphine, the 5-hydroxytryptamine agonist, quipazine, and the alpha 2-adrenoceptor agonist, clonidine. Repeated electroconvulsive shock enhanced the locomotor activity produced by either quipazine (25 mg/kg i.p.) or apomorphine (0.2 mg/kg s.c.) compared to sham-shocked controls. This treatment also attenuated the hypoactivity produced by clonidine (0.5 mg/kg i.p.). These changes are identical to those produced in normal rats by repeated electroconvulsive shock. Hypophysectomy, therefore, did not abolish the increased 5-hydroxytryptaminergic and dopaminergic behavioural responses neither did it prevent the decreased functional activity of central alpha 2-adrenoceptors, which may be presynaptic. These data suggest that although electroconvulsive shock has been reported to stimulate the secretion of various pituitary hormones, this process is not essential for the development of the enhanced monoamine-mediated behavioural responses studied.

Intracerebroventricular administration of 5,7-dihydroxytryptamine to mice increases both head-twitch response and the number of cortical 5-HT2 receptors.

5-Hydroxytryptamine-containing (5-HT) neurones in brain of the mouse were selectively destroyed by intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT, 50 micrograms). Sham-lesioned controls received vehicle (2 microliters, i.c.v.). Two weeks later the head-twitch response induced by 5-methoxy-N,N-dimethyltryptamine (2.0 mg/kg) and mediated by 5-HT2 receptors was markedly enhanced in the lesioned mice. Furthermore, lesioning also increased 5-HT2 binding sites in the cortex, assessed by the binding of [3H]ketanserin in these animals, and decreased levels of 5-HT in the cortex (70%) and mid/hindbrain (64%) regions. A second group of mice, lesioned with less 5,7-DHT (5-20 micrograms, i.c.v.) showed unaltered head-twitch responses to 5-methoxy-N, N-dimethyltryptamine (2.0 mg/kg) and did not have increased 5-HT2 receptor binding in the cortex. Depletions of 5-HT were 32 and 40% in the cortex and mid/hindbrain, respectively. Comparison of the extent of depletion of 5-HT in the mid/hindbrain after lesioning, with the increase in head-twitch response, suggested that depletions of less than 40% did not affect this behaviour. However, depletions greater than 40% produced marked increases in this response and there was a good correlation between these two variables (r=0.701, P less than 0.01). In conclusion, these data suggest that enhanced head-twitch responses occurring after lesioning with 5,7-DHT may result from increased 5-HT2 receptors in brain. Moreover, the magnitude of the observed behavioural enhancement was dependent upon the extent of depletion of 5-HT produced by the lesioning.

A new and highly sensitive method for measuring 3-methoxytyramine using HPLC with electrochemical detection. Studies with drugs which alter dopamine metabolism in the brain.

3-Methoxytyramine (3-MT) is a minor metabolite of dopamine which is suggested to reflect the turnover and utilization of dopamine. A novel, isocratic HPLC method has been developed which can be used to analyse 3-MT in homogenates of rat brain without the need for additional purification procedures. Furthermore, the coulometric electrochemical detection system is sensitive enough to measure 3 pg of 3-MT (equivalent to 0.6 ng/g tissue wet weight). 3-Methoxytyramine was measured in the striatum and n. accumbens after decapitation and rapid freezing, using 3-methoxy-4-hydroxybenzylamine as the internal standard. The effects of dopaminergic and other drugs on this metabolite were examined using this method. alpha-Methyl-p-tyrosine (200 mg/kg i.v.) produced parallel linear decreases in dopamine and 3-MT in naive rats, but not those pretreated with tranylcypromine (5 mg/kg i.p.). Methamphetamine (0.3-10 mg/kg i.p.) and amphetamine (0.3-10 mg/kg i.p.) both dose-dependently increased 3-MT in naive and tranylcypromine-pretreated rats. In naive animals, 3-MT was not altered by intraperitoneal injection of the dopamine reuptake inhibitors, bupropion (10 mg/kg) and nomifensine (10 mg/kg) or by sibutramine HCl (3 mg/kg), amitriptyline (10 mg/kg), desipramine (10 mg/kg) and zimeldine (10 mg/kg). 3-Methoxytyramine was decreased by apomorphine (5 mg/kg i.p.) and also by large doses of the selective D2 antagonist, BRL 34778 (5 mg/kg i.p.) or L-DOPA (50 mg/kg i.p.). The selective D1 antagonist, SCH 23390 (0.1 or 5 mg/kg i.p.) was without effect. In tranylcypromine-pretreated rats, 3-MT was dose-dependently reduced and increased by apomorphine (0.01-5 mg/kg i.p.) and BRL 34778 (0.1-5 mg/kg i.p.), respectively. The drug SCH 23390 (0.1-5 mg/kg i.p.) produced much smaller increases in 3-MT which were probably mediated through the striatonigral pathway. Overall, the data suggest that measurement of 3-MT, after inhibition of monoamine oxidase, is a useful index of the release and utilization of dopamine. However, after substantial and prolonged depletion of dopamine, levels of 3-MT in naive animals are a better index. Also, the formation of 3-MT in naive rats rats provides a sensitive method for distinguishing between dopamine releasing agents and reuptake inhibitors.

Reserpinization severs the cooperative but not the oppositional interaction between D1 and D2 receptors.

Dopamine D1 and D2 receptors in rat brain interact synergistically to produce stereotypy and antagonistically to induce atypical jerking. This study showed that repeated reserpine treatment (5 daily injections of 1 mg/kg, s.c.), which depleted dopamine stores by 98%, rendered D1 and D2 receptors independent with respect to the production of stereotypy, i.e. either D1- or D2-selective agonists given alone induced stereotypy. In contrast, the atypical jerking induced by the D2 agonist, quinpirole, was still inhibited by the D1 agonist, SKF 82958, indicating that reserpine treatment did not render these two receptors independent with respect to initiation of this behavior.

[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.

The effects of the peptide-coupling agent, EEDQ, on 5-HT2A receptor binding and function in rat frontal cortex.

This ex vivo study in rat frontal cortex determined the influence of 5-HT receptor agonists and antagonists on EEDQ-induced depletion of 5-HT2A binding sites and reduction in their functional coupling to phospholipid hydrolysis. Twenty-four hours after EEDQ (6 mg/kg) administration a marked reduction (66%) of cortical 5-HT2A binding sites with no change in binding affinity was observed. The 5HT2A antagonists ritanserin (1 mg/kg), ketanserin (1 and 5 mg/kg), metergoline (3 mg/kg) or the 5HT2A agonist, DOI (3 and 10 mg/kg) also significantly reduced (by 15-44%) these binding sites 24 h after injection. Thirty minute pretreatment with ritanserin, ketanserin, metergoline or DOI (at the doses above) afforded 49-65% protection against the loss of 5-HT2A binding sites induced by EEDQ (6 mg/kg). DOI (10 mg/kg) pretreatment (-24 h) decreased by 26% the accumulation of [3H]inositol phosphates (IPs) evoked by 5-HT (100 microM), but did not affect that produced by DOI (100 microM). Ketanserin (5 mg/kg, -24 h) decreased 5-HT- and DOI-induced IP formation by 65% and 53%, respectively. The EEDQ (6 mg/kg, -24 h)-evoked reductions (-50%) of 5-HT- and DOI-induced IP formation were not altered by DOI (10 mg/kg) or ketanserin (5 mg/kg) given 30 min before EEDQ. G-protein-stimulated IP accumulation was unaffected by EEDQ (6 mg/kg). Overall, EEDQ reduces 5-HT2A binding sites and function in rat frontal cortex, whereas its effects on binding were attenuated by various 5-HT receptor antagonists and agonists, its effects on function was unaltered by these drugs.

The beta 2-adrenoceptor agonists clenbuterol and salbutamol enhance the hypothermic action of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) in mice by a central mechanism.

The hypothermic response of mice to injection of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) was enhanced by injection of the beta 2-adrenoceptor agonist clenbuterol with an ED50 of 0.4 mg/kg. This effect of clenbuterol is through a central mechanism since salbutamol, a beta 2-adrenoceptor agonist with poor penetration into the brain, had no effect at a dose of 2 mg/kg, whereas intracerebroventricular injection of clenbuterol (3 micrograms) or salbutamol (2 micrograms), produced a significant enhancement. The enhancing effect of clenbuterol was unaffected by pretreatment with the beta 1-adrenoceptor antagonist metoprolol but was totally antagonised by the beta 2-adrenoceptor antagonist ICI 118,551 and to a lesser extent by butoxamine. Clenbuterol therefore enhances the function of the presynaptic 5-HT1 receptor through a beta 2-adrenoceptor mechanism.

[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.

Elevation of extracellular cortical noradrenaline may contribute to the antidepressant activity of zotepine: an in vivo microdialysis study in freely moving rats.

The antipsychotic, zotepine, as well as possessing affinity for dopamine D1- and D2-1ike receptors, has high affinity for the noradrenaline (NA) transporter and inhibits [3H]NA uptake by rat frontal cortex synaptosomes, in vitro. The present studies investigated the effects of zotepine on extracellular NA in the frontal cortex of freely moving rats using in vivo microdialysis. Removal of calcium from the perfusate reduced extracellular NA by 70.5% and prevented the 50 mM KCl-stimulated increase in NA levels. Zotepine (0.5-1.5 mg kg(-1) i.p.), evoked biphasic, dose-dependent rises in extracellular NA with maximal increases observed at 60 min (+ 171.0%) and 240 min (+ 211.5%) post-treatment. The increases in NA levels were sustained for up to 100 min post-dosing. Clozapine (10.0 mg kg(-1) i.p.), resulted in a smaller, transient increase in NA levels (+ 72.0%) which lasted for 20 min post-treatment. Neither ziprasidone (3.0 mg kg(-1) i.p.) nor olanzapine (1.0 mg kg(-1) i.p.) influenced extracellular NA. Systemic treatment with the antidepressant desipramine (0.3 mg kg(-1) i.p.) resulted in a prolonged elevation of NA levels over 240 min (maximal increase of + 354.3%), whilst local infusion of nisoxetine (1-100 microM) through the dialysis probe increased NA levels in a concentration-dependent manner (up to 587.8% of control values). These data suggest that the inhibition of NA uptake by zotepine and its subsequent prolonged elevation of extracellular cortical NA may underlie the reported antidepressant properties of zotepine in schizophrenic patients.

Sibutramine does not decrease the number of 5-HT re-uptake sites in rat brain and, like fluoxetine, protects against the deficits produced by dexfenfluramine.

The effect of sibutramine and dexfenfluramine on 5-HT re-uptake sites, labelled with [(3)H]paroxetine, have been determined in various rat brain regions. In addition, the ability of fluoxetine and sibutramine to protect against the changes in [(3)H]paroxetine binding produced by dexfenfluramine was examined. Sibutramine (9 mg/kg, p.o.) and dexfenfluramine (1, 3 and 10 mg/kg, p.o.) were administered twice daily (before 09.00 h and after 16.00 h) for four days, followed by a 14 day drug-free period. In the protection studies, fluoxetine (10 mg/kg, i.p.) and sibutramine (9 mg/kg, p.o.) were given 1 h prior to dexfenfluramine (10 mg/kg, p.o.) using the same dosing regimen as described above. Sibutramine (9 mg/kg, p.o.; three times its ED(50) to inhibit food intake at 2 h) had no significant effect on the number or affinity of 5-HT re-uptake sites the brain regions studied. In contrast, dexfenfluramine at an equivalent dose (3 mg/kg, p.o.) significantly decreased the number of 5-HT re-uptake sites in frontal cortex (by 35%), hippocampus (by 47%) and hypothalamus (by 27%). This effect was dose-dependent with marked decreases (by 58-84%) in the number of sites following 10 mg/kg, p.o. These effects were not associated with changes in binding affinity. Fluoxetine (10 mg/kg, i.p.) completely blocked the effect of dexfenfluramine (10 mg/kg, p.o.) without having any significant effect alone. Sibutramine (9 mg/kg, p.o.) also blocked the effects of dexfenfluramine, although the reversal was only partial in frontal cortex, hippocampus and hypothalamus. Thus sibutramine, unlike dexfenfluramine, does not alter brain 5-HT re-uptake sites. Furthermore, sibutramine and fluoxetine protect against the deficits in 5-HT re-uptake sites produced by dexfenfluramine. These data provide further evidence that sibutramine is a 5-HT re-uptake inhibitor and it does not have neurotoxic potential.

The influence of L-triiodothyronine (T3) on the effects of repeated administration of desipramine or electroconvulsive shock on alpha 2- and beta-adrenoceptor function in the brain of the rat: implications for the potentiation of antidepressant therapy by T3.

Repeated, daily administration of either an electroconvulsive shock (ECS; 110 V, 1 sec) or desipramine (DMI; 5 mg/kg X 2) to rats caused a progressive decrease in the function of presynaptic alpha 2-adrenoceptors, assessed by the hypoactivity (sedation) response to clonidine (0.2 mg/kg). This attenuation required approximately 7 days' administration of either treatment for maximum effect. A single injection of triiodothyronine (T3; 100 micrograms/kg) on day 1 of the treatment markedly accelerated the decreased responses to clonidine induced by DMI or electroconvulsive shock, but did not alter the maximum attenuation. By itself T3 did not affect the hypoactivity responses. alpha 2-Adrenoceptors, measured by the binding of [3H]idazoxan in the cortex, which are believed to be predominantly postsynaptic, were decreased by 14 days of DMI or electroconvulsive shock for 10 days, but not 2 days of either treatment. Triiodothyronine did not influence the decreased number of alpha 2-adrenoceptors induced by DMI or electroconvulsive shock but may have delayed the onset produced by DMI. Binding to beta-adrenoceptors in the cortex was measured using [3H]dihydroalprenolol. This was significantly decreased by 14 days administration of DMI, but not significantly by electroconvulsive shock for 10. Down-regulation of beta-adrenoceptors, induced by DMI was rapid, being observed after 1 day of treatment. Injection of T3 did not influence the final decreases produced by DMI or electroconvulsive shocks but moderately delayed their onset. Triiodothyronine alone caused a 25% reduction in cortical beta-adrenoceptors 24 hr after injection.(ABSTRACT TRUNCATED AT 250 WORDS)