Associations between inattention and impulsivity ADHD symptoms and disordered eating risk in a community sample of young adults

BACKGROUND

Symptoms of attention deficit hyperactivity disorder (ADHD) and trait impulsivity have been associated with disordered eating but are seldom assessed in community studies, or longitudinally and little is known about the mediating mechanisms.

METHODS

We tested associations between ADHD symptoms and disordered eating cross-sectionally and between trait impulsivity and disordered eating longitudinally. We utilised data from a normative cohort of young adults (642 participants: 65% female, M_age = 23 years). Participants were classified as high risk or low risk for disordered eating using the SCOFF instrument. In the first two steps of both cross-sectional and longitudinal hierarchical logistic regression models, demographics and covariates were entered. For the cross-sectional regression, Adult ADHD self-report scale (ASRS) scores, separated into inattentive and hyperactive/impulsive symptoms, were entered in the third step. In a separate longitudinal model, Barratt impulsivity scale subscales (attentional, motor and non-planning impulsivity) were entered in the third step. Depression, as assessed by the moods and feelings questionnaire (MFQ), was examined as a mediator.

RESULTS

Cross-sectionally, sex, MFQ score and inattentive symptoms predicted disordered eating risk (model R² = 20%). Longitudinally, sex, MFQ score and attentional impulsivity predicted disordered eating risk (model R² = 16%). The relationship between inattentive symptoms and the disordered eating risk was partially mediated by MFQ score, whereas the relationship between attentional impulsivity and the disordered eating risk was fully mediated by MFQ scores.

CONCLUSIONS

These data highlight (1) a specific role for inattentive symptoms of ADHD and (2) the importance of both depression and impulsivity in predicting eating disorder risk.

Investigating virtual reality navigation in amnestic mild cognitive impairment using fMRI

Spatial navigation requires a well-established network of brain regions, including the hippocampus, caudate nucleus, and retrosplenial cortex. Amnestic Mild Cognitive Impairment (aMCI) is a condition with predominantly memory impairment, conferring a high predictive risk factor for dementia. aMCI is associated with hippocampal atrophy and subtle deficits in spatial navigation. We present the first use of a functional Magnetic Resonance Imaging (fMRI) navigation task in aMCI, using a virtual reality analog of the Radial Arm Maze. Compared with controls, aMCI patients showed reduced activity in the hippocampus bilaterally, retrosplenial cortex, and left dorsolateral prefrontal cortex. Reduced activation in key areas for successful navigation, as well as additional regions, was found alongside relatively normal task performance. Results also revealed increased activity in the right dorsolateral prefrontal cortex in aMCI patients, which may reflect compensation for reduced activations elsewhere. These data support suggestions that fMRI spatial navigation tasks may be useful for staging of progression in MCI.

Effects of awareness that food intake is being measured by a universal eating monitor on the consumption of a pasta lunch and a cookie snack in healthy female volunteers

To date, there have been no studies that have explicitly examined the effect of awareness on the consumption of food from a Universal Eating Monitor (UEM - hidden balance interfaced to a computer which covertly records eating behaviour). We tested whether awareness of a UEM affected consumption of a pasta lunch and a cookie snack. 39 female participants were randomly assigned to either an aware or unaware condition. After being informed of the presence of the UEM (aware) or not being told about its presence (unaware), participants consumed ad-libitum a pasta lunch from the UEM followed by a cookie snack. Awareness of the UEM did not significantly affect the amount of pasta or cookies eaten. However, awareness significantly reduced the rate of cookie consumption. These results suggest that awareness of being monitored by the UEM has no effect on the consumption of a pasta meal, but does influence the consumption of a cookie snack in the absence of hunger. Hence, energy dense snack foods consumed after a meal may be more susceptible to awareness of monitoring than staple food items.

Effects of the 5-HT2C receptor agonist meta-chlorophenylpiperazine on appetite, food intake and emotional processing in healthy volunteers

RATIONALE

The treatment of obesity is an increasing global health priority, yet few effective drug treatments are currently available. The discovery of novel anti-obesity therapies could be assisted by the validation of experimental (translational) medicine models in healthy volunteers that assess efficacy and safety at an early stage of drug development.

OBJECTIVES

The aim of this study was to examine the effects of the 5-HT2C receptor agonist meta-chlorophenylpiperazine (mCPP) in an experimental medicine model assessing both appetite and mood.

METHODS

Using a between-subjects, double-blind, placebo-controlled design, 24 male and 24 female participants were randomly assigned to either placebo, 15- or 30-mg mCPP treatment groups. Lunch was eaten from a Universal Eating Monitor (UEM) that measured eating rate, and the participants completed the P1vital® Oxford Emotional Test Battery (ETB) and a series of appetite and mood ratings.

RESULTS

mCPP reduced appetite and, in women, enhanced measures of satiation. The drug also enhanced memory for emotional material in the word recall and recognition memory tasks of the ETB.

CONCLUSIONS

The results provide new insight into the effects of mCPP on appetite, satiety and memory in humans. In addition, our data provide an illustration of the value of measuring changes in appetite and mood in healthy volunteers to determine the potential efficacy and safety of novel anti-obesity drugs.

The effects of ketamine and risperidone on eye movement control in healthy volunteers

The non-competitive N-methyl-D-aspartate receptor antagonist ketamine leads to transient psychosis-like symptoms and impairments in oculomotor performance in healthy volunteers. This study examined whether the adverse effects of ketamine on oculomotor performance can be reversed by the atypical antipsychotic risperidone. In this randomized double-blind, placebo-controlled study, 72 healthy participants performed smooth pursuit eye movements (SPEM), prosaccades (PS) and antisaccades (AS) while being randomly assigned to one of four drug groups (intravenous 100 ng ml(-1) ketamine, 2 mg oral risperidone, 100  ng ml(-1) ketamine plus 2 mg oral risperidone, placebo). Drug administration did not lead to harmful adverse events. Ketamine increased saccadic frequency and decreased velocity gain of SPEM (all P < 0.01) but had no significant effects on PS or AS (all P > or = 0.07). An effect of risperidone was observed for amplitude gain and peak velocity of PS and AS, indicating hypometric gain and slower velocities compared with placebo (both P < or = 0.04). No ketamine by risperidone interactions were found (all P > or = 0.26). The results confirm that the administration of ketamine produces oculomotor performance deficits similar in part to those seen in schizophrenia. The atypical antipsychotic risperidone did not reverse ketamine-induced deteriorations. These findings do not support the cognitive enhancing potential of risperidone on oculomotor biomarkers in this model system of schizophrenia and point towards the importance of developing alternative performance-enhancing compounds to optimise pharmacological treatment of schizophrenia.

The effects of sibutramine on the microstructure of eating behaviour and energy expenditure in obese women

Given the suggestion that many potential anti-obesity drugs may enhance within-meal satiation, few studies have directly measured the effects of any drug on the microstructure of human eating behaviour. The effects of 7 days dosing with sibutramine 10 mg and 15 mg a day on appetite and energy balance were determined in 30 obese women (BMI 34.6 +/- 3.3 kg/m2, age 46.0 +/- 12.9 years) using a Universal Eating Monitor (UEM) and indirect calorimetry, in a double-blind, placebo-controlled crossover study. At day 7, sibutramine 10 mg and 15 mg reduced food intake by 16.6% and 22.3%, respectively (p < 0.001), compared with placebo. Sibutramine reduced eating rate compared with placebo rather than meal length (10 mg p < 0.05; 15 mg p < 0.001). In addition, sibutramine 10 mg significantly reduced hunger later in the meal (p < 0.05) and sibutramine 15 mg increased fullness early in the meal (p < 0.01), both of which are consistent with enhanced within-meal satiation. Sibutramine had little effect on resting metabolic rate, although 15 mg did significantly reduce respiratory quotient at several time points during the test day. These results provide novel evidence that decreased consumption of a test meal induced by sibutramine is primarily because of reduced eating rate, enhancing the deceleration in cumulative food intake within a meal associated with the development of satiety. Changes in within-meal appetite ratings appear particularly sensitive to drug-induced enhancement of satiation, and may provide key indices for assessing the therapeutic potential of novel anti-obesity drugs.

Serotonin 1B and 2C receptor interactions in the modulation of feeding behaviour in the mouse

RATIONALE

To examine the functional relationship between 5-HT1B receptors (5-HT1B-R) and 5-HT2C receptors (5-HT2C-R) in the control of food intake.

OBJECTIVES

To compare the hypophagic effect of the 5-HT(2C/1B)-R agonist m-chlorophenylpiperazine (mCPP), with that of the selective 5-HT1B-R agonist CP-94,253 in both wildtype (WT) and 5-HT2C knockout (KO) mice.

METHODS

The hypophagic effects of mCPP (1, 3 and 5.6 mg/kg) and CP-94,253 (5, 10 and 20 mg/kg) were assessed in WT and 5-HT2C KO mice using the behavioural satiety sequence paradigm. The effects of pre-treatment with the selective 5-HT2C-R antagonist SB 242,084 (0.5 and 1.5 mg/kg) were assessed in two groups of WT mice, with each group given only mCPP or CP-94,253.

RESULTS

The 5-HT(2C/1B) receptor agonist mCPP and the selective 5-HT1B receptor agonist CP-94,253 both suppressed food intake in WT mice. 5-HT2C KO mice were insensitive to the hypophagic effects of mCPP but were more sensitive to CP-94,253-induced hypophagia than WT controls. mCPP induced a significant increase in post-prandial activity in 5-HT2C KO mice, but this effect was absent in 5-HT2C KO mice who were given CP-94,253. Data from WT mice, who were pre-treated with the 5-HT2C receptor antagonist SB 242,084 and then challenged with either mCPP or CP-94,253, were similar to those obtained from 5-HT2C KO mice.

CONCLUSIONS

5-HT2C-R and 5-HT1B-R activation are each sufficient to induce a hypophagic response. However, concurrent 5-HT2C-R inactivation can potentiate the hypophagic response to 5-HT1B-R activation, consistent with an inhibitory role for the 5-HT2C-R in behaviour mediated by the activation of other 5-HT receptors. These results also confirm that 5-HT1B-R activation alone cannot account for the hyperactive response of 5-HT2C KO mice to mCPP.

Identification of 4-methyl-1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indoles as 5-HT2C receptor agonists

Synthesis and evaluation of the activity of new 4-methyl-1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indoles as 5-HT(2C) receptor agonists are described. Appropriately substituted, several analogs displayed selectivity against the other 5-HT(2) receptor subtypes of 1 order of magnitude or more. Selectivity was improved for several compounds versus the lead 1, increasing the therapeutic interest in this series of 5-HT(2C) receptor agonists.

Indoline derivatives as 5-HT(2C) receptor agonists

A series of 1-(1-indolinyl)-2-propylamines was synthesised and evaluated as 5-HT(2C) receptor agonists for the treatment of obesity. The general methods of synthesis of the precursor indoles are described. The functional efficacy and radioligand binding data for all of the compounds at 5-HT(2) receptor subtypes are reported. A number of compounds were found to reduce food intake in rats after oral administration.

mCPP-induced hyperactivity in 5-HT2C receptor mutant mice is mediated by activation of multiple 5-HT receptor subtypes

The serotonin receptor agonist mCPP induces hyperlocomotion in 5-HT2C receptor knockout (KO) mice or in the presence of a 5-HT2C receptor antagonist. In the present group of experiments, we evaluate the role of 5-HT1A, 5-HT1B and 5-HT2A receptors in mCPP-induced hyperactivity in 5-HT2C KO mice. We also assess the ability of agonists at these receptors to induce hyperactivity in wildtype (WT) mice pre-treated with a selective 5-HT2C receptor antagonist. As previously reported, mCPP (3 mg/kg) induced hyperactivity in 5-HT2C KO mice. A combination of the 5-HT1B receptor agonist CP-94,253 (20 mg/kg) and the 5-HT1A receptor agonist 8-OH-DPAT (0.5 mg/kg) induced marked hyperactivity in WT but not in 5-HT2C KO mice, nor in mice treated with the selective 5-HT2C receptor antagonist, SB 242084 (1.5 mg/kg). Neither CP-94,253 nor 8-OH-DPAT had any intrinsic effect on locomotion in WTs. mCPP-induced hyperactivity was attenuated in 5-HT2C KO mice by the 5-HT1B receptor antagonist SB 224289 (2.5 mg/kg), and the 5-HT2A receptor antagonists ketanserin (0.3 mg/kg) and M100907 (0.01 mg/kg) but not by the 5-HT1A receptor antagonist WAY 100635 (1 mg/kg). The 5-HT(2A/2B/2C) receptor agonist, Ro 60-0175 (3 mg/kg), induced a modest increase in locomotor activity in WT mice pre-treated with SB 242084. However, the combination of Ro 60-0175 with CP-94,253 induced a substantial increase in activity in 5-HT2C KO mice, an effect comparable to mCPP-induced hyperactivity. Thus, joint activation of 5-HT1A and 5-HT1B receptors stimulates locomotion in WT mice but this response is dependent on a functional 5-HT2C receptor population and hence is absent in 5-HT2C KO mice. By contrast, mCPP-induced hyperactivity depends on the inactivation of a separate 5-HT2C receptor population and is mediated by 5-HT2A and 5-HT1B receptor activation.

Discovery of nonxanthine adenosine A2A receptor antagonists for the treatment of Parkinson's disease

During a program to investigate the biochemical basis of side effects associated with the antimalarial drug mefloquine, the authors made the unexpected discovery that the (-)-(R,S)-enantiomer of the drug is a potent adenosine A2A receptor antagonist. Although the compound was ineffective in in vivo animal models of central adenosine receptor function, it provided a unique nonxanthine adenosine A2A receptor antagonist lead structure and encouraged the initiation of a medicinal chemistry program to develop novel adenosine A2A antagonists for the management of Parkinson's disease (PD). The authors have synthesized and screened more than 2,000 chemically diverse and novel adenosine A(2A antagonists. Early examples from two distinct chemical series are the thieno[3,2-dy]pyrimidine VER-6623 and the purine compounds VER-6947 and VER-7835, which have high affinity at adenosine A2A receptors (K(i) values 1.4, 1.1, and 1.7 nmol/L, respectively) and act as competitive antagonists. In particular, VER-6947 and VER-7835 demonstrate potent in vivo activity reversing the locomotor deficit caused by the D2 receptor antagonist haloperidol, with minimum effective doses comparable with that of KW6002 (0.3 to 1 mg/kg). In conclusion, the authors have discovered potent, selective, and in vivo active nonxanthine adenosine A2A antagonists that have considerable promise as a new therapy for PD.

Oral administration of the 5-HT2Creceptor agonist, mCPP, reduces body weight gain in rats over 28 days as a result of maintained hypophagia

RATIONALE

The 5-HT(2C) receptor subtype has been implicated extensively in the regulation of ingestive behaviour.

OBJECTIVE

To assess whether chronic administration of the preferential 5-HT(2C) receptor agonist, mCPP, reduces rat body weight gain and to determine if this effect is wholly or partially attributable to the effect of the drug on daily food intake.

METHODS

Animals were orally dosed with mCPP (10 mg/kg P.O., b.i.d.) or d-fenfluramine (2.5 mg/kg P.O., b.i.d.) for 28 days. Further groups of animals received drug treatments for the first 14 days and then received vehicle for the remainder of the experiment. Locomotor activity was assessed on days 2, 14, and 28. In a second study, animals received mCPP or d-fenfluramine for a 14-day period (dose and route were identical to the previous study). A group of pair-fed controls were included to determine whether the effects on body weight gain were attributable entirely to drug-induced hypophagia.

RESULTS

Both mCPP and d-fenfluramine reduced body weight relative to vehicle-treated controls over the 28-day period. Withdrawal of the drugs on day 14 resulted in a significant rebound weight gain. Neither mCPP nor d-fenfluramine induced significant changes in locomotor activity compared to controls on any of the days tested (2, 14 or 28). In the second, 14-day study, changes in the body weights of pair-fed controls closely paralleled those of their drug-treated counterparts.

CONCLUSION

These data indicate that chronic oral treatment with mCPP and d-fenfluramine significantly reduces rat body weight gain, an effect that is reversible upon withdrawal and wholly attributable to maintained hypophagia.

Preferential effects of the cannabinoid CB1 receptor antagonist, SR 141716, on food intake and body weight gain of obese (fa/fa) compared to lean Zucker rats

RATIONALE

The selective CB(1) receptor antagonist, SR 141716, has been demonstrated to reduce food consumption in a range of animal species.

OBJECTIVE

To assess the effect of chronic administration of SR 141716 on body weight and ingestive behaviour of lean and obese (fa/fa) Zucker rats.

METHODS

Lean and obese Zucker rats were orally dosed with SR 141716 (3, 10, 30 mg/kg PO), sibutramine (5 mg/kg PO) or vehicle for one week. Pair-fed controls provided insight as to whether the effect of SR 141716 on body weight was attributable to drug-induced hypophagia. Subsequently, the effect of chronic oral administration of SR 141716 (1, 3, 10 mg/kg) was assessed for 28 days. At the end of this period, all animals were given vehicle for 14 days. The incidence of wet-dog shakes, yawning, scratching, and grooming behaviours, was assessed after acute administration and at weekly intervals thereafter for 4 weeks.

RESULTS

SR 141716 dose-dependently decreased food intake and body weight gain in both lean and obese animals. The inhibition of food intake and body weight gain was greater in obese Zuckers than in lean Zucker controls. Changes in the body weights of pair-fed controls closely paralleled those of their drug-treated counterparts. Chronic 28-day treatment led to a maintained reduction of body weight gain. Withdrawal of SR 141716 on day 28 resulted in rebound hyperphagia and a significant weight gain. On acute administration, SR 141716 dose-dependently induced motor behaviours that showed tolerance upon repeated administration.

CONCLUSION

These data indicate that chronic oral treatment with SR 141716 significantly reduces the food intake and body weight gain of obese and lean Zucker rats, an effect that is greater in obese animals and reversible upon drug withdrawal.

Evidence that hypophagia induced by d-fenfluramine and d-norfenfluramine in the rat is mediated by 5-HT2C receptors

The present series of studies is the first to investigate the pharmacological mechanisms underlying d-fenfluramine- and d-norfenfluramine-induced hypophagia in the rat using highly selective serotonin 5-HT2 receptor antagonists. Administration of d-fenfluramine, and its major metabolite d-norfenfluramine, suppresses food intake in animals. Both compounds stimulate the release of serotonin and are potent inhibitors of the re-uptake of 5-HT into nerve terminals. In addition, d-norfenfluramine also acts as a direct 5-HT(2B/2C) receptor agonist. Pre-treatment with the selective 5-HT2C receptor antagonist, SB-242084 (0.3-3 mg/kg), dose-dependently inhibited both d-fenfluramine- (3 mg/kg) and d-norfenfluramine-induced (2 mg/kg) hypophagia. In contrast, the hypophagic effect of d-fenfluramine and d-norfenfluramine was unaffected by prior treatment with the highly selective 5-HT2B receptor antagonists, SB-215505 (0.3-3 mg/kg) and RS-127445 (1-3 mg/kg) or the 5-HT2A receptor antagonists MDL 100,907 (0.003-0.03 mg/kg) and ketanserin (0.2, 0.5 mg/kg). In addition, the 5-HT1A receptor antagonist WAY-100635 (0.3, 1 mg/kg) and the 5-HT1B receptor antagonists GR-127935 (1, 2 mg/kg) and SB-224289 (2-10 mg/kg) did not affect d-fenfluramine-induced hypophagia. These data provide unequivocal evidence for an important role of the 5-HT2C receptor in the mediation of d-fenfluramine and d-norfenfluramine-induced hypophagia in the rat and do not support the involvement of 5-HT1A/1B/2A/2B receptors.

Double-blind, placebo-controlled study of amantadine hydrochloride in the treatment of children with autistic disorder

OBJECTIVE

To test the hypothesis that amantadine hydrochloride is a safe and effective treatment for behavioral disturbances--for example, hyperactivity and irritability--in children with autism.

METHOD

Thirty-nine subjects (intent to treat; 5-19 years old; IQ > 35) had autism diagnosed according to DSM-IV and ICD-10 criteria using the Autism Diagnostic Interview-Revised and the Autism Diagnostic Observation Schedule-Generic. The Aberrant Behavior Checklist-Community Version (ABC-CV) and Clinical Global Impressions (CGI) scale were used as outcome variables. After a 1-week, single-blind placebo run-in, patients received a single daily dose of amantadine (2.5 mg/kg per day) or placebo for the next week, and then bid dosing (5.0 mg/kg per day) for the subsequent 3 weeks.

RESULTS

When assessed on the basis of parent-rated ABC-CV ratings of irritability and hyperactivity, the mean placebo response rate was 37% versus amantadine at 47% (not significant). However, in the amantadine-treated group there were statistically significant improvements in absolute changes in clinician-rated ABC-CVs for hyperactivity (amantadine -6.4 versus placebo -2.1; p = .046) and inappropriate speech (-1.9 versus 0.4; p = .008). CGI scale ratings were higher in the amantadine group: 53% improved versus 25% (p = .076). Amantadine was well tolerated.

CONCLUSIONS

Parents did not report statistically significant behavioral change with amantadine. However, clinician-rated improvements in behavioral ratings following treatment with amantadine suggest that further studies with this or other drugs acting on the glutamatergic system are warranted. The design of these and similar drug trials in children with autistic disorder must take into account the possibility of a large placebo response.

Case series: amantadine open-label treatment of impulsive and aggressive behavior in hospitalized children with developmental disabilities

OBJECTIVE

A growing body of literature implicates interactions between glutamatergic and neostriatal dopaminergic neurotransmitter systems in the development and expression of impulsivity, hyperactivity, and stereotypy. Amantadine hydrochloride, a drug used in young children for influenza prophylaxis, acts both as an indirect dopamine agonist as well as an N-methyl-D-aspartate (NMDA) receptor antagonist. Thus an open clinical trial of this medication for the treatment of symptoms of impulse control disorders in children was performed.

METHOD

A total of eight children (seven with neurodevelopmental disorders and all inpatients) with target behaviors refractory to other treatments were selected after parental informed consent. All patients were male and ranged in age from 4 to 12 years. Outcome was based on subjective consensus clinical ratings by the multidisciplinary treatment team.

RESULTS

For four of the children, amantadine was associated with marked clinical improvement. In the remainder, improvement was also observed. Amantadine was well tolerated.

CONCLUSIONS

On the basis of this experience, it appears that amantadine hydrochloride or related NMDA antagonists may warrant additional study in this and related populations.

Similarities in the action of Ro 60-0175, a 5-HT2C receptor agonist and d-fenfluramine on feeding patterns in the rat

RATIONALE

Activation of 5-HT2C receptors is thought to enhance satiety and to mediate the action of the prototypical anorectic drug d-fenfluramine.

OBJECTIVE

Four experiments investigated the role of the 5-HT2C receptor in the modulation of feeding by comparison of the effects of the putative selective 5-HT2C receptor agonist Ro 60-0175 and d-fenfluramine on feeding behaviour.

METHODS

Microstructural analyses of meal patterning and drinking of a palatable solution were made over a range of drug doses administered to male Lister hooded rats.

RESULTS

Ro 60-0175 increased the latency to the first meal (3 mg/kg) and reduced meal size (1 mg/kg). d-Fenfluramine (1 mg/kg) produced a similar behavioural pattern, but 3 mg/kg produced a more profound hypophagia that persisted for 10-12 h. Ro 60-0175 (1, 3 mg/kg) and d-fenfluramine (1.5 mg/kg) reduced ingestion of a palatable glucose/saccharin solution, by a reduction in the number of bouts of licking, with little effect on the size of individual bouts. d-Fenfluramine-induced hypophagia (2.1 mg/kg) was challenged by the administration of the selective 5-HT2C receptor antagonist SB 242084 (1, 3 mg/kg) in the meal patterning paradigm. SB 242084 significantly attenuated the decrease in feeding rate and increase in latency to feed produced by d-fenfluramine, but had no effect on the fenfluramine-induced reduction in meal size. A similar pattern of results was obtained when Ro 60-0175-induced hypophagia (3 mg/kg) was challenged by SB 242084 (1, 3 mg/kg).

CONCLUSIONS

These results demonstrate that Ro 60-0175 is a useful probe of the importance of 5-HT2C activation in the control of food intake and support the hypothesis that activation of 5-HT2C receptors is a critical aspect of the hypophagic action of d-fenfluramine. The 5-HT2C receptor may prove to be a useful target in the development of clinically effective drugs for the treatment of obesity.

Comparative effects of continuous infusion of mCPP, Ro 60-0175 and d-fenfluramine on food intake, water intake, body weight and locomotor activity in rats

1. The aim of the study was to compare the effects of 14 day subcutaneous infusion of the 5-HT(2C) receptor agonists, m-chlorophenylpiperazine (mCPP, 12 mg kg(-1) day(-1)) and Ro 60-0175 (36 mg kg(-1) day(-1)) and the 5-HT releasing agent and re-uptake inhibitor, d-fenfluramine (6 mg kg(-1) day(-1)), on food and water intake, body weight gain and locomotion in lean male Lister hooded rats. 2. Chronic infusion of all three drugs significantly reduced food intake and attenuated body weight gain. In contrast, drug infusion did not lead to significant reductions in locomotor activity in animals assessed 2 and 13 days after pump implantation. 3. In a subsequent 14 day study that was designed to identify possible tolerance during days 7 - 14, animals were given a subcutaneous infusion of mCPP (12 mg kg(-1) day(-1)) or d-fenfluramine (6 mg kg(-1) day(-1)) for either 7 or 14 days. During the first 7 days both drugs significantly reduced body weight gain compared to saline-infused controls; however, from day 7 onwards animals withdrawn from drug treatment exhibited an increase in body weight such that by day 14 they were significantly heavier than their 14-day drug-treated counterparts. 4. Both mCPP and d-fenfluramine reduced daily food intake throughout the infusion periods. For 14-day treated animals this hypophagia was marked during the initial week of the study but only minor during the second week. In light of the sustained drug effect on body weight, the data suggest that weight loss by 5-HT(2C) receptor stimulation may be only partly dependent on changes in food consumption and that 5-HT(2C) receptor agonists may have effects on thermogenesis. 5. These data suggest tolerance does not develop to the effects of d-fenfluramine, mCPP and Ro 60-0175 on rat body weight gain.

Measurement of anxiety in transgenic mice

A wide range of approaches has been used to study anxiety in mice. All presuppose that aversive stimuli, such as foot shock or novelty, induce a central state of fear, which can be quantified through specific behavioural and physiological measures. This review discusses the validity of the various approaches in terms of their similarity to different human anxiety disorders, their ability to detect compounds which modulate human anxiety, and their relevance to animal defensive processes. The most commonly used models of anxiety suitable for screening transgenic and knockout mice are discussed, with an emphasis placed on controlling for factors which could confound results. As all models used to date have limitations and no single paradigm adequately models all aspects of anxiety, this review recommends the use of a broad range of anxiety models in order to provide a comprehensive characterisation of the behavioural phenotype of transgenic mice.

Reduced satiating effect of d-fenfluramine in serotonin 5-HT(2C) receptor mutant mice

RATIONALE

d-Fenfluramine stimulates the release of serotonin (5-HT) and is a potent inhibitor of the re-uptake of 5-HT into nerve terminals. Administration of d-fenfluramine suppresses food intake in both animals and humans.

OBJECTIVE

We have investigated the role of the 5-HT2C receptor in mediating the effect of d-fenfluramine on mouse food intake and the behavioural satiety sequence.

METHODS

Mutant mice lacking serotonin 5-HT2C receptors and wild-type animals were habituated to a daily presentation of wet mash. Animals were non-deprived and received d-fenfluramine (3-30 mg/kg) 30 min prior to being assessed for the presence of stereotypy and presented with wet mash. The behaviour of animals was observed for the subsequent 40 min and food intake was recorded.

RESULTS

d-Fenfluramine dose-dependently inhibited the consumption of a palatable wet mash by the mice. d-Fenfluramine (3 mg/kg) significantly reduced the amount of wet mash consumed by wild-type mice and induced a temporal advance in the behavioural satiety sequence consistent with an enhancement of satiety. Mutant mice were less sensitive to the satiating effects of 3 mg/kg d-fenfluramine. Hence, this dose of d-fenfluramine had a reduced effect on both food consumption and the behavioural satiety sequence in the 5-HT2C mutant mice. In contrast, mutant mice showed an increased sensitivity to the stereotypy induced by high doses of d-fenfluramine (10, 30 mg/kg) compared to that of wild-type littermates.

CONCLUSION

These data demonstrate a role for the 5-HT2C receptor in mediating d-fenfluramine-induced satiety.

Utility of ethological analysis to overcome locomotor confounds in elevated maze models of anxiety

The elevated plus-maze is a commonly used model to identify putative anxiolytic and anxiogenic drugs. However, the validity of elevated plus-maze and other recently developed variants such as the elevated zero-maze has recently been questioned on the grounds that both the reference anxiolytic drug chlordiazepoxide and the psychostimulant d-amphetamine increase open arm exploration and stimulate locomotor activity. These findings suggest that measures of "anxiety" in the elevated maze cannot be adequately dissociated from simple changes in locomotor activity, which may confound the interpretation of results obtained using these models. A variety of approaches to assess drug effects on locomotor activity in the elevated maze have been suggested, including the use of total and closed arm entries, as well as supplementary tests such as exploration of the holeboard apparatus. However, all these approaches utilise the measurement of exploration in a novel environment, and as such, could potentially be influenced by either changes in anxiety or locomotor activity. Recently, it has been shown that ethological measures of "risk assessment", such as stretched-attend postures and head-dipping, are sensitive indicators of drug-effects in the elevated maze. The present study assessed the utility of ethological analysis in dissociating locomotor activity from "anxiety" by comparing the effects of d-amphetamine to those of chlordiazepoxide in the rat elevated zero-maze. The results showed that both chlordiazepoxide and d-amphetamine increase the amount of time spent in the open arms and reduce "risk assessment" without increasing line crossing or rearing. These results confirm that under certain test conditions, psychostimulants are capable of producing "false-positives" in elevated maze models, and that both traditional methods and the ethological measures used in this study fail to unequivocally dissociate drug effects on anxiety from effects on locomotor activity. Further studies using other species and different classes of psychostimulants are warranted to determine the generality of these findings.

Blockade of pre- and post-synaptic 5-HT1A receptors does not modify the effect of fluoxetine or 5-hydroxytryptophan on ethanol and food intake in rats

Selective serotonin reuptake inhibitors (SSRIs) or serotonin precursors inhibit ethanol and food intake by increasing the synaptic availability of 5-HT in the central nervous system. However, these agents can also increase 5-HT levels at somatodendritic 5-HT1A autoreceptors, with negative effects on serotonergic transmission. (+)WAY100135 [N-ter-butyl 3-4-(2-methoxy-phenyl) piperazin-1-yl-2-phenylpropanamide dihydrochloride] is a selective antagonist both at pre- and post-synaptic 5-HT1A receptors. The present study investigated the effect on ethanol and food intake of (+)WAY100135, given alone or coadministered with the SSRI fluoxetine or the 5-HT precursor 5-hydroxytryptophan (5-HTP) in genetically selected alcohol-preferring rats. Blockade of presynaptic 5-HT1A receptors after injection of (+)WAY100135, 0.1 or 1 microgram/rat, into the dorsal raphe did not significantly modify ethanol, food or total fluid intake. The same doses of (+)WAY100135 did not modify the inhibition of ethanol and food intake induced by intraperitoneal (i.p.) injection of fluoxetine, 5 mg/kg. Subcutaneous (s.c.) administration of (+)WAY100135 (1 or 10 mg/kg) did not affect the 3-h, or the overnight intake of ethanol, food or total fluids. Given together with i.p. fluoxetine (5 mg/kg) or s.c. 5-HTP (100 mg/kg plus carbidopa. 12.5 mg/kg), the same s.c. doses of (+)WAY100135 did not modify their inhibitory effect on ethanol and food consumption. Present findings suggest that blockade either of pre- or of pre- and postsynaptic 5-HT1A receptors does not potentiate the inhibitory effect of fluoxetine or 5-HTP on ethanol and food intake.

WAY100635 and latent inhibition in the rat: selective effects at preexposure

The influence of the selective, silent 5HT1a antagonist WAY100635 (Wyeth Research Ltd) on the latent inhibition effect was examined in a within-subject, on-baseline conditioned suppression procedure in rats. WAY100635 was found to enhance the latent inhibition effect, producing a retardation in the acquisition of conditioned suppression following a level of stimulus preexposure known to be insufficient to produce a latent inhibition effect in control animals. This influence of the drug was restricted to its actions during the preexposure phase of the experiment, and the drug also abolished the unconditioned suppression of lever pressing that occurs on the first presentation of a novel auditory stimulus. These findings are discussed in terms of the possible influence of serotonergic manipulations on contextual processing, and also have important implications for current animal models of schizophrenia which stress the role of dopaminergic mechanisms in latent inhibition.

Behavioural and pharmacological characterisation of the canopy stretched attend posture test as a model of anxiety in mice and rats

The behavioural element, stretched attend posture (SAP), is an important component of the "risk-assessment" repertoire of defensive behaviour in rodents. The present experimental paradigm was devised as a novel and simple method of eliciting high levels of SAP in mice and rats. The SAP test apparatus comprised an elevated black Perspex circular platform. A smaller clear red Perspex circular "Canopy" was supported directly above the platform by a central pillar, thus dividing the platform into an inner, dimly lit covered zone and an outer, brightly lit exposed zone. In both the rat and mouse version of this model, vehicle-treated animals exhibited a marked preference for exploring the covered zone and also exhibited high baseline levels of SAP, particularly at the covered zone boundary whilst they investigated the exposed zone. In the mouse SAP test, the benzodiazepine receptor agonists, diazepam (0.5 mg/kg s.c.) and chlordiazepoxide (2 mg/kg s.c.), and the 5-HT1A receptor agonists, buspirone (1 and 3 mg/kg s.c.), ipsapirone (3 mg/kg s.c.) and 8-OH-DPAT (0.2 mg/kg s.c.), all significantly decreased the frequency of SAP without impairing motor activity. In the rat SAP test, diazepam (0.5 mg/kg s.c.) significantly decreased, whilst the anxiogenic 5-HT2C/1B receptor agonist, mCPP (0.25 and 0.5 mg/kg s.c.), significantly increased, the frequency of SAP. Ipsapirone (3 mg/kg s.c.) induced a non-specific behavioural inhibition. These data suggest that the "Canopy" SAP test is a useful paradigm to investigate risk assessment behaviour in both rats and mice, and may provide a sensitive novel rodent model of anxiety.

Devazepide attenuates dl-fenfluramine-induced suppression of gastric emptying but not food intake in the 17 h food-deprived rat

Recently a number of studies have provided evidence which suggests that CCK and 5-HT interact in the control of food intake. The present experiments further examine this mechanism and the possibility that CCK and 5-HT interact in the control of gastric emptying. The selective CCK-A receptor antagonist, devazepide, (0.03-3.0 mg/kg) administered alone had no intrinsic effect on gastric emptying. Devazepide (0.1 and 0.3 mg/kg) blocked dl-fenfluramine-induced (3.0 mg/kg) suppression of gastric emptying. However, devazepide (0.03-3.0 mg/kg) failed to attenuate the anorectic effect of the same dose of dl-fenfluramine. These results suggest that under the present experimental conditions CCK and 5-HT interact in the regulation of gastric emptying but not food intake. Thus the interaction between CCK and 5-HT in the regulation of gastric emptying appears not to affect the control of ingestive behaviour.

Effects of 5-HT1A receptor agonists, partial agonists and a silent antagonist on the performance of the conditioned emotional response test in the rat

In the present study, the effects of 5-HT1A receptor ligands with varying degrees of intrinsic activity at the 5-HT1A receptor were examined in the conditioned emotional response (CER) test and their effects compared to those of the benzodiazepine receptor agonists, diazepam and chlordiazepoxide. Diazepam (3.0 mg/kg) and chlordiazepoxide (3.0 mg/kg), and the 5-HT1A receptor partial agonists, ipsapirone (10.0 mg/kg) and gepirone (3.0 mg/kg), alleviated conditioned suppression of lever pressing. The 5-HT1A receptor partial agonist, buspirone (0.1-1.0 mg/kg), the 5-HT1A receptor agonist, 8-OH-DPAT (0.01-0.10 mg/kg), and the 5-HT1A receptor antagonist, WAY-100635 (0.03-3.0 mg/kg), had no effects on conditioned fear. Neither enhancing the level of food deprivation nor pretreatment with the amnesic agent scopolamine induced anxiolytic-like effects in the present CER test. The anxiolytic-like effects of ipsapirone in this test were completely reversed by WAY-100635. These results indicate that 5-HT1A agonist, but not antagonist actions, induce an anxiolytic effect in the CER test in rats.

Lack of interaction between devazepide and 8-OH-DPAT-induced hyperphagia in the rat

Recently, a number of studies have provided evidence suggesting that CCK and 5-HT interact in the control of food intake. However, the majority of these studies have relied on the administration of exogenous CCK to investigate potential interactions. The aim of the present study was to focus on the potential role of endogenous CCK in 5-HT-CCK interactions. Our prediction was that the CCKA antagonist, devazepide, alone would potentiate the hyperphagic effect of the 5-HT1A agonist, 8-OH-DPAT, in free-feeding rats. The results showed that devazepide, at a dose that had no intrinsic effect (1.0 mg/kg), did not enhance the hyperphagic effect of 8-OH-DPAT (100 and 300 micrograms/kg). This suggests that when serotonergic inhibitory activity is reduced by 5-HT1A-receptor stimulation, there is no compensatory increase of endogenous CCK activity to excite 5-HT neurons and thereby inhibit food intake.

Effects of the selective angiotensin II receptor antagonists losartan and PD123177 in animal models of anxiety and memory

There is increasing interest in the potential functional role of the octapeptide angiotensin II (AII) in psychiatric and cognitive disorders. The novel angiotensin II (AII) receptor antagonists, losartan and PD123177, selective for the AT1 and AT2 receptor subtypes respectively, constitute important pharmacological tools for the assessment of the behavioural consequences of modulation of AII function. The present series of studies investigated the effects of each compound in two animal models of anxiety, the rat elevated zero-maze and mouse light/dark box, and two models of working memory in the rat, the operant delayed matching to position (DMTP) task and the spatial reinforced alternation test in the T-maze. Our data indicate that both compounds (0.01-10 mg/kg s.c.) were without significant effect in any of the behavioural assays. Using the present methods and strains of laboratory rodents, these findings provide no support for the involvement of AII receptor function in the mediation of anxiety of working memory.

Behavioural evidence that d-fenfluramine-induced anorexia in the rat is not mediated by the 5-HT1A receptor subtype

These studies investigated the involvement of the 5-HT1A receptor in mediating d-fenfluramine-induced anorexia in the rat. Non-deprived, d-fenfluramine-treated (3.0 mg/kg) rats consumed a reduced amount of a palatable wet mash and showed a temporal advance in the behavioural sequence consistent with satiety. Thus, rats treated with d-fenfluramine ceased feeding and began resting before corresponding controls. Pretreatment with the selective 5-HT1A receptor antagonist WAY-100,635 (1.0 mg/kg) had no effect on either the reduced mash consumption or behavioural satiety sequence of d-fenfluramine-treated animals at a dose which was found to attenuate the anorexia induced by the 5-HT1A receptor agonist 8-OH-DPAT (0.5 mg/kg). Pretreatment with the non-selective 5-HT antagonist metergoline (1.0 mg/kg) attenuated the d-fenfluramine-induced reduction of mash consumption and the advanced offset of feeding. Metergoline pretreatment had no effect on the advanced onset of resting observed in d-fenfluramine-treated animals. These data suggest that d-fenfluramine reduces food intake, perhaps by enhancing satiety, via a mechanism which does not involve the 5-HT1A receptor subtype. The implications of these results to the utility of the behavioural satiety sequence as a measure of postprandial satiety are discussed.

Dissociation between cognitive and motor/motivational deficits in the delayed matching to position test: effects of scopolamine, 8-OH-DPAT and EAA antagonists

The effects of the muscarinic antagonists scopolamine HBr and MeBr, the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), and the N-methyl-d-aspartate (NMDA) antagonists MK-801 and CGS-19755 on performance of rats in a delayed matching-to-position task were examined. Pretreatment with scopolamine HBr (0.05 and 0.1 mg/kg), resulted in a delay-dependent decrease in the percentage of correct responses and discriminability (log d), but had no effect on either the latency to complete trials, or the rate of trial completion during the fixed duration session. Scopolamine MeBr (0.1 mg/kg) did not impair percent correct or increase the response latency but did decrease the rate of trial completion. 8-OH-DPAT (up to 0.3 mg/kg), had no effect on percent correct, but did induce a small decrease in discriminability. The impairment in discriminability occurred only at a dose that substantially reduced the rate of trial completion. Both MK-801 (0.05 mg/kg) and CGS 19755 (10 mg/kg) induced a delay-independent impairment in percent correct, discriminability and a reduction in the rate of trial completion without affecting latency. A lower dose of CGS 19755 (5.0 mg/kg) induced a slight impairment in discriminability without significantly affecting the other measures. Taken together, these results demonstrate some dissociation between drug-induced cognitive and motor/motivational deficits in the DMTP test. However, the data question the specificity of putative cognitive impairments reported in many previous studies with the 5-HT1A agonist 8-OH-DPAT.

Electrophysiological, biochemical, neurohormonal and behavioural studies with WAY-100635, a potent, selective and silent 5-HT1A receptor antagonist

Although considerable progress has been made in characterising the 5-HT1A receptor using agonists, partial agonists or non-selective antagonists, further studies of 5-HT1A receptor function have been hindered by the lack of highly selective antagonists. The term 'silent' antagonist has been used for such compounds in order to distinguish them unequivocally from several 5-HT1A receptor partial agonists which were initially designated 'antagonists'. In this report we provide a comprehensive review of the biochemical, pharmacological and behavioural properties of the first potent, selective and silent 5-HT1A receptor antagonist, WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-N-(2- pyridinyl)cyclohexanecarboxamide trihydrochloride). WAY-100635 had an IC50 (displacement of specific [3H]8-OH-DPAT binding to 5-HT1A receptors in the rat hippocampus) of 1.35 nM and was > 100-fold selective for the 5-HT1A site relative to a range of other CNS receptors. [3H]WAY-100635 was also characterised as the first 5-HT1A antagonist radioligand, displaying the same regional distribution of binding sites as [3H]8-OH-DPAT in rat brain. As would be expected for the binding of an antagonist to a G-protein-coupled receptor, the Bmax of [3H]WAY-100635 specific binding was consistently 50-60% greater than that of the agonist radioligand, [3H]8-OH-DPAT. Mn2+, but not guanine nucleotides, inhibited [3H]WAY-100635-specific binding. [3H]WAY-100635 was also shown to bind selectively to brain 5-HT1A receptors in vivo, following intravenous administration to mice. In vitro electrophysiological studies demonstrated that WAY-100635 had no 5-HT1A receptor agonist actions, but dose-dependently blocked the effects of agonists at both the postsynaptic 5-HT1A receptor in the CA1 region of the hippocampus, and the somatodendritic 5-HT1A receptor located on dorsal raphe 5-HT neurones. In vivo, WAY-100635 also dose-dependently blocked the ability of 8-OH-DPAT to inhibit the firing of dorsal raphe 5-HT neurones, and to induce the '5-HT syndrome', hypothermia, hyperphagia and to elevate plasma ACTH levels. In the mouse light/dark box anxiety model, WAY-100635 induced anxiolytic-like effects. WAY-100635 had no intrinsic effect on cognition in the delayed-matching-to-position model of short-term memory in the rat, but reversed the disruptive effects of 8-OH-DPAT on motor motivational performance. These data clearly demonstrate that WAY-100635 is the first potent, selective and silent 5-HT1A receptor antagonist. Furthermore, [3H]WAY-100635 is the first antagonist radioligand to become available for 5-HT1A receptor binding studies both in vitro and in vivo. The positive effects of WAY-100635 in an anxiety model also indicate that a postsynaptic 5-HT1A receptor antagonist action may contribute to the anxiolytic properties of 5-HT1A receptor partial agonists.

Multiple serotonin receptors: opportunities for new treatments for obesity?

Recent progress in the molecular pharmacology of 5-HT receptors and the development of selective ligands for various 5-HT receptor subtypes has advanced our understanding of the role of 5-HT mechanisms in the control of food intake and bodyweight. The most intensively investigated 5-HT receptor subtypes have been the 5-HT1A receptor, the 5-HT1B receptor and the 5-HT2C receptor. The overall pattern of results to date suggests that selective 5-HT2C agonists may be novel anorectic drugs and prove useful in the treatment of obesity. However, a number of issues remain unresolved, particularly regarding potential side-effects, as the 5-HT2C receptor agonist mCPP has been reported to induce anxiety and nausea in humans, actions that would clearly limit its therapeutic utility. In addition, the possible role of recently cloned 5-HT receptor subtypes such as 5-ht5, 5-ht6 and 5-ht7, remains unexplored and the development of selective ligands for these sites has the potential to lead to new treatments for obesity.

Differential effects of WAY-100135 on the decrease in 5-hydroxytryptamine release induced by buspirone and NAN-190

1-(2-Methoxyphenyl)-4-[(phthalimido)butyl] piperazine (NAN-190) and 8-[4-[4-(2-pyrimidinyl)-1-piperazinyl]butyl]-8-azaspiro[4.5] decane-7,9-dione (buspirone) are 5-HT1A receptor partial agonists which decrease 5-hydroxytryptamine (5-HT) release in vivo. In order to assess whether these ligands decrease 5-HT release by stimulating 5-HT1A receptors we examined the ability of the selective 5-HT1A receptor antagonist N-tert-butyl 3-4-(2-methoxyphenyl) piperazin-1-yl-2-phenylpropanamide dihydrochloride (WAY-100135) to block their inhibitory effects on 5-HT. NAN-190 (0.1 mg/kg s.c.) and buspirone (1.0 mg/kg s.c.) significantly decreased extracellular levels of 5-HT in hippocampal dialysates. WAY-100135 (10.0 mg/kg s.c.) attenuated the effect of buspirone but had no significant effect on the NAN-190-induced decreased in 5-HT release. These data demonstrate that buspirone is an agonist at the somatodendritic 5-HT1A receptor but that the inhibitory effects of NAN-190 on 5-HT release may be mediated via a mechanism other than, or in addition to, 5-HT1A receptor agonism.

Comparisons between the effects of 5-HT and DL-fenfluramine on food intake and gastric emptying in the rat

5-Hydroxytryptamine (5-HT) dose-dependently increased gastric emptying in rats, whereas DL-fenfluramine produced a biphasic dose response curve for gastric emptying. Thus, fenfluramine increased gastric emptying at a dose of 0.1 mg/kg but decreased it at doses of 1 and 3 mg/kg. Both 5-HT and DL-fenfluramine produced significant decreases in food intake. As 5-HT produced opposing effects on gastric emptying and food intake, it appears that the anorectic effect of 5-HT may not depend on changes in the rate of gastric emptying. In contrast, doses of DL-fenfluramine that decreased feeding also decreased gastric emptying, which suggests that reduced food intake may at least partly result from decreased gastric emptying. Taken together, these results suggest that the effects of 5-HT and DL-fenfluramine on feeding and gastric emptying may be mediated by different mechanisms.

The influence of 5-hydroxytryptamine re-uptake blockade on CCK receptor antagonist effects in the rat elevated zero-maze

In this study, the elevated zero-maze model of anxiety was used to investigate CCK receptor antagonist effects on the behaviour of male Lister-hooded rats and to demonstrate, by administering antagonists in the presence or absence of selective 5-hydroxytryptamine (5-HT) re-uptake inhibitors, the involvement of 5-HT in the mediation of these effects. Devazepide, a selective CCKA receptor antagonist, L-365,260 (3R(+)-N-2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepin- 3-yl-N1- (3-methyl-phenyl)urea) or CI-988 (4-([2-[[3-(1H-indol-3-yl)-2-methyl-1- oxo-2-[[(tricyclo[3.3.1.1.(3.7)]-dec-2-yloxy)-carbonyl]-amin o]- propyl]-amino]-1-phenylethyl]-amino)-4-oxo-[R-(R*,R*)]-butanoate- N-methyl-D-glucamine), both selective CCKB receptor antagonists, were administered 30 min prior to testing. Behavioural analysis during testing included measures of risk-assessment behaviours (e.g. stretched-attend posture) in addition to time spent on the open quadrants. Devazepide induced significant anxiolytic effects, whereas CI-988 produced inconsistent results and L-365,260 was ineffective. When administered simultaneously with the 5-HT re-uptake inhibitors zimelidine or Wy 27587 (N-[[[1-[(6- fluoro-2-naphthalenyl)methyl]-4-piperidinyl]amino] carbonyl]-3-pyridine carboxamide methyl sulphonate salt), the significant anxiolytic effect induced by devazepide was dose-dependently and significantly attenuated. Zimelidine and Wy27587 had little effect alone on zero-maze behaviour at the lower of two doses given. These data show that the elevated zero-maze, in conjunction with the analysis of 'risk-assessment' behaviours, is an anxiety model which is sensitive to the anxiolytic effects of CCK receptor antagonism.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of 8-OH-DPAT-induced elevation of plasma corticotrophin by the 5-HT1A receptor antagonist WAY100635

Numerous studies have demonstrated the stimulatory effect of 5-HT1A receptor agonists, such as 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), on plasma corticotrophin (ACTH) levels in the rat. However, until recently the lack of a selective 5-HT1A receptor antagonist has hampered mechanistic studies in this area. In this study we examined the effects of the selective 5-HT1A receptor antagonist N-[2-[4-(2-methoxyphenyl)-1- piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride (WAY100635) on plasma ACTH levels and on the elevation of ACTH induced by the 5-HT1A receptor agonist 8-OH-DPAT in the conscious rat. The basal plasma ACTH level was 41.0 +/- 1.8 pg/ml. 8-OH-DPAT increased ACTH levels at doses of 100 and 300 micrograms/kg with maximum increases of 551 and 546% respectively occurring 10 min post-injection. WAY100635 had no effects per se on plasma ACTH at doses up to 100 micrograms/kg, indicating it has no 5-HT1A receptor agonist properties. WAY100635 dose-dependently blocked the elevation of ACTH induced by 8-OH-DPAT, the minimum effective dose being 10 micrograms/kg. The present results indicate that 8-OH-DPAT elevates plasma ACTH levels by stimulating 5-HT1A receptors, a conclusion that is consistent with the findings of previous studies using non-selective 5-HT1A receptor antagonists such as pindolol.

Behavioural and pharmacological characterisation of the elevated "zero-maze" as an animal model of anxiety

The elevated "zero-maze" is a modification of the elevated plus-maze model of anxiety in rats which incorporates both traditional and novel ethological measures in the analysis of drug effects. The novel design comprises an elevated annular platform with two opposite enclosed quadrants and two open, removing any ambiguity in interpretation of time spent on the central square of the traditional design and allowing uninterrupted exploration. Using this model, the reference benzodiazepine anxiolytics, diazepam (0.125-0.5 mg/kg) and chlordiazepoxide (0.5-2.0 mg/kg) significantly increased the percentage of time spent in the open quadrants (% TO) and the frequency of head dips over the edge of the platform (HDIPS), and reduced the frequency of stretched attend postures (SAP) from the closed to open quadrants. In contrast, the anxiogenic drug m-chlorophenyl-piperazine (mCPP; 0.25-1.0 mg/kg) induced the opposite effects, decreasing %TO and HDIPS, and increasing SAP. The 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.001-0.1 mg/kg) had no effects on either %TO or HDIPS, but did decrease SAP at 0.01 mg/kg although not at higher or lower doses. Similarly, the 5-HT3 receptor antagonist, ondansetron (0.0001-1.0 mg/kg) decreased SAP and increased %TO at 0.01 mg/kg, but not at other doses. The present data suggest that a combination of the novel "zero-maze" design and a detailed ethological analysis provides a sensitive model for the detection of anxiolytic/anxiogenic drug action.

Effects of the selective 5-HT1A receptor antagonist WAY100135 and its enantiomers on 8-OH-DPAT-induced hyperglycaemia in conscious rats

8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) increases plasma glucose levels in conscious rats probably by stimulation of central 5-HT1A receptors. We have examined the effects of WAY100135 (N-tert-butyl-3-[4-(2-methoxyphenyl)piperazin-1-yl]-2-phenylpropan amide), a selective 5-HT1A receptor antagonist and its enantiomers on plasma glucose levels and on the hyperglycaemia induced by 8-OH-DPAT. (R,S)-WAY100135 (minimum effective dose (MED) 3 mg/kg i.v.) and (S)-WAY100135 (MED 1 mg/kg i.v.) dose-dependently attenuated 8-OH-DPAT-induced hyperglycaemia. In contrast, (R)-WAY100135 at doses up to 3 mg/kg i.v. was unable to block hyperglycaemia induced by 8-OH-DPAT. When the antagonists were examined for intrinsic effects on plasma glucose levels only (S)-WAY100135 (3 mg/kg i.v.) caused a significant but transient hyperglycaemia (20% increase). These results are consistent with previous suggestions that (R,S)-WAY100135 and (S)-WAY100135 are selective 5-HT1A receptor antagonists and that 8-OH-DPAT-induced hyperglycaemia is mediated by 5-HT1A receptors. The antagonist action of WAY100135 is stereoselective, and more potent activity being observed with the (S) enantiomer.

In vivo characterization of the putative 5-HT1A receptor antagonist SDZ 216,525 using two models of somatodendritic 5-HT1A receptor function

SDZ 216,525 has been proposed to be a silent 5-HT1A receptor antagonist. The present study examined the potential intrinsic agonist action of SDZ 216,525 using two in vivo models of somatodendritic 5-HT1A autoreceptor function: 5-HT release using microdialysis and feeding behaviour of satiated animals. SDZ 216,525 (1 mg/kg s.c.) and the alpha 1-adrenoceptor antagonist prazosin (1 mg/kg s.c.) significantly decreased hippocampal 5-HT release. In addition, SDZ 216,525 (3 and 10 mg/kg s.c.) and prazosin (3 and 10 mg/kg s.c.) significantly increased food intake in satiated rats. The selective 5-HT1A receptor antagonist (RS)-WAY100135 (10 mg/kg s.c.) which has been demonstrated to block the effects of 8-OH-DPAT on 5-HT release and food intake had no significant effect on the response induced by SDZ 216,525. In contrast, the non-selective 5-HT1A receptor antagonist (-)-pindolol (8 mg/kg s.c.) attenuated both SDZ 216,525 responses. The decrease in hippocampal 5-HT release and increase in food intake induced by SDZ 216,525 suggest that the compound may be a 5-HT1A receptor partial agonist. However, the failure of the 5-HT1A receptor antagonist (RS)-WAY100135 to block the SDZ 216,525 responses suggests that SDZ 216,525 decreases 5-HT release and increases food intake by a mechanism other than 5-HT1A receptor agonism. The high affinity of SDZ 216,525 for the alpha 1-adrenoceptor, and the ability of prazosin to decrease 5-HT release and increase food intake, suggest that the effects of SDZ 216,525 may be mediated via an alpha 1-adrenoceptor antagonist action.

The angiotensin converting enzyme inhibitors captopril and enalapril inhibit apomorphine-induced oral stereotypy in the rat

The possible functional interaction between angiotensin and dopamine mechanisms in the rat was investigated by examining the effects of the angiotensin converting enzyme inhibitors captopril and enalapril on apomorphine-induced stereotypy. Apomorphine-induced behaviour was observed, and recorded using a keypad linked to a microcomputer. In agreement with previous findings, low doses of apomorphine induced a syndrome of vacuous mouth movements, penile grooming, yawning and immobility whereas at higher doses the yawning syndrome disappeared to be replaced with sniffing, licking and gnawing. Two antagonism studies were carried out. In the first the effects of captopril on apomorphine-induced behaviour were compared with those of the classical neuroleptic haloperidol, and in the second dose-response curves for the effects of captopril and enalapril on apomorphine-induced behaviour were determined. Captopril had no effect on the apomorphine-induced yawning syndrome whereas this was blocked by haloperidol. In contrast, both captopril and haloperidol blocked oral stereotypy (licking and gnawing) induced by apomorphine but had no effect on sniffing induced by the dopamine agonist. Selective blockade of apomorphine-induced oral stereotypy by angiotensin converting enzyme inhibition was confirmed in the second study in which both captopril and enalapril were observed to antagonize apomorphine-induced gnawing. The inhibition of apomorphine-induced gnawing by enalapril correlated with inhibition of brain angiotensin converting enzyme, but not lung angiotensin converting enzyme, by the drug as assessed by ex vivo penetration studies. These data suggest that angiotensin converting enzyme inhibition modulates the expression of apomorphine-induced oral stereotypy, a response that is thought to be mediated by postsynaptic dopamine receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

An examination of the behavioural specificity of hypophagia induced by 5-HT1B, 5-HT1C and 5-HT2 receptor agonists using the post-prandial satiety sequence in rats

Previous studies have shown that administration of 5-HT1B, 5-HT1C or 5-HT2 agonists decreases food intake in rats. However, it has not been established whether these drugs induce satiety or decrease feeding by a non-specific mechanism. In the present study the post-prandial satiety sequence was used to characterise the actions of the 5-HT2 receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), the 5-HT1B/5-HT1C receptor agonists, 1-(3-chorophenyl) piperazine (mCPP) and 1-[3-(trifluoromethyl)phenyl] piperazine (TFMPP), and the 5-HT1B agonist, 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)H-indole (RU 24969), on feeding in rats. All four compounds reduced food intake in rats that had been food deprived overnight. The 5-HT1B/5-HT1C agonists, TFMPP (at a dose of 1.0 mg/kg) and mCPP (at a dose of 3.0 mg/kg), appeared to produce satiety as their effects on the satiety sequence were similar to those induced by a food pre-load. In contrast, the 5-HT1B agonist RU 24969 and the 5-HT2 agonist DOI did not produce behavioural profiles that resembled satiety. Thus, RU 24969 elevated active behaviours and did not accelerate resting whereas DOI appeared to induce hypophagia by a non-specific fragmentation of behaviour. The results suggest that simultaneous activation of 5-HT1B and 5-HT1C receptors may be sufficient to elicit behaviourally specific satiety in the rat. In contrast, selective activation of 5-HT2 receptors does not induce satiety but elicits active behaviours and decreases feeding by response competition.

Silent 5-HT1A receptor antagonists: utility as research tools and therapeutic agents

The 5-hydroxytryptamine 5-HT1A receptor has been the focus of considerable research effort for over a decade. However, the definitive classification of this receptor and the full characterization of its pharmacology have awaited the development of highly selective 5-HT1A receptor antagonists. The only compounds available until recently have been either nonselective or partial 5-HT1A receptor agonists (or a combination of both). Confusion has arisen owing to the use of different pharmacological models in examining the functional activity of 5-HT1A receptor ligands. Several partial agonists display only antagonist activity in models of postsynaptic 5-HT1A receptor function, whereas their agonist properties are revealed in models of presynaptic, somatodendritic 5-HT1A autoreceptor function. In view of these considerations, the term 'silent antagonist' has been introduced to distinguish true 5-HT1A receptor antagonists from partial agonists. Allan Fletcher and colleagues review the pharmacological properties of the first selective silent 5-HT1A receptor antagonists that have been recently discovered and discuss the potential therapeutic utility of these novel compounds.

The effects of CCKA and CCKB antagonists on activity in the black/white exploration model of anxiety in mice

In view of evidence suggesting that cholecystokinin (CCK) may have a role in the mediation of human panic disorders, it was predicted that CCK receptor antagonists may have anxiolytic-like activity in an animal model of anxiety, the black/white exploration test. Data revealed that, in mice, the CCKA receptor antagonist, devazepide (formerly L-364,718, MK-329), produced a clear anxiolytic-like profile with an inverted U-shaped dose-response curve centered around 5 micrograms/kg. Similarly, L-365,031, a specific, but less potent, CCKA antagonist, also produced a profile consistent with weak anxiolysis but only at 5 micrograms/kg. By direct contrast, the potent and specific CCKB antagonist L-365,260 had no robust anxiolytic-like effects in this test. Therefore, these data suggest that devazepide has the greatest effects in this model, that L-365,031 is only marginally active, and that L-365,260 is without influence. These results suggest that CCKA receptor mechanisms are involved in the mediation of anxiolytic-like effects in the black/white model of exploration in mice.

Neurochemical profile of the selective and silent 5-HT1A receptor antagonist WAY100135: an in vivo microdialysis study

The neurochemical profile of the selective 5-HT1A receptor antagonist WAY100135 [N-tert-butyl 3-4-(2-methoxyphenyl) piperazin-1-yl-2-phenylpropanamide dihydrochloride] and its enantiomers at the somatodendritic 5-HT1A receptor was determined by studying the effects of these compounds on 5-HT (5-hydroxytryptamine, serotonin) release in the rat hippocampus using in vivo microdialysis. (+/-)-WAY100135, (+)-WAY100135 and (-)-WAY100135 (all at 10 mg/kg s.c.) had no significant effect on extracellular levels of 5-HT in the hippocampus demonstrating that these compounds are devoid of 5-HT1A receptor agonist properties. In contrast, the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (0.1 mg/kg s.c.) and the partial agonists BMY 7378 (1.0 mg/kg s.c.) and buspirone (5 mg/kg s.c.) significantly decreased hippocampal 5-HT. Pretreatment with (+/-)-WAY100135 (at 10 mg/kg s.c.) and (+)-WAY100135 (at 1.0-10 mg/kg s.c.) completely blocked the 8-OH-DPAT-induced decrease in 5-HT release demonstrating that these compounds are antagonists at the somatodendritic 5-HT1A autoreceptor. (-)-WAY100135 at a dose of 10 mg/kg s.c. had no significant effect on the 8-OH-DPAT-induced inhibition of 5-HT release. (+/-)-WAY100135 had no significant effect on extracellular levels of dopamine in the rat hippocampus but significantly increased extracellular levels of noradrenaline. The mechanism underlying the increase in noradrenaline is unknown at present.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the putative 5-HT1A receptor antagonist NAN-190 on free feeding and on feeding induced by the 5-HT1A receptor agonist 8-OH-DPAT in the rat

The effects of the putative 5-HT1A receptor antagonist NAN-190 on feeding and spontaneous locomotor activity in rats were examined. The drug elicited a robust, dose-dependent (0.01-10 mg/kg) increase in food consumption in free feeding animals. Microstructural analysis of feeding induced by NAN-190 (3 mg/kg) revealed that the drug increased the duration of feeding and number of feeding bouts but decreased the feeding rate. The increase in feeding induced by 3 mg/kg of NAN-190 was not apparent until 2-4 h after injection. This prolonged latency to onset of the feeding response appeared to be due to response competition. Thus, a 'neuroleptic-like' action of the drug on spontaneous motor activity was observed during the the initial 2 h following injection. A dopamine receptor antagonist action of NAN-190 was also indicated by the results of studies in which the drug was observed to block oral stereotypy induced by the dopamine receptor agonist apomorphine. In interaction studies, NAN-190 (0.1 and 10 mg/kg) failed to block the feeding response induced by the prototypical 5-HT1A receptor agonist 8-OH-DPAT (0.0625 and 1.0 mg/kg) and indeed, appeared to have an additive effect with 8-OH-DPAT on consummatory behaviour. These data suggest that NAN-190 may act as a partial agonist rather than an antagonist at the 5-HT1A receptor and also provide the first evidence that the drug has dopamine receptor antagonist properties in vivo.

Drinking induced by subcutaneous injection of angiotensin II in the rat is blocked by the selective AT1 receptor antagonist DuP 753 but not by the selective AT2 receptor antagonist WL 19

The role of AT1 and AT2 receptors in mediating the drinking response induced by angiotensin II in the rat was examined. Angiotensin II (0.1-1.0 mg/kg s.c.) caused a dose-dependent increase in drinking in water-replete rats. The angiotensin Il-induced drinking response was dose dependently blocked by the selective AT1 receptor antagonist DuP 753 (1-30 mg/kg s.c.). In contrast, the selective AT2 receptor antagonist WL 19 failed to block angiotensin II-induced drinking up to doses of 100 mg/kg s.c. and significantly enhanced the response at 3 and 100 mg/kg. These data suggest that drinking induced by angiotensin II is mediated by AT1 receptors and that AT2 receptor activation may inhibit the drinking response.

CCK antagonists and CCK-monoamine interactions in the control of satiety

The introduction of potent cholecystokinin (CCK) receptor antagonists, selective for either the CCK-A or the CCK-B subtype, has provided a great impetus to the study of activity of endogenous CCK in relation to the control of feeding. This paper reviews experiments in which devazepide (a selective CCK-A receptor antagonist) and L-365,260 (a selective CCK-B-gastrin receptor antagonist) have been used. Both compounds increase food consumption (under certain conditions) and postpone the onset of satiety. L-365,260 is the more potent, suggesting a role for central CCK-B type receptors in satiety. In addition, use of CCK antagonists permits the study of important functional interactions between CCK and other neurochemical factors that serve to control feeding. Thus, devazepide, but not L-365,260, blocked the anorectic effect of either d-fenfluramine or serotonin. Hence, CCK-A type receptors appear to be involved in the anorectic effect of these drugs. This result serves as an example to illustrate a principle of cooperativity in the satiety-inducing effects of diverse neurochemical signals.