Profiles of visuospatial memory dysfunction in opioid-exposed and dependent populations

BACKGROUND

Chronic opioid exposure is common world-wide, but behavioural performance remains under-investigated. This study aimed to investigate visuospatial memory performance in opioid-exposed and dependent clinical populations and its associations with measures of intelligence and cognitive impulsivity.

METHODS

We recruited 109 participants: (i) patients with a history of opioid dependence due to chronic heroin use (n = 24), (ii) heroin users stabilised on methadone maintenance treatment (n = 29), (iii) participants with a history of chronic pain and prescribed tramadol and codeine (n = 28) and (iv) healthy controls (n = 28). The neuropsychological tasks from the Cambridge Neuropsychological Test Automated Battery included the Delayed Matching to Sample (DMS), Pattern Recognition Memory, Spatial Recognition Memory, Paired Associate Learning, Spatial Span Task, Spatial Working Memory and Cambridge Gambling Task. Pre-morbid general intelligence was assessed using the National Adult Reading Test.

RESULTS

As hypothesised, this study identified the differential effects of chronic heroin and methadone exposures on neuropsychological measures of visuospatial memory (p < 0.01) that were independent of injecting behaviour and dependence status. The study also identified an improvement in DMS performance (specifically at longer delays) when the methadone group was compared with the heroin group and also when the heroin group was stabilised onto methadone. Results identified differential effects of chronic heroin and methadone exposures on various neuropsychological measures of visuospatial memory independently from addiction severity measures, such as injecting behaviour and dependence status.

Evidence that mesoaccumbens dopamine and locomotor responses to nicotine in the rat are influenced by pretreatment dose and strain

RATIONALE

Sensitisation of the mesoaccumbens dopamine response to nicotine has been implicated in the development of nicotine dependence. This study explored the doses of nicotine that elicit the response in two strains of rats that differ in their baseline levels of activity.

METHODS

Male Sprague-Dawley and Lister hooded rats were pretreated with daily subcutaneous injections of (-)-nicotine for 7 days at doses ranging from 0.03 mg/kg to 0.90 mg/kg. Microdialysis studies were performed on day 9 in conscious freely moving rats, placed in an activity box and challenged with 0.4 mg/kg nicotine.

RESULTS

The acute administration of nicotine to drug-naive rats stimulated dopamine overflow in the accumbal shell but not the core. Sprague-Dawley rats, pretreated with nicotine (0.03 mg/kg/day and 0.10 mg/kg/day) showed increased basal overflow of dopamine in the accumbal core. Pretreatment with 0.10 mg/kg/day or 0.30 mg/kg/day, but not 0.03 mg/kg/day or 0.90 mg/kg/day, also caused sensitisation of the response to a nicotine challenge on the test day. Sensitisation of the locomotor response to nicotine exhibited a simple dose-response relationship, with the largest sensitisation being observed in animals pretreated with 0.90 mg/kg/day. In Lister hooded rats, pretreatment with nicotine reduced basal dopamine overflow in the accumbal core and did not cause sensitisation to a subsequent challenge with nicotine.

CONCLUSIONS

Sensitisation of the mesoaccumbens dopamine response to nicotine is influenced by pre-treatment dose and the strain of rats used. It is not related directly to the expression of sensitised locomotor responses to the drug and, therefore, may be implicated in other psychopharmacological properties of the drug, including dependence.

The pharmacology underlying pharmacotherapy for tobacco dependence: a focus on bupropion

Tobacco dependence remains the major preventable cause of early mortality and morbidity in the developed world. The primary reinforcer of the dependence is the nicotine present in tobacco smoke and, for many smokers, successful treatment depends upon breaking this dependence. Until recently, the only specific pharmacotherapy available for tobacco dependence was nicotine replacement therapy (NRT). Although this approach does significantly increase long-term cessation rates, it is by no means a panacea for the many smokers who require help to quit. Recently, a new drug, bupropion (Zyban), has been licensed as an additional pharmacological aid for smoking cessation. This commentary discusses the mechanisms that may account for its efficacy in this indication and considers the impact its introduction may have on the approach of healthcare systems to the treatment of tobacco dependence.

The putative role of extra-synaptic mesolimbic dopamine in the neurobiology of nicotine dependence

A majority of habitual tobacco smokers find it very difficult to quit the habit because they become addicted to the nicotine present in tobacco smoke. Nicotine, like other psychostimulant drugs of abuse, increases dopamine release in the principal terminal field of the mesolimbic system, the nucleus accumbens, and there is evidence that this mediates the 'rewarding' properties of the drug, which reinforce its self-administration. This review focuses on the working hypothesis that addiction to nicotine, and other psychostimulant drugs, depends upon their ability to evoke a sustained increase in dopamine release directly into the extracellular space which lies between the cells in the nucleus accumbens where it stimulates extra-synaptic dopamine receptors. It is suggested that increased stimulation of these receptors is associated with increased incentive learning or the attribution of increased incentive salience to the cues associated with acquisition and delivery of the drug. The hypothesis proposes that these cues can become conditioned reinforcers of drug-taking behaviour. The receptors, which mediate the effects of nicotine on mesoaccumbens dopamine neurones, are desensitised by sustained exposure to nicotine at concentrations commonly found in the plasma of habitual smokers. It is proposed that, at times when the plasma nicotine concentration is sufficiently high to cause desensitisation of the receptors, tobacco smoking is maintained by the conditioned reinforcers present in the tobacco smoke. The hypothesis predicts, therefore, that conditioned reinforcement may play a more important role in the addiction to tobacco than for most other addictive behaviours. As a result, studies with nicotine have the potential to contribute to our understanding of the neurobiology of addiction which cannot easily be explored using drugs, such as cocaine and amphetamine, which invariably increase dopamine overflow in the forebrain.

The effects of nicotine on neural pathways implicated in depression: a factor in nicotine addiction?

The prevalence of tobacco smoking varies considerably between different groups within the community, tobacco smoking being particularly prevalent in patients with depressive disorder. This review will focus on results, derived from animal studies, which suggest that, in addition to its primary reinforcing properties, nicotine also exerts effects in stressful environments, which may account for its enhanced addictive potential in depressed patients. It focuses on the evidence that depression sensitises patients to the adverse effects of stressful stimuli, and that this can be relieved by drugs that stimulate dopamine release in the forebrain. This mechanism, it is proposed, contributes to the increased craving to smoke in abstinent smokers exposed to such stimuli, because they become conditioned to use this property of nicotine to produce rapid alleviation of the adverse effects of the stress. The review also explores the possibility that chronic exposure to nicotine elicits changes in 5-HT formation and release in the hippocampus which are depressogenic. It is postulated that smokers are protected from the consequences of these changes, while they continue to smoke, by the antidepressant properties of nicotine. However, they contribute to the symptoms of depression experienced by many smokers when they first quit the habit.

The influence of lobeline on nucleus accumbens dopamine and locomotor responses to nicotine in nicotine-pretreated rats

In vivo brain microdialysis was used to investigate the influence of lobeline on dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) overflow in the core of the nucleus accumbens of freely-moving rats pretreated with nicotine (0.4 mg x kg(-1), s.c., once per day for 5 days). Locomotion was also recorded. Lobeline, at doses of 0.7, 4.0 and 10.0 mg x kg(-1), i.p., failed to elicit any significant changes in extracellular dopamine or dihydroxyphenylacetic acid levels during the 60 min following its administration and did not stimulate locomotor. The dopamine responses to nicotine (0.4 mg x kg(-1), s.c.), were abolished (P<0.01) if the nicotine challenge was administered 10 min but not 60 min, after lobeline doses of 4.0 and 10.0 mg kg(-1), i.p., but were unaffected following lobeline at the lowest dose tested (0.7 mg x kg(-1), i.p.) at either time. The increase in locomotor activity was significantly attenuated (P<0.01), to a similar extent, when the nicotine was injected 10 min, but not 60 min, after all three doses of lobeline (0.7, 4.0 and 10.0 mg kg(-1), i.p.) when compared with the saline-treated rats. The results suggest that lobeline is a short-acting antagonist of the nicotinic AChRs which mediate the effects of nicotine on mesolimbic dopamine activity and locomotor stimulation.

The influence of nicotine pretreatment on mesoaccumbens dopamine overflow and locomotor responses to D-amphetamine

Pretreatment with psychostimulant drugs causes sensitisation of their effects on locomotor activity and dopamine (DA) overflow in the nucleus accumbens (NAcc) and there is evidence for similarities in the mechanisms involved. This study used in vivo microdialysis in conscious freely moving rats to investigate the extent to which pretreatment with nicotine causes sensitisation to D-amphetamine. Pretreatment with nicotine (0.4 mg/kg s.c. daily for 5 days) caused sensitisation of the locomotor responses to D-amphetamine (0.1-0.5 mg/kg s.c.) but not cocaine (15 mg/kg i.p.). Nicotine pretreatment did not influence the increase in DA overflow into dialysis probes, located in the core of the NAcc, evoked by systemic injections of D-amphetamine or cocaine (15 mg/kg i.p.) but decreased the overflow evoked by the administration of D-amphetamine (1 x 10(-6) M) through the dialysis probe. The results provide further evidence for a dissociation between the expression of sensitised locomotor responses to psychostimulant drugs and sensitisation of their stimulatory effects on DA overflow in the core of the NAcc. The results suggest that the sensitisation of the effects of nicotine on DA overflow in this subdivision of the NAcc may be pharmacologically specific to nicotinic drugs.

Sensitization of the mesoaccumbens dopamine response to nicotine

This article reviews the evidence that pretreatment with nicotine causes a regionally selective sensitization of its stimulatory effects on a pathway, the mesoaccumbens dopamine (DA) system, which has been implicated in the locomotor stimulant response to nicotine and its ability to reinforce self-administration. The sensitization evoked by daily injections of nicotine is associated with a regionally selective downregulation of the control of mesoaccumbens DA neurons by inhibitory autoreceptors and depends upon co-stimulation of NMDA glutamatergic receptors. It is suggested that the sensitization is related to enhanced burst firing of mesoaccumbens neurons, which results in an enhancement of DA release into the extracellular space between the cells where it acts upon putative extrasynaptic dopamine receptors. The studies with NMDA receptor antagonists revealed a dissociation between the expression of sensitized mesoaccumbens DA and locomotor responses to nicotine. It is proposed, therefore, that the sensitized mesoaccumbens DA responses to nicotine may be implicated in psychopharmacological responses to drug concerned more closely with nicotine dependence.

Society for Research on Nicotine and Tobacco

The proceedings of the second annual scientific conference of the Society for Research on Nicotine and Tobacco are summarized. The goal of the annual conference was to disseminate information about ongoing nicotine research from biological, behavioral and social perspectives. Data were presented describing our current understanding of the structure and function of neuronal nicotinic acetylcholine receptors, by which nicotine exerts most, if not all, of its effects in the brain. The conformational complexity of receptor subunits expressed in different brain areas contributes significantly to the complexity of responses observed to nicotinic agonists. Nicotine is being developed as a medication that might be used to maintain smoking cessation and to treat various medical diseases. The potential toxicity of nicotine, apart from cigarette smoking, is an important variable in assessing the benefits and risks of such therapeutic applications. The risks of nicotine-containing medications appear to be far less than those associated with tobacco use. Recent data indicate that cigarette smoking is increasing among young in the United States. Adolescent smokers are interested in quitting and make frequent quit attempts, but are usually not successful. Effective methods are needed to manage adolescent smokers before they become heavily addicted. Nicotine replacement as a pharmacological treatment for smoking cessation has made a significant contribution in improving quit rates. New medications have been developed that target specific populations of smokers.

Regional variation in the effects of nicotine on catecholamine overflow in rat brain

The effects of acute, repeated intermittent and continuous administration of nicotine on the overflow of noradrenaline in the ventral hippocampus and dopamine in the nucleus accumbens and striatum have been studied. Daily injections of nicotine (0.4 mg/kg(-1) for 5 days) enhanced noradrenaline and dopamine overflow in the ventral hippocampus and nucleus accumbens respectively (P < 0.01 and P < 0.05) but not dopamine in the striatum in response to a nicotine challenge. The responses in the ventral hippocampus and nucleus accumbens were attenuated (P < 0.01) by the constant infusion of nicotine at a dose of 1 mg kg(-1) per day; the dopamine response in the striatum required a higher dose (4 mg kg(-1) per day) before desensitisation was observed. The data suggest that the dopamine projections to the striatum are less sensitive to both stimulation and desensitisation by nicotine than the catecholamine projections to the ventral hippocampus and nucleus accumbens.

Effects of acute D-CPPene on mesoaccumbens dopamine responses to nicotine in the rat

Acute administration of the NMDA receptor antagonist, D-CPPene (SDZ EAA 494; 3-(2-carboxypiperazin-4-yl)-1-propenyl-1-phosphonic acid; 2 mg/kg), abolished (P < 0.01) the sensitised mesoaccumbens dopamine response to nicotine (0.4 mg/kg) measured using in vivo microdialysis, but not the increased locomotor activity, observed in rats pretreated with nicotine prior to the test day. D-CPPene enhanced (P < 0.01) the mesoaccumbens dopamine response, but not the locomotor response, to acute nicotine given to drug-naive rats. The data suggest that sensitised mesoaccumbens dopamine responses to nicotine involve co-stimulation of NMDA receptors but that this effect is not closely related to sensitisation of the locomotor response to the drug.

Neurochemical and behavioural interactions between ibogaine and nicotine in the rat

1. In vivo brain microdialysis has been employed to investigate the effects of ibogaine on nicotine-induced changes in dopamine overflow in the nucleus accumbens (NAc) of freely moving rats. The effects of the compound on locomotor responses to nicotine and behaviour in the elevated plus-maze were also examined. 2. No changes were observed in the dopamine overflow or the locomotor activity of the animals following the administration of ibogaine (40 mg kg-1, i.p.). However, ibogaine, administered 22 h earlier, significantly (P < 0.01) attenuated the increase in dopamine overflow but not the hyperlocomotion, evoked by nicotine. 3. In the elevated plus-maze test, significant reductions in the open:total runway entries in both saline-treated controls (P < 0.05) and nicotine-treated (P < 0.01) rats were obtained when the animals were tested 22 h after pretreatment with ibogaine (40 mg kg-1, i.p.). The total activity was significantly (P < 0.01) greater in the nicotine-treated rats but this response was not affected by ibogaine pretreatment. 4. Administration of ibogaine was associated with reductions in the tissue levels of 5-hydroxyindoleacetic acid (5-HIAA) in the NAc (P < 0.01) and striatum (P < 0.05) and an increase in the level of this metabolite in the medial prefrontal cortex (mPFC) (P < 0.01) while the levels of dopamine and 5-hydroxytryptamine (5-HT) in the mPFC were reduced (P < 0.05). The DOPAC/dopamine (P < 0.05) and 5-HIAA/5-HT (P < 0.01) ratios were significantly increased in the mPFC for at least 7 days after a single treatment with ibogaine. 5. Ibogaine attenuates the nicotine-induced increases in dopamine overflow in the NAc and may, therefore, inhibit the rewarding effects of this drug. However, the long lasting anxiogenesis induced by ibogaine warrant further investigation before its use could be recommended for smokers.

Pharmacology of nicotine and its therapeutic use in smoking cessation and neurodegenerative disorders

During the last decade, nicotine has been used increasingly as an aid to smoking cessation and has been found to be a safe and efficacious treatment for the symptoms of nicotine withdrawal. This period has also seen significant advances in our understanding of the mechanisms underlying the psychopharmacological responses to nicotine, including, particularly, those that have been implicated in nicotine addiction. This paper reviews this decade of progress in the specific context of the therapeutic application of nicotine to the treatment of smoking cessation. Other putative future applications, particularly in the treatment of neurodegenerative disorders, are also reviewed.

Desensitization of the nicotine-induced mesolimbic dopamine responses during constant infusion with nicotine

1. The effects of constant nicotine infusions (0.25, 1.0 and 4.0 mg kg-1 day-1) on extracellular dopamine levels in the nucleus accumbens (NAc) and on locomotor activity have been compared with the changes evoked by repeated daily injections (0.4 mg kg-1 day-1 for 5 days) of the drug. 2. The extracellular dopamine concentration in the NAc was significantly increased (P < 0.05) following a challenge dose of nicotine (0.4 mg kg-1, s.c.) in animals which had been pretreated with daily injections of the drug. This effect was accompanied by an enhanced locomotor response to nicotine. 3. The stimulant effects of nicotine on mesolimbic dopamine secretion and on locomotor activity were significantly inhibited (P < 0.01) by the prior administration of mecamylamine (2.0 mg kg-1, s.c.) but not by hexamethonium (2.0 mg kg-1, s.c.). 4. The constant infusion of nicotine at a rate of 1 and 4 but not 0.25 mg kg-1 day-1 abolished the sensitized dopamine response in the NAc to an injection of nicotine in animals pretreated with the drug. The locomotor responses to nicotine in the nicotine-pretreated rats were significantly attenuated by the infusion of nicotine at all 3 doses, although the nicotine induced locomotor activity, in the rats infused with 0.25 mg kg-1 day-1 was also significantly (P < 0.05) higher than that observed in the rats treated acutely with nicotine. 5. Significantly (P<0.01) enhanced mesolimbic dopamine responses, to a challenge injection of nicotine(0.4 mg kg-1, s.c.), were observed 2 and 7 days after termination of the infusion of nicotine (4 mg kg-1 day-1 for 14 days); locomotor responses were enhanced (P<0.01) 1, 2 and 7 days after termination of the infusion.6. The results suggest that sensitized mesolimbic dopamine responses to nicotine occur as a result of stimulation of centrally located nicotinic receptors but that these receptors may be desensitized during periods of chronic exposure to nicotine at doses which may be relevant to smoking.

Neural mechanisms underlying nicotine dependence

There is little doubt that many habitual smokers find it difficult to quit the habit because they have become addicted to the nicotine present in the smoke. This paper addresses some of the pharmacological mechanisms underlying this addiction and discusses how an understanding of these mechanisms may contribute to the more effective use of nicotine replacement therapy during smoking cessation. It considers critically the evidence that the "rewarding" properties of nicotine, which serve to reinforce drug-seeking behaviour, are related to stimulation of the mesolimbic dopamine system of the brain. The critique focuses specifically on the evidence that many central nicotinic receptors, including those which mediate the effects of the drug on dopamine secretion, are readily desensitized by chronic exposure to agonist and that hypotheses which assume that nicotine inhaled from tobacco smoke invariably results in stimulation of the receptors must be treated with caution. Nicotinic receptors in the brain are, however, heterogeneous in nature with different molecular structures and pharmacologies. It is concluded that the reinforcing properties of nicotine sought by smokers may reflect both stimulation and desensitization of the different nicotinic receptor populations, and that smokers may adjust their smoking habits to achieve the balance of receptor stimulation and desensitization which they find most reinforcing. It seems likely that the efficacy of the different nicotine formulations during the treatment of smoking cessation may also reflect their ability to stimulate or desensitize brain nicotinic receptors.

Behavioural and neurochemical adaptations to nicotine in rats: influence of NMDA antagonists

1. The repeated co-administration of the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (0.1 and 0.3 mg kg-1, i.p.) with nicotine (0.4 mg kg-1, s.c.) attenuated the development of tolerance to the locomotor depressant effect of the nicotine in rats. 2. The repeated co-administration of the competitive NMDA antagonist D-CPPene (SDZ EAA 494; 3-(2-carboxypiperazin-4-yl)-1-propenyl-1-phosphonic acid, 2 and 8 mg kg-1, i.p.) also attenuated tolerance to the locomotor depressant effect of nicotine. 3. Dizocilpine (0.3 mg kg-1, i.p.) pretreatment attenuated sensitization to the locomotor stimulant effect of nicotine (0.4 mg kg-1, s.c.) and prevented sensitization of nicotine-induced dopamine release in the nucleus accumbens. However, pretreatment with dizocilpine alone caused a modest enhancement of the behavioural response to a subsequent acute dose of nicotine. 4. D-CPPene (2.0 mg kg-1, i.p.) pretreatment prevented sensitization to the nicotine-induced dopamine release in the nucleus accumbens. There was no enhanced locomotor response that could be attributed to nicotine pretreatment when D-CPPene was co-administered with nicotine. However, pretreatment with D-CPPene alone enhanced the locomotor response to an acute dose of nicotine. 5. The results suggest the involvement of NMDA receptors in adaptations of the behavioural and neurochemical effects of nicotine that occur as a result of repeated administration of the drug.

Studies on the influence of nicotine infusions on mesolimbic dopamine and locomotor responses to nicotine

The present study examined the effects of constant nicotine infusions on dopamine overflow in the nucleus accumbens and on locomotor activity and compared them with the changes evoked by repeated daily injections (one injection per day for 5 days) of the drug. The putative anxiolytic properties of nicotine have also been examined using the elevated plus-maze test of anxiety. Repetitive daily subcutaneous injections of nicotine (0.4 mg/kg) enhanced (P < 0.01) the overflow of dopamine evoked by a challenge dose of the drug (0.4 mg/kg) and increased (P < 0.01) its stimulatory effects on locomotor activity. The constant infusion of nicotine, at doses of 1 and 4 mg/kg per day, abolished (P < 0.05) the effects of a bolus injection of nicotine on extracellular dopamine and attenuated (P < 0.01) the enhanced locomotor response evoked by daily pretreatment with nicotine boli. The mesolimbic dopamine response to a bolus injection of nicotine was not significantly attenuated by nicotine infusions when the dose was reduced to 0.25 mg/kg per day. The locomotor responses in these rats were significantly (P < 0.05) less than those seen in the animals pretreated with nicotine injections alone but were also higher (P < 0.05) than those seen in saline-treated control rats given a bolus injection of nicotine. Neither the constant infusion (4 mg/kg per day) nor the injection of nicotine (0.4 mg/kg) evoked an anxiolytic or anxiogenic effect in the elevated plus-maze test. However, the nicotine infusions did abolish the locomotor stimulant effects of the drug in this apparatus.(ABSTRACT TRUNCATED AT 250 WORDS)

The differential effects of circulating norepinephrine and neuronally released norepinephrine on sodium excretion in humans

The renal effects of incremental infusions of norepinephrine (placebo, 0.025 mu/kg/min), 0.075 micrograms/kg/min, phenylephrine (placebo, 0.5 micrograms/kg/min, 2.5 micrograms/kg/min), and tyramine (placebo, 2 micrograms/kg/min, 15 micrograms/kg/min) were examined in three respective groups (n = 9, 8, and 8) of normotensive male subjects undergoing water diuresis. Tyramine is an indirect sympathetic agent that causes neuronal release of endogenous norepinephrine. Increases in mean arterial pressure during each high-dose infusion were comparable in all three groups. Both norepinephrine and phenylephrine caused a decrease in urinary sodium excretion and effective renal plasma flow, with no changes in glomerular filtration rate. Proximal tubular sodium reabsorption, as assessed by both lithium clearance and solute-free water clearance methods, was increased by pressor doses of norepinephrine and phenylephrine. In contrast, a similar pressor dose of tyramine was associated with a pressure natriuresis, an increase in effective renal plasma flow, and a decrease in proximal tubular sodium reabsorption. Our data indicate that, in normotensive humans, circulating catecholamines (norepinephrine and phenylephrine) have opposite effects on renal sodium handling from neuronally released norepinephrine (tyramine).

Effect of noradrenaline on renal sodium and water handling in euhydrated and overhydrated man

1. The renal effects of incremental doses of intravenously infused noradrenaline were evaluated in normal subjects during two different water loads, 5 ml/kg (n = 6) and 20 ml/kg (n = 9), producing conditions of euhydration and overhydration, respectively. 2. Noradrenaline infusion rates ranged from 0.015 to 0.075 microgram min-1 kg-1. In the euhydrated subjects, noradrenaline caused a dose-dependent fall in urinary sodium excretion and an increase in urinary flow rate. During overhydration similar doses of noradrenaline caused a fall in urinary sodium excretion but a decrease in urinary flow rate. 3. Although there was no detectable change in glomerular filtration rate, a dose-dependent fall in effective renal plasma flow was observed in both hydration states during noradrenaline infusion. 4. Noradrenaline infusion was associated with a dose-dependent increase in proximal tubular sodium reabsorption as assessed by the lithium clearance method. Fractional reabsorption of sodium by the distal nephron was, however, unchanged by noradrenaline in both hydration states. 5. Plasma vasopressin concentration was unchanged by noradrenaline in euhydrated subjects. The renin-angiotensin-aldosterone axis was stimulated by noradrenaline in both euhydrated and overhydrated subjects. 6. Thus we conclude that plasma circulating noradrenaline has a dose-dependent antinatriuretic effect in man. The antinatriuretic effect of noradrenaline is mediated mainly at the proximal tubule in man. We have also shown that during overhydration, noradrenaline decreased urinary flow rate. In contrast, in euhydrated subjects, noradrenaline increased urinary flow rate with no accompanying changes in plasma vasopressin concentration, which suggests a direct effect of noradrenaline on the renal tubular permeability to water.

Development of PharmTest: a unique personal computer-mediated tool for assessment of pharmacology

This report concerns the development of an assessment* model (PharmTest) for further evaluation by academic pharmacologists. The content area chosen for this model is the pharmacology of affective disorders. The components of the PharmTest system are: 1) a cognitive map of the content area used to develop the learning objectives (Figure): 2) both lower- and higher-level objectives developed jointly by basic and clinical faculty; 3) a bank of multiple choice questions (MCQ) judged to be congruent to the objectives by an expert panel; 4) a software program (SP) to manage the testing process; and 5) an annotated self-study document to aid students in their review after computer self-testing. PharmTest is designed to assist faculty in producing tests, making possible student self-testing and study. PharmTest was developed during a 6-month cooperative project between a faculty member from the University of North Carolina (HJB) and faculty of the University of Dundee. This report presents the learning objectives and cognitive map developed for the model content topic of "Pharmacology of Affective Disorders." Also it suggests a recipe for development of other content areas of pharmacology based on this project. Also, it presents the development process for PharmTest. Finally a plan for collecting evaluation data from academic pharmacology faculty is presented. Implications of the increased efficiency to faculty in linking learning objectives and testing are discussed, and a suggestion is made for national evaluation of learning in pharmacology.

Enalapril blunts the antinatriuretic effect of circulating noradrenaline in man

OBJECTIVE

The present study examines the effect of angiotensin converting enzyme inhibition on the renal haemodynamic and sodium excretory responses to noradrenaline in man.

DESIGN

We studied the effects of intravenous noradrenaline (0.075 micrograms/kg per min) and enalapril pretreatment (5 mg/day for 5 days), alone and in combination, on urinary sodium excretion, effective renal plasma flow, glomerular filtration rate and segmental tubular function in nine normal subjects.

METHODS

The subjects were studied during maximal water diuresis. The clearance of inulin and of para-aminohippurate were used to estimate the glomerular filtration rate and effective renal plasma flow, respectively. Segmental tubule handling of sodium was assessed by the lithium clearance method.

RESULTS

Noradrenaline alone decreased urinary sodium excretion (P < 0.01) and the effective renal plasma flow (P < 0.01) without altering the glomerular filtration rate. Enalapril pretreatment significantly attenuated this fall in sodium excretion (P < 0.05) and effective renal plasma flow (P < 0.05), and had a similar attenuating effect on the noradrenaline-induced decrease in the fractional excretion of lithium. The pressor response to noradrenaline infusion was not, however, influenced by the enalapril pretreatment.

CONCLUSIONS

Enalapril blunts the renal vasoconstrictive effect and the antinatriuretic effect of noradrenaline in man. Our results indicate that there is an important interaction between the sympathetic nervous system and the renin-angiotensin system in the kidneys in man.

Influence of tetrodotoxin and calcium on changes in extracellular dopamine levels evoked by systemic nicotine

The influence of tetrodotoxin (TTX) and calcium on the increase of extracellular dopamine (DA) levels in the nucleus accumbens (NAcc), evoked by the systemic administration of nicotine, cocaine and d-amphetamine, have been studied in conscious, freely moving rats using in vivo microdialysis. TTX (10(-6) M), administered via the dialysis probe, completely abolished (P < 0.01) the elevations in extracellular DA, DOPAC and HVA seen following nicotine (0.4 mg/kg SC). The removal of calcium with the inclusion of diaminoethanetetraacetic acid (EDTA 10(-4) M) in the Ringer solution was also associated with inhibition (P < 0.01) of the nicotine-induced changes in these parameters. The systemic administration of cocaine (15 mg/kg IP) and d-amphetamine (0.5 mg/kg SC) caused elevations in extracellular DA (P < 0.01) accompanied by significant decreases (P < 0.01) in HVA levels. DOPAC levels were also significantly (P < 0.01) lowered by d-amphetamine treatment. The presence of TTX and removal of calcium with addition of EDTA completely abolished the changes in NAcc DA and HVA induced by cocaine. TTX had no influence on the d-amphetamine evoked responses in NAcc DA. However, the metabolites, which were markedly reduced by the TTX, were not further decreased by the systemic administration of d-amphetamine. NAcc DA was significantly (P < 0.01) raised following d-amphetamine in the absence of calcium and presence of EDTA. However, this was significantly (P < 0.01) attenuated in comparison to that seen in the presence of calcium. The results support the conclusion that, at the dose tested, nicotine evokes increases in extracellular NAcc DA levels by calcium and impulse-dependent mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Prazosin blunts the antinatriuretic effect of circulating angiotensin II in man

OBJECTIVE

The present study examines the role of alpha 1-adrenoceptors in determining the renal haemodynamic and sodium excretory responses to a physiological dose of angiotensin II in man.

DESIGN

The effects of a low-dose infusion of angiotensin II (1 ng/kg per min) and a non-depressor dose of prazosin (0.25 mg), alone and in combination, on urinary sodium excretion (UNaV), effective renal plasma flow (ERPF), glomerular filtration rate (GFR) and segmental tubular function were studied in eight normal male subjects.

METHODS

Subjects were studied undergoing maximal water diuresis. Clearances of inulin and para-aminohippurate were employed to estimate GFR and ERPF, respectively. Segmental tubular handling was assessed by both lithium clearance (CLi) and solute-free water methods.

RESULTS

Angiotensin II decreased UNaV without altering ERPF and GFR. Angiotensin II caused a significant fall in fractional CLi, which may indicate a proximal tubular effect of angiotensin II. Angiotensin II alone also increased fractional reabsorption of sodium delivered to the distal nephron, as evaluated by both the CLi method and by estimation of solute-free water clearance. When angiotensin II was given in combination with prazosin, which on its own had no apparent effects on any renal parameters, the antinatriuretic and tubular effects of angiotensin II were significantly blunted.

CONCLUSIONS

These findings suggest that low doses of circulating angiotensin II are able to modulate UNaV by increasing sodium reabsorption in the proximal and, to some extent, the distal nephron segment in man. The study also showed that a non-depressor dose of prazosin blunted the renal effects of angiotensin II, thereby providing tentative evidence of a renal interaction between alpha-adrenoceptors and angiotensin II in man.

Prazosin attenuates the natriuretic response to atrial natriuretic factor in man

The effect of alpha-1-adrenoceptor blockade with 0.25 mg oral prazosin on the renal response to atrial natriuretic factor (ANF) 5 pmol/kg/min was examined in eight healthy male volunteers undergoing maximal water diuresis. ANF on its own decreased mean arterial blood pressure (P less than 0.05) without altering heart rate or increasing plasma norepinephrine. ANF increased urinary sodium excretion by 130% (P less than 0.01) from baseline value with accompanying 18% decrease (P less than 0.05) in PAH clearance (ERPF) without changing inulin clearance (GFR). When compared to placebo infusion, ANF infusion caused a significant increase in fractional excretion lithium (FELi), a marker of proximal tubular function. Fractional distal delivery of sodium, another marker of proximal tubular outflow as determined by free water clearance, was also increased during ANF infusion. As expected, ANF decreased distal nephron fractional sodium reabsorption as evaluated by both the "lithium method" and by the conventional "solute-free water method." Prazosin on its own had no effect on blood pressure, renal function or hormonal parameters. When given in combination with ANF, prazosin blunted the natriuretic effect of ANF from 130% to 35% (P less than 0.01). However, prazosin pretreatment did not influence the ANF-induced fall in blood pressure or ERPF nor the ANF-induced suppression of plasma aldosterone. We have therefore found evidence to support the hypothesis that at basal levels of sympathetic tone, the natriuretic effect of ANF in man is dependent on an intact sympathetic nervous system, since sympathetic blockade by prazosin blunts its sodium excretory effects.

The effects of acute and repeated nicotine treatment on nucleus accumbens dopamine and locomotor activity

1. The effects of acute and subchronic nicotine and (+)-amphetamine on the extracellular levels of dopamine and its metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in nucleus accumbens (NAc) have been studied in conscious, freely-moving rats by use of in vivo microdialysis. 2. In rats which had been habituated to the test apparatus for approximately 80 min, the acute subcutaneous (s.c.) administration of nicotine (0.1 or 0.4 mg kg-1) caused a dose-dependent increase (P less than 0.01) in spontaneous activity and evoked significant increases (P less than 0.05) in the extracellular levels of DOPAC and HVA. 3. Measurements made 24 h after the last injection of nicotine showed that pretreatment with the higher doses tested (0.4 mg kg-1) resulted in increased basal levels of dopamine (P less than 0.01) and decreased basal levels of DOPAC (P less than 0.05) in the NAc dialysates. 4. Pretreatment with nicotine (0.1 or 0.4 mg kg-1 daily for 5 days) enhanced the effects of the drug on spontaneous locomotor activity and enhanced the effects of the drug on extracellular levels of dopamine to the extent that the response became significant (P less than 0.05). 5. If a dopamine uptake inhibitor, nomifensine, was added to the Ringer solution used to dialyse the probe, the s.c. administration of both acute and subchronic nicotine (0.4 mg kg-1) resulted in significant increases (P less than 0.05) in the dopamine concentration in the dialysate. Under these conditions, pretreatment with nicotine prior to the test day prolonged (P less than 0.05) the dopamine response to a challenge dose of nicotine.6. Subcutaneous injections of (+)-amphetamine (0.2 or 0.5 mg kg-') evoked dose-dependent increases in both spontaneous activity and the concentration of dopamine in NAc dialysates. These responses were unaffected by 5 days pretreatment with the drug.7. The results of this study support the conclusion that the enhanced locomotor response to nicotine observed in animals pretreated with the drug prior to the test day is associated with potentiation of its effects on dopamine secretion in the NAc.

The influence of stress on psychopharmacological responses to nicotine

This essay considers the mechanisms which may mediate the apparent anxiolytic properties of nicotine and which are thought to be responsible for the 'calming' effect of tobacco smoke experienced by many smokers. It summarizes the evidence that, in many tests for anxiolytic activity, the effects of nicotine do not resemble those of established anxiolytic drugs such as diazepam and concludes that it is likely that neural systems other than those which mediate the responses to the benzodiazepines are responsible for the putative anxiolytic properties of nicotine. Circumstantial evidence which suggests that the increase in mesolimbic dopamine secretion evoked by nicotine may not only be rewarding per se but may also contribute to the ability of the drug to alleviate the effects of stress is presented. The essay also summarizes results which suggest that chronic nicotine evokes changes in the mesolimbic dopamine system which resemble those seen in animals treated chronically with antidepressant drugs and proposes that the mechanisms which mediate the ability of antidepressant drugs to alleviate the effects of stress may also mediate the apparent anxiolytic properties of nicotine. The possible consequences of this hypothesis for future research are considered.

A comparison of the effects of nicotine and (+)-amphetamine on rat behaviour in an unsignalled Sidman avoidance schedule

In agreement with the results of previous studies, the withdrawal of nicotine from rats trained on an unsignalled Sidman avoidance schedule under the influence of the drug (0.4 mg kg-1 given subcutaneously 3 min before each training session) was associated with a reduction in lever-pressing responses (P less than 0.05) and an increase in the number of shocks received (P less than 0.01). The number of shocks received by the withdrawn rats was also greater (P less than 0.05) than the number of shocks received by rats trained and tested with saline, whereas the number of lever-pressing responses recorded for saline-treated rats was not influenced significantly by the drug used during training. The subcutaneous administration of (+)-amphetamine (0.5 mg kg-1 30 min before the test session) stimulated lever-pressing in rats trained with saline or nicotine and abolished the increase in the number of shocks received by the nicotine-withdrawn rats, but had no significant effect on the number of shocks received by rats trained with saline. The number of shocks received by the rats trained on the schedule with (+)-amphetamine but tested after an injection of saline was also greater (P less than 0.05) than the number of shocks received by rats trained and tested with saline. It is concluded that the disruption in shock avoidance performance observed for the nicotine- and (+)-amphetamine-withdrawn rats may reflect the development of dependence upon the stimulant properties of these drugs.

Modulation of the GABAA receptor by barbiturates and pregnane steroids: differential effects of the influence of assay temperature

The effect of temperature on the modulation of the GABAA receptor by barbiturates and steroids has been investigated in-vitro using a radioreceptor binding assay. Displaceable [3H]muscimol binding to a crude membrane preparation from rat cerebral cortex was enhanced by the endogenous steroid metabolite, 5 beta-pregnan-3 alpha-ol-20-one, by the synthetic steroid, alphaxalone, and by pentobarbitone in a dose-dependent manner. Hydrocortisone and corticosterone had no significant effect on [3H]muscimol binding. Analysis of binding data using a curve-fitting program ('Ligand') showed that both pentobarbitone (1 mM) and 5 beta-pregnan-3 alpha-ol-20-one (10 microM) increased the apparent number of high affinity binding sites in the membrane but had no effect on the affinity of [3H]muscimol binding (Kd approx. 11 nM). Increasing the assay temperature from 0 degrees C to 35 degrees C decreased [3H]muscimol binding and decreased the enhancement of binding by pentobarbitone but had no effect on 5 beta-pregnan-3 alpha-ol-20-one enhancement of binding. 5 alpha-Pregnan-3 alpha-ol-20-one increased the apparent rate of association of [3H]muscimol binding to its receptor whereas pentobarbitone had no effect. These different effects on the apparent association rate and the different responses to temperature, suggest that the barbiturate and steroid may interact with the GABAA receptor through different binding sites.

Smoking-associated changes in the serotonergic systems of discrete regions of human brain

This paper describes the results of a postmortem study of the effects of tobacco smoking on the concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) as well as the binding of [3H]-8-hydroxy-(di-n-propylamino)-tetralin ([3H]-8-OH-DPAT) and [3H]-ketanserin in six discrete regions of human brain. Smoking was associated with significant decreases in the concentrations of 5-HIAA in the hippocampal neocortex (P less than 0.001), hippocampal formation (P less than 0.05) and the median raphe nuclei (P less than 0.05). The 5-HT level of the hippocampal formation was also significantly reduced in smokers (P less than 0.05). These changes were accompanied by significant increases in the binding of [3H]-8-OH-DPAT in the hippocampal neocortex (P less than 0.01) and hippocampal formation (P less than 0.05). [3H]-Ketanserin binding in the brain regions studied was unaffected by smoking. It is concluded that smoking is associated with a regionally selective decrease in the activity of the serotonergic system of the human hippocampus.

Aversive environmental stimuli as a factor in the psychostimulant response to nicotine

Saline-treated rats tested on an elevated open platform were less active (p less than 0.01) than those tested on an enclosed platform of the same dimensions. Acute nicotine (0.05, 0.1 and 0.4 mg/kg SC) increased the activity (p less than 0.01) of rats tested on the open platform but had no effect on activity measured on the enclosed platform. When injected chronically, the highest dose tested increased the activity of rats tested on both platforms, whereas the two lower doses continued to exert selective effects on the activity of rats tested on the open platform. d-Amphetamine (0.1 to 0.5 mg/kg SC) and cocaine (5 and 15 mg/kg IP) evoked dose-dependent increases in activity which were independent of the test environment used. It is concluded that nicotine appeared to be a more effective psychostimulant in the rats tested on the open platform because, at doses lower than those needed to evoke general psychostimulation, it attenuated the reduction in activity caused by exposure to the more aversive environment.

The effect of atrial natriuretic factor on urinary albumin and beta 2-microglobulin excretion in man

The effect of a 20-min infusion of atrial natriuretic factor (ANF) 99-126, 0.4 microgram/kg per min, on both urinary albumin and beta 2-microglobulin excretion was examined in nine normal male subjects during stable water diuresis. ANF caused a rise in urinary albumin in excretion (from 4.19 +/- 0.66 to 13.49 +/- 3.07 ng/min, P less than 0.01) without any significant change in either creatinine clearance of beta 2-microglobulin excretion. These findings suggest that ANF may enhance glomerular permeability to albumin in man.

Physiological increases in circulating noradrenaline are antinatriuretic in man

Low-dose (0.025 micrograms/kg per min) noradrenaline infusion, resulting in a physiological plasma increment (280 pg/ml), was antinatriuretic in normal salt-replete male subjects. The reduction in sodium excretion (-20%, P less than 0.01) occurred without any change in the glomerular filtration rate but was associated with a significant (P less than 0.02) decline in lithium clearance. These results suggest that changes in circulating noradrenaline, within the physiological range, can decrease sodium excretion in man by enhancing proximal tubular sodium reabsorption. These findings extend previous investigations in man which used pharmacological doses of noradrenaline and are in agreement with animal evidence for a renal tubular antinatriuretic effect of the sympathetic nervous system.

Evidence that tobacco smoking increases the density of (-)-[3H]nicotine binding sites in human brain

In a postmortem study of nicotinic receptors in human brain, cigarette smoking was found to be associated with increased (-)-[3H]nicotine binding to membranes prepared from gyrus rectus (Brodmann area 11) (p less than 0.001), hippocampal neocortex (Brodmann area 27), cerebellar cortex (p less than 0.01), hippocampal formation (Ammon's horn + subiculum), and the median raphe nuclei of the midbrain (p less than 0.05) but not the medulla oblongata. Analysis of the binding data suggested that the increased binding reflected an increase in the density of the receptors rather than a change in their affinity for (-)-nicotine. The effects of smoking were not influenced significantly by either the sex or age of the subject. It is concluded that smoking evokes an increase in high-affinity nicotine binding similar to that observed previously in animals treated chronically with nicotine and that the effect of smoking on these sites is probably caused by the nicotine present in the tobacco smoke.

The role of hippocampal 5-HT in the effects of nicotine on habituation to an X-maze

Neither the chronic administration (40 daily subcutaneous injections) of nicotine (0.4 mg/kg) nor its withdrawal (3 days) influenced avoidance of the more aversive open runways of an elevated X-maze in rats which had been habituated to the apparatus. Lesions of the serotonergic fibres innervating the hippocampus increased total activity (P less than 0.05). However, analysis of covariance indicated that reduced 5-hydroxytryptamine secretion in the hippocampus was probably not the mechanism by which nicotine stimulated total activity in these rats.

The effects of diazepam on brain 5-HT and 5-HIAA in stressed and unstressed rats

Diazepam, administered to rats at a high dose (25 mg/kg PO) has been shown to have no effect on the plasma corticosterone response to the stress of an elevated open platform. It did however, reduce the plasma corticosterone in rats repeatedly exposed to the apparatus. Diazepam-withdrawal from stress-habituated rats increased plasma corticosterone (p less than 0.01) whereas withdrawal of diazepam from unstressed rats had no effect on plasma corticosterone. It is concluded that this effect of diazepam-withdrawal may reflect the development of dependence upon the drug. Significant effects were not observed following the administration of a lower non-selective dose (5 mg/kg PO) of diazepam and, therefore, it is not clear whether dependence to its sedative, rather than the anxiolytic properties have been measured. Acute diazepam (25 mg/kg) increased (p less than 0.05) hippocampal 5-hydroxyindoleacetic acid; its withdrawal from unstressed rats after 40 days reduced (p less than 0.01) hypothalamic 5-hydroxytryptamine. There was no evidence that the effects of diazepam or its withdrawal on plasma corticosterone in stressed rats were associated directly with changes in brain 5-hydroxyindoles.

Spontaneous activity and brain 5-hydroxyindole levels measured in rats tested in two designs of elevated X-maze

The spontaneous activity of rats tested both acutely and chronically (15 minutes per day for 25 days) in an elevated X-maze composed entirely of open runways was found to be significantly less (P less than 0.01) than that measured for rats tested in a maze of similar dimensions composed entirely of enclosed runways. Acute exposure to both mazes caused significant increases (P less than 0.01) in plasma corticosterone when compared with unstressed control rats. Chronic exposure to the open, but not the enclosed maze caused a significant (P less than 0.01) attenuation of this response. Chronic exposure to the open maze caused significant increases (P less than 0.01) in the concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in hippocampus, hypothalamus and cerebral cortex when compared with unstressed control rats. When compared with the data for the rats tested repeatedly in the enclosed maze, chronic exposure to the open maze increased the 5-HT concentrations in hypothalamus (P less than 0.05) and cerebral cortex (P less than 0.01) and the 5-HIAA concentrations in hypothalamus (P less than 0.01) and hippocampus (P less than 0.01). The spontaneous locomotor activity of the rats tested in the open maze, correlated significantly (P less than 0.01) with plasma corticosterone and the 5-HIAA concentrations in hippocampus (P less than 0.01), hypothalamus (P less than 0.05) and cerebral cortex (P less than 0.01). In the rats tested in the enclosed maze, spontaneous activity only correlated significantly (P less than 0.01) with hippocampal 5-HIAA. It is concluded that the study has revealed clear differences in the behavioral, plasma corticosterone and brain 5-hydroxyindole responses to the two mazes but that the results do not provide unequivocal evidence that these differences occurred because the open maze was more aversive than the enclosed. It is also concluded that the study provides further support for the hypothesis that 5-HT turnover in the hippocampus may be directly related to the level of spontaneous locomotor activity.

Behavioural and adrenocortical responses to nicotine measured in rats with selective lesions of the 5-hydroxytryptaminergic fibres innervating the hippocampus

The effects of acute and subchronic (7) injections of nicotine (0.4 mg kg-1, s.c.) and of selective lesions of the 5-hydroxytryptaminergic (5-HTergic) pathways innervating the hippocampus on the spontaneous behaviour of rats in an elevated X-maze composed of two open and two enclosed runways have been examined. Subchronic, but not acute, nicotine increased total spontaneous activity. Neither acute nor subchronic nicotine altered the ratio of open:closed runway entries. Destruction of the 5-HTergic pathways innervating the hippocampus with 5,7-dihydroxytryptamine caused a reduction in the ratio of open:enclosed runway entries. Acute, but not subchronic, nicotine caused a significant increase in plasma corticosterone. The lesion had no effects on the plasma levels of this hormone. No significant interactions between the lesion and the responses to nicotine were observed. The data failed to provide any evidence that hippocampal 5-HTergic systems may be implicated in the effects of nicotine on the spontaneous behaviour of the rat.

Studies on the possible role of brain 5-HT systems and adrenocortical activity in behavioural responses to nicotine and diazepam in an elevated X-maze

Subchronic (6 days) but not acute injections of nicotine (0.4 mg/kg SC) increased spontaneous activity (P less than 0.01) in an elevated X-maze composed of two open and two enclosed runways. Neither acute nor subchronic nicotine altered significantly the ratio of open:enclosed runway entries (O/E ratio). Diazepam (5 mg/kg PO) had no significant effects on spontaneous activity but increased the O/E ratio (P less than 0.05). Acute nicotine increased (P less than 0.01) whereas subchronic nicotine caused a small decrease (P less than 0.05) in the plasma corticosterone concentration. Both acute and subchronic diazepam decreased the levels of the hormone (P less than 0.01 and P less than 0.05, respectively) although the reduction elicited by chronic diazepam was less than that caused by acute diazepam (P less than 0.05). In the experiments with diazepam the plasma corticosterone concentration correlated negatively with the O/E ratio (r = -0.58; P less than 0.05), whereas in the experiments with nicotine plasma corticosterone correlated negatively (r = -0.46; P less than 0.05) with enclosed runway entries. Nicotine injections were associated with a regionally-selective reduction in the 5-hydroxyindole acetic acid (5-HIAA) concentration in the hippocampus (P less than 0.05) and a reduction in hippocampal 5-hydroxytryptamine (5-HT) which approached statistical significance. Chronic, but not acute, diazepam increased (P less than 0.01) hypothalamic 5-HT. The changes in 5-HT and 5-HIAA did not appear to be directly related to the behavioural or adrenocortical responses to either of the drugs.

Central nicotine binding sites: a study of post-mortem stability

The effect of post-mortem treatment on the binding of d, I-[3H]nicotine, to rat cerebrocortical membranes, has been evaluated. Neither freezing [-70 degrees C] and thawing, a four hour post-mortem period at room temperature, nor refrigeration for up to 96 hrs at 4 degrees C caused any significant changes in the density or properties of nicotine binding sites in cerebrocortical membranes. The results suggest that nicotine binding to membranes in brain is unlikely to be affected by the usual postmortem delays experienced before human necropsies.

An investigation of amphetamine-induced release of 5-HT from rat hippocampal slices

The spontaneous release of [3H]5-HT from hippocampal slices, preincubated with [3H]5-HT, was increased by dopamine (P less than 0.001) and d-amphetamine (P less than 0.001) in a dose-dependent way. d-Amphetamine (10(-5) M) also increased (P less than 0.05) the release evoked by KCl (26 mM) whereas dopamine did not. The effects of dopamine and d-amphetamine on spontaneous [3H]5-HT release were antagonised by haloperidol and cis-flupenthixol. The release of [3H]HT evoked by KCl (26 mM) was reduced by noradrenaline (P less than 0.001) for conc. of 10(-5) M. It is concluded that the effects of d-amphetamine on [3H]5-HT release are probably mediated, in part by presynaptic dopamine receptors located on the 5-HT nerve terminals and that this response may depend upon the release of dopamine from adjacent terminals.

Lysine vasopressin fails to alter (3H)-noradrenaline uptake or release from hippocampal tissue in vitro

Lysine vasopressin (5.2 and 10.4 microM) failed to significantly alter the spontaneous release of (3H)-noradrenaline from hippocampal slices in vitro or the release observed after stimulation with potassium chloride (15 and 25 mM). Uptake of (3H)-noradrenaline by synaptosomes prepared from hippocampal tissue was not significantly changed by incubation with vasopressin (5.2 and 10.4 mu M). Our results fail to support the hypothesis, derived from behavioural and in vivo biochemical studies, that vasopressin modulates the activity of noradrenergic nerve terminals in this part of the limbic system.

The influence of age on lithium efficacy and side-effects in out-patients

One hundred and sixty-six unipolar and bipolar out-patients (21-78 years) on long-term lithium treatment were studied on a prospective basis. Although there was a possible tendency for manic attacks to increase in prevalence and severity with age, it was difficult to demonstrate a general age-related decline in lithium efficacy. There was a tendency for the prevalence and severity of fine hand tremor to increase with age. This was not seen with polydipsia/polyuria, the other typical lithium side-effect.

The effects of nicotine administration on 5-HT uptake and biosynthesis in rat brain

The effects of acute and chronic nicotine administration and its withdrawal on the rates of uptake and formation of 5-HT and the uptake of L-tryptophan, by synaptosomes prepared from discrete brain regions, have been studied in the rat. Both the acute and chronic (40 days) administration of nicotine (0.4 mg/kg s.c.) caused a decrease in the rate of formation of 5-HT by hippocampal synaptosomes (P less than 0.05) while 24 h withdrawal of the drug from chronically treated rats resulted in a partial recovery of this effect. Chronic nicotine treatment also reduced the rate of L-tryptophan uptake by hippocampal synaptosomes (P less than 0.01) an effect which appeared to be the result of a reduction in the number of L-tryptophan carrier molecules in the synaptosomal membrane. This effect, which was not reversed by withdrawal of the drug for 24 h, was not seen in synaptosomes prepared from other regions of the rat brain.