Evidence concerning the involvement of 5-hydroxytryptamine in the locomotor activity produced by amphetamine or tranylcypromine plus L-DOPA

Effects of dopamine and serotonin synthesis inhibitors on the ketamine-, d-amphetamine-, and cocaine-induced locomotor activity of preweanling and adolescent rats: sex differences

The pattern of ketamine-induced locomotor activity varies substantially across ontogeny and according to sex. Although ketamine is classified as an NMDA channel blocker, it appears to stimulate the locomotor activity of both male and female rats via a monoaminergic mechanism. To more precisely determine the neural mechanisms underlying ketamine's actions, male and female preweanling and adolescent rats were pretreated with vehicle, the dopamine (DA) synthesis inhibitor ∝-methyl-_DL-p-tyrosine (AMPT), or the serotonin (5-HT) synthesis inhibitor 4-chloro-_DL-phenylalanine methyl ester hydrochloride (PCPA). After completion of the pretreatment regimen, the locomotor activating effects of saline, ketamine, d-amphetamine, and cocaine were assessed during a 2 h test session. In addition, the ability of AMPT and PCPA to reduce dorsal striatal DA and 5-HT content was measured in male and female preweanling, adolescent, and adult rats. Results showed that AMPT and PCPA reduced, but did not fully attenuate, the ketamine-induced locomotor activity of preweanling rats and female adolescent rats. Ketamine (20 and 40 mg/kg) caused a minimal amount of locomotor activity in male adolescent rats, and this effect was not significantly modified by AMPT or PCPA pretreatment. When compared to ketamine, d-amphetamine and cocaine produced different patterns of locomotor activity across ontogeny; moreover, AMPT and PCPA pretreatment affected psychostimulant- and ketamine-induced locomotion differently. When these results are considered together, it appears that both dopaminergic and serotonergic mechanisms mediate the ketamine-induced locomotor activity of preweanling and female adolescent rats. The dichotomous actions of ketamine relative to the psychostimulants in vehicle-, AMPT-, and PCPA-treated rats, suggests that ketamine modulates DA and 5-HT neurotransmission through an indirect mechanism.

Pharmacological models of ADHD

For more than 50 years, heavy metal exposure during pre- or post-natal ontogeny has been known to produce long-lived hyperactivity in rodents. Global brain injury produced by neonatal hypoxia also produced hyperactivity, as did (mainly) hippocampal injury produced by ontogenetic exposure to X-rays, and (mainly) cerebellar injury produced by the ontogenetic treatments with the antimitotic agent methylazoxymethanol or with polychlorinated biphenyls (PCBs). More recently, ontogenetic exposure to nicotine has been implicated in childhood hyperactivity. Because attention deficits most often accompany the hyperactivity, all of the above treatments have been used as models of attention deficit hyperactivity disorder (ADHD). However, the causation of childhood hyperactivity remains unknown. Neonatal 6-OHDA-induced dopaminergic denervation of rodent forebrain also produces hyperactivity - and this model, or variations of it, remain the most widely-used animal model of ADHD. In all models, amphetamine (AMPH) and methylphenidate (MPH), standard treatments of childhood ADHD, typically attenuate the hyperactivity and/or attention deficit. On the basis of genetic models and the noted animal models, monoaminergic phenotypes appear to most-closely attend the behavioral dysfunctions, notably dopaminergic, noradrenergic and serotoninergic systems in forebrain (basal ganglia, nucleus accumbens, prefrontal cortex). This paper describes the various pharmacological models of ADHD and attempts to ascribe a neuronal phenotype with specific brain regions that may be associated with ADHD.

Serotoninergics attenuate hyperlocomotor activity in rats. Potential new therapeutic strategy for hyperactivity

Hyperactivity is thought to be associated with an alteration of dopamine (DA) neurochemistry in brain. This conventional view became solidified on the basis of observed hyperactivity in DA-lesioned animals and effectiveness of the dopaminomimetics such amphetamine (AMP) in abating hyperactivity in humans and in animal models of hyperactivity. However, because AMP releases serotonin (5-HT) as well as DA, we investigated the potential role of 5-HT in an animal model of hyperactivity. We found that a greater intensity of hyperactivity was produced in rats when both DA and 5-HT neurons were damaged at appropriate times in ontogeny. Therefore, previously we proposed this as an animal model of attention deficit hyperactivity disorder (ADHD) - induced by destruction of dopaminergic neurons with 6-hydroxydopamine (6-OHDA) (neonatally) and serotoninergic neurons with 5,7-dihydroxytryptamine (5,7-DHT) (in adulthood). In this model effects similar to that of AMP (attenuation of hyperlocomotion) were produced by m-chlorophenylpiperazine (m-CPP) but not by 1-phenylbiguanide (1-PG), respective 5-HT2 and 5-HT3 agonists. The effect of m-CPP was shown to be replicated by desipramine, and was largely attenuated by the 5-HT2 antagonist mianserin. These findings implicate 5-HT neurochemistry as potentially important therapeutic targets for treating human hyperactivity and possibly childhood ADHD.

The pharmacology and clinical pharmacology of 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy")

The amphetamine derivative (+/-)-3,4-methylenedioxymethamphetamine (MDMA, ecstasy) is a popular recreational drug among young people, particularly those involved in the dance culture. MDMA produces an acute, rapid enhancement in the release of both serotonin (5-HT) and dopamine from nerve endings in the brains of experimental animals. It produces increased locomotor activity and the serotonin behavioral syndrome in rats. Crucially, it produces dose-dependent hyperthermia that is potentially fatal in rodents, primates, and humans. Some recovery of 5-HT stores can be seen within 24 h of MDMA administration. However, cerebral 5-HT concentrations then decline due to specific neurotoxic damage to 5-HT nerve endings in the forebrain. This neurodegeneration, which has been demonstrated both biochemically and histologically, lasts for months in rats and years in primates. In general, other neurotransmitters appear unaffected. In contrast, MDMA produces a selective long-term loss of dopamine nerve endings in mice. Studies on the mechanisms involved in the neurotoxicity in both rats and mice implicate the formation of tissue-damaging free radicals. Increased free radical formation may result from the further breakdown of MDMA metabolic products. Evidence for the occurrence of MDMA-induced neurotoxic damage in human users remains equivocal, although some biochemical and functional data suggest that damage may occur in the brains of heavy users. There is also some evidence for long-term physiological and psychological changes occurring in human recreational users. However, such evidence is complicated by the lack of knowledge of doses ingested and the fact that many subjects studied are or have been poly-drug users.

Brain structures involved in the behavioral stimulant effect of central serotonin release

Drugs such as p-chloroamphetamine or a combination of tranylcypromine and tryptophan release serotonin in the central nervous system and produce a behavioral serotonin syndrome. However, in the presence of methysergide or following destruction of descending spinal serotonergic projections by 5,7-dihydroxytryptamine, central serotonin release produces hyperlocomotion. This supports the hypothesis that release of serotonin in the brain promotes locomotion but that the expression of this effect can be blocked by concomitant intraspinal effects of serotonin release. Hyperlocomotion induced by serotonin release is attenuated or blocked by: (a) pretreatment with p-chlorophenylalanine; (b) acute surgical lesions of the basal diencephalon; (c) chronic lesions of the ventromedial midbrain tegmentum by local injection of 5,7-dihydroxytryptamine; and (d) acute surgical decortication. Medial decortication tends to be more effective then lateral decortication. Hyperlocomotion produced by methamphetamine is also attenuated or blocked by acute basal diencephalic lesions or decortication. It is suggested that ascending serotonergic and dopaminergic projections collaborate in the generation of spontaneous voluntary motor activity.

Facilitatory and inhibitory effects of harmaline on the tryptophan-induced 5-hydroxytryptamine syndrome and body temperature changes in pargyline-pretreated rats

The effects of harmaline on tryptophan-induced 5-hydroxytryptamine (5HT) syndrome and body temperature changes in pargyline-pretreated rats were investigated. When administered i.p. 60 min after pargyline treatment (50 mg/kg, i.p.), tryptophan, at 100 mg/kg but not 10 mg/kg, induced the 5-HT syndrome. Tryptophan at 100 mg/kg also produced hypothermia followed by hyperthermia in pargyline-pretreated rats. Administration of harmaline (10 mg/kg, i.p.) 30 min after pargyline not only potentiated the 100 mg/kg tryptophan-induced 5-HT syndrome and body temperature changes, but also produced the syndrome following administration of 10 mg/kg tryptophan in pargyline-pretreated rats. In contrast, when administered 30 min before parygline, 10 mg/kg harmaline completely suppressed the syndrome and body temperature changes caused by mg/kg tryptophan. Tryptophan (100 mg/kg, i.p.) administration significantly increased 5-HT levels and decreased 5-hydroxyindole acetic and levels and 5-HT turnover in the brain of pargyline-pretreated rats. Harmaline administration 30 min after pargyline did not significantly affect the tryptophan-induced changes in 5-HT levels and 5-HT turnover, whereas when administered 30 min before pargyline, harmaline significantly blocked the effect of tryptophan. These results suggest that mechanisms underlying the inhibitory action of harmaline on the tryptophan-induced 5-HT syndrome and body temperature changes in pargyline-pretreated rats differ from those by which harmaline potentiates the effects of tryptophan.

Review of the pharmacology and clinical pharmacology of 3,4-methylenedioxymethamphetamine (MDMA or "Ecstasy")

3,4-Methylenedioxymethamphetamine (MDMA or "Ecstasy") was first synthesised 80 years ago, but has recently received prominence as an illegally synthesised recreational drug of abuse. There is a widely held belief among misusers that it is safe. In the last 2-3 years there have been a number of reports of the drug producing severe acute toxicity and death and there are concerns that it may cause long term toxic damage to 5-hydroxytryptamine (5-HT) nerve terminals. There is a considerable literature on the acute pharmacological effects of MDMA in experimental animals, and this is reviewed. The drug produces both hyperthermia and the "serotonin syndrome", a series of behavioural changes which result from increased 5-HT function. Acute clinical toxicity problems following MDMA ingestion also include hyperthermia and the appearance of the serotonin syndrome. The hyperthermia appears to precipitate other severe clinical problems and the outcome can be fatal. In agreement with others, we suggest that the recent increase in the number of reports of MDMA toxicity probably results from the widespread use of the drug at all night dance parties or "raves". The phenomenon of amphetamine aggregation toxicity in mice was reported 40 years ago. If applicable to MDMA-induced toxicity in humans, all the conditions necessary to induce or enhance toxicity are present at raves: crowded conditions (aggregation), high ambient temperature, loud noise and dehydrated subjects. Administration of MDMA to rodents and non-human primates results in a long term neurotoxic decrease in 5-HT content in several brain regions and there is clear biochemical and histological evidence that this reflects neurodegeneration of 5-HT terminals. Unequivocal data demonstrating that similar changes occur in human brain do not exist, but limited and indirect clinical evidence gives grounds for concern. There are also data suggesting that long term psychiatric changes can occur, although there are problems of interpretation and these are reviewed. Suggestions for the rational treatment of the acute toxicity are made on the basis of both pharmacological studies in animals and current clinical practice. Cases presenting clinically are usually emergencies and unlikely to allow carefully controlled studies. Proposals include decreasing body temperature (possibly with ice), the use of dantrolene and anticonvulsant and sedative medication, particularly benzodiazepines. The use of neuroleptics requires care because of the theoretical risk of producing the neuroleptic malignant syndrome and the possibility of precipitating seizures. In rats, chlormethiazole antagonises the hyperthermia produced by MDMA and has been shown clinically to block MDMA-induced convulsive activity.

Proposed animal model of attention deficit hyperactivity disorder

Dopamine (DA) neurons are implicated in the hyperlocomotion of neonatal 6-hydroxydopamine (6-OHDA)-lesioned rats, an animal model of attention deficit hyperactivity disorder (ADHD). Because serotonin (5-HT) neurons mediate some DA agonist effects, we investigated the possible role of 5-HT neurons on locomotor activity. Rats were treated at 3 days after birth with vehicle or 6-OHDA (134 micrograms ICV; desipramine pretreatment, 20 mg/kg IP, 1 h), and at 10 weeks with vehicle or 5,7-dihydroxytryptamine (5,7-DHT; 75 micrograms ICV; pretreatment with desipramine and pargyline, 75 mg/kg IP, 30 min), to destroy DA and/or 5-HT fibers. Intense spontaneous hyperlocomotor activity was produced in rats lesioned with both 6-OHDA and 5,7-DHT. Locomotor time in this group was 550 +/- 17 s in a 600 s session, vs. 127 +/- 13 s in the 6-OHDA group and < 75 s in 5,7-DHT and intact control groups (p < 0.001). Oral activity dose-effect curves established that 5,7-DHT attenuated DA D1 receptor supersensitivity and further sensitized 5-HT2c receptors. Acute treatment with dextroamphetamine (0.25 mg/kg SC) reduced locomotor time in 6-OHDA + 5,7-DHT-lesioned rats to 76 +/- 37 s (p < 0.001). Striatal DA was reduced by 99% and 5-HT was reduced by 30% (vs. 6-OHDA group). Because combined 6-OHDA (to neonates) and 5,7-DHT (to adults) lesions produce intense hyperlocomotion that is attenuated by amphetamine, we propose this as a new animal model of ADHD. The findings suggest that hyperactivity in ADHD may be due to injury or impairment of both DA and 5-HT neurons.

5-HT loss in rat brain following 3,4-methylenedioxymethamphetamine (MDMA), p-chloroamphetamine and fenfluramine administration and effects of chlormethiazole and dizocilpine

1. The present study has investigated whether the neurotoxic effects of the relatively selective 5-hydroxytryptamine (5-HT) neurotoxins, 3,4-methylenedioxymethamphetamine (MDMA or 'Ecstasy'), p-chloroamphetamine (PCA) and fenfluramine on hippocampal and cortical 5-HT terminals in rat brain could be prevented by administration of either chlormethiazole or dizocilpine. 2. Administration of MDMA (20 mg kg-1, i.p.) resulted in an approximate 30% loss of cortical and hippocampal 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) content 4 days later. Injection of chlormethiazole (50 mg kg-1) 5 min before and 55 min after the MDMA provided complete protection in both regions, while dizocilpine (1 mg kg-1, i.p.) protected only the hippocampus. 3. Administration of a single dose of chlormethiazole (100 mg kg-1) 20 min after the MDMA also provided complete protection to the hippocampus but not the cortex. This regime also attenuated the sustained hyperthermia (approx +2.5 degrees C) induced by the MDMA injection. 4. Injection of PCA (5 mg kg-1, i.p.) resulted in a 70% loss of 5-HT and 5-HIAA content in hippocampus and cortex 4 days later. Injection of chlormethiazole (100 mg kg-1, i.p.) or dizocilpine (1 mg kg-1, i.p.) 5 min before and 55 min after the PCA failed to protect against the neurotoxicity, nor was protection afforded by chlormethiazole when a lower dose of PCA (2.5 mg kg-1, i.p.) was given which produced only a 30% loss of 5-HT content. Chlormethiazole did prevent the hyperthermia induced by PCA (5 mg kg-1), while the lower dose of PCA (2.5 mg kg-1) did not produce a change in body temperature.5. Neither chlormethiazole nor dizocilpine prevented the neurotoxic loss of hippocampal or cortical 5-HT neurones measured 4 days following administration of fenfluramine (25 mg kg-1, i.p.).6. In general, chlormethiazole and dizocilpine were effective antagonists of the 5-HT-mediated behaviours of head weaving and forepaw treading which appeared following injection of all three neurotoxins.7. Both chlormethiazole and dizocilpine have previously been shown to prevent the neurotoxic effects ofa high dose of methamphetamine on cerebral 5-HT and dopamine pathways. These drugs also prevent MDMA-induced neurotoxicity of 5-HT pathways, but not that induced by injection of PCA or fenfluramine. This suggests that the mechanisms of neurotoxic damage to 5-HT pathways produced by substituted amphetamines cannot be identical. The monoamine loss does not appear to result from the hyperthermia produced by the neurotoxic compounds.

Disulfiram treatment of patients with both alcohol dependence and other psychiatric disorders: a review

In treatment of alcohol dependence, disulfiram is most useful in conjunction with a structured, supervised, aftercare program. However, it has been reported to cause psychiatric side effects and to interact with various psychiatric medications. Many patients with alcohol dependence suffer from other psychiatric disorders and are treated with such psychiatric medications. This paper reviews the pertinent clinical pharmacology of disulfiram and the literature on potential psychiatric complications and drug interactions of disulfiram. At the usual dosage, about 250 mg/day, disulfiram does not appear to increase significantly the risk of psychiatric complications or of psychiatric drug interactions. Therefore, it can be considered a treatment option for patients with alcohol dependence and other psychiatric disorders.

Tremorogenesis by LON-954 [N-carbamoyl-2-(2,6-dichlorophenyl) acetamidine hydrochloride]: evidence for the involvement of 5-hydroxytryptamine

LON-954 [N-carbamoyl-2-(2,6-dichlorophenyl) acetamidine hydrochloride], a novel tremorogen known to affect the central dopaminergic system, has been investigated in rats for tremor and 5-hydroxytryptamine (5-HT) metabolism. Five, 10 and 20 mg/kg of LON-954 IP caused a reproducible and consistent tremor with a high frequency (16 Hz) within 2 minutes and lasting 30-45 minutes. 5-HT content of the tuberculum olfactorium and basal ganglia was found to be increased significantly at a time when 5-hydroxyindoleacetic acid (5-HIAA) content showed a decrease. 5-HT and 5-HIAA of medulla oblongata showed significant changes only after 15 minutes. The alterations in the levels of the indoleamine in tuberculum olfactorium and its relationship with dosage as well as duration and intensity of LON-954 tremor indicate the involvement of the mesolimbic system in its action. A direct role of 5-HT in LON-tremor was evidenced since the drug failed to produce tremor in rats pretreated with p-chlorophenylalanine (300 mg/kg IP) for 3 days.

Neurochemical and neuropharmacological properties of 4-fluorotranylcypromine

1. The 4-fluoro analogue of the monoamine oxidase-inhibiting antidepressant tranylcypromine was compared to the parent drug with regard to the following: inhibition of monoamine oxidases A and B in vitro and ex vivo; levels of both drugs in brain, liver, and blood after injection of equimolar doses; and effects on brain levels of the amines 2-phenylethylamine, tryptamine, norepinephrine, dopamine, and 5-hydroxytryptamine. 2. 4-Fluorotranylcypromine was found to be 10 times more potent than tranylcypromine at inhibiting monoamine oxidases A and B in vitro in rat brain homogenates. 3. After administration (0.1 mmol/kg, ip), 4-fluorotranylcypromine attained higher brain and liver levels and provided greater availability than did tranylcypromine after the injection of an equimolar amount. 4. At the dose employed, the ex vivo monoamine oxidases A and B inhibitory profiles in brain and liver over a 24-hr period following tranylcypromine and 4-fluorotranylcypromine treatment were not different from each other. 5. Although the drugs had similar effects on inhibition of brain MAO ex vivo, they differed from one another at several time intervals in the increases in concentrations of 2-phenylethylamine, tryptamine, norepinephrine, dopamine, and 5-hydroxytryptamine produced in brain. 6. In conclusion, fluorination of tranylcypromine in the 4 position of the phenyl ring produced a drug which was more potent than the parent drug at inhibiting MAO in vitro and attained higher levels in brain than did tranylcypromine itself after intraperitoneal injection of equimolar amounts of the drugs. 4-Fluorotranylcypromine increased the concentrations of trace amines, catecholamines, and 5-hydroxytryptamine in brain at most time intervals following intraperitoneal injection, and at some time intervals there were differences from tranylcypromine with regard to the amine concentrations produced.

Determination of 3-methoxytyramine in rat brain by HPLC with electrochemical detection and its correlation with dopamine function after administration of a monoamine oxidase inhibitor and L-3,4-dihydroxyphenylalanine

3-Methoxytyramine (3-MT), normally a minor metabolite of 3,4-dihydroxyphenylethylamine (dopamine) in brain, becomes the sole product of metabolism following the administration of a monoamine oxidase (MAO) inhibitor. A simplified reverse-phase HPLC method for 3-MT employing electrochemical detection is fully described. This method has a detection limit of 0.1 microgram/g brain wet weight and is sensitive enough to detect 3-MT in individual brain regions after rats have been pretreated with an MAO inhibitor. Administration of tranylcypromine (TCP, 10 mg/kg) and L-3,4-dihydroxyphenylalanine (L-DOPA) (10-50 mg/kg) produced a dose-dependent linear increase in 3-MT concentrations in the dopaminergic brain regions n. caudatus (r = 0.95; p less than 0.01) and n. accumbens (r = 0.96; p less than 0.01). This treatment also produced a dose-dependent increase in behavioural activity in rats (r = 0.88; p less than 0.01). Furthermore, a good correlation was found between the activity responses of individual rats and the accumulation of 3-MT after TCP/L-DOPA in both n. caudatus (r = 0.76; p less than 0.01) and n. accumbens (r = 0.84; p less than 0.01). These data describe a simple and sensitive HPLC analysis technique for 3-MT and demonstrate that following administration of an MAO inhibitor this metabolite may provide a useful monitor of central dopamine function.

Effects of serotonergic activity in nucleus accumbens septi on drug-induced circling

The effects of injections of 5-hydroxytryptamine (5-HT) into the nucleus accumbens and lesions of the nucleus accumbens induced by 5,7-dihydroxytryptamine (5,7-DHT) on drug-induced circling were investigated in rats with unilateral nigrostriatal lesions induced by 6-hydroxydopamine (6-OHDA). Injections of 5-HT (60-120 micrograms in 1 microliter; 1 microliter/min) into the nucleus accumbens caused a significant decrease in the circling response to 5.0 mg/kg of d-amphetamine (s.c.). The distribution of radioactivity after intracerebral injections of [3H]5-HT using these parameters showed that although much of the injected material was retained in the nucleus accumbens there was also considerable spread to the frontal cortex. However, in further behavioural experiments, using an injection procedure (0.5 microliter; 0.11 microliter/min) which caused much greater retention of injected material in the nucleus accumbens, with minimal spread to the frontal cortex, the ability of 5-HT injected into the accumbens to block amphetamine-induced circling was not diminished. Moreover, injections of 5-HT into the frontal cortex did not have any effect on amphetamine-induced circling. Lesions of the nucleus accumbens induced by 5,7-DHT caused a significant enhancement of the contralateral circling response to 1.0 mg/kg of apomorphine and a similar but non-significant tendency to increase the circling responses to several other doses of apomorphine and amphetamine. The results provide evidence that serotonergic mechanisms in the nucleus accumbens inhibit circling behaviour generated by unilateral activation of nigrostriatal dopaminergic mechanisms.

Interactions of non-selective monoamine oxidase inhibitors, tranylcypromine and nialamide, with inhibitors of 5-hydroxytryptamine, dopamine or noradrenaline re-uptake

Rats pretreated with tranylcypromine and given clomipramine, developed head and body twitches, forelimb flexor-extensor movements and wet dog shakes, phenomena which failed to develop when pretreatment incorporated p-chlorophenylalanine (PCPA) but were unabated when this included alpha-methyl-p-tyrosine (AMPT). Locomotor activity, itself enhanced by tranylcypromine, was further and significantly elevated compared to saline, by clomipramine or imipramine in grouped rats (n = 3) but not in single or paired rats; desipramine lacked such action. This effect of clomipramine was prevented when PCPA was incorporated into the pretreatment and that of imipramine by including PCPA or AMPT. Brain monoamine oxidase (MAO) A inhibition was 92% and that of MAO B, 80%. Cortical hydroxytryptamine (5-HT) and noradrenaline concentrations as well as hypothalamic 5-HT, were significantly elevated by tranylcypromine, as was dopamine in the striatum, nucleus accumbens and tuberculum olfactorium. Hyperthermia developed in tranylcypromine pretreated rats given paroxetine or fluoxetine. Myoclonic phenomena were elicited by paroxetine, fluoxetine, clomipramine or imipramine in nialamide pretreated rats but these were less intense than in rats pretreated with phenelzine or tranylcypromine. Fatalities were fewer than in rats pretreated with tranylcypromine or phenelzine. Brain MAO A inhibition was 92% and that of MAO B, 69%.

Mechanisms of PCA-induced hypothermia, ejaculation, salivation and irritability in rats

Injections of p-chloramphetamine (PCA, 5 mg/kg) induced hypothermia, ejaculation, salivation and irritability in male rats kept at an ambient temperature of 20 +/- 1 degree C. PCA-induced hypothermia was attenuated by pretreatment with the 5-hydroxytryptamine (5-HT) uptake blockers Lundbeck 10-171 (Lu 10-171, 10 mg/kg) and chlorimipramine (CMI, 20 mg/kg) and the 5-HT synthesis inhibitor parachlorophenylalanine (PCPA, 150 mg/kg daily for 3 days); it was potentiated by pretreatment with the noradrenaline uptake blocker Lundbeck 5-003 (Lu 5-003, 10 mg/kg) and the catecholamine synthesis inhibitor alpha-methyl-p-tyrosine (AMPT, 50 mg/kg every 3 hr for 9 hr). PCA- induced ejaculation was attenuated by pretreatment with Lu 10-171 and CMI. PCA-induced salivation was attenuated by pretreatment with Lu 10-171 and CMI and potentiated by pretreatment with Lu 5-003. PCA-induced irritability was potentiated by pretreatment with PCPA. These results suggest that both 5-HT and the catecholamines play a role in PCA-induced hypothermia, ejaculation, and salivation.

A behavioural and biochemical study in rats of 5-hydroxytryptamine receptor agonists and antagonists, with observations on structure-activity requirements for the agonists

1 The effect of the putative 5-hydroxytryptamine (5-HT) receptor antagonists, methysergide, methergoline, mianserin, cyproheptadine, cinanserin (all at 10 mg/kg), methiothepin (5 mg/kg) and (-)-propranolol (20 mg/kg) on the behavioural responses to tranylcypromine (10 mg/kg) followed 30 min later by L-tryptophan (100 mg/kg) was examined.2 Methysergide, methergoline, methiothepin and (-)-propranolol inhibited head weaving, forepaw treading and hind-limb abduction. Methysergide and methergoline increased reactivity. In contrast, cypropheptadine, cinanserin and mianserin had no effects on the behaviour.3 Similar findings were obtained when the behaviours were elicited by administration of tranylcypromine (10 mg/kg) followed by the putative 5-HT receptor agonist, 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) (2 mg/kg).4 When the behaviours were elicited by the putative 5-HT receptor agonist, quipazine (50 mg/kg), all the drugs effectively inhibited head weaving and forepaw treading.5 When the dose of cypropheptadine was doubled to 20 mg/kg an inhibition of the tranylcypromine/L-tryptophan induced behaviours was seen.6 Methiothepin produced a marked inhibition of apomorphine-induced locomotor activity whilst all the others enhanced this response, suggesting that only methiothepin inhibits the 5-HT behaviours by dopamine antagonism and that the increased reactivity seen following tranylcypromine/L-tryptophan after pretreatment with methysergide or methergoline might be due to enhanced dopamine function.7 Pretreatment with p-chlorophenylalanine resulted in enhanced behavioural responses to both 5-MeODMT and quipazine.8 Both methergoline and methiothepin decreased the rate of 5-HT synthesis in whole brain but not spinal cord and methergoline decreased spinal cord 5-HIAA concentration. None of the other drugs had any significant effects on the concentration of 5-HT, 5-HIAA or 5-HT synthesis rate in brain or spinal cord.9 Experiments with compounds structurally related to quipazine and with molecular models suggested that quipazine produces behavioural changes probably by stimulating the 5-HT receptor in a similar way to 5-HT but that it would bind weakly, in agreement with ligand-receptor binding studies.10 It is suggested, therefore, that cyproheptadine, cinanserin and mianserin fail to inhibit 5-HT and 5-MeODMT-induced behaviours because they are weak antagonists whilst they are able to inhibit the same behaviours induced by quipazine because it is a weak agonist.11 These data indicate that extreme care should be taken in accepting or rejecting 5-HT as a mediator of behaviours or of other responses unless several antagonists or agonists have been examined.

On the neurochemical basis of self-stimulation with midbrain raphe electrode placements

Bar-pressing for electrical stimulation of the median raphe nucleus in rats was not attenuated by 5HT receptor blockade with metergoline or cyproheptadine, by 5HT depletion induced with parachloroamphetamine or by prior destruction of ascending 5HT pathways with intracerebral microinjections of 5,7-dihydroxytryptamine. Furthermore, in a shuttle box paradigm in which rats could both initiate and terminate stimulation, parachlorophenylalanine did not antagonize initiation of stimulation. It is concluded that the rewarding effects of raphe stimulation are not mediated by serotonergic mechanisms. In contrast to these results, alpha-methyl-paratyrosine induced catecholamine depletion exerted an inhibitory effect on initiation behaviour without impairing termination of stimulation. It is concluded that the rewarding component of raphe stimulation is mediated by catecholamines. Termination of (escape from) stimulation was not materially affected by catecholamine or 5HT depletion suggesting the aversive component of raphe stimulation may not be mediated by these monoamines.

A sensitive and rapid fluorimetric assay for monoamine oxidase utilizing high pressure liquid chromatography

A rapid and sensitive assay for the measurement of monoamine oxidase (MAO) activity was developed. This method utilizes high pressure liquid chromatography with fluorescence excitation at 280 nm and detection of 330 nm at pH 5.0 of indoleacetic acid and 5-hydroxyindoleacetic acid, the deaminated products of two substrates for MAO, tryptamine, and serotonin, respectively. The assay allows for the complete separation of metabolites from either of the two substrates. The method has been used to determine MAO activity in the frontal cortex and caudate nucleus of rat brain using tryptamine and serotonin as substrates. The ease and rapidity of this assay make it sutable for use where routine enzyme determinations are required.

Ketamine-induced rotation: interaction with GABA-transaminase inhibitors and picrotoxin

Ketamine in a dose of 100 mg/kg (IP) produced stereotypic behavior and vigorous rotation in adult male Sprague-Dawley rats. The first rotation phase, accompanied by head swinging, was short and terminated by the anesthetic phase which lasted 20-30 min. The second rotation phase began 1-3 min after the end of the anesthetic phase. A single dose of GABA-T inhibitors, gamma-vinyl GABA (1200 mg/kg, IP) or gamma-acetylenic GABA (100 mg/kg, IP) administered 4 hours prior to ketamine, shortened the first rotation phase, increased the anesthetic phase, changed the pattern of postanesthetic rotation and reduced total and net rotation scores. Picrotoxin (3 mg/kg) given 10 min prior to ketamine tended to act in the opposite direction although none of its effects reached statistical significance.

The effects of drugs on the processes regulating the functional activity of brain monoamines

1. By study of the synthesis and turnover of brain monoamines and with the use of behavioral models which indicate the functional activity of brain 5HT and dopamine, it is possible to unravel the mechanisms by which some drugs produce behavioral effects. 2. Using these techniques the acute and chronic effects of certain neuroleptics, propranolol and other beta-adrenergic blocking agents, repeated electroconvulsive shock, and lithium upon the functional activity of brain 5HT and dopamine are examined. 3. The clinical relevance of these studies is discussed.

The effects of putative 5-hydroxytryptamine antagonists on the behaviour produced by administration of tranylcypromine and L-tryptophan or tranylcypromine and L-DOPA to rats

1 The putative 5-hydroxytryptamine (5-HT) receptor blocking drugs methysergide (10 mg/kg) and methergoline (5 mg/kg) were found to abolish some components of the hyperactivity syndrome, including head weaving and forepaw treading, which follow administration to rats of tranylcypromine (20 mg/kg) and L-tryptophan (100 mg/kg). Hyperactivity and hyper-reactivity were potentiated with a resultant increase in automated locomotor activity counts. In contrast (-)-propranolol (20 mg/kg) inhibited all features of the syndrome. The same results were obtained with these drugs when the behaviour was elicited by p-chloroamphetamine (10 mg/kg) or by tranylcypromine and tryptamine (10 mg/kg). 2 Methysergide and methergoline had similar effects on the syndrome produced by tranylcypromine and L-DOPA (50 mg/kg) whereas propranolol was without effect. 3 None of the putative 5-HT receptor antagonists affected brain 5-HT turnover as assessed by rate of accumulation of 5-HT following monoamine oxidase inhibition with tranylcypromine. 4 Microinjections of 5,7-dihydroxytryptamine into the spinal cord resulted in a 70% fall in cord 5-HT concentrations without an effect on brain 5-HT concentrations. The behavioural response to the putative 5-HT receptor agonist, 5-methoxy N,N-dimethyltryptamine (2 mg/kg), was potentiated in these animals suggesting that 5-HT receptors become supersensitive on denervation, and that some components of the behavioural syndrome are mediated by spinal cord 5-HT receptors. 5 Pretreatment with alpha-methyl p-tyrosine (2 X 200 mg/kg) delayed the onset of all components of the behaviour elicited by tranylcypromine/L-tryptophan by 60 min, indicating an involvement of catecholamines in the syndrome. 6 p-Chloroamphetamine-induced 5-HT depletion had no effect on any component of the tranylcypromine-L-DOPA behaviour.

Neuroleptic drugs block both the hyperactivity and the increase in caudate nucleus cyclic AMP concentration produced by the administration of tranylcypromine and L-dopa to rats

Injection of rats with tranylcypromine and L-dopa increased brain dopamine concentrations and produced a behavioural syndrome that includes hyperactivity. It also elevated caudate nucleus cyclic AMP concentrations by approximately 50% in vivo, probably by stimulating dopamine receptors. Pretreatment with chlorpromazine inhibited both the tranylcypromine/L-dopa-induced behaviour and elevated cyclic AMP concentrations in a dose-dependent manner. Haloperidol and alpha-flupenthixol also inhibited both effects, while beta-flupenthixol and pimozide were without effect. Since none of these drugs altered the tranylcypromine/L-dopa-induced rise of brain dopamine, it is likely that they produced their effect by inhibiting dopamine-sensitive adenylate cyclase. A good correlation was found to exist between the neuroleptic inhibition of both the increased behavioural activity and the increased caudate nucleus cyclic AMP concentrations produced by tranylcypromine and L-dopa.

Repeated exposure of rats to the convulsant agent flurothyl enhances 5-hydroxytryptamine- and dopamine-mediated behavioural responses

1 Rats were convulsed once daily for 7 days by exposure to the inhalant convulsant agent, flurothyl (Indoklon, bis (2,2,2-trifluouroethyl)ether). Twenty four hours after the final convulsion the rats were injected with tranylcypromine (20 mg/kg) followed 30 min later by L-DOPA (50 mg/kg), a procedure which increases brain dopamine concentrations. The flurothyl-treated rats showed a greater locomotor activity response than rats that had not been convulsed.2 This enhanced response appears to be due to increased postsynaptic dopamine receptor sensitivity since flurothyl-treated rats also showed enhanced locomotor responses to methamphetamine (2 mg/kg) and apomorphine (2 mg/kg).3 Enhanced 5-hydroxytryptamine-induced activity responses following administration of tranylcypromine (20 mg/kg) and L-tryptophan (50 mg/kg) were also seen 24 h after the last of 10 daily flurothyl-induced convulsions.4 The increased 5-hydroxytryptamine response also appears to be due to increased postsynaptic sensitivity since the flurothyl-treated rats showed increased hyperactivity following administration of tranylcypromine (20 mg/kg) and the suggested 5-hydroxytryptamine agonist, 5-methoxy N,N-dimethyltryptamine (2 mg/kg).5 No change in the brain concentration of 5-hydroxytryptamine, 5-hydroxyindoleacetic acid, tryptophan, dopamine or noradrenaline was observed 24 h after the last of 10 daily flurothyl-induced convulsions, compared to untreated rats. The rate of 5-hydroxytryptamine accumulation after tranylcypromine/L-tryptophan treatment and of dopamine and noradrenaline accumulation after tranylcypromine/L-DOPA treatment was similar in both groups.6 Repeated flurothyl convulsion has the same effects on these behavioural tests as repeated electroconvulsive shock. Since both treatments have been used successfully to treat depression, it is suggested that the mechanism of action of electroconvulsive therapy may be by increasing postsynaptic responses to the monoamine neurotransmitters.

Mesolimbic dopamine neurons: effects of 6-hydroxydopamine-induced destruction and receptor blockade on drug-induced rotation of rats

Bilateral injections of 6-hydroxydopamine (6-OHDA) into the nucleus accumbens greatly reduced the dopamine content of this nucleus and the olfactory tubercle and blocked the ipsilateral rotation induced by amphetamine and methamphetamine in rats with unilateral 6-OHDA lesions of the caudate nucleus. In contrast, apomorphine-induced contralateral rotation was enhanced. Similar results were obtained when the destruction of forebrain noradrenergic neurons, normally produced by the nucleus accumbens 6-OHDA lesion, was prevented by desipramine (DMI) pretreatment. Microinjections of the dopamine receptor antagonist heloperidol into the nucleus accumbens did not spread to the olfactory tubercle, as assessed by the distribution of 3H-haloperidol, and blocked circling induced by amphetamine and apomorphine. Amphetamine-induced circling was less effectively blocked by haloperidol injected into the olfactory tubercle. These results suggest that activity at nucleus accumbens dopamine receptors can greatly affect circling behavior, perhaps by amplifying asymmetries of nigrostriatal activity.

Effects of levodopa and dopamine of plasma glucose concentration in mice

In nialamide-treated, fasted mice levodopa produced a dose-dependent hypoglycaemic response. The response was also seen in pargyline-treated mice but not in animals which were not treated with a monoamine oxidase inhibitor. Dopamine did not affect plasma glucose under these conditons. In doses which were ineffective when injected i.v., both levodopa and dopamine produced hypoglycemia when injected intracerebroventriculary (i.c.v.). The hypoglycaemic response to levodopa was prevented by the dopamine antagonists, haloperidol and pimozide. The possible involvement of 5HT in the hypoglycaemic response to levodopa was suggested by the blockade of the response by cyproheptadine and methysergide together with the observations that hypoglycaemia is produced by 5HTP and by i.c.v. 5HT. p-Chlorophenylalanine (PCPA) also reduced the response to levodopa but the usefulness of PCPA as an inhibitor of 5HT synthesis in these experiments in doubtful since it also inhibited the hypoglycaemic effects of 5HTP and i.c.v. 5HT. Hypoglycaemia produced by levodopa did not appear to involve stimulation of insulin secretion since plasma IRI levels were not increased by levodopa and the hypoglycaemia was accompanied by a elevation of plasma FFA and no significant change in the liver glycogen content. It is suggested that the hypoglycaemic effect of levodopa is mediated through dopamine acting in the brain, although the involvement of 5HT in the response and the mechanisms involved remain to be determined.

Single and repeated administration of neuroleptic drugs to rats: effects on striatal dopamine-sensitive adenylate cyclase and locomotor activity produced by tranylcypromine and L-tryptophan or L-Dopa

Injection of tranylcypromine and L-tryptophan results in rats displaying behavioural changes including hyperactivity, probably due to stimulation of post-synaptic 5-hydroxytryptamine (5-HT) receptors. Increased locomotor activity of a different type is elicited by injection of tranylcypromine and L-dopa, a procedure which increased dopaminergic function in the brain. It has now been demonstrated that the neuroleptic drugs, chlorpromazine, alpha-flupenthixol, haloperidol and spiroperidol block both syndromes. The inhibition produced by these drugs on 5-HT-induced hyperactivity is probably because a dopaminergic system is involved in the behavioural expression of the 5-HT induced hyperactivity. The structurally related drugs with no neuroleptic activity (ethopropazine, promethazine and beta-flupenthixol)are without effect on thses hyperactivity syndromes. Also ineffective were the neuroleptics pimozide and clozapine. Striatal dopamine sensitive adenylate cyclase activity in vitro was inhibited by the administration of chlorpromazine (100 mg/kg) in vivo. Rats treated for 4 or more days with chlorpromazine, alpha-flupenthixol, spiroperidol and haloperidol subsequently showed enhanced locomotor activity in response to tranylcypromine and L-Dopa. Administration of those drugs which did not block hyperactivity acutely did not result in enhancement. Only chlorpromazine, when given for 4 days, enhanced the hyperactivity response following tranylcypromine and L-tryptophan, probably because the drug also blocks 5-HT receptors. In rats displaying enhanced behavioural responses no evidence was found for enhanced sensitivity of striatal adenylate cyclase to dopamine.