ON THE RELATION OF TRYPTAMINIC AND SEROTONERGIC MECHANISMS TO AMPHETAMINE INDUCED ABNORMAL BEHAVIOUR

Effects of tryptophan deficiency on prepulse inhibition of the acoustic startle in rats

RATIONALE

Serotonin (5-HT) plays a key role in the pathophysiology of psychotic disorders, presumably through a modulation of dopamine (DA) transmission. Reduction of 5-HT signaling has been suggested to enhance dopaminergic responses in animal models of psychosis. An intriguing naturalistic strategy to reduce 5-HT brain content is afforded by the dietary restriction to its precursor, l-tryptophan (TRP).

OBJECTIVE

We investigated the impact of a TRP-deficient diet in rats on the prepulse inhibition of the startle (PPI), a measure of sensorimotor gating which is typically impaired by psychotomimetic substances.

MATERIALS AND METHODS

After either short-term (6 h) or long-term (14 days) TRP deprivation, rats were tested for startle reflex and PPI. Moreover, we assessed the impact of both TRP deprivation regimens on PPI reduction induced by the psychotomimetic substance d-amphetamine (AMPH).

RESULTS

Both TRP-deficient regimens failed to significantly affect PPI responses. However, chronic, but not short-term, TRP-deficient diet induced a significant sensitization to the effects of AMPH (1.25-2.5 mg/kg, subcutaneous). The enhanced predisposition to PPI disruption elicited by prolonged TRP deprivation was completely reversed 24 h after reinstatement of TRP in the diet, as well as pretreatment with antipsychotic drugs haloperidol (0.1 mg/kg, intraperitoneal) and clozapine (5 mg/kg, intraperitoneal), which exert their therapeutic action mostly through blockade of DA D(2) receptors.

CONCLUSIONS

The present results confirm and extend previous findings on the impact of serotonergic signaling in the modulation of DA transmission in schizophrenia and point to chronic TRP deprivation as a potential model of environmental manipulation that may produce a sensitization to psychotic-like symptoms induced by dopaminergic activation.

Coordination of side-to-side head movements and walking in amphetamine-treated rats: a stereotyped motor pattern as a stable equilibrium in a dynamical system

Rats injected with 5.0 mg/kg (+)-amphetamine perform, at one stage of the drug's influence, rhythmic side-to-side head movements while walking. This makes them an interesting preparation for investigating how stereotyped motor patterns emerge from the coordination of periodic movements. We report here such a pattern we have isolated: the left foreleg and the right hindleg land on the ground as the head reaches the peak of its movement to the right, and vice versa (contra-lateral pattern). We show that this pattern can be explained as a stable equilibrium in a simple, nonlinear dynamical model, similar to models developed for tapping with both hands in human subjects. The model also accounts for sequences of behavior that are not in the contra-lateral pattern, explaining them as a flow of the system back towards the stable equilibrium after a disturbance. Motor patterns that constitute the building blocks of unconstrained behavior are often defined as fixed phase relations between movements of the parts of the body. This study applies the paradigm of Dynamic Pattern Generation to free (unconstrained) behavior: motor patterns are defined as stable equilibria in dynamical systems, assembled by mutual influence of concurrent movements. Our findings suggest that this definition is more powerful for the description of free behavior. The amphetamine-treated rat is a useful preparation for investigating this notion in an unconstrained animal whose behavior is still not as complex and variable as that of the normal animal.

Serotonin depletion causes long-term reduction of exploration in the rat

This study assessed the effects of central serotonergic depletion on exploratory activity at baseline, as well as after administration of d-amphetamine or the anxiogenic beta-carboline FG-7142. Intraventricular 5,7-dihydroxytryptamine (5,7-DHT) induced an almost complete depletion of serotonin [5-hydroxytryptamine (5-HT)] in the medial prefrontal cortex, nucleus accumbens, medial corpus striatum, and hippocampus with no changes in norepinephrine, dopamine or dihydroxyphenylacetic acid concentrations. 5-HT-depleted rats demonstrated reduced spontaneous and d-amphetamine-augmented exploration 3-10 weeks postoperatively. An effect on FG-7142-induced inhibition of exploratory activity was not apparent. These data implicate 5-HT systems in the expression of different aspects of exploratory and amphetamine-augmented motor behaviors.

Comparison of the acute actions of amine-depleting drugs and dopamine receptor antagonists on dopamine function in the brain in rats

The effects of the monoamine depleting drugs oxypertine, tetrabenazine and reserpine were compared with those of the dopamine receptor antagonists, chlorpromazine and trifluoperazine, on behavioural and biochemical indices of dopamine function in the brain. Oxypertine (0.625-20 mg/kg, i.p.), chlorpromazine (0.625-20 mg/kg i.p.) and trifluoperazine (0.0625-2.0 mg/kg i.p.), administered to rats 1 hr previously, inhibited stereotyped behaviour induced by both amphetamine (5.0 mg/kg i.p.) and apomorphine (1.0 mg/kg, s.c.) in a dose-dependent manner. Tetrabenazine (0.625-20 mg/kg i.p., 1 hr previously) inhibited stereotypy induced by amphetamine but not that induced by apomorphine. Reserpine (0.1 10 mg/kg i.p., 6 hr previously) did not inhibit, but in larger doses, tended to enhance the stereotyped responses to both amphetamine and apomorphine. Oxypertine (10 mg/kg, i.p., 1 hr previously), tetrabenazine (5 mg/kg i.p., 1 hr previously) and reserpine (2.5 mg/kg i.p., 6 hr previously) reduced the content of dopamine in the striatum but increased the concentrations of homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC). Chlorpromazine (5 mg/kg i.p.) and trifluoperazine (0.5 mg/kg i.p.), given 1 hr previously, did not alter concentrations of dopamine in the striatum but increased those of HVA and DOPAC. Oxypertine, chlorpromazine and trifluoperazine weakly inhibited dopamine-stimulated adenylate cyclase in homogenates of the striatum in the rat. Tetrabenazine and reserpine had no effect. Similarly, trifluoperazine and chlorpromazine displaced the specific binding of [3H]piflutixol to membranes from the striatum. Oxypertine also was weakly effective, but tetrabenazine and reserpine were without effect. Trifluoperazine, chlorpromazine and oxypertine displaced specific binding of [3H]spiperone and [3H]N,n-propylnorapomorphine (NPA) to preparations of the striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral aspects of serotonin-dopamine interaction in the monkey

The effects of serotonin (5-hydroxytryptamine; 5-HT) antagonists and 5-HT uptake inhibitors on the behavioral response to amphetamine and haloperidol in monkeys (cercopithecus aethiops) were investigated. Amphetamine increased locomotor activity and reactivity and induced repetitive movements of head, limbs and trunk, but no oral hyperkinesia. Haloperidol induced dystonia and parkinsonism. Pretreatment with the 5-HT antagonists cyproheptadine and mianserin increased amphetamine-induced locomotor activity, reactivity and repetitive movements and decreased haloperidol-induced dystonia and parkinsonism. Conversely the 5-HT uptake inhibitors paroxetine and CGP 6085 A decreased amphetamine-induced repetitive movements and aggravated haloperidol-induced dystonia and parkinsonism. The 5-HT uptake inhibitors produced oral hyperkinesia resembling human tardive dyskinesia, which was intensified by amphetamine and blocked by haloperidol. These findings support the suggestion that 5-HT inhibits dopamine functions and may imply that 5-HT antagonists could have a beneficial effect against acute extrapyramidal side-effects of neuroleptic treatment. 5-HT uptake inhibitors in the monkey may serve as a model for tardive dyskinesia.

Stimulant drug effects in developmental disorders and hyperactivity--toward a resolution of disparate findings

An attempt is made to integrate data from a variety of clinical populations and from the animal literature. Evidence is presented suggesting that mentally retarded and autistic children generally show a poor response to stimulant medication, whereas hyperactive and normal children respond beneficially. Cognitive research in mentally retarded and autistic children is reviewed, and it is suggested that both diagnostic groups suffer from attentional difficulties, the mechanisms of which may be very similar. The literature on stimulant-induced stereotypy in animals is discussed, with emphasis on the clinical implications for autism and mental retardation. An attentional model is proposed to account for type of therapeutic response to stimulant medication. This is followed by a possible method for testing the model and by specific predictions relating to subject characteristics and response.

Susceptibility to amphetamine-elicited dyskinesias following chronic methadone treatment in monkeys

Eight rhesus monkeys that had drunk subdependence-producing doses of methadone daily for 10-22 months, and had subsequently been drug-free for 2-17 months, were injected with low doses of methamphetamine (MA). They immediately exhibited oral dyskinesias resembling the symptoms of tardive dyskinesia in humans, a condition resulting from chronic blockade of striatal dopamine receptors by neuroleptics. Eleven control monkeys failed to develop dyskinesias during prolonged MA administration. Control monkeys then received parenteral methadone, chlorpromazine, haloperidol, or saline for 45 days. Upon subsequent retest with MA, the methadone and chlorpromazine monkeys immediately displayed oral dyskinesias. Dopaminergic antagonists blocked MA-elicited dyskinesis, whereas neither a noradrenergic blocker nor sedative doses of phenobarbital and diazepam had any effect on dyskinesias. We suggest that receptor supersensitivity is produced by chronic treatment with methadone or other dopamine receptor blockers. Following treatment, stimulation of hypersensitive striatal receptors by the dopamine released by MA results in oral dyskinesias. The clinical implications for methadone maintenance treatment program patients are discussed.

Dyskinesias in monkeys: interaction of methamphetamine with prior methadone treatment

Rhesus monkeys with a history of drinking methadone, but presently drug-free, were injected with low doses of methamphetamine (MA). They immediately developed oral dyskinesias resembling the symptoms of tardive dyskinesia in humans, a condition resulting from chronic blockade of striatal dopamine receptors by neuroleptics. Nine of 11 control monkeys failed to develop dyskinesias during prolonged MA administration. A stressful stimulus intensified the MA-elicited oral dyskinesias, an effect analogous to exacerbation of tardive dyskinesias by emotional stress. Control monkeys were then injected with methadone, chlorpromazine, haloperidol, or saline for 45 days. Ten days following this chronic treatment, MA immediately elicted oral dyskinesias in the methadone and chlorpromazine monkeys. Acute administration of the dopaminergic blocking agents chlorpromazine, spiroperidol, and clozapine eliminated MA-elicited dyskinesias, whereas the alpha-adrenergic blocker phentolamine was ineffective. Physostigmine blocked the dyskinesias in 1 of 2 cases. Sedative doses of phenobarbital and diazepam had no effect on oral dyskinesias. These data indicate that chronic treatment with methadone or other dopamine receptor blocking agents leads to receptor supersensitivity to the actions of MA.

Behavioral effects of 5, 7-dihydroxytryptamine lesions of ascending 5-hydroxytryptamine pathways

In protriptyline (25 mg/kg) pretreated rats stereotactic 5,7-dihydroxytryptamine (5,7-DHT) lesions of the medial plus laternal 5-hydroxytryptamine (5-HE) bundles in the mesencephalon increased the 5-HT fluorescence in these bundles, and reduced the in vitro uptake of [3H] 5-HT in the hypothalamus to 16% of control values after 2 mug 5,7-DHT/4mul and 12% after 4 mug 5,7-DHT/4mul, and in the cortex cerebri to 35 and 34% of control values, respectively. Selective lesion of the medial 5-HT bundle reduced [3H] 5-HT uptake both in hypothalamus and in cortex cerebri to 45-48% of control values, while selective lesion of the lateral 5-HT bundles significantly reduced [3H] 5-HT uptake only in cortex (to 73-75%). No significant change was observed in [3H] noradreanaline uptake after any injection, or in [3H] 5-HT uptake after vehicle injections. Locomotor activity in an open field 3-10 days postoperatively was significantly reduced by lesions of the medial plus lateral 5-HT bundles. 5-Hdroxytryptophan (50 mg/kg) and a peripheral decarboxylase inhibitor (MK 486, 75 mg/kg) 17 days postoperatively induced a pronounced behavioral "5-HT syndrome" in these rats with medial plus lateral lesions but not in controls. Pain sensitivity, as measured by the hot plate test, was not changed by any lesion, even when tryptophan hydroxylase was partly inhibited with alpha-propyldopacetamide (100 mg/kg). Morphine analgesia and acquisition of a one-way avoidance response also were unchanged. Apomorphine (2 mg/kg)-induced locomotor activity and stereotyped behavior, as measured in an Animex activity meter, were not significantly different from control values in the 5,7-DHT groups. It was concluded that the medial 5-JT BUNDLE INNERVATES BOTH THE HYPOTHALAMUS AND THE CORTEX CEREBRI AND THE LATERAL 5-HT bundle mainly the cortex. These ascending 5-HT neurons are involved in maintaining open field ambulation. No wupport was obtained for the view that they are involved in pain mechanisms, in morphine-induced analgesia, in apomorphine-induced motor behavior, or in one-way avoidance learning.

Evidence for involvement of 5-hydroxytryptamine in the actions of amphetamine

1 Pargyline treatment, 1 h before (+)-amphetamine (1 mg/kg), reduced amphetamine-stimulated motor activity. This inhibition was reversed in animals pretreated with p-chlorophenylalanine (PCPA).2 Following treatment with PCPA or 5,6-dihydroxytryptamine (5,6-DHT), amphetamine-induced locomotor activity was significantly potentiated. The increased response to amphetamine in PCPA-treated rats was reversed in animals pretreated with 5-hydroxytryptophan.3 The inhibition of amphetamine-stimulated locomotor activity by treatment with 6-hydroxydopamine was not reversed by PCPA treatment.4 Stereotypies produced by amphetamine were not found to be altered by depletion of 5-hydroxytryptamine.5 Induction of adrenal tyrosine hydroxylase activity produced by chronic amphetamine administration was significantly potentiated by PCPA, emphasizing the involvement of a 5-hydroxytryptamine inhibitory system in more than one action of amphetamine.

A comparison of the effects of varying dose levels of oxypertine on mood and physical performance of trained athletes

Oxypertine (also known as Win. 18,501–2) is a member of a series of alkyl indolyl-4-phenyl piperazines (Archer et al., 1962), and is 1-[2-(5,6 -Dimethoxy-2-methyl-3-indolyl) ethyl]-4-phenylpiperazine.