The effect of dopamine and noradrenaline antagonists on amphetamine induced locomotor activity in mice and rats

Dihydroergotamine protects against ischemic stroke by modulating microglial/macrophage polarization and inhibiting inflammation in mice

OBJECTIVES

The search for drugs that can protect the brain tissue and reduce nerve damage in acute ischemic stroke has emerged as a research hotspot. We investigated the potential protective effects and mechanisms of action of dihydroergotamine against ischemic stroke.

METHODS

C57BL/6 mice were subjected to middle cerebral artery occlusion (MCAO), and dihydroergotamine at a dose of 10 mg/kg/day was intraperitoneally injected for 14 days. Adhesive removal and beam walking tests were conducted 1, 3, 5, 7, 10, and 14 days after MCAO surgery. Thereafter, the mechanism by which dihydroergotamine regulates microglia/macrophage polarization and inflammation and imparts ischemic stroke protection was studied using enzyme-linked immunosorbent assay, immunofluorescence staining, and western blotting.

RESULTS

From the perspective of a drug repurposing strategy, dihydroergotamine was found to inhibit oxygen-glucose deprivation damage to neurons, significantly improve cell survival rate, and likely exert a protective effect on ischemic brain injury. Dihydroergotamine significantly improved neural function scores and survival rates and reduced brain injury severity in mice. Furthermore, dihydroergotamine manifests its protective effect on ischemic brain injury by reducing the expression of TNF-α and IL-1β in mouse ischemic brain tissue, inhibiting the polarization of microglia/macrophage toward the M1 phenotype and promoting polarization toward the M2 phenotype.

CONCLUSION

This study is the first to demonstrate the protective effect of dihydroergotamine, a first-line treatment for migraine, against ischemic nerve injury in vitro and in vivo.

The Involvement of Norepinephrine in Behaviors Related to Psychostimulant Addiction

Although it is generally accepted that the abuse-related effects of amphetamines and cocaine result from the activation of the brain dopaminergic (DA) system, the psychostimulants also alter other neurotransmitter systems. In particular, they increase extracellular levels of norepinephrine (NE) and serotonin by inhibiting respective plasma membrane transporters and/or inducing release. The present review will discuss the preclinical findings on the effects of the NE system modulation (lesions, pharmacological and genetic approaches) on behaviors (locomotor hyperactivity, behavioral sensitization, modification of intracranial self-stimulation, conditioned place preference, drug self-administration, extinction/reinstatement of drug seeking behavior) related to the psychostimulant addiction.

Dopamine and the mechanisms of cognition: Part II. D-amphetamine effects in human subjects performing a selective attention task

BACKGROUND

A neural network computer model described in a companion paper predicted the effects of increased dopamine transmission on selective attention under two different hypotheses.

METHODS

To evaluate these predictions we conducted an empirical study in human subjects of D-amphetamine effects on performance of the Eriksen response competition task. Ten healthy volunteers were tested before and after placebo or D-amphetamine in a double-blind cross-over design.

RESULTS

D-amphetamine induced a speeding of reaction time overall and an improvement of accuracy at fast reaction times but only in the task condition requiring selective attention.

CONCLUSIONS

This pattern of results conforms to the prediction of the model under the hypothesis that D-amphetamine primarily affects dopamine transmission in cognitive rather than motor networks. This suggests that the principles embodied in parallel distributed processing models of task performance may be sufficient to predict and explain specific behavioral effects of some drug actions in the central nervous system.

No major differences in locomotor responses to dexamphetamine in high and low responders to novelty: a study in Wistar rats

The aim of the study was to compare locomotor responses to acute and sub-chronic dexamphetamine in two distinct types of Wistar rats, namely the Nijmegen high responders to novelty (HR) and Nijmegen low responders to novelty (LR). HR and LR were chosen because they differ in neurochemical processes relevant to the control of the locomotor effects of dexamphetamine, such as the dopaminergic and adrenergic activity in the nucleus accumbens. In experiment 1, a dexamphetamine dose-response curve (0.0-2.0 mg/kg/i.p.) was established using standard activity boxes. The dose-response curve slightly, but significantly, differed between HR and LR: especially the increase elicited by 1.5 mg/kg dexamphetamine was significantly greater in HR than in LR. In experiment 2, locomotor effects of sub-chronic administration of dexamphetamine (1.0 mg/kg/i.p.) were analyzed in HR and LR for 5 consecutive days. HR showed a higher locomotor response to dexamphetamine than LR; however, the two groups did not differ in their sensitization rate. It is concluded that there are neither major HR-LR differences in the locomotor response to acute administration of various doses of dexamphetamine nor HR-LR differences in the rate of sensitization of this locomotor response to sub-chronic administration of dexamphetamine. Type-specific differences in the mutual interaction between corticosteroids and dexamphetamine as well as the nature of the chosen dependent variable, namely locomotor activity, are hypothesized to underlie the results of the present study.

Differential effects of classical and newer antipsychotics on the hypermotility induced by two dose levels of D-amphetamine

The inhibitory effects of a variety of established and putative antipsychotic compounds on the hypermotility induced by D-amphetamine at two dose levels (0.5 and 2.0 mg/kg) have been studied. Classical antipsychotics (haloperidol, fluphenazine and cis(Z)-flupentixol) and the selective dopamine D2 receptor antagonist remoxipride inhibit hypermotility in the two conditions with similar potencies, whereas sertindole, clozapine, risperidone, ziprasidone and olanzapine preferentially inhibit the effect of the low dose of D-amphetamine (selectivity ratios between 6.5 and 18). Seroquel, amperozide and the selective 5-HT2A receptor antagonist MDL 100.151 ((+/-)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-p iperidine - methanol) have no effect on D-amphetamine 2.0 mg/kg, but inhibit the response to D-amphetamine 0.5 mg/kg. The alpha 1-adrenoceptor antagonist prazosin inhibits the motility response to D-amphetamine 0.5 mg/kg with slightly higher potency than that to D-amphetamine 2.0 mg/kg, whereas the 5-HT2A/2C receptor antagonist ritanserin selectively inhibits the effect of D-amphetamine 0.5 mg/kg. The histamine H1 receptor antagonist mepyramine is ineffective in both models. All compounds, except remoxipride, MDL 100.151 and ritanserin (which are ineffective) inhibit spontaneous locomotor activity at dose levels close to those inhibiting the response to D-amphetamine 2.0 mg/kg. Prazosin has partial inhibitory effect. In conclusion, dopamine antagonism has similar inhibitory effect on hyperactivity induced by low and high D-amphetamine dosages, alpha 1-adrenoceptor antagonism also contributes to both effects, whereas 5-HT2 receptor antagonism selectively interacts with the low D-amphetamine dose. This indicates that the responses to D-amphetamine 0.5 and 2.0 mg/kg are differently modulated by these neurotransmitters.(ABSTRACT TRUNCATED AT 250 WORDS)

Thioperamide, the selective histamine H3 receptor antagonist, attenuates stimulant-induced locomotor activity in the mouse

The effects of the selective histamine H3 receptor agonist (R)-alpha-methylhistamine and antagonist thioperamide on stimulant-induced locomotor activity in the mouse were examined. Amphetamine (1 mg.kg-1 s.c.), apomorphine (2 mg.kg-1 s.c.) or cocaine (5 mg.kg-1 s.c.) increased locomotor activity. Neither thioperamide (10 mg.kg-1 i.p.) nor (R)-alpha-methylhistamine (20 mg.kg-1 i.p.) affected spontaneous locomotor activity in their own right. (R)-alpha-Methylhistamine (0.3, 3 or 20 mg.kg-1 i.p.) also had no effect on amphetamine (1 mg.kg-1 s.c.)-induced locomotor activity. In contrast, thioperamide (0.2-10 mg.kg-1 i.p. or 0.3-20 micrograms i.c.v.) inhibited, in a dose-dependent manner, the hyperactivity response induced by amphetamine (1 mg.kg-1 s.c.). (R)-alpha-Methylhistamine (20 mg.kg-1 i.p.) completely reversed the inhibitory response to thioperamide (2 mg.kg-1 i.p.). Thioperamide (2 or 10 mg.kg-1 i.p.) also inhibited apomorphine (2 mg.kg-1 s.c.)- and, to a lesser extent, cocaine (5 mg.kg-1 s.c.)-induced hyperactivity. We therefore conclude that antagonism of the central histamine H3 receptor inhibits, to a varying degree, the effects of locomotor stimulants.

Role of catecholamines in the modafinil and amphetamine induced wakefulness, a comparative pharmacological study in the cat

Seventeen adult cats were chronically implanted with electrodes for polygraphic recordings in order to assess the role of catecholamines in the arousal effects of oral administrations of modafinil, a presumed noradrenergic agonist, and amphetamine, a well-known catecholamine-releasing agent. Whereas both modafinil (1, 2.5 and 5 mg/kg) and amphetamine (0.25, 0.5 and 1 mg/kg) caused a significant and dose-dependent increase in wakefulness and brain temperature, amphetamine, but not modafinil, elicited marked signs of behavioral excitation. Pretreatments with alpha-methyl-DL-p-tyrosine methyl ester (50 mg/kg, i.p.), an inhibitor of catecholamine synthesis, almost completely prevented the effects of amphetamine (0.25 and 1 mg/kg), but only slightly reduced the duration of the waking effect of modafinil (2.5 and 5 mg/kg). Pretreatments with phentolamine (10 mg/kg, i.p.), prazosin (1.5 mg/kg, per os) and propranolol (5 mg/kg, i.p.), an alpha-, alpha 1- and beta-receptor antagonist, respectively, attenuated significantly the arousal effect of modafinil (1 mg/kg, the same as below) but not of amphetamine (0.25 mg/kg, the same as below). Intraperitoneal injections of haloperidol (0.5 mg/kg), a dopamine-receptor antagonist, blocked significantly the arousal of amphetamine but not of modafinil. The effects of both modafinil and amphetamine were enhanced by a pretreatment with yohimbine (1 mg/kg, i.p.), an alpha 2-receptor antagonist. These results suggest that the arousal effect of modafinil does not depend on the availability of the endogenous catecholamines but results from an enhancement of alpha 1- and beta-receptor activity and that the waking and behavioral effects of amphetamine may be mainly due to an increase in dopamine release.

Microinjections of a nicotinic agonist into dopamine terminal fields: effects on locomotion

Nicotine induces locomotion, a behavior associated with the mesocorticolimbic dopamine system. The present study determined the effects on locomotion of direct microinjections of the nicotinic agonist cytisine into four DA terminal fields were nicotinic receptors have been localized: nucleus accumbens (NAS, n = 20), caudate putamen (CPU, n = 9), olfactory tubercle (OT, n = 8), and medial prefrontal cortex (MPC, n = 12). Male Long-Evans rats were injected with cytisine (0.1, 1, 10 and 100 nanomoles per 0.5 microliters per side) or vehicle through indwelling cannulae, and locomotor activity was recorded during a 60-minute test session; each animal was tested with each dose in counterbalanced order. NAS injections of the three highest doses of cytisine increased locomotion relative to vehicle injections; injections in the CPU, dorsal to the NAS, were ineffective, as were MPC and OT injections. The data support the notion that systemic nicotine may interact with dopaminergic projections to the NAS to produce increases in locomotor activity.

Central alpha 1-adrenergic stimulation in relation to the behaviour stimulating effect of modafinil; studies with experimental animals

Single administration of the new drug modafinil was followed by an increase in locomotor activity in mice and in nocturnal activity in monkeys. Stereotyped behaviour in mice and rats, and potentiation of amphetamine-induced stereotyped behaviour were not observed; however, at the highest dose used, a slight potentiation of apomorphine-induced stereotyped behaviour was observed in rats. The modafinil-induced increase in locomotor activity in mice was prevented by the centrally acting alpha 1-adrenoceptor antagonists, prazosin and phenoxybenzamine, and by reserpine but not by the mixed dopamine D-1/D-2 antagonist, haloperidol, the dopamine D-2 antagonist, sulpiride, the peripherally acting alpha 1-adrenoceptor antagonist, phentolamine, the alpha 2-adrenoceptor antagonist, yohimbine, the beta-adrenoceptor antagonist, propranolol, or by the catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine. Likewise, the modafinil-induced increase in nocturnal activity in monkeys was prevented by prazosin. Interestingly, modafinil did not produce obvious peripheral sympathetic effects in mice and rats (no salivation, no contraction of the pilomotor muscles, slight mydriasis only at high doses). Therefore, modafinil appears to produce a strong stimulating effect in rodents and in primates. These effects could be linked to modulation (stimulation) of central alpha 1-adrenoceptors unaccompanied by peripheral sympathetic effects, which is unexpected.

Effects of amperozide on induced turning behaviour in 6-OHDA lesioned rats

The effect of amperozide on DA synapses was studied in 6-OHDA lesioned rats exhibiting a specific turning behaviour in response to the DA agonists apomorphine and pergolide or indirectly acting stimulating agents like amphetamine. Amperozide, unlike classical neuroleptics, failed to antagonize apomorphine induced turning behaviour in a regular fashion, but showed pergolide antagonism within the D2 receptor selective dose range, suggesting a type of selective interference with dopaminergic nerve transmission which differs from that caused by classical neuroleptics. Furthermore, amperozide antagonized the turning behaviour induced by amphetamine, presumably by interfering with the availability of newly synthesized DA and NA suggesting a similar influence also on other DA releasing agents. Although amperozide potentiated the effects of alpha-MPT, the drug seemed not to influence the reserpine sensitive pool of DA.

The effect of dopamine receptor blockade on the development of sensitization to the locomotor activating effects of amphetamine and morphine

The effect of dopamine (DA) receptor blockade on the development of sensitization to the locomotor activating effects of systemic amphetamine and intra-ventral tegmental area (intra-VTA) morphine was investigated. Rats were pretreated with the D-1 DA receptor antagonist, SCH-23390 (0.04 or 0.2 mg/kg, i.p.) or one of two D-2 DA receptor antagonists, pimozide (0.5 mg/kg, i.p.) and Ro 22-2586 (0.2 mg/kg, i.p.), prior to each of 5 exposures to the sensitizing drug. SCH-23390 blocked the development of sensitization to amphetamine but not to intra-VTA morphine. Pimozide had the opposite effect and Ro 22-2586 had no effect on the development of sensitization to either amphetamine or intra-VTA morphine. All 3 antagonists, at the doses tested, completely blocked the acute locomotor activating effects of these two drugs. Pretreatment in separate animals with low autoreceptor doses of sulpiride (25 mg/kg, i.p. with amphetamine and 10 mg/kg, i.p. with intra-VTA morphine) slightly potentiated the acute locomotor effect and produced a slight enhancement of the sensitized response to amphetamine and intra-VTA morphine. Pretreatment with a higher dose of sulpiride (50 mg/kg, i.p.) blocked the acute locomotor effect of intra-VTA morphine but had no effect on the development of sensitization to this drug. These results suggest that the mechanisms underlying the development of sensitization to the locomotor activating effects of amphetamine and intra-VTA morphine are different even though these may ultimately result in similar changes in the activity of mesencephalic DA neurons. Implications of these findings for the differential involvement of D-1 and D-2 DA receptors and for neural hypotheses of behavioral sensitization are discussed.

Central noradrenaline depletion attenuates amphetamine-induced locomotor behavior

Male rats were given 6-hydroxydopamine-induced lesions of the locus coeruleus (LC) or the dorsal noradrenergic bundle (DNAB), prior to the measurement of locomotor and rearing activity induced by D-amphetamine. The increased locomotor activity induced by D-amphetamine (1.8 mg/kg) was significantly attenuated by both the LC and the DNAB lesions. The stimulatory effect of the 7.2 mg/kg dose of amphetamine was attenuated by the LC lesion, whereas the DNAB lesion potentiated this effect. The LC lesion also attenuated rearing induced by the 7.2 mg/kg dose of amphetamine. These results suggest some involvement of central noradrenergic neurons in the activity induced by amphetamine in the rat.

Central noradrenaline depletion antagonizes aspects of d-amphetamine-induced hyperactivity in the rat

The effects of noradrenaline (NA) depletion upon amphetamine-induced hyperactivity were examined in five experiments. Central NA depletion via either systemic DSP4 or neonatal 6-OHDA antagonised the amphetamine-induced (2 mg/kg SC) increase in rearing behaviour, whereas lesions of the dorsal noradrenergic bundle using 6-hydroxydopamine antagonised the increase in locomotor activity. Peripheral NA depletion following systemic 6-hydroxydopamine to adult rats did not cause any changes in motor activity after acute amphetamine administration. Desipramine, the selective NA uptake inhibitor, blocked the effects of DSP4 upon amphetamine-induced rearing. NA depletion antagonised hyperactivity produced by the 2 mg/kg dose of amphetamine, but not the hyperactivity (rearing or locomotion) effects of amphetamine at 1, 4 or 8 mg/kg.

Changes in rat dopamine- and serotonin function in vivo after prolonged administration of the specific 5-HT uptake inhibitor, citalopram

The effect of prolonged administration of the potent and specific 5-HT uptake inhibitor citalopram on behavioural measures of dopaminergic and serotonergic activity has been studied in rats. Administration of citalopram in the diet at a daily dose of 99 mumol/kg led to supersensitivity to d-amphetamine-induced hypermotility and stereotypy and to subsensitivity to apomorphine-induced hypomotility 2 h after withdrawal. Forepaw clonus induced by 5-methoxy-N,N-dimethyltryptamine was decreased 2 h and 24 h after withdrawal and the number of head shakes induced by 1-5-HTP and citalopram were decreased 24 h after withdrawal. The d-amphetamine potentiation was still seen after 24 h, whereas the response had returned to normal 3 and 7 days after withdrawal. The content of amphetamine in three different brain regions was about 50% higher compared with controls 24 h after withdrawal of prolonged citalopram administration. At this time citalopram had been eliminated, and citalopram itself could not affect amphetamine metabolism. Other experiments indicated a linear relation between d-amphetamine brain concentration and motility level. Thus, a 50% increase in citalopram-treated rats cannot alone account for 3-fold increase in d-amphetamine-induced motility. Potentiation of d-amphetamine-induced hypermotility was also found after citalopram in a daily dietary dose of 25 mumol/kg for 13 days and after oral bolus injection (49 mumol/kg twice daily for 14 days). Acute citalopram injection had no effect in any of these models. The results suggest increased responsiveness of dopaminergic mechanisms mediating hypermotility, and decreased sensitivity of dopamine receptors mediating sedation (proposed autoreceptors). Sensitivity of 5-HT receptors was also decreased. The mechanisms by which citalopram induces d-amphetamine supersensitivity as well as subsensitivity to apomorphine and 5-HT agonists are presently unknown, since no changes in dopaminergic and serotonergic receptor binding have been found after an identical dose regimen.

Dopamine receptor agonistic and antagonistic effects of 3-PPP enantiomers

The pharmacological profile of the enantiomers of the proposed selective dopamine (DA) autoreceptor agonist 3-PPP [3-(3-hydroxyphenyl)-N-n-propylpiperidine] has been studied. In vitro both enantiomers showed weak DA agonistic activity, and (--)-3-PPP some DA antagonistic effect on DA-stimulated adenylate cyclase activity. Both enantiomers in low doses had a similar profile in vivo: Inhibition of locomotor activity of mice and rats, induction of contralateral circling behaviour in 6-hydroxy-DA-lesioned rats and an emetic effect in dogs. At higher doses, differential effects of the enantiomers were found: (+)-3-PPP induced hyperactivity, weak stereotyped behaviour and ipsilateral circling in hemitransected rats. (--)-3-PPP had depressant effects in high doses, inhibited d-amphetamine-induced hyperactivity and d-amphetamine-, methylphenidate- and apomorphine-induced stereotyped licking/biting in rats and antagonized apomorphine-induced emesis in dogs. However, (+)-3-PPP also showed a weak antagonistic activity against d-amphetamine-induced hyperactivity and d-amphetamine- and apomorphine-induced stereotypy in rats and inhibited apomorphine-induced emesis in dogs. It is suggested that both enantiomers have significant effects on postsynaptic DA receptors in high doses: (--)-3-PPP with weak antagonistic activity in some test models and (+)-3-PPP with agonistic and antagonistic effect. Since these effects of (+)-3-PPP were of low intensity at high doses, (+)-3-PPP may be a partial DA agonist at postsynaptic receptors in high doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential activity of enantiomers of amphetamine in rats

Administration of single doses of d-amphetamine (0.5-4.0 mg/kg i.p.) to adult, male rats produced the expected dose-related increases in spontaneous motor activity. This effect was reduced by pretreatment with alpha-methylparatyrosine (alpha MT) and virtually unaffected by pretreatment with pargyline or parachlorophenylalanine (PCPA). Single doses of l-amphetamine (0.25-8.0 mg/kg) evoked an initial decrease in activity followed by increased activity of smaller magnitude than that caused by the d-isomer. The depressant effects of the l-isomer were prolonged by pretreatment with alpha MT, and abolished by pretreatment with pargyline or PCPA.

Possible DA agonist properties of naloxone

Naloxone is widely if not universally considered to be a pharmacologically 'pure' opiate (mu) receptor antagonist virtually devoid of agonist action when administered in moderate dosages. However, naloxone (NX) appears to possess a striking number of DA agonist properties. Thus, some investigators have found NX capable of inducing stereotyped rearing and locomotor activity in habituated rats (a controversial finding), and decrease serum prolactin levels, improve Parkinsonism, enhance copulatory performance in sexually sluggish animals, and increase striatal HVA levels, in mimicry of centrally acting DA agonists. NX can also significantly potentiate the central effects induced by DA agonists including DA agonist (d-amphetamine) induced 3H-dopamine release, and antagonize a number of the central effects elicited by DA release inhibiting agents. Finally, virtually all of the central effects of morphine reversible by NX have also been found to be antagonized by a variety of dopamine agonists; while DA release inhibiting agents can abolish the ability of NX to antagonize morphine induced effects. Thus, NX may be exerting its central effects through a dopaminergic mechanism. Since NX does not bind DA receptors, it is quite likely that NX may ultimately antagonize the central effects of morphine by enhancing DA release from DA terminals upon which opiate receptors are localized. The same opiate receptors, shown to be localized on DA nerve terminals, have already been implicated in opiate mediated modulation of DA release.

Loss of eye movements abolishes light entrainment of circadian mesolimbic catecholamine excitability: a function for REM?

Light entrainment of the circadian rhythm of mesolimbic dopamine excitability, measured by the amphetamine-induced locomotor response, and the circadian feeding rhythm was abolished following section of the extraocular muscles of the rat. Endogenous (free-running) circadian rhythms were preserved. The results are consistent with electrophysiologic evidence that the rapid eye movements during paradoxical sleep transmit light-modulated electrical potentials to regions of the brain that influence circadian rhythms and dopamine release.

Alterations in the stages of continuous amphetamine intoxication produced by lesions of locus coeruleus and substantia nigra

1. Slow-release silicone pellets containing d-amphetamine base were implanted subcutaneously in rats 20 days following radio-frequency lesions of the locus coeruleus (LC), substantia nigra (SN), or control operations. 2. LC-lesioned rats exhibited enhanced motor stereotypies soon after implantation, while SN-lesioned animals showed increased locomotion but decreased stereotypy and anorexia. 3. The later behavioral stages of continuous amphetamine intoxication were attenuated in both lesioned groups as controls then entered the most intense stereotypy, showed the greatest withdrawal to the burrows, and maximally exhibited the increase in socially disruptive behaviors which appear following four days of constant amphetamine intoxication. 4. The integrity of both dopaminergic and noradrenergic systems was necessary for the full expression of the late stages of this animal model of amphetamine psychosis.

Amphetamine psychosis and schizophrenia: a dual model

Several of the behavioral consequences of acute and chronic amphetamine treatment were evaluated and related to the underlying neurochemical correlates of drug treatment. It was suggested that decreased noradrenergic activity after long-term amphetamine treatment influences stimulus sampling, whereas enhanced dopaminergic activity was responsible for the progressive augmentation of stereotypy and self-stimulation behavior observed after long-term exposure to amphetamine. It was hypothesized that amphetamine-induced psychosis and the symptomatology associated with schizophrenia are related to alterations in both norepinephrine and dopamine activity.

A comparison of the effects of neuroleptics on phencyclidine-induced behaviors in the rat

The dose-response effects of neuroleptic pretreatment on phencyclidine (PCP; 3 or 5 mg/kg)-induced locomotor activity, stereotyped behaviors and ataxia were quantified in groups of male rats using rating scales recently developed in this laboratory. Three butyrophenone neuroleptics consistently produced dose-dependent antagonism of the behavioral effects of PCP administration. Fluphenazine antagonized the behavioral effects produced by 3 mg/kg PCP but not those produced by 5 mg/kg PCP. Each of the other neuroleptics examined (chlorpromazine, thioridazine, mesoridazine, triflupromazine, cis-flupenthixol) had no consistent antagonistic effect or actually enhanced one or more of the behavioral effects of PCP. Some neuroleptics slightly reduced PCP locomotion or stereotypies at high doses, but these effects were probably a non-specific consequence of the synergistic ataxia-producing properties of these drugs. In a second set of experiments, atropine sulfate pretreatment increased PCP-induced locomotor activity and stereotyped behaviors but had no effect on ataxia; pretreatment with physostigmine produced opposite effects. Combined pretreatment with haloperidol and atropine sulfate significantly reduced only haloperidol antagonism of PCP-induced ataxia, thus suggesting that non-dopoaminergic effects of neuroleptics may interfere with their ability to antagonize PCP.

The effect of varying doses of d-amphetamine on activity levels of prepubertal mice

The effect of varying doses of d-amphetamine on the activity level of C57BL/6J mice (known for their high activity level), DBA/1J, C3H/HeJ, and C3D2F1 mice was investigated (all mice were 25 to 30 days old). Activity was measured by the use of an activity cage with a revolving drum. After determination of baseline activity level, the animals were assigned to the following set of i.p. injections: (1) normal saline, (2) d-amphetamine 0.2 mg/kg, (3) d-amphetamine 0.5 mg/kg, (4) d-amphetamine 5 mg/kg. The mean activity level of the C57BL/6J mice was significantly higher than that of the other strains. The mean activity level after 5 mg/kg was significantly lower than after other dosages in all strains. All strains responded similarly to d-amphetamine as is apparent from the parallel profiles for the dose-response curves. The response of the developing mice to d-amphetamine is at variance with the known response of mature mice.

Differential behavioral responses of spontaneously hypertensive (SHR) and normotensive (WKY) rats to d-amphetamine

A comparison was made in the behavioral responses of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats to d-amphetamine. Animals were tested at a young age (6 weeks) to minimize the effects of elevated blood pressure on drug responsiveness. SHR rats were more active than WKY rats after injections of 1.0, 2.0, and 4.0 mg/kg d-amphetamine. A significant strain difference in stereotypy was also noted; rearing occurred in SHR rats while lateral or vertical head movements (head waving) occurred in WKY rats. The lack of significant strain differences in the behavioral responses of rats to apomorphine, a direct acting dopamine agonist, suggested that the differential behavioral responses to d-amphetamine were not a result of differences between strains in receptor sensitivity. Pretreatment of rats with reserpine eliminated the strain differences in behavioral responses to d-amphetamine. Pretreatment of rats with alpha-methyl-p-tyrosine prior to administration of d-amphetamine elminated the strain differences in stereotyped behavior; however, WKY rats remained less active than SHR rats. Pretreatment of SHR rats with parachlorophenylalanine had no effect on the behavioral responses to d-amphetamine. In contrast, pretreatment of WKY rats with parachlorophenylalanine resulted in an increase in rearing and a decrease in head waving following an injection of d-amphetamine. These findings suggest that the differences in responses to d-amphetamine of SHR and WKY rats are due in part to variations in the activities of central catecholaminergic and serotonergic neurons.

The effect of dopamine and noradrenaline blockade on amphetamine-induced behaviour in the marmoset

Acute administration of 4 mg/kg d-amphetamine in the marmoset results in a large increase in small head movements (checking), an almost total suppression of purposeful activities and social interaction, but little change in the amount of locomotion. Checking behaviour is blocked in a dose dependent manner by 0.03--0.18 mg/kg haloperidol but not by propranolol, aceperone or diazepam, suggesting dopaminergic mediation of this behaviour. The loss of activities and social interaction after amphetamine is not antagonized by any of the drugs used in this study. Locomotion is decreased by haloperidol, propranolol and diazepam in amphetamine treated animals and by haloperidol and aceperone in normal animals.

Dissociated effects of inhibition of catecholamine synthesis on motor activity, "emotionality," and aggression in mice

The inhibitor of catecholamine synthesis at the tyrosine hydroxylase level, alpha-methyltyrosine, administered in daily doses of 250 mg/kg IP, altered motor activity and aggressive behavior of isolated male mice in ten-minute paired encounter tests conducted on nine successive days. Motor activity was determined by an electromagnetic activity meter which measures fine and coarse movements separately. Coarse motor activity correlated significantly with aggressive behavior. Nonaggressive fine motor activity was significantly increased, while all the parameters of aggressive behavior showed a significant decrease in aggression. Increased escape behavior, heterogrooming, squeaking, and two cases of stupor were observed, suggesting possible equivalents of anxiousness. The defecation rate did not differ from that of the control group, victors having had a higher rate than losers. Results are discussed in connection with the "construct of emotionality" and the hypothesis of there being several categories of aggression with corresponding biochemical correlations.

Antagonism of morphine-induced central stimulation in mice by small doses of catecholamine-receptor agonists

The morphine (75 mg/kg i.p.) induced stimulation of motor activity in mice was significantly suppressed by small doses of central catecholamine (CA) receptor agonists, apomorphine (0.2 mg/kg) and clonidine (0.05 mg/kg). In the same dose, and at the same time interval as the behavioural stimulation was obtained, morphine did not significantly affect the in vivo rate of tyrosine hydroxylation in two dopamine (DA)-rich mouse brain regions, the corpus striatum and in the limbic system, or in the noradrenaline (NA)-rich, but DA-poor hemispheres, measured as the Dopa-accumulation during 30 min after inhibition of aromatic amino-acid decarboxylase by 3-hydroxybenzylhydrazine (NSD 1015) 150 mg/kg. The apomorphine induced reduction in Dopa accumulation in the DA-rich brain regions was not significantly affected by morphine. The disappearance rate of brain NA after inhibition of tyrosine hydroxylase by alpha-methyltyrosine methylester (250 mg/kg), the utilization of NA, was accelerated by morphine, whereas that of DA was not affected. Clonidine (0.05 mg/kg) retarded selectively brain NA utilization, and also suppressed the morphine-induced increase in NA utilization. In conclusion, morphine's stimulation of motor activity in mice, an effect which previously has been found to be correlated with its dependence producing action, could be inhibited by apomorphine or clonidine in small doses which inhibit brain DA- and NA-neurons, respectively. Thus, we have now shown the psychomtor stimulation by two euphoriant and dependence-producing drugs, ethanol and morphine, to be suppressed by CA "autoreceptor" activation.

Influence of catecholamines on dexamphetamine-induced changes in locomotor activity

In the mouse, central noradrenaline receptor stimulation by clonidine, or intracerebroventricular injection of noradrenaline or alpha-methylnoradrenaline, caused marked enhancement of the locomotor stimulant effects of dexamphetamine in doses that were without effect when given alone. A minimally locomotor-stimulant dose of apomorphine reduced the effect of dexamphetamine. Pimozide and phenoxybenzamine each virtually abolished locomotor stimulation after dexamphetamine, while FLA63 caused significant reduction. Phenoxybenzamine also abolished the enhancement by clonidine. The intensity of the dexamphetamine effect was dose-related, while in the case of apomorphine the duration rather than the intensity was related to the dose administered. Clonidine potentiated apomorphine locomotor stimulation; following this drug combination, the nature of the movements more closely resembled those seen after dexamphetamine. The results suggest the involvement of both noradrenaline and dopamine in the dexamphetamine response.

Alterations of spontaneous neuronal activity in the caudate-putamen, nucleus accumbens and amygdaloid complex of rats produced by D-amphetamine

Changes in spontaneous neuronal activity in the caudate-putamen, accumbens nucleus and amygdaloid complex of immunobilized, locally anesthetized rats were recorded following intraperitoneal injection of 2.5 mg/kg d-amphetamine sulfate. In each site, d-amphetamine typically produced a prolonged depression of firing rate which, in most cases, occurred after an inital, brief potentiation of activity. However, the onset of the amphetamine-induced depression occurred signficantly later in the amygdala. Subsequent IP administration of either 5.0 mg/kg chlorpromazine or 2.0 mg/kg haloperidol reversed, to varying degrees, the amphetamine-induced depression of neuronal activity in each area. These results are discussed in terms of the known biochemical effects of amphetamine on catecholaminergic transmission and the alleged role of the nigro-neostriatal mesolimbic dopamine systems in the amphetamine behavioral response.

Further analysis of the resistance of the diabetic rat to d-amphetamine

Rats that were made diabetic by the subcutaneous injection of alloxan monohydrate were found to be resistant to the anorexic action of d-amphetamine. This resistance to amphetamine anorexia did not appear attributable to an increased hunger motivation of the diabetic rats, but rather seemed due to a diminished action of the drug in alloxan-injected animals. This conclusion was supported by further experiments indicating that alloxan-injected rats show diminished locomotor activity and stereotyped behavior following amphetamine administration. Furthermore, the amphetamine resistance appears to be the result of the diabetic state, since amphetamine-induced stereotyped behavior could be reinstated in alloxan-injected rats by the administration of protamine zinc insulin for ten days. The results of these investigations suggest that there exists an altered central nervous system response to d-amphetamine in the diabetic rat. These possibility of an abnormal functioning of central catecholamine-containing neurons in such animals is discussed.

Locomotor stimulation by L-dopa: relative importance of noradrenaline receptor activation

The importance of brain noradrenaline synthesis and receptor activation for the hyperkinesia induced by carbidopa plus L-Dopa in reserpine-treated or normal mice was analyzed in four different models. After pretreatment with reserpine and the monoamine oxidase inhibitor nialamide, the hyperkinesia induced by L-Dopa (25 mg/kg i.p.) was partly mediated via stimulation of noradrenaline receptors since it was significantly antagonized by the noradrenaline receptor-blocking agent phenoxybenzamine. Treatment with reserpine plus L-Dopa (125 mg/kg i.p.) produced an increase in motor activity probably due to stimulation of dopamine receptors since it was not accompanied by an accumulation of noradrenaline and it was not inhibited by phenoxybenzamine. The hyperkinesia following treatment with reserpine and a higher dose of L-Dopa (250 mg/kg i.p.) was probably due to stimulation of both dopamine and noradrenaline receptors since the dopamine-beta-hydroxylase inhibitor FLA-63 partly reduced the effect of L-Dopa. Phenoxybenzamine potentiated the motor stimulation by L-Dopa (125 mg/kg i.p.) in mice not pretreated with reserpine, perhaps depending on a slight enhancement of the net accumulation of brain dopamine. Thus, noradrenaline receptor activation is of importance for the L-Dopa-induced hyperkinesia, at least after high doses or after monoamine oxidase inhibition.

Effects of locus coeruleus lesions upon cerebral monoamine content, sleep-wakefulness states and the response to amphetamine in the cat

The purpose of the present study was to investigate the effects of complete lesions of the noradrenaline locus coeruleus neurons upon wakefulness and paradoxical sleep. Radiofrequency lesions of the nucleus were performed in 8 chronically implanted cats which were continuously recorded with an EEG for 5 days prior to and 21 days following the lesions, when they were sacrificed. In 3 of these animals amphetamine (2 mg/kg) was administered on one control day and on the 10th day post-lesion. Following sacrifice, monoamine content was assayed in discrete brain regions, and the lesion was examined in Nissl-stained sections of the pons. (1) The majority (x 69%) of the locus coeruleus was bilaterally destroyed by the lesions which only minimally exceeded the boundaries of the nucleus within the dorsolateral pontine tegmentum. Noradrenaline was depleted by a mean of 85% in the paleo- and neocortex and by a mean of 60% in the thalamus and midbrain. (2) EEG activation reappeared within 12-48 h following the lesion and represented a normal percentage of recording time on the 3rd and subsequent days post-lesion. The behavioral arousal and long-lasting EEG activation produced by amphetamine was qualitatively and quantitatively the same pre- and post-lesion. (3) Despite alteration of certain components, paradoxical sleep reappeared within 48 h and recovered to normal amounts by the second week post-lesion. Muscle atonia was permanently absent in 7 animals. Ponto-geniculo-occipital (PGO) spiking was acutely redistributed across all states and chronically reduced in frequency (by a mean of 50%) within paradoxical sleep. These results indicate that the noradrenaline locus coeruleus neurons are not necessary for the tonic maintenance of EEG activation that occurs in normal wakefulness and in amphetamine-produced arousal. Furthermore, these neurons are not necessary for the occurrence of paradoxical sleep, although they may be involved in modulation of PGO spiking.

Modification of the L-DOPA reversal of reserpine akinesia by inhibitors of dopamine-beta-hydroxylase

The effect of the dopamine-beta-hydroxylase inhibitors (DBHI) FLA-63 and U10,157 on the reversal of reserpine akinesia by L-DOPA in mice was investigated both behaviourally and by measurement of the cerebral amines dopamine and noradrenaline. Pretreatment of reserpinised animals with intraperitoneal, but not oral, FLA-63 produced hypermotility in the first hour after L-DOPA administration, compared to animals receiving L-DOPA alone. This enhanced activity was associated with an increase in dopamine, but no significant change in the noradrenaline content of whole brain. Pretreatment with both oral and intraperitoneal FLA-63 caused dose-dependent suppression of locomotor activity in the second and third hours after L-DOPA. This suppression was associated with a significant decrease in brain noradrenaline in the presence of a significant elevation in brain dopamine. Pretreatment of animals with U10,157 produced similar but less marked behavioural responses. The results do not appear to be due to stressful effects of DBHI's, causing release of corticosteroids; neither corticosterone nor beta-methasone had any significant effect on L-DOPA-induced locomotor activity in reserpinised animals, although they did increase spontaneous motor activity in normal animals. The data presented support the concept that both noradrenaline and dopamine are responsible for the gross motor activity induced by L-DOPA in the reserpinised mouse.

Role of DA in the stimulant effect of DITA in mice; comparison with d-amphetamine

The effect of DL-alpha methyltyrosine (alpha-MT), 6-hydroxydopa (6-OH DOPA), haloperidol, phenoxybenzamine and propranolol on the stimulant activity of the anorexigenic agents (3',4'-dichloro-2-(2-imidazolin-2-yl-thio)-acetophenone HBr) (DITA) and d-amphetamine was studied in male mice. The pretreatment of mice with alpha-MT, (32, 64 mg/kg i.p.), significantly reduced the increase in motor activity induced by DITA or d-amphetamine. On the other hand, pretreatment of mice with 6-OH DOPA, (100, 150 mg/kg, i.v.), did not significantly after the stimulant effect of either DITA or d-amphetamine. In the case of haloperidol, it significantly reduced the increase of motor activity induced by DITA or d-amphetamine; propranolol and phenoxybenzamine were ineffective. Our results support the hypothesis that the stimulant effect of DITA and d-amphetamine depends mainly on the integrity of the central dopaminergic rather than the noradrenergic system.

Inhibition of circling behavior by neuroleptic drugs in mice with unilateral 6-hydroxydopamine lesions of the striatum

The development of circling behavior to apomorphine, amphetamine and L-Dopa in mice with unilateral 6-hydroxydopamine lesions of the dopaminergic nerve terminals in the striatum has been studied, and the effect of a range of neuroleptic and sedative drugs on this circling behaviour has been investigated. Circling induced by all the stimulant drugs was inhibited in a dose-dependent manner by haloperidol, pimozide, chlorpromazine, metoclopramide and clozapine (in descending rank order of potency), but not by phenoxybenzamine, diazepam, promethazine and pentobarbitone sodium. This relatively simple animal model appears useful for screening neuroleptic drugs which may block striatal dopamine receptors, thereby predicting their potency to cause unwanted extrapyramidal effects but not their antipsychotic efficacy.

Central catecholamine receptor blocking actions of BE-2254 ('heat'): comparison with chlorpromazine and haloperidol

BE-2254, 2-[beta-(4-hydroxyphenyl)-ethylaminomethyl]-tetralone, (ED50 = 3.4 mg/kg i.p.) was about equal to chlorpromazine (ED50 = 4.4) as an antagonist of central noradrenergic receptor stimulation produced by clonidine (enhancement of the flexor reflex in spinalized rats). Haloperidol and phentolamine had essentially no effect at 9 mg/kg i.p...