Comparative behavioural effects of typical and atypical antipsychotic drugs in rhesus monkey

Behavioural effects of typical and atypical antipsychotic agents were compared in unrestrained rhesus monkey (Macaca mulatta) living in social colonies. The behaviours were categorized as social, solitary and abnormal. They were studied with the help of video cameras fixed in the observation chamber. The behavioural effects were recorded on videotape and analyzed for significant changes. Chlorpromazine (2.5-10 mg/kg, i.m.), haloperidol (0.01-0.04 mg/kg, i.m.), risperidone (0.05-0.2 mg/kg, p.o.) and clozapine (5-20 mg/kg, p.o.) induced significant alterations in parameters of social and solitary behaviour. Chlorpromazine produced a marked decrease in locomotor activity whereas haloperidol showed marked extrapyramidal effects. Risperidone produced minimal extrapyramidal effects and sedation compared to haloperidol and chlorpromazine. Clozapine had intermediate extrapyramidal effects similar to those of chlorpromazine but it produced hypersalivation and dose-related sedation. Thus, risperidone had advantages over the other antipsychotics used in this study because it did not produce salivation, had minimal extrapyramidal effects and caused less sedation. These antipsychotic drugs produced many behavioural effects in the rhesus monkey that were similar to their clinically observed effects. A study of behavioural effects in the monkey can thus be a useful predictive tool in the preclinical development of new antipsychotics.     

Chlorpromazine as a discriminative stimulus in rats: Generalization to typical and atypical antipsychotics

The discriminative stimulus properties of the typical antipsychotic chlorpromazine were examined in a two‐lever drug discrimination procedure for food reward. Six of nine rats readily acquired the discrimination between 1.0 mg/kg chlorpromazine (i.p.) and vehicle in a mean of 29.7 training sessions. The chlorpromazine generalization curve was dose‐dependent and yielded an ED₅₀ of 0.305 mg/kg (95% confidence interval (CI) = 0.201–0.463 mg/kg). The chlorpromazine cue generalized to the atypical antipsychotics clozapine (ED₅₀ for the clozapine curve was 0.258 mg/kg [95% CI = 0.047–1.420 mg/kg]) and olanzapine (ED₅₀ for the olanzapine curve was 0.199 mg/kg [95% CI = 0.076–0.522 mg/kg]) and to the typical antipsychotic thioridazine (ED₅₀ for the thioridazine curve was 3.103 mg/kg [95% CI = 1.993–4.832 mg/kg]). Haloperidol (a typical antipsychotic) and raclopride (an atypical antipsychotic) did not substitute for chlorpromazine. It is clear from the present results that the discriminative stimulus properties of chlorpromazine share similarities both with the atypical antipsychotics clozapine and olanzapine and with the typical antipsychotic thioridazine. The extent to which the discriminative stimulus properties of antipsychotic drugs reflect or are predictive of their therapeutic effects in schizophrenic patients remains unclear. Drug Dev. Res. 48:38–44, 1999. © 1999 Wiley‐Liss, Inc.     

Combined treatment of quetiapine with haloperidol in animal models of antipsychotic effect and extrapyramidal side effects: comparison with risperidone and chlorpromazine

Rationale Quetiapine, an atypical neuroleptic, has beneficial antipsychotic effects in schizophrenic patients, but with a lower incidence of extrapyramidal symptoms (EPS) compared with typical antipsychotics. While typical antipsychotics are often switched to atypical agents when adverse effects become limiting, there is little preclinical information to support this strategy, both in terms of efficacy and side effects.Objectives The antipsychotic effects and EPS during concomitant administration of quetiapine with haloperidol, a typical antipsychotic agent, were evaluated in mice and compared with chlorpromazine and risperidone.Methods We first investigated the antipsychotic effects and EPS liability of quetiapine, risperidone, chlorpromazine, and haloperidol when administered alone to select optimal doses for subsequent combination studies. The second study was designed to evaluate the antipsychotic efficacy and EPS profile of concomitant administration of quetiapine, risperidone, or chlorpromazine with haloperidol. Antipsychotic effects were evaluated with the methamphetamine-induced hyperlocomotion test, and EPS liability was evaluated in a catalepsy-induction model.Results Quetiapine, risperidone, chlorpromazine, and haloperidol dose-dependently reduced methamphetamine-induced hyperlocomotion, with ED₅₀ values of 5.6, 0.020, 1.8, 0.035 mg/kg, respectively. In the catalepsy test, quetiapine only weakly induced catalepsy at the highest dose of 100 mg/kg, whereas risperidone, chlorpromazine, and haloperidol dose-dependently induced catalepsy with ED₅₀ values of 0.25, 4.6, and 0.10 mg/kg, respectively. While the combination of quetiapine (6 mg/kg) and haloperidol (0.04 mg/kg) significantly reduced methamphetamine-induced hyperlocomotion in comparison with haloperidol alone, quetiapine (10, 32 mg/kg) plus haloperidol did not potentiate the cataleptogenic activity of haloperidol. In contrast, risperidone (0.1, 0.32 mg/kg) or chlorpromazine (3.2 mg/kg) significantly augmented catalepsy induced by haloperidol. Catalepsy induced by co-administration of quetiapine (10 mg/kg) and haloperidol (0.1 mg/kg) was significantly potentiated by WAY100635, a 5-HT_1A antagonist, and catalepsy induced by co-administration of risperidone (0.1 mg/kg) and haloperidol (0.1 mg/kg) was significantly antagonized by 8-OH-DPAT, a 5-HT_1A agonist.Conclusion The present study demonstrated that the combined administration of quetiapine with haloperidol did not aggravate EPS, possibly because of its affinity for 5-HT_1A receptors. This finding may have the clinical implication that quetiapine could provide a successful regimen in switching from typical antipsychotic agents in the symptom management of schizophrenia, or even in adjunctive therapy with other antipsychotic agents.     

The effect of antipsychotic drugs and their clinically inactive analogs on dopamine metabolism.

Changes in dopamine metabolite levels in the rat striatum and tuberculum olfactorium, following the administration of three non-antipsychotic butyrophenones (AL-499, AHR-1900 and U-25,927) and a non-antipsychotic benzazepine (SCH-12,679), were compared to the effects seen following the antipsychotics haloperidol, chlorpromazine and clozapine. The non-antipsychotics, although clinically ineffective, were reported as active in a variety of animal screening tests. Haloperidol, chlorpromazine and clozapine produced a dose-dependent increase in 3,4-dihydroxyphenylacetic acid (DOPAC) levels in both regions. Of the non-antipsychotic drugs only AHR-1900 significantly elevated the level of DOPAC, however, the slope of its dose-response curve was atypically flat in comparison to the dose-response curves of drugs with known antipsychotic efficacy. Moreover, the maximal effect of AHR-1900 observed at a dose of 40 mg/kg was less than the ED50 effect of haloperidol which occurs at a 250 fold lower dose. It is concluded that the dose-dependent elevation of DOPAC in the striatum and tuberculum olfactorium of the rat is a good predictor of antipsychotic efficacy.     

Neuroleptic-induced hypersensitivity of striatal dopamine receptors in the rat as a model of tardive dyskinesias. Effects of clozapine,haloperidol, loxapine and chlorpromazine

The present study has compared the abilities of clozapine, haloperidol, chlorpromazine and loxapine to induce dopamine (DA)-receptor hypersensitivity in rats, as measured by the apomorphine response after withdrawal of the antipsychotic drugs. Haloperidol, chlorpromazine and loxapine, but not clozapine, potentiated the apomorphine response during 1–2 weeks after withdrawal. Clozapine, given prior to apomorphine, reduced the responses of the haloperidol and loxapine groups to the control level. The effects of haloperidol and clozapine were quantified in rats with unilateral striatal lesions.Biochemical investigations showed that tolerance developed to the increase in striatal homovanillic acid (HVA) after chronic treatment with haloperidol, chlorpromazine and loxapine, whereas clozapine (20 mg/kg p.o.) failed to affect the HVA content, and no tolerance developed to the increase seen at 80 mg/kg. Cross-tolerance to the rise in HVA was seen with haloperidol, chlorpromazine and loxapine, but chronic pretreatment with clozapine failed to affect the rise in HVA induced by a single dose of the former compounds.On the basis of these results, it is predicted that tardive dyskinesias are unlikely to develop after this drug, and that clozapine may attenuate or abolish neuroleptic-induced tardive dyskinesias.Part of this work was presented at the IXth Congress of the C.I.N.P. in Paris, July 1974.     

Effects of amisulpride, risperidone and chlorpromazine on auditory and visual latent inhibition, prepulse inhibition, executive function and eye movements in healthy volunteers

In view of the evidence that cognitive deficits in schizophrenia are critically important for long-term outcome, it is essential to establish the effects that the various antipsychotic compounds have on cognition, particularly second-generation drugs. This parallel group, placebo-controlled study aimed to compare the effects in healthy volunteers (n = 128) of acute doses of the atypical antipsychotics amisulpride (300 mg) and risperidone (3 mg) to those of chlorpromazine (100 mg) on tests thought relevant to the schizophrenic process: auditory and visual latent inhibition, prepulse inhibition of the acoustic startle response, executive function and eye movements. The drugs tested were not found to affect auditory latent inhibition, prepulse inhibition or executive functioning as measured by the Cambridge Neuropsychological Test Battery and the FAS test of verbal fluency. However, risperidone disrupted and amisulpride showed a trend to disrupt visual latent inhibition. Although amisulpride did not affect eye movements, both risperidone and chlorpromazine decreased peak saccadic velocity and increased antisaccade error rates, which, in the risperidone group, correlated with drug-induced akathisia. It was concluded that single doses of these drugs appear to have little effect on cognition, but may affect eye movement parameters in accordance with the amount of sedation and akathisia they produce. The effect risperidone had on latent inhibition is likely to relate to its serotonergic properties. Furthermore, as the trend for disrupted visual latent inhibition following amisulpride was similar in nature to that which would be expected with amphetamine, it was concluded that its behaviour in this model is consistent with its preferential presynaptic dopamine antagonistic activity in low dose and its efficacy in the negative symptoms of schizophrenia.     

Effects of antipsychotic drugs on latent inhibition: sensitivity and specificity of an animal behavioral model of clinical drug action

Latent inhibition (LI) of a conditioned emotional response (CER) has been proposed as a quantitative measure of selective attention. We have assessed the parallels of the pharmacology of LI in rats with the clinical pharmacology of schizophrenia. Drug and vehicle treated rats were divided into groups and preexposed 20 times to cage illumination as a CS, or not preexposed. All groups were conditioned with 2 CS-footshock pairings. The following day CER, as measured by interruption of drinking in response to CS presentation, was recorded. LI was observed as a decreased CER in preexposed relative to non-preexposed animals. LI was enhanced by haloperidol 0.3 mg/kg after 7 or 14 daily treatments, but not after a single acute dose. Haloperidol doses of 0.3 and 0.03 mg/kg enhanced LI, while doses of 0.003 and 3.0 mg/kg had no effect. Haloperidol enhancement of LI was unaffected by the coadministration of the anticholinergic agent trihexyphenidyl. Enhancement of LI is exhibited by the antipsychotic drugs fluphenazine, chlorpromazine, thiothixene, thioridazine, mesoridazine, and metoclopramide but not clozapine. The non-antipsychotic drugs pentobarbital, imipramine, chlordiazepoxide, trihexyphenidyl, and promethazine failed to enhance LI. LI exhibits striking parallels to the clinical pharmacology of schizophrenia.Preliminary data were presented in part at the Society for Neuroscience Annual Meeting, Phoenix, AZ, 1989     

Prepulse inhibition as a screening test for potential antipsychotics

Startle response amplitude is greatly reduced by a low intensity pulse presented 100 msec prior to the startle stimulus. The magnitude of this prepulse inhibition (PPI) is reduced in schizophrenic patients. In rats, apomorphine disrupts PPI; haloperidol antagonizes apomorphine's effects. We tested the antipsychotic drugs haloperidol, chlorpromazine, clozapine, and risperidone, and the non-antipsychotic psychopharmacological agents diazepam, buspirone, and imipramine for their ability to antagonize apomorphine's effects on PPI of the acoustic startle reflex. Haloperidol, chlorpromazine, and risperidone antagonized apomorphine's blockade of PPI. Clozapine antagonized apomorphine's effect only at a dose that decreased startle amplitude by 82%. Imipramine and diazepam did not antagonize apomorphine's effect at behaviorally relevant doses. Buspirone weakly antagonized apomorphine blockade of PPI, but, like apomorphine, disrupted PPI when given alone. These results suggest that this PPI test may provide a useful screening procedure for compounds wtih antipsychotic activity. However, the lack of a robust clozapine effect needs to be investigated.     

Pharmacological treatment of psychotic agitation

The presentation of agitated psychotic patients to psychiatric emergency services is a common occurrence. The traditionally accepted treatment for such patients involves the use of a typical antipsychotic, generally haloperidol. More recently benzodiazepines, such as lorazepam, have been used in combination with antipsychotics due to their sedative properties and relatively benign adverse effect profiles. Standard clinical protocol at many institutions involves the intramuscular administration of 5 to 10mg of haloperidol and 1 to 2mg of lorazepam. Atypical antipsychotics have gained acceptance as first-line treatments for psychotic disorders. These drugs are seen as an improvement over traditional antipsychotics because of their increased efficacy and reduced extrapyramidal effects. The utility of atypical antipsychotics in the emergency setting has been relatively unexplored because slow titration schedules or dose-limiting adverse effects for some members of the class have made this form of treatment impractical. However, the recent availability of oral liquid and rapidly dissolving tablet preparations of some atypical agents has provided useful alternatives in some cases. Nevertheless, for many patients a parenteral drug is the only desirable or feasible treatment option. Intramuscular preparations of the atypical antipsychotics olanzapine and ziprasidone have been developed, and are close to launch in the US. The availability of a rapid-acting intramuscular preparation of an atypical antipsychotic could represent a significant advancement in the treatment of agitation associated with psychosis.     

The effects of atypical antipsychotics and phencyclidine (PCP) on rotorod performance.

A series of six experiments were conducted to determine the effects of haloperidol, clozapine, olanzapine, and phencyclidine (PCP) on rotorod performance. Rodents were trained to walk on a rotorod to avoid a mild shock to a criterion of 20 rpm for 3 min. None of the vehicles of any of these drugs disrupted rotorod performance. Haloperidol disrupted rotorod performance at doses of 0.03, 0.1, and 0.3 mg/kg, and olanzapine disrupted rotorod performance at doses of 3.0 and 10.0 mg/kg. Clozapine produced a much milder disruption across all three doses (3.0, 10.0, and 30.0 mg/kg). PCP produced a consistent and severe disruption of rotorod performance at doses of 4.0 and 6.0 mg/kg, but not at a dose of 2.0 mg/kg. Twenty-four hours postinjection there were no residual PCP effects on rotorod performance. Coadministration of either haloperidol or olanzapine with PCP did not reverse PCP-induced disruption in rotorod performance, while clozapine produced a partial reversal at only one dose. These findings indicate that olanzapine functions similarly to classic antipsychotics with respect to their effects on locomotion and balance.     

Seroquel, clozapine and chlorpromazine restore sensorimotor gating in ketamine-treated rats

Sensorimotor gating of the startle reflex – measured by prepulse inhibition (PPI) – is impaired in schizophrenia patients and in rats treated with either dopamine (DA) agonists or with N-methyl-D-aspartate (NMDA) antagonists. While both typical and atypical antipsychotics restore PPI in DA agonist-treated rats, studies thus far have demonstrated that only atypical antipsychotics restore PPI in rats treated with NMDA antagonists. This model for predicting atypical antipsychotic properties has been studied extensively in rats, and there is interest in moving these studies into humans, where the NMDA antagonist ketamine is also reported to significantly reduce PPI. In anticipation of such studies, and to facilitate the use of this model in humans, we examined the effects of high and low potency typical antipsychotics (haloperidol and chlorpromazine), the atypical antipsychotic clozapine, and the putative atypical antipsychotic, Seroquel, on ketamine-disrupted PPI in rats, across a range of ketamine that produced submaximal, as well as maximal disruptions of PPI. Ketamine dose-dependently reduced PPI, and this effect was significantly opposed by Seroquel, clozapine and chlorpromazine, but not haloperidol. The effects of chlorpromazine on ketamine-disrupted PPI demonstrate that the ability of antipsychotics to restore PPI in NMDA antagonist-treated rats is not specific to clinically atypical antipsychotics. Receptor properties shared by Seroquel, clozapine and chlorpromazine, but not haloperidol, may implicate critical substrates in the NMDA antagonist-induced disruption of PPI. Received: 31 December 1997/Final version: 11 March 1998     

Antipsychotic medication: effects on regulation of glucose and lipids

Since the introduction of chlorpromazine in the 1950s, antipsychotics have been used for the treatment of schizophrenia. The phenothiazines were followed by the butyrophenones, particularly haloperidol. With all the movement disorder side effects of these medications (extrapyramidal syndrome, akathisia, tardive dyskinesia), the pharmaceutical industry has gradually released atypical antipsychotics. This class includes clozapine (released in the USA in 1990), risperidone (1994), olanzapine (1996), quetiapine (1998) and ziprasidone (2001). However, the rate of diabetes mellitus in patients with schizophrenia appeared to increase with the availability of this class of medications. In reviewing rate and degree of changes in weight, glucose control and lipid levels induced by typical and atypical antipsychotics, it was found that in contrast to case reports, there is a dearth of retrospective, open and controlled studies. However, in studies as early as 1964, significant weight increases were found to be associated with use of chlorpromazine. While the phenothiazines may have some effect on patients with chemical diabetes, there is little evidence of the typical antipsychotics producing diabetes mellitus de novo, or worsening diabetes that is already been discovered. Ziprasidone appears to be the antipsychotic with the most beneficial combination of effects: no weight gain, no change in glucose utilisation and reductions in cholesterol and serum triglycerides (TGs).     

Antagonism of amphetamine-induced disruption of latent inhibition in rats by haloperidol and ondansetron: Implications for a possible antipsychotic action of ondansetron

Latent inhibition (LI) is a behavioural phenomenon whereby preexposure to a stimulus without reinforcement interferes with the formation of subsequent associations to that stimulus. Using preexposure to a tone stimulus which subsequently serves as a conditioned stimulus for suppression of licking, we have confirmed that LI is disrupted by a low dose of amphetamine. Haloperidol was able to prevent this effect of amphetamine. Ondansetron, a selective and potent 5HT₃ receptor antagonist, was also shown to be effective at blocking the amphetamine-induced disruption of LI at a dose of 0.01 mg/kg, but not at 0.1 mg/kg. In addition, it was demonstrated that ondansetron could enhance LI; using only ten preexposures, no LI was obtained in the saline group, but was apparent in animals given ondansetron, an effect which has been previously shown with haloperidol. Haloperidol, at the higher dose used, reduced suppression of licking, however, ondansetron at the effective dose had no such effect. It is concluded that ondansetron is able to attenuate increases in dopamine activity, produced pharmacologically with amphetamine without affecting baseline dopamine activity. The implications of these findings for a possible antipsychotic action of ondansetron are discussed.     

U-74500A (lazaroid), a 21-aminosteroid attenuates neuroleptic-induced orofacial dyskinesia

21-Aminosteroid, or lazaroid, is one of a novel class of antioxidant drugs designed to inhibit iron-dependent lipid peroxidation in biological lipid environments. They have shown promising results in several animal models of traumatic, ischemic and hemorrhagic injury of the central nervous system. Neuroleptic-induced orofacial dyskinesia is an animal model of tardive dyskinesia whose pathophysiology has been related to oxidative stress in the basal ganglia. In this study, we have examined the protective role of U-74500A [pregna-1,4,9(11)-triene-3,20-dione, 21-(4-(5,6-bis(diethylamino)-2-pyridinyl)-1-piperazinyl)-16-ethyl-HCl (16-alpha)], a 21-aminosteroid having antioxidant property in attenuating the behavioral and biochemical effects of chronic haloperidol and chlorpromazine administration. Haloperidol (1 mg/kg/day i.p.) and chlorpromazine (5 mg/kg/day i.p.) administered for 21 days caused a significant increase in vacuous chewing movements (VCMs), tongue protrusion (TP) and the number of facial twitchings (FT) observed on day 22. U-74500A (1, 2 and 5 mg/kg i.p.), administered every day, along with haloperidol (1 mg/kg/day i.p.) and chlorpromazine (5 mg/kg/day), attenuated the increase of VCMs and related behaviors on day 22. Haloperidol and chlorpromazine significantly increased lipid peroxidation in various brain areas such as the cortex, striatum and subcortical parts characterized by an increase in MDA levels. The coadministration of U-74500A limited the effect of haloperidol and chlorpromazine on MDA levels in the cortex and striatum but not in the subcortical parts. U-74500A, an aminosteroid, may have therapeutic use in typical neuroleptic-induced tardive dyskinesia-like effects.     

Haloperidol decanoate. A preliminary review of its pharmacodynamic and pharmacokinetic properties and therapeutic use in psychosis

Haloperidol decanoate is a depot preparation of haloperidol, a commonly used butyrophenone derivative with antipsychotic activity. Haloperidol decanoate has no intrinsic activity: its pharmacodynamic actions are those of haloperidol--primarily that of central antidopamine activity. The monthly administered depot formulation has several clinical and practical advantages over oral haloperidol: better compliance and more predictable absorption; more controlled plasma concentrations; fewer extrapyramidal side effects; less frequent reminders of condition; and reduced medical workload. In open and controlled studies, haloperidol decanoate has produced adequate maintenance or improvement of the condition of patients with psychoses (mainly schizophrenia) when an abrupt change from orally administered haloperidol or other antipsychotic drugs has been instituted. Limited comparative studies indicate that the depot and oral forms of haloperidol are equally effective, and that haloperidol decanoate is at least as effective as depot forms of fluphenazine, pipothiazine, flupenthixol and perphenazine in controlling the symptoms of psychosis. Extrapyramidal side effects and the need for concomitant anti-Parkinsonian drugs may be a problem, but may be less frequent than with oral haloperidol or other depot antipsychotics. Thus, haloperidol decanoate offers a useful alternative in the treatment of psychoses to orally administered haloperidol or to other depot antipsychotic drugs.     

Discriminative stimulus properties in rats of the novel antipsychotic quetiapine

Rats discriminated the novel antipsychotic quetiapine (Seroquel). Full generalization was seen with the novel ("atypical") antipsychotics, clozapine, olanzapine, and risperidone. Generalization was not seen with the older "typical" antipsychotics, haloperidol, chlorpromazine, and loxapine, or with the novel atypical antipsychotic, amisulpride. The pattern of generalization resembled that seen in rats trained to discriminate a low dose (1.25 mg/kg) of clozapine, which dissociates most novel antipsychotics from typical antipsychotics. However, the failure of the novel antipsychotic amisulpride to generalize demonstrates that this bioassay does not detect all novel antipsychotics. These data suggest that the discrimination of antipsychotics such as quetiapine may be of value in the development of novel antipsychotics, although the relationship between the discriminative properties of such drugs and their clinical actions is unclear.     

Parametric and pharmacological modulations of latent inhibition in mouse inbred strains

Latent inhibition (LI) is a cross species selective attention phenomenon, which is disrupted by amphetamine and enhanced by antipsychotic drugs (APDs). Accumulating data of LI in gene-modified mice as well as in mouse inbred strains suggest genetic component of LI. Here we study modulation of LI in mouse inbred strains with spontaneously disrupted LI by parametric manipulations (number of pre-exposures and conditioning trials) and pharmacological treatments with antipsychotics and NMDA modulator, D-serine. C3H/He and CBA/J inbred mice showed disrupted LI under conditions with 40 pre-exposures (PE) and 2 trials of the conditioned stimulus-unconditioned stimulus (CS-US) due to either loss of the pre-exposure effect or a ceiling effect of poor learning, respectively. The increased number of pre-exposures and/or number of conditioning trials corrected expression of LI in these inbred mice. The disrupted LI was also reversed by haloperidol in both inbred strains at 1.2 mg/kg but not at 0.4 mg/kg, as well as by clozapine (at 3 mg/kg in C3H/He and at 9 mg/kg in CBA/J mice). D-serine potentiated LI in C3H/He mice at 600 mg/kg, but not in the CBA/J at both studied doses (600 and 1800 mg/kg). Desipramine (10 mg/kg) had no effect on LI in both inbred mouse strains. Our findings demonstrated some resemblance between the effects of parametric and pharmacological manipulations on LI, suggesting that APDs may affect the capacity of the brain processes environmental stimuli in LI. Taken together, LI may offer a translational strategy that allows prediction of drug efficacy for cognitive impairments in schizophrenia.     

Mood alteration following oral and intravenous haloperidol and relationship to drug concentration in normal subjects

Haloperidol was administered to 12 subjects intravenously (0.125 mg/kg) and to nine subjects orally (0.5 mg/kg). These doses produced sedation in most subjects. A minimal decrease in orthostatic blood pressure was observed. Administration of the Profile of Mood States to these subjects revealed effects on factor 4, vigor-activity, and factor 6, confusion-bewilderment, but many subjects could not complete testing due to excessive sedation. Haloperidol concentrations were obtained during testing and correlated moderately with scores of these subscales. Correlation was also noted between haloperidol concentration and chlorpromazine effect as measured by the Addiction Research Center Inventory. Extrapyramidal reactions, mainly acute dystonic reactions and akathisia, were common. Dystonia occurred in four subjects after intravenous, and three subjects, after oral administration. Akathisia occurred in eight subjects after intravenous, and three subjects after oral administration. Extrapyramidal reactions tended to occur relatively early or relatively late, at times when drug concentrations were far less than peak values.     

Effect of neuroleptic drugs on central catecholamine turnover assessed using tyrosine- and dopamine- -hydroxylase inhibitors

The effects of some neuroleptic drugs on the noradrenaline turnover in the rat brain and spinal cord were studied biochemically and histochemically with the help of a new inhibitor of the enzyme dopamine-β-hydroxylase, bis(4-methyl-1-homopiperazinyl-thiocarbonyl) disulphide; (FLA-63). Haloperidol (1 mg/kg, i.p.), chlorpromazine (5–10 mg/kg, i.p.), pimozide (1–5 mg/kg, i.p.) and fluspirilene (1–5 mg/kg, i.p.) produced an acceleration of the noradrenaline disappearance induced by FLA-63. Clothiapine (1 mg/kg, i.p.) was ineffective. The lowering of brain dopamine after treatment with α-methyltyrosine methylester (H44/68) was markedly enhanced by haloperidol (5 mg/kg, i.p.) and slightly so by chlorpromazine (5 mg/kg, i.p.), whereas both drugs simultaneously caused a significant increase in the noradrenaline loss. Thus, the same results were obtained with dopamine-β-hydroxylase and tyrosine-hydroxylase inhibition on the influence of neuroleptic drugs on the noradrenaline turnover. The acceleration seen after haloperidol and chlorpromazine, but not after pimozide and fluspirilene, could be due to a compensatory activation of noradrenaline neurons produced by a noradrenaline receptor blockade.