Neuroleptic classification: implications for tardive dyskinesia

Brain neuromediator systems in the immune response control: pharmacological analysis of pre- and postsynaptic mechanisms

The involvement of the dopaminergic (DAergic), GABAergic and serotoninergic (5-HTergic) synaptic mechanisms in neuroimmunomodulation are considered. It is shown that the central DA- and GABAergic systems exert a stimulatory influence on the immune reactivity. Activation of postsynaptic DA receptors with apomorphine and (+)(3-hydroxyphenyl)-N-n-propylpiperidine [(+)-3-PPP] at high doses, D2 receptor activation with quinpirole, as well as DA reuptake blockade with amantadine and bupropion, resulted in an increase in the immune response. The intensity of the immune response was also increased during activation of the GABAergic system with the GABA agonist muscimol or the benzodiazepine agonists diazepam and tazepam. On the other hand, decreases in the activity of either system by different drugs inhibiting DAergic and GABAergic neurotransmission (antagonists of DA postsynaptic receptors haloperidol at 1.0 mg/kg and (-)-3-PPP at 6.8 mg/kg, agonists of DA autoreceptors apomorphine at 0.02 mg/kg, (-)- and (+)-3-PPP at 1.7 and 3.4 mg/kg, antagonist of GABA receptors bicuculline, blocker of chloride channels picrotoxin, blockers of benzodiazepine receptors Ro 15-1788 and Ro 15-3505) produce suppression of the immune response. The 5-HTergic system is involved in the inhibitory mechanism of neuroimmunomodulation. 5-HT reuptake blockade with 4-(5,6-dimethyl-R-benzophuranil)-piperidine (CGP-6085A) and sertraline led to immunosuppression.

Chronic treatment with chlorpromazine, thioridazine or haloperidol increases striatal enkephalins and their release from rat brain

The aim of this paper is to study the effect of 1, 2 or 3 months' administration of chlorpromazine (CPZ), thioridazine (TDZ) (2 or 6 mg/kg) or haloperidol (HAL) (0.25 or 1 mg/kg) IP on the level of leu- and met-enkephalin (ENK) in striatum. A dose- and time-dependent increase of striatal ENK level was observed after chronic administration of the neuroleptics (NL), but 8 days after withdrawal of chronically administered NL striatal ENK was decreased. Apomorphine pretreatment significantly attenuated the elevation in ENK produced by chronic injections of NL. In perfusion fluid obtained from the lateral ventricle of animals treated 1 month with HAL a dose-dependent increase of ENK levels was observed, which was augmented by potassium ions. It is concluded that: 1) Chronic administration of neuroleptic drugs that block dopamine receptors increases the level and the release of striatal enkephalins; 2) The results support the hypothesis that activation of dopaminergic neurons tonically inhibits the synthesis of enkephalins in the striatum.

Behavioral interactions between muscimol and compounds selective for the D1 and D2 dopamine receptor subtypes

The present study investigated the effects of the GABA agonist muscimol on the behaviors produced by acute injections of selective D1 and D2 agonists and antagonists. Muscimol potentiated the intensity of stereotyped behaviors shown by rats treated with the D2 agonist quinpirole; in contrast, it suppressed the repetitive bouts of grooming shown by rats treated with SKF38393. Muscimol potentiated the catalepsy produced by either a D1 (SCH23390) or D2 (metoclopramide) antagonist, suggesting that the cataleptic behaviors produced by these compounds may contain a common GABAergic mechanism.

Effects of the selective dopamine D-2 receptor agonist, quinpirole on sleep and wakefulness in the rat

The effects of the dopamine D-2 receptor agonist, quinpirole, were compared with those produced by dopamine D-2 antagonist, YM-09151-2, in rats implanted with electrodes for chronic sleep recordings. Quinpirole (0.015-1.0 mg/kg) induced biphasic effects such that low doses decreased wakefulness and increased sleep, while higher doses induced the opposite effects. At 0.015 mg/kg, YM-09151-2 slightly augmented wakefulness, while at 1.0-2.0 mg/kg it significantly increased light sleep but depressed REM sleep. Pretreatment with YM-09151-2 in a dose which preferentially acts at presynaptic sites reversed the suppressant effects of a low dose of quinpirole on wakefulness and slow wave sleep. In contrast, the administration of YM-09151-2 in a dose which blocks postsynaptic D-2 receptors prevented the effect of a high dose of quinpirole on wakefulness and slow wave sleep; the depression of REM sleep was not affected. The opposite effects observed on the waking EEG after activation of either dopamine autoreceptors or postsynaptic D-2 receptors with adequate doses of quinpirole tend to indicate an active role for DA in the control of the waking state.

Profile of in vitro binding affinities of neuroleptics at different rat brain receptors: cluster analysis comparison with pharmacological and clinical profiles

A series of 21 neuroleptics with different chemical structures (phenothiazines, thioxanthenes, dibenzodiazepines, butyrophenones, benzamides, etc.) was examined for their in vitro interactions with 12 neurotransmitter binding sites in the rat brain (alpha- and beta-noradrenergic, dopaminergic, muscarinic, serotoninergic, histaminic, and opioid receptors, calcium channels, and serotonin uptake binding sites). The biochemical profile obtained from the binding data was compared with reported pharmacological and clinical profiles for this class of compounds by cluster analysis. Cluster analysis on binding data classified the compounds in three main subgroups: benzamides, compounds with an affinity mainly for DA2 and 5-HT2 receptors and inactive at muscarinic receptors, and compounds with a high affinity for alpha 1-adrenergic receptors and muscarinic receptors. The main subgroups resulting from cluster analysis of previously published pharmacological and clinical data for neuroleptics contain compounds common to the present study, with some correlations. The results extend previous observations that a complete binding profile corresponds to the pharmacological and clinical profile of this class of compounds.

Haloperidol- and SCH23390-induced dopaminergic supersensitivities are not additive in the rat

The effect of chronic D-1 and/or D-2 dopamine receptor blockade on apomorphine-induced behaviors was studied in rats treated for 21 days with the selective D-1 antagonist SCH23390, the predominantly D-2 antagonist haloperidol, and the combination of the two drugs at the same daily doses (0.1 and 1 mg/kg respectively). Apomorphine (0.3 mg/kg) 4 days following the last injection of the drugs increased (49-70%) stereotypic behavior in all animals as compared to saline-treated controls. Although the SCH23390-induced increase was lower than haloperidol-induced supersensitivity, stereotypies after combined administration of both drugs did not differ significantly from either, suggesting that the effects of the two drugs are not additive. Underlying receptor changes and modified D-1/D-2 receptor interactions may account for the participation of both receptor subtypes to the development of neuroleptic-induced dopaminergic supersensitivity.

Can the supersensitivity of rodents to dopamine be regarded as a model of tardive dyskinesia?

1. The paper presents arguments derived from both, clinical work and animal experiments, for or against the traditional hypothesis suggesting that tardive dyskinesia (TD) is caused by supersensitivity to dopamine. The main aim of this study was to answer the question posed in the title - whether the supersensitivity to dopamine evoked in rodents by neuroleptics can be regarded as an adequate pharmacological model of TD. 2. The data presented here prove that chronic administration of neuroleptics to schizophrenic patients cannot be the only factor inducing TD; furthermore, symptoms similar or identical to those of TD are also observed in the course of other disorders, not connected with neuroleptics, e.g. aging or schizophrenia itself. 3. Clinical data offer no clear evidence for the existence of a direct cause-effect relationship between super-sensitivity to dopamine and occurrence of TD. 4. The role of brain degeneration, caused by different factors but in particular by the process of aging, in the pathogenesis of dyskinetic disorders, including TD, has been stressed. 5. Pharmacological and biochemical data show that chronic administration of classic neuroleptics to animals induces an increase in the density of dopamine D-2 receptors (Bmax). It seems that this receptor-mediated supersensitivity may concern both the postsynaptic and the presynaptic D-2 dopamine receptors. On the other hand, it is not clear enough whether a dopamine D-1 receptor-mediated supersensitivity might also be a causal factor of TD. 6. The analysis in animals, of biochemical and pharmacological effects of neuroleptics which do not induce TD showed that in some situations these drugs may also evoke the receptor-mediated supersensitivity concerning dopamine D-2 receptors. 7. The method of a prolonged (approx. 1 year) oral administration of neuroleptics seems to differentiate those which induce TD from those which do not, at least regarding the induction of an increase of Bmax for butyrophenone neuroleptics and an increase of apomorphine-induced stereotypy, however, some exceptions are noted. 8. The above analysis of clinical and experimental data suggests that the supersensitivity to dopamine in rats treated chronically with neuroleptics cannot be accepted as a model which reflects the etiopathogenesis of TD. Neither a positive nor a negative result obtained in this test is reliable enough, and either depends on the tested parameters (apomorphine stereotypy and [3H]spiperon binding seem to be the most reliable), route of neuroleptic administration, duration of treatment and, probably, a number of other, still unknown factors.(ABSTRACT TRUNCATED AT 400 WORDS)

Attenuation of D-1 antagonist-induced D-1 receptor upregulation by concomitant D-2 receptor blockade

The effect of chronic selective D-1 and/or D-2 dopamine receptor blockade on regional D-1 receptor binding was studied in rat brain following chronic treatment with the specific D-1 antagonist SCH 23390 and/or the predominantly D-2 antagonist haloperidol. D-1 receptor density and affinity were evaluated by quantitative autoradiography using 125I-SCH 23982. Chronic SCH 23390 treatment increased D-1 receptor density by 30 to 40% in the striatum, accumbens and tuberculum olfactorium; receptor affinity remained unchanged. Haloperidol had no effect on D-1 receptor Bmax or Kd values, although, when administered with SCH 23390, reduced the D-1 receptor upregulation induced by the D-1 antagonist in striatum and tuberculum olfactorium, but not in nucleus accumbens. These results may be attributable to D-1/D-2 dopamine receptor interactions occurring in the striatum and tuberculum olfactorium and may have implications for the prevention and treatment of drug-induced extrapyramidal disorders.

D1 dopamine receptor--the search for a function: a critical evaluation of the D1/D2 dopamine receptor classification and its functional implications

The present review focuses on the hypothesized D1/D2 dopamine (DA) receptor classification, originally based on the form of receptor coupling to adenylate cyclase activity. The pharmacological effects of compounds exhibiting putative selective agonist or antagonist profiles at those DA receptors positively coupled to adenylate cyclase activity (D1 DA receptors) are extensively reviewed. Comparisons are made with the effects of putative selective D2 DA receptor agonists and antagonists, and on the basis of this work, the DA receptor classification is critically evaluated. A variety of biochemical, behavioral, and electrophysiological evidence is presented which supports the view that D1 and D2 DA receptors can interact in both an opposing and synergistic fashion. Particular attention is focused on the possibility that D1 receptor stimulation is required to enable the expression of certain D2 receptor-mediated effects, and the functional consequences of this form of interaction are considered. A hypothetical model is presented which considers how both the opposing and enabling forms of interaction between D1 and D2 DA receptors can control behavioral expression. Finally, the clinical relevance of this work is discussed and the potential use of selective D1 receptor agonists and antagonists in the treatment of psychotic states and Parkinson's disease is considered.

Effect of prolonged treatment with neuroleptics on dopamine D-1 and D-2 receptor density in corpus striatum of mice

The effects of long-term treatment with neuroleptics on D-1 and D-2 receptor parameters in corpus striatum were studied in mice. Mice were treated daily for 12 days with the selective D-1 antagonist, the benzazepine SCH 23390, the mixed D-1/D-2 antagonist zuclopenthixol or the selective D-2 antagonist haloperidol. Three days after withdrawal Bmax and KD for 3H-SCH 23390 binding to D-1 receptors and 3H-spiperone binding to D-2 receptors were determined. The study showed that the density of D-2 receptors increased after haloperidol whereas no changes were seen after SCH 23390 or zuclopenthixol. No changes in D-1 receptor density were seen after either treatment. The results are in full agreement with published behavioural results where haloperidol induces tolerance whereas SCH 23390 or zuclopenthixol do not. Some changes in KD values were seen. The cause and meaning of these changes await further investigation.

Chronic neuroleptic treatment increases D-2 but not D-1 receptors in rat striatum

In vitro binding of [3H]cis(Z)-flupentixol (FPT) to rat striatal membranes was evaluated as an assay for D-1 receptors. It was found that under the appropriate assay conditions [3H]FPT bound to a single saturable site which was most abundant in striatum and bound dopaminergic agonists in the potency order that these drugs demonstrate for adenylate cyclase. These data support previous work suggesting that [3H]FPT labels the D-1 receptor. Next, rats received haloperidol or fluphenazine for 54 days and striatal dopamine receptors were assayed 72 h later. The drug treatments increased the density of D-2 receptors as measured by [3H]spiperone binding by 40% and 25% respectively. However, no change was observed in D-1 receptor density. We conclude that effects of chronic neuroleptic treatment that depend upon increased dopamine receptor density are mediated via the D-2 receptor subtype.

Receptor-binding profiles of neuroleptics

Dopamine-receptor blockade seems to be a prominent effect of neuroleptics. Blockade of other receptors might, however, contribute to the therapeutic effect. A series of neuroleptics have been tested for affinity to DA D-1 and D-2 receptors, serotonin receptors (S2), alpha-adrenoceptors (alpha 1), histamine receptors (H1), and muscarinic cholinergic receptors. According to the affinity to DA D-1 and D-2 receptors, neuroleptics can be divided into different groups. Thioxanthenes have affinity for both D-1 and D-2 receptors; phenothiazines have affinity for D-2 receptors and considerably lower affinity for D-1 receptors; and butyrophenones, diphenylbutylpiperidines, and benzamides have affinity only for D-2 receptors. Concerning affinity to other receptors the only consistent finding is affinity for S2 receptors. The clinical significance of these findings is speculative. In several behavioral tests the D-1/D-2 classification is also observed, and it is suggested that D-1-receptor activation is responsible for dyskinesia, and that thioxanthenes - due to their D-1 receptor blocking effect-induce less dyskinesia than other neuroleptics.

Functional evidence for selective dopamine D-1 receptor blockade by SCH 23390

The selectivity of a new specific dopamine D-1 receptor antagonist SCH 23390, (R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin -7-ol hemimaleate, was investigated in functional neurochemical models. Inhibition of the activity of dopamine-stimulated adenylate cyclase in striatal homogenates of the rat represented an effect at dopamine D-1 receptors, whereas reversal of the decrease in electrically-induced release of tritium from striatal slices of the rabbit, preloaded with [3H]dopamine or [3H]choline by apomorphine, represented D-2 pre- and postsynaptic effects, respectively. The selectivity of the methods was checked by using known D-1 and D-2 agonists, SKF 38393 (2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine hydrochloride) and LY 141865 or LY 171555 (racemate and (-)-enantiomer, respectively; trans-4,4a,5,6,7,8,8a,9-octahydro-5-propyl-2H-pyrazolo [3,4-g]quinoline dihydrochloride), respectively. It was found that SCH 23390 competitively inhibited the activity of dopamine-stimulated adenylate cyclase with a Ki-value of 0.004 microM. In contrast to haloperidol, a specific dopamine D-2 antagonist, which inhibited the decline in release of both ligands from preloaded slices induced by apomorphine, SCH 23390 was without effect on this release from slices loaded with [3H]dopamine but had effect on release from slices loaded with [3H]choline, in concentrations 350 times greater than those of haloperidol (IC50 = 0.63 microM). The results confirm the dopamine D-1-selective blockade by SCH 23390, previously shown using dopamine-receptor binding techniques.

The citalopram/5-HTP-induced head shake syndrome is correlated to 5-HT2 receptor affinity and also influenced by other transmitters

Combination of the 5-HT-uptake inhibitor, citalopram, with 1-5-HTP induced a characteristic head shake syndrome in rats. This was blocked by a range of 5-HT antagonists, including the selective 5-HT2 antagonists, ketanserin and pirenperone and was also blocked by the alpha 1-adrenoceptor antagonists, prazosin and WB 4101, and the alpha 2-adrenoceptor agonist, clonidine. 1-5-HTP-antagonistic effect was also recorded for 26 neuroleptic drugs. Their inhibitory potencies showed close correlation to 5-HT2-receptor affinity in vitro and, slightly weaker, to alpha 1-adrenoceptor affinity. In contrast, no correlation to dopamine D-2 receptor affinity was found, indicating that the cataleptogenic and motility-inhibitory properties of neuroleptics did not unspecifically influence 1-5-HTP-induced head shakes. These were not influenced by a histaminic antagonist, muscarinic antagonist or alpha 2-adrenoceptor antagonist, but were inhibited by beta-adrenoceptor blockers, GABA agonists, a benzodiazepine and morphine. The results indicate that 1-5-HTP-induced head shakes are most sensitive to 5-HT2 antagonists, but that the syndrome is influenced by other neuronal systems. Since 5-HT2 affinity and alpha 1-adrenoceptor affinity of many compounds is found concomitantly, caution is needed to evaluate the relative importance of these properties for 1-5-HTP antagonism.

Pharmacological effects of a specific dopamine D-1 antagonist SCH 23390 in comparison with neuroleptics

Neuroleptics such as thioxanthenes (cis(Z)-flupentixol and cis(Z)-clopenthixol) and phenothiazines (fluphenazine and perphenazine), which block both dopamine (DA) D-1 and D-2 receptors and the butyrophenones (haloperidol and spiroperidol), which block D-2 receptors only, are equipotent both behaviorally and clinically. A new compound SCH 23390 which selectively blocks DA D-1 receptors, resembles many neuroleptics in its pharmacological profile: antistereotypic effects in mice, rats and dogs, cataleptogenic effect and inhibitory effect on amphetamine circling. In contrast SCH 23390 has no effect on apomorphine-induced vomiting in dogs and little effects on 6-OHDA-denervated supersensitive DA receptors, stimulated by the DA agonist 3-PPP. In a series of experiments where methylphenidate-induced stereotyped gnawing in mice was inhibited by neuroleptics, it was shown that concomitant treatment with scopolamine or diazepam attenuated the effect of butyrophenones (D-2 antagonists). The same treatment attenuated the effect of phenothiazines, to a lesser extent, and hardly attenuated the effect of thioxanthenes and SCH 23390 at all. It is concluded that DA D-1 receptors are as important as D-2 receptors for the expression of neuroleptic activity in most animal models believed to be predictive of antipsychotic and extrapyramidal side-effect potential. However, the D-1 antagonist is less sensitive than D-2 antagonists to antimuscarinic compounds and benzodiazepines.