Designing a non-neuroleptic antischizophrenic drug: the noradrenergic strategy

Novel antipsychotic agents with dopamine autoreceptor agonist properties: synthesis and pharmacology of 7-[4-(4-phenyl-1-piperazinyl)butoxy]-3,4-dihydro-2(1H)-quinolinone derivatives

To develop a novel antipsychotic agent which is an agonist of dopamine (DA) autoreceptors and an antagonist of postsynaptic DA receptors, a series of 7-[4-[4-(substituted phenyl)-1-piperazinyl]butoxy]-3,4-dihydro-2 (1H)-quinolinones was synthesized and their dual activities were examined. The postsynaptic DA receptor antagonistic activities of the compounds were evaluated by their ability to inhibit stereotypy induced by apomorphine in mice, and the autoreceptor agonist activities were determined by their effects on the gamma-butyrolactone (GBL)-induced increase in L-dihydroxyphenylalanine (DOPA) synthesis in the mouse brain. Many compounds inhibited the stereotypic behavior, and several compounds reversed the GBL-induced increase in the DOPA synthesis. Among them, 7-[4-[4-(2,3-dichlorophenyl)-1-piperazinyl]-butoxy]-3,4-dihydro-2 (1H)-quinolinone (28, aripiprazole, OPC-14597) was found to have these two activities. This compound reversed the GBL-induced DOPA synthesis (ED50 values of 5.1 mumol/kg p.o.) and inhibited the APO induced stereotypy (ED50 values of 0.6 mumol/kg p.o.). Compound 28 induced catalepsy at 10 times higher dose than that required for the antagonism of APO-induced stereotypy (ED50 value of 7.8 mumol/kg p.o.).

L-dopa helps positive but not negative features of neuroleptic-insensitive chronic schizophrenia

L-dopa (Sinemet-110 in a final dose equivalent to - 4 g per day) added to maintenance chlorpromazine, produced a small antipsychotic effect in a group of eight severely impaired male chronic schizophrenic in-patients. Negative symptoms were unaffected by L-dopa, although the improvement in psychotic behaviour and positive symptoms was restricted to the four patients with the most severe negative symptoms measured during the control treatment period. These L-dopa responders also tended to improve slightly when the dose of chlorpromazine was halved, an indication of their poor, or even counter-therapeutic response to conventional neuroleptic medication given in relatively high dosage. Signs of increased dopaminergic activity (raised eye blink rate and reduced plasma prolactin) were not observed in subjects showing an antipsychotic response to L-dopa. This raises the possibility that L-dopa may exert an antipsychotic effect in neuroleptic-insensitive subjects by altering noradrenergic activity in the brain.

Locus ceruleus morphometry in aging and schizophrenia

The locus ceruleus (LC), a pigmented brainstem nucleus rich in noradrenergic neurons, has been proposed to be involved in the pathophysiology of aging and schizophrenia. We undertook a quantitative neuropathological study of the LC in these two conditions. A computing planimeter was employed to count the total number of neurons and measure the volume of the LC, neuronal cross-sectional area, and percent of neuronal area occupied by neuromelanin in the brains of 39 subjects; 13 "normative", 15 leucotomized schizophrenic (most had died in the preneuroleptic era), and 11 leucotomized non-schizophrenic control patients, ranging in age from 11 to 94 years. There was a significant inverse correlation between age and total number of LC neurons, neuronal size, and LC volume, and a significant positive correlation between age and the percentage of neuronal area occupied by neuromelanin. Although schizophrenics did not differ significantly from control groups on any of the parameters of LC morphology, there was a trend for reduced LC volume in schizophrenic brains. Also, the LC of leucotomized patients tended to have increased neuromelanin content and slightly increased cell counts compared to normals, although the importance of this finding is not clear.

Further studies of the mechanism behind scopolamine-induced reversal of antistereotypic and cataleptogenic effects of neuroleptics in rats

Scopolamine is known to attenuate the amphetamine antagonistic and cataleptogenic effect of selective DA D-2 antagonists. To study further the influence of other receptor systems three approaches were taken: concomitant treatment with receptor blockers (scopolamine, prazosin and ketanserin) and a selective D-2 antagonist YM 09151-2, testing of a neuroleptic droperidol, with mixed D-2, alpha 1 and 5-HT2 antagonistic properties and testing a selective D-1 antagonist SCH 23390. Scopolamine markedly attenuated both effects of YM 09151-2 and droperidol. In contrast neither prazosin nor ketanserin influenced the effects of YM 09151-2. Furthermore, prazosin did not influence the interaction between scopolamine and YM 09151-2 in the tests of stereotypy and catalepsy. Scopolamine did not change the amphetamine antagonistic potency of SCH 23390, but decreased moderately its cataleptogenic potency. It is concluded that 5-HT2 and alpha 1-adrenergic receptor blockade are of minor importance in order to determine the sensitivity of a DA D-2 antagonist to the reversal induced by scopolamine. Thus, our earlier hypothesis, that DA D-1 receptor blockade is the main mechanism stabilizing these neuroleptic effects against scopolamine reversal, are further supported by the present experiments.

Locus coeruleus norepinephrine-containing neurons: effects produced by acute and subchronic treatment with antipsychotic drugs and amphetamine

Extracellular single-unit recording techniques were used to determine whether chronic treatment with either a typical antipsychotic drug (APD), haloperidol (HAL) or an atypical APD clozapine (CLOZ) causes a time-dependent reduction of spontaneously active norepinephrine (NE) neurons in the locus coeruleus (LC). Neither HAL nor CLOZ, after prolonged treatment, reduced NE activity. In addition, subchronic amphetamine (AMP) treatment did not increase NE activity. If these results can be extended to humans, they suggest that NE hyperactivity is not the cause for schizophrenic symptoms. Interestingly, chronic CLOZ markedy increased NE activity which may contribute to its low potential for causing extrapyramidal side-effects.

The neurochemistry and pharmacology of extinction behavior

The role of various neurotransmitter systems in the brain in extinction behavior is examined. An attempt is made to suggest psychological mechanisms (such as attention, secondary reinforcement or internal inhibition) by which the neurotransmitter systems or drugs act to produce the observed alteration in extinction behavior. The putative neurotransmitters acetylcholine, noradrenaline, dopamine, serotonin, endorphins and the peptides are reviewed, as are pharmacological agents such as the benzodiazepines, the barbiturates, the psychodelics, the neuroleptics, the psychomotor stimulants and cannabinoids. Other treatments and factors are considered such as peripheral hormones and the adrenal-pituitary axis. It is suggested that the noradrenergic system may be involved in the expression of extinction behavior by a role in selective attention, the dopamine system via an involvement with secondary reinforcement, the cholinergic system by a mechanism of response inhibition and the barbiturates and benzodiazepines by a block of nonreward.