The Mechanism of Action of Novel Antipsychotic Drugs

257

138

The modulating effects of serotonin on dopamine neurotransmission are not well understood, particularly in acute psychotic states. Positron emission tomography was used to examine the effect of psilocybin on the in vivo binding of [ 11 C]raclopride to D 2 -dopamine receptors in the striatum in healthy volunteers after placebo and a psychotomimetic dose of psilocybin (n ϭ 7). Psilocybin is a potent indoleamine hallucinogen and a mixed 5-HTPsilocybin, a potent indoleamine hallucinogen and 5-HT receptor stimulating agent, has been reported to produce a psychosis-like syndrome in man resembling the first manifestation of schizophrenia in certain respects [for review see (Fischman 1983;Gouzoulis-Mayfrank et al. 1998)]. Particularly, ego-disorders (Rüm-mele and Gnirss 1961;Vollenweider et al. 1997), affective changes (Rümmele and Gnirss 1961), loosened associations (Spitzer et al. 1996) and perceptual alterations commonly seen in psilocybin-induced psychosis are also observed in incipient acute schizophrenic stages (Bowers and Freedman 1966;Heimann, 1986;Gouzoulis et al. 1994). In support of these suggested clinical similarities, we recently found that psilocybin produced a marked prefrontal and anterior cingulate activation in normal subjects comparable to the hyperfrontal pattern observed in some (Cleghorn et al. 1989;Ebmeier et al. 1993Ebmeier et al. , 1995Catafau et al. 1994 1994;Ebmeier et al. 1995;Sabri et al. 1997) but not all (Andreasen et al. 1992;Buchsbaum et al. 1992;Liddle et al. 1992;Siegel et al. 1993) acute schizophrenic patients. A number of functional animal studies have suggested that indoleamine (psilocybin, LSD) and phenylethylamine (DOI, mescaline) hallucinogens produce their psychotomimetic effects primarily through excessive stimulation of 5-HT, and 5-HT 2A receptors in particular (McKenna et al. 1989;Pierce and Peroutka 1989;Aghajanian 1994;Sipes and Geyer 1994;Padich et al. 1996). This assumption was corroborated in a recent human study demonstrating that the psychotomimetic effects of psilocybin can be blocked dose-dependently by pretreatment with the preferential 5-HT 2A receptor antagonist ketanserin (Vollenweider et al. 1998). However, pretreatment with the D 2 -antagonist haloperidol also reduces some of the positive symptoms of psilocybin psychosis. This raises the possibility that symptoms of psilocybin are secondary responses to increased dopaminergic transmission (Vollenweider et al. 1998).Hence, a contribution of the dopamine systems to the effects of psilocybin, presumably through a serotonindopamine interaction, cannot be ruled out. Functional interactions between central serotonin (5-HT) and dopamine (DA) systems have been well documented. Electrophysiological, biochemical, and behavioral evidence suggests that the ascending serotonergic pathways from the medial and dorsal raphe modulate or control the function of the mesolimbic and mesostriatal dopamine systems (Joyce 1993;Zazpe et al. 1994;Kapur and Remington 1996). The modulating effect of serotonin on striatal dopamine release...

Section: Discussionsupporting

confidence: 75%

5-HT Modulation of Dopamine Release in Basal Ganglia in Psilocybin-Induced Psychosis in Man—A PET Study with [11C]raclopride

Vollenweider

1999

257

138

“…Despite this, it is unclear what molecular mechanism(s) might make a drug atypical (see Arnt and Skarsfeldt 1998). Some of the more generally accepted mechanisms include concomitant D 2 ր5-HT 2 receptor antagonist activity (Meltzer 1991) or selectivity for the D 3 or D 4 receptor (Sokoloff et al 1990;. In addition, it has been hypothesized that effective antipsychotic action may be caused by occupation of one of several types of noradrenergic receptors, although this is less well understood (Cohen and Lipinski 1986;Van Kammen et al 1990).…”

Section: Discussionmentioning

confidence: 99%

Interactions of the Novel Antipsychotic Aripiprazole (OPC-14597) with Dopamine and Serotonin Receptor Subtypes

Lawler

Prioleau

Lewis

et al. 1999

376

298

cells; C-6 cells; SchizophreniaSchizophrenia is a chronic psychiatric illness with two major types of symptoms-positive or psychotic symptoms, such as hallucinations and delusions, and negative or deficit symptoms, such as amotivation, apathy, and asociality. Approximately 1% of the population suffers from schizophrenia (Kaplan and Sadock 1988). The serendipitous discovery of chlorpromazine four decades ago not only provided the first efficacious therapeutic intervention, but also opened horizons into research about the etiology and therapy of this disease. It was soon hypothesized that chlorpromazine and similar drugs worked by being pharmacological antagonists of the neurotransmitter dopamine (Seeman et al. 1976;Creese et al. 1976), a hypothesis that ultimately provided the foundation for the commonly accepted division of dopamine receptors into two classes (Garau et al. 1978), now often called D 1 and D 2 (Kebabian and Calne 1979).During the past decade, molecular cloning studies have resulted in the identification of several genes coding for dopamine receptors. There now are at least two From the Departments of Pharmacology (CP, RBM) and Psychiatry (CPL, RBM), and Medicinal Chemistry (RBM), Curricula in Toxicology (CPL, RBM), and Neurobiology (MML, RBM), UNC Neuroscience Center (CPL, CP, MML, RBM), University of North Carolina School of Medicine, Chapel Hill, North Carolina; and Molecular Neuropharmacology Section (CM, DJ, JAS, AMG, DRS), National Institutes of Neurological Disorders and Stroke, Bethesda, Maryland.Address correspondence to: Dr. Cindy Lawler, CB #7250; UNC Neuroscience Center, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7250. Received April 17, 1998; revised August 27, 1998; accepted September 21, 1998. (Zhou et al. 1990;Monsma et al. 1990;Sunahara et al. 1990;Dearry et al. 1990) and D 1B (Tiberi et al. 1991) or D 5 (Sunahara et al. 1991], both of these linked functionally to stimulation of cAMP synthesis, and preferentially recognizing 1-phenyl-tetrahydrobenzazepines (e.g., SCH23390). The D 2 -like receptors come from at least three genes and include multiple splice variants. The D 2 -like receptors [D 2S (Bunzow et al. 1988), D 2L (Giros et al. 1989;Monsma et al. 1989), D 3 (Sokoloff et al. 1990, and D 4 ] sometimes are linked to inhibition of cAMP synthesis and have a different pharmacological specificity from the D 1 -like receptors (i.e., having much higher affinity for spiperone or sulpiride).The traditional view of antipsychotic drug efficacy posits a primary role for pharmacological antagonism of D 2 -like receptors. Despite the demonstrable effectiveness of dopamine D 2 receptor antagonists, however, a substantial number (up to 20%) of patients are considered unresponsive to these typical antipsychotics (Kane et al. 1988). Furthermore, the typical antipsychotics have significant and serious side effects that make them less than optimal therapeutic agents (see Peacock and Gerlach 1996). For example, they cause acute drug-induced parkinsonian symptoms (...

“…There is also the hypothesis that clozapine interacts differently at the nigrostriatal pathway versus the mesolimbic pathway and that this selective mesolimbic action accounts for the absence of the EPS effects (reviewed in Meltzer 1991). Results from in vivo imaging studies note that clozapine does not seem to increase occupancy of striatal D-2 receptors once it reaches a plateau of approximately 60%, unlike the Ͼ 80% occupancy observed with the other high-affinity neuroleptics (e.g., in Kapur et al 1999;Seeman and Tallerico 1999).…”

mentioning

confidence: 99%

Evaluation of Dopamine D-2 Receptor Occupancy by Clozapine, Risperidone, and Haloperidol In Vivo in the Rodent and Nonhuman Primate Brain Using 18F-Fallypride

Mukherjee

Christian

Narayanan

et al. 2001