Comparison of the novel antipsychotic ziprasidone with clozapine and olanzapine: inhibition of dorsal raphe cell firing and the role of 5-HT1A receptor activation.
Ziprasidone is a novel antipsychotic agent which binds with high affinity to 5-HT1A receptors (Ki = 3.4 nM), in addition to 5-HT1D, 5-HT2, and D2 sites. While it is an antagonist at these latter receptors, ziprasidone behaves as a 5-HT1A agonist in vitro in adenylate cyclase measurements. The goal of the present study was to examine the 5-HT1A properties of ziprasidone in vivo using as a marker of central 5-HT1A activity the inhibition of firing of serotonin-containing neurons in the dorsal raphe nucleus. In anesthetized rats, ziprasidone dose-dependently slowed raphe unit activity (ED50 = 300 micrograms/kg i.v.) as did the atypical antipsychotics clozapine (ED50 = 250 micrograms/kg i.v.) and olanzapine (ED50 = 1000 micrograms/kg i.v.). Pretreatment with the 5-HT1A antagonist WAY-100,635 (10 micrograms/kg i.v.) prevented the ziprasidone-induced inhibition; the same dose of WAY-100,635 had little effect on the inhibition produced by clozapine and olanzapine. Because all three agents also bind to alpha 1 receptors, antagonists of which inhibit serotonin neuronal firing, this aspect of their pharmacology was assessed with desipramine (DMI), a NE re-uptake blocker previously shown to reverse the effects of alpha 1 antagonists on raphe unit activity. DMI (5 mg/kg i.v.) failed to reverse the inhibitory effect of ziprasidone but produced nearly complete reversal of that of clozapine and olanzapine. These profiles suggest a mechanism of action for each agent, 5-HT1A agonism for ziprasidone and alpha 1 antagonism for clozapine and olanzapine. The 5-HT1A agonist activity reported here clearly distinguishes ziprasidone from currently available antipsychotic agents and suggests that this property may play a significant role in its pharmacologic actions.
Sprouse
J S
JS
Department of Neuroscience, Pfizer Inc., Groton, CT 06340, USA.
Reynolds
L S
LS
Braselton
J P
JP
Rollema
H
H
Zorn
S H
SH
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology; D000818:Animals; D001569:Benzodiazepines; D003024:Clozapine / Q000494:pharmacology*; D003891:Desipramine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D000077152:Olanzapine; D010879:Piperazines / Q000494:pharmacology*; D010890:Pirenzepine / Q000031:analogs & derivatives* / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011903:Raphe Nuclei / Q000737:chemistry / Q000166:cytology / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000502:physiology*; D044263:Receptors, Serotonin, 5-HT1; D012702:Serotonin Antagonists / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology*
D018759:Adrenergic Uptake Inhibitors; D001569:Benzodiazepines; D003024:Clozapine; D003891:Desipramine; D000077152:Olanzapine; D010879:Piperazines; D010890:Pirenzepine; D011725:Pyridines; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D017367:Selective Serotonin Reuptake Inhibitors; D013844:Thiazoles; C092292:ziprasidone; C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide