| In Vitro | In vitro activity: Clozapine (10, 20 mg/kg) significantly increases the number of Fos-positive neurons in the nucleus accumbens, medial prefrontal cortex and lateral septal nucleus. Clozapine induces zif268 but not c-fos mRNA in rat striatum, while Haloperidol induces c-Fos-like immunoreactivity in the caudate-putamen. Clozapine is more selective for D4 receptors compared to D2 receptors. Clozapine is a mixed but weak D1/D2 antagonist. Clozapine produces a marked facilitation (300-400%) of NMDA-evoked responses in a concentration-dependent manner with EC50 of 14 nM. Clozapine, but not haloperidol, produces bursts of excitatory postsynaptic potentials (EPSPs), which are blocked by glutamate receptor antagonists, suggesting that these EPSPs are the result of increasing release of excitatory amino acids. Clozapine is a full agonist at the muscarinic M4 receptor (EC50 = 11 nM), producing inhibition of forskolin-stimulated cAMP accumulation. Clozapine potently antagonizes agonist-induced responses at the other four muscarinic receptor subtypes. |
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| Animal model | Mice: Mice are treated chronically (21 days) with 25 mg/kg/day clozapine. Experiments are conducted 1, 7, 14, and 21 days after the last clozapine administration. [3H]Ketanserin binding and 5-HT2A mRNA expression are determined in mouse somatosensory cortex. Head-twitch behavior, expression of c-fos, which is induced by all 5-HT2A agonists, and expression of egr-1 and egr-2, which are LSD-like specific, are assayed |
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