Brain neurotransmitter receptor-binding characteristics in rats after oral administration of haloperidol, risperidone and olanzapine

The present study was conducted to characterize the binding of neurotransmitter receptors (dopamine D2, serotonin 5-HT2, histamine H1, adrenaline α1 and muscarine Ml receptors) in the rat's brain after the oral administration of haloperidol, risperidone, and olanzapine. Haloperidol at 1 and 3 mg/kg displayed significant activity to bind the D2 receptor (increase in the Kd value for [3H]raclopride binding) in the corpus striatum with little change in the activity toward the 5-HT2 receptor (binding parameters for [3H]ketanserin). In contrast, risperidone (0.1–3 mg/kg) showed roughly 30 times more affinity for the 5-HT2 receptor than D2 receptor. Also, olanzapine (1–10 mg/kg) was most active toward the H1 receptor in the cerebral cortex, corpus striatum, and hippocampus, was less active in binding 5-HT2 and D2 receptors, and showed the least affinity for α1 and M1 receptors. In conclusion, haloperidol and risperidone administered orally selectively bind D2 and 5-HT2 receptors, respectively, in the rat brain, while olanzapine binds H1, 5-HT2, and D2 receptors more than α1 and M1 receptors.