Alteration of Monoaminergic Neuronal Firing by Acute Administration of Cariprazine: An In Vivo Electrophysiological Study

Abstract

Cariprazine is a novel dopamine (DA) and serotonin (5-HT) partial agonist with an in vitro receptor affinity profile that endows it with the potential to be used successfully in the treatment of both unipolar and bipolar disorders. The objective of this study was to determine whether in vitro findings with cariprazine lead to functional alterations of monoamine systems in the intact rat brain. In vivo electrophysiological recordings were carried out in male Sprague-Dawley rats under chloral hydrate anesthesia. Dorsal raphé nucleus (DRN), locus coeruleus (LC), and hippocampus cornu ammonis region 3 (CA3) pyramidal neurons were recorded and cariprazine was administered systemically by intravenous injection or locally through iontophoresis. In the DRN, cariprazine induced a complete inhibition of the firing of 5-HT neurons, which was fully reversed by the selective 5-HT1A antagonist WAY100.635. In the LC, the inhibitory effect of the preferential 5-HT2A agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) was reversed by cariprazine with an ED50 value of 67 µg/kg, i.v., and it did not block the inhibitory effect of the α2-adrenergic agonist clonidine. In the hippocampus, when cariprazine was administered by iontophoresis, it inhibited the firing of pyramidal neurons, but it did not dampen the suppressant effect of 5-HT. These results indicate that, in vivo, cariprazine acts as a 5-HT1A agonist in the DRN, as an antagonist on 5-HT2A receptors controlling the firing of NE neurons, and is a full agonist at 5-HT1A receptors located on pyramidal neurons of the hippocampus. The modulatory actions of cariprazine on the 5-HT and NE systems may contribute to its reported effectiveness in depressive episodes.