Serotonin modulates fast-spiking interneuron and synchronous activity in the rat prefrontal cortex through 5-HT1A and 5-HT2A receptors

Abstract

Alterations of the serotonergic system in the prefrontal cortex (PFC) are implicated in psychiatric disorders such as schizophrenia and depression. Although abnormal synchronous activity is observed in the PFC of these patients, little is known about the role of serotonin (5-HT) in cortical synchrony. We found that 5-HT, released by electrical stimulation of the dorsal raphe nucleus (DRN) in anesthetized rats, regulates the frequency and the amplitude of slow (<2 Hz) waves in the PFC via 5-HT2A receptors (5-HT 2ARs). 5-HT also modulates prefrontal gamma (30-80 Hz) rhythms through both 5-HT1ARs and 5-HT2ARs, but not 5-HT 2CRs, inducing an overall decrease in the amplitude of gamma oscillations. Because fast-spiking interneurons (FSi) are involved in the generation of gamma waves, we examined serotonergic modulation of FSi activity in vivo. Most FSi are inhibited by serotonin through 5-HT1ARs, while a minority is activated by 5-HT2ARs, and not 5-HT2CRs. In situ hybridization histochemistry confirmed that distinct populations of FSi in the PFC express 5-HT1ARs and 5-HT2ARs, and that the number of FSi expressing 5-HT2CRs is negligible. We conclude that 5-HT exerts a potent control on slow and gamma oscillations in the PFC. On the one hand, it shapes the frequency and amplitude of slow waves through 5-HT 2ARs. On the other hand, it finely tunes the amplitude of gamma oscillations through 5-HT2AR- and 5-HT1AR-expressing FSi, although it primarily down-regulates gamma waves via the latter population. These results may provide insight into impaired serotonergic control of network activity in psychiatric illnesses such as schizophrenia and depression. Copyright © 2010 the authors.