Mechanisms of 5‐HT 1A receptor‐mediated transmission in dorsal raphe serotonin neurons

In the dorsal raphe nucleus, it is known that serotonin release activates metabotropic 5‐HT 1A autoreceptors located on serotonin neurons that leads to an inhibition of firing through the activation of G‐protein‐coupled inwardly rectifying potassium channels. We found that in mouse brain slices evoked serotonin release produced a 5‐HT 1A receptor‐mediated inhibitory postsynaptic current (IPSC) that resulted in only a transient pause in firing. While spillover activation of receptors contributed to evoked IPSCs, serotonin reuptake transporters prevented pooling of serotonin in the extrasynaptic space from activating 5‐HT 1A ‐IPSCs. As a result, the decay of 5‐HT 1A ‐IPSCs was independent of the intensity of stimulation or the probability of transmitter release. These results indicate that evoked serotonin transmission in the dorsal raphe nucleus mediated by metabotropic 5‐HT 1A autoreceptors may occur via point‐to‐point synapses rather than by paracrine mechanisms.