Different tonic regulation of neuronal activity in the rat dorsal raphe and medial prefrontal cortex via 5-HT1A receptors

It has been established that 5-HT1A receptors are expressed both presynaptically as autoreceptors by 5-HT containing neurones, and postsynaptically by a variety of other neurones. Activation of either somatodendritic 5-HT1A autoreceptors or postsynaptic 5-HT,A receptors induces hyperpolarisation and inhibition of action potential discharge of the neurones, but it is unclear whether 5-HT,A receptors are under a general tonic influence by 5-HT. In the present study, using single unit recordings from both anesthetized acid non-anesthetized rats, we show that the activity of neurones in the medial prefrontal cortex is not altered by systemic administration of the selective 5-HT1A receptor antagonist, WAY 100635. In contrast, WAY 100635 increased the firing rate of 5-HT neurones in the dorsal raphe nucleus. Our findings indicate a tonic activation of presynaptic somatodendritic but not postsynaptic cortical 5-HT1A receptors. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.