Abstract

Research has shown that there are important neurochemical differences between the mesocortical and mesostriatal dopamine systems. The work reported in this paper has sought to compare the regulation of dopamine release in the medial prefrontal cortex and the anterior caudate-putamen. In vivo microdialysis was used to recover dialysate fluid for subsequent assay for dopamine concentrations. The responses to D2 antagonist (haloperidol) administration, which has been shown to increase impulse-dependent dopamine release, were compared. Results demonstrated a diminished effect of systemic haloperidol administration on dopamine efflux in the prefrontal cortex. The responses to systemic administration of a nonimpulse-dependent, transporter-mediated, dopamine releaser (d-amphetamine) were also contrasted. Results again demonstrated a diminished pharmacological effect in the cortex. The potential interaction of stimulation of these two types of dopamine release was examined by coadministration of these compounds. Haloperidol pretreatment dramatically potentiated the dopamine-releasing effect of amphetamine administration. This effect was observed in both the cortex and the striatum. Subsequent work demonstrated that this effect of haloperidol was mediated by D2-like receptors in the prefrontal cortex. These results are discussed in relation to other neurochemical and neuroanatomical studies demonstrating sparse densities of dopamine transporter sites and dopamine D2 receptors in the cortex compared with the striatum. They demonstrate a functional correlate to the recently reported, largely extrasynaptic localization of dopamine transporter sites in the prefrontal cortex. Furthermore, they demonstrate the existence of cortical D2-like autoreceptors that may normally be “silent” under basal conditions.