Characterization of dopamine release in the rat medial prefrontal cortex as assessed by in vivo microdialysis: Comparison to the striatum

Using the technique of perfusion microdialysis combined with a small-bore liquid chromatography system we have measured the basal and drug-induced fluxes of extracellular dopamine in the medial prefrontal cortex of chloral hydrate-anesthetized rats and have compared our findings in the cortex to that observed in the striatum. The results were as follows. (1) At a flow rate of 2 μ1/min, the basal level of dopamine in the medial prefrontal cortex was 0.28 ±0.1 (n = 32) fmol/μl perfusate, which was nearly an order of magnitude less than that obtained from the striatum. (2) alpha-Methyl-para-tyrosine (150 mg/kg, i.v.) significantly decreased the extracellular levels of striatal and cortical dopamine. The magnitude and duration of the responses were similar in both regions. (3) Local perfusion with 30 mM K⁺ had a more profound effect on dopamine release in the striatum than in the medial prefrontal cortex. The K⁺-induced release in both regions was significantly attenuated in the absence of Ca²⁺. (4) The anxiogenic beta carboline FG 7142 (15 mg/kg, i.p.) enhanced the release of cortical dopamine by about 50% while it was without an effect in the striatum. (5) Amphetamine (1 mg/kg, i.v.) significantly elevated, while reserpine (5 mg/kg, i.p.) rapidly attenuated, the dopamine level in the medial prefrontal cortex. These studies demonstrate that perfusion microdialysis, in conjunction with small-bore liquid chromatography with electrochemical detection, can be used to measure the basal release of dopamine in the rat medial prefrontal cortex and that the dopamine release process in this region, as has been shown in the striatum, is sensitive to stimulation conditions and pharmacological manipulations. The significance of variations in the pharmacological responsiveness of the dopamine released in the medial prefrontal cortex and striatum is discussed.