Catecholamine release and uptake in the mouse prefrontal cortex

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Abstract
Monitoring the release and uptake of catecholamines from terminals in weakly innervated brain regions is an important step in understanding their importance in normal brain function. To that end, we have labeled brain slices from transgenic mice that synthesize placental alkaline phosphatase (PLAP) on neurons containing tyrosine hydroxylase with antibody–fluorochrome conjugate, PLAP‐Cy5. Excitation of the fluorochrome enables catecholamine neurons to be visualized in living tissue. Immunohistochemical fluorescence with antibodies to tyrosine hydroxylase and dopamine β‐hydroxylase revealed that the PLAP labeling was specific to catecholamine neurons. In the prefrontal cortex (PFC), immunohistochemical fluorescence of the PLAP along with staining for dopamine transporter (DAT) and norepinephrine transporter (NET) revealed that all three exhibit remarkable spatial overlap. Fluorescence from the PLAP antibody was used to position carbon‐fiber microelectrodes adjacent to catecholamine neurons in the PFC. Following incubation with l‐DOPA, catecholamine release and subsequent uptake was measured and the effect of uptake inhibitors examined. Release and uptake in NET and DAT knockout mice were also monitored. Uptake rates in the cingulate and prelimbic cortex are so slow that catecholamines can exist in the extracellular fluid for sufficient time to travel ∼100 µm. The results support heterologous uptake of catecholamines and volume transmission in the PFC of mice.