Uptake and subcellular localization of neurotransmitters in the brain

Nerve terminals in the brain possess specialized uptake mechanisms for a variety of putative neurotransmitters, such as dopamine (DA), norepinephrine (NE), serotonin, γ-aminobutyric acid (GABA) and, possibly, for glutamic acid and glycine. This chapter describes the specific uptake mechanisms for several putative neurotransmitters in the brain and their use in labeling and separating synaptosomes storing different putative neurotransmitters. The chapter proposes to use these uptake systems for labeling the endogenous transmitter pools with exogenous, radioactive neurotransmitters, labeling one class of synaptosomes with ³H-transmitter and another with ¹⁴C-transmitter. Kinetic studies elucidate the optimal conditions for nerve endings in brain slices or in isolated, pinched-off form (synaptosomes) to accumulate selectively their specific transmitter. The synaptosomal populations are separated with density gradient centrifugal procedures in the same brain region storing different transmitters or in different brain region storing the same transmitter. The electron microscopic studies reveal specific morphological features for the varying synaptosomal populations.