Monitoring neurotransmitter release from isolated retinas using online microdialysis-capillary electrophoresis

Release of neurotransmitters and other primary amine-containing analytes from intact, isolated larval salamander (Ambystoma tigrinum) retinas maintained in a 6.5-microL perfusion chamber was monitored using online microdialysis-capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). Primary amines were derivatized online with o-phthaldialdehyde (OPA) and beta-mercaptoethanol. With the use of overlapping injections, the perfusate was sampled every approximately 10 s. Although separation conditions were optimized using 20 mM hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD) for a number of important neuromessengers including D- and L-serine, D- and L-asparate, glutamate, GABA, serotonin, dopamine, norepinephrine, and taurine, only glutamate (0.48 +/- 0.27 microM), GABA (0.25 +/- 0.12 microM), taurine (5.5 +/- 2.1 microM), and l-serine (2.8 +/- 1.0 microM) were identified in the perfusate. Elevated levels of glutamate, GABA, and taurine were detected during stimulation with 60 mM K+. This method is the first to directly sample multiple neurotransmitters from perfused, isolated retinas and to observe changes in efflux of these neurotransmitters as a result of pharmacological stimulation.