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-μL 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 β-mercaptoethanol. With the use of overlapping injections, the perfusate was sampled every ∼10 s. Although separation conditions were optimized using 20 mM hydroxypropyl-γ-cyclodextrin (HP-γ-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 μM), GABA (0.25 ± 0.12 μM), taurine (5.5 ± 2.1 μM), and L-serine (2.8 ± 1.0 μM) 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.