CHANGES in the concentration of intracellular free calcium ([Ca 2ϩ ] i ) regulate activation and control of many cellular processes, including excitability, neuronal development, and secretion of neurotransmitters.As such, increased [Ca 2ϩ ] i can be considered a surrogate measure for neuronal activation and has been applied to examine the effects of mechanical, thermal, and chemical stimulation of sensory neurons cultured from dorsal root ganglia (DRG).1,2 Transient depolarization of DRG neurons increases inward Ca 2ϩ currents, with a linear relation between magnitude of current and increase in [Ca 2ϩ ] i up to approximately 300 nM, beyond which complex buffering mechanisms result in a nonlinear relation.3 We describe a method, using fluorometric measurement of [Ca 2ϩ ] i by videomicroscopy, to examine inhibitory pharmacology in individual DRG neurons.Previous studies using this method have examined stimuli such as capsaicin exposure, 1 which only activate some nociceptive neurons or can only be applied once because of rapid desensitization.The method we describe can be used to rapidly examine inhibitory pharmacology in populations of individually identified DRG neurons, whose receptor and neurotransmitter phenotype could be subsequently identified using immunocytochemistry.
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Duflo et al. (2004) studied this question.