Concurrent release of ATP and substance P within guinea pig trigeminal ganglia in vivo

Neurons within sensory ganglia have been proposed to communicate via non-synaptic release of a diffusible chemical messenger, but the identity of the chemical mediator(s) remains unknown [J. Neurosci. 16 (1996) 4733-474]. The present study addressed the possibility of co-released ATP and substance P (SP) within sensory ganglia to further advance the hypothesis of non-synaptic communication between sensory neurons. Microdialysis probes inserted into trigeminal ganglia (TRGs) of anesthetized guinea pigs were perfused with artificial cerebrospinal fluid and the collected perfusate analyzed for ATP and SP content using the firefly luciferin-luciferase (L/L) assay and radioimmunoassay, respectively. Significant reversible increases in ATP and SP levels were observed after infusion of 100 mM KCI or I mM capsaicin. Ca2+-free ACSF produced an eightfold increase in ATP levels, interpreted as a decrease in activity of Ca2+-dependent ecto-nucleotidases that degrade ATR In contrast, KCI-induced release of ATP in the presence of normal Ca2+ was blocked by Cd2+, a voltage-gated Ca2+ channel blocker, illustrating Ca2+-dependence of evoked AT? release. Since ganglionic release of ATP could arise from several neuronal and non-neuronal sources we directly tested acutely dissociated TRG neuron somata for ATP release. Neuron-enriched dissociated TRG cells were plated onto glass tubes and tested for ATP release using the L/L assay. Robust ATP release was evoked with 5 muM capsaicin. These data suggest that ATP is released concurrently with SP from the somata of neurons within sensory ganglia. (C) 2001 Elsevier Science BY. All rights reserved.