Functional role of the ATP receptor-mediated signaling in the solitary network

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It was attempted to clarify the functional role of extracellular ATP-mediated signaling in the central cardiorespiratory network in the solitary complex in which abundant expression of P2X (ATP-gated non-specific cation channels) has been demonstrated histochemically. The whole-cell current was recorded from neurons visually identified with infra-red videomicroscopy in the thick brainstem slice of rats (10-30 days old). The following conclusions were drawn.1. Involvement of ATP-mediated synaptic transmission in the synapse from solitary tract (TS) to second-order neurons in the nucleus of the solitary tract (NTS) seems to be little. I failed to detect component resistant to CNQX, AP5, bicuculline and strychnine in the TS stimulation-evoked post-synaptic current (PSC). In addition, on contrary to those demonstrated using freshly dissociated NTS cells, no NTS neuron showed inward current with ATP (n=10).2. However, ATP and its analogues modified PSCs evoked by TS stimulation of the second-order NTS neurons, indicating that P2X receptors are involved in presynaptic regulation of the input gain of afferent information.3. About 70% of the large diameter (>*30 mum) neurons in dorsal motor nucleus of vagus (dmnX) showed ATP-induced TTX-resistant inward currents together with burst-like PSCs. Bicuculline abolished most of Recording with CsCl in the patch solution indicated that these are mainly GABAergic and partly glutaminergic PSCs. The PSCs activated by ATP was abolished with TTX.This is a novel finding indicating that, in addition to the parasympathetic preganglionic cells, the GABAergic and glutaminergic premotor neurons sending synaptic connections to these cells also express P2X receptors.