Abstract
Histochemical and electrophysiological studies have reported the presence of P2X purinoceptors in the area postrema (AP). In this study, we sought to clarify the purinergic modulation of AP neuronal excitability using a patch-clamp technique in rat brain slices. Voltage-clamp recordings were obtained from 40 neurons in the presence of TTX (1 μM) at a holding potential of –50 mV. Each cell was tested whether it displays the hyperpolarization-activated cation current (Ih) or not. Twenty of 40 cells tested showed excitatory responses to ATP (up to 1 mM), including cells displaying 1) ATP-induced inward currents with significant changes in the frequency of miniature EPSCs (mEPSCs) (n=14, including 1 cell displaying Ih and 13 cells not displaying Ih), 2) ATP-induced inward currents without significant changes in the frequency of mEPSCs (n=1, cells not displaying Ih), and 3) marked increases in the frequency of mEPSCs without any direct postsynaptic currents (n=5, including 4 cells displaying Ih and 1 cell not displaying Ih). PPADS (10-20 μM), selective P2X purinoceptor antagonist, abolished the responses of AP neurons to the bath application of ATP in all cells tested (n=10). These results indicate that P2X purinoceptors are present both pre- and post- and/or extrasynaptically in the AP. Further this study suggests the different localization of purinoceptors between pacemaker cells displaying Ih and cells not displaying Ih. [Jpn J Physiol 55 Suppl:S188 (2005)]
