Direction character of ¡°critical sensitivity¡± phenomena in neural firing pacemaker

    YANG Jing, DUAN Yuª²Bin, XING Junª²Ling, HU Sanª²Jue

    1PLA Institute of Neurosciences, 2Department of Physiology, School of Basic Medicine, Fourth Military Medical University, Xi¬ðan 710033, China

    ¡¾Abstract¡¿ AIM: To explore the direction characteristics of ¡°critical sensitivity¡± phenomena in neural firing pacemaker. METHODS: Interspike intervals (ISIs) sequence of Aª²type fiber discharge was recorded from the neural firing pacemaker of chronic constriction of sciatic nerve in rats. Under calciumª²free condition, the ISIs sequence branched into periodª²adding bifurcation and certain concentration of EGTA (a kind of calcium chelator) of the perfusion solution stabilized the firing pattern at period state, critical state before bifurcation and critical state after bifurcation. Response to electrical field stimulus at different dynamic states was observed. RESULTS: At critical state before bifurcation, excitatory electrical field stimulus of certain intensity induced an obvious increase of firing rate and a transition of firing pattern. Inhibitory electrical field stimulus of the same intensity, however, decreased the firing rate slightly but with no transition of firing pattern. At critical state after bifurcation, inhibitory electrical field stimulus of certain intensity resulted in a markedly decrease of firing rate with a transition of firing pattern, but excitatory electrical field stimulus of the same intensity increased the firing rate slightly but with no transition of firing pattern. CONCLUSION: The ¡°critical sensitivity¡± phenomena in neural firing pacemaker have direction characteristics. ......