FUNCTIONAL-CHARACTERIZATION OF CAUDAL HYPOGLOSSAL NEURONS BY SPECTRALPATTERNS OF NEURONAL DISCHARGES IN THE RAT

This study evaluated the spectral characteristics of neuronal discharg es in the caudal hypoglossal nucleus and their physiological relevance in adult, male Sprague-Dawley rats which were anaesthetized and maint ained with pentobarbital sodium. Based on auto-spectral analysis of ex tracellular single-neuron activity, three spectral patterns were ident ified in the spontaneous discharges of hypoglossal neurons. Neurons th at exhibited a rhythmic pattern manifested a concentrated peak in the auto-spectrogram that corresponded to the mean discharge rate. A major ity of hypoglossal neurons displayed the modulated pattern, which was manifested either as scattered power densities (wide-band modulated pa ttern) or with a peak frequency component that was different from the mean discharge rate (narrow-band modulated pattern). Neurons that exhi bited a mixed pattern displayed both rhythmic and modulated spectral p atterns. Cross-spectral analysis further revealed that respiratory mod ulation constituted a major physiological influence on caudal hypoglos sal neurons. The respiratory modulated pattern, however, could be conv erted to a mixed pattern in the presence of a central dipsogen, angiot ensin III. The results suggest that the spectral patterns of neuronal discharges in caudal hypoglossal neurons represent manifestations of m ultiple physiological information, including that regarding respiratio n and dipsogenesis, which is encoded in these neurons. It was also sho wn that this information may only be revealed by auto-spectral and cro ss-spectral analysis of neuronal discharge signals. (C) 1997 IBRO.