Fig. 9.
VTA novel wide-spike neurons exhibited a circadian rhythm in impulse activity. These neurons were characterized by their wide waveforms and tonically fast-firing impulse activity. (A) Digitized waveform (upper left), spike train (upper right). (B) Novel wide-spike neuron proportions through the circadian cycle. Each point represents the proportion of total novel wide-spike neurons found during that respective CT range. (C) Novel wide-spike neurons in active and resting phases are plotted as a function of their firing rate and spike widths. Horizontal dotted line indicates 10 spikes/s, the minimum firing rate of a neuron categorized as a novel wide-spike. More novel wide-spike neurons were recorded during the active phase than in the resting phase (P < 0.05). (D) The number of spontaneously active novel wide-spike neurons per electrode track as recorded during each circadian phase. Bars are SEM; *P = 0.02. Novel wide-spike neurons selectively fired during the active circadian phase.