A previous study has demonstrated that during cortical spreading depression (CoSD), locus coeruleus (LC) neurons in adult rats reveal antidromic burst activity consisting of multiple initial segment (IS) spikes and IS-somatodendritic (SD) spikes with a distinct IS-SD break. In addition, the spontaneous firing rate of the neurons was reduced during CoSD. In the present experiments, we studied developmental changes in the electrical activity of LC neurons during CoSD. Since stable and repetitive DC shifts occurred in rats older than postnatal day 13 (PD13), the electrical activity of LC neurons at developmental stages later than PD13 was examined. The CoSD-related burst activity similar to that observed in adults was recorded at all stages of development, and the proportion of LC neurons showing the burst activity was nearly the same through all developmental stages and in adults. The frequency of IS spikes in the burst activity at PD13-P15 was not different from that in adults. However, the spontaneous firing rate of LC neurons at early developmental stages remained unchanged during CoSD. Based on these findings, it is conceivable that the mechanism of the generation of multiple IS spikes during CoSD at early developmental stages is different from that at later developmental stages and in adults.
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