Burst Firing Patterns Of Hippocampal CA1 Neurons In Vivo

Burst is a unique firing pattern of neurons in the central nervous system. Using multi-channel recording techniques, we investigated the characteristics of the burst firing patterns of hippocampal CA1 neurons in mice during two different behavioral states: exploration and slow-wave sleep. The results showed that both pyramidal cells and interneurons in hippocampal CA1 have burst activity, but there are some differents between them, including burst type and the relationship with field potential.The brust type of pyramidal cells in hippocampal CA1 is unitary. A burst consists of a series of two to seven individual spikes, in which the amplitude of individual extracellularly recorded spikes decrease during the series. In the different behavioral states, burst type doesn't change much, during the exploration and slow-wave sleep, burst can both easily be observded. Some cells fire bursts respectively related to theta rhythm and high-frequency ripple.The burst types of interneurons in hippocampal CA1 are more multiplex. According to the spike number in a burst, the interspike interval in a burst and the decreasing of spike amplitude, they are divided to four patterns, respectively named I, II,III and IV. Pattern I is similar to that of pyramidal cells: there are two to seven spikes in a burst, but no decrease in spike amplitude. Bursts of pattern III,III and IV are obviously different that usually a burst is composed of more spikes of which the amplitude does not decrease.Compared with that of pyramidal cells, interneuron bursts are more influenced by different behavioral states. Bursts of pattern III,III are more likely to fire during slow-wave sleep, and the exact firing time is close related to high-frequency ripple, each ripple is corresponding to a burst. While bursts of pattern IV are more often observed during exploration, moreover they are correlative to the theta rhythm, each theta cycle corresponds a burst which is composed of five to sixteen spikes.The diversity of burst patterns of pyramidal cells and interneurons in hippocampal CA1 suggests that they are likely playing different roles on the neural coding and neural network modulation.