Relationship between Dorsal Raphe Nucleus Neuronal Population Activity with Cortical Rhythms

Studies have shown that the firing activity of single neurons in the dorsal raphe nucleus (DRN) brain region is linked to slow wave oscillations in the cortex, especially the frontal cortex. However, most studies consist of either single DRN neuronal or single-channel electrocorticogram (ECoG) recording. Hence, it is unclear how a population of DRN neurons with electrophysiologically diverse characteristics can coordinate and relate to the oscillatory rhythms in different cortical regions. In this work, in anaesthetized mice, we simultaneously record extracellularly a group of DRN neurons and three cortical regions using electrocorticogram (ECoG). The cortical regions are the two bi-hemispheric frontal and one (right) occipital regions. Using coherence analysis, we investigate the relationship between DRN neurons and cortical rhythms. We then found the coherence between firing activities of DRN neurons to quantify the relationship. We found that most slow firing DRN neurons with regular and irregular spiking characteristics have significantly stronger relationship with cortical ECoG signals at frequencies of oscillation around 0.5-1 Hz and 3.5-3.8 Hz, especially with the frontal cortex. Moreover, the simultaneously recorded DRN neurons were generally found to be weakly correlated with each other. In summary, these findings suggest that slow firing DRN neurons, potentially 5-HT neurons, exhibit strong relations with frontal cortical activities even though the neurons have weak correlation with each other. Future work will investigate using more samples and to identify the specific types of DRN neurons, for example, whether they are serotonergic neurons.