In a recent study, the metabolic function of the hippocampal sharp wave-ripple was examined. The hippocampus has been known to play a role in both cognitive and endocrine functions. In the study, the electrophysiological activity from the hippocampus and interstitial glucose concentrations in the body were simultaneously measured in freely behaving rats. The goal was to identify an activity pattern that might link both cognitive and endocrine functions. The results suggest that clusters of sharp wave-ripples (SPW-R) recorded from the hippocampus reliably predict a decrease in peripheral glucose concentrations within about 10 minutes. The correlation was not dependent on ultradian, circadian, or meal-triggered fluctuations. In addition to the SPW-R rates, the potential contribution of theta power, discretized brain state (non-rapid eye movement (NREM) sleep, or wake), continuous measures of brain state (power spectrum slope and theta/delta ratio), movement (head accelerometer), electromyogram, and linear combinations of these variables were also assessed using several predictive modelling approaches. In all cases, SPW-R rate was the most predictive variable. The findings suggest that the function of the SPW-R is to modulate peripheral glucose homeostasis and offer a mechanism for a link between sleep disruption and blood glucose dysregulation in type 2 diabetes.
Tingley et al. Nature 2021:1-25. Abstract