Characteristics of ventromedial thalamic neuronal activity during sleep-wake cycle in mice

To investigate the characteristics of ventromedial thalamus (VM) neuronal activity during sleep-wake cycles.

Both the oscillation state of electrical activity in the parietal cortex and three-dimensional acceleration of the head and neck were employed to determine the brain states of male mouse (n=4). The brain states were classified into three types: wakefulness, non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. In vivo multi-electrode arrays were utilized to record the firing activity of VM and ventrolateral thalamus (VL) neurons in these three distinctive brain states and during their switching process.

①The firing rates of VM neurons (n=50) during wakefulness (4.13±0.47) Hz were significantly higher than in either NREM sleep (2.46±0.34 Hz, P<0.01) or REM sleep (2.35±0.32 Hz, P<0.01). There was no significant difference as to the firing rates between NREM and REM sleep state (P>0.05). ②The firing rates of VM neurons (n=50) increased significantly from NREM sleep state to wakefulness (P<0.001) and evidently reduced from wakefulness to NREM sleep state (P<0.01). However, there was no obvious difference from NREM sleep state to REM sleep state (P>0.05). ③The firing rates of VL neurons (n=40) during NREM sleep state (3.68±0.62) Hz were lower than in either wakefulness (10.42±1.03 Hz, P<0.01) or REM sleep condition (8.95±0.89 Hz, P<0.01). In contrast, the firing rates of VL neurons significantly increased from NREM sleep stated to either wakefulness (P<0.01) or REM sleep state (P<0.01).

The wakefulness state has the greatest firing activities of VM neurons. The firing activities of VM neurons reduce during the transition from wakefulness to sleep state, whereas the activities increase during the transition from sleep state to wakefulness state.