Abstract
The aim of the present study was (1) to investigate how the tongue reflex is modulated during wakefulness and sleep and (2) to examine if modulation of the tongue reflex activities during active sleep is related with respiratory phases or rapid eye movements in the freely moving rabbit. Electromyographic (EMG) activity of tongue muscle was recorded in the genioglossus (tongue-protruder, GG) muscle, and the GG reflex was evoked by electrical stimulation of the inferior alveolar nerve. The current intensity of stimulus was set at 1.5 times threshold to evoke the reflex to evaluate the modulatory mode of GG reflex. Peak to peak amplitude of EMGs in the reflex was compared among wakefulness and sleep stages.GG activity showed a wide variation, some had respiratory-related activity and others did not. However, in all animals, the reflex was suppressed during sleep, and the inhibition was significantly stronger during active sleep than that during quiet sleep. In some cases, the reflex was completely suppressed during active sleep. Furthermore, during this sleep stage, the reflex amplitude during inspiratory phase was larger than that during expiratory phase. On the other hand, the rapid eye movements during active sleep were not related to the changes in the reflex activity during active sleep. Not only basic but also clinical studies have paid attention to loss of tone in upper airway muscles including tongue muscles during sleep. The neuronal mechanisms controlling tongue muscle activity in sleep were discussed. [Jpn J Physiol 54 Suppl:S178 (2004)]
