New pathways and data on REM sleep behaviour disorder in a rat model.

OBJECTIVE: An abnormality in auditory evoked responses localised to the inferior colliculus (IC) has been reported in rapid eye movement (REM) sleep behaviour disorder (RBD) patients. The external cortex of the inferior colliculus (ICX) has been demonstrated not only to be involved in auditory processing, but also to participate in the modulation of motor activity. METHODS: Rats were surgically implanted with electrodes for electroencephalography (EEG) and electromyography (EMG) recording and guide cannulae aimed at the ICX for drug infusions. Drug infusions were conducted after the animals recovered from surgery. Polysomnographic recordings with video were analysed to detect normal and abnormal sleep states. RESULTS: Baclofen, a gamma-aminobutyric acid B (GABA(B)) receptor agonist, infused into the ICX increased phasic motor activity in slow wave sleep (SWS) and REM sleep and tonic muscle activity in REM sleep; it also elicited RBD-like activity during the infusion and post-infusion period. In contrast, saclofen, a GABA(B) receptor antagonist, did not produce significant changes in motor activities in sleep. Baclofen infusions in ICX also significantly increased REM sleep during the post-infusion period, while saclofen infusions did not change the amount of any sleep-waking states. CONCLUSIONS: This study suggests that GABA(B) receptor mechanisms in the ICX may be implicated in the pathology of RBD.