Pharmacogenetic inhibition of the subcoeruleus region influences rem sleep and cataplexy in narcoleptic mice

Abstract

Cataplexy – the sudden involuntary loss of skeletal muscle tone – is a defining feature of narcolepsy. A longstanding, but untested, hypothesis is that cataplexy results from intrusion of REM sleep paralysis into wakefulness. This hypothesis is built on the assumption that cataplexy and REM sleep paralysis share a common neural mechanism. The current study aimed to determine if cataplexy is influenced by direct manipulation of REM sleep circuitry. We did this by pharmacogenetically inhibiting cells in the subcoeruleus – a region important for REM paralysis – while monitoring REM sleep and cataplexy in narcoleptic mice. Virally-mediated transduction of hM4D-Gi/o was bilaterally targeted to the subcoeruleus (Sub-C) in hypocretin knockout mice ( n = 7). Standard electrophysiological (i.e., EEG/EMG) and behavioural criteria were used to characterize cataplexy and REM sleep. Intraperitoneal administration of clozapine-n-oxide (CNO, 10 mg/kg) was used to inhibit Sub-C cells expressing hM4D-Gi/o. Saline injections served as controls for CNO administration. Histological and immunohistochemistry were used to verify hM4D-Gi/o expression in the left/right Sub-C. Sub-C inhibition markedly influenced REM sleep and cataplexy. Compared to saline, Sub-C inhibition increased REM sleep amounts by increasing both the number ( p = 0.001) and duration of REM episodes ( p < 0.0001). This intervention also triggered increases in basal levels of muscle tone during REM sleep, i.e., it blocked REM sleep paralysis ( p < 0.05). Silencing Sub-C cells also lead to marked sleep fragmentation by increasing the number of NREM to REM transitions. Sub-C inhibition lead to an 88% decrease ( p = 0.04) in time spent in cataplexy as well as 75% fewer cataplexy episodes ( p = 0.025). There were no measureable changes in the duration of cataplectic events ( p > 0.05 for all variables). Pharmacogenetic manipulation of the Sub-C influences REM sleep expression as well as cataplexy expression in narcoleptic mice. At first glance, these preliminary data suggest that REM sleep paralysis and cataplexy may be mediated by a similar neural mechanism.