Neuromelanin-sensitive imaging in patients with idiopathic rapid eye movement sleep behaviour disorder

Abstract

This scientific commentary refers to ‘The coeruleus/subcoeruleus complex in idiopathic rapid eye movement sleep behaviour disorder’, by Ehrminger et al. (doi: 10.1093/brain/aww006 )

Figure 1

Schematic depicting key aspects of normal REM sleep and REM sleep without atonia (the electrophysiological substrate for REM sleep behaviour disorder) associated with neurodegenerative disease in humans. Normal REM sleep ( A ). The glutaminergic sublaterodorsal nucleus is in the subcoeruleus area (just caudal to the locus coeruleus), and is part of the REM-on region. The sublaterodorsal nucleus (or homologous nucleus in humans) projects to spinal interneurons (‘direct route’, denoted by the line from the sublaterodorsal nucleus to spinal interneurons). The ‘indirect route’, denoted by the line from the sublaterodorsal nucleus to the magnocellular reticular formation to the anterior horn cells of the spinal cord, may also contribute to muscle atonia. Either or both routes represent the final common pathway(s) that cause active inhibition of the cranial motor nuclei (not shown) and anterior horn cells of the spinal cord, resulting in suppression of skeletal muscle activity in REM sleep. REM sleep without atonia ( B ). According to the schema by Braak et al. (2003) , the locus coeruleus, sublaterodorsal nucleus and magnocellular reticular formation degenerate early in the course of Lewy body disease underlying evolving Parkinson’s disease (stage 2), and prior to significant changes in the substantia nigra (stage 3). A similar topography of degeneration may explain REM sleep behaviour disorder associated with multiple system atrophy. The loss of active inhibition of the sublaterodorsal nucleus ± magnocellular reticular formation on the anterior horn cells of the spinal cord combines with influences by the locomotor generators (not shown) to cause REM sleep without atonia and the syndrome of REM sleep behaviour disorder. Excitatory projections represented by encircled ‘plus’ sign, inhibitory projections represented by encircled ‘minus’ sign, with the size of these symbols representing the relative effect of each projection on the synapsing nuclei. Nuclei are represented by circles or ovals, with solid coloured circles and ovals reflecting those with normal populations of neurons, and speckled circles and ovals reflecting those with significantly reduced populations of neurons. The relative tonic influences of each projection are represented by line thickness, with thicker lines depicting stronger influences, thinner lines depicting weaker influences, and dashed and dotted lines depicting weak influences due to damage to neurons in the respective nuclei. AHC = anterior horn cell; EMG = electromyographic; LC = locus coeruleus; MCRF = magnocellular reticular formation; SLD = sublaterodorsal nucleus; SN = substantia nigra.