GABAergic neurons in prepositus hypoglossi regulate REM sleep by its action on locus coeruleus in freely moving rats

GABA in locus coeruleus modulates REM sleep. Apart from the presence of int erneurons, locus coeruleus also receives GABAergic inputs from prepositus h ypoglossi in the medulla, where the presence of REM-ON-like neurons have be en reported. Therefore, it was hypothesized that GABAergic projections from prepositus hypoglossi to locus coeruleus may modulate REM sleep. The exper iments were conducted on chronic rats prepared for recording EEG, EOG, and EMG in freely moving conditions. Bipolar stimulating electrodes were implan ted in prepositus hypoglossi bilaterally, while chemitrodes were implanted bilaterally in locus coeruleus. The prepositus hypoglossi were bilaterally stimulated (3 Hz, 250 mu sec, 100 muA) for 8 h in the presence and absence of picrotoxin (0.25 mug/250 nl) microinjection bilaterally in locus coerule us, followed by poststimulation recording for 4 h. It was observed that sti mulation of prepositus hypoglossi alone significantly increased REM sleep p rimarily by increasing the REM sleep duration per episode. However, when it was stimulated in the presence of picrotoxin in LC, REM sleep decreased, p redominantly due to decreased REM sleep duration per episode. The results o f this study suggest that GABAergic inputs from prepositus hypoglossi act o n locus coeruleus and regulate REM sleep, possibly by inhibition of REM-OFF neurons. (C) 2001 Wiley-Liss, Inc.