Normally rapid eye movement sleep (REMS) does not appear during waking or non-REMS. Isolated, independent studies showed that elevated noradrenaline (NA) inhibits REMS and induces REMS loss-associated cyto-molecular, -morphological, psycho-somatic changes and associated symptoms. However, the source of NA and its target in the brain for REMS-regulation and -function in health and diseases remained to be confirmed in vivo. Using tyrosine hydroxylase (TH)-siRNA and virus-coated TH-shRNA, in normal freely moving rats we down-regulated NA synthesis in locus coeruleus (LC) REM-OFF neurons in vivo. These TH down-regulated rats showed increased REMS, which was prevented by infusing NA into the pedunculo-pontine tegmentum (PPT), the site of REM-ON neurons; normal REMS returned after recovery. Moreover, unlike normal or control siRNA or shRNA injected rats, upon REMS deprivation (REMSD) TH down-regulated rats’ brain did not show elevated Na-K ATPase (molecular changes) expression and activity. To the best of our knowledge these are the first in vivo findings in an animal model confirming NA from the LC REM-OFF neurons a) acts on the PPT REM-ON neurons to prevent appearance of REMS; and b) are responsible for inducing REMSD-associated molecular changes and symptoms. These observations clearly show neuro-physio-chemical mechanism why normally REMS does not appear during waking and that LC-neurons are the primary source of NA which in-turn causes some if not many, REMSD-associated symptoms and behavioral changes. The findings are proof-of-principle for the first-time and hold potential to be exploited for confirmation towards treating REMS-disorder and amelioration of REMS loss-associated symptoms in patients.
Significance Statement: Reciprocal interaction among REM-ON and REM-OFF neurons in PPT and LC, respectively, has been proposed to regulate REMS. Findings from isolated, independent studies led to the proposition that NA from the latter inhibits the former to prevent REMS, its withdrawal initiates REMS by disinhibiting the former, while excess NA causes REMS-loss associated symptoms. However, evidence from direct in vivo studies confirming this idea was lacking. Using RNAi-technology in vivo, we show that NA from LC neurons prevents REMS by inhibiting PPT neurons and those LC neurons are the source of NA for inducing REMS-loss associated symptoms. These confirmatory findings in animal models are first proof-of-principle, which hold potential for exploitation in ameliorating REMS loss-associated symptoms in patients.
All authors declare no conflict of interest.
J C Bose Fellowship; Department of Science and Technology (DST), Govt of India; UGC and Institutional Grants to the University under DST-PURSE and FIST; DBT-BUILDER; UGC-UPE, DRS and Networking, India.