Role of noradrenergic and GABA-ergic inputs in pedunculopontine tegmentum for regulation of rapid eye movement sleep in rats

doi:10.1016/j.neuropharm.2006.02.006

Neuropharmacology

Volume 51, Issue 1, July 2006, Pages 1-11

https://doi.org/10.1016/j.neuropharm.2006.02.006 Get rights and content

Abstract

Rapid eye movement (REM) sleep disturbance is associated with several psycho-behavioral disorders, hence, it is important to understand its neural mechanism of regulation. Although it was known that the noradrenergic (NA-ergic) neurons from locus coeruleus (LC) project to the pedunculopontine tegmentum (PPT), the role of noradrenaline (NA) alone and in association with GABA, an inhibitory neurotransmitter, in PPT for REM sleep regulation was not known and was investigated in this study in freely moving normally behaving rats. Rats were surgically prepared for electrophysiological sleep–wake recording and simultaneous bilateral microinjections into PPT. 200 nl of prazosin (α1-antagonist) or clonidine (α2-agonist) or propranolol (β-antagonist) or combination of picrotoxin (GABA-A antagonist) and clonidine or vehicle (control) was microinjected bilaterally into PPT using a remote-controlled pump and the effects on REM sleep compared. Prazosin, clonidine and propranolol increased the total time spent in REM sleep whereas co-injection of picrotoxin and clonidine did not affect REM sleep. The results suggest that NA in PPT tonically inhibits REM sleep, possibly by acting on the cholinergic REM-ON neurons, while GABA inhibits the release of NA for REM sleep regulation. A model of neural connections explaining such regulation has been presented.

Introduction

REM-OFF and REM-ON neurons interact to regulate rapid eye movement (REM) sleep (Steriade and McCarley, 1990), however, the neuropharmacological basis and mechanism(s) of such regulation are matter of intense investigations. The cholinergic REM-ON neurons located in the laterodorsal/pedunculopontine tegmentum (LDT/PPT) remains shut throughout the sleep–wake cycle except during REM sleep when they are active, while the noradrenergic (NA-ergic) REM-OFF neurons located in the locus coeruleus (LC) are active all through but shut off only during REM sleep (Jacobs, 1986, Steriade and McCarley, 1990). It was hypothesized that GABA plays a role in the inhibition of those REM sleep related neurons for REM sleep regulation (Alam et al., 1993, Mallick et al., 1999). The hypothesis was confirmed for neurons in LC through a series of in vivo studies (Kaur et al., 2001, Kaur et al., 2004, Mallick et al., 2001). Subsequently, direct and indirect studies from others (Maloney et al., 1999, Torterolo et al., 2002, Ulloor et al., 2004, Vazquez and Baghdoyan, 2004) and this laboratory (Pal and Mallick, 2004) also supported the involvement of GABA in PPT for REM sleep regulation, although the mechanism of action was unknown.

The proposed executive role of cholinergic REM-ON neurons (Steriade and Hobson, 1990) in the generation of REM sleep may be supported by the studies showing that lesion (Webster and Jones, 1988) and electrical stimulation (Thakkar et al., 1996) of the site containing REM-ON neurons eliminated and increased REM sleep, respectively. The cholinergic neurons in the PPT receive NA-ergic inputs from LC (Rye et al., 1987) and in vitro studies showed that noradrenaline (NA) inhibits as well as excites distinct population of those neurons (Muhlethaler et al., 1990). The PPT also possesses both GABA-ergic neurons (Ford et al., 1995) as well as terminals (Rye et al., 1987). Thus, the cholinergic neurons in the PPT receive two inhibitory inputs i.e., NA-ergic and GABA-ergic, and independent isolated studies have shown that both affect REM sleep (Gottesmann, 2002, Pal et al., 2005). Although the tonic effect of GABA in PPT on REM sleep has been studied, the tonic role of NA and the subtypes of adrenoceptors in PPT involved in the regulation of REM sleep were unknown. Further, the knowledge about the interactions between NA and GABA in PPT in behaving animals for the regulation of REM sleep was also lacking. Knowledge on such interaction between neurotransmitters is important because they are likely to play very important role in psychosomatic disorders, some of which are associated with REM sleep disorders that have so far remained unexplained. The present microinjection study in freely moving normally behaving rats was conducted to better understand the interactions of neurotransmitters and the adrenergic receptor subtypes involved in PPT for REM sleep regulation. Results have been presented at the Interim Congress of World Federation of Sleep Research and Sleep Medicine Societies as a preliminary report (Pal and Mallick, 2005).

Section snippets

Surgical procedure and implantation of electrodes

All the studies were conducted on chronically prepared freely moving normally behaving male Wistar rats (n = 24) weighing 275–300 g. The animals were maintained on 12:12 h light/dark cycle with food and water ad libitum. The rats were prepared for electrophysiological sleep–wakefulness recording and microinjection of drugs into PPT as described earlier (Mallick et al., 2001, Pal and Mallick, 2004). Under surgical anesthesia (ketamine hydrochloride 80 mg/kg and xylazine hydrochloride 10 mg/kg, i.p.)

Results

The presence of cannula track and pontamine sky blue dye spots amidst ChAT-immunopositive neurons confirmed that the injection sites were amidst cholinergic neurons in PPT and also that the neurons around the cannula were not damaged by the injections (Fig. 2). The PPT sites that modulated REM sleep (effective sites) and the adjacent sites that did not affect REM sleep (control sites) are shown in an anatomical reconstruction diagram (Fig. 3). The baseline sleep–wakefulness data of the control

Discussion

The results showed that REM sleep was increased either by reducing the release of NA by applying the NA-ergic α2-agonist, clonidine, or by preventing spontaneously released NA to act on its receptors by applying the α1-antagonist, prazosin, or β-antagonist, propranolol, into PPT. These findings suggest that: (i) normally NA is available and tonically inhibits the PPT REM-ON neurons preventing the expression of REM sleep; (ii) if such tonic inhibitory effect of NA on PPT neurons was withdrawn,

Acknowledgment

The financial support from Council of Scientific and Industrial Research to B.N.M. is duly acknowledged.

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Role of noradrenergic and GABA-ergic inputs in pedunculopontine tegmentum for regulation of rapid eye movement sleep in rats

Abstract

Introduction

Section snippets

Surgical procedure and implantation of electrodes

Results

Discussion

Acknowledgment

Neurol. Clin.

Brain Res. Brain Res. Rev.

Prog. Neurobiol.

Neuroscience

Neuroscience

Neuroscience

Prog. Neurobiol.

Behav. Brain Res.

Brain Res.

Brain Res.

Neuroscience

Behav. Brain Res.

Neurosci. Lett.

Brain Res.

Biol. Psychiat.

Neurosci. Res.

Neuroscience

Brain Res.

Bull.

Prog. Brain Res.

Brain Res.

Brain Res.

Role of GABA in acetylcholine induced locus coeruleus mediated increase in REM sleep

Sleep Res.

Modulation of desynchronized sleep through microinjection of alpha1-adrenergic agonists and antagonists in the dorsal pontine tegmentum of the cat

Eur. J. Physiol.

Sleep-wake states and cortical synchronization control by pregnenolone sulfate into the pedunculopontine nucleus

J. Neurosci. Res.

Excitation of the brain stem pedunculopontine tegmentum cholinergic cells induces wakefulness and REM sleep

J. Neurophysiol.