The rat ponto‐medullary network responsible for paradoxical sleep onset and maintenance: a combined microinjection and functional neuroanatomical study

Abstract

The neuronal network responsible for paradoxical sleep (PS) onset and maintenance has not previously been identified in the rat, unlike the cat. To fill this gap, this study has developed a new technique involving the recording of sleep-wake states in unanaesthetized head-restrained rats whilst locally administering pharmacological agents by microiontophoresis from glass multibarrel micropipettes, into the dorsal pontine tegmentum and combining this with functional neuroanatomy. Pharmacological agents used for iontophoretic administration included carbachol, kainic acid, bicuculline and gabazine. The injection sites and their efferents were then identified by injections of anterograde (phaseolus vulgaris leucoagglutinin) or retrograde (cholera toxin B subunit) tracers through an adjacent barrel of the micropipette assembly and by C-Fos immunostaining. Bicuculline, gabazine and kainic acid ejections specifically into the pontine sublaterodorsal nucleus (SLD) induced within a few minutes a PS-like state characterized by a continuous muscle atonia, low voltage EEG and a lack of reaction to stimuli. In contrast, carbachol ejections into the SLD induced wakefulness. In PHA-L, glycine and C-Fos multiple double-labelling experiments, anterogradely labelled fibres originating from the SLD were seen apposed on glycine and C-Fos positive neurons (labelled after 90 min of pharmacologically induced PS-like state) from the ventral gigantocellular and parvicellular reticular nuclei. Altogether, these data indicate that the SLD nuclei contain a population of neurons playing a crucial role in PS onset and maintenance. Furthermore, they suggest that GABAergic disinhibition and glutamate excitation of these neurons might also play a crucial role in the onset of PS.

Electrophysiological characterization of neurons in the dorsolateral pontine rapid-eye-movement sleep induction zone of the rat: Intrinsic membrane properties and responses to carbachol and orexins

“…Application of the cholinergic agonist carbachol to this area in the cat causes, at short latency, a pharmacologically induced state virtually indistinguishable from REM sleep, including the muscle atonia component (Mitler and Dement, 1974;Baghdoyan et al, 1987;Vanni-Mercier et al, 1989;Yamamoto et al, 1990). In the rat, carbachol does not normally cause a REM-like state when injected into the SubC but a state similar to REM can be induced by application of the GABA A receptor antagonists, bicuculline and GABAzine (Boissard et al, 2002;Pollock and Mistlberger, 2003). (Thakkar et al, 1999).…”

“…Early transection studies by Jouvet and coworkers in the cat identified the pons as being critical for REM sleep (Jouvet, 1962). Further investigation by the Jouvet group and others identified a region ventral to the locus coeruleus (LC), lateral to the midline and mediodorsal to the trigeminal motor nucleus which plays a critical role in at least two aspects of REM sleep, namely muscle atonia and PGO spikes (Mouret et al, 1967;Marks et al, 1980;Baghdoyan et al, 1984;Morrison, 1988;Yamamoto et al, 1990;Boissard et al, 2002). In the cat this region has been called the peri-LC, subcoeruleus alpha and subcoeruleus whereas in the rat it encompasses the regions termed dorsal subcoeruleus (SubCD) and subcoeruleus alpha part (SubCA) by Paxinos and Watson (Paxinos and Watson, 1998).…”

“…In the cat this region has been called the peri-LC, subcoeruleus alpha and subcoeruleus whereas in the rat it encompasses the regions termed dorsal subcoeruleus (SubCD) and subcoeruleus alpha part (SubCA) by Paxinos and Watson (Paxinos and Watson, 1998). Recently this same area in the rat has been termed the sublaterodorsal nucleus (SLD) by Boissard et al (Boissard et al, 2002). In this manuscript we will use the term SubC to refer to this area, which is shown in figure 1.…”

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

“…Fos staining refined the understanding by implicating a specific pontine cell population, in rodents an area named the sublaterodorsal nucleus (SubC), as the point of induction and maintenance of REM sleep and REM sleep atonia [8][9][10][11]. The SubC is a small pontine nucleus representing a mix of glutamateric and GABAergic neurons; located ventral to the locus coeruleus (LC), medial to the trigeminal motor nucleus (MO5) and ventromedial to the laterodorsal tegmental nucleus (LDT) and the parabrachial nucleus (PB).…”

“…Anterograde tracing studies have shown that one subset of glutamatergic SubC REM-on neurons have projections downstream to the alpha and ventral gigantocellular (GiA/GiV) neurons as well as spinal interneurons of the ventral horn [10]. These descending pathways have been shown to play a role in REM atonia [30,31].…”