c-fosExpression in Brainstem Premotor Interneurons during Cholinergically Induced Active Sleep in the Cat

Abstract

The present study was undertaken to identify trigeminal premotor interneurons that become activated during carbachol-induced active sleep (c-AS). Their identification is a critical step in determining the neural circuits responsible for the atonia of active sleep. Accordingly, the retrograde tracer cholera toxin subunit B (CTb) was injected into the trigeminal motor nuclei complex to label trigeminal interneurons. To identify retrograde-labeled activated neurons, immunocytochemical techniques, designed to label the Fos protein, were used. Double-labeled (i.e., CTb(+), Fos(+)) neurons were found exclusively in the ventral portion of the medullary reticular formation, medial to the facial motor nucleus and lateral to the inferior olive. This region, which encompasses the ventral portion of the nucleus reticularis gigantocellularis and the nucleus magnocellularis, corresponds to the rostral portion of the classic inhibitory region of. This region contained a mean of 606 +/- 41.5 ipsilateral and 90 +/- 32.0 contralateral, CTb-labeled neurons. These cells were of medium-size with an average soma diameter of 20-35 micrometer. Approximately 55% of the retrogradely labeled cells expressed c-fos during a prolonged episode of c-AS. We propose that these neurons are the interneurons responsible for the nonreciprocal postsynaptic inhibition of trigeminal motoneurons that occurs during active sleep.

Nitrergic ventro-medial medullary neurons activated during cholinergically induced active (rapid eye movement) sleep in the cat

“…These procedures were similar to those reported in previous work (see for example Morales et al, 1999). Animals were prepared for recording states of sleep and wakefulness and for the delivery of substances within the brainstem.…”

“…This structure contains a chemically diverse population of neurons that contain glutamate, glycine, GABA, Acetilcholine and several neuropeptides (Fort et al, 1989 and 1990; Holstege, 1996; Morales et al, 1999). In addition, numerous nitrergic neurons, named that way because they express the neuronal isoform of the enzyme nitric oxide synthase (nNOS), have been described in this region (Vincent and Kimura, 1992; Rodrigo et al, 1994; Batten et al, 2000; Pose et al, 2005; Travers et al, 2005).…”

“…Many studies indicate that this region of the reticular formation is involved in the generation of the motor atonia that occurs during the state of active sleep (AS; see for example Morales et al, 1999 and references therein). We have shown that it contains trigeminal premotor neurons that express c-fos during carbachol-induced active sleep (C-AS).…”

“…A subpopulation of these premotor neurons is glycinergic and appears to be responsible for the postsynaptic inhibition of motoneurons during AS (ibid, Morales et al, 2006). These studies were carried out in animals in which carbachol was injected in the Nucleus Pontis Oralis (NPO) to evoke long-lasting (1-2 hours) episodes of C-AS (Baghdoyan et al, 1987 and 1989; Morales et al, 1999). …”

Use of c-fos to identify activity-dependent spinal neurons after stepping in intact adult rats

“…These data demonstrate a pattern of activity that is similar to the last-order premotor interneurons that have been suggested to be responsible for producing locomotion. 33 Step-induced FOS pattern progressed rostrocaudally in the lumbar spinal cord The number of FOS þ neurons increased in the rostrocaudal direction with increasing duration of quadrupedal treadmill stepping. The largest number of FOS þ neurons were observed in the lumbar enlargement segments L3-L5.…”