Atropine microdialysis within or near the pre-Bötzinger Complex increases breathing frequency more during wakefulness than during NREM sleep

Abstract

Muere C, Neumueller S, Miller J, Olesiak S, Hodges MR, Pan L, Forster HV. Atropine microdialysis within or near the pre-Bötzinger Complex increases breathing frequency more during wakefulness than during NREM sleep. J Appl Physiol 114: 694-704, 2013. First published December 27, 2012 doi:10.1152/japplphysiol.00634.2012.-Normal activity of neurons within the medullary ventral respiratory column (VRC) in or near the pre-Bötzinger Complex (preBötC) is dependent on the balance of inhibitory and excitatory neuromodulators acting at their respective receptors. The role of cholinergic neuromodulation during awake and sleep states is unknown. Accordingly, our objective herein was to test the hypotheses that attenuation of cholinergic modulation of VRC/ preBötC neurons in vivo with atropine would: 1) decrease breathing frequency more while awake than during non-rapid-eye-movement (NREM) sleep and 2) increase other excitatory neuromodulators. To test these hypotheses, we unilaterally dialyzed mock cerebrospinal fluid (mCSF) or 50 mM atropine in mCSF in or near the preBötC region of adult goats during the awake (n ϭ 9) and NREM sleep (n ϭ 7) states. Breathing was monitored, and effluent dialysate was collected for analysis of multiple neurochemicals. Compared with dialysis of mCSF alone, atropine increased (P Ͻ 0.05) breathing frequency while awake during the day [ϩ10 breaths (br)/min] and at night (ϩ9 br/min) and, to a lesser extent, during NREM sleep (ϩ5 br/min). Atropine increased (P Ͻ 0.05) effluent concentrations of serotonin (5-HT), substance P (SP), and glycine during the day and at night. When atropine was dialyzed in one preBötC and mCSF in the contralateral preBötC, 5-HT and SP increased only at the site of atropine dialysis. We conclude: 1) attenuation of a single neuromodulator results in local changes in other neuromodulators that affect ventilatory control, 2) effects of perturbations of cholinergic neuromodulation on breathing are state-dependent, and 3) interpretation of perturbations in vivo requires consideration of direct and indirect effects.neuromodulators; control of breathing; acetylcholine; non-rapid-eyemovement sleep THE NEUROMODULATOR ACETYLCHOLINE (ACh) is involved in a variety of central and peripheral neural circuits, including the control of breathing and sleep (7,12,16,19,25,39). The effects of ACh are mediated through either nicotinic or muscarinic receptors coupled to second messenger pathways (6, 10, 13, 42). There are five known muscarinic ACh receptor (mAChR) subtypes (M 1 to M 5 ) expressed in the brain stem, differing in expression profiles and in effects on breathing (2,9,11,13,33,34). For example, the pontine respiratory group (PRG) nuclei express M 1 -M 3 mAChRs (34). The predominant effect of cholinergic modulation of PRG neurons within the Kölliker-Fuse Nucleus (KFN) appears to be excitatory, since reverse dialysis of the nonselective mAChR antagonist atropine reduced minute ventilation (V I ) and breathing frequency in both the awake state and during non-rapid-eye-movement (NREM...

Severe peri-ictal respiratory dysfunction is common in Dravet syndrome

“…Muscarinic receptors in the medulla play an important role in respiratory control (51, 52) and central respiratory CO 2 chemoreception (53,54). Depending on the site of action, muscarinic receptor activation can either stimulate or inhibit breathing (51,52,54,69,70). Acetylcholinesterase inhibitors block central respiratory rhythm generation via an effect in the brain stem (69,71), and this central apnea can be prevented by atropine (72).…”

Blockade of neurokinin-1 receptors in the ventral respiratory column does not affect breathing but alters neurochemical release

“…All effluent dialysate samples were analyzed by a core assay lab, as previously described (28). Briefly, glutamine (GLN), glycine (GLY), GABA, and 5-HT were measured via reverse-phase high-performance liquid chromatography with a Waters Resolve C 18 column.…”

“…The present studies were carried out by identical methodologies and under the same conditions as time control studies (28). We have decided to reuse and reanalyze these control data for two important reasons: 1) to minimize the number of goats used, since repetition of control experiments may violate policies regarding using the smallest number of animals to address scientific questions, and 2) we believe that direct comparisons between time control data and data from the present study are necessary for scientific interpretation and to frame our present results in context with previous findings.…”

“…Furthermore, studies in anesthetized mice suggest that tonic activation of NK1Rs in the preBötC becomes particularly important when ␣1 noradrenergic receptors and serotonin (5-HT) type 2 receptors are blocked (10). Finally, our group has previously found that reverse dialysis of a muscarinic cholinergic receptor antagonist (atropine) in the ventral respiratory column (VRC) of intact goats, during wakefulness and sleep, elicits a significant increase in breathing frequency (28). This increase in frequency may have been mediated by concurrent increases in 5-HT and SP (28), perhaps due to corelease of these neurochemicals from a subset of raphé serotonergic neurons that colocalize SP and project to the preBötC (33).…”

“…Finally, our group has previously found that reverse dialysis of a muscarinic cholinergic receptor antagonist (atropine) in the ventral respiratory column (VRC) of intact goats, during wakefulness and sleep, elicits a significant increase in breathing frequency (28). This increase in frequency may have been mediated by concurrent increases in 5-HT and SP (28), perhaps due to corelease of these neurochemicals from a subset of raphé serotonergic neurons that colocalize SP and project to the preBötC (33). If such were the case, these findings would be consistent with the concept of neuromodulator interdependence, whereby attenuation of one neuromodulator is locally compensated for by changes in other neuromodulators (e.g., an increase in excitatory neurochemicals or a decrease in inhibitory neurotransmitters).…”