Alpha4* nicotinic receptors in preBotzinger complex mediate cholinergic/nicotinic modulation of respiratory rhythm.
Acetylcholine and nicotine can modulate respiratory patterns by acting on nicotinic acetylcholine receptors (nAChRs) in the preBötzinger complex (preBötC). To further explore the molecular composition of these nAChRs, we studied a knock-in mouse strain with a leucine-to-alanine mutation in the M2 pore-lining region (L9'A) of the nAChR alpha4 subunit; this mutation renders alpha4-containing receptors hypersensitive to agonists. We recorded respiratory-related rhythmic motor activity from hypoglossal nerve (XIIn) and patch-clamped preBötC inspiratory neurons in an in vitro medullary slice preparation from neonatal mice. Nicotine affected respiratory rhythm at concentrations approximately 100-fold lower in the homozygous L9'A knock-in mice compared with wild-type mice. Bath application of 5 nm nicotine increased the excitability of preBötC inspiratory neurons, increased respiratory frequency, and induced tonic/seizure-like activities in XIIn in L9'A mice, effects similar to those induced by 1 microM nicotine in wild-type mice. In L9'A mice, microinjection of low nanomolar concentrations of nicotine into the preBötC increased respiratory frequency, whereas injection into the ipsilateral hypoglossal (XII) nucleus induced tonic/seizure-like activity. The alpha4*-selective nAChR antagonist dihydro-beta-erythroidine produced opposite effects and blocked the nicotinic responses. These data, showing that nAChRs in the preBötC and XII nucleus in L9'A mice are hypersensitive to nicotine and endogenous ACh, suggest that functional alpha4* nAChRs are present in the preBötC. They mediate cholinergic/nicotinic modulation of the excitability of preBötC inspiratory neurons and of respiratory rhythm. Furthermore, functional alpha4* nAChRs are present in XII nucleus and mediate cholinergic/nicotinic modulation of tonic activity in XIIn.
Shao
Xuesi M
XM
Department of Neurobiology, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, California 90095-1763, USA. mshao@ucla.edu
Tan
Wenbin
W
Xiu
Joanne
J
Puskar
Nyssa
N
Fonck
Carlos
C
Lester
Henry A
HA
Feldman
Jack L
JL
D000818:Animals; D004079:Dihydro-beta-Erythroidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009474:Neurons / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009538:Nicotine / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000494:pharmacology*; D018733:Nicotinic Antagonists / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D010507:Periodicity; D021122:Protein Subunits / Q000235:genetics* / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000235:genetics* / Q000378:metabolism; D012119:Respiration / Q000187:drug effects / Q000235:genetics; D012125:Respiratory Center / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D014982:Xenopus laevis
D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D021122:Protein Subunits; D011978:Receptors, Nicotinic; D004079:Dihydro-beta-Erythroidine; D009538:Nicotine