Nicotine differentially activates inhibitory and excitatory neurons in the dorsal spinal cord.
Nicotinic agonists have well-documented antinociceptive properties when administered subcutaneously or intrathecally in mice. However, secondary mild to toxic effects are observed at analgesic doses, as a consequence of the activation of the large family of differentially expressed nicotinic receptors (nAChRs). In order to elucidate the action of nicotinic agonists on spinal local circuits, we have investigated the expression and function of nAChRs in functionally identified neurons of neonate mice spinal cord. Molecular markers, amplified at the single-cell level by RT-PCR, distinguished two neuronal populations in the dorsal horn of the spinal cord: GABAergic/glycinergic inhibitory interneurons, and calbindin (CA) or NK1 receptor (NK1-R) expressing, excitatory interneurons and projection neurons. The nicotinic response to acetylcholine of single cells was examined, as well as the pattern of expression of nAChR subunit transcripts in the same neuron. Beside the most expressed subunits alpha4, beta2 and alpha7, the alpha2 subunit transcript was found in 19% of neurons, suggesting that agonists targeting alpha2* nAChRs may have specific actions at a spinal level without major supra-spinal effects. Both inhibitory and excitatory neurons responded to nicotinic stimulation, however, the nAChRs involved were markedly different. Whereas GABA/glycine interneurons preferentially expressed alpha4alpha6beta2* nAChRs, alpha3beta2alpha7* nAChRs were preferentially expressed by CA or NK1-R expressing neurons. Recorded neurons were also classified by firing pattern, for comparison to results from single-cell RT-PCR studies. Altogether, our results identify distinct sites of action of nicotinic agonists in circuits of the dorsal horn, and lead us closer to an understanding of mechanisms of nicotinic spinal analgesia.
Cordero-Erausquin
Matilde
M
Récepteurs et Cognition, CNRS URA2182, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris Cedex 15, France.
Pons
Stéphanie
S
Faure
Philippe
P
Changeux
Jean-Pierre
JP
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000344:Afferent Pathways / Q000187:drug effects* / Q000502:physiology; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D015415:Biomarkers; D064026:Calbindins; D003712:Dendrites / Q000187:drug effects / Q000502:physiology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005998:Glycine / Q000378:metabolism; D066298:In Vitro Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009538:Nicotine / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology; D010146:Pain / Q000188:drug therapy* / Q000503:physiopathology; D020671:Posterior Horn Cells / Q000187:drug effects* / Q000502:physiology; D021122:Protein Subunits / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D018040:Receptors, Neurokinin-1 / Q000235:genetics; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000235:genetics; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D000700:Analgesics; D015415:Biomarkers; D064026:Calbindins; D021122:Protein Subunits; D012333:RNA, Messenger; D018040:Receptors, Neurokinin-1; D011978:Receptors, Nicotinic; D064030:S100 Calcium Binding Protein G; D005680:gamma-Aminobutyric Acid; D009538:Nicotine; D005998:Glycine