Neuronal nitric oxide synthase is upregulated in a subset of primary sensory afferents after nerve injury which are necessary for analgesia from alpha2-adrenoceptor stimulation.
alpha2-Adrenoceptor (AR) agonists increase in analgesic potency and efficacy after peripheral nerve injury, and their effects are blocked by neuronal nitric oxide synthase (nNOS) inhibitors and M4 muscarinic receptor antagonists only after injury. We tested whether nNOS and M4 muscarinic receptors are co-expressed in the spinal cord, and whether destruction of a subset of sensory afferents which are essential to alpha2-AR analgesia would also destroy nNOS and M4 receptor expression. Male Sprague-Dawley rats underwent left L5 and L6 spinal nerve ligation. Lumbar spinal cord was removed and immunostained for M4 muscarinic receptors and nNOS alone and for co-expression. Others received intrathecal injection of saporin linked to an antibody to the neurotrophin receptor p75(NTR), which eliminates cells expressing this receptor and the analgesic effects of alpha2-AR agonists. nNOS staining of fibers in the superficial dorsal horn was dramatically increased after spinal nerve ligation, and this was abolished by saporin linked anti-p75(NTR) treatment. In contrast, nNOS staining in dorsal horn neurons was unaltered by these manipulations. M4 receptors were present on neurons in the dorsal horn, some of which co-expressed nNOS, but their pattern of expression was not altered by these manipulations. Peripheral nerve injury increases nNOS expression in fibers in the superficial dorsal horn, some of which likely express p75(NTR), and alpha2-AR agonists may reduce injury-induced sensitization by activation of nNOS in these fibers In contrast, changes in nNOS and M4 receptor location on spinal cord neurons are not responsible for increased analgesic potency of alpha2-AR agonists after nerve injury.
Ma
Weiya
W
Department of Anesthesiology and Center for the Study of Pharmacologic Plasticity in the Presence of Pain, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157-1009, USA.
Eisenach
James C
JC
D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D004195:Disease Models, Animal; D005727:Ganglia, Spinal / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D008026:Ligation; D008297:Male; D009437:Neuralgia / Q000188:drug therapy / Q000378:metabolism / Q000503:physiopathology; D009475:Neurons, Afferent / Q000187:drug effects / Q000378:metabolism*; D009498:Neurotoxins / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism*; D009619:Nociceptors / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010523:Peripheral Nervous System Diseases / Q000188:drug therapy / Q000378:metabolism* / Q000503:physiopathology; D020671:Posterior Horn Cells / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D043588:Receptor, Muscarinic M4 / Q000187:drug effects / Q000378:metabolism; D020800:Receptor, Nerve Growth Factor / Q000187:drug effects / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D013126:Spinal Nerve Roots / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D013127:Spinal Nerves / Q000293:injuries / Q000378:metabolism / Q000503:physiopathology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D009498:Neurotoxins; D043588:Receptor, Muscarinic M4; D020800:Receptor, Nerve Growth Factor; D018341:Receptors, Adrenergic, alpha-2; D009569:Nitric Oxide; D052248:Nitric Oxide Synthase Type I