Sensitization of spinal cord nociceptive neurons with a conjugate of substance P and cholera toxin.
BACKGROUND
Several investigators have coupled toxins to neuropeptides for the purpose of lesioning specific neurons in the central nervous system. By producing deficits in function these toxin conjugates have yielded valuable information about the role of these cells. In an effort to specifically stimulate cells rather than kill them we have conjugated the neuropeptide substance P to the catalytic subunit of cholera toxin (SP-CTA). This conjugate should be taken up selectively by neurokinin receptor expressing neurons resulting in enhanced adenylate cyclase activity and neuronal firing.


RESULTS
The conjugate SP-CTA stimulates adenylate cyclase in cultured cells that are transfected with either the NK1 or NK2 receptor, but not the NK3 receptor. We further demonstrate that intrathecal injection of SP-CTA in rats induces the phosphorylation of the transcription factor cyclic AMP response element binding protein (CREB) and also enhances the expression of the immediate early gene c-Fos. Behaviorally, low doses of SP-CTA (1 microg) injected intrathecally produce thermal hyperalgesia. At higher doses (10 microg) peripheral sensitivity is suppressed suggesting that descending inhibitory pathways may be activated by the SP-CTA induced sensitization of spinal cord neurons.


CONCLUSIONS
The finding that stimulation of adenylate cyclase in neurokinin receptor expressing neurons in the spinal cord produces thermal hyperalgesia is consistent with the known actions of these neurons. These data demonstrate that cholera toxin can be targeted to specific cell types by coupling the catalytic subunit to a peptide agonist for a g-protein coupled receptor. Furthermore, these results demonstrate that SP-CTA can be used as a tool to study sensitization of central neurons in vivo in the absence of an injury.
Caudle
Robert M
RM
Department of Oral and Maxillofacial Surgery and Diagnostic Sciences, University of Florida College of Dentistry, Gainesville, FL 32610, USA. caudle@ufl.edu
Mannes
Andrew J
AJ
Keller
Jason
J
Perez
Federico M
FM
Suckow
Shelby K
SK
Neubert
John K
JK
D000262:Adenylyl Cyclases / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D016466:CHO Cells; D002772:Cholera Toxin / Q000008:administration & dosage*; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D006930:Hyperalgesia / Q000503:physiopathology*; D007278:Injections, Spinal; D008297:Male; D009475:Neurons, Afferent / Q000187:drug effects*; D009619:Nociceptors / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D018040:Receptors, Neurokinin-1 / Q000378:metabolism*; D013116:Spinal Cord / Q000187:drug effects / Q000503:physiopathology*; D013373:Substance P / Q000008:administration & dosage*
D004338:Drug Combinations; D018040:Receptors, Neurokinin-1; D013373:Substance P; D002772:Cholera Toxin; D000262:Adenylyl Cyclases