Systemic administration of anti-NGF increases A-type potassium currents and decreases pancreatic nociceptor excitability in a rat model of chronic pancreatitis.
We have previously shown that pancreatic sensory neurons in rats with chronic pancreatitis (CP) display increased excitability associated with a decrease in transient inactivating potassium currents (I(A)), thus accounting in part for the hyperalgesia associated with this condition. Because of its well known role in somatic hyperalgesia, we hypothesized a role for the nerve growth factor (NGF) in driving these changes. CP was induced by intraductal injection of trinitrobenzene sulfonic acid (TNBS) in rats. After 3 wk, anti-NGF antibody or control serum was injected intra-peritoneally daily for 1 wk. This protocol was repeated in another set of experiments in control rats (receiving intraductal PBS instead of TNBS). Pancreatic nociceptors labeled with the dye Dil were identified, and patch-clamp recordings were made from acutely dissociated DRG neurons. Sensory neurons from anti-NGF-treated rats displayed a lower resting membrane potential, increased rheobase, decreased burst discharges in response to stimulatory current, and decreased input resistance compared with those treated with control serum. Under voltage-clamp condition, neuronal I(A) density was increased in anti-NGF-treated rats compared with rats treated with control serum. However, anti-NGF treatment had no effect on electrophysiological parameters in neurons from control rats. The expression of Kv-associated channel or ancillary genes Kv1.4, 4.1, 4.2, 4.3, and DPP6, DPP10, and KCHIPs 1-4 in pancreas-specific nociceptors was examined by laser-capture microdissection and real-time PCR quantification of mRNA levels. No significant differences were seen among those. These findings emphasize a key role for NGF in maintaining neuronal excitability in CP specifically via downregulation of I(A) by as yet unknown mechanisms.
Department of Medicine, Division of Gastroenterology and Hepatology, Stanford University School of Medicine, Stanford, California 94305, USA.
Yaohui
Y
Zhu
Kshama
K
Mehta
Cuiping
C
Li
Guang-Yin
GY
Xu
Liansheng
L
Liu
Tugba
T
Colak
Mohan
M
Shenoy
Pankaj Jay
PJ
Pasricha
D000818:Animals; D015536:Down-Regulation / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D020932:Nerve Growth Factor / Q000037:antagonists & inhibitors*; D009619:Nociceptors / Q000187:drug effects*; D050500:Pancreatitis, Chronic / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D015221:Potassium Channels / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011984:Sensory Receptor Cells / Q000502:physiology
D015221:Potassium Channels; D020932:Nerve Growth Factor