Increased sensitivity to the antinociceptive activity of (+/-)-baclofen in an animal model of chronic neuropathic, but not chronic inflammatory hyperalgesia.
Modulation of sensory afferent inputs to the spinal cord by GABA appears to be an important physiological mechanism and may provide an antinociceptive control system. In the present study we have evaluated the antinociceptive activity of the GABAB receptor agonist, (+/-)-baclofen, in rats with unilateral chronic inflammatory or neuropathic hyperalgesia. (+/-)-Baclofen was antinociceptive in untreated control animals and both animal models. In the neuropathic model the sensitivity to (+/-)-baclofen was significantly increased by 3-fold in the ipsilateral limb. By contrast, in animals with chronic inflammation no difference in sensitivity between ipsilateral and contralateral limbs to (+/-)-baclofen was observed. Receptor autoradiographic analysis in spinal cord sections revealed no increase in the density of GABAB receptor binding sites and no change in receptor affinity in the neuropathic model.
Department of Gastrointestinal Pharmacology, Glaxo Group Research Ltd, Ware, Herts., U.K.
G D
GD
Smith
S M
SM
Harrison
P J
PJ
Birch
P J
PJ
Elliott
M
M
Malcangio
N G
NG
Bowery
D000700:Analgesics / Q000627:therapeutic use*; D000818:Animals; D001345:Autoradiography; D001418:Baclofen / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D058786:GABA-B Receptor Agonists; D006930:Hyperalgesia / Q000188:drug therapy* / Q000209:etiology* / Q000473:pathology; D007249:Inflammation / Q000150:complications* / Q000473:pathology; D008297:Male; D009422:Nervous System Diseases / Q000150:complications* / Q000473:pathology; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects; D051381:Rats; D018080:Receptors, GABA-B / Q000378:metabolism; D012584:Sciatic Nerve / Q000502:physiology
D000700:Analgesics; D058786:GABA-B Receptor Agonists; D018080:Receptors, GABA-B; D001418:Baclofen