Plastic changes of calcitonin gene-related peptide in morphine tolerance: behavioral and immunohistochemical study in rats.
The present study was undertaken to investigate the plasticity of calcitonin gene-related peptide (CGRP) in antinociception after morphine tolerance in rats. The hindpaw withdrawal latencies (HWLs) to both thermal and mechanical stimulation increased significantly after intracerebroventricular injection of 2.5 nmol of CGRP in opioid-naive rats, indicating that CGRP produces an antinociceptive effect in the brain. Furthermore, there was an antinociceptive effect after intracerebroventricular injection of 2.5 nmol of CGRP in morphine-tolerant rats. Interestingly, the antinociceptive effect induced by intracerebroventricular injection of CGRP was lower in morphine-tolerant rats than that in opioid-naive rats at the same dose. At the same time, there was downregulation of CGRP-like immunoreactivity in both lateral septal nucleus and central nucleus of amygdala tested by immunohistochemical methods, whereas no significant changes were observed in arcuate nucleus of hypothalamus and periaqueductal gray after morphine treatment in rats. The present study demonstrates plastic changes in both CGRP-induced antinociception and CGRP-like immunoreactivity in rat brain after morphine tolerance, suggesting that CGRP may play an important role in morphine tolerance.
College of Life Sciences, Center for Brain and Cognitive Science and National Laboratory of Biomembrane and Membrane Biotechnology, Peking University, Beijing, People's Republic of China.
Xiang
X
Zhou
Jin-Ju
JJ
Li
Long-Chuan
LC
Yu
D000222:Adaptation, Physiological; D000679:Amygdala / Q000378:metabolism; D000700:Analgesics / Q000378:metabolism*; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism*; D015536:Down-Regulation; D004361:Drug Tolerance / Q000502:physiology*; D007150:Immunohistochemistry; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology; D010147:Pain Measurement; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time; D020665:Septum of Brain / Q000378:metabolism
D000700:Analgesics; D000701:Analgesics, Opioid; D009020:Morphine; D015740:Calcitonin Gene-Related Peptide