Excitatory amino acid release in the locus coeruleus during naloxone-precipitated morphine withdrawal in adjuvant arthritic rats.

Objective: Excitatory amino acid levels in the locus coeruleus (LC) and the behavioral signs during naloxone-precipitated withdrawal in arthritic rats treated with chronic morphine were investigated by in vivo microdialysis.

Methods: Increases in glutamate (Glu) and aspartate (Asp) were noted after naloxone (48 nmol/5 microl, LC)-precipitated withdrawal from normal and adjuvant arthritic rats which had been intracerebroventricularly infused for 3 days with morphine (26 nmol/l microl/h).

Results: The increases in Glu and Asp levels on morphine withdrawal in normal rats were attenuated following naloxone challenge in the morphine-dependent arthritic rats. Moreover, behavioral signs during morphine withdrawal were detected following the naloxone challenge in both the morphine-dependent normal and adjuvant arthritic rats, but not in the saline-infused controls.

Conclusions: These results show that the attenuation of Glu and Asp release from the LC in the adjuvant arthritic rats might explain the anti-inflammatory and analgesic effects of mu-opioids in adjuvant arthritic rats.