title: Cerebrospinal fluid beta-endorphin in models of hyperalgesia in the rat.
abstract: Cerebrospinal fluid (CSF) obtained by acute percutaneous puncture of the cisternal membrane of the halothane anesthetized rat has low but measurable concentrations of beta-endorphin-like immunoreactivity (beta-EPir: 32.8 +/- 3.0 pmol/l). Chromatographic separation of beta-EPir showed that authentic beta-endorphin1-31 was the main component of beta-EPir in cisternal CSF. Subcutaneous injection of 5% formalin in the hind paws did not increase beta-EPir in cisternal CSF. Rats with tactile paw hyperalgesia evoked by unilateral ligation of the L5/6 nerve roots 2 weeks earlier had beta-EPir concentrations that did not differ from sham operated or unoperated control animals. In contrast, capsaicin injected in the hindpaws increased the mean beta-EPir concentration compared to saline injections (P = 0.006) 45 min after emerging from anesthesia following injection. These results show that acute activation of C fibers (by capsaicin) will evoke the release of beta-endorphin into the CSF, suggesting activation of the beta-endorphin terminal systems in the brain/midbrain. The failure of formalin injections to release beta-EPir to CSF may be due to specificity of the afferent stimulus evoking beta-EPir release, a lower stimulus intensity, and/or the duration of the stimulus generated by formalin. The normal concentrations of beta-EPir found in the hyperalgesic state following nerve injury suggest that the supraspinal beta-endorphin system does not display tonic changes under such conditions.
authors.affiliation: Anesthesiology Research Laboratory, University of California San Diego, La Jolla, CA 92093-0818, USA.
authors.forename: F W
authors.initials: FW
authors.lastname: Bach
authors.forename: S R
authors.initials: SR
authors.lastname: Chaplan
authors.forename: J
authors.initials: J
authors.lastname: Jang
authors.forename: T L
authors.initials: TL
authors.lastname: Yaksh
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004195:Disease Models, Animal; D006930:Hyperalgesia / Q000134:cerebrospinal fluid*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D001615:beta-Endorphin / Q000134:cerebrospinal fluid*
chemical_list: D001615:beta-Endorphin