title: Microdialysis of extracellular endogenous opioid peptides from rat brain in vivo.
abstract: The combination of microdialysis and a highly sensitive radioimmunoassay was developed in order to monitor the in vivo extracellular levels of endogenous opioid peptides from discrete regions of the rat brain. The radioimmunoassay cross-reacts 100% with peptides with alpha N-acetyl Tyr.Gly.Gly.Phe-Met or -Leu at the N terminus and thus recognizes all known endogenous opioid peptide fragments following acetylation of the sample. The assay was conducted on solid phase with antibody bound via protein A to 96-well plates and provided a limit of detection of approximately 0.2 fmol. A variety of dialysis membranes were evaluated with respect to their efficiency in recovering opioid peptides in vitro. Custom-made probes (4 mm active length) manufactured from polyacrylonitrile membranes and commercially available polycarbonate membrane probes proved most suitable with relative recoveries for [Met]- and [Leu]enkephalin in the range 6-10% at a flow rate of 2.7 microliters/min. Probes implanted in the globus pallidus/ventral pallidum of halothane/N2O anaesthetized rats recovered approximately 1.5 fmol of immunoreactive opioid material per 30-min sample in the absence of peptidase inhibitors. The majority of this immunoreactivity co-eluted with [Met]- and [Leu]enkephalin on reverse-phase high-performance liquid chromatography. A 2-min pulse of 100 mM K(+)-containing artificial cerebrospinal fluid in the perfusion medium during a 30-min sampling period increased the recovered immunoreactive material to 43.9 fmol +/- 12.4 S.E.M. A second stimulation 3 h later also resulted in elevated levels with an S2:S1 ratio of 0.64 +/- 0.03. The second stimulation was completely blocked by perfusion of a 10 mM EGTA-containing medium, basal release on average remaining unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Psychiatry and Behavioral Sciences, Stanford University Medical Center, CA 94305.
authors.forename: N T
authors.initials: NT
authors.lastname: Maidment
authors.forename: D R
authors.initials: DR
authors.lastname: Brumbaugh
authors.forename: V D
authors.initials: VD
authors.lastname: Rudolph
authors.forename: E
authors.initials: E
authors.lastname: Erdelyi
authors.forename: C J
authors.initials: CJ
authors.lastname: Evans
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives* / Q000378:metabolism; D004745:Enkephalins / Q000378:metabolism*; D008297:Male; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D004745:Enkephalins; D004744:Enkephalin, Methionine; C027511:enkephalin-Met, Arg(6)-Phe(7)-; C033453:enkephalin-Met, Arg(6)-Gly(7)-Leu(8)-