Microdialysis studies of purine and monoamine release from the central nervous system in vivo

Ogilvy, Hilary V. (1996) Microdialysis studies of purine and monoamine release from the central nervous system in vivo. PhD thesis, University of Glasgow.

Abstract

The effects of kainic acid and potassium on the release of endogenous adenosine and its metabolites, inosine, hypoxanthine and xanthine, from the rat hippocampus have been studied by in vivo microdialysis. In the hippocampus of rats anaesthetised with urethane the concentration of extracellular adenosine was estimated to be 0.8muM during the first two hrs after insertion of the dialysis probe. Kainic acid (0.1-25mM) in the perfusate evoked a concentration-dependent release of adenosine with an EC50 of 0.94mM. A 5min pulse of ImM kainic acid in the perfusate, during a sampling period of one hour, increased the 20mul dialysate levels from 3.68 +/- 0.21 to 7.66 +/- 0.82 pmol (mean +/- sem). A second stimulation (S2) 3hrs (hours) after the first stimulation (SI) also induced adenosine release. The S2/S1 ratio was 0.46 +/- 0.02. Kainate- evoked release of adenosine was shown to involve the production of action potentials since TTX (tetrodotoxin) significantly reduced the S2/S1 ratio by 53.85%. The release was reduced by incorporation into the perfusate of CNQX (6-cyano-7-nitroquinoxaline-2,3-dione), a non-NMDA (N-methyl-D-aspartate) receptor antagonist, but not by NMDA receptor blockers, (+)-MK-801 (dizocilpine) or (+/-)-AP-5 ((+/-)-2-amino-5-phosphonopentanoic acid), indicating a non-NMDA receptor mediated process. The kappa agonist, U50 488H (trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benzeneactemide methanesulphonate hydrochloride), significantly reduced the S2/S1 ratio by 55.77%. Release was reduced significantly by 44.23% by ascorbic acid (an antioxidant), 48.08% by glutathione (a scavenger of hydroperoxides) and 71.15% by oxypurinol (a xanthine oxidase inhibitor) indicating the involvement of free radicals in kainate-evoked adenosine release. Neither the adenosine A1 receptor antagonist CPT (8-cyclopentyl-1,3-dimethylxanthine) nor the A1 receptor agonist R-PIA (R(-) N6-(2-phenylisopropyl)adenosine) affected kainate-evoked release of adenosine. This indicates that activation of A1 receptors, by endogenous adenosine or an agonist, does not inhibit kainate-evoked release of adenosine. The present results indicate that kainate-evoked release of adenosine may be mediated by non-NMDA receptor activation, possibly requiring the propagation of action potentials and free radical production.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Neurosciences
• Colleges/Schools: College of Medical Veterinary and Life Sciences
• Supervisor's Name: Stone, Professor Trevor
• Date of Award: 1996
• Depositing User: Enlighten Team
• Unique ID: glathesis:1996-71737
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 17 May 2019 09:31
• Last Modified: 08 Apr 2022 16:46
• Thesis DOI: 10.5525/gla.thesis.71737
• URI: https://theses.gla.ac.uk/id/eprint/71737