Excitatory transmitter amino acid release from the ischemic rat cerebral cortex: effects of adenosine receptor agonists and antagonists.
The effects of selective adenosine receptor agonists [N6-cyclopentyladenosine (CPA) and N-ethylcarboxamidoadenosine (NECA)] and antagonists [8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and 9-chloro-2-(2-furanyl)-5,6-dihydro-1,2,4-triazolo[1,5-c]quinazoline-5-im ine (CGS-15943A)] on aspartate and glutamate release from the ischemic rat cerebral cortex were studied with the cortical cup technique. Cerebral ischemia (for 20 min) was elicited by four-vessel occlusion. Excitatory amino acid releases were compared from control ischemic rats and drug-treated rats. Basal levels of aspartate and glutamate release were not greatly affected by pretreatment with the adenosine receptor agonists or antagonists. However, CPA (10(-10) M) and NECA (10(-9) M) significantly inhibited the ischemia-evoked release of aspartate and glutamate into cortical superfusates. The ability to block ischemia-evoked release of excitatory amino acids was not evident at higher concentrations of CPA (10(-6) M) or NECA (10(-5) M). The selective A1 receptor antagonist DPCPX also had no effect on release when administered at a low dosage (0.01 mg/kg, i.p.) but blocked the ischemia-evoked release of aspartate and glutamate at a higher dosage (0.1 mg/kg). Evoked release was inhibited by the selective A2 receptor antagonist CGS-15943A (0.1 mg/kg, i.p.). Thus, adenosine and its analogs may suppress ischemia-evoked release of excitatory neurotransmitter amino acids via high-affinity A1 receptors, whereas coactivation of lower-affinity A2 receptors may block (or reverse) the A1-mediated response.
Simpson
R E
RE
Department of Physiology, School of Medicine, Wayne State University, Detroit, Michigan.
O'Regan
M H
MH
Perkins
L M
LM
Phillis
J W
JW
D000241:Adenosine / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology; D019830:Adenosine-5'-(N-ethylcarboxamide); D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism*; D002545:Brain Ischemia / Q000378:metabolism*; D002540:Cerebral Cortex / Q000378:metabolism*; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D008297:Male; D018377:Neurotransmitter Agents / Q000378:metabolism; D058914:Purinergic Antagonists; D011799:Quinazolines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011983:Receptors, Purinergic / Q000502:physiology*; D014230:Triazoles / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
D005971:Glutamates; D018377:Neurotransmitter Agents; D058914:Purinergic Antagonists; D011799:Quinazolines; D011983:Receptors, Purinergic; D014230:Triazoles; D014970:Xanthines; D001224:Aspartic Acid; D019830:Adenosine-5'-(N-ethylcarboxamide); D018698:Glutamic Acid; C048599:N(6)-cyclopentyladenosine; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000241:Adenosine; C052410:9-chloro-2-(2-furyl)-(1,2,4)triazolo(1,5-c)quinazolin-5-imine