Effects of morphine-3-glucuronide and morphine on the K+-evoked release of [3H]-glutamic acid and [14C]-gamma-aminobutyric acid from rat brain synaptosomes.
The effects of morphine-3-glucuronide (M3G) and morphine on the K+-evoked release of [14C]-gamma-aminobutyric acid (GABA) and [3 H]-glutamic acid were investigated in rat brain synaptosomes using superfusion techniques. K+-evoked release of both [14C]-GABA and [3H]-glutamic acid from rat brain synaptosomes was eliminated in the absence of calcium, indicating that K+-evoked neurotransmitter release was from vesicular stores in a manner analagous to that which occurs in vivo following an action potential (1). Addition of M3G or morphine in a range of concentrations (0.1-10 microM) to the superfusion medium did not alter the K+-evoked release of [14C]-GABA or [3H]-glutamic acid from rat brain synaptosomes, suggesting that the CNS excitation observed following central administration of M3G (2-5) and supra-analgesic doses of morphine (2,3,6,7) does not occur by a generalized inhibition of GABA release or facilitation of glutamic acid release from pre-synaptic nerve terminals.
Bartlett
S E
SE
Department of Pharmacy, The University of Queensland, Brisbane, Queensland, Australia.
Smith
M T
MT
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001921:Brain / Q000502:physiology*; D002122:Calcium Chloride / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009022:Morphine Derivatives / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D009022:Morphine Derivatives; D014316:Tritium; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D009020:Morphine; D004492:Edetic Acid; D002122:Calcium Chloride; C018108:morphine-3-glucuronide; D011188:Potassium