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pubmed:abstractText |
Electrical stimulation (3 Hz, 2 msec duration, 5-12 V for 2 min every 20 min) of cortical slices from the rat, previously incubated with [3H]noradrenaline, evoked a release of tritium which was inhibited by morphine, normorphine, Tyr-D-Ala-Gly-MePhe-NH(CH2) 2OH ( RX783006 ) and D-Ala2-D-Leu5-enkephalin ( pIC30 5.90, 6.32, 7.45 and 6.74 respectively). Naloxone did not affect the release of tritium when given alone but antagonised the actions of the opioids, giving a Ke value of about 3 nM irrespective of the particular agonist used, which suggests an action at mu receptors. The delta opioid receptor blocker, ICI154129 , antagonised the opioids only in large concentrations (Ke 21300 nM). In slices previously incubated with [3H]5-hydroxytryptamine, electrical stimulation increased overflow of tritium but neither naloxone nor the opioid agonists affected evoked overflow of tritium at concentrations which were effective in slices incubated with [3H]noradrenaline. It is concluded that stimulation of mu opioid receptors may inhibit release of noradrenaline from central noradrenergic neurones and that these receptors are not present in significant numbers on neurones releasing 5-hydroxytryptamine in the cortex.
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