Abstract
The effects of dynorphin-A, dermorphine and morphine on the secretion of transmitter from the toad ( Bufo marinus) motor nerve terminal have been determined. Intracellular recordings of miniature end plate potentials (m.e.p.p.s) and evoked end plate potentials (e.p.p.s) were used to estimate quantal content ( m ̄ ) and binomial parameters p and n. Dynorphin-A, and to a lesser extent morphine, decreased ( m ̄ ) while dermorphine had no significant effect on m ̄ . Dynorphin-A (ED 50 = 24 μM) was 21 times more potent then morphine (ED 50 = 510 μM) in decreasing m ̄ . The decrease in m ̄ produced by dynorphin-A and morphine was accompanied by a greater decrease in the variance ( S 2) of number of quanta secreted per stimulation over the recording period. The decrease in m ̄ produced by dynorphin-A, and to a lesser extent by morphine, is probably mediated by the opiates acting on κ-opioid receptors.
Published Version
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