Morphine induces a spontaneous and evoked bursting activity in rat cortical neurons by adding a postsynaptic active mechanism to the synaptic input: an intracellular study in vivo.
The action of morphine on spontaneous and stimulus-evoked postsynaptic potentials was investigated in rat cortical neurons recorded intracellularly in vivo. Iontophoretically applied, morphine increased supra-threshold evoked depolarizing postsynaptic potentials inducing bursts of spikes, but only slightly increased weak (subthreshold) potentials. Spontaneous excitatory postsynaptic potentials were affected in a similar way, but their frequency did not change. Inhibitory postsynaptic potentials were only subsequently modified. Membrane hyperpolarization, induced by negative current injection, counteracts the morphine-induced burst generation. We suggest that the action of this alkaloid on threshold postsynaptic events involves a voltage-dependent mechanism, which may be triggered by synaptic currents.
Clinica Neurologica, II Universita' di Roma, Italy.
P
P
Stanzione
A
A
Stefani
G
G
Bernardi
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009020:Morphine / Q000494:pharmacology*; D009044:Motor Cortex / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D013003:Somatosensory Cortex / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*
D009020:Morphine