Potentiation of postsynaptic potentials in motoneurons of the frog,Rana ridibunda, by gallamine
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The potentiating effect of gallamine on postsynaptic potentials was studied intracellularly on the preparation of the isolated spinal cord of the frog,Rana ridibunda. The amplitude both of afferentPSP (stimulation of DR) and of descendingPSP (stimulation of LC and VC) increased to 200–600% of the initial value. The responses reached 20 mV, and a convulsive effect developed. Both early (mono- and disynaptic) and late components were considerably potentiated. New components, absent prior to the gallamine application, appeared. Responses to a shortterm application of glutamate were potentiated much less than PSP in the same cell. NMDAresponses were not potentiated. Brain treatment with EAA blockers showed that potentiation and convulsive effect might appear under conditions of blockage of NMDA receptors but not under conditions of blockage of non-NMDA receptors. Gallamine eliminated inhibition evoked by the agents that block EAA. After gallamine application the duration of antidromic and orthodromic AP did not change substantially, while after-depolarization increased considerably, which resulted in generation of 2-3 AP in response to a single stimulus. A competitive blocker of cholinergic transmission, d-tubocurarine, did not potentiate PSP but increased synaptic noise. Mechanisms of gallamine action are discussed.
KeywordsNMDA Receptor Evolutionary Biochemistry Bicucullin Normal Solution Ventral Root
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