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Abstract:
Potential changes were investigated which follow the intra- and extracellular electrophoretic injection of NH4 + and also the intravenous application of neutral ammonium salts. The common effect found in all kinds of application is a depolarizing shift of the IPSP-equilibrium potential (EIPSP) towards the resting potential. Inhibitory transmission is preserved but produces considerably reduced hyperpolarizing potential changes at normal resting potentials. In addition, ammonium ions produce short term shifts of resting and overshoot potentials with intracellular application. The latter changes can be explained under the assumption that NH4 + partly substitutes for Na+ as for the action potential generation.
The observed reversible reduction of EIPSP has high sensitivity towards extracellular and systemic NH4 + application as compared to intracellular injection. The time course of the depolarizing shift of EIPSP, especially its restitution, was shortest in extracellular application. It is suggested that ammonium release from the internal site produces the long term effects observed on the IPSP after intracellular injection. The externally effective dosages correspond to intracerebral NH4 +-concentrations which are reported for preconvulsive states of various kinds of metabolically induced epilepsies.
