Excitatory and inhibitory autaptic currents in isolated hippocampal neurons maintained in cell culture.

Individual rat hippocampal neurons, grown in isolation from other neurons on small spots of permissive substrate, were studied in order to characterize the electrical properties of the synapses that such cells formed with themselves (autapses). Excitatory (probably glutamatergic) or inhibitory (probably type A gamma-aminobutyratergic) autapses were frequently found. Excitatory autaptic currents reversed near the potential expected for monovalent cations were blocked by the glutamatergic antagonist kynurenic acid, and possessed a slow component with the pharmacological profile of N-methyl-D-aspartate-type channels. These currents also exhibited trial-to-trial statistical fluctuations in their amplitudes, this being well-described by quantal analysis. Inhibitory autaptic currents reversed at hyperpolarized potentials, as expected for chloride-permeable pores and were blocked by picrotoxin, a type A gamma-aminobutyric receptor antagonist. It is concluded that autaptic currents in culture are identical to those found at synapses.