A depolarizing inhibitory potential in neurones of the olfactory cortex in vitro.

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Abstract
Stable intracellular recordings were obtained from neurons in slices of the guinea pig olfactory cortex maintained in vitro. Single stimuli applied to the lateral olfactory tract (LOT) produced an excitatory post-synaptic potential (EPSP) usually generating a single spike. The EPSP was followed by a long (200-500 ms) after-depolarization (LAD) of peak amplitude 5-16 mV. This was accompanied by a vary large conductance increase and was associated with an inhibition of the intracellularly recorded EPSP and of spike generation. The LAD was more susceptible than the EPSP to depression by repetitive LOT stimulation and raising external [Mg2+]. The LAD could be generated without a preceding spike. At an average resting membrane potential of -74 mV the average reversal potential for the LAD (Elad) was -63 mV. Elad became more positive on reducing [Cl-]out or on using KCl-filled electrodes. Apparently the LAD represents a Cl--mediated inhibitory postsynaptic potential, generated through deep-lying recurrent inhibitory loops.