Intracellularly-recorded effects of glutamate and aspartate on neurones in the guinea-pig olfactory cortex slice

The effects of bath-applied glutamate, aspartate (and some related amino acids) on neurones of the guinea pig olfactory cortex slice were recorded intracellularly. Neurones were activated either by intracellularly-applied current or orthodromically by stimulating the lateral olfactory tract. In response to orthodromic stimuli several neurones displayed a late hyperpolarizing potential (LHP) after the usual sequence of EPSP, spike and IPSP. Glutamate and aspartate evoked 3 types of response: (a) a depolarization with apparent increase in input conductance; (b) a depolarization with no detectable conductance change; and (c) a hyperpolarization with conductance increase. Some possible mechanisms by which these 3 response-types could be generated are discussed. Depolarizations evoked by the glutamate analogue, kainate, were usually irreversible. Our results emphasize that glutamate and aspartate can evoke a variety of neuronal responses from olfactory cortex neurones. Several of these responses were previously undetected in experiments based on extracellular recordings.