Synaptic delay and conduction time in brain during exposure to simulated high altitudes.

Abstract

RELATIVELY few techniques are available for the investigation of the long-term effects of physiological variables on conduction times and synaptic delay in the brain. The lateral olfactory tract (LOT) and prepyriform cortex provide a system whereby these parameters may be measured in rats chronically implanted with electrodes1. Fibres of the LOT synapse with dendrites of the prepyriform pyramidal cells2. When the LOT is electrically stimulated by a single shock, both the presynaptic LOT potential and the postsynaptic prepyriform response may be recorded from electrodes placed in the prepyriform cortex (Fig. 1). As the LOT potential first approaches and then invades the recording area, the adjacent cortex acts first as a current source and then as a sink; hence the presynaptic potential is biphasic—first positive, then negative. The time from stimulus artefact to negative crest of the presynaptic potential is a measure of conduction time along the LOT and the time from the negative peak to beginning of the prepyriform response is a measure of synaptic delay (Fig. 1).