Long-term potentiation in the piriform cortex is blocked by lead

Abstract

1. Long-term potentiation (LTP) is a prolonged increase in synaptic efficacy that is triggered by a brief tetanic stimulation at certain central synapses. LTP is one of the best available model systems available to the neurophysiologist of neuronal plasticity such as that underlying learning and memory. 2. We have studied the susceptibility of LTP to blockade by lead as a test of the hypothesis that the negative effect of lead on intelligence in children may result from interference with this process. LTP was studied in slices of rat piriform cortex. At this site, as in many other central synapses, LTP requires activation of postsynaptic N-methyl-D-aspartate (NMDA) receptors, and we investigated whether lead actions, if any, were mediated via effects on NMDA-activation ion channels or, alternatively, at voltage-activated calcium channels. 3. We find that lead blocks LTP at low micromolar concentrations. However, concentrations of lead that totally block LTP had no apparent effect on either NMDA-activated responses or presynaptic calcium channels, as monitored by transmitter release from presynaptic terminals. 4. While the mechanism of lead blockade of LTP remains to be determined, these observations are consistent with the hypothesis that the cognitive effects of lead neurotoxicity may result from effects on LTP.