Inhibition of TEA-induced LTP by aluminum

Brief application of tetraethylammonium (TEA) to hippocampal slices causes long-term potentiation (TEA LTP) at synapses of CA1 pyramidal neurons characterized by a long-lasting increase of field excitatory postsynaptic potential (fEPSP) slope and population spike (PS) amplitude. Since this kind of potentiation requires the activation of voltage-dependent calcium channels, we examined the effect of the inorganic calcium channel blocker aluminum, which has been shown to impair tetanus-induced LTP (eLTP). We found that Al inhibited in a concentration-dependent manner both fEPSP slope and PS amplitude potentiation by TEA; 0.68 microgram/ml A1 attenuated TEA LTP, while a complete block of long-lasting potentiation was obtained for 2.7 micrograms/ml Al. Occlusion experiments revealed that both concentrations of Al allowed the induction of eLTP 60 min after TEA/Al exposure. However, longer application (15 min) of 2.7 micrograms/ml Al before the induction of TEA LTP prevented the subsequent induction of eLTP although no significant differences concerning the action on TEA LTP were observed. This indicates a general loss of neuronal plasticity which might be due to progressive neuronal cell damage. Since the effective concentration range of Al is directly comparable to the action of Al on eLTP, our data provide evidence for shared mechanisms of both potentiations. Although based on different induction mechanisms, Ca2+ is assumed to be a general intracellular trigger for both forms of LTP and thus it can be hypothesized that the neurotoxic action of Al is due to interference with Ca(2+)-dependent processes by inhibition of calcium conductances.