Two different forms of long-term potentiation at CA1-subiculum synapses

Distinct functional roles in learning and memory are attributed to certain areas of the hippocampus and the parahippocampal region. The subiculum as a part of the hippocampal formation is the principal target of CA1 pyramidal cell axons and serves as an interface in the information processing between the hippocampus and the neocortex. Subicular pyramidal cells have been classified as bursting and regular firing cells. Here we report fundamental differences in long-term potentiation (LTP) between both cell types. Prolonged high-frequency stimulation induced NMDA receptor-dependent LTP in both cell types. While LTP relied on postsynaptic calcium in regular firing neurons, no increase in postsynaptic calcium was required in bursting cells. Furthermore, paired-pulse facilitation revealed that the site of LTP expression was postsynaptic in regular firing neurons, while presynaptic in burst firing neurons. Our findings on synaptic plasticity in the subiculum indicate that regular firing and bursting cells represent two functional units with distinct physiological roles in processing hippocampal output.