Adding it All Up

Abstract

Wang et al. investigated use-dependent changes in dendritic integration and discovered increases in excitatory postsynaptic potential (EPSP) summation after stimulus paradigms that led to long-term potentiation (LTP). They also found decreases in EPSP summation after stimulus paradigms that led to long-term depression (LTD). Neurons integrate excitatory and inhibitory signals to determine whether or not to fire an impulse. Use-dependent changes in synaptic efficacy, such as those in LTP and LTD, can tip the balance toward excitation or inhibition, respectively. Wang et al. used perforated whole-cell recording to examine dendritic integration of EPSPs in rat hippocampal slices before and after eliciting LTP or LTD. LTP was accompanied by a persistent input-specific increase in the spatial summation of synchronous EPSPs, whereas LTD was accompanied by a decrease in spatial summation. The authors used a combination of electrophysiological and pharmacological analysis to show that changes in dendritic integration required activation of N -methyl-D-aspartate (NMDA) receptors, as do LTP and LTD. The magnitude of changes in dendritic summation did not positively correlate with the magnitude of LTP or LTD, however, and the increase in summation was more sensitive than LTP to inhibition of protein kinase C or calcium-calmodulin-dependent protein kinase II. Pharmacological analysis implicated modification of NMDA receptors and hyperpolarization-activated cation (I h ) channels in the changes in dendritic summation. Blocking I h channels, which inhibited the increase in summation, had no significant effect on LTP itself. These data suggest that synergistic changes in dendritic integration occur simultaneously with changes in synaptic efficacy through distinct mechanisms mediated through different signaling pathways. Z. Wang, N.-L. Xu, C.-P. Wu, S. Duan, M.-M. Poo, Bidirectional changes in spatial dendritic integration accompanying long-term synaptic modifications. Neuron 37 , 463-472 (2003). [Online Journal]