Dendritic Na+ spikes enable cortical input to drive action potential output from hippocampal CA2 pyramidal neurons

摘要

Cells called neurons carry information—in the form of electrical signals—around the brain. These cells connect to each other in complex networks and each neuron is able to form junctions, or synapses, with many neighbors. In a neuron, small electrical signals start from synapses at the tips of branched structures called dendrites. From there, these signals travel to the cell body of the neuron to activate a larger electrical signal—called an action potential—that travels along a long tail-like extension, called the axon, to reach synapses with other neurons. In the dendrites, the small electrical signals can be amplified by rapid changes in the concentration of sodium ions, known as Na+ spikes. Although they were first recorded over 40 years ago, it is not clear how important the Na+ spikes are for triggering action potentials. In this study, Sun et al. studied a type of neuron in the hippocampus called CA2 pyramidal neurons, which are involved in social memory and aggression. Unlike most other neurons in this region, CA2 neurons are strongly activated by signals from a neighboring region of the brain called the entorhinal cortex. The experiments show that Na+ spikes are able to travel from the dendrites to the cell body of these neurons, where they are required to trigger action potentials. However, this is not the case for other neurons in the hippocampus, where the Na+ spikes are very weak by the time they reach the cell body. Sun et al. used a computational modeling technique to compare the different types of neurons in the hippocampus. The dendrites of these cells have different branching patterns and shapes, and the model suggests that this may explain the differences in how well the Na+ spikes travel to the cell body. The next major challenge is to understand the role of the Na+ spikes in social memory and other complex behaviors that are controlled by CA2 neurons.