Electric role of dendritic spikes

Work performed at Northwestern University has given fresh insight into the role of dendrites in brain function – this role having remained poorly understood for the past century.  A paper has been published in Nature by William Kath and his team that details how dendritic spines contribute during synaptic transmission.  Essentially, the spines on dendrites are now thought to have a role in the modulation of synaptic signals – hence they are described as ‘electrical compartments’.  This is crucial in the constant crosstalk occurring within the brain’s neuronal network.

Each neuron in the brain communicates with others via its branching dendrites; one dendrite may receive input from up to 1000 other neurons.   It has been understood for decades that dendritic spines participate in the chemical transmission taking place at the neuronal synapse.  Receptors on the spines are bound by neurotransmitters such as GABA and glutamate.  The work at Northwestern postulates an electrical component that may now be experimentally assessed.   Kath, a professor of engineering sciences and mathematics at Northwestern, states that the paper gives ‘conclusive’ evidence.

Researchers carried out their experiments in the hippocampi of rats.  This brain region is involved in learning and memory formation.  Microelectrodes were used to probe the dendrites’ voltage; a current was administered and the corresponding voltage alteration measured.  Another method was ‘glutamate uncaging’ – glutamate is released at specific sites to evoke the response that would occur in vivo.  Lastly, calcium-sensitive dyes were injected into the synaptic site to monitor calcium levels, which indicate electrical fluctuations during an action potential.  These methods allowed assessment of dendritic electrical activity.

The researchers also used computational models of real neurons; these built a 3D representation of the neuron, giving details of each dendrite’s diameter, placement and electrical properties. The simulations indicated that the electrical resistance of  spines is consistent throughout their dendrite – this is regardless of location on the dendritic tree.

It is hoped that the success in examining dendritic properties in further detail will help to cast more light on the astounding computational capacity of the brain.  Anomalies in communication could be implicated in diseases such as Parkinson’s and Alzheimer’s.  Hence further understanding would improve models of the diseased brain.