Researchers discovered a strange new type of brain cell that sends signals by bypassing the cell body altogether. The findings were published in journal Neuron on 17 September 2014.
The new cells were discovered in the hippocampus of a mouse. Humans have the same general brain structure and types of hippocampus cells as mice.
Generally, in typical brain cell the branched dendrites receive electrical signals from other neurons. These signals are passed onto other neurons along the axon once they are processed.
Now, researchers discovered a brain cell shape where the axon arises directly from one of the dendrites.
Research conducted by the neuroscientists
To study the effect of signals received at these axon-carrying dendrites, the team injected a neurotransmitter called glutamate into the brain tissue of mice that can be activated by light pulses. Using a high-resolution microscope, the team directed the light beam directly to a specific dendrite and then activated the neurotransmitter to simulate an input signal.
Resultantly, it was found that dendrites which are directly connected to the axon actively propagate even small input stimuli and activate the neuron. This effect is evident when the information flow from other dendrites to the axon is suppressed by inhibitory input signals at the cell body.
Information transmitted by this special dendrite influences the behaviour of the nerve cell more than input from any other dendrite.
• Neurons come in different shapes and sizes but the basic blueprint consists of a cell body from which dendrites and axons protrude.
• Dendrites are branchlike structures that receive signals from other nerve cells and deliver them to the cell body. The neuron then processes the signals and moves along information to the next cell via a long projection called the axon.
• However , the newly discovered cells have a different unknown process. In these cells, the signals skip the cell body altogether instead of travelling along an axon that projects directly from one of the dendrites.
• The team coloured the places of origin of axons of pyramidal cells in the hippocampus, a brain region involved in memory. In more than half of the cells, they found that the axon does not emerge from the cell body but originates at a dendrite instead.
However, after the discovery, a question loomed large that why these hippocampus cells need these special bypasses that skip over the cell body. The unique shape seems to make the cells stronger and less prone to situations when their responses inhibit rather than neurons that operate on the traditional pathway.
However, it is still not yet clear which signals use this privileged channel and why.