Dendrodendritic synapse
Dendrodendritic synapses are connections between the
History
In 1966 Wilfrid Rall, Gordon Shepherd, Thomas Reese, and Milton Brightman found a novel pathway, dendrites that signaled to dendrites.[3] While studying the mammalian olfactory bulb, they found that there were active dendrites that couple and send signals to each other. The topic was then only explored sporadically due to difficulties with techniques and technology available to further investigate dendrodendritic synapses. Investigations into this phenomenon of active dendrites has resurfaced with vigor at the start the 21st century.
The study of dendrodendritic synapses in the olfactory bulb provided some early examples of ideas about neuronal organization relating to dendritic spines[4]
- One spine could serve as an input-output unit
- One neuron could contain multiple dendritic spines
- These spines are widely spaced, indicating some independent function
- Synaptic input-output events can occur without axonal stimulation
Location
Dendrodendritic synapses have been found and studied in both the
Olfactory bulb
Dendrodendritic synapses have been studied extensively in the olfactory bulb of rats where it is believed they help in the process of differentiating smells. The granule cells of the olfactory bulb communicate exclusively through dendrodendritic synapses because they lack axons. These granule cells form dendrodendritic synapses with mitral cells to convey odor information from the olfactory bulb. Lateral inhibition from the granule cell spines helps to contribute to contrasts between odors and in odor memory.[5]
Dendrodendritic synapses have also been found to have similar effects on olfactory input from the glomeruli of the antennal lobe of insects.
Retina
The spatial and color contrast systems of the retina operate in a similar manner. Dendrodendritic homologous gap junctions have been found as a way of communication between dendrites in the retinal α-type Ganglion cells to produce a faster method of communication to modulate the color contrast system.[6] Using bidirectional electrical synapses in the dendrodendrtic synapses they modulate inhibition of different signals thus allowing for a modulation of the color contrast system. This dendritic function is an alternative modulatory system to that of pre-synaptic inhibition which is presumed to also help differentiate different contrast in the visual sense.[7]
Neuroplasticity
Dendrodendritic synapses can play a role in