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Thalamic microcircuits: presynaptic dendrites form two feedforward inhibitory pathways in thalamus.
Shane R Crandall1, Charles L Cox
1Department of Pharmacology, University of Illinois, Urbana, IL, USA.
Journal of Neurophysiology
|April 26, 2013
Summary
Researchers discovered two distinct inhibitory responses in the visual thalamus, mediated by different glutamate receptor types on presynaptic dendrites. This finding impacts understanding of visual information processing.
Area of Science:
- Neuroscience
- Visual System
- Synaptic Transmission
Background:
- Feedforward inhibition in the visual thalamus regulates sensory information flow from retina to neocortex.
- This inhibitory pathway is uniquely dominated by presynaptic dendrites (F2 terminals).
- F2 terminal output is known to be modulated by ionotropic and metabotropic glutamate receptors.
Purpose of the Study:
- To investigate whether ionotropic and metabotropic glutamate receptors regulate output from the same or distinct F2 terminals.
- To characterize the different types of F2 responses in the rat visual thalamus.
Main Methods:
- Utilized focal glutamate uncaging combined with whole-cell recordings in rat visual thalamus.
- Differentiated F2 responses based on the types of glutamate receptors involved.
Main Results:
- Identified two distinct F2 responses: Type-A (ionotropic glutamate receptors only) and Type-B (ionotropic and metabotropic glutamate receptors, specifically mGluR5).
- Both response types were observed in the same postsynaptic neurons, distinct from neurons lacking these responses.
- Results suggest distinct F2 terminals or small clusters are responsible for the two observed inhibitory responses.
Conclusions:
- Distinct F2 terminals likely mediate the Type-A and Type-B inhibitory responses in the visual thalamus.
- The efficacy of retinal communication with the thalamus is predicted to be regulated by retinogeniculate axon activity and the specific F2 terminals activated.
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