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Opioid receptor subtype expression defines morphologically distinct classes of hippocampal interneurons
K R Svoboda1, C E Adams, C R Lupica
1Department of Pharmacology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
Summary
Opioid receptors (mu and delta) in the hippocampus inhibit interneurons, modulating pyramidal cell activity. Mu-opioid receptors target interneurons near pyramidal cell bodies, while delta-opioid receptors target those in dendritic layers, influencing neuronal excitability.
Area of Science:
- Neuroscience
- Cellular Neuroscience
- Neuropharmacology
Background:
- Hippocampal pyramidal cells are regulated by GABAergic interneurons.
- Opioid receptor activation in the hippocampus influences neuronal excitability.
Purpose of the Study:
- To classify hippocampal interneurons based on opioid receptor expression and axonal projection.
- To determine how mu- and delta-opioid receptor activation differentially affects interneuron activity and pyramidal cell excitability.
Main Methods:
- Whole-cell patch-clamp recordings in hippocampal slices.
- Application of selective mu- and delta-opioid receptor agonists.
- Biocytin filling and post hoc morphological analysis of interneurons.
Main Results:
- Opioid receptor activation induced inhibitory currents in most interneurons.
- Interneurons projecting to pyramidal cell bodies predominantly expressed mu-opioid receptors.
- Interneurons targeting pyramidal dendritic layers showed higher expression of delta-opioid receptors.
Conclusions:
- Mu-opioid receptor activation inhibits interneurons innervating pyramidal cell somata, increasing cell excitability.
- Delta-opioid receptor activation inhibits interneurons in dendritic layers, enhancing afferent signal transmission.
- Morphological segregation of interneurons underlies differential effects of mu and delta opioid receptor signaling on hippocampal circuits.