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Layer selective presynaptic modulation of excitatory inputs to hippocampal cornu Ammon 1 by mu-opioid receptor

A R McQuiston1

  • 1Department of Anatomy and Neurobiology, Virginia Commonwealth University Medical Center, Richmond, VA 23298, USA. amcquiston@vcu.edu

Neuroscience
|December 11, 2007
PubMed

Insights

Activation of mu-opioid receptors (MOR) in the hippocampus affects inhibitory interneurons. MOR activation is more potent in specific CA1 layers, impacting synaptic plasticity and spatial memory.

Area of Science:

  • Neuroscience
  • Neuropharmacology
  • Synaptic Plasticity

Background:

  • Mu-opioid receptors (MOR) in hippocampal CA1 disrupt neural rhythms, synaptic plasticity, and spatial memory.
  • MORs hyperpolarize inhibitory interneurons, suppress synaptic transmission, and increase CA1 excitatory activity.
  • The precise anatomical locations of MOR actions within CA1 remain unclear.

Purpose of the Study:

  • To investigate the anatomical sites of mu-opioid receptor (MOR) activation within the hippocampal CA1 region.
  • To determine how MOR activation affects GABA receptor function and inhibitory synaptic transmission in different CA1 layers.
  • To elucidate the impact of MOR activation on excitatory postsynaptic potentials (EPSPs) across CA1 layers.

Main Methods:

  • Utilized voltage-sensitive dye imaging and whole-cell patch clamping in rat hippocampus slices.
  • Employed photolysis of caged GABA to assess direct GABA receptor activation.
  • Applied electrical stimulation to isolated CA1 layers to evoke EPSPs and tested the effects of MOR agonist DAMGO.

Main Results:

  • MOR activation did not alter direct GABA receptor activation but suppressed GABAergic inhibitory postsynaptic potentials, indicating presynaptic action.
  • MOR activation significantly increased EPSP areas in stratum radiatum (SR), stratum pyramidale (SP), and stratum oriens (SO) compared to stratum lacunosum-moleculare (SLM).
  • The effect of MOR activation was proportionally larger in SR, SP, and SO than in SLM, suggesting layer-specific modulation.

Conclusions:

  • MOR activation primarily acts presynaptically to inhibit interneuron function in hippocampal CA1.
  • MOR-mediated inhibition of GABA release is less effective in the stratum lacunosum-moleculare (SLM) compared to other CA1 layers.
  • These findings clarify the anatomical specificity of MOR actions in CA1, contributing to understanding their role in synaptic plasticity and memory.

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