Activation of β-adrenergic receptors in rat visual cortex expands astrocytic processes and reduces extracellular space volume

Ang Doma Sherpa, Fanrong Xiao, Neethu Joseph, Chiye Aoki, Sabina Hrabetova

Research output: Contribution to journalArticle

Abstract

Brain extracellular space (ECS) is an interconnected channel that allows diffusion-mediated transport of signaling molecules, metabolites, and drugs. We tested the hypothesis that β-adrenergic receptor (βAR) activation impacts extracellular diffusion-mediated transport of molecules through alterations in the morphology of astrocytes. Two structural parameters of ECS—volume fraction and tortuosity—govern extracellular diffusion. Volume fraction (α) is the volume of ECS relative to the total tissue volume. Tortuosity (λ) is a measure of the hindrance that molecules experience in the ECS, compared to a free medium. The real-time iontophoretic (RTI) method revealed that treatment of acutely prepared visual cortical slices of adult female rats with a βAR agonist, DL-isoproterenol (ISO), decreases α significantly, from 0.22 ± 0.03 (mean ± SD) for controls without agonist to 0.18 ± 0.03 with ISO, without altering λ (control: 1.64 ± 0.04; ISO: 1.63 ± 0.04). Electron microscopy revealed that the ISO treatment significantly increased the cytoplasmic area of astrocytic distal endings per unit area of neuropil by 54%. These findings show that norepinephrine decreases α, in part, through an increase in astrocytic volume following βAR activation. Norepinephrine is recognized to be released within the brain during the awake state and increase neurons’ signal-to-noise ratio through modulation of neurons’ biophysical properties. Our findings uncover a new mechanism for noradrenergic modulation of neuronal signals. Through astrocytic activation leading to a reduction of α, noradrenergic modulation increases extracellular concentration of neurotransmitters and neuromodulators, thereby facilitating neuronal interactions, especially during wakefulness. Synapse 70:307–316, 2016.

Original languageEnglish (US)
Pages (from-to)307-316
Number of pages10
JournalSynapse
Volume70
Issue number8
DOIs
StatePublished - Aug 1 2016

    Fingerprint

Keywords

  • adrenergic system
  • astrocyte
  • diffusion
  • electron microscopy
  • extracellular space
  • isoproterenol
  • real-time iontophoretic method
  • sleep-wake cycle
  • tortuosity
  • volume fraction

ASJC Scopus subject areas

  • Cellular and Molecular Neuroscience

Cite this