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Astrocytes respond to inhibitory neurotransmitter GABA
Researchers from the University of Padova in Italy have discovered that cortical astrocytes respond to the inhibitory neurotransmitter GABA through GABAB receptor-mediated calcium oscillations in developing and adult mice.
This response recruits Gi/o protein and inositol 1,4,5-triphosphate (IP3) signalling pathways, which triggers glutamate release, leading to evoked neuronal slow inward currents (SICs).
Glial cell astrocytes were traditionally believed to form supporting functions in the central nervous system, but not to contribute to the fundamental functions of the brain. However, over the last decade or so, this theory has been challenged. It is now known that astrocytes can regulate neuronal network activities by responding to the excitatory neurotransmitter glutamate with Ca2+ elevations.
Until this recent study, published in Glia, the response of astrocytes to inhibitory neurotransmitters, such as GABA remained largely unexplored. Through confocal and two-photon laser scanning microscopy of the somatosensory and temporal cortex, the researchers were able to show that in vitro the application of GABA or Baclofen (a GABA agonist) evoked Ca2+ oscillations in the soma of a subpopulation of astrocytes.
These findings were developed through in vivo experiments of astrocytes, that also exhibited GABA receptor mediated calcium elevations.
Through patch clamp recordings, the research group were able to show that Baclofen induced Ca2+ oscillations caused the release of glutamate from the astrocytes and SICs in associated pyramidal cells. This disappeared if the mice didn’t express the type 2 IP3 receptor (IP3R2).
These findings suggest that cortical astrocytes respond to GABAergic interneurons in the living brain and can contribute to the fundamental phenomena of the brain by integrating these inputs into neurons. Further studies of how different GABAergic interneurons interact with astrocytes will further explain the role of cortical astrocytes to neuronal activity.
The research was led by corresponding author Giorgio Carmignoto from the Department of Biomedical Sciences at the University of Padova.
Two-photon brain slice imaging experiments were conducted using Scientifica’s Multiphoton Imaging System, equipped with a pulsed infrared laser. Wavelengths of 780 or 910 nm were used to excite Fluo-4 AM and GCaMP3 respectively. Images were acquired in cortical layers II–III and V at a resolution of 512 × 512 at 1-2 frames per second.
Single and dual cell recordings were partly performed under the Scientifica Multiphoton Imaging System. A MultiClamp 700B amplifier enabled recordings in both voltage-clamp and current-clamp configurations. The signals were filtered at 1 kHz and sampled at 10 kHz with a Digidata interface and pCLAMP software.