Cortical layer 1 and layer 2/3 astrocytes exhibit distinct calcium dynamics in vivo.
Cumulative evidence supports bidirectional interactions between astrocytes and neurons, suggesting glial involvement of neuronal information processing in the brain. Cytosolic calcium (Ca(2+)) concentration is important for astrocytes as Ca(2+) surges co-occur with gliotransmission and neurotransmitter reception. Cerebral cortex is organized in layers which are characterized by distinct cytoarchitecture. We asked if astrocyte-dominant layer 1 (L1) of the somatosensory cortex was different from layer 2/3 (L2/3) in spontaneous astrocytic Ca(2+) activity and if it was influenced by background neural activity. Using a two-photon laser scanning microscope, we compared spontaneous Ca(2+) activity of astrocytic somata and processes in L1 and L2/3 of anesthetized mature rat somatosensory cortex. We also assessed the contribution of background neural activity to the spontaneous astrocytic Ca(2+) dynamics by investigating two distinct EEG states ("synchronized" vs. "de-synchronized" states). We found that astrocytes in L1 had nearly twice higher Ca(2+) activity than L2/3. Furthermore, Ca(2+) fluctuations of processes within an astrocyte were independent in L1 while those in L2/3 were synchronous. Pharmacological blockades of metabotropic receptors for glutamate, ATP, and acetylcholine, as well as suppression of action potentials did not have a significant effect on the spontaneous somatic Ca(2+) activity. These results suggest that spontaneous astrocytic Ca(2+) surges occurred in large part intrinsically, rather than neural activity-driven. Our findings propose a new functional segregation of layer 1 and 2/3 that is defined by autonomous astrocytic activity.
Takata
Norio
N
Hirase Research Unit, Neuronal Circuit and Mechanisms Research Group, RIKEN Brain Science Institute, Wako, Japan. takata@brain.riken.jp
Hirase
Hajime
H
D000818:Animals; D001253:Astrocytes / Q000166:cytology* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002540:Cerebral Cortex / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D004569:Electroencephalography; D008297:Male; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
D002118:Calcium