title: Hemodynamic responses evoked by neuronal stimulation via channelrhodopsin-2 can be independent of intracortical glutamatergic synaptic transmission.
abstract: Maintenance of neuronal function depends on the delivery of oxygen and glucose through changes in blood flow that are linked to the level of ongoing neuronal and glial activity, yet the underlying mechanisms remain unclear. Using transgenic mice expressing the light-activated cation channel channelrhodopsin-2 in deep layer pyramidal neurons, we report that changes in intrinsic optical signals and blood flow can be evoked by activation of a subset of channelrhodopsin-2-expressing neurons in the sensorimotor cortex. We have combined imaging and pharmacology to examine the importance of glutamatergic synaptic transmission in this form of neurovascular coupling. Blockade of ionotropic glutamate receptors with the antagonists CNQX and MK801 significantly reduced forepaw-evoked hemodynamic responses, yet resulted in no significant reduction of channelrhodopsin-evoked hemodynamic responses, suggesting that stimulus-dependent coupling of neuronal activity to blood flow can be independent of local excitatory synaptic transmission. Together, these results indicate that channelrhodopsin-2 activation of sensorimotor excitatory neurons produces changes in intrinsic optical signals and blood flow that can occur under conditions where synaptic activation of neurons or other cells through ionotropic glutamate receptors would be blocked.
authors.affiliation: Kinsmen Laboratory of Neurological Research, Department of Psychiatry, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Nadia A
authors.initials: NA
authors.lastname: Scott
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Murphy
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000098:blood supply / Q000187:drug effects / Q000502:physiology*; D000075402:Channelrhodopsins; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects*; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology*; D018698:Glutamic Acid / Q000378:metabolism; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology*; D007834:Lasers; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D011725:Pyridines / Q000494:pharmacology; D012039:Regional Blood Flow / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects*
chemical_list: D000075402:Channelrhodopsins; D018683:Excitatory Amino Acid Agents; D011725:Pyridines; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; C121465:6-methyl-2-(phenylethynyl)pyridine