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Correlation between hemodynamics and neuronal activity during altered brain states

Lecrux C, Sandoe C, Neupane S, Kropf P, Toussay X, Tong X-K, Shmuel A, Hamel E (2014) Correlation between hemodynamics and neuronal activity during altered brain states. Neuroscience 2014 Abstracts 352.03. Society for Neuroscience, Washington, DC.

Summary: Introduction: Changes in neuronal activity are spatially and temporally replicated by concurrent alterations in cerebral blood flow (CBF) under physiological conditions, a phenomenon known as neurovascular coupling (NVC) which forms the basis of several brain imaging techniques. However, virtually nothing is known about NVC under conditions of altered brain states. Using the whisker-to-barrel pathway, we tested whether the coupling between neuronal activity and cerebral perfusion would be affected by changes in cortical states triggered by varying acetylcholine (ACh) tone. Methods: Sensory stimulation was induced in rats by mechanical whisker stimulation. In the barrel cortex, CBF was measured by laser-Doppler flowmetry and somatosensory evoked potentials (SEPs) were recorded with a multichannel electrode. Activated neurons were identified by double-immunohistochemistry for c-Fos and markers of pyramidal cells or GABA interneurons. ACh tone was increased pharmacologically (physostigmine 0.1mg/kg, subcutaneous; linopirdine, 10mg/kg, intraperitoneal) or through basal forebrain (BF) electrical stimulation. ACh tone was decreased using a selective cholinotoxin (saporin, 4mg/2mL, icv). Under enhanced ACh tone, muscarinic (scopolamine, 0.1mg/kg, intravenous) or central nicotinic (chlorisondamine dichloride, 12mg/5mL, icv) receptors were selectively blocked. Results: Whisker-evoked CBF responses were altered by changes in ACh tone induced by linopirdine (+31±4%, p<0.001), physostigmine (+40±8%, p<0.01), BF stimulation (+52±18%, p<0.05) or saporin (-41%, p<0.001) compared to their respective controls. These changes reflected alterations in the activity or extent, but not in the identity, of the neuronal network of cortical pyramidal cells and specific GABA interneurons selectively recruited by whisker stimulation. Under enhanced or decreased ACh tone, whisker-evoked CBF responses accurately mirrored changes in neuronal activity, and correlated with corresponding changes in the amplitude of the SEPs in cortical layers II/III and IV. Moreover, a positive correlation was observed between hemodynamic changes and band-limited power in the high gamma band in cortical layers II/III. The enhanced CBF response under high ACh tone required muscarinic ACh receptor activation. Conclusions: Changes in neuronal and vascular signals upon sensory stimulation remain tightly correlated under enhanced or reduced ACh tone, and reflect altered activity of the neuronal network selectively recruited by sensory stimulation. These subtle changes are reliably captured by superficial hemodynamic signals.

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