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Systemic blood pressure alters cortical blood flow and neurovascular coupling during nociceptive processing in the primary somatosensory cortex of the rat.

Systemic blood pressure alters cortical blood flow and neurovascular coupling during nociceptive processing in the primary somatosensory cortex of the rat.
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Uchida S, Bois S, Guillemot JP, Leblond H, Piché M,


Uchida S, Bois S, Guillemot JP, Leblond H, Piché M, (click to view)

Uchida S, Bois S, Guillemot JP, Leblond H, Piché M,

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Neuroscience 2016 12 18343() 250-259 pii S0306-4522(16)30704-7
Abstract

Inference on nociceptive and pain-related processes from functional magnetic resonance imaging is made with the assumption that the coupling of neuronal activity and cerebral hemodynamic changes is stable. However, since nociceptive stimulation is associated with increases in systemic arterial pressure, it is essential to determine whether this coupling remains the same during different levels of nociception and pain. The main objective of the present study was to compare the amplitude of local field potentials (LFP) and cerebral blood flow (CBF) changes in the primary somatosensory cortex during nociceptive electrical stimulation of the contralateral or ipsilateral forepaw in isoflurane-anesthetized rats, while manipulating mean arterial pressure (MAP). MAP changes induced by nociceptive stimulation were manipulated by transecting the spinal cord at the upper thoracic segments (T1-T2), which interrupts sympathetic pathways and prevents nociception-related MAP increases, while sensory pathways between the forepaws and the brain remain intact. Intensity-dependent increases in MAP and CBF were observed and these effects were abolished or significantly decreased after spinal transection (p<0.001 and p<0.05, respectively). In contrast, the intensity-dependent changes in LFP amplitude were decreased for the contralateral stimulation but increased for the ipsilateral stimulation after spinal transection (p<0.05). Thus, neurovascular coupling was altered differently by stimulus-induced MAP changes, depending on stimulus intensity and location. This demonstrates that CBF changes evoked by nociceptive processing do not always match neuronal activity, which may lead to inaccurate estimation of neuronal activity from hemodynamic changes. These results have important implications for neuroimaging of nociceptive and pain-related processes.

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