The effects of graded hypercapnia on the activation flow coupling responsedue to forepaw stimulation in alpha-chloralose anesthetized rats

Activation flow coupling (AFC), changes in cerebral blood flow (CBF) due to changes in neural activity with functional stimulation, provides the physi ological basis of many neuroimaging techniques. Hypercapnia leads to an inc rease in CBF while neural activity remains unaffected. Laser Doppler (LD) f lowmetry was used to measure CBF changes (LDCBF) in the somatosensory corte x due to periodic electrical forepaw stimulation (4 s in duration) before a nd during graded hypercapnia (3% CO2, 5% CO2 and 10% CO2). With increasing CO2 concentrations, the baseline LDCBF progressively increased. The peak he ight (PH) of the LDCBF response, expressed as a percent change from the obs erved baseline for each hypercapnic state, significantly decreased (P <0.05 ) with increasing CO2 concentrations. However, the absolute magnitude of th e LD CBF change was independent of CO2 concentration. The temporal dynamics of the LD response during hypercapnia were significantly prolonged compare d to baseline conditions (P <0.05). (C) 2001 Elsevier Science B.V. All righ ts reserved.