title: Functional MRI of calcium-dependent synaptic activity: cross correlation with CBF and BOLD measurements.
abstract: Spatial specificities of the calcium-dependent synaptic activity, hemodynamic-based blood oxygenation level-dependent (BOLD) and cerebral blood flow (CBF) fMRI were quantitatively compared in the same animals. Calcium-dependent synaptic activity was imaged by exploiting the manganese ion (Mn++) as a calcium analog and an MRI contrast agent at 9.4 T. Following forepaw stimulation in alpha-chloralose anesthetized rat, water T1 of the contralateral forepaw somatosensory cortex (SI) was focally and markedly reduced from 1.99 +/- 0.03 sec to 1.30 +/- 0.18 sec (mean +/- SD, N = 7), resulting from the preferential intracellular Mn++ accumulation. Based on an in vitro calibration, the estimated contralateral somatosensory cortex [Mn++] was approximately 100M, which was 2-5-fold higher than the neighboring tissue and the ipsilateral SI. Regions with the highest calcium activities were localized around cortical layer IV. Stimulus-induced BOLD and CBF changes were 3.4 +/- 1.6% and 98 +/- 33%, respectively. The T1 synaptic activity maps extended along the cortex, whereas the hemodynamic-based activation maps extended radially along the vessels. Spatial overlaps among the synaptic activity, BOLD, and CBF activation maps showed excellent co-registrations. The center-of-mass offsets between any two activation maps were less than 200 microm, suggesting that hemodynamic-based fMRI techniques (at least at high field) can be used to accurately map the spatial loci of synaptic activity.
authors.affiliation: Department of Radiology, University of Minnesota School of Medicine, Minneapolis 55455, USA.
authors.forename: T Q
authors.initials: TQ
authors.lastname: Duong
authors.forename: A C
authors.initials: AC
authors.lastname: Silva
authors.forename: S P
authors.initials: SP
authors.lastname: Lee
authors.forename: S G
authors.initials: SG
authors.lastname: Kim
mesh_terms: D000818:Animals; D001931:Brain Mapping; D002118:Calcium / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004558:Electric Stimulation; D005552:Forelimb / Q000294:innervation*; D006439:Hemodynamics; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010100:Oxygen / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow; D013003:Somatosensory Cortex / Q000098:blood supply / Q000502:physiology*
chemical_list: D010100:Oxygen; D002118:Calcium