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1 Laboratory of Cerebrovascular Biology and Stroke, Departments of Neurology and 2 Neuroscience, University of Minnesota Medical School, Minneapolis, Minnesota 55455
Crus II is an area of the cerebellar
cortex that receives trigeminal afferents from the perioral region. We
investigated the mechanisms of functional hyperemia in cerebellum using
activation of crus II by somatosensory stimuli as a model. In
particular, we sought to determine whether stimulation of the perioral
region increases cerebellar blood flow
(BFcrb) in crus II and, if so, whether the response depends on activation of
2-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-kainate
receptors and nitric oxide (NO) production. Crus II was exposed in
anesthetized rats, and the site was superfused with Ringer. Field
potentials were recorded, and
BFcrb was measured by
laser-Doppler flowmetry. Crus II was activated by electrical stimulation of the perioral region (upper lip). Perioral stimulation evoked the characteristic field potentials in crus II and increased BFcrb (34 ± 6%; 10 Hz-25 V;
n = 6) without changing arterial
pressure. The BFcrb increases were
associated with a local increase in glucose utilization (74 ± 8%;
P < 0.05;
n = 5) and were attenuated by the
AMPA-kainate receptor antagonist
2,3-dihydroxy-6-nitro-7-sulfamoylbenzo-[f]quinoxaline (
71 ± 3%; 100 µM; P < 0.01; n = 5). The neuronal NO synthase inhibitor 7-nitroindazole (7-NI, 50 mg/kg;
n = 5) virtually abolished the
increases in BFcrb
(90 ± 2%; P < 0.01) but did not affect the amplitude of the field potentials. In
contrast, 7-NI attenuated the increase in neocortical cerebral blood
flow produced by perioral stimulation by 52 ± 6%
(P < 0.05;
n = 5). We conclude that crus II
activation by somatosensory stimuli produces localized increases in
local neural activity and BFcrb
that are mediated by activation of glutamate receptors and NO. Unlike
in neocortex, in cerebellum the vasodilation depends almost exclusively
on NO. The findings underscore the unique role of NO in the mechanisms
of synaptic function and blood flow regulation in cerebellum.
cerebral circulation; laser-Doppler flowmetry; glucose utilization; vasodilation; glutamate receptors
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