Local and Propagated Vascular Responses Evoked by Focal Synaptic Activity in Cerebellar Cortex

Abstract

We investigated the local and remote vascular changes evoked by activation of the cerebellar parallel fibers (PFs). The PFs were stimulated (25-150 microA, 30 Hz) in halothane-anesthetized rats equipped with a cranial window. The changes in arteriolar and venular diameter produced by PF stimulation were measured with the use of a videomicroscopy system. Cerebellar blood flow (BFcrb) was monitored by laser Doppler flowmetry and the field potentials evoked by PF stimulation were recorded with the use of microelectrodes. PF stimulation increased the diameter of local arterioles (+26 +/- 1%, mean +/- SE) in the activated folium (n = 10, P < 0.05). The vasodilation was greatest in smaller arterioles (16.5 +/- 0.8 microm), was graded with the intensity of stimulation, and was less marked than the vasodilation produced by hypercapnia in comparably sized vessels (+58 +/- 5%, CO2 pressure = 50-60 mmHg, n = 8). In addition, the vasodilation was greatest along the horizontal beam of activated PFs and was reduced in arterioles located away from the stimulated site in a rostrocaudal direction. The increases in vascular diameter were associated with increases in BFcrb in the activated area (+55 +/- 4%, n = 5). PF stimulation increased vascular diameter (+10 +/- 0.5%, n = 10) also in larger arterioles (30-40 microm) located in the folium adjacent to that in which the PFs were stimulated. Higher-order branches of these arterioles supplied the activated area. No field potentials were evoked by PF stimulation in the area where these upstream vessels were located. The data suggest that increased synaptic activity in the PF system produces a "local" hemodynamic response mediated by synaptic release of vasoactive agents and a "remote" response that is propagated to upstream arterioles from vessels residing in the activated folium. These propagated vascular responses are important in the coordination of segmental vascular resistance that is required to increase flow effectively during functional brain hyperemia.

Relative changes of cerebral arterial and venous blood volumes during increased cerebral blood flow: Implications for BOLD fMRI

“…To validate our NMR measurements of relative arterial and venous CBV changes during hypercapnia, diameters of arteries and veins were measured in vivo using methods described in detail previously (14). A different group of Sprague Dawley rats (275-300 g; n ϭ 8) were initially anesthetized with 5% halothane in 100% oxygen and maintained with 1-2% halothane.…”

“…Nevertheless, it has been proposed that the change in venous blood volume dominates the total CBV change during altered CBF by neural stimulation and hypercapnia (8,12). However, this assumption is questionable since small arterioles are known to dilate during increased CBF (13)(14)(15).…”

“…Relative arterial and venous CBV (rCBV) were determined by diffusionweighted 19 F NMR, while relative CBF (rCBF) was measured using a two-coil continuous arterial spin labeling method (17). To correlate our NMR results, changes in arterial and venous vessel diameters induced by hypercapnia were also measured by in vivo optical microscopy (14). (16), only a brief summary is included here.…”

How accurate is magnetic resonance imaging of brain function?

“…In addition, when blood flow to a volume of tissue increases, flow in the large arterial and venous blood vessel that supply or drain blood from that particular volume of tissue must also increase, because of conservation of mass. It is, therefore, not surprising that blood vessel dilation produced by neuronal activation propagates to more distant blood vessels [28]. However, the effects in large vessel can be suppressed by magnetic resonance techniques to yield accurate perfusion mapsin other words, maps that report on water delivery to the capillary bed and, by exchange across the capillary wall, to the surrounding tissue.…”

Sustained conduction of vasomotor responses in rat mesenteric arteries in a two‐compartment in vitro set‐up

“…Conduction of vasomotor responses in resistance artery networks has been widely described 17, 18, 19, 20. These responses are believed to play an important role in coordination of arterial tone in response to stimuli such as metabolic demand during exercise, thus regulating blood flow 1.…”