Comparison between Pial and Intraparenchymal Vascular Responses to Cervical Sympathetic Stimulation in Cats. Part 1. Under Normal Resting Conditions

Abstract

Summary:To investigate the role of sympathetic regula tion in both resistance and capacitance vessels in cerebral circulation, the responses of pial and intraparenchymal vessels to sympathetic nerve stimulation were simulta neously examined in 14 cats by means of a newly devel oped video camera photoelectric system. The system consisted of a video camera system for measurement of pial vascular diameters and a photoelectric apparatus for estimating regional cerebral blood volume in the intrapa renchymal vessels. The ipsilateral superior cervical gan glion was electrically stimulated for 5 min. Initially. both the pial and intraparenchymal vessels constricted. TheIt is well documented that sympathetic nerves derived from the superior cervical ganglion con strict cerebral vessels down to the pial arterioles and venules (Auer et aI. , 1982) and exert a protec tive effect against breakthrough of autoregulation of CBF during acute hypertension (Bill and Linder, 1976). However, the role of the sympathetic nerves in the regulation of the resting CBF is still disputed Purves, 1978). This controversy seems to depend partly on the method ological limitations of measuring CBF and on the homeostatic mechanism of cerebral circulation. Harper et al. (1972) hypothesized that under most circumstances, sympathetic constriction of the ex traparenchymal and pial vessels might be com pen- 342large pial arteries (173 ± 25 f.Lm, mean ± SEM) remained constricted throughout the stimulation. whereas the in traparenchymal vessels began to dilate after the initial constriction and exceeded the control level at 175 ± 25 s despite continued stimulation. In conclusion. such sym pathetic nerve stimulation is considered to exert a con strictive effect on the intraparenchymal as well as the pial vessels at the early stage. The compensatory dilation of the intraparenchymal vessels was delayed 3 min after ini tiation of the stimulation. Key Words: Cerebral blood volume-Escape phenomenon-Pial vessel-Sympa thetic stimulation. sated for by a metabolic dilation of the intraparen chymal vessels and that CBF might be kept con stant. Recently, we developed a video camera photoelectric system that permits simultaneous and continuous measurement of pial vascular diameter and changes in regional cerebral blood volume (CBV). In the present study, to test Harper et al. 's hypothesis, we compared the responses of pial and intraparenchymal vessels to superior cervical gan glion stimulation by using this new method. MATERIALS AND METHODSExperiments were performed on 14 cats weighing from 2.3 to 3.4 kg, anesthetized by intraperitoneal injection of a-chloralose (50 mg/kg) and urethane (5 00 mg/kg). The bilateral femoral arteries and one femoral vein were can nulated for monitoring arterial blood pressure (BP). ana lyzing blood gases. and injection of drugs. The animals were subjected to tracheostomy and were ventilated with a respirator (Harvard 662) after immobilization with al curonium chloride (2 mg i.v.). The animal's head was fixed in a stereotactic head ho...

The Locus Coeruleus-Norepinephrine Network Optimizes Coupling of Cerebral Blood Volume with Oxygen Demand

“…Although early studies suggest NE-mediated regulation of cortical blood flow derives from superior cervical ganglion projections to pial vessels and penetrating arterioles (Gotoh et al, 1986), later analysis showed that LC projections are closely associated with cerebral arterioles and capillaries (Cohen et al, 1997) and also directly affect blood flow (Ohta et al, 1991;Raichle et al, 1975). Ultrastructural analysis suggests that LC neurons do not directly innervate vessels but rather form varicosities in the paravascular space adjacent to arterioles and capillaries (Cohen et al, 1997).…”

Effect of Stellate Ganglion Block on the Cerebrovascular System

“…[12][13][14][15] Various animal studies have failed to show that sympathetic nerve activity modulates CBF, 16 -19 yet others have reported changes in CBF as a result of sympathetic stimulation. 7,20,21 The inconsistencies observed in previous reports may be due to the methods used to investigate the effects of SGB on the cerebral vasculature.…”

Differential Effects of Increasing Doses of α‐Trinositol on Cerebral Blood Flow Autoregulation

“…Large pial arteries constrict, whereas intraparenchymal vessels undergo compensatory dilatation. This explains the constant baseline cerebral blood flow while the limits of autoregulation are shifted (Baumbach & Heistad 1983;Gotoh et al 1986). The response of cerebral vessels to sympathetic nerve stimulation has been considered to be due to release of norepinephrine (Auer et al 1983).…”