論文

Effects of inhibition of nitric oxide (NO) synthesis on the cerebrovascular autoregulatory vasodilator response to hypotension were studied in conscious rats. Cerebral blood flow (CBF) was determined with [14C]iodoantipyrine in a saline-treated control group and in three groups following inhibition of NO synthase activity by twice daily intraperitoneal injections of 50 mg/kg of NG-nitro-L-arginine methyl ester (L-NAME) for four days. In the saline-control group (n = 8) and in the L-NAME-treated Group (a) (n = 8) CBF was determined while systemic mean arterial blood pressure (MABP) remained at its resting level (means +/- S.D., 128 +/- 6 and 151 +/- 11 mmHg, respectively). In the other groups CBF was determined after MABP was reduced by blood withdrawal to 118 +/- 9 and 88 +/- 8 mmHg in Groups (b) (n = 8) and (c) (n = 8), respectively. Despite the elevated MABP, global CBF was significantly lower in L-NAME-treated Group (a) than in the saline-controls (P < 0.005), indicating cerebral vasoconstriction resulting from inhibition of NO synthesis. Global CBF was not significantly reduced further in the two groups with hypotension. Local CBF in the hypotensive rats showed no significant reductions below values in L-NAME-treated control rats (Group (a)) in 31 of 32 brain structures; the only exception was in the auditory cortex of the severely hypotensive rats (Group (c)). The autoregulatory mechanism for cerebral vasodilatation to compensate for reduced arterial blood pressure is maintained following inhibition of NO synthesis.

Local cerebral blood flow (ICBF) was measured with [14C]iodoantipyrine in conscious, unrestrained rats during electrical stimulation of the fastigial nucleus (FN). Electrode position in the FN was determined by blood pressure (MABP) responses to stimulation under anesthesia. In nine rats in which MABP responses had been variable under anesthesia, bipolar stimulation (50 Hz, 0.5 ms, 1 s on/1 s off) with currents of 30-100 microA after recovery from anesthesia produced stereotypic behavior but little effect on MABP and ICBF. In seven other conscious rats currents could be raised to 75-200 microA without inducing seizures, resulting in sustained MABP elevations during the ICBF measurement and significantly increased ICBF in the sensory-motor (+45%), parietal (+31%), and frontal cortices (+56%) and the caudate-putamen (+27%) above control values (n = 9). Glucose utilization, measured with [14C]deoxyglucose, in rats similarly stimulated was significantly increased in six structures, including some of the above, indicating increases in ICBF due to metabolic activation. Unilateral or bilateral electrolytic lesions of the FN, placed 6-7 days before ICBF measurement, had negligible effects on resting ICBF and on autoregulation in conscious rats. These results fail to support a specific role for the FN in physiological regulation of cerebral blood flow in unanesthetized rats.

Effects of inhibition of nitric oxide (NO) synthase by NG-nitro-L-arginine methyl ester (L-NAME) on the increases in local cerebral blood flow (LCBF) produced in the whisker-to-barrel sensory pathway by vibrissal stimulation were studied in conscious rats with the autoradiographic iodo[14C]antipyrine method. Unilateral whisker stroking increased LCBF in the ipsilateral trigeminal spinal and principal sensory nuclei, contralateral ventral posteromedial thalamic nucleus, and contralateral somatosensory barrel cortex. Intravenous L-NAME (30 mg/kg) lowered baseline LCBF without altering the percent increases due to stimulation. Intracisternal infusions of L-NAME in doses about 10 times the molar content of free arginine in brain inhibited brain NO synthesis activity by 88%, but the percent augmentations of LCBF by stimulation remained unchanged. Chronic treatment with L-NAME (50 mg/kg ip twice daily for 4 days) inhibited NO synthase activity in brain by 84% but also failed to reduce the percent increases in LCBF due to stimulation. These results indicate that NO does not mediate the increases in LCBF associated with functional activation.

The present experimental study was undertaken to investigate the effects of locus coeruleus stimulation on the dynamic changes of intraparenchymal vessels and pial vessels. Twelve cats were anaesthetized with alpha-chloralose and urethane. For stimulation of the locus coeruleus, a concentric stainless-steel needle electrode was inserted stereotaxically. During the stimulation, volumetric changes of the intraparenchymal vessels were monitored by a photoelectric method for estimating the cerebral blood volume (CBV) (6 cats), and the diameters of pial arteries were measured continuously using a video camera system (6 cats). The CBV followed a decreasing course during the stimulation of the locus coeruleus. The decrease in CBV from the control value (6.3 vol%) was 0.14 +/- 0.04 vol% at 80 s (p less than 0.05), 0.15 +/- 0.05 vol% at 100 s (p less than 0.05), and 0.15 +/- 0.03 vol% at 120 s (p less than 0.01). After cessation of the stimulation, CBV showed a gradual recovery. On the other hand, the diameters of the pial arteries did not change during or after the stimulation of the locus coeruleus. The above results suggest that the locus coeruleus has a vasoconstrictive effect on the intraparenchymal vessels, although it exerts no apparent influence on the pial arteries.

SAH後の脳血管攣縮に対するノルアドレナリン(NA)作動性神経系の関与を明らかにするため,実験的SAHにおける上頸部交感神経節(SCG)節前線維の電気活動を検討した.成猫13匹を用い,SCG近傍で節前線維を切断後,中枢側から活動電位を導出し,pulse density variation法を用いて連続的に解析した.実験的SAHは大槽内に自家血0.3 mlを注入し作製した(SAH群8例),対照群(5例)では生理食塩水0.3 mlを注入をした.SAH群では節前線維の放電頻度はSAH作製後,前値に比し有意に増加した(10分後:186.9±48.1%,mean±SEM, 30分後:328.4±88.5%,90分後:296.3±132.0%,各々p<0.05),対照群の放電頻度は有意な変化を示さなかった.なお,経過中両群とも全身血圧に有意な変動を認めなかった.SAH急性期において,脳軟膜血管壁に分布するNA作動性神経系の電気活動亢進が示唆された

成猫5匹を用い一側青斑核電気刺激に対する両側大脳皮質血液含量(CBV)の変化を検討した結果,青斑核適正刺激は脳実質内血管に対して収縮作用を有することを認めた

Intracellular Na+ concentration plays an important role in the regulation of cellular energy metabolism; i.e., increased intracellular Na+ concentration stimulates glucose utilization both in cultured neurons and astrocytes. Both high KCI and veratridine, which have been known to cause neuronal damage, elicit increased glucose utilization, presumably via increased intracellular Na+ concentration. In the present study, we examined the role of intracellular Na+ influx in the mechanisms of neuronal cell damage induced by high KCl or veratridine assayed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric method. Rat primary cultures of striatal neurons were incubated with high KCl (final concentrations: 25, 50 mM) or veratridine (0.1-100 microM) with or without various inhibitors. High KCl depolarizes cell membrane, thus, leading to Na+ influx through an activation of voltage-sensitive Na+ channels, while veratridine elicits Na+ influx by directly opening these channels. After 24-h incubation with elevated [K+]o or veratridine, glucose contents in the medium decreased significantly (approximately by 7 mM), but remained higher than 18 mM. High [K+]o reduced percent cell viability significantly (approximately 50% at 25 mM, approximately 40% at 50 mM [K+]o, P<0.01), but tetrodotoxin (100 nM) had no protective effect, indicating that Na+ influx was not essential to high K+ -induced cell death. DL-2-Amino-5-phosponovaleric acid (APV) (1 mM) completely blocked cell death induced by elevated [K+]o, while 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10 microM) did not. In contrast, veratridine (>10 microM) caused cell damage in a dose-dependent and tetrodotoxin-sensitive manner, but none of APV, CNQX, or bepridil (Na+ -Ca2+ exchanger blocker) had any protective effect. Nifedipine (50 approximately 100 microM), however, reduced percent cell damage induced by veratridine.

Membrane depolarization by elevated extracellular K+ concentration ([K+]o) causes rapid Na+ influx through voltage-sensitive Na+ channels into excitable cells. The consequent increases in intracellular Na+ concentration ([Na+]i) and/or [K+]o stimulate Na+,K+-ATPase activity, which in turn stimulates energy metabolism and rates of glucose utilization (CMR[glc]) in neurons. We previously reported that in cultured cells elevated [K+]o stimulated CMR(glc) in neurons but not astroglia; but increasing [Na+]i by opening voltage-sensitive Na+ channels with veratridine stimulated CMR(glc) in both. These results indicated that Na+ influx plays a key role in the regulation of energy metabolism in neurons and astroglia, but that depolarization of astroglial membranes by elevated [K+]o does not open voltage-sensitive Na+ channels as it does in neurons. To examine this possibility directly we have measured the effects of increased [K+]o and of veratridine on Na+ influx into cultured rat astroglia and neurons. Cells were incubated in bicarbonate buffer containing ouabain (1 mM), tracer amounts of 22NaCl, and various concentrations (5.4, 28, 56 mM) of K+ or 75 microM veratridine for 0-60 min. Cells were digested and assayed for intracellular 22Na+ content. Elevated extracellular K+ stimulated tetrodotoxin-sensitive 22Na+ accumulation in cultured neurons but inhibited 22Na+ influx in astroglia. Veratridine-stimulated Na+ influx in both astroglia and neurons (144% and 133%, respectively), and these effects were completely blocked by 10 microM tetrodotoxin. These results indicate that increased [K+]o does not open voltage-sensitive Na+ channels and may inhibit Na+ influx in astroglia.