Takehiko Adachi

Nitric oxide (NO) is involved in increased cerebral cortical blood flow following stimulation of the nucleus basalis of Meynert in anesthetized rats

The effects of i.v. administration of a nitric oxide (NO) synthase inhibitor, L-NG-nitroarginine (L-NOArg), on the increase in cerebral cortical blood flow (cortical BF), following either electrical stimulation of the nucleus basalis of Meynert (NBM), whose cholinergic fibers project to the cortex, or hypercapnia with 10% CO2 inhalation, were studied in anesthetized rats. Cortical BF was measured using laser Doppler flowmetry. The threshold intensity of electrical stimulation of the NBM (0.5 ms, 50 Hz for 10 s) that induced an increase in regional cortical BF was defined as 1T. The cortical BF was increased on a stimulus intensity dependent manner at 1T-5T intensities tested. L-NOArg was administered cumulatively i.v. starting from 0.3 mg/kg, then 3 mg/kg, and 30 mg/kg. Time interval between each cumulative administration of L-NOArg was approximately 40 min. Three and 30 mg/kg of L-NOArg significant reduced the NBM stimulation-induced increase of cortical BF at intensities of 2T and 3T. The response at an intensity of 5T was reduced only by 30 mg/kg of L-NOArg to about half the control response. The reduced responses at 2T, 3T, and 5T were reversed following the i.v. administration of a physiological precursor of NO, L-arg (300 mg/kg). Inhalation of 10% CO2 for 15 s induced an increase in cortical BF which was not influenced by L-NOArg and L-Arg. These results suggest that NO is a necessary factor in the vasodilation of the cortical BF that is brought about by cholinergic fibers originating in the NBM.

Macrophage migration inhibitory factor activates hypoxia-inducible factor in a p53-dependent manner.

Background Macrophage migration inhibitory factor (MIF) is not only a cytokine which has a critical role in several inflammatory conditions but also has endocrine and enzymatic functions. MIF is identified as an intracellular signaling molecule and is implicated in the process of tumor progression, and also strongly enhances neovascularization. Overexpression of MIF has been observed in tumors from various organs. MIF is one of the genes induced by hypoxia in an hypoxia-inducible factor 1 (HIF-1)-dependent manner. Methods/Principal Findings The effect of MIF on HIF-1 activity was investigated in human breast cancer MCF-7 and MDA-MB-231 cells, and osteosarcoma Saos-2 cells. We demonstrate that intracellular overexpression or extracellular administration of MIF enhances activation of HIF-1 under hypoxic conditions in MCF-7 cells. Mutagenesis analysis of MIF and knockdown of 53 demonstrates that the activation is not dependent on redox activity of MIF but on wild-type p53. We also indicate that the MIF receptor CD74 is involved in HIF-1 activation by MIF at least when MIF is administrated extracellularly. Conclusion/Significance MIF regulates HIF-1 activity in a p53-dependent manner. In addition to MIFs potent effects on the immune system, MIF is linked to fundamental processes conferring cell proliferation, cell survival, angiogenesis, and tumor invasiveness. This functional interdependence between MIF and HIF-1α protein stabilization and transactivation activity provide a molecular mechanism for promotion of tumorigenesis by MIF.

Xenon has greater inhibitory effects on spinal dorsal horn neurons than nitrous oxide in spinal cord transected cats.

UNLABELLED Xenon (Xe) suppresses wide dynamic range neurons in cat spinal cord to a similar extent as nitrous oxide (N2O). The antinociceptive action of N2O involves the descending inhibitory system. To clarify whether the descending inhibitory system is also involved in the antinociceptive action of Xe, we compared the effects of Xe on the spinal cord dorsal horn neurons with those of N2O in spinal cord-transected cats anesthetized with alpha-chloralose and urethane. We investigated the change of wide dynamic range neuron responses to touch and pinch by both anesthetics. Seventy percent Xe significantly suppressed both touch- and pinch-evoked responses in all 12 neurons. In contrast, 70% N2O did not show significant suppression in touch- and pinch-evoked responses. These results suggest that the antinociceptive action of Xe might not be mediated by the descending inhibitory system, but instead may be produced by the direct effect on spinal dorsal horn neurons. IMPLICATIONS Xenon (Xe) is an inert gas with anesthetic properties. We examined the antinociceptive effects of Xe and nitrous oxide (N2O) in spinal cord-transected cats. Our studies indicate that Xe has a direct antinociceptive action on the spinal cord that is greater than that of N2O.

Isoflurane and Sevoflurane Augment Norepinephrine Responses to Surgical Noxious Stimulation in Humans

Background Suppression of hypertensive response to noxious stimulation by volatile anesthetics may be a result of suppression of the stimulation‐induced norepinephrine response or that of the cardiovascular response to catecholamines, or both. The suppression of the cardiovascular response is established, but that of norepinephrine response has not been confirmed. The authors hypothesized that the suppression of cardiovascular response but not that of norepinephrine response plays a major role in suppressing the noxious stimulation‐induced hypertensive response by volatile anesthetics. Methods Forty healthy donors for living‐related liver transplantation were allocated to four groups: receiving 1.2% (end‐tidal) isoflurane in oxygen and nitrogen, 2.0% isoflurane, 1.7% sevoflurane, or 2.8% sevoflurane. The intraoperative plasma norepinephrine and epinephrine concentrations, arterial blood pressure and pulse rate were measured for the first 15 min of surgery and were compared with the preoperative values. Results Norepinephrine and epinephrine concentrations both increased intraoperatively in all four groups. The values of maximum increase the area under the concentration‐versus‐time curve of norepinephrine were greater in the high dose groups of both anesthetics. The intraoperative blood pressure did not differ by different doses of anesthetics, and the degree of increase of blood pressure was not proportional to the plasma catecholamine concentrations. Conclusion The effects of isoflurane and sevoflurane on the surgical noxious stimulation‐induced norepinephrine response were inversely proportional to the dose. The suppression of noxious stimulation‐induced blood pressure response by anesthetics that were studied may be the result of suppression of the responses of vascular smooth muscle and myocardium to catecholamines.

Effects of sevoflurane on central nervous system electrical activity in cats.

We analyzed the effect of a new volatile anesthetic, sevoflurane (2%-5% in oxygen) on the electroencephalogram (EEG) of the neocortex, amygdala, and hippocampus, cortical somatosensory evoked potential (SEP), and brainstem reticular multiunit activity (R-MUA) in cats. Sevoflurane suppressed the background activity of the neocortex more than the amygdala and hippocampus. With increasing concentration of sevoflurane, the cortical EEG progressed from high-amplitude slow waves to a suppression-burst pattern, which was followed by an isoelectric pattern and then spikes with isoelectricity. The amplitude of the SEP was augmented and the R-MUA was suppressed by sevoflurane in a dose-related manner. Repetitive peripheral electrical stimulation induced generalized seizures at 5% sevoflurane in 2 of 13 cats. These results suggest that sevoflurane suppresses the background central nervous system electrical activities in a dose-related manner, leaving the reactive capabilities facilitated at deep anesthesia.

Nitric Oxide Synthase Inhibitor Does Not Reduce Minimum Alveolar Anesthetic Concentration of Halothane in Rats

Nitric oxide (NO) synthase inhibitor (Nω-nitro-L-arginine methyl ester [L-NAME]) has been reported to reduce minimum alveolar anesthetic concentration (MAC) of halothane when administered intravenously (IV) and to reduce thermal hyperalgesia, or produce antinociception in the formalin test, when administered intracerebroventricularly (ICV) or intrathecally (IT). This study attempts to identify the site(s) in the central nervous system (CNS) where L-NAME acts to reduce the halothane MAC. For this purpose, we examined the effects of IV, ICV, and IT administration of L-NAME on the halothane MAC in rats. In contrast to an earlier study, we did not observe any decrease in the halothane MAC after IV (10–30 mg/kg) administration of L-NAME. ICV (100 pg) and IT (100 pg and 1 mg) administration of L-NAME also did not alter the halothane MAC. These findings indicate that the L-arginine-NO pathway is not involved in the mechanism of action of halothane to suppress mechanical nociceptive response or in the nociceptive neural mechanism of mechanical stimulation.

Activation of the cortical and medullary dopaminergic systems by nitrous oxide in rats: a possible neurochemical basis for psychotropic effects and postanesthetic nausea and vomiting.

To provide a neurochemical basis for the central nervous system actions of nitrous oxide, the changes of brain dopamine (DA), serotonin (5‐HT), norepinephrine (NE), and metabolites of DA and 5‐HT were studied in rats. Thirty male Wistar rats were assigned to one of five groups according to the type of gas and the duration of gas exposure. The rats in one group, which served as control, were exposed to air for 30 min, and the rats in four other groups were exposed to 75% nitrous oxide in oxygen for 0.5, 1, 2, and 4 h, respectively. Animals were killed with microwave irradiation, and the brains were divided into seven sections: the cerebral cortex, cerebellum, striatum, hippocampus, midbrain‐thalamus, hypothalamus, and medullapons. The contents of NE, DA, 3,4‐dihydroxyphenylalanine (DOPAC), homovanillic acid (HVA), 5‐HT, and 5‐hydroxyindoleacetic acid (5‐HIAA) in each discrete area were measured with high‐performance liquid chromatography. Nitrous oxide had no significant effect on the contents of NE, 5‐HT, nor 5‐HIAA, but decreased that of DA in the striatum and midbrainthalamus after 4 h of exposure (P < 0.05). Levels of DOPAC, but not DA, in the cerebral cortex and medulla‐pons were increased significantly at exposures up to 2 h (P < 0.05), but were not significant from control levels after a 4‐h exposure. Increased levels of DOPAC indicate that nitrous oxide increases dopaminergic neuronal activities in the mesocortical projection and the medullary network. The euphoric properties of nitrous oxide may be a reflection of the activation of mesocortical dopaminergic projection, whereas the increased incidence of postexposure emesis may be a reflection of the activation of the medullary dopaminergic system. The attenuation after 4 h of exposure may correlate with development of acute tolerance to nitrous oxide actions.

Stimulation of the nucleus basalis of Meynert and substantia innominata produces widespread increases in cerebral blood flow in the frontal, parietal and occipital cortices

The effect of a focal stimulation of the magnocellular nucleus of the basal forebrain at two different areas, the nucleus basalis of Meynert (NBM) and the substantia innominata (SI), on local cerebral blood flow (CBF) in the frontal, parietal and occipital cortices was examined in urethane-anesthetized rats. The stimulation, either electrically or chemically, of both the NBM and SI produced significant CBF increase in all these 3 cortices ipsilateral to the stimulation site. This fact suggests that activation of neurons originating in the NBM and SI produces widespread increases in local CBF in the ipsilateral cerebral cortex.

Cutaneous stimulation regulates blood flow in cerebral cortex in anesthetized rats.

The effect of noxious or innocuous mechanical stimulation of cutaneous areas (face, forelimb and paw, back, hindlimb and paw) on cerebral blood flow in cortex was examined with laser Doppler flowmetry in anesthetized rats. Pinching of the face, forepaw and hindpaw for 15 s produced significant increases of systemic blood pressure and of cortical blood flow, whereas pinching of the back or brushing of any cutaneous area produced no significant changes in either parameter. Following spinal transection at the first thoracic level, the blood pressure response to forepaw pinching was suppressed, whereas the increase in cortical blood flow still took place. Thus the results suggest that the increase in cortical blood flow following cutaneous noxious stimulation is, in part at least, independent of changes in blood pressure and of any concomitant vasodilatation.

Persisting mild hypothermia suppresses hypoxia-inducible factor-1alpha protein synthesis and hypoxia-inducible factor-1-mediated gene expression.

The transcription factor hypoxia-inducible factor-1 (HIF-1) plays an essential role in regulating gene expression in response to hypoxia-ischemia. Ischemia causes the tissue not only to be hypoxic but also to be hypothermic because of the hypoperfusion under certain circumstances. On the other hand, the induced hypothermia is one of the most common therapeutic modalities to extend tolerance to hypoxia. Although hypoxia elicits a variety of cellular and systemic responses at different organizational levels in the body, little is known about how hypoxia-induced responses are affected by low temperature. We examined the influence of mild hypothermic conditions (28-32 degrees C) on HIF-1 in both in vitro and in vivo settings. In vitro experiments adopting cultured cells elucidated that hypoxia-induced HIF-1 activation was resistant to 4-h exposure to the low temperature. In contrast, exposure to the low temperature as long as 24 h suppressed HIF-1 activation and the subsequent upregulation of HIF-1 target genes such as VEGF or GLUT-1. HIF-1alpha protein stability in the cell was not affected by hypothermic treatment. Furthermore, intracellular ATP content was reduced under 1% O(2) conditions but was not largely affected by hypothermic treatment. The evidence indicates that reduction of oxygen consumption is not largely involved in suppression of HIF-1. In addition, we demonstrated that HIF-1 DNA-binding activity and HIF-1-dependent gene expressions induced under 10% O(2) atmosphere in mouse brain were not influenced by treatment under 3-h hypothermic temperature but were inhibited under 5-h treatment. On the other hand, we indicated that warming ischemic legs of mice for 24 h preserved HIF-1 activity. In this report we describe for the first time that persisting low temperature significantly reduced HIF-1alpha neosynthesis under hypoxic conditions, leading to a decrease in gene expression for adaptation to hypoxia in both in vitro and in vivo settings.