Michio Miyoshi

Angiotensin type 1 receptor antagonist inhibits lipopolysaccharide-induced stimulation of rat microglial cells by suppressing nuclear factor κB and activator protein-1 activation

We investigated whether angiotensin (ANG) II and its receptors contribute to lipopolysaccharide (LPS)‐induced microglial activation through activation of the proinflammatory transcription factors nuclear factor κB (NF‐κB) and activator protein‐1 (AP‐1). Using primary microglial cell cultures, we examined whether losartan [ANG type 1 receptor (AT1) antagonist] alters the effects of LPS on: the production of interleukin‐1 (IL‐1) and nitric oxide, cell morphology, and NF‐κB and AP‐1 activities. Reverse transcription‐polymerase chain reaction revealed that LPS‐stimulated microglial cells exhibited marked mRNA expression for AT1, ANG type 2 receptor (AT2) and the ANG II precursor angiotensinogen, whereas non‐stimulated microglial cells expressed only those for AT2 and angiotensinogen. We further demonstrated marked peptide/protein expression for AT1 and ANG II in LPS‐activated microglial cells. LPS (100 ng/mL)‐stimulated microglial cells showed increased concentrations of IL‐1 and nitrite (a relatively stable metabolite of nitric oxide), and increased expression of IL‐1 mRNA as well as a morphological change from an amoeboid shape to a multipolar (mostly bipolar but sometimes tripolar) rod shape. These effects were all significantly inhibited by losartan treatment (10−5 m or less). NF‐κB and AP‐1 activities were enhanced in LPS‐stimulated microglial cells, effects that were significantly suppressed by losartan (10−5 m). ANG II application enhanced the LPS‐induced increases in IL‐1 and nitrite concentrations, as well as the LPS‐induced morphological changes and AP‐1 activation, and these enhancements were inhibited by losartan (10−5 m). These results suggest that endogenous ANG II enhances LPS‐induced microglial activities through stimulation of the microglial AT1, which itself evokes activation of the transcription factors NF‐κB and AP‐1.

Systemic administration of [6]-gingerol, a pungent constituent of ginger, induces hypothermia in rats via an inhibitory effect on metabolic rate

We investigated the effects of systemic administrations of ginger (Zingiber officinale Roscoe, Zingiberaceae) or its pungent constituent, [6]-gingerol, on resting body temperature in rats. Rats given ginger-containing rat chow for 5 days showed no changes in their day-night cycle of body temperature or physical activity. However, a single intraperitoneal (i.p.) injection of [6]-gingerol (2.5 or 25 mg/kg) induced a rapid, marked drop in body temperature in a dose-related manner, with no change in physical activity. A significant decrease in metabolic rate was observed immediately after an i.p. injection of [6]-gingerol (25 mg/kg), although heat-loss responses underwent no alteration (versus vehicle). These results suggest that in rats: (a) a decrease in metabolic rate is responsible for the [6]-gingerol-induced hypothermia, and (b) [6]-gingerol modulates or interferes with the mechanisms underlying body temperature regulation, while other bioactive constituents of ginger may counteract the hypothermic effect of [6]-gingerol.

Green odor inhalation by rats down-regulates stress-induced increases in Fos expression in stress-related forebrain regions

In the present study, on rats, a quantitative analysis of Fos protein immunohistochemistry was performed as a way of investigating the effects of inhalation of green odor (a mixture of equal amounts of trans-2-hexenal and cis-3-hexenol) on the neuronal activations in stress-related forebrain regions induced by acute and repeated stress. Rats were exposed to restraint stress for 90 min each day for 1, 2, 4, 7, or 11 consecutive days. The hypothalamic paraventricular nucleus (PVN), amygdala, hippocampus and paraventricular thalamic nucleus (PVT) were examined. Both acute and repeated restraint stress increased Fos-positive cells in the entire hypothalamic PVN, in the central and medial amygdala, and in PVT, although these responses declined upon repeated exposure to such stress. The stress-induced Fos responses were much weaker in rats that inhaled green odor during each days restraint. No increases in Fos-positive cells were observed in the hippocampus in acutely stressed rats. The Fos-immunoreactive response to acute stress shown by the piriform cortex did not differ significantly between the vehicle+stress and green+stress groups. Green odor had inhibitory effects on the stress-induced corticosterone response, body-weight loss, and adrenal hypertrophy. These results suggest that in rats, green odor inhalation may, in an as yet unknown way, act on the brain to suppress activity in the neuronal networks involved in stress-related responses (such as activation of the hypothalamo-pituitary-adrenocortical axis and activation of the sympathetic nervous system, as well as stress-induced fear responses).

Effects of head-down tilt on the intracranial pressure in conscious rabbits.

Head-down tilt (HDT) causes a fluid shift towards the upper body, which increases intracranial pressure (ICP). In the present study, the time course of ICP changes during prolonged exposure to HDT was investigated in conscious rabbits through a catheter chronically implanted into the subarachnoid space. The production of cerebrospinal fluid (CSF) after exposure to 7-days HDT was also examined by a ventriculo-cisternal perfusion method. The ICP increased from 4.3+/-0.4 (mean+/-S.E.M.) mmHg to 8.0+/-0.8 mmHg immediately after the onset of 45 degrees HDT, reached a peak value of 15.8+/-1.9 mmHg at 11 h, and then decreased to 10.4+/-1.1 mmHg at 24 h. During 7-days HDT, it also increased from 4.8+/-0.9 mmHg to 9.2+/-1.6 mmHg immediately after the onset of 45 degrees HDT, reached a peak value of 12.8+/-2.5 mmHg at 12 h of HDT, and then decreased gradually towards the pre-HDT baseline value for 7 days. The rate of CSF production was 10.1+/-0.6 microl/min in rabbits exposed to 7-days HDT, and 9.7+/-0.5 microl/min in control rabbits. These results suggest that the rabbits begin to adapt to HDT within a few days and that the production of CSF is preserved after exposure to 7-days HDT. The time course of ICP changes during HDT in conscious rabbits seems to be considerably different from that in anesthetized rabbits.

Enhancement of local anaesthesia action by organic acid salts (I) : possible change of excitability in nerve fibre membrane

Measurements of action potentials recorded from giant nerve fibres of the crayfish abdomen showed that by addition of an organic acid salt to a local anaesthetic solution, the onset of anaesthetic action became more rapid and the duration of action was prolonged. Similar results were also obtained in rat vagal nerves. The chemical structure of compounds having these enhancing effects was found to have, in common, a carboxyl group connected with either a benzene ring or an aliphatic hydrocarbon. Topical application of anaesthetic solutions to the skin of flexor side of the forearm in humans revealed that the duration of anaesthesia evaluated by the apparent decrease of the number of pain points was significantly prolonged by the addition of salicylate. The use of local anaesthetics combined with organic acid salts would be promising in clinical practice to enhance their action greatly.

Green odor and depressive-like state in rats: Toward an evidence-based alternative medicine?

It is widely accepted that mental stress is an important factor in the development of psychological disorders such as depression. On pre-existing evidence, the so-called green odor may have a relieving and sedative effect on animals exposed to stressful situations. Using two behavioral models of depression, the forced-swim test and learned helplessness paradigm, we investigated whether inhalation of green odor (a 50:50 mixture of trans-2-hexenal and cis-3-hexenol) might alleviate and/or prevent experimentally induced depressive-like states in rats. A 3-min swim every day for 7 days resulted in significant prolongation of immobility time (vs. day 1). Inhaling green odor, but not vehicle, thereafter for 10 days (without swimming) led to the prolonged immobility time being significantly reduced and the hippocampal level of brain-derived neurotrophic factor (BDNF) being significantly increased. In the learned helplessness paradigm, the failure number and time spent in the shock compartment seen in the active avoidance test were both significantly attenuated in those rats that inhaled green odor for 11 days after the postshock screening test (vs. vehicle-exposed rats). Finally, for 10 consecutive days rats continuously exposed to green odor or vehicle swam for 3 min/day. Immobility time was significantly shorter in the green-odor group than in the vehicle-exposed group on days 6-10. These results suggest that green odor has not only a therapeutic, but also a preventive effect on depressive-like states in rats. These effects may be at least in part due to a green odor-induced upregulation of BDNF in the hippocampus.

Chronic restraint stress in rats suppresses sweet and umami taste responses and lingual expression of T1R3 mRNA

Effects of chronic restraint stress on the taste responses to five basic taste qualities were investigated electrophysiologically in the rat chorda tympani. In addition, the mRNA expression for T1R3, the common G-protein-coupled receptor (GPCR) for sweet and umami tastes, was studied quantitatively by RT-PCR after such stress. Rats were restrained in a small cylindrical restrainer made of steel wire for 8h daily for 14 successive days. The integrated responses to sweet and umami tastes, as recorded from the chorda tympani, were significantly suppressed after such stress, but the other three basic taste responses were unaffected. Expression of T1R3 mRNA in the fungiform papillae, as estimated by RT-PCR, was slightly reduced by the stress, and a quantitative real time RT-PCR study revealed a significant suppression of T1R3 mRNA expression in the stress group. These results suggest that the observed stress-induced changes in taste sensation could be caused by a peripheral disorder of the transduction mechanism in taste-receptor cells, involving in particular a stress-induced inhibition of T1R3 expression.

Effect of Natriuretic Peptide Receptor Antagonist on Lipopolysaccharide-Induced Fever in Rats: Is Natriuretic Peptide an Endogenous Antipyretic?

We investigated whether natriuretic peptide (NP) acts as an endogenous antipyretic inside and/or outside the blood-brain barrier in rats made febrile by systemic administration of bacterial endotoxin (lipopolysaccharide; LPS). Intravenous (i.v.) injection of LPS induced a triphasic fever, the second phase of which was significantly enhanced by an i.v. injection of the NP receptor (A-type and B-type) antagonist HS-142-1, a glucose-caproic acid polymer. In contrast, the same antagonist (i.v.) had no effect on the fever induced by i.v. injection of interleukin (IL)-1β. An i.v. administration of HS-142-1 enhanced the LPS (i.v.)-induced IL-1β response in the rat spleen. An i.v. treatment with atrial NP (ANP) significantly attenuated the second phase of the LPS-induced fever. On the other hand, i.c.v. injection of the above-mentioned NP receptor antagonist resulted in an augmentation of the third phase of the fever induced by i.v. administration of LPS, the same phase that was attenuated by ANP given i.c.v. When given intracerebro-ventricularly (i.c.v.), the antagonist had no effect on the fever induced by i.v. IL-1β. Finally, the fever induced by i.c.v. injection of LPS was not affected even by an i.c.v. administration of the antagonist. These results suggest that the production of pyrogenic cytokines (such as IL-1β) that follows i.v. LPS injection may be inhibited by NP acting outside the blood-brain barrier, leading to an inhibition of the fever. In contrast, inside the blood-brain barrier NP may inhibit cytokine-independent mechanisms present within the rat brain that mediate LPS (i.v.)-induced fever.

Systemic administration of lipopolysaccharide upregulates angiotensin II expression in rat renal tubules: Immunohistochemical and ELISA studies

We investigated whether angiotensin II (AII) peptide is induced in the rat kidney under endotoxemic conditions. Immunohistochemistry revealed strong AII-like immunoreactivity in the renal tubules of rats given high-dose lipopolysaccharide (LPS; 1000 microg/kg) intraperitoneally (i.p.). AII-like immunoreactivity in renal tubules was slight at 1h after the LPS injection, but marked at 3 h. There were few signals in the kidney in saline-injected control rats. When injected at 0.1, 10, or 1000 microg/kg i.p., LPS-induced a dose-related increase in AII-like immunoreactivity in renal tubules that was unaffected by treatment with the prostaglandin-synthesis blocker indomethacin. ELISA measurement of the AII concentration in the whole kidney supported the above findings. These results suggest that systemically administered LPS induces AII peptide expression in renal tubules by a prostaglandin-independent mechanism.

Exercise pressor reflex function in female rats fluctuates with the estrous cycle

In women, sympathoexcitation during static handgrip exercise is reduced during the follicular phase of the ovarian cycle compared with the menstrual phase. Previous animal studies have demonstrated that estrogen modulates the exercise pressor reflex, a sympathoexcitatory mechanism originating in contracting skeletal muscle. The present study was conducted in female rats to determine whether skeletal muscle contraction-evoked reflex sympathoexcitation fluctuates with the estrous cycle. The estrous cycle was judged by vaginal smear. Plasma concentrations of estrogen were significantly (P < 0.05) higher in rats during the proestrus phase of the estrus cycle than those during the diestrus phase. In decerebrate rats, either electrically induced 30-s continuous static contraction of the hindlimb muscle or 30-s passive stretch of Achilles tendon (a maneuver that selectively stimulates mechanically sensitive muscle afferents) evoked less renal sympathoexcitatory and pressor responses in the proestrus animals than in the diestrus animals. Renal sympathoexcitatory response to 1-min intermittent (1- to 4-s stimulation to relaxation) bouts of static contraction was also significantly less in the proestrus rats than that in the diestrus rats. In ovariectomized female rats, 17β-estradiol applied into a well covering the dorsal surface of the lumbar spinal cord significantly reduced skeletal muscle contraction-evoked responses. These observations demonstrate that the exercise pressor reflex function and its mechanical component fluctuate with the estrous cycle in rats. Estrogen may cause these fluctuations through its attenuating effects on the spinal component of the reflex arc.