Pain threshold, learning and formation of brain edema in mice lacking the angiotensin II type 2 receptor.

The main biological role of angiotensin II type 2 receptor (AT2) has not been established. We made use of targeted disruption of the mouse AT2 gene to examine the functional role of the AT2 receptor in the central nervous system (CNS). We have previously shown that AT2-deficient mice displayed anxiety-like behavior in comparisons with wild-type mice. In the present study, we analyzed the pain threshold, learning behavior and brain edema formation using the tail-flick test, the tail-pinch test, the passive avoidance task and cold injury, respectively. In the passive avoidance task and cold injury, no differences were found between wild-type mice and AT2-deficient mice. In contrast, the pain threshold was significantly lower in AT2-deficient mice, compared with findings in wild-type mice. The immunohistochemical distribution of beta-endorphin in the brain was analyzed quantitatively in AT2-deficient mice and wild-type mice, using microphotometry. The fluorescence intensity of beta-endorphin in the arcuate nucleus of the medial basal hypothalamus (ARC) was significantly lower in AT2-deficient mice, compared with findings in wild-type mice. We found that the AT2 receptor does not influence learning behavior and brain edema formation. As AT2-deficient mice have increased sensitivity to pain and decreased levels of brain beta-endorphin, AT2 receptors may perhaps mediate regulation of the pain threshold.

Anxiety-like behavior in mice lacking the angiotensin II type-2 receptor.

The main biological role of angiotensin II type 2 receptor (AT2) has not been established. We made use of targeted disruption of the mouse AT2 gene to examine the role of the AT2 receptor in the central nervous system (CNS). AT2-deficient mice displayed anxiety-like behavior compared with wild-type mice. However, AT2-deficient mice showed no depressant-like activity and no change in hexobarbital-induced sleeping time as compared with findings in wild-type mice. Both noradrenergic and corticotropin-releasing factor (CRF) neuronal systems appear to be involved in this anxiety-like behavior. Diazepam, captopril (angiotensin I converting enzyme inhibitor), prazosin (alpha1 antagonist) reversed the anxiety-like behavior in these AT2-deficient mice, whereas yohimbine (alpha2 antagonist), phenylephrine (alpha1 agonist), clonidine (alpha2 agonist), isoproterenol (beta1/beta2 agonist), propranolol (beta1/beta2 antagonist) and alpha-helical CRF9-41 (CRF receptor antagonist) has no apparent effects on anxiety-like behavior in AT2-deficient mice. In addition, concentrations of plasma adrenocorticotropic hormone (ACTH) and corticosterone in AT2-deficient mice did not differ from these in wild-type mice, hence, there are probably no endocrine abnormalities involving the hypothalamic-pituitary-adrenal axis (HPA). The amygdala appears to play an important role in many of the responses to fear and anxiety. The number of [3H]prazosin but not [125I]CRF binding sites in the amygdala was significantly reduced in AT2-deficient mice. These findings indicate that the noradrenergic system is involved in mediating the anxiety-like behavior in AT2-deficient mice.

Reduction of depressive-like behavior in mice lacking angiotensinogen.

We made use of targeted disruption of the mouse angiotensinogen (ATN) gene to examine the functional role of the ATN in the central nervous system. Both male and female ATN-deficient mice displayed the reduction of depressive-like behavior in the behavioral despair swim tests and spontaneous locomotor activity diminished. However, both male and female ATN-deficient mice showed no anxiogenic-like or memory-deficit behavior and there was no change in the pain threshold. We propose that endogenous ATN in the central nervous system may regulate the depressant state in the brain.

Role of the angiotensin II type-2 receptor in the mouse central nervous system.

There are two known major angiotensin II receptor subtypes, type 1 (AT1) and type 2 (AT2), both of which are present in the brain. AT1 and AT2 receptors occur in characteristic distributions that are highly correlated with the distribution of angiotensin II-like immunoreactivity in nerve terminals. Acting through the AT1 receptor in the central nervous system, angiotensin II has effects on fluid and electrolyte homeostasis, neuroendocrine systems, autonomic pathways regulating cardiovascular function and behavior. While the role of the AT2 receptor in the brain is less well understood, recent knockout studies point to their involvement in behavioral and cardiovascular functions. We discuss here evidence regarding the function of the AT2 receptor in the brain, determined using mice lacking the AT2 receptor.

Motor discoordination and increased susceptibility to cerebellar injury in GLAST mutant mice.

To study the function of GLAST, a glutamate transporter highly expressed in the cerebellar Bergmann astrocytes, the mouse GLAST gene was inactivated. GLAST-deficient mice developed normally and could manage simple coordinated tasks, such as staying on a stationary or a slowly rotating rod, but failed more challenging task such as staying on a quickly rotating rod. Electrophysiological examination revealed that Purkinje cells in the mutant mice remained to be multiply innervated by climbing fibres even at the adult stage. We also found that oedema volumes in the mutant mice increased significantly after cerebellar injury. These results indicate that GLAST plays active roles both in the cerebellar climbing fibre synapse formation and in preventing excitotoxic cerebellar damage after acute brain injury.

Functions of the two glutamate transporters GLAST and GLT-1 in the retina.

In the retina, the glutamate transporter GLAST is expressed in Müller cells, whereas the glutamate transporter GLT-1 is found only in cones and various types of bipolar cells. To investigate the functional role of this differential distribution of glutamate transporters, we have analyzed GLAST and GLT-1 mutant mice. In GLAST-deficient mice, the electroretinogram b-wave and oscillatory potentials are reduced and retinal damage after ischemia is exacerbated, whereas GLT-1-deficient mice show almost normal electroretinograms and mild increased retinal damage after ischemia. These results demonstrate that GLAST is required for normal signal transmission between photoreceptors and bipolar cells and that both GLAST and GLT-1 play a neuroprotective role during ischemia in the retina.

Peptic ulcer therapy with lansoprazole and Helicobacter pylori eradication.

This study investigated the relationship between the clearance of Helicobacter pylori and the healing rate of ulcers after treatment with lansoprazole. Lansoprazole 30 mg/day was administered to 124 gastric ulcer (GU) patients and 57 duodenal ulcer (DU) patients. The healing rates were 89.6% in GU and 96.5% in DU. The rate of shift to the S2 stage of healing was 33.1% in GU and 38.6% in DU. The H. pylori-positive rate was 69.7% in GU and 74.5% in DU. H. pylori clearance rates after lansoprazole treatment were 43.4% in GU and 51.2% in DU. In GU, the ulcer healing rate in the H. pylori-positive to -negative group was significantly higher than that in the group that remained H. pylori-positive, but there were no significant differences in the rate of shift to the S2 stage of ulcer healing. In DU, there were no significant differences in either the healing rates or the rates of shift to the S2 stage of ulcer healing. This suggests that the clearance of H. pylori results in a high healing rate in GU.

NE-100, a novel sigma receptor ligand: effect on phencyclidine-induced behaviors in rats, dogs and monkeys.

Phencyclidine (PCP)-induced psychosis is a useful animal model for studies on schizophrenia. N, N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)-phenyl]- ethylamine monohydrochloride (NE-100) had no effect on conditioned avoidance responses (CAR) in rats, whereas, the PCP-induced impairment of avoidance inhibition was attenuated by NE-100. The PCP-induced ataxia or decreased attention in rhesus monkeys was to some extent overcome by NE-100. In dogs, PCP-induced either head-weaving behavior or ataxia, effects which were blocked by NE-100. Administration of PCP led to an increase in beta-2 and a decrease in delta relative power (RP) activity in cortical background spectral electroencephalographics (ECoG) in dogs. While NE-100 in itself showed no significant change in beta-2 and delta RP, NE-100 did block the PCP-induced beta-2 increase and delta decrease. These findings indicate that NE-100 attenuates the effect of PCP in experimental animals. This drug is being considered as a therapeutic for the treatment of patients in the schizophrenia.

The effect of VA-045 on disturbance in consciousness in experimental animal models.

The effect of VA-045, a novel apovincaminic acid derivative, on disturbance in consciousness was investigated in mice and rats. VA-045 and thyrotropin-releasing hormone (TRH) shortened the duration of pentobarbital-induced sleeping in rats. VA-045 and TRH improved head impact-induced disturbed behavior in mice. The duration of action of the improving effect of VA-045 was longer than that of TRH. VA-045 and TRH also ameliorated the global cerebral ischemia-induced neurological deficits. Global cerebral ischemia was produced by a 10 min occlusion of both common carotid arteries 24 hr after the permanent electrocauterization of bilateral vertebral arteries. VA-045, but not TRH, attenuated the global cerebral ischemia-induced decreased step through latency (STL) in a passive avoidance task in rats. TRH enhanced spontaneous locomotor activity in mice, whereas VA-045 had no effect on it. The pharmacological effects of VA-045 on disturbance in consciousness will be discussed.

Effect of VA-045 on a closed head injury model in rats.

The effect of VA-045, a novel apovincaminic acid derivative, was studied in a model of closed head injury (CHI) in rats. CHI was induced by dropping a 400 g weight through a tube from 70 cm above a steel helmet placed on the vertex. Intravenous administration of VA-045 and thyrotropin-releasing hormone (TRH) reduced both the duration of loss of righting reflex and the duration of disruption of spontaneous movement caused by CHI. VA-045, but not TRH attenuated the CHI-induced decreased step through latency (STL) on a passive avoidance task. Over the same time schedule, however, VA-045 did not attenuate the scopolamine-induced decreased STL. CHI-induced reduction of the amplitude of somatosensory evoked potentials (SEP) was recovered by VA-045 but not by TRH. These findings indicate that VA-045 may be useful for treating patients with CHI-induced disturbance in consciousness.

[The analgesic and antipyretic effects of a non-steroidal anti-inflammatory drug, oxaprozin, in experimental animals].

The analgesic and antipyretic effects of oxaprozin were investigated in comparison with those of indomethacin, ibuprofen, phenylbutazone and aspirin. On the various writhing tests in mice, the analgesic effect of oxaprozin was about 2 to 9 times more potent than those of ibuprofen, phenylbutazone and aspirin. On the other hand, the analgesic and antipyretic effects of oxaprozin in rats were roughly equivalent to those of aspirin, but less effective than those of the other drugs tested. On the urate synovitis test in dogs, only oxaprozin showed a prophylactic effect. Therefore, The effect of oxaprozin in mice and dogs was more potent than ibuprofen, phenylbutazone and aspirin. The metabolic rate of oxaprozin in rats is 3.5 and 7.2 times more rapid than in mice and dogs, respectively, and its blood level in rats is low. Moreover, the biological half-life of oxaprozin is 39 to 43 hr and 49 to 69 hr in dogs and humans, respectively. From these results, it is suggested that oxaprozin is more potent than ibuprofen, phenylbutazone and aspirin, and in clinical use, it is a long acting anti-inflammatory drug.

[Influence of hydrocortisone 17-butyrate 21-propionate on the visual and the auditory organs (author's transl)].

The visual toxicity and the ototoxicity of hydrocortisone 17-butyrate 21-propionate (HBP), a newly synthesized anti-inflammatory steroid, was investigated using rats and dogs. (1) Electroretinogram (ERG) and visually evoked potential (VEP) in rats were not changed when HBP was administered intravenously and intraperitoneally, even at the semilethal doses. Consequently, it was suggested that HBP had no effect on the visual nervous system. (2) Similar to other corticosteroids, the intra ocular pressure rose in the dogs received HBP. Nevertheless, these dogs showed neither the remarkable changes in ERG, in the fundus of the eye, in the histological examination, nor the turbidity of the cornea and the lens. Based on these facts, it was reasonable to think that the the rise in the intra ocular pressure caused by HBP was not so severe that induce the secondary influence to other visual functions. (3) The rats received HBP did not show any changes in the auditory function by the audiometry. As the result, HBP was thought to be one of the rather safety corticosteroids concerning the visual toxicity and the ototoxicity.