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Biomedical subjects

M Ichikawa

Publications and source records attributed to M Ichikawa.

At least 343 records · Page 19Linked to original sources
PubMed1984

Axonal microtubules necessary for generation of sodium current in squid giant axons: I. Pharmacological study on sodium current and restoration of sodium current by microtubule proteins and 260K protein.

Effects of the reagents suppressing or supporting axoplasmic microtubule assembly were studied on the Na ionic current of squid giant axons by perfusing the axon internally with the solution containing the reagent. Among the reagents suppressing the assembly, colchicine, vinblastine, podophyllotoxin, sulfhydryl reagents such as DTNB and NEM, and chaotropic anions such as iodide and bromide, were examined. These reagents reduced maximum Na conductance and shifted the voltage dependence of steady-state Na activation in a depolarizing direction along the voltage axis. They also made the voltage dependence less steep, but did not affect sodium inactivation appreciably. Effects on Na ionic current of reagents which support microtubule assembly (Taxol, DMSO, D2O and temperature) were opposite the effects of those agents suppressing assembly. At the same time, we demonstrated that after Na currents were partially reduced, they could be restored by internally perfusing the axon with a solution containing microtubule proteins, 260K proteins and cAMP under conditions favorable for microtubule assembly. For full restoration, it was found that the following conditions were necessary: (1) The microenvironment within the axon is suitable for microtubule assembly. (2) Tubulins incorporated into microtubules are fully tyrosinated at their C-termini. (3) A peripheral protein having a molecular weight of 260,000 daltons (260K protein) is indispensable. These results suggest that axoplasmic microtubules and 260K proteins in the structure underlying the axolemma play a role in generating Na currents in squid giant axons.

Alkaloids↗
PubMed1984

Axonal microtubules necessary for generation of sodium current in squid giant axons: II. Effect of colchicine upon asymmetrical displacement current.

Effect of internal colchicine on asymmetrical displacement currents was studied by internally perfusing squid giant axons with a solution containing colchicine. It was found that (1) asymmetrical displacement currents were composed of two parts; colchicine-sensitive and colchicine-resistant; that (2) the colchicine-sensitive part had a definite rising phase while the colchicine-resistant one showed an instantaneous jump, followed by exponential decay; and that (3) the colchicine-sensitive part related to normal Na channels.

Animals↗
PubMed1984

Effects of feed restriction and switching the diet on proteinuria in male Wistar rats.

The effects of different dietary regimens on proteinuria in aging male Wistar rats were examined. When rats were given 50% restricted diets from the weanling and young adult (80-days-old) period, they excreted a physiologically normal level of less than 10 mg/day of urinary protein throughout life, and the electrophoretic pattern of their excreted proteins was also normal. This effect of dietary restriction in preventing proteinuria was due to simultaneous restrictions of total energy and protein intake. When rats of middle age (430-days-old) suffering from proteinuria were given 50% restricted diets, their urinary protein excretion decreased rapidly to 20 mg/day, but not further, and then the electrophoretic pattern of their excreted proteins was similar to that of rats with proteinuria. Results on the effect of switching from a commercial diet to 20% casein diet given ad libitum suggested that proteinuria in aging rats may be prevented by dietary control of certain nutrients besides total energy and/or protein intake.

Animals↗
PubMed1984

Endogenous nitrogen excretion in male highlanders of Papua New Guinea.

Endogenous nitrogen excretion was examined in highlanders of Papua New Guinea. Eight highlanders were fed a semisynthetic protein-free diet with about 49 kcal/kg of energy for 11 days. At the end of this period they excreted 29.2 +/- 4.0 mg N/kg of urinary nitrogen and 13.9 +/- 2.5 mg N/kg of fecal nitrogen per day. When the values were expressed per basal metabolic rate (BMR), they were 1.25 +/- 0.19 mg N/kcal BMR for urine and 0.59 +/- 0.08 mg N/kcal BMR for feces. The total amount was calculated as 43.1 +/- 4.3 mg N/kg (1.84 +/- 0.18 mg N/kcal BMR). Endogenous urinary nitrogen excretion in highlanders was the lowest so far reported; the effects of ethnic and nutritional backgrounds on obligatory urinary N loss were examined but no clear explanation was found for the highlanders' low value.

Adult↗
PubMed1984

Antipsychotic and prophylactic effects of acetazolamide (Diamox) on atypical psychosis.

We investigated the antipsychotic and prophylactic effects of acetazolamide (Diamox) on atypical psychosis. Acetazolamide was given to 30 patients: Type I, puberal periodic psychosis, a psychosis whose onset occurs during the period of puberty and which appears repetitively with psychosis-like condition at about the same interval as the menstrual cycle (6 cases); Type II, a) presenile atypical psychosis which initially appears in patients in their 20s or 30s accompanied by manic-depressive cycles and shows acute confusional and dreamy states in the presenile period, incurable cases (7), b) atypical psychosis, in the narrow sense, cases which show acute hallucination, delusion, confusional and dreamy states accompanied by affective symptoms (8 cases); Type III, repetitively the atypical manic and depressive states, and atypical manic-depressive psychosis, and transient changes in consciousness, refractory cases (2); Type IV, atypical schizophrenia, which is considered to be schizophrenia but shows the abnormalities in electroencephalogram and emotional disorders (7 cases). Among these cases, some extent of the therapeutic effects of acetazolamide (500-1,000 mg/day) was obtained in about 70%. The high therapeutic effects were particularly observed in Types I, II and III. It was less effective against atypical schizophrenia. Acetazolamide showed the effectiveness in 10 cases out of 13 cases to which lithium carbonate and carbamazepine were ineffective. The high therapeutic effects of acetazolamide were shown in the cases whose symptoms were aggravated at the interval of the menstrual cycle. No correlation was observed between the electroencephalographic abnormalities and the therapeutic effects. In addition, the prophylactic effects of acetazolamide on the periodic crisis were observed in 9 cases. From these results, acetazolamide was considered to have the antipsychotic and prophylactic effects on atypical psychosis. Since side effects due to acetazolamide were rarely observed, the present drug was considered to have a high safety margin.

Acetazolamide↗
PubMed1984

Ambulatory long-term vasodilator therapy for chronic refractory heart failure: hemodynamic evaluation and clinical response.

We evaluated long-term combined vasodilator therapy (hydralazine or ecarazine + isosorbide dinitrate) in 29 patients with chronic congestive heart failure resistant to the optimal conventional therapy. There were 24 men and 5 women, aged 28 to 76 years (mean 52 y/o). The etiology of heart failure was congestive cardiomyopathy in 24 patients, ischemic cardiomyopathy in 4 patients and advanced mitral regurgitation due to calcified mitral annulus in 1 patient. There were 21 patients in NYHA class III and 8 patients in NYHA class IV. All patients continued their previous therapeutic regimen during the period of this study. Hemodynamic measurements were performed with a triple lumen flow-directed balloon-tipped catheter in 20 patients to evaluate the effects of vasodilator therapy. In the rest of 9 patients, heart rate, blood pressure, chest X-ray examination for heart size (CTR) and M-mode echocardiograms for ejection fraction (EF) were monitored. The hemodynamic responses to the combined vasodilator therapy in 20 patients showed significant decreases in afterload and preload concomitant with an increase in cardiac output. The noninvasive evaluation of combined vasodilator therapy in 9 patients resulted in significant improvement in CTR and EF. We also noted a significant improvement in their symptoms of 29 patients. Side effects and drug toxicity were uncommon during vasodilator therapy. It is concluded that the combined vasodilator therapy is most useful adjunctive therapy in the management of severe refractory heart failure. Moreover, long-term nonparenteral vasodilators can be administered even at outpatient clinic without hemodynamic monitoring.

Adult↗
PubMed1983

Light and electron microscopic demonstration of guanylate cyclase in rat brain.

Guanylate cyclase (GTP pyrophosphate-lyase (cyclizing), EC4.6.1.2.) was histochemically demonstrated in rat brain with light and electron microscopes by using a specific monoclonal antibody to soluble guanylate cyclase from rat brain. Under a light microscope, intense reactions were seen in caudate-putamen complex, neocortex and cerebellar cortex. Immunoreactive cells were mainly some types of neurons such as small neurons in caudate-putamen complex, Purkinje cells in cerebellar cortex and pyramidal cells in neocortex. Some astroglial cells were also stained. Not all neurons or glial cells exhibited the positive guanylate cyclase reactivity. Electron microscopic examination revealed that guanylate cyclase was localized within postsynaptic components (perikaryon and dendrites) in neurons and in the cytoplasm and plasma membrane of astroglia. Presynaptic terminals were free of reaction. The observation supports a possibility that cyclic GMP is involved in the postsynaptic events of neuronal transmission and the regulation of intracellular processes.

Animals↗
PubMed1983

A Golgi study of Bergmann glial cells in developing rat cerebellum.

In order to examine the relationship between the Bergmann glial cells and the migrating granule cells, the postnatal development of the Bergmann glial cells in the rat cerebellum was analysed by a rapid Golgi method. In newborn rats where immature Purkinje cells occupied a rather thick zone (about 8 cells thick) between the thin molecular layer and the intermediate zone, immature Bergmann glial cells were recognized by the irregularly contoured somata situated within the deep part of the zone of Purkinje cells and by several perpendicular thin fibers (filiform fibers) which traversed the external granular layer (EGL) to terminate at the pial surface. After day 2 of the postnatal age (PD2), both somata and fibers of Bergmann glial cells showed gradual or fairly abrupt changes. The somata migrated upwards toward the molecular layer on PD2 and on PD4 were situated just beneath the Purkinje cells which had become arranged in a single layer. After PD6 the distance between the pial surface and the somata situated in the Purkinje cell layer and concomitantly the length of the Bergmann glial fibers, progressively increased in accordance with the thickening of the molecular layer. Between PD0 and PD8 the somata were irregularly contoured with short protoplasmic processes extending radially. After PD8 they gradually lost these short processes and became smooth. The Bergmann glial fibers were rather smooth with a few beady enlargements and tiny bud-like excrescences on their surface between PD0 and PD8. On PD12 the bushy expansions, characteristic of matured Bergmann glial fibers, suddenly increased in number on most fibers. After PD12 they continued to augment until PD25, when most fibers were entirely covered with the expansions. The number of fibers issuing from each Bergmann glial cell and entering the EGL increased postnatally reaching a peak on PD8, and then decreased gradually. These changes in the number of Bergmann glial fibers corresponded well with those in the number of external granule cells, suggesting the presence of developmental interactions between these two kinds of cells.

Animals↗
PubMed1983

Spatial and temporal pattern of postnatal proliferation of Bergmann glial cells in rat cerebellum: an autoradiographic study.

In order to examine the relationship between the Bergmann glial cells and the migrating granule cells, the development of the Bergmann glial cells in the rat cerebellum was studied with 3H-thymidine autoradiography. 3H-thymidine was injected intraperitoneally into rats on two days successively between days 2 and 21 of the postnatal age (PD2 and PD21). All animals were sacrificed on PD25 and the vermis of the cerebellum was embedded in epoxy resin. Semithin sections were cut sagittally for autoradiography. The labeling index of the Bergmann glial cells in lobules I, II, III, IV, V, VIa, VIII, IX, and X reached the peak on PD6-7, and in lobules VIb and VII on PD8-9. Moreover, the lobules could be divided into three groups according to the day when cumulative labeling indices reached 50% of the total ones (LI50): The early-developing group (LI50; PD4.4-5.2) contained lobules I, II, III, IV, and V, the intermediate group (LI50; PD5.3-6.1) lobules VIa, VIII, IX, and X, and the late-developing group (LI50; PD6.6-7.8) lobules VIb and VII. The regional gradient of LI50 in the Bergmann glial cells corresponded approximately to the regional gradient in the ratio of late-forming granule cells; that is, the later the LI50 of the Bergmann glial cells, the higher is the ratio of the late-forming granule cells. This suggests that an intimate relationship exists between these two kinds of cells.

Age Factors↗
PubMed1983

Spatial and temporal pattern of postnatal proliferation of glial cells in the parietal cortex of the rat.

Rats were injected with [3H]thymidine on different postnatal days (PD 0 approximately PD 16) and sacrificed after 6 h. Parietal cortices were embedded in epoxy resin and then semithin sections for autoradiography and ultrathin ones for electron microscopy were made alternately. On the day of birth (PD 0), about 70% of total labeled cells within the cortical gray, which were proved to be glial cells, were observed in the inner half of the cortical width. On PD 4, however, the intracortical distribution of labeled cells was reversed, i.e. about 70% of labeled cells were found in the outer half. Thereafter, on PD 6 and PD 8, no significant difference of the number of the labeled cells could be noted between the outer and the inner halves of the cortical gray. The pattern of glial proliferation in the parietal cortex of early postnatal rat thus showed an inside-out tendency, although not so distinctive as that of prenatal neurogenesis in the neocortex. Electron microscopy of the labeled cells revealed that on earliest days, they showed the condensation of nuclear chromatin and abundant free ribosomes, both suggesting the immaturity of cells, while, on later days, the nuclear chromatin became dispersed and free ribosomes decreased, indicating the progress of cellular differentiation as glial cells.

Animals↗
PubMed1983

Cellular mechanism involved in the synthesis of cyclic GMP in nervous tissues.

Intracellular cyclic GMP content responds to the stimulation of muscarinic receptor in a variety of tissues. Several aspects of the cellular mechanism involved in the synthesis of cyclic GMP were investigated. 1. In cultured bovine chromaffin cells, acetylcholine as well as muscarine stimulated the 32Pi incorporation into phosphatidic acid, induced Ca2+ mobilization across the cells, and, in parallel, elevated intracellular cyclic GMP content. Phosphatidic acid added to culture medium also stimulated the efflux and influx of Ca2+ and the synthesis of cyclic GMP in bovine chromaffin cells and in neuroblastoma cells in the same fashion as acetylcholine. 2. We have succeeded in a purification of an endogenous activator for guanylate cyclase from rat brain and identified it as L-arginine. L-Arginine, but not D-arginine, activated soluble guanylate cyclase 10- to 20-fold at a low concentration (1-2 X 10(-5) M). The activation of the enzyme by L-arginine seemed to require Ca2+. Calcium accumulated in cells in response to muscarinic stimulation would activate guanylate cyclase in collaboration with L-arginine. 3. Using a specific monoclonal antibody, we demonstrated the cellular and subcellular localizations of guanylate cyclase in rat brain. An intense reaction was observed in the brain regions which were rich in muscarinic receptor. Electron microscopic examination revealed that guanylate cyclase was concentrated in the postsynaptic perikaryon and dendrites of some type of neurons indicating its involvement in neural transmission.

Acetylcholine↗