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Biomedical subjects

H Niki

Publications and source records attributed to H Niki.

At least 109 records · Page 6Linked to original sources
PubMed1985

Insulin release independent of a rise in cytosolic free Ca2+ by forskolin and phorbol ester.

The role of cytosolic free Ca2+ in insulin release was evaluated using isolated rat pancreatic islets permeabilized with digitonin and incubated in Ca-EGTA buffers to fix free Ca2+ concentration at arbitrary levels. Ca2+ induced insulin release in a concentration-dependent manner with the threshold being between 0.1 and 1 microM. The hormone release was increased by forskolin and 12-O-tetradecanoyl phorbol-13-acetate (TPA), a potent activator of adenylate cyclase and that of protein kinase C, respectively. The findings suggest that activation of both protein kinase A and protein kinase C modulate insulin release without a concomitant increase in cytosolic free Ca2+.

Animals↗
PubMed1985

Hippocampal unit activity and delayed response in the monkey.

Single unit activity was recorded from the hippocampus while Japanese monkeys (Macaca fuscata, n = 4) were performing a delayed response (DR) task. A total of 272 units showed an obvious change in discharge rate in relation to the events of the DR task. These 272 related units were classified into 6 groups: cue-light related units (n = 24), cue- and choice-light related units (n = 41), choice-light related units (n = 21), response-related units (n = 51), reward-error units (n = 17), and delay units (n = 118). Reward-error units contained reward-related and error-related units. Error-related units showed changes in firing after incorrect responses and/or after omission of reward on correct trials. It is noteworthy that 43.4% of the related units are delay units which showed increased or decreased firing preferentially during the delay period. Some units showed a differential firing pattern during cue or delay period depending on the spatial position of the cue. The results of the present study are interpreted as an experimental evidence for the involvement of the hippocampus in DR task.

Animals↗
PubMed1979

Prefrontal and cingulate unit activity during timing behavior in the monkey.

Single unit activity was recorded from the dorsolateral prefrontal cortex and the anterior cingulate cortex while monkeys were performing a modified differential reinforcement of long latencies (DRLL) task. A total of 252 prefrontal units and 218 anterior cingulate units showed an obvious change in discharge rate (increase or decrease) in association with one or more of the events of a DRLL task. Related units were classified into 3 main groups: S--R event units, reward-error units, and timing units. S--R event units consisted of three subtypes: stimulus-related, response-related, and stimulus--response-related units. Reward-error units contained reward-related units and error-recognition units. Error-recognition units showed a vigorous increase in firing only after incorrect responses. These units were also responsive to omission of reinforcement on correct trials. Three types of timing units were distinguishable. The first one showed an anticipatory change prior to stimulus onset, and the second one exhibited a gradual anticipatory change preceding the time of responding. The third one manifested a sustained change during delay and an abrupt cessation of change in firing at the time of response initiation.

Animals↗
PubMed1978

Effect of alpha-D-mannose and equilibrated D-mannose of insulin release.

The effects on insulin release of alpha-D-mannose and equilibrated D-mannose were studied in the isolated perfused rat pancreas. Although phosphomannose isomerase, in contrast to phosphoglucose isomerase, is stereospecific for beta-D-mannose-6-phosphate, the alpha anomer of D-mannose (2 mg/ml) was significantly more effective than equilibrated D-mannose in stimulating insulin release. The finding does not seem to accord with the view that the signal for hexose-induced insulin release arises from the glycolytic pathway, and suggests the existence of the stereospecific glucoreceptor(s) on the pancreatic B-cell membrane.

Animals↗
PubMed1977

Tritiated thymidine autoradiographic study on the origin and renewal of argentaffin cells in the pyloric gland of hamsters.

The origin and renewal of the argentaffin cells in the pyloric glands of hamsters were studied by flash, cumulative and pulse labelling autoradiography with 3H-thymidine. The argentaffin cells were identified by the Diazo Method using Fast Red B Salt. By flash labelling autoradiography, it was shown that the argentaffin cells located from the middle to the lower level of the pyloric mucosa were not labelled with 3H-thymidine, indicating that this cell type has no proliferative activity. On the 10th and the 20th day of cumulative labelling, 31% and 63% of the argentaffin cells in the gland were found to be labelled, respectively. The labelled argentaffin cells were concentrated in the upper part of the gland (around the region of the isthmus), and no label was found over nuclei of the cells at the lowermost level of the gland. These labelled cells were shown to undergo a downward migration in the days following pulse labelling. They were replaced by unlabelled (and weakly or very weakly labelled) cells which arose at the region of the isthmus. The argentaffin cells in the pyloric gland are thought to arise from epithelial precursor cells at the region of the isthmus. The labelled argentaffin cells in the gland were found to decrease in number almost exponentially after pulse labelling. This indicates that the life span of argentaffin cells is not fixed, but their renewal conforms to the "random loss system". The half time of turnover of this cell population was 15 days on average.

Animals↗
PubMed1977

Enzymatic oxidation of isethionate to sulfoacetaldehyde in bacterial extract.

Isethionate degradation in a bacterial extract was shown by the isolation of enzymes and by identification of an intermediate to take place in two steps; dehydrogenation to sulfoacetaldehyde and desulfonation leading to the formation of sulfite and acetate. The enzyme responsible for isethionate oxidation in the presence of FAD was particulate in nature and a solubilized preparation obtained by extraction with buffer of low ionic strength had oxidizing activities against only isethionate and n-butanol among compounds tested. The enzyme was inhibited by thiol and carbonyl reagents.

Acetaldehyde↗
PubMed1976

Prefrontal unit activity and delayed response: relation to cue location versus direction of response.

Two monkeys were trained to perform 3 kinds of spatial tasks (right-left DR, up-down DR, and conditional position discrimination with delay). In the conditional position task, the animal was required to respond to the right (left) choice key when the cue had been presented on the upper (lower) position. Single unit activity was recorded from the principalis area of the dorsolateral prefrontal cortex while the animal was performing the tasks. Once a differential delay unit (i.e., unit showing specificity during the delay period for two kinds of trials) was found in right-left DR (or up-down DR), the same unit was tested in the other tasks. A total of 32 differential delay units were investigated sufficiently to allow comparison of all 3 conditions. The results indicate that there are two types of differential delay units. The first type showed a clear dependence on the cue location, while the second type was related to the direction of the impending response. Activity of the second type of differential delay unit during the delay period served to predict the occurrence of errors, whereas this relation between unit discharge and correct or incorrect responses was not seen for the first type of differential delay unit.

Animals↗
PubMed1976

Interaction of alloxan and anomers of D-glucose on glucose-induced insulin secretion and biosynthesis in vitro.

The direct effects of alloxan on glucose-induced insulin secretion and biosynthesis and the interaction of alloxan and D-glucose anomers were studied in vitro by use of isolated islets from rat pancreas. Islets were pretreated by incubation for five minutes in media containing alloxan (0.2 mg./ml.) alone or alloxan with either the alpha or beta anomer of D-glucose (3 mg./ml.). After washing, batches of five islets were incubated in the medium supplemented with glucose (1.8 mg./ml.) for 60 minutes to observe insulin secretion and for 90 minutes to observe insulin biosynthesis. Prior exposure to alloxan alone produced marked inhibition of subsequent glucose-induced insulin secretion and biosynthesis. A significantly greater protection against these inhibitory effects of alloxan was observed by using the alpha anomer of D-glucose than the beta anomer. The anomeric preference of D-glucose for protecting islet cells from the inhibitory effect of alloxan on glucose-induced insulin secretion and biosynthesis was similar to that for triggering insulin secretion. Possible mechanisms of the inhibitory effect of alloxan and the protective effect of D-glucose anomers in connection with those of other sugars are discussed. It is suggested that a glucoreceptor, stereospecific to the alpha anomer of D-glucose, may exist for both insulin secretion and biosynthesis.

Alloxan↗
PubMed1975

Uptake of radioactive D-glucose anomers by pancreatic islets.

Isolated rat islets were incubated in media containing either the alpha or beta anomer of D-[1-3H]glucose for 5 min at 37 degrees. The amounts of the two anomers incorporated were determined using L-[1-14C]glucose as an extracellular space marker. The incorporation of beta-D-glucose was about twice that of alpha-D-glucose. Our previous and present results suggest that the two anomers of D-glucose each have a preferential function in pancreatic beta cells; alpha-D-glucose stimulates insulin secretion, and beta-D-glucose is transported into the cells.

Animals↗