Search PubMed⌕ Search

Biomedical subjects

K Naka

Publications and source records attributed to K Naka.

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

Signal transmission in the catfish retina. I. Transmission in the outer retina.

Extrinsic current, either pulsatile or white-noise modulated, was injected into the (cone) horizontal-cell soma and axon, and resulting responses were recorded from nearby points. In the case of white-noise inputs, signal transmission between the two points was characterized by Wiener kernels. The signal transmission within the lamina, the S-space, formed by the (cone) horizontal-cell somas and axons is quasi-linear and very fast, indicating that the laminae are purely resistive networks within the frequency range of the light-evoked response. There exists signal transaction between the lamina formed by the somas and axons. The forward transmission is constant gain, low pass, but there is a filter for the reverse transmission to impede the backflow of high-frequency components. Signals in the horizontal-cell soma are transmitted to the bipolar cells. The transmission is sign noninverting for the on-center bipolar cells and sign inverting for the offcenter cells. The transmission is quasi-linear excluding complex mechanisms in the transmission. We believe that the forward and direct transmission of signals from the horizontal to bipolar cells is the most straightforward interpretation of the observation. The transfer functions between the horizontal and bipolar cells differ considerably from one bipolar cell to the next.

Animals↗
PubMed1985

Signal transmission in the catfish retina. II. Transmission to type-N cell.

Responses from channel catfish type-N (sustained amacrine) cells were evoked either by step changes in illuminance, i.e. brightening or dimming from a mean illuminance, or by a white-noise modulated light stimulus. Current injected into the horizontal-cell soma or axon produced responses in type-N cells that were very similar to those produced by light stimuli. Light- and current-evoked responses had linear and second- and third-order nonlinear components; the former contributed 40-50%, whereas the latter contributed 20-30% to the total response. The remainder of the response could have been due to higher-order nonlinearities or to intrinsic as well as extrinsic noise. Nonlinear components in the light- and current-evoked responses were sharp transient peaks, which were prominent in white-noise-evoked responses, and oscillatory wavelets. The high-frequency components in the cell's response, which result from nonlinearity, were absent in the responses from bipolar and horizontal cells. The nonlinear responses were predicted by the second- and third-order kernels. The type-N cell response was complex because the response had both linear and nonlinear components, and because of the complexities of second- and, probably, third-order kernels. The cell's complex response reflects the complex nature of the cell's function as well as its synaptic organization.

Animals↗
PubMed1985

Signal transmission in the catfish retina. III. Transmission to type-C cell.

Current injected into horizontal-cell somas and axons produced transient (on-off) depolarizations from type-C cells (commonly known as transient amacrine cells) similar to those produced by light. Both the light- and current-induced responses had very small linear components and nonlinear components as represented by the second-order kernels, which reproduced the cell's response with a reasonable degree of accuracy. The second-order kernels were well defined and stereotyped. The quadratic nature of the nonlinear component is reflected in the frequency doubling response as well as the very steep input-output relationship of the cell. Type-C cell's responses evoked by light and current differed in a subtle but distinct fashion, and this difference appeared in the signature of the second-order kernels. The light-produced kernels had two diagonal positive peaks and off-diagonal valleys ("four-eye" structure), whereas the current-produced kernels had a single on-diagonal positive peak with off-diagonal negative valleys ("three-eye" structure). The difference in the kernel configuration was reflected in the cell's step-evoked response. Some type-C cells produced faster responses whereas others produced slower responses, whether evoked by light or by current. Our past and present results show that type-C cells produce a very nonlinear response that is not necessarily complex.

Animals↗
PubMed1985

Yuta (shaman) and community mental health on Okinawa.

This study reports on the relations between the yuta (shaman) and the community mental health activities on Okinawa, Japan. Focus is on the process of initiation of the yuta and its meanings from the mental health viewpoints, the functions of the yuta in the particular cultural background of the island, and the importance of admitting the existence of the yuta in its relations to the psychiatric treatment in a mental hospital. The discussion is based on the authors' research findings which were obtained mostly through their therapeutic activities and their field studies. The authors' assumption is that each culture has in it a certain social background that is unique in that culture by which a stress or insanity is increased or brought about, but in the same culture there are ways to decrease the stress and to cure the insanity.

Cultural Characteristics↗
PubMed1985

[Fundamental and clinical studies on aztreonam in the field of obstetrics and gynecology].

Aztreonam (SQ 26,776, AZT), a new monobactam antibiotic, was fundamentally and clinically studied with the following results. Uterine and adnexal concentrations of AZT after intravenous injection of 1 g were highest 3 hours after administration in the ranges of between 18.6-23.4 micrograms/g 16.5-28.2 micrograms/g, respectively, and and rapidly decreased thereafter. Penetration of AZT into the pelvic dead space exudate was quickly recognized after intravenous injection of 1 g and its concentration 30 minutes after administration was 14.08 +/- 7.08 micrograms/ml and highest (22.35 +/- 5.85 micrograms/ml) 2 hours after administration. It gradually decreased to 8.50 +/- 2.07 micrograms/ml 6 hours after administration. Clinical effect was studied by administering 1-3 g of AZT twice a day for 3-16 days by intravenous drip infusion for 18 patients with various infections in the field of obstetrics and gynecology. Efficacy of AZT for 9 genital infection cases were excellent for 4 cases, good for 4 cases and poor for 1 case, with an overall efficacy rate of 88.9%. For 2 UTI cases, it was excellent for one case and good for the other, and for 4 pelvioperitonitis cases, excellent for 3 cases and good for 1 case. For 2 inflammation cases of the pelvic dead space, efficacy of AZT was excellent for both of them. With regard to side effect, there was only one rash case experienced. It was considered from the above results that AZT is sufficiently useful for the infections in the field of obstetrics and gynecology and also useful for various gynecologic surgery cases.

Adult↗
PubMed1984

Turtle and catfish horizontal cells show different dynamic response.

Horizontal cell responses of catfish and turtle have been found to differ in a characteristic way. These characteristics established by white-noise analysis show that the impulse response (first order Wiener kernel) of the catfish horizontal cell has a substantially shorter latency as well as peak response time than that of the turtle. The turtle horizontal cell, on the other hand, has a dynamic gain which is twice that of the catfish. Since these differences were established under conditions of ambient illumination, they may be expected to be functionally important in the visual experience of the animals under normal environmental conditions.

Action Potentials↗
PubMed1984

Effects of background and spatial pattern on incremental sensitivity of catfish horizontal cells.

Incremental sensitivity of cones and horizontal cells was examined in the retina of the channel catfish (Ictalurus punctatus). In horizontal cells, steady full-field background illumination made the spot-evoked dynamic response larger and faster. The "enhancement" of incremental sensitivity was maximal at background levels of 20-50 microW/cm2. Similar changes in response were obtained by enlarging the diameter of the test spot (to 4 mm) without background illumination. In cones, no such enhancement with background was observed and small (0.4 mm) and large (4.0 mm) spots produced similar responses. Similar enhancement by a steady background has been observed also in the proximal neurons of catfish retina.

Animals↗
PubMed1983

A comparison of spatio-temporal receptive fields of ganglion cells in the retinas of the tadpole and adult frog.

Receptive fields formed by ganglion cells were measured simultaneously in time and space in the adult and tadpole retinas. The spatio-temporal receptive-fields (STRFs) were measured by cross-correlating the spatio-temporal white-noise stimulus with the cells' spike discharges. Crosscorrelation was made photographically to extract the first order STRF kernel (approximately linear component of the STRFs). The time-course of STRF formed by the frog ganglion cells was twice as fast as that of the tadpole cells. The STRF formed by the tadpole ganglion cells was either a center-brightening or a center-dimming type whereas in the frog there was another class of cells which produced either complex STRFs or did not show any linear component in their STRFs. Size of the STRFs in frog and tadpole was similar in both frog and tadpole retinas.

Action Potentials↗
PubMed1983

A new photographic method for mapping spatio-temporal receptive field using television snow stimulation.

A means was devised to measure simultaneously spatial as well as temporal characteristics of visual receptive fields by stimulating the retina with the noise obtained on an unused television channel. The input, television snow, and the output, neural response, were recorded on a video tape. The tape was played back to obtain the (linear) spatio-temporal Wiener kernel by cross-correlating the input with the output. This method can be applied to extract the linear part of the visual responses in time and space.

Animals↗
PubMed1983

Decreased sensitivity of platelets to prostacyclin in patients with diabetes mellitus.

In order to ascertain the platelet sensitivity to prostacyclin (PGI2) in patients with diabetes mellitus, we determined the percentage inhibition of platelet aggregation and platelet ATP secretion following PGI2 addition in an in vitro system. The percentage inhibition of platelet aggregation caused by PGI2 in final concentration of 1.25, 2.5, or 5.0 ng/ml was significantly lower in diabetics than in healthy controls. That of platelet ATP secretion by 1.25 or 2.5 ng/ml of PGI2 was also significantly lower in diabetics. These data suggested that in patients with diabetes mellitus, the decreased sensitivity of platelets to PGI2 will bring about hypercoagulability and may become one of the risk factors of diabetic microangiopathy in cooperation with lowered vascular PGI2 generation.

Adenosine Triphosphate↗
PubMed1983

Salivary urea nitrogen as an index to renal function: a test-strip method.

To investigate the feasibility of using salivary urea nitrogen as an index of renal glomerular filtration rate, we developed and applied a new analytical system consisting of a urease-containing test strip and an automatic reflectance spectrometer. The concentrations of urea nitrogen so determined correlate well (r = 0.93) with concentrations in serum. These preliminary data suggest that our method can be used routinely as a simple and reliable means of detecting abnormalities of renal function.

Adolescent↗
PubMed1982

Spatio-temporal visual receptive fields as revealed by spatio-temporal random noise.

A means was devised to visualize the retinal receptive fields in time and space using the noise on unused television channels as spatio-temporal inputs and performing correlation between the input and output photographically. The method was applied to characterize the receptive fields of catfish retinal ganglion cells. The results were 1) there were two major types of receptive fields, circular and elliptical, 2) shapes and sizes of the field components changed with time (latency), and 3) a field's surround was often localized as hot spots.

Acoustic Stimulation↗