Kyoji Tasaki

A simple, direct and rapid method for filling microelectrodes ☆ ☆☆

Abstract A new direct and rapid method for filling single and multibarreled drawn glass capillary microelectrodes is described.

The dual nature of the octopus electroretinogram

Abstract Micro-electrodes inserted through the octopus retina detect a sustained negative response on the anterior surface, next an equipotential area, and still deeper a sustained positive response. On the basis of differences between the two responses with respect to stimulus variables, especially wavelength, the existence of at least two potential origins in the octopus retina was suggested. Although there is evidence that in the squid retina the receptor cells act as a dipole, the assumption of only one dipole is not enough to account for the data from the octopus retina.

Duplex system in the simple retina of a gastropod mollusc,Limax flavus L.

SummaryThe ERG and optic nerve discharge of a slug,Limax flavus L., were recorded from the optic nerve with a glass capillary suction electrode (Fig. 1). The intensity-amplitude function of the ERG was found to consist of two sections, each being expressed by a power function of stimulus intensity (Fig. 3). By using spike discharges from the optic nerve as a criterion response, spectral sensitivity curves were obtained under dark adapted and light adapted states. The λmax for the dark adapted retina was 480 nm, but a shift of λmax to 460 nm occurred when the sensitivity at 480 nm was lowered by light adaptation by about 3 log units (Figs. 4, 5).During dark adaptation the retinal sensitivity increased rapidly at first, then gradually, and after about 10 min, the sensitivity increase occurred suddenly, showing a break in the dark adaptation curve. These results suggest the presence of two processes in theLimax retina which might represent the activities of two morphologically distinct cell groups, type I and type II.

Inhibitory retinal efferents from dopaminergic cells in the optic lobe of the octopus

The effect of dopamine (DA) and its related compounds upon retinal activities of the octopus was compared with that of repetitive stimulation of the optic nerve, while recording ERGs and light-elicited spike discharges. Retinal perfusion with DA or its agonist, apomorphine, markedly enhanced ERGs. The effect appeared at about 10(-8) M and saturated at 10(-6) M. Norepinephrine and L-DOPA had very little effect. Intraretinal injections of DA at different depths revealed that the site of DA action was in the plexiform layer. ERGs were also enhanced by optic nerve stimulation, which inhibited spike discharges. This inhibitory effect was particularly evident when discharges were weak. Consequently the inhibitory effect of optic nerve stimulation was exerted predominantly to the peripheral areas of the receptive field of a nerve bundle, thus resulting in a considerable reduction in the size of the receptive field. These observations suggest that the spatial resolution of this animal may be improved by the efferent activity.

An investigation of the lateral spread of potentials in the octopus retina

Abstract A radial organization was found in the spread of the normally positive responses recorded from deep (near the sclera) portions of the octopus retina. Around a locally illuminated region, positive responses are recorded toward the center of the retina and negative responses toward the near periphery. A unique central area of the retina was also found.

Response of rabbit horizontal cells to a contrast reversal stimulus.

Retinal ganglion cells of cats 4, rhesus monkeys 2 and rabbits 1,s can be segregated into two types based on whether they demonstrate linear (X-cells) or non-linear (Ycells) spatial summation. The neural network which gives rise to these two types of response patterns has not been determined although it has been suggested that X-cells receive their main input from bipolar cells, while Y-cells receive their main input from amacrine cells 10. What role the horizontal cells might play in determining the linearity of spatial summation by the ganglion cells has been largely ignored, although it is known that current (hyperpolarizing and depolarizing) injected into horizontal cells can alter the firing pattern of ganglion cells of catfish 12, carp 13 and pikOL In order to detemine whether horizontal cells in the rabbit retina show linear or non-linear spatial summation, we recorded the responses elicited by a contrast reversal or alternating phase stimulus placed at different positions in the receptive field 7,9. In an earlier study s, we showed that with the same stimulus, rabbit ganglion cells can be segregated into linear X-cells and non-linear Y-cells. We wish to report here that at low stimulus intensity levels, horizontal cells show linear spatial summation and the response pattern resembles that of the X ganglion cells. At higher intensities, the horizontal cells demonstrate non-linear spatial summation. The non-linearity is seen as a doubling of the frequency which is characteristic of the Y ganglion cells in cats 9 and rabbits s. Experiments were conducted on the isolated eye-cup preparation (retina, choroid and sclera) of rabbits. The preparation was maintained in a Ringer-Locke incubating medium, and good responses were obtained up to 12 h after enucleation (for complete details, see ref. 8). Bevelled glass microelectrodes (40-80 M ~ after bevelling) were used to record intracellularly from horizontal cells 16. Responses were identified as arising from horizontal cells by the following criteria. First, the response