Sensory processes最新文献

The membrane current of single rod outer segments in pieces of isolated toad retina was recorded with a glass suction electrode. Light evoked a slow net outward photocurrent consisting of a reduction in the steady inward dark current. In very dim light, the photocurrent broke up into discrete shot effects with a rounded shape and an amplitude of about 1 pA. These events were shown to result from photoisomerization of single rhodopsin molecules. The current in darkness showed fluctuations consisting of (a) discrete events apparently resulting from thermal isomerization of rhodopsin molecules, and (b) smaller amplitude shot effects shaped by two of the four rate processes of the light response.

Seven color-opponent bipolar and 50 color-opponent amacrine cells were identified in the carp retina and their spectral responses examined by using procion-dye-filled micropipets for staining and recording. Four of the bipolar cells had a +R-G-and three a +Y-B-type chromatic center. Six of the bipolar cells showed hyperpolarizing non-color-opponent surrounds, while one +R-G-type cell had a +Y-RB-type surround. This cell showed the greatest complexity of all bipolar cells identified so far, and its spectral property strongly suggests the existence of an intimate relation between it and +Y-RB-type horizontal cells. Examination and classification of the 50 amacrine cells revealed that 17 belonged to the +R-G, 16 to the -R+G, 6 to the +Y-B, and 11 to the -Y + B type. Most of these cells showed non-color-opponent surrounds. Yet, the similarity of the chromatic arrangement of their centers with that of the ganglion cells shows that the four basic types of color channels are already in existence in the amacrine cells where they seem to originate.

Responses of on-center bipolar cells and horizontal cells were recorded simultaneously in the carp retina, and the effect of polarization of horizontal cells on the bipolar cells was studied. Hyperpolarization by extrinsic current of horizontal cells elicited in the bipolar cells a hyperpolarizing response which, unlike the electrical coupling betweeen adjacent horizontal cells, was accompanied by a change in membrane conductance. The bipolar cell responses elicited by polarization of external horizontal cells showed a negative reversal potential, while those elicited by polarization of intermediate horizontal cells showed a positive reversal potential. It was suggested that the external horizontal cells modify the cone-bipolar transmission which involves the conductance change of subsynaptic potassium and/or chloride channels, while the intermediate horizontal cells modify the rod-bipolar transmission which involves the conductance change of sodium channels.

The effects of catecholamines (CA) and certain related compounds on the horizontal cell membrane potential were examined in the retina of the teleost (Eugerres plumieri). Each CA compound (dopamine, noradrenaline, and adrenaline) had a similar effect on each class of horizontal cell (photopic L- and C-type, scotopic L-type). The threshold effect, seen with 25-50 microM CA, was an enlargement of both center and surround responses in general. At higher concentrations (100-200 microM), CA augmented the center response and attenuated the surround considerably; these reciprocal changes usually were associated with moderate depolarization. Recovery took place in 15-20 min. The results indicate that up to a certain concentration CA do not affect directly the transmission from photoreceptors to horizontal cells. The lateral propagation of S-potential, however, appears selectively affected by CA. alpha-Methylnoradrenaline, 5-hydroxydopamine, and serotonin caused the same effect on horizontal cells as CA. Reserpine, clonidine, and L-dopa mimic the CA effect only after prior application of CA. Phentolamine blocked while propranolol, haloperidol, and pimozide did not influence the DA effect. We conclude that alpha-adrenergic receptors probably are involved in the CA-induced changes observed in horizontal cells.

The frequency-response characteristics of channels used in human vibrotaction were studied by using a psychophysical tuning-curve paradigm derived from auditory research. Sinusodial 200-msec vibratory bursts delivered to the thenar eminence of the hand were detected in the presence of sinusodial maskers delivered to the same skin area either continuously or pulsed in forward masking. Psychophysical tuning curves were obtained by determining the intensity of maskers of varied frequency necessary to mask a 10-dB SL test stimulus of fixed frequency. The results support the notion that at least two independent channels operate in human vibrotaction. There was no evidence for frequency selective mechanisms other than those at the periphery. Psychophysical tuning curves were similar to neural tuning curves for individual cutaneous mechanoreceptors.