Sensory processes最新文献

Reversal potentials were measured for the center and surround responses of on-center bipolar cells in the carp retina. In the scotopic condition, the center response showed a reversal at 29 +/- 13mV, the surround response at 38 +/- 13 mV. The result suggests that both the center and surround responses were -53 +/- 11 mV and -59 +/- 11 mV, respectively. These responses were sensitive to the red light. It is therefore suggested that both the center and surround responses contributed by rods are mediated by changes in conductance of Na+ channels but in opposite ways. In the photopic condition, reversal potentials of the center and surround responses contributed by red cones are mediated by changes in conductance of K+ and/or Cl- channels, but in opposite ways. The responses in the mesopic condition showed the complex electrical properties as a consequence of interaction between the two ionic components described above.

Elemental analysis was made on the rod outer segments and fuscin granules in the frog eye by means of an energy-dispersive X-ray spectrometer combined with an electron microscope. The materials were prepared from the unfixed fresh retina by means of air-dried or freeze-dried cryosection, freeze-substitution, or the freeze-drying embedding method. An outer segment in the air-dried cryosection showed P, K, S, Cl, and Ca peaks. The dry section of freeze-substituted or freeze-dried embedded outer segment showed P, K, S, and Cl; K was lost in the wet section. The fuscin granules showed prominent peaks of Ca and Zn constantly, in addition to S, Cl, Mg, K, and occasionally Cu. The K peak was also lost in the wet section.

The three-dimensional organization of Müller cells in the retina of various vertebrates was investigated by means of high-voltage electron microscope stereoscopy using 2-5 micrometer-thick Golgi preparations. The alveolar compartments constituted by thin lamellar processes of the Müller cell were seen in the outer and inner nuclear layers. The radial process of the Müller cell has many irregular appendages which attenuate into thin lamellae to invade the neuropile. The functional significance of the characteristic morphological features of the Müller cell is discussed.

The electrical responses of rods are analyzed in different ionic environments. It is shown that the dark level of the membrane potential is predominantly determined by a sodium current, while the peak of responses to bright light is controlled by the concentration of external potassium. The sag from the peak to the plateau of photoresponses seems to be generated by different ionic mechanism. The effects produced by substituting the external calcium with EGTA are also analyzed. It is suggested that calcium plays a role in different mechanisms of generation of electrical responses.

Single units were recorded through glass microelectrodes placed on the optic disk or on the retina of the opened eye of the frog (Rana catesbiana). Units were classified as A-, B-, and C-fibers according to conduction velocities. By the method of collision between naturally elicited and electrically elicited impulses, many of the B-fibers and some A- and C-fibers, which showed unusual behavior to photic stimulation, were found to be efferent fibers. Retinal effects of the efferent nerves were studied by repetitive stimulation and cooling of the optic nerve. The effects were found to be both inhibitory and excitatory.

When a transient depolarization was evoked in horizontal cells by a transretinal current pulse, a small hyperpolarizing deflection (probably IPSP) was detected in cones. The IPSP was abolished by superfusion of the retina with GABA-containing Ringer solution, which also hyperpolarized the cones. These results suggest that, in the dark, a GABA-mediated negative feedback was operating from horizontal cells to cones, and terminated in the light. Application of GABA also caused remarkable changes in spectral response curves of horizontal cells, mainly because of suppression of responses to monochromatic lights of longer wavelengths. Therefore, it was concluded that the feedback plays an important role in mechanisms of conversion from the trichromatic process in cones to the opponent color process in horizontal cells.

Electrically evoked responses (E-responses) of L-and C-type horizontal cells produced by transretinal stimulation were studied under chromatic illumination in the carp retina. From the examination of E-S relations (E-response verus S-potential) and of the shape of both responses the following results were obtained: (1) Equilibrium potential of subsynaptic membrane is estimated as 0 to 10 mV above zero membrane potential. (2) L-cells receive signals from red-and probably from green-sensitive cones and feed them back to the former. (3) The depolarizing response to red light of C-cells is produced by delayed and reversed signals from L-cells. Thus the model proposed by W.K. Stell, D. O. Lightfoot, and T. G. Wheeler (Science, 1975, 190,989-990) is supported.

Goldfish mixed bipolar cells, which contact both rods and cones, comprise two types; Ma, with axon terminals in the distal sublamina(a) and Mb, with axon terminals in the proximal sublamina(b) of the inner synaptic layer. Type Ma cells make only wide-cleft junctions (WCJ), whereas type Mb cells make only narrow-cleft junctions (NCJ) with rods and cores. It follows that WCJs mediate sign-conserving synaptic transmission to the center hyperpolarizing Ma cells, whereas NCJs mediate sign-inverting transmission to the center depolarizing Mb cells. Bipolar cell (BC) surrounds may be mediated largely through horizontal cell (HC) pathways. Type Ma BCs appear to be influenced primarily through HC feedback at cones and both feedback and nonribbon feedforward contacts at rods; in contrast most Mb BCs may be influenced by both HC feedback and ribbon-associated feedforward contacts at rods and cones, accounting for the greater complexity of Mb BC surrounds. BC subtypes Mal and Mbl, which contact only red-sensitive cones (+ rods), are likely to have red-opponent (non-color-coded) surrounds mediated by H1 (L-type) cone HCs; while subtypes Ma2 and Mb2 and 3, which contact also green-sensitive cones, are likely to have red + green-opponent (color-coded) surrounds mediated by H1 and H2 (R/G C-type) cone HCs.