Abstract
1. Synaptic transfer between the retinal input and output was studied in turtle eyecups by injecting rectangular current pulses into a single cone or rod while recording externally from a ganglion cell.
2. When a receptor was activated with weak steps of polarizing current, the probability of obtaining a ganglion cell impulse rose after an S-shaped delay to a peak at about 0·1 sec and then declined. This suggests that the transmission chain behaves like an electrical band-pass filter containing delay and differentiating elements.
3. To further characterize the kinetics of excitation in the subthreshold region, the duration and polarity of the polarizing current pulses were varied while determining the magnitude of the threshold current and the delay to the ganglion cell impulses. The results of these experiments were described with linear models which assume that synaptic transfer occurs over a cascade of first-order delay stages and a single differentiating stage.
4. The pathways which relay off responses to light from rods and red-sensitive cones were formally similar, but the time scale in the rod path was several times slower. The path carrying off responses from the red-sensitive cones was faster than the on path. These kinetic differences indicate that independent pathways mediate each of the three categories of response and suggest that the kinetics of each path are `matched' to the input signals generated by light.
5. The strength—latency relations for the responses of on-centre ganglion cells to flashes and steps of light were approximately predicted from the description of synaptic transfer developed here and the description of visual transduction in red-sensitive cones from a previous study.
6. It is suggested that the retinal paths have kinetics which might be useful in transmitting light-evoked signals whilst attenuating noise present near the input.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Baylor D. A., Fettiplace R. Light path and photon capture in turtle photoreceptors. J Physiol. 1975 Jun;248(2):433–464. doi: 10.1113/jphysiol.1975.sp010983. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Baylor D. A., Fettiplace R. Transmission from photoreceptors to ganglion cells in turtle retina. J Physiol. 1977 Oct;271(2):391–424. doi: 10.1113/jphysiol.1977.sp012006. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Baylor D. A., Hodgkin A. L. Detection and resolution of visual stimuli by turtle photoreceptors. J Physiol. 1973 Oct;234(1):163–198. doi: 10.1113/jphysiol.1973.sp010340. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Baylor D. A., Hodgkin A. L., Lamb T. D. The electrical response of turtle cones to flashes and steps of light. J Physiol. 1974 Nov;242(3):685–727. doi: 10.1113/jphysiol.1974.sp010731. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Copenhagen D. R., Owen W. G. Functional characteristics of lateral interactions between rods in the retina of the snapping turtle. J Physiol. 1976 Jul;259(2):251–282. doi: 10.1113/jphysiol.1976.sp011465. [DOI] [PMC free article] [PubMed] [Google Scholar]
- DE LANGE DZN H. Research into the dynamic nature of the human fovea-cortex systems with intermittent and modulated light. I. Attenuation characteristics with white and colored light. J Opt Soc Am. 1958 Nov;48(11):777–784. doi: 10.1364/josa.48.000777. [DOI] [PubMed] [Google Scholar]
- Lamb T. D., Simon E. J. The relation between intercellular coupling and electrical noise in turtle photoreceptors. J Physiol. 1976 Dec;263(2):257–286. doi: 10.1113/jphysiol.1976.sp011631. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schwartz E. A. Electrical properties of the rod syncytium in the retina of the turtle. J Physiol. 1976 May;257(2):379–406. doi: 10.1113/jphysiol.1976.sp011374. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schwartz E. A. Responses of single rods in the retina of the turtle. J Physiol. 1973 Aug;232(3):503–514. doi: 10.1113/jphysiol.1973.sp010283. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Simon E. J., Lamb T. D., Hodgkin A. L. Spontaneous voltage fluctuations in retinal cones and bipolar cells. Nature. 1975 Aug 21;256(5519):661–662. doi: 10.1038/256661a0. [DOI] [PubMed] [Google Scholar]