Abstract
The pallial nerves of Spisula solidissima each contain a single afferent nerve fiber which responds directly to illumination of the nerve, and apparently mediates the "shadow" response of siphon retraction. These units show constant-frequency spontaneous activity in the dark; illumination abruptly inhibits this discharge, and cessation of the light stimulus then evokes a prolonged burst of impulses at high frequency (the off-response). Impulses are initiated at a point near the visceral ganglion, and propagated unidirectionally toward it. Stimulation with monochromatic light has revealed that more than one photoreceptor pigment is involved, since the discharge patterns evoked are wavelength-specific. Inhibition is relatively prominent at short wavelengths, excitation at long wavelengths. Following selective adaptation with blue light, "on" responses can be produced with red stimuli, demonstrating the unmasking of an excitatory event which takes place during illumination. The two photoreceptor pigments may be segregated in two or more cells presynaptic to the recorded unit, or,—more likely—may both be contained in the same cell. The spectral sensitivity function for inhibition shows a single maximum at 540 mµ, and is probably dependent upon a carotenoid pigment. No photoreceptor function has been demonstrated for a hemoprotein, apparently identical with cytochrome h, which occurs in high concentration in Spisula nerve.
Full Text
The Full Text of this article is available as a PDF (1.3 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- BROWN P. K., BROWN P. S. Visual pigments of the octopus and cuttlefish. Nature. 1958 Nov 8;182(4645):1288–1290. doi: 10.1038/1821288a0. [DOI] [PubMed] [Google Scholar]
- HUBBARD R., ST GEORGE R. C. The rhodopsin system of the squid. J Gen Physiol. 1958 Jan 20;41(3):501–528. doi: 10.1085/jgp.41.3.501. [DOI] [PMC free article] [PubMed] [Google Scholar]