Electrical Activity of Perfused and Freely Swimming Squids as Compared with in vitro Responses

Abstract

The in vitro and in situ electroretinogram of squid (Todarodes pacificus Steenstrup) was investigated with microelectrodes. The electroretinogram recorded from the retinal surface was a sustained negative potential, but the response from the deeper layer was a positive potential (deep response), indicating that the receptor cell acts as an electric dipole. By moving a spot of light along a line passing over the microelectrode, it was shown that the deep response spread laterally from an illuminated area into surrounding unilluminated areas. From an experiment of selective adaptation by a polarized light, two sensitive planes were found in the squid retina, one responding maximally to a horizontally vibrating e-vector and the other being maximally sensitive to a vertical e-vector. The peaking wavelength in the spectral response curve of the electroretinogram is 480 mμ and agrees to absorption maximum of squid rhodopsin. Recording from freely swimming squid with an implanted electrode revealed the existence of marked oscillatory potential which occurred either spontaneously or responding to photic stimulation. This oscillation was considered to be attributed to summated impulses of the optic nerve fibers. Thus it was concluded that the axons of primary sensory cells convey impulses spontaneously to the central nervous system.