Decremental conduction of the visual signal in barnacle lateral eye

Abstract

SUMMARY1. There are problems associated with the notion that slow potentials alone are used to transmit information in the early stages of some visual systems. This idea and alternatives have been tested on the barnacle lateral ocellus, a simple eye with only three photoreceptors, each with its own axon about 1 cm long.2. All of the receptors have very similar properties including spectral sensitivity, and are also electrically coupled together. Impulses cannot be recorded from any of the cell bodies, all ofwhici have been impaled as shown by dye marking.3. No impulses can be recorded externally from most of the ocellar nerve or intracellularly from the receptor axon terminals. Impulses driven by light, sometimes recorded in the final part of the nerve, are believed to originate in other axons.4. During illumination of the eye, current enters the receptor soma and leaves via the rest of the axon. This is consistent with the idea that the axon acts as a purely passive cable. The passive behaviour was also demonstrated in a comparison of the relative attenuation down the axon, of hyperpolarizations and depolarizations.5. Calculations based on the supposed electrical constants of the somas showed that the slow potential itself was unlikely to be the visual signal, since it would be enormously attenuated by passive spread down the long thin axons. To check this, the axon terminals in the supraoesophageal ganglion were penetrated and identified by electrical and dye-marking criteria. In fact, the slow potential was attenuated in the most favourable

Saturation of the response to light in Limulus ventral photoreceptor.

“…Hence, ri is 1*70 x 107 Q cm-1. Since the axon of the ventral photoreceptor appears not to conduct action potentials it probably resembles the axon of the barnacle photoreceptor in having a long space constant (Shaw, 1972). If we take A = 5 mm, then Rin = 8-5 MQ.…”

Cellular synthesis and axonal transport of gamma‐aminobutyric acid in a photoreceptor cell of the barnacle.

“…1 A). As the receptor cells are electrically coupled to some extent (Brown, Hagiwara, Koike & Meech, 1971;Shaw, 1972), although a direct contact or a gap junction between the cells was not demonstrated (Fahrenbach, 1965), it might not be surprising to find some movement of GABA between the cells. Such a movement was demonstrated between the electrically coupled Retzius cells of the leech (Rieske, Schubert & Kreutzberg, 1975).…”

“…The photoreceptor cell in the lateral ocellus of B. eburneus has a long axon (up to 9 mm in length; Shaw, 1972). The movement of intracellularly injected radioactive substances along the axon can be followed by autoradiography (cf.…”

“…This large size enabled stable intra-cellular recordings (Gwilliam, 1963(Gwilliam, , 1965Brown, Hagiwara, Koike & Meech, 1970; , as well as intra-axonal recordings (Shaw, 1972; Ozawa, Hagiwara, Nicolaysen & Stuart, 1976;Hudspeth, Poo & Stuart, 1977; Hudspeth Ross & Stuart, 1978). These studies have revealed that illumination causes a slow, sustained depolarization but no spike 0022-3751/80/1090-0414 $07.50 © 1980 The Physiological Society H. KOIKE AND K. TSUDA potentials in the photoreceptor cell and its axon, and that this depolarizing receptor potential spreads electrotonically towards the axon terminal which is several millimetres away from the cell body (Shaw, 1972;. In response to the depolarization of the receptor, a hyperpolarization with membrane conductance increase is recorded from post-synaptic cells in the supra-esophageal ganglion (I cell of Stuart & Oertel, 1978).…”

Facilitation in arthropod photoreceptors.

“…Facilitation was first reported in 1954 by Ruck and Jahn for isopod crustaceans. Subsequently, facilitation has been reported for: arthropods of two other classes (spiders-DeVoe, 1972;insects-Giulio and Lucaroni, 1967;Ventura and Puglia, 1977); the barnacle (Stratten and Ogden, 1971;Shaw, 1972); and cephalopod mollusks (Hartline and Lange, 1974). Facilitation has never been reported for vertebrate photoreceptors, although the effect of light in temporarily reducing sensitivity has been intensively investigated.…”