Proceedings of The Physiological Society
University of Central Lancashire (2002) J Physiol 543P, S229
Intracellular recordings from the photoreceptors of the cuttlefish, Sepia officinalis
G. Groeger and R. Williamson
The Marine Biological Association of the UK, The Laboratory, Citadel Hill, Plymouth PL1 2PB and Department of Biological Sciences, University of Plymouth, Plymouth PL4 8AA, UK
Cuttlefish eyes are similar in size and visual performance to those of many vertebrates. Like its vertebrate analogue, it is a single chamber eye, with a variable pupil and accommodating lens, and is controlled by a complex set of oculomotor muscles. The retina has a foveal-like area, containing closely packed photoreceptors. However, the organisation of the cuttlefish retina is much simpler than equivalent vertebrate retinas as it contains only photoreceptors and some supporting cells. The bipolar, horizontal, amacrine and ganglion cells of the vertebrate eye have their analogues within the cuttlefish brain. As part of a larger study to investigate visual processing in the cuttlefish, we examine here the intracellular response of the retinal photoreceptors in Sepia officinalis to controlled flashes of light.
For experiments, an animal was anaesthetised by immersion in 2 % ethanol in seawater, humanely killed by decapitation, and then the eyes excised. The anterior portion of the eye was removed and pieces of retina, approximately 1 cm2, dissected free and placed in a recording dish perfused with chilled, artificial seawater. Intracellular recordings were obtained from photoreceptors using glass pipettes of about 100 MΩ resistances, when filled with 4 M potassium acetate.
Intracellular recordings from individual photoreceptors showed that they had membrane resting potentials of -61 ± 16.4 mV (mean ± S.D.; n = 20) in the dark-adapted condition, and that they responded to a controlled flash of light with a depolarising response of up to 45 mV. The shape and duration of the response is illustrated in Fig. 1. In about half of the recordings, a clear burst of action potentials was observed in response to the flash stimulus. As the flash duration was increased from 1 to 50 ms, the maximum amplitude of the response increased from 2 to 37 mV. Flashes longer than 50 ms produced a plateau in the response. For flash intensities within the range 1
Where applicable, experiments conform with Society ethical requirements