Richard F. Olivo

Brief exposure to light initiates screening pigment migration in retinula cells of the crayfish,Procambarus

SummaryExposure of eyes excised from dark-adapted crayfish (Procambarus clarkii) to white light for 30s (Fig. 1) or 5s (Fig. 3) elicits migration of screening pigment in retinula cells; migration continues in the dark without requiring further exposure to light, and reaches completion within 5 to 10 min. For a 5-s exposure to light, the threshold illuminance is about 200 lx and the saturating illuminance is about 20,000 lx (Fig. 2). Between these limits, the extent of migration increases with illuminance, but the rate of migration remains relatively constant (Fig. 3). The calculated velocity of pigment granule transport is about 0.7 μm/s, which is comparable to the velocities reported for much smaller migration distances in some insect eyes.Since migration continues long after depolarization has ended, transport cannot be by electrophoresis, as Stavenga (1975) proposes. Control of migration by calcium ions is proposed as a likely hypothesis; calcium could act by activating a transport system or by causing the disassembly of microtubules.

Monitoring animals’ movements using digitized video images

An animal’s movements can be monitored continuously using video digitization techniques. We outline the differences between video frame-grabbers and column-scan digitizers, and describe two applications using column-scanners: detecting episodes of spontaneous locomotion and tracking the position of a moving appendage. Strategies are discussed for increasing the speed of software and for compressing the information in the video images into an analog motion signal to be displayed and stored for later analysis. Finally, the advantages and limitations of frame-grabbers and column-scan digitizers are assessed.

Spectral sensitivity of screening-pigment migration in retinula cells of the crayfish Procambarus.

Abstract In photoreceptors of insects and some other arthropods, the migration of screening pigment granules has been shown to have the same spectral- or polarization-sensitivity as the visual response. We demonstrate that for a crustacean, the crayfish Procambarus clarkii . the sensitivity spectrum of pigment migration matches the sensitivity spectrum of the electroretinogram. This provides further support for the theory that the visual response initiates the migration of screening pigment.

The effects of serotonin and octopamine on behavioral arousal in the crayfish

1. In the crayfish, behavioral arousal is known to elicit walking and to enhance compensatory eye movements. n n2. To see if serotonin and octopamine modulate arousal, we measured their effects on walking and eye movements in tethered crayfish, Procambarus clarkii. Serotonin strongly suppresses both walking and eye movements. n n3. In contrast, octopamine elicits an arousal-like state of continuous jittery leg movements and increased eye movements. n n4. Serotonins effect on arousal is uncertain, but octopamine remains a plausible modulator of behavioral arousal.

Proprioception provides a major input to the horizontal oculomotor system of crayfish

Abstract Compensatory eye movements in the horizontal (yaw) plane in crayfish are driven by the visual system and by proprioceptors in the legs. We used sinusoidal oscillation of a striped drum around the animal or a turntable beneath its legs to elicit eye movements. The striped drum produced the stronger response at low velocities; the turntable produced the stronger response at high velocities. When both vision and proprioception were stimulated together, the responses summed. The range of velocities of our experimental stimuli (2–35 deg/sec) matched the range of turning velocities generated spontaneously by freely-moving crayfish. Thus, during natural locomotion, proprioception could play a major role in stabilizing the eyes in the horizontal plane.

A practical and inexpensive frame-numbering device for use with automatic oscilloscope cameras

Abstract 1. 1. A circuit is described to provide sequential frame numbers for labelling photographs made with automatic oscilloscope recording cameras (such as the Grass C4). 2. 2. The device employs readily available digital integrated circuits to count frames and to drive seven-segment incandescent readout displays, which are positioned in view of the camera beneath the oscilloscope screen.