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Polarization analysis in the crayfish visual system

Raymon M. Glantz

Department of Biochemistry and Cell Biology, Rice University, PO Box 1892, Houston, TX 77251, USA

View larger version (34K): [in a new window]   Fig. 1. Transient and dynamic polarization sensitivity in a lamina monopolar neuron. (A) Hyperpolarizing responses of lamina monopolar neurons (LMCs) to successive 0.2s flashes of polarized light at 1s-1 as the polarizer rotates through 540°. The lower trace is the response of a photodiode, which captures a small fraction of the stimulus signal from behind a vertically oriented polarizer. The largest pulses on the lower trace (arrows) indicate vertical polarization (=0°) and the smallest pulses (arrowheads) indicate horizontal polarization (=90°). Because the photodiode response is highly nonlinear, the amplitudes indicated in the stimulus trace do not reflect the correct intensity of the vertical e-vector in this or any of the figures. (B) Response of the same LMC (upper trace) to a changing e-vector (at the same intensity as in A) produced by a rotating polarizer. The stimulus light comes on at the left of the panel (t=2.0s) and polarizer rotation commences 5.5s later. The peaks and troughs of the lower trace indicate polarization angles of 0° (vertical) and 90° (horizontal), respectively. The dashed line corresponds to the membrane resting potential of the LMC (modified from Glantz, 1996a). (C) Response of a different LMC to a rotating polarizer with steady-state exposures at =90° at the left of the panel and =10° at the right. Note the very modest differences between the two steady-state responses compared with the response to the same two e-vectors during polarizer rotation.

View larger version (29K): [in a new window]   Fig. 2. Transient and dyn'amic responses of a tangential neuron (Tan1) to polarized light at varied e-vector orientations. (A) Tangential cell responses (top trace) to 0.2s flashes (at 0.5s-1) of polarized light at varied e-vector angles. The lower trace indicates stimulus timing and e-vector orientation (as described in Fig.1). (B) Response of the same tangential cell to a changing e-vector. The stimulus light (lower trace) comes on at t=1.0s and two cycles of polarizer rotation are separated by a steady-state exposure of 9s (modified from Glantz, 1996b). (C) Comparison of the steady-state (solid line) and dynamic (broken line) responses as a function of e-vector angle. Vertical bars are ± 1.0 S.E.M. Each point is the mean of five observations.

View larger version (48K): [in a new window]   Fig. 3. Sustaining fiber steady-state and dynamic responses to polarized light at varied e-vector angles. (A) The eye was exposed to continuous illumination and the e-vector was changed in a stepwise manner from the vertical (0°) at the left in four steps to horizontal (at t=25s, the lowest step on the polarization trace) and back to the vertical (modified from Glantz and McIsaac, 1998). (B) Sustaining fiber response to a changing e-vector. Polarizer rotation commences from a horizontal orientation at t=3.3s (start of the first rotation cycle) and undergoes 4.5 cycles of 180° rotation. Rotation is stopped at the vertical orientation.

View larger version (28K): [in a new window]   Fig. 4. Comparison of sustaining fiber and dimming fiber dynamic responses. (A) Sustaining fiber response to polarizer rotation. Note the approach of the membrane potential to the resting potential (0 mV on the ordinate) as approaches 90° (arrowhead). (B) Dimming fiber response to polarizer rotation. Note the hyperpolarizing inhibitory postsynaptic potentials (arrows) as the e-vector approaches the vertical.

View larger version (19K): [in a new window]   Fig. 5. Functional interaction between sustaining fiber (SF) O38 and a head-down motoneuron (HDMN). (A) Simultaneous recording of responses of SF O38 and an HDMN to a step increase in illumination delivered to the dorsoposterior quadrant of the visual field. (B) Cross-correlation histogram of SF O38 and the HDMN responses to a 5-minute exposure to continuous illumination. The ordinate is the conditional probability of a motoneuron impulse in a 1.0ms time bin following a sustaining fiber impulse. The abscissa is the time lag from the sustaining fiber impulse. The dashed line indicates the expected conditional probability of a motoneuron impulse on the basis of its mean firing rate (9impulsess-1) and assuming that motoneuron impulses occur at random times after a sustaining fiber impulse. The peak of the correlogram is at +5ms and the total conduction time to and from the inferred synapse in the brain is 3–4ms (modified from Glantz et al., 1984).

View larger version (49K): [in a new window]   Fig. 6. Head-down motoneuron response to a changing e-vector. The light beam was directed to the dorsal surface of the eye. The lower trace monitors polarizer rotation. The maximum signal indicates an e-vector orientation parallel to the long axis of the eyestalk, and the minimum signal indicates an e-vector orientation parallel to the equatorial axis of the cornea. Note the tendency of the discharge rate to peak as the e-vector orientation approaches the long axis of the eyestalk.

View larger version (22K): [in a new window]   Fig. 7. Measurement of the polarization sensitivity of a head-down motoneuron. (A) The post-stimulus time histograms represent responses to 1.0s flashes at 12 e-vector angles. 0° is parallel to the long axis of the eyestalk. Each histogram indicates the firing rate over a 2.0s span at 20ms per bin and averaged over 40 responses. The bar beneath each histogram indicates the timing of the light flash and the number adjacent to each histogram is the e-vector angle in degrees. The histogram labeled 135° is presented for comparison. It is identical to the histogram at –45°. (B) Peak impulse rate versus e-vector angle. (C) Peak impulse rate versus the intensity of unpolarized illumination. Unit intensity was 1.2mWcm-2.