| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
The Journal of Neurophysiology Vol. 80 No. 5 November 1998, pp. 2571-2583
Copyright ©1998 by the American Physiological Society
Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005
 |
ABSTRACT |
|---|
 Abstract
 Introduction
Methods
Results
Discussion
References
|
|---|
Glantz, Raymon M. and Andy McIsaac. Two-channel polarization analyzer in the sustaining fiber-dimming fiber ensemble of crayfish visual system. J. Neurophysiol. 80: 2571-2583, 1998. Polarization sensitivity (PS) was examined in two classes of neurons, sustaining fibers and dimming fibers, in the medulla externa (second optic neuropile) of the crayfish, Pacifasticus leniusculus. Visual responses were recorded intracellularly and extracellularly. The influence of e-vector orientation (
) was probed in steady-state responses, with brief flashes and with a rotating polarizer. The results indicate that the entire sustaining fiber population appears to be maximally sensitive to vertically polarized light. Although the evidence is less complete for dimming fibers, they appear to be maximally inhibited by vertically polarized light and excited by horizontally polarized light. Thus the sustaining fibers and dimming fibers form a two-channel polarization analyzer that captures the main features of the polarization system established in photoreceptors and lamina monopolar cells. The available evidence suggests that this two-channel system has the same characteristics across most or all of the retinula. Lateral inhibition in sustaining fibers is differentially sensitive to . Inhibition is substantial at = 90° (horizontal) and essentially absent at = 0°. The details of the sustaining fiber polarization response closely follow features established in more peripheral neurons, including the magnitude of PS, enhanced responsiveness to a changing e-vector, and modest directionality to a changing e-vector in~40% of the cells.
A notable feature of many arthropod and cephalopod visual systems is the sensitivity to the e-vector orientation ( This study is based on intracellular and extracellular recordings in the crayfish Pacifasticus leniusculus. The animals were prepared as in Glantz (1996b) Recording procedures
Intracellular recordings from sustaining fibers were made with micropipettes filled with 3.0 M potassium acetate (tip resistances of 100-200 M
Stimulus system
Visual stimuli were generated by two optical channels alternately accessible via a 45° mirror. One channel, consisting of a 7.0-mW helium-neon laser and directed by galvanometer controlled mirrors, was used to locate the receptive field. The sustaining fibers were identified on the basis of receptive field location, after the methods of Wiersma and Yamaguchi (1967) Experimental protocols
Because previous reports (Leggett 1976 Data acquisition and analysis
Data acquisition was performed with a Data Translation A/D card and a PC computer. Intracellular recordings were digitized at 500 Hz. For extracellular recordings the action potentials were isolated with a time-amplitude window discriminator and digitized at 300 Hz, which is the maximum discharge rate.
PS in the response to a stationary e-vector
Rotating a polarizer elicits transient responses, as in Fig. 1 (first 25 s), synchronized to the changes in e-vector angle. As Distribution of The
Sustaining fiber response to a changing e-vector
The sustaining fiber response to temporal variations in
PS in the inhibitory surround
The intensity dependence of PS described in Fig. 4 and the insensitivity of
PS in dimming fibers
Dimming fibers are spontaneously active in the dark and exhibit an OFF response to intensity decrements. Increments of illumination elicit a graded hyperpolarization and a pause in the discharge, as shown in Fig. 9. With polarized light, the hyperpolarizations elicited by pulses at
The principal purpose of this study was to examine the transfer of polarization-related information from the more distal nonspiking visual neurons to the sustaining fibers and dimming fibers. Toward this end, aspects of PS, previously measured in lamina monopolar cells and tangential cells, were examined with the same procedures in sustaining and dimming fibers. Both monopolar cells and tangential cells make indirect functional connections to sustaining fibers (Wang-Bennett and Glantz 1987a
INTRODUCTION
Abstract
Introduction
Methods
Results
Discussion
References
) of polarized light (Shashar and Cronin 1996
; Waterman 1981, 1984; Wehner 1989). This capacity arises from photoreceptors structurally specialized for the discrimination of (Shaw 1966, 1969; Waterman 1981). Arthropod retinula may contain two to four distinct e-vector channels (Marshall et al. 1991; Shaw 1966; Wehner 1983). Furthermore, polarization analysis may be extended by rotation of the retinula via head and eyestalk movements.
), the detection of specular reflections (Schwind 1991), and optomotor reflexes (Schöne and Schöne 1961; von Philipsborn and Labhart 1990; Wolf et al. 1980). The neuronal mechanisms that encode polarization-related signals are only partially understood. In crayfish, the retinular cells and lamina monopolar neurons form the basis of two parallel pathways that signal orthogonal s (Glantz 1996a; Nässel and Waterman 1977; Sabra and Glantz 1985; Waterman and Fernandez 1970). A subsequent stage consists of "tangential cells," which are components of the lamina-medulla externa (second optic neuropile) circuitry (Strausfeld and Nässel 1981; Wang-Bennett and Glantz 1987b). In one subclass of these cells PS is enhanced by an opponency mechanism, and the second subclass is directionally selective for a changing e-vector (Glantz 1996b). Tangential cells modulate the visual signals of the sustaining fibers (tonic ON neurons) (Wang-Bennett and Glantz 1987b), which in turn synapse on optomotor neurons (Glantz and Nudelman 1988; Glantz et al. 1984). The sustaining fibers and dimming fibers (tonic OFF neurons) are the principal output neurons of the medulla externa (Kirk et al. 1982; Wiersma and Yamaguchi 1966, 1967).
) and the crayfish Procambarus clarkii (Yamaguchi et al. in Waterman 1984) indicate strong sensitivity to a changing e-vector. PS was not examined in the dimming fibers. This study describes the stationary and dynamic polarization response of sustaining fibers and dimming fibers in Pacifasticus leniusculus. The results indicate a stationary PS profile with a single peak near the vertical for the entire population of sustaining fibers. Conversely, dimming fibers are inhibited by vertically polarized light and discharge maximally at a horizontal .
METHODS
Abstract
Introduction
Methods
Results
Discussion
References
. The eyestalks were glued in their sockets with cyanoacrylate adhesive. The blood was replaced with oxygenated saline during a 1-h perfusion at 8°C. The optic lobe was exposed by excision of the dorsal cuticle of the eyestalk. The animal was clamped in a Plexiglas chamber (containing 2 frosted glass windows, 2 cm on a side) and bathed in oxygenated saline at 20°C. One of the eyes was centered in front of a window at 15 mm from the frosted glass.
) and led to an Axoclamp B1 amplifier. The signals were stored on magnetic tape. All cells were impaled in the medulla externa (Kirk et al. 1982). The same procedures were also used to characterize dimming fibers and medullary amacrine neurons (Waldrop and Glantz 1985).
View larger version (56K):
[in a new window]
FIG. 1.
Response of sustaining fiber 019 to a changing e-vector orientation ( ) [clockwise (CW) polarizer rotation] and to stationary s. Membrane resting potential is 
65 mV and is indicated by zero on the left-hand ordinate. Bottom trace monitors polarizer rotation. = 0° (vertical) is up, and orientation is read from the right-hand ordinate.
View larger version (27K):
[in a new window]
FIG. 2.
Mean impulse rates vs. e-vector angle of cell described in Fig. 1. A: responses to stationary e-vector. Rates in pulses/s (pps) are based on 5.0-s samples between 3 and 8 s after each new is established; n = 10. Circles are at ±1.0 SD B: impulse rate vs. time as polarizer is rotated through two 360° cycles (bottom trace). Bottom trace, 
: e-vector angle of 150°. Scale for e-vector angle is on the right-hand ordinate. C: dynamic phase associated with peak impulse rate vs. stationary e-vector angle of maximum response (max) for 21 sustaining fibers. Note 4 data points are superposed. Continuous line is the least-squares regression with slope of 0.95. Correlation coefficient is 0.86.
View larger version (31K):
[in a new window]
FIG. 3.
Sustaining fiber (01) polarization response profiles to stationary flashes at varied e-vector angle. A: subthreshold responses. Log I = 4.7. Membrane resting potential is 60 mV and indicated by zero on the left-hand ordinate. Bottom trace: e-vector angle (right-hand ordinate) CW rotation. B: poststimulus time histograms (PSTs) of suprathreshold impulse trains elicited at 15° intervals. max is 15°. Each PST is based on 20 responses to 0.5-s flashes, and was varied from 40 to 120°. The peak transient discharge of each PST is aligned with the stimulus on the abscissa. C: PSTs at = 0° for 5 stimulus intensities. PS for the responses in B are determined from the ratio of intensities required for equal magnitude responses at max and min. D: polarization response profile of another cell (sustaining fiber 014). Note peaks at s of 20 and 100°. Data are organized as in B.
. The stimulus was controlled with an electromagnetic shutter and neutral density wedge.
; Waterman 1984; Yamaguchi et al. 1976) indicated that crustacean visual neurons are insensitive to the e-vector angle of a stationary flash, two protocols were developed to explore this issue. These procedures examine the steady-state and transient responses to variations in e-vector angle.
is presented for 8-10 s, and the polarizer is then rotated to another angle. Each rotation is associated with a transient burst of~1.0 s in duration. The -dependent variations in mean rate were assessed for the interval from 3.0 to 8.0 s after the establishment of each . The responses to each were measured 10 times.
was measured with a scanning procedure. Responses were elicited with brief (0.5-0.7 s) pulses of illumination, and the polarizer was rotated to successive angles in steps of 12-22°. For synaptic potential measurements, the responses to four to six stimulus cycles were averaged. For impulse trains, the responses to 20 cycles were averaged to form poststimulus time histograms (PSTs) at each e-vector angle. To avoid saturation, these experiments were performed at intensities <10% of the saturation intensity.
max necessary to generate comparable responses at max and min. To determine the dependence of PS on stimulus intensity (I), the response-intensity functions were measured at max and min. For any response magnitude PS = I(min)/I(max). For each neuron the average magnitude of PS was determined for the intensity range from 0.5 log units above threshold to just below saturation intensity. The PS of dimming fibers was measured in seven cells from the size of the light-elicited inhibitory postsynaptic potential (IPSP).
was examined with a rotating polarizer. The influence of both the rate and direction of change was examined in 30 preparations. The responses were evaluated from the phase and amplitude of the oscillatory membrane potential and from variations in the impulse rate relative to .
.
). During excited states measurements were suspended until the control baseline rate resumed.
= 0.03 s) separated action potentials from the compound excitatory postsynaptic potential (EPSP). The filtered signals were then averaged with the stimulus trace as a temporal reference. The action potential sequences were converted into a train of unitary events and used to derive mean impulse rates and to form PSTs. Temporal variations in the impulse rate were derived from the impulse probability divided by the PST binwidth. Extracellular recordings were evaluated from their mean impulse rates and from PSTs.
View larger version (39K):
[in a new window]
FIG. 4.
Response-intensity functions of sustaining fiber EPSP at = 0 and 90°. A: signal-averaged EPSP of sustaining fiber 019 for log intensities 4.0 to 1.0 in 0.5 log unit steps at = 0°. Flashes indicated by bar at bottom of figure and were 0.4 s in duration. Each trace is the average of 5 responses. Impulses were removed with a low-pass filter before signal averaging. B: as in A for = 90°. C: transient response amplitude vs. intensity at = 0° (
) and = 90° (- - -). D: plateau phase amplitude at = 0° () and 90° (- - -). E: mean impulse rate vs. log intensity at = 0° () and 90° (- - -). Vertical bars are ±1.0 SD.
RESULTS
Abstract
Introduction
Methods
Results
Discussion
References
approaches 0°, the membrane depolarizes, and there is a burst of impulses. As approaches 90°, the membrane repolarizes, and the impulse rate declines toward a minimum. Modest changes in e-vector angle (10-30°), produce changes in membrane potential and in mean impulse rate that persist for 
20 s, as shown in Fig. 1. At each stepwise change in between 0 and 60° the membrane potential and the impulse rate decline. Conversely, successive steps between 60 and 180° produce depolarization and increased impulse rates. Figure 2A shows the mean rate (subsequent to the transient burst) for each of 6 s. At max (between 150 and 0°) the mean rate was 3.6 times that at min (60°), and PS was 7.0.
max and min near 150° () and 60°, respectively, and a 3.4-fold difference in responsiveness. Thus continuous rotation augments the discharge, but the ratio of impulse rates at max and min are similar. The similarity between max measured at stationary e-vector angles and the phase of the peak response elicited with a slowly rotating polarizer was observed for nearly all neurons so examined (as in Fig. 2C). Thus, when a crayfish rotates in a field of polarized light, the elements of the sustaining fiber ensemble will each discharge at a rate proportional to the proximity to max.
max (0°) to 2.0 mV at min. At suprathreshold intensities the discharge is evaluated with the PST, and PS is interpolated from the intensity-response function. Figure 3B shows -dependent variations in firing rate. The peak impulse rate at max (15°) is about 2.2 times that at min (105°), and PS is 4.0 as determined by the variations in the intensity dependence of the peak rate in Fig. 3C. At moderate intensities, 3 of 33 cells tested exhibited a two-peak sensitivity profile, as in Fig. 3D, with the peaks spaced ~90° apart. An additional five cells exhibited this pattern at higher intensities. Thus there is evidence for convergent input from the orthogonal channels in 10-25% of the cells.
max and min, as shown in Fig. 4. In this cell PS increases with stimulus intensity. The responses in Fig. 4, A and B, are averaged compound EPSPs at max and min. At the lowest intensities, both the transient and plateau responses exhibit only modest PS (2.0, as in Fig. 4, C and D). At higher intensities however the response to flashes at = 0° is saturated yet remains 30-50% greater than the response to flashes at = 90°. This result implies an intensity dependence in PS. The discontinuity at log I = 3.0 may reflect a high-threshold opponency mechanism. Sustaining fibers are subject to intensity-dependent lateral inhibition (Glantz and Nudelman 1976; Waldrop and Glantz 1985). At high stimulus intensities, the EPSP traces in Fig. 4, A and B, exhibit a dip in the membrane potential (arrow in Fig. 4A) between the peak and plateau phases of the response. A similar dip in the PST has been previously shown (Glantz and Nudelman 1976) to reflect a delayed action from the inhibitory surround. Furthermore, the dip occurs over the same range of stimulus intensities associated with the divergence of the response functions at max and min (in Fig. 4, C and D). More direct evidence for PS in the surround inhibitory mechanism is described below.
3, and saturation (as in Fig. 4E) exhibit an average PS of 5.6 ± 2.0 (SD). Intensity-response functions at max and min were examined in 12 neurons and revealed an average PS of 4.8 ± 3.0, which is comparable with the PS of receptors and lamina cells in Pacifasticus (Glantz 1996a).
max in sustaining and dimming fibers
max of sustaining fibers clusters near the vertical as previously inferred by Yamaguchi et al. (1976) from dynamic responses. The distribution of max values for 48 cells measured with a stationary polarizer is shown in Fig. 5A. The data sample includes 9 of 14 sustaining fiber subtypes (receptive field locations) identified by Wiersma and Yamaguchi (1967). When these results are segregated by receptive field location (dorsal vs. ventral, anterior vs. posterior) the result is similar for each subgroup and similar to Fig. 5A (data not shown). A striking feature of the distribution is the paucity of max observations near 90°. Only 2 of 48 cells exhibited max within ±15° of the horizontal. This distribution contrasts markedly with those of receptors and lamina monopolar cells (Glantz 1996a) in which both orthogonal max values are well represented in the cell populations. The preference for a vertical e-vector is quite robust. When the stimulus is centered in the inhibitory surround such that only the internally reflected light reaches the excitatory field, the distribution of e-vector maxima remains clustered about the vertical. An interesting feature of PS in dimming fibers is that the distribution of max for inhibition, Fig. 5B, is similar to that for excitation in sustaining fibers.
View larger version (16K):
[in a new window]
FIG. 5.
A: distribution of max values from stationary flash measurements for 48 sustaining fibers. B: distribution of max values for the elicited inhibitory postsynaptic potential (IPSP) of 14 dimming fibers. Seven measurements were based on the scanning method, and 7 were based on the associated with maximum hyperpolarization in response to a slowing rotating polarizer.
reflects both the stationary PS profile and the direction and rate of change of (as in Figs. 1 and 2). Figure 6 shows the subthreshold response to polarizer rotation at 76 and 146°/s in the clockwise (CW) and counterclockwise (CC) directions. The oscillations in synaptic potential are modestly larger (30-50%) for CC rotations and at the higher velocity. Directionality and sensitivity to rates of change were examined in 30 neurons. Thirteen cells exhibited a consistent directional bias similar to that shown in Fig. 6 and with responses in one direction exceeding that in the opposite direction by 40-100%. Most cells were also sensitive to the rate of change of the e-vector, with a maximum response at 100-180°/s and diminished responses at lower and higher rates of change (data not shown).
View larger version (44K):
[in a new window]
FIG. 6.
Sustaining fiber 01 subthreshold response to a rotating polarizer. The shutter is opened at t = 2.2 s (bottom trace) eliciting a transient depolarization that decays to a plateau phase (top trace). The membrane resting potential was 60 mV, and it is indicated by zero on the left-hand ordinate. Polarizer rotation commences at t = 12 s in the CW direction at 76°/s, followed by counterclockwise (CC) rotation at 76 and 146°/s and CW rotation at 146°/s. Bottom trace is stimulus monitor, and e-vector angle is indicated on the right-hand ordinate.
max to stimulus location may have a common basis in sustaining fiber surround inhibition (Waldrop and Glantz 1985; Wiersma and Yamaguchi 1967). If the inhibitory mechanism is polarization sensitive with max near 90°, the PS profiles for net excitation would be shifted toward 0°. The results of two types of experiments suggest that the sustaining fiber inhibitory mechanism is polarization sensitive and that max for inhibition is ~90°.
max for excitation was assessed with a rotating polarizer (30-60°/s) and with the light beam focused on the excitatory field. After a control measurement (as in Fig. 7A) the inhibitory field was illuminated with constant polarized light from a second beam at = 0° or = 90°, as seen in Fig. 7, B and C, respectively. When the inhibitory stimulus is polarized to = 0°, there is little or no evidence of inhibition. When the inhibitory field was illuminated at = 90°, both the peak and mean rates, elicited by the excitatory stimulus, were substantially diminished. Similar results were obtained in three of four experiments. An inhibitory stimulus at = 90° was 20-50% more effective than one at 0°. The fourth cell revealed no evidence of inhibition at any .
View larger version (26K):
[in a new window]
FIG. 7.
Dependence of lateral inhibition on . A: control response of sustaining fiber 038 (left-hand ordinate) to CW polarizer rotation (bottom trace, right-hand ordinate). Mean rate is 10.9 ± 0.1 impulse/s. B: as in A but with continuous illumination of the inhibitory surround at = 0°. Mean rate is 9.7 ± 1.1 impulses/s. C: as in B but illumination of inhibitory field is at = 90°. Mean rate is 5.3 ± 2.3 impulses/s.
), was examined with a stationary or slowly rotating polarizer as in Fig. 8. In this cell, max was at 78°, as shown in Fig. 8A. Three of six cells exhibited a max near 90°, and only one revealed a max near 0°. The max, evaluated from the response to a rotating polarizer, depends on the e-vector rate of change. A max near 90° obtains at rates of up to 120°/s (as in Fig. 8B) but not at higher rates (as in Fig. 8, C and D).
View larger version (16K):
[in a new window]
FIG. 12.
Schematic diagram of connections in the crayfish visual system related to PS. RH and RV are retinular cells sensitive to the horizontal and vertical e-vector angles, respectively. There are 4 RVs and 3 RHs in each ommatidium. Lamina monopolar cells M3 [1 per lamina (LM) cartridge] receive sign-inverting, receptor input exclusively from 4 RVs originating in a single ommatidium (Nässel and Waterman 1977 ), and M4 is exclusively innervated by 3 RH cells per ommatidium. Monopolar cells project retinotopically to the medulla externa (ME) and synapse on columnar transmedullary neurons (TM). Cholinergic transmedullary cells (TM-A) with horizontal e-vector sensitivity (innervated by M4) provide depolarizing (sign-conserved) synaptic input to broad field medullary amacrine neurons. TM-A with a vertical e-vector preference (innervated by M3) provides a sign-inverting (hyperpolarizing) input to dimming fibers. Sustaining fibers are excited by glutamatergic transmedullary cells (TM-GL) with V-sensitivity. TM-GL are inhibited by medullary amacrine cells, which is the basis of the H-sensitivity in sustaining fiber lateral inhibition. In the brain [supraesophageal ganglion (SG)], sustaining fibers excite optomotor neurons or indirectly inhibit motoneurons via nonspiking interneurons.
View larger version (23K):
[in a new window]
FIG. 8.
Response of nonspiking medullary amacrine neuron to CW polarizer rotation at 53°/s (A), 120°/s (B), 218°/s (C), and 300°/s (D). Note at the lowest velocity the maximum depolarization obtains at = 78°, and phase lag increases at successively higher rates of e-vector change. Each trace is the average of 5 (A) or 10 (B-D) responses. Membrane resting potential is 50 mV, indicated by 0 on left-hand ordinate. Broken traces are from the stimulus monitor and scaled on the right-hand ordinate.
= 0° (as in Fig. 9, right column) are larger than those obtained with pulses at 90° (as in Fig. 9, left column), and the -dependent difference generally increases with stimulus intensity, as in Fig. 9G.
View larger version (29K):
[in a new window]
FIG. 9.
Dimming fiber IPSPs elicited with 2.0-s pulses of light at = 90° (left column) and 0° (right column) and at log intensity 3 (A and B), 2 (C and D), and 1 (E and F). Note that the IPSP increases progressively with intensity at = 0° but not at = 90°. Lower bar indicates stimulus timing. G: IPSP amplitude vs. intensity at = 0° () and = 90° (- - -). Circles are at ±1.0 SD.
and max for inhibition is ~0°. The IPSP at of 0° is ~60% larger than that at 90°, and the response varies as a cos2 function, as in Fig. 10B. The average PS of dimming fibers was 4.9 ± 3.0 (n = 7). max for inhibition was determined with the scanning method, as in Fig. 10, or from the response to a slowly rotating polarizer, as in Fig. 11. In 12 of 14 cells so tested, max was within ±15° of 0°, as in Fig. 5B. Thus dimming fibers are inhibited, and sustaining fibers are excited at the same max. For a changing e-vector, inhibition at = 0° hyperpolarizes the cell as approaches 0°, and the cell depolarizes (recovers from inhibition) as approaches 90°, as shown in Fig. 11. Although the -dependent variation in membrane potential is a modest 1.0-3.0 mV (as in Fig. 11, B and C), it is sufficient to maximize the impulse rate as approaches 90°.
View larger version (43K):
[in a new window]
FIG. 10.
A: dimming fiber responses to flashes (0.6-s duration, at 2-s intervals) of constant intensity and with varied in 17 steps per 180°. Log I = 1.0. Lower trace is the stimulus monitor, and stimulus scale is on the right-hand ordinate. Polarizer rotation is CW. B: average polarization response profile for the dimming fiber IPSP at log I = 1.0. : mean response amplitude for 5 stimulus cycles. 
are at ±SE. - - -: cos2 function with max of 11°. PS for this neuron was 2.4, and comparable response ratios were obtained at log I = 1.5 and 2.0.
View larger version (28K):
[in a new window]
FIG. 11.
A: dimming fiber response to polarizer rotation at 45°/s. Note depolarization and peak impulse rate near = 90°. Membrane resting potential is 54 mV, indicated by 0 on left-hand ordinate. Dashed line monitors the e-vector angle (right-hand ordinate). Rotation is CW. B and C: signal averages of synaptic potential responses to polarizer rotation at 30 and 67°/s, respectively. Note maximum hyperpolarization near = 0°.
DISCUSSION
Abstract
Introduction
Methods
Results
Discussion
References
,b).
s (Fig. 12) and enhanced responsiveness to a changing e-vector. The sustaining fiber polarization response is similar to that of only one class of lamina monopolars (with max ~0°, as in Table 1). The absence of a horizontal e-vector channel in sustaining fibers implies a highly selective pattern of innervation. Because the dimming fiber max at 90° results from inhibition at = 0°, the dimming fiber input must also come from a subset of columnar cells with max = 0°. Excitation of sustaining fibers is mediated by glutamate (Pfeiffer-Linn and Glantz 1991), but inhibition of dimming fibers requires acetylcholine (Pfeiffer and Glantz 1989). Thus the two synaptic actions, which have similar dependence, must be mediated by different transmedullary cells, as shown in Fig. 12. It is likely however, that these cholinergic and glutamatergic transmedullary cells are excited by common lamina monopolar neurons (M3 in Fig. 12). Another inference from these studies is that the glutamatergic transmedullary cells (Pfeiffer-Linn and Glantz 1991), which are presynaptic to sustaining fibers (TM-GL, in Fig. 12), are likely to exhibit a max near 0°.
View this table:
TABLE 1.
Comparison of the polarization-sensitive properties in four classes of neurons
max, and the representation of PS for the entire panoramic visual field.
in a local area will effect particular sustaining and dimming fibers in a manner that is indistinguishable from a change in local intensity. There are several possible resolutions to this problem, and each requires assumptions about the behavioral context. One possibility is that, in a restricted environment, local intensity and may be correlated. Alternatively, the PS in this system may enhance contrast detection (caused by reflected polarized light) in circumstances in which intensity contrast is absent (Bernard and Wehner 1977; Leggett 1976). In this context it may be immaterial whether the source of the contrast is a difference in or local intensity.
). The cells are insensitive to the stationary e-vector angle but highly sensitive to e-vector change and/or the direction of change. In contrast to the crayfish sustaining and dimming fibers, however, the crab neuron's response is not modulated with variations in . The opposite extreme is found in the cricket medulla, which contains three classes of polarization-sensitive neurons with max separated by ~60° (Labhardt 1988). Stationary PS is enhanced by an opponency mechanism (Labhardt and Petzold 1993). It is notable that three arthropods analyze polarization signals in homologous structures (the second optic neuropile) but with very different strategies.
) PS is largely restricted to the ommatidia on the dorsal face of the compound eye, and the distribution of analyzers is consistent with a matched filter for skylight polarization. This organization provides a basis for navigation by polarized skylight. The more homogeneous distribution of PS in crayfish eye may indicate a different function such as contrast enhancement in an aquatic environment.
| |
ACKNOWLEDGEMENTS |
|---|
We thank S. Rabinowitz for assistance in preparation of the manuscript.
This research was supported by a National Science Foundation Grant IBN-9507878.
| |
FOOTNOTES |
|---|
Address for reprint requests: R. M. Glantz, Dept. of Biochemistry and Cell Biology, Rice University, 6100 Main St., Houston, TX 77005.
Received 25 August 1997; accepted in final form 23 July 1998.
| |
REFERENCES |
|---|
|
Abstract
Introduction
Methods
Results
Discussion
References
|
|---|
This article has been cited by other articles:
|
|
 |
|
  J. C. Tuthill and S. Johnsen Polarization sensitivity in the red swamp crayfish Procambarus clarkii enhances the detection of moving transparent objects J. Exp. Biol., May 1, 2006; 209(9): 1612 - 1616. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. M. Glantz Polarization analysis in the crayfish visual system J. Exp. Biol., March 9, 2002; 204(14): 2383 - 2390. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
