POLARIZATION SENSITIVITY IN CRAYFISH LAMINA MONOPOLAR NEURONS

1. Polarization sensitivity (PS) was examined in photoreceptors and la mina monopolar cells (LMCs) in two species of crayfish, Procambarus cl arkii and Pacifasticus leniusculus. The measurements were made with in tracellular recordings and broad field illumination. 2. PS is about 40 % greater in Pacifasticus than in Procambarus (Table 1). In both speci es the LMC stationary PS profiles (estimated with flashes) are similar to those of receptors (Figs. 1 and 2). Both receptor and LMC sensitiv ity profiles are well described by cos(2) theta functions (Fig. 3). PS was observed in all receptors and 78% of LMCs. 3. When stimulated wit h a rotating polarizer, receptors and LMCs exhibit membrane potential modulation with phase predicted by the stationary PS profile (Fig.5). In photoreceptors, the polarization-elicited percent modulation falls off steeply as intensity increases. The LMC modulation is stronger tha n that in receptors and relatively insensitive to the mean intensity ( Figs. 6 to 8). For low intensities the LMC modulation is 100%. The LMC dynamic behavior is consistent with either an opponency mechanism or strong but polarization-insensitive lateral inhibition. 4. Receptors a nd LMCs exhibit steady-state differential sensitivity to stationary e- vector orientation (Fig. 9). 5. About 10% of the LMC neurons exhibit P S maxima separated by 90 degrees. These results imply a nonlinear summ ation of signals from orthogonal receptor channels (Fig. 10).