ALBERT

Notes: Abstract Two new recombinant haplotypes of the rat major histocompatibility system,RT1, have been detected in [LEW.1A (RT1 a ) ×LEW.1W (RT1 u )] × LEW 1N(RT1 n ) segregating hybrids. Recombinantr3 carries theRTL1. A region (determining classical transplantation antigens) and theRT1.B region (determining strong mixed lymphocyte reactivity and genetic control of antipolypeptide immune responsiveness) of the RT1a parent, bur rejects RT1a skin grafts. Recombinantr4 carries theA andB regions of the RT1u parent, but rejects RT1u skin grafts. The two histocompatibility genes detected are allelic to each other. The relevant locus, designated asH-C, maps to theB-region side of theRT1 system and appears to mark a thirdRT1 gene region,RT1.C. Availability of haplotypes r3 andr4 allowed the definition of a histocompatibility locus in theB region,H-B. The products ofH-C, H-B and of the previously describedH-A gene vary in antigenic strength.

Notes: Abstract The influence of the quantum size effect (QSE) in very thin Pd and Au films (0.5〈d〈10 [nm]) deposited on glass tips is studied by means of field emission at various anode potentials. The thickness-dependent field emission current characteristics show short periodic variations with a period of about 0.3 nm for both Pd and Au. The measured QSE oscillations and their amplitudes differ strongly from those expected qualitatively from model calculations for the smallest thicknesses. A model for the metal film based on a modification of the uniform background model is presented, and the thickness dependence of the conductance and the field emission current density are qualitatively discussed. Possible explanations of some discrepancies between calculations and the measured field emission current characteristics are proposed.

Notes: BOOK REVIEWS

Notes: Summary We used microspectrophotometry, together with some associated electrophysiological measurements, to characterize the photopigments of R1–6 receptors in living, white-eyedDrosophila. Measurements were from the deep pseudopupil, an optical visualization of photopigment-containing rhabdomeres. Transmission changes associated with photointerconversion of rhodopsin (R480) and its stable metarhodopsin (M570) are easily seen (Fig. 1). Such transmission changes were measured to produce a difference specrum (Fig. 2); the isosbestic wavelength is about 502 nm. A photoequilibrium spectrum (Fig. 3), analyzed together with sensitivity data (Fig. 4a), was used to determine the fraction of M570 in photoequilibria established with various monochromatic wavelengths. From this, the quantum efficiency for M570 to R480 conversion relative to R480 to M570 efficiency was determined to be about 0.71. No dark regeneration of M570 to R480 occurred within a period of 60min (Fig. 4a, b). The extent of conversion related to incident energy was estimated as a function of wavelength (Figs. 5 and 6). These experiments yielded the photosensitivity spectrum of the visual pigment (Fig. 6). Assuming that the absorption spectrum of rhodopsin (R480) is the same as the sensitivity spectrum as determined by electrophysiology, this photosensitivity spectrum was used to derive the spectrum of metarhodopsin (M570) (Fig. 7). The maximal extinction of M570 is about 1.43 times the maximal extinction of R480. The spectra of both states of the photopigment fit the Ebrey-Honig nomogram in the long wavelength band. Both of the photosensitivity spectra, measured in the living eye, associated with R480 and M570 respectively have a major UV maximum.

Notes: Summary Drosophila have three types of photoreceptors in their compound eyes: R1–6, R7, and R8. In addition they have simple eyes, ocelli, with another type of photoreceptor. The role of each type of receptor and the possible interaction of their inputs were examined in an innate visual preference task, fast walking phototaxis. Flies were found to be attracted to light, i.e., positively phototactic. We compared the strength of the photopositive response and the spectral preference of normal fly strains and mutant fly strains lacking functional ocelli, R1–6, or R7, singly or in combination. Electroretinographic measures were used to confirm the specificity of deficits in visual mutant strains and the normal functioning of intact receptors. The strength of the photopositive response was strong, as indicated by the high correlation between increases in the intensity of the variable stimulus and increasing numbers of flies attracted toward it. Nearly all strains with or without intact receptor types showed high correlations whether the constant intensity stimulus offered as the alternative choice was bright 467 nm light (Figs. 1 and 2) or dim 572 nm light (Figs. 3 and 4). These constant stimuli were selected so that data in relevant intensity ranges of receptor function would be obtained. An important exception to the high correlations in the intensityresponse functions occurred with flies lacking function in all receptor types except R8; their positive phototaxis was extremely weak in dim light (Fig. 3). Analyses of the phototactic spectral sensitivities (Figs. 5 and 6), as well as comparisons with known electrophysiological spectral sensitivities, were used to determine the inputs from compound eye receptors and to demonstrate central interaction of these inputs with ocellar input. Several experiments with converging evidence suggest that R7 (when present) and R8 dominate fast phototaxis in the conditions of our experiment. R1–6 is the predominant compound eye receptor type in ERG measures; however, its behavioral input is clearly demonstrated only as enhancing R8 dominance of phototaxis in experiments using a dim constant stimulus and as enhancing R7 dominance of phototaxis in experiments using a bright constant stimulus. Similarly, the presence of ocellar receptors also facilitates R8 input in dim light and R7 input in bright light. The data substantiating these respective conclusions are: (1) a lack of dim light phototaxis in a mutant strain with only R8 functional (Fig. 3); and (2) a lack of an ultraviolet (UV) maximum from R7 in bright light phototaxis in a mutant strain with only R7 and R8 functional (Fig. 5c). Generally, absence of the ocelli and R1–6 had remarkably little effect on fast phototactic behavior except for the interaction with R7 and R8 inputs. This interaction is consistent with a theory that ocelli serve to modulate compound eye sensitivity.

Notes: Summary Ectopic eyes were produced on the fleshfly,Sarcophaga bullata by transplantation of imaginal eye discs. Electrophysiological and histological observations of these supernumerary eyes indicate the absence of synaptic connections between retinular cells and higher order neurons.