Color vision extracts spectral information by comparing signals from photoreceptors with different visual pigments. Such comparisons are encoded by color-opponent neurons that are excited at one ...wavelength and inhibited at another. Here, we examine the circuit implementation of color-opponent processing in the Drosophila visual system by combining two-photon calcium imaging with genetic dissection of visual circuits. We report that color-opponent processing of UVshort/blue and UVlong/green is already implemented in R7/R8 inner photoreceptor terminals of “pale” and “yellow” ommatidia, respectively. R7 and R8 photoreceptors of the same type of ommatidia mutually inhibit each other directly via HisCl1 histamine receptors and receive additional feedback inhibition that requires the second histamine receptor Ort. Color-opponent processing at the first visual synapse represents an unexpected commonality between Drosophila and vertebrates; however, the differences in the molecular and cellular implementation suggest that the same principles evolved independently.
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•Physiological recordings reveal early stages of color opponency•R7 and R8 photoreceptors of the same type of ommatidia mutually inhibit each other•HisCl1 histamine receptor mediates direct inhibition between R7 and R8•Ort histamine receptor is required for feedback inhibition
The Drosophila visual system extracts different spectral information at the level of the first synapse, reminiscent of processing in the vertebrate retina.
Effortless learning during sleep is everybody's dream. Several studies found that presenting odor cues during learning and selectively during slow wave sleep increases learning success. The current ...study extends previous research in three aspects to test for optimization and practical applicability of this cueing effect: We (1) performed a field study of vocabulary-learning in a regular school setting, (2) stimulated with odor cues during the whole night without sleep monitoring, and (3) applied the odor additionally as retrieval cue in a subsequent test. We found an odor cueing effect with comparable effect sizes (d between 0.6 and 1.2) as studies with sleep monitoring and selective cueing. Further, we observed some (non-significant) indication for a further performance benefit with additional cueing during the recall test. Our results replicate previous findings and provide important extensions: First, the odor effect also works outside the lab. Second, continuous cueing at night produces similar effect sizes as a study with selective cueing in specific sleep stages. Whether odor cueing during memory recall further increases memory performance hast to be shown in future studies. Overall, our results extend the knowledge on odor cueing effects and provide a realistic practical perspective on it.
Color vision is an important sensory capability of humans and many animals. It relies on color opponent processing in visual circuits that gradually compare the signals of photoreceptors with ...different spectral sensitivities. In Drosophila, this comparison begins already in the presynaptic terminals of UV-sensitive R7 and longer wavelength-sensitive R8 inner photoreceptors that inhibit each other in the medulla. How downstream neurons process their signals is unknown. Here, we report that the second order medulla interneuron Dm8 is inhibited when flies are stimulated with UV light and strongly excited in response to a broad range of longer wavelength (VIS) stimuli. Inhibition to UV light is mediated by histaminergic input from R7 and expression of the histamine receptor ort in Dm8, as previously suggested. However, two additional excitatory inputs antagonize the R7 input. First, activation of R8 leads to excitation of Dm8 by non-canonical photoreceptor signaling and cholinergic neurotransmission in the visual circuitry. Second, activation of outer photoreceptors R1–R6 with broad spectral sensitivity causes excitation in Dm8 through the cholinergic medulla interneuron Mi1, which is known for its major contribution to the detection of spatial luminance contrast and visual motion. In summary, Dm8 mediates a second step in UV/VIS color opponent processing in Drosophila by integrating input from all types of photoreceptors. Our results demonstrate novel insights into the circuit integration of R1–R6 into color opponent processing and reveal that chromatic and achromatic circuitries of the fly visual system interact more extensively than previously thought.
•Calcium imaging reveals a second step in color opponent processing in Drosophila•Dm8 antagonistically processes R7 (UV) and R8 + R1–R6 (UV to VIS) inputs•Activation of R8 causes excitation in Dm8 by non-canonical photoreceptor signaling•R1–R6 convey “achromatic” input to Dm8 through cholinergic Mi1 neurons
Pagni et al. reveal physiological insight into color opponent processing in a second order visual interneuron in Drosophila. Chromatic and achromatic circuits interact extensively to enable UV/VIS color opponent processing in this cell type that can explain its role in spectral behavior.
Dm9 neurons in
have been proposed as functional homologs of horizontal cells in the outer retina of vertebrates. Here we combine genetic dissection of neuronal circuit function, two-photon calcium ...imaging in Dm9 and inner photoreceptors, and immunohistochemical analysis to reveal novel insights into the functional role of Dm9 in early visual processing. Our experiments show that Dm9 receive input from all four types of inner photoreceptor R7p, R7y, R8p, and R8y. Histamine released from all types R7/R8 directly inhibits Dm9 via the histamine receptor Ort, and outweighs simultaneous histamine-independent excitation of Dm9 by UV-sensitive R7. Dm9 in turn provides inhibitory feedback to all R7/R8, which is sufficient for color-opponent processing in R7 but not R8. Color opponent processing in R8 requires additional synaptic inhibition by R7 of the same ommatidium via axo-axonal synapses and the second
histamine receptor HisCl1. Notably, optogenetic inhibition of Dm9 prohibits color opponent processing in all types of R7/R8 and decreases intracellular calcium in photoreceptor terminals. The latter likely results from reduced release of excitatory glutamate from Dm9 and shifts overall photoreceptor sensitivity toward higher light intensities. In summary, our results underscore a key role of Dm9 in color opponent processing in
and suggest a second role of Dm9 in regulating light adaptation in inner photoreceptors. These novel findings on Dm9 are indeed reminiscent of the versatile functions of horizontal cells in the vertebrate retina.
In animals, successful production of the visual chromophore (11-cis-retinal or derivatives thereof such as 11-cis-3-hydroxy-retinal) is essential for photoreceptor cell function and survival. These ...carotenoid-derived compounds must combine with a protein moiety (the opsin) to establish functional visual pigments. Evidence from cell culture systems has implicated that the retinal pigment epithelium protein of 65 kDa (RPE65) is the long-sought all-trans to 11-cis retinoid isomerase. RPE65 is structurally related to nonheme iron oxygenases that catalyze the conversion of carotenoids into retinoids. In vertebrate genomes, two carotenoid oxygenases and RPE65 are encoded, whereas in insect genomes only a single representative of this protein family, named NinaB (denoting neither inactivation nor afterpotential mutant B), is encoded. We here cloned and functionally characterized the ninaB gene from the great wax moth Galleria mellonella. We show that the recombinant purified enzyme combines isomerase and oxygenase (isomerooxygenase) activity in a single polypeptide. From kinetics and isomeric composition of cleavage products of asymmetrical carotenoid substrates, we propose a model for the spatial arrangement between substrate and enzyme. In Drosophila, we show that carotenoid-isomerooxygenase activity of NinaB is more generally found in insects, and we provide physiological evidence that carotenoids such as 11-cis-retinal can promote visual pigment biogenesis in the dark. Our study demonstrates that trans/cis isomerase activity can be intrinsic to this class of proteins and establishes these enzymes as key components for both invertebrate and vertebrate vision.
In animals, visual pigments are essential for photoreceptor function and survival. These G-protein-coupled receptors consist of a protein moiety (opsin) and a covalently bound 11-cis-retinylidene ...chromophore. The chromophore is derived from dietary carotenoids by oxidative cleavage and trans-to-cis isomerization of double bonds. In vertebrates, the necessary chemical transformations are catalyzed by two distinct but structurally related enzymes, the carotenoid oxygenase β-carotenoid-15,15′-monooxygenase and the retinoid isomerase RPE65 (retinal pigment epithelium protein of 65 kDa). Recently, we provided biochemical evidence that these reactions in insects are catalyzed by a single enzyme family member named NinaB. Here we show that in the fly pathway, carotenoids are mandatory precursors of the chromophore. After chromophore formation, the retinoid-binding protein Pinta acts downstream of NinaB and is required to supply photoreceptors with chromophore. Like ninaE encoding the opsin, ninaB expression is eye-dependent and is activated as a downstream target of the eyeless/pax6 and sine oculis master control genes for eye development. The requirement for coordinated synthesis of chromophore and opsin is evidenced by analysis of ninaE mutants. Retinal degeneration in opsin-deficient photoreceptors is caused by the chromophore and can be prevented by restricting its supply as seen in an opsin and chromophore-deficient double mutant. Thus, our study identifies NinaB as a key component for visual pigment production and provides evidence that chromophore in opsin-deficient photoreceptors can elicit retinal degeneration.
In the present study we provide evidence that SRP-35, a protein we identified in rabbit skeletal muscle sarcoplasmic reticulum, is an all-trans-retinol dehydrogenase. Analysis of the primary ...structure and tryptic digestion revealed that its N-terminus encompasses a short hydrophobic sequence bound to the sarcoplasmic reticulum membrane, whereas its C-terminal catalytic domain faces the myoplasm. SRP-35 is also expressed in liver and adipocytes, where it appears in the post-microsomal supernatant; however, in skeletal muscle, SRP-35 is enriched in the longitudinal sarcoplasmic reticulum. Sequence comparison predicts that SRP-35 is a short-chain dehydrogenase/reductase belonging to the DHRS7C dehydrogenase/reductase (short-chain dehydrogenase/reductase family) member 7C subfamily. Retinol is the substrate of SRP-35, since its transient overexpression leads to an increased production of all-trans-retinaldehyde. Transfection of C2C12 myotubes with a fusion protein encoding SRP-35-EYFP (enhanced yellow fluorescent protein) causes a decrease of the maximal Ca²⁺ released via RyR (ryanodine receptor) activation induced by KCl or 4-chloro-m-chresol. The latter result could be mimicked by the addition of retinoic acid to the C2C12 cell tissue culture medium, a treatment which caused a significant reduction of RyR1 expression. We propose that in skeletal muscle SRP-35 is involved in the generation of all-trans-retinaldehyde and may play an important role in the generation of intracellular signals linking Ca2+ release (i.e. muscle activity) to metabolism.
Rod and cone visual pigments use 11- cis- retinal, a vitamin A derivative, as their chromophore. Light isomerizes 11- cis- into all- trans- retinal, triggering a conformational transition of the ...opsin molecule that initiates phototransduction. After bleaching all- trans- retinal leaves the opsin, and light sensitivity must be restored by regeneration of 11- cis- retinal. Under bright light conditions the retinal G protein-coupled receptor (RGR) was reported to support this regeneration
by acting as a photoisomerase in a proposed photic visual cycle. We analyzed the contribution of RGR to rhodopsin regeneration
under different light regimes and show that regeneration, during light exposure and in darkness, is slowed about 3-fold in
Rgr -/- mice. These findings are not in line with the proposed function of RGR as a photoisomerase. Instead, RGR, independent of
light, accelerates the conversion of retinyl esters to 11- cis- retinal by positively modulating isomerohydrolase activity, a key step in the âclassicalâ visual cycle. Furthermore, we find
that light accelerates rhodopsin regeneration, independent of RGR.
A potential role of the sympathetic nervous system in progression of renal failure has received little attention. This study examined whether nonhypotensive doses of moxonidine, an agent that reduces ...sympathetic activity, affects glomerulosclerosis, urine albumin excretion, and indices of renal handling of norepinephrine (NE) in subtotally nephrectomized (SNX) rats. Sprague Dawley rats were SNX or sham-operated (control). SNX rats were either left untreated or treated with moxonidine in a dose (1.5 mg/kg body wt per d) that did not modify telemetrically monitored 24-h BP. Glomerular and renal morphology were evaluated by quantitative histology, immunohistochemistry, and in situ hybridization. Urine albumin excretion rate was analyzed by enzyme-linked immunosorbent assay, and kidney angiotensin II and NE content were measured using HPLC, (3)H-NE uptake, and release. Body and kidney weight and BP were not significantly different between SNX with or without moxonidine. The glomerulosclerosis index was significantly lower in moxonidine-treated (0.88 +/- 0.09) compared with untreated (1.55 +/- 0.28) SNX rats, as was the index of vascular damage (0.32 +/- 0.14 versus 0.67 +/- 0.16). The number of proliferating cell nuclear antigen-positive glomerular and tubular cells per area was significantly higher in untreated SNX rats than in controls and moxonidine-treated SNX rats. The same was true for urine albumin excretion rate. Renal angiotensin II tissue concentration was not affected by moxonidine. In untreated SNX rats, renal nerve stimulation and exogenous NE induced an increase in isolated kidney perfusion pressure (102 +/- 21 versus 63 +/- 8 mmHg). Renal endogenous NE content was significantly lower in SNX rats than in controls (86 +/- 14 versus 140 +/- 17 pg/mg wet weight). Cortical uptake of (3)H-NE was not different, but cortical NE release was significantly higher in SNX rats than in controls. Reduced function of presynaptic inhibitory alpha-adreno-receptors is unlikely because an alpha(2)-adrenoceptor antagonist increased NE release. At subantihypertensive doses, moxonidine ameliorates renal structural and functional damage in SNX animals, possibly through central inhibition of efferent sympathetic nerve traffic. In kidneys of SNX rats, indirect evidence was found for increased activity of a reduced number of nerve fibers.
An enzyme‐based cyclic pathway for trans to cis isomerization of the chromophore of visual pigments (11‐cis‐retinal) is intrinsic to vertebrate cone and rod vision. This process, called the visual ...cycle, is mostly characterized in rod‐dominated retinas and essentially depends on RPE65, an all‐trans to 11‐cis‐retinoid isomerase. Here we analysed the role of RPE65 in zebrafish, a species with a cone‐dominated retina. We cloned zebrafish RPE65 and showed that its expression coincided with photoreceptor development. Targeted gene knockdown of RPE65 resulted in morphologically altered rod outer segments and overall reduced 11‐cis‐retinal levels. Cone vision of RPE65‐deficient larvae remained functional as demonstrated by behavioural tests and by metabolite profiling for retinoids. Furthermore, all‐trans retinylamine, a potent inhibitor of the rod visual cycle, reduced 11‐cis‐retinal levels of control larvae to a similar extent but showed no additive effects in RPE65‐deficient larvae. Thus, our study of zebrafish provides in vivo evidence for the existence of an RPE65‐independent pathway for the regeneration of 11‐cis‐retinal for cone vision.
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