Drosophila melanogaster has long been a popular model insect species, due in large part to the availability of genetic tools and is fast becoming the model for insect colour vision. Key to understanding colour reception in Drosophila is in-depth knowledge of spectral inputs and downstream neural processing. While recent studies have sparked renewed interest in colour processing in Drosophila, photoreceptor spectral sensitivity measurements have yet to be carried out in vivo. We have fully characterised the spectral input to the motion and colour vision pathways, and directly measured the effects of spectral modulating factors, screening pigment density and carotenoid-based ocular pigments. All receptor sensitivities had significant shifts in spectral sensitivity compared to previous measurements. Notably, the spectral range of the Rh6 visual pigment is substantially broadened and its peak sensitivity is shifted by 92 nm from 508 to 600 nm. We show that this deviation can be explained by transmission of long wavelengths through the red screening pigment and by the presence of the blue-absorbing filter in the R7y receptors. Further, we tested direct interactions between inner and outer photoreceptors using selective recovery of activity in photoreceptor pairs.
14Drosophila melanogaster has long been a popular model insect species, due in large part to 15 the availability of genetic tools and is fast becoming the model for insect colour vision. Key 16 to understanding colour reception in Drosophila is in-depth knowledge of spectral inputs 17 and downstream neural processing. While recent studies have sparked renewed interest in 18 colour processing in Drosophila, photoreceptor spectral sensitivity measurements have yet 19 to be carried out in vivo. We have fully characterised the spectral input to the motion and 20 colour vision pathways, and directly measured the effects of spectral modulating factors, 21 screening pigment density and carotenoid-based ocular pigments. All receptor sensitivities 22 had significant shifts in spectral sensitivity compared to previous measurements. Notably, 23 the spectral range of the Rh6 visual pigment is substantially broadened and its peak 24 sensitivity is shifted by 92 nm from 508 to 600 nm. We propose that this deviation can be 25 explained by transmission of long wavelengths through the red screening pigment and by 26 the presence of the blue-absorbing filter in the R7y receptors. Further, we tested direct 27 interactions between photoreceptors and found evidence of interactions between inner and 28 outer receptors, in agreement with previous findings of cross-modulation between receptor 29 outputs in the lamina. 30
Akin to all damselflies, Calopteryx (family Calopterygidae), commonly known as jewel wings or demoiselles, possess dichoptic (separated) eyes with overlapping visual fields of view. In contrast, many dragonfly species possess holoptic (dorsally fused) eyes with limited binocular overlap. We have here compared the neuronal correlates of target tracking between damselfly and dragonfly sister lineages and linked these changes in visual overlap to premotor neural adaptations. While dragonflies attack prey dorsally, we show that demoiselles attack prey frontally. We identify demoiselle Target Selective Descending Neurons (TSDNs) with matching frontal visual receptive fields, anatomically and functionally homologous to the dorsally-positioned dragonfly TSDNs. By manipulating visual input using eyepatches and prisms, we show that moving target information at the premotor level depends on binocular summation in demoiselles. Consequently, demoiselles encode directional information in a binocularly fused frame of reference such that information of a target moving towards the midline in the left eye is fused with information of the target moving away from the midline in the right eye. This contrasts with dragonfly TSDNs where receptive fields possess a sharp midline boundary, confining responses to a single visual hemifield in a sagittal frame of reference (i.e. relative to the midline). Our results indicate that although TSDNs are conserved across Odonata, their neural inputs, and thus the upstream organization of the target tracking system, differs significantly and match divergence in eye design and predatory strategies.
Insulin‐like growth factor‐I (IGF‐I) signaling plays a key role in neuroinflammation. Here we show that IGF‐1 also regulates phagocytosis of reactive astrocytes through p110α isoform of phosphatidylinositol 3‐kinase (PI3K), differentially in both sexes. Systemic bacterial lipopolysaccharide (LPS)‐treatment increased the expression of GFAP, a reactive astrocyte marker, in the cortex of mice in both sexes and was blocked by IGF‐1 only in males. In primary astrocytes, LPS enhanced the mRNA expression of Toll‐like receptors (TLR2,4) and proinflammatory factors: inducible nitric oxide synthase (iNOS), chemokine interferon‐γ‐inducible protein‐10 (IP‐10) and cytokines (IL‐1β, IL‐6, and IL‐10) in male and female. Treatment with IGF‐1 counteracted TLR4 but not TLR2, iNOS, and IP10 expression in both sexes and cytokines expression in males. Furthermore, reactive astrocyte phagocytosis was modulated by IGF‐1 only in male astrocytes. IGF‐1 was also able to increase AKT‐phosphorylation only in male astrocytes. PI3K inhibitors, AG66, TGX‐221, and CAL‐101, with selectivity toward catalytic p110α, p110β, and p110δ isoforms respectively, reduced AKT‐phosphorylation in males. All isoforms interact physically with IGF‐1‐receptor in both sexes. However, the expression of p110α is higher in males while the expression of IGF‐1‐receptor is similar in male and female. AG66 suppressed the IGF‐1 effect on cytokine expression and counteracted the IGF‐1‐produced phagocytosis decrease in male reactive astrocytes. Results suggest that sex‐differences in the effect of IGF‐1 on the AKT‐phosphorylation could be due to a lower expression of the p110α in female and that IGF‐1‐effects on the inflammatory response and phagocytosis of male reactive astrocytes are mediated by p110α/PI3K subunit.
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