The contribution of cortical feedback projections to sensory representations in the mouse primary visual cortex

"As visual information travels along the cortical hierarchy, our brain builds representations of the outside world, which ultimately guide behavior. Areas in the cortical hierarchy communicate through reciprocal cortical connections. While the role of feedforward connections in visual processing is reasonably understood, the contributions of feedback connections are less clear. The main source of feedback inputs to the mouse’s primary visual cortex (V1) is a set of higher-order visual areas (HVAs). HVAs modulate the activity of V1 and have been implicated in visual perception and contextual modulations. Nevertheless, the impact of HVAs in V1 has been traditionally studied by inhibiting their activity, rendering these studies unable to distinguish the contributions of direct cortico-cortical feedback and indirect pathways.(...)

Prenatal caffeine intake differently affects synaptic proteins during fetal brain development

Caffeine is the psychostimulant most consumed worldwide. However, little is known about its effects during fetal brain development. In this study, adult female Wistar rats received caffeine in drinking water (0.1, 0.3 and 1.0 g/L) during the active cycle in weekdays, two weeks before mating and throughout pregnancy. Cerebral cortex and hippocampus from embryonic stages 18 or 20 (E18 or E20, respectively) were collected for immunodetection of the following synaptic proteins: brain-derived neurotrophic factor (BDNF), TrkB receptor, Sonic Hedgehog (Shh), Growth Associated Protein 43 (GAP-43) and Synaptosomal-associated Protein 25 (SNAP-25). Besides, the estimation of NeuN-stained nuclei (mature neurons) and non-neuronal nuclei was verified in both brain regions and embryonic periods. Caffeine (1.0 g/L) decreased the body weight of embryos at E20. Cortical BDNF at E18 was decreased by caffeine (1.0 g/L), while it increased at E20, with no major effects on TrkB receptors. In the hippocampus, caffeine decreased TrkB receptor only at E18, with no effects on BDNF. Moderate and high doses of caffeine promoted an increase in Shh in both brain regions at E18, and in the hippocampus at E20. Caffeine (0.3 g/L) decreased GAP-43 only in the hippocampus at E18. The NeuN-stained nuclei increased in the cortex at E20 by lower dose and in the hippocampus at E18 by moderate dose. Our data revealed that caffeine transitorily affect synaptic proteins during fetal brain development. The increased number of NeuN-stained nuclei by prenatal caffeine suggests a possible acceleration of the telencephalon maturation. Although some modifications in the synaptic proteins were transient, our data suggest that caffeine even in lower doses may alter the fetal brain development

Commensal bacteria and essential amino acids control food choice behavior and reproduction

<div><p>Choosing the right nutrients to consume is essential to health and wellbeing across species. However, the factors that influence these decisions are poorly understood. This is particularly true for dietary proteins, which are important determinants of lifespan and reproduction. We show that in <i>Drosophila melanogaster</i>, essential amino acids (eAAs) and the concerted action of the commensal bacteria <i>Acetobacter pomorum</i> and <i>Lactobacilli</i> are critical modulators of food choice. Using a chemically defined diet, we show that the absence of any single eAA from the diet is sufficient to elicit specific appetites for amino acid (AA)-rich food. Furthermore, commensal bacteria buffer the animal from the lack of dietary eAAs: both increased yeast appetite and decreased reproduction induced by eAA deprivation are rescued by the presence of commensals. Surprisingly, these effects do not seem to be due to changes in AA titers, suggesting that gut bacteria act through a different mechanism to change behavior and reproduction. Thus, eAAs and commensal bacteria are potent modulators of feeding decisions and reproductive output. This demonstrates how the interaction of specific nutrients with the microbiome can shape behavioral decisions and life history traits.</p></div

Loss of peripheral synthesis of nonessential amino acids (neAAs) increases yeast appetite.

<p>(A) Schematic depicting the biosynthesis of tyrosine (Tyr) in <i>Drosophila</i>. (B) Feeding preference of control and <i>Henna</i> whole-animal knockdown flies upon removal of all amino acids (AAs), all neAAs, or all neAAs with 1x and 2x Tyr added back. (C) Feeding preference of control and <i>Henna</i> fat body knockdown flies upon removal of either all neAAs or all AAs. (B and C) Circles represent yeast preference in single assays, with a line representing the median and whiskers representing the interquartile range. <i>n</i> = 15–20. Significance was tested using the Kruskal–Wallis test followed by Dunn’s multiple comparison test. Not significant (ns) <i>p</i> > 0.05, * <i>p</i> < 0.05, ** <i>p</i> < 0.01, *** <i>p</i> < 0.001. Underlying data used in this Fig are provided in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2000862#pbio.2000862.s013" target="_blank">S1 Data</a>.</p

Flies specifically increase yeast appetite upon single essential amino acid (eAA) deprivation.

<p>(A) Feeding preference of flies kept on holidic medium or holidic medium lacking all amino acids (AAs), all nonessential amino acids (neAAs), or single eAAs in the context of no neAAs. Circles represent yeast preference in single assays, with a line representing the median and whiskers representing the interquartile range. <i>n</i> = 26. Significance was tested using the Kruskal–Wallis test followed by Dunn’s multiple comparison test. (B) Cumulative intake measurement of yeast extract and sucrose using the capillary feeder (CAFE) assay. Flies were prefed a holidic diet containing either all AAs, no AAs, all AAs except valine (Val), or all AAs except arginine (Arg). Dots represent means and error bars represent the standard error of the mean. <i>n</i> = 10. Significance was tested using the unpaired <i>t</i> test with Bonferroni correction for the intake volume at 4 h. For yeast extract intake in (B), Val and Arg deprivation have the same effect when compared to the complete holidic medium. There was also no significant effect of the different diets on sucrose intake. Not significant (ns) <i>p</i> > 0.05, * <i>p</i> < 0.05, ** <i>p</i> < 0.01, *** <i>p</i> < 0.001. Underlying data used in this Fig are provided in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2000862#pbio.2000862.s013" target="_blank">S1 Data</a>.</p