Neuronal differentiation is regulated by neuronal activity. Here, we analyzed dendritic and axonal growth of Basket cells (BCs) and non-Basket cells (non-BCs) using sparse transfection of channelrhodopsin-YFP and repetitive optogenetic stimulation in slice cultures of rat visual cortex. Neocortical interneurons often display axon-carrying dendrites (AcDs). We found that the AcDs of BCs and non-BCs were, on average, the most complex dendrites. Further, the AcD configuration had an influence on BC axonal development. Axons originating from an AcD formed denser arborizations with more terminal endings within the dendritic field of the parent cell. Intriguingly, this occurred already in unstimulated BCs, and complexity was not increased further by optogenetic stimulation. However, optogenetic stimulation exerted a growth-promoting effect on axons emerging from BC somata. The axons of non-BCs neither responded to the AcD configuration nor to the optogenetic stimulation. The results suggest that the formation of locally dense BC plexuses is regulated by spontaneous activity. Moreover, in the AcD configuration, the AcD and the axon it carries mutually support each other's growth.

Objectives: Saccharomyces boulardii CNCM I-745, a probiotic yeast, is effectively used for the treatment of acute diarrhea as well as for the prevention and treatment of traveller‘s diarrhea and diarrhea under tube feeding. The underlying mechanisms are not fully elucidated. Both antitoxic and regulatory effects on the intestinal barrier, mediated either by the yeast or yeast-derived substrates, have been discussed. Methods: To examine the effects of Saccharomyces boulardii released substrates (S.b.S) on gastrointestinal (GI) barrier function, a murine small intestinal organoid cell model under stress was used. Stress was induced by lipopolysaccharide (LPS) exposure or withdrawal of growth factors from cell culture medium (GF_Red). Stressed organoids were treated with S.b.S (200 µg/mL), and markers of GI barrier and inflammatory response were assessed. Results: GF_Red-induced stress was characterized by disturbances in selected tight junction (TJ) (p < 0.05), adherent junction (AJ) (p < 0.001), and mucin (Muc) formation (p < 0.01), measured by gene expressions, whereby additional S.b.S treatment was found to reverse these effects by increasing Muc2 (from 0.22 to 0.97-fold change, p < 0.05), Occludin (Ocln) (from 0.37 to 3.5-fold change, p < 0.0001), and Claudin (Cldn)7 expression (from 0.13 ± 0.066-fold change, p < 0.05) and by decreasing Muc1, Cldn2, Cldn5, and junctional adhesion molecule A (JAM-A) expression (all p < 0.01). Further, S.b.S normalized expression of nucleotide binding oligomerization domain (Nod)2- (from 44.5 to 0.51, p < 0.0001) and matrix metalloproteinase (Mmp)7-dependent activation (from 28.3 to 0.02875 ± 0.0044 ** p < 0.01) of antimicrobial peptide defense and reduced the expression of several inflammatory markers, such as myeloid differentiation primary response 88 (Myd88) (p < 0.01), tumor necrosis factor α (Tnfα) (p < 0.01), interleukin (IL)-6 (p < 0.01), and IL-1β (p < 0.001). Conclusions: Our data provide new insights into the molecular mechanisms by which Saccharomyces boulardii CNCM I-745-derived secretome attenuates inflammatory responses and restores GI barrier function in small intestinal organoids.

(1) Background: Tannacomp^® is a drug consisting of tannin albuminate, a complex of tannic acid (TA) and ethacridine lactate (Eta) used for treating acute and traveler’s diarrhea. TA is thought to modulate gastrointestinal barrier function, but the underlying mechanisms and whether Eta has similar effects remains unclear. (2) Methods: to investigate the effects of TA and Eta on the intestinal barrier, stress responses were induced in murine intestinal organoids by lipopolysaccharide (LPS) exposure or withdrawal of growth factors from cell culture medium (GF_Red). Further, organoids were exposed to either TA (0.01 mg/mL) or Eta (0.002 mg/mL) and markers of inflammatory response and gut barrier function were assessed. (3) Results: TA and Eta reduced several inflammatory markers such as interleukin 6, interleukin 1β, tumor necrosis factor α, and myeloid differentiation primary response 88 in stressed organoids. In addition, TA and Eta attenuated LPS- and GF_Red-mediated gut barrier dysfunctions, with normalization of tight junction, adherent junction and mucin gene expression and reduction of Nod2- and matrix metalloproteinase 7-dependent activation of antimicrobial peptides. (4) Conclusions: our data show that TA and Eta modulate markers of inflammation and the intestinal barrier and suggest novel mechanisms of action of this drug that could broaden its treatment indications.

Neuronal differentiation is regulated by neuronal activity. Here, we analyzed dendritic and axonal growth of Basket cells and non-Basket cells using sparse transfection of channelrhodopsin-YFP and repetitive optogenetic stimulation in slice cultures of rat visual cortex. Neocortical interneurons often display axon-carrying dendrites (AcDs). We found that the AcDs of Basket cells and non-Basket cells were on average their most complex dendrite. Further, the AcD configuration had an influence on Basket cell axonal development. Axons originating from an AcD formed denser arborizations with more terminal endings within the dendritic field of the parent cell. Intriguingly, this occurred already in unstimulated Basket cells, and complexity was not increased further by optogenetic stimulation. However, optogenetic stimulation exerted a growth-promoting effect on axons emerging from Basket cell somata. The axons of non-Basket cells neither responded to the AcD configuration nor to the optogenetic stimulation. The results suggest that the formation of locally dense Basket cell plexuses is regulated by spontaneous activity. Moreover, in the AcD configuration, the AcD and the axon it carries mutually support each others growth. Teaser: Textbooks usually draw cortical neurons with axons emerging from the cell body. Axons emerging from dendrites have been considered a caprice of nature until recent work demonstrated that axon-carrying dendrites are neither a rare nor a random phenomenon. Rather, this morphological configuration awards specific functional properties. Here, we discovered a morphogenetic role of the AcD configuration in developing Basket neurons which deliver axo-somatic inhibition to pyramidal neurons. Driven by spontaneous activity, AcD and the axon mutually promote each others growth such that the axon rapidly forms a denser presynaptic terminal field. Basket cells with axons from the cell body achieve the same complexity with technical assistance via an optogenetic stimulation. This way, a dendritic origin accelerates Basket cell axonal development.