Literature context: 47; RRID:AB_1142794 Rabbit-anti-c-Fos Cell Signalin
The efficacy and duration of memory storage is regulated by neuromodulatory transmitter actions. While the modulatory transmitter serotonin (5-HT) plays an important role in implicit forms of memory in the invertebrate Aplysia, its function in explicit memory mediated by the mammalian hippocampus is less clear. Specifically, the consequences elicited by the spatio-temporal gradient of endogenous 5-HT release are not known. Here we applied optogenetic techniques in mice to gain insight into this fundamental biological process. We find that activation of serotonergic terminals in the hippocampal CA1 region both potentiates excitatory transmission at CA3-to-CA1 synapses and enhances spatial memory. Conversely, optogenetic silencing of CA1 5-HT terminals inhibits spatial memory. We furthermore find that synaptic potentiation is mediated by 5-HT4 receptors and that systemic modulation of 5-HT4 receptor function can bidirectionally impact memory formation. Collectively, these data reveal powerful modulatory influence of serotonergic synaptic input on hippocampal function and memory formation.
Literature context: ti-5-HT (Abcam, ab66047, 1:500; RRID:AB_1142794) and rabbit anti-FosB (Santa Cr
Freud-1/Cc2d1a represses the gene transcription of serotonin-1A (5-HT1A) autoreceptors, which negatively regulate 5-HT tone. To test the role of Freud-1 in vivo, we generated mice with adulthood conditional knock-out of Freud-1 in 5-HT neurons (cF1ko). In cF1ko mice, 5-HT1A autoreceptor protein, binding and hypothermia response were increased, with reduced 5-HT content and neuronal activity in the dorsal raphe. The cF1ko mice displayed increased anxiety- and depression-like behavior that was resistant to chronic antidepressant (fluoxetine) treatment. Using conditional Freud-1/5-HT1A double knock-out (cF1/1A dko) to disrupt both Freud-1 and 5-HT1A genes in 5-HT neurons, no increase in anxiety- or depression-like behavior was seen upon knock-out of Freud-1 on the 5-HT1A autoreceptor-negative background; rather, a reduction in depression-like behavior emerged. These studies implicate transcriptional dysregulation of 5-HT1A autoreceptors by the repressor Freud-1 in anxiety and depression and provide a clinically relevant genetic model of antidepressant resistance. Targeting specific transcription factors, such as Freud-1, to restore transcriptional balance may augment response to antidepressant treatment.SIGNIFICANCE STATEMENT Altered regulation of the 5-HT1A autoreceptor has been implicated in human anxiety, major depression, suicide, and resistance to antidepressants. This study uniquely identifies a single transcription factor, Freud-1, as crucial for 5-HT1A autoreceptor expression in vivo Disruption of Freud-1 in serotonin neurons in mice links upregulation of 5-HT1A autoreceptors to anxiety/depression-like behavior and provides a new model of antidepressant resistance. Treatment strategies to reestablish transcriptional regulation of 5-HT1A autoreceptors could provide a more robust and sustained antidepressant response.
Literature context: ab66047, RRID:AB_1142794 rabbit ant
Lgr5+ adult intestinal stem cells are highly proliferative throughout life. Single Lgr5+ stem cells can be cultured into three-dimensional organoids containing all intestinal epithelial cell types at near-normal ratios. Conditions to generate the main cell types (enterocyte, goblet cells, Paneth cells, and M cells) are well established, but signals to induce the spectrum of hormone-producing enteroendocrine cells (EECs) have remained elusive. Here, we induce Lgr5+ stem cell quiescence in vitro by blocking epidermal growth factor receptor (EGFR) or mitogen-associated protein kinase (MAPK) signaling pathways in organoids and show that their quiescent state is readily reverted. Quiescent Lgr5+ stem cells acquire a distinct molecular signature biased toward EEC differentiation. Indeed, combined inhibition of Wnt, Notch, and MAPK pathways efficiently generates a diversity of EEC hormone-expressing subtypes in vitro. Our observations uncouple Wnt-dependent stem cell maintenance from EGF-dependent proliferation and provide an approach for the study of the elusive EECs in a defined environment.
Literature context: # ab66047 RRID:AB_1142794; Abcam]. F
The primary sweet sensor in mammalian taste cells for sugars and noncaloric sweeteners is the heteromeric combination of type 1 taste receptors 2 and 3 (T1R2+T1R3, encoded by Tas1r2 and Tas1r3 genes). However, in the absence of T1R2+T1R3 (e.g., in Tas1r3 KO mice), animals still respond to sugars, arguing for the presence of T1R-independent detection mechanism(s). Our previous findings that several glucose transporters (GLUTs), sodium glucose cotransporter 1 (SGLT1), and the ATP-gated K(+) (KATP) metabolic sensor are preferentially expressed in the same taste cells with T1R3 provides a potential explanation for the T1R-independent detection of sugars: sweet-responsive taste cells that respond to sugars and sweeteners may contain a T1R-dependent (T1R2+T1R3) sweet-sensing pathway for detecting sugars and noncaloric sweeteners, as well as a T1R-independent (GLUTs, SGLT1, KATP) pathway for detecting monosaccharides. However, the T1R-independent pathway would not explain responses to disaccharide and oligomeric sugars, such as sucrose, maltose, and maltotriose, which are not substrates for GLUTs or SGLT1. Using RT-PCR, quantitative PCR, in situ hybridization, and immunohistochemistry, we found that taste cells express multiple α-glycosidases (e.g., amylase and neutral α glucosidase C) and so-called intestinal "brush border" disaccharide-hydrolyzing enzymes (e.g., maltase-glucoamylase and sucrase-isomaltase). Treating the tongue with inhibitors of disaccharidases specifically decreased gustatory nerve responses to disaccharides, but not to monosaccharides or noncaloric sweeteners, indicating that lingual disaccharidases are functional. These taste cell-expressed enzymes may locally break down dietary disaccharides and starch hydrolysis products into monosaccharides that could serve as substrates for the T1R-independent sugar sensing pathways.
Literature context: bridge MA; RRIDs: AB_300798 and AB_1142794, respectively; see Tableâ€‹Table1
The raphe nuclei provide serotonergic innervation widely in the brain, thought to mediate a variety of neuromodulatory effects. The mammalian olfactory bulb (OB) is a prominent recipient of serotonergic fibers, particularly in the glomerular layer (GL), where they are thought to gate incoming signals from the olfactory nerve. The dorsal raphe nucleus (DRN) and the median raphe nucleus (MRN) are known to densely innervate the OB. The majority of such projections are thought to terminate in the GL, but this has not been explicitly tested. We sought to investigate this using recombinant adeno-associated viruses (rAAV)-mediated expression of green fluorescent protein (GFP)-synaptophysin targeted specifically to neurons of the DRN or the MRN. With DRN injections, labeled fibers were found mostly in the granule cell layer (GCL), not the GL. Conversely, dense labeling in the GL was observed with MRN injections, suggesting that the source of GL innervation is the MRN, not the DRN, as previously thought. The two raphe nuclei thus give dual innervation within the OB, with distinct innervation patterns.