Biology subjects

Bauer, J. P.

Publications and source records attributed to Bauer, J. P..

3 recordsLinked to original sources

bioRxiv2022

Glucagon-like peptide-1 receptor differentially controls mossy cell activity across the dentate gyrus longitudinal axis

Understanding the role of dentate gyrus (DG) mossy cells (MCs) in learning and memory has rapidly evolved due to increasingly precise methods for targeting MCs and for in vivo recording and activity manipulation in rodents. These studies have shown MCs are highly active in vivo, strongly remap to contextual manipulation, and that their inhibition or hyperactivation impairs pattern separation and location or context discrimination. What is not well understood is how MC activity is modulated by neurohormonal mechanisms, which might differentially control the participation of MCs in cognitive functions during discrete states, such as hunger or satiety. In this study, we demonstrate that glucagon-like peptide-1 (GLP-1), a neuropeptide produced in the gut and the brain that regulates food consumption and hippocampal-dependent mnemonic function, might regulate MC function through selective expression of its receptor, GLP-1R. RNA-seq demonstrated that most Glp1r in hippocampal principal neurons is expressed in MCs, and in situ hybridization revealed strong expression of Glp1r in hilar neurons. Glp1r-ires-Cre mice crossed with Ai14D reporter mice followed by co-labeling for the MC marker GluR2/3 revealed that almost all MCs in the ventral DG expressed Glp1r and that almost all Glp1r-expressing hilar neurons were MCs. However, only ~60% of dorsal DG MCs expressed Glp1r, and Glp1r was also expressed in small hilar neurons that were not MCs. Consistent with this expression pattern, peripheral administration of the GLP-1R agonist exendin-4 (5 g/kg) increased cFos expression in ventral but not dorsal DG hilar neurons. Finally, whole-cell patch-clamp recordings from ventral MCs showed that bath application of exendin-4 (200 nM) depolarized MCs and increased action potential firing. Taken together, this study identifies a potential neurohormonal mechanism linking a critically important satiety signal with activity of MCs in the ventral DG that might have functional effects on learning and memory during distinct states.

neuroscience↗

bioRxiv2020

Ventral hippocampal mossy cell hyperactivity degrades dorsal hippocampal mnemonic function via longitudinal projections

BackgroundThe anterior hippocampus of individuals with early psychosis or schizophrenia is hyperactive, as is the ventral hippocampus in rodent models for schizophrenia risk. Hyperactive ventral hippocampal projections to extrahippocampal brain regions contribute to schizophrenia symptoms, but less is known about the functional effects of hyperactive projections within the hippocampal formation long axis. We approached this question by testing whether hyperactivation of ventral dentate gyrus (DG) mossy cells (MCs), which densely project intrahippocampally to the dorsal DG, influences spatial memory, a cognition dependent on intact dorsal DG function. MethodsIn CD-1 mice, we targeted dorsal DG-projecting ventral DG MCs using an adeno-associated virus intersectional strategy. In vivo fiber photometry recording of ventral DG MCs was performed during exploratory behaviors. We targeted excitatory chemogenetic constructs to ventral DG MCs and tested whether their hyperactivation impaired encoding in a spatial memory task. ResultsVentral DG MCs were activated during behavior related to environmental information gathering (rearing) but not during non-exploratory motor behaviors. Ventral DG MCs made functional monosynaptic inputs to dorsal DG granule cells, with chemogenetic activation of ventral DG MCs leading to increased activity of dorsal DG granule cells. Finally, chemogenetic activation of ventral DG MCs during the encoding phase of an object location memory task impaired retrieval 24 hours later, without effects on locomotion or other exploratory behaviors. ConclusionsThese data suggest that localized hippocampal hyperactivity may have longitudinal intrahippocampal functional consequences, supporting study of longitudinal circuits as targets to mitigate cognitive deficits associated with schizophrenia.

neuroscience↗

bioRxiv2020

Food-Poisoning Bacteria Employ a Citrate Synthase and a Type II NRPS to Synthesize Bolaamphiphilic Lipopeptide Antibiotics

Mining the genome of the food-spoiling bacterium Burkholderia gladioli pv. cocovenenans revealed five non-ribosomal peptide synthetase (NRPS) gene clusters, including an orphan gene locus (bol). Gene inactivation and metabolic profiling linked the bol gene cluster to novel bolaamphiphilic lipopeptides with antimycobacterial activity. A combination of chemical analyses and bioinformatics elucidated the structures of bolagladin A and B, lipocyclopeptides featuring an unusual dehydro-{beta}-alanine enamide linker fused to an unprecedented tricarboxylic fatty acid tail. Through a series of targeted gene deletions we proved the involvement of a designated citrate synthase (CS), priming ketosynthases (KS III), a type II NRPS including a novel desaturase for enamide formation, and a multimodular NRPS generating the cyclopeptide. Network analyses revealed the evolutionary origin of the CS and identified cryptic CS/NRPS gene loci in various bacterial genomes.

microbiology↗