Biology subjects

Melzer, S.

Publications and source records attributed to Melzer, S..

7 recordsLinked to original sources

bioRxiv2026

PACAP engages distinct signaling programs across cortical neuronal and non-neuronal cell types

Neuropeptides form modulatory communication channels that tune neuronal circuits and their functions, often through selective targeting of distinct cell populations. Pituitary adenylate cyclase-activating polypeptide (PACAP) is an important neuropeptidergic regulator of fear and stress. However, its receptors are surprisingly ubiquitous across most brain areas and cell types, making the physiological roles and functional mechanisms difficult to predict. Here, we investigate the cell type-specific effects of PACAP in the temporal association cortex (TeA), a brain region implicated in fear learning and memory. Adcyap1r1, encoding the PACAP receptor PAC1, was broadly expressed across the majority of neuronal and non-neuronal cells. Yet, PACAP engaged highly diverse molecular pathways across functionally distinct cell types that were differentially recruited during auditory fear learning and retrieval, providing a framework for how broad receptor expression can yield specific network modulation. Our data underscore the importance of dissecting cellularly resolved peptidergic signaling to understand functional mechanisms of neuropeptides.

neuroscience↗

bioRxiv2026

Temporal cortex astrocytic Gi-GPCR signaling regulates learned threat responses

Astrocytes are increasingly recognized as dynamic modulators of brain circuit function, memory processing, and behavior. Emerging evidence suggests that astrocytic G-protein-coupled receptors (GPCRs) are key regulators of these processes through their influence on intracellular signaling and neuron-glia interactions. Here, we show that the repertoire of functionally expressed GPCRs in cortical astrocytes is broader than previously appreciated. Yet, how distinct GPCR pathways contribute to behavioral regulation remains unknown for most brain areas and behavioral contexts. We therefore investigated the role of astrocytic GPCR signaling in the temporal cortex, a region that integrates multimodal sensory information and learned fear associations. Using chemogenetic tools to selectively activate distinct GPCR pathways in astrocytes, we demonstrate that Gi-coupled GPCR signaling, but not Gs- or Gq-coupled signaling, enhances fear memory retrieval. In vivo fiber photometry revealed that temporal cortex astrocytes exhibit robust Ca2+ transients to neutral, conditioned auditory and aversive sensory stimuli. Notably, astrocytic Gi-GPCR activation attenuated cue-evoked Ca2+ transients during memory retrieval. Together, these findings identify astrocytic GPCR signaling as a pathway-specific regulator of fear memory retrieval and suggest that astrocytic Gi-GPCR signaling modulates the processing of sensory cues to drive defensive behavior.

neuroscience↗

bioRxiv2025

Tether-mediated extraction of myelinoid bodies by microglia and astrocytes can maintain myelin integrity

Oligodendrocytes make myelin for the electrical insulation of axons and saltatory impulse conduction. Myelin lipids and proteins undergo a slow turnover, but exactly how the multilamellar and compacted membrane sheaths are remodeled without compromising myelin sheath integrity has remained puzzling, in particular at advanced age when myelin abnormalities increase. Earlier EM studies had suggested myelin membranes are shed and subsequently phagocytosed by microglia. However, the formation of multilamellar myelinoid bodies (MBs), leaving a well-ordered myelin sheath behind, is difficult to reconcile with simple shedding mechanisms. Here, we show by three-dimensional FIB-SEM reconstructions of optic nerves in mice and by two-photon live-imaging of myelinated cortical slices that MBs are initially connected to their parental sheaths by long tethers, which are stretched by trogocytosing microglia and astrocytes. We observe ruptured tethers attached to both MBs and sheaths, suggesting a novel mechanism of tension-driven tether scission. Importantly, the successive fusion of the corresponding innermost myelin membranes in an extended tether can preserve myelin sheath integrity. Thus, the remodeling by tether-mediated MB extraction emerges as a mechanism of physiological maintenance of myelin sheaths in the CNS.

neuroscience↗

bioRxiv2024

Efficient and Versatile Rapeseed Transformation for New Breeding Technologies

Many gene functions are widely studied and understood in Arabidopsis; however, the lack of efficient transformation systems often limits the application and verification of this knowledge in crop plants. Brassica napus L., a member of the Brassicaceae family, is usually transformed by Agrobacterium-mediated hypocotyl transformation, but not all growth types are equally amenable to transformation. In particular, winter-type rapeseed, which requires vernalization to initiate flowering, is recalcitrant to in vitro regeneration and transformation. The analysis of gene functions in rapeseed is further complicated by the allotetraploid nature of its genome and the genome triplication within the Brassica genus, which has led to the presence of a large number of gene homologs for each Arabidopsis ortholog. We have established a transformation method that facilitates the regeneration of winter-type rapeseed by using the WUSCHEL gene from Beta vulgaris. This allowed us to efficiently transform winter-type and spring-type rapeseed in small-scale experiments. As proof of principle, we targeted Bna.CLV3 and Bna.SPL9/15 with CRISPR/Cas9 and showed that entire gene families are effectively edited using this transformation protocol. This allowed us to simultaneously study many redundantly acting homologous genes in rapeseed. We observed mutant phenotypes for Bna.CLV3 and Bna.SPL9/15 in primary transformants, indicating that biallelic knockouts were obtained for up to eight genes. This allowed an initial phenotypic characterization to be performed already a few months after starting the experiment.

plant biology↗

bioRxiv2024

Oxytocin facilitates social behavior of female rats via selective modulation of interneurons in the medial prefrontal cortex

The hypothalamic neuropeptide oxytocin is best known for its prosocial behavioral effects. However, the precise anatomical and cellular targets for oxytocin in the cortex during social behavior remain elusive. Here we show that oxytocin neurons project directly to the medial prefrontal cortex where evoked axonal oxytocin release facilitates social behaviors in adult female rats. In conjunction, we report that local oxytocin receptor-expressing (OTR+) cells are predominantly interneurons, whose activation promotes social interaction. Notably, this prosocial effect persists even under physiological challenge (hunger), pointing to a dedicated prosocial circuit capable of overriding primary survival drives. We further demonstrate that activation of these OTR+ interneurons inhibits principal cells specifically projecting to the basolateral amygdala, thus providing a putative mechanism of selective oxytocin action in this sociability-promoting cortical network.

neuroscience↗

bioRxiv2024

Probing PAC1 receptor activation across species with an engineered sensor

Class-B1 G protein-coupled receptors (GPCRs) are an important family of clinically relevant drug targets that remain difficult to investigate via high-throughput screening and in animal models. Here, we engineered PAClight1P78A, a novel genetically-encoded sensor based on a class-B1 GPCR (the human PAC1 receptor, hmPAC1R) endowed with high dynamic range ({Delta}F/F0 = 1100%), excellent ligand selectivity and rapid activation kinetics ({tau}ON = 1.15 sec). To showcase the utility of this tool for in vitro applications, we thoroughly characterized and compared its expression, brightness and performance between PAClight1P78A transfected and stably-expressing cells. Demonstrating its use in animal models, we show robust expression and fluorescence responses upon exogenous ligand application ex vivo and in vivo in mice, as well as in living zebrafish larvae. Thus, the new GPCR-based sensor can be used for a wide range of applications across the life sciences empowering both basic research and drug development efforts.

neuroscience↗

bioRxiv2020

Bombesin-like peptide recruits disinhibitory cortical circuits and enhances fear memories

Disinhibitory neurons throughout the mammalian cortex are powerful enhancers of circuit excitability and plasticity. The differential expression of neuropeptide receptors in disinhibitory, inhibitory and excitatory neurons suggests that each circuit motif is controlled by distinct neuropeptidergic systems. Here, we reveal that a bombesin-like neuropeptide, gastrin-releasing peptide (GRP), recruits disinhibitory cortical microcircuits through selective targeting and activation of vasoactive intestinal peptide (VIP)-expressing cells. Using a newly-developed genetically-encoded GRP sensor and trans-synaptic tracing we reveal that GRP regulates VIP cells via extrasynaptic diffusion from several putative local and long-range sources. In vivo photometry and CRISPR/Cas9-mediated knockout of the GRP receptor (GRPR) in auditory cortex indicate that VIP cells are strongly recruited by novel sounds and aversive shocks, and that GRP-GRPR signaling enhances auditory fear memories. Our data establish peptidergic recruitment of selective disinhibitory cortical microcircuits as a mechanism to regulate fear memories.

neuroscience↗