Biology subjects

Homberg, J.

Publications and source records attributed to Homberg, J..

5 recordsLinked to original sources

bioRxiv2024

The Neural Blueprint of Stress Susceptibility: Brain-wide neuronal activity associated with the consequences of stress

Understanding the neurobiological mechanisms of stress susceptibility is key to advancing our insight into stress-related psychopathology like post-traumatic stress disorder (PTSD). Preclinical animal models however typically lack translationally relevant brain readouts. Here, we used a mouse model for severe stress, segregating mice into stress-susceptible and resilient groups. We analyzed and contrasted their whole-brain neuronal activity pre-, peri- and post-stress exposure and compared functional connectivity of the salience (SN), default mode (DMN) and executive control network (lateral cortical network (LCN) in rodents). We found that stress-susceptible mice exhibited pre-existing hyperactivity in the lateral orbital area, a potential risk factor for stress vulnerability, and heightened retrosplenial cortex activity peri- and post-stress, potentially contributing to maladaptive fear memory. Upon stress exposure, susceptible mice showed strong recruitment of visual and memory-related areas, whereas resilient mice displayed marked reductions in retrosplenial activity and increased activation in the agranular insula and ventral striatum. Observations of enhanced intra-SN and SN-DMN connectivity in susceptible mice mirrored those observed in individuals with PTSD. Moreover, susceptible mice displayed aberrant DMN-LCN network pre- and peri-stress. These findings highlight the importance of dynamic network interactions in stress susceptibility and suggest novel brain region targets for (early) intervention.

neuroscience↗

bioRxiv2024

Unravelling the neurocognitive mechanisms underlying counterconditioning in humans

Counterconditioning (CC) aims to enhance extinction of threat memories by establishing new associations of opposite valence. While its underlying neurocognitive mechanisms remain largely unexplored, previous studies suggest qualitatively different mechanisms from regular extinction. In this functional MRI study, participants underwent categorical threat conditioning (CS+/CS-: images of animals/tools), followed by either CC (CS+ images reinforced with monetary rewards, n=24) or regular extinction (n=24). The following day, we assessed spontaneous recovery of threat responses and episodic memory for CS+ and CS-category exemplars. While the ventromedial prefrontal cortex (vmPFC) was activated during regular extinction, participants undergoing CC showed persistent CS+-specific deactivation of the vmPFC and hippocampus, and CS+-specific activation of the nucleus accumbens (NAcc). The following day, physiological threat responses returned in the regular extinction group, but not in the CC group. Counterconditioning furthermore strengthened episodic memory for CS+ exemplars presented during CC, and retroactively also for CS+ exemplars presented during the threat conditioning phase. Our findings confirm that CC leads to more persistent extinction of threat memories, as well as altered consolidation of the threat conditioning episode. Crucially, we show a qualitatively different activation pattern during CC versus regular extinction, with a shift away from the vmPFC and towards the NAcc.

neuroscience↗

bioRxiv2023

Estimating foraging behavior in rodents using a modified paradigm measuring threat imminence dynamics

Animals display defensive behaviors in response to threats to avoid danger and approach rewards. In nature, these responses did not evolve alone but are always accompanied by motivational conflict. A semi-naturalistic threat imminence continuum model models the approach-avoidance conflict and is able to integrate multiple defensive behaviors into a single paradigm. However, its comprehensive application is hampered by the lack of a detailed protocol and data about some fundamental factors including sex, age, and motivational level. Here, we modified a previously established paradigm measuring threat imminence continuum dynamics, involving modifications of training and testing protocols, and utilization of commercial materials combined with open science codes, making it more standardized and easier to replicate. We demonstrate that foraging behavior is modulated by age, hunger level, and sex. This paradigm can be used to study defensive behaviors in animals in a more naturalistic manner with relevance to human approach-avoid conflicts and associated psychopathologies. HighlightsO_LIWe provide detailed guidance for setting up a modified paradigm for the threat imminence continuum model with commercial materials and open-source codes. C_LIO_LIWe propose a modified paradigm for the threat imminence continuum model to quantify foraging behaviors. C_LIO_LIOur method enables comparison between groups as a function of multiple factors including age and food restriction. C_LI Graphic Summary O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=93 SRC="FIGDIR/small/550314v1_ufig1.gif" ALT="Figure 1"> View larger version (14K): org.highwire.dtl.DTLVardef@f4be92org.highwire.dtl.DTLVardef@b7f6dorg.highwire.dtl.DTLVardef@db0dc1org.highwire.dtl.DTLVardef@1640cce_HPS_FORMAT_FIGEXP M_FIG C_FIG

animal behavior and cognition↗

bioRxiv2022

TPH2 knockout male rats are aggressive, show less anxiety, and exhibit an altered oxytocin system

The central serotoninergic system is critical for stress responsivity and social behavior, and its dysregulations has been centrally implicated in virtually all neuropsychiatric disorders. Genetic serotonin depletion animal models could provide a tool to elucidate the causes and mechanisms of diseases and to develop new treatment approaches. Previously mice lacking tryptophan hydroxylase 2 (Tph2) have been developed, showing altered behaviors and neurotransmission. However, the effect of congenital serotonin deficiency on emotional and social behavior in rats is still largely unknown, as are the underlying mechanisms. In this study, we used Tph2 knockout (Tph2-/-) male rat model to study how the lack of serotonin in the rat brain affects anxiety-like and social behaviors. Since oxytocin is centrally implicated in these behaviors, we furthermore explored whether effects of Tph2 knockout on behavior would relate to changes in the oxytocin system. We show that Tph2-/- rats display reduced anxiety-like behavior and a high level of aggression in social interactions. In addition, oxytocin receptor expression was increased in the infralimbic and prelimbic cortex, paraventricular nucleus, dorsal raphe nucleus and some subregions of hippocampus, which was paralleled by increased levels of oxytocin in the medial frontal cortex, paraventricular nucleus, but not the dorsal raphe nucleus, central amygdala and hippocampus. In conclusion, our study demonstrated reduced anxiety but exaggerated aggression in Tph2-/- male rats and reveals for the first time a potential involvement of altered oxytocin system function. SIGNIFICANCE STATEMENTWe explored the changes in behavior and oxytocin system functioning in the tryptophan hydroxylase 2 (Tph2) knockout rat model, lacking serotonin in the brain. This rat model contributes to our understanding of the role of serotonin in psychiatric transdiagnostic features and underlying mechanisms. We found that Tph2 knockout male rats are aggressive, less anxious, and exhibit an altered oxytocin system. The observed changes in oxytocin signaling may lead to a new target for the treatment of diseases caused by genetic serotonin deficiency.

neuroscience↗

bioRxiv2020

Serotonin transporter knockout in rats modulates category learning

Lower function of the serotonin transporter (5-HTT) has a strong relationship with the development of autism spectrum disorder (ASD) in humans. One characteristic of ASD is the repetitive and restrictive behavior, which may form the basis for better memory and savant skills in some people with ASD. This characteristic in ASD may reflect a tendency towards an exploitation strategy rather than an exploration strategy during learning. Using a rat model, we developed a touchscreen-based task for testing 5-HTT knockout effects on stimulus category learning. By analyzing the data with a reinforcement learning drift diffusion model, we find that 5-HTT knockout rats show a lower learning rate and apply more of an exploitation versus exploration strategy compared to WT rats during category learning. The decision bound of decision-making during stimulus generalization indicates that more 5-HTT knockout rats than WT rats exploit irrelevant information to categorize stimuli. The touchscreen-based task we developed greatly increases the translational value from animals to humans and helps to understand the behavioral mechanisms underlying repetitive behavior in ASD.

neuroscience↗