The Impact of Ethologically Relevant Stressors on Adult Mammalian Neurogenesis

BMP Antagonist Gremlin 2 Regulates Hippocampal Neurogenesis and Is Associated with Seizure Susceptibility and Anxiety

The Bone Morphogenetic Protein (BMP) signaling pathway is vital in neural progenitor cell proliferation, specification, and differentiation. The BMP signaling antagonist Gremlin 2 (Grem2) is the most potent natural inhibitor of BMP expressed in the adult brain; however its function remains unknown. To address this knowledge gap, we have analyzed mice lacking Grem2 via homologous recombination (Grem2-/- ). Histological analysis of brain sections revealed significant scattering of CA3 pyramidal cells within the dentate hilus in the hippocampus of Grem2-/- mice. Furthermore, the number of proliferating neural stem cells and neuroblasts was significantly decreased in the subgranular zone of Grem2-/- mice compared with that of wild-type (WT) controls. Due to the role of hippocampal neurogenesis in neurological disorders, we tested mice on a battery of neurobehavioral tests. Grem2-/- mice exhibited increased anxiety on the elevated zero maze in response to acute and chronic stress. Specifically, male Grem2-/- mice showed increased anxiogenesis following chronic stress, and this was correlated with higher levels of BMP signaling and decreased proliferation in the dentate gyrus. Additionally, when chemically challenged with kainic acid, Grem2-/- mice displayed a higher susceptibility to and increased severity of seizures compared with WTs. Together, our data indicate that Grem2 regulates BMP signaling and is vital in maintaining homeostasis in adult hippocampal neurogenesis and structure. Furthermore, the lack of Grem2 contributes to the development and progression of neurogenesis-related disorders such as anxiety and epilepsy.

Single administration of a psychedelic [(R)-DOI] influences coping strategies to an escapable social stress

Psychedelic compounds have potentially rapid, long-lasting anxiolytic, antidepressive and anti-inflammatory effects. We investigated whether the psychedelic compound (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI], a selective 5-HT2A receptor partial agonist, decreases stress-related behavior in male mice exposed to repeated social aggression. Additionally, we explored the likelihood that these behavioral changes are related to anti-inflammatory properties of [(R)-DOI]. Animals were subjected to the Stress Alternatives Model (SAM), an escapable social stress paradigm in which animals develop reactive coping strategies - remaining in the SAM arena (Stay) with a social aggressor, or dynamically initiated stress coping strategies that involve utilizing the escape holes (Escape) to avoid aggression. Mice expressing these behavioral phenotypes display behaviors like those in other social aggression models that separate animals into stress-vulnerable (as for Stay) or stress-resilient (as for Escape) groups, which have been shown to have distinct inflammatory responses to social stress. These results show that Stay animals have heightened cytokine gene expression, and both Stay and Escape mice exhibit plasma and neural concentrations of the inflammatory cytokine tumor necrosis factor-α (TNFα) compared to unstressed control mice. Additionally, these results suggest that a single administration of (R)-DOI to Stay animals in low doses, can increase stress coping strategies such as increasing attention to the escape route, promoting escape behavior, and reducing freezing during socially aggressive interaction in the SAM. Lower single doses of (R)-DOI, in addition to shifting behavior to suggest anxiolytic effects, also concomitantly reduce plasma and limbic brain levels of the inflammatory cytokine TNFα.

Modulating chronic outcomes after pediatric traumatic brain injury: Distinct effects of social and environmental enrichment

Impairments in social and cognitive function are a common consequence of pediatric traumatic brain injury (TBI). Rehabilitation has the potential to promote optimal behavioral recovery. Here, we evaluated whether an enhanced social and/or cognitive environment could improve long-term outcomes in a preclinical model of pediatric TBI. Male C57Bl/6 J mice received a moderately-severe TBI or sham procedure at postnatal day 21. After one week, mice were randomized to different social conditions (minimal socialization, n = 2/cage; or social grouping, n = 6/cage), and housing conditions (standard cage, or environmental enrichment (EE), incorporating sensory, motor, and cognitive stimuli). After 8 weeks, neurobehavioral outcomes were assessed, followed by post-mortem neuropathology. We found that TBI mice exhibited hyperactivity, spatial memory deficits, reduced anxiety-like behavior, and reduced sensorimotor performance compared to age-matched sham controls. Pro-social and sociosexual behaviors were also reduced in TBI mice. EE increased sensorimotor performance, and the duration of sociosexual interactions. Conversely, social housing reduced hyperactivity and altered anxiety-like behavior in TBI mice, and reduced same-sex social investigation. TBI mice showed impaired spatial memory retention, except for TBI mice exposed to both EE and group housing. In the brain, while TBI led to significant regional tissue atrophy, social housing had modest neuroprotective effects on hippocampal volumes, neurogenesis, and oligodendrocyte progenitor numbers. In conclusion, manipulation of the post-injury environment has benefit for chronic behavioral outcomes, but the benefits are specific to the type of enrichment available. This study improves understanding of modifiable factors that may be harnessed to optimize long-term outcomes for survivors of early-life TBI.

Genetic adaptation to urban living: molecular DNA analyses of wild boar populations in Budapest and surrounding area

Studies of wild boar, Sus scrofa Linnaeus 1758, in urban and suburban areas of Budapest, Hungary, have indicated that these populations do not have continuous contact. Based on the assumption that the city has a discrete population, we hypothesized that the urban wild boar would differ genetically from those in suburban areas. Analysis of single-nucleotide polymorphism (SNP) data using the GeneSeek Genomic Profiler (GGP) Porcine 50 K system (Neogen, Scotland, UK) differentiated three populations: Buda (B) from the Western bank of the Danube; Buda Surrounding (BS); and Valkó (V) from the Eastern bank of the Danube. The coefficient of genetic differentiation (FST) for the B and BS populations was low. The inbreeding coefficients of the populations BS and V were close to zero, while population B had a high positive value reflecting the influence of founders and the inbreeding of the continuous urban population. The genome regions that were most differentiated between the B and BS populations were analyzed based on the FST values of the SNP markers using a mixed linear multi-locus model and BayeScan software. The most differentiated marker, WU_10.2_18_56278226, was found on chromosome 18. The surrounding region contained several candidate genes that could play important roles in adaptations related to human-induced stress. Two of these, encoding the adenylate cyclase 1 (ADCY1) and inhibin beta A chain precursor (INHBA) genes, were sequenced. While IHBA gene did not display variation, the allele distribution of the ADCY1 gene in the B population was significantly different from that of the BS population supporting the parapatric differentiation of wild boar.

Nucleus Reuniens Lesion and Antidepressant Treatment Prevent Hippocampal Neurostructural Alterations Induced by Chronic Mild Stress in Male Rats

The hippocampus-prefrontal cortex circuit plays a major role in stress and in the neurobiology of depression and its treatment. Disruption of this circuit by lesioning the thalamic nucleus reuniens (RE) has been shown to prevent the detrimental effects of chronic mild stress on prefrontal cortex neuroplasticity indices in male rats. However, it remains unknown whether hippocampal neurostructural response to stress is modified by RE lesion. In the present study, adult male rats were subjected to the chronic mild stress model of depression and were treated with either vehicle or an antidepressant (i.e. sertraline). Moreover, a group of animals was subjected to RE lesion before stress exposure with or without sertraline treatment. We demonstrated that chronic mild stress induced hippocampal CA1 dendritic atrophy and this was prevented by pre-stress RE lesion to the same extent that antidepressant treatment reversed it. The present findings highlight the importance of hippocampal-prefrontal cortex communication in chronic stress effects on hippocampal neuroplasticity and contribute to the elucidation of the role of RE in neurostructural changes underlying stress-driven depression and its treatment.

Keel bone fractures induce a depressive-like state in laying hens

In commercial flocks of laying hens, keel bone fractures (KBFs) are prevalent and associated with behavioural indicators of pain. However, whether their impact is severe enough to induce a depressive-like state of chronic stress is unknown. As chronic stress downregulates adult hippocampal neurogenesis (AHN) in mammals and birds, we employ this measure as a neural biomarker of subjective welfare state. Radiographs obtained longitudinally from Lohmann Brown laying hens housed in a commercial multi-tier aviary were used to score the severity of naturally-occurring KBFs between the ages of 21-62 weeks. Individual birds' transitions between aviary zones were also recorded. Focal hens with severe KBFs at 3-4 weeks prior to sampling (n = 15) had lower densities of immature doublecortin-positive (DCX+) multipolar and bipolar neurons in the hippocampal formation than focal hens with minimal fractures (n = 9). KBF severity scores at this time also negatively predicted DCX+ cell numbers on an individual level, while hens that acquired fractures earlier in their lives had fewer DCX+ neurons in the caudal hippocampal formation. Activity levels 3-4 weeks prior to sampling were not associated with AHN. KBFs thus lead to a negative affective state lasting at least 3-4 weeks, and management steps to reduce their occurrence are likely to have significant welfare benefits.