Assessment of behavioral, neuroinflammatory, and histological responses in a model of rat repetitive mild fluid percussion injury at 2 weeks post-injury.

Repetitive mild traumatic brain injury (rmTBI) is a prominent public health concern, with linkage to debilitating chronic sequelae. Developing reliable and well-characterized preclinical models of rmTBI is imperative in the investigation of the underlying pathophysiological mechanisms, as models can have varying parameters, affecting the overall pathology of the resulting injury. The lateral fluid percussion injury (FPI) model is a reliable and frequently used method of TBI replication in rodent subjects, though it is currently relatively underutilized in rmTBI research. In this study, we have performed a novel description of a variation of the lateral repetitive mild FPI (rmFPI) model, showing the graded acute behavioral impairment and histopathology occurring in response to one, two or four mild FPI (1.25 atm) or sham surgeries, implemented 24h apart. Beam walking performance revealed significant motor impairment in injured animals, with dysfunction increasing with additional injury. Based upon behavioral responses and histological observations, we further investigated the subacute pathophysiological outcomes of the dual FPI (dFPI). Immunoreactivity assessments showed that dFPI led to regionally-specific reductions in the post-synaptic protein neurogranin and increased subcortical white matter staining of the presynaptic protein synaptophysin at 2 weeks following dFPI. Immunohistochemical assessments of the microglial marker Iba-1 showed a striking increase in in several brain regions, and assessment of the astrocytic marker GFAP showed significantly increased immunoreactivity in the subcortical white matter and thalamus. With this study, we have provided a novel account of the subacute post injury outcomes occurring in response to a rmFPI utilizing these injury and frequency parameters, and thereby also demonstrating the reliability of the lateral FPI model in rmTBI replication.

All-trans Retinoic Acid has Limited Therapeutic Effects on Cognition and Hippocampal Protein Expression After Controlled Cortical Impact.

Traumatic brain injury (TBI) is known to impair synaptic function, and subsequently contribute to observed cognitive deficits. Retinoic Acid (RA) signaling modulates expression of synaptic plasticity proteins and is involved in hippocampal learning and memory. All trans-retinoic acid (ATRA), a metabolite of Vitamin A, has been identified as a potential pharmacotherapeutic for other neurological disorders due to this role. This study conducted an ATRA dose response to determine its therapeutic effects on cognitive behaviors and expression of hippocampal markers of synaptic plasticity and RA signaling proteins after experimental TBI. Under isoflurane anesthesia, adult male Sprague Dawley rats received either controlled cortical impact (CCI, 2.5 mm deformation, 4 m/s) or control surgery. Animals received daily intraperitoneal injection of 0.5, 1, 5, or 10 mg/kg of ATRA or vehicle for 2 weeks. Animals underwent motor and spatial learning and memory testing. Hippocampal expression of synaptic plasticity proteins neurogranin (Ng), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA1 sub-unit, as well as RA signaling proteins STRA6, ADLH1a1, CYP26A1 and CYP26B1 were evaluated by western blot at 2-weeks post-injury. ATRA treatment significantly recovered Ng synaptic protein expression, while having no effect on motor performance, spatial learning, and memory, and GluA1 expression after TBI. RA signaling protein expression is unchanged 2 weeks after TBI. Overall, ATRA administration after TBI showed limited therapeutic benefits compared to the vehicle.

Captive Asian short-clawed otters (Aonyx cinereus) learn to exploit unfamiliar natural prey.

Foraging plays a vital role in animal life histories, and learning whether unfamiliar food items are palatable is a key part of this process. Animals that engage in extractive foraging must also learn how to overcome the protective measures of their prey. While otters (subfamily Lutrinae) are a taxon known for their extractive foraging behaviour, how they learn about prey palatability and acquire extractive foraging techniques remains poorly understood. Here we investigated (i) how captive Asian short-clawed otters (Aonyx cinereus) learned to interact with, and extract meat from, unfamiliar natural prey and (ii) how their exploitation of such prey compared to their ability to overcome artificial foraging tasks containing familiar food rewards. Network-based diffusion analysis showed that otters learned to interact with unfamiliar natural prey by observing their group mates. However, once interacting with the prey, they learned to extract the meat mainly asocially. In addition, otters took longer to overcome the protective measures of unfamiliar natural prey than those of extractive food puzzles. Asian short-clawed otter populations are declining in the wild. Increasing our understanding of how they learn to overcome novel foraging challenges could help develop pre-release training procedures as part of reintroduction programmes for otter conservation.

Effects of food type and abundance on begging and sharing in Asian small-clawed otters (Aonyx cinereus).

Begging for food, a conspicuous solicitation display, is common in a variety of taxa, and it has received extensive research attention in a parent-offspring context. Both theoretical models and empirical evidence suggest that offspring begging can be an honest signal of hunger or a mediator of competition between siblings. At a behavioural mechanistic level, begging for food can be a form of harassment aimed at persuading those in possession of food to share. Food sharing, defined as the transfer of a defendable food item from one individual to another, can vary considerably between species, age-classes and food type and abundance. We investigated the determinants of begging and food-sharing behaviours in Asian small-clawed otters (Aonyx cinereus), a group-living species that commonly exhibits begging in captivity. We presented two captive otter populations with three food types that varied in exploitation complexity, in three different abundances. We predicted that begging rates would be highest when food was in lowest abundance and hardest to exploit, and that increased begging would lead to increased food sharing. We found that, over time, increased begging rates were indeed correlated with increased food transfers, but neither food type complexity nor abundance affected begging or sharing rates. However, age category was significantly associated with begging and food sharing rates: juvenile otters begged more and shared less than adult otters. The results from this first experimental study on begging and food sharing within the Mustelid family begin to reveal some of the drivers of these behaviours.

Discovery of Ubonodin, an Antimicrobial Lasso Peptide Active against Members of the Burkholderia cepacia Complex.

We report the heterologous expression, structure, and antimicrobial activity of a lasso peptide, ubonodin, encoded in the genome of Burkholderia ubonensis. The topology of ubonodin is unprecedented amongst lasso peptides, with 18 of its 28 amino acids found in the mechanically bonded loop segment. Ubonodin inhibits RNA polymerase in vitro and has potent antimicrobial activity against several pathogenic members of the Burkholderia genus, most notably B. cepacia and B. multivorans, causative agents of lung infections in cystic fibrosis patients.

Discovery and structure of the antimicrobial lasso peptide citrocin.

We report the identification of citrocin, a 19-amino acid-long antimicrobial lasso peptide from the bacteria Citrobacter pasteurii and Citrobacter braakii We refactored the citrocin gene cluster and heterologously expressed it in Escherichia coli We determined citrocin's NMR structure in water and found that is reminiscent of that of microcin J25 (MccJ25), an RNA polymerase-inhibiting lasso peptide that hijacks the TonB-dependent transporter FhuA to gain entry into cells. Citrocin has moderate antimicrobial activity against E. coli and Citrobacter strains. We then performed an in vitro RNA polymerase (RNAP) inhibition assay using citrocin and microcin J25 against E. coli RNAP. Citrocin has a higher minimal inhibition concentration than microcin J25 does against E. coli but surprisingly is ∼100-fold more potent as an RNAP inhibitor. This suggests that citrocin uptake by E. coli is limited. We found that unlike MccJ25, citrocin's activity against E. coli relied on neither of the two proton motive force-linked systems, Ton and Tol-Pal, for transport across the outer membrane. The structure of citrocin contains a patch of positive charge consisting of Lys-5 and Arg-17. We performed mutagenesis on these residues and found that the R17Y construct was matured into a lasso peptide but no longer had activity, showing the importance of this side chain for antimicrobial activity. In summary, we heterologously expressed and structurally and biochemically characterized an antimicrobial lasso peptide, citrocin. Despite being similar to MccJ25 in sequence, citrocin has an altered activity profile and does not use the same outer-membrane transporter to enter susceptible cells.