Progressive structuring of a branched antimicrobial peptide on the path to the inner membrane target.

In recent years, interest has grown in the antimicrobial properties of certain natural and non-natural peptides. The strategy of inserting a covalent branch point in a peptide can improve its antimicrobial properties while retaining host biocompatibility. However, little is known regarding possible structural transitions as the peptide moves on the access path to the presumed target, the inner membrane. Establishing the nature of the interactions with the complex bacterial outer and inner membranes is important for effective peptide design. Structure-activity relationships of an amphiphilic, branched antimicrobial peptide (B2088) are examined using environment-sensitive fluorescent probes, electron microscopy, molecular dynamics simulations, and high resolution NMR in solution and in condensed states. The peptide is reconstituted in bacterial outer membrane lipopolysaccharide extract as well as in a variety of lipid media mimicking the inner membrane of Gram-negative pathogens. Progressive structure accretion is observed for the peptide in water, LPS, and lipid environments. Despite inducing rapid aggregation of bacteria-derived lipopolysaccharides, the peptide remains highly mobile in the aggregated lattice. At the inner membranes, the peptide undergoes further structural compaction mediated by interactions with negatively charged lipids, probably causing redistribution of membrane lipids, which in turn results in increased membrane permeability and bacterial lysis. These findings suggest that peptides possessing both enhanced mobility in the bacterial outer membrane and spatial structure facilitating its interactions with the membrane-water interface may provide excellent structural motifs to develop new antimicrobials that can overcome antibiotic-resistant Gram-negative pathogens.

Early Neurodevelopmental Outcomes Following Exposure to General Anesthesia in Infancy: EGAIN, a Prospective Cohort Study.

BACKGROUND: General anesthesia (GA) is known to worsen neural outcomes in animals, but human research assessing early-life GA exposure and neurodevelopment show inconsistent findings. We investigated the effects of a single GA exposure for minor surgery on the neurodevelopment of healthy children at multiple time-points, using clinical assessments along with behavioral and neurophysiological measures rarely used in human research. METHODS: GA-exposed children were a prospective cohort of 250 full-term, healthy infants who underwent GA for minor surgery before 15 months. Nonexposed children were from a separate cohort of similar age, sex, ethnicity, and maternal education. In both cohorts, clinical measures (Bayley Scales of Infant and Toddler Development-III [BSID-III] and Child Behavior Checklist [CBCL1½-5]) were assessed at 24 months, and experimental tests (memory and attentional) and neurophysiology (event-related potentials) at 6 and 18 months. RESULTS: At 24 months, there were no differences between GA-exposed and nonexposed children in the cognitive, language, motor, and socioemotional domains of the BSDI-III; however, GA-exposed children had poorer parental-reported scores in BSID-III general adaptability (94.2 vs. 99.0 [mean difference, 4.77; 97.3% confidence interval, -9.29, -0.24]; P =0.020) and poorer internalizing behavior scores on CBCL1½-5 (52.8 vs. 49.4 [mean difference, 3.35; 97.3% confidence interval, 0.15-6.55]; P =0.021). For experimental measures, GA-exposed children showed differences in 4 tests at 6 and 18 months. CONCLUSIONS: GA-exposed children did not differ from unexposed children in cognitive, language or motor outcomes at 24 months, but exhibited poorer parent-reported behavior scores. Differences in infant behavior and neurophysiology were detected at 6 and 18 months. Neurophysiological assessments may complement clinically relevant assessments to provide greater insights into neurodevelopment following early GA exposure.

Independent Mobility Achieved through a Wireless Brain-Machine Interface.

Individuals with tetraplegia lack independent mobility, making them highly dependent on others to move from one place to another. Here, we describe how two macaques were able to use a wireless integrated system to control a robotic platform, over which they were sitting, to achieve independent mobility using the neuronal activity in their motor cortices. The activity of populations of single neurons was recorded using multiple electrode arrays implanted in the arm region of primary motor cortex, and decoded to achieve brain control of the platform. We found that free-running brain control of the platform (which was not equipped with any machine intelligence) was fast and accurate, resembling the performance achieved using joystick control. The decoding algorithms can be trained in the absence of joystick movements, as would be required for use by tetraplegic individuals, demonstrating that the non-human primate model is a good pre-clinical model for developing such a cortically-controlled movement prosthetic. Interestingly, we found that the response properties of some neurons differed greatly depending on the mode of control (joystick or brain control), suggesting different roles for these neurons in encoding movement intention and movement execution. These results demonstrate that independent mobility can be achieved without first training on prescribed motor movements, opening the door for the implementation of this technology in persons with tetraplegia.

High-frequency stimulation of the globus pallidus interna nucleus modulates GFRα1 gene expression in the basal ganglia.

Deep brain stimulation (DBS) is an established therapy for movement disorders such as Parkinson's disease (PD). Although the efficacy of DBS is clear, its precise molecular mechanism remains unknown. The glial cell line derived factor (GDNF) family of ligands has been shown to confer neuroprotective effects on dopaminergic neurons, and putaminal infusion of GDNF have been investigated in PD patients with promising results. Despite the potential therapeutic role of GDNF in alleviating motor symptoms, there is no data on the effects of electrical stimulation on GDNF-family receptor (GFR) expression in the basal ganglia structures. Here, we report the effects of electrical stimulation on GFRα1 isoforms, particularly GFRα1a and GFRα1b. Wistar rats underwent 2 hours of high frequency stimulation (HFS) at the globus pallidus interna nucleus. A control group was subjected to a similar procedure but without stimulation. The HFS group, sacrificed 24 hours after treatment, had a threefold decrease in mRNA expression level of GFRα1b (p=0.037), but the expression level reverted to normal 72 hours after stimulation. Our preliminary data reveal the acute effects of HFS on splice isoforms of GFRα1, and suggest that HFS may modulate the splice isoforms of GFRα1a and GFRα1b to varying degrees. Going forward, elucidating the interactions between HFS and GFR may shed new insights into the complexity of GDNF signaling in the nervous system and lead to better design of clinical trials using these signaling pathways to halt disease progression in PD and other neurodegenerative diseases.