There is compelling evidence that acute ethanol exposure stimulates ventral tegmental area (VTA) dopamine cell activity and that VTA-dependent dopamine release in terminal fields within the nucleus accumbens plays an integral role in the regulation of ethanol drinking behaviors. Unfortunately, due to technical limitations, the specific temporal dynamics linking VTA dopamine cell activation and ethanol self-administration are not known. In fact, establishing a causal link between specific patterns of dopamine transmission and ethanol drinking behaviors has proven elusive. Here, we sought to address these gaps in our knowledge using a newly developed viral-mediated gene delivery strategy to selectively express Channelrhodopsin-2 (ChR2) on dopamine cells in the VTA of wild-type rats. We then used this approach to precisely control VTA dopamine transmission during voluntary ethanol drinking sessions. The results confirmed that ChR2 was selectively expressed on VTA dopamine cells and delivery of blue light pulses to the VTA induced dopamine release in accumbal terminal fields with very high temporal and spatial precision. Brief high frequency VTA stimulation induced phasic patterns of dopamine release in the nucleus accumbens. Lower frequency stimulation, applied for longer periods mimicked tonic increases in accumbal dopamine. Notably, using this optogenetic approach in rats engaged in an intermittent ethanol drinking procedure, we found that tonic, but not phasic, stimulation of VTA dopamine cells selectively attenuated ethanol drinking behaviors. Collectively, these data demonstrate the effectiveness of a novel viral targeting strategy that can be used to restrict opsin expression to dopamine cells in standard outbred animals and provide the first causal evidence demonstrating that tonic activation of VTA dopamine neurons selectively decreases ethanol self-administration behaviors.

We apply light torques to single optically trapped glass nanorods suspended in water. The resulting motion is studied experimentally and consists of two distinct regimes: a linear regime where the rod angle increases linearly with time and a nonlinear regime where the rod angle changes nonlinearly, experiencing accelerations and rapid reversals. We present a detailed theoretical treatment for the motion of such nanorods, which agrees extremely well with the observed motion. The experiments are carried out so that the trapped and torqued nanorods move without influence from surfaces. Such a model system is critical to understanding the more complex motion that occurs near a surface. Studying such nonlinear motion both free of, and near, a surface is important for understanding nanofluidics and hydrodynamic motion at the nanoscale.

Next-generation sequencing (NGS) machines can sequence millions of DNA strands in a single run, such as oligonucleotide (oligo) libraries comprising millions to trillions of discrete oligo sequences. Capillary electrophoresis is an attractive technique to select tight binding oligos or “aptamers” because it requires minimal sample volumes (e.g., 100 nL) and offers a solution-phase selection environment through which enrichment of target-binding oligos can be determined quantitatively. We describe here experiments using capillary transient isotachophoresis (ctITP)-based nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) as a method for selecting aptamers from a randomized library containing a known (29mer) thrombin-binding aptamer. Our capillary electrophoresis (CE)-selected samples were sequenced by the Ion Torrent Personal Genome Machine (PGM) and analyzed for selection efficiency. We show that a single round of CE selection can enrich a randomer synthetic DNA oligo mixture for thrombin-binding activity from 0.4 % aptamer content before selection to >15 % aptamer content.

Electrospun nanofibers manufactured from biocompatible materials are used in numerous bioengineering applications, such as tissue engineering, creating organoids or dressings, and drug delivery. In many of these applications, the morphological and mechanical properties of the single fiber affect their function. We used a combined atomic force microscope (AFM)/optical microscope technique to determine the mechanical properties of nanofibers that were electrospun from a 50:50 fibrinogen:PCL (poly-ε-caprolactone) blend. Both of these materials are widely available and biocompatible. Fibers were spun onto a striated substrate with 6 μm wide grooves, anchored with epoxy on the ridges and pulled with the AFM probe. The fibers showed significant strain softening, as the modulus decreased from an initial value of 1700 MPa (5–10% strain) to 110 MPa (>40% strain). Despite this extreme strain softening, these fibers were very extensible, with a breaking strain of 100%. The fibers exhibited high energy loss (up to 70%) and strains larger than 5% permanently deformed the fibers. These fibers displayed the stress–strain curves of a ductile material. We provide a comparison of the mechanical properties of these blended fibers with other electrospun and natural nanofibers. This work expands a growing library of mechanically characterized, electrospun materials for biomedical applications.

Chromatin motions depend on and may regulate genome functions, in particular the DNA damage response. In yeast, DNA double-strand breaks (DSBs) globally increase chromatin diffusion, whereas in higher eukaryotes the impact of DSBs on chromatin dynamics is more nuanced. We mapped the motions of chromatin microdomains in mammalian cells using diffractive optics and photoactivatable chromatin probes and found a high level of spatial heterogeneity. DNA damage reduces heterogeneity and imposes spatially defined shifts in motions: Distal to DNA breaks, chromatin motions are globally reduced, whereas chromatin retains higher mobility at break sites. These effects are driven by context-dependent changes in chromatin compaction. Photoactivated lattices of chromatin microdomains are ideal to quantify microscale coupling of chromatin motion. We measured correlation distances up to 2 µm in the cell nucleus, spanning chromosome territories, and speculate that this correlation distance between chromatin microdomains corresponds to the physical separation of A and B compartments identified in chromosome conformation capture experiments. After DNA damage, chromatin motions become less correlated, a phenomenon driven by phase separation at DSBs. Our data indicate tight spatial control of chromatin motions after genomic insults, which may facilitate repair at the break sites and prevent deleterious contacts of DSBs, thereby reducing the risk of genomic rearrangements.