All organisms react to noxious and mechanical stimuli but we still lack a complete understanding of cellular and molecular mechanisms by which somatosensory information is transformed into appropriate motor outputs. The small number of neurons and excellent genetic tools make Drosophila larva an especially tractable model system in which to address this problem. We developed high throughput assays with which we can simultaneously expose more than 1,000 larvae per man-hour to precisely timed noxious heat, vibration, air current, or optogenetic stimuli. Using this hardware in combination with custom software we characterized larval reactions to somatosensory stimuli in far greater detail than possible previously. Each stimulus evoked a distinctive escape strategy that consisted of multiple actions. The escape strategy was context-dependent. Using our system we confirmed that the nociceptive class IV multidendritic neurons were involved in the reactions to noxious heat. Chordotonal (ch) neurons were necessary for normal modulation of head casting, crawling and hunching, in response to mechanical stimuli. Consistent with this we observed increases in calcium transients in response to vibration in ch neurons. Optogenetic activation of ch neurons was sufficient to evoke head casting and crawling. These studies significantly increase our understanding of the functional roles of larval ch neurons. More generally, our system and the detailed description of wild type reactions to somatosensory stimuli provide a basis for systematic identification of neurons and genes underlying these behaviors.

We show that gas diffusion nuclear magnetic resonance (GD-NMR) provides a powerful technique for probing the structure of porous media. In random packs of glass beads, using both laser-polarized and thermally polarized xenon gas, we find that GD-NMR can accurately measure the pore space surface-area-to-volume ratio, S/V rho, and the tortuosity, alpha (the latter quantity being directly related to the system's transport properties). We also show that GD-NMR provides a good measure of the tortuosity of sandstone and complex carbonate rocks.

We demonstrate a minimally invasive nuclear magnetic resonance (NMR) technique that enables determination of the surface-area-to-volume ratio (S/V) of soft porous materials from measurements of the diffusive exchange of laser-polarized 129 Xe between gas in the pore space and 129 Xe dissolved in the solid phase. We apply this NMR technique to porous polymer samples and find approximate agreement with destructive stereological measurements of S/V obtained with optical confocal microscopy. Potential applications of laser-polarized xenon interphase exchange NMR include measurements of in vivo lung function in humans and characterization of gas chromatography columns.Porous media are ubiquitous in nature, e.g., granular materials, foams, ceramics, oil-or waterbearing 'reservoir' rocks, and animal and human lungs. Determining the structure of these materials is relevant to a wide range of scientific and technological problems, ranging from the coarsening of foams to the transport properties of subsurface fluids to cardiopulmonary physiology and medicine. In this letter we demonstrate a non-invasive technique for characterizing the surface-area-to-volume ratio (S/V) [1] of 'soft' porous media: i.e., materials in which there is significant gas solubility in the solid phase. Such a description applies to many different materials, including porous polymer granulates used for filtering, porous polymer bead packs used for radio-immunoassay, resin columns used for chromatographic separation, and lung and sinus tissue in humans and animals.S/V influences numerous interactions within porous media, including fluid diffusion and transport, electric charge distribution, and chemical exchange. For example, S/V is important in determining pulmonary function since the lung is the site of O 2 and CO 2 exchange between the body and the external environment. There are numerous techniques for measuring S/V in porous media, including stereology [2] with traditional and confocal microscopy, light scattering [4,5], and mercury intrusion porosimetry [5]. However, only nuclear magnetic resonance (NMR) provides a non-invasive and non-destructive technique for determining three-dimensional structure, including S/V [6]. In particular, NMR measurements of the time-dependent diffusion coefficient of a liquid filling the pore space has been used to determine S/V in a variety of porous media [7,8] including glass beads [9], reservoir rocks [10], and biological samples [11]. Recently, we extended this technique to NMR measurements of xenon gas diffusion within porous media [12,13], thereby probing longer length scales than with traditional liquid-infused diffusion measurements [9,10] because of fast gas diffusion and long xenon spin polarization lifetimes. Gas diffusion NMR may also be used to study porous media that are not compatible with water saturation, such as non-wetting polymers and in vivo lungs. However, for materials with pore size less than about 300 μm (such as lung alveoli), the high diffusivity of gases causes systematic erro...

NMR images of laser polarized 3He gas were obtained at 21 G using a simple, homebuilt instrument. At such low fields magnetic resonance imaging (MRI) of thermally polarized samples (e.g., water) is not practical. Low-field noble gas MRI has novel scientific, engineering, and medical applications. Examples include portable systems for diagnosis of lung disease, as well as imaging of voids in porous media and within metallic systems.