Active haptic sensation is critical for object identification, but its neural circuit basis is poorly understood. We combined optogenetics, two-photon imaging, and high-speed behavioral tracking in mice solving a whisker-based object orientation discrimination task. We found that orientation discrimination required animals to summate input from multiple whiskers specifically along the whisker arc. Animals discriminated the orientation of the stimulus per se as their performance was invariant to the location of the presented stimulus. Populations of barrel cortex neurons summated across whiskers to encode each orientation. Finally, acute optogenetic inactivation of the barrel cortex and cell-type-specific optogenetic suppression of layer 4 excitatory neurons degraded performance, implying that infragranular layers alone are not sufficient to solve the task. These data suggest that spatial summation over an active haptic array generates representations of an object’s orientation, which may facilitate encoding of complex three-dimensional objects during active exploration.

Epilepsy remains a significant healthcare problem associated with significant morbidity and mortality. Electroencephalograms (EEGs) provide a means of identifying ongoing seizures. However, specialized equipment is needed to obtain and interpret data. There remains a need for technologies that are easily utilized and interpreted for the purpose of monitoring children in the time periods before, during and after seizure activity. NIRS cerebral oximetry works as a noninvasive measurement that allows continuous measurement of cerebral oxygen availability. This monitor serves as a surrogate to invasive measures of venous pO2, often obtained from the jugular vein to estimate cerebral oxygen levels. We recently published NIRS-EEG data with a limited number of NIRS probes in four patients with medically refractory epilepsy undergoing pre-surgical evaluation with ages ranging from 5 to 17 years. The purpose of this pilot study is to describe the relationship of regional cerebral oximetry and cytoximetry, measured using MULTICHANNEL NIRS (near-infrared spectroscopy) in the peri-ictal period in children with epilepsy. The hypothesis is: 1. Regional cerebral saturation of oxygen and/or cytochrome oxidase redox state will increase prior to the onset of seizure activity; 2. Regional cerebral saturation of oxygen and/or cytochrome oxidase redox state will have a varied response during seizure activity depending on the seizure type; 3. Regional cerebral saturation of oxygen and/or cytochrome oxidase redox state will return to baseline following cessation of seizure activity. The three goals for the research study are to: 1. Quantify the magnitude and direction of change of cerebral oxygen saturation and cytochrome oxidase redox state during the peri-ictal period in children with epilepsy; 2. Quantify the temporal relationship, magnitude and direction of change of cerebral oxygenation and cytochrome oxidase redox state in relationship to seizure type; 3. Measure the association of cerebral oxygenation and cytochrome oxidase redox state with systemic oxygen saturation, EEG findings and clinical status. Study subjects will include pediatric patients from birth to 18 years of age with a known seizure disorder who are being admitted to the epilepsy monitoring unit (EMU) or the ICU at CHW for further workup or medication management of their epilepsy. Children will be monitored per standard of care for the duration of their hospitalization, which typically is 3–5 days with the additional NIRS-EEG array added to their monitoring. Preliminary data shows varied regional cerebral oxygen saturation and/or cytochrome oxidase redox state during interictal period and seizure activity depending on the seizure type. The increased blood flow clearly coincided with epileptiform activity and continued to increase as the epileptiform activity built up. Regional cerebral oxygen saturation increased in the epileptogenic focus, perhaps due to loss of cerebrovascular autoregulation.

Targeted manipulation of activity in specific populations of neurons is important for investigating the neural circuit basis of behavior. Optogenetic approaches using light-sensitive microbial rhodopsins have permitted manipulations to reach a level of temporal precision that is enabling functional circuit dissection. As demand for more precise perturbations to serve specific experimental goals increases, a palette of opsins with diverse selectivity, kinetics, and spectral properties will be needed. Here, we introduce a novel approach of "topological engineering"-inversion of opsins in the plasma membrane-and demonstrate that it can produce variants with unique functional properties of interest for circuit neuroscience. In one striking example, inversion of a Channelrhodopsin variant converted it from a potent activator into a fast-acting inhibitor that operates as a cation pump. Our findings argue that membrane topology provides a useful orthogonal dimension of protein engineering that immediately permits as much as a doubling of the available toolkit.

Canola is a new crop for many inland Pacific Northwest U.S. wheat growers to consider for integration into their wheat-dominated systems. Both crops have winter and spring varieties that can fill niches in different precipitation zones across the region, and they both efficiently extract available water to depths of 4 to 6 ft if soil depth allows. Yet, physiological and morphological differences dictate necessary changes in 4R N management approaches and recommendations when transitioning from wheat to canola. Additional differences in water and N use efficiency are also key factors that contribute to region-specific N recommendations. And so, the saying goes in the inland Pacific Northwest that canola “is not your father's wheat.” Earn 1 CEU in Nutrient Management by reading this article and taking the quiz at www.agronomy.org/education/classroom/classes/410

Behavior has molecular, cellular, and circuit determinants. However, because many proteins are broadly expressed, their acute manipulation within defined cells has been difficult. Here, we combined the speed and molecular specificity of pharmacology with the cell type specificity of genetic tools. DART (drugs acutely restricted by tethering) is a technique that rapidly localizes drugs to the surface of defined cells, without prior modification of the native target. We first developed an AMPAR antagonist DART, with validation in cultured neuronal assays, in slices of mouse dorsal striatum, and in behaving mice. In parkinsonian animals, motor deficits were causally attributed to AMPARs in indirect spiny projection neurons (iSPNs) and to excess phasic firing of tonically active interneurons (TANs). Together, iSPNs and TANs (i.e., D2 cells) drove akinesia, whereas movement execution deficits reflected the ratio of AMPARs in D2 versus D1 cells. Finally, we designed a muscarinic antagonist DART in one iteration, demonstrating applicability of the method to diverse targets.

Dendritic release of dopamine activates dopamine D2 autoreceptors, which are inhibitory G protein-coupled receptors (GPCRs), to decrease the excitability of dopamine neurons. This study used tagged D2 receptors to identify the localization and distribution of these receptors in living midbrain dopamine neurons. GFP-tagged D2 receptors were found to be unevenly clustered on the soma and dendrites of dopamine neurons within the substantia nigra pars compacta (SNc). Physiological signaling and desensitization of the tagged receptors were not different from wild type receptors. Unexpectedly, upon desensitization the tagged D2 receptors were not internalized. When tagged D2 receptors were expressed in locus coeruleus neurons, a desensitizing protocol induced significant internalization. Likewise, when tagged µ-opioid receptors were expressed in dopamine neurons they too were internalized. The distribution and lack of agonist-induced internalization of D2 receptors on dopamine neurons indicate a purposefully regulated localization of these receptors.

We recently demonstrated that the collaterals of substantia nigra (SN) projection neurons can implement divisive feedback inhibition, or gain control (Brown et al., 2014). While in vivo recordings were consistent with divisive feedback inhibition, a causal test was lacking. A gain control model of the nigral microcircuit implies behavioral effects of disrupting intranigral inhibition that are distinct from previous functional models. To test the model predictions experimentally, we develop a chemogenetic approach that can selectively suppress synaptic release within the substantial nigra without affecting the propagation of activity to extranigral targets. We observe behavioral consequences of suppressing intranigral inhibition that are uniquely consistent with a gain control model. Our data further suggest that if endogenous metabotropic signaling can modulate intranigral synapses, this would provide a circuit mechanism for an exploitation/exploration trade-off in which the timing and variability of goal-directed movements are controlled independently of changes in action.

Dysfunction of the basal ganglia produces severe deficits in the timing, initiation, and vigor of movement. These diverse impairments suggest a control system gone awry. In engineered systems, feedback is critical for control. By contrast, models of the basal ganglia highlight feedforward circuitry and ignore intrinsic feedback circuits. In this study, we show that feedback via axon collaterals of substantia nigra projection neurons control the gain of the basal ganglia output. Through a combination of physiology, optogenetics, anatomy, and circuit mapping, we elaborate a general circuit mechanism for gain control in a microcircuit lacking interneurons. Our data suggest that diverse tonic firing rates, weak unitary connections and a spatially diffuse collateral circuit with distinct topography and kinetics from feedforward input is sufficient to implement divisive feedback inhibition. The importance of feedback for engineered systems implies that the intranigral microcircuit, despite its absence from canonical models, could be essential to basal ganglia function.