The Transcription Factor Shox2 Shapes Neuron Firing Properties and Suppresses Seizures by Regulation of Key Ion Channels in Thalamocortical Neurons.

Thalamocortical neurons (TCNs) play a critical role in the maintenance of thalamocortical oscillations, dysregulation of which can result in certain types of seizures. Precise control over firing rates of TCNs is foundational to these oscillations, yet the transcriptional mechanisms that constrain these firing rates remain elusive. We hypothesized that Shox2 is a transcriptional regulator of ion channels important for TCN function and that loss of Shox2 alters firing frequency and activity, ultimately perturbing thalamocortical oscillations into an epilepsy-prone state. In this study, we used RNA sequencing and quantitative PCR of control and Shox2 knockout mice to determine Shox2-affected genes and revealed a network of ion channel genes important for neuronal firing properties. Protein regulation was confirmed by Western blotting, and electrophysiological recordings showed that Shox2 KO impacted the firing properties of a subpopulation of TCNs. Computational modeling showed that disruption of these conductances in a manner similar to Shox2's effects modulated frequency of oscillations and could convert sleep spindles to near spike and wave activity, which are a hallmark for absence epilepsy. Finally, Shox2 KO mice were more susceptible to pilocarpine-induced seizures. Overall, these results reveal Shox2 as a transcription factor important for TCN function in adult mouse thalamus.

Dynamics of adrenergic signaling in cardiac myocytes and implications for pharmacological treatment.

Dense innervation of the heart by the sympathetic nervous system (SNS) allows cardiac output to respond appropriately to the needs of the body under varying conditions, but occasionally the abrupt onset of SNS activity can trigger cardiac arrhythmias. Sympathetic activity leads to the release of norepinephrine (NE) onto cardiomyocytes, activating ß1-adrenergic receptors (ß1-ARs) and leading to the production of the second messenger cyclic AMP (cAMP). Upon sudden activation of ß1-ARs in experiments, intracellular cAMP can transiently rise to a high concentration before converging to a steady state level. Although changes to cellular cAMP concentration are important in modulating the overall cardiovascular response to sympathetic tone, the underlying mechanisms of the cAMP transients and the parameters that control their magnitude are unclear. We reduce a detailed computational model of the ß1-adrenergic signaling cascade to a system of two differential equations by eliminating extraneous variables and applying quasi-steady state approximation. The structure of the reduced model reveals that the large cAMP transients associated with abrupt ß1-AR activation are generated by the interplay of production/degradation of cAMP and desensitization/resensitization of ß1-ARs. The reduced model is used to predict how the dynamics of intracellular cAMP depend on the concentrations of norepinephrine (NE), phosphodiesterases 3 and 4 (PDE3,4), G-protein coupled receptor kinase 2 (GRK2), and ß1-AR, in healthy conditions and a simple model of early stages of heart failure. The key findings of the study are as follows: 1) Applying a reduced model of the dynamics of cardiac sympathetic signaling we show that the concentrations of two variables, cAMP and non-desensitized ß1-AR, capture the overall dynamics of sympathetic signaling; 2) The key factors influencing cAMP production are AC activity and PDE3,4 activity, while those that directly impact ß1-AR phosphorylation are GRK2 and PKA1. Thus, disease states that affect sympathetic control of the heart can be thoroughly assessed by studying AC activity, PDE3,4, GRK2 and PKA activity, as these factors directly impact cAMP production/degradation and ß1-AR (de) phosphorylation and are therefore predicted to comprise the most effective pharmaceutical targets in diseases affecting cardiac ß1-adrenergic signaling.

Neuroscience needs behavior: inferring psychophysical strategy trial by trial.

Tools quantifying dynamic behavior are important to understand brain function. In this issue of Neuron, Roy et al. (2021) extended the available repertoire with PsyTrack, which tracks, trial by trial, how subjects performing psychophysical tasks adjust the way they weigh stimuli and task covariates or change their biases.

Dopamine receptor 1 neurons in the dorsal striatum regulate food anticipatory circadian activity rhythms in mice.

Daily rhythms of food anticipatory activity (FAA) are regulated independently of the suprachiasmatic nucleus, which mediates entrainment of rhythms to light, but the neural circuits that establish FAA remain elusive. In this study, we show that mice lacking the dopamine D1 receptor (D1R KO mice) manifest greatly reduced FAA, whereas mice lacking the dopamine D2 receptor have normal FAA. To determine where dopamine exerts its effect, we limited expression of dopamine signaling to the dorsal striatum of dopamine-deficient mice; these mice developed FAA. Within the dorsal striatum, the daily rhythm of clock gene period2 expression was markedly suppressed in D1R KO mice. Pharmacological activation of D1R at the same time daily was sufficient to establish anticipatory activity in wild-type mice. These results demonstrate that dopamine signaling to D1R-expressing neurons in the dorsal striatum plays an important role in manifestation of FAA, possibly by synchronizing circadian oscillators that modulate motivational processes and behavioral output.

Recent progress in understanding hydrophobic interactions.

We present here a brief review of direct force measurements between hydrophobic surfaces in aqueous solutions. For almost 70 years, researchers have attempted to understand the hydrophobic effect (the low solubility of hydrophobic solutes in water) and the hydrophobic interaction or force (the unusually strong attraction of hydrophobic surfaces and groups in water). After many years of research into how hydrophobic interactions affect the thermodynamic properties of processes such as micelle formation (self-assembly) and protein folding, the results of direct force measurements between macroscopic surfaces began to appear in the 1980s. Reported ranges of the attraction between variously prepared hydrophobic surfaces in water grew from the initially reported value of 80-100 Angstrom to values as large as 3,000 Angstrom. Recent improved surface preparation techniques and the combination of surface force apparatus measurements with atomic force microscopy imaging have made it possible to explain the long-range part of this interaction (at separations >200 Angstrom) that is observed between certain surfaces. We tentatively conclude that only the short-range part of the attraction (<100 Angstrom) represents the true hydrophobic interaction, although a quantitative explanation for this interaction will require additional research. Although our force-measuring technique did not allow collection of reliable data at separations <10 Angstrom, it is clear that some stronger force must act in this regime if the measured interaction energy curve is to extrapolate to the measured adhesion energy as the surface separation approaches zero (i.e., as the surfaces come into molecular contact).

Origin of the long-range attraction between surfactant-coated surfaces.

We compare the "long-range hydrophobic forces" measured (i) in the "symmetric" system between two mica surfaces that had been rendered hydrophobic by the adsorption of a double-chained cationic surfactant, and (ii) between one such hydrophobic surface and a hydrophilic surface of bare mica ("asymmetric" case). In both cases, the forces were purely attractive, stronger than van der Waals, and of long-range, as previously reported, with those of the asymmetric, hydrophobic-hydrophilic system being even stronger and of longer range. Atomic force microscopy images of these surfaces show that the monolayers transform into patchy bilayers when the surfaces are immersed in water, and that the resulting surfaces contain large micrometer-sized regions of positive charges (bilayer) and negative charges (bare mica) while remaining overall neutral. The natural alignment of oppositely charged domains as two such surfaces approach would result in a long-range electrostatic attraction in water, but the short-range, "truly hydrophobic" interaction is not explained by these results.

Measurement of the long- and short-range hydrophobic attraction between surfactant-coated surfaces.

We have measured the attractive long-range 'hydrophobic' forces in water between double-chained surfactant monolayers physisorbed on mica. We used both normal and high-speed video cameras to follow the dynamics and possible rate-dependence of force-distance profiles in the distance regime from 1000 A to adhesive contact, including the short-distance regime below 100 A-the regime of greatest biological interest. We find that the hydrophobic interaction follows a double-exponential function down to separations of approximately 50 A, after which point the attractive force appears to become considerably stronger.

Effects of dissolved gas on the hydrophobic attraction between surfactant-coated surfaces.

The effect of dissolved gas on the hydrophobic attraction between double-chained surfactant monolayers physisorbed on mica has been studied using a surface forces apparatus (SFA). Distance vs time data were obtained over the full distance regime from D approximately 1000 A down to contact using the dynamic SFA method. Removal of dissolved gas was seen to reduce the range of the attraction while the short-range attraction (under approximately 250 A) remained unchanged. The implications for the possibility of two distinct force regimes in the interactions between hydrophobic surfaces are discussed.

Spectroscopic and photophysical properties of hexanuclear rhenium(III) chalcogenide clusters.

The electronic, vibrational, and excited-state properties of hexanuclear rhenium(III) chalcogenide clusters based on the [Re(6)(mu(3)-Q)(8)](2+) (Q = S, Se) core have been investigated by spectroscopic and theoretical methods. Ultraviolet or visible excitation of [Re(6)Q(8)](2+) clusters produces luminescence with ranges in maxima of 12 500-15 100 cm(-)(1), emission quantum yields of 1-24%, and emission lifetimes of 2.6-22.4 microseconds. Nonradiative decay rate constants and the luminescence maxima follow the trend predicted by the energy gap law (EGL). Examination of 24 clusters in solution and 14 in the solid phase establish that exocluster ligands engender the observed EGL behavior; clusters with oxygen- or nitrogen-based apical ligands achieve maximal quantum yields and the longest lifetimes. The excited-state decay mechanism was investigated by applying nonradiative decay models to temperature-dependent emission experiments. Solid-state Raman spectra were recorded to identify vibrational contributions to excited-state deactivation; spectral assignments were enabled by normal coordinate analysis afforded from Hartree-Fock and DFT calculations. Excited-state decay is interpreted with a model where normal modes largely centered on the [Re(6)Q(8)](2+) core induce nonradiative relaxation. Hartree-Fock and DFT calculations of the electronic structure of the hexarhenium family of compounds support such a model. These experimental and theoretical studies of [Re(6)Q(8)](2+) luminescence provide a framework for elaborating a variety of luminescence-based applications of the largest series of isoelectronic clusters yet discovered.

A luminescent heterometallic dirhodium-silver chain.

A novel one-dimensional (1D) heterometallic chain, [[Rh(2)(dfpma)(2)(MeCN)(4)](2)[Ag(MeCN)(4)]][PF(6)](5) (1), is afforded from the in situ reaction of [ClRh(cod)](2) with [Ag(MeCN)(4)][PF(6)] and dfpma (dfpma = bis(difluorophosphine)methylamine). Dichroic crystals, which are obtained from MeCN/Et(2)O solutions, crystallize in the monoclinic space group C2/m with a = 13.570(5) A, b = 20.895(9) A, c = 13.810(6) A, beta = 104.904(7) degrees, V = 3784(3) A(3), Z = 4. X-ray diffraction studies reveal an asymmetric unit comprising two Rh(I)(2) dimers and a square planar Ag(I) cation; this subunit propagates to form a 1D heterometallic chain. Compound 1 displays novel spectroscopic properties in the solid state, including temperature-dependent luminescence.