Achieving temporally precise, noninvasive control over specific neural cell types in the deep brain would advance the study of nervous system function. Here we use the potent channelrhodopsin ChRmine to achieve transcranial photoactivation of defined neural circuits, including midbrain and brainstem structures, at unprecedented depths of up to 7 mm with millisecond precision. Using systemic viral delivery of ChRmine, we demonstrate behavioral modulation without surgery, enabling implant-free deep brain optogenetics.Certain symptoms of neurological and psychiatric disease can be treated by modulation of pathological brain activity in both preclinical and clinical settings [1][2][3][4] . However, existing methods for neuromodulation are not cell type specific (for example, transcranial magnetic or direct current stimulation) and/or are invasive (for example, electrical deep brain stimulation) 2,3 . In basic research settings, optogenetics with microbial channelrhodopsins (ChRs) enables cell type-specific excitation or inhibition of neuronal activity with light, permitting the tuning of cellular activity in terms of levels, ratios and rhythms with improved precision, which in many cases results in symptom-relevant treatment via optical neuromodulation [4][5][6] . However, the delivery of visible light often requires invasive implantation of foreign materials and devices into the brain, which damages tissue and increases infection and ischemia risk 1,7 . To improve long-term biocompatibility, optogenetic effects can be recruited by light delivered external to a thinned skull 8 . However, light attenuation by scattering and absorption in bone and tissue currently limits transmission of sufficient photon densities to stimulate neural activity in deep brain structures, even with fast ChR variants engineered to respond to lower intensity and/or longer wavelengths of light for access to deeper tissue [9][10][11] . Engineered ChRs with slow off-kinetics (for example, stable step-function opsins) can integrate photons for modulation of distal neural populations, but cannot provide the high temporal control enabled by fast opsins 12 .We recently described the potent fast red-shifted opsin ChRmine, which exhibits extremely large photocurrents with hundred-fold improved operational light sensitivity compared with existing fast red-shifted variants and rapid off-kinetics suitable for millisecond-scale control over neural activity 13 (Supplementary Table 1)-photophysical properties that may be suitable for deep transcranial optogenetics. To determine whether ChRmine can enable safe and rapid transcranial deep brain photoactivation, we performed optically paired in vivo extracellular electrophysiology in the ventral tegmental area (VTA), 4.5 mm deep from the skull surface (Fig. 1a,b). We used ChRmine targeted to somata with a Kv2.1 peptide tag to minimize axonal localization and antidromic activation (AAV8-CamKIIα::ChRmine-oScarlet-Kv2.1; Extended Data Fig. 1a). A 400-µm fiber optic was positioned directly above the surface of th...

Current drug treatments for epilepsy attempt to broadly restrict excitability to mask a symptom, seizures, with little regard for the heterogeneous mechanisms that underlie disease manifestation across individuals. Here, we discuss the need for a more complete view of epilepsy, outlining how key features at the cellular and microcircuit level can significantly impact disease mechanisms that are not captured by the most common methodology to study epilepsy, electroencephalography (EEG). We highlight how major advances in neuroscience tool development now enable multi-scale investigation of fundamental questions to resolve the currently controversial understanding of seizure networks. These findings will provide essential insight into what has emerged as a disconnect between the different levels of investigation and identify new targets and treatment options.

Thiolactomycin inhibits bacterial cell growth through inhibition of the β-ketoacyl-ACP synthase activity of type II fatty acid synthases. The effect of modifications of the 5-position isoprenoid side chain on both IC 50 and MIC were determined. Synthesis and screening of a structurally diverse set of 5-position analogues revealed very little tolerance for substitution in purified enzyme assays but a few analogues retained MIC, presumably through another target. Even subtle modifications such as reducing one or both double bonds of the diene were not tolerated. The only permissible structural modifications were removal of the isoprene methyl group or addition of a methyl group to the terminus. Co-crystallization of these two inhibitors with the condensing enzyme from E. coli revealed that they retained the TLM binding mode at the active site with reduced affinity. These results suggest a strict requirement for a conjugated, planar side chain inserting within the condensing enzyme active site.