Luminopsins are fusion proteins of luciferase and opsin that allow interrogation of neuronal circuits at different temporal and spatial resolutions by choosing either extrinsic physical or intrinsic biological light for its activation. Building on previous development of fusions of wild-type Gaussia luciferase with channelrhodopsin, here we expanded the utility of luminopsins by fusing bright Gaussia luciferase variants with either channelrhodopsin to excite neurons (luminescent opsin, LMO) or a proton pump to inhibit neurons (inhibitory LMO, iLMO). These improved LMOs could reliably activate or silence neurons in vitro and in vivo. Expression of the improved LMO in hippocampal circuits not only enabled mapping of synaptic activation of CA1 neurons with fine spatiotemporal resolution but also could drive rhythmic circuit excitation over a large spatiotemporal scale. Furthermore, virus-mediated expression of either LMO or iLMO in the substantia nigra in vivo produced not only the expected bidirectional control of single unit activity but also opposing effects on circling behavior in response to systemic injection of a luciferase substrate. Thus, although preserving the ability to be activated by external light sources, LMOs expand the use of optogenetics by making the same opsins accessible to noninvasive, chemogenetic control, thereby allowing the same probe to manipulate neuronal activity over a range of spatial and temporal scales.luciferase | bioluminescence | neural circuitry | substantia nigra | hippocampus

The contribution of basal ganglia outputs to consummatory behavior remains poorly understood. We recorded from the substantia nigra pars reticulata (SNR), the major basal ganglia output nucleus, during self-initiated drinking. The firing rates of many lateral SNR neurons were time-locked to individual licks. These neurons send GABAergic projections to the deep layers of the orofacial region of the lateral tectum (superior colliculus, SC). Many tectal neurons are also time-locked to licking, but their activity is usually antiphase to that of SNR neurons, suggesting inhibitory nigrotectal projections. We used optogenetics to selectively activate the GABAergic nigrotectal afferents in the deep layers of the SC. Photo-stimulation of the nigrotectal projections transiently inhibited the activity of the lick-related tectal neurons, disrupted their licking-related oscillatory pattern, and suppressed self-initiated drinking. These results demonstrate that GABAergic nigrotectal projections play a crucial role in coordinating drinking behavior.

Considerable evidence implicates the basal ganglia in interval timing, yet the underlying mechanisms remain poorly understood. Using a novel behavioral task, we demonstrate that head-fixed mice can be trained to show the key features of timing behavior within a few sessions. Single-trial analysis of licking behavior reveals stepping dynamics with variable onset times, which is responsible for the canonical Gaussian distribution of timing behavior. Moreover, the duration of licking bouts decreased as mice became sated, showing a strong motivational modulation of licking bout initiation and termination. Using optogenetics, we examined the role of the basal ganglia output in interval timing. We stimulated a pathway important for licking behavior, the GABAergic output projections from the substantia nigra pars reticulata to the deep layers of the superior colliculus. We found that stimulation of this pathway not only cancelled licking but also delayed the initiation of anticipatory licking for the next interval in a frequency-dependent manner. By combining quantitative behavioral analysis with optogenetics in the head-fixed setup, we established a new approach for studying the neural basis of interval timing.

Most adaptive behaviors require precise tracking of targets in space. In pursuit behavior with a moving target, mice use distance to target to guide their own movement continuously. Here, we show that in the sensorimotor striatum, parvalbumin-positive fast-spiking interneurons (FSIs) can represent the distance between self and target during pursuit behavior, while striatal projection neurons (SPNs), which receive FSI projections, can represent self-velocity. FSIs are shown to regulate velocity-related SPN activity during pursuit, so that movement velocity is continuously modulated by distance to target. Moreover, bidirectional manipulation of FSI activity can selectively disrupt performance by increasing or decreasing the self-target distance. Our results reveal a key role of the FSI-SPN interneuron circuit in pursuit behavior and elucidate how this circuit implements distance to velocity transformation required for the critical underlying computation.

25Most adaptive behaviors require precise tracking of targets in space. In pursuit 26 behavior with a moving target, mice use distance to target to guide their own movement 27 continuously. Here we show that in the sensorimotor striatum, parvalbumin-positive fast-28 spiking interneurons (FSIs) can represent the distance between self and target during 29 pursuit behavior, while striatal projection neurons (SPNs), which receive FSI projections, 30 can represent self-velocity. FSIs are shown to regulate velocity-related SPN activity during 31 pursuit, so that movement velocity is continuously modulated by distance to target. 32 Moreover, bidirectional manipulation of FSI activity can selectively disrupt performance 33 by increasing or decreasing the self-target distance. Our results reveal a key role of the 34 FSI-SPN interneuron circuit in pursuit behavior, and elucidate how this circuit implements 35 distance to velocity transformation required for the critical underlying computation. 36 37 38 39 40 41 42 43 44 45 46 47 48 50Whether pursuing a prey or approaching a mate, natural behaviors often involve 51 continuous tracking of targets in space. Yet the neural substrates of such pursuit behavior remain 52 poorly understood. Technical limitations have prevented the study of natural pursuit behavior in 53 freely moving animals [1][2][3][4] . In this study we designed a new behavioral task for freely moving 54 mice. In this task, mice follow a continuously moving target that delivers sucrose reward. Using 55 3D motion capture, we were able to track not only the position of the animal but also the distance 56 to target, a crucial variable for accurate pursuit. This task allows us to compare, for the first 57 time, continuous behavioral variables and neural activity recorded at the same time in freely 58 moving animals. 59 We studied the contribution of the inhibitory interneuron circuit in the sensorimotor 60 striatum to pursuit behavior. The striatum is a major basal ganglia (BG) nucleus that has been 61 implicated in motor control, compulsive behavior, and habit formation [5][6][7][8][9] . A critical circuit in 62 the striatum is formed by the parvalbumin positive GABAergic fast-spiking interneurons (FSIs) 63 and striatal projection neurons (SPNs) 10, 11 . FSIs, which constitute less than 1% of the striatal 64 neuronal population, receive glutamatergic inputs from the cerebral cortex and project to many 65 SPNs, which make up over 90% of the population 12, 13 . The sensorimotor striatum is 66 characterized by the highest expression of FSIs. Reduced numbers of FSIs is associated with 67 neuropsychiatric disorders such as Tourette's syndrome and obsessive-compulsive disorder 14, 15 . 68 Behavioral studies have also implicated the FSIs in choice behavior and habitual lever pressing 69 13, 16 . 70 Recent work has shown that sensorimotor SPN activity is often highly correlated with 71 movement velocity 17, 18 , and stimulation of striatal output alters movement velocity frequency-72 dependently 19 ....