On-Off direction selective retinal ganglion cells (DSGCs) encode the axis of visual motion. They respond strongly to an object moving in a preferred direction and weakly to an object moving in the opposite, ‘null’, direction. Historically, On-Off DSGCs were classified into 4 subtypes according to their directional preference (anterior, posterior, superior or inferior). Here, we compare two genetically identified populations of On-Off DSGCs: DRD4-DSGCs and TRHR-DSGCs. We find that although both populations are tuned for posterior motion, they can be distinguished by a variety of physiological and anatomical criteria. First, the directional tuning of TRHR-DSGCs is broader than that of DRD4-DSGCs. Second, whereas both populations project similarly to the dorsal lateral geniculate nucleus, they project differently to the ventral lateral geniculate nucleus and the superior colliculus. Moreover, TRHR-DSGCs, but not DRD4-DSGCs, also project to the zona incerta, a thalamic area not previously known to receive direction-tuned visual information. Our findings reveal unexpected diversity among mouse On-Off DSGC subtypes that uniquely process and convey image motion to the brain.

How specific features in the environment are represented within the brain is an important unanswered question in neuroscience. A subset of retinal neurons, called direction selective ganglion cells (DSGCs) are specialized for detecting motion along specific axes of the visual field1. Despite extensive study of the retinal circuitry that endows DSGCs with their unique tuning properties2,3, their downstream circuitry in the brain and thus their contribution to visual processing has remained unclear. In mice, several different types of DSGCs connect to the dorsal lateral geniculate nucleus (dLGN),4,5,6 the visual thalamic structure that harbors cortical relay neurons. Whether direction selective information computed at the level of the retina is routed to cortical circuits and integrated with other visual channels, however, is unknown. Here we show using viral trans-synaptic circuit mapping7,8 and functional imaging of visually-driven calcium signals in thalamocortical axons, that there is a di-synaptic circuit linking DSGCs with the superficial layers of primary visual cortex (V1). This circuit pools information from multiple types of DSGCs, converges in a specialized subdivision of the dLGN, and delivers direction-tuned and orientation-tuned signals to superficial V1. Notably, this circuit is anatomically segregated from the retino-geniculo-cortical pathway carrying non-direction-tuned visual information to deeper layers of V1, such as layer 4. Thus, the mouse harbors several functionally specialized, parallel retino-geniculo-cortical pathways, one of which originates with retinal DSGCs and delivers direction- and orientation-tuned information specifically to the superficial layers of primary visual cortex. These data provide evidence that direction and orientation selectivity of some V1 neurons may be influenced by the activation of DSGCs.

Axons in the mammalian central nervous system (CNS) fail to regenerate after injury. Here we show that if retinal ganglion cell (RGC) activity is increased by visual stimulation or using chemogenetics, their axons regenerate. We also show that if enhancement of neural activity is combined with elevation of the cell growth-promoting pathway involving mammalian target of rapamycin (mTOR), RGC axons regenerate the long distances necessary to re-innervate the brain. Analysis of genetically-labeled RGCs revealed this regrowth can be target specific: RGC axons navigated back to their correct visual targets and avoided targets incorrect for their function. Moreover, these regenerated connections were successful in partially rescuing a subset of visual behaviors. Our findings indicate that combining neural activity with activation of mTOR can serve as powerful tool for enhancing axon regeneration and they highlight the remarkable capacity of CNS neurons to re-establish accurate circuit connections in the adult brain.

When the head rotates, the image of the visual world slips across the retina. A dedicated set of retinal ganglion cells (RGCs) and brainstem visual nuclei termed the "accessory optic system" (AOS) generate slip-compensating eye movements that stabilize visual images on the retina and improve visual performance. Which types of RGCs project to each of the various AOS nuclei remain unresolved. Here we report a new transgenic mouse line, Hoxd10 -GFP, in which the RGCs projecting to all the AOS nuclei are fluorescently labeled. Electrophysiological recordings of Hoxd10 -GFP RGCs revealed that they include all three subtypes of On direction-selective RGCs (On-DSGCs), responding to upward, downward, or forward motion. Hoxd10 -GFP RGCs also include one subtype of On-Off DSGCs tuned for forward motion. Retrograde circuit mapping with modified rabies viruses revealed that the On-DSGCs project to the brainstem centers involved in both horizontal and vertical retinal slip compensation. In contrast, the On-Off DSGCs labeled in Hoxd10 -GFP mice projected to AOS nuclei controlling horizontal but not vertical image stabilization. Moreover, the forward tuned On-Off DSGCs appear physiologically and molecularly distinct from all previously genetically identified On-Off DSGCs. These data begin to clarify the cell types and circuits underlying image stabilization during self-motion, and they support an unexpected diversity of DSGC subtypes.

SUMMARY Neural circuits consist of highly precise connections among specific types of neurons that serve a common functional goal. How neurons distinguish among different synaptic targets to form functionally precise circuits remains largely unknown. Here, we show that during development, the adhesion molecule cadherin-6 (Cdh6) is expressed by a subset of retinal ganglion cells (RGCs) and also by their targets in the brain. All of the Cdh6-expressing retinorecipient nuclei mediate non-image-forming visual functions. A screen of mice expressing GFP in specific subsets of RGCs revealed that Cdh3-RGCs which also express Cdh6 selectively innervate Cdh6-expressing retinorecipient targets. Moreover, in Cdh6-deficient mice, the axons of Cdh3-RGCs fail to properly innervate their targets and instead project to other visual nuclei. These findings provide functional evidence that classical cadherins promote mammalian CNS circuit development by ensuring that axons of specific cell types connect to their appropriate synaptic targets.

Summary How axons select their appropriate targets in the brain remains poorly understood. Here we explored the cellular mechanisms of axon-target matching in the developing visual system by comparing four transgenic mouse lines, each with a different population of genetically labeled retinal ganglion cells (RGCs) that connect to unique combinations of brain targets. We discovered that the time when an RGC axon arrives in the brain is correlated with its target selection strategy. Early-born, early-arriving RGC axons initially innervate multiple targets. Subsequently, most of those connections were removed. By contrast, later born, later-arriving RGC axons were highly accurate in their initial target choices. These data reveal the diversity of cellular mechanisms axons use to pick their targets and they highlight the key role of birthdate and outgrowth timing for influencing this precision. Timing-based mechanisms may underlie the assembly of the other sensory pathways and complex neural circuitry in the brain.

SUMMARY The mammalian eye-to-brain pathway includes more than twenty parallel circuits, each consisting of precise long-range connections between specific sets of retinal ganglion cells (RGCs) and target structures in the brain. The mechanisms that drive assembly of these parallel connections, and the functional implications of their specificity remain unresolved. Here we show that in absence of contactin 4 (CNTN4) or one of its binding partners, amyloid precursor protein (APP), a subset of direction selective retinal ganglion cells fail to target the nucleus of the optic tract (NOT) - the accessory optic system (AOS) target controlling horizontal image stabilization. Conversely, ectopic expression of CNTN4 biases RGCs to arborize in the NOT, and that process also requires APP. Our data reveal critical and novel roles for CNTN4/APP in promoting target-specific axon arborization and they highlight the importance of this process for functional development of a behaviorally-relevant parallel visual pathway.

Environmental DNA (eDNA) detection of aquatic invasive species using quantitative polymerase chain reaction (qPCR) is a powerful tool for resource managers, but qPCR has traditionally been confined to laboratory analysis. Laboratory results often take days or weeks to be produced, limiting options for rapid management response. To circumvent laboratory delay, we combined a purpose‐built eDNA filtration system (Smith‐Root eDNA‐Sampler) with a field DNA extraction and qPCR analysis platform (Biomeme) to form a complete field eDNA sampling and detection process. A controlled laboratory study involving serial dilutions of New Zealand mudsnail (Potamopyrgus antipodarum; Gray, 1843) eDNA was conducted to compare the detection capabilities of the field system with traditional bench qPCR. Additionally, field validation studies were conducted to determine whether field eDNA analysis can be used to map mudsnail eDNA distribution and quantify temporal fluctuations. In the laboratory experiment, both qPCR platforms (Biomeme, bench qPCR) lost the ability to reliably detect mudsnail eDNA at the same dilution level, with starting quantity values as low as 21 DNA copies/reaction. A strong linear relationship was observed between the average quantification cycle values of the two platforms (slope = 1.101, intercept = −1.816, R2 = 0.997, p < 0.001). Of the 80 field samples collected, 44 (55%) tested positive for mudsnail eDNA with Biomeme, and results identified both spatial and temporal fluctuations in mudsnail eDNA/L. However, the average qPCR inhibition rate with Biomeme was 28% for field samples, and up to 39% in the temporal dataset. With additional optimization to reduce inhibition, the eDNA‐Sampler/Biomeme system has potential to be a rapid and highly effective detection/quantification tool for aquatic invasive species.