An imaging-coupled 3D printing methodology for the design, optimization, and fabrication of a customized nerve repair technology for complex injuries is presented. The custom scaffolds are deterministically fabricated via a microextrusion printing principle which enables the simultaneous incorporation of anatomical geometries, biomimetic physical cues, and spatially controlled biochemical gradients in a one-pot 3D manufacturing approach.

SUMMARY Cerebellar outputs take polysynaptic routes to reach the rest of the brain, impeding conventional tracing. Here, we quantify pathways between the cerebellum and forebrain by using transsynaptic tracing viruses and a whole-brain analysis pipeline. With retrograde tracing, we find that most descending paths originate from the somatomotor cortex. Anterograde tracing of ascending paths encompasses most thalamic nuclei, especially ventral posteromedial, lateral posterior, mediodorsal, and reticular nuclei. In the neocortex, sensorimotor regions contain the most labeled neurons, but we find higher densities in associative areas, including orbital, anterior cingulate, prelimbic, and infralimbic cortex. Patterns of ascending expression correlate with c-Fos expression after optogenetic inhibition of Purkinje cells. Our results reveal homologous networks linking single areas of the cerebellar cortex to diverse forebrain targets. We conclude that shared areas of the cerebellum are positioned to provide sensory-motor information to regions implicated in both movement and nonmotor function.

Highlights d Ambient warmth activates DRN Vgat neurons d DRN Vgat neurons regulate energy expenditure through locomotion and thermogenesis d DRN Vgat neurons exhibit vast projections and polysynaptically innervate brown fat d DRN Vgat projections differentially regulate food intake and energy expenditure

The use of viruses as transneuronal tracers has become an increasingly powerful technique for defining the synaptic organization of neural networks. Although a number of recombinant alpha herpesviruses are known to spread selectively in the retrograde direction through neural circuits only one strain, the H129 strain of herpes simplex virus type 1, is reported to selectively spread in the anterograde direction. However, it is unclear from the literature whether there is an absolute block or an attenuation of retrograde spread of H129. Here we demonstrate efficient anterograde spread, and temporally delayed retrograde spread, of H129 and three novel recombinants. In vitro studies revealed no differences in anterograde and retrograde spread of parental H129 and its recombinants through superior cervical ganglion neurons. In vivo injections of rat striatum revealed a clear bias of anterograde spread, although evidence of deficient retrograde transport was also present. Evidence of temporally delayed retrograde transneuronal spread of H129 in the retina was observed following injection of the lateral geniculate nucleus. The data also demonstrated that three novel recombinants efficiently express unique fluorescent reporters and have the capacity to infect the same neurons in dual infection paradigms. From these experiments we conclude that H129 and its recombinants efficiently infect neurons through anterograde transneuronal passage, but also are capable of temporally delayed retrograde transneuronal spread. In addition, the capacity to produce dual infection of projection targets following anterograde transneuronal passage provides an important addition to viral transneuronal tracing technology.

Highlights d Cellular resolution imaging of IL-NAc projection neurons in rats d IL-NAc neurons display spatial and temporal selectivity during drug seeking d After a drug-free period, drug motivation is high and neural coding is degraded