A comprehensive excitatory input map of the striatum reveals novel functional organization.

The striatum integrates excitatory inputs from the cortex and the thalamus to control diverse functions. Although the striatum is thought to consist of sensorimotor, associative and limbic domains, their precise demarcations and whether additional functional subdivisions exist remain unclear. How striatal inputs are differentially segregated into each domain is also poorly understood. This study presents a comprehensive map of the excitatory inputs to the mouse striatum. The input patterns reveal boundaries between the known striatal domains. The most posterior striatum likely represents the 4th functional subdivision, and the dorsomedial striatum integrates highly heterogeneous, multimodal inputs. The complete thalamo-cortico-striatal loop is also presented, which reveals that the thalamic subregions innervated by the basal ganglia preferentially interconnect with motor-related cortical areas. Optogenetic experiments show the subregion-specific heterogeneity in the synaptic properties of striatal inputs from both the cortex and the thalamus. This projectome will guide functional studies investigating diverse striatal functions.

In vivo time-lapse imaging reveals extensive neural crest and endothelial cell interactions during neural crest migration and formation of the dorsal root and sympathetic ganglia.

During amniote embryogenesis the nervous and vascular systems interact in a process that significantly affects the respective morphogenesis of each network by forming a "neurovascular" link. The importance of neurovascular cross-talk in the central nervous system has recently come into focus with the growing awareness that these two systems interact extensively both during development, in the stem-cell niche, and in neurodegenerative conditions such as Alzheimer's Disease and Amyotrophic Lateral Sclerosis. With respect to the peripheral nervous system, however, there have been no live, real-time investigations of the potential relationship between these two developing systems. To address this deficit, we used multispectral 4D time-lapse imaging in a transgenic quail model in which endothelial cells (ECs) express a yellow fluorescent marker, while neural crest cells (NCCs) express an electroporated red fluorescent marker. We monitored EC and NCC migration in real-time during formation of the peripheral nervous system. Our time-lapse recordings indicate that NCCs and ECs are physically juxtaposed and dynamically interact at multiple locations along their trajectories. These interactions are stereotypical and occur at precise anatomical locations along the NCC migratory pathway. NCCs migrate alongside the posterior surface of developing intersomitic vessels, but fail to cross these continuous streams of motile ECs. NCCs change their morphology and migration trajectory when they encounter gaps in the developing vasculature. Within the nascent dorsal root ganglion, proximity to ECs causes filopodial retraction which curtails forward persistence of NCC motility. Overall, our time-lapse recordings support the conclusion that primary vascular networks substantially influence the distribution and migratory behavior of NCCs and the patterned formation of dorsal root and sympathetic ganglia.

A comprehensive thalamocortical projection map at the mesoscopic level.

The thalamus relays sensori-motor information to the cortex and is an integral part of cortical executive functions. The precise distribution of thalamic projections to the cortex is poorly characterized, particularly in mouse. We employed a systematic, high-throughput viral approach to visualize thalamocortical axons with high sensitivity. We then developed algorithms to directly compare injection and projection information across animals. By tiling the mouse thalamus with 254 overlapping injections, we constructed a comprehensive map of thalamocortical projections. We determined the projection origins of specific cortical subregions and verified that the characterized projections formed functional synapses using optogenetic approaches. As an important application, we determined the optimal stereotaxic coordinates for targeting specific cortical subregions and expanded these analyses to localize cortical layer-preferential projections. This data set will serve as a foundation for functional investigations of thalamocortical circuits. Our approach and algorithms also provide an example for analyzing the projection patterns of other brain regions.

A selective 5-HT1a receptor agonist improves respiration in a mouse model of Rett syndrome.

Rett syndrome is a neurological disorder caused by loss of function mutations in the gene that encodes the DNA binding protein methyl-CpG-binding protein 2 (Mecp2). A prominent feature of the syndrome is disturbances in respiration characterized by frequent apnea and an irregular interbreath cycle. 8-Hydroxy-2-dipropylaminotetralin has been shown to positively modulate these disturbances (Abdala AP, Dutschmann M, Bissonnette JM, Paton JF, Proc Natl Acad Sci U S A 107: 18208-18213, 2010), but the mode of action is not understood. Here we show that the selective 5-HT1a biased agonist 3-chloro-4-fluorophenyl-(4-fluoro-4-{[(5-methylpyrimidin-2-ylmethyl)-amino]-methyl}-piperidin-1-yl)-methanone (F15599) decreases apnea and corrects irregularity in both heterozygous Mecp2-deficient female and in Mecp2 null male mice. In whole cell voltage-clamp recordings from dorsal raphe neurons, F15599 potently induced an outward current, which was blocked by barium, reversed at the potassium equilibrium potential, and was antagonized by the 5-HT1a antagonist WAY100135. This is consistent with somatodendritic 5-HT1a receptor-mediated activation of G protein-coupled inwardly rectifying potassium channels (GIRK). In contrast, F15599 did not activate 5-HT1b/d receptors that mediate inhibition of glutamate release from terminals in the nucleus accumbens by a presynaptic mechanism. Thus F15599 activated somatodendritic 5-HT1a autoreceptors, but not axonal 5-HT1b/d receptors. In unanesthetized Mecp2-deficient heterozygous female mice, F15599 reduced apnea in a dose-dependent manner with maximal effect of 74.5 ± 6.9% at 0.1 mg/kg and improved breath irrregularity. Similarly, in Mecp2 null male mice, apnea was reduced by 62 ± 6.6% at 0.25 mg/kg, and breathing became regular. The results indicate respiration is improved with a 5-HT1a agonist that activates GIRK channels without affecting neurotransmitter release.

IKAP/Elp1 is required in vivo for neurogenesis and neuronal survival, but not for neural crest migration.

Familial Dysautonomia (FD; Hereditary Sensory Autonomic Neuropathy; HSAN III) manifests from a failure in development of the peripheral sensory and autonomic nervous systems. The disease results from a point mutation in the IKBKAP gene, which encodes the IKAP protein, whose function is still unresolved in the developing nervous system. Since the neurons most severely depleted in the disease derive from the neural crest, and in light of data identifying a role for IKAP in cell motility and migration, it has been suggested that FD results from a disruption in neural crest migration. To determine the function of IKAP during development of the nervous system, we (1) first determined the spatial-temporal pattern of IKAP expression in the developing peripheral nervous system, from the onset of neural crest migration through the period of programmed cell death in the dorsal root ganglia, and (2) using RNAi, reduced expression of IKBKAP mRNA in the neural crest lineage throughout the process of dorsal root ganglia (DRG) development in chick embryos in ovo. Here we demonstrate that IKAP is not expressed by neural crest cells and instead is expressed as neurons differentiate both in the CNS and PNS, thus the devastation of the PNS in FD could not be due to disruptions in neural crest motility or migration. In addition, we show that alterations in the levels of IKAP, through both gain and loss of function studies, perturbs neuronal polarity, neuronal differentiation and survival. Thus IKAP plays pleiotropic roles in both the peripheral and central nervous systems.