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Determining the cellular content of the nervous system in terms of cell types and the rules of their connectivity represents a fundamental challenge to the neurosciences. The recent advent of high-throughput techniques, such as single-cell RNA-sequencing has allowed for greater resolution in the identification of cell types and/or states. Although most of the current neuronal classification schemes comprise discrete clusters, several recent studies have suggested that, perhaps especially, within the striatum, neuronal populations exist in continua, with regards to both their molecular and electrophysiological properties. Whether these continua are stable properties, established during development, or if they reflect acute differences in activity-dependent regulation of critical genes is currently unknown. We set out to determine whether gradient-like molecular differences in the recently described Pthlh-expressing inhibitory interneuron population, which contains the Pvalb-expressing cells, correlate with differences in morphological and connectivity properties. We show that morphology and long-range inputs correlate with a spatially organized molecular and electrophysiological gradient of Pthlh-interneurons, suggesting that the processing of different types of information (by distinct anatomical striatal regions) has different computational requirements.

Variance in IQ is associated with a wide range of health outcomes, and 1% of the population are affected by intellectual disability. Despite a century of research, the fundamental neural underpinnings of intelligence remain unclear. We integrate results from genome-wide association studies (GWAS) of intelligence with brain tissue and single cell gene expression data to identify tissues and cell types associated with intelligence. GWAS data for IQ (N = 78,308) were meta-analyzed with a study comparing 1247 individuals with mean IQ ~170 to 8185 controls. Genes associated with intelligence implicate pyramidal neurons of the somatosensory cortex and CA1 region of the hippocampus, and midbrain embryonic GABAergic neurons. Tissue-specific analyses find the most significant enrichment for frontal cortex brain expressed genes. These results suggest specific neuronal cell types and genes may be involved in intelligence and provide new hypotheses for neuroscience experiments using model systems.

Intelligence is highly heritable 1 and a major determinant of human health and well-being 2 . Recent genome-wide meta-analyses have identified 24 genomic loci linked to variation in intelligence 3-7 , but much about its genetic underpinnings remains to be discovered. Here, we present a large-scale genetic association study of intelligence (n = 269,867), identifying 205 associated genomic loci (190 new) and 1,016 genes (939 new) via positional mapping, expression quantitative trait locus (eQTL) mapping, chromatin interaction mapping, and gene-based association analysis. We find enrichment of genetic effects in conserved and coding regions and associations with 146 nonsynonymous exonic variants. Associated genes are strongly expressed in the brain, specifically in striatal medium spiny neurons and hippocampal pyramidal neurons. Gene set analyses implicate pathways related to nervous system development and synaptic structure. We confirm previous strong genetic correlations with multiple health-related outcomes, and Mendelian randomization analysis results suggest protective effects of intelligence for Alzheimer's disease and ADHD and bidirectional causation with pleiotropic effects for schizophrenia. These results are a major step forward in understanding the neurobiology of cognitive function as well as genetically related neurological and psychiatric disorders.

SummaryRecent work suggests that cortical interneuron diversity arises from genetic mechanisms guided by the interplay of intrinsic developmental patterning and local extrinsic cues. Individual genetic programs underlying subtype identity are at least partly established in postmitotic neural precursors, prior to their tangential migration and integration in the cortical circuitry. Nevertheless, it is unclear how distinct interneuron identities are maintained during their migration and maturation. Sox6 is a transcription factor with an established role in MGE-derived interneuron maturation and positional identity. To determine its role in maintaining somatostatin (Sst)-expressing interneurons’ subtype identity, we conditionally removed Sox6 in migrating Sst interneurons and assessed the effects on their mature identity using single-cell RNA-sequencing (scRNAseq), in situ hybridization and electrophysiology. Sox6 removal prior to migration in Sst-expressing neurons reduced subtype diversity without affecting overall number of neurons. Seven out of nine Sst-expressing molecular subtypes were absent in the mature primary somatosensory cortex of Sox6-cKO mice, including the Chodl-Nos1-expressing type which has been shown to be specified at, or shortly after, cell cycle exit. The remaining Sst-expressing subtypes in the Sox6-cKO cortex comprised three molecular subtypes, Crh-C1ql3 and Hpse-Cbln4, and a third subtype that seemed to be a molecular hybrid of these subtypes. Moreover, Sox6-cKO cells still expressed genes enriched within the entire class of Sst-expressing neurons, such as Sst, Lhx6, Satb1, Elfn1 and Mafb. Removal of Sox6 at P7, after cells have reached their final destination and begin integration into the network, did not disrupt Chodl-Nos1 marker expression. Our findings suggest that expression of Sox6 during the migratory phase of cortical interneurons is necessary for maintenance of Sst+ subtype identity, indicating that subtype maintenance during migration requires active transcriptional programs.

In the nervous system, BCL11B is crucial for the development of deep layer corticospinal projection neurons and striatal medium spiny neurons and is often used as a marker for the aforementioned cell types. However, the expression of BCL11B in subtypes of non-excitatory neurons in the primary somatosensory cortex (S1) has not been reported in the mouse. In this study we show that BCL11B is extensively expressed in S1 GABAergic interneurons, throughout the three main subgroups (somatostatin-, parvalbumin- and 5HT3a-expresssing). Almost all BCL11B positive cells in the upper S1 layers were GABAergic interneurons and surprisingly, almost 40% of the BCL11B positive neurons in layer V were GABAergic interneurons. Single cell mRNA sequencing data revealed higher Bcl11b expression in S1 interneurons compared to deep layer pyramidal neurons. The highest levels of Bcl11b expression were found within the 5HT3a population, specifically in putative neurogliaform interneuron subclasses (5HT3a-positive but not expressing vasoactive intestinal peptide). In the light of our findings we suggest caution using BCL11B as a single marker to identify neurons.

Understanding the function of a tissue requires knowing the spatial organization of its constituent cell types. In the cerebral cortex, single-cell RNA sequencing (scRNA-seq) has revealed the genome-wide expression patterns that define its many, closely related cell types, but cannot reveal their spatial arrangement. Here we introduce probabilistic cell typing by in situ sequencing (pciSeq), an approach that leverages prior scRNA-seq classification to identify cell types using multiplexed in situ RNA detection. We applied this method to map the inhibitory neurons of hippocampal area CA1, a cell system critical for memory function, for which ground truth is available from extensive prior work identifying the laminar organization of subtly differing cell types. Our method confidently identified 16 interneuron classes, in a spatial arrangement closely matching ground truth. This method will allow identifying the spatial organization of fine cell types across the brain and other tissues.

Summary Striatal locally projecting neurons, or interneurons, act on nearby circuits and shape functional output to the rest of the basal ganglia. We performed single-cell RNA sequencing of striatal cells enriching for interneurons. We find seven discrete interneuron types, six of which are GABAergic. In addition to providing specific markers for the populations previously described, including those expressing Sst/Npy, Th, Npy without Sst, and Chat, we identify two small populations of cells expressing Cck with or without Vip. Surprisingly, the Pvalb-expressing cells do not constitute a discrete cluster but rather are part of a larger group of cells expressing Pthlh with a spatial gradient of Pvalb expression. Using PatchSeq, we show that Pthlh cells exhibit a continuum of electrophysiological properties correlated with expression of Pvalb. Furthermore, we find significant molecular differences that correlate with differences in electrophysiological properties between Pvalb-expressing cells of the striatum and those of the cortex., Graphical Abstract, Highlights • Single-cell RNA sequencing of striatal interneurons reveals seven main classes • Subclass-specific latent factor analysis reveals gradients of gene expression • Pvalb neurons are not a discrete class but belong to a class expressing Pthlh • Interneuron classes vary in their similarity to counterparts from cortex/hippocampus, Muñoz-Manchado et al. describe the molecular and electrophysiological diversity of interneurons from the striatum. They find that in contrast to many other brain regions, cells expressing the gene Pvalb are not a discrete class of cells. This affects the interpretation of studies on striatal networks and their function.

Insomnia is the second-most prevalent mental disorder, with no sufficient treatment available. Despite a substantial role of genetic factors, only a handful of genes have been implicated and insight into the associated neurobiological pathways remains limited. Here, we use an unprecedented large genetic association sample (N=1,331,010) to allow detection of a substantial number of genetic variants and gain insight into biological functions, cell types and tissues involved in insomnia complaints. We identify 202 genome-wide significant loci implicating 956 genes through positional, eQTL and chromatin interaction mapping. We show involvement of the axonal part of neurons, of specific cortical and subcortical tissues, and of two specific cell-types in insomnia: striatal medium spiny neurons and hypothalamic neurons. These cell-types have been implicated previously in the regulation of reward processing, sleep and arousal in animal studies, but have never been genetically linked to insomnia in humans. We found weak genetic correlations with other sleep-related traits, but strong genetic correlations with psychiatric and metabolic traits. Mendelian randomization identified causal effects of insomnia on specific psychiatric and metabolic traits. Our findings reveal key brain areas and cells implicated in the neurobiology of insomnia and its related disorders, and provide novel targets for treatment.

With few exceptions, the marked advances in knowledge about the genetic basis of schizophrenia have not converged on findings that can be confidently used for precise experimental modeling. By applying knowledge of the cellular taxonomy of the brain from single-cell RNA sequencing, we evaluated whether the genomic loci implicated in schizophrenia map onto specific brain cell types. We found that the common-variant genomic results consistently mapped to pyramidal cells, medium spiny neurons (MSNs) and certain interneurons, but far less consistently to embryonic, progenitor or glial cells. These enrichments were due to sets of genes that were specifically expressed in each of these cell types. We also found that many of the diverse gene sets previously associated with schizophrenia (genes involved in synaptic function, those encoding mRNAs that interact with FMRP, antipsychotic targets, etc.) generally implicated the same brain cell types. Our results suggest a parsimonious explanation: the common-variant genetic results for schizophrenia point at a limited set of neurons, and the gene sets point to the same cells. The genetic risk associated with MSNs did not overlap with that of glutamatergic pyramidal cells and interneurons, suggesting that different cell types have biologically distinct roles in schizophrenia.

Cellular diversity in the brain revealed The mammalian brain has an extraordinarily large number of cells. Although there are quite a few different cell types, many cells in any one category tend to look alike. Zeisel et al. analyzed the transcriptomes of mouse brain cells to reveal more than meets the eye. Interneurons of similar type were found in dissimilar regions of the brain. Oligodendrocytes that seemed to be all of one class were differentiated by their molecular signatures into a half-dozen classes. Microglia associated with blood vessels were distinguished from look-alike perivascular macrophages. Thus, the complex microanatomy of the brain can be revealed by the RNAs expressed in its cells. Science , this issue p. 1138

Synaptic protein -synuclein (-SYN) modulates neurotransmission in a complex and poorly understood manner and aggregates in the cytoplasm of degenerating neurons in Parkinsons disease. Here, we report that -SYN present in dopaminergic nigral afferents is essential for the normal cycling and maintenance of neural stem cells (NSCs) in the brain subependymal zone of adult male and female mice. We also showthat premature senescence of adult NSCs into non-neurogenic astrocytes in mice lacking-SYN resemblesthe effects of dopaminergic fiber degeneration resulting from chronic exposure to 1-methyl-4-phenyl-1,2,3,6-tetra-hydropyridine or intranigral inoculation of aggregated toxic -SYN. Interestingly, NSC loss in -SYN-deficient mice can be prevented by viral delivery of human -SYN into their sustantia nigra or by treatment with L-DOPA, suggesting that -SYN regulates dopamine availability to NSCs. Our data indicatethat-SYN, presentin dopaminergic nerveterminals supplyingthe subependymal zone, acts as a niche componentto sustainthe neurogenic potential of adult NSCs and identify -SYN and DA as potential targets to ameliorate neurogenic defects in the aging and diseased brain., This work was supported by Ministerio de Economía y Competitividad Spanish Grants SAF2014-54581 and SAF2016-77541 and Instituto de Salud Carlos III (PI12/02574, PI13/01390, Centro de Investigacio´n Biome´dica en Red de Enfermedades Neurodegenerativas, Centro de Investigacio´n Biome´dica en Red de Salud Mental and RETIC Tercel)toM.V.,J.J.T-A., A.B., and I.F;Junta de Andalucía(Proyectos de Excelencia)toJ.J.T-A.; Generalitat Valenciana (Programa Prometeo) to I.F.; European Regional Development Fund; and European Union (E.U.) to A.B. R.S.-C. and G.B. received Spanish Ministerio de Educación FPU predoctoral fellowships. Work in the I.F. laboratory is supported by Fundacio´n Botín-Banco Santander.

Intelligence is highly heritable1 and a major determinant of human health and well-being2. Recent genome-wide meta-analyses have identified 24 genomic loci linked to intelligence3–7, but much about its genetic underpinnings remains to be discovered. Here, we present the largest genetic association study of intelligence to date (N=279,930), identifying 206 genomic loci (191 novel) and implicating 1,041 genes (963 novel) via positional mapping, expression quantitative trait locus (eQTL) mapping, chromatin interaction mapping, and gene-based association analysis. We find enrichment of genetic effects in conserved and coding regions and identify 89 nonsynonymous exonic variants. Associated genes are strongly expressed in the brain and specifically in striatal medium spiny neurons and cortical and hippocampal pyramidal neurons. Gene-set analyses implicate pathways related to neurogenesis, neuron differentiation and synaptic structure. We confirm previous strong genetic correlations with several neuropsychiatric disorders, and Mendelian Randomization results suggest protective effects of intelligence for Alzheimer’s dementia and ADHD, and bidirectional causation with strong pleiotropy for schizophrenia. These results are a major step forward in understanding the neurobiology of intelligence as well as genetically associated neuropsychiatric traits.

Neuroticism is an important risk factor for psychiatric traits including depression1, anxiety2,3, and schizophrenia4–6. Previous genome-wide association studies7–12 (GWAS) reported 16 genomic loci10–12. Here we report the largest neuroticism GWAS meta-analysis to date (N=449,484), and identify 136 independent genome-wide significant loci (124 novel), implicating 599 genes. Extensive functional follow-up analyses show enrichment in several brain regions and involvement of specific cell-types, including dopaminergic neuroblasts (P=3×10-8), medium spiny neurons (P=4×10-8) and serotonergic neurons (P=1×10-7). Gene-set analyses implicate three specific pathways: neurogenesis (P=4.4×10-9), behavioural response to cocaine processes (P=1.84×10-7), and axon part (P=5.26×10-8). We show that neuroticism’s genetic signal partly originates in two genetically distinguishable subclusters13 (depressed affect and worry, the former being genetically strongly related to depression, rg=0.84), suggesting distinct causal mechanisms for subtypes of individuals. These results vastly enhance our neurobiological understanding of neuroticism, and provide specific leads for functional follow-up experiments.

Background:Integrating rare variation from trio family and case/control studies has successfully implicated specific genes contributing to risk of neurodevelopmental disorders (NDDs) including autism spectrum disorders (ASD), intellectual disability (ID), developmental disorders (DD), and epilepsy (EPI). For schizophrenia (SCZ), however, while sets of genes have been implicated through study of rare variation, only two risk genes have been identified.Methods:We used hierarchical Bayesian modeling of rare variant genetic architecture to estimate mean effect sizes and risk-gene proportions, analyzing the largest available collection of whole exome sequence (WES) data for schizophrenia (1,077 trios, 6,699 cases and 13,028 controls), and data for four NDDs (ASD, ID, DD, and EPI; total 10,792 trios, and 4,058 cases and controls).Results:For SCZ, we estimate 1,551 risk genes, more risk genes and weaker effects than for NDDs. We provide power analyses to predict the number of risk gene discoveries as more data become available, demonstrating greater value of case-control over trio samples. We confirm and augment prior risk gene and gene set enrichment results for SCZ and NDDs. In particular, we detected 98 new DD risk genes at FDR < 0.05. Correlations of risk-gene posterior probabilities are high across four NDDs (ρ > 0.55), but low between SCZ and the NDDs (ρ < 0.3). In depth analysis of 288 NDD genes shows highly significant protein-protein interaction (PPI) network connectivity, and functionally distinct PPI subnetworks based on pathway enrichments, single-cell RNA-seq (scRNAseq) cell types and multi-region developmental brain RNA-seq.Conclusions:We have extended a pipeline used in ASD studies and applied it to infer rare genetic parameters for SCZ and four NDDs. We find many new DD risk genes, supported by gene set enrichment and PPI network connectivity analyses. We find greater similarity among NDDs than between NDDs and SCZ. NDD gene subnetworks are implicated in postnatally expressed presynaptic and postsynaptic genes, and for transcriptional and post-transcriptional gene regulation in prenatal neural progenitor and stem cells.

Variance in IQ is associated with a wide range of health outcomes, and 1% of the population are affected by intellectual disability. Despite a century of research, the fundamental neural underpinnings of intelligence remain unclear. We integrate results from genome-wide association studies (GWAS) of intelligence with brain tissue and single cell gene expression data to identify tissues and cell types associated with intelligence. GWAS data for IQ (N = 78,308) were meta-analyzed with an extreme-trait cohort of 1,247 individuals with mean IQ ∼170 and 8,185 controls. Genes associated with intelligence implicate pyramidal neurons of the somatosensory cortex and CA1 region of the hippocampus, and midbrain embryonic GABAergic neurons. Tissue-specific analyses find the most significant enrichment for frontal cortex brain expressed genes. These results suggest specific neuronal cell types and genes may be involved in intelligence and provide new hypotheses for neuroscience experiments using model systems.

Histological and morphological studies indicate that approximately 5% of striatal neurons are cholinergic or γ-aminobutyric acidergic (GABAergic) interneurons (gINs). However, the number of striatal neurons expressing known interneuron markers is too small to account for the entire interneuron population. We therefore studied the serotonin (5HT) receptor 3a-enhanced green fluorescent protein (5HT3a(EGFP)) mouse, in which we found that a large number of striatal gINs are labeled. Roughly 20% of 5HT3a(EGFP)-positive cells co-express parvalbumin and exhibit fast-spiking (FS) electrophysiological properties. However, the majority of labeled neurons do not overlap with known molecular interneuron markers. Intrinsic electrical properties reveal at least 2 distinct novel subtypes: a late-spiking (LS) neuropeptide-Y (NPY)-negative neurogliaform (NGF) interneuron, and a large heterogeneous population with several features resembling low-threshold-spiking (LTS) interneurons that do not express somatostatin, NPY, or neuronal nitric oxide synthase. Although the 5HT3a(EGFP) NGF and LTS-like interneurons have electrophysiological properties similar to previously described populations, they are pharmacologically distinct. In direct contrast to previously described NPY(+) LTS and NGF cells, LTS-like 5HT3a(EGFP) cells show robust responses to nicotine administration, while the 5HT3a(EGFP) NGF cell type shows little or no response. By constructing a molecular map of the overlap between these novel populations and existing interneuron populations, we are able to reconcile the morphological and molecular estimates of striatal interneuron numbers.

Key points • The carotid body (CB) is a key chemoreceptor organ that mediates the hyperventilatory response to hypoxia, and contributes to the process of acclimatisation to chronic hypoxaemia. • Knowledge of CB physiology at the cellular and molecular levels has advanced considerably in recent times thanks to studies on lower mammals; however, information on humans is practically absent. Here we describe the properties of human CB cells in slice preparations or after enzymatic dispersion. • Besides glomus (type I) and glia-like, sustentacular (type II) cells, adult human CBs contain nestin-positive neural progenitor cells. The human CB also expresses high levels of glial cell line-derived neurotrophic factor. These properties are maintained at an advanced age. • Human glomus cells contain a relatively high density of voltage-dependent Na+, Ca2+ and K+ channels. Membrane depolarisation with high extracellular K+ induces an increase of cytosolic [Ca2+] and quantal catecholamine release. • Human glomus cells are responsive to hypoxia and hypoglycaemia, both of which induce an increase in cytosolic [Ca2+] and transmitter release. Chemosensory responses of glomus cells are also preserved at an advanced age. • These findings on the cellular and molecular physiology of the CB provide novel perspectives for the systematic study of pathologies involving this organ in humans. Abstract The carotid body (CB) is the major peripheral arterial chemoreceptor in mammals that mediates the acute hyperventilatory response to hypoxia. The CB grows in response to sustained hypoxia and also participates in acclimatisation to chronic hypoxaemia. Knowledge of CB physiology at the cellular level has increased considerably in recent times thanks to studies performed on lower mammals, and rodents in particular. However, the functional characteristics of human CB cells remain practically unknown. Herein, we use tissue slices or enzymatically dispersed cells to determine the characteristics of human CB cells. The adult human CB parenchyma contains clusters of chemosensitive glomus (type I) and sustentacular (type II) cells as well as nestin-positive progenitor cells. This organ also expresses high levels of the dopaminotrophic glial cell line-derived neurotrophic factor (GDNF). We found that GDNF production and the number of progenitor and glomus cells were preserved in the CBs of human subjects of advanced age. Moreover, glomus cells exhibited voltage-dependent Na+, Ca2+ and K+ currents that were qualitatively similar to those reported in lower mammals. These cells responded to hypoxia with an external Ca2+-dependent increase of cytosolic Ca2+ and quantal catecholamine secretion, as reported for other mammalian species. Interestingly, human glomus cells are also responsive to hypoglycaemia and together these two stimuli can potentiate each other's effects. The chemosensory responses of glomus cells are also preserved at an advanced age. These new data on the cellular and molecular physiology of the CB pave the way for future pathophysiological studies involving this organ in humans.

Aims: A major limiting factor for cell therapy in Parkinson’s disease is that the survival of grafted dopaminergic neurons is very poor, which may be improved by administration of GDNF, for which the carotid body is a good source. Materials & methods: Rats with total unilateral dopaminergic denervation were grafted with a cell suspension of rat dopaminergic neuroblasts with or without cell aggregates from the rat carotid body. At 1, 2 and 3 months after grafting, the rats were tested in the cylinder and the rotometer and killed 4 months after grafting. Results: We observed that the survival of dopaminergic neurons and graft-derived dopaminergic innervation were higher in rats that received mixed grafts. Both grafted groups showed complete recovery in the amphetamine-induced rotation test. However, rats with cografts performed significantly better in the cylinder test. Conclusion: Cografting of carotid body cells may constitute a useful strategy for cell therapy in Parkinson’s disease.

GABAergic interneurons are key regulators of hippocampal circuits, but our understanding of the diversity and classification of these cells remains controversial. Here we analyze the organization of interneurons in the CA1 area, using the combinatorial patterns of gene expression revealed by single-cell mRNA sequencing (scRNA-seq). This analysis reveals a 5-level hierarchy of cell classes. Most of the predicted classes correspond closely to known interneuron types, allowing us to predict a large number of novel molecular markers of these classes. In addition we identified a major new interneuron population localized at the border of strata radiatum and lacunosum-moleculare that we term "R2C2 cells" after their characteristic combinatorial expression of Rgs12, Reln, Cxcl14, and Cpne5. Several predictions of this classification scheme were verified using in situ hybridization and immunohistochemistry, providing further confidence in the gene expression patterns and novel classes predicted by the single cell data.

Intrastriatal grafts of CB cells can produce important recovery in different preclinical models of Parkinson’s disease (PD). The carotid body (CB) is a bilateral neural crest‐derived chemoreceptor organ that is composed of a cluster of highly dopaminergic glomus cells. Although anti‐Parkinsonian CB cell therapy was originally thought to be a dopamine‐replacement approach, different studies have demonstrated that the beneficial action exerted by the CB implant is mainly due to a trophic action on the nigrostriatal pathway rather than to the mere release of dopamine. Accordingly, it has been shown that CB implants produce high levels of glial cell line neurotrophic factor (GDNF). In addition, the trophic action induced by the graft shows a dose‐dependent relation with respect to the size and GDNF expression of the implant. Thus, dopaminergic CB glomus cells appear to be ideally suited for the endogenous release of GDNF, and probably other trophic factors, in PD. In parallel with the preclinical studies, two Phase I/II clinical trials have shown that CB autotransplantation can improve motor symptoms in PD patients although with less efficiency than in experimental models. In this chapter, we review the different preclinical and clinical studies performed on CB transplantation in PD, paying special attention to the mechanisms underlying the grafts’ actions.

Intrastriatal transplantation of dopaminergic carotid body (CB) cells ameliorates parkinsonism in animal models and, with less efficacy, in Parkinson's disease patients. CB-based cell therapy was initially proposed because of its high dopamine content. However, later studies suggested that its beneficial effect might be due to a trophic action exerted on nigrostriatal neurons. Compatible with this concept are the high levels of neurotrophic factors encountered in CB cells. To test experimentally this idea, unilateral striatal transplants were performed with a sham graft in the contralateral striatum, as a robust internal control. Thereafter, the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6, -tetrahydropyridine was injected during 3 months. CB grafts protected from degeneration ipsilateral nigral dopaminergic neurons projecting to the transplant in a dose-dependent manner regarding size and glial cell line-derived neurotrophic factor expression. Grafts performed at different times after the onset of the neurotoxic treatment demonstrated with histological and behavioral methods protection and repair of the nigrostriatal pathway by CB transplants. This study provides a mechanistic explanation for the action of CB transplants on parkinsonian models. It should also help to improve cell therapy approaches to Parkinson's disease. © 2013 Elsevier Inc., This study was supported by grants from the Spanish Government (FIS, Red TERCEL, CIBERNED, MEC, and MICINN), the Andalusian Government (Excellence projects) and the Marcelino Botín Foundation.

One size does not fit all Oligodendrocytes are best known for their ability to myelinate brain neurons, thus increasing the speed of signal transmission. Marques et al. surveyed oligodendrocytes of developing mice and found unexpected heterogeneity. Transcriptional analysis identified 12 populations, ranging from precursors to mature oligodendrocytes. Transcriptional profiles diverged as the oligodendrocytes matured, building distinct populations. One population was responsive to motor learning, and another, with a different transcriptome, traveled along blood vessels. Science , this issue p. 1326