Its ligand Sema3e is expressed by vGlut2on thalamic but not vGlut1on cortical afferents (Figure 7B). Genetic elimination of either presynaptic Sema3e or postsynaptic PlxnD1 leads to increased thalamostriatal input specifically to D1-MSNs but not D2-MSNs assessed by electrophysiology and anatomy. This work highlights that at the

mechanistic level, the same molecular pathway is employed for the regulation of synaptic specificity in basal ganglia circuits and sensory-motor connectivity in the spinal cord. Whereas in the spinal cord, presynaptic PlxnD1 expression in proprioceptors prevents the establishment of direct synaptic contacts with postsynaptic Compound Library purchase Sema3e-expressing Cm motor neurons (Pecho-Vrieseling et al., 2009) (Figure 6A), thalamostriatal synapses use the same ligand-receptor pair but with switched pre- and postsynaptic localization to regulate synaptic specificity. Dopaminergic input from the SN to the striatum gates the shift of MSNs between active up and inactive down states (Gerfen and Surmeier, 2011, Grillner et al., 2005 and Kreitzer and Malenka, 2008). Dopaminergic neurons in the midbrain exhibit functional heterogeneity, at least in part originating from differential synaptic input to these neurons mediated by dendritic arborization (Henny et al., 2012). Analysis

of anatomical and functional properties of dopaminergic neurons with cell bodies positioned in SN pars compacta (SNc) differentiates two main most types. Neurons with dendrites extending into the neighboring SN pars reticulata (SNr) exhibit a higher proportion of GABAergic MG 132 inputs than the ones with dendrites confined to SNc, a feature tightly correlating with in vivo responses to aversive stimuli (Henny et al., 2012). These findings provide additional support for the notion that the elaboration of dendritic arbors during development profoundly influences assembly of presynaptic input and neuronal function. Ascending spinal pathways concerned with motor control are involved in reporting predicted future action

and past events assessed through sensory feedback. Internal monitoring of motor behavior exists at a multitude of hierarchical levels and was studied in many species (Poulet and Hedwig, 2007 and Sommer and Wurtz, 2008). While the briefly summarized studies on pathways carrying ascending information to the cerebellum are based on work carried out over many years, they clearly illustrate the existence of spatially confined and task-related reporting channels of spinal origin. They also highlight the lack of knowledge about genetic and developmental pathways involved in specification and connectivity of these important neuronal populations. In the cervical spinal cord, a specialized group of C3-C4 propriospinal neurons was characterized using a combination of electrophysiological, anatomical, and behavioral approaches in cat and monkey (Alstermark et al., 2007 and Pettersson et al., 2007).