Daily rhythms of mammalian physiology, metabolism, and behavior parallel the day-night cycle. They are orchestrated by a central circadian clock in the brain, the suprachiasmatic nucleus (SCN). Transcription of clock genes is sensitive to metabolic changes in reduction and oxidation (redox); however, circadian cycles in protein oxidation have been reported in anucleate cells, where no transcription occurs. We tested whether the SCN also expresses redox cycles and how such metabolic oscillations might affect neuronal physiology. We detected self-sustained circadian rhythms of SCN redox state that required the molecular clockwork. The redox oscillation could determine the excitability of SCN neurons through non-transcriptional modulation of multiple K+ channels. Thus, dynamic regulation of SCN excitability appears to be closely tied to metabolism that engages the clockwork machinery.

The thalamic relay to neocortex is dynamically gated. The inhibitory interneuron, which we have studied in the lateral geniculate nucleus, is important to this process. In addition to axonal outputs, these cells have dendritic terminals that are both presynaptic and postsynaptic. Even with action potentials blocked, activation of ionotropic and metabotropic glutamate receptors on these terminals increases their output, whereas activation of metabotropic (M2 muscarinic) but not nicotinic cholinergic receptors decreases their output. These actions can strongly affect retinogeniculate transmission.

Efficient derivation of large-scale motor neurons (MNs) from human pluripotent stem cells is central to the understanding of MN development, modelling of MN disorders in vitro and development of cell-replacement therapies. Here we develop a method for rapid (20 days) and highly efficient (B70%) differentiation of mature and functional MNs from human pluripotent stem cells by tightly modulating neural patterning temporally at a previously undefined primitive neural progenitor stage. This method also allows high-yield (4250%) MN production in chemically defined adherent cultures. Furthermore, we show that Islet-1 is essential for formation of mature and functional human MNs, but, unlike its mouse counterpart, does not regulate cell survival or suppress the V2a interneuron fate. Together, our discoveries improve the strategy for MN derivation, advance our understanding of human neural specification and MN development, and provide invaluable tools for human developmental studies, drug discovery and regenerative medicine.

Detailed information regarding the contribution of individual ␥-aminobutyric acid (GABA)-containing inhibitory neurons to the overall synaptic activity of single postsynaptic cells is essential to our understanding of fundamental elements of synaptic integration and operation of neuronal circuits. For example, GABA-containing cells in the thalamic reticular nucleus (nRt) provide major inhibitory innervation of thalamic relay nuclei that is critical to thalamocortical rhythm generation. To investigate the contribution of individual nRt neurons to the strength of this internuclear inhibition, we obtained whole-cell recordings of unitary inhibitory postsynaptic currents (IPSCs) evoked in ventrobasal thalamocortical (VB) neurons by stimulation of single nRt cells in rat thalamic slices, in conjunction with intracellular biocytin labeling. Two types of monosynaptic IPSCs could be distinguished. ''Weak'' inhibitory connections were characterized by a significant number of postsynaptic failures in response to presynaptic nRt action potentials and relatively small IPSCs. In contrast, ''strong'' inhibition was characterized by the absence of postsynaptic failures and significantly larger unitary IPSCs. By using miniature IPSC amplitudes to infer quantal size, we estimated that unitary IPSCs associated with weak inhibition resulted from activation of 1-3 release sites, whereas stronger inhibition would require simultaneous activation of 5-70 release sites. The inhibitory strengths were positively correlated with the density of axonal swellings of the presynaptic nRt neurons, an indicator that characterizes different nRt axonal arborization patterns. These results demonstrate that there is a heterogeneity of inhibitory interactions between nRt and VB neurons, and that variations in gross morphological features of axonal arbors in the central nervous system can be associated with significant differences in postsynaptic response characteristics.Intrathalamic rhythmic activities that are prominent in sleep and certain pathophysiological conditions (reviewed in ref. 1) are a consequence of both the intrinsic properties of thalamic neurons and the reciprocal synaptic connectivity between excitatory cells in thalamic relay nuclei and inhibitory neurons in the thalamic reticular nucleus (nRt) (or analogous perigeniculate nucleus) (2-5). Most thalamic neurons are capable of firing action potentials in robust phasic bursts that are key elements in rhythm generation. Burst behavior, in turn, depends on the presence of a low-threshold transient Ca 2ϩ current (6, 7) that is inactivated at resting membrane potentials and deinactivated by inhibitory postsynaptic potentials that hyperpolarize the involved neurons (2, 3, 8). The ␥-aminobutyric acid (GABA)-ergic inhibitory innervation onto thalamocortical relay neurons from nRt (3, 9-13) thus forms a key element in the generation of oscillatory activities.In this scheme of thalamic operation, it becomes critical to define the factors that regulate the inhibitory drive from nRt neur...