Circadian Integration of Glutamatergic Signals by Little SAAS in Novel Suprachiasmatic Circuits

Neuropeptides are critical integrative elements within the central circadian clock in the suprachiasmatic nucleus (SCN), where they mediate both cell-to-cell synchronization and phase adjustments that cause light entrainment. Forward peptidomics identified little SAAS, derived from the proSAAS prohormone, among novel SCN peptides, but its role in the SCN is poorly understood.Little SAAS localization and co-expression with established SCN neuropeptides were evaluated by immunohistochemistry using highly specific antisera and stereological analysis. Functional context was assessed relative to c-FOS induction in light-stimulated animals and on neuronal circadian rhythms in glutamate-stimulated brain slices. We found that little SAAS-expressing neurons comprise the third most abundant neuropeptidergic class (16.4%) with unusual functional circuit contexts. Little SAAS is localized within the densely retinorecipient central SCN of both rat and mouse, but not the retinohypothalamic tract (RHT). Some little SAAS colocalizes with vasoactive intestinal polypeptide (VIP) or gastrin-releasing peptide (GRP), known mediators of light signals, but not arginine vasopressin (AVP). Nearly 50% of little SAAS neurons express c-FOS in response to light exposure in early night. Blockade of signals that relay light information, via NMDA receptors or VIP- and GRP-cognate receptors, has no effect on phase delays of circadian rhythms induced by little SAAS.Little SAAS relays signals downstream of light/glutamatergic signaling from eye to SCN, and independent of VIP and GRP action. These findings suggest that little SAAS forms a third SCN neuropeptidergic system, processing light information and activating phase-shifts within novel circuits of the central circadian clock

SCHEDULING TRAINS ON A RAILWAY NETWORK USING A DISCRETE EVENT MODEL OF RAILWAY TRAFFIC

This paper develops a local feedback-based travel advance strategy for computing railway network schedules. The strategy uses a discrete event model of train advances along lines of the railway. This approach can quickly handle perturbations in the schedule and is shown to perform well on three time-performance criteria while maintaining the local nature of the strategy. If the local strategy leads to a deadlock, a capacity check algorithm is applied that prevents deadlock, but requires additional nonlocal information. Extensions to the strategy are developed for networks with double-track sections and with variable train characteristics and priorities. The approach also is shown to be computationally efficient

Scheduling trains on a railway network using a discrete event model of railway traffic

Scheduling trains in a railway network is a fundamental operational problem in the railway industry. A local feedback-based travel advance strategy is developed using a discrete event model of train advances along lines of the railway. This approach can quickly handle perturbations in the schedule and is shown to perform well on three time-performance criteria while maintaining the local nature of the strategy. If the local strategy leads to a deadlock, a capacity check algorithm is applied that prevents deadlock, but requires additional nonlocal information. Extensions to the strategy are developed for networks with double-track sections and with variable train characteristics and priorities.