Interplay between biochemical processes and network properties generates neuronal up and down states at the tripartite synapse.

Neuronal up and down states have long been known to exist both in vitro and in vivo. A variety of functions and mechanisms have been proposed for their generation, but there has not been a clear connection between the functions and mechanisms. We explore the potential contribution of cellular-level biochemistry to the network-level mechanisms thought to underlie the generation of up and down states. We develop a neurochemical model of a single tripartite synapse, assumed to be within a network of similar tripartite synapses, to investigate possible function-mechanism links for the appearance of up and down states. We characterize the behavior of our model in different regions of parameter space and show that resource limitation at the tripartite synapse affects its ability to faithfully transmit input signals, leading to extinction-down states. Recovery of resources allows for "reignition" into up states. The tripartite synapse exhibits distinctive "regimes" of operation depending on whether ATP, neurotransmitter (glutamate), both, or neither, is limiting. Our model qualitatively matches the behavior of six disparate experimental systems, including both in vitro and in vivo models, without changing any model parameters except those related to the experimental conditions. We also explore the effects of varying different critical parameters within the model. Here we show that availability of energy, represented by ATP, and glutamate for neurotransmission at the cellular level are intimately related, and are capable of promoting state transitions at the network level as ignition and extinction phenomena. Our model is complementary to existing models of neuronal up and down states in that it focuses on cellular-level dynamics while still retaining essential network-level processes. Our model predicts the existence of a "final common pathway" of behavior at the tripartite synapse arising from scarcity of resources and may explain use dependence in the phenomenon of "local sleep." Ultimately, sleeplike behavior may be a fundamental property of networks of tripartite synapses.

A Standardized Checklist Improves the Transfer of Stroke Patients from the Neurocritical Care Unit to Hospital Ward.

BACKGROUND AND PURPOSE: The transfer of patients with ischemic stroke from the intensive care unit (ICU) to noncritical care inpatient wards involves detailed information sharing between care teams. Our local transfer process was not standardized, leading to potential patient risk. We developed and evaluated an "ICU Transfer Checklist" to standardize communication between the neurocritical care team and the stroke ward team. METHODS: Retrospective review of consecutive patients with ischemic stroke admitted to the neurocritical care unit who were transferred to the stroke ward was used to characterize transfer documentation. A multidisciplinary team developed and implemented an ICU Transfer Checklist that contained a synthesis of the patient's clinical course, immediate "to-do" action items, and a system-based review of active medical problems. Postintervention checklist utilization was recorded for 8 months, and quality metrics for the postintervention cohort were compared to the preintervention cohort. Providers were surveyed pre- and postintervention to characterize perceived workflow and quality of care. RESULTS: Patients before (n = 52) and after (n = 81) ICU Transfer Checklist implementation had similar demographic and clinical characteristics. In the postchecklist implementation period, the ICU Transfer Checklist was used in over 85% of patients and median hospital length of stay (LOS) decreased (8.6 days vs 5.4 days, P = .003), while ICU readmission rate remained low. The checklist was associated with improved perceptions of safety and decreased time needed to transfer patients. CONCLUSIONS: Use of the standardized ICU Transfer Checklist was associated with decreased hospital LOS and with improvements in providers' perceptions of patient safety.