General anesthesia is typically considered to be a rapidly and completely reversible state. The demonstration of anesthetic preconditioning against ischemia makes it clear, however, that anesthetic agents can alter molecular and synaptic events in the central nervous system for days. Along similar lines, our research shows that in rodents general anesthesia produces enduring cognitive impairment, with the old recovering more slowly. The mechanisms of this post-anesthetic cognitive dysfunction are unclear but evidence points to lasting changes in processes involved in synaptic plasticity. We have evidence that the volatile anesthetic isoflurane produces profound and persistent down-regulation of drebrin, an F-actin binding protein involved in formation of dendritic spines and excitatory synapses, loss of dendritic spines, and reduced neuronal release of tPA, an enzyme that regulates synthesis of the neurotrophin BDNF, implying that isoflurane interferes with neurotrophic support and synaptogenesis. Moreover, isoflurane decreases proliferation of neural progenitors both in vitro and in vivo, possibly leading to reduced cellular plasticity in the mature brain. Accordingly, using in vitro models of cultured mature and immature neurons and hippocampal slices from young and old animals, as well as a behaviorally well-characterized in vivo model, we propose to systematically examine anesthetic effects on dendritic spine morphogenesis, synaptogenesis, and neurogenesis to test the hypotheses that isoflurane but not propofol 1. causes sustained disruption of mechanisms underlying spine and synapse formation;and 2. reduces the capacity for synaptic and cellular remodeling, particularly in the aged brain. There has been little attention to these aspects of anesthetic action previously and elucidating how general anesthetics interfere acutely and persistently with morphological and functional indices of synaptic communication may provide a morphological / molecular basis for their lingering short- and long-term effects on brain function. This proposal is a logical extension of our previous efforts and, by improving understanding of the impact of general anesthetics on the aged brain, may eventually help improve cognitive outcomes after surgery and general anesthesia in elders, the group most vulnerable to postoperative cognitive morbidity.
These studies are designed to investigate the cause of persistent neuroplastic and cognitive changes in the aged brain following general anesthesia. This work may help to prevent or treat postoperative cognitive dysfunction in the aged.
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