• Anesthetic Imprinting of the Developing Brain

    The ability to pharmacologically render patients insensible to noxious stimulation using general anesthetics and sedatives represents one of the greatest discoveries in medicine. Advanced physiological monitoring and meticulous administration of modern anesthetic drugs have facilitated surgical interventions to mitigate life-threatening conditions in very young children. Moreover, sedation during mechanical ventilation and for painful procedures in intensive care units has shielded neonates from the deleterious effects of pain and suffering. Accordingly, every year, anesthetics and sedatives are used in millions of young children worldwide to ablate the stress response to noxious stimulation and to mitigate potential, stress-related morbidity during painful procedures and imaging studies.

    However, recent findings in laboratory animals have demonstrated structural alterations, such as a widespread increase in apoptotic brain cell death, an inborn cell suicide program, immediately following exposure to all currently and commonly used sedatives and anesthetics. Moreover, several preclinical studies have also observed alterations in synaptic formation and subsequent impairment in neurocognitive function. These findings in newborn animals have led to significant concerns among pediatric anesthesiologists and parents.

    Given the potentially serious consequences of long-term neurological sequelae following uneventful pediatric surgery with anesthesia, our research aims to clarify the underlying mechanisms and to delineate the selectivity of anesthesia-induced neuroapoptosis, which will be critical for assessing human relevance of this phenomenon, and if necessary, for developing mitigating strategies.

    Along those lines, our laboratory has demonstrated similar neuronal apoptosis following prolonged exposure to equipotent doses of the three most commonly used anesthetics: Desflurane, Isoflurane and Sevoflurane. Furthermore, we were able to demonstrate that anesthetics selectively affect immature neurons, explaining the shift in brain regional vulnerability, changing with age. We characterized the age of susceptible neurons to be around two weeks of age. Given the phenomenon’s potential dramatic clinical impact, we will continue our research efforts to improve the understanding of the underlying mechanism, to delineate human applicability, and to determine alternative anesthetic techniques. Our translational efforts are geared toward examining the effects of surgery with anesthesia early in life on subsequent brain structure and function using noninvasive imaging technology and validated individualized testing.

  • A six-hour exposure to Desflurane, Isoflurane or Sevoflurane increases apoptotic cell death in neonatal mice, compared with fasted, unanesthetized littermates (no anesthesia).

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  • Anesthesia triggers cell death in newly generated dentate granule cells, as identified by their location and phenotypic markers, irrespective of the age of the animal. Representative photomicrograph composites of dentate gyrus from a 21 day-old mouse (A-D), following an isoflurane anesthetic, stained for the apoptotic marker caspase 3 (green,A), the mature granule cell marker Calbindin (red, B), the immature granule cell marker Calretinin (blue, C), and a merged image (D). Caspase 3+, apoptotic neurons are predominantly located in the subgranular zone (arrows), and express the immature marker Calretinin and not the mature marker Calbindin. Bar graphs (E) represent the fraction of apoptotic, caspase 3+ dentate granule cells colocalizing the respective maturational stage-specific markers [caspase 3+ cells co-labeled with one of the four respective markers divided by the total number of caspase 3+ cells]. Apoptotic dentate granule cells are identified as late progenitors and immature granule cells, but not as radial glia-like progenitors or mature neurons. Schematic (F) demonstrating dentate granule cell (DCG) maturation progressing from radial glia-like progenitor cells, located close to the hilus and expressing Sox2, to transient amplifying cells and neuroblasts, located in the subgranular zone (SGZ) and expressing NeuroD1, to immature neurons with small dendritic tree, located in the SGZ and expressing Calretinin, and lastly to Calbindin-expressing mature neurons migrating into the granule cell layer (GCL) and extending dendrites into the molecular layer (ML). Similar composite photomicrographs from a young adult mouse (P49, G to J), and bar graphs of characterization (K) identifying apoptotic cells as late progenitors and immature granule cells. All scale bars = 50 µm.

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