General anesthesia (GA) allows for care of sick and premature children, but its use during critical stages of brain development (i.e. synaptogenesis) induces apoptotic death of immature neurons and long-term neurocognitive and behavioral impairments. The formation of functional neuronal networks during brain development depends on timely and proper neuronal axon selection and pruning, a process highly dependent on neuronal activity and homeostasis of neurotrophic factors, especially brain-derived neurotrophic factor (BDNF). Since GA is a potent inhibitor of neuronal activity and a potent modulator of BDNF homeostasis, our general hypothesis is that transient exposure to GA during critical stages of brain development causes long-term impairments of proper axon selection and pruning in neurons that survive the initial apoptotic `attack'. This, in turn, causes lasting impairments in formation of functional neuronal networks among the remaining (`normal') neurons. Our long-term goals are to understand how GA modulates the formation of functional neuronal networks responsible for long-term memory storage and consolidation and to establish the links between GA- induced BDNF-modulated axon pruning and synaptic neurotransmission. The rationale is that this understanding will enable pharmacological targeting of critical steps in axon pruning and formation of neuronal circuitries to prevent GA- induced impairment of synaptogenesis and memory/learning deficits. Using in vivo rat models of GA-induced developmental neurotoxicity we will focus on the infrapyramidal bundle (IPB) of mossy fiber projections in the hippocampus (from granular neurons in the dentate gyrus to pyramidal neurons in the CA3 region), a neuronal circuitry that plays a crucial role in learning and memory and is well established as a model of axon pruning. We will address specific hypothesis that GA impairs BDNF-p75NTR signaling, thereby hampering proper selection of axons and ultimately impairing synaptic neurotransmission.
Specific Aim #1 : will examine two intravenous anesthetics commonly used in children and having distinct mechanisms of action: the NMDA antagonist ketamine and the GABAA agonist propofol via morphometric analyses of the IPB and its synaptic contacts using light and electron microscopy. Our preliminary data suggest that ketamine impairs developmental IPB pruning that coincides with a significant down-regulation of BDNF and pro-BDNF. We will examine the importance of BDNF and p75NTR on GA-induced impairment in IPB pruning using BDNF+/- and Ngfr-/- (p75NTR-/-) mutant mice. The importance of the BDNF-p75NTR cascade will be examined using the p75NTR pharmacologic antagonist TAT-Pep5 to block p75NTR or the viral vector LV-syn-p75NTR to knock-in (`restore') p75NTR in dentate gyrus of p75NTR-/- mice.
Specific Aim #2 : will determine the functional link between GA-induced impairments in axon pruning and selection and the impairment of synaptic plasticity in IPB neuronal circuits. We will examine GA effects in p75NTR-/- and BDNF+/- mutant mice and their wild type (WT) counterparts using ex-vivo patch clamp slice recordings of synaptic neurotransmission in CA3 and dentate gyrus of the hippocampus. We will attempt to potentiate the effect of GA in WT mice on synaptic transmission using the p75NTR antagonist TAT-Pep5 and will attempt to block the effects of GA by knocking-in p75NTR in the dentate gyrus of p75NTR-/- mice.

Public Health Relevance

Early exposure to clinical anesthesia can be detrimental to the developing brain, resulting in long-term cognitive impairments. Guided by our preliminary findings we propose that transient exposure to anesthesia during critical stages of brain development impairs the homeostasis of brain derived neurotrophic factor (BDNF) and hampers proper axon selection and pruning with deleterious effects on the formation of neuronal circuitries responsible for long-term memory storage and consolidation. Hence, we plan to examine the mechanistic aspects and functional consequences of anesthesia-induced BDNF- modulated impairments of axon pruning and maintenance with the ultimate goal being timely prevention of anesthesia-induced damage to neuronal network formation during critical stages of synaptogenesis.

Agency
National Institute of Health (NIH)
Institute
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21HD080281-03
Application #
9021552
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Zajicek, Anne
Project Start
2015-04-01
Project End
2017-03-31
Budget Start
2016-04-01
Budget End
2017-03-31
Support Year
3
Fiscal Year
2016
Total Cost
Indirect Cost
Name
University of Colorado Denver
Department
Anesthesiology
Type
Schools of Medicine
DUNS #
041096314
City
Aurora
State
CO
Country
United States
Zip Code
80045
Obradovic, Aleksandar Lj; Atluri, Navya; Dalla Massara, Lorenza et al. (2018) Early Exposure to Ketamine Impairs Axonal Pruning in Developing Mouse Hippocampus. Mol Neurobiol 55:164-172
Jevtovic-Todorovic, Vesna; Brambrick, Ansgar (2018) General Anesthesia and Young Brain: What is New? J Neurosurg Anesthesiol 30:217-222
Jevtovic-Todorovic, Vesna (2018) Exposure of Developing Brain to General Anesthesia: What Is the Animal Evidence? Anesthesiology 128:832-839
Maloney, Susan E; Creeley, Catherine E; Hartman, Richard E et al. (2018) Using animal models to evaluate the functional consequences of anesthesia during early neurodevelopment. Neurobiol Learn Mem :
Zanghi, Christine N; Jevtovic-Todorovic, Vesna (2017) A holistic approach to anesthesia-induced neurotoxicity and its implications for future mechanistic studies. Neurotoxicol Teratol 60:24-32
Dalla Massara, Lorenza; Osuru, Hari Prasad; Oklopcic, Azra et al. (2016) General Anesthesia Causes Epigenetic Histone Modulation of c-Fos and Brain-derived Neurotrophic Factor, Target Genes Important for Neuronal Development in the Immature Rat Hippocampus. Anesthesiology 124:1311-1327