The effects of neonatal isoflurane exposure in mice on brain cell viability, adult behavior, learning, and memory.
BACKGROUND
Volatile anesthetics, such as isoflurane, are widely used in infants and neonates. Neurodegeneration and neurocognitive impairment after exposure to isoflurane, midazolam, and nitrous oxide in neonatal rats have raised concerns regarding the safety of pediatric anesthesia. In neonatal mice, prolonged isoflurane exposure triggers hypoglycemia, which could be responsible for the neurocognitive impairment. We examined the effects of neonatal isoflurane exposure and blood glucose on brain cell viability, spontaneous locomotor activity, as well as spatial learning and memory in mice.


METHODS
Seven-day-old mice were randomly assigned to 6 h of 1.5% isoflurane with or without injections of dextrose or normal saline, or to 6 h of room air without injections (no anesthesia). Arterial blood gases and glucose were measured. After 2 h, 18 h, or 11 wk postexposure, cellular viability was assessed in brain sections stained with Fluoro-Jade B, caspase 3, or NeuN. Nine weeks postexposure, spontaneous locomotor activity was assessed, and spatial learning and memory were evaluated in the Morris water maze using hidden and reduced platform trials.


RESULTS
Apoptotic cellular degeneration increased in several brain regions early after isoflurane exposure, compared with no anesthesia. Despite neonatal cell loss, however, adult neuronal density was unaltered in two brain regions significantly affected by the neonatal degeneration. In adulthood, spontaneous locomotor activity and spatial learning and memory performance were similar in all groups, regardless of neonatal isoflurane exposure. Neonatal isoflurane exposure led to an 18% mortality, and transiently increased Paco(2), lactate, and base deficit, and decreased blood glucose levels. However, hypoglycemia did not seem responsible for the neurodegeneration, as dextrose supplementation failed to prevent neuronal loss.


CONCLUSIONS
Prolonged isoflurane exposure in neonatal mice led to increased immediate brain cell degeneration, however, no significant reductions in adult neuronal density or deficits in spontaneous locomotion, spatial learning, or memory function were observed.
Loepke
Andreas W
AW
Department of Anesthesia, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA. andreas.loepke@cchmc.or
Istaphanous
George K
GK
McAuliffe
John J
JJ
Miles
Lili
L
Hughes
Elizabeth A
EA
McCann
John C
JC
Harlow
Kathryn E
KE
Kurth
C Dean
CD
Williams
Michael T
MT
Vorhees
Charles V
CV
Danzer
Steve C
SC
D018685:Anesthetics, Inhalation / Q000633:toxicity*; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects*; D001522:Behavior, Animal / Q000187:drug effects*; D001786:Blood Glucose / Q000187:drug effects; D001921:Brain / Q000187:drug effects* / Q000473:pathology / Q000503:physiopathology; D002245:Carbon Dioxide / Q000097:blood; D002470:Cell Survival / Q000187:drug effects; D005260:Female; D005947:Glucose / Q000008:administration & dosage; D006863:Hydrogen-Ion Concentration; D007530:Isoflurane / Q000633:toxicity*; D019344:Lactic Acid / Q000097:blood; D008297:Male; D018782:Maze Learning / Q000187:drug effects*; D008568:Memory / Q000187:drug effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D009043:Motor Activity / Q000187:drug effects; D009410:Nerve Degeneration / Q000139:chemically induced* / Q000473:pathology / Q000503:physiopathology; D009474:Neurons / Q000187:drug effects / Q000473:pathology; D010100:Oxygen / Q000097:blood; D013997:Time Factors
D018685:Anesthetics, Inhalation; D001786:Blood Glucose; D002245:Carbon Dioxide; D019344:Lactic Acid; D007530:Isoflurane; D005947:Glucose; D010100:Oxygen