Rats exposed to isoflurane in utero during early gestation are behaviorally abnormal as adults

Abstract

Background: Preclinical evidence suggests that commonly used anesthetic agents induce long-lasting neurobehavioral changes when administered early in life, but there has been virtually no attention to the neurodevelopmental consequences for the fetus of maternal anesthesia. This study tested the hypothesis that fetal rats exposed to isoflurane during maternal anesthesia on gestational day 14, which corresponds to the second trimester in humans, would be behaviorally abnormal as adults.

Methods: Timed, pregnant rats were randomly assigned on gestational day 14 to receive 1.4% isoflurane in 100% oxygen (n = 3) or 100% oxygen (n = 2) for 4 h. Beginning at 8 weeks of age, male offspring (N = 12-14 in control and anesthesia groups, respectively) were evaluated for spontaneous locomotor activity, hippocampal-dependent learning and memory (i.e., spontaneous alternations, novel object recognition, and radial arm maze), and anxiety (elevated plus maze).

Results: Isoflurane anesthesia was physiologically well tolerated by the dams. Adult rats exposed prenatally to isoflurane were not different than controls on spontaneous locomotor activity, spontaneous alternations, or object recognition memory, but made more open arm entries on the elevated plus maze and took longer and made more errors of omission on the radial arm maze.

Conclusions: Rats exposed to isoflurane in utero at a time that corresponds to the second trimester in humans have impaired spatial memory acquisition and reduced anxiety, compared with controls. This suggests the fetal brain may be adversely affected by maternal anesthesia, and raises the possibility that vulnerability to deleterious neurodevelopmental effects of isoflurane begins much earlier in life than previously recognized.

Figure 1

Maternal weight at the time of anesthesia (E 14) and one day before delivery (E 21). There were no differences between the groups (P > 0.05). Data are expressed as mean ± SEM for 2 control and 3 anesthetized dams.

Figure 2

Spontaneous locomotor activity. There were no differences in either the distance traveled (Panel A) or the mean speed (Panel B) between adult rats exposed to isoflurane in utero (N = 14) and age-matched controls (N = 12) (P = 0.07 and 0.06, respectively). Data are expressed as mean ± SEM.

Figure 3

Spontaneous alternation behavior. Adult rats exposed to isoflurane in utero (N = 14) were no different than controls (N = 12) either in the number of arm entries (P = 0.03, not significant after Benjamini-Hochberg correction) or in the percent alternation score, calculated by dividing the actual number of alternations by the number of possible alternations (not shown). Data are expressed as mean ± SEM.

Figure 4

Performance in the elevated plus maze. Adult rats exposed to isoflurane in utero (N = 13) made more open arm entries (P = 0.005, significant after Benjamini-Hochberg correction; Panel A) though there were no differences in the time spent in the open arms (P = 0.02, not significant; Panel B) compared to controls (N = 11). Data are expressed as mean ± SEM.

Figure 5

Performance on the radial arm maze. There were no differences in the total number of arm entries on the maze between the groups but animals exposed to isoflurane in utero (N = 14) made more omission errors than the controls (N = 11; P = 0.005, significant after Benjamini-Hochberg correction)(A). On time to complete the maze (B), there was an effect of anesthesia condition (P = 0.001, significant after Benjamini-Hochberg correction), with rats exposed to isoflurane in utero taking longer to complete the maze than age-matched controls. There were no differences in the number of choices made before the first error in both groups (P = 0.03; C). Data are expressed as mean ± SEM and were analyzed using linear mixed models in which anesthetic condition (control or anesthetized) was modeled as a fixed effect and dam was modeled as a random, repeated-measures effect to account for non-independence of observations among pups born to the same dam.