Background: Recent studies in rodents suggest that repeated and prolonged anesthetic exposure at early stages of development leads to cognitive and behavioral impairments later in life. However, the underlying mechanism remains unknown. In this study, we tested whether exposure to general anesthesia during early development will disrupt the maturation of synaptic circuits and compromise learning-related synaptic plasticity later in life.
Methods: Mice received ketamine-xylazine (20/3 mg/kg) anesthesia for one or three times, starting at either early (postnatal day 14 [P14]) or late (P21) stages of development (n = 105). Control mice received saline injections (n = 34). At P30, mice were subjected to rotarod motor training and fear conditioning. Motor learning-induced synaptic remodeling was examined in vivo by repeatedly imaging fluorescently labeled postsynaptic dendritic spines in the primary motor cortex before and after training using two-photon microscopy.
Results: Three exposures to ketamine-xylazine anesthesia between P14 and P18 impair the animals' motor learning and learning-dependent dendritic spine plasticity (new spine formation, 8.4 ± 1.3% [mean ± SD] vs. 13.4 ± 1.8%, P = 0.002) without affecting fear memory and cell apoptosis. One exposure at P14 or three exposures between P21 and P25 has no effects on the animals' motor learning or spine plasticity. Finally, enriched motor experience ameliorates anesthesia-induced motor learning impairment and synaptic deficits.
Conclusions: Our study demonstrates that repeated exposures to ketamine-xylazine during early development impair motor learning and learning-dependent dendritic spine plasticity later in life. The reduction in synaptic structural plasticity may underlie anesthesia-induced behavioral impairment.