Evaluation of spinal toxicity and long-term spinal reflex function after intrathecal levobupivaciane in the neonatal rat

Background: Neuraxial anesthesia is utilized in children of all ages. Local anesthetics produce dose-dependent toxicity in certain adult models, but the developing spinal cord may also be susceptible to drug-induced apoptosis. In postnatal rodents, we examined the effects of intrathecal levobupivacaine on neuropathology and long-term sensorimotor outcomes. Methods: Postnatal day 3 (P3) or P7 rat pups received intrathecal levobupivacaine 2.5 mg/kg (0.5%) or saline. Mechanical withdrawal thresholds and motor block were assessed. Spinal cord tissue analysis included apoptosis counts (activated caspase-3, Fluoro-Jade C) at 24 h, glial reactivity at 7 days, and histopathology in cord and cauda equina at 24 h and 7 days. Long-term spinal function in young adults (P35) was assessed by hind limb withdrawal thresholds, electromyography responses to suprathreshold stimuli, and gait analysis. Results: Intrathecal levobupivacaine produced spinal anesthesia at P3 and P7. No increase in apoptosis or histopathological change was seen in the cord or cauda equina. In the P3 saline group, activated caspase-3 (mean ± SEM per lumbar cord section 6.1 ± 0.3) and Fluoro-Jade C (12.1 ± 1.2) counts were higher than at P7, but were not altered by levobupivacaine (P = 0.62 and P = 0.11, two-tailed Mann-Whitney test). At P35, mechanical withdrawal thresholds, thermal withdrawal latency, and electromyographic reflex responses did not differ across P3 or P7 levobupivacaine or saline groups (one way ANOVA with Bonferroni comparisons). Intrathecal bupivacaine at P3 did not alter gait. Conclusion: Single dose intrathecal levobupivacaine 0.5% did not increase apoptosis or produce spinal toxicity in neonatal rat pups. This study provides preclinical safety data relevant to neonatal use of neuraxial local anesthesia.