Adverse Behavioral Changes in Adult Mice Following Neonatal Repeated Exposure to Pain and Sucrose

Sucrose is recommended for the treatment of pain during minor procedures in preterm infants in the neonatal intensive care unit (NICU) and is currently used worldwide as the standard of care. We recently reported that adult mice repetitively exposed to sucrose compared to water during the first week of life, irrespective of exposure to an intervention, had significantly smaller brain volumes in large white matter, cortical and subcortical structures (e.g., hippocampus, striatum, fimbria). These structures are important for stress regulation and memory formation. Here, we report the effects of repeated neonatal exposure to pain and sucrose on adult behavior in mice. Neonatal C57BL/6J mice (N = 160, 47% male) were randomly assigned to one of two treatments (sucrose, water) and one of three interventions (needle-prick, tactile, handling). Pups received 10 interventions daily from postnatal day 1 (P1) to P6. A single dose of 24% sucrose or water was given orally 2 min before each intervention. At adulthood (P60-85) mice underwent behavioral testing to assess spatial memory, anxiety, motor function, pain sensitivity, and sugar preference. We found that mice that had received sucrose and handling only, had poorer short-term memory in adulthood compared to water/handling controls (p < 0.05). When exposed to pain, mice treated with repetitive sucrose or water did not differ on memory performance (p = 0.1). A sugar preference test showed that adult mice that received sucrose before an intervention as pups consumed less sugar solution compared to controls or those that received water before pain (p < 0.05). There were no significant group differences in anxiety, motor, or pain sensitivity. In a mouse model that closely mimics NICU care, we show for the first time that memory in adulthood was poorer for mice exposed to pain during the first week of life, irrespective of sucrose treatment, suggesting that sucrose does not protect memory performance when administered for pain. In the absence of pain, early repetitive sucrose exposure induced poorer short-term memory, highlighting the importance of accurate pain assessment

Neonatal Pain-Related Stress Predicts Cortical Thickness at Age 7 Years in Children Born Very Preterm

Background Altered brain development is evident in children born very preterm (24–32 weeks gestational age), including reduction in gray and white matter volumes, and thinner cortex, from infancy to adolescence compared to term-born peers. However, many questions remain regarding the etiology. Infants born very preterm are exposed to repeated procedural pain-related stress during a period of very rapid brain development. In this vulnerable population, we have previously found that neonatal pain-related stress is associated with atypical brain development from birth to term-equivalent age. Our present aim was to evaluate whether neonatal pain-related stress (adjusted for clinical confounders of prematurity) is associated with altered cortical thickness in very preterm children at school age. Methods 42 right-handed children born very preterm (24–32 weeks gestational age) followed longitudinally from birth underwent 3-D T1 MRI neuroimaging at mean age 7.9 yrs. Children with severe brain injury and major motor/sensory/cognitive impairment were excluded. Regional cortical thickness was calculated using custom developed software utilizing FreeSurfer segmentation data. The association between neonatal pain-related stress (defined as the number of skin-breaking procedures) accounting for clinical confounders (gestational age, illness severity, infection, mechanical ventilation, surgeries, and morphine exposure), was examined in relation to cortical thickness using constrained principal component analysis followed by generalized linear modeling. Results After correcting for multiple comparisons and adjusting for neonatal clinical factors, greater neonatal pain-related stress was associated with significantly thinner cortex in 21/66 cerebral regions (p-values ranged from 0.00001 to 0.014), predominately in the frontal and parietal lobes. Conclusions In very preterm children without major sensory, motor or cognitive impairments, neonatal pain-related stress appears to be associated with thinner cortex in multiple regions at school age, independent of other neonatal risk factors

Constrained principal component analysis loadings for the 7 neonatal clinical factors to explain variance in cortical thickness.

<p>Predictor loadings were computed as correlations between component scores and the set of neonatal clinical variables.</p><p>C.I. = 95% confidence interval; Pain = number of skin-breaking procedures exposure; Morphine = cumulative daily dose in milligrams adjusted for daily body weight; Ventilation = number of days on mechanical ventilation; Surgery = number of surgeries; Infection = number of culture proven infection; SNAP-II = score for neonatal acute physiology; GA = gestational age.</p>†<p><i>p</i>-value threshold for significance adjusted for multiple comparisons with a false discovery rate (FDR) correction set at 5%; <i>p</i>-values and confidence intervals were computed by bootstrapping 1000 times.</p

GENLIN results for the 21/66 cortical regions significantly associated with neonatal pain-related stress (adjusted for clinical confounders).

<p>R, right hemisphere; L, left hemisphere; Infection = number of culture proven infection; Pain = number of skin-breaking procedures exposure; Ventilation = number of days on mechanical ventilation; Morphine = cumulative daily dose in milligrams adjusted for daily body weight; SNAP-II = score for neonatal acute physiology; Surgery = number of surgeries; GA = gestational age.</p><p>B values are unstandardized. Number of days on mechanical ventilation was winsorized (replaced the outlier value with the closest value within the ±3 standard deviation range) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0076702#pone.0076702-Tukey1" target="_blank">[84]</a>.</p>†<p>Bold text represents statistical significance; <i>p</i>-value threshold for significance adjusted for multiple comparisons with a false discovery rate (FDR) correction set at 5%.</p