Effects Of Neonatal Repetitive Procedural Pain On Emotion And Cognition And Its Mechanism

Pain is referred as an unpleasant sensory and emotional experience associated with actual or potential tissue damage,or described in terms of such damage.With medical and technological progress,the survival of infants born extremely premature has increased substantially.As part of their life-saving care,these infants are often exposed to uncontroled repetitive invasive procedures,causing acute pain in the neonatal period.Exposing to repetitive and prolonged procedure pain can not only alter pain responsiveness,impair the behavioral development,and cause emotional and cognitive abnormity,but also can become heavy burden to the family and society.So it has been a great challenge to explore the impacts of neonatal repetitive procedural pain on children health and underlying mechanism as well as improve the perceptions of pain management among pediatrician and nurses,thus to establish neonatal pain management guideline in China.In children population,the behavioral development parallels with the neuropsychological development.Since the behavioral development is a reflection of maturation of central nervous system especially brain,the structure and function of brain can be affected by various biological and environmental factors.Early period of life is a critical window for brain development,which is of great plasticity.The central nervous system is more vulnerable for preterm infants.Early life adverse experiences such as early child abuse,maternal separation,low maternal care and perinatal stress cause permanent modification of phenotype including learning,memory,cognition and emotion in adulthood.Hippocampus,as a part of limbic system,plays an important role in these changes mentioned above.However,the effect of neonatal repetitive procedural pain on the cognition,emotion and its mechanism is not yet clear.Given a large amount of neonatal procedural pain occurs in the critical time of brain development,we aim to investigate the effects of neonatal pain on children behavioral development and underlying mechanism in this study.We used the animal model to analyze the alternations in behavior,hippocampal synaptic plasticity and neurotransmitters after neonatal repetitive needle stick pain exposure in pubertal and adult rats.The findings will help to enhance the medical personnel's perceptions regarding long-term consequences of pain in human neonates,thus providing scientific evidences for early prevention and intervene of neonatal pain.ObjectiveUse animal models,examine the effects of neonatal repetitive procedural pain on emotional and cognition behavior,the hippocampal synaptic plasticity and neurotransmitters in prepubertal and adult rats.Methods SPF pregnant Sprague-Dawley(SD)rats were used.Male rat pups were randomly assigned to either group.Neonatal rat pups were stimulated four times each day on postnatal days 0-7(P0-P7),by either needle stick(Needle group)or cotton-tipped swab(Tactile group).Mechanical sensitivity was tested by the von Frey mechanical test.All subjects were tested on P24 and P87 for behavioral tests such as trace fear conditioning test for learning and memory,as well as Open Field(OF),Tail Suspension Test and Forced Swimming Test for anxiety-and depression-like behavior.Long-term potentiation(LTP)of hippocampus was recorded for hippocampal synaptic plasticity.5-HT and 5-HIAA levels were tested by HPLC.Expression of mRNA and protein of NR1?GluR1?NR2A?NR2B is tested by PCR and WB.Results1.From P8 to P85,mechanical hypersensitivity of the bilateral hind paws was observed in the Needle group than the Tactile group.2.Training:Needle group showed significant fewer freezing behavior in training period in 12 weeks,but no difference in 3 weeks.Contextual FC:Needle group rat exhibited fewer contextual freezing behavior(24h post-training)in both 3w and 12w,and showed fewer freezing behavior in novel context(48h post-training)in 12w.Trace fear conditioning was also affected in Needle/Tactile rat,Needle rat showed fewer freezing behavior in both 3w and 12w.3.The distance in inner and outer area,the speed in outer area and number in inner area were significantly increased in the Needle group than the Tactile group in 3w in the OF.Also the duration and distance in inner area,number and speed both in inner and outer area were significantly increased in the Needle group compared with the Tactile group in 12w in the OF.Further more,the immobility time for the Needle group was significantly longer than the Tactile group in 3w but not in 12w in the Tail suspension test.4.There was a significant decrease in LTP induced by high frequency stimulation(HFS)in the CA1 region of hippocampal slices in Needle group rat compare to Tactile group rat in both 3 w and 12w.The hippocampal NR1?GluR1?NR2A?NR2B mRNA and protein expression were significantly decreased in the Needle group compared to the Tactile group in 3w and 12w.5.The Needle group rats showed a decrease in 5-HT level while an increase in 5-HIAA level in hippocampus in 3w and both decreased in 12w.The Needle group rats show a decrease of HVA,DOPAC and 5-HIAA level of CSF in 3w,but an increase in 12w.The hippocampal 5-HT1A and 5-HT7R mRNA expression are significantly decreased in the Needle group compared to the Tactile group in 3 w and 12w.ConclusionNeonatal repetitive procedural pain causes persistent mechanical hypersensitivity,impairs learning ability,and persistent anxiety-and depression-like behavior from prepuberty to adulthood,along with dysfunction in hippocampal synaptic plasticity and 5-HT and DA metabolism.