Long-Term Consequences of Neonatal Injury

Infant pain vs. pain with parental suppression: Immediate and enduring impact on brain, pain and affect

BACKGROUND

In the short term, parental presence while a human infant is in pain buffers the immediate pain responses, although emerging evidence suggests repeated social buffering of pain may have untoward long-term effects.

METHODS/FINDING

To explore the short- and long-term impacts of social buffering of pain, we first measured the infant rat pup's [postnatal day (PN) 8, or 12] response to mild tail shock with the mother present compared to shock alone or no shock. Shock with the mother reduced pain-related behavioral activation and USVs of pups at both ages and reduced Fos expression in the periaqueductal gray, hypothalamic paraventricular nucleus, and the amygdala at PN12 only. At PN12, shock with the mother compared to shock alone differentially regulated expression of several hundred genes related to G-protein-coupled receptors (GPCRs) and neural development, whereas PN8 pups showed a less robust and less coherent expression pattern. In a second set of experiments, pups were exposed to daily repeated Shock-mother pairings (or controls) at PN5-9 or PN10-14 (during and after pain sensitive period, respectively) and long-term outcome assessed in adults. Shock+mother pairing at PN5-9 reduced adult carrageenan-induced thermal hyperalgesia and reduced Fos expression, but PN10-14 pairings had minimal impact. The effect of infant treatment on adult affective behavior showed a complex treatment by age dependent effect. Adult social behavior was decreased following Shock+mother pairings at both PN5-9 and PN10-14, whereas shock alone had no effect. Adult fear responses to a predator odor were decreased only by PN10-14 treatment and the infant Shock alone and Shock+mother did not differ.

CONCLUSIONS/SIGNIFICANCE

Overall, integrating these results into our understanding of long-term programming by repeated infant pain experiences, the data suggest that pain experienced within a social context impacts infant neurobehavioral responses and initiates an altered developmental trajectory of pain and affect processing that diverges from experiencing pain alone.

Developmental impact of peripheral injury on neuroimmune signaling

A peripheral injury drives neuroimmune interactions at the level of the injury and throughout the neuraxis. Understanding these systems will be beneficial in the pursuit to target persistent pain that involves both neural and immune components. In this review, we discuss the impact of injury on the development of neuroimmune signaling, along with data that suggest a possible cellular immune memory. We also discuss the parallel effects of injury in the nervous system and immune related areas including bone marrow, lymph node and central nervous system-related cells. Finally, we relate these findings to patient populations and current research that evaluates human tissue.

Sestrin2 prevents neonatal incision pain and re-incision enhanced hyperalgesia in adult rats

BACKGROUND

Improving the methods for recognizing pain is important for infants admitted to the neonatal intensive care unit. Sestrin2 is a novel stress-inducible protein with a neuroprotective role that functions as a molecular mediator of hormesis. Nevertheless, the role of sestrin2 in the pain process is still unclear. The following study examined the role of sestrin2 on mechanical hypersensitivity after pups incision, as well as enhanced pain hyperalgesia after adulthood re-incision in rats.

METHODS

The experiment was divided into two parts: (1) studying the effect of sestrin2 in the neonatal incision; (2) studying the priming effect in adulthood re-incision. An animal model was established in seven-day-old rat pups with a right hind paw incision. Pups were intrathecally administrated rh-sestrin2 (exogenous sestrin2). Paw withdrawal threshold testing was performed to assay mechanical allodynia; tissue was analyzed in ex vivo using Western blot and immunofluorescence. SB203580 was further used to inhibit microglial function and evaluate the sex-dependent effect in adulthood.

RESULTS

Sestrin2 expression increased transitorily in the spinal dorsal horn in pups after incision. Administration of rh-sestrin2 improved pups' mechanical hypersensitivity by regulating the AMPK/ERK pathway and alleviated re-incision-induced enhanced hyperalgesia in male and female adult rats. After administration of SB203580 in pups, the mechanical hyperalgesia following re-incision in adult rats was prevented in males but not females; however, the protective effect of SB203580 in males was counteracted by silencing sestrin2.

CONCLUSIONS

These data suggest that sestrin2 prevents neonatal incision pain and re-incision enhanced hyperalgesia in adult rats. Moreover, microglia inhibition affects enhanced hyperalgesia only in adult males, which may be regulated through the sestrin2 mechanism. To sum up, these sestrin2 data may be a potential common molecular target for treating re-incision hyperalgesia in different sexes.

Neonatal injury modulates incisional pain sensitivity in adulthood: An animal study

Neonatal pain experiences including traumatic injury influences negatively on development of nociceptive circuit developments, resulting in persistent pain hypersensitivity in adults. However, the detailed mechanism is not yet well understood. In the present study, to clarify the pathogenesis of orofacial pain hypersensitivity associated with neonatal injury, the involvement of the voltage-gated sodium channel (Na_v) 1.8 and the C-C chemokine ligand 2 (CCL2)/C-C chemokine receptor 2 (CCR2) signaling in the trigeminal ganglion (TG) in facial skin incisional pain hypersensitivity was examined in 190 neonatal facial-injured and sham male rats. The whisker pad skin was incised on postnatal day 4 and week 7 (Incision-Incision group). Compared to the group without neonatal incision (Sham-Incision group), mechanical hypersensitivity in the whisker pad skin was enhanced in Incision-Incision group. The number of Na_v1.8-immunoreactive TG neurons and the amount of CCL2 expressed in the macrophages and satellite glial cells in the TG were increased on day 14 after re-incision in the Incision-Incision group, compared with Sham-Incision group. Blockages of Na_v1.8 in the incised region and CCR2 in the TG suppressed the enhancement of mechanical hypersensitivity in the Incision-Incision group. Administration of CCL2 into the TG enhanced mechanical hypersensitivity in the Sham-Sham, Incision-Sham and Sham-Incision group. Our results suggest that neonatal facial injury accelerates the TG neuronal hyperexcitability following orofacial skin injury in adult in association with Na_v1.8 overexpression via CCL2 signaling, resulting in the enhancement of orofacial incisional pain hypersensitivity in the adulthood.

Early life nociceptive stimulus and fentanyl exposure increase hippocampal neurogenesis and anxiety but do not affect spatial learning and memory

This study aimed to determine whether preemptive fentanyl administration in neonatal rats reduces the impact of a nociceptive stimulus initiated during the first day of life (P1) on hippocampal neurogenesis, behavior, and learning. At P1, Wistar rat pups received either a subcutaneous injection of fentanyl (F) before intraplantar injection of complete Freund’s adjuvant (CFA) (CFA + F group), an isolated injection of CFA (CFA group), or subcutaneous injection of fentanyl without CFA injection (F). Control animals received saline injections using the same route and volume as the treatment groups. Hippocampal neurogenesis was evaluated by 5′ –bromo-2′-deoxyuridine (BrdU) staining on P10 and P39 to assess neuronal proliferation and survival, respectively. Anxiety behavior in adulthood was assessed using an open field test (OF) and an elevated plus maze test (EPM). Spatial memory was assessed on a Morris water maze test (MWM), where the animals were trained for seven days, beginning on P81, and the probe trial was performed to evaluate memory retention. Although the CFA + F group showed an increased number of proliferative cells on P10, this finding did not persist on P39. The CFA + F group spent more time in the closed arms in the EPM, revealing more anxious behavior, although the early noxious experience, both with and without fentanyl, did not alter neurogenesis in adolescence and learning in adulthood. This study highlights that the impact of pain in early life pain combined with fentanyl on hippocampal neurogenesis on P10 did not persist on P39. In addition, this combined intervention during the first week of life was associated with higher anxiety levels.

Evidence-Based Nursing Practices for the Prevention of Newborn Procedural Pain in Neonatal Intensive Therapy-An Exploratory Study

BACKGROUND

Due to the progress in neonatology, in particular, in the past three decades, the mortality rate among patients of intensive care units has decreased. However, this is connected not only with newborns needing to stay longer in the unit, but also with the exposure of newborns to many painful procedures and stresses. Lack of or insufficient pain prevention has a negative impact on the sensory or locomotor development of newborns. Despite the presence of guidelines based on scientific evidence, the use of pharmacological and non-pharmacological pain-management methods in newborns is still insufficient.

AIM

The aim of the study was to: identify the knowledge nurses/midwives have of recommended non-pharmacological and/or pharmacological methods, in particular, in relation to medical intervention procedures; assess the interventions for pain relief applied by midwives/nurses most often in their clinical practice; examine the role of age, general work experience, education level and years of work of medical professionals on a neonatal ward, as well as the referral level of a unit, versus the application of pharmacological and non-pharmacological methods.

METHODS

A descriptive and quantitative study conducted in 2019 among Polish nurses/midwives working at neonatal intensive care units.

RESULTS

The analysis of the material reflected the deficit of knowledge and the insufficient daily use of recommended pain-relief measures among the respondents.

CONCLUSIONS

The interpretation of data indicates that despite the clear and easily available recommendations of scientific societies concerning the mode of conduct in particular medical procedures, medical personnel do not apply those recommendations in their everyday practice. It is necessary to plan and implement education strategies for nurses/midwives on standard pain-management interventions during painful medical procedures.

Selective Targeting of Serotonin 5-HT1a and 5-HT3 Receptors Attenuates Acute and Long-Term Hypersensitivity Associated With Neonatal Procedural Pain

Neonatal painful procedures causes acute pain and trigger long-term changes in nociceptive processing and anxiety behavior, highlighting the need for adequate analgesia during this critical time. Spinal serotonergic receptors 5-HT1a and 5-HT3 play an important role in modulating incoming nociceptive signals in neonates. The current study aims to attenuate acute and long-term hypersensitivity associated with neonatal procedural pain using ondansetron (a 5-HT3 antagonist) and buspirone (a 5-HT1a agonist) in a well-established rat model of repetitive needle pricking. Sprague-Dawley rat pups of both sexes received ondansetron (3 mg/kg), buspirone (3 mg/kg) or saline prior to repetitive needle pricks into the left hind-paw from postnatal day 0-7. Control animals received tactile stimulation or were left undisturbed. Acute, long-term, and post-operative mechanical sensitivity as well as adult anxiety were assessed. Neonatal 5-HT1a receptor agonism completely reverses acute hypersensitivity from P0-7. The increased duration of postoperative hypersensitivity after re-injury in adulthood is abolished by 5-HT3 receptor antagonism during neonatal repetitive needle pricking, without affecting baseline sensitivity. Moreover, 5-HT1a and 5-HT3 receptor modulation decreases adult state anxiety. Altogether, our data suggests that targeted pharmacological treatment based on the modulation of spinal serotonergic network via the 5-HT1a and 5-HT3 receptors in neonates may be of use in treatment of neonatal procedural pain and its long-term consequences. This may result in a new mechanism-based therapeutic venue in treatment of procedural pain in human neonates.

Early Life Painful Procedures: Long-Term Consequences and Implications for Farm Animal Welfare

Farm animals routinely undergo painful husbandry procedures early in life, including disbudding and castration in calves and goat kids, tail docking and castration in piglets and lambs, and beak trimming in chicks. In rodents, inflammatory events soon after birth, when physiological systems are developing and sensitive to perturbation, can profoundly alter phenotypic outcomes later in life. This review summarizes the current state of research on long-term phenotypic consequences of neonatal painful procedures in rodents and farm animals, and discusses the implications for farm animal welfare. Rodents exposed to early life inflammation show a hypo-/hyper-responsive profile to pain-, fear-, and anxiety-inducing stimuli, manifesting as an initial attenuation in responses that transitions into hyperresponsivity with increasing age or cumulative stress. Neonatal inflammation also predisposes rodents to cognitive, social, and reproductive deficits, and there is some evidence that adverse effects may be passed to offspring. The outcomes of neonatal inflammation are modulated by injury etiology, age at the time of injury and time of testing, sex, pain management, and rearing environment. Equivalent research examining long-term phenotypic consequences of early life painful procedures in farm animals is greatly lacking, despite obvious implications for welfare and performance. Improved understanding of how these procedures shape phenotypes will inform efforts to mitigate negative outcomes through reduction, replacement, and refinement of current practices.

Model-Informed Bayesian Estimation Improves the Prediction of Morphine Exposure in Neonates and Infants

BACKGROUND

Pain control in infants is an important clinical concern, with potential long-term adverse neurodevelopmental effects. Intravenous morphine is routinely administered for postoperative pain management; however, its dose-concentration-response relationship in neonates and infants has not been well characterized. Although the current literature provides dosing guidelines for the average infant, it fails to control for the large unexplained variability in morphine clearance and response in individual patients. Bayesian estimation can be used to control for some of this variability. The authors aimed to evaluate morphine pharmacokinetics (PKs) and exposure in critically ill neonates and infants receiving standard-of-care morphine therapy and compare a population-based approach to the model-informed Bayesian techniques.

METHODS

The PKs and exposure of morphine and its active metabolites were evaluated in a prospective opportunistic PK study using 221 discarded blood samples from 57 critically ill neonates and infants in the neonatal intensive care unit. Thereafter, a population-based PK model was compared with a Bayesian adaptive control strategy to predict an individual's PK profile and morphine exposure over time.

RESULTS

Among the critically ill neonates and infants, morphine clearance showed substantial variability with a 40-fold range (ie, 2.2 to 87.1, mean 23.7 L/h/70 kg). Compared with the observed morphine concentrations, the population-model based predictions had an R of 0.13, whereas the model-based Bayesian predictions had an R of 0.61.

CONCLUSIONS

Model-informed Bayesian estimation is a better predictor of morphine exposure than PK models alone in critically ill neonates and infants. A large variability was also identified in morphine clearance. A further study is warranted to elucidate the predictive covariates and precision dosing strategies that use morphine concentration and pain scores as feedbacks.

Safety and effectiveness of parent- or nurse-controlled analgesia in neonates: a systematic review

OBJECTIVE

The aim of this systematic review was to determine the safety and effectiveness of parent- or nurse-controlled analgesia on neonatal patient outcomes. More specifically, the objective was to determine the effect of parent- or nurse-controlled analgesia on neonatal pain scores, analgesic use, and incidence of iatrogenic withdrawal syndrome, as well as any opioid-associated adverse events.

INTRODUCTION

Despite recent innovations in neonatology leading to significant improvements in short- and long-term outcomes for newborns requiring intensive care, optimal management of pain and distress remains a challenge for the treating multidisciplinary team. The inability of neonates to communicate pain easily, inconsistent practice among health professionals, insufficient analgesic prescriptions, and delays in medical reviews all impact effective pain management. Exploring the effect of parent- or nurse-controlled analgesia may identify a modality that negates these concerns and improves the pharmacological management of pain in newborns.

INCLUSION CRITERIA

This review considered experimental and observational studies evaluating the safety and effectiveness of parent- or nurse-controlled analgesia that included babies born at 23 weeks' gestation to four weeks post-term. The interventions considered for inclusion were any type of analgesia delivered by an infusion pump that allowed bolus dosing or a continuous analgesic infusion with bolus dosing as required. Studies using algorithms and protocols to guide timing and dosage were eligible for inclusion. Comparators included the standard management of pain for neonates in the newborn intensive care unit. A modification to the a priori protocol was made to include all neonates nursed outside of a neonatal intensive care unit to ensure all studies that examined the use of parent- or nurse-controlled analgesia in the neonatal population were included in the review.

METHODS

An extensive search of six major databases was conducted (CINAHL, Cochrane Library, Embase, PubMed, PsycINFO, and Web of Science). Studies published from 1997 to 2020 in English were considered for inclusion in this review. Databases searched for unpublished studies included MedNar and ProQuest Dissertations and Theses.

RESULTS

Fourteen studies were included in this review: two randomized controlled trials, six quasi-experimental studies, one case-control study, and five case series. There was considerable heterogeneity in the interventions and study outcome measures within the studies, resulting in an inability to statistically pool results. The small sample sizes and inability to distinguish data specific to neonates in six of the studies resulted in low quality of evidence for the safety and effectiveness of parent- or nurse-controlled analgesia in neonates. However, studies reporting neonatal data demonstrated low pain scores and a trend in reduced opioid consumption when parent- or nurse-controlled analgesia was used.

CONCLUSIONS

The use of parent- or nurse-controlled analgesia in the neonatal population has shown some effect in reducing the amount of opioid analgesia required without compromising pain relief or increasing the risk of adverse events. Due to the paucity of evidence available, certainty of the results is compromised; therefore, larger trials exploring the use of parent- or nurse-controlled analgesia in neonates and the development of nurse-led models for analgesia delivery are needed.

SYSTEMATIC REVIEW REGISTRATION NUMBER

PROSPERO CRD42018114382.

Microglial activation in the trigeminal spinal subnucleus interpolaris/caudalis modulates orofacial incisional mechanical pain hypersensitivity associated with orofacial injury in infancy

PURPOSE

Infantile tissue injury induces sensory deficits in adulthood. Infantile facial incision (IFI) was reported to cause an enhancement of incision-induced mechanical hypersensitivity in adulthood due to acceleration of the trigeminal ganglion neuronal excitability. However, the effects of IFI on activation of microglia in the spinal trigeminal nucleus and its involvement in facial pain sensitivity is not well known.

METHODS

A facial skin incision was made in the left whisker pad in infant (IFI) and/or adult rats (AFI). Mechanical head withdrawal threshold and microglial activation in the trigeminal spinal nucleus were analyzed.

RESULTS

Mechanical pain hypersensitivity induced by AFI was significantly exacerbated and prolonged by IFI. The number of Iba1-immunoreactive cells in the trigeminal spinal nucleus following AFI was increased by IFI, suggesting that IFI facilitates microglial hyperactivation following AFI. Intraperitoneal administration of minocycline, a microglial activation inhibitor, suppressed the facial incision-induced microglial hyperactivation in the trigeminal spinal nucleus and the exacerbation of the facial mechanical pain hypersensitivity induced by IFI.

CONCLUSION

These results suggest that facial trauma in infants causes hyperactivation of microglia in the trigeminal spinal nucleus following AFI, leading to the prolongation of the facial mechanical pain hypersensitivity.

Tapentadol for the Treatment of Moderate-to-Severe Acute Pain in Children Under the Age of Two Years

Background

Pharmacokinetics (PK), efficacy, and safety of the opioid analgesic tapentadol in the treatment of moderate-to-severe acute pain have so far not been investigated in pediatric patients <2 years of age.

Patients and Methods

Two multicenter, open-label trials assessed the pharmacokinetic profile, safety, tolerability, and efficacy of single doses of tapentadol oral solution (OS; NCT02221674; n=19) or intravenous infusion (IV, EudraCT 2014-002259-24; n=38) in children from birth to <2 years of age. Of these, 8 preterm neonates were included in the IV trial. A third randomized, double-blind, placebo-controlled trial (NCT02081391) investigated the efficacy and safety of multiple tapentadol OS doses in patients from birth to <2 years (placebo n=4, tapentadol n=11) using an immediate rescue trial design. Patients in all three trials underwent surgery that, in the investigator’s opinion, reliably produced moderate-to-severe pain requiring opioid treatment.

Results

Administration of single tapentadol doses resulted in tapentadol serum concentrations within the targeted range known to be safe and efficacious in adults and compared well to the range observed for children aged 2 to <18 years. Pain intensity already improved 15 min after administration. In the multiple dose trial, amounts of supplemental opioid analgesic medication within the first 24 h after start of trial medication were low (placebo 0.02 mg/kg, tapentadol 0.05 mg/kg). All patients stopped treatment with the trial medication because opioid analgesics were no longer required. Treatment-emergent adverse events occurred in 42.1% (tapentadol OS single dose), 28.9% (tapentadol IV), and 75% of placebo and 54.5% of tapentadol patients (tapentadol OS multiple doses), none of them serious.

Conclusion

Tapentadol showed a favorable PK and safety profile in children <2 years of age. Multiple tapentadol OS dosing is efficacious and generally well tolerated in children ≥2 years and might also be a useful treatment option for children <2 years in need of strong analgesics.

Neonatal complete Freund's adjuvant-induced inflammation does not induce or alter hyperalgesic priming or alter adult distributions of C-fibre dorsal horn innervation

Introduction:

Inflammation during the neonatal period can exacerbate pain severity following reinjury in adulthood. This is driven by alterations in the postnatal development of spinal and supraspinal nociceptive circuitry. However, the contribution of alterations in peripheral nociceptor function remains underexplored.

Objectives:

We examined whether neonatal complete Freund's adjuvant (CFA)-induced inflammation induced or altered adult development of hyperalgesic priming (inflammation-induced plasticity in nonpeptidergic C fibres) or altered postnatal reorganization of calcitonin gene-related peptide (CGRP)-expressing and isolectin B4 (IB4)-binding C fibres in the spinal dorsal horn (DH).

Methods:

After intraplantar injection of CFA at postnatal day (P) 1, we assessed mechanical thresholds in adult (P60) rats before and after intraplantar carrageenan. One week later, intraplantar PGE₂-induced hypersensitivity persisting for 4 hours was deemed indicative of hyperalgesic priming. CGRP expression and IB4 binding were examined in adult rat DH after CFA.

Results:

P1 CFA did not alter baseline adult mechanical thresholds, nor did it change the extent or duration of carrageenan-induced hypersensitivity. However, this was slower to resolve in female than in male rats. Rats that previously received carrageenan but not saline were primed, but P1 hind paw CFA did not induce or alter hyperalgesic priming responses to PGE₂. In addition, CFA on P1 or P10 did not alter intensity or patterns of CGRP or IB4 staining in the adult DH.

Conclusion:

Complete Freund's adjuvant-induced inflammation during a critical period of vulnerability to injury during early postnatal development does not induce or exacerbate hyperalgesic priming or alter the broad distribution of CGRP-expressing or IB4-binding afferent terminals in the adult dorsal horn.

Neonatal morphine exposure and maternal deprivation alter nociceptive response and central biomarkers' levels throughout the life of rats

In the present study, we investigated the effect of repeated neonatal morphine exposure and/or maternal deprivation(MD) on the nociceptive response and central biomarkers' BDNF, IL-1β, and IL-4 levels at postnatal days 16(PND16), 30(PND30), and 60(PND60). At birth, the litters were standardized to contain 8 pups/dam (n = 58). From PND1 to PND10, the pups of the deprived groups were separated daily from their mothers for 3 h and divided into 5 groups: control(C), saline(S), morphine(M), deprived-saline(DS), and deprived-morphine(DM). The pups received subcutaneous injections of saline/morphine (5 μg) in the mid-scapular area between PND8 and PND14. Nociceptive responses were assessed by hot plate(HP) and tail-flick(TFL) tests and biomarker levels by ELISA. Thermal hyperalgesia(HP) was found in all assessments for the M, DS, and DM groups, and a decrease in nociceptive threshold(TFL) was found in the DS group at PND16; M and DM groups at PND30; and M, DS, and DM groups at PND60. There were interactions between treatment/deprivation/timepoint in all central biomarkers' levels. The current study indicates that neonatal exposure to morphine and MD, which occurs in the pediatric ICU, can alter the nociceptive and neuroinflammatory responses.

Effects of Massage on Postoperative Pain in Infants With Complex Congenital Heart Disease

BACKGROUND

Pain management is an essential component of care for pediatric patients following surgery. Massage reduces self-reported postoperative pain in adults with heart disease but has received little attention in postoperative pediatric patients with complex congenital heart disease (CCHD).

OBJECTIVES

The aim of the study was to evaluate the effectiveness of massage compared to a rest period on postoperative pain scores and physiological responses in infants with CCHD.

METHODS

We used a two-group randomized clinical trial design with a sample of 60 infants with CCHD between 1 day and 12 months of age following their first cardiothoracic surgery. Both groups received standard postoperative care. Group 1 received a daily 30-minute restriction of nonessential caregiving (quiet time), and Group 2 received a daily 30-minute massage. Interventions continued for seven consecutive days. Pain was measured six times daily using the Face, Legs, Activity, Cry, Consolability Pain Assessment Tool (FLACC). Average daily doses of analgesics were recorded. Heart rates (HRs), respiratory rates (RRs), and oxygen saturations (SpO2) were recorded continuously. Daily averages, pre- and postintervention FLACC scores, and physiological responses were analyzed using descriptive statistics, generalized linear mixed models repeated measures, latent growth models, and/or regression discontinuity analysis. Fentanyl-equivalent narcotic values were used as a time-varying covariate.

RESULTS

Adjusted pain scores were lower for the massage group on all days except Day 7. Overall, there were no group effects on level of pain or differential rate of change in pain. However, the massage group had lower daily pain scores with small to medium effect size differences, largest at Days 4, 5, and 6, and lower average daily HR and RR. There was little difference between groups in SpO2. Infants demonstrated immediate effects of massage, with HR and RR decreasing and oxygen saturations increasing.

DISCUSSION

This study provides beginning evidence that postoperative massage may reduce pain and improve physiological parameters in infants with congenital heart disease. This nonpharmacological adjunct to pain management may provide a particular benefit for this population by reducing demand on the cardiorespiratory system.

The effect of early burn injury on sensitivity to future painful stimuli in dairy heifers

Animals that experience painful procedures as neonates are more sensitive to pain later in life. We evaluated whether disbudding with a heated iron at 3 (n = 12), 35 (n = 9), or 56 (n = 20) d of age affected heifers’ pain responses to vaccine injections at 11 mo of age. Heifers responded to the injection procedure with struggling and changes in eye temperature and heart rate variability compared to a sham procedure the day before, and still had a heightened response 6 d later, regardless of disbudding age. However, some heart rate variability indices suggested increased sympathetic dominance in heifers disbudded at 35 d, compared to the other 2 age groups, independent of the injection procedure. We also found that heifers disbudded at 3 or 35 d had a higher mean heart rate after the injection procedure compared to those disbudded at 56 d. We conclude that: (1) heifers find injections aversive; and (2) there is some evidence that disbudding age influences autonomic nervous system activity later in life.

Early Neonatal Pain-A Review of Clinical and Experimental Implications on Painful Conditions Later in Life

Modern health care has brought our society innumerable benefits but has also introduced the experience of pain very early in life. For example, it is now routine care for newborns to receive various injections or have blood drawn within 24 h of life. For infants who are sick or premature, the pain experiences inherent in the required medical care are frequent and often severe, with neonates requiring intensive care admission encountering approximately fourteen painful procedures daily in the hospital. Given that much of the world has seen a steady increase in preterm births for the last several decades, an ever-growing number of babies experience multiple painful events before even leaving the hospital. These noxious events occur during a critical period of neurodevelopment when the nervous system is very vulnerable due to immaturity and neuroplasticity. Here, we provide a narrative review of the literature pertaining to the idea that early life pain has significant long-term effects on neurosensory, cognition, behavior, pain processing, and health outcomes that persist into childhood and even adulthood. We refer to clinical and pre-clinical studies investigating how early life pain impacts acute pain later in life, focusing on animal model correlates that have been used to better understand this relationship. Current knowledge around the proposed underlying mechanisms responsible for the long-lasting consequences of neonatal pain, its neurobiological and behavioral effects, and its influence on later pain states are discussed. We conclude by highlighting that another important consequence of early life pain may be the impact it has on later chronic pain states-an area of research that has received little attention.

Involvement of TNFα in the enhancement of hypersensitivity in the adulthood-injured face associated with facial injury in infancy

To evaluate the mechanisms underlying acceleration of hypersensitivity in the adulthood-injured face following facial injury in infants, we developed the rats model with facial skin injury in infants and adulthoods (incision + incision), and facial skin suture in infants and facial skin injury in adulthoods (sham + incision), and analyzed the mechanical head-withdrawal threshold (MHWT) of the facial skin, immunohistochemical analysis of trigeminal ganglion (TG) and the effects of intra-ganglionic administration of neutralizing ant-TNFα antibody and recombinant TNFα on nocifensive behavior. The MHWT became considerably lower in incision + incision rats than in sham + incision rats at 10-14 days after the surgery. We observed many TG neurons encircled by glial fibrillary acidic protein-immunoreactive (GFAP-IR) cells and those exhibited TNFα immunoreactivity. TNFα was also expressed in GFAP-IR cells in incision + inicision TG. TNFα protein levels and the relative number of TNFα-IR cells were significantly higher in incision + incision rats than in sham + incision rats. The MHWT was significantly recovered during the intra-ganglionic administration of neutralizing anti-TNFα antibody 4-14 days after the incision. Furthermore, the MHWT was significantly decreased in sham + incision rats following the intra-ganglionic administration of recombinant TNFα. The present findings suggest that the neuron-satellite glial cell communication via TNFα is a critical mechanism in the enhancement of mechanical hypersensitivity in the adulthood-injured face following facial injury in infants.

Current state of science in machine learning methods for automatic infant pain evaluation using facial expression information: study protocol of a systematic review and meta-analysis

INTRODUCTION

Infants can experience pain similar to adults, and improperly controlled pain stimuli could have a long-term adverse impact on their cognitive and neurological function development. The biggest challenge of achieving good infant pain control is obtaining objective pain assessment when direct communication is lacking. For years, computer scientists have developed many different facial expression-centred machine learning (ML) methods for automatic infant pain assessment. Many of these ML algorithms showed rather satisfactory performance and have demonstrated good potential to be further enhanced for implementation in real-world clinical settings. To date, there is no prior research that has systematically summarised and compared the performance of these ML algorithms. Our proposed meta-analysis will provide the first comprehensive evidence on this topic to guide further ML algorithm development and clinical implementation.

METHODS AND ANALYSIS

We will search four major public electronic medical and computer science databases including Web of Science, PubMed, Embase and IEEE Xplore Digital Library from January 2008 to present. All the articles will be imported into the Covidence platform for study eligibility screening and inclusion. Study-level extracted data will be stored in the Systematic Review Data Repository online platform. The primary outcome will be the prediction accuracy of the ML model. The secondary outcomes will be model utility measures including generalisability, interpretability and computational efficiency. All extracted outcome data will be imported into RevMan V.5.2.1 software and R V3.3.2 for analysis. Risk of bias will be summarised using the latest Prediction Model Study Risk of Bias Assessment Tool.

ETHICS AND DISSEMINATION

This systematic review and meta-analysis will only use study-level data from public databases, thus formal ethical approval is not required. The results will be disseminated in the form of an official publication in a peer-reviewed journal and/or presentation at relevant conferences.

PROSPERO REGISTRATION NUMBER

CRD42019118784.

Early Pain Exposure Influences Functional Brain Connectivity in Very Preterm Neonates

Background

Early exposure to nociceptive events may cause brain structural alterations in preterm neonates, with long-lasting consequences on neurodevelopmental outcome. Little is known on the extent to which early pain may affect brain connectivity. We aim to evaluate brain functional connectivity changes in preterm neonate that underwent multiple invasive procedures during the postnatal period, and to correlate them with the neurodevelopmental outcome at 24 months.

Methods

In this prospective case-control study, we collected information about exposure to painful events during the early postnatal period and resting-state BOLD-fMRI data at term equivalent age from two groups of preterm neonate: 33 subjected to painful procedures during the neonatal intensive care (mean gestational age 27.9 ± 1.8 weeks) and 13 who did not require invasive procedures (average gestational age 31.2 ± 2.1 weeks). A data-driven principal-component-based multivariate pattern analysis (MVPA) was used to investigate the effect of early pain exposure on brain functional connectivity, and the relationship between connectivity changes and neurodevelopmental outcome at 24 months, assessed with Griffiths, Developmental Scale-Revised: 0-2.

Results

Early pain was associated with decreased functional connectivity between thalami and bilateral somatosensory cortex, and between the right insular cortex and ipsilateral amygdala and hippocampal regions, with a more evident effect in preterm neonate undergoing more invasive procedures. Functional connectivity of the right thalamocortical pathway was related to neuromotor outcome at 24 months (P = 0.003).

Conclusion

Early exposure to pain is associated with abnormal functional connectivity of developing networks involved in the modulation of noxious stimuli in preterm neonate, contributing to the neurodevelopmental consequence of preterm birth.

The challenge of developing pain medications for children: therapeutic needs and future perspectives

It is broadly accepted that children of all age groups including (preterm) neonates and young infants can perceive pain and that there is an absolute need to treat their pain safely and effectively. The approved treatment options for children, particularly (preterm) neonates and young infants, are very limited with only a few medications specifically labelled for this population. This article presents the challenges of developing pain medications for children. A short overview gives information on pain in children, including pain perception, prevalence of pain and the long-term consequences of leaving pain untreated in this vulnerable population. Current pain management practices are briefly discussed. The challenges of conducting pediatric clinical trials in general and trials involving analgesic medications in particular within the regulatory framework available to develop these medications for children are presented. Emphasis is given to the operational hurdles faced in conducting a pediatric clinical trial program. Some suggestions to overcome these hurdles are provided based on our experience during the pediatric trial program for the strong analgesic tapentadol used for the treatment of moderate to severe acute pain.

[Evaluation of pain in children of 2, 4 and 6 months after the application of non-pharmacological analgesia methods during vaccination]

INTRODUCTION

Young children perceive pain as much, or even more than adults, and the pain may have short- and long-term consequences. The literature describes the use of non-pharmacological interventions to alleviate pain during vaccination. The aim of this study was to assess 3such interventions for analgesia during vaccination: non-nutritive sucking (NNS), breastfeeding (BF), and administration of a 50% dextrose solution (D50W).

MATERIALS AND METHODS

A prospective, non-randomised cohort study was carried out on infants aged 2, 4 and 6 months that received 1, 2, or 3 vaccines, respectively, according to the routine immunisation schedule. There were 3treatments: NNS, BF, and 2mL of D50W combined with NNS. Pain was assessed using the LLANTO scale, and the duration of crying.

RESULTS

The study included 387 infants. The mean scores in the LLANTO scale at ages 2 and 6 months were significantly lower in breastfed infants compared to infants managed with NNS (P=.025 and P<.001, respectively), or infants given D50W (P=.025 and P=.001), and the difference was not statistically significant at age 4 months (P=.21 and P=.27). There were no significant differences between infants managed with NNS and D50W at 2, 4, and 6 months (P=.66, P=.93 and P=.45, respectively). The duration of crying was significantly lower at age 6 months in breastfeed infants compared to infants managed with NNS or D50W (P=.013 and P=.017). No breastfed child (n=129) experienced side effects.

CONCLUSIONS

In infants born to term with adequate weight for gestational age, breastfeeding reduces pain on the administration of 1 or 2 vaccines. When 3 vaccines are given, the reduction is minimal. Administration of D50W does not have any additional analgesic effect in infants compared to being held by a parent combined with NNS during vaccination. BF during vaccination is not associated with any side effects.

The impact of fibromyalgia syndrome and the role of comorbidity with mood and post-traumatic stress disorder in worsening the quality of life

BACKGROUND:

The aim is to measure the association between fibromyalgia syndrome (FMS) and post-traumatic stress disorder (PTSD), mood and anxiety disorders using reliable psychiatric diagnoses according to Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV) and with a case-control design.

METHODS:

Case-control study with cases (71 consecutive female patients with FMS) and controls (284 subjects without FMS), randomly drawn after a gender- and age-matching technique from the database of an epidemiological survey. Psychiatric diagnoses were conducted according to DSM-IV and carried out by clinical staff using a structured interview (Advanced Neuropsychiatric Tools and Assessment Schedule). QoL was measured by Short Form Health Survey (SF-12).

RESULTS:

The lifetime prevalence of major depressive disorder (MDD; 43.7% vs 8.1%, p < .0001), bipolar disorder (BD; 21.1% vs 0.7%, p  < .0001), PTSD (8.4% vs 1.4%, p < .0001) and panic disorder (28.2% vs 5.6%, p < .001) was higher in people with FMS than in controls. People with FMS showed a poorer QoL than controls on the SF-12 (26.43 ± 6.04 vs 37.45 ± 5.80, p < .0001). Those with comorbidity with MDD and BD showed a mean SF-12 score of 24.75 ± 6.31 versus 29.52 ± 4.84 ( N = 25) of people with FMS without any mood disorder ( p = .002). The attributable burden of FMS in worsening QoL was found comparable to that of serious chronic diseases such as multiple sclerosis.

CONCLUSION:

FMS is a disorder that 'in itself' can have a devastating impact on an individual's life. The frequency of the association with major depressive and bipolar disorders increases the impact on the QoL of people with FMS. One of the causes of this association appears to be the extreme vulnerability to chronic stress that this disorder involves. The findings have important clinical significance: the physician must interpret in the right dimension and with dignity the suffering of the people with FMS.

Neonatal pain and stress disrupts later-life pavlovian fear conditioning and sensory function in rats: Evidence for a two-hit model

Early life trauma has been linked to increased risks for anxiety, depression, and chronic pain. We used rodent models of acute and inflammatory neonatal pain to explore effects on fear conditioning and somatosensory function. Hindpaw needle pricks or handling on postnatal days (PNDs) 1-7 caused lasting impacts on affective and somatosensory function when assessed at later ages, PNDs 24 (postweaning), 45 (adolescence), or 66 (adulthood). First, auditory, but not contextual, freezing was mildly disrupted regardless of age. Second, a profound postfear conditioning tactile hypersensitivity was observed in neonatally stressed, postweaning rats. In the absence of fear conditioning, the mechanical hypersensitivity was not observed, consistent with a two-hit model of psychopathology. Injections of 2% α-carrageenan did not have the same lasting impact but was slightly protective against observed effects of neonatal vehicle injections. Basal and elicited corticosterone levels postweaning were not altered by neonatal pain or handling. These data demonstrate that neonatal adversity can have lasting impacts on affective and somatosensory function that differs regardless of age.

Validation of the Échelle Douleur Inconfort Nouveau-Né for Brazilian culture

OBJECTIVE

To evaluate the reliability and validity of the Brazilian version of the Échelle Douleur Inconfort Nouveau-Né, which measures prolonged pain in neonates.

METHOD

A methodological study carried out with 96 neonates. The Brazilian versions of the Échelle Douleur Inconfort Nouveau-Né and the Children's and Infants' Postoperative Pain Scale were used for data collection. For reliability, equivalence measured by intraobserver agreement and homogeneity were considered. To evaluate the validity, the convergent construct approach was considered correlating the Brazilian versions of the Échelle Douleur Inconfort Nouveau-Né and the Children's and Infants' Postoperative Pain Scale.

RESULTS

In assessing reliability, the coefficient of agreement between observers varied between 0.64 and 0.85 for the items that make up the instrument, and 0.96 for the total score. Cronbach's alpha was 0.82. Regarding the convergent validity evaluation, Spearman correlation coefficient between the values found for both scales was 0.79 (p< 0.0001).

CONCLUSION

The Brazilian version of the Échelle Douleur Inconfort Nouveau-Né is a reliable and valid instrument for assessing prolonged pain in neonates.

Microglia in health and pain: impact of noxious early life events

NEW FINDINGS

What is the topic of this review? This review discusses the origins and development of microglia, and how stress, pain or inflammation in early life disturbs microglial function during critical developmental periods, leading to altered pain sensitivity and/or increased risk of chronic pain in later life. What advances does it highlight? We highlight recent advances in understanding how disrupted microglial function impacts the developing nervous system and the consequences for pain processing and susceptibility for development of chronic pain in later life. The discovery of microglia is accredited to Pío del Río-Hortega, who recognized this 'third element' of CNS cells as being morphologically distinct from neurons and astrocytes. For decades after this finding, microglia were altogether ignored or relegated as simply being support cells. Emerging from virtual obscurity, microglia have now gained notoriety as immune cells that assume a leading role in the development, maintenance and protection of a healthy CNS. Pioneering studies have recently shed light on the origins of microglia, their role in the developing nervous system and the complex roles they play beyond the immune response. These studies reveal that altered microglial function can have a profoundly negative impact on the developing brain and may be a determinant in a range of neurodevelopmental disorders and neurodegenerative diseases. The realization that aberrant microglial function also critically underlies chronic pain, a debilitating disorder that afflicts over 1.5 billion people worldwide, was a major conceptual leap forward in the pain field. Adding to this advance is emerging evidence that early life noxious experiences can have a long-lasting impact on central pain processing and adult pain sensitivity. With microglia now coming of age, in this review we examine the association between adverse early life events, such as stress, injury or inflammation, and the influence of sex differences, on the role of microglia in pain physiology in adulthood.

The management of fibromyalgia from a psychosomatic perspective: an overview

Fibromyalgia (FM) is a central sensitization syndrome characterized by chronic widespread pain. FM is often comorbid with psychiatric disorders, as well as psychological distress that worsens the quality-of-life of people affected. The aim was to collect current evidence about the management of FM from a psychosomatic perspective. The literature was synthesized and summarized in a narrative format. The literature search was carried out in PubMed; review articles, meta-analysis, overview, and guidelines published in the last 10 years written in English were included. Five main topics (Diagnostic criteria of FM; Pathogenesis of chronic widespread pain in FM; Early stress and trauma as predisposing factors for central sensitization; FM and Psychiatric comorbidity; Implications for treatment) were pointed out and discussed. Much evidence underlies the importance of considering and treating the comorbidity of FM with psychiatric disorders and psychological factors that affect pain management. Validation of FM as a central sensitization syndrome by a clinician facilitates therapeutic strategies that involve patients as active participants in the pain management process, likely leading to improved outcomes.

Defining pain in newborns: need for a uniform taxonomy?

A framework for defining pain terms such as acute, persistent, prolonged or chronic pain to newborns was derived from the scientific literature on neonatal pain assessments, previous attempts to define chronic pain and the clinical and neurophysiological features of neonatal pain. This novel framework incorporates the temporal features, localising characteristics, and secondary effects of the pain experienced, as well as the behavioural and physiological response patterns of newborns.

CONCLUSION

Although not evidence-based, this framework provides an initial starting point for defining commonly used neonatal pain terms. It will require future revision/refinement based on the accumulating evidence for non-acute pain.

Chemotherapy-Induced Neuropathy in Cancer Survivors

CONTEXT

Evidence suggests that chemotherapy-induced neuropathy (CIN) is a significant problem for cancer survivors. However, a detailed phenotypic characterization of CIN in cancer survivors is not available.

OBJECTIVES

To evaluate between-group differences in demographic and clinical characteristics, as well as in measures of sensation, function, and postural control, in a sample of cancer survivors who received a platinum and/or a taxane-based CTX regimen and did (n = 426) and did not (n = 197) develop CIN.

METHODS

Survivors completed self-report questionnaires and underwent objective testing (i.e., light touch, pain sensation, cold sensation, vibration, muscle strength, grip strength, Purdue Pegboard test, Timed Get Up and Go test, Fullerton Advanced Balance test). Parametric and nonparametric statistics were used to compare between-group differences in study outcomes.

RESULTS

Of the 426 survivors with CIN, 4.9% had CIN only in their upper extremities, 27.0% only in their lower extremities, and 68.1% in both their upper and lower extremities. Demographic and clinical characteristics associated with CIN included the following: older age, lower annual income, higher body mass index, a higher level of comorbidity, being born prematurely, receipt of a higher cumulative dose of chemotherapy, and a poorer functional status. Survivors with CIN had worse outcomes for all of the following objective measures: light touch, pain, temperature, vibration, upper and lower extremity function, and balance.

CONCLUSIONS

This study is the first to provide a detailed phenotypic characterization of CIN in cancer survivors who received a platinum and/or a taxane compound. These data can serve as a benchmark for future studies of CIN in cancer survivors.

Neonatal Injury Results in Sex-Dependent Nociceptive Hypersensitivity and Social Behavioral Deficits During Adolescence, Without Altering Morphine Response

Neonatal injury is associated with persistent changes in sensory function and altered nociceptive thresholds that give rise to aberrant pain sensitivity in later life. Although these changes are well documented in adult rodents, little is known about the consequences of neonatal injury during adolescence. Because adolescence is a critical developmental period during which persistent pain conditions can arise, we examined the effect of neonatal injury on nociception, social behavior, and response to morphine in adolescent Sprague Dawley rats. Male and female rats exposed to plantar incision injury at postnatal day 3 displayed mechanical hypersensitivity that resolved by 24 hours after incision. When these animals reached adolescence (postnatal day 28-40), neonatally-injured male rats showed ipsilaterally restricted mechanical, heat, and cold hypersensitivity, as well as social behavioral deficits. In contrast, these effects were not seen in female rats. Neonatal injury did not alter acute morphine antinociception or the development of analgesic tolerance in either sex. Morphine-induced conditioned place preference, behavioral sensitization, and physical withdrawal were also not affected by neonatal incision. Thus, early-life injury results in sex-dependent pain-related hypersensitivity and social behavior deficits during adolescence, without altering the response to opioids.

PERSPECTIVE

Neonatal surgery has greater effects on adolescent male than female rats, resulting in pain-related hypersensitivity and social behavioral deficits. Neonatal surgery does not alter the antinociceptive effects of morphine or abuse liability.

Long-Term Effects of Chronic Buspirone during Adolescence Reduce the Adverse Influences of Neonatal Inflammatory Pain and Stress on Adaptive Behavior in Adult Male Rats

Neonatal pain and stress induce long-term changes in pain sensitivity and behavior. Previously we found alterations in pain sensitivity in adolescent rats exposed to early-life adverse events. We tested whether these alterations have long-lasting effects and if those effects can be improved by the 5-hydroxytryptamine 1A (5-HT1A) receptor agonist buspirone injected chronically during the adolescent period. This study investigates: (1) effects of inflammatory pain (the injection of formalin into the pad of a hind paw) or stress (short maternal deprivation-isolation, MI), or their combination in 1-2-day-old rats on the adult basal pain, formalin-induced pain, anxiety and depression; (2) effects of adolescent buspirone in adult rats that experienced similar early-life insults. Changes in nociceptive thresholds were evaluated using the hot plate (HP) and formalin tests; levels of anxiety and depression were assessed with the elevated plus maze and forced swim tests respectively. Both neonatal painful and stressful treatments induced long-term alterations in the forced swim test. Other changes in adult behavioral responses were dependent on the type of neonatal treatment. There was a notable lack of long-term effects of the combination of early inflammatory pain and stress of MI on the pain responses, anxiety levels or on the effects of adolescent buspirone. This study provides the first evidence that chronic injection of buspirone in adolescent rats alters antinociceptive and anxiolytic effects limited to adult rats that showed behavioral alterations induced by early-life adverse treatments. These data highlight the role of 5-HT1A receptors in long-term effects of neonatal inflammatory pain and stress of short MI on adaptive behavior and possibility of correction of the pain and psychoemotional behavior that were altered by adverse pain/stress intervention using buspirone during critical adolescent period.

Beyond Acute Pain: Understanding Chronic Pain in Infancy

This topical review presents the current challenges in defining chronic pain in infants, summarizes evidence from animal and human infant studies regarding the biological processes necessary for chronic pain signaling, and presents observational/experiential evidence from clinical experts. A literature search of four databases (CINAHL, EMBASE, PsycINFO, and MEDLINE) was conducted, along with hand searches of reference lists. Evidence from animal studies suggest that important neurophysiological mechanisms, such as the availability of key neurotransmitters needed for maintenance of chronic pain, may be immature or absent in the developing neonate. In some cases, human infants may be significantly less likely to develop chronic pain. However, evidence also points to altered pain perception, such as allodynia and hyperalgesia, with significant injury. Moreover, clinicians and parents in pediatric intensive care settings describe groups of infants with altered behavioral responses to repeated or prolonged painful stimuli, yet agreement on a working definition of chronic pain in infancy remains elusive. While our understanding of infant chronic pain is still in the rudimentary stages, a promising avenue for the future assessment of chronic pain in infancy would be to develop a clinical tool that uses both neurophysiological approaches and clinical perceptions already presented in the literature.

A "Wear and Tear" Hypothesis to Explain Sudden Infant Death Syndrome

Sudden infant death syndrome (SIDS) is the leading cause of death among USA infants under 1 year of age accounting for ~2,700 deaths per year. Although formally SIDS dates back at least 2,000 years and was even mentioned in the Hebrew Bible (Kings 3:19), its etiology remains unexplained prompting the CDC to initiate a sudden unexpected infant death case registry in 2010. Due to their total dependence, the ability of the infant to allostatically regulate stressors and stress responses shaped by genetic and environmental factors is severely constrained. We propose that SIDS is the result of cumulative painful, stressful, or traumatic exposures that begin in utero and tax neonatal regulatory systems incompatible with allostasis. We also identify several putative biochemical mechanisms involved in SIDS. We argue that the important characteristics of SIDS, namely male predominance (60:40), the significantly different SIDS rate among USA Hispanics (80% lower) compared to whites, 50% of cases occurring between 7.6 and 17.6 weeks after birth with only 10% after 24.7 weeks, and seasonal variation with most cases occurring during winter, are all associated with common environmental stressors, such as neonatal circumcision and seasonal illnesses. We predict that neonatal circumcision is associated with hypersensitivity to pain and decreased heart rate variability, which increase the risk for SIDS. We also predict that neonatal male circumcision will account for the SIDS gender bias and that groups that practice high male circumcision rates, such as USA whites, will have higher SIDS rates compared to groups with lower circumcision rates. SIDS rates will also be higher in USA states where Medicaid covers circumcision and lower among people that do not practice neonatal circumcision and/or cannot afford to pay for circumcision. We last predict that winter-born premature infants who are circumcised will be at higher risk of SIDS compared to infants who experienced fewer nociceptive exposures. All these predictions are testable experimentally using animal models or cohort studies in humans. Our hypothesis provides new insights into novel risk factors for SIDS that can reduce its risk by modifying current infant care practices to reduce nociceptive exposures.

Long-Term Effects of Neonatal Pain and Stress on Reactivity of the Nociceptive System

The influence of inflammatory pain and/or weaning stress at different terms of neonatal development on functional activity of the nociceptive system during adulthood was studied in rats. Repeated stress in 1-2-day-old rat pups (a premature baby model) enhanced pain sensitivity to peripheral inflammation in both males and females. Repeated inflammatory pain experienced by male pups aged 1-2 or 7-8 days (models of preterm and full-term baby), even in presence of mother, enhanced pain behavior under conditions of repeated inflammatory pain in adulthood. Pain sensitivity in adult animals before (hot plate test) and after formation of the inflammatory focus (formalin test) depended on the age when the animals were subjected to the injury, type of exposure, and on animal sex. The priority data obtained by us will help to understand the mechanisms of long-term effects of early injuries and are important for pediatricians and neonatologists.

Melatonin as a potential counter-effect of hyperalgesia induced by neonatal morphine exposure

Morphine administration in the neonatal period can induce long-term effects in pain circuitry leading to hyperalgesia induced by the opioid in adult life. This study explored a new pharmacological approach for reversing this effect of morphine. We focused on melatonin owing its well-known antinociceptive and anti-inflammatory effects, and its ability to interact with the opioid system. We used the formalin test to assess the medium and long-term effects of melatonin administration on hyperalgesia induced by morphine in early life. Newborn rats were divided into two groups: the control group, which received saline, and the morphine group, which received morphine (5μg subcutaneously [s.c.]) in the mid-scapular area, once daily for 7days, from P8 (postnatal day 8) until P14. At postnatal days 30 (P30) and 60 (P60), both groups were divided in two subgroups, which received melatonin or melatonin vehicle 30min before the formalin test. The nociceptive responses were assessed by analyzing the total time spent biting, flicking, and licking the formalin-injected hind paw; these responses were recorded during the first 5min (neurogenic/acute phase) and from 15 to 30min (inflammatory/tonic phase). Initially, animals in the morphine/vehicle group showed increased nociceptive behavior in phase II (inflammatory) of the formalin test at P30, and in the neurogenic and inflammatory phases at P60. These increased nociceptive responses were fully reversed by melatonin administration at either age. These findings show that melatonin administration is a potential means for countering hyperalgesia induced by neonatal morphine exposure in young and adult rats.