Long-term effects of neonatal pain on nociceptive systems

Impact of neonatal pain and opiate administration in animal models: A meta-analysis concerning pain threshold

BACKGROUND AND AIM

Neonatal intensive care treatment, including frequently performed painful procedures and administration of analgesic drugs, can have different effects on the neurodevelopment. This systematic review and meta-analysis aimed to investigate the influence of pain, opiate administration, and pre-emptive opiate administration on pain threshold in animal studies in rodents, which had a brain development corresponding to preterm and term infants.

METHODS

A systematic literature search of electronic data bases including CENTRAL (OVID), CINAHL (EBSCO), Embase.com, Medline (OVID), Web of Science, and PsycInfo (OVID) was conducted. A total of 42 studies examining the effect of pain (n = 38), opiate administration (n = 9), and opiate administration prior to a painful event (n = 5) in rodents were included in this analysis.

RESULTS

The results revealed that pain (g = 0.42, 95%CI 0.16-0.67, p = 0.001) increased pain threshold leading to hypoalgesia. Pre-emptive opiate administration had the opposite effect, lowering pain threshold, when compared to pain without prior treatment (g = -1.79, 95%CI -2.71-0.86, p = 0.0001). Differences were found in the meta regression for type of stimulus (thermal: g = 0.66, 95%CI 0.26-1.07, p = 0.001; vs. mechanical: g = 0.13, 95%CI -0.98-1.25, p = 0.81) and gestational age (b = -1.85, SE = 0.82, p = 0.027). In addition, meta regression indicated an association between higher pain thresholds and the amount of cumulative pain events (b = 0.06, SE = 0.03, p = 0.05) as well as severity of pain events (b = 0.94, SE = 0.28, p = 0.001).

CONCLUSION

Neonatal exposure to pain results in higher pain thresholds. However, caution is warranted in extrapolating these findings directly to premature infants. Further research is warranted to validate similar effects in clinical contexts and inform evidence-based practices in neonatal care.

A nociceptive neuronal ensemble in the dorsomedial prefrontal cortex underlies pain chronicity

Pain chronicity involves unpleasant experience in both somatosensory and affective aspects, accompanied with the prefrontal cortex (PFC) neuroplastic alterations. However, whether specific PFC neuronal ensembles underlie pain chronicity remains elusive. Here we identify a nociceptive neuronal ensemble in the dorsomedial prefrontal cortex (dmPFC), which shows prominent reactivity to nociceptive stimuli. We observed that this ensemble shows distinct molecular characteristics and is densely connected to pain-related regions including basolateral amygdala (BLA) and lateral parabrachial nuclei (LPB). Prolonged chemogenetic activation of this nociceptive neuronal ensemble, but not a randomly transfected subset of dmPFC neurons, induces chronic pain-like behaviors in normal mice. By contrast, silencing the nociceptive dmPFC neurons relieves both pain hypersensitivity and anxiety in mice with chronic inflammatory pain. These results suggest the presence of specific dmPFC neuronal ensembles in processing nociceptive information and regulating pain chronicity.

Hydromorphone Prescription for Pain in Children-What Place in Clinical Practice?

While morphine is the gold standard treatment for severe nociceptive pain in children, hydromorphone is increasingly prescribed in this population. This review aims to assess available knowledge about hydromorphone and explore the evidence for its safe and effective prescription in children. Hydromorphone is an opioid analgesic similar to morphine structurally and in its pharmacokinetic and pharmacodynamic properties but 5-7 times more potent. Pediatric pharmacokinetic and pharmacodynamic data on hydromorphone are sorely lacking; they are non-existent in children younger than 6 months of age and for oral administration. The current data do not support any advantage of hydromorphone over morphine, both in terms of efficacy and safety in children. Morphine should remain the treatment of choice for moderate and severe nociceptive pain in children and hydromorphone should be reserved as alternative treatment. Because of the important difference in potency, all strategies should be taken to avoid inadvertent administration of hydromorphone when morphine is intended.

Maternal separation with neonatal pain influences later-life fear conditioning and somatosenation in male and female rats

Early life adversity, including that which occurs in a medical setting, has been increasingly shown to have lasting consequences on both physical and mental health. In order to understand the lasting effects of early-life adversity, such as that might occur in the neonatal intensive care unit (NICU), several rodent models have been developed including maternal separation, neonatal handling, and repeated needle prick pain. However, in the clinical scenario, these stressors are often combined. Thus, the current study seeks to observe the lasting impacts of both neonatal pain and maternal separation in a rodent model. Rats were separated from their dam for 6 h per day during the first 7 days of life, during which they were subjected to repeated needle prick pain or handling. A separate group was left undisturbed. All rats were subsequently tested for threat processing using a 3-day Pavlovian fear conditioning model and for somatosensation using measures of mechanical and thermal thresholds. Results indicated that rats subjected to maternal separation and pain had enhanced fear conditioning in adolescence as well as displaying a modest age-independent tactile hypersensitivity compared to undisturbed controls. These data show that experiencing combined neonatal pain and maternal separation may create a latent vulnerability to subsequent stressors.

Embodied Ethics: Phenomenology of the NICU Nurse's Touch

This study was a phenomenological exploration of the ethics of the nurse's touch in the Neonatal Intensive Care Unit (NICU). I explore several examples of touching encounters as gathered from NICU nurses through interview and observation, and organize the lived meanings around several thematic statements. These include the learning touch: finding a way to hold the baby, the marking touch: when touch lingers long after physical contact, the missing touch: touching without physical contact, the gnostic touch: the possibility of knowing an other and ourselves, and the call of touch: drawn to hold. Exploring the touching gestures of NICU nurses discloses the relational ethics inherent to caring practices. By attempting to articulate these practices, the hope is that the significance and contribution of the nurse's touch might be recognized and brought forward to our individual and professional consciousness, conversations, and curricula.

Migraine in Children Under 7 Years of Age: a Review

PURPOSE OF REVIEW

Despite the accumulation of a significant amount of data on pediatric headache, few studies have been conducted on its occurrence in children under 7 years of age. Within primary headaches in this age, migraine especially, turns out to be a disorder affecting up to 4% of the general population. An underestimate of its true prevalence can be due to lack of specific diagnostic markers, the frequent difficulty of describing pain in childhood, and the necessity of reliable parents' reports. Thus, migraine in children under 7 years of age represents an important challenge for clinicians. The objective of this manuscript is to provide a comprehensive review of epidemiologic, clinic, and therapeutic aspects of migraine in this age.

RECENT FINDINGS

Current literature data show that migraine has some differences, especially in clinical and therapeutic terms, in this age group compared to subsequent ages. Furthermore, some evidences showing that an early onset of migraine may play an unfavorable role in its natural history, suggest an early identification and management of migraine in younger children. Moreover, we highlight the role that factors of prenatal and perinatal development can play in the predisposition and anticipation of migraine onset. Finally, open questions related to the several undefined features of migraine in this age are reported. Migraine in this pediatric population is absolutely not rare, represents an importan clinical challenge and probably has a negative predictive role.

Evaluation of prolonged pain in preterm infants with pneumothorax using heart rate variability analysis and EDIN (Échelle Douleur Inconfort Nouveau-Né, neonatal pain and discomfort scale) scores

Purpose

The EDIN scale (Échelle Douleur Inconfort Nouveau-Né, neonatal pain and discomfort scale) and heart rate variability has been used for the evaluation of prolonged pain. The aim of our study was to assess the value of the newborn infant parasympathetic evaluation (NIPE) index and EDIN scale for the evaluation of prolonged pain in preterm infants with chest tube placement due to pneumothorax.

Methods

This prospective observational study assessed prolonged pain in preterm infants with a gestational age between 33 and 35 weeks undergoing installation of chest tubes. Prolonged pain was assessed using the EDIN scale and NIPE index.

Results

There was a significant correlation between the EDIN scale and NIPE index (r=-0.590, P=0.003). Prolonged pain is significantly more severe in the first 6 hours following chest tube installation (NIPE index: 60 [50–86] vs. 68 [45–89], P<0.002; EDIN score: 8 [7–11] vs. 6 [4–8], P<0.001).

Conclusion

Prolonged pain can be accurately assessed with the EDIN scale and NIPE index. However, evaluation with the EDIN scale is time-consuming. The NIPE index can provide instantaneous assessment of prolonged and continuous pain.

The manual orienting response habituation to repeated tactile stimuli in preterm neonates: Discrimination of stimulus locations and interstimulus intervals

Preterm infants frequently develop atypical sensory profiles, the tactile modality being particularly affected. However, there is a lack of recent investigation of neonatal tactile perception in a passive context, especially in preterms who are particularly exposed to this tactile stimuli. Our aims were to provide evidence of orienting responses (behavioral modifications directing subject's attention towards stimuli) and habituation to passive tactile stimuli in preterm neonates, to explore their ability to perceive spatial and temporal aspects of the stimulus, and to evaluate the effect of clinical factors on these abilities. We included 61 preterm neonates, born between 32 and 34 weeks of gestational age. At 35 weeks of corrected gestational age, we measured orienting responses (forearm, hand, and fingers movements) during vibrotactile stimulation of their hand and forearm; during a habituation and dishabituation paradigm, the dishabituation being either a location change or a pause in the stimulation sequence. Preterm newborns displayed a manual orienting response to vibrotactile stimuli which significantly decreased when the stimulus was repeated, regardless of the stimulated location on the limb. Habituation was delayed in subjects born at a younger gestational age, smaller birth weight, and having experienced more painful care procedures. Preterm neonates perceived changes in stimulus location and interstimulus time interval. Our findings provide insights on several aspects of the perception of repeated tactile stimuli by preterm neonates, and the first evidence of the early development of temporal processing abilities in the tactile modality. Future work will investigate the links between this ability and neurodevelopmental disorders.

Hypersensitivity of Prelimbic Cortex Neurons Contributes to Aggravated Nociceptive Responses in Rats With Experience of Chronic Inflammatory Pain

Previous experience of chronic pain causes enhanced responses to upcoming noxious events in both humans and animals, but the underlying mechanisms remain unclear. In the present study, we found that rats with complete Freund's adjuvant (CFA)-induced chronic inflammatory pain experience exhibited aggravated pain responses to later formalin test. Enhanced neuronal activation upon formalin assaults and increased phosphorylated cAMP-response element binding protein (CREB) were observed in the prelimbic cortex (PL) of rats with chronic inflammatory pain experience, and inhibiting PL neuronal activities reversed the aggravated pain. Inflammatory pain experience induced persistent p38 mitogen-activated protein kinase (MAPK; p38) but not extracellular regulated protein kinase (ERK) or c-Jun N-terminal kinase (JNK) hyperphosphorylation in the PL. Inhibiting the p38 phosphorylation in PL reversed the aggravated nociceptive responses to formalin test and down-regulated enhanced phosphorylated CREB in the PL. Chemogenetics identified PL-periaqueductal gray (PAG) but not PL-nucleus accumbens (NAc) as a key pathway in inducing the aggravated formalin pain. Our results demonstrate that persistent hyperphosphorylation of p38 in the PL underlies aggravated nociceptive responses in rats with chronic inflammatory pain experience.

Applying a Lifespan Developmental Perspective to Chronic Pain: Pediatrics to Geriatrics

An ideal taxonomy of chronic pain would be applicable to people of all ages. Developmental sciences focus on lifespan developmental approaches, and view the trajectory of processes in the life course from birth to death. In this article we provide a review of lifespan developmental models, describe normal developmental processes that affect pain processing, and identify deviations from those processes that lead to stable individual differences of clinical interest, specifically the development of chronic pain syndromes. The goals of this review were 1) to unify what are currently separate purviews of "pediatric pain," "adult pain," and "geriatric pain," and 2) to generate models so that specific elements of the chronic pain taxonomy might include important developmental considerations.

PERSPECTIVE

A lifespan developmental model is applied to the forthcoming Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks-American Pain Society Pain Taxonomy to ascertain the degree to which general "adult" descriptions apply to pediatric and geriatric populations, or if age- or development-related considerations need to be invoked.

Age-Dependent Sexual Dimorphism in Susceptibility to Develop Chronic Pain in the Rat

Neonatal pain has been suggested to contribute to the development and/or persistence of adult pain. Observations from animal models have shown that neonatal inflammation produces long-term changes in sensory neuron function, which can affect the susceptibility of adults to develop persistent pain. We used a preclinical model of transition to chronic pain, hyperalgesic priming, in which a previous inflammatory stimulus triggers a long-lasting increase in responsiveness to pro-algesic mediators, prototypically prostaglandin E₂ (PGE₂), to investigate if post-natal age influences susceptibility of adult rats to develop chronic pain. Priming was induced by tumor necrosis factor alpha (TNFα), in male and female rats, 1, 2, 3, 4, 5 or 7weeks after birth. When adults (8weeks after birth), to evaluate for the presence of priming, PGE₂ was injected at the same site as TNFα. In males that had received TNFα at post-natal weeks 1, 2 or 3, priming was attenuated compared to the 4-, 5- and 7-week-old treated groups, in which robust priming developed. In contrast, in females treated with TNFα at post-natal week 1, 2, 3, or 4, but not at 5 or 7, priming was present. This age and sex difference in the susceptibility to priming was estrogen-dependent, since injection of TNFα in 3-week-old males and 5-week-old females, in the presence of the estrogen receptor antagonist ICI 182,780, did produce priming. These results suggest that estrogen levels, which vary differently in males and females over the post-natal period, until they stabilize after puberty, impact pain as an adult.

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.

Missed Opportunities for Sedation and Pain Management at a Level III Neonatal Intensive Care Unit, India

BACKGROUND

Neonates in the neonatal intensive care unit (NICU) undergo a multitude of painful and stressful procedures during the first days of life. Stress from this pain can lead to neurodevelopmental problems that manifest in later childhood and should be prevented.

OBJECTIVE

To determine the number of painful procedures performed per day for each neonate, to verify documentation of painful procedures performed, and to, subsequently, note missed opportunities for providing pain relief to neonates.

METHODS

We conducted a cross-sectional study at a level III NICU located in a rural part of western India. A total of 69 neonates admitted for more than 24 h were included. Twenty-nine neonates were directly observed for a total of 24 h each, and another 40 neonatal records were retrospectively reviewed for the neonate's first 7 days of admission. All stressful and painful procedures performed on the neonate were recorded. Also recorded were any pharmaceutical pain relief agents or central nervous system depressants administered to the neonate before or at the time of the procedures. Average nurse-patient ratio was also calculated. Data were analyzed using descriptive statistics.

RESULTS

A documentation deficit of 2.2% was observed. The average nurse-patient ratio was 1.53:1. A total of 13711 procedures were recorded, yielding 44.1 (38.1 stressful, 3.8 mildly painful, and 2.2 moderately painful) procedures per patient day. Common stressful procedures were position changing (2501) and temperature recording (2208). Common mildly and moderately painful procedures were heel prick (757) and endotracheal suctioning (526), respectively. Use of pharmacological agents coincided with 33.48% of the procedures. The choice of drug and time of administration were inappropriate, indicating that the pharmacological agents were intended not for pain relief but rather for a coexisting pathology or as sedation from ventilation with no analgesia.

CONCLUSION

Stressful procedures are common in the NICU; mildly and moderately painful procedures fairly common. Almost two-thirds of the times, no pharmaceutical pain relief methods were used, and when administered, the pharmaceutical agents were seldom intended for pain relief; this implies poor pain management practices and emphasizes the imperative need for educating NICU nurses, residents, fellows, and attendings.

Long-term and trans-generational effects of neonatal experience on sheep behaviour

Early life experiences can have profound long-term, and sometimes trans-generational, effects on individual phenotypes. However, there is a relative paucity of knowledge about effects on pain sensitivity, even though these may impact on an individual's health and welfare, particularly in farm animals exposed to painful husbandry procedures. Here, we tested in sheep whether neonatal painful and non-painful challenges can alter pain sensitivity in adult life, and also in the next generation. Ewes exposed to tail-docking or a simulated mild infection (lipopolysaccharide (LPS)) on days 3–4 of life showed higher levels of pain-related behaviour when giving birth as adults compared with control animals. LPS-treated ewes also gave birth to lambs who showed decreased pain sensitivity in standardized tests during days 2–3 of life. Our results demonstrate long-term and trans-generational effects of neonatal experience on pain responses in a commercially important species and suggest that variations in early life management can have important implications for animal health and welfare.

Systemic Progesterone Administration in Early Life Alters the Hyperalgesic Responses to Surgery in the Adult: A Study on Female Rats

BACKGROUND

There has recently been a substantial increase in the survival of prematurely born neonates and an increase of in utero surgeries. Noxious stimulation in the newborn alters the pain response to injury in adult life. Progesterone, an effective antihyperalgesic agent in the adult, is at high concentration in the pregnant mother. Therefore, we investigated the effects of early-life progesterone on postsurgical outcomes in adult rats.

METHODS

Female rat pups were administered progesterone or vehicle during the first 7 days postpartum (P1-P7). A second control group had no injections. Half of each of these groups received an incision of the hindpaw at P3 and the other half did not. At P60, all groups of these now adult rats received a second paw incision. Tactile sensitivity and thermal sensitivity were measured weekly at P14-P42 (period I), at P60 (just before the second incision), and every 2 days of P61-P70 (period II). At P67, rats were fixed by systemic paraformaldehyde perfusion and their spinal cords taken for staining and immunocytochemical analysis of activated p-p38 mitogen-activated protein kinase.

RESULTS

Rats with surgery at P3 had greater tactile and thermal hyperalgesia in period I than the nonoperated rats, a difference abolished by progesterone treatment. P3 incision also resulted in long-lasting tactile and thermal hyperalgesia after the P60 incision (period II), both of which were markedly smaller in degree and faster to resolve in rats receiving early progesterone. Even in rats that were not operated on in period I, neonatal progesterone lessened the tactile hyperalgesia in period II. More spinal cells showed p-p38 staining in vehicle-treated rats as a result of the early-life incision but not in those treated with progesterone.

CONCLUSIONS

These findings suggest that endogenously high progesterone in utero may have a similarly protective action and that the development of nociceptive circuitry can be strongly influenced by neonatal progesterone.

Neuroimmune mechanisms of stress: sex differences, developmental plasticity, and implications for pharmacotherapy of stress-related disease

The last decade has witnessed profound growth in studies examining the role of fundamental neuroimmune processes as key mechanisms that might form a natural bridge between normal physiology and pathological outcomes. Rooted in core concepts from psychoneuroimmunology, this review utilizes a succinct, exemplar-driven approach of several model systems that contribute significantly to our knowledge of the mechanisms by which neuroimmune processes interact with stress physiology. Specifically, we review recent evidence showing that (i) stress challenges produce time-dependent and stressor-specific patterns of cytokine/chemokine expression in the CNS; (ii) inflammation-related genes exhibit unique expression profiles in males and females depending upon individual, cooperative or antagonistic interactions between steroid hormone receptors (estrogen and glucocorticoid receptors); (iii) adverse social experiences incurred through repeated social defeat engage a dynamic process of immune cell migration from the bone marrow to brain and prime neuroimmune function and (iv) early developmental exposure to an inflammatory stimulus (carageenin injection into the hindpaw) has a lasting influence on stress reactivity across the lifespan. As such, the present review provides a theoretical framework for understanding the role that neuroimmune mechanisms might play in stress plasticity and pathological outcomes, while at the same time pointing toward features of the individual (sex, developmental experience, stress history) that might ultimately be used for the development of personalized strategies for therapeutic intervention in stress-related pathologies.

Probiotic Lactobacillus rhamnosus GG (LGG) and prebiotic prevent neonatal inflammation-induced visceral hypersensitivity in adult rats

BACKGROUND

Increasing evidence indicates a positive effect of probiotics on the nervous system. The objective of this study was to determine if probiotic Lactobacillus rhamnosus GG (LGG) and/or prebiotics polydextrose/galactooligosaccharide (PDX/GOS) can alter the colonic sensitivity in a neonatal rat model of chronic visceral hyperalgesia and to determine whether altered sensitivity is associated with changes in neurotransmitter levels in the brain.

METHODS

Chronic visceral hyperalgesia was induced in rats by intracolonic administration of zymosan for 3 days during postnatal day 14-16 (P14-P16). After weaning (P21), these pups were divided into groups that received either (1) control diet (CD), (2) PDX/GOS, (3) LGG, or (4) PDX/GOS + LGG. These diets were continued until visceral sensitivity was tested at P60. The viscero-motor response (VMR) to graded colorectal distension (CRD) was determined by measuring the electromyographic (EMG) activity from the abdominal external oblique muscles. The levels of neurotransmitters and biogenic amines were quantified in the frontal cortex, subcortex, brain stem, and cerebellum.

KEY RESULTS

At P60, the VMR to CRD in the neonatal zymosan-treated rats was significantly higher than neonatal saline-treated rats. In contrast, neonatal zymosan-treated rats that received PDX/GOS or LGG did not exhibit visceral hyperalgesia. The levels of serotonin, noradrenaline, and dopamine were significantly altered in LGG-treated rats compared to other groups.

CONCLUSIONS & INFERENCES

Results document that in rats LGG can attenuate neonatally induced chronic visceral pain measured in adulthood. Prolonged intake of LGG alters some key brain neurotransmitters and biogenic amines that could be involved in pain modulation.

Variation of opioid use in pediatric inpatients across hospitals in the U.S

CONTEXT

Appropriate use of opioids is essential to manage moderate-to-severe pain in children safely and effectively, yet published guidance regarding opioid treatment for pediatric patients is limited, potentially resulting in excessive variation in opioid use in pediatric patients across hospitals in the U.S.

OBJECTIVES

The aim was to evaluate hospital variation in opioid use in pediatric inpatients.

METHODS

Using data from the Pediatric Health Information System and the Premier Perspective Database regarding all pediatric inpatients in 626 hospitals, we examined hospital variation in opioid use and the length of opioid use, adjusting for patient demographic and clinical characteristics and for hospital type (children's vs. general) and hospital patient volume, using multilevel generalized linear regression modeling.

RESULTS

Overall, 41.2% of all pediatric hospitalizations were exposed to opioids. Among the exposed patients, the mean length of exposure was 4.6 days. Exposure proportion and exposure length varied substantially across hospitals, even after accounting for patient demographic and clinical characteristics, hospital type and hospital patient volume, especially among terminal hospitalizations. For patients discharged alive vs. died, the adjusted exposure percentage for each hospital ranged from 0.7% to 99.1% (interquartile range [IQR]: 35.3%-59.9%) vs. 0.1% to 100.0% (IQR: 29.2%-66.2%), respectively, and the adjusted exposure length ranged from 1.0 to 8.4 days (IQR: 2.2-2.7 days) vs. 0.9 to 35.2 days (IQR: 4.0-7.4 days).

CONCLUSION

The substantial hospital-level variation in opioid use in pediatric inpatients suggests room for improvement in clinical practice.

Predisposing effects of neonatal visceral pain on abuse-related effects of morphine in adult male Sprague Dawley rats

RATIONALE

Adverse early life experiences are risk factors for drug abuse and addiction. Changes in brain opioid systems have been demonstrated in response to neonatal visceral pain (NVP), but the impact of these changes on abuse-related effects of morphine are unknown. The NVP procedure used models chronic visceral hyperalgesia persisting across development.

OBJECTIVES

Intravenous self-administration, drug discrimination, and locomotor activity were used to compare the abuse-related effects of morphine in NVP and control rats.

METHODS

Rats self-administered 0.3 mg/kg/inj morphine under an FR1 schedule, and dose-effect functions for morphine were then established. Separate rats were trained to discriminate 3.2 mg/kg morphine from saline under an FR20 schedule, and morphine dose-effect functions were then determined in the absence and presence of 0.1 mg/kg naltrexone. A third group of rats was tested with a range of morphine doses in an assay of locomotor activity, then injected daily with 10 mg/kg morphine to assess locomotor sensitization.

RESULTS

NVP rats self-administered more morphine than controls at reinforcing doses. Discriminative stimulus effects of morphine were similar between groups, but in the presence of naltrexone, the ED50 for morphine was more than 12× greater in control rats than in NVP animals. Morphine did not stimulate locomotor activity at any tested dose in NVP rats, although significant effects were observed in controls. Finally, significant locomotor sensitization was observed only in NVP rats.

CONCLUSIONS

NVP-induced changes in brain opioid systems have persistent pharmacological consequences into adulthood and may increase sensitivity to abuse-related effects of opioids across development.

Procedural sedation and analgesia in pediatric patients

A spectrum of conditions requires sedation and analgesia in pediatric population. Ineffective treatment of pain may result in physiological and behavioral responses that can adversely affect the developing nociceptive system. The recognition of pain in children can be facilitated by different pain scales. This article reviews the procedural sedation and analgesia (PSA) practices in children along with pharmacology of the drugs used for this purpose.

Interactions between glia, the immune system and pain processes during early development

Pain is a serious problem for infants and children and treatment options are limited. Moreover, infants born prematurely or hospitalized for illness likely have concurrent infection that activates the immune system. It is now recognized that the immune system in general and glia in particular influence neurotransmission and that the neural bases of pain are intimately connected to immune function. We know that injuries that induce pain activate immune function and suppressing the immune system alleviates pain. Despite this advance in our understanding, virtually nothing is known of the role that the immune system plays in pain processing in infants and children, even though pain is a serious clinical issue in pediatric medicine. This brief review summarizes the existing data on immune-neural interactions in infants, providing evidence for the immaturity of these interactions.

[Impact of the instrumental vaginal delivery on pain perception at two months]

INTRODUCTION

Although instrumental vaginal delivery reduces the risk of neonatal mortality, it increases the risk of specific morbidity including prolonged neonatal discomfort. Previous studies suggest that neonatal exposure to acute pain could have long-term effects on the pain response later in life. The aim of the study was to investigate whether instrumental vaginal delivery may alter the response to a noxious stimulus at the age of two months.

METHOD

Newborn infants were enrolled in this prospective observational study after parental consent. A group of children born by instrumental vaginal delivery (group 2) were compared to matched controls born by vaginal delivery (group 1). Pain was assessed in each newborn infant between two and four hours after birth using the scale of pain and discomfort of the newborn baby (EDIN). These children were reassessed for pain response to immunizations (Infanrix(®) and Prevenar(®)) at two months of age using the DAN scale.

RESULTS

Thirteen children were enrolled in this study, six in group 1 and seven in group 2. Gestational age, birth weight, Apgar score, and umbilical arterial blood were similar in both groups. The EDIN measured between H2 and H4 was significantly higher in group 2 (median, 4 [IQ, 3] versus 0 [3.25], P<0.05). While the DAN score before and during immunization was similar in the two groups, it was statistically higher in group 2 than in group 1 (4 [3] versus 2 [2.25], P<0.01) within the15 min following the injections.

CONCLUSION

These results indicate that birth by instrumental vaginal delivery causes discomfort after birth and increases the pain response to immunization at the age of two months. This study supports the hypothesis that instrumental vaginal delivery may alter pain perception later in life.

Neonatal bee venom exposure induces sensory modality-specific enhancement of nociceptive response in adult rats

OBJECTIVE

Previous studies have shown that inflammatory pain at the neonatal stage can produce long-term structural and functional changes in nociceptive pathways, resulting in altered pain perception in adulthood. However, the exact pattern of altered nociceptive response and associated neurochemical changes in the spinal cord in this process is unclear.

METHOD

In this study, we used an experimental paradigm in which each rat first received intraplantar bee venom (BV) or saline injection on postnatal day 1, 4, 7, 14, 21, or 28. This was followed 2 months later by a second intraplantar bee venom injection in the same rats to examine the difference in nociceptive responses.

RESULTS

We found that neonatal inflammatory pain induced by the first BV injection significantly reduced baseline paw withdrawal mechanical threshold, but not baseline paw withdrawal thermal latency, when rats were examined 2 months from the first BV injection. Neonatal inflammatory pain also exacerbated mechanical, but not thermal, hyperalgesia in response to the second BV injection in these same rats. Rats exposed to neonatal inflammation also showed up-regulation of spinal NGF, TrkA receptor, BDNF, TrkB receptor, IL-1β, and COX-2 expression following the second BV injection, especially with prior BV exposure on postnatal day 21 or 28.

CONCLUSION

These results indicate that neonatal inflammation produces sensory modality-specific changes in nociceptive behavior and alters neurochemistry in the spinal cord of adult rats. These results also suggest that a prior history of inflammatory pain during the developmental period might have an impact on clinical pain in highly susceptible adult patients.

DA-9701: A New Multi-Acting Drug for the Treatment of Functional Dyspepsia

Motilitone^® (DA-9701) is a new herbal drug that was launched for the treatment of functional dyspepsia in December 2011 in Korea. The heterogeneous symptom pattern and multiple causes of functional dyspepsia have resulted in multiple drug target strategies for its treatment. DA-9701, a compound consisting of a combination of Corydalis Tuber and Pharbitidis Semen, has being developed for treatment of functional dyspepsia. It has multiple mechanisms of action such as fundus relaxation, visceral analgesia, and prokinetic effects. Furthermore, it was found to significantly enhance meal-induced gastric accommodation and increase gastric compliance in dogs. DA-9701 also showed an analgesic effect in rats with colorectal distension induced visceral hypersensitivity and an antinociceptive effect in beagle dogs with gastric distension-induced nociception. The pharmacological effects of DA-9701 also include conventional effects, such as enhanced gastric emptying and gastrointestinal transit. The safety profi le of DA-9701 is also preferable to that of other treatments.

Neonatal injury rapidly alters markers of pain and stress in rat pups

Less than 60% of infants undergoing invasive procedures in the neonatal intensive care unit receive analgesic therapy. These infants show long-term decreases in pain sensitivity and cortisol reactivity. In rats, we have previously shown that inflammatory pain experienced on the day of birth significantly decreases adult somatosensory thresholds and responses to anxiety- and stress-provoking stimuli. These long-term changes in pain and stress responsiveness are accompanied by two-fold increases in central met-enkephalin and β-endorphin expression. However, the time course over which these changes in central opioid peptide expression occur, relative to the time of injury, are not known. The present studies were conducted to determine whether the observed changes in adult opioid peptide expression were present within the first postnatal week following injury. The impact of neonatal inflammation on plasma corticosterone, a marker for stress reactivity, was also determined. Brain, spinal cord, and trunk blood were harvested at 24 h, 48 h, and 7 d following intraplantar administration of the inflammatory agent carrageenan on the day of birth. Radioimmunoassay was used to determine plasma corticosterone and met-enkephalin and β-endorphin levels within the forebrain, cortex, midbrain, and spinal cord. Within 24 h of injury, met-enkephalin levels were significantly increased in the midbrain, but decreased in the spinal cord and cortex; forebrain β-endorphin levels were significantly increased as a result of early life pain. Corticosterone levels were also significantly increased. At 7 d post-injury, opioid peptides remained elevated relative to controls, suggesting a time point by which injury-induced changes become programmed and permanent.

Salivary biomarkers are not suitable for pain assessment in newborns

BACKGROUND AND AIMS

Newborns admitted to the neonatal intensive care unit are repeatedly subjected to painful or stressful procedures; therefore, objective assessment of their pain is essential. An increasing number of scales for neonatal pain assessment have been developed, many of which are based on physiological and behavioral factors. Recently, salivary biomarkers have been used to assess stress in adults and older infants. This study aimed to determine whether salivary biomarkers can be useful objective indices for assessing newborn pain.

STUDY DESIGN

A total of 47 healthy newborns were enrolled 3-4days after birth. Heel lancing was performed to collect blood for a newborn screening test. Before and after heel lancing, saliva was collected to analyze hormone levels, a video was recorded for behavioral observations, and heart rate was recorded. Two investigators independently assessed newborn pain from the video observations using the Neonatal Infant Pain Scale (NIPS). Salivary chromogranin (sCgA) and salivary amylase (sAA) levels were measured using an enzyme-linked immunosorbent assay kit and a dry chemistry system, respectively.

RESULTS

No definite changes in salivary biomarkers (sCgA or sAA) were detected before and after heel lancing. However, newborn sCgA levels were markedly higher than reported adult levels, with large inter- and intra-subject variability, whereas newborn sAA levels were lower than adult levels. NIPS score and heart rate were dramatically increased after heel lancing.

CONCLUSIONS

NIPS score (behavioral assessment) and heart rate are useful stress markers in newborns. However, neither sCgA nor sAA is suitable for assessing newborn pain.

Low formalin concentrations induce fine-tuned responses that are sex and age-dependent: a developmental study

The formalin test is increasingly applied as a model of inflammatory pain using high formalin concentrations (5–15%). However, little is known about the effects of low formalin concentrations on related behavioural responses. To examine this, rat pups were subjected to various concentrations of formalin at four developmental stages: 7, 13, 22, and 82 days of age. At postnatal day (PND) 7, sex differences in flinching but not licking responses were observed with 0.5% formalin evoking higher flinching in males than in females. A dose response was evident in that 0.5% formalin also produced higher licking responses compared to 0.3% or 0.4% formalin. At PND 13, a concentration of 0.8% formalin evoked a biphasic response. At PND 22, a concentration of 1.1% evoked higher flinching and licking responses during the late phase (10–30 min) in both males and females. During the early phase (0–5 min), 1.1% evoked higher licking responses compared to 0.9% or 1% formalin. 1.1% formalin produced a biphasic response that was not evident with 0.9 or 1%. At PND 82, rats displayed a biphasic pattern in response to three formalin concentrations (1.25%, 1.75% and 2.25%) with the presence of an interphase for both 1.75% and 2.25% but not for 1.25%. These data suggest that low formalin concentrations induce fine-tuned responses that are not apparent with the high formalin concentration commonly used in the formalin test. These data also show that the developing nociceptive system is very sensitive to subtle changes in formalin concentrations.

Stress and pain response of neonates after spontaneous birth and vacuum-assisted and cesarean delivery

OBJECTIVE

The objective of the study was to compare the stress response and pain expression of newborns (NBs) in the early postpartum period.

STUDY DESIGN

This was a prospective study with 280 NBs enclosed at 3 Swiss university hospitals. Stress response and pain reaction were analyzed according to the mode of delivery: elective cesarean section (ELCS), spontaneous vaginal delivery, and assisted vaginal delivery by vacuum extraction (VE). Saliva cortisol and clinical pain expression were evaluated after delivery and before and after heel prick for metabolic screening.

RESULTS

Significant differences were evident during the first 72 hours postpartum with highest nominations in the VE group. Meconium-stained amniotic fluid was the only intrapartum stress factor with an impact on clinical pain expression.

CONCLUSION

NBs delivered vaginally show a higher incidence of stress response and pain expression than infants of the ELCS group. The long-term impact of these findings remains to be determined.

Are there long-term consequences of pain in newborn or very young infants?

Physiologic studies indicate that very early pain or stress experiences have more than immediate consequences for infants. Assessment and care of pain are complex subjects made even more complex and challenging when the individual experiencing pain is a very young infant. This review provides evidence that significant and long-lasting physiological consequences may follow painful insults in the very young, including changes in the central nervous system and changes in responsiveness of the neuroendocrine and immune systems to stress at maturity.

Neonatal nociception elevated baseline blood pressure and attenuated cardiovascular responsiveness to noxious stress in adult rats

Neonatal nociception has significant long-term effects on sensory perception in adult animals. Although neonatal adverse experience affect future responsiveness to stressors is documented, little is known about the involvement of early nociceptive experiences in the susceptibility to subsequent nociceptive stress exposure during adulthood. The aim of this study is to explore the developmental change in cardiovascular regulating activity in adult rats that had been subjected to neonatal nociceptive insults. To address this question, we treated neonatal rats with an intraplantar injection of saline (control) or carrageenan at postnatal day 1. The carrageenan-treated rats exhibited generalized hypoalgesia at basal state, and localized hyperalgesia after re-nociceptive challenge induced by intraplantar injections of complete Freund's adjuvant (CFA) as adults. Then we recorded baseline cardiovascular variables and 24-h responsiveness to an injection of CFA in the free-moving adult rats with telemetric technique. The carrageenan-treated rats showed significantly higher basal blood pressures (110.3±3.16 vs. control 97.0±4.28 mmHg). In control animals, baroreceptor reflex sensitivity (BRS) decreased, sympathetic vasomotor activity increased, and parasympathetic activity was inhibited after CFA injection. Blood pressure elevation was evident (107.0±2.75 vs. pre-injection 97.0±4.28 mmHg). Comparatively, the carrageenan-treated rats showed a higher BRS (BrrLF 1.03±0.09 vs. control 0.70±0.06 ms/mmHg) and higher parasympathetic activity [0.93±0.17 vs. control 0.32±0.02 ln(ms²)] after CFA injection. The change in blood pressure is negligible (111.9±4.05 vs. pre-injection 110.3±3.16 mmHg). Our research has shown that neonatal nociception alters future pain sensation, raises basal blood pressure level, and attenuates cardiovascular responsiveness to nociceptive stress in adult rats.

Adult-age inflammatory pain experience enhances long-term pain vigilance in rats

BACKGROUND

Previous animal studies have illustrated a modulatory effect of neonatal pain experience on subsequent pain-related behaviors. However, the relationship between chronic pain status in adulthood and future pain perception remains unclear.

METHODOLOGY/PRINCIPAL FINDINGS

In the current study, we investigated the effects of inflammatory pain experience on subsequent formalin-evoked pain behaviors and fear conditioning induced by noxious stimulation in adult rats. Our results demonstrated an increase of the second but not the first phase of formalin-induced pain behaviors in animals with a history of inflammatory pain that have recovered. Similarly, rats with persistent pain experience displayed facilitated acquisition and prolonged retention of pain-related conditioning. These effects of prior pain experience on subsequent behavior were prevented by repeated morphine administration at an early stage of inflammatory pain.

CONCLUSIONS/SIGNIFICANCE

These results suggest that chronic pain diseases, if not properly and promptly treated, may have a long-lasting impact on processing and perception of environmental threats. This may increase the susceptibility of patients to subsequent pain-related disorders, even when chronic pain develops in adulthood. These data highlight the importance of treatment of chronic pain at an early stage.

Comprehensive pain management protocol reduces children's memory of pain at discharge from the pediatric ED

BACKGROUND

Historically, pain has been poorly managed in the pediatric emergency department (ED) (PED), resulting in measurable psychosocial issues both acute and delayed.

OBJECTIVE

The aim of the study was to measure the impact of protocolized pain management on patients with painful conditions or undergoing painful procedures in the PED.

METHODS

We performed an analysis before and after the implementation of the protocol, dubbed the "Comfort Zone." Validated, age-appropriate pain scales were performed. Validation (using Cronbach α, confirmatory factor analysis) was followed by comparison of responses between the pre- and posttests collected (χ(2) and Wilcoxon rank sum tests). Pain scores were collected at triage and at discharge. At triage, patients were asked to report pain levels. At discharge, they were asked to report their current pain and recall the level of pain during their stay. At triage, parents were asked to report about their perception of the child's pain. At discharge, they were asked to report about their perception of the child's current pain and recall the level of pain during the stay and during procedures, if done.

RESULTS

Five hundred thirty-one patients were enrolled in the preprotocol group; 47% were women with a median age of 5 years (range, 30 days-18 years). Two hundred sixty-three patients were enrolled in the protocol group; 39% were women with a median age of 6 years (range, 30 days-18 years). Patient-recalled pain scores of the ED visit in the protocol group were significantly lower than those of the preprotocol group (Wong-Baker Faces Pain Scale, 5.07-4.01; P < .001); yet parent estimates of pain did not show a significant change at any point. Patient assessment of pain at ED discharge did not show a significant change either (Wong-Baker Faces Pain Scale, 1.99-1.56; P = .09). The Faces scale is not well validated for patients younger than 4, so that group had only parental assessment of pain and, consistent with the larger data set, showed no significant pain scale reduction at any point.

CONCLUSION

Protocolized pain management reduces patients' memory of pain during PED visits but may not affect parental memory of perceived pain or parent- and patient-reported pain at discharge.

The impact of prenatal stress on basal nociception and evoked responses to tail-docking and inflammatory challenge in juvenile pigs

The consequences of tail-docking (at 2-4 days) and prenatal stress (maternal social stress during the 2nd third of pregnancy) on baseline nociceptive thresholds and responses to acute inflammatory challenge were investigated in juvenile pigs in two studies. Nociceptive thresholds were assessed on the tail root and on the hind foot using noxious mechanical and cold stimulation before and after acute inflammatory challenge by intradermal injection of 30 μg capsaicin (study 1) or 3% carrageenan (study 2) into the tail root. Four groups of 8 (study 1, n=14-16 pigs/treatment) or 5 (study 2, n=6 pigs/treatment/sex) week-old pigs were exposed to the main factors: maternal stress and treatment (docked vs. intact tails). In study 1, tail docking did not significantly alter thresholds to noxious mechanical stimulation, whilst prenatally stressed pigs had significantly higher baseline thresholds to noxious mechanical stimulation on the tail root and on the hind foot than unstressed pigs, whether tail-docked or intact. Capsaicin injection induced localised mechanical allodynia around the tail root in all treatment groups, but had no effect on noxious plantar mechanical responses; however prenatally stressed offspring exhibited significantly attenuated response thresholds to capsaicin compared to controls. In study 2 tail docking did not alter thresholds to either mechanical or noxious cold stimulation. Baseline response durations to noxious cold stimulation of the tail root were significantly shorter in both sexes of prenatally stressed pigs, whilst male but not female prenatally stressed pigs exhibited significantly higher baseline thresholds to mechanical stimulation than controls, although results in female pigs tended towards significance. Carrageenan injection into the tail root induced localised mechanical and cold allodynia in all treatment groups, effects that were attenuated in prenatally stressed pigs. Collectively, these findings indicate that prenatal stress can induce long-term alterations in nociceptive responses, manifest as a reduced sensitivity to noxious mechanical and cold stimulation and evoked inflammatory allodynia. Neonatal tail-docking does not lead to long-term alterations in nociception in pigs.

Endpoints in pediatric pain studies

Assessing pain intensity in (preverbal) children is more difficult than in adults. Tools to measure pain are being used as primary endpoints [e.g., pain intensity, time to first (rescue) analgesia, total analgesic consumption, adverse effects, and long-term effects] in studies on the effects of analgesic drugs. Here, we review current and promising new endpoints used in pediatric pain assessment studies.

Stress and tension-type headache mechanisms

Stress is widely demonstrated as a contributing factor in tension-type headache (TTH). The mechanisms underlying this remain unclear at present. Recent research indicates the importance of central pain processes in tension-type headache (TTH) pathophysiology. Concurrently, research with animals and healthy humans has begun to elucidate the relationship between stress and pain processing in the central nervous system, including central pain processes putatively dysfunctional in TTH. Combined, these two fields of research present new insights and hypotheses into possible mechanisms by which stress may contribute to TTH. To date, however, there has been no comprehensive review of this literature. The present paper provides such a review, which may be valuable in facilitating a broader understanding of the central mechanisms by which stress may contribute to TTH.