Alvares, D., Torsney, C., Beland, B., Reynolds, M., and Fitzgerald, M. (2000). Modeling the prolonged eff ects of neonatal pain. Prog Brain Res, 129 , 365 \200\223373 . Faturi, C. B., Tiba, P. A., Kawakami, S. E., Catallani, B., Kerstens, M., and Suchecki, D. (2010). Disruptions of the mother-infant relationship and stress-related behaviors: altered corticosterone secretion does not explain everything. Neurosci Biobehav Rev, 34 , 821 \200 \223834 . Anand, K. J., Coskun, V., Th rivikraman, K. V., Nemeroff , C. B., and Plotsky, P. M. (1999) . Long-term behavioral eff ects of repetitive pain in neonatal rat pups. Physiol Behav, 66 , 627 \200\223637 . Anand, K. J., Garg, S., Rovnaghi, C. R., Narsinghani, U., Bhutta, A. T., and Hall, R. W. (2 007). Ketamine reduces the cell death following infl ammatory pain in newborn rat brain. Pe diatr Res, 62 , 283 \200\223290 . Fitzgerald, M. and Walker, S. M. (2009). Infant pain management: a developmental neurobiolo gical approach. Nat Clin Pract Neurol, 5 , 35 \200\22350 . SECTION 1 introduction 28 Moss, A., Alvares, D., Meredith-Middleton, J., Robinson, M., Slater, R., Hunt, S. P., et al . (2005). Ephrin-A4 inhibits sensory neurite outgrowth and is regulated by neonatal skin w ounding. Eur J Neurosci, 22 , 2413 \200\2232421 . Fox, M. D. (2011). Wound care in the neonatal intensive care unit. Neonatal Netw, 30 , 291 \200\223303 . Hathway, G. J., Koch, S., Low, L., and Fitzgerald, M. (2009). Th e changing balance of brai nstem-spinal cord modulation of pain processing over the fi rst weeks of rat postnatal life . J Physiol, 587 , 2927 \200\2232935 . Nagarajan, R., Darlington, R. B., Finlay, B. L., and Clancy, B. (2010). ttime: an R package for translating the timing of brain development across mammalian species. Neuroinformatics , 8 , 201 \200\223205 . Hathway, G. J., Vega-Avelaira, D., and Fitzgerald, M. (2012). A critical period in the supr aspinal control of pain: opioid-dependent changes in brainstem rostroventral medulla functi on in preadolescence. Pain, 153 , 775 \200\223783 . Hensch, T. K. (2004). Critical period r egulation. Annu Rev Neurosci, 27 , Negrigo, A., Medeiros, M., Guinsburg, R., and Covolan, L. (2011). Long- term gender behavio ral vulnerability aft er nociceptive neonatal formalin stimulation in rats. Neurosci Lett, 490 , 196 \200\223199 . 549 \200\223579 . Hohmann, A. G., Neely, M. H., Pina, J., and Nackley, A. G. (2005). Neonatal chronic hind pa w infl ammation alters sensitization to intradermal capsaicin in adult rats: a behavioral a nd immunocytochemical study. J Pain, 6 , 798 \200\223808 . Rahman, W., Fitzgerald, M., Aynsley-Green, A., and Dickenson, A. (1997). Th e eff ects of n eonatal exposure to infl ammation and/or morphine on neuronal responses and morphine analge sia in adult rats. In T. S. Jensen, J. A. Turner, and Z. Wiesenfeld-Hallin (eds) Proceeding s of the 8th World Congress on Pain. Progress in Pain Research and Management. Vol 8 , pp. 783 \200\223794. Seattle : IASP Press. Howard, R. F., Walker, S. M., Mota, P. M., and Fitzgerald, M. (2005). Th e ontogeny of neur opathic pain: postnatal onset of mechanical allodynia in rat spared nerve injury (SNI) and chronic constriction injury (CCI) models. Pain, 115 , 382 \200\223389 . Randich, A., Uzzell, T., Deberry, J. J., and Ness, T. J. (2006). Neonatal urinary bladder i nfl ammation produces adult bladder hypersensitivity. J Pain, 7 , 469 \200\223479 . Jiang, M. C. and Gebhart, G. F. (1998). Development of mustard oil-induced hyperalgesia in rats. Pain, 77 , 305 \200\223313 . Ren, K., Anseloni, V., Zou, S. P., Wade, E. B., Novikova, S. I., Ennis, M., et al . (2004). Characterization of basal and re-infl ammation-associated long- term alteration in pain re sponsivity following short-lasting neonatal local infl ammatory insult. Pain, 110 , 588 \200\223596 . Kalinichev, M., Easterling, K. W., and Holtzman, S. G. (2002). Early neonatal experience of Long-Evans rats results in long-lasting changes in reactivity to a novel environment and m orphine-induced sensitization and tolerance. Neuropsychopharmacology, 27 , 518 \200\223533 . Ren, K., Novikova, S. I., He, F., Dubner, R., and Lidow, M. S. (2005). Neonatal local noxio us insult aff ects gene expression in the spinal dorsal horn of adult rats. Mol Pain, 1 , 2 7 . Kehlet, H., Jensen, T. S., and Woolf, C. J. (2006). Persistent postsurgical pain: risk factors and prevention. Lancet, 367 , 1618 \200\2231625 . LaPrairie, J. L., Johns, M. E., and Murphy, A. Z. (2008). Preemptive morphine analgesia att enuates the long-term consequences of neonatal infl ammation in male and female rats. Pedia tr Res, 64 , 625 \200\223630 . Reynolds, M., Alvares, D., Middleton, J., and Fitzgerald, M. (1997). Neonatally wounded ski n induces NGF-independent sensory neurite outgrowth in vitro. Brain Res Dev Brain Res, 102 , 275 \200\223283 . Reynolds, M. L. and Fitzgerald, M. (1995). LaPrairie, J. L. and Murphy, A. Z. (2007). Female rats are more vulnerable to the long-term consequences of neonatal infl ammatory injury. Pain, 132 (Suppl. 1) , S124 \200\223133 . Long-term sensory hyperinnervation following neonatal skin wounds. J Comp Neurol, 358 , 487 \200\223498 . LaPrairie, J. L. and Murphy, A. Z. (2009). Neonatal injury alters adult pain sensitivity by increasing opioid tone in the periaqueductal gray. Front Behav Neurosci, 3 , 31 . Ririe, D. G. and Eisenach, J. C. (2006). Age-dependent responses to nerve injury-induced me chanical allodynia. Anesthesiology, 104 , 344 \200\223350 . Ririe, D. G., Vernon, T. L., To bin, J. R., and Eisenach, J. C. (2003). Age- dependent responses to thermal hyperalgesia an d mechanical allodynia in a rat model of acute postoperative pain. Anesthesiology, 99 , 443 \200\223448 . LaPrairie, J. L. and Murphy, A. Z. (2010). Long-term impact of neonatal injury in male and female rats: Sex diff erences, mechanisms and clinical implications. Front Neuroendocrinol, 31 , 193 \200\223202 . Le Bars, D., Gozariu, M., and Cadden, S. W. (2001). Animal models of Roizenblatt, S., Andersen, M. L., Bignotto, M., D \200\231almeida, V., Martins, P. J., and Tufi k, S. (2010). Neonatal arthritis disturbs sleep and behavior of adult rat off spring a nd their dams. Eur J Pain, 14 , 985 \200\223991 . nociception. Pharmacol Rev, 53 , 597 \200\223652 . Lee, D. H. and Chung, J. M. (1996). Neuropathic pain in neonatal rats. Neurosci Lett, 209 , 140 \200\223142 . Rovnaghi, C. R., Garg, S., Hall, R. W., Bhutta, A. T., and Anand, K. J. (2008). Ketamine an algesia for infl ammatory pain in neonatal rats: a factorial randomized trial examining lon g-term eff ects. Behav Brain Funct, 4 , 35 . Lidow, M. S., Song, Z. M., and Ren, K. (2001). Long-term eff ects of short- lasting early l ocal infl ammatory insult. Neuroreport, 12 , 399 \200\223403 . Lim, E. J., Back, S. K., Kim, M. A., Li, C., Lee, J., Jeong, K. Y., et al . (2009). Long-la sting neonatal inflammation enhances pain responses to subsequent infl ammation, but not pe ripheral nerve injury in adult rats. Int J Dev Neurosci, 27 , 215 \200\223222 . Ruda, M. A., Ling, Q. D., Hohmann, A. G., Peng, Y. B., and Tachibana, T. (2000). Altered no ciceptive neuronal circuits aft er neonatal peripheral infl ammation. Science, 289 , 628 \200\223631 . Schwetz, I., McRoberts, J. A., Coutinho, S. V., Bradesi, S., Gale, G., Fanselow, M., et al . (2005). Corticotropin-releasing factor receptor 1 mediates acute and delayed stress-induc ed visceral hyperalgesia in maternally separated Long-Evans rats. Am J Physiol Gastrointest Liver Physiol, 289 , G704 \200\2237012 . Lin, C. and Al-Chaer, E. D. (2003). Long-term sensitization of primary aff erents in adult rats exposed to neonatal colon pain. Brain Res, 971 , 73 \200\22382 . Low, L. A. and Fitzgerald, M. (2012). Acute pain and a motivational pathway in adult rats: infl uence of early life pain experience. PLoS ONE, 7 , e34316 . Sorkin, L. S. and Yaksh, T. L. (2009). Behavioral models of pain states evoked by physical injury to the peripheral nerve. Neurotherapeutics, 6 , 609 \200\2236019 . McCutcheon, J. E. and Marinelli, M. (2009). Age matters. Eur J Neurosci, 29 , 997 \200\2231014 . McKelvy, A. D. and Sweitzer, S. M. (2009). Endothelin-1 exposure on postnatal day 7 alters expression of the endothelin B receptor and behavioral sensitivity to endothelin-1 on postn atal day 11. Neurosci Lett, 451 , 89 \200\22393 . McLaughlin, C. R., Lichtman, A. H., Fanse low, M. S., and Cramer, C. P. (1990). Tonic nociception in neonatal rats. Pharmacol Biochem Behav, 36 , 859 \200\223862 . Spencer, S. J., Galic, M. A., and Pittman, Q. J. (2011). Neonatal programming of innate imm une function. Am J Physiol Endocrinol Metab, 300 , E11 \200\223118 . Sternberg, W. F. and Ridgway, C. G. (2003). Eff ects of gestational stress and neonatal han dling on pain, analgesia, and stress behavior of adult mice. Physiol Behav, 78 , 375 \200 \223383 . Miranda, A., Peles, S., Shaker, R., Rudolph, C., and Sengupta, J. N. (2006). Neonatal nocic eptive somatic stimulation diff erentially modifi es the activity of spinal neurons in rats and results in altered somatic and visceral sensation. J Physiol, 572 , 775 \200\223787 . Sternberg, W. F., Scorr, L., Smith, L. D., Ridgway, C. G., and Stout, M. (2005). Long-term eff ects of neonatal surgery on adulthood pain behavior. Pain, 113 , 347 \200\223353 . CHAPTER 3 long-term effects of early pain and injury: animal models 29 Wang, G., Ji, Y., Lidow, M. S., and Traub, R. J. (2004). Neonatal hind paw injury alters pr ocessing of visceral and somatic nociceptive stimuli in the adult rat. J Pain, 5 , 440 \200 \223449 . Tachibana, T., Ling, Q. D., and Ruda, M. A. (2001). Increased Fos induction in adult rats t hat experienced neonatal peripheral infl ammation. Neuroreport, 12 , 925 \200\223957 . Wang, J., Gu, C., and Al-Chaer, E. D. (2008). Altered behavior and digestive outcomes in ad ult male rats primed with minimal colon pain as neonates. Behav Brain Funct, 4 , 28 . Tjong, Y. W., Ip, S. P., Lao, L., Wu, J., Fong, H. H., Sung, J. J., Berman, B., and Che, C. T. (2010). Neonatal maternal separation elevates thalamic corticotrophin releasing factor type 1 receptor expression response to colonic distension in rat. Neuro Endocrinol Lett, 31 , 215 \200\223220 . Wang, K. C., Wang, S. J., Fan, L. W., Cai, Z., Rhodes, P. G., and Tien, L. T. (2011). Inter leukin-1 receptor antagonist ameliorates neonatal lipopolysaccharide-induced long-lasting h yperalgesia in the adult rats. Toxicology, 279 , 123 \200\223129 . Torsney, C. and Fitzgerald, M. (2002). Age-dependent eff ects of peripheral infl ammation o n the electrophysiological properties of neonatal rat dorsal horn neurons. J Neurophysiol, 87 , 1311 \200\2231317 . Winston, J., Shenoy, M., Medley, D., Naniwadekar, A., and Pasricha, P. J. (2007). Th e vani lloid receptor initiates and maintains colonic hypersensitivity induced by neonatal colon i rritation in rats. Gastroenterology, 132 , 615 \200\223627 . Torsney, C. and Fitzgerald, M. (2003). Spinal dorsal horn cell receptive fi eld size is inc reased in adult rats following neonatal hindpaw skin injury. J Physiol, 550 , 255 \200\2232 61 . Walker, C. D., Kudreikis, K., Sherrard, A., and Johnston, C. C. (2003). Repeated neonatal p ain infl uences maternal behavior, but not stress responsiveness in rat off spring. Brain R es Dev Brain Res, 140 , 253 \200\223261 . Wood, S. L., Beyer, B. K., and Cappon, G. D. (2003). Species comparison of postnatal CNS de velopment: functional measures. Birth Defects Res B Dev Reprod Toxicol, 68 , 391 \200\22340 7 . Walker, C. D., Xu, Z., Rochford, J., and Johnston, C. C. (2008). Naturally occurring variat ions in maternal care modulate the eff ects of repeated neonatal pain on behavioral sensiti vity to thermal pain in the adult off spring. Pain, 140 , 167 \200\223176 . Young, E. E., Baumbauer, K. M., Hillyer, J., and Joynes, R. L. (2007). Local anesthetic tre atment signifi cantly attenuates acute pain responding but does not prevent the neonatal in jury-induced reduction in adult spinal behavioral plasticity. Behav Neurosci, 121 , 1073 \200\2231081 . Walker, S. M., Meredith-Middleton, J., Cooke-Yarborough, C., and Fitzgerald, M. (2003). Neo natal infl ammation and primary aff erent terminal plasticity in the rat dorsal horn. Pain, 105 , 185 \200\223195 . Young, E. E., Baumbauer, K. M., Hillyer, J. E., Patterson, A. M., Hoy, K. C., Jr., Mintz, E . M., et al . (2008). Th e neonatal injury-induced spinal learning defi cit in adult rats: central mechanisms. Behav Neurosci, 122 , 589 \200\223600 . Walker, S. M., Meredith-Middleton, J., Lickiss, T., Moss, A., and Fitzgerald, M. (2007). Pr imary and secondary hyperalgesia can be diff erentiated by postnatal age and ERK activation in the spinal dorsal horn of the rat pup. Pain, 128 , 157 \200\223168 . Zhang, Y. H., Wang, X. M., and Ennis, M. (2010). Eff ects of neonatal infl ammation on desc ending modulation from the rostroventromedial medulla. Brain Res Bull, 83 , 16 \200\22322 . Walker, S. M., Tochiki, K. K., and Fitzgerald, M. (2009). Hindpaw incision in early life in creases the hyperalgesic response to repeat surgical injury: critical period and dependence on initial aff erent activity. Pain, 147 , 99 \200\223106 . CHAPTER 4 Long-term e \200 ects of pain in children Ruth E. Grunau Introduction Major advances in high-technology medical care have led to greatly increased s urvival of medically fragile infants born extremely pre- term, or with major congenital ano malies or other life-threatening conditions. Th ese infants are exposed to procedural, surg ical, and post-surgical pain. For millennia human infancy was a prolonged period of adult p rotection, with pain rarely encountered early in life. While the biological mechanisms for perception of pain develop during the fetal period, endogenous capacities to dampen pain ma ture later. Until relatively recently, this biological substrate was a good fi t, matching the environment of infancy. However, the revolution in medical care has led to unforeseen c hallenges to understand and manage infant pain. In full-term infants, the pri- mary concern is whether early pain alters later pain sensitivity. In contrast, due to the immaturity of the developing nervous system, the greatest impact of pain is likely to occur in the least maturely born infants. Th erefore, in infants born very preterm who undergo lengthy hospit alization, pain may aff ect multiple aspects of devel- opment. Th is chapter focuses on lon g-term eff ects of early pain on subsequent pain perception, neurodevelopment, brain develo p- ment, and programming of stress systems in the context of clinical studies, and whether caregiving factors may ameliorate potential long-term adverse eff ects. pain, boys who had been circumcised (regardless of analgesia) displayed greater pain behavi or to immunization at age 4 to 6 months, compared to uncircumcised boys (Taddio et al., 199 5). Th en a prospective randomized controlled study was conducted in which boys underwent n eonatal circumcision with either local anesthetic lidocaine-prilocaine 5% cream (EMLA ) or placebo, or were not circumcised. Th ese three groups of boys were studied later during immunization at age 4 to 6 months (Taddio et al., 1997). Circumcised boys who had received placebo showed higher facial actions, cry duration, and observer visual analog scale (VAS) pain ratings in response to immunization compared to the uncir- cumcised group. Importantly, using quantitative sensory testing, adult penile sen- sitivity did not diff er in men who had or had not been circumcised as neonates (Bleustein et al., 2005). Long-term eff ects of circumci- sion on pain threshold may be transitory. Th ere is scant research o n this question, given that placebo studies for neonatal circumcision studies are no longer ethical by current standards. Further studies are needed that compare later pain threshold s among infants that receive varying pain relief for circumcision (e.g. lidocaine-prilo- ca ine 5% cream versus penile block). Moreover, caregiver behav- iours during immunization sho uld be measured to rule out possible confounding factors between parents who choose to circ umcise their newborn boys, compare to those who do not. Major surgery Long aft er surgery early in life, there appear to be changes in later tactil e sensitivity that vary depending on the type of surgery, and whether in the region of surg ery or elsewhere, indicating both local and global eff ects. In a combined sample of childr en born full- term or preterm, skin sensitivity was tested at age 9 to 12 years in a group of children who had chest surgery in infancy, and com- pared with children who had no surge ry (Schmelzle-Lubiecki et al., 2007). Th ose who had surgery showed hyposensitivity to touc h, cold, and heat in the region of the surgery, and subtle abnormali- ties in everyday sens ations. In contrast to these long-term changes, Andrews and Fitzgerald (2002) found that in fants who had abdom- inal surgery showed hyper sensitivity to touch, both in the wound area and the contralateral side of the body in the fi rst 24 postop- erative hours. In another study, infants who underwent surgery in Full-term infants: early pain and later pain thresholds Stimulation of peripheral nocicepto rs can trigger long-term changes in circuitry of the central nervous system (CNS; Fitzgeral d and Walker, 2009). To better understand the potential long-lasting changes associated wit h early pain in infants born full-term, studies of the eff ects of circumcision, major surg ery and burns on tactile and pain thresholds later in childhood have been conducted. Circumcision One line of investigation to evaluate whether neonatal pain has long-term eff ects in healthy infants born full-term, has been fol- low-up of subsequent pain sensitivity in boys circumcised early in life. In a post hoc analysis of behavioral response to immuni zation CHAPTER 4 long-term effects of pain in children 31 the fi rst 3 months of life, and then subsequent surgery in the same dermatome 15 (range 8 \200\22370; median: 10th \200\22390th percentile) weeks later, needed more intraoperative f entanyl, had higher behavioral pain scores, had greater noradrenaline plasma concentrations , and needed more postoperative morphine than infants with no prior surgery (Peters et al., 2005). In contrast, in that study, infants who previously underwent surgery in a diff eren t dermatome had only higher postoperative analgesic requirements and noradrenaline plasma c oncentrations. Th ese studies suggest spinal and supraspi- nal changes following early surg ery. Th e long-term consequences of surgery in early infancy appear to be greater in areas of prior tissue damage, suggesting neurobiological changes with clinical impli- cations for subsequent pain management. However, importantly no diff erences were found in heart rate, cortisol, or behavioral responses to vaccination in toddlers who had surgery early in life (Peters et al., 2003). endogenous controls are immature (Fitzgerald and Walker, 2009), and pain induces diff use a ctivation across multiple brain regions (Fabrizi et al., 2011) therefore preterm infants ar e potentially most susceptible to pain and long-term eff ects of pain during the devel- opm ental period corresponding to the late second and entire third trimester of fetal life. Pre term neonates display lower thresholds (i.e. are more sensitive) and greater refl ex respon ses to peripheral stimuli compared to full-term infants (Fitzgerald and Beggs, 2001). With repeated stimulation, refl ex thresholds may drop even fur- ther (see Walker and Baccei, Ch apter 6, this volume, for details of peripheral and central mechanisms of refl ex sensitiza tion). Importantly, sensitization to repeated tactile stimulation is great- est below 33 we eks postconceptional age (Andrews and Fitzgerald, 1994). Due to altered touch thresholds an d sensitization, even non-invasive handling such as diaper change can elicit pain-like beha vioral and autonomic responses in very premature infants, if the diaper change follows bloo d collection even aft er a 30-min rest period in between the procedures (Holsti et al., 200 5). Similarly, when diaper change preceded blood collection, pain response to heel lance wa s heightened compared to blood collection aft er at least 1 h undisturbed (Holsti et al., 2 006). In this way, sensitization may provide one mechanism whereby repetitive pain and hand ling lays the groundwork for ongoing pain and discomfort during neo- natal intensive care. It is likely that eff ects of surgery will be related to age at surgery, the severity of th e intervention, provision of eff ective pain manage- ment, how well surgery and the hospita l stay were managed emo- tionally and cognitively for the young child, as well as the type and timing of subsequent evaluation. Taken together, it appears that early surgery can indu ce changes in peripheral and central tactile and pain processing; however, the direction, m agnitude, and nature of the functional impact depend on multiple factors. In some of these studies samples of infants born preterm and full-term were combined. It is unknown whether physiological and brain matu- rity at the time of surgery (i.e. varying duration of gestati on) con- tributes to the long-term impact on later pain threshold. Moreover, very preterm i nfants who undergo neonatal surgery also have been exposed to multiple other invasive proce dures due to their prema- turity, Studies on eff ects of early surgery on sensitivity to pa in later in childhood that account for multiple sources of early pain expe- rience during h ospitalization are needed to uncover diff erences between infants born preterm and full-ter m. Later pain thresholds Evidence for long-term eff ects of neonatal pain on later tactile and pain perception has now been demonstrated in multiple studies. Whereas the early work on l ong-term eff ects of neonatal pain on later pain sensitivity utilized parent report (Grunau et al., 1994a) or pictures (Grunau et al., 1998), more recent studies have directly compar ed behavioral and autonomic pain responses in infants born very preterm compared to healthy infants born at full-term. Findings diff er depending on age at testing. Contrary to expec ta- tion, aft er hospital discharge, preterm infants showed little diff er- ence in reactiv ity to pain at 4 months corrected age (CA), either to a pain-na ve site of fi nger lance (Oberlander et al., 2000), or to more intense pain of immunization injections (Grunau et a l., 2010). However, at 8 months CA, pain responses diverged in that the pre- term group sho wed brief initial facial hyperresponsiveness to a fi n- ger lance, followed by faster behav ioral and heart-rate recovery (Grunau et al., 2001). Th is rapid dampening evident at 8 mon ths CA may underlie the appearance of reduced pain response to everyday bumps, scrapes, and falls reported by parents of preterms born at 800g or less compared to full-term toddlers (Grunau et al., 1994a). Diff erences may emerge across time, as reported in animal studies (e.g. Ren et al., 2004; see also Walker, Chapter 3, this volume). Burns Children who had suff ered burns early in life (at 6 \200\22324 months), displayed al tered mechanical and pain sensitivity later in child- hood at age 9 to 16 years, that varie d by severity of the initial injury (Wollgarten-Hadamek et al., 2009). Compared to controls , children with moderate burns in infancy showed higher mechanical detec- tion thresholds ( hyposensitivity), lower mechanical pain thresholds (hypersensitivity), and greater sensitiz ation to repetitive mechani- cal stimuli; however, no signifi cant changes were found for t hermal stimuli. In contrast, compared to controls, severely burned children showed elevated thermal pain thresholds, whereas mechanical pain sensitivity was not consistently diff ere nt. Th e authors concluded that this diff erential pattern of altered sensory and pain sens itiv- ity may refl ect diff erences in stress, pain, and analgesic treatment between modera tely and severely burned infants. Importantly, early traumatic and painful injuries, such a s burns, can induce glo- bal long-term alterations in tactile and pain processing. At later ages, detection and pain thresholds for thermal, mechan- ical, and pressure stimul i have been studied, providing converging evidence of altered sensation in children born pr eterm. Pressure points were tested with a dolorimeter to measure later pain thresh- old, re vealing that adolescents born preterm had more tender points and lower pain threshold (Busk ila et al., 2003). Using quan- titative sensory testing, both hyperreactivity (enhanced sen sitivity) and hyporeactivity (reduced sensitivity) to pain have been reported at ages 9 to 14 years in children born preterm compared to full- term. Th e direction and the extent of eff ects varied depending on the type of pain stimulus and whether the pain was short-lasti ng or ongoing (Hermann et al., 2006; S. M. Walker et al., 2009). Preterms Neonatal pain in preterm infants Very preterm infants born 2 to 4 months before their due d ate spend weeks to months in the neonatal intensive care unit (NICU), outside the protectiv e intrauterine environment. During this time the syn- aptic connections, integrated circuit s, and descending modulatory SECTION 1 introduction 32 and full-terms exposed to NICU care both diff ered from full-term healthy controls displayi ng increased baseline thermal thresholds (i.e. reduced sensitivity), but a greater degree o f sensitization fol- lowing prolonged heat at non-injured sites, suggestive of central chan ges. Findings of both baseline hyporeactivity but hyperreactiv- ity to a noxious stimulus i n these human studies are consistent with the animal literature on long-term eff ects of ea rly pain (Ren et al., 2004; see also Walker, Chapter 3, this volume). of pain problems in adulthood, and the role that environmental life stresses may play in th is population. Neurodevelopment Infants born very preterm spend weeks to months in the NICU during a perio d of extremely rapid brain development and pro- gramming of stress systems, rendering them far more vulnerable to environmental perturbations such as neonatal pain, than infants born at term. For the tiniest, most fragile infants, the period of pain exposure is prolonged, during the last trimester of \200\230fetal \200\231 life, a time of very complex and rapid brain development. Neurodevelopmental problems including cognitive, language, visual-perce ptual, visual- motor, attention and learning defi cits as well as motor dysfunc- tion are c ommon in children born prematurely (e.g. Allen, 2008; Grunau et al., 2002), persisting to a dulthood (e.g. Hack et al., 2002; Grunau et al., 2004a). Two mechanisms have been identifi ed that may potentially link neonatal pain exposure to altered neurodevel- opment in this v ulnerable population, namely changes to the devel- oping brain and programming of stress sy stems. It is known that immature neurons are more sensitive to neurotoxic environmental inf l uences (see Lagercrantz et al., 2010). Atypicalities in structural and functional brain d evelopment are evident in preterm infants (e.g. Ment et al., 2009, S. P. Miller and Ferrier o, 2009), however the causes are unclear. Importantly, the study of preterm infants born at less than 26 weeks of gestation (S. M. Wa lker et al., 2009) was the fi rst to diff erentiate those who had neonatal surgery. While t here were generalized diff erences between the children born preterm com- pared to full-ter m in heat and cold thresholds and also in response to mechanical stimulation adjacent to sc ars, it was the preterms that had neonatal surgery that primarily accounted for those fi nd ings. While the extent of tissue damage may be the most salient diff er- ence in those extr eme preterms micropremies exposed to surgery, it is also possible that those requiring surg ery may have been sicker and may have been exposed to more cumulative procedural pain durin g their NICU care. Further research is needed to elucidate the role of neonatal surgery in the long-term eff ects of altered pain thresholds in children born extremely preterm. Using functional magnetic resonance imaging (fMRI) while children were exposed to pain stim ulation, children born pre- term showed greater cortical and subcortical brain activation ( Hohmeister et al., 2010). In response to heat stimuli of moder- ate pain intensity, preterm but not full-term children that had required NICU care as neonates, exhibited signifi cant activations in a number of brain regions (thalamus, anterior cingulate cortex, cerebellum, basal ganglia, and periaqueductal gray) that were not signifi cantly activated in non-NICU exposed full-term controls. Moreover, the preterms showed signifi cantly greater activatio n than controls in primary somatosensory cortex, anterior cingulate cortex, and insula. Th is exaggerated brain response in preterms was pain-specifi c. Greater neonatal pain exposure, defi ned as the cumulative number of skin-breaking procedur es from birth to term equivalent, was found to be associated with poorer motor and cognitiv e devel- opment to 18 months CA, aft er adjusting for medical neonatal con- founders (Gruna u et al., 2009). Th is is consistent with evidence in another longitudinal cohort that repe ated neonatal pain was associ- ated with alterations in the developing preterm brain (Brumm elte et al., 2012). Furthermore, prolonged exposure to repeated neonatal pain in preterm in fants appears to contribute to altered program- ming of the hypothalamic \200\223pituitary \200\223adrenocortical (HPA) axis across the fi rst 2 years of life (Grunau et al., 2004b, 2007), which has important implications for brain function. Recurrent pain in the long run: children, adolescents, and young adults Self-report is cons idered the \200\230gold standard \200\231 for pain assessment. Surprisingly, given the alt ered sensory thresholds described earlier, there have been several reports that adolescents and young adults born preterm report few if any diff erences in recurrent pain in daily li fe compared to their peers born healthy at full-term (Buskila et al., 2003; Saigal et al., 1996, 2007; Schmelzle-Lubiecki et al., 2007; S. M. Walker et al., 2009). However, given the high prevalence of abdominal pain, headaches, limb pain, and other non-specifi c pain comp laints in children in the general population, it is diffi cult to evaluate diff erences in these relatively small studies. Similarly, by parent report, greater somatization (function al pain complaints with no medical explanation) was more common in young preterm children a t age 5 years (Grunau et al., 1994b; Sommerfelt et al., 1996); however, in a longitudinal c ohort these diff erences were no longer apparent in later childhood at age 9 years (Whitfi eld et al., 1997) or in late adolescence at 17 years (Grunau et al., 2004a). Th us, althoug h touch and pain thresholds diff er in children born preterm, and brain activity in respons e to pain diff ers in preterms, contrary to expectations, there is little evidence at this point for long-term functional pain problems that impact daily life. However, further resea rch is needed to evaluate gender diff erences in the emergence Pain and the immature developing brain Brain reactivity to procedures Th e brain undergoes very rapid developmental changes in mac- rostructure, microstructure, and connectivity duri ng the time that infants born extremely preterm are undergoing neonatal intensive care. An example of the progression of structural brain matura- tion from 28 weeks of gestation to t erm-equivalent age is shown in Figure 4.1 . Magnetic resonance imaging (MRI) studies have r evealed atypical brain development in neonates born very preterm, e.g. smaller volume of th e brain and specifi c regions, abnormalities in white matter microstructure, reduced cortic al thickness, distur- bances of the thalamocortical system, and altered development of the cerebellum and other structures (e.g. see Ball et al., 2011; Volpe 2009; see also Poorun an d Slater, Chapter 39, this volume). Th ere has been long-standing concern that procedures conducted as part of life-saving care of preterm neonates may adversely aff ect brain development. Th irty years ago, Perlman an d Volpe (1983) reported that endotracheal suctioning aff ected neonatal cerebral blood fl o w. In recent years there have been a number of impor- tant studies of cortical activity dur ing procedural intervention in the NICU, utilizing near infrared spectroscopy to examine ce rebral blood fl ow and electroencephalography (EEG) to measure electrical CHAPTER 4 long-term effects of pain in children 33 A B Figure 4.1 Structural maturation of the developing brain in one preterm infant from 28 week s (A) to term equivalent age (B) MRI images courtesy of Dr Steven Miller. activity, demonstrating that blood collection evokes responses in the cortex (Bartocci et a l., 2006; Fabrizi et al., 2011; Slater et al., 2006, 2010; Tombini et al., 2009; Vanhatalo et al., 2009). Fabrizi et al. (2011) reported increased incidence of widely dispersed non- specifi c neuronal bursts of EEG activity in response to touch and pain in preterm infants, rather than the typical focused-evoked somatosensory potentials, maximal at the central el ectrodes that were evident in full-term neonates. Th is study is very important for underst anding the vulnerability of preterm neonates, as it under- scores the sensitivity of the pr eterm neonate to both mechanical and nociceptive stimulation. Th is phenomenon of responses wide- spread across the brain contributes to understanding why diaper change can evoke as much behavioral and autonomic reactivity as blood collection in preterm neonates while in t he NICU (Holsti et al., 2005). It is challenging to record specifi c brain activity in resp onse to painful procedures in young infants, since even aft er excluding overt movement art ifacts, tensing of muscles in the face and limbs may aff ect the signal, given the proximit y of the motor and somatosensory regions of the cortex (Maimon et al., 2013). carried out shortly aft er birth and again at term equivalent age in neonates born at 24 to 32 weeks of gestation. Aft er adjusting for multiple clinical confounding factors, such as gestational age at birth, infections, brain injury, and surgery, higher exposure to pro- c edural pain was associated with reduced development of white matter (indexed by fractional anisotropy (FA)) and subcortical gray matter (measured by N-acetylaspartate to choline rati o (NAA/ choline) \200\224a marker of cerebral metabolism and density). Reduced FA was predi cted by early pain prior to the fi rst brain scan, whereas lower NAA/choline was predicted by pain exposure throughout the neonatal course, suggesting a primary and early eff ect on subcor- tical structures with secondary white matter changes. Th is study appears to be the fi rst in human infants to show that neonatal pain is associated with adverse brain develo pment. Until now, relation- ships between pain and brain development in preterm infants wer e speculative. In the fi rst study to examine whether neonatal pain is associ- ated with brain activity la ter in childhood, in a diff erent longi- tudinal cohort of preterm infants followed from bi rth to school age, Grunau and colleagues found an association between greater cumulative ne onatal pain and spontaneous oscillatory brain activ- ity under resting conditions using mag netoencephalography at age 7 years (Doesburg et al., 2013). In turn, the cortical activity was associated with cognitive function. Importantly, in this study the link between neonata l pain and brain function was evident in infants born extremely preterm at 24 to 28 weeks, but not in more mature preterm infant born 29 to 32 weeks. It is well established that ther e are progressive changes in the maturation of oscillatory brain activity throughout the pr eterm period, as shown in the spec- tral composition of EEG recordings (Okumura et al., 200 3). Th e fi nding that neonatal pain was associated with brain activity in infants born at 24 to 28 weeks, but not later, may refl ect the distinct phases of development occurring wi thin thalamocortical systems within the 24- to 28- and 29- to 32-week gestational periods, and the implications for how pain is processed within the developing CNS (Kostovic and Juda s, 2010). In the only fMRI study of the brain during pain stimulation, at age 9 to 14 years children born preterm showed greater activa- tion in the somatosensory cortex and several other brai n regions compared to children born full-term with or without early hospi- talization (Hohm eister et al., 2010; see also Hermann, Chapter 40, this volume). More research is needed to explicate relationships between brain, behavior, and autonomic reactivity in the preterm n eonate under various conditions across post-conceptional age in the NICU. Neonatal pain and brain development Utilizing state-of-the-art brain imaging techniques to study micro- structure development from early in life to term equivalent age, Grunau and co lleagues found an association between greater exposure to pain-related stress in preterm in fants in the NICU and poorer neonatal brain development (Brummelte et al., 2012). In a long itudinal design, serial MRI and diff usion tensor imaging was SECTION 1 introduction 34 Sleep Sleep \200\223waking states develop during the third trimester of fetal life, and thu s are emerging during the period that preterm infants are exposed to repeated procedural pa in in the NICU. Th ere is long- standing interest in eff ects of sleep disruption on the de veloping CNS (e.g. Anders and Roff warg, 1973; Scher et al., 2005). Sleep plays an essentia l role in brain development (Blumberg and Seelke, 2010). Shift s in sleep state occur in re sponse to pain in the NICU, thus have become a key part of pain assessment (e.g. Holsti et al., 2008; Stevens et al., 2010), however little is known about eff ects of pain and pain m anagement on sleep in preterm neonates. Importantly, opioids for pain management aff ect sl eep structure, for example, decreasing rapid eye movement sleep (Axelin et al., 2010). Fabr izi et al. (2011) reported that the occurrence of noxious- specifi c EEG potentials was not state dependent, since the propor- tion of awake infants was the same for those who did an d did not exhibit the noxious-specifi c EEG response. However, very preterm infants typical ly spend little time awake in the NICU. Further EEG and behavioral studies of eff ects of p ain on sleep are needed, to elucidate the role of pain in preterm infants on brain developm ent via disruption of sleep.