Pain assessment in infants and children

The science of pain assessment for infants and children has grown substantially in the past several decades to the point that valid and reliable methods for pain assessment are available for use in clinical settings. Accurate pain assessment requires consideration of children's developmental level, type of pain experienced, history and context of pain, family influences, and interaction with the health care team. Research is needed to improve the sensitivity, specificity, and generalizability of pain-assessment tools and to more fully incorporate contextual factors into the objective assessment process. Finally, the improvement of pain assessment in the clinical setting can be viewed as a patient care quality issue, and continuous quality improvement methods can be used effectively to incorporate pain assessment as an integral component of every infant's and child's health care.

Treatment of pain in the neonatal intensive care unit

Pain is a disruptive influence on infants in the NICU. The most obvious and effective strategy to decrease infant pain in the NICU is to stringently limit the frequency of painful procedures, especially those that are most commonly reported (i.e., heel lances and endotracheal suctioning), and have these performed on infants that are most unstable or critically ill by the most experienced person available. Organizational concerns over the cost of NICU care have forced a re-evaluation of the necessity of certain diagnostic and care procedures and a limiting of procedures to those that can be documented to positively affect clinical outcome. Pharmacologic and nonpharmacologic strategies are essential to the prevention and management of neonatal pain, and these should be considered for complementary use for every infant. Research has shown the safety and effectiveness of some of the strategies in reducing mild pain caused by brief invasive procedures; however, many of the studies had methodologic limitations. Therefore, more research is required to determine the comparative efficacy of the various strategies and to document additive or synergistic effects when combined.

Response of Schwann cells to action potentials in development

Sensory axons become functional late in development when Schwann cells (SC) stop proliferating and differentiate into distinct phenotypes. We report that impulse activity in premyelinated axons can inhibit proliferation and differentiation of SCs. This neuron-glial signaling is mediated by adenosine triphosphate acting through P2 receptors on SCs and intracellular signaling pathways involving Ca2+, Ca2+/calmodulin kinase, mitogen-activated protein kinase, cyclic adenosine 3',5'-monophosphate response element binding protein, and expression of c-fos and Krox-24. Adenosine triphosphate arrests maturation of SCs in an immature morphological stage and prevents expression of O4, myelin basic protein, and the formation of myelin. Through this mechanism, functional activity in the developing nervous system could delay terminal differentiation of SCs until exposure to appropriate axon-derived signals.

Impact of preoperative education on pain management outcomes after coronary artery bypass graft surgery: a pilot

Patients have been found to receive inadequate analgesia despite moderate to severe pain after coronary artery bypass graft (CABG) surgery. The purpose of this pilot study was to evaluate a preadmission educational booklet for patients undergoing their first uncomplicated CABG. A randomized controlled trial (RCT) was undertaken at the largest cardiovascular centre in Canada. Repeated measures were used to compare data from 3 interviews: at baseline, day 3, and day 5. Patients were randomly assigned to one of 3 groups at the preadmission clinic 2 to 7 days before surgery: (1) generic hospital booklet and videotape (control), (2) control + pain booklet, or (3) control + pain booklet and interview; 45 subjects completed all 3 interviews. Measures were the McGill Pain Questionnaire-Short Form and the American Pain Society Patient Outcome Questionnaire. For all groups, analgesic administration was inadequate (19.89[13.37] mg morphine equivalents/24 hours) despite unrelieved pain (6.63[2.46], 0-10). However, patients receiving the interventions in addition to control care received 46% more analgesia than patients receiving control care alone and had fewer concerns about asking for help and taking analgesia. Changes were not required in the intervention booklet or measures.

Sucrose for analgesia in newborn infants undergoing painful procedures

BACKGROUND

Management of pain for neonates is less than optimal. The administration of sucrose with and without non-nutritive sucking (pacifiers) has been the most frequently studied non-pharmacological intervention for relief of procedural pain in neonates.

OBJECTIVES

To determine the efficacy, effect of dose, and safety of sucrose for relieving procedural pain as assessed by physiologic and/or behavioural indicators.

SEARCH STRATEGY

Standard methods as per the Neonatal Collaborative Review Group. A MEDLINE search was carried out for relevant randomized controlled trials (RCTs) published from January 1966 - November 1, 1997; EMBASE from 1993-1997; Reference Update search on November 11, 1997 and search of the Cochrane Library Issue 4 on November 11, 1997. Key words and (MeSH) terms included, infant/newborn, pain, analgesia and sucrose. Personal files, bibliographies, the most recent relevant neonatal and pain journals and conference proceedings were searched manually. Unpublished studies were not included. Language restrictions were not imposed.

SELECTION CRITERIA

RCTs in which term and/or preterm neonates undergoing heel lance, venepuncture or intramuscular injection (immunization) received sucrose or water/placebo or no intervention.

DATA COLLECTION AND ANALYSIS

Trial quality was assessed according to the methods of the Neonatal Collaborative Review Group. Quality measures included; blinding of randomization, blinding of intervention, completeness of follow up and blinding of outcome measurement. Data were abstracted and independently checked for accuracy by the two investigators. The inconsistency in outcome measures and differences in the statistical reporting of results made meta-analysis impossible. We were not able to identify two studies in which the same physiologic and/or behavioral outcomes following a noxious stimulus (heel-lance, venepuncture, intramuscular injection) were measured and reported in an identical fashion using means and standard deviations (or standard errors). The results are therefore reported for each accepted study separately.

MAIN RESULTS

Fifteen studies were identified for possible inclusion in this systematic review. Five studies were excluded; three RCTs were excluded as in these trials the number of infants randomized to treatment vs. placebo groups were not reported; one study was not an RCT, and in one RCT the neonates did not undergo a painful procedure. Ten RCTs were included in this review. Sucrose in a wide range of dosages was generally found to decrease univariate physiologic (heart rate) and behavioural (the mean percent time crying, total cry duration, duration of first cry, and facial action) pain indicators and multivariate [Premature Infant Pain Profile (PIPP)] pain outcomes in neonates undergoing heelstick or venepuncture. An optimal dose of sucrose to reduce pain associated with procedures in preterm and term neonates could not be identified through this systematic review.

REVIEWER'S CONCLUSIONS

Sucrose reduces physiologic and/or behavioral indicators of stress/pain in neonates following procedural pain stimuli (heel lance, venepuncture, immunization). There was inconsistency in the dose of sucrose that was effective and an optimal dose to be used in preterm and/or term infants could not be identified. Considerations for future research are to describe the painful procedure and intervention in detail, to use appropriate sample size to show a statistically significant reduction in pain, to use a multidimensional conceptualization of pain, to select outcome measures that are reliable and valid pain indicators and to account for the variation in the infant's response and context in which the pain is experienced. The use of repeated administrations of sucrose in neonates needs to be investigated. Use of sucrose in neonates that are very low birth weight, unstable and/or ventilated also needs to be addressed. (ABSTRACT TRUNCATED)

Validation of the premature infant pain profile in the clinical setting

OBJECTIVE

The Premature Infant Pain Profile (PIPP) is a 7-indicator composite measure developed to assess acute pain in preterm and term neonates. It has been validated in studies using synchronized videotaping of infants undergoing procedures. The purpose of this study was to establish (a) construct validity of the PIPP and (b) inter- and intrarater reliability of the PIPP prospectively in the clinical environment.

DESIGN

A randomized, crossover design was used.

SETTING

The study was conducted in a Level III outborn neonatal intensive care unit.

PARTICIPANTS

A convenience sample of 43 neonates, stratified by gestational age, was studied.

INTERVENTIONS

Each infant experienced three separate, randomly ordered events: baseline, a painful event, and a nonpain event. Infants were videotaped and scored at the bedside using the PIPP by the nurse caring for the infant and the clinical nurse specialist who bad expertise in infant pain. The videotapes were later reviewed by two additional experts; one in real time and one using a second-to-second stop frame technique.

RESULTS

Repeated-measures analysis of the main effects and interactions yielded a statistically significant main effect for event (pain, nonpain, baseline), thus differentiating pain from nonpain and baseline events (F = 48, p = 0.0001) and establishing construct validity. Interrater reliability analysis of individual event scores of the PIPP yielded reliability coefficients of 0.93-0.96. Intrarater reliability coefficients analysis for individual events were equally high at 0.94-0.98.

CONCLUSIONS

This study demonstrates that the PIPP is a pain measure with good construct validity and excellent inter- and intrarater reliability for the assessment of procedural pain of preterm and term infants in clinical settings.

Reliability of an intravenous intermittent access port (saline lock) for obtaining blood samples for coagulation studies

BACKGROUND

Patients admitted to rule out myocardial infarction often receive a heparin infusion that requires measurement of partial thromboplastin time every 6 to 8 hours until coagulation values stabilize. If the patient's acuity at admission does not necessitate placement of arterial or central catheters, insertion of an intermittent intravenous access port (saline lock) would decrease the need for frequent venipuncture. Many studies on obtaining blood samples via arterial and central catheters have been reported, but no reports have described the method of using a saline lock or the amount of blood discarded during that procedure.

OBJECTIVE

To evaluate the efficacy of inserting a saline lock specifically for obtaining blood samples and to determine the amount of blood that must be discarded in order to obtain prothrombin and partial thromboplastin times that match the values from blood samples obtained via venipuncture.

METHODS

Coagulation values determined with 2 consecutive blood samples obtained via the saline lock after the first 0.5 mL of blood withdrawn was discarded were compared with measurements determined with a blood sample obtained via venipuncture.

RESULTS

Prothrombin and partial thromboplastin times were not significantly different among the 3 blood samples.

CONCLUSION

The untoward effects of frequent venipunctures to obtain blood samples for measurement of prothrombin and partial thromboplastin times can be lessened by using an 18-gauge saline lock to obtain blood samples and discarding the first 0.5 mL of blood withdrawn before the samples for coagulation studies are collected.

Reliability of an intravenous intermittent access port (saline lock) for obtaining blood samples for coagulation studies

BACKGROUND: Patients admitted to rule out myocardial infarction often receive a heparin infusion that requires measurement of partial thromboplastin time every 6 to 8 hours until coagulation values stabilize. If the patient's acuity at admission does not necessitate placement of arterial or central catheters, insertion of an intermittent intravenous access port (saline lock) would decrease the need for frequent venipuncture. Many studies on obtaining blood samples via arterial and central catheters have been reported, but no reports have described the method of using a saline lock or the amount of blood discarded during that procedure. OBJECTIVE: To evaluate the efficacy of inserting a saline lock specifically for obtaining blood samples and to determine the amount of blood that must be discarded in order to obtain prothrombin and partial thromboplastin times that match the values from blood samples obtained via venipuncture. METHODS: Coagulation values determined with 2 consecutive blood samples obtained via the saline lock after the first 0.5 mL of blood withdrawn was discarded were compared with measurements determined with a blood sample obtained via venipuncture. RESULTS: Prothrombin and partial thromboplastin times were not significantly different among the 3 blood samples. CONCLUSION: The untoward effects of frequent venipunctures to obtain blood samples for measurement of prothrombin and partial thromboplastin times can be lessened by using an 18-gauge saline lock to obtain blood samples and discarding the first 0.5 mL of blood withdrawn before the samples for coagulation studies are collected.

Management of pain from heel lance with lidocaine-prilocaine (EMLA) cream: is it safe and efficacious in preterm infants?

Hospitalized preterm infants undergo multiple painful heel lances. A two-phase, randomized, controlled trial was undertaken to determine the safety and efficacy of lidocaine-prilocaine 5% cream (EMLA, Astra Pharmaceuticals, L.P, Westborough, MA) for relieving pain from heel lance. One hundred twenty infants were randomly assigned to receive 0.5 g of EMLA or placebo cream for 30 minutes (Phase 1) or 60 minutes (Phase 2) before a routine heel lance. Efficacy was assessed using the Premature Infant Pain Profile (PIPP). Safety was determined by methemoglobin concentration 8 hours after EMLA application and by clinical signs of methemoglobinemia. No significant differences existed on PIPP scores between EMLA and placebo groups in Phase 1 (p < .480) or Phase 2 (p < .831). No infant had any clinical signs of methemoglobinemia. The mean methemoglobin concentration was 1.19% (.47). Approximately 10% of infants had minor skin reactions, and approximately 20% of EMLA-treated infants had blanching at the application site. The authors conclude that EMLA is safe but not efficacious for relieving pain from heel lance in preterm infants.

Do cry features reflect pain intensity in preterm neonates? A preliminary study

The purpose of this study was to investigate if cries from preterm neonates would reflect changes in pain intensity following interventions. The cries from 25 preterm neonates from an original sample of 122 were audiorecorded while the infant was undergoing heelstick during a randomized crossover design testing the efficacy of: pacifier with sucrose or water, or prone position as compared to standard care. Both pacifier conditions reduced procedural pain according to a validated composite pain measure (the Premature Infant Pain Profile). There were proportionately fewer cries in the two pacifier groups compared to the prone positioning and standard care groups, and cry duration was positively correlated with PIPP scores. However, neither cry duration nor fundamental frequency reflected group differences. Further research is needed to determine if cry is a sensitive and valid indicator of pain in preterm infants.

Health services research in workers' compensation medical care: policy issues and research opportunities

OBJECTIVE

To describe some of the unique aspects of medical care offered under workers' compensation insurance systems and discuss the major policy considerations relevant to health services researchers undertaking investigations in this area.

BACKGROUND AND FINDINGS

State-based workers' compensation (WC) insurance systems requiring employers to pay for medical care and wage replacement for workplace injuries and illnesses were first developed between 1910 and 1920 in the United States. Employers are generally required to purchase state-regulated workers' compensation insurance that includes first-dollar payment for all medical and rehabilitative services and payment of lost wages to workers with work-related illness or injury. Injured workers have variable but usually limited latitude in choosing their health care provider. Employers and workers' compensation insurers have incentives for controlling both the cost of medical care and lost wages.

CONCLUSION

The major policy issues in WC medical care--the effect of patient choice of provider and delivery system structure, the ensuring of high-quality care, the effect of integrating benefits, and investigation of the interrelationships between work, health, and productivity--can be informed by current studies in health services research and by targeted future studies of workers' compensation populations. These studies must consider the extent of patient choice of physician, the regulatory environment, the unique role of the workplace as a risk and modifying factor, and the complex interaction between health and disability insurance benefits.

The efficacy of developmentally sensitive interventions and sucrose for relieving procedural pain in very low birth weight neonates

BACKGROUND

Procedural pain management for very low birth weight (VLBW) neonates has been minimal or nonexistent in most neonatal intensive care units (NICUs).

OBJECTIVES

To compare the efficacy of developmentally sensitive behavioral interventions (nonnutritive sucking via a pacifier, positioning) and sucrose for relieving procedural pain in VLBW infants and to determine the influence of contextual factors (gestational age, postnatal age, birth weight, severity of illness, frequency of painful procedures) on pain response.

METHOD

In a prospective randomized crossover trial, pain was assessed in 122 VLBW neonates using the Premature Infant Pain Profile following four randomly ordered interventions during consecutive routine heel lance procedures.

RESULTS

Significant differences in pain existed among treatment interventions (F = 16.20, p < .0001). The pacifier with sucrose (F = 24.09, p < .0001) and pacifier with sterile water (F = 9.00, p = .003) significantly reduced pain. Prone positioning did not decrease pain (F = 2.24, p = .137). Frequency of painful procedures approached significance in influencing pain response (F = 3.59, p = .01).

CONCLUSIONS

The most efficacious interventions for reducing pain from single painful events were the pacifier with sucrose and the pacifier with sterile water. Research on the efficacy and safety of implementing these interventions, alone and in combination, for repeated painful procedures is needed. In addition, research is needed on the influence of implementing these interventions on pain response and clinical outcomes (e.g., health status and neurodevelopmental status) in VLBW neonates in the NICU.

Control of myelination by specific patterns of neural impulses

A cell culture preparation equipped with stimulating electrodes was used to investigate whether action potential activity can influence myelination of mouse dorsal root ganglia axons by Schwann cells. Myelination was reduced to one-third of normal by low-frequency impulse activity (0.1 Hz), but higher-frequency stimulation (1 Hz) had no effect. The number of Schwann cells and the ultrastructure of compact myelin were not affected. The frequency of stimulation that inhibited myelination decreased expression of the cell adhesion molecule L1, and stimulation under conditions that prevented the reduction in L1 blocked the effects on myelination. This link between myelination and functional activity in the axon at specific frequencies that change axonal expression of L1 could have important consequences for the structural and functional relationship of myelinating axons.

Pigeon fanciers' lung: the mucin antigen is present in pigeon droppings and pigeon bloom

BACKGROUND

Pigeon intestinal mucin has been implicated as an important antigen pigeon fanciers' lung. This study investigated whether mucin is detectable in pigeon droppings and bloom, the likely antigenic sources in disease.

METHODS

Soluble extracts of a number of materials found in a pigeon loft were prepared and specific IgG subclass antibodies to these antigens were measured in 14 antibody-positive pigeon fanciers. Cross-reactivity between these materials and purified pigeon intestinal mucin was investigated by inhibition of anti-mucin ELISA. Mucin was purified from the soluble extracts of these crude antigen mixtures by CsCl density gradient centrifugation.

RESULTS

The patterns of IgG subclass responses to purified pigeon intestinal mucin and to the four materials collected from the pigeon loft were similar. Subclass differences between symptomatic and asymptomatic individuals, demonstrable against purified mucin, were similarly seen against pigeon droppings and pigeon bloom. Both pigeon droppings and pigeon bloom were capable of inhibiting IgG binding to purified pigeon mucin, and mucin inhibited substantially the binding of IgG to these materials. Glycoprotein with a density similar to that described for pigeon intestinal mucin was purified from each source.

CONCLUSION

Pigeon intestinal mucin is present in a variety of materials found in the environment of the pigeon loft in a form capable of reacting with anti-mucin antibodies in the sera of exposed individuals. Reduction in exposure to these materials may decrease the likelihood of developing pigeon fanciers' lung and minimise reactions in sensitised individuals.

Assessment of pain in the neonate

This article critically reviews the measures developed for assessing pain in the human neonate. Information was gathered with a computerized literature search of published articles and abstracts, a manual review of relevant conference proceedings, recently published journals, unpublished reports and manuscripts, and personal files. This identified 16 measures that were critically examined for their psychometric properties (reliability and validity) and clinical use. Special emphasis was placed on the feasibility of using neonatal pain assessment measures for clinical practice to address the research-practice gap. Although considerable progress has been made in the field of neonatal pain assessment, few measures have adequately established psychometric properties and clinical utility. Furthermore, most measures have been developed for research and not for the clinical setting. Issues regarding sensitivity, specificity, and the ability to detect clinically important changes have not been addressed. A sufficient number of infant pain measures have now been developed to assess acute pain. There is a paucity of measures to assess chronic pain in infants, and measures for infants who are low birth weight, critically ill, or ventilated. Future research should be aimed at strengthening the properties of existing measures, and at the development of measures for those infants with chronic pain or special needs.

NGF and LIF both regulate galanin gene expression in primary DRG cultures

Both target-derived and injury-induced factors could be involved in the axotomy-induced increases in galanin expression in dorsal root, ganglion (DRG) neurons. Galanin mRNA levels were studied in primary cultures of E13.5 embryos, grown for 14 days in culture, in response to two candidate molecules, nerve growth factor (NGF) and leukemia inhibitory factor (LIF). In these cultures, NGF withdrawal alone resulted in a significant increase in galanin mRNA. Addition of LIF onto NGF-containing cultures did not produce a significant increase, while addition of LIF to NGF-deprived cultures caused an upregulation of galanin mRNA which was significantly stronger than that of NGF withdrawal alone. Thus, NGF withdrawal and LIF increase act together to up-regulate galanin gene transcription in DRG neurons.

Managing pain after coronary artery bypass surgery

Nurses are responsible for assessing patients' pain and intervening with modalities such as opioids. However, after coronary artery bypass surgery, patients experience moderate to severe pain and receive inadequate analgesia. These practices are problematic as unrelieved acute pain is harmful and may result in negative consequences that influence recovery. Consistent with the subjectivity and multidimensionality of pain, as described in Gate Control Theory, patients need to be involved as participants in their care where possible. Pain policies and education programs need to reflect current professional guidelines and be proactive in addressing staff and patient gaps in pain knowledge and misbeliefs.

Evidence-based pain management for infants

The impact of pain on infants has been the topic of increasing research interest over the past decade. Although pain is now known to be stressful and the source of immediate and long term consequences, inadequate progress has been made in infant pain management. Research evidence provides the basis for effective pain management. However, the quality of the evidence, inconsistent findings, and the perceived lack of clinical relevance may have hindered the utilization of research on infant pain management in clinical practice. Reconceptualization of the definition of pain, increased methodologic rigor, validated assessment approaches, and systematic reviews of research studies on pain management may provide the opportunity for improved pain management using evidence-based practice.

A systematic review of lidocaine-prilocaine cream (EMLA) in the treatment of acute pain in neonates

OBJECTIVE

Neonates routinely undergo painful cutaneous procedures as part of their medical treatment. Lidocaine-prilocaine 5% cream (EMLA) is a topical anesthetic that may be useful for diminishing the pain from these procedures. EMLA is routinely used in children and adults. There is substantial apprehension about its use in neonates because of concerns that it may cause methemoglobinemia. The objective of this review was to determine the efficacy and safety of EMLA as an analgesic for procedural pain treatment in neonates and provide evidence-based recommendations for clinical practice.

METHODS

Systematic review techniques were used. Studies were identified using manual and computer-aided searches (Medline, EMBASE, Reference Update, personal files, scientific meeting proceedings). Behavioral (eg, facial action, crying) and physiologic (eg, heart rate, oxygen saturation, blood pressure, respiratory rate) outcome data from prospective nonrandomized controlled studies and randomized controlled trials in full-term and preterm neonates were accepted for inclusion to establish efficacy of EMLA. The risk of methemoglobinemia (defined as methemoglobin concentration >5% and requiring medical intervention) was estimated from all prospective studies.

RESULTS

Eleven studies of the efficacy of EMLA were included in the analysis. Infant gestational age at the time of delivery ranged from 26 weeks to full-term. Two studies included data from both neonates and older infants. The following procedures were studied: circumcision (n = 3), heel lancing (n = 4), venipuncture (n = 1), venipuncture and arterial puncture (n = 1), lumbar puncture (n = 1), and percutaneous venous catheter placement (n = 1). Nine studies were randomized controlled trials. The total sample size for each study ranged from 13 to 110 neonates. The dose of EMLA used was 0.5 g to 2 g in 9 studies, and was not specified in the others. The duration of application ranged from 10 minutes to 3 hours. The three studies that investigated the efficacy of EMLA for decreasing the pain of circumcision used a randomized controlled trial design. All of them demonstrated significantly reduced crying time during the procedure in the infants in the EMLA group compared with the infants in the control group. Facial grimacing, assessed in two of the studies, was also significantly lower in the EMLA group. Using meta-analytic techniques, the heart rate outcome data for two studies was summarized. Increases in heart rate compared with baseline values were 12 to 27 beats per minute less for the EMLA group than in the placebo group during various stages of the surgical procedure. Three studies that investigated the pain from heel lancing were randomized controlled trials; the other was a nonrandomized controlled study. None demonstrated a significant benefit of EMLA for any of the outcome measures used to assess pain (ie, behavioral pain scores, infant crying, heart rate, blood pressure, respiratory rate, oxygenation parameters). One randomized controlled study of the pain from venipuncture showed that infants treated with EMLA had significantly lower heart rates and cry duration compared with infants treated with a placebo. In one nonrandomized study, a significantly lower behavioral pain score was observed for infants treated with EMLA compared with the control group. Infant heart rate, however, did not differ between the groups. In one randomized controlled study of pain from percutaneous venous catheter placement, EMLA resulted in a significantly lower increase in heart rate and respiratory rate. Behavioral pain scores were significantly lower during arterial puncture in one nonrandomized controlled study. EMLA did not reduce physiologic changes or behavioral pain scores in one randomized controlled trial in infants undergoing lumbar puncture. Meta-analytic techniques revealed that methemoglobin concentrations did not differ between EMLA-treated and placebo-treated infants (weighted mean di

Comparison of the uptake of fine and ultrafine TiO2 in a tracheal explant system

To examine the relationship between particle uptake by pulmonary epithelial cells and particle size, we exposed rat tracheal explants to fine particles (FPs; 0.12 micron) or ultrafine particles (UFPs; 0.021 micron) of titanium dioxide for 3 or 7 days. By electron microscopy, particles were found in the epithelium at both time points, but in the subepithelial tissues, they were found only at 7 days. The volume proportion of both FPs and UFPs in the epithelium increased from 3 to 7 days; it was greater for UFPs at 3 days but was greater for FPs at 7 days. The volume proportion of particles in the subepithelium at 7 days was equal for both dusts, but the ratio of epithelial to subepithelial volume proportion was approximately 2:1 for FPs and 1:1 for UFPs. Mean volume of individual particle aggregates was similar for both dusts at 3 days but was markedly smaller for FPs at 7 days. These observations suggest that the behavior of particles of different size is complex: UFPs persist in the tissues as relatively large aggregates, whereas the size of FP aggregates becomes smaller over time. UFPs appear to enter the epithelium faster, and once in the epithelium, a greater proportion of them is translocated to the subepithelial space compared with FPs. However, if it is assumed that the volume proportion is representative of particle number, the number of particles reaching the interstitial space is directly proportional to the number applied; i.e., overall, there is no preferential transport from lumen to interstitium by size.

Activity-dependent regulation of N-cadherin in DRG neurons: differential regulation of N-cadherin, NCAM, and L1 by distinct patterns of action potentials

Cell adhesion molecule (CAM) expression is highly regulated during nervous system development to control cell migration, neurite outgrowth, fasciculation, and synaptogenesis. Using electrical stimulation of mouse dorsal root ganglion (DRG) neurons in cell culture, this work shows that N-cadherin expression is regulated by neuronal firing, and that expression of different CAMs is regulated by distinct patterns of neural impulses. N-cadherin was down-regulated by 0.1 or 1 Hz stimulation, but NCAM mRNA and protein levels were not altered by stimulation. L1 was down-regulated by 0.1 Hz stimulation, but not by 0.3 Hz, 1 Hz, or pulsed stimulation. N-cadherin expression was lowered with faster kinetics than L1 (1 vs. 5 days), and L1 mRNA returned to higher levels after terminating the stimulus. The RSLE splice variant of L1 was not regulated by action potential stimulation, and activity-dependent influences on L1 expression were blocked by target-derived influences. The results are consistent with changes in firing pattern accompanying DRG development and suggest that functional activity can influence distinct developmental processes by regulating the relative abundance of different CAMs.