The Analgesic Effects of Maternal Milk Odor on Newborns: A Meta-Analysis

Registered Nurses' Association of Ontario (RNAO) best practice guideline on the assessment and management of vascular access devices

INTRODUCTION

Vascular access is the most common invasive procedure performed in health care. This fundamental procedure must be performed in a safe and effective manner. Vascular access devices (VADs) are often the source of infections and other complications, yet there is a lack of clear guidance on VADs for health providers across different settings. A Best Practice Guideline (BPG) was developed by the Registered Nurses' Association of Ontario (RNAO) to provide evidence-based recommendations on the assessment and management of VADs.

METHODS

RNAO BPGs are based on systematic reviews of the literature following the GRADE approach. Experts on the topic of vascular access were selected to form a panel. Systematic reviews were conducted on six research areas: education, vascular access specialists, blood draws, daily review of peripheral VADs, visualization technologies, and pain management. A search for relevant research studies published in English limited to January 2013 was applied to eight databases. All studies were independently assessed for eligibility and risk of bias by two reviewers based on predetermined inclusion and exclusion criteria. The GRADE approach was used to determine certainty of the evidence.

RESULTS

Over 65,000 articles were screened related to the six priority research questions. Of these, 876 full-text publications were examined for relevance, with 174 articles designated to inform nine recommendations in the BPG on the subject areas of: comprehensive health teaching, practical education for health providers, blood draws, daily review of peripheral VADs, visualization technologies, and pain management. In June 2021, the RNAO published the BPG on vascular access, which included the recommendations and other supporting resources.

CONCLUSION

The vascular access BPG provides high quality guidance and updated recommendations, and can serve as a primary resource for health providers assessing and managing VADs.

[Evidence-based guideline for neonatal pain management in China (2023)]

Pain disrupts neonatal vital signs and internal environment homeostasis and affects the recovery process, and recurrent pain stimulation is one of the important risk factors for neurodevelopmental disorders and some chronic diseases. In order to standardize pain management practice in neonatal wards in China and effectively prevent and reduce the adverse effects of pain on the physical and mental development of neonates, National Clinical Research Center for Child Health and Diseases (Children's Hospital of Chongqing Medical University) convened a multidisciplinary panel to formulate the evidence-based guideline for neonatal pain management in China (2023 edition) following the principles and methods for the guideline development issued by the World Health Organization. Based on the best evidence and expert consensus, this guideline gives 26 recommendations for nine clinical issues, i.e., the classification and definition of neonatal pain, common sources of pain, pain assessment principles, pain assessment methods, analgesic principle, non-pharmaceutical analgesic methods, pharmaceutical analgesic methods, parental participation in pain management, and recording methods for pain management, so as to provide medical staff with guidance and a decision-making basis for neonatal pain assessment and analgesia management.

Efficacy and safety of non-pharmacological interventions for neonatal pain: an overview of systematic reviews

OBJECTIVES

To synthesise current evidence from systematic reviews (SRs) regarding the efficacy and safety of non-pharmacological interventions to prevent and treat pain in newborn infants.

DESIGN

Overview of SRs.

DATA SOURCES

We searched PubMed, Embase, Cochrane Library, Web of Science, CINAHL, Chinese National Knowledge Infrastructure (CNKI), Chinese Biomedical Literature Database (CBM), Wanfang Database, Chinese Science and Technology Periodical Database (VIP) and Google Scholar to identify all relevant SRs published in the last 5 years.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

We included SRs that evaluated the efficacy and safety of non-pharmacological interventions for neonatal pain.

DATA EXTRACTION AND SYNTHESIS

Two reviewers independently extracted the data, assessed the methodological quality using a Measurement Tool to Assess Systematic Reviews (AMSTAR) 2 and graded the evidence quality with the Grading of Recommendations Assessment, Development and Evaluation (GRADE).

RESULTS

A total of 29 SRs were included in this overview, of which 28 focused on procedural pain and only 1 focused on postoperative pain. Based on AMSTAR 2, seven reviews were found to be of 'high quality', eight of 'moderate quality', five of 'low quality' and nine of 'critically low quality'. The GRADE results suggested that facilitated tucking, kangaroo care, sweet solutions, familiar odour or combined non-pharmacological interventions, such as a combination of sucrose and non-nutritive sucking, were effective and safe in reducing pain from medical procedures in neonates. However, sucrose alone was less effective than local anaesthesia or a combination of the two during circumcision.

CONCLUSIONS

Facilitated tucking, small volumes of sweet solutions, kangaroo care and familiar odour were recommended. Scientific implementation strategies should be developed to promote the clinical use of these effective non-pharmacological interventions. Meanwhile, further rigorous trials and SRs are needed to identify the best non-pharmacological approaches for pain from common surgery and illnesses in neonates.

PROSPERO REGISTRATION NUMBER

CRD42021292583.

Efficacy of Breast Milk Olfactory and Gustatory Interventions on Neonates’ Biobehavioral Responses to Pain during Heel Prick Procedures

This study aimed to evaluate the efficacy of breast milk odor either alone or in combination with breast milk taste (via syringe-feeding) to alleviate neonates’ biobehavioral responses to pain during heel-prick procedures. This prospective randomized controlled trial recruited 114 neonates by convenience sampling from a newborn unit of a medical center in Taiwan. Neonates were randomly assigned to three groups: control (gentle touch + human voice), control + breast milk odor, and control + breast milk odor + breast milk taste. Heart rate, oxygen saturation, and voice recordings of crying were measured across heel-prick procedures: baseline, no stimuli (stage 0); during heel prick (Stages 1–4); and recovery (Stages 5–10). Generalized estimating equations and Kaplan–Meier survival analysis compared differences in changes between groups for heart rate, oxygen saturation, and time to crying cessation. Changes in mean heart rate and oxygen saturation in neonates receiving breast milk odor or breast milk odor + breast milk taste were significantly less than those at the corresponding stage for the control group. Among neonates receiving breast milk odor or breast milk odor + breast milk taste, hazard rate ratios for crying cessation were 3.016 and 6.466, respectively. Mother’s breast milk olfactory and gustatory interventions could stabilize the biobehavioral responses to pain during heel prick procedures in neonates.

Breastmilk as a Multisensory Intervention for Relieving Pain during Newborn Screening Procedures: A Randomized Control Trial

The study aim was to explore the effects of multisensory breastmilk interventions on short-term pain of infants during newborn screening. This is a randomized controlled trial. A total of 120 newborns were recruited and assigned by randomization to one of three treatment conditions: Condition 1 = routine care (gentle touch + verbal comfort); Condition 2 = breastmilk odor + routine care; or Condition 3 = breastmilk odor + taste + routine care. Pain was scored with the Neonatal Infant Pain Scale (NIPS). Data were collected from video recordings at 1 min intervals over the 11 phases of heel sticks: phase 1, 5 min before heel stick without stimuli (baseline); phase 2 to phase 6 (during heel stick); and phase 7 to phase 11 (recovery). Generalized estimating equations compared differences in pain scores for newborns over phases among the three conditions. Compared with the routine care, provision of the odor and taste of breastmilk reduce NIPS scores during heel sticks (B = −4.36, SE = 0.45, p < 0.001 [phase₆]), and during recovery (B = −3.29, SE = 0.42, p < 0.001 [phase₇]). Our findings provide new data, which supports the use of multisensory interventions that include breastmilk odor and taste in combination with gentle touch and verbal comfort to relieve pain in infants undergoing newborn screening.

Human Milk Microbiota and Oligosaccharides: A Glimpse into Benefits, Diversity, and Correlations

Human milk represents a cornerstone for growth and development of infants, with extensive array of benefits. In addition to exceptionally nutritive and bioactive components, human milk encompasses a complex community of signature bacteria that helps establish infant gut microbiota, contributes to maturation of infant immune system, and competitively interferes with pathogens. Among bioactive constituents of milk, human milk oligosaccharides (HMOs) are particularly significant. These are non-digestible carbohydrates forming the third largest solid component in human milk. Valuable effects of HMOs include shaping intestinal microbiota, imparting antimicrobial effects, developing intestinal barrier, and modulating immune response. Moreover, recent investigations suggest correlations between HMOs and milk microbiota, with complex links possibly existing with environmental factors, genetics, geographical location, and other factors. In this review, and from a physiological and health implications perspective, milk benefits for newborns and mothers are highlighted. From a microbiological perspective, a focused insight into milk microbiota, including origins, diversity, benefits, and effect of maternal diet is presented. From a metabolic perspective, biochemical, physiological, and genetic significance of HMOs, and their probable relations to milk microbiota, are addressed. Ongoing research into mechanistic processes through which the rich biological assets of milk promote development, shaping of microbiota, and immunity is tackled.

Pain, Smell, and Taste in Adults: A Narrative Review of Multisensory Perception and Interaction

Every day our sensory systems perceive and integrate a variety of stimuli containing information vital for our survival. Pain acts as a protective warning system, eliciting a response to remove harmful stimuli; it may also be a symptom of an illness or present as a disease itself. There is a growing need for additional pain-relieving therapies involving the multisensory integration of smell and taste in pain modulation, an approach that may provide new strategies for the treatment and management of pain. While pain, smell, and taste share common features and are strongly linked to emotion and cognition, their interaction has been poorly explored. In this review, we provide an overview of the literature on pain modulation by olfactory and gustatory substances. It includes adult human studies investigating measures of pain threshold, tolerance, intensity, and/or unpleasantness. Due to the limited number of studies currently available, we have structured this review as a narrative in which we comment on experimentally induced and clinical pain separately on pain–smell and pain–taste interaction. Inconsistent study findings notwithstanding, pain, smell, and taste seem to interact at both the behavioral and the neural levels. Pain intensity and unpleasantness seem to be affected more by olfactory substances, whereas pain threshold and tolerance are influenced by gustatory substances. Few pilot studies to date have investigated these effects in clinical populations. While the current results are promising for the future, more evidence is needed to elucidate the link between the chemical senses and pain. Doing so has the potential to improve and develop novel options for pain treatment.

The effect of inhaling mother's breast milk odor on the behavioral responses to pain caused by hepatitis B vaccine in preterm infants: a randomized clinical trial

Background

Nowadays, it is generally assumed that non-pharmacologic pain relief in preterm infants is an important measure to consider. Research findings suggest that familiar odors have soothing effects for neonates. The aim of this study was to compare the effect of maternal breast milk odor (MBMO) with that of another mother’s breast milk odor (BMO) on the behavioral responses to pain caused by hepatitis B (HB) vaccine injection in preterm infants.

Methods

This single-blind randomized clinical trial was performed over the period between February 2019 and March 2020 in the neonatal intensive care unit of Babol Rouhani Hospital, Iran. Ninety preterm infants, who were supposed to receive their HB vaccine, were randomly assigned into three groups: MBMO (A), another mother’s BMO (B), and control with distilled water(C). Oxygen saturation (SaO2), blood pressure (BP) and heart rate (HR) were recorded for all participants through electronic monitoring. In addition, premature infant pain profiles (PIPP) were determined through video recording for all three groups during intervention. The chi-square, ANOVA and ANCOVA were used for analyzing the data, and P < 0.05 was considered significant in this study.

Results

No significant differences were found between the three groups in mean ± SD of HR, BP, and Sao2 before the intervention (P > 0.05). After the intervention, however, the means for heart rate in groups A, B, and C were 146 ± 14.3, 153 ± 17.5 and 155 ± 17.7, respectively (P = 0.012). Moreover, the means for PIPP scores in groups A, B and C were 6.6 ± 1.3, 10 ± 2, and 11.4 ± 1.9, respectively (P < 0.001). There was no significant difference found between groups in their means of SaO2, systolic and diastolic blood pressure after the intervention (P > 0.05).

Conclusions

The results indicate that stimulation with MBMO is effective in reducing pain in preterm infants; therefore, it can be postulated that this technique can be considered in less invasive procedures such as needling.

Trial registration

IRCT, IRCT20190220042771N1. Registered 18 May 2019- Retrospectively registered,

A Randomized Controlled Trial: The Effect of Own Mother's Breast Milk Odor and Another Mother's Breast Milk Odor on Pain Level of Newborn Infants

Objective: Our research was conducted empirically to determine whether another mother's breast milk could be used to reduce the pain of newborns who were not able to access their own mother's milk for any reason. Materials and Methods: The sample group of the research included 90 newborns [smell of own mother's milk (30), smell of another mother's milk (30), and the control group (30)] hospitalized in the unit. A neonatal information form was used as the data collection tool, the Neonatal Pain, Agitation, and Sedation Scale (N-PASS) was used to assess the newborn's pain, and an evaluation form prepared by the researcher was used to record the findings. Results: The group which was exposed to their own mother's milk had a significantly lower N-PASS mean score compared to other groups and the group which was exposed to another mother's milk was observed to have a significantly lower N-PASS mean score compared to the control group (p < 0.05). While the median values for the total time spent crying of the "own mother's milk" group and the "another mother's milk" group were similar; the total time spent crying of the control group had a significantly higher median value. Conclusion: Our research determined that, while the most effective method for reducing pain in newborns was the smell of their own mother's breast milk, for newborns who were not able to access their own mother's breast milk, the smell of breast milk from a different mother could also be used.

Non-pharmacological care for opioid withdrawal in newborns

BACKGROUND

The prevalence of substance use, both prescribed and non-prescribed, is increasing in many areas of the world. Substance use by women of childbearing age contributes to increasing rates of neonatal abstinence syndrome (NAS). Neonatal opioid withdrawal syndrome (NOWS) is a newer term describing the subset of NAS related to opioid exposure. Non-pharmacological care is the first-line treatment for substance withdrawal in newborns. Despite the widespread use of non-pharmacological care to mitigate symptoms of NAS, there is not an established definition of, and standard for, non-pharmacological care practices in this population. Evaluation of safety and efficacy of non-pharmacological practices could provide clear guidance for clinical practice.

OBJECTIVES

To evaluate the safety and efficacy of non-pharmacological treatment of infants at risk for, or having symptoms consistent with, opioid withdrawal on the length of hospitalization and use of pharmacological treatment for symptom management. Comparison 1: in infants at risk for, or having early symptoms consistent with, opioid withdrawal, does non-pharmacological treatment reduce the length of hospitalization and use of pharmacological treatment? Comparison 2: in infants receiving pharmacological treatment for symptoms consistent with opioid withdrawal, does concurrent non-pharmacological treatment reduce duration of pharmacological treatment, maximum and cumulative doses of opioid medication, and length of hospitalization?

SEARCH METHODS

We used the standard search strategy of Cochrane Neonatal to search CENTRAL (2019, Issue 10); Ovid MEDLINE; and CINAHL on 11 October 2019. We also searched clinical trials databases and the reference lists of retrieved articles for randomized controlled trials (RCTs), quasi-RCTs, and cluster trials.

SELECTION CRITERIA

We included trials comparing single or bundled non-pharmacological interventions to no non-pharmacological treatment or different single or bundled non-pharmacological interventions. We assessed non-pharmacological interventions independently and in combination based on sufficient similarity in population, intervention, and comparison groups studied. We categorized non-pharmacological interventions as: modifying environmental stimulation, feeding practices, and support of the mother-infant dyad. We presented non-randomized studies identified in the search process narratively.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. We used the GRADE approach to assess the certainty of evidence. Primary outcomes in infants at risk for, or having early symptoms consistent with, opioid withdrawal included length of hospitalization and pharmacological treatment with one or more doses of opioid or sedative medication. Primary outcomes in infants receiving opioid treatment for symptoms consistent with opioid withdrawal included length of hospitalization, length of pharmacological treatment with opioid or sedative medication, and maximum and cumulative doses of opioid medication.

MAIN RESULTS

We identified six RCTs (353 infants) in which infants at risk for, or having symptoms consistent with, opioid withdrawal participated between 1975 and 2018. We identified no RCTs in which infants receiving opioid treatment for symptoms consistent with opioid withdrawal participated. The certainty of evidence for all outcomes was very low to low. We also identified and excluded 34 non-randomized studies published between 2005 and 2018, including 29 in which infants at risk for, or having symptoms consistent with, opioid withdrawal participated and five in which infants receiving opioid treatment for symptoms consistent with opioid withdrawal participated. We identified seven preregistered interventional clinical trials that may qualify for inclusion at review update when complete. Of the six RCTs, four studies assessed modifying environmental stimulation in the form of a mechanical rocking bed, prone positioning, non-oscillating waterbed, or a low-stimulation nursery; one study assessed feeding practices (comparing 24 kcal/oz to 20 kcal/oz formula); and one study assessed support of the maternal-infant dyad (tailored breastfeeding support). There was no evidence of a difference in length of hospitalization in the one study that assessed modifying environmental stimulation (mean difference [MD) -1 day, 95% confidence interval [CI) -2.82 to 0.82; 30 infants; very low-certainty evidence) and the one study of support of the maternal-infant dyad (MD -8.9 days, 95% CI -19.84 to 2.04; 14 infants; very low-certainty evidence). No studies of feeding practices evaluated the length of hospitalization. There was no evidence of a difference in use of pharmacological treatment in three studies of modifying environmental stimulation (typical risk ratio [RR) 1.00, 95% CI 0.86 to 1.16; 92 infants; low-certainty evidence), one study of feeding practices (RR 0.92, 95% CI 0.63 to 1.33; 49 infants; very low-certainty evidence), and one study of support of the maternal-infant dyad (RR 0.50, 95% CI 0.13 to 1.90; 14 infants; very low-certainty evidence). Reported secondary outcomes included neonatal intensive care unit (NICU) admission, days to regain birth weight, and weight nadir. One study of support of the maternal-infant dyad reported NICU admission (RR 0.50, 95% CI 0.13 to 1.90; 14 infants; very low-certainty evidence). One study of feeding practices reported days to regain birth weight (MD 1.10 days, 95% CI 2.76 to 0.56; 46 infants; very low-certainty evidence). One study that assessed modifying environmental stimulation reported weight nadir (MD -0.28, 95% CI -1.15 to 0.59; 194 infants; very low-certainty evidence) and one study of feeding practices reported weight nadir (MD -0.8, 95% CI -2.24 to 0.64; 46 infants; very low-certainty evidence).

AUTHORS' CONCLUSIONS

We are uncertain whether non-pharmacological care for opioid withdrawal in newborns affects important clinical outcomes including length of hospitalization and use of pharmacological treatment based on the six included studies. The outcomes identified for this review were of very low- to low-certainty evidence. Combined analysis was limited by heterogeneity in study design and intervention definitions as well as the number of studies. Many prespecified outcomes were not reported. Although caregivers are encouraged by experts to optimize non-pharmacological care for opioid withdrawal in newborns prior to initiating pharmacological care, we do not have sufficient evidence to inform specific clinical practices. Larger well-designed studies are needed to determine the effect of non-pharmacological care for opioid withdrawal in newborns.

The Calming Effect of Maternal Breast Milk Odor on Term Infant: A Randomized Controlled Trial

Purpose: This study was carried out to assess the effect of the odor of breast milk and formula milk on reducing the acute pain of newborn infants during the heel-prick blood sampling. Methods: Eighty-four newborn were randomly assigned into two groups (formula milk group and breast milk group) with 42 infant searches. The pain that the newborn felt before, during, and after heel-prick blood sampling was assessed using Neonatal Infant Pain Scale; their heart rate and blood oxygen saturation were measured with a pulse oximeter. Saliva samples were taken from newborns before and after sampling, and their salivary cortisol level was measured. During sampling, the crying duration of newborn was recorded with a chronometer. Results: The pain threshold and heart rates of the newborn in the breast milk group were significantly lower than those in the formula milk group (p < 0.001). Salivary cortisol in the formula milk group increased and oxygen saturation levels in these infants decreased significantly more as compared to the breast milk group (p < 0.05). Conclusions: The odor of breast milk may be helpful in reducing the pain of newborn during heel-prick blood sampling.

Maternal odor reduces the neural response to fearful faces in human infants

Maternal odor is known to play an important role in mother-infant-interaction in many altricial species such as rodents. However, we only know very little about its role in early human development. The present study therefore investigated the impact of maternal odor on infant brain responses to emotional expression. We recorded the electroencephalographic (EEG) signal of seven-month-old infants watching happy and fearful faces. Infants in two control groups exposed to no specific odor (control 1) or the odor of a different infant’s mother (control 2) showed the expected EEG fear response. Crucially, this response was markedly absent in the experimental group exposed to their mother’s odor. Thus, infants respond differently to fear signals in the presence of maternal odor. Our data therefore suggest that maternal odor can be a strong modulator of social perception in human infants.

Systematic review and meta-analysis of olfactive stimulation interventions to manage procedural pain in preterm and full-term neonates

BACKGROUND

Preterm and full-term neonates undergo many painful procedures during their hospitalization in the neonatal intensive care unit. Unrelieved and repeated pain can have important repercussions on their motor and intellectual development. Still, pain management interventions are limited for neonates.

OBJECTIVE

This systematic review aimed to evaluate the effectiveness of olfactive stimulation interventions on the pain response of preterm and full-term infants during painful procedures.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

An electronic search was conducted from inception to August 2019 in PubMed, MEDLINE, Embase, CINAHL, PsycINFO, Web of Sciences, CENTRAL, Scopus and ProQuest.

REVIEW METHODS

Study selection, data extraction, assessment of risk of bias and quality of evidence were performed by two independent reviewers.

RESULTS

3311 studies were screened. Of the 14 studies included studies (n = 1028 infants), results from 10 were combined in meta-analysis. The latter demonstrated that olfactive stimulation interventions using a familiar odor were effective compared to standard care on pain reactivity (SMD -0.69; 95% CI -0.93 to -0.44; I² = 20%, p < 0.00001), pain regulation (SMD -0.40; 95% CI -0.66 to -0.14; I² = 13%, p = 0.002), crying duration during (SMD -0.42; 95% CI -0.73 to -0.10; I² = 47%, p = 0.009) and after the procedure (SMD -0.37; 95% CI -0.68 to -0.07; I² = 0%, p = 0.01), heart rate after the procedure (MD -3.87; 95% CI -7.36 to -0.38; I² = 99%, p = 0.03), oxygen saturation during (MD -0.47; 95% CI -0.86 to -0.08; I² = 91%, p = 0.02) and after the procedure (MD -0.56; 95% CI -0.99 to -0.13; I² = 99%, p = 0.01). No adverse event was reported.

CONCLUSION

These findings are based on low to very low quality of evidence limiting our confidence in effect estimates. More rigorous trials with a larger sample size are needed to enhance the comprehension of the mechanisms underlying olfactive stimulation interventions and the interventions' efficacy.

Effects of Combined Use of Mother's Breast Milk, Heartbeat Sounds, and Non-Nutritive Sucking on Preterm Infants' Behavioral Stress During Venipuncture: A Randomized Controlled Trial

PURPOSE

Even routine procedures can cause pain and stress, and can be harmful to the fast-growing brain of preterm infants. Mitigating pain and stress with sucrose and analgesics has side effects; thus, an alternate choice is the use of natural breast milk and infants' sensory capabilities. Therefore, this study examined the effects of different integrations of sensory experiences-mother's breast milk odor and taste (BM-OT), heartbeat sounds (HBs), and non-nutritive sucking (NNS)-on preterm infant's behavioral stress during venipuncture.

DESIGN

This study was a prospective, randomized controlled trial.

METHODS

Infants born preterm (<37 weeks' gestational age) were enrolled in the study through convenience sampling, and randomly assigned to the following conditions: (condition 1) routine care (n = 36); (condition 2) BM-OT (n = 33); (condition 3) BM-OT + HBs (n = 33); or (condition 4) BM-OT + HBs + NNS (n = 36). Crying duration from puncture to recovery period was recorded using a voice recorder. Facial actions and body movements were measured using an infant behavioral coding scheme and transformed into frequencies during seven stages: baseline (stage 0), disinfecting (stage 1), venipuncture (stage 2), and the recovery period for 10 minutes (stages 3-6).

FINDINGS

Data were analyzed for 138 preterm infants. The corresponding median times to stop crying for conditions 1, 2, 3, and 4 were 137, 79, 81, and 39 s, respectively; the instantaneous occurrence rates of stopping crying for conditions 2, 3, and 4 were 1.469, 1.574, and 2.996 times greater than for condition 1, respectively. Infants receiving conditions 3 and 4 had significantly fewer occurrences of facial actions (stage 6 and stages 4-6, respectively) and body movements (stages 3-6 for both); however, there were no significant reductions in stress behaviors for condition 2 (BM-OT).

CONCLUSIONS

The combination of BM-OT, HBs, and NNS could be provided to preterm infants as interventions to prevent and reduce behavioral stress, and facilitate pain recovery during venipuncture procedures.

CLINICAL RELEVANCE

Clinicians should be educated about how to recognize preterm infants' behavioral stress, and to incorporate different sensory combinations of respective mothers' BM, HBs, and NNS into painful procedures to help preterm infants recover from distress.

Differential olfactory bulb methylation and hydroxymethylation are linked to odor location memory bias in injured mice

Chronic pain is often linked to comorbidities such as anxiety and cognitive dysfunction, alterations that are reflected in brain plasticity in regions such as the prefrontal cortex and the limbic area. Despite the growing interest in pain-related cognitive deficits, little is known about the relationship between the emotional valence of the stimulus and the salience of its memory following painful injuries. We used the tibia fracture model of chronic pain in mice to determine whether pleasant and unpleasant odor location memories differ in their salience seven weeks following the onset of the painful injury. Our results indicate that injured mice show a bias toward recalling unpleasant memories, thereby propagating the vicious cycle of chronic pain and negative affect. Next, we linked these behavioral differences to mechanisms of molecular plasticity by measuring the levels of global methylation and hydroxymethylation in the olfactory bulb. Compared to controls, global methylation levels were shown to be increased, while hydroxymethylation levels were decreased in the olfactory bulb of injured mice, indicative of overall changes in DNA regulation machinery and the subsequent alterations in sensory systems.