Naloxone prevents cell-mediated immune alterations in adult mice following repeated mild stress in the neonatal period

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

BACKGROUND AND AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

Naloxone Diminishes the Virulence and Modifies the Cellular Immune Responses of BALB/c Mice Infected with Leishmania major

PURPOSE

Leishmania major-infected BALB/c mice display strong susceptibility to the infection due to the induction of Th2 response. The aim of this study was to assess the effects of naloxone on virulence of L. major in BALB/c mice and the ensued cellular immune response.

METHODS

The effects of injection of a single dose of naloxone in the footpad of L. major-infected BALB/c mice were investigated by evaluating the lesion sizes, the parasite burden, cell proliferation, secreted cytokines (IFN-γ, IL-4, IL-10 and IL-12) and their genes expressions due to naloxone treatment while the untreated mice were used as a control.

RESULTS

Significantly lower lesion sizes and less parasite burden were measured in the treated mice. Significantly decreased productions of IFN-γ, IL-12, IL-4, and IL-10 were also observed in the treated mice at week 4 post-infection while the production IL-10 remained significantly hindered till 8 weeks post-infection.

CONCLUSION

Our data indicated that although the treatment of L. major-infected BALB/c mice with a single dose of naloxone was unable to improve the cellular immune response, it led to lower virulence, confirmed by significantly reduced lesions and parasite load.

Effect of Intermittent and Mild Cold Stimulation on the Immune Function of Bursa in Broilers

Cold stress causes growth performance to decrease and increases production costs. Cold adaptation can enhance immune function and alleviate the negative impact caused by the stress condition. The study investigated the effect of intermittent and mild cold stimulation on the immune function of the bursa of Fabricius in broilers. A total of 400 healthy one-day-old broilers were divided into the control group (CC) and cold stimulation (CS) groups. The CC group was raised at a conventional raising temperature of broilers, while the CS groups were raised at 3°C below the temperature of the CC for three-, four-, five-, or six-hour periods at one-day intervals from 15 to 35 days of age (D35), denoted CS3, CS4, CS5, and CS6, respectively. Subsequently, they were raised at 20°C from 36 to 49 days of age (D49). The expression levels of TLRs, cytokines, and AvBDs were determined to access the immune function of bursa in broilers. After 21-day IMCS (at D36), the expression levels of TLR1, TLR15 and TLR21, interleukin (IL)-8, and interferon (IFN)-γ, as well as AvBD8 in CS groups, were lower than those in CC (p < 0.05). The expression levels of TLR3, TLR4 and TLR7, were decreased in the CS3, CS5, and CS6 groups (p < 0.05), but there were no significant differences in both the CC and CS4 groups (p > 0.05). When the IMCS ended for 14 days (at D49), the expression levels of TLR2, TLR3, TLR5, TLR7, TLR15, and TLR21, and IL-8, as well as AvBD2, AvBD4 and AvBD7 in CS groups, were lower than those in CC (p < 0.05). In addition to CS4, the expression levels of TLR1, IFN-γ, and AvBD8 in CS3, CS5, and CS6 were still lower than those in CC (p < 0.05). We concluded that the intermittent and mild cold stimulation could regulate immunoreaction by modulating the production of TLRs, cytokines, and AvBDs in the bursa, which could help broilers adapt to low ambient temperature and maintain homeostasis.

Early life stress in mice is a suitable model for Irritable Bowel Syndrome but does not predispose to colitis nor increase susceptibility to enteric infections

Neonatal period is characterized by an immature intestinal barrier. Scattered evidence suggests that early life stressful events induce long lasting alterations of intestinal homeostasis mimicking Irritable Bowel Syndrome (IBS). Those observations highlighting defect of intestinal barrier by early life stress questioned its potential role as a risk factor for gastrointestinal disorders such as colitis and infections. In this study, we aimed to analyze if maternal separation (MS) in mice mimicks IBS main features. We next addressed whether MS could trigger or exacerbate colitis in genetically predisposed mice and/or enhance susceptibility to gastrointestinal infections in wild type mice. MS induced main features of IBS in adult wild type male mice i.e. intestinal hyperpermeability, visceral hypersensitivity, microbiota dysbiosis, bile acid malabsorption and low grade inflammation in intestine associated with a defect of Paneth cells and the ILC3 population. This breach in mucosal barrier functions in adults was associated with a systemic IgG response against commensal E. coli and increased IFNγ secretion by splenocytes. However, in IL10^-/- mice, MS did not trigger nor worsen colitis. Furthermore, wild type mice submitted to MS did not show increase susceptibility to gastrointestinal infections (S. Typhimurium, L. monocytogenes or T. gondii) compared to controls. Altogether, our results identify MS in mice as a good experimental model for IBS mimicking all the main features. In addition, early life stress, even though it has long lasting consequences on intestinal homeostasis, does not constitute a facilitating factor to colitis in predisposed individuals nor to gastrointestinal infections in wild type mice.

Etiopathogenesis and Pharmacological Prevention of a Type-2 Diabetes Model in Male Mice

We describe a stress-derived type-2 diabetes model in male mice, and formulate new hypotheses on how the model was induced, how diabetes-like alterations were prevented through specific pharmacological treatments, and how its possible neuroendocrine pathogenesis could be hypothesized. Pregnant females arrived in our laboratory on their 14th day of conceptional age. After birth, control mice never showed any apparent behavioral-metabolic-endocrine alterations. However, application of postnatal stress (brief mother deprivation, plus sham injection, daily from birth to weaning), was followed in adult male mice by two series of diabetes-like alterations. Some alterations (e.g., body overweight, immune, neurophysiologic, neurobehavioral alterations) were selectively prevented by opioid antagonist naloxone daily administered during nursing period. The aforementioned alterations plus several others (e.g., hyperglycemia, neuroendocrine alterations) were prevented by administration of specific antisense oligodeoxinucleotide, which modulated synthesis-hyperfunction of proopiomelanocortin-derived corticotropin (ACTH)-corticosterone and endorphins in the pituitary. Surprisingly, together with metabolic alterations, enduring increment of neurophysiologic/neurobehavioral brain performances were observed, accompanied by energy compensative reactions, and brain mitochondria hyperfunction. Thus, increased glycemia/lipidemia appeared to furnish fuel necessary to cope with increased request of energy. Diabetes-like alterations were accompanied by enduring hyperfunction of opioid- and ACTH-corticosterone-endogenous structures in the brain, which were apparently due to failure of negative feedback hormone mechanisms in the pituitary, for the control of the hypothalamus-pituitary-adrenal axis. In conclusion, for the first time we can hypothesize that a diabetes-like syndrome is produced by enduring hyperfunction of two proopiomelanocortin-dependent endogenous systems (brain opioid- and ACTH-corticosterone systems), following failure of pituitary feedback hormonal control, after complex stress procedures.

Antisense versus proopiomelanocortin mRNA reduces vascular risk in a murine model of type-2 diabetes following stress exposure in early post-natal life

Mechanisms of vascular complications in type-2 diabetes patients and animal models are matter of debate. We previously demonstrated that a double-stress model applied to male mice during nursing period produces enduring hyperfunction of endogenous opioid and adrenocorticotropin (ACTH)-corticosteroid systems, accompanied by type-2 diabetes-like alterations in adult animals. Administration of the opioid receptor antagonist naloxone, or of an antisense oligodeoxynucleotide versus proopiomelanocortin mRNA, capable to block the pro-opiomelanocortin-derived peptides β-endorphin and ACTH, selectively prevent these alterations. Here, we investigated alterations produced by our stress model on aorta endothelium-dependent relaxation and contractile responses. Mice, stressed during nursing period, showed in the adulthood hormonal and metabolic type-2 diabetes-like alterations, including hyperglycemia, increased body weight and increased plasma ACTH and corticosterone levels. Ex vivo isolated aorta rings, gathered from stressed mice, were less sensitive to noradrenaline-induced contractions versus controls. This effect was blocked by nitric-oxide synthase-inhibitor l-N(G)-nitroarginine added to bath organ solution. Aorta rings relaxation caused by acetylcholine was enhanced in stressed mice versus controls, but following treatment with the nitric-oxide donor sodium nitroprusside, concentration-relaxation curves in aorta from stressed groups were similar to controls. Therefore, vascular response alterations to physiologic-pharmacologic stimuli were apparently due to nitric-oxide hyperfunction-dependent mechanisms. Aorta functional alterations, and plasma stress hormones enhancement, were prevented in mice stressed and treated with antisense oligodeoxinucleotide, addressed to reduce ACTH- and corticosteroid-mediated hyperfunction. This study demonstrates the key role of ACTH-corticosteroid axis hyperfunction for the triggering of vascular conditions in male adult rodents following postnatal stress in a type-2 diabetes model.

Stress in the adult rat exacerbates muscle pain induced by early-life stress

BACKGROUND

Early-life stress and exposure to stressful stimuli play a major role in the development of chronic widespread pain in adults. However, how they interact in chronic pain syndromes remains unclear.

METHODS

Dams and neonatal litters were submitted to a restriction of nesting material (neonatal limited bedding [NLB]) for 1 week. As adults, these rats were exposed to a painless sound stress protocol. The involvement of sympathoadrenal catecholamines interleukin 6 (IL-6) and tumor necrosis factor alpha (TNFα) in nociception was evaluated through behavioral and enzyme-linked immunosorbent assays, surgical interventions, and intrathecal antisense treatments.

RESULTS

Adult NLB rats exhibited mild muscle hyperalgesia, which was markedly aggravated by sound stress (peaking 15 days after exposure). Adrenal medullectomy did not modify hyperalgesia in NLB rats but prevented its aggravation by sound stress. Sustained administration of epinephrine to NLB rats mimicked sound stress effect. Intrathecal treatment with antisense directed to IL-6 receptor subunit gp130 (gp130), but not to tumor necrosis factor receptor type 1 (TNFR1), inhibited hyperalgesia in NLB rats. However, antisense against either gp130 or TNFR1 inhibited sound stress-induced enhancement of hyperalgesia. Compared with control rats, NLB rats exhibit increased plasma levels of IL-6 but decreased levels of TNFα, whereas sound stress increases IL-6 plasma levels in control rats but not in NLB rats.

CONCLUSIONS

Early-life stress induces a persistent elevation of IL-6, hyperalgesia, and susceptibility to chronic muscle pain, which is unveiled by exposure to stress in adults. This probably depends on an interaction between adrenal catecholamines and proinflammatory cytokines acting at muscle nociceptor level.

Enhanced brain performance in mice following postnatal stress

The double postnatal stress model (brief maternal separation plus sham injection daily applied from birth to weaning) induces metabolic alterations similar to type 2 diabetes in young-adult male mice. We verify whether 1) the stress also induces brain metabolic-functional alterations connected to diabetes and 2) different alterations are modulated selectively by two stress-damaged endogenous systems (opioid- and/or ACTH-corticosteroid-linked). Here, diabetes-like metabolic plus neurophysiologic-neurometabolic parameters are studied in adult mice following postnatal stress and drug treatment. Surprisingly, together with 'classic' diabetes-like alterations, the stress model induces in young-adult mice significantly enhanced brain neurometabolic-neurophysiologic performances, consisting of decreased latency to flash-visual evoked potentials (- ~8%); increased level (+ ~40%) and reduced latency (- ~30%) of NAD(P)H autofluorescence postsynaptic signals following electric stimuli; enhanced passive avoidance learning (+ ~135% latency); and enhanced brain-derived neurotrophic factor level (+ ~70%). Postnatal treatment with the opioid receptor antagonist naloxone prevents some alterations, moreover the treatment with antisense (AS; AS vs proopiomelanocortin mRNA) draws all parameters to control levels, thus showing that some alterations are bound to endogenous opioid-system hyper-functioning, while others depend on ACTH-corticosterone system hyper-functioning. Our stress model induces diabetes-like metabolic alterations coupled to enhanced brain neurometabolic-neurophysiologic performances. Taken all together, these findings are compatible with an 'enduring acute-stress' reaction, which puts mice in favorable survival situations vs controls. However, prolonged hormonal-metabolic imbalances are expected to also produce diabetes-like complications at later ages in stressed mice.

Cytokines and irritable bowel syndrome: where do we stand?

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder, which presents with one or more gastrointestinal symptoms without any structural or organic abnormality. The etiology and pathophysiological mechanisms of IBS remain uncertain. Residual or reactivated inflammation at the molecular level is considered the underlying mechanism of post-infectious IBS. On the other hand, genetic variations in the immunological components of the body, including cytokine gene polymorphisms, are proposed as a potential mechanism of IBS even in patients without previous gastrointestinal infection. Several studies have suggested imbalanced cytokine signaling as an etiology for IBS. In this review, recent findings on cytokine profiles and cytokine gene polymorphisms in patients with IBS are described and the role of cytokines in animal models of IBS is discussed.

The CB₁ receptor antagonist SR141716A reverses adult male mice overweight and metabolic alterations induced by early stress

Perinatal stress may cause metabolic and hormonal disruptions during adulthood. The aim of this study was to evaluate the effects of early postnatal nociceptive stimulation (NS) on body weight and other metabolic parameters during adulthood and to determine whether CB₁ endocannabinoid receptors (CB₁Rs) may be involved in these effects. Male mice were subjected to NS during lactation with a daily subcutaneous injection of saline solution. Subsequently, both control and NS-mice were treated from day 40 to 130, with an oral dose (1 µg/g body weight) of SR141716A, a specific CB₁R antagonist/inverse agonist. Mice body weight and food intake was periodically evaluated. Adult animals were then killed to evaluate epididymal fat pads and metabolic parameters. NS did not influence food intake in adult animals, but caused significant increases in body weight, epididymal fat pads, and circulating levels of leptin, corticosterone, and triglycerides (TGs). Chronic treatment with SR141716A normalized these parameters, with the exception of corticosterone levels. This treatment also reduced plasma levels of glucose, insulin, and total cholesterol in both adult control and NS-mice. In addition, fatty acid (FA) amide hydrolase (FAAH) activity (the enzyme able to hydrolyze endocannabinoids) from liver and epididymal fat of adult NS-mice was decreased by 40-50% in comparison to activities found in same tissues of control mice. Results suggest that overactive liver and epididymal fat CB₁R due to early NS may be involved in late metabolic alterations, which are sensitive to chronic treatment with SR141716A.

Post-natal stress-induced endocrine and metabolic alterations in mice at adulthood involve different pro-opiomelanocortin-derived peptides

In previous investigations we added a physical stress (mild pain) to the "classical" post-natal psychological stress in male mice, and we found that this combination produced a series of dysmetabolic signs very similar to mild human type-2 diabetes. Here, for the first time we demonstrate that within this diabetes model at least two groups of signs depend on the unbalance of two different endogenous systems. Newborn male mice were daily exposed to stressful procedures for 21 days (brief mother separation plus sham injection). Other groups underwent the same procedure, and also received naloxone (Na) to block μ-δ endogenous receptors, or a phosphorothioate antisense oligonucleotide (AS) directed against pro-opiomelanocortin (POMC)-mRNA [to block adrenocorticotropin (ACTH)- and POMC-derived opioid peptides]. Adult mice which received only post-natal stress increased body weight (+7.5%), abdominal overweight (+74%), fasting glycemia (+43%), plasma corticosterone (+110%), plasma (+169%) and pituitary (+153%) ACTH levels. Conversely, hypothalamic ACTH and corticotropin-releasing hormone (CRH) were reduced (-70% and -75%, respectively). Neonatal AS administration reverted all parameters to control values. Neonatal naloxone had little or no influence on glucose, corticosterone, ACTH, CRH levels, whereas it prevented body overweight and abdominal overweight. We conclude that, within this type-2 diabetes model in male mice at least two endocrino-neurohumoral systems are damaged, one concerning the opioid system, and the other concerning HPA hormones. The use of the two drugs was of primary importance to demonstrate this statement, and to demonstrate that these two groups of signs could be defined as "separate entities" following our complex post-natal stress model.

Plasma cytokine profiles in females with irritable bowel syndrome and extra-intestinal co-morbidity

OBJECTIVES

Irritable bowel syndrome (IBS) is a functional disorder that is associated with a number of extra-intestinal co-morbidities and a pro-inflammatory profile. This study was designed to examine the cytokine profile among a group of IBS patients with the extra-intestinal co-morbidities fibromyalgia, premenstrual dysmorphic disorder, and chronic fatigue syndrome.

METHODS

In all, 100 female IBS patients with these co-morbidities, 21 IBS subjects without co-morbidity ("pure" IBS; Rome II), and 54 age-matched female controls took part in the study. Blood was drawn for measurement of the plasma cytokines interleukin (IL)-1β, IL-6, IL-8, IL-10, IL-12p70, IL-13, tumor necrosis factor (TNF)α, and interferon γ. The presence of the selected extra-intestinal manifestations was assessed using standard international criteria.

RESULTS

Patients with IBS have increased plasma levels of IL-6 and IL-8; those with these extra-intestinal co-morbidities were found to have, in addition, increased levels of IL-1β and TNFα. No associations were evident between cytokine profiles and the nature of the co-morbidity or number of extra-intestinal co-morbidities present.

CONCLUSIONS

Although IBS is characterized by a pro-inflammatory profile featuring the pro-inflammatory cytokines IL-6 and IL-8, IBS patients with certain extra-intestinal co-morbid conditions are distinguished by additional elevations in IL-1β and TNFα.

Sexual dimorphic evolution of metabolic programming in non-genetic non-alimentary mild metabolic syndrome model in mice depends on feed-back mechanisms integrity for pro-opiomelanocortin-derived endogenous substances

Previously, we showed that our post-natal handling model induces pro-opiomelanocortin-derived (POMC) endogenous systems alterations in male mice at weaning. These alterations last up to adult age, and are at the basis of adult hormonal and metabolic conditions similar to mild metabolic syndrome/type-2 diabetes. Here, we evaluate how sex influences post-natal programming in these metabolic conditions. Subjects are adult control (non-handled) female (NHF) and male (NHM) CD-1 mice; adult post-natal handled female (HF) and male (HM) mice. Handling consists of daily maternal separation (10 min) plus sham injection, from birth to weaning (21 days). In adult handled males (90-days old) we find not only POMC-derived hormones alterations (enhanced basal plasma corticosterone (+91%) and ACTH (+109%)) but also overweight (+5.4%), fasting hyperglycemia (+40%), hypertriglyceridemia (+21%), enhanced brain mRNA expression of hydroxysteroid(11-beta)dehydrogenase type-1 (HSD11B1) (+49%), and decreased mRNA-HSD11B2 (-39%). Conversely, uric acid, creatinine, HDL(C), total cholesterol, glucose and insulin incremental area under-the-curve are not affected. In females, post-natal handling does not produce both hormonal and dysmetabolic diabetes-like changes; but handling enhances n3- and n6-poly-unsaturated, and decreases saturated fatty acids content in erythrocyte membrane composition in HF versus NHF. In conclusion, for the first time we show that female sex in mice exerts effective protection against the hypothalamus-pituitary-adrenal homeostasis disruption induced by our post-natal handling model on POMC cleavage products; endocrine disruption is in turn responsible for altered metabolic programming in male mice. The role of sex hormones is still to be elucidated.

Maternal and early life stress effects on immune function: relevance to immunotoxicology

Stress is triggered by a variety of unexpected environmental stimuli, such as aggressive behavior, fear, forced physical activity, sudden environmental changes, social isolation or pathological conditions. Stressful experiences during very early life (particularly, maternal stress during fetal ontogeny) can permanently alter the responsiveness of the nervous system, an effect called programming or imprinting. Programming affects the hypothalamic-pituitary-adrenocortical (HPA) axis, brain neurotransmitter systems, sympathetic nervous system (SNS), and the cognitive abilities of the offspring, which can alter neural regulation of immune function. Prenatal or early life stress may contribute to the maladaptive immune responses to stress that occur later in life. This review focuses on the effect of maternal and early life stress on immune function in the offspring across life span. It highlights potential mechanisms by which prenatal stress impacts immune functions over life span. The literature discussed in this review suggests that psychosocial stress during pre- and early postnatal life may increase the vulnerability of infants to the effects of immunotoxicants or immune-mediated diseases, with long-term consequences. Neural-immune interactions may provide an indirect route through which immunotoxicants affect the developing immune system. A developmental approach to understanding how immunotoxicants interact with maternal and early life stress-induced changes in immunity is needed, because as the body changes physiologically across life span so do the effects of stress and immunotoxicants. In early and late life, the immune system is more vulnerable to the effects of stress. Stress can mimic the effects of aging and exacerbate age-related changes in immune function. This is important because immune dysregulation in the elderly is more frequently and seriously associated with clinical impairment and death. Aging, exposure to teratogens, and psychological stress interact to increase vulnerability and put the elderly at the greatest risk for disease.

Neurobiology of pain in children: an overview

The evaluation of pain in the newborn and the infant is difficult because pain is mainly a subjective phenomenon. Until a few years ago, several myths persisted. First, the myth that children, especially infants, do not feel pain the way adults do, therefore there is no untoward consequences for them. Second, lack of assessment and reassessment for the presence of pain. Third, misunderstanding of how to conceptualise and quantify a subjective experience. Fourth, lack of knowledge of pain treatment. Fifth, the notion that addressing pain in children takes too much time and effort, in ultimate analysis resulting in wasting time. Sixth, fears of hidden -and not easy to diagnose or prevent- adverse effects of analgesic medications, including respiratory depression and addiction. Finally, from a conceptual point of view, high thresholds of pain in neonates and infants were considered to be present by natural character, and useful in protecting infant from pain during birth and transit through the narrow vaginal channel.The present review is focused on the description of different theories on the pain pathogenesis in children.

Early life stress alters behavior, immunity, and microbiota in rats: implications for irritable bowel syndrome and psychiatric illnesses

BACKGROUND

Adverse early life events are associated with a maladaptive stress response system and might increase the vulnerability to disease in later life. Several disorders have been associated with early life stress, ranging from depression to irritable bowel syndrome. This makes the identification of the neurobiological substrates that are affected by adverse experiences in early life invaluable.

METHODS

The purpose of this study was to assess the effect of early life stress on the brain-gut axis. Male rat pups were stressed by separating them from their mothers for 3 hours daily between postnatal days 2-12. The control group was left undisturbed with their mothers. Behavior, immune response, stress sensitivity, visceral sensation, and fecal microbiota were analyzed.

RESULTS

The early life stress increased the number of fecal boli in response to a novel stress. Plasma corticosterone was increased in the maternally separated animals. An increase in the systemic immune response was noted in the stressed animals after an in vitro lipopolysaccharide challenge. Increased visceral sensation was seen in the stressed group. There was an alteration of the fecal microbiota when compared with the control group.

CONCLUSIONS

These results show that this form of early life stress results in an altered brain-gut axis and is therefore an important model for investigating potential mechanistic insights into stress-related disorders including depression and IBS.

A new model of neonatal stress which produces lasting neurobehavioral effects in adult rats

BACKGROUND

During critical care in neonatal intensive care units (NICU), infants experience stressors and treatments that may produce lasting effects on adult health. An animal model simulating the NICU experience is needed to understand the impact of specific neonatal stressors.

OBJECTIVE

We combined approaches to develop a neonatal rat model simulating NICU stressors in order to examine the hypothesis that early stress and morphine sulfate (MS) exposure would affect development and alter adult behavior.

METHODS

Rat pups were exposed to stressors and given twice daily MS injections (2 mg/kg s.c.) for 5 days (postnatal days 3-7). Stress included daily maternal separation (from 08.00 to 16.00 h), hand feedings, a daily hypoxia/hyperoxia episode (100% N(2) for 8 min, then 100% O(2) for 4 min), and cold exposure (4 degrees C for 20 min/day). Five treatment groups were formed: (1) 'control control' (dam reared and untreated); (2) control vehicle; (3) stress vehicle; (4) control morphine, and (5) stress morphine. Early growth and developmental indices were measured. Adult neurobehavioral tests were paw flick, passive avoidance, and forced swimming. Neonatal MS pharmacokinetics, neonatal and adult corticosterone levels, and adult hematocrit and blood pressure values were measured.

RESULTS

Neonatal stress significantly increased the mortality. Neonatal stress and MS treatment slowed early growth. Neonatal MS impaired passive avoidance learning and increased frequency, duration, and distance of forced swimming. There were no differences in corticosterone, hematocrit, or blood pressure values.

CONCLUSIONS

This model simulates NICU stressors and enables measurement of acute physiological and long-term neurobehavioral indices. Neonatal MS treatment impaired the adult cognitive functioning.

Administration of antisense oligonucleotide against pro-opiomelanocortin prevents enduring hormonal alterations induced by neonatal handling in male mice

Early life events have been implicated in the programming of adult chronic diseases. Several investigations suggest that the role of early environment in influencing development mainly involves the hypothalamic-pituitary-adrenal axis. Therefore, we examined whether 1) daily neonatal handling, applied from birth to weaning induces HPA hormones alterations in mice lasting up to the adult age; and 2) if the administration of an antisense oligodeoxynucleotide versus pro-opiomelanocortin (As-POMC) prevents hormonal alterations observed in previously handled mice (Handled). In the adult phase (90 days), Handled are overweight and have higher basal plasma immuno-reactive (ir)-corticosterone and adrenocorticotropin (ir-ACTH), and higher pituitary ir-ACTH; while they have lower hypothalamic ir-ACTH and corticotropin-releasing hormone (ir-CRH) in comparison with the non-handled mice. As-POMC (0.05-0.1 nmol/g body weight per day) administered during the same period dose-dependently prevents the increase in body weight, in plasma ir-corticosterone, ir-ACTH, and pituitary ir-ACTH, also preventing the decrease in hypothalamic ir-CRH and ir-ACTH; while the mismatch oligonucleotide is nearly inactive. This data indicates that pharmacological treatment in neonatal life may have enduring effects, reducing the alterations in hormonal homeostatic programming mechanisms induced by early repeated handling.

Neonatal maternal deprivation promotes Nippostrongylus brasiliensis infection in adult rats

Neonatal stress is known to alter immune responses in adults and parasitic infection is modulated by the immune status of the host. The present study aimed to establish whether neonatal maternal deprivation affects the time course of Nippostrongylus brasiliensis infection and associated intestinal alterations in adult rats. Rat pups were separated from their dam 3h daily during postnatal days 2-14, or left undisturbed. At 12 weeks of age, N. brasiliensis infection was induced by subcutaneous administration of 3000 L3 larvae. At 7 and 12 days after primary infection, the number of intestinal adult worms, fecal egg output, jejunal paracellular permeability, and myeloperoxidase (MPO) activity were measured. On days 7 and 12 after a secondary infection, numbers of adult worms and egg production were determined. Maternal deprivation increased the number of jejunal adult worms and fecal eggs and larvae on day 7 after primary infection, and exacerbated the increase in jejunal MPO activity induced by the infection. On day 12, adult worms were only observed in deprived rats. N. brasiliensis infection did not potentiate the increase in jejunal paracellular permeability induced by maternal deprivation. After the second infection, no egg was detected in both control and deprived rats. In conclusion, maternal deprivation in rats facilitates primary infection by N. brasiliensis and enhances the inflammatory response of the jejunum, but does not induce severe breakdown of immunity to N. brasiliensis.

Overweight and metabolic and hormonal parameter disruption are induced in adult male mice by manipulations during lactation period

Neonatal manipulations (10 min of maternal separation plus s.c. sham injection, daily for the first 21 d of life) determine overweight in male adult mice. In this work, we investigated the mechanisms underlying mild obesity and the alteration of caloric balance. Neonatally manipulated mice become overweight after onset of maturity, showing increased fat tissue and hypertrophic epididymal adipocytes. Increase in body weight occurs in the presence of a small increase in daily food intake (significant only in the adult period) and the absence of a decrease in spontaneous locomotor activity, while the calculated caloric efficiency is higher in manipulated mice, especially in adulthood. Fasting adult animals show hyperglycemia, hyperinsulinemia, hypertriglyceridemia, hypercholesterolemia, and hyperleptinemia. Soon after weaning and in the adulthood, plasma corticosterone and adrenocorticotropin (ACTH) are also significantly increased. Thus, neonatal manipulations in nongenetically susceptible male mice program mild obesity, with metabolic and hormonal alterations that are similar to those found in experimental models of diabetes mellitus, suggesting that this metabolic derangement may have at least part of its roots early on in life and, more interestingly, that psychological and nociceptive stimuli induce these features.

Adolescence as possible critical temporal window for blood pressure short term monitoring in boys and girls

Adolescence is a critical temporal window for the development of obesity in adult age. We studied this period for short-term monitoring of blood pressure in both genders. Weight, height, body mass index (BMI), systolic and diastolic blood pressure (SBP, DBP) were recorded in 937 adolescents, 474 boys and 463 girls aged 12 years, and again 2 years later in the same subjects. Boys with BP values > or = 95th percentile at both ages (no. = 8) showed at 12 years weight (kg 61.4) height (cm 159.5) and BMI (23.5), and also at 14 years (77.0, 172.4, 25.6) values consistently higher than boys with high BP values at either ages taken singularly (no. = 32 + 32) (mean 49.2, 154.4, 21.5, respectively, at 12 years, and 62.1, 167.0, 22.2 at 14 years). These 64 boys, had values higher than boys with BP always below the 95th percentile (no. = 402) (45.5, 151.4, 19.7 at 12 years, and 56.9, 164.6, 20.9 at 14 years). This was confirmed for weight and BMI in girls. Stepwise logistic regression revealed that weight at 12 years and high BP values at 12 years were predictive independent risk factors for hypertension at 14 years. Odds ratio indicated that increment of body weight unit (1 kg) at 12 years predicted an average increase of 4% of risk for high BP values at 14 years, while high BP values at 12 years was predictive for a 2.19 times risk for high BP values at 14 years. Body weight, BMI and BP at 12 years of age may give useful indications for the prevision (and possible prevention) of hypertension and overweight at 14 years of age.

Suppressed fever and hypersensitivity responses in chicks prenatally exposed to opiates

We have established procedures to reliably induce opiate dependence in the chick embryo via in ovo injection, early in embryonic development, of the long-acting and potent opiate N-desmethyl-l-alpha-noracetylmethadol (NLAAM). Prior studies found that there is continual exposure to NLAAM throughout embryogenesis and shortly after hatching there are signs of spontaneous withdrawal. In the present study, we used three doses of NLAAM (2.5, 5, and 10 mg/kg egg weight) to determine if prenatal opiate exposure followed by postnatal withdrawal interfered with appropriate neural-endocrine-immune interactions in the young chick. To ensure that effects were not a consequence of inappropriately large doses, we first examined acute and chronic toxicity and additional characteristics of postnatal opiate withdrawal. We then measured the corticosterone and fever responses to LPS stimulation during the withdrawal period. After the conclusion of opiate withdrawal, we assessed the hypersensitivity response to phytohemagglutinin (PHA). The fever response to LPS and the hypersensitivity response to PHA were suppressed by prenatal opiate exposure and postnatal withdrawal. The corticosterone response to LPS was not affected, but there were exaggerated corticosterone responses to saline injection in chicks exposed in ovo to NLAAM. It was unlikely that the effects of prenatal NLAAM were the result of toxicity, as little chronic toxicity was seen with the lower two doses of NLAAM, doses that yielded significant suppressions of neural-endocrine-immune responses. However, effects found in the chicks treated with 10 mg NLAAM/kg may have been partly related to the greater toxicity and/or protracted postnatal withdrawal in this group.

Taurine administration during lactation modifies hippocampal CA1 neurotransmission and behavioural programming in adult male mice

Taurine plays a role in neuronal development. In this study, we examined whether postnatal taurine administration influences the long-term consequences induced by mild neonatal stressors (10 min maternal deprivation plus sham injection, applied daily to neonatal mice up to 21 days). At 30 days of age stressed mice showed higher pain threshold both in the tail-flick--which measures mostly the spinal mechanisms of pain--and in the hot-plate test--which reflects mainly the supraspinal mechanisms of pain. The latter effect was prevented completely by neonatal taurine administration, while the tail-flick test was not affected, thus suggesting that spinal pain is not sensitive to taurine treatment. At 140 days of age, mice which were stressed during the neonatal period showed consistent decrease in immobility time in forced swimming test, and taurine did not influence this parameter. At the same age, the fear/anxiety axis, measured with elevated plus maze test, did not show any consistent changes. Electrophysiological experiments in brain slices obtained from adult mice showed that input-output curves in hippocampal CA1 were increased by taurine administration in lactation. Hence, neonatal administration of taurine might permanently modify the functioning of hippocampus, a brain area which is known to be crucial for learning and memory.

Neonatal maternal deprivation triggers long term alterations in colonic epithelial barrier and mucosal immunity in rats

BACKGROUND

Stressful events in the early period of life (for example, maternal deprivation) have been shown to modify adult immune and gastrointestinal tract functions. The present study aimed to establish whether maternal deprivation affects colonic epithelial barrier and the development of an experimental colitis in adult rats.

METHODS

Male Wistar rat pups were separated during postnatal days 2-14 or left undisturbed with their dam. At 12 weeks of age, we assessed colonic paracellular permeability, bacterial translocation, myeloperoxidase (MPO) activity, mucosal mast cell density, cytokine (interleukin (IL)-1 beta, IL-2, IL-4, IL-10, and interferon gamma (IFN-gamma)) mRNA expression, and macroscopic damage. Total gut permeability, MPO activity, and macroscopic damage were also assessed four days after intracolonic administration of 2,4,6-trinitrobenzenesulphonic acid (TNBS).

RESULTS

Maternal deprivation triggered a significant increase in colonic permeability associated with bacterial translocation into the mesenteric lymph nodes, liver, and spleen. These alterations were associated with some macroscopic damage and an increase in colonic MPO activity, mucosal mast cell density, and cytokine mRNA expression. Intracolonic infusion of TNBS induced a significantly higher inflammatory reaction in separated animals, as judged by enhanced MPO colonic levels, total gut permeability, and macroscopic lesions.

CONCLUSIONS

Maternal deprivation promotes long term alterations in the colonic epithelial barrier associated with an exaggerated immune response to an external immune stimulus. This suggests a role for early psychological factors in the regulation of colonic mucosal barrier in later life.

Vas deferens response to selective opioid receptor agonists in adult mice is impaired following postnatal repeated mild stress

Mild stress repeatedly applied to neonatal rodents induces alterations of central nervous system functions, persisting up to the adult age. Most alterations may be mediated through hormones and neuromediators active on the autonomic nervous system, therefore we tested the efficacy of selective opioid receptor agonists on the vas deferens of adult mice that, as neonates, had undergone daily mild stress until weaning (brief isolation and solvent injection). We found in the adult mouse (90 days old) decreased sensitivity of vas deferens to selective mu-, delta- and kappa-opioid receptor agonist drugs. The neonatal administration of an antisense oligodeoxynucleotide adrenocorticotropin-synthesis-inhibitor partly prevented these effects.