Long-term changes induced by neonatal handling in the nociceptive threshold and body weight in mice

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.

Experimental study of pre- and postnatal caffeine exposure and its observable effects on selected neurotransmitters and behavioural attributes at puberty : Caffeine exposure and its observable effects on selected neurotranmitters and behaviour

Caffeine is globally consumed as a stimulant in beverages. It is also ingested in purified forms as power and tablets. Concerns have been raised about the potential consequences of intrauterine and early life caffeine exposure on brain health. This study modeled caffeine exposure during pregnancy and early postanal life until puberty, and the potential consequences. Caffeine powder was dissolved in distilled water. Thirty-two (n = 32) pregnant mice (Mus musculus) (dams) were divided into four groups- A, B, C and D. Group A animals served as a control, receiving placebo. Caffeine doses in mg/kg body weight were administered as follows: Group B, 10 mg/kg; Group C, 50 mg/kg; Group D, 120 mg/kg. Prenatal caffeine exposure [phase I] lasted throughout pregnancy. Half the number of offspring (pups) were sacrificed at birth; the rest were recruited into phase II and the experiment continued till day 35, marking puberty. Brain samples were processed following sacrifice. γ-aminobutyric acid (GABA), acetylcholine (ACh), and serotonin (5Ht) neurotransmitters were assayed in homogenates to evaluate functional neurochemistry. Anxiety and memory as neurobehavioural attributes were observed using the elevated plus and Barnes' mazes respectively. Continuous caffeine exposure produced positive effects on short and long-term memory parameters; the pattern interestingly was irregular and appeared more effective with the lowest experimental dose. Anxiety test results showed no attributable significant aberrations. Caffeine exposure persistently altered the neurochemistry of selected neurotransmitters including ACh and 5Ht, including when exposure lasted only during pregnancy. ACh significantly increased in group B^C+ to 0.3475μgg-¹ relative to control's 0.2508μgg-¹; pre-and continuous postnatal exposure in Group B increased 5Ht to 0.2203 μgg-¹ and 0.2213 μgg-¹ respectively relative to control's 0.1863 μgg-¹. From the current investigation, caffeine exposure in pregnancy had persistent effects on brain functional attributes including neurotransmitters activities, memory and anxiety. Caffeine in moderate doses affected memory positively but produced negative effects at the higher dosage including increased anxiety tendencies.

The burden of early life stress on the nociceptive system development and pain responses

For a long time, the capacity of the newborn infant to feel pain was denied. Today it is clear that the nociceptive system, even if still immature, is functional enough in the newborn infant to elicit pain responses. Unfortunately, pain is often present in the neonatal period, in particular in the case of premature infants which are subjected to a high number of painful procedures during care. These are accompanied by a variety of environmental stressors, which could impact the maturation of the nociceptive system. Therefore, the question of the long-term consequences of early life stress is a critical question. Early stressful experience, both painful and non-painful, can imprint the nociceptive system and induce long-term alteration in brain function and nociceptive behavior, often leading to an increase sensitivity and higher susceptibility to chronic pain. Different animal models have been developed to understand the mechanisms underlying the long-term effects of different early life stressful procedures, including pain and maternal separation. This review will focus on the clinical and preclinical data about early life stress and its consequence on the nociceptive system.

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.

Laboratory environmental factors and pain behavior: the relevance of unknown unknowns to reproducibility and translation

The poor record of basic-to-clinical translation in recent decades has led to speculation that preclinical research is "irreproducible", and this irreproducibility in turn has largely been attributed to deficiencies in reporting and statistical practices. There are, however, a number of other reasonable explanations of both poor translation and difficulties in one laboratory replicating the results of another. This article examines these explanations as they pertain to preclinical pain research. I submit that many instances of apparent irreproducibility are actually attributable to interactions between the phenomena and interventions under study and "latent" environmental factors affecting the rodent subjects. These environmental variables-often causing stress, and related to both animal husbandry and the specific testing context-differ greatly between labs, and continue to be identified, suggesting that our knowledge of their existence is far from complete. In pain research in particular, laboratory stressors can produce great variability of unpredictable direction, as stress is known to produce increases (stress-induced hyperalgesia) or decreases (stress-induced analgesia) in pain depending on its parameters. Much greater attention needs to be paid to the study of the laboratory environment if replication and translation are to be improved.

Postnatal Stress in Mice: Effects on Body Fat, Plasma Lipids, Glucose and Insulin

Mice pups were exposed to stressful stimuli everyday during the first 3 weeks of life. Body weight, food intake and spontaneous locomotor activity, triglycerides, cholesterol, phospholipids, glucose and insulin basal levels, as well as epididymal fat pad weight and its cell volume were measured in stressed and control animals. Results indicated that postnatal stressful manipulations induced an increase in body weight, epididymal fat pad weight and its cell volume, as well as in insulin, glucose, cholesterol and triglycerides plasma levels, at 4 months of age. No significant changes in food consumption, locomotor activity and phospholipids plasma levels were found. Present data suggest that early stressful manipulations may induce residual effects on lipid and glucid metabolism.

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.

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.

Enhancement of synaptic transmission and nociceptive behaviour in HPC-1/syntaxin 1A knockout mice following peripheral nerve injury

Our previous analysis of HPC-1/syntaxin 1A knockout (KO) mice indicated that HPC-1/syntaxin 1A plays an important role in the synaptic plasticity of the hippocampus in vitro and learning behaviour in vivo. In order to gain further insights into the physiological functions of HPC-1/syntaxin 1A, we studied the changes in the plasticity of synaptic transmission in the superficial dorsal horn of the spinal cord following a peripheral nerve injury in HPC-1/syntaxin 1A KO and wild-type (WT) mice. The von Frey filament test revealed that partial ligation of the sciatic nerve caused neuropathic pain in both WT and KO mice. However, KO mice showed significant enhancement of mechanical allodynia as compared with WT mice. Tight-seal whole-cell recordings were obtained from neurons in the superficial dorsal horn of the spinal cord slices. Electrical stimulus-evoked excitatory postsynaptic currents (EPSCs), asynchronous EPSCs (aEPSCs) in the presence of strontium, and spontaneously occurring miniature EPSCs (mEPSCs) were analysed. Prior to peripheral nerve ligation, no significant differences were observed in the properties of evoked EPSCs, aEPSCs and mEPSCs in KO and WT mice. Seven-14 days after partial ligation, the amplitude of evoked EPSCs and the frequency of aEPSCs and mEPSCs in KO mice were significantly greater than those in WT mice; however, the amplitude of aEPSCs and mEPSCs remained unchanged in both groups. Enhanced allodynia behaviour and significant enhancement of excitatory synaptic transmission following peripheral nerve ligation in KO mice suggest that HPC-1/syntaxin 1A might play a role in synaptic plasticity in the nociceptive pathway.

Behavioral, cognitive and biochemical responses to different environmental conditions in male Ts65Dn mice, a model of Down syndrome

Ts65Dn mouse is the most widely accepted model for Down syndrome. We previously showed that environmental enrichment improved spatial learning in female but deteriorated it in male Ts65Dn mice. This study analyzed the factors contributing to the disturbed cognition of male Ts65Dn mice after enriched housing, by allocating male control and Ts65Dn mice in four conditions after weaning: small (n = 2-3) and large group (n = 8-10) housing, and enriched housing in small (2-3) and large groups (8-10). Learning, aggressive behavior, anxiety-like behavior and biochemical correlates of stress were evaluated when Ts65Dn and control mice were 4-5 months old. Environmental enrichment in large mixed colonies of Ts65Dn and diploid littermates disturbed behavioral and learning skills of Ts65Dn mice in the Morris water maze. ACTH and testosterone levels were not modified in any group of mice. Ts65Dn and control mice subjected to enriched housing in large groups and Ts65Dn mice housed in large groups showed higher corticosterone levels. Aggressive behavior was evaluated by measuring the number of attacks performed in the presence of an intruder. Ts65Dn mice performed less attacks than controls in all conditions, especially after enriched housing, indicating subordination. In the plus maze, cognitive aspects (i.e. risk assessment) and motor components (open arm avoidance) of anxiety behavior were evaluated; no difference in any condition was found. It is suggested that an excess of social and/or physical stimulation in Ts65Dn mice may affect cognition by disturbing the emotional and behavioral components of the learning process.

The development of nociceptive circuits

The study of pain development has come into its own. Reaping the rewards of years of developmental and molecular biology, it has now become possible to translate fundamental knowledge of signalling pathways and synaptic physiology into a better understanding of infant pain. Research has cast new light on the physiological and pharmacological processes that shape the newborn pain response, which will help us to understand early pain behaviour and to design better treatments. Furthermore, it has shown how developing pain circuitry depends on non-noxious sensory activity in the healthy newborn, and how early injury can permanently alter pain processing.

Internal and External Factors Affecting the Development of Neuropathic Pain in Rodents. Is It All About Pain?

It is important to know the factors that will influence animal models of neuropathic pain. A good reproducibility and predictability in different strains of animals for a given test increases the clinical relevance and possible targeting. An obligatory requirement for enabling comparisons of results of different origin is a meticulous definition of the specific sensitivities of a model for neuropathic pain and a description of the test conditions. Factors influencing neuropathic pain behavior can be subdivided in external and internal factors. The most important external factors are; timing of the measurement of pain after induction of neuropathy, circadian rhythms, seasonal influences, air humidity, influence of order of testing, diet, social variables, housing and manipulation, cage density, sexual activity, external stress factors, and influences of the experimenter. The internal factors are related to the type of animal, its genetic background, gender, age, and the presence of homeostatic adaptation mechanisms to specific situations or stress. In practice, the behavioral presentations to pain depend on the combination of genetic and environmental factors such as accepted social behavior. It also depends on the use of genetic manipulation of the animals such as in transgenic animals. These make the interpretation of data even more difficult. Differences of pain behavior between in- and outbred animals will be better understood by using modern analysis techniques. Substrains of animals with a high likelihood for developing neuropathic pain make the unraveling of specific pathophysiological mechanisms possible. Concerning the effect of stress on pain, it is important to differentiate between external and internal stress such as social coping behavior. The individual dealing with this stress is species sensitive, and depends on the genotype and the social learning. In the future, histo-immunological and genetic analysis will highlight similarities of the different pathophysiological mechanisms of pain between different species and human subjects. The final objective for the study of pain is to describe the genetics of the eliciting pain mechanisms in humans and to look for correlations with the knowledge from basic research. Therefore, it is necessary to know the genetic evolution of the different mechanisms in chronic pain. In order to be able to control the clinical predictability of a putative treatment the evolutionary pharmacogenomic structure of specific transmitters and receptors must be clarified.

[Clinical characteristics of children with chronic pain in a pediatric pain unit: oncologic pain versus non-oncologic pain]

BACKGROUND

Despite undoubted scientific advances in the field of chronic pain in children, there is no evidence of clinical application of this knowledge.

OBJECTIVE

To describe the experience of a pediatric pain unit (PPU) specifically dedicated to the treatment of chronic pain in children.

MATERIAL AND METHODS

We performed an analytic, observational, retrospective, cohort study of the clinical features of the first 42 patients treated for chronic pain in the PPU during a two-year period. The patients were assigned to two groups: an oncologic group and a non-oncologic group. ANOVA was used to analyze quantitative variables and the Chi-square test was used to analyze qualitative variables.

RESULTS

No significant differences were found between the two groups in the demographic variables studied (age and sex). Concerning the type of treatment used, no significant differences were found in effectiveness or compliance. However, treatment duration was significantly longer in the non-oncologic group than in the oncologic group (74.2 days vs 37.5 days, p(0.008). The duration of non-oncologic chronic pain before attending the PPU (mean: 557 days) influenced the effectiveness (r 5 0.781; p 5 0.0001) and duration of treatment (r 5 0.61; p 5 0.0051). However, the duration of previous chronic oncologic pain was significantly shorter (mean: 34 days) and showed no influence on treatment effectiveness or duration.

CONCLUSIONS

The pediatric population presents chronic pain syndromes that can be appropriately treated in a PPU with conventional, easy to manage analgesics. We recommend the establishment of pediatric pain units similar to those for adults, using a multidisciplinary approach to mitigate children's suffering.

Identification and ranking of genetic and laboratory environment factors influencing a behavioral trait, thermal nociception, via computational analysis of a large data archive

Laboratory conditions in biobehavioral experiments are commonly assumed to be 'controlled', having little impact on the outcome. However, recent studies have illustrated that the laboratory environment has a robust effect on behavioral traits. Given that environmental factors can interact with trait-relevant genes, some have questioned the reliability and generalizability of behavior genetic research designed to identify those genes. This problem might be alleviated by the identification of the most relevant environmental factors, but the task is hindered by the large number of factors that typically vary between and within laboratories. We used a computational approach to retrospectively identify and rank sources of variability in nociceptive responses as they occurred in a typical research laboratory over several years. A machine-learning algorithm was applied to an archival data set of 8034 independent observations of baseline thermal nociceptive sensitivity. This analysis revealed that a factor even more important than mouse genotype was the experimenter performing the test, and that nociception can be affected by many additional laboratory factors including season/humidity, cage density, time of day, sex and within-cage order of testing. The results were confirmed by linear modeling in a subset of the data, and in confirmatory experiments, in which we were able to partition the variance of this complex trait among genetic (27%), environmental (42%) and genetic x environmental (18%) sources.

Neurobehavioral development of two mouse lines commonly used in transgenic studies

The present study was aimed at establishing the differences in the neurodevelopmental profile between two F2 lines derived from two F1 hybrid mouse strains (129 x C57BL/6 and C57BL/6 x SJL). The choice of the given strains was based on the frequent use of these mice in transgenic research. For the neurodevelopment phenotyping, we employed a test battery consisting of 23 somatometric, sensorial and motor tests. Significant variations between the strains were established in different functional domains. Some specific delays in the appearance of developmental landmarks were observed in F2 mice derived from crosses of F1 C57BL/6 x 129, whereas they acquired early developmental functions, such as the righting reflex, sooner than C57BL/6 x SJL-derived mice. C57BL/6 x 129 F2 offspring were spontaneously hypoactive, and their poorer motor performance was confirmed by low performance in the negative geotaxis test. However, there were no differences in the general psychomotor development as shown by the good performance in the homing test in both F2 lines. Both strains were susceptible to the handling procedures used, presenting a similar alteration in the response observed in the homing test as compared to nonhandled control mice. In conclusion, our work highlights the importance of the genetic background for transgenesis experiments and also the need for well-established testing protocols to obtain sufficient information at the first stage of behavioral screening of genetically modified mice.

Postnatally induced differences in adult pain sensitivity depend on genetics, gender and specific experiences: reversal of maternal deprivation effects by additional postnatal tactile stimulation or chronic imipramine treatment

Postnatal endotoxin exposure, handling or maternal deprivation produce long-lasting individual differences in various neuroendocrine and behavioural responses. However, the impact of postnatal experiences on adult pain sensitivity and its reversibility by postnatal additional tactile stimulation or antidepressants in adulthood is not well understood. Therefore, postnatal endotoxin application as a model for infection, maternal deprivation as a model for depression, and postnatal handling as a model for stimulation were compared with respect to the effects on pain sensitivity in adult Fischer 344 (F344) and Lewis (LEW) rats. Handling increased hot plate latencies in adult F344 and LEW rats, while maternal deprivation shortened hot plate latencies only in LEW rats. Prophylactic treatment strategies, such as tactile stimulation of the dorsal neck region of pups directly after maternal deprivation, or chronic treatment of adult maternally deprived rats using imipramine, successfully provide protection against the maternal deprivation-induced shortening of hot plate latencies. Thus, there is considerable specificity of certain postnatal experiences in modulating adult pain sensitivity and the maternal deprivation-induced hyperalgesia is reversible by different interventional regimes. These findings may explain some of the individual differences in pain sensitivity of humans and the differential efficacy of antidepressants in pain syndromes.

delta-Opioid modulation of social interactions in juvenile mice weaned at different ages

The environmental stimulus of weaning has been shown to affect both the developmental expression of social behavior and the maturation of the opioid delta-receptors' subpopulation in altricial rodents. The aim of this study was to address both these issues by using the social interaction paradigm. Separate groups of male and female mice were randomly assigned to three different weaning ages -- early (Wean-15), regular (Wean-20), and delayed (Wean-25) -- and assessed when 30 days old under intraperitoneal administration of the selective delta-opioid agonist SNC80 (0, 0.1, or 0.3 mg/kg). Wean-15 male and female subjects were much more involved in investigating the partner as well as the cage environment compared to the regular Wean-20 group. An increased social investigation was also found as a consequence of delayed weaning in the female group. The neurobehavioral changes induced by the manipulation of weaning age were also reflected in an altered responsivity to the effects of SNC80 administration. The drug-induced increase in the expression of investigative and affiliative social interactions was further magnified by early weaning. A delayed weaning time was instead associated with reduced sensitivity to the drug, which suggests a delayed maturation of the system. As a whole, the present results indicate that the time of weaning is able to markedly affect the expression of social interactions of adolescent mice by possibly exerting a direct modulatory role on the development of the still plastic delta-opioid system.

Effects of neonatal handling on sympathoadrenal activity and body composition in adult male rats

Neonatal handling permanently alters the hypothalamic-pituitary-adrenal (HPA) response to stress. Because the sympathetic nervous system (SNS) and adrenal medulla also participate in stress responses, the impact of daily handling between birth and weaning on SNS and adrenal medullary function was examined in adult rats using techniques of [(3)H]norepinephrine ([(3)H]NE) turnover and urinary catecholamine excretion. Handled animals exhibited a 23% reduction in [(3)H]NE turnover in heart and a 53% decrease in spleen. [(3)H]NE turnover in brown adipose tissue, stomach, and kidney did not differ between handled and nonhandled animals. In contrast, urinary epinephrine (Epi) excretion was significantly greater in handled rats in response to a 3-day fast than in nonhandled animals. Although body weight, weight gain in response to dietary enrichment with sucrose or lard, or body fat content did not differ in handled and nonhandled animals, handled rats displayed heavier abdominal fat depots than nonhandled animals, implying a difference in body fat distribution. Neonatal handling thus leads to decreased sympathetic activity within specific subdivisions of the SNS and, by contrast, to increased adrenal medullary responsiveness.

Short-term effects of postnatal manipulation on central beta-adrenoceptor transmission

Neonatal handling is known to induce long-lasting changes in behavioral and neuroendocrine responses to stress. Since the central noradrenergic system participates in the adaptive responses to stressful conditions we have analyzed the effects of postnatal handling on beta-adrenoceptor binding sites and isoprenaline- and forskolin-stimulated cyclic AMP accumulation in cerebral cortex, hippocampus and cerebellum of rats at 1 and 3 months of age. Handled animals showed reduced emotional reactivity and lower ACTH and corticosterone secretion after stress. Binding studies using [(3) H]CGP12-177 revealed increased beta-adrenoceptor binding sites in handled rats in cerebellum and cerebral cortex with no changes in hippocampus, and decreased affinity in all cerebral regions. Handling reduced basal levels of cyclic AMP in hippocampus and cerebellum but not in cerebral cortex. The concentration-response curves of cyclic AMP to isoprenaline were displaced to the right in cerebellum of handled rats without differences in Emax; however, Emax was significantly reduced in cerebral cortex and hippocampus. Direct stimulation of the catalytic subunit of adenylyl cyclase by forskolin reduced the efficiency in hippocampus and cerebellum, but not in cerebral cortex of handled animals. It is concluded that neonatal handling reduces the binding properties of beta-adrenoceptor and its primary biochemical responses in the young rat brain, which may account for the reduced responsiveness to stress attained in the handled rats, and may explain the persistence of the effect. The present study emphasizes the role of the central noradrenergic system in modulating the behavioral and neurendocrine responses to neonatal handling.

Effects of neonatal treatment with Tyr-MIF-1 and naloxone on the long-term body weight gain induced by repeated postnatal stressful stimuli

Stressful stimuli repeatedly applied during the first postnatal weeks can induce body weight gain in the mouse during adulthood. This effect can be prevented by injecting naloxone concomitantly with stress. The peptides belonging to the Tyr-MIF-1 family have a great modulating activity on numerous stress-induced phenomena. The aim of the present work was to compare the effect of repeated neonatal injections of Tyr-MIF-1 or naloxone on the long-term body weight gain induced by a stressing procedure applied daily during the first three weeks of life. The results indicate that although naloxone blocked the development of the stress-induced effects, Tyr-MIF-1 potentiated them.

Effect of neonatal handling on brain enkephalin-degrading peptidase activities

Neonatal handling decreases neutral endopeptidase 24.11 activity in the amygdala. However, this procedure does not affect aminopeptidase activities in any of the brain areas studied. Neonatal handling has been one of the most commonly used strategies to study the plasticity of the nervous system. The crucial role of the opioids in the control of different aspects of behaviour and development has been well documented. Regarding this subject, the endogenous opioid system might mediate some of the effects induced by neonatal handling. In this work, we have studied the effects of neonatal handling on several enkephalin-degrading peptidases, including soluble and membrane-bound aminopeptidases (puromycin-sensitive and -insensitive) and neutral endopeptidase 24.11 in different rat brain areas. Tyrosine aminopeptidase activities were measured fluorimetrically using tyrosine-beta-naphthylamide as substrate and puromycin as selective inhibitor of one of the membrane-enzymes. Dansyl-D-Ala-Gly-Phe(pNO2)-Gly was the fluorogenic substrate for neutral endopeptidase. The reduced neutral endopeptidase 24.11 activity in the amygdala of neonatal handled rats could reduce enkephalin catabolism in this area and it could be responsible for some of the effects induced by neonatal handling.

Infantile handling eliminates reversal learning deficit in rats prenatally exposed to alcohol

Prenatal exposure to ethanol results in learning deficits and alters physiological response to stress. Neonatal handling and stimulation. on the other hand, produce long-lasting physiological and behavioral changes in response to stress. To determine whether early handling, consisting of daily separation and tactile stimulation for the first 3 weeks, can modify fetal alcohol effects on learning ability of young adult rats, offspring of rats chronically exposed to ethanol throughout pregnancy and control animals were trained in a T-maze to learn a position response and then to reverse the learned response. The nonhandled, ethanol-treated rats were deficient on reversal, but the ethanol-treated rats that were handled during the first 3 weeks of postnatal development showed no deficit in learning to reverse their previously learned responses. Postnatal handling had no effect on acquisition in alcohol-treated rats. Neither reversal nor acquisition was affected by infantile handling in pair-fed or normal control animals. Early handling may have eliminated the reversal deficit in the ethanol-treated offspring by altering their physiological and behavioral reactivity to stress.

Short- and long-periods of neonatal maternal separation differentially affect anxiety and feeding in adult rats: gender-dependent effects

Environmental manipulations during early development can induce permanent alterations in hypothalamic-pituitary-adrenal (HPA) and behavioral responses to stressors. However, little is known about the impact of early life experiences on appetitive responses. The present investigation assessed the effects of brief handling/separation or protracted separation from the dams, on feeding and anxiety responses during development. During the first 3 weeks post-partum, Sprague-Dawley rat pups were exposed daily to either brief (15 min) handling/isolation (H), a more protracted (3 h) period of maternal separation (MS), or were not handled (NH). When tested on the elevated plus-maze (at 5-6 weeks) H groups displayed less anxiety than NH gender-matched controls. Surprisingly, so did the MS females. At weaning (Day 22), the MS rats weighed significantly less than both the H and NH animals; the difference between the H and MS was more robust and persisted throughout the experiment (D 62). The H animals of both genders, and the females of the MS group, consumed more of the palatable 'snack' than their NH counterparts. The feeding suppressant response to the various satiety peptides (bombesin, cholecystokinin, and amylin) was not affected by the early life experience, with exception of cholecystokinin (CCK) effects, which were more pronounced in H and MS males. These results suggest that early life events may contribute to anxiety and/or ingestive disorders such as anorexia nervosa, bulimia and obesity.

Prenatal alcohol exposure results in hyperactivity of the hypothalamic-pituitary-adrenal axis of the offspring: modulation by fostering at birth and postnatal handling

Exposure of fetal rats to alcohol results in permanent hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. In contrast, postnatal handling or fostering have been reported to restrain HPA activity. Because of the deleterious consequences of a hyperresponsive HPA axis, we thought that the possibility that postnatal manipulations might be able to reverse the influence of prenatal alcohol treatment deserved investigation. To test this hypothesis, we exposed rat dams to alcohol by inhalation during the second week of gestation. At birth, pups were either fostered or remained with their dam. For the first 3 weeks, litters were handled daily for 15 min or left undisturbed. At 22 days of age, male and female pups were decapitated under basal conditions, after 10 min of mild electro-footshock, or 10 min after footshock had been terminated. As expected, prenatal exposure to alcohol induced increased adrenocorticotropin (ACTH) secretion in response to footshock, and postnatal handling of control pups resulted in a suppression of corticosterone and ACTH release, although changes in this latter hormone did not reach statistical significance. Surprisingly, however, pups exposed to alcohol that were also fostered and handled after birth, showed an ACTH response to footshock stress that was significantly larger than all other groups. This unexpected response may be due to alterations in maternal-pup behaviors and may indicate that these manipulations act on different neuronal substrates within the central HPA of young rats. Further studies are needed to determine whether adrenal regulation is also altered in animals exposed to alcohol prenatally and reared in a similar manner.

Endogenous opiates: 1995

This article is the eighteenth installment of our annual review of research concerning the opiate system. It includes articles published during 1995 reporting the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects. The specific topics covered this year include stress: tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.