Postnatal stress is associated with impaired fear conditioning and extinction, and heightened hippocampal fibroblast growth factor 2, in mother rats

Rats exposed to early-life maternal separation (MS) exhibit later alterations in fear conditioning and impairments in fear extinction. As MS creates long-lasting anxiety in the mother, the present study assessed the influence of MS on fear conditioning and extinction in mother rats. It also examined whether estrous cycle effects on extinction, which are robust in nulliparous rats, but abolished in primiparous rats, re-emerge after MS. Following parturition, pups were removed from their mothers for 3 h daily from postpartum day 2-14 (MS), or remained housed with their mothers (standard reared condition, SR). Pups were weaned at postpartum day 24, and three months later, mothers received fear conditioning, extinction training, and test for extinction recall over three days. Extinction training took place during Proestrus (high estradiol and progesterone) or Metestrus (low estradiol and progesterone). Similar to past findings in non-stressed mothers, estrous cycle was not associated with conditioned fear expression (indexed by fear responses at the start of extinction training) or extinction recall in either MS or SR mothers. However, MS mothers exhibited weaker conditioned fear expression and impaired extinction recall, relative to SR mothers. Hippocampal fibroblast growth factor-2, a neurotrophin involved in stress regulation and fear expression, was elevated in MS relative to SR mothers. These results indicate that postnatal stress has long-lasting consequences for neural and behavioral systems involved in fear learning and inhibition without altering the involvement of ovarian hormones in these processes.

Infant stranger fear trajectories predict anxious behaviors and diurnal cortisol rhythm during childhood

Although a robust literature has linked stable, high levels of fear across childhood to increased risk for anxiety problems, less is known about alternative pathways to anxiety. We tested two putatively normative developmental pathways of early fearfulness for their distinct associations with behavioral (anxiety-related behaviors and symptoms) and biological (diurnal cortisol) markers of anxiety risk in middle childhood in a community-based sample (n = 107). Steeper increases in fear from 6 to 36 months predicted more parent-reported anxiety symptoms at age 8 years. In addition, children who exhibited steep increases in fear during infancy were overrepresented among children with diagnoses of separation anxiety disorder at age 8 years. Finally, we showed that steeper increases in fearfulness in infancy predicted flatter slopes of diurnal cortisol at age 8 years for girls. Thus, differences in stranger fear across infancy may indicate varying degrees of risk for anxious behaviors in later childhood.

Is social dispersal stressful? A study in male crested macaques (Macaca nigra)

In gregarious species, dispersal events represent one of the most dramatic changes in social life and environment an animal will experience during life due to increased predation risk, aggression from unfamiliar conspecifics and the lack of social support. However, little is known about how individuals respond physiologically to dispersal and whether this process is stressful for the individuals involved. We therefore studied the physiological stress response during dispersal in the crested macaque, a primate species in which males often change groups. Over a period of 14months and 14 dispersal events in 4 groups, we determined faecal glucocorticoid metabolite (FGCM) levels during the process of immigration into a new group and examined a variety of factors (e.g. male age, rank achieved, number of males in the group) potentially affecting FGCM levels during this process. We found that FGCM levels were significantly elevated in the first few days upon immigration, after which levels returned quickly to baseline. FGCM response levels upon immigration were significantly and positively influenced by the number of males in the group. The rank a male achieved upon immigration, aggression received, as well as the proximity to other males did not significantly influence FGCM levels. Our data confirm previous findings on other species demonstrating that in crested macaques immigration into a new social group is associated with an acute endocrine stress response. However, given that stress hormone levels remained elevated only for a short period of time, we do not expect males to experience high physiological costs during immigration. Given our limited knowledge on the physiological responses to dispersal in animals, this study contributes to our understanding of dispersal more generally, and particularly inter-individual differences in the stress response and the potential physiological costs associated with these.

Behavioural and biochemical changes in maternally separated Sprague-Dawley rats exposed to restraint stress

Early life adversity has been associated with the development of various neuropsychiatric disorders in adulthood such as depression and anxiety. The aim of this study was to determine if stress during adulthood can exaggerate the depression-/anxiety-like behaviour observed in the widely accepted maternally separated (MS) Sprague-Dawley (SD) rat model of depression. A further aim was to determine whether the behavioural changes were accompanied by changes in hippocampal brain-derived neurotrophic factor (BDNF) and the protein profile of the prefrontal cortex (PFC). Depression-/anxiety-like behaviour was measured in the elevated plus maze, open field and forced swim test (FST) in the MS SD rats exposed to chronic restraint stress in adulthood. As expected, MS increased immobility of SD rats in the FST but restraint stress did not enhance this effect of MS on SD rats. A proteomic analysis of the PFC revealed a decrease in actin-related proteins in MS and non-separated rats subjected to restraint stress as well as a decrease in mitochondrial energy-related proteins in the stressed rat groups. Since MS during early development causes a disruption in the hypothalamic-pituitary-adrenal axis and long-term changes in the response to subsequent stress, it may have prevented restraint stress from exerting its effects on behaviour. Moreover, the decrease in proteins related to mitochondrial energy metabolism in MS rats with or without subsequent restraint stress may be related to stress per se and not depression-like behaviour, because rats subjected to restraint stress displayed similar decreases in energy-related proteins and spent less time immobile in the FST than control rats.

Cortisol regulation in 12-month-old human infants: associations with the infants' early history of breastfeeding and co-sleeping

Experiences during early life are suggested to affect the physiological systems underlying stress responses, including the hypothalamic-pituitary-adrenal axis (HPA axis). While stressful early experiences have been associated with dysregulated HPA-axis functioning, positive early experiences, i.e. high maternal caregiving quality, contribute to more optimal HPA-axis functioning. Influences of other early caregiving factors, however, are less well documented. The goal of this study was to examine whether breastfeeding and co-sleeping during the first 6 months of life were associated with infant cortisol regulation, i.e. cortisol reactivity and recovery, to a stressor at 12 months of age. Participants were 193 infants and their mothers. Information on breastfeeding and co-sleeping was collected using weekly and daily sleep diaries, respectively, for the first 6 months of life. Co-sleeping was defined as sleeping in the parents' bed or sleeping in the parents' room. At 12 months of age, infants were subjected to a psychological stressor [Strange Situation Procedure (SSP); Ainsworth et al. 1978]. Salivary cortisol was measured prestressor and at 25, 40, and 60 min poststressor to measure reactivity and recovery. Regression analyses showed that after controlling for maternal sensitivity, infant attachment status, feeding, and sleeping arrangements at 12 months of age and other confounders, more weeks of co-sleeping predicted lower infant cortisol reactivity to the SSP. Also, more weeks of breastfeeding predicted quicker cortisol recovery. These results indicate that an early history of co-sleeping and breastfeeding contributes positively to cortisol regulation in 12-month-olds.

Bifidobacterium breve with α-linolenic acid and linoleic acid alters fatty acid metabolism in the maternal separation model of irritable bowel syndrome

The aim of this study was to compare the impact of dietary supplementation with a Bifidobacterium breve strain together with linoleic acid & α-linolenic acid, for 7 weeks, on colonic sensitivity and fatty acid metabolism in rats. Maternally separated and non-maternally separated Sprague Dawley rats (n = 15) were orally gavaged with either B. breve DPC6330 (10(9) microorganisms/day) alone or in combination with 0.5% (w/w) linoleic acid & 0.5% (w/w) α-linolenic acid, daily for 7 weeks and compared with trehalose and bovine serum albumin. Tissue fatty acid composition was assessed by gas-liquid chromatography and visceral hypersensitivity was assessed by colorectal distension. Significant differences in the fatty acid profiles of the non-separated controls and maternally separated controls were observed for α-linolenic acid and arachidonic acid in the liver, oleic acid and eicosenoic acid (c11) in adipose tissue, and for palmitoleic acid and docosahexaenoic acid in serum (p<0.05). Administration of B. breve DPC6330 to MS rats significantly increased palmitoleic acid, arachidonic acid and docosahexaenoic acid in the liver, eicosenoic acid (c11) in adipose tissue and palmitoleic acid in the prefrontal cortex (p<0.05), whereas feeding B. breve DPC6330 to non separated rats significantly increased eicosapentaenoic acid and docosapentaenoic acid in serum (p<0.05) compared with the NS un-supplemented controls. Administration of B. breve DPC6330 in combination with linoleic acid and α-linolenic acid to maternally separated rats significantly increased docosapentaenoic acid in the serum (p<0.01) and α-linolenic acid in adipose tissue (p<0.001), whereas feeding B. breve DPC6330 with fatty acid supplementation to non-separated rats significantly increased liver and serum docosapentaenoic acid (p<0.05), and α-linolenic acid in adipose tissue (p<0.001). B. breve DPC6330 influenced host fatty acid metabolism. Administration of B. breve DPC6330 to maternally separated rats significantly modified the palmitoleic acid, arachidonic acid and docosahexaenoic acid contents in tissues. The effect was not observed in non-separated animals.

Infant anticipatory stress

In humans, anticipatory stress involves activation of the limbic-hypothalamic-pituitary-adrenal axis, which releases stress hormones such as cortisol in response to an impending stressor. Conditioning of the stress response to anticipate and prepare for future challenges is a hallmark of adaptation. It is unknown whether human infants in the first year of life have developed the neural circuitry to support the anticipation of stressful events in an attachment context. Here, we show that human infants at six months of age produce an anticipatory stress response, as indicated by the release of stress hormones, when re-exposed after 24 h to a context in which they demonstrated a stress response to a disruption in the parent-infant relationship. Although infant stress response (cortisol elevation) was greater to the stressful event (parent unresponsiveness) than to the second exposure to the stress context (room, chair, presence of parent and experimenter, etc.), it was greater in the stress group than in the control group on both days. Results suggest that human infants have the capacity to produce an anticipatory stress response that is based on expectations about how their parents will treat them in a specific context.

Controlled cross-over study in normal subjects of naloxone-preceding-lactate infusions; respiratory and subjective responses: relationship to endogenous opioid system, suffocation false alarm theory and childhood parental loss

BACKGROUND

The expanded suffocation false alarm theory (SFA) hypothesizes that dysfunction in endogenous opioidergic regulation increases sensitivity to CO2, separation distress and panic attacks. In panic disorder (PD) patients, both spontaneous clinical panics and lactate-induced panics markedly increase tidal volume (TV), whereas normals have a lesser effect, possibly due to their intact endogenous opioid system. We hypothesized that impairing the opioidergic system by naloxone could make normal controls parallel PD patients' response when lactate challenged. Whether actual separations and losses during childhood (childhood parental loss, CPL) affected naloxone-induced respiratory contrasts was explored. Subjective panic-like symptoms were analyzed although pilot work indicated that the subjective aspect of anxious panic was not well modeled by this specific protocol.

METHOD

Randomized cross-over sequences of intravenous naloxone (2 mg/kg) followed by lactate (10 mg/kg), or saline followed by lactate, were given to 25 volunteers. Respiratory physiology was objectively recorded by the LifeShirt. Subjective symptomatology was also recorded.

RESULTS

Impairment of the endogenous opioid system by naloxone accentuates TV and symptomatic response to lactate. This interaction is substantially lessened by CPL.

CONCLUSIONS

Opioidergic dysregulation may underlie respiratory pathophysiology and suffocation sensitivity in PD. Comparing specific anti-panic medications with ineffective anti-panic agents (e.g. propranolol) can test the specificity of the naloxone+lactate model. A screen for putative anti-panic agents and a new pharmacotherapeutic approach are suggested. Heuristically, the experimental unveiling of the endogenous opioid system impairing effects of CPL and separation in normal adults opens a new experimental, investigatory area.

Panic, suffocation false alarms, separation anxiety and endogenous opioids

This review paper presents an amplification of the suffocation false alarm theory (SFA) of spontaneous panic [Klein DF (1993). False suffocation alarms, spontaneous panics, and related conditions. An integrative hypothesis. Arch Gen Psychiatry; 50:306-17.]. SFA postulates the existence of an evolved physiologic suffocation alarm system that monitors information about potential suffocation. Panic attacks maladaptively occur when the alarm is erroneously triggered. That panic is distinct from Cannon's emergency fear response and Selye's General Alarm Syndrome is shown by the prominence of intense air hunger during these attacks. Further, panic sufferers have chronic sighing abnormalities outside of the acute attack. Another basic physiologic distinction between fear and panic is the counter-intuitive lack of hypothalamic-pituitary-adrenal (HPA) activation in panic. Understanding panic as provoked by indicators of potential suffocation, such as fluctuations in pCO(2) and brain lactate, as well as environmental circumstances fits the observed respiratory abnormalities. However, that sudden loss, bereavement and childhood separation anxiety are also antecedents of "spontaneous" panic requires an integrative explanation. Because of the opioid system's central regulatory role in both disordered breathing and separation distress, we detail the role of opioidergic dysfunction in decreasing the suffocation alarm threshold. We present results from our laboratory where the naloxone-lactate challenge in normals produces supportive evidence for the endorphinergic defect hypothesis in the form of a distress episode of specific tidal volume hyperventilation paralleling challenge-produced and clinical panic.

Maternal separation of rat pups increases the risk of developing depressive-like behavior after subsequent chronic stress by altering corticosterone and neurotrophin levels in the hippocampus

Children that are abused have an increased risk for developing psychiatric disorders later in life, because of the negative effects of stress on the developing brain. We used a maternal separation model in rats to see how neurotrophins, stress hormones, behavior and the anti-oxidant potential of serum are affected. Rat pups were separated from their mothers for 3h/day on days 2-14. Maternal separation caused changes in levels of NGF and NT-3 in the dorsal and ventral hippocampus, increased basal corticosterone levels and decreased ACTH levels after acute restraint stress. The anti-oxidant potential of the rat serum was significantly lower in the maternal separation group. Depressive-like behavior, measured during a forced swim test, was seen in maternally separated rats after additional chronic stress during adulthood. Maternal separation caused downregulation of neurotrophins in the ventral hippocampus, possibly as an effect of high corticosterone levels, but compensatory mechanisms against cell death may be involved as neurotrophin levels increased in the dorsal hippocampus. Decreased anti-oxidant potential of serum could have been an effect of downregulated neurotrophin levels.

Gene-environment interaction affects substance P and neurokinin A in the entorhinal cortex and periaqueductal grey in a genetic animal model of depression: implications for the pathophysiology of depression

Evidence implies a role for corticotropin-releasing hormone (CRH) and tachykinins, e.g. substance P (SP) and neurokinin A (NKA) in the pathophysiology of depression. We have previously shown that SP- and NKA-like immunoreactivity (-LI) concentrations were altered in the frontal cortex and striatum of the congenitally 'depressed' Flinders Sensitive Line (FSL) compared to the Flinders Resistant Line (FRL) control rats. It is also known that environmental stress may affect brain levels of tachykinins. In view of these results we decided to superimpose maternal deprivation, an early life environmental stressor, onto the genetically predisposed 'depressed' FSL rats and the FRL control rats and use this paradigm as a model of gene-environment interaction. The adult animals were sacrificed, adrenal glands and brains dissected out and SP-, NKA- and CRH-LI levels were determined in ten discrete brain regions. Maternal deprivation led to a marked increase in SP-LI and NKA-LI levels in the periaqueductal grey (PAG) and entorhinal cortex of the 'depressed' FSL strain while it had no significant effect in the FRL controls. Furthermore, specific strain differences in peptide-LI content were confirmed. No difference was found in relative adrenal gland weight, which is consistent with the finding that CRH-LI levels in the hypothalamus were similar across strains, and insensitive to stress in either strain. Taken together, these data are in line with behavioural experiments showing ameliorating effects of NK1 and NK2 receptor antagonists against anxiety and depression-like symptoms in rodents, and therefore further implicate the tachykinin systems in the pathophysiology of depression and adult life psychopathology.

Anxiolytic-like properties of the anandamide transport inhibitor AM404

The endocannabinoids anandamide and 2-arachidonoyglycerol (2-AG) may contribute to the regulation of mood and emotion. In this study, we investigated the impact of the endocannabinoid transport inhibitor AM404 on three rat models of anxiety: elevated plus maze, defensive withdrawal and separation-induced ultrasonic vocalizations. AM404 (1-5 mg kg(-1), intraperitoneal (i.p.)) exerted dose-dependent anxiolytic-like effects in the three models. These behavioral effects were associated with increased levels of anandamide, but not 2-AG, in the prefrontal cortex and were prevented by the CB(1) cannabinoid antagonist rimonabant (SR141716A), suggesting that they were dependent on anandamide-mediated activation of CB(1) cannabinoid receptors. We also evaluated whether AM404 might influence motivation (in the conditioned place preference (CPP) test), sensory reactivity (acoustic startle reflex) and sensorimotor gating (prepulse inhibition (PPI) of the startle reflex). In the CPP test, AM404 (1.25-10 mg kg(-1), i.p.) elicited rewarding effects in rats housed under enriched conditions, but not in rats kept in standard cages. Moreover, AM404 did not alter reactivity to sensory stimuli or cause overt perceptual distortion, as suggested by its lack of effect on startle or PPI of startle. These results support a role of anandamide in the regulation of emotion and point to the anandamide transport system as a potential target for anxiolytic drugs.

Effects of early life stress on [11C]DASB positron emission tomography imaging of serotonin transporters in adolescent peer- and mother-reared rhesus monkeys

Peer-reared (PR) rhesus monkeys with early maternal separation later exhibit aggressiveness, impaired impulse control, alcohol abuse, and low CSF 5-hydroxyindoleacetic acid. This study compared regional brain serotonin transporter (SERT) binding between nine PR and seven mother-reared rhesus monkeys with [11C]DASB positron emission tomography (PET) imaging. Parametric images of binding potential (BP) (which is proportional to Bmax/KD, in which Bmax is transporter density and KD is dissociation constant) and relative blood flow (R1) were generated by the two-parameter multilinear reference tissue model. R1 images were used for coregistration and normalization of PET parametric data to the magnetic resonance imaging template space. Group BP differences were analyzed voxelwise by Student's t test in SPM2. Region of interest-based parameter values were also calculated to obtain the magnitude of regional BP differences between the two groups. For the PR group, SERT BP was decreased by 10-23% across a range of brain areas consisting of the raphe, thalamus, hypothalamus, caudate and putamen, globus pallidum, anterior cingulate gyrus, and medial temporal regions, including amygdala and hippocampus (cluster-level corrected p = 0.002). For the latter three regions, BP was decreased in the right hemisphere. These results agree with the hypothesis that early maternal deprivation affects the development of the serotonergic system and suggest that decreased serotonergic innervations in the critical brain regions may explain some of the behavioral and biochemical abnormalities in PR monkeys.

Social withdrawal behaviors in nonhuman primates and changes in neuroendocrine and monoamine concentrations during a separation paradigm

This study investigated relationships between withdrawal behaviors in rhesus macaques and changes in monoamine metabolite and endocrine concentrations during repeated psychosocial stress. Rhesus monkeys (N = 71) experienced maternal separation in which four separations took place during four consecutive weeks. Behavioral observations were made, as well as plasma concentrations of cortisol and cerebrospinal fluid concentrations of the serotonin, dopamine, and norepinephrine metabolites were obtained. Animals were assigned to high, moderate, and low withdrawal groups, defined using baseline durations of withdrawal behaviors. Highly withdrawn animals showed less reduction than nonwithdrawn animals in serotonin metabolite concentrations over repeated separations. Highly withdrawn macaques also failed to significantly reduce cortisol concentrations across separation weeks. More adaptation in central serotonin functioning and cortisol concentrations was seen in nonwithdrawn primates than in highly withdrawn primates; these findings have implications for increased risk of developing anxiety disorders in highly inhibited children.

Childhood parental loss and cortisol levels in adult men

Although data from animal studies show that early rearing experiences can have lasting effects on the hypothalamic-pituitary-adrenal (HPA) axis, little is known about the relationship between childhood parental loss and adult cortisol levels in humans. In the current study, 57 healthy adult men completed a telephone interview concerning parental loss or separations before age 17. Salivary cortisol measures, taken 10 times a day for 5 days in the daily environment, were available from an earlier study. Nine subjects had experienced the death of a parent during childhood. Compared to levels in 38 subjects who had experienced neither loss nor a separation > two weeks, parental loss by death was associated with higher cortisol throughout the day (F(1,44) = 4.73, p = 0.035). Men who had lost a parent scored no higher than those with no loss or separation on trait anxiety or current depressive symptoms, and the effect of parental loss on cortisol remained significant after controlling for these variables. Cortisol patterns in men who had been temporarily separated from one or both parents (n = 10) were inconsistent. Limitations include a lack of systematic information concerning the quality of care after parental death and other forms of childhood adversity. The sample was too small to assess effects of maternal vs. paternal loss or age at loss. Results suggest that parental death during childhood may have lasting effects on the HPA axis, even in the absence of psychopathology.

Behavioral, hormonal and histological stress markers of anxiety-separation in postnatal rats are reduced by prepro-thyrotropin-releasing hormone 178-199

We investigated in the present study whether systemic injections of prepro-thyrotropin-releasing-hormone 178-199 (PPTRH 178-199) in postnatal 3-days old rat pups can provide ameliorative effects in a model of anxiety-separation disorder. The pups were individually separated from their mother and placed in a novel environment. PPTRH 178-199-treated animals started exploring the novel environment in a significantly shorter time and elicited significantly less distress vocalizations than control animals. PPTRH 178-199-treated animals also had markedly lower serum adrenocorticotropic hormone and corticosterone compared to control animals. Furthermore, we observed a significant increase in PPTRH 178-199 immunoreactive cell bodies in the hypothalamus of PPTRH 178-199-treated animals compared to controls, suggesting that the peptide crossed the blood-brain barrier. PPTRH 178-199 treatment can help to reduce behavioral and hormonal disturbances associated with anxiety-separation situations.

Prenatal stress alters early neurobehavior, stress reactivity and learning in non-human primates: a brief review

In this paper we review three prospective longitudinal studies from our laboratory examining the effects of prenatal stress on early neuro behavior, stress reactivity and learning performance in rhesus monkeys. Either a noise stressor or ACTH treatment was administered to pregnant monkeys during specific periods of pregnancy and offspring were examined repeatedly across development. In all three studies, the prenatally stressed monkeys showed reduced attention and impaired neuromotor functioning during the first month of life compared to controls from undisturbed pregnancies. When the monkeys were separated from their mothers or peers at 6-8 months of age, prenatally stressed monkeys exhibited more disturbance behavior and showed hypothalamic-pituitary-adrenal axis dysregulation. During adolescence, they exhibited impairments in learning, compared to controls.

The role of childhood trauma in the neurobiology of mood and anxiety disorders: preclinical and clinical studies

Epidemiologic studies indicate that children exposed to early adverse experiences are at increased risk for the development of depression, anxiety disorders, or both. Persistent sensitization of central nervous system (CNS) circuits as a consequence of early life stress, which are integrally involved in the regulation of stress and emotion, may represent the underlying biological substrate of an increased vulnerability to subsequent stress as well as to the development of depression and anxiety. A number of preclinical studies suggest that early life stress induces long-lived hyper(re)activity of corticotropin-releasing factor (CRF) systems as well as alterations in other neurotransmitter systems, resulting in increased stress responsiveness. Many of the findings from these preclinical studies are comparable to findings in adult patients with mood and anxiety disorders. Emerging evidence from clinical studies suggests that exposure to early life stress is associated with neurobiological changes in children and adults, which may underlie the increased risk of psychopathology. Current research is focused on strategies to prevent or reverse the detrimental effects of early life stress on the CNS. The identification of the neurobiological substrates of early adverse experience is of paramount importance for the development of novel treatments for children, adolescents, and adults.

Periodic maternal separation of neonatal rats produces region- and gender-specific effects on biogenic amine content in postmortem adult brain

Early environment exerts profound effects on mammalian behavioral and neural development. The aim of this study was to describe changes in adult neurochemistry in the rat following repeated neonatal maternal separation (RMS) during the preweaning period, a procedure known to induce enduring behavioral effects. Following RMS, rats show an attenuated locomotor response to novelty, to D-amphetamine, and attenuated behavioral responses for conditioned incentives as adults. These behavioral effects are broadly opposite in direction to those found following postweaning isolation rearing. Isolation rearing-induced behavioral changes are associated with profound changes in central monoamine function. Following RMS, adult rats had increased tissue levels of dopamine in both dorsal and ventral striatum. The turnover of dopamine, as determined by the ratio of DOPAC to dopamine, was decreased in the mPFC of RMS subjects. Serotonin levels were reduced in dorsal hippocampus of RMS rats of both sexes and in the mPFC of male RMS rats. Noradrenaline levels were increased in the dorsal hippocampus in female, but not in male, RMS rats. These data provide evidence that, in addition to the adult behavioral consequences, RMS leads to profound, region-, and gender-specific changes in brain monoamine content. The developmental specificity of these results is discussed with respect to their possible role in altered behavioral development and psychopathology.

NGF expression in the developing rat brain: effects of maternal separation

A number of studies have shown that mothering style in rodents can produce neuroendocrine, neurochemical and behavioural changes in the adult, although the basic mechanisms initiating this cascade of events still need to be investigated. Long term changes in neuronal function might be due to alterations in the expression of neurotrophins which have been shown to promote neuronal survival, differentiation and function during development, such as Nerve Growth Factor (NGF). NGF is essential for proper development of sympathetic and neural crest-derived sensory neurons of the peripheral nervous system as well as of central cholinergic neurons. In previous studies, using a maternal separation paradigm, we have shown that NGF expression is increased in the dentate gyrus and the hilus of the hippocampus as a result of brief (45 min) maternal separations. In the present study neonatal rats were separated for longer periods of time (up to 3 h) and at different ages during development (9 and 16 days postnatally). Results indicate that the effects of maternal separation on NGF expression are stronger with longer separations and are not restricted to the hippocampal region but can be seen also in other brain areas. Overall these results indicate that external factors, such as the presence/absence of the mother, can modify neurotrophic factor's availability in the brain, thus indicating NGF as a potential player in environmentally-mediated brain plasticity during development.

[Serotonergic dysfunction caused by social isolation. Implications for the development of aggressiveness and alcoholism]

Dysfunction of serotonergic neurotransmission has been associated with two different psychopathological syndromes--impulsive aggressivity resulting form a lack of stimulation of the "behavior inhibition system" on the one hand and the manifestation of clinical depression and compulsive syndromes on the other. The examination of primate behavior provides a model which may reconciliate these seemingly contradictory hypotheses. According to primate experiments, monoaminergic depletion results in anxious and desperate behavior only if the individual has previously been exposed to social isolation stress, which in turn induces a decrease in the central serotonin turnover rate. Young non-human primates who experience early social separation stress are anxious and fearful, while as adults they tend to be aggressive, consume excessive amounts of alcohol and are less intoxicated by alcohol intake. These observation indicate the importance of social separation stress in the pathogenesis of alcoholism and antisocial behavior and may point to prophylactic and pharmacological treatment strategies.

Biogenic amine activity in response to fluoxetine and desipramine in differentially reared rhesus monkeys

BACKGROUND

It has been hypothesized that adverse early experience may be a mechanism by which children become vulnerable to later psychopathology via alteration of neurochemical or hormonal systems associated with such disorders. Such effects may in turn affect later responses to pharmacologic agents that act on these systems.

METHODS

In this study, 18 mother-reared (MR) and 18 peer-reared (PR) rhesus monkeys experienced six 1-week separations from cagemates interspersed with 1-week reunions, while housed in like-reared groups of 3. Within rearing groups, equal numbers of animals received either fluoxetine (2 mg/kg), desipramine (5 mg/kg) or placebo delivered daily beginning 4 weeks before the first separation. Levels of norepinephrine (NE), the NE metabolite MHPG, the dopamine metabolites DOPAC and HVA, and the serotonin metabolite 5HIAA were measured in CSF samples collected approximately every 2 to 3 weeks during these procedures.

RESULTS

Following treatment, DMI increased NE and decreased MHPG in the DMI-treated groups, while 5HIAA was decreased in the fluoxetine-treated groups following treatment. The increase in NE was followed by a sharp decline over the course of treatment, which was accompanied by an increase in MHPG. The rearing groups did not show a differential response to the drug treatments, and the separation manipulation itself had few effects. The mother-reared group showed higher levels of NE and DOPAC over all samples and higher levels of HVA in most samples.

CONCLUSIONS

These rearing effects on biogenic amine activity were observed even in the presence of pharmacologic treatments that effectively altered the activity of these systems, and are consistent with previous findings from the same subject. The higher NE values observed in mother-reared infants over separations and reunions may have been due to higher basal levels of NE than peer-reared monkeys or to greater responsiveness to the stress of repeated social disruption or both. These findings agree with other primate studies showing that rearing differences persist beyond the infancy period and add to growing evidence of the important influence of the early social environment on neurobiologic development in primates.

Effects of rearing condition on HPA axis response to fluoxetine and desipramine treatment over repeated social separations in young rhesus monkeys

Normal hypothalamic-pituitary-adrenal (HPA) axis activity is disrupted in several types of human psychiatric disorders, and has been widely reported to be altered as a result of early experience in rodents. In this study the effects of early social experience on later response of the HPA axis to separations from cagemates and pharmacologic treatments were examined in rhesus monkeys. HPA axis activity was measured in mother-reared and peer-reared monkey infants in conjunction with six repeated separations from and reunions with their cagemates. Within each rearing group, infants were assigned to one of three treatment groups that received continuous treatment with either fluoxetine (2 mg/kg), desipramine (DMI, 5 mg/kg) or placebo (saline) beginning 2 weeks prior to separations. At 2 weeks after drug treatment, fluoxetine increased ACTH and cortisol in the treated groups, while DMI decreased ACTH and cortisol in both treated groups; however, these effects were not persistent over the separations. While these treatment effects tended to be more pronounced in the mother-reared group, the rearing groups did not show a clearly differential response to either of the treatments. The most prominent finding was that mother-reared monkeys showed significantly higher ACTH and cortisol levels than peer-reared monkeys over all samples, an effect that may have mitigated a potential rearing group difference in treatment response. The results add to growing evidence for the influence of primate mothers on the functional development of psychobiological systems in their infants, and suggest that the HPA axis is among the more sensitive of these systems to postnatal experience.

The stressfulness of separation among nine-month-old infants: effects of social context variables and infant temperament

This manuscript reports on the results of 2 experiments dealing with behavioral and adrenocortical responses to separation among 9-month-old human infants. In both experiments the social context of separation was manipulated. The results of Experiment 1 yielded evidence of a statistically significant adrenocortical response to 30 min of separation under conditions in which the substitute caregiver responded sensitivity to infant distress, but was busy and relatively noninteractive when babies were not distressed during the separation period. Altering the behavior of the substitute caregiver such that she was warm, responsive, and interactive throughout the separation produced a significant reduction in adrenocortical activity and in negative affect. In fact, these measures were not significantly different than those obtained when the mother and infant remained together in the playroom (No Separation). In Experiment 2, the effects of group versus singleton care were examined using the less stressful mode of substitute caregiving as described above. No significant condition differences in behavioral distress or cortisol were found. Furthermore, neither condition elicited a significant increase in cortisol over basal levels. Finally, these data provide evidence that maternal reports of infant Distress to Limits temperament, using Rothbart's Infant Behavior Questionnaire, predict adrenocortical responses to separation, while reports of Fear of Novelty do not.