Oligodendrocyte gene expression is reduced by and influences effects of chronic social stress in mice.

Oligodendrocyte gene expression is downregulated in stress-related neuropsychiatric disorders, including depression. In mice, chronic social stress (CSS) leads to depression-relevant changes in brain and emotional behavior, and the present study shows the involvement of oligodendrocytes in this model. In C57BL/6 (BL/6) mice, RNA-sequencing (RNA-Seq) was conducted with prefrontal cortex, amygdala and hippocampus from CSS and controls; a gene enrichment database for neurons, astrocytes and oligodendrocytes was used to identify cell origin of deregulated genes, and cell deconvolution was applied. To assess the potential causal contribution of reduced oligodendrocyte gene expression to CSS effects, mice heterozygous for the oligodendrocyte gene cyclic nucleotide phosphodiesterase (Cnp1) on a BL/6 background were studied; a 2 genotype (wildtype, Cnp1+/- ) × 2 environment (control, CSS) design was used to investigate effects on emotional behavior and amygdala microglia. In BL/6 mice, in prefrontal cortex and amygdala tissue comprising gray and white matter, CSS downregulated expression of multiple oligodendroycte genes encoding myelin and myelin-axon-integrity proteins, and cell deconvolution identified a lower proportion of oligodendrocytes in amygdala. Quantification of oligodendrocyte proteins in amygdala gray matter did not yield evidence for reduced translation, suggesting that CSS impacts primarily on white matter oligodendrocytes or the myelin transcriptome. In Cnp1 mice, social interaction was reduced by CSS in Cnp1+/- mice specifically; using ionized calcium-binding adaptor molecule 1 (IBA1) expression, microglia activity was increased additively by Cnp1+/- and CSS in amygdala gray and white matter. This study provides back-translational evidence that oligodendrocyte changes are relevant to the pathophysiology and potentially the treatment of stress-related neuropsychiatric disorders.

Altered emotionality and neuronal excitability in mice lacking KCTD12, an auxiliary subunit of GABAB receptors associated with mood disorders.

Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the brain, is fundamental to brain function and implicated in the pathophysiology of several neuropsychiatric disorders. GABA activates G-protein-coupled GABAB receptors comprising principal GABAB1 and GABAB2 subunits as well as auxiliary KCTD8, 12, 12b and 16 subunits. The KCTD12 gene has been associated with bipolar disorder, major depressive disorder and schizophrenia. Here we compare Kctd12 null mutant (Kctd12(-/-)) and heterozygous (Kctd12(+/-)) with wild-type (WT) littermate mice to determine whether lack of or reduced KCTD12 expression leads to phenotypes that, extrapolating to human, could constitute endophenotypes for neuropsychiatric disorders with which KCTD12 is associated. Kctd12(-/-) mice exhibited increased fear learning but not increased memory of a discrete auditory-conditioned stimulus. Kctd12(+/-) mice showed increased activity during the inactive (light) phase of the circadian cycle relative to WT and Kctd12(-/-) mice. Electrophysiological recordings from hippocampal slices, a region of high Kctd12 expression, revealed an increased intrinsic excitability of pyramidal neurons in Kctd12(-/-) and Kctd12(+/-) mice. This is the first direct evidence for involvement of KCTD12 in determining phenotypes of emotionality, behavioral activity and neuronal excitability. This study provides empirical support for the polymorphism and expression evidence that KCTD12 confers risk for and is associated with neuropsychiatric disorders.

The impaired coping induced by early deprivation is reversed by chronic fluoxetine treatment in adult fischer rats.

The symptoms of depression include feelings of reduced coping ability and increased helplessness. Early life adversity increases vulnerability to depression. In rats, the quantification of ability to cope with adverse challenge can be achieved using preexposure to an inescapable aversive stimulus and subsequent assessment of escape or avoidance deficits in the same environment. Here we investigated the predictive validity of a model in which, in the Fischer rat strain, postnatal isolation leads in adulthood to a state of increased sensitivity to develop an escape or avoidance deficit. On days 1-14 rat pups were isolated for 4 hours (early deprivation, ED) or for 15 minutes (early handling, EH), or were left completely undisturbed (non-handling, NH). In adulthood, subjects were placed in a shuttle box and half were exposed to brief, mild foot shocks (preexposure, PE) and the other half were non-preexposed (NPE). Half of the PE and NPE subjects were then treated for 21 days with fluoxetine and the other half with vehicle. In males, although there was no overall preexposure effect on avoidance behaviour, ED-PE and ED-NPE and EH-PE and EH-NPE demonstrated an avoidance deficit relative to NH. Fluoxetine attenuated this deficit and most notably in ED-PE. In females, vehicle ED-PE demonstrated an avoidance deficit relative to NH-PE; fluoxetine attenuated this ED effect. These findings provide supportive evidence for the predictive validity of this depression model.

Amphetamine withdrawal does not produce a depressive-like state in rats as measured by three behavioral tests.

Administration of amphetamine (AMPH) can induce symptoms of psychosis in humans and locomotor sensitization in rats; in contrast, withdrawal from a period of AMPH intake is most often associated with symptoms of human endogenous depression. The aim of this study was to determine whether AMPH withdrawal produces a depressive-like state in rats. The present study examined the effects of withdrawal from an escalating-dose AMPH schedule (ESC; three daily injections over 6 days, 1-5 mg/kg, i.p.) and an intermittent-dose AMPH schedule (INT; one daily injection over 6 days, 1.5 mg/kg, i.p.) on animals' performance in three behavioral paradigms related to depression: the Porsolt swim test, the learned helplessness assay and operant responding for sucrose on a progressive ratio schedule. ESC and INT AMPH withdrawal had no effect on any of these tests or on stress responsiveness as measured by increased plasma levels of corticosterone (CORT) and adrenocorticotropin following the swim test, although basal CORT levels were higher in AMPH-withdrawn animals compared to controls. Finally, we confirmed the presence of locomotor sensitization for both AMPH schedules after 30 days of withdrawal. Our results suggest that the ability of AMPH withdrawal to produce symptoms of depression may not be evident in all behavioral screens for depressive symptoms in the rat.

Peripartum sex steroid profiles and endocrine correlates of postpartum maternal behavior in captive gorillas (Gorilla gorilla gorilla).

An association between pregnancy levels of estrogen and progesterone and maternal behavior has been demonstrated in several taxonomic orders of nonprimate and primate mammals, but has not so far been investigated in the gorilla. In this study we investigated whether prepartum titers of urinary estrone conjugates (E1C) or pregnanediol-3alpha-glucuronide (PdG) were related to postpartum maternal behavior in eight multiparous Western lowland gorilla females (Gorilla gorilla gorilla) housed in four zoological gardens. Urine samples were collected from each study animal for 14 days prepartum and 14 days postpartum, and measures of maternal responsiveness were scored during the first 15 days postpartum. Urine samples were assayed with radioimmunoassay for E1C and PdG. Results for the peripartum profiles of urinary E1C, as well as postpartum profiles of PdG, agree with previous findings for the gorilla, while results for late-pregnancy profiles of urinary PdG were inconclusive in confirming a prepartum increase or decrease. Neither prepartum levels of E1C or PdG, nor the E1C/PdG ratio were found to be related to measures of postpartum maternal behavior. This lack of association between late-pregnancy E1C titers per se and postpartum maternal behavior is contrary to findings in nonprimate and other primate species.

Comparison of the effects of early handling and early deprivation on maternal care in the rat.

It has been reported in the rat that postnatal manipulations can induce robust and persistent effects on offspring neurobiology and behavior, mediated in part via effects on maternal care. There have, however, been few studies of the effects of postnatal manipulations on maternal care. Here, we describe and compare the effects on maternal behavior on postnatal days 1-12 of two manipulations, early handling (EH, 15-min isolation per day) and early deprivation (ED, 4-hr isolation per day), relative to our normal postnatal husbandry procedure. Maternal behavior was measured at five time points across the dark phase of the reversed L:D cycle. EH yielded an increase in arched-back nursing across several time points but did not affect any other behavior. ED stimulated a bout of maternal behavior such that licking and arched-back nursing were increased at the time of dam-litter reunion, although not at any other time point. Neither EH nor ED affected weaning weight significantly. Importantly, within-treatment variation was high relative to these between-treatment effects.

Comparison of the effects of infant handling, isolation, and nonhandling on acoustic startle, prepulse inhibition, locomotion, and HPA activity in the adult rat.

This study examined whether early isolation (EI), early handling (EH), or early nonhandling (NH) in infant rats alters (a) prepulse inhibition (PPI) of the acoustic startle response (ASR) or its disruption by apomorphine, (b) motor activity or its stimulation by amphetamine, or (c) corticosterone activity (because of its modulation of dopamine activity), in adulthood and in comparison with a normal-husbandry postnatal control environment. EI did not affect PPI, reduced PPI disruption by apomorphine in males, and increased amphetamine-stimulated activity in males. NH increased the ASR, reduced activity in the open field, and increased corticosterone reactivity in males. In all paradigms, the effects of EH were similar to those of the control environment. This study provides an important contribution to the evidence on the relationship between postnatal experience and long-term neurobehavioral development in the rat and the relevance of this approach to animal models of neuropsychiatric disorder.

Lack of effect of an early stressful life event on sensorimotor gating in adult rats.

Hypotheses of the etiology of schizophrenia emphasize the important role of perinatal insults in predisposing individuals to the development of the disease, so that an animal model in which a discrete postnatal manipulation of the infant social environment yields schizophrenia-like behavior in adulthood would be valuable in terms of the study of the neural substrate and treatment of schizophrenia. Schizophrenics demonstrate a deficit in sensorimotor gating (prepulse inhibition), and a similar phenomenon has been described in adult rats following the administration of direct and indirect dopamine agonists. Recently it has been reported that a 24 h separation of rat pups from the mother results in a disruption of prepulse inhibition at adulthood. Here we report a study which investigated the same phenomenon but which, in contrast to the previous study, utilized unrelated subjects all derived from different dams. Maternal separation was conducted for 24 h with pups aged 4, 9 or 18 days and these subjects, together with non-separated controls, were tested at age 3 months in terms of their prepulse inhibition in the acoustic startle response paradigm. Maternal separation did not disrupt prepulse inhibition. Comparison of males and females (with a maximum of one opposite-sex sibling) demonstrated that acoustic startle response and prepulse inhibition of this response was enhanced in males relative to females. This study indicates that 24 h maternal separation does not provide a robust model for studying the effects of early environmental insults on the long-term abnormal development of sensorimotor gating.

Lewis/Fischer rat strain differences in endocrine and behavioural responses to environmental challenge.

The Lewis (LEW) and Fischer (F344) rat strains provide a comparative model of hypothalamic-pituitary-adrenal (HPA) function in which LEW is relatively hypoactive at homeostasis and hyporeactive to environmental challenge. The present study describes a comparison of LEW and F344 rats, males and females, in terms of their corticosterone (CORT) or behavioural responses to a range of behavioural tasks, where each of the tasks used contains a stressor component and has been demonstrated to be sensitive to corticotropin releasing factor (CRF) and/or CORT manipulation: acoustic startle response (ASR), elevated plus maze, schedule-induced polydipsia, and fear-conditioned suppression of drinking. Our aim was to determine to what extent the LEW trait of HPA axis hyporesponsiveness is associated with strain differences in behavioural responsiveness to environmental challenge. As expected, young (2-3 months)-mature (5-10 months) LEW males and females exhibited a lesser CORT response to restraint and novel confinement than did F344 males and females, although in old adulthood (18 months) the CORT stress response was equable in LEW/F344 males and actually higher in LEW than in F344 females. In young-mature adults, the ASR was greater in LEW males than in the other groups; all groups spent a low proportion of time on the open arms of the elevated plus maze; polydipsia was greater in F344 females than in the other groups; and fear-conditioned suppression of drinking was greater in F344 males and females than in LEW males and females. Therefore, relative hyporeactivity of the HPA axis in LEW rats is clearly not associated with uniform behavioural hyporeactivity, including CRF-dependent behaviours. Rather, this study suggests further evidence that environmental reactivity reflects a number of distinct emotional states and underlying neural circuits.

The maternal separation paradigm and adult emotionality and cognition in male and female Wistar rats.

A single 24-h maternal separation (MS) in the rat during the stress hyporesponsive period alters adult behavior and neuroendocrine stress response. The age of the animal at MS might be a crucial factor for effects in adulthood. We report here on adult behavioral effects of MS performed on postnatal day 4 (MS4), 9 (MS9), or 18 (MS18) in male and female Wistar rats. Unrelated subjects were used to avoid confounding litter effects. Subjects were tested on paradigms of unconditioned fear/anxiety, i.e., open field and elevated plus-maze, and on paradigms involving learning in an aversive situation, i.e., conditioned freezing, active avoidance, and water maze. In line with our predictions we obtained (a) sex differences that were consistent with enhanced fear/anxiety in males relative to females, (b) evidence that MS4 yielded deficits in active avoidance learning and conditioned freezing (trend level), whereas MS9 yielded enhanced active avoidance and water maze learning, (c) evidence (at trend level) that these effects of MS are greater in males than in females. There was no evidence for an effect of MS on paradigms of unconditioned fear/anxiety. We conclude that MS, irrespective of the age at separation, does not provide a robust environmental model of modified behavior in aversive situations.

Effect of sex on fear conditioning is similar for context and discrete CS in Wistar, Lewis and Fischer rat strains.

Enhanced fear in males relative to females, both innate and conditioned, is a well-described characteristic of behavior in the laboratory rat. In the case of aversive conditioning to foot shock in Long-Evans rats, it has been described that conditioning to general (nondiscrete) contextual cues is greater in male rats relative to female rats, whereas conditioning to a discrete, predictive stimulis (CS) is not. These findings have been combined with evidence for greater levels of hippocampal LTP in males in Sprague-Dawley rats to derive a model of hippocampal-LTP-mediated contextual and not CS, fear conditioning. The present study reports on an analysis of the effect of sex in contextual and discrete CS conditioning to foot shock, assessed via measurement of freezing behavior in a novel automated paradigm, in three rat strains: Wistar, Fischer, and Lewis. In Wistar rats, there was a consistent but nonsignificant tendency for males to demonstrate both more contextual and more CS conditioning than females; in Fischer rats, males demonstrated both more contextual and more CS conditioning than females; in Lewis rats, a markedly enhanced acquisition of freezing in males did not translate into a sex difference in either context or CS conditioning at expression. Therefore, within each strain the effect of sex was consistent between context and CS conditioning. These findings, taken together with the hippocampal LTP evidence, suggest that the latter mediates both contextual and discrete CS aversive conditioning, and contributes to sex differences in both these forms of conditioning, in those strains where these sex differences exist.

Hematology and serum chemistry values in captive Goeldi's monkeys (Callimico goeldii).

Hematologic and biochemical reference values were obtained from 27 healthy, captive, nonanesthetized Goeldi's monkeys (Callimico goeldii), a threatened South American primate, using automated techniques. The merits of nonparametric statistical analysis of values over the more common parametric method were demonstrated.

Hormonal monitoring of age at sexual maturation in female Goeldi's monkeys (Callimico goeldii) in their family groups.

The aim of this study was to determine whether or not sexual maturation is attained in the family group in captive-born Goeldi's monkey (Callimico goeldii) and if so, at what age and body weight. To monitor ovarian activity in 14 female Goeldi's monkeys, urinary content of pregnanediol-3alpha-glucuronide (PdG) was determined using radioimmunoassay. Urinary samples were collected between the ages of 6 and 70 weeks. Subjects became sexually mature while still housed in their family groups, at a median age of 57 weeks (48-< 70 weeks). Median body weight at the age of sexual maturity was 473 g (N=10; 420-543 g). This corresponded to 90% of the median non-pregnant body weight of breeding females in our colony (526 g, N=8). Therefore, Goeldi's monkey is similar to Leontopithecus but different from Cebuella, Callithrix, and Saguinus, in terms of daughters ovulating in the family group and at a relatively young age.

Peripheral benzodiazepine receptors in cerebral cortex, but not in internal organs, are increased following inescapable stress and subsequent avoidance/escape shuttle-box testing.

Stress-induced alterations in peripheral benzodiazepine receptor (PBR) density have been reported in humans and in rats. However, the PBR response is highly specific, and its function remains largely unexplained. The aim of the present study was to investigate the relationship between behavior in the two-way active avoidance paradigm (2WAA) and post-test PBR densities in adrenal, testis, kidney, and cerebral cortex. Adult male Wistar rats were tested in the 2WAA either in the naive state (AA) or 24 h following shock preexposure (PE), known to interfere with avoidance/escape response acquisition, and decapitated immediately after testing. Control subjects were decapitated without experimental experience. The stressful characteristic of the experiment was validated by significantly increased post-test corticosterone levels in AA and PE subjects compared with controls, with a trend towards higher corticosterone levels in PE relative to AA rats. Similarly, PE compared with AA subjects tended to show retarded acquisition of the escape/avoidance response. PBR densities in adrenal, kidney, and testis and central benzodiazepine receptors (CBR) in the cerebral cortex remained unaffected by avoidance testing. Cerebral cortex PBR density was significantly increased in PE subjects. These findings suggest that avoidance testing, although stressful to the animals, led to changes confined to cerebral cortex PBR, indicating that the hypothalamic-pituitary-adrenal (HPA) response occurs independently of the PBR response in peripheral organs, and also suggest that the opportunity for coping alters the impact of the stressor on the subject and prevents the expression of PBR response in peripheral organs.

Sex differences in the acoustic startle response and prepulse inhibition in Wistar rats.

The prepulse inhibition paradigm (PPI) is based on the phenomenon that the acoustic startle response (ASR) to an acoustic stimulus is reduced when the stimulus is preceded by a weak prepulse. It has been shown that PPI is dramatically disrupted in patients with schizotypic disorders. Since PPI can be easily tested in animals as well as in humans it is a widely used model to investigate the neurobiological mechanisms underlying those disorders. In humans it has been demonstrated that men show increased PPI at weak prepulses relative to women. Only very few studies have investigated PPI sex differences in rats and these report negative findings. Studies are reported on here where consistent differences have been found in ASR and PPI between adult male and female Wistar rats. Compilation of data from a series of experiments demonstrates that ASR and PPI are both greater in males than in females in this rat strain, a finding which is largely in line with the human evidence. This study therefore adds weight to the argument that PPI of the ASR provides an animal model with high validity for the study of important human disorders which are characterized by sensorimotor gating deficits.

Evidence from urinary cortisol that maternal behavior is related to stress in gorillas.

By studying western lowland gorillas (Gorilla gorilla gorilla, n = 8) in zoological gardens via ethological and non-invasive physiological techniques, we have demonstrated that their postpartum maternal behavior is related negatively to their postpartum urinary titers of cortisol. On the basis of this finding, it is proposed that postpartum stress contributes to disrupted maternal behavior in the gorilla in captivity. Morning urine samples were collected with a mean sampling interval of 1.6 days from Day 14 prepartum to Day 14 postpartum (n = 11 pregnancies). Creatinine-indexed (Cr) urinary cortisol titers declined significantly between Day 9 to 1 prepartum (0.634 +/- 0.014 microg/mg of Cr, mean +/- SEM) and Day 1 to 6 postpartum (0.396 +/- 0.030 microg/mg of Cr, mean +/- SEM; p < 0.01-0.001). For each pregnancy, the relative postpartum decline in urinary cortisol was calculated as (microg of cortisol/mg of Cr Day 1 to 4)/(microg of cortisol/mg of Cr Day -4 to -1). Values ranged from 0.35 to 1.12, were independent of absolute prepartum cortisol titers, and were interpreted as evidence of inter-female differences in postpartum hypothalamo-pituitary-adrenal axis activity and, therefore, postpartum stress. This postpartum stress index was negatively correlated with the amount of time (0-100%) that females carried and supported their 0-14 day-old infants in a ventral position during locomotion (r(s) = -0.68, p < 0.05) and tended to be negatively correlated with the total amount of time (0-100%) they spent in ventro-ventral contact with their infants (r(s) = -0.58; p < 0.10). This study provides the first physiological evidence that postpartum stress is an important etiologic factor in gorilla maternal failure in captive environments.

Physiological Responses to parental separation and a strange situation are related to parental care received in juvenile Goeldi's monkeys (Callimico goeldii).

The relationship between parental care received and physiological and behavioral responses to parental separation, isolation, and reunion was investigated in seven juvenile Goeldi's monkey living in their family groups. Physiological responses were measured non-invasively: the hypothalamic-pituitary-adrenal axis via urinary cortisol output and the autonomic nervous system via piloerection on the tail. Parent-infant aggression demonstrated high intergroup variation and predicted: (a) an increase in urinary cortisol output, r(s) = 0.86, p = 0.04, and duration of piloerection, r(s) = 0.71, p = 0.08, at initial separation-isolation; (b) adaptation of piloerection, r(s) = -0.89, p = 0.03, to repeated separation-isolation. Juvenile Goeldi's monkeys that had received high parental aggression were more physiologically responsive to separation; they also sought more contact with their mothers at reunion, rs = 0.93, p = 0.02. We propose that these data are consistent with the hypothesis that high emotional reactivity is related to insecure attachment to aggressive parents in this New world primate.

Monitoring and controlling reproduction in captive common marmosets on the basis of urinary oestrogen metabolites.

Non-invasive methods for routine monitoring of reproductive states and reproduction control in large colonies of captive Callithrix jacchus have been developed. Immunoactive urinary oestrone-3-conjugates (E1C) were measured during non-conception cycles (n = 5) and pregnancy (n = 7). Using plasma progesterone levels to time ovulation, ovulation was quantitatively estimated by a) calculating the first E1C rise and b) by establishing an E1C threshold. Ovulation was thus defined as taking place 4 days preceding a) the first rise of E1C above follicular-phase levels, or b) a concentration > or = 4.5 micrograms E1C/mg creatinine. Early pregnancy could be determined after day 20 by continued luteal-phase levels of E1C. Secondly, the luteolytic effect of cloprostenol, injected over a wide range of doses and between days 1 and 64 after ovulation/conception, was analysed. Luteolysis was achieved when cloprostenol was administered after day 5 post-ovulation; the luteolytic effect was found not to be dose-dependent. The success of cloprostenol treatment was 87% as confirmed by endocrine monitoring. The methods described are effective and minimize intervention, and are therefore suitable for long-term applications, particularly in combination with behavioural studies.

An investigation into sexual motivation and behavior in female Goeldi's monkey (Callimico goeldii): effect of ovarian state, mate familiarity and mate choice.

Four adult female Callimico were studied in terms of their sexual motivation relative to three unrelated adult males using an operant paradigm followed by a pair test or a two-male choice test. Reductions in urinary cortisol concentrations and the duration of immobility were used as indicators of subjects' adjustment to the experimental situation. When females were tested with unfamiliar males there was no effect of ovarian state on operant or species-typical measures of female sexual motivation. When females were retested with the same males after a 1-week familiarization, sexual motivation was higher during the peri-ovulatory phase than during the post-ovulatory phase in terms of operant but not in terms of species-typical proceptive behavior or in terms of receptive behavior. During the familiarization periods, female sociopositive behavior and sexual motivation demonstrated marked variation depending on the identity of the male. Males with which females demonstrated high sexual motivation during familiarization were the object of equal amounts of female operant behavior during pair tests and two-male choice tests; males with which females had demonstrated low sexual motivation were the objects of less female sexual motivation under conditions of female choice than in pair tests.