Dynamic microglial alterations underlie stress-induced depressive-like behavior and suppressed neurogenesis.

The limited success in understanding the pathophysiology of major depression may result from excessive focus on the dysfunctioning of neurons, as compared with other types of brain cells. Therefore, we examined the role of dynamic alterations in microglia activation status in the development of chronic unpredictable stress (CUS)-induced depressive-like condition in rodents. We report that following an initial period (2-3 days) of stress-induced microglial proliferation and activation, some microglia underwent apoptosis, leading to reductions in their numbers within the hippocampus, but not in other brain regions, following 5 weeks of CUS exposure. At that time, microglia displayed reduced expression of activation markers as well as dystrophic morphology. Blockade of the initial stress-induced microglial activation by minocycline or by transgenic interleukin-1 receptor antagonist overexpression rescued the subsequent microglial apoptosis and decline, as well as the CUS-induced depressive-like behavior and suppressed neurogenesis. Similarly, the antidepressant drug imipramine blocked the initial stress-induced microglial activation as well as the CUS-induced microglial decline and depressive-like behavior. Treatment of CUS-exposed mice with either endotoxin, macrophage colony-stimulating factor or granulocyte-macrophage colony-stimulating factor, all of which stimulated hippocampal microglial proliferation, partially or completely reversed the depressive-like behavior and dramatically increased hippocampal neurogenesis, whereas treatment with imipramine or minocycline had minimal or no anti-depressive effects, respectively, in these mice. These findings provide direct causal evidence that disturbances in microglial functioning has an etiological role in chronic stress-induced depression, suggesting that microglia stimulators could serve as fast-acting anti-depressants in some forms of depressive and stress-related conditions.

Sleep does not enhance the recovery of deprived eye responses in developing visual cortex.

Monocular deprivation (MD) during a critical period of visual development triggers a rapid remodeling of cortical responses in favor of the open eye. We have previously shown that this process is enhanced by sleep and is inhibited when the sleeping cortex is reversibly inactivated. A related but distinct form of cortical plasticity is evoked when the originally deprived eye (ODE) is reopened, and the non-deprived eye is closed during the critical period (reverse monocular deprivation (RMD)). Recent studies suggest that different mechanisms regulate the initial loss of deprived eye responses following MD and the recovery of deprived eye responses following RMD. In this study we investigated whether sleep also enhances RMD plasticity in critical period cats. Using polysomnography combined with microelectrode recordings and intrinsic signal optical imaging in visual cortex we show that sleep does not enhance the recovery of ODE responses following RMD. These findings add to the growing evidence that different forms of plasticity in vivo are regulated by distinct mechanisms and that sleep has divergent roles upon different types of experience-dependent cortical plasticity.

Specific and time-dependent effects of glucocorticoid receptor agonist RU28362 on stress-induced pro-opiomelanocortin hnRNA, c-fos mRNA and zif268 mRNA in the pituitary.

This study examined the effects of the glucocorticoid receptor (GR) agonist RU28362 on stress-induced gene expression in the pituitary of rats to investigate mechanisms of glucocorticoid negative feedback in vivo. In an initial experiment, acute restraint stress produced rapid (within 15 min) induction of c-fos mRNA, zif268 mRNA and pro-opiomelanocortin (POMC) hnRNA within the anterior and intermediate/posterior pituitary as determined by quantitative real-time polymerase chain reaction. Treatment with RU28362 (150 microg/kg, i.p.) 60 min before restraint inhibited adrenocorticotrophic hormone (ACTH) and corticosterone secretion and selectively suppressed the stress-induced increase in POMC hnRNA in the anterior pituitary gland. The failure of RU28362 to surpress the stress-induced rise in c-fos and expression of zif268 mRNA suggests that the central release of ACTH secretagogues was not affected at this time point by treatment with the GR agonist. Rather, the inhibition of ACTH release appeared to be due to a direct effect of RU28362 within the pituitary. A follow-up time-course study varied the interval (10, 60 or 180 min) between RU28362 pretreatment and the onset of restraint. The stress-induced increase in POMC hnRNA was completely blunted by RU28362 treatment within 10 min of treatment, although the stress induced hormone secretion, c-fos mRNA and zif268 mRNA were unaffected. The rapid inhibition of the stress-induced rise in POMC hnRNA in the anterior pituitary appears to reflect direct, GR-mediated suppression of POMC gene expression. RU28362 pretreatment 180 min before restraint onset was sufficient to suppress the stress-induced expression in the anterior pituitary gland of all three genes examined. Thus, the delayed negative feedback effects on hypothalamic-pituitary-adrenal axis activity that emerged after 180 min after glucocorticoid treatment were not evident at 60 min. Taken together, the data suggest that the inhibition of the stress-induced release of ACTH apparent within the first hour of glucocorticoid exposure is effected at the level of the pituitary gland. The delayed glucocorticoid effects evident 180 min after RU28362 treatment may include glucocorticoid actions in the brain and additional actions within the pituitary.

Clinical response augments NK cell activity independent of treatment modality: a randomized double-blind placebo controlled antidepressant trial.

BACKGROUND: Major depressive disorder (MDD) has been associated with alterations in immune function. Suppression of natural killer (NK) cell activity (NKCA) reliably characterizes immunological alterations observed in MDD. Antidepressant pharmacotherapy has been associated with modulation of NKCA. Previous investigations into antidepressant modulation of NKCA have not employed randomized double-blind placebo controlled designs. Thus, it is unknown whether treatment-associated changes in immune function are due to drug, placebo, or spontaneous remission effects. The present investigation examined the effect of antidepressant treatment on NKCA utilizing a randomized double-blind placebo controlled experimental design. METHOD: Patients (N = 16) met DSM-IV criteria for MDD and were randomly assigned to drug (N = 8; citalopram, 20 mg/day) or placebo (N = 8) under double-blind conditions. Severity and pattern of depressive symptoms were assessed by the Hamilton Depression Rating Scale (HDRS). NK cell function was measured using a standard chromium-release assay and NK cell number assessed by flow cytometry. HDRS scores, NK cell function, and NK cell numbers were collected at 0, 1, 2 and 4 weeks of treatment. RESULTS: Clinical response was associated with augmented NKCA independent of treatment condition. Failure to respond to treatment resulted in significantly reduced NKCA over treatment interval. CONCLUSIONS: The present results suggest that alterations in the depressive syndrome, regardless of therapeutic modality, may be sufficient to modulate NKCA during antidepressant trials and thus may significantly impact on co-morbid health outcomes in MDD.

Infusion of nerve growth factor (NGF) into kitten visual cortex increases immunoreactivity for NGF, NGF receptors, and choline acetyltransferase in basal forebrain without affecting ocular dominance plasticity or column development.

Intracerebroventricular or intracortical administration of nerve growth factor (NGF) has been shown to block or attenuate visual cortical plasticity in the rat. In cats and ferrets, the effects of exogenous NGF on development and plasticity of visual cortex have been reported to be small or nonexistent. To determine whether locally delivered NGF affects ocular dominance column formation or the plasticity produced by monocular deprivation in cats at the height of the critical period, we infused recombinant human NGF into the primary visual cortex of kittens using an implanted cannula minipump. NGF had no effect on the normal developmental segregation of geniculocortical afferents into ocular dominance columns as determined both physiologically and anatomically. The plasticity of binocular visual cortical responses induced by monocular deprivation was also normal in regions of immunohistochemically detectable NGF infusion, as measured using intrinsic signal optical imaging and single-unit electrophysiology. Immunohistochemical analysis of the basal forebrain regions of the same animals demonstrated that the NGF infused into cortex was biologically active, producing an increase in the number of NGF-, TrkA-, p75(NTR)-, and choline acetyltransferase-positive neurons in basal forebrain nuclei in the hemisphere ipsilateral to the NGF minipump compared to the contralateral basal forebrain neurons. We conclude that NGF delivered locally to axon terminals of cholinergic basal forebrain neurons resulted in increases in protein expression at the cell body through retrograde signaling.

Levels of monocyte reactive oxygen species are associated with reduced natural killer cell activity in major depressive disorder.

Major depressive disorder (MDD) is associated with reductions in natural killer cell activity (NKCA), however the mechanism(s) mediating reduced NKCA in MDD has yet to be determined. In light of evidence that MDD is associated with an inflammatory immune response, we propose that reactive oxygen species (ROS), generated by inflammatory leukocytes (monocytes and/or neutrophils), may mediate the suppression of NKCA in MDD. Intracellular levels of monocyte ROS were significantly associated with reductions in NKCA in outpatients (n = 15) diagnosed with MDD. Sleep disturbance was also significantly correlated with reductions in NKCA. Elevated levels of ROS may be an additional characteristic of a subset of depressed patients in whom an inflammatory response persists and elevations in ROS may, in part, mediate the associations observed between MDD, cardiovascular disease, and cancer.

Sleep enhances plasticity in the developing visual cortex.

During a critical period of brain development, occluding the vision of one eye causes a rapid remodeling of the visual cortex and its inputs. Sleep has been linked to other processes thought to depend on synaptic remodeling, but a role for sleep in this form of cortical plasticity has not been demonstrated. We found that sleep enhanced the effects of a preceding period of monocular deprivation on visual cortical responses, but wakefulness in complete darkness did not do so. The enhancement of plasticity by sleep was at least as great as that produced by an equal amount of additional deprivation. These findings demonstrate that sleep and sleep loss modify experience-dependent cortical plasticity in vivo. They suggest that sleep in early life may play a crucial role in brain development.

Monocyte 5-HT1A receptors mediate pindobind suppression of natural killer cell activity: modulation by catalase.

Serotonin (5-hydroxytryptamine; 5-HT) modulates constituents of the immune system. 5-HT1A receptor antagonists potently suppress lymphocyte function. NK cell activity (NKCA) was measured after exposure of mononuclear cells to the 5-HT1A receptor antagonist pindobind and the 5-HT(1C/2) receptor antagonist ketanserin. Elutriated monocytes were exposed to pindobind, incubated with peripheral blood lymphocytes (PBL) in the presence or absence of an H2O2 scavenger catalase, and NKCA measured. Pindobind, but not ketanserin, suppressed NKCA in vitro. Pindobind-treated monocytes suppressed NKCA, whereas pindobind treatment of PBL did not affect NKCA. Catalase inhibited pindobind-induced suppression of NKCA. These data are consistent with previous results that 5-HT modulates NKCA via 5-HT1A receptors on monocytes and suggest that 5-HT may abrogate monocyte suppression of NKCA by inhibiting monocyte signals such as H2O2.

Prenatal nicotine alters vigilance states and AchR gene expression in the neonatal rat: implications for SIDS.

Maternal smoking is a major risk factor for sudden infant death syndrome (SIDS). The mechanisms by which cigarette smoke predisposes infants to SIDS are not known. We examined the effects of prenatal nicotine exposure on sleep/wake ontogenesis and central cholinergic receptor gene expression in the neonatal rat. Prenatal nicotine exposure transiently increased sleep continuity and accelerated sleep/wake ontogeny in the neonatal rat. Prenatal nicotine also upregulated nicotinic and muscarinic cholinergic receptor mRNAs in brain regions involved in regulating vigilance states. These findings suggest that the nicotine contained in cigarette smoke may predispose human infants to SIDS by interfering with the normal maturation of sleep and wake.

The forced-choice paradigm and the perception of facial expressions of emotion.

The view that certain facial expressions of emotion are universally agreed on has been challenged by studies showing that the forced-choice paradigm may have artificially forced agreement. This article addressed this methodological criticism by offering participants the opportunity to select a none of these terms are correct option from a list of emotion labels in a modified forced-choice paradigm. The results show that agreement on the emotion label for particular facial expressions is still greater than chance, that artifactual agreement on incorrect emotion labels is obviated, that participants select the none option when asked to judge a novel expression, and that adding 4 more emotion labels does not change the pattern of agreement reported in universality studies. Although the original forced-choice format may have been prone to artifactual agreement, the modified forced-choice format appears to remedy that problem.

The effects of St. John's Wort (Hypericum perforatum) on NK cell activity in vitro.

St. John's Wort (Hypericum perforatum; H. perforatum) is a popular herbal supplement used to treat mild to moderate depression. H. perforatum possesses serotonergic properties such as inhibition of serotonin (5-hydroxytryptamine; 5-HT) reuptake. Serotonergic pharmacotherapy is associated with amelioration of depression as well as increases in natural killer (NK) cell activity (NKCA). Also, 5-HT and 5-HT analogs augment NKCA in vitro. Considering the serotonergic properties of H. perforatum, the effects of H. perforatum on NKCA were assessed in vitro. Mononuclear cells (MNCs) from normal donors were exposed in vitro to an extract of H. perforatum (LI160s) or established 5-HT stimulators of NKCA. After an overnight incubation, cells were washed and a standard 51Cr-release cytotoxicity assay performed to assess NKCA. LI160s at all concentrations failed to augment NKCA. However, in corroboration of previous studies, 5-HT, the selective serotonin reuptake inhibitors (SSRIs), paroxetine and norfluoxetine, and alpha-interferon augmented NKCA above control levels. Though an efficacious treatment for mild to moderate depression, H. perforatum differs from commonly prescribed serotonergic antidepressants insofar as H. perforatum fails to enhance NKCA in vitro. Therefore, the present results are consistent with pharmacologic studies indicating that H. perforatum possesses, at best, weak serotonergic activity.

Enhancing images of facial expressions.

Facial images can be enhanced by application of an algorithm--the caricature algorithm--that systematically manipulates their distinctiveness (Benson & Perrett, 1991c; Brennan, 1985). In this study, we first produced a composite facial image from natural images of the six facial expressions of fear, sadness, surprise, happiness, disgust, and anger shown on a number of different individual faces (Ekman & Friesen, 1975). We then caricatured the composite images with respect to a neutral (resting) expression. Experiment 1 showed that rated strength of the target expression was directly related to the degree of enhancement for all the expressions. Experiment 2, which used a free rating procedure, found that, although caricature enhanced the strength of the target expression (more extreme ratings), it did not necessarily enhance its purity, inasmuch as the attributes of nontarget expressions were also enhanced. Naming of prototypes, of original exemplar images, and of caricatures was explored in Experiment 3 and followed the pattern suggested by the free rating conditions of Experiment 2, with no overall naming advantage to caricatures under these conditions. Overall, the experiments suggested that computational methods of compositing and caricature can be usefully applied to facial images of expression. Their utility in enhancing the distinctiveness of the expression depends on the purity of expression in the source image.

Antidepressants augment natural killer cell activity: in vivo and in vitro.

Depressed mood has been associated with reduced natural killer cell activity (NKCA). Further, amelioration of depressive symptoms by pharmacotherapy has resulted in augmented NKCA. Serotonin, an indoleamine implicated in the pathophysiology of affective disorders, enhances NKCA in vitro and lymphocytes possess serotonin transporters and receptors. The present study evaluated NKCA in depressed outpatients before and during treatment with the selective serotonin reuptake inhibitor (SSRI) fluoxetine (Prozac(R)). Further, the SSRIs, fluoxetine and paroxetine (Paxil(R)), were also incubated in vitro with lymphoid cells to evaluate possible direct effects of SSRIs on NKCA. Depressed outpatients were administered fluoxetine (20 mg/day) for 4 weeks. NKCA and severity of depression were evaluated at weeks 0, 1, 2, and 4. Serum concentrations of fluoxetine and norfluoxetine were obtained as well. Mononuclear cells obtained from nonpatient volunteers were incubated with pharmacologic concentrations of fluoxetine or paroxetine and NKCA measured with a standard chromium release assay. Fluoxetine treatment resulted in decreased symptoms of depression and increased serum concentrations of fluoxetine and norfluoxetine. Further, fluoxetine treatment was associated with augmented NKCA in a subgroup of depressed outpatients exhibiting low NKCA at baseline. Fluoxetine had no effect on NKCA in depressed individuals exhibiting high NKCA at baseline. Incubation of mononuclear cells with fluoxetine and paroxetine augmented NKCA in vitro. The enhancing effects of antidepressants on NKCA in vivo and in vitro indicate a possible direct drug interaction with lymphoid cells during pharmacotherapy, suggesting that pharmacologic treatment of depression may result in enhanced immune competence as indexed by enhanced NKCA and that NKCA could be pharmacologically augmented with antidepressants in individuals with compromised immune function.

Effects of sleep deprivation in neonatal rats.

This investigation represents the first systematic study of sleep homeostasis in developing mammals that spans the preweaning and postweaning periods. Neonatal rats from 12 to 24 days of postnatal life (P12-P24) were anesthetized with Metofane (methoxyflurane) and implanted with miniaturized electroencephalographic (EEG) and electromyographic electrodes. After 48 h of recovery, neonatal rats were sleep deprived for 3 h by either gentle handling or forced locomotion. We find that 3-h sleep deprivation produces dramatically different compensatory responses at different stages of postnatal development. In striking contrast to adult rats, sleep deprivation does not increase slow-wave sleep EEG delta (0.5-4.0 Hz) activity in rats younger than P24. However, P12-P20 rats do show evidence of sleep regulation because they show compensatory increases in sleep time and sleep continuity during recovery. In P12 rats, approximately 90% of total slow wave sleep time lost during the sleep-deprivation period was recovered during subsequent sleep. A similar recovery of active sleep time was observed in P20-P24 rats. These findings suggest not only that sleep is regulated in neonatal rats but that the accumulation and/or discharge of sleep need changes dramatically between the third and fourth postnatal weeks.

Neonatal treatments with the serotonin uptake inhibitors clomipramine and zimelidine, but not the noradrenaline uptake inhibitor desipramine, disrupt sleep patterns in adult rats.

Chronic postnatal exposure to clomipramine (CMI), a monoamine uptake inhibitor, results in persistent alterations in adult rat REM sleep. These effects have been ascribed to CMI's ability to block neonatal active sleep (AS). However, these effects have not been obtained with other anti-depressants which also block neonatal AS. We compared the long-term effects on adult rat sleep after postnatal treatments (P8-P21) with either CMI or zimelidine (ZMI, a selective serotonin uptake inhibitor) or desipramine (DMI, a selective noradrenaline uptake inhibitor). ZMI and CMI increased the frequency and decreased the duration of REM sleep bouts, increased the number of nonREM-REM transitions, and increased sigma power in REM and nonREM sleep EEGs in adulthood. In contrast, DMI had no effect on any adult sleep parameters. Since ZMI, DMI and CMI all reduce AS to similar levels, these results suggest that neonatal AS suppression is not responsible for the sleep deficits following CMI or ZMI treatment. However, since ZMI and CMI, but not DMI, increase synaptic concentrations of serotonin, elevated serotonin levels during development may instead be responsible for the long-lasting sleep deficits.

Development of diurnal organization of EEG slow-wave activity and slow-wave sleep in the rat.

This study characterizes the development of diurnal patterns of slow-wave sleep (SWS) distribution and SWS electroencephalographic (EEG) delta-power (DP) density in 12- to 24-day-old rats (P12-P24). Diurnal organization in sleep-wake distribution was established by P20. A decline in SWS DP across the light phase did not appear until P24. Before P20, SWS DP increased across the light phase in a pattern inverse to that typically seen in adult rats. At P20, SWS DP was evenly distributed across the light phase, and at P24, SWS DP declined across the light phase. The transient dissociation between diurnal organization in sleep-wake cycles and SWS DP suggests that circadian and homeostatic sleep regulatory mechanisms develop at different rates in the postnatal period.

Development of REM and slow wave sleep in the rat.

Active sleep (AS) in the neonate has been considered to be an immature form of rapid eye movement (REM) sleep. Quiet sleep (QS) has been thought to represent an immature form of slow wave sleep (SWS). To determine the relationship between the behaviorally determined states of AS and QS and electrographically determined REM sleep and SWS, we examined sleep ontogeny in the developing rat using an experimental routine that permitted long-term recordings and minimized the effects of maternal separation. Under these conditions, a transient state that included electroencephalographic slow wave activity and phasic motor activity was eventually replaced with the mature SWS pattern. Our work suggests that neonatal QS is not an immature form of SWS and that AS is best considered as an undifferentiated behavioral state from which both SWS and REM sleep develop.

The ability to detect deceit generalizes across different types of high-stake lies.

The authors investigated whether accuracy in identifying deception from demeanor in high-stake lies is specific to those lies or generalizes to other high-stake lies. In Experiment 1, 48 observers judged whether 2 different groups of men were telling lies about a mock theft (crime scenario) or about their opinion (opinion scenario). The authors found that observers' accuracy in judging deception in the crime scenario was positively correlated with their accuracy in judging deception in the opinion scenario. Experiment 2 replicated the results of Experiment 1, as well as P. Ekman and M. O'Sullivan's (1991) finding of a positive correlation between the ability to detect deceit and the ability to identify micromomentary facial expressions of emotion. These results show that the ability to detect high-stake lies generalizes across high-stake situations and is most likely due to the presence of emotional clues that betray deception in high-stake lies.

The effects of REM sleep-inhibiting drugs in neonatal rats: evidence for a distinction between neonatal active sleep and REM sleep.

Neonatal active sleep (AS) has been considered to be homologous and continuous with rapid-eye-movement (REM) sleep in adult animals. We have recently proposed an alternative view that AS is an undifferentiated sleep state distinct from REM sleep. To test these opposing views on the relationship of AS and REM sleep, neonatal rats (P11, P14 and P20) were systemically injected with compounds that inhibit REM sleep in adults. Zimelidine (ZMI) and desipramine (DMI) are monoamine uptake inhibitors which increase synaptic concentrations of serotonin and norepinephrine, respectively. Serotonin and norepinephrine inhibit brainstem cholinergic neurons important in REM sleep generation. Atropine (ATR) is a muscarinic receptor antagonist that blocks the post-synaptic effects of cholinergic projections. Only DMI (5 mg/kg) suppressed AS at P11. ZMI (6 mg/kg) and ATR (6 mg/kg) did not suppress AS until P14. These data suggest that serotonergic and cholinergic regulation of AS are absent before P14. The fact that AS in P11 rats is not affected by cholinergic antagonists supports the hypothesis that AS and REM sleep represent different sleep states.