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.

Acute alcohol intoxication suppresses natural killer cell activity and promotes tumor metastasis.

Alcohol consumption is associated with increased morbidity and mortality related to infectious diseases and malignancy (1-5), although immune mediation of these relationships is controversial. Specifically, the activity of natural killer (NK) cells, which are involved in the resistance to infections and metastasis, can be suppressed in the presence of ethanol in vitro. However, acute consumption or infusion of ethanol in vivo exerts no effects on NK activity assessed in vitro thereafter. Therefore, we have developed and used a method to study the effects of ethanol on NK activity in living rats by using an NK-sensitive metastatic process and selective depletion of NK cells in vivo. Acute ethanol intoxication caused a marked suppression of NK activity in vivo and a tenfold increase in the number of MADB106 tumor metastases. Ethanol had no effect in rats selectively depleted of NK cells or when an NK-insensitive tumor (C4047) was used. These findings suggest that even acute ethanol intoxication markedly suppresses NK activity in the living organism. This suppression may underlie some aspects of the association between alcoholism, infectious disease and malignancies.

Brain interleukin-1 mediates chronic stress-induced depression in mice via adrenocortical activation and hippocampal neurogenesis suppression.

Several lines of evidence implicate the pro-inflammatory cytokine interleukin-1 (IL-1) in the etiology and pathophysiology of major depression. To explore the role of IL-1 in chronic stress-induced depression and some of its underlying biological mechanisms, we used the chronic mild stress (CMS) model of depression. Mice subjected to CMS for 5 weeks exhibited depressive-like symptoms, including decreased sucrose preference, reduced social exploration and adrenocortical activation, concomitantly with increased IL-1 beta levels in the hippocampus. In contrast, mice with deletion of the IL-1 receptor type I (IL-1rKO) or mice with transgenic, brain-restricted overexpression of IL-1 receptor antagonist did not display CMS-induced behavioral or neuroendocrine changes. Similarly, whereas in wild-type (WT) mice CMS significantly reduced hippocampal neurogenesis, measured by incorporation of bromodeoxyuridine (BrdU) and by doublecortin immunohistochemistry, no such decrease was observed IL-1rKO mice. The blunting of the adrenocortical activation in IL-1rKO mice may play a causal role in their resistance to depression, because removal of endogenous glucocorticoids by adrenalectomy also abolished the depressive-like effects of CMS, whereas chronic administration of corticosterone for 4 weeks produced depressive symptoms and reduced neurogenesis in both WT and IL-1rKO mice. The effects of CMS on both behavioral depression and neurogenesis could be mimicked by exogenous subcutaneous administration of IL-1 beta via osmotic minipumps for 4 weeks. These findings indicate that elevation in brain IL-1 levels, which characterizes many medical conditions, is both necessary and sufficient for producing the high incidence of depression found in these conditions. Thus, procedures aimed at reducing brain IL-1 levels may have potent antidepressive actions.

Stress and pain responses in rats lacking CCK1 receptors.

UNLABELLED: CCK involvement in stress- and pain-responsiveness was examined by studying the behavior of infant (11-12-days-old) and adult OLETF rats that do not express CCK1 receptors. Infant odor- and texture-preferences were also assessed. We hypothesized that OLETF rats will show behavioral patterns similar to those previously observed after CCK1 antagonist administration. Rate of separation-induced ultrasonic vocalization was significantly greater in OLETF compared to controls, in two separate studies. Infant pups of the two strains did not differ in odor- and texture-preference tests. OLETF rats showed consistently longer hot-plate paw-lift (as infants, in two separate studies) and paw-lick (as adults) latencies. SUMMARY: OLETF pups vocalized in isolation more than controls and showed relative hypoalgesic responses, evident also in adulthood, in concordance with the pharmacological literature.

Cytokine-associated emotional and cognitive disturbances in humans.

BACKGROUND: Infectious, autoimmune, and neurodegenerative diseases are associated with profound psychological disturbances. Studies in animals clearly demonstrate that cytokines mediate illness-associated behavioral changes. However, the mechanisms underlying the respective psychological alterations in humans have not been established yet. Therefore, we investigated the effects of low-dose endotoxemia, a well-established and safe model of host-defense activation, on emotional, cognitive, immunological, and endocrine parameters. METHODS: In a double-blind, crossover study, 20 healthy male volunteers completed psychological questionnaires and neuropsychological tests 1, 3, and 9 hours after intravenous injection of Salmonella abortus equi endotoxin (0.8 ng/kg) or saline in 2 experimental sessions. Blood samples were collected hourly, and rectal temperature and heart rate were monitored continuously. RESULTS: Endotoxin had no effects on physical sickness symptoms, blood pressure, or heart rate. Endotoxin caused a mild increase in rectal temperature (0.5 degrees C), and increased the circulating levels of tumor necrosis factor alpha (TNF-alpha), soluble TNF receptors, interleukin (IL)-6, IL-1 receptor antagonist, and cortisol. After endotoxin administration, the subjects showed a transient significant increase in the levels of anxiety (effect size [ES] = 0.55) and depressed mood (ES = 0.66). Verbal and nonverbal memory functions were significantly decreased (ES = 0.55 to 0.64). Significant positive correlations were found between cytokine secretion and endotoxin-induced anxiety (r = 0.49 to r = 0.60), depressed mood (r = 0.40 to r = 0.75), and decreases in memory performance (r = 0.46 to r = 0.68). CONCLUSIONS: In humans, a mild stimulation of the primary host defense has negative effects on emotional and memory functions, which are probably caused by cytokine release. Hence, cytokines represent a novel target for neuropsychopharmacological research.

Antisense prevention of neuronal damages following head injury in mice.

Closed head injury (CHI) is an important cause of death among young adults and a prominent risk factor for nonfamilial Alzheimer's disease. Emergency intervention following CHI should therefore strive to improve survival, promote recovery, and prevent delayed neuropathologies. We employed high-resolution nonradioactive in situ hybridization to determine whether a single intracerebro-ventricular injection of 500 ng 2'-O-methyl RNA-capped antisense oligonucleotide (AS-ODN) against acetylcholinesterase (AChE) mRNA blocks overexpression of the stress-related readthrough AChE (AChE-R) mRNA splicing variant in head-injured mice. Silver-based Golgi staining revealed pronounced dendrite outgrowth in somatosensory cortex of traumatized mice 14 days postinjury that was associated with sites of AChE-R mRNA overexpression and suppressed by anti-AChE AS-ODNs. Furthermore, antisense treatment reduced the number of dead CA3 hippocampal neurons in injured mice, and facilitated neurological recovery as determined by performance in tests of neuromotor coordination. In trauma-sensitive transgenic mice overproducing AChE, antisense treatment reduced mortality from 50% to 20%, similar to that displayed by head-injured control mice. These findings demonstrate the potential of antisense therapeutics in treating acute injury, and suggest antisense prevention of AChE-R overproduction to mitigate the detrimental consequences of various traumatic brain insults.

The role of endogenous interleukin-1 in stress-induced adrenal activation and adrenalectomy-induced adrenocorticotropic hormone hypersecretion.

To examine the role of IL-1 in the regulation of the hypothalamo-pituitary-adrenal (HPA) axis, mice with knockout of the IL-1 receptor type I (IL-1rKO) were exposed to psychological and metabolic stressors. When exposed to mild stressors (auditory stress or a low dose of 2-deoxyglucose), IL-1rKO mice displayed a significantly diminished corticosterone secretion, compared with wild-type (WT) controls. In response to more severe stressors (60-min restraint or a high dose of 2-deoxyglucose), both groups exhibited a similar increase in corticosterone secretion. To examine the role of IL-1 in HPA axis feedback regulation, serum ACTH levels were measured after adrenalectomy (ADX) in IL-1rKO mice and in mice with transgenic overexpression of IL-1 receptor antagonist within the brain (IL-1raTG). As expected, WT controls exhibited ADX-induced ACTH hypersecretion, whereas IL-1rKO and IL-1raTG mice showed no increase in ACTH levels, suggesting that brain IL-1 has a critical role in ADX-associated ACTH hypersecretion. Similarly, WT mice that were chronically exposed to IL-1ra in utero displayed a diminished ADX-induced ACTH hypersecretion, compared with vehicle-treated controls, suggesting a developmental role of IL-1 in HPA axis regulation. In conclusion, our results suggest that endogenous IL-1 plays a critical role in HPA axis activation after stress and ADX.

Effects of antidepressant drugs on the behavioral and physiological responses to lipopolysaccharide (LPS) in rodents.

Antidepressants produce various immunomodulatory effects, as well as an attenuation of the behavioral responses to immune challenges, such as lipopolysaccharide (LPS). To explore further the effects of antidepressants on neuroimmune interactions, rats were treated daily with either fluoxetine (Prozac) or saline for 5 weeks, and various behavioral, neuroendocrine, and immune functions were measured following administration of either LPS or saline. Chronic fluoxetine treatment significantly attenuated the anorexia and body weight loss, as well as the depletion of CRH-41 from the median eminence and the elevation in serum corticosterone levels induced by LPS. Chronic treatment with imipramine also attenuated LPS-induced adrenocortical activation. In rats and in mice, which normally display a biphasic body temperature response to LPS (initial hypothermia followed by hyperthermia), chronic treatment with fluoxetine completely abolished the hypothermic response and facilitated and strengthened the hyperthermic response. The effects of antidepressants on the responsiveness to LPS are probably not mediated by their effects on peripheral proinflammatory cytokine production, because LPS-induced expression of TNFalpha and IL-1beta mRNA in the spleen (assessed by semiquantitative in situ hybridization) was not altered following chronic treatment with either fluoxetine or imipramine. The effects of antidepressants on the acute phase response may have important clinical implications for the psychiatric and neuroendocrine disturbances that are commonly associated with various medical conditions.

Fetal alcohol exposure attenuates interleukin-1beta-induced fever: neuroimmune mechanisms.

Central mechanisms for the attenuating effects of fetal alcohol exposure (FAE) on interleukin-1beta (IL-1beta)-induced fever were studied in adult male offspring of dams fed a liquid diet supplemented with ethanol (E), in pair-fed (P) control and in normal (N) offspring. Hypothalamic levels of IL-1 were significantly lower in E than in N rats at 2 h, but not at 4 and 6 h, after intraperitoneal administration of lipopolysaccharide. Fever induced by intracerebroventricular (i.c.v.) IL-1 was significantly lower in E than in N and P rats. In contrast, E rats showed a normal febrile response to i.c.v. prostaglandin-E2. Thus, whereas FAE does not affect central thermoregulatory mechanisms, per se, FAE alters the kinetics of hypothalamic IL-1 production/appearance and decreases the responsiveness of central mechanisms which mediate the febrile response to IL-1.

Intracerebroventricular interleukin-1beta impairs clearance of tumor cells from the lungs: role of brain prostaglandins.

We have previously demonstrated that central administration of interleukin (IL)-1beta suppresses natural killer (NK) cell activity, impairs NK-mediated lung clearance of tumor cells, and enhances tumor colonization. The central pathways activated by IL-1beta are as yet unknown. Using an in vivo model of tumor colonization, this study examined the role of central noradrenergic, opioid and prostaglandin mechanisms in mediating the effect of IL-1beta on lung clearance of tumor cells. We demonstrate that central noradrenergic and opioid systems are not critically involved in this effect. Neither depletion of central noradrenergic pathways, or administration of the opioid antagonist, naltrexone (50 ug), blocked the impaired lung clearance of MADB106 tumor cells induced by central administration of IL-1beta (20 ng). Central prostaglandins (PGs) do, however, appear to play a critical role. Central administration of the prostaglandin antagonist, diclofenac (250 ug), but not ibuprofen, completely blocked the effect of IL-1beta on lung clearance of tumor cells. Antagonism of the effects of IL-1beta was shown to be due to the effects of centrally and not of peripherally acting prostaglandins.

The EAE-associated behavioral syndrome: II. Modulation by anti-inflammatory treatments.

EAE is associated with sickness behavior symptoms that are temporally correlated with inflammatory processes. To further elucidate the role of inflammatory mediators in the behavioral syndrome, EAE mice were injected daily with anti-inflammatory drugs, beginning at disease onset. Dexamethasone or interleukin-1 (IL-1) receptor antagonist or the prostaglandins synthesis inhibitor indomethacin attenuated the behavioral symptoms. Administration of the tumor necrosis-factor alpha (TNF-alpha) synthesis inhibitor pentoxifylline or targeted deletion of the type I TNF receptor had no behavioral effects whereas administration of pentoxifylline in IL-1ra-treated mice further reversed the behavioral depression. These findings demonstrate the critical involvement of pro-inflammatory cytokines and prostaglandins in the EAE-associated behavioral syndrome, and may have implications for understanding and treating the neuropsychiatric disturbances in multiple sclerosis (MS) patients.

The EAE-associated behavioral syndrome: I. Temporal correlation with inflammatory mediators.

To elucidate the mechanisms underlying the EAE-associated behavioral syndrome (EBS), we examined the temporal correlation between the behavioral alterations and inflammatory processes. Onset of the behavioral syndrome was associated with the onset of brain infiltration, as well as mRNA expression of interleukin 1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF-alpha) and elevated production of interleukin 1 beta protein and prostaglandin E(2) (PGE(2)). Sickness behavior symptoms coincided with peak cytokine expression. Behavioral recovery was associated with a reduction of cytokine expression, but not infiltration, PGE(2) production or motor disturbances. These results suggest that inflammatory processes in general, and the production of pro-inflammatory cytokines in particular, are involved in mediating EAE-associated sickness behavior.

Behavioral aspects of experimental autoimmune encephalomyelitis.

Acute inflammation is known to induce a depressive-like sickness behavior syndrome in humans and in experimental animals. In the present study, we sought to determine whether a chronic neuroautoimmune inflammation is also associated with a similar behavioral syndrome. Experimental autoimmune encephalomyelitis (EAE) was induced in SJL/J female mice by adoptive transfer of lymph node cells, and sickness behavior symptoms, including anorexia, loss of body weight, reduced social exploration, and decreased preference for sucrose solution were measured. We report that these components of sickness behavior were induced during the acute phase of the disease, and recovered in later phases. Moreover, the onset and recovery of the behavioral symptoms preceded the onset and recovery of the neurological signs, respectively. Since EAE is considered a model for multiple sclerosis (MS), it is suggested that EAF-induced behavioral changes may serve as a model for the depressive symptomatology that characterizes most MS patients.

A novel permissive role for glucocorticoids in induction of febrile and behavioral signs of experimental herpes simplex virus encephalitis.

Herpes simplex virus type 1 (HSV-1) encephalitis may present with fever and behavioral changes, to the extent of a psychotic state and psychomotor agitation. We developed a clinically relevant experimental model of HSV-1 encephalitis and investigated host brain responses associated with its clinical signs and whether these responses depend on the presence of circulating glucocorticoids. Intracerebral inoculation of HSV-1 in rats induced fever, motor hyperactivity and aggressive behavior. In adrenalectomized rats HSV-1 failed to induce these signs, although mortality rate was identical to sham-operated rats. Hypophysectomy or blocking glucocorticoid receptors also prevented HSV-1-induced fever. Dexamethasone replacement therapy to adrenalectomized rats restored the HSV-1-induced fever and behavioral abnormalities. HSV-1 inoculation produced hyperproduction of prostaglandin E(2) by brain slices. This effect was abolished in adrenalectomized rats and was restored by dexamethasone treatment. In intact rats HSV-1 induced brain interleukin-1beta (IL-1beta) gene expression. Adrenalectomy alone caused brain IL-1beta expression, which did not increase after HSV-1 infection. Similarly, HSV-1 induced IL-1beta expression in astrocyte cultures. Removal of cortisol from the culture medium caused basal IL-1beta mRNA expression which was not increased by infection. In conclusion, fever, motor hyperactivity and aggressive behavior during experimental HSV-1 encephalitis are dependent on brain responses, including prostaglandin E(2) and IL-1beta synthesis. Circulating glucocorticoids play an essential permissive role in the induction of these host brain responses.

Influence of socioeconomic status on behavioral, emotional and cognitive effects of rubella vaccination: a prospective, double blind study.

A double-blind prospective design was used to investigate the immediate and prolonged psychological effects of a specific viral infection, and the role of immune activation in mediating these effects. Subjects were 240 female teenager girls who were vaccinated with rubella vaccine. Based on analysis of levels of antibodies to rubella, subjects were divided into two groups. An experimental group (n = 60), which included subjects who were initially seronegative and were infected following vaccination, and a control group (n = 180), which included subjects who were already immune to rubella before vaccination. Compared with the control group and to their own baseline, low socioeconomic status (SES) subjects within the experimental group showed a significant increase in the severity of depressed mood, social and attention problems, and delinquent behavior. Ten weeks post-vaccination there were no differences between the experimental and control groups in serum levels of interleukin-1 beta, interferon-gamma, soluble interleukin-2 receptors (sIL-2r), and cortisol. However, a significant negative correlation was found between fatigue-related symptoms and sIL-2r levels in the experimental (r = -0.325), but not the control group (r = -0.046). These findings suggest that viral infection can produce prolonged behavioral, emotional and cognitive problems mainly in subjects belonging to the low SES.

Endotoxin-induced changes in food consumption in healthy volunteers are associated with TNF-alpha and IL-6 secretion.

This study examined the effects of endotoxin administration on food and water consumption in humans, and the associations between these changes and endotoxin-induced secretion of cytokines, cortisol, and fever. Twenty healthy male volunteers received an i.v. injection of Salmonella abortus equi endotoxin (0.8 ng/kg) or saline in two experimental sessions. Blood samples were collected hourly, and rectal temperature was monitored continuously. Food consumption was significantly reduced at 0-4 h and significantly elevated at 4-5 h after the endotoxin injection. Endotoxin administration had no significant effect on water consumption. Endotoxin-induced secretion of TNF-alpha and IL-6 was positively associated with the decrease in food consumption (r=0.61 and 0.68), and negatively associated with the rebound increase in food consumption (r=-0.53 and -0.45). Neither the febrile response, nor the secretion of cortisol was associated with the changes in food consumption. These results suggest that TNF-alpha and IL-6 are involved in endotoxin-induced anorexia in humans.

Salt preference in rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain).

Brattleboro rats are homozygous for diabetes insipidus (HO-DI), lacking the ability to synthesize vasopressin. Besides increasing water consumption, HO-DI rats may compensate for their excessive renal water loss by reducing their intake of and preference for substances that elevate plasma osmolarity. In two experiments we assessed this possibility. In Experiment 1, salt preference of HO-DI and control Long-Evans (LE) rats was measured by presenting the rats with two tubes: one filled with water and the other with NaCl. In the first part of the experiment, 18 NaCl concentrations were presented in increasing order (from 6 to 300 mM). In the second part, other groups of HO-DI and LE rats were presented with 6 concentrations of NaCl, ranging from 6 to 450 mM in either increasing or decreasing order of concentrations. In Experiment 2, preference for 6 concentrations of citric acid ranging from 0.1 to 6 mM was assessed. With NaCl concentrations greater than 100 mM, intake and preference declined rapidly for the HO-DI group but very gradually for the LE group. In contrast, the HO-DI rats preferred all citric acid solutions more than LE rats. The results suggest that HO-DI rats compensate for their inability to concentrate urine not only by increasing water consumption, but also by decreasing consumption of and preference for salty solutions.

Intake of and preference for sweet solutions are attenuated in morphine-withdrawn rats.

The hypothesis that intake of sweet solutions is partially controlled by endogenous opioid peptides was tested in 2 experiments that examined the effects of repetitive morphine administration and withdrawal on subsequent intake of and preference for saccharin solutions in rats. Experiment 1 established that 17 hr after morphine withdrawal, rats consumed less saccharin, but not less water, than did controls. The groups did not differ 8 days later. In Experiment 2, using a 2-bottle saccharin-preference test, rats exhibited a reduced preference to saccharin solutions (1, 3, 9, 30, or 60 mM) for 6 days after morphine withdrawal. The difference between the groups was most pronounced at the most preferred concentrations (9 and 30 mM). The results suggest that cross-tolerance occurs between morphine and the opioid-mediated hedonic effects of sweet solutions.

Conditioned taste aversions are not readily disrupted by external excitation.

Thirsty male rats were given saccharin water followed by delayed illness. During the delay, some of the rats were exposed to events designed to stimulate their external systems (i.e., the system that processes external events such as auditory and tactile stimulation). Access to females, mild footshocks, and pain from hypertonic saline injections did not interfere with either the acquisition or extinction of a taste aversion. In fact, when administered intraperitoneally, the hypertonic saline slightly increased the strength of the aversion. Exposure to heat, which changed both skin temperature and core temperature, slightly attenuated the formation of the aversion. Overall, these results emphasize the independence of the internal system (i.e., the system that deals with internal events such as taste, illness, and core temperature) and the external system. Furthermore, the associating of events related to the internal system is not readily interfered with by events related to the external system.

Stress-induced suppression of natural killer cell cytotoxicity in the rat: a naltrexone-insensitive paradigm.

The suppression of natural killer (NK) cell cytotoxicity by footshock stress can be attenuated by opioid antagonists, implicating endogenous opioids in its mediation. A stress paradigm that induces NK suppression that is not blocked by the opioid antagonist naltrexone is reported. This stress paradigm is also shown to cause analgesia and elevated plasma corticosterone levels that are not attenuated by naltrexone. In the first experiment, a significant suppression of NK cell cytotoxicity after forced swimming was demonstrated in Fischer 344 rats treated with either saline or naltrexone, compared with nonstressed controls. Significantly higher corticosterone levels were evident in both stressed groups. In the second experiment, the same stress paradigm was shown to cause significant analgesia in the tail-flick test, whereas no differences were seen between groups pretreated with saline and naltrexone. It is concluded that opioids need not always be involved in the suppression of NK cell cytotoxicity by stress.