Neonatal immune system activation with lipopolysaccharide enhances behavioural sensitization to the dopamine agonist, quinpirole, in adult female but not male rats

Neonatal brain inflammation enhances methamphetamine-induced reinstated behavioral sensitization in adult rats analyzed with explainable machine learning

Neonatal brain inflammation produced by intraperitoneal (i.p.) injection of lipopolysaccharide (LPS) results in long-lasting brain dopaminergic injury and motor disturbances in adult rats. The goal of the present work is to investigate the effect of neonatal systemic LPS exposure (1 or 2 mg/kg, i.p. injection in postnatal day 5, P5, male rats)-induced dopaminergic injury to examine methamphetamine (METH)-induced behavioral sensitization as an indicator of drug addiction. On P70, subjects underwent a treatment schedule of 5 once daily subcutaneous (s.c.) administrations of METH (0.5 mg/kg) (P70-P74) to induce behavioral sensitization. Ninety-six hours following the 5th treatment of METH (P78), the rats received one dose of 0.5 mg/kg METH (s.c.) to reintroduce behavioral sensitization. Hyperlocomotion is a critical index caused by drug abuse, and METH administration has been shown to produce remarkable locomotor-enhancing effects. Therefore, a random forest model was used as the detector to extract the feature interaction patterns among the collected high-dimensional locomotor data. Our approaches identified neonatal systemic LPS exposure dose and METH-treated dates as features significantly associated with METH-induced behavioral sensitization, reinstated behavioral sensitization, and perinatal inflammation in this experimental model of drug addiction. Overall, the analysis suggests that the implementation of machine learning strategies is sensitive enough to detect interaction patterns in locomotor activity. Neonatal LPS exposure also enhanced METH-induced reduction of dopamine transporter expression and [3H]dopamine uptake, reduced mitochondrial complex I activity, and elevated interleukin-1β and cyclooxygenase-2 concentrations in the P78 rat striatum. These results indicate that neonatal systemic LPS exposure produces a persistent dopaminergic lesion leading to a long-lasting change in the brain reward system as indicated by the enhanced METH-induced behavioral sensitization and reinstated behavioral sensitization later in life. These findings indicate that early-life brain inflammation may enhance susceptibility to drug addiction development later in life, which provides new insights for developing potential therapeutic treatments for drug addiction.

Delayed effects of neonatal immune activation on brain neurochemistry and hypothalamic-pituitary-adrenal axis functioning

During the postnatal period, the brain is highly sensitive to stress and inflammation, which are hazardous to normal growth and development. There is increasing evidence that inflammatory processes in the early postnatal period increase the risk of psychopathologies and cognitive impairment later in life. On the other hand, there are few studies on the ability of infectious agents to cause long-term neuroinflammation, leading to changes in the hypothalamic-pituitary-adrenal axis functioning and an imbalance in the neurotransmitter system. In this review, we examine short- and long-term effects of neonatal-induced inflammation in rodents on glutamatergic, GABAergic and monoaminergic systems and on hypothalamic-pituitary-adrenal axis activity.

Alterations in gut microbiota affect behavioral and inflammatory responses to methamphetamine in mice

RATIONALE AND OBJECTIVES

Methamphetamine (METH) is a highly addictive and widely abused drug that causes severe neuroinflammation in the human brain. The gut microbiota has a tremendous impact on the core symptoms of neuropsychiatric disorders via the microbiota-gut-brain (MGB) axis. However, it is not clear whether alterations in the gut microbiota are involved in METH exposure.

METHODS

We established a mouse model with chronic, escalating doses of METH exposure. Intervene in gut microbiota with antibiotics to observe the changes of locomotor activity caused by METH exposure in mice. qPCR and 16S rRNA gene sequencing were used to analyze the gut microbiota profiles. In addition, we tested the levels of inflammatory factors in the nucleus accumbens (NAc), prefrontal cortex (mPFC), hippocampus (HIp), and spleen. Finally, short-chain fatty acids (SCFAs) were supplemented to determine the interaction between behavior changes and the structure of gut microbiota.

RESULTS

In this research, METH increased the locomotor activity of mice, while antibiotics changed the effect. Antibiotics enhanced the expression of pro-inflammatory cytokines in mPFC, HIp, and spleen of METH-exposed mice. METH altered the gut microbiota of mice after antibiotic treatment, such as Butyricicoccus and Roseburia, which are related to butyrate metabolism. Supplementation with SCFAs changed the behavior of METH-exposed mice and decreased Parabacteroides and increased Lactobacillus in METH-exposed mice gut.

CONCLUSIONS

This research showed that antibiotics affected the behavior of METH-exposed mice and promoted inflammation. Our findings suggest that SCFAs might regulate METH-induced gut microbiota changes and behavior.

The effect of early life immune challenge on adult forced swim test performance and hippocampal neurogenesis

Many psychiatric diseases can be considered neurodevelopmental in nature and accumulating evidence links immune system dysfunction to disease etiology. Yet, it is currently unknown how the immune system alters brain function through development to increase susceptibility to psychiatric illness. Neonatal immune challenge in rodents is a neurodevelopmental model that has been associated with long-term molecular and behavioural changes in stress-reactivity. As enhanced stress-reactivity is associated with the emergence of depressive-like behaviours concurrent with hippocampal pathology, we measured depressive-like behaviour in the forced swim test and hippocampal neurogenesis in adult mice neonatally exposed to lipopolysaccharide LPS; 0.05 mg/kg, i.p. on postnatal days 3 and 5. As there are important functional differences along the ventral-dorsal hippocampus axis, ventral and dorsal hippocampal neurogenesis were measured separately. Our findings reveal a sexually-dimorphic response to early-life LPS challenge. Male LPS-mice spent less time immobile in the forced swim test, suggesting altered reactivity to swim stress. This was accompanied by an increase in doublecortin-positive cells in the dorsal hippocampus of female mice. These findings demonstrate that exposure to an immune challenge during critical developmental time periods leads to long-term sexually-dimorphic alterations in stress-reactivity that are accompanied by changes to adult hippocampal neurogenesis.

Impact of Season of Birth on Psychiatric Disorder Susceptibility and Drug Abuse Incidence in a Population from the Köppen Tropical Savanna Region of Brazil

BACKGROUND

Despite much evidence that season of birth (SOB) my influence the vulnerability to psychiatric disorders, divergence has been reported, in particular between populations born in the northern and southern hemispheres. We analyzed the potential modified risk by SOB to psychiatric disorder or drug addiction comorbidity in a population born in the Triângulo Mineiro region, a southern hemisphere Köppen tropical savanna region in Brazil.

METHOD

We accessed the records of 98,457 of patients and healthy controls of the National Datacenter of Medical Promptuary to evaluate the influence of SOB as a modifying factor on the occurrence of mental disorders and drug abuse conditions among individuals born from the year 2000 to 2016.

RESULTS

The data revealed significant modification of the relative incidence of major depressive disorder (MDD) (F11, 72 = 2.898; p = 0.003; eta-squared, ES = 0.313; ⍺ = 0.97), anxiety-related disorder (ARD) (F11, 81 =2.389; p = 0.013; ES = 0.241; ⍺ = 0.932), and schizophrenia (SZ) (F11, 83 = 2.764; p = 0.005; ES = 0.303; α = 0.963), while there was no increase in the number of healthy controls born in any month of the year (F11, 71 = 1.469; p = 0.163). Post hoc analyses indicated a significant higher vulnerability to MDD or ARD if the patient was born in August, or October to December, respectively. A relative increase in the incidence of SZ was also observed in patients born from August to October, compared to patients born from November to January.

CONCLUSIONS

SOB may influence the risk for psychiatric disorders in the TMR population. Regional particularities associated with the climatic regime may account for the apparent divergence between studies.

Early-life inflammation with LPS delays fear extinction in adult rodents

A large body of evidence has been brought forward connecting developmental immune activation to abnormal fear and anxiety levels. Anxiety disorders have extremely high lifetime prevalence, yet susceptibility factors that contribute to their emergence are poorly understood. In this research we investigated whether an inflammatory insult early in life can alter the response to fear conditioning in adulthood. Fear learning and extinction are important and adaptive behaviors, mediated largely by the amygdala and its interconnectivity with cortico-limbic circuits. Male and female rat pups were given LPS (100μg/kg i.p.) or saline at postnatal day 14; LPS activated cFos expression in the central amygdala 2.5h after exposure, but not the basal or lateral nuclei. When tested in adulthood, acquisition of an auditory cued or contextual learned fear memory was largely unaffected as was the extinction of fear to a conditioned context. However, we detected a deficit in auditory fear extinction in male and female rats that experienced early-life inflammation, such that there is a significant delay in fear extinction processes resulting in more sustained fear behaviors in response to a conditioned cue. This response was specific to extinction training and did not persist into extinction recall. The effect could not be explained by differences in pain threshold (unaltered) or in baseline anxiety, which was elevated in adolescent females only and unaltered in adolescent males and adult males and females. This research provides further evidence for the involvement of the immune system during development in the shaping of fear and anxiety related behaviors.

Antipsychotic-induced sensitization and tolerance: Behavioral characteristics, developmental impacts, and neurobiological mechanisms

Antipsychotic sensitization and tolerance refer to the increased and decreased drug effects due to past drug use, respectively. Both effects reflect the long-term impacts of antipsychotic treatment on the brain and result from the brain's adaptive response to the foreign property of the drug. In this review, clinical evidence of the behavioral aspect of antipsychotic sensitization and tolerance is selectively reviewed, followed by an overview of preclinical literature that examines these behavioral characteristics and the related pharmacological and nonpharmacological factors. Next, recent work on the developmental impacts of adolescent antipsychotic sensitization and tolerance is presented and recent research that delineates the neurobiological mechanisms of antipsychotic sensitization and tolerance is summarized. A theoretical framework based on "drug learning and memory" principles is proposed to account for the phenomena of antipsychotic sensitization and tolerance. It is maintained that antipsychotic sensitization and tolerance follow basic principles of learning or acquisition ("induction") and memory ("expression"). The induction and expression of both effects reflect the consequences of associative and nonassociative processing and are strongly influenced by various pharmacological, environmental, and behavioral factors. Drug-induced neuroplasticity, such as functional changes of striatal dopamine D2 and prefrontal serotonin (5-HT)2A receptors and their mediated signaling pathways, in principle, is responsible for antipsychotic sensitization and tolerance. Understanding the behavioral characteristics and neurobiological underpinnings of antipsychotic sensitization and tolerance has greatly enhanced our understanding of mechanisms of antipsychotic action, and may have important implications for future drug discovery and clinical practice.

Differential effects of intermittent versus continuous haloperidol treatment throughout adolescence on haloperidol sensitization and social behavior in adulthood

Animal work on the behavioral effects of antipsychotic treatment suggests that different dosing regimens could affect drug sensitivity differently, with an intermittent treatment regimen tending to cause a sensitization effect, while a continuous treatment causing a tolerance. In this study, we explored how haloperidol (HAL) sensitization induced throughout adolescence and tested in adulthood was differentially impacted by these two dosing regimens in the conditioned avoidance response (CAR) test. We also examined how these two dosing regiments affected social interaction and social memory in adulthood. Male adolescent Sprague-Dawley rats were treated with HAL via either osmotic minipump (HAL-0.25 CONT; 0.25 mgkg(-1)day(-1), n = 14) or daily injection (HAL-0.05 INT; 0.05 mgkg(-1)day(-1) injection, sc, n = 14), or sterile water (n = 14) from postnatal days (PND) 44 to 71. HAL sensitization was assessed in a challenge test in which all rats were injected with HAL (0.025 and 0.05 mg/kg, sc) on PND 80 and PND 82. Two days later, half of the rats from each group (n = 7/group) were assayed in two 4-trial social interaction tests in which a subject rat was given four 5-min social encounters with a familiar or novel juvenile rat (PND 35-40) at 10 min intervals. Another half were tested in a quinpirole-induced hyperlocomotion assay to assess the potential HAL-induced change in D2-mediated function. Results show that only the intermittent dosing group under the HAL 0.05 mg/kg challenge showed a robust sensitization effect as rats in this group made significantly fewer avoidance responses than those in the vehicle and HAL-0.25 CONT groups. Adolescent HAL treatment did not affect social behavior and social memory, as rats from all 3 groups exhibited a similar level of social interaction and showed a similar level of sensitivity to the change of social stimuli. Similarly, adolescent HAL treatment also did not produce a long-lasting change in D2 function, as all 3 groups exhibited a similar level of increase in motor activity under quinpirole challenge. These findings suggest that HAL sensitization is a dosing-specific phenomenon. It is more likely to be seen under an intermittent dosing regimen than under a continuous dosing one. The findings that the intermittent HAL treatment did not impair social functioning and did not alter D2 function suggest a dissociation between drug-induced alterations in drug sensitivity and those in social function and neuroreceptors.

Long-lasting sensitization induced by repeated risperidone treatment in adolescent Sprague-Dawley rats: a possible D2 receptor mediated phenomenon?

RATIONALE

Risperidone use in children and adolescents for the treatment of various neuropsychiatric disorders (e.g., schizophrenia, autism, disruptive behavior, etc.) has increased substantially in recent decades. However, its long-term effect on the brain and behavioral functions is not well understood.

OBJECTIVE

The present study investigated how a short-term risperidone treatment in adolescence impacts antipsychotic response in adulthood in the conditioned avoidance response and phencyclidine (PCP)-induced hyperlocomotion tests.

METHODS

Male adolescent Sprague-Dawley rats (postnatal days [P] 40-44 or 43-48) were first treated with risperidone (0.3, 0.5, or 1.0 mg/kg, subcutaneously (sc)) and tested in the conditioned avoidance or PCP (3.2 mg/kg, sc)-induced hyperlocomotion model daily for five consecutive days. After they became adults (~P 76-80), they were challenged with risperidone (0.3 mg/kg, sc) to assess their sensitivity to risperidone reexposure. A quinpirole (a D2/3 receptor agonist, 1.0 mg/kg, sc)-induced hyperlocomotion test was later conducted to assess the risperidone-induced functional changes in D2 receptor.

RESULTS

In the risperidone challenge test in adulthood, adult rats previously treated with risperidone in adolescence made significantly fewer avoidance responses and exhibited significantly lower PCP-induced hyperlocomotion than those previously treated with vehicle. They also appeared to be more hyperactive than the vehicle-pretreated ones in the quinpirole-induced hyperlocomotion test. Prepulse inhibition of acoustic startle or fear-induced 22 kHz ultrasonic vocalizations in adulthood was not altered by adolescence risperidone treatment.

CONCLUSIONS

Adolescent risperidone exposure induces a long-term increase in behavioral sensitivity to risperidone that persists into adulthood. This long-lasting change might be due to functional upregulation of D2-mediated neurotransmission.

Time-dependence of risperidone and asenapine sensitization and associated D2 receptor mechanism

When an antipsychotic drug is given repeatedly and intermittently, there is often a long-term increase in its behavioral efficacy, termed antipsychotic sensitization. With the passage of time, the magnitude of antipsychotic sensitization may increase or decrease based on the principle of time-dependent sensitization (TDS) or memory decay, respectively. In the present study, we examined the time-dependent feature and possible dopamine D2 receptor mechanism of sensitization induced by risperidone and asenapine in the conditioned avoidance response test. Well-trained male adult Sprague-Dawley rats were first repeatedly treated with risperidone (1.0mg/kg) or asenapine (0.2mg/kg) and tested for avoidance response daily for 5 consecutive days. Eight, 18 or 38 days after the 5th drug treatment, all rats were retested drug-free to assess the long-term impact of prior risperidone or asenapine treatment. Drug-pretreated rats had significantly lower avoidance than vehicle-pretreated ones on this test, and the group differences increased with the passage of time. In the subsequent drug challenge test at 10, 20 or 40 days after the 5th drug treatment, all rats were injected with a low dose of risperidone (0.3mg/kg) or asenapine (0.1mg/kg). Drug-pretreated rats again made significantly fewer avoidances than controls, confirming the antipsychotic sensitization effect. Finally, in the quinpirole (a D2/3 receptor agonist, 1.0mg/kg, sc)-induced hyperlocomotion test, risperidone-pretreated rats exhibited a significantly higher level of motor activity than the vehicle-pretreated ones. These findings suggest that risperidone and asenapine sensitization is long-lasting, follows the TDS principle, and is likely mediated by D2 receptor supersensitivity.

Impacts of early intervention with fluoxetine following early neonatal immune activation on depression-like behaviors and body weight in mice

Several reports have suggested that early neonatal immune activation adversely influences the hypothalamic-pituitary-adrenal (HPA) axis development in humans and animal models. In addition, there have been several studies indicating that early intervention with fluoxetine (FLX) can alter HPA axis development and function, and prevent occurrence of behavioral abnormalities induced by common early-life insults. The present study aims to investigate the effects of early intervention with FLX following early neonatal immune activation on depression-like behaviors and body weight in mice. Neonatal mice in their postnatal days (PNDs) 3 and 5 received either lipopolysaccharide (LPS; 50 μg/kg, s.c.) or saline treatment, then male and female mice of both neonatal intervention groups received oral administration of FLX (5 and 10 mg/kg/day) or water via regular drinking bottles during the periadolescent period (PNDs 35-65). The results showed that neonatal LPS exposure elevated depression-like behaviors accompanied by increasing corticosterone levels in adulthood and decreasing body weight during neonatal and adolescent periods. Furthermore, the periadolescent FLX treatment inhibited the depression-like behaviors induced by neonatal infection in both sexes. This study obtained some experimental evidence indicating the potential adverse impacts of the FLX on normal behavioral development in male control animals. In conclusion, our findings suggest that an early pharmacological intervention with FLX may prevent emergence of depression-like behaviors induced by neonatal immune challenge without any detrimental effect on health in a sex- and dose-dependent manner in mice.

Neonatal exposure to lipopolysaccharide enhances vulnerability of nigrostriatal dopaminergic neurons to rotenone neurotoxicity in later life

Brain inflammation in early life has been proposed to play important roles in the development of neurodegenerative disorders in adult life. To test this hypothesis, we used a neonatal rat model of lipopolysaccharide (LPS) exposure (1000 EU/g body weight, intracerebral injection on P5) to produce brain inflammation. By P70, when LPS-induced behavioral deficits were spontaneously recovered, animals were challenged with rotenone, a commonly used pesticide, through subcutaneous mini-pump infusion at a dose of 1.25 mg/kg per day for 14 days. This rotenone treatment regimen ordinarily does not produce toxic effects on behaviors in normal adult rats. Our results show that neonatal LPS exposure enhanced the vulnerability of nigrostriatal dopaminergic neurons to rotenone neurotoxicity in later life. Rotenone treatment resulted in motor neurobehavioral impairments in rats with the neonatal LPS exposure, but not in those without the neonatal LPS exposure. Rotenone induced losses of tyrosine hydroxylase immunoreactive neurons in the substantia nigra and decreased mitochondrial complex I activity in the striatum of rats with neonatal LPS exposure, but not in those without this exposure. Neonatal LPS exposure with later exposure to rotenone decreased retrogradely labeled nigrostriatal dopaminergic projecting neurons. The current study suggests that perinatal brain inflammation may enhance adult susceptibility to the development of neurodegenerative disorders triggered later on by environmental toxins at an ordinarily non-toxic or sub-toxic dose. Our model may be useful for studying mechanisms involved in the pathogenesis of nonfamilial Parkinson's disease and the development of potential therapeutic treatments.

Neonatal exposure to lipopolysaccharide enhances methamphetamine-induced reinstated behavioral sensitization in adult rats

Our previous studies have shown that neonatal exposure to lipopolysaccharide (LPS) resulted in long-lasting dopaminergic injury and enhanced methamphetamine (METH)-induced increase of locomotion in the adult male rat. To further investigate the effect of neonatal LPS exposure-induced dopaminergic injury, we used our neonatal rat model of LPS exposure (1mg/kg, intracerebral injection in postnatal day 5, P5, rats) to examine the METH sensitization as an indicator of drug addiction in the adult rats. On P70, animals began a treatment schedule of 5 daily subcutaneous (s.c.) administration of METH (0.5mg/kg) or saline (P70-P74) to induce behavioral sensitization. Ninety-six hours after the 5th treatment with METH or saline (P78), animals received a single dose of 0.5mg/kg METH (s.c.) or saline. Neonatal LPS exposure enhanced the level of development of behavioral sensitization including distance traveled, rearing events and stereotypy to METH administration in both male and female rats. Neonatal LPS exposure also enhanced the reinstated behavioral sensitization in both male and female rats after the administration had ceased for 96h. However, neonatal LPS exposure induced alteration in the reinstated behaviors sensitization of distance traveled and rearing events to METH administration appears to be greater in male than in female rats. These results indicate that neonatal brain LPS exposure produces a persistent lesion in the dopaminergic system, as indicated by enhanced METH-induced locomotor and stereotyped behavioral sensitization in later life. These findings show that early-life brain inflammation may enhance susceptibility to the development of drug addiction in later life.

Dopaminergic neuronal injury in the adult rat brain following neonatal exposure to lipopolysaccharide and the silent neurotoxicity

Our previous studies have shown that neonatal exposure to lipopolysaccharide (LPS) resulted in motor dysfunction and dopaminergic neuronal injury in the juvenile rat brain. To further examine whether neonatal LPS exposure has persisting effects in adult rats, motor behaviors were examined from postnatal day 7 (P7) to P70 and brain injury was determined in P70 rats following an intracerebral injection of LPS (1 mg/kg) in P5 Sprague-Dawley male rats. Although neonatal LPS exposure resulted in hyperactivity in locomotion and stereotyped tasks, and other disturbances of motor behaviors, the impaired motor functions were spontaneously recovered by P70. On the other hand, neonatal LPS-induced injury to the dopaminergic system such as the loss of dendrites and reduced tyrosine hydroxylase immunoreactivity in the substantia nigra persisted in P70 rats. Neonatal LPS exposure also resulted in sustained inflammatory responses in the P70 rat brain, as indicated by an increased number of activated microglia and elevation of interleukin-1β and interleukin-6 content in the rat brain. In addition, when challenged with methamphetamine (METH, 0.5 mg/kg) subcutaneously, rats with neonatal LPS exposure had significantly increased responses in METH-induced locomotion and stereotypy behaviors as compared to those without LPS exposure. These results indicate that although neonatal LPS-induced neurobehavioral impairment is spontaneously recoverable, the LPS exposure-induced persistent injury to the dopaminergic system and the chronic inflammation may represent the existence of silent neurotoxicity. Our data further suggest that the compromised dendritic mitochondrial function might contribute, at least partially, to the silent neurotoxicity.

A developmental characterization of mesolimbocortical serotonergic gene expression changes following early immune challenge

An immunogenic challenge during early postnatal development leads to long-term changes in behavioural and physiological measures reflecting enhanced emotionality and anxiety. Altered CNS serotonin (5-HT) signalling during the third postnatal week is thought to modify the developing neurocircuitry governing anxiety-like behaviour. Changes in 5-HT signalling during this time window may underlie increased emotionality reported in early immune challenge rodents. Here we examine both the spatial and temporal profile of 5-HT related gene expression, including 5HT1A, 2A, 2C receptors, the 5-HT transporter (5HTT), and tryptophan hydroxylase 2 (TPH2) during early development (postnatal day [P]14, P17, P21, P28) in mice challenged with lipopolysaccharide (LPS) during the first postnatal week. Expression levels were measured using in situ hybridization in regions associated with mediating emotive behaviours: the dorsal raphe (DR), hippocampus, amygdala, and prefrontal cortex (PFC). Increased TPH2 and 5HTT expression in the ventrolateral region of the DR of LPS-mice accompanied decreased expression of ventral DR 5HT1A and dorsal DR 5HTT. In the forebrain, 5HT1A and 2A receptors were increased, whereas 5HT2C receptors were decreased in the hippocampus. Decreased mRNA expression of 5HT2C was detected in the amygdala and PFC of LPS-treated pups; 5HT1A was increased in the PFC. The majority of these changes were restricted to P14-21. These transient changes in 5-HT expression coincide with the critical time window in which 5-HT disturbance leads to permanent modification of anxiety-related behaviours. This suggests that alterations in CNS 5-HT during development may underlie the enhanced emotionality associated with an early immune challenge.

Early-life programming of later-life brain and behavior: a critical role for the immune system

The immune system is well characterized for its critical role in host defense. Far beyond this limited role however, there is mounting evidence for the vital role the immune system plays within the brain, in both normal, “homeostatic” processes (e.g., sleep, metabolism, memory), as well as in pathology, when the dysregulation of immune molecules may occur. This recognition is especially critical in the area of brain development. Microglia and astrocytes, the primary immunocompetent cells of the CNS, are involved in every major aspect of brain development and function, including synaptogenesis, apoptosis, and angiogenesis. Cytokines such as tumor necrosis factor (TNF)α, interleukin [IL]-1β, and IL-6 are produced by glia within the CNS, and are implicated in synaptic formation and scaling, long-term potentiation, and neurogenesis. Importantly, cytokines are involved in both injury and repair, and the conditions underlying these distinct outcomes are under intense investigation and debate. Evidence from both animal and human studies implicates the immune system in a number of disorders with known or suspected developmental origins, including schizophrenia, anxiety/depression, and cognitive dysfunction. We review the evidence that infection during the perinatal period of life acts as a vulnerability factor for later-life alterations in cytokine production, and marked changes in cognitive and affective behaviors throughout the remainder of the lifespan. We also discuss the hypothesis that long-term changes in brain glial cell function underlie this vulnerability.

Neonatal endotoxin exposure modifies the acoustic startle response and circulating levels of corticosterone in the adult rat but only following acute stress

A variety of early life stressors have consistently been implicated in the development of psychopathology in adulthood. The current study investigates a rarely considered form of early life stress, bacterial infection, for its ability to induce psychopathology-like symptoms in adult rat. Specifically, neonatal rats were exposed to a simulated bacterial infection. In adulthood the acoustic startle response of these animals was evaluated both prior to and following exposure to restraint stress. Our results indicate that animals neonatally exposed to infection exhibit a significantly exaggerated acoustic startle response but only following exposure to stress. Additionally, we observed that adult animals neonatally exposed to infection, exhibited increased production of circulating corticosterone following stress, indicating potentiated hypothalamic pituitary adrenal axis activity as well as altered novelty seeking behaviour and locomotor activity. These results extend upon existing pre-clinical findings that indicate certain stressful early life events can predispose the adult animal to exhibit abnormal behaviour in adulthood.