Maternal separation disrupts dendritic morphology of neurons in prefrontal cortex, hippocampus, and nucleus accumbens in male rat offspring

Long-term effects of maternal deprivation on the neuronal soma area in the rat neocortex

Early separation of rat pups from their mothers (separatio a matrem) is considered and accepted as an animal model of perinatal stress. Adult rats, separated early postnatally from their mothers, are developing long-lasting changes in the brain and neuroendocrine system, corresponding to the findings observed in schizophrenia and affective disorders. With the aim to investigate the morphological changes in this animal model we exposed 9-day-old (P9) Wistar rats to a 24 h maternal deprivation (MD). At young adult age rats were sacrificed for morphometric analysis and their brains were compared with the control group bred under the same conditions, but without MD. Rats exposed to MD had a 28% smaller cell soma area in the prefrontal cortex (PFCX), 30% in retrosplenial cortex (RSCX), and 15% in motor cortex (MCX) compared to the controls. No difference was observed in the expression of glial fibrillary acidic protein in the neocortex of MD rats compared to the control group. The results of this study demonstrate that stress in early life has a long-term effect on neuronal soma size in cingulate and retrosplenial cortex and is potentially interesting as these structures play an important role in cognition.

Brief maternal separation affects brain α1-adrenoceptors and apoptotic signaling in adult mice

Exposure to adversity during early life is a risk factor for the development of different mood and psychiatric disorders, including depressive-like behaviors. Here, neonatal mice were temporarily but repeatedly (day 1 to day 13) separated from mothers and placed in a testing environment containing a layer of odorless clean bedding (CB). We assessed in adult animals the impact of this early experience on binding sites and mRNA expression of α1-adrenergic receptor subtypes, heat shock proteins (HSPs) and proapoptotic and antiapoptotic members of the Bcl-2 family proteins in different brain regions involved in processing of olfactory information and rewarding stimuli. We found that repeated exposure to CB experience produced anhedonic-like behavior in terms of reduced saccharin intake and α1-adrenoceptor downregulation in piriform and somatosensory cortices, hippocampus, amygdala and discrete thalamic nuclei. We also found a selective decrease of α1B-adrenoceptor binding sites in the cingulate cortex and hippocampus and an increase of hippocampal α1A and α1B receptor, but not of α1D-adrenoceptor, mRNA levels. Moreover, while a significant decrease of antiapoptotic heat shock proteins Hsp72 and Hsp90 was identified in the prefrontal cortex, a parallel increase of antiapoptotic members of Bcl-2 family proteins was found at the hippocampal level. Together, these data provide evidence that the early exposure to CB experience produced enduring downregulation of α1-adrenoceptors in the prefrontal-limbic forebrain/limbic midbrain network, which plays a key role in the processing of olfactory information and reaction to rewarding stimuli. Finally, these data show that CB experience can "prime" the hippocampal circuitry and promote the expression of antiapoptotic factors that can confer potential neuroprotection to subsequent adversity.

Long-lasting Consequences of Early Life Stress on Brain Structure, Emotion and Cognition

During the perinatal period, the brain undergoes substantial structural changes, synaptic rearrangements, and development of neuronal circuits which ultimately determine brain function and behavior. Environmental factors-such as exposure to adverse experiences-have major impact on brain function and structure during this sensitive period. These alterations can be long-lasting, and have been implicated in psychopathology such as cognitive decline and emotional dysfunction. Here we briefly review how early postnatal adversity determines structure and function of the hippocampus, amygdala, and prefrontal cortex (PFC) areas, which are crucial for proper cognitive and emotional function.

Prenatal nicotine and maternal deprivation stress de-regulate the development of CA1, CA3, and dentate gyrus neurons in hippocampus of infant rats

Adverse experiences by the developing fetus and in early childhood are associated with profound effects on learning, emotional behavior, and cognition as a whole. In this study we investigated the effects of prenatal nicotine exposure (NIC), postnatal maternal deprivation (MD) or the combination of the two (NIC+MD) to determine if hippocampal neuron development is modulated by exposure to drugs of abuse and/or stress. Growth of rat offspring exposed to MD alone or NIC+MD was repressed until after weaning. In CA1 but not CA3 of postnatal day 14 (P14) pups, MD increased pyramidal neurons, however, in dentate gyrus (DG), decreased granule neurons. NIC had no effect on neuron number in CA1, CA3 or DG. Unexpectedly, NIC plus MD combined caused a synergistic increase in the number of CA1 or CA3 neurons. Neuron density in CA regions was unaffected by treatment, but in the DG, granule neurons had a looser packing density after NIC, MD or NIC+MD exposure. When septotemporal axes were analyzed, the synergism of stress and drug exposure in CA1 and CA3 was associated with rostral, whereas MD effects were predominantly associated with caudal neurons. TUNEL labeling suggests no active apoptosis at P14, and doublecortin positive neurons and mossy fibers were diminished in NIC+MD relative to controls. The laterality of the effect of nicotine and/or maternal deprivation in right versus left hippocampus was also analyzed and found to be insiginificant. We report for the first time that early life stressors such as postnatal MD and prenatal NIC exposure, when combined, may exhibit synergistic consequences for CA1 and CA3 pyramidal neuron development, and a potential antagonistic influence on developing DG neurons. These results suggest that early stressors may modulate neurogenesis, apoptosis, or maturation of glutamatergic neurons in the hippocampus in a region-specific manner during critical periods of neurodevelopment.

Comparing development of synaptic proteins in rat visual, somatosensory, and frontal cortex

Two theories have influenced our understanding of cortical development: the integrated network theory, where synaptic development is coordinated across areas; and the cascade theory, where the cortex develops in a wave-like manner from sensory to non-sensory areas. These different views on cortical development raise challenges for current studies aimed at comparing detailed maturation of the connectome among cortical areas. We have taken a different approach to compare synaptic development in rat visual, somatosensory, and frontal cortex by measuring expression of pre-synaptic (synapsin and synaptophysin) proteins that regulate vesicle cycling, and post-synaptic density (PSD-95 and Gephyrin) proteins that anchor excitatory or inhibitory (E-I) receptors. We also compared development of the balances between the pairs of pre- or post-synaptic proteins, and the overall pre- to post-synaptic balance, to address functional maturation and emergence of the E-I balance. We found that development of the individual proteins and the post-synaptic index overlapped among the three cortical areas, but the pre-synaptic index matured later in frontal cortex. Finally, we applied a neuroinformatics approach using principal component analysis and found that three components captured development of the synaptic proteins. The first component accounted for 64% of the variance in protein expression and reflected total protein expression, which overlapped among the three cortical areas. The second component was gephyrin and the E-I balance, it emerged as sequential waves starting in somatosensory, then frontal, and finally visual cortex. The third component was the balance between pre- and post-synaptic proteins, and this followed a different developmental trajectory in somatosensory cortex. Together, these results give the most support to an integrated network of synaptic development, but also highlight more complex patterns of development that vary in timing and end point among the cortical areas.

Early-life stress affects the structural and functional plasticity of the medial prefrontal cortex in adolescent rats

Early life experiences are crucial factors that shape brain development and function due to their ability to induce structural and functional plasticity. Among these experiences, early-life stress (ELS) is known to interfere with brain development and maturation, increasing the risk of future psychopathologies, including depression, anxiety, and personality disorders. Moreover, ELS may contribute to the emergence of these psychopathologies during adolescence. In this present study, we investigated the effects of ELS, in the form of maternal separation (MS), on the structural and functional plasticity of the medial prefrontal cortex (mPFC) and anxiety-like behavior in adolescent male rats. We found that the MS procedure resulted in disturbances in mother-pup interactions that lasted until weaning and were most strongly demonstrated by increases in nursing behavior. Moreover, MS caused atrophy of the basal dendritic tree and reduced spine density on both the apical and basal dendrites in layer II/III pyramidal neurons of the mPFC. The structural changes were accompanied by an impairment of long-term potentiation processes and increased expression of key proteins, specifically glutamate receptor 1, glutamate receptor 2, postsynaptic density protein 95, αCa(2+) /calmodulin-dependent protein kinase II and αCa(2+)/calmodulin-dependent protein kinase II phosphorylated at residue Thr305, that are engaged in long-term potentiation induction and maintenance in the mPFC. We also found that the MS animals were more anxious in the light/dark exploration test. The results of this study indicate that ELS has a significant impact on the structural and functional plasticity of the mPFC in adolescents. ELS-induced adaptive plasticity may underlie the pathomechanisms of some early-onset psychopathologies observed in adolescents.

Early life stress-induced histone acetylations correlate with activation of the synaptic plasticity genes Arc and Egr1 in the mouse hippocampus

Early life stress (ELS) programs the developing organism and influences the development of brain and behavior. We tested the hypothesis that ELS-induced histone acetylations might alter the expression of synaptic plasticity genes that are critically involved in the establishment of limbic brain circuits. Maternal separation (MS) from postnatal day 14-16 was applied as ELS and two immediate early genes underlying experience-induced synaptic plasticity, Arc and early growth response 1 (Egr1) were analyzed. We show here that repeated ELS induces a rapid increase of Arc and Egr1 in the mouse hippocampus. Furthermore, immunoblotting revealed that these changes are paralleled by histone modifications, reflected by increased acetylation levels of H3 and H4. Most importantly, using native Chromatin immunoprecipitation quantitative PCR (nChIP-qPCR), we show for the first time a correlation between elevated histone acetylation and increased Arc and Egr1 expression in response to ELS. These rapid epigenetic changes are paralleled by increases of dendritic complexity and spine number of hippocampal CA3 pyramidal neurons in ELS animals at weaning age. Our results are in line with our working hypothesis that ELS induces activation of synaptic plasticity genes, mediated by epigenetic mechanisms. These events are assumed to represent early steps in the adaption of neuronal networks to a stressful environment.

Wistar rats subjected to chronic restraint stress display increased hippocampal spine density paralleled by increased expression levels of synaptic scaffolding proteins

The aim of this study was to investigate whether the previously reported effect of chronic restraint stress (CRS) on hippocampal neuron morphology and spine density is paralleled by a similar change in the expression levels of synaptic scaffolding proteins. Adult male Wistar rats were subjected either to CRS (6 h/day) for 21 days or to control conditions. The resulting brains were divided and one hemisphere was impregnated with Golgi-Cox before coronal sectioning and autometallographic development. Neurons from CA1, CA3b, CA3c, and dentate gyrus (DG) area were reconstructed and subjected to Sholl analysis and spine density estimation. The contralateral hippocampus was used for quantitative real-time polymerase chain reaction and protein analysis of genes associated with spine density and morphology (the synaptic scaffolding proteins: Spinophilin, Homer1-3, and Shank1-3). In the CA3c area, CRS decreased the number of apical dendrites and their total length, whereas CA1 and DG spine density were significantly increased. Analysis of the contralateral hippocampal homogenate displayed an increased gene expression of Spinophilin, Homer1, Shank1, and Shank2 and increased protein expression of Spinophilin and Homer1 in the CRS animals. In conclusion, CRS influences hippocampal neuroplasticity by modulation of dendrite branching pattern and spine density paralleled by increased expression levels of synaptic scaffolding proteins.

Maternal deprivation induces deficits in temporal memory and cognitive flexibility and exaggerates synaptic plasticity in the rat medial prefrontal cortex

Early life adverse events can lead to structural and functional impairments in the prefrontal cortex (PFC). Here, we investigated whether maternal deprivation (MD) alters PFC-dependent executive functions, neurons and astrocytes number and synaptic plasticity in adult male Long-Evans rats. The deprivation protocol consisted of a daily separation of newborn Long-Evans pups from their mothers and littermates 3h/day postnatal day 1-14. Cognitive performances were assessed in adulthood using the temporal order memory task (TMT) and the attentional set-shifting task (ASST) that principally implicates the PFC and the Morris water maze task (WMT) that does not essentially rely on the PFC. The neurons and astrocytes of the prelimbic (PrL) area of the medial PFC (mPFC) were immunolabelled respectively with anti-NeuN and anti-GFAP antibodies and quantified by stereology. The field potentials evoked by electrical stimulation of ventral hippocampus (ventral HPC) were recorded in vivo in the PrL area. In adulthood, MD produced cognitive deficits in two PFC-dependent tasks, the TMT and ASST, but not in the WMT. In parallel, MD induced in the prelimbic area of the medial PFC an upregulation of long-term potentiation (LTP), without any change in the number of neurons and astrocytes. We provide evidence that MD leads in adults to an alteration of the cognitive abilities dependent on the PFC, and to an exaggerated synaptic plasticity in this region. We suggest that this latter phenomenon may contribute to the impairments in the cognitive tasks.

Individual variations in maternal care early in life correlate with later life decision-making and c-fos expression in prefrontal subregions of rats

Early life adversity affects hypothalamus-pituitary-adrenal axis activity, alters cognitive functioning and in humans is thought to increase the vulnerability to psychopathology--e.g. depression, anxiety and schizophrenia--later in life. Here we investigated whether subtle natural variations among individual rat pups in the amount of maternal care received, i.e. differences in the amount of licking and grooming (LG), correlate with anxiety and prefrontal cortex-dependent behavior in young adulthood. Therefore, we examined the correlation between LG received during the first postnatal week and later behavior in the elevated plus maze and in decision-making processes using a rodent version of the Iowa Gambling Task (rIGT). In our cohort of male and female animals a high degree of LG correlated with less anxiety in the elevated plus maze and more advantageous choices during the last 10 trials of the rIGT. In tissue collected 2 hrs after completion of the task, the correlation between LG and c-fos expression (a marker of neuronal activity) was established in structures important for IGT performance. Negative correlations existed between rIGT performance and c-fos expression in the lateral orbitofrontal cortex, prelimbic cortex, infralimbic cortex and insular cortex. The insular cortex correlations between c-fos expression and decision-making performance depended on LG background; this was also true for the lateral orbitofrontal cortex in female rats. Dendritic complexity of insular or infralimbic pyramidal neurons did not or weakly correlate with LG background. We conclude that natural variations in maternal care received by pups may significantly contribute to later-life decision-making and activity of underlying brain structures.

Stress during development alters dendritic morphology in the nucleus accumbens and prefrontal cortex

The long-term effects of stress during development have been well characterized. However, the effects of developmental stress on the underlying neurological mechanisms related to the reward system are not well understood. The present report studied the long term effects of stress during development on the structural plasticity in the cortical and subcortical regions. Rats exposed to stress during embryonic development (prenatal stress; PS) or soon after birth (maternal separation; MS) were studied for structural alteration at the neuronal level in the nucleus accumbens (NAc), orbital frontal cortex (OFC), and medial prefrontal cortex (mPFC). The findings show that stress during development increased dendritic branching, length, and spine density in the NAc, and subregions of the PFC. PS experience increased dendritic branching and length in the mPFC apical and basilar dendrites. In contrast, a PS-associated decrease in dendritic branching and length was observed in the basilar branches of the OFC. MS resulted in an increase in dendritic growth and spine density in the subregions of the PFC. The effect of PS on neuroanatomy was more robust than MS despite the shorter duration and intensity. The altered dendritic growth and spine density associated with stress during development could have potential impact on NAc and PFC related behaviors.

Maternal care received by individual pups correlates with adult CA1 dendritic morphology and synaptic plasticity in a sex-dependent manner

Maternal care is an important environmental factor for rats early in life. Adult offspring from dams exhibiting extremely high versus low maternal care differ remarkably in dendritic complexity and long-term synaptic potentiation in the CA1 area. However, >70% of the pups do not belong to these extreme categories of maternal care, questioning the general relevance of these observations. Therefore, the present study investigated whether the influence of maternal care is discernable over its entire range and can serve as an index predicting later CA1 structure and function. The amount of licking and grooming (%LG) received was determined for each pup during the first postnatal week. In males, both total apical branch length and dendritic complexity correlated significantly and positively with %LG. In females, we observed a nonsignificant negative correlation, also when controlled for variations in oestradiol and progesterone levels. The correlation in females was significantly different from that in males. No significant correlation was observed between the %LG and the amount of synaptic potentiation, either in male or in female offspring, regardless of whether slices had been treated with corticosterone or vehicle. However, in male rats, the degree of potentiation seen after corticosterone compared to vehicle treatment was almost significantly related to the %LG received early in life; this differed significantly from that observed in females. The data from the present study suggest that %LG received early in life results in mild, yet sex-dependent effects on adult CA1 structure and function.

Corticostriatal-limbic gray matter morphology in adolescents with self-reported exposure to childhood maltreatment

OBJECTIVE

To study the relationship between self-reported exposure to childhood maltreatment (CM) and cerebral gray matter (GM) morphology in adolescents without psychiatric diagnoses.

DESIGN

Associations were examined between regional GM morphology and exposure to CM (measured using a childhood trauma self-report questionnaire for physical, emotional, and sexual abuse and for physical and emotional neglect).

SETTING

University hospital.

PARTICIPANTS

Forty-two adolescents without psychiatric diagnoses.

MAIN OUTCOME MEASURES

Correlations between childhood trauma self-report questionnaire scores and regional GM volume were assessed in voxel-based analyses of structural magnetic resonance images. Relationships among GM volume, subtypes of exposure to CM, and sex were explored.

RESULTS

Childhood trauma self-report questionnaire total scores correlated negatively (P < .005) with GM volume in prefrontal cortex, striatum, amygdala, sensory association cortices, and cerebellum. Physical abuse, physical neglect, and emotional neglect were associated with rostral prefrontal reductions. Decreases in dorsolateral and orbitofrontal cortices, insula, and ventral striatum were associated with physical abuse. Decreases in cerebellum were associated with physical neglect. Decreases in dorsolateral, orbitofrontal, and subgenual prefrontal cortices, striatum, amygdala, hippocampus, and cerebellum were associated with emotional neglect. Decreases in the latter emotion regulation regions were also associated with childhood trauma self-report questionnaire scores in girls, while caudate reductions (which may relate to impulse dyscontrol) were seen in boys.

CONCLUSIONS

Exposure to CM was associated with corticostriatal-limbic GM reductions in adolescents. Even if adolescents reporting exposure to CM do not present with symptoms that meet full criteria for psychiatric disorders, they may have corticostriatal-limbic GM morphologic alterations that place them at risk for behavioral difficulties. Vulnerabilities may be moderated by sex and by subtypes of exposure to CM.

Gut memories: towards a cognitive neurobiology of irritable bowel syndrome

The brain and the gut are engaged in continual crosstalk along a number of pathways collectively termed the 'brain-gut axis'. Over recent years it has become increasingly clear that dysregulation of the axis at a number of levels can result in disorders such as irritable bowel syndrome (IBS). With recent advances in neuroimaging technologies, insights into the neurobiology of IBS are beginning to emerge. However the cognitive neurobiology of IBS has remained relatively unexplored to date. In this review we summarise the available data on cognitive function in IBS. Moreover, we specifically address three key pathophysiological factors, namely; stress, immune activation and chronic pain, together with other factors involved in the manifestation of IBS, and explore how each of these components may impact centrally, what neurobiological mechanisms might be involved, and consider the implications for cognitive functioning in IBS. We conclude that each factor addressed could significantly impinge on central nervous system function, supporting the view that future research efforts must be directed towards a detailed assessment of cognitive function in IBS.

Nonsteroidal anti-inflammatory treatment prevents delayed effects of early life stress in rats

BACKGROUND

Early developmental insults can cause dysfunction within parvalbumin (PVB)-containing interneurons in the prefrontal cortex. The neuropsychiatric disorders associated with such dysfunction might involve neuroinflammatory processes. Cyclooxygenase-2 (COX-2) is a key mediator of inflammation and is therefore a potential target for preventive treatment. Here, we investigated whether the developmental trajectories of PVB expression and COX-2 induction in the prelimbic region of the prefrontal cortex are altered after maternal separation stress in male rats.

METHODS

Male rat pups were separated from their mother and littermates for 4 hours/day between postnatal Days 2 and 20. Western blotting and immunohistochemistry were used to analyze PVB and COX-2 expression in the prefrontal cortex and hippocampus. A separate cohort of animals was treated with a COX-2 inhibitor during preadolescence and analyzed for PVB, COX-2, and working memory performance.

RESULTS

We demonstrate that maternal separation causes a reduction of PVB and an increase in COX-2 expression in the prefrontal cortex in adolescence, with concurrent working memory deficits. Parvalbumin was not affected earlier in development. Prophylactic COX-2 inhibition preadolescence prevents PVB loss and improves working memory deficits induced by maternal separation.

CONCLUSIONS

These data are the first to show a preventive pharmacological intervention for the delayed effects of early life stress on prefrontal cortex interneurons and working memory. Our results suggest a possible mechanism for the relationship between early life stress and interneuron dysfunction in adolescence.

Prenatal bystander stress induces neuroanatomical changes in the prefrontal cortex and hippocampus of developing rat offspring

The rapid period of growth and development that occurs prenatally renders the brain vulnerable to experiences that may disrupt cortical plasticity. Although there is extensive literature examining anatomical changes in fully matured brain, there has been very little investigation of younger offspring. The current study used an indirect prenatal bystander stress and analyzed neuroanatomical changes in postnatal day 21 (P21) Long Evans rats. Dendritic architecture (dendritic length, branch order, and spine density) along with cell quantification (neuron and glia) was generated for layer 3 pyramidal cells of the medial prefrontal cortex (mPFC/Cg3), orbital prefrontal cortex (OFC/AID), and CA1 of the hippocampus. We found that prenatal bystander stress significantly altered the complexity and length of dendritic arbor, the density of excitatory spines and the actual volume of neuronal and glial cell numbers in the mPFC, OFC, and CA1 of developing rat offspring. Neuroanatomical changes of this extent occurring at such a critical time period will likely impact healthy maturation of the brain and long-term development.

Infant maternal separation impairs adult cognitive performance in BALB/cJ mice

RATIONALE

Early life adversity, such as early abuse or parental loss, is thought to increase risk for developing psychiatric disorders in adulthood including mood and anxiety disorders. Human retrospective studies also suggest that early life adversity predicts poor response to antidepressants in adulthood.

OBJECTIVES

We used the infant maternal separation (IMS) paradigm to examine the effects of early adversity on adult emotional behavior, the antidepressant response, and cognitive performance in BALB/cJ mice.

METHODS

Mice were subjected to either standard facility rearing (SFR) or 3 h of daily separation from the dam from postnatal days 2-15. During adulthood, SFR and IMS mice received chronic treatment (∼3 weeks) with the selective serotonin reuptake inhibitor (SSRI) fluoxetine (18 mg/kg/day), and were assessed for anxiety- and depression-related behavior in the light/dark test and forced swim tests (FST), respectively. We then evaluated the effects of IMS on cognition in the fear conditioning, novel object recognition, and T-maze spatial learning and reversal learning tasks.

RESULTS

Chronic fluoxetine treatment produced robust antidepressant effects in both SFR and IMS mice in the FST. IMS did not affect the antidepressant response, or emotional behavior in the light/dark test or FST. However, IMS reduced fear conditioning to the tone and context, disrupted novel object recognition in females, and impaired both spatial and reversal learning in males.

CONCLUSIONS

Our findings suggest that IMS induces deficits in adult emotional, episodic, and spatial memory and reversal learning, but does not alter adult emotional behavior or the response to chronic SSRI treatment in mice.

Maternal separation altered behavior and neuronal spine density without influencing amphetamine sensitization

We studied the long-term influence of maternal separation (MS) on periadolescent behavior, adult amphetamine (AMPH) sensitization, and structural plasticity in the corticolimbic regions in rats. Male and female pups, separated daily for 3h from the dam during postnatal day 3-21, were tested for periadolescent exploratory, emotional, cognitive, and social behaviors. The development and persistence of drug-induced behavioral sensitization were tested by repeated AMPH administration and a challenge, respectively. The spine density was examined in the nucleus accumbens (NAc), the medial prefrontal cortex (mPFC), and the orbital frontal cortex (OFC) from Golgi-Cox stained neurons. The results showed that MS enhanced anxiety-like behavior in males. MS abolished the sex difference in playful attacks observed in controls with resultant feminization of male play behavior. Furthermore, the probability of complete rotation defense to face an attack was decreased in females. AMPH administration resulted in the development of behavioral sensitization that persisted at least for two weeks. Sensitization was not influenced by MS. MS increased the spine density in the NAc, the mPFC, and the OFC. Repeated AMPH administration increased the spine density in the NAc and the mPFC, and decreased it in the OFC. MS blocked the drug-induced alteration in these regions. In sum, MS during development influenced periadolescent behavior in males, and structurally reorganized cortical and subcortical brain regions without affecting AMPH-induced behavioral sensitization.

Lithium ameliorates nucleus accumbens phase-signaling dysfunction in a genetic mouse model of mania

Polymorphisms in circadian genes such as CLOCK convey risk for bipolar disorder. While studies have begun to elucidate the molecular mechanism whereby disruption of Clock alters cellular function within mesolimbic brain regions, little remains known about how these changes alter gross neural circuit function and generate mania-like behaviors in Clock-Δ19 mice. Here we show that the phasic entrainment of nucleus accumbens (NAC) low-gamma (30-55 Hz) oscillations to delta (1-4 Hz) oscillations is negatively correlated with the extent to which wild-type (WT) mice explore a novel environment. Clock-Δ19 mice, which display hyperactivity in the novel environment, exhibit profound deficits in low-gamma and NAC single-neuron phase coupling. We also demonstrate that NAC neurons in Clock-Δ19 mice display complex changes in dendritic morphology and reduced GluR1 expression compared to those observed in WT littermates. Chronic lithium treatment ameliorated several of these neurophysiological deficits and suppressed exploratory drive in the mutants. These results demonstrate that disruptions of Clock gene function are sufficient to promote alterations in NAC microcircuits, and raise the hypothesis that dysfunctional NAC phase signaling may contribute to the mania-like behavioral manifestations that result from diminished circadian gene function.

Effects of maternal separation, early handling, and gonadal sex on regional metabolic capacity of the preweanling rat brain

This is the first study to assess the effects of mother-infant separation on regional metabolic capacity in the preweanling rat brain. Mother-infant separation is generally known to be stressful for rat pups. Holtzman adolescent rats show a depressive-like behavioral phenotype after maternal separation during the preweanling period. However, information is lacking on the effects of maternal separation on the brains of rat pups. We addressed this issue by mapping the brains of preweanling Holtzman rat pups using cytochrome oxidase histochemistry, which reflects long-term changes in brain metabolic capacity, following two weeks of repeated, prolonged maternal separation, and compared this to both early handled and non-handled pups. Quantitative image analysis revealed that maternal separation reduced cytochrome oxidase activity in the medial prefrontal cortex and nucleus accumbens shell. Maternal separation reduced prefrontal cytochrome oxidase to a greater degree in female pups than in males. Early handling reduced cytochrome oxidase activity in the posterior parietal cortex, ventral tegmental area, and subiculum, but increased cytochrome oxidase activity in the lateral frontal cortex. The sex-dependent effects of early handling on cytochrome oxidase activity were limited to the medial prefrontal cortex. Regardless of separation group, females had greater cytochrome oxidase activity in the habenula and ventral tegmental area compared to males. These findings suggest that early life mother-infant separation results in dysfunction of prefrontal and mesolimbic regions in the preweanling rat brain that may contribute to behavioral changes later in life.