The hippocampal formation--orbitomedial prefrontal cortex circuit in the attentional control of active memory

Structural brain abnormalities in borderline personality disorder: a voxel-based morphometry study

Imaging studies using region-of-interest morphometry and positron emission tomography have contributed to our understanding of structural and functional abnormalities in borderline personality disorder (BPD); however, both methods have practical limitations to their usefulness for exploratory studies of brain-behavior relationships. We used voxel-based morphometry (VBM) in 34 subjects with BPD and 30 healthy control (HC) subjects to study effects of diagnosis, gender, childhood sexual abuse, depressed mood, impulsivity and aggression on group differences. VBM is a computer-based method for whole brain analysis that combines the advantages of a functional study with a structural method. The BPD subjects, diagnosed with the Diagnostic Interview for Borderline Patients and the International Personality Disorders Examination, were compared with 30 HC subjects, with age and gender covaried. Analyses were repeated separately by gender and, in women, by histories of childhood sexual abuse. Depressed mood, impulsivity, and aggression were covaried in separate analyses. Compared with HC, BPD subjects had significant bilateral reductions in gray matter concentrations in ventral cingulate gyrus and several regions of the medial temporal lobe, including the hippocampus, amygdala, parahippocampal gyrus, and uncus. BPD women (and abused BPD women), but not BPD men, had significant reductions in medial temporal lobe, including the amygdala. BPD men, but not BPD women, showed diminished gray matter concentrations in the anterior cingulate gyrus compared with findings in HC subjects. Covarying for depressed mood rendered group differences non-significant in the ventral cingulate but had little effect on differences in medial temporal cortex. Covarying for aggression (LHA) had relatively little effect on group differences, while covarying for impulsivity, as determined by the Barratt Impulsiveness Scale, rendered all previously noted voxel-level group differences non-significant. Diminished gray matter in the prefrontal cortex and the medial temporal cortex may mediate the dysregulation of impulse and affect in BPD. Group differences varied greatly by gender, levels of depression, and impulsivity. VBM is an efficient method for exploratory study of brain-behavior relationships.

Consequences of different housing conditions on brain morphology in laying hens

The aim of this study was to analyze the impact of physical and social stress on the avian forebrain morphology. Therefore, we used laying hens kept in different housing systems from puberty (approximately 16 weeks old) until the age of 48 weeks: battery cages, small littered ground pen, and free range system. Cell body sizes and catecholaminergic and serotonergic innervation patterns were investigated in brain areas expected to be sensitive to differences in environmental stimulation: hippocampal substructures and the nidopallium caudolaterale (NCL), a functional analogue of the prefrontal cortex. Our analysis shows both structures differing in the affected morphological parameters. Compared to battery cage hens, hens in the free range system developed larger cells in the dorsomedial hippocampus. Only these animals exhibited an asymmetry in the tyrosine hydroxylase density with more fibres in the left dorsomedial hippocampus. We assume that the higher spatial complexity of the free range system is the driving force of these changes. In contrast, in the NCL the housing systems affected only the serotonergic innervation pattern with highest fibre densities in free range hens. Moreover hens of the free range system displayed the worst plumage condition, which most likely is caused by feather pecking causing an altered serotonergic innervation pattern. Considering the remarkable differences between the three housing conditions, their effects on hippocampal structures and the NCL were surprisingly mild. This observation suggests that the adult brain of laying hens displays limited sensitivity to differences in social and physical environment induced post-puberty, which warrants further studies.

The stop null mice model for schizophrenia displays [corrected] cognitive and social deficits partly alleviated by neuroleptics

Recently evidence has accumulated that schizophrenia can arise from primary synaptic defects involving structural proteins particularly, microtubule associated proteins. Previous experiments have demonstrated that a STOP (stable tubule only peptide) gene deletion in mice leads to a phenotype mimicking some aspects of positive symptoms classically observed in schizophrenic patients. In the current study, we determined if STOP null mice demonstrate behavioral abnormalities related to the social and cognitive impairments of schizophrenia. Compared with wild-type mice, STOP null mice exhibited deficits in the non-aggressive component of social recognition, short term working memory and social and spatial learning. As described in humans, learning deficits in STOP null mice were poorly sensitive to long term treatment with typical neuroleptics. Since social and cognitive dysfunction have consistently been considered as central features of schizophrenia, we propose that STOP null mice may provide a useful model to understand the neurobiological correlates of social and cognitive defects in schizophrenia and to develop treatments that better target these symptoms.

Neonatal lesions of the entorhinal cortex induce long-term changes of limbic brain regions and maze learning deficits in adult rats

We here investigated the effects of neonatal lesions of the entorhinal cortex (EC) in rats on maze learning and on structural alterations of its main projection region, the hippocampus, as well as other regions with anatomical connections to the EC that are involved in maze learning. Since early brain damage is considered to be involved in certain neuropsychiatric diseases, this approach sought to model certain aspects of this etiopathogenesis. Bilateral neonatal lesions were induced on postnatal day 7 by microinjection of ibotenic acid (1.3 microg/0.2 microl phosphate-buffered saline (PBS)) into the EC. Naive and sham-lesioned rats served as controls. Rats were trained and tested on an eight-arm radial maze for allocentric and egocentric learning. Subsequently, gold-chloride staining and immunohistochemical staining for the microtubule-associated protein MAP-2 was used to assess myelination and dendritic density in the hippocampus, striatum and medial prefrontal cortex (mPFC) of these rats. Additionally, parvalbumin-expressing, presumably GABAergic interneurons, were evaluated in these regions. Performance in both the allocentric and the egocentric strategy was disturbed after neonatal EC lesion as shown by an increase of repeated arm entries, which indicates disturbed working memory. Histological evaluation revealed that the density of parvalbumin-immunopositive neurons and myelin sheaths was reduced in the hippocampus but not in the striatum and mPFC in neonatally lesioned rats. Density of MAP-2 staining did not differ between groups in all regions tested. Since structural alterations were only found in the EC and hippocampus our findings support their eminent role in working memory and show that no functional restoration occurs after neonatal lesions.

Spatial organization of direct hippocampal field CA1 axonal projections to the rest of the cerebral cortex

The spatial distribution of axonal projections descending from rat field CA1 to thalamus and hypothalamus was analyzed previously with the PHAL method [Cenquizca, L.A., Swanson, L.W. 2006. An analysis of direct hippocampal cortical field CA1 axonal projections to diencephalon in the rat. J Comp Neurol 497:101-114.]. The same experimental material was used here to define the topography of field CA1 association projections to other cerebral cortical areas. First, the results confirm and extend known intrahippocampal formation inputs to dentate gyrus, subiculum, presubiculum, parasubiculum, and entorhinal area, which are arranged generally along the formation's transverse axis and dominated by the subicular projection-by far the densest established by field CA1 anywhere in the brain. And second, field CA1 innervates a virtually complete ring of extrahippocampal formation cortex via three routes. A dorsal pathway from the dorsal third of field CA1 innervates moderately the retrosplenial area; a moderately strong ventral pathway from the ventral two thirds of field CA1 passing through the longitudinal association bundle sends offshoots to visual, auditory, somatosensory, gustatory, main and accessory olfactory, and visceral areas-as well as the basolateral amygdalar complex and the agranular insular and orbital areas; and a cortical-subcortical-cortical pathway through the fornix from the whole longitudinal extent of field CA1 innervates rather strongly a rostral region that includes the tenia tecta along with the anterior cingulate, prelimbic, infralimbic, and orbital areas. The functional consequences of long-term potentiation in field CA1 projection neurons remain to be explored.

5HT2A receptor binding is increased in borderline personality disorder

BACKGROUND

Postmortem studies in suicide victims demonstrate an increase in the number of post-synaptic 5-HT(2A) receptor binding sites in ventral lateral and orbital frontal cortex. Diminished metabolic responses to serotonergic activation are noted in these areas in impulsive subjects with borderline personality disorder (BPD), a group at high risk for suicidal behaviors. We examined 5HT(2A) receptor binding potential (BP) in impulsive subjects with BPD, with positron emission tomography neuroimaging with [(18)F] altanserin.

METHODS

Fourteen female subjects with BPD were assessed for Axis I comorbidity, depressed mood, impulsivity, aggression, suicidality, childhood abuse, and compared with 11 healthy female control subjects. The 5HT(2A) receptor binding was evaluated in prefrontal cortex, anterior cingulate, hippocampus, temporal lobe, occipital cortex, and thalamus. Data were analyzed with Logan graphical analysis and a four-compartment (4C) model.

RESULTS

Hippocampal 5HT(2A) receptor binding was significantly increased in BPD subjects compared with control subjects in both Logan and 4C analyses, covarying for age. Hippocampal BP values were related to comorbid major depressive episode, with highest values found in non-depressed BPD subjects and lowest in healthy control subjects. The BP values were not related to depressed mood, impulsivity, aggression, suicidality, or childhood abuse.

CONCLUSIONS

5HT(2A) receptor binding is increased in the hippocampus of BPD subjects independent of depressed mood, impulsivity, aggression, suicidality, or childhood abuse. Dysregulation of serotonergic function in hippocampus might contribute to affective and behavioral symptoms in BPD.

The prefrontal cortex as a key target of the maladaptive response to stress

Research on the detrimental effects of stress in the brain has mainly focused on the hippocampus. Because prefrontal cortex (PFC) dysfunction characterizes many stress-related disorders, we here analyzed the impact of chronic stress in rats on the integrity of the hippocampal-PFC pathway, monitored by behavioral and electrophysiological function and morphological assessment. We show that chronic stress impairs synaptic plasticity by reducing LTP induction in the hippocampal-PFC connection; in addition, it induces selective atrophy within the PFC and severely disrupts working memory and behavioral flexibility, two functions that depend on PFC integrity. We also demonstrate that short periods of stress exposure induce spatial reference memory deficits before affecting PFC-dependent tasks, thus suggesting that the impairment of synaptic plasticity within the hippocampus-to-PFC connection is of relevance to the stress-induced PFC dysfunction. These findings evidence a fundamental role of the PFC in maladaptive responses to stress and identify this area as a target for intervention in stress-related disorders.

Paradoxical influence of hippocampal neurogenesis on working memory

To explore the function of adult hippocampal neurogenesis, we ablated cell proliferation by using two independent and complementary methods: (i) a focal hippocampal irradiation and (ii) an inducible and reversible genetic elimination of neural progenitor cells. Previous studies using these methods found a weakening of contextual fear conditioning but no change in spatial reference memory, suggesting a supportive role for neurogenesis in some, but not all, hippocampal-dependent memory tasks. In the present study, we examined hippocampal-dependent and -independent working memory using different radial maze tasks. Surprisingly, ablating neurogenesis caused an improvement of hippocampal-dependent working memory when repetitive information was presented in a single day. These findings suggest that adult-born cells in the dentate gyrus have different, and in some cases, opposite roles in distinct types of memory.

Bidirectional modulation of goal-directed actions by prefrontal cortical dopamine

Instrumental actions are a vital cognitive asset that endows an organism with sensitivity to the consequences of its behavior. Response-outcome feedback allows responding to be shaped in order to maximize beneficial, and minimize detrimental, outcomes. Lesions of the medial prefrontal cortex (mPFC) result in behavior that is insensitive to changes in outcome value in animals and compulsive behavior in several human psychopathologies. Such insensitivity to changes in outcome value is a defining characteristic of instrumental habits: responses that are controlled by antecedent stimuli rather than goal expectancy. Little is known regarding the neurochemical substrates mediating this sensitivity. The present experiments used sensitivity to posttraining outcome devaluation to index the action-habit status of instrumental responding. Infusions of dopamine into the ventral mPFC (vmPFC), but not dorsal mPFC, restored outcome sensitivity bidirectionally-decreasing responding following outcome devaluation and increasing responding when the outcome was not devalued. This bidirectionality makes the possibility that these infusions nonspecifically dysregulated vmPFC dopamine transmission unlikely. VmPFC dopamine promoted instrumental responding appropriate to outcome value. Reinforcer consumption data indicated that this was not a consequence of altered sensitivity to the reinforcer itself. We suggest that vmPFC dopamine reengages attentional processes underlying goal-directed behavior.

Neuropsychological impairment in major depression: its nature, origin and clinical significance

Neuropsychological impairment is well established as a feature of major depressive disorder (MDD) but studies have shown a variable pattern of impairment. This paper seeks first to clarify this by examining methodological and clinical factors that give rise to variability in study findings. Second, it examines theories of the origin of these neuropsychological abnormalities. Third, it reviews evidence regarding the clinical significance of different patterns of deficit. A selective review was undertaken of the literature with a particular emphasis on methodological factors, the influence of clinical subtypes and prevalent theories of neuropsychological abnormality. Methodological issues and the heterogeneity of MDD account for considerable variability in results. Specific investigation of the subtypes of psychotic MDD, melancholic MDD and bipolar depression reduces this heterogeneity and results are more consistent in the elderly. Hypothalamic-pituitary-adrenal axis dysfunction is associated with neuropsychological dysfunction in MDD although evidence of direct causation is not definitive at present. Impairment of executive and psychomotor function is a consistent finding, particularly in the elderly, and may reflect frontostriatal-limbic dysfunction. There is growing evidence that this may have clinical significance. It is suggested that future research take very careful account of the exact phenotype of MDD. Classification based on neuropsychological profile may, in fact, be useful. Further research should examine further the clinical importance of patterns of neuropsychological impairment.

Stroop tasks associated with differential activation of anterior cingulate do not differentiate psychopathic and non-psychopathic offenders

Attentional models of psychopathy hold that psychopathic individuals fail to process information that conflicts with goal-directed behavior. However, they display normal interference on color-word Stroop tasks. To determine whether psychopathic individuals' attention deficits are specific to conditions associated with the anterior cingulate (ACC) conflict monitoring system, we administered a Stroop task with a mostly-congruent condition associated with ACC activation, and a mostly-incongruent condition that is not, to 128 criminal offenders assessed for psychopathy using Hare's (2003) PCL-R. Despite replicating previous condition Effects associated with differential ACC activation (Carter et al., 2000), psychopathic offenders and controls performed very similarly in both conditions. Results do not support an association between ACC-related deficits in conflict monitoring and the attention deficits of psychopathic offenders.

Neural correlates of anosognosia for cognitive impairment in Alzheimer's disease

We explored the neural substrate of anosognosia for cognitive impairment in Alzheimer's disease (AD). Two hundred nine patients with mild to moderate dementia and their caregivers assessed patients' cognitive impairment by answering a structured questionnaire. Subjects rated 13 cognitive domains as not impaired or associated with mild, moderate, severe, or very severe difficulties, and a sum score was calculated. Two measures of anosognosia were derived. A patient's self assessment, unconfounded by objective measurements of cognitive deficits such as dementia severity and episodic memory impairment, provided an estimate of impaired self-evaluative judgment about cognition in AD. Impaired self-evaluation was related to a decrease in brain metabolism measured with 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) in orbital prefrontal cortex and in medial temporal structures. In a cognitive model of anosognosia, medial temporal dysfunction might impair a comparison mechanism between current information on cognition and personal knowledge. Hypoactivity in orbitofrontal cortex may not allow AD patients to update the qualitative judgment associated with their impaired cognitive abilities. Caregivers perceived greater cognitive impairments than patients did. The discrepancy score between caregiver's and patient's evaluations, an other measure of anosognosia, was negatively related to metabolic activity located in the temporoparietal junction, consistent with an impairment of self-referential processes and perspective taking in AD.

Cannabinoids and prefrontal cortical function: Insights from preclinical studies

Marijuana use has been associated with disordered cognition across several domains influenced by the prefrontal cortex (PFC). Here, we review the contribution of preclinical research to understanding the effects of cannabinoids on cognitive ability, and the mechanisms by which cannabinoids may affect the neurochemical processes in the PFC that are associated with these impairments. In rodents, acute administration of cannabinoid agonists produces deficits in working memory, attentional function and reversal learning. These effects appear to be largely dependent on CB1 cannabinoid receptor activation. Preclinical studies also indicate that the endogenous cannabinoid system may tonically regulate some mnemonic processes. Effects of cannabinoids on cognition may be mediated via interaction with neurochemical processes in the PFC and hippocampus. In the PFC, cannabinoids may alter dopaminergic, cholinergic and serotonergic transmission. These mechanisms may underlie cognitive impairments observed following marijuana intake in humans, and may also be relevant to other disorders of cognition. Preclinical research will further enhance our understanding of the interactions between the cannabinoid system and cognitive functioning.

Longitudinal change in memory performance associated with HTR2A polymorphism

We present a fresh approach to evaluating association with candidate genes and cognitive change by testing association for parameters describing individual growth curves from twins. Moderate genetic influences on memory in aging adults has been shown in quantitative genetic studies. A recently reported, association of a HTR2A polymorphism with episodic memory in young unrelated adults led us to investigate the association between a nearby polymorphism and longitudinal memory performance in the Swedish Adoption/Twin Study of Aging (SATSA). Analysis of growth curve parameters suggests that both how well individuals perform on figural memory at age 65 years and nonlinear change in figural memory performance across age are associated with HTR2A. Individuals with two copies of the common G allele demonstrated higher figural memory performance longitudinally than those with the less frequent A allele, with performance trajectories differing by 2-6% per year. These findings imply a role for the 5-HT2A serotonin receptor on the formation of episodic memories in older adults.

Distinctive morphology of hippocampal CA1 terminations in orbital and medial frontal cortex in macaque monkeys

The fine morphology of hippocampal connections to the orbital and medial frontal cortex (OMFC) was investigated by placing injections of anterograde tracers in the CA1 in two monkeys. The axons terminated mainly in layers 2 and 3, of areas 11, 13, 14c, 25, and 32, and were widely divergent in these layers, traversing 2-4 mm. Boutons were scattered along the main axon, but also occurred as distinctive small, spherical clusters of terminations ("mini-clusters"; diameter <50 microm). Occasional larger terminal arbors were observed in layer 3 and these were often unusually tortuous or convoluted. These features may imply a specialized microcircuitry of hippocampal-OMFC connections, including an origin from a particular subpopulation of CA1 projection neurons.

Dopamine-dependent interactions between limbic and prefrontal cortical plasticity in the nucleus accumbens: disruption by cocaine sensitization

The prefrontal cortex and the hippocampus exhibit converging projections to the nucleus accumbens and have functional reciprocal connections via indirect pathways. As a result, information processing between these structures is likely to be bidirectional. Using evoked potential measures, we examined the interactions of these inputs on synaptic plasticity within the accumbens. Our results show that the direction of information flow between the prefrontal cortex and limbic structures determines the synaptic plasticity that these inputs exhibit within the accumbens. Moreover, this synaptic plasticity at hippocampal and prefrontal inputs selectively involves dopamine D1 and D2 activation or inactivation, respectively. Repeated cocaine administration disrupted this synaptic plasticity at hippocampal and prefrontal cortical inputs and goal-directed behavior in the spatial maze task. Thus, interactions of limbic-prefrontal cortical synaptic plasticity and its dysfunction within the accumbens could underlie complex information processing deficits observed in individuals following psychostimulant administration.

The relationship between hippocampal EEG theta activity and locomotor behaviour in freely moving rats: effects of vigabatrin

The relationship between hippocampal electroencephalogram (EEG) theta activity and locomotor speed in both spontaneous and forced walking conditions was studied in rats after vigabatrin injection (500 mg/kg i.p.). Vigabatrin increased the percentage of time that rats spent being immobile. During spontaneous walking in the open field, the speed of locomotion was increased by vigabatrin, while theta peak frequency was decreased. Vigabatrin also reduced the theta peak frequency during forced (speed controlled) walking. There was only a weak positive correlation (r=0.22) between theta peak frequency and locomotor speed for the saline condition. Furthermore, vigabatrin abolishes the weak relationship between speed of locomotion and theta peak frequency. Vigabatrin and saline did not differ in the slope of the regression line, but showed different offset points at the theta peak frequency axis. Thus, other factors than speed of locomotion seem to be involved in determination of the theta peak frequency.

Activity and plasticity in the CA1, the dentate gyrus, and the amygdala following controllable vs. uncontrollable water stress

The level of controllability has been shown to modulate the effects of stress on physiology and behavior. In the present study, we investigated the effects of controllable vs. uncontrollable stressors on plasticity in hippocampal CA1, the dentate gyrus (DG), and basal amygdala nucleus (B) in the rat, using the electrophysiological procedure of long-term potentiation (LTP). A naive group was left undisturbed until the electrophysiological recording commenced. Rats of the two controllable stress groups were trained in the Morris water maze to locate an invisible underwater platform (the first group), or visible platform (the second group), thus escaping from the water, before the recording. The uncontrollable stress group underwent the same procedure (exposure time to water was adjusted to the averaged exposure time of the first controllable group) without the escape platform. We first assessed the effects of stress and controllability on LTP in CA1. Both controllable stressors and the uncontrollable stress impaired CA1 LTP, with a more robust effect induced by the uncontrollable stress. We further assessed the effects of the same procedures on LTP in DG and B. The uncontrollable stress enhanced LTP in DG and increased baseline responses (suggesting uncontrollable stress-induced plasticity) in the amygdala. All the stressors decreased amygdalar LTP. An assessment of plasma levels of corticosterone (CORT), following the behavioral procedures, revealed an enhancement in CORT release following the uncontrollable, but not controllable stress, indicating the uncontrollable condition as the most stressful. These findings provide insight into the differential effects of stress and stress controllability on different hippocampal subregions and the amygdala.

Neurodevelopment, neuroplasticity, and new genes for schizophrenia

Schizophrenia is a complex, debilitating neuropsychiatric disorder. Epidemiological, clinical, neuropsychological, and neurophysiological studies have provided substantial evidence that abnormalities in brain development and ongoing neuroplasticity play important roles in the pathogenesis of the disorder. Complementing these clinical studies, a range of cytoarchitectural, morphometric, ultrastructural, immunochemical, and gene expression methods have been applied in investigations of postmortem brain tissues to characterize the cellular and molecular profile of putative developmental and plastic abnormalities in schizophrenia. While findings have been diverse and many are in need of replication, investigations focusing on higher cortical and limbic brain regions are increasingly demonstrating abnormalities in the structural and molecular integrity of the synaptic complex as well as glutamate-related receptors and signal transduction pathways that play critical roles in brain development, synaptogenesis, and synaptic plasticity. Most exciting have been recent associations of schizophrenia with specific genes, such as neuregulin-1, dysbindin-1, and AKT-1, which are vital to synaptic development, neurotransmission, and plasticity.

Differential effects of infralimbic vs. ventromedial orbital PFC lidocaine infusions in CD-1 mice on defensive responding in the mouse defense test battery and rat exposure test

The ventromedial prefrontal cortex (vmPFC) is extremely sensitive to a variety of stressful situations and threatening events, and has been suggested to be an associative cortical brain system processing the integration of anxiety-related cognitive, affective and motivated behavior in rodents, primates and humans. In addition, recent evidence suggests that (a) anxiety-related affective processing appears to be lateralized to the right hemisphere vmPFC; and (b) there appears to be functional heterogeneity within the rodent vmPFC. The present study evaluated the possibility that distinct sub-areas of the right hemisphere ventral PFC might differentially influence anxiety-like defensive responding in two different predator stress situations following transient inactivation of the ventromedial orbital (vMO) or infralimbic (IL) vmPFC in CD-1 mice. In week 1, IL vmPFC lidocaine infusions reduced anxiety-like defensive responding in mice (enhanced approach and contact) confronted with a hand-held anesthetized rat stimulus in the mouse defense test battery (vMO inactivation exerted minimal effects). In week 2, vMO lidocaine infusions enhanced anxiety-like defensive responding (enhanced avoidance and protected risk assessment) toward a barricaded live rat in the rat exposure test (IL inactivation exerted minimal effects). Although it is unclear whether week 1 mouse defense test battery testing influenced week 2 rat exposure test results, these preliminary data suggest functional differences within the mouse right hemisphere ventral PFC related to cautious evaluation of predator threat. Given the dense unilateral reciprocal connectivity between the IL and vMO subregions of the PFC, both associative ventromedial cortical areas may exert complimentary yet dissociable roles in the processing of threat stimuli. This suggests that while the IL vmPFC may mediate cautious evaluation of threat situations (risk assessment), the vMO PFC may inhibit prepotent avoidance responses to facilitate such IL-mediated adaptive behavioral responses.

Introduction of a retention interval in a sustained attention task in rats: effects of a visual distracter and increasing the inter-trial interval

The impact of manipulating explicit attentional demands on working memory has not been well studied in rodents. The present experiment was designed to test the effects of incorporating a retention interval in a two-lever sustained attention task that requires discrimination of visual signals and non-signals and that has previously been shown to yield valid measures of attention in the rat. Upon establishing baseline performance, additional manipulations, including presentation of a visual distracter and increasing the length and variability of the inter-trial interval were conducted. During baseline conditions, accurate detection of signals, but not non-signals, decreased as the retention interval was increased. Presentation of a flashing houselight throughout the session eliminated delay-dependent detection of signals. Increasing the inter-trial interval improved detection of signals and decreased detection of non-signals at the longest retention interval. Finally, increasing the variability of the inter-trial interval did not have significant effects on performance above and beyond the effects of increasing the inter-trial interval. The present experiment demonstrates that manipulation of explicit attentional demands can alter working memory performance in the rat. This task may be employed to understand the neuropharmacological and neuroanatomical substrates mediating memory while attentional load is systematically varied.

Role of estrogen in balancing contributions from multiple memory systems

In addition to modulating memory per se, estrogen alters the learning strategy used to solve a task, thereby regulating the quality of information processed by the brain. This review discusses estrogen's actions on cognition within a memory systems framework, highlighting our work with a variety of paradigms showing that learning strategy is sensitive to estrogen even when learning rate is not. Specifically, high levels of gonadal steroids, in particular, elevations in estrogen, bias female rats toward using hippocampal-sensitive approaches while low levels of gonadal steroids promote the use of non-hippocampal sensitive strategies. In light of findings from a variety of approaches involving the hippocampus in allocentric and the striatum in egocentric response patterns, it is likely that estrogen alters the relative participation of these, and most undoubtedly other, neural systems during cognition. Changes in neuromodulators such as acetylcholine that regulate other processes such as inhibitory tone and excitability reflect one mechanism by which estrogen may orchestrate learning and memory.

Stress induces activation of stress-activated kinases in the mouse brain

Stress is a part of daily life. However, molecular mechanisms underlying the activation of limbic-hypothalamic-pituitary-adrenal (LHPA) axis remains unknown. In this study, we explored whether activation of the mitogen-activated kinase kinase 4 (MKK4)-c-Jun-N-terminal kinase (JNK) signaling pathway may play a role in the activation of the LHPA axis. We found that forced-swim stress induced elevation of activated MKK4 in the hippocampal formation, amygdala, and hypothalamus. Unlike MKK4, a high basal level of JNK activity is present in many brain areas of unstressed mice. Forced-swim stress significantly elevated JNK activity in the hypothalamus and amygdala and, to a lesser extent, in the cortex, CA1 and CA3 regions, and the dentate gyrus. To further investigate the role of MKK4 and JNK in induction of stress responses, we investigated whether a different stress, namely, restraint stress, induced activation of MKK4 or JNK in the brain. We found that restraint stress also induced elevation of activated MKK4 and JNK in the hippocampal formation, amygdala, and hypothalamus. Because MKK4 and JNK were activated within 5 min following stress, we propose that the MKK4-JNK signaling may be an early neural event in the initiation of neuroendocrine, autonomic and behavioral stress responses.

Decreased hippocampal 5-HT2A receptor binding in major depressive disorder: in vivo measurement with [18F]altanserin positron emission tomography

BACKGROUND

Serotonin 5-HT(2A) receptors play an important role in the regulation of many functions that are disturbed in patients with major depressive disorder. Postmortem and positron emission tomography studies have reported both increased and decreased 5-HT(2A) receptor binding in different limbic and paralimbic regions.

METHODS

We conducted a quantitative 5-HT(2A) receptor binding study using positron emission tomography and [(18)F]altanserin of four regions hypothesized to have altered levels of 5-HT(2A) receptors in major depressive disorder. Using a four-compartment model, the 5-HT(2A) receptor distribution was estimated by calculating the regional [(18)F]altanserin k(3)/k(4) ratio in which k(3) is the rate of binding to the receptor and k(4) is the rate of dissociation from the receptor. Forty-six antidepressant-free patients with major depressive disorder and 29 healthy control subjects were enrolled.

RESULTS

5-HT(2A) receptor binding in the hippocampus was reduced by 29% in depressed subjects (p =.004). In other regions, 5-HT(2A) receptor binding was decreased (averaging 15%) but not significantly. Both groups had similar age-dependent decreases in 5-HT(2A) receptors throughout all brain regions.

CONCLUSIONS

Altered serotoninergic function in the hippocampus is likely involved in the disturbances of mood regulation in major depressive disorder, although the specific role of the 5-HT(2A) receptor changes is still unclear.

The role of prelimbic cortex in instrumental conditioning

Numerous studies have implicated human and primate prefrontal cortex in the ability to hold and manipulate goal or outcome-related information in working memory to guide the performance of forthcoming actions. Here we report that cell-body lesions of prelimbic cortex impair the ability of rats to select an action based on previously encoded action-outcome associations. Rats were food deprived and trained to press two levers, one delivering food pellets and the other a sucrose solution. All rats acquired the lever-press response although the initial acquisition in the prelimbic rats was significantly slower than in sham controls. Furthermore, whereas in sham-lesioned rats, post-training devaluation of one of the two outcomes using a specific satiety procedure produced a selective reduction in performance on the lever that in training delivered the prefed outcome, prelimbic rats failed to show a selective devaluation effect and appeared to reduce performance on both levers non-selectively. Importantly, this impairment only emerged in extinction; in subsequent experiments it was found that, when a specific action-outcome association was cued either by presentation of the outcome itself or by presenting a stimulus previously paired with the outcome, rats demonstrated an ability to select the associated action. These results suggest that action-outcome encoding may be intact in prelimbic rats and that the lesion impaired their ability to retain this learning in working memory in order to establish a course of action. Alternatively, the lesion may have altered the relative contribution of action-outcome and outcome-action associations to instrumental performance. On this account, prelimbic lesions affect action-outcome encoding but leave outcome-action associations intact providing the basis for outcome-mediated initiation of an action sufficient, perhaps, to support acquisition and performance in the lesioned rats.

Effects of interval duration on temporal processing in schizophrenia

INTRODUCTION

Temporal processing has received scant attention in the literature pertaining to cognitive deficits in patients with schizophrenia. Previous research suggests that patients with schizophrenia exhibit temporal perception deficits on both auditory and visual stimuli. The current study investigated the effects of interval manipulation to (1) replicate the original findings with a larger sample and an increased number of trials (2) assess the degree to which both patients and controls can differentiate temporal changes in a range of experimental interstimulus intervals, and (3) explore whether different interstimulus interval durations pose different levels of difficulty for the patients with schizophrenia.

METHODS

Participants were asked to decide whether temporal intervals were shorter or longer than standard intervals on a computer-based auditory temporal perception task. The standard interval remained the same duration throughout the various tasks. The interstimulus interval separating the standard and experimental intervals varied in the range of 500, 1000, or 3000 ms. Data are presented for a sample of 16 patients with schizophrenia and 15 controls.

RESULTS

Data suggest that patients with schizophrenia exhibit deficits in differentiating interval durations across all paradigms compared to their control-group peers on a range of auditory tasks (p<.001).

CONCLUSIONS

These results are consistent with a general temporal deficit in schizophrenia. However, the roles of medication and localization are also addressed.

Effect of chronic stress on spatial memory in rats is attenuated by lithium treatment

Stress is known to alter cognitive functions, such as memory, and it has been linked to the pathophysiology of mood and anxiety disorders. Chronic lithium treatment is used in some psychiatric disorders and has been suggested to act upon mechanisms which can enhance neuronal viability. The purpose of this work is to investigate a possible effect of lithium treatment in a chronic stress model. Adult male Wistar rats were divided in two groups, control and chronically stressed, treated either with normal chow or with chow containing LiCl for 40 days. Stress treatment was a chronic variable stress model, consisting of different stressors which were applied in a random fashion, once a day, every day. Memory was assessed by using the water maze task. The results demonstrated a marked decrease in reference memory in the water maze task in chronically stressed rats. This effect was attenuated by lithium treatment in all the parameters considered. No effect was observed in the working memory. These results indicate that lithium treatment may counteract some effects of chronic stress situations, particularly concerning spatial memory.

Infralimbic D2 receptor influences on anxiety-like behavior and active memory/attention in CD-1 mice

Ventromedial prefrontal cortical (vmPFC) dopamine (DA) influences attentional aspects of cognition and anxiety-like behavioral responding in rodents. The present study investigated the role of D2 receptors on spontaneous alternation in the Y-maze and anxiety-like behavior in a two-trial elevated plus-maze (EPM) procedure in CD-1 mice following vmPFC infusions of the D2 antagonist, sulpiride, and the D2 agonist, quinpirole. Pretrial 1 quinpirole infusions did not influence any anxiety measure (with the exception that the lowest dose increased protected stretch attends), but reduced protected exploration activity (closed-arm entry/time ratios and wall rearing). In Trial 2 24 h later (no injection), quinpirole exerted an anxiolytic behavioral profile relative to Trial 2 control mice (enhanced open-arm entry/time ratios, unprotected head dips), with no effects on protected exploration or risk assessment activity. Pretrial 1 sulpiride infusions enhanced unprotected exploration (open-arm entry/time ratios, unprotected stretch attend, and head dips), but did not influence protected exploration or risk assessment in the EPM. In Trial 2, 24 h later (no injection), sulpiride extended this anxiolytic profile to reduced protected exploration and risk assessment activity (closed-time ratio, protected stretch attend, and head dips). In the Y-maze, whereas quinpirole disrupted alternation performance (5- and 10-nmol dose) concomitant with marked repetitive same-arm returns (SAR) at the highest dose, sulpiride disrupted alternation performance concomitant with marked repetitive SAR behavior at the lowest dose only. These data indicate that although infralimbic (IL) quinpirole and sulpiride infusions similarly disrupted alternation performance in the Y-maze and reduced Trial 2 anxiety-like responding in the EPM, these drugs differentially produced these effects.

Excitotoxic lesions of the medial prefrontal cortex attenuate fear responses in the elevated-plus maze, social interaction and shock probe burying tests

Previous research investigating the effects of medial prefrontal cortex (MPFC) lesions on fear- and anxiety-related behavior has yielded an inconsistent body of findings. Behavioral studies have reported increases, decreases, and no effect on anxiety. In addition, many studies are complicated by the use of lesioning techniques that destroy fibers of passage, and the use of conditioned fear tests, which may introduce the confounding effects of learning and memory. Therefore, the present study examined the effects of ibotenic acid lesions of the MPFC (including prelimbic, infralimbic and anterior cingulate) on three wide-ranging and well-validated behavioral assays of anxiety: the elevated plus maze (EPM), social interaction (SI) and the shock-probe tests (SP). In the EPM test, lesioned rats showed a significantly higher percentage of open arm entries and open arm time than controls. In a version of the SI test sensitive to anxiolytic effects, lesioned rats were found to spend a significantly greater amount of time in active interaction with a conspecific; while another version of the SI test sensitive to anxiogenic effects did not show any differences between lesioned and non-lesioned controls. In the SP test, lesioned rats exhibited significantly lower rates of burying. In contrast, retention of shock probe avoidance was not affected. No effects of lesions on measures of locomotor activity or shock reactivity were found. The concordant anxiolytic-like effects found in the three behavioral assays strongly suggests a general reduction in fear responsiveness in MPFC lesioned rats.

Behavioral transitions modulate hippocampal electroencephalogram correlates of open field behavior in the rat: support for a sensorimotor function of hippocampal rhythmical synchronous activity

A clear relationship exists between moment-to-moment behavioral elements and hippocampal rhythmical synchronous activity (RSA) (theta rhythm). However, behavioral elements are not isolated events but are part of behavioral sequences in a context of behavioral activity. By concurrently monitoring open field behavior and hippocampal EEG, EEG correlates of open field behavior in relation to preceding and following behavior were studied in Sprague Dawley rats to determine whether the behavioral context influences EEG correlates of behavior. Results show that preceding and subsequent behavioral patterns influenced the spectral power correlates of behavior. RSA power was increased when a "type 1 behavior" (voluntary movement) preceded the behavior compared with when a "type 2 behavior" (automatic movement, awake immobility) preceded it. The modulating effect of behavioral transitions was shown for several types of behaviors, and systematic modulation of hippocampal EEG correlates of behavior was demonstrated. The present report shows that the strong and systematic relationship between hippocampal RSA and behavior is modulated by the behavioral-sequential context. Thus, in addition to the well established relationship between RSA and motor activity, a second nonmotor process seems to contribute to hippocampal RSA. A likely candidate is a sensory process, which is in accordance with theories on the sensorimotor function of hippocampal RSA.

Reduced hippocampal anisotropy related to anteriorization of alpha EEG in schizophrenia

Dysfunctions of the hippocampus have been suggested to be related to schizophrenia, and reduced connectivity with other brain regions may be a key for the pathophysiology. The aim of this study was to investigate the effect of white matter anomalies in the hippocampus, as a sign of altered connectivity, on the brain electrical activity. We investigated seven first episode schizophrenic patients and seven age, gender and education-matched controls with diffusion tensor imaging and resting EEG. Fractional anisotropy was computed based on diffusion tensor imaging data for the right and left hippocampus for both groups. No group differences were found in hippocampal fractional anisotropy, EEG spectral power and topography. However a significant correlation was found between more anterior alpha activity and lower fractional anisotropy of both hippocampi in schizophrenics, but not in controls. More anterior alpha activity has been described in schizophrenia. We conclude that this feature might depict a group of schizophrenic patients with reduced hippocampal connectivity.

Helplessness and escape performance: glutamate-adenosine interactions in the frontal cortex

Adenosine has been implicated as a proximate mediator of escape deficits in the learned helplessness paradigm, suggesting that neuronal overactivation-a typical precursor to adenosine release-precedes the inescapable shock-induced impairment (T. R. Minor, W. C. Chang, & J. L. Winslow, 1994). In the present experiments, glutamate (100 microg) injection into the rat frontal cortex produced a deficit in escape performance. Pretest treatment with the adenosine receptor antagonist caffeine (7 mg/kg ip) reversed the effect of glutamate when infused 1 hr. but not 72 hr, after glutamate injection. Finally, microinjection of 2-amino-5-phosphonovaleric acid (5 ng) into the frontal cortex prior to inescapable shock prevented the escape deficit. These findings are consistent with the involvement of N-methyl-D-aspartate receptor activation in the frontal cortex in the helplessness effect.

Perceptual attentional set-shifting is impaired in rats with neurotoxic lesions of posterior parietal cortex

The posterior parietal cortex (PPC) is believed to be involved in the representation of spatial information, including spatial attentional processing. Because the PPC is extensively interconnected with frontal cortical regions involved in attention and executive function, we sought to determine whether PPC was involved in nonspatial attentional processes such as those of the frontal areas to which it projects. Lesions of the medial frontal cortex (in rats) or lateral prefrontal cortex (in nonhuman primates) impair the ability to shift attention from one perceptual dimension of a stimulus to another (referred to as an extradimensional shift). Rats with neurotoxic lesions of the PPC tested in an attentional set-shifting paradigm demonstrated a pattern of impairment identical to that of rats with medial frontal cortex lesions: they were selectively impaired on the extradimensional shift phase of the task. Performance in other phases of the task was indistinguishable from that of control rats, including the ability to reverse a previously learned discrimination. These findings are consistent with models that assign the PPC a prominent role in cortical attentional processing networks, as well as a role for the PPC in processing information about expectancy and surprise. They also suggest, importantly, that the interaction between the PPC and the frontal cortex is not limited to spatial attentional processing.