Deficits In Associative Learning Research Articles

Associative Learning in Subclinical Hypothyroidism at Different Ranges of Thyroid Stimulating Hormone: A Cambridge Neuropsychological Test Automated Battery (CANTAB) Study of Visual Paired Association Learning Task.

Associative learning deficits are constantly found in subclinical hypothyroidism (SCH). Despite achieving normal thyroid stimulating hormone (TSH) levels, a considerable number of patients undergoing levothyroxine (LT-4) treatment frequently complain about memory retrieval. The Paired Association Learning (PAL) task involves computerised testing on the CANTAB- Cambridge Neuropsychological Test Automated Battery, also considered a screening tool for Alzheimer's disease (AD). This study aimed to investigate the impact of different levels of TSH on visual associative learning in SCH and determine if these impairments were reversed with LT-4. A total of 134 participants were included in this cross-sectional study. Group 1: 35 healthy controls; patients with SCH (Group 2: 33 newly identified cases; Group 3: 32 patients on LT-4 with elevated TSH; Group 4: 34 euthyroid but on LT-4). A thyroid profile and a neuropsychological clinical assessment were done. The visual PAL task was performed on CANTAB. PAL was significantly impaired (p = <0.05) in all 3 patient groups as compared to Group 1. The PAL total errors (adjusted) scores were significantly higher in Groups 2 and 3, indicating that associative learning is definitely impaired in SCH, reaching levels previously seen in patients with AD. Our findings encourage screening for visual associative learning or memory retrieval in patients with SCH. The study present has established a more reasonable threshold of TSH 2.5mIU/L to encourage examination of associative learning and the initiation of LT-4 in SCH. Poor PAL task performance in patients with SCH may have significant implications in clinical settings for suspecting AD.

Impairment in acquisition of conditioned fear in people with depressive symptoms.

Depression is one of the primary global public health issues, and there has been a dramatic increase in depression levels among young people over the past decade. The neuroplasticity theory of depression postulates that a malfunction in neural plasticity, which is responsible for learning, memory, and adaptive behavior, is the primary source of the disorder's clinical manifestations. Nevertheless, the impact of depression symptoms on associative learning remains underexplored. We used the differential fear conditioning paradigm to investigate the effects of depressive symptoms on fear acquisition and extinction learning. Skin conductance response (SCR) is an objective evaluation indicator, and ratings of nervousness, likeability, and unconditioned stimuli (US) expectancy are subjective evaluation indicators. In addition, we used associability generated by a computational reinforcement learning model to characterize the skin conductance response. The findings indicate that individuals with depressive symptoms exhibited significant impairment in fear acquisition learning compared to those without depressive symptoms based on the results of the skin conductance response. Moreover, in the discrimination fear learning task, the skin conductance response was positively correlated with associability, as estimated by the hybrid model in the group without depressive symptoms. Additionally, the likeability rating scores improved post-extinction learning in the group without depressive symptoms, and no such increase was observed in the group with depressive symptoms. The study highlights that individuals with pronounced depressive symptoms exhibit impaired fear acquisition and extinction learning, suggesting a possible deficit in associative learning. Employing the hybrid model to analyze the learning process offers a deeper insight into the associative learning processes of humans, thus allowing for improved comprehension and treatment of these mental health problems.

Antagonism of D2 receptors via raclopride ameliorates amphetamine-induced associative learning deficits in male mice

Dopamine levels in the dorsomedial striatum (DMS) are highly dynamic and are thought to underly the encoding of action-outcome associations. Although it is known that amphetamine disrupts the learning that is required for goal-directed action, the role of D1 and D2 receptors in this process has not been established. In this study, we examined the role of D1 and D2 receptor antagonists on learning in response to amphetamine. We used the outcome-specific devaluation task to examine goal-directed action in male C57BL6/J mice treated systemically with either a D1 antagonist (SCH-23990; 0.01 mg/kg) or a D2 antagonist (raclopride; 0.5 mg/kg) and then administered amphetamine (1 mg/kg). The mice were injected repeatedly throughout the instrumental training phase of the task to assess the impact on the learning of action-outcomes, and the subsequent choice test assessing performance of goal-directed action was conducted drug free. Effects of chronic drug administration on locomotor behaviour was assessed before and after the choice test. Treatment during learning with either amphetamine, or the D1 or D2 antagonists, impaired the subsequent performance of goal-directed action. The amphetamine-induced impairment in goal-directed action was reversed in mice treated with raclopride, but not when treated with SCH-23990. By contrast, amphetamine-induced hyperactivity was reversed in mice treated with SCH-23990, but not in mice treated with raclopride. Taken together, these data support the role of a balance of dopamine receptor signalling after amphetamine treatment. While overall D1 receptor availability is necessary to promote learning, in a state of elevated dopamine, modifying D2 receptor function can ameliorate learning deficits.

Single vascular insult exacerbates disease pathology in APPswe Mice.

AbstractBackgroundVascular insults, such as microinfarcts play a major role in mixed dementia including Alzheimer’s disease (AD). Neuroimaging from longitudinal studies have shown involvement of white matter hyperintensities due to blood brain barrier (BBB) breakdown. In patients with AD the combined neurotoxic effects of amyloid‐β (Aβ) converge on brain vasculature synergistically leading to neuronal and synaptic dysfunction, which in turn leads to cognitive impairment. In the present study we examined the effect of vascular insult induced by enothelin‐1 (ET‐1, a vasoconstrictor peptide) on Aβ pathology in mouse models of AD. We further studied behavioral deficits during reduced cerebral blood flow changes and structural changes in BBB components.MethodWe injected 2µg/2μl of ET‐1 bilaterally into lateral ventricles APPswe mice carrying point mutation for APP. Behavioral assays were performed to compare associative learning and spatial memory deficits, if any after 30 days of ET‐1 injection. Immunohistochemistry for markers of endothelial cells and pericytes were done to look at the structural changes in BBB. Aβ ELISA and plaque load were tested to understand the effect of vascular insult on AD pathology.ResultVasoconstriction following ET‐1 injection after 30 days leads to memory deficits in AD mice while wildtype mice recovered. There were structural changes in BBB showing decreased expression of endothelial and pericyte marker, however these changes were not observed in wildtype mice. Aβ levels were increased in brain lysates of APPswe mice injected with ET‐1.ConclusionSingle vascular insult was adequate to bring about impairment in learning and memory in APPswe mice and structural changes in BBB, which were not seen in WT type mice indicating that ET‐1 induced cerebral hypoperfusion accelerated AD pathogenesis.

Sex-dependent deficits in associative learning across multiple LPS doses

Activation of the immune system by administration of the bacterial endotoxin lipopolysaccharide (LPS) impairs cognitive and neural plasticity processes. For instance, acute LPS exposure has been reported to impair memory consolidation, spatial learning and memory, and associative learning. However, the inclusion of both males and females in basic research is limited. Whether LPS-induced cognitive deficits are comparable in males and females is currently unclear. Therefore, the present study evaluated sex differences in associative learning following administration of LPS at a dose (i.e., 0.25 mg/kg) that impairs learning in males and higher LPS doses (i.e., 0.325 – 1 mg/kg) across multiple experiments. Adult male and female C57BL/6J mice were trained in a two-way active avoidance conditioning task following their respective treatments. Results showed that LPS had sex-dependent effects on associative learning. The 0.25 mg/kg LPS dose impaired learning in males, consistent with prior work. However, LPS, at any of the doses employed across three experiments, did not disrupt associative learning in females. Female mice were resistant to learning deficits despite showing heightened levels of select proinflammatory cytokines in response to LPS. Collectively, these findings demonstrate that the learning impairments resulting from acute LPS exposure are sex-dependent.

Sex difference in evolution of cognitive decline: studies on mouse model and the Dominantly Inherited Alzheimer Network cohort

Women carry a higher burden of Alzheimer’s disease (AD) compared to men, which is not accounted entirely by differences in lifespan. To identify the mechanisms underlying this effect, we investigated sex-specific differences in the progression of familial AD in humans and in APPswe/PS1ΔE9 mice. Activity dependent protein translation and associative learning and memory deficits were examined in APPswe/PS1ΔE9 mice and wild-type mice. As a human comparator group, progression of cognitive dysfunction was assessed in mutation carriers and non-carriers from DIAN (Dominantly Inherited Alzheimer Network) cohort. Female APPswe/PS1ΔE9 mice did not show recall deficits after contextual fear conditioning until 8 months of age. Further, activity dependent protein translation and Akt1-mTOR signaling at the synapse were impaired in male but not in female mice until 8 months of age. Ovariectomized APPswe/PS1ΔE9 mice displayed recall deficits at 4 months of age and these were sustained until 8 months of age. Moreover, activity dependent protein translation was also impaired in 4 months old ovariectomized APPswe/PS1ΔE9 mice compared with sham female APPswe/PS1ΔE9 mice. Progression of memory impairment differed between men and women in the DIAN cohort as analyzed using linear mixed effects model, wherein men showed steeper cognitive decline irrespective of the age of entry in the study, while women showed significantly greater performance and slower decline in immediate recall (LOGIMEM) and delayed recall (MEMUNITS) than men. However, when the performance of men and women in several cognitive tasks (such as Wechsler’s logical memory) are compared with the estimated year from expected symptom onset (EYO) we found no significant differences between men and women. We conclude that in familial AD patients and mouse models, females are protected, and the onset of disease is delayed as long as estrogen levels are intact.

Neuronal deletion of CaV1.2 is associated with sex-specific behavioral phenotypes in mice

The gene CACNA1C, which encodes the pore forming subunit of the L-type calcium channel CaV1.2, is associated with increased risk for neuropsychiatric disorders including schizophrenia, autism spectrum disorder, major depression, and bipolar disorder. Previous rodent work identified that loss or reduction of CaV1.2 results in cognitive, affective, and motor deficits. Most previous work has either included non-neuronal cell populations (haploinsufficient and Nestin-Cre) or investigated a discrete neuronal cell population (e.g. CaMKII-Cre, Drd1-Cre), but few studies have examined the effects of more broad neuron-specific deletion of CaV1.2. Additionally, most of these studies did not evaluate for sex-specific effects or used only male animals. Here, we sought to clarify whether there are sex-specific behavioral consequences of neuron-specific deletion of CaV1.2 (neuronal CaV1.2 cKO) using Syn1-Cre-mediated conditional deletion. We found that neuronal CaV1.2 cKO mice have normal baseline locomotor function but female cKO mice display impaired motor performance learning. Male neuronal CaV1.2 cKO display impaired startle response with intact pre-pulse inhibition. Male neuronal CaV1.2 cKO mice did not display normal social preference, whereas female neuronal CaV1.2 cKO mice did. Neuronal CaV1.2 cKO mice displayed impaired associative learning in both sexes, as well as normal anxiety-like behavior and hedonic capacity. We conclude that deletion of neuronal CaV1.2 alters motor performance, acoustic startle reflex, and social behaviors in a sex-specific manner, while associative learning deficits generalize across sexes. Our data provide evidence for both sex-specific and sex-independent phenotypes related to neuronal expression of CaV1.2.

Recovery of Angelman syndrome rat deficits with UBE3A protein supplementation

We recently generated a novel Angelman syndrome (AS) rat model with a complete Ube3a gene deletion, that recapitulates the loss of UBE3A protein and shows cognitive and EEG deficits. We also recently published the identification of extracellular UBE3A protein within the brain using microdialysis. Here we explored the effects of supplementation of exogenous UBE3A protein to hippocampal slices and intrahippocampal injection of AS rats. We report that the AS rat model demonstrates deficits in hippocampal long-term potentiation (LTP) which can be recovered with the application of exogenous UBE3A protein. Furthermore, injection of recombinant UBE3A protein into the hippocampus of the AS rat can rescue the associative learning and memory deficits seen in the fear conditioning task. These data suggest that extracellular UBE3A protein may play a role in synaptic function, LTP induction and hippocampal-dependent memory formation.

Deletion of the voltage-gated calcium channel, CaV 1.3, causes deficits in motor performance and associative learning.

L-type voltage-gated calcium channels are important regulators of neuronal activity and are widely expressed throughout the brain. One of the major L-type voltage-gated calcium channel isoforms in the brain is CaV 1.3. Mice lacking CaV 1.3 are reported to have impairments in fear conditioning and depressive-like behaviors, which have been linked to CaV 1.3 function in the hippocampus and amygdala. Genetic variation in CaV 1.3 has been linked to a variety of psychiatric disorders, including autism and schizophrenia, which are associated with altered motor learning, associative learning and social function. Here, we explored whether CaV 1.3 plays a role in these behaviors. We found that CaV 1.3 knockout mice have deficits in rotarod learning despite normal locomotor function. Deletion of CaV 1.3 is also associated with impaired gait adaptation and associative learning on the Erasmus Ladder. We did not observe any impairments in CaV 1.3 knockout mice on assays of anxiety-like, depression-like or social preference behaviors. Our results suggest an important role for CaV 1.3 in neural circuits involved in motor learning and concur with previous data showing its involvement in associative learning.

Anticipation: An Essential Feature of Anhedonia.

The following essay addresses the evolution of the term "anhedonia" as a key construct in biological psychiatry, especially as it pertains to positive emotional and motivational states central to mental health and well-being. In its strictest definition, anhedonia was intended to convey an inability to experience "pleasure" derived from ingestion of sweet tastes or the experience of pleasant odors and tactile sensations, among a host of positive sensations. However, this definition has proved to be too restrictive to capture the complexity of key psychological factors linked to major depression, schizophrenia, and substance use disorders it was originally intended to address. Despite the appeal of the elegant simplicity of the term anhedonia, its limitations soon became apparent when used to explain psychological constructs including aspects of learning, memory, and incentive motivation that are major determinants of success in securing the necessities of life. Accordingly, the definition of anhedonia has morphed into a much broader term that includes key roles in the disturbance of motivation in the form of anergia, impaired incentive motivation, along with deficits in associative learning and key aspects of memory, on which the ability to predict the consequences of one's actions are based. Here we argue that it is this latter capacity, namely predicting the likely consequences of motivated behavior, which can be termed "anticipation," that is especially important in the key deficits implied by the general term anhedonia in the context of neuropsychiatric conditions.

Alcohol and Vaporized Nicotine Co-exposure During Adolescence Contribute Differentially to Sex-Specific Behavioral Effects in Adulthood.

Co-occurrence of e-cigarette use and alcohol consumption during adolescence is frequent. Here, we examined whether adolescent co-exposure to alcohol drinking and vaporized nicotine would impact reward- and cognition-related behaviors in adult male and female rats during adulthood. Four groups of male and female Sprague Dawley rats (n = 8-11/group/sex) received either nicotine (JUUL 5% nicotine pods) or vehicle vapor for 10 minutes daily between postnatal days 30-46, while having continuous voluntary access to ethanol and water during this time in a two-bottle preference design. Upon reaching adulthood, all rats underwent behavioral testing (ie, Pavlovian conditioned approach testing, fear conditioning and a two-bottle alcohol preference). A sex-dependent effect, not related to adolescent nicotine or alcohol exposure, on alcohol drinking in adulthood was found, such that females had a higher intake and preference for alcohol compared to males; both male and female adult rats also had greater alcohol preference compared to their alcohol preference as adolescents. Male rats exposed to vaporized nicotine with or without alcohol drinking during adolescence exhibited altered reward-related learning in adulthood, evidenced by enhanced levels of sign-tracking behavior. Male rats that drank alcohol with or without nicotine vapor in adolescence showed deficits in associative fear learning and memory as adults. In contrast, these effects were not seen in female rats exposed to alcohol and nicotine vapor during adolescence. The present study provides evidence that co-exposure to alcohol and vaporized nicotine during adolescence in male, but not female, rats produces long-term changes in reward- and cognition-related behaviors. These findings enhance our understanding of the effects of alcohol drinking and nicotine vapor exposure in adolescence. Moreover, they highlight potential sex differences that exist in the response to alcohol and nicotine vapor, underscoring the need for follow-up studies elucidating the neurobiological mechanisms that drive these sex differences, as well as the long-term effects of alcohol and nicotine vapor use.

Blood brain barrier dysfunction caused by repeated Endothelin-1 injection leads to irreversible memory impairment.

Vascular dysfunction is being increasingly recognized as a major contributor to dementia burden. Repeated occurrence of vascular insults in small vessels results in Blood Brain Barrier (BBB) dysfunction potentially contributing to cognitive impairments. The small vessel infracts is seen as white matter hyperintensities in MRI of many patients. Postmortem studies have shown BBB damage in dementia including AD and accumulation blood-derived proteins as well as loss of BBB associated cells like pericytes. In view of such a scenario we wanted to establish an animal model to study multiple small vessel insults impacting BBB leading to learning and memory deficits. C57/BL6J mice aged 4-5 months was implanted with cannula on left side of the hemisphere. ET-1 (Endothelin- 1), a 21 amino acid vasoconstricting peptide was infused through guide cannula into the intracerebroventricular space of lateral ventricle. Mice were injected for 3 doses of ET-1 at intervals of 3 weeks over a period of 9 weeks. The animals were assessed for associative learning and spatial memory deficits with different behavioral task. Animals were perfused and brain was processed for immunohistochemistry to assess vascular pathology. To simulate the clinical conditions the animals were injected over a period of three weeks to make sure that animal completely recovers from first vascular insult and then subsequent insults were given. There was BBB leakage, discrepancies in the blood vessel integrity and loss of pericytes after multiple ET-1 injection. Further there was significant memory deficits in novel object task, contextual fear conditioning test and Morris water maze. Our results demonstrated that chronic vascular insults cause BBB dysfunction and cognitive deficits seen as memory impairment. We were able to establish that repeated vasoconstriction by ET-1 in small vessels leads to BBB breach resulting in irreversible learning and memory deficits. This animal model could help us to study molecular underpinnings of white matter hyperintensities.

Persistent exercise fatigue and associative learning deficits in combination with transient glucose dyshomeostasis in a mouse model of Gulf War Illness

AimsTo characterize exercise fatigue, metabolic phenotype and cognitive and mood deficits correlated with brain neuroinflammatory and gut microbiome changes in a chronic Gulf War Illness (GWI) mouse model. The latter have been described in an accompanying paper [1]. Main methodsAdult male C57Bl/6N mice were exposed for 28 days (5 days/week) to pyridostigmine bromide: 6.5 mg/kg, b.i.d., P.O. (GW1) or 8.7 mg/kg, q.d., P.O. (GW2); topical permethrin (1.3 mg/kg in 100% DMSO) and N,N-diethyl-meta-toluamide (DEET 33% in 70% EtOH) and restraint stress (5 min). Exercise, metabolic and behavioral endpoints were compared to sham stress control (CON/S). Key findingsRelative to CON/S, GW2 presented persistent exercise intolerance (through post-treatment (PT) day 161), deficient associative learning/memory, and transient insulin insensitivity. In contrast to GW2, GW1 showed deficient long-term object recognition memory, milder associative learning/memory deficit, and behavioral despair. SignificanceOur findings demonstrate that GW chemicals dose-dependently determine the presentation of exercise fatigue and severity/type of cognitive/mood-deficient phenotypes that show persistence. Our comprehensive mouse model of GWI recapitulates the major multiple symptom domains characterizing GWI, including fatigue and cognitive impairment that can be used to more efficiently develop diagnostic tests and curative treatments for ill Gulf War veterans.

Multimodal mechanisms of human socially reinforced learning across neurodegenerative diseases.

Social feedback can selectively enhance learning in diverse domains. Relevant neurocognitive mechanisms have been studied mainly in healthy persons, yielding correlational findings. Neurodegenerative lesion models, coupled with multimodal brain measures, can complement standard approaches by revealing direct multidimensional correlates of the phenomenon.To this end, we assessed socially reinforced and non-socially reinforced learning in 40 healthy participants as well as persons with behavioural variant frontotemporal dementia (n = 21), Parkinson’s disease (n = 31) and Alzheimer’s disease (n = 20). These conditions are typified by predominant deficits in social cognition, feedback-based learning and associative learning, respectively, although all three domains may be partly compromised in the other conditions. We combined a validated behavioural task with ongoing EEG signatures of implicit learning (medial frontal negativity) and offline MRI measures (voxel-based morphometry).In healthy participants, learning was facilitated by social feedback relative to non-social feedback. In comparison with controls, this effect was specifically impaired in behavioural variant frontotemporal dementia and Parkinson’s disease, while unspecific learning deficits (across social and non-social conditions) were observed in Alzheimer’s disease. EEG results showed increased medial frontal negativity in healthy controls during social feedback and learning. Such a modulation was selectively disrupted in behavioural variant frontotemporal dementia. Neuroanatomical results revealed extended temporo-parietal and fronto-limbic correlates of socially reinforced learning, with specific temporo-parietal associations in behavioural variant frontotemporal dementia and predominantly fronto-limbic regions in Alzheimer’s disease. In contrast, non-socially reinforced learning was consistently linked to medial temporal/hippocampal regions. No associations with cortical volume were found in Parkinson’s disease. Results are consistent with core social deficits in behavioural variant frontotemporal dementia, subtle disruptions in ongoing feedback-mechanisms and social processes in Parkinson’s disease and generalized learning alterations in Alzheimer’s disease. This multimodal approach highlights the impact of different neurodegenerative profiles on learning and social feedback.Our findings inform a promising theoretical and clinical agenda in the fields of social learning, socially reinforced learning and neurodegeneration.

Age group differences in learning-related activity reflect task stage, not learning stage

Healthy aging is accompanied by declines in the ability to learn associations between events, even when their relationship cannot be described. Previous functional magnetic resonance imaging (fMRI) studies have attributed these implicit associative learning (IAL) deficits to differential engagement of the hippocampus and basal ganglia in older relative to younger adults in early and late stages of the task, respectively. However, these task stages have been confounded with age group differences in learning performance that emerge later and to a lesser degree in older adults. To disentangle the effects of task stage from learning stage (i.e., when there is significant evidence of learning) on age group differences in the neural substrates of IAL, we acquired fMRI data while 28 younger (20.8 ± 2.3 years) and 22 older (73.6 ± 6.8 years) healthy adults completed the Triplets Learning Task, in which the location of two cues predicted the location of a target with high (HF) or low (LF) frequency. When matched for task stage, results revealed worse learning performance and increased IAL-related activity in the hippocampus during the early stage and in the globus pallidum during the late stage in older relative to younger adults. However, when matched for learning stage, there were no significant age group differences in learning performance or IAL-related activity. Thus, although learning emerges later for older adults, they are engaging similar brain regions as younger adults when learning the associations, suggesting that previous reports of age group differences reflect effects of age on task stage, but not learning stage.

Associative Learning Requires Neurofibromin to Modulate GABAergic Inputs to Drosophila Mushroom Bodies.

Cognitive dysfunction is among the hallmark symptoms of Neurofibromatosis 1, and accordingly, loss of the Drosophila melanogaster ortholog of Neurofibromin 1 (dNf1) precipitates associative learning deficits. However, the affected circuitry in the adult CNS remained unclear and the compromised mechanisms debatable. Although the main evolutionarily conserved function attributed to Nf1 is to inactivate Ras, decreased cAMP signaling on its loss has been thought to underlie impaired learning. Using mixed sex populations, we determine that dNf1 loss results in excess GABAergic signaling to the central for associative learning mushroom body (MB) neurons, apparently suppressing learning. dNf1 is necessary and sufficient for learning within these non-MB neurons, as a dAlk and Ras1-dependent, but PKA-independent modulator of GABAergic neurotransmission. Surprisingly, we also uncovered and discuss a postsynaptic Ras1-dependent, but dNf1-independnet signaling within the MBs that apparently responds to presynaptic GABA levels and contributes to the learning deficit of the mutants.

Gulf War Agent Exposure Causes Dose‐Dependent Impairment of Memory Formation and Exercise Intolerance in a Mouse Model of Gulf War Illness

Gulf War Illness (GWI) is a chronic multi-symptom condition that still affects a third of veterans who served in the 1991 Persian Gulf War (GW). Latently-emerging and persistent symptoms fall into 5 general domains: neurological/cognition/mood, muscle/joint pain, respiratory, gastrointestinal disturbances and especially chronic fatigue. In particular, veterans exhibit CNS deficits in the neuropsychological domains of visuospatial abilities, attention/executive functioning, and learning/memory. GWI remains untreated due its poorly understood etiology and pathophysiology. It is suggested that GWI is a result of continuous exposure of military personnel to GW agents (pyridostigmine bromide, (PB), permethrin (PER), diethyltoluamide (DEET) and deployment/combat stress. To further investigate the cognitive manifestations of GWI pathophysiology, we studied the effects of chronic GW agent exposure in adult C57Bl/6N males utilizing a repeated measures design. The dosing paradigm consisted of 5 d/week for 28d of exposure to two doses of PB (6.5 mg/kg/d, 2x/d and 8.7 mg/kg/d, 1x/d; po), PER (1.3 mg/kg/d; top) in 70% ETOH, DEET (1650 mg/kg/d in DMSO) and stress 5 min/d (n=5–7/group). Two controls were included: sham (saline po, 70% ETOH and DMSO top) and sham/stress. Behavioral endpoints were measured at different timepoints post treatment (PT) up to PT160d. The 8.7 mg/kg/d dose was more effective in modeling cognitive deficits on the passive avoidance test since this group failed to avoid the aversive dark chamber at the 24h, and 7d and/or 3d retention timepoints at PT70. A repeat test at PT120 indicated that the 8.7 and sham/stress (P<.01) but not the 6.5 mg/kg/d group displayed retention of emotional reactivity memory at all test timepoints. In the novel object recognition test, performed at PT17, GW groupsbut not sham/stress displayed deficient memory retention at 24h (P<.01). On the Barnes Maze, no GW exposure effects on reference memory were noted during acquisition training nor a 24h acquisition probe trial. Since the neuropsychological deficits seen in GW chemical exposures can be exacerbated by comorbid mood-related conditions, animals were tested for anxiety and depression but no GW-specific effects were found. To model chronic fatigue, using a 5-day exercise endurance test we found that 8.7 mg/kg/d showed decreased latency to exhaustion at PT23 and PT161 compared to sham/stress (P<.05, P<.01). This effect could not be attributed to problems with motor coordination as measured on Suok and rotarod tests. In summary, the GW agent exposure paradigm produces specific cognitive deficits in associative aversive learning and novel object recognition memory but not visuospatial (reference) memory. GW agents also cause mice to tire faster during exercise without deficits in motor coordination. This animal model may be useful in examining common mechanisms underlying deficient cognitive performance and chronic fatigue in GWI.

Transgenic mice with an R342X mutation in Phf6 display clinical features of Börjeson-Forssman-Lehmann Syndrome.

The PHF6 mutation c.1024C > T; p.R342X, is a recurrent cause of Börjeson-Forssman-Lehmann Syndrome (BFLS), a neurodevelopmental disorder characterized by moderate-severe intellectual disability, truncal obesity, gynecomastia, hypogonadism, long tapering fingers and large ears (MIM#301900). Here, we generated transgenic mice with the identical substitution (R342X mice) using CRISPR technology. We show that the p.R342X mutation causes a reduction in PHF6 protein levels, in both human and mice, from nonsense-mediated decay and nonsense-associated alternative splicing, respectively. Magnetic resonance imaging studies indicated that R342X mice had a reduced brain volume on a mixed genetic background but developed hydrocephaly and a high incidence of postnatal death on a C57BL/6 background. Cortical development proceeded normally, while hippocampus and hypothalamus relative brain volumes were altered. A hypoplastic anterior pituitary was also observed that likely contributes to the small size of the R342X mice. Behavior testing demonstrated deficits in associative learning, spatial memory and an anxiolytic phenotype. Taken together, the R342X mice represent a good preclinical model of BFLS that will allow further dissection of PHF6 function and disease pathogenesis.

Inhibition of mTOR signaling by genetic removal of p70 S6 kinase 1 increases anxiety-like behavior in mice

The mechanistic target of rapamycin (mTOR) is a ubiquitously expressed kinase that acts through two complexes, mTORC1 and mTORC2, to regulate protein homeostasis, as well as long lasting forms of synaptic and behavioral plasticity. Alteration of the mTOR pathway is classically involved in neurodegenerative disorders, and it has been linked to dysregulation of cognitive functions and affective states. However, information concerning the specific involvement of the p70 S6 kinase 1 (S6K1), a downstream target of the mTORC1 pathway, in learning and memory processes and in the regulation of affective states remains scant. To fill this gap, we exposed adult male mice lacking S6K1 to a battery of behavioral tests aimed at measuring their learning and memory capabilities by evaluating reference memory and flexibility with the Morris water maze, and associative memory using the contextual fear conditioning task. We also studied their anxiety-like and depression-like behaviors by, respectively, performing elevated plus maze, open field, light-dark emergence tests, and sucrose preference and forced swim tests. We found that deleting S6K1 leads to a robust anxious phenotype concomitant with associative learning deficits; these symptoms are associated with a reduction of adult neurogenesis and neuronal atrophy in the hippocampus. Collectively, these results provide grounds for the understanding of anxiety reports after treatments with mTOR inhibitors and will be critical for developing novel compounds targeting anxiety.

Single bilateral injection of endothelin‐1 leads to temporary deficits in memory and synaptic dysfunction

AbstractBackgroundCerebral small vessel disease (SVD) has gained prominence worldwide as a major factor for cognitive impairment seen in dementia. Micro infracts causing elusive changes in cognitive function clinically will not get diagnosed are found to be the main risk factor for SVD. We were interested in creating micro infarcts rather than a severe insult to replicate small vessel damage, so we opted for Intra cerebroventricular (ICV) bilateral stereotaxic injection of endothelin‐1 (ET‐1) into lateral ventricles. Sub cortical injections of ET‐1 in brain has been used in many studies to accomplish long lasting vasoconstriction and gradual reperfusion causing lesion. Therefore, we tried to overcome this by injecting into lateral ventricles allowing it to spread through cerebrospinal fluid.MethodET‐1 (Endothelin‐ 1) a 21 amino acid vasoconstricting peptide was injected bilaterally into lateral ventricles of C57 mice. Some animals were injected unilaterally to see whether there are any motor deficits. Expression of CD31, a marker of endothelial cells was done by immunohistochemistry to assess vasoconstriction. Contextual fear conditioning, object recognition and Morris water maze task was performed to examine associative learning and spatial memory deficits. Gait and rotarod was performed to examine if there are any motor deficits. Synaptic plasticity was evaluated as activity dependent protein translation was measured in synaptoneurosomes prepared from hippocampus.ResultThe obstruction in cerebral blood flow due to vasoconstriction caused by ET‐1 injection leads to deficits in associative learning and spatial memory after 7 days. There was no change in gait or rotarod performance indicating no effect on motor function. However, the behavioral dysfunction was temporary and reversed after 30 days of ET‐1 treatment once the blood flow was restored. These changes were demonstrated as drop in the activity dependent protein translation after 7 days of ET‐1 injection and raise after 30 days of treatment as it is an indicator for synaptic plasticity.ConclusionBilateral injection of ET‐1 leads to prominent associative and spatial memory deficit and decline in activity dependent protein translation in hippocampus. Still these defects are reversible once the blood flow is restored. Unilateral injection of ET‐1 did not show any motor dysfunction.