Impact Forces and Patterns of Axonal Injury Differ Between Two Models of TBI

Traumatic brain injury (TBI) affects approximately 3.8 million Americans a year and results in complex neuropathological and neurocognitive sequelae. Animal models of TBI attempt to replicate the impact forces and pathology of injury in humans. However, in these models, the forces generated at the time of impact are poorly understood. Nonetheless, a variety of shear and strain forces generated at the time of impact can produce diffuse axonal injury. Injury to axons and neurons across a variety of brain regions resulting from axonal injury underlies the cognitive and behavioral impairments observed after TBI. Three critical brain regions, the corpus callosum (CC), cerebellum (Cb), and the locus coeruleus (LC), are critical for interhemispheric communication, motor coordination, and regulation of higher cognitive function. However, axonal injury in these brain regions is poorly studied across animal injury models. To address these gaps in our knowledge, we determined head acceleration forces generated in two common experimental TBI models and quantified patterns of neuronal injury markers in the CC, Cb, and LC produced by these models. Specifically, a closed head-electronic controlled cortical impact (CH-eCCI) model and a frontal- impact Maryland weight drop (MWD) model were used to compare different impact trajectories. Force data were correlated with neurosilver stain markers to identify injured fibers and cell bodies of injured neurons. We found that g-force increased with both higher CH-eCCI impact velocities and vertical impact depth. Similarly, acceleration forces increased with higher drop heights and horizontal impact throw in the MWD model. G-force measurements exceeded device limits (400Gs) before standard laboratory parameters for mild or moderate CH-eCCI could be evaluated (i.e., 2.5 mm or 3.5 mm @ 5.5m/s). Neurosilver labeling of axonal injury in the CC, Cb, and LC after CH-eCCI injury was found to be dependent on the severity of injury. Although there was a clear relationship between injury severity and silver staining in the CC and Cb, more data is needed to determine whether the same relationship exists for labeling in the LC. These studies suggest that in these animal models, acceleration g-forces are 4-8 fold higher than those found in sports-related injuries (i.e.90-100Gs). Furthermore, axonal injury in the Cb and LC may be a critical contributor to the motor and cognitive deficits reported following injury

Psychostimulants as Cognitive Enhancers: The Prefrontal Cortex, Catecholamines and Attention Deficit Hyperactivity Disorder

Psychostimulants exert behavioral-calming and cognition-enhancing actions in the treatment of attention deficit hyperactivity disorder (ADHD). Contrary to early views, extensive research demonstrates that these actions are not unique to ADHD. Specifically, when administered at low and clinically-relevant doses, psychostimulants improve a variety of behavioral and cognitive processes dependent on the prefrontal cortex (PFC) in subjects with and without ADHD. Despite the longstanding clinical use of these drugs, the neural mechanisms underlying their cognition-enhancing/therapeutic actions have only recently begun to be examined. At behaviorally-activating doses, psychostimulants produce large and widespread increases in extracellular levels of brain catecholamines. In contrast, cognition-enhancing doses of psychostimulants exert regionally-restricted actions, elevating extracellular catecholamine levels and enhancing neuronal signal processing preferentially within the PFC. Additional evidence suggests a prominent role of PFC α2- and D1 receptors in the behavioral and electrophysiological actions of low-dose psychostimulants. These and other observations indicate a pivotal role of PFC catecholamines in the cognition-enhancing and therapeutic actions of psychostimulants as well as other drugs used in the treatment of ADHD. This information may be particularly relevant for the development of novel pharmacological treatments for ADHD and other conditions associated with PFC dysregulation

Locus ceruleus regulates sensory encoding by neurons and networks in waking animals

Substantial evidence indicates that the locus ceruleus (LC)–norepinephrine (NE) projection system regulates behavioral state and state-dependent processing of sensory information. Tonic LC discharge (0.1–5.0 Hz) is correlated with levels of arousal and demonstrates an optimal firing rate during good performance in a sustained attention task. In addition, studies have shown that locally applied NE or LC stimulation can modulate the responsiveness of neurons, including those in the thalamus, to nonmonoaminergic synaptic inputs. Many recent investigations further indicate that within sensory relay circuits of the thalamus both general and specific features of sensory information are represented within the collective firing patterns of like-modality neurons. However, no studies have examined the impact of NE or LC output on the discharge properties of ensembles of functionally related cells in intact, conscious animals. Here, we provide evidence linking LC neuronal discharge and NE efflux with LC-mediated modulation of single-neuron and neuronal ensemble representations of sensory stimuli in the ventral posteriomedial thalamus of waking rats. As such, the current study provides evidence that output from the LC across a physiologic range modulates single thalamic neuron responsiveness to synaptic input and representation of sensory information across ensembles of thalamic neurons in a manner that is consistent with the well documented actions of LC output on cognition

Prefrontal Corticotropin-Releasing Factor (CRF) Neurons Act Locally to Modulate Frontostriatal Cognition and Circuit Function.

The PFC and extended frontostriatal circuitry support higher cognitive processes that guide goal-directed behavior. PFC-dependent cognitive dysfunction is a core feature of multiple psychiatric disorders. Unfortunately, a major limiting factor in the development of treatments for PFC cognitive dysfunction is our limited understanding of the neural mechanisms underlying PFC-dependent cognition. We recently demonstrated that activation of corticotropin-releasing factor (CRF) receptors in the caudal dorsomedial PFC (dmPFC) impairs higher cognitive function, as measured in a working memory task. Currently, there remains much unknown about CRF-dependent regulation of cognition, including the source of CRF for cognition-modulating receptors and the output pathways modulated by these receptors. To address these issues, the current studies used a viral vector-based approach to chemogenetically activate or inhibit PFC CRF neurons in working memory-tested male rats. Chemogenetic activation of caudal, but not rostral, dmPFC CRF neurons potently impaired working memory, whereas inhibition of these neurons improved working memory. Importantly, the cognition-impairing actions of PFC CRF neurons were dependent on local CRF receptors coupled to protein kinase A. Additional electrophysiological recordings demonstrated that chemogenetic activation of caudal dmPFC CRF neurons elicits a robust degradation of task-related coding properties of dmPFC pyramidal neurons and, to a lesser extent, medium spiny neurons in the dorsomedial striatum. Collectively, these results demonstrate that local CRF release within the caudal dmPFC impairs frontostriatal cognitive and circuit function and suggest that CRF may represent a potential target for treating frontostriatal cognitive dysfunction

Antenatal nutritional supplementation and autism spectrum disorders in the Stockholm youth cohort:population based cohort study

Abstract Objective To determine whether nutritional supplementation during pregnancy is associated with a reduced risk of autism spectrum disorder (ASD) with and without intellectual disability in offspring. Design Observational prospective cohort study using multivariable logistic regression, sibling controls, and propensity score matching. Setting Stockholm County, Sweden. Participants 273 107 mother-child pairs identified through population registers. The study sample was restricted to children who were aged 4 to 15 years by the end of follow-up on 31 December 2011 and were born between 1996 and 2007. Exposures Multivitamin, iron, and folic acid supplement use was reported at the first antenatal visit. Main outcome measure Diagnosis of ASD with and without intellectual disability in children determined from register data up to 31 December 2011. Results Prevalence of ASD with intellectual disability was 0.26% (158 cases in 61 934) in the maternal multivitamin use group and 0.48% (430 cases in 90 480) in the no nutritional supplementation use group. Maternal multivitamin use with or without additional iron or folic acid, or both was associated with lower odds of ASD with intellectual disability in the child compared with mothers who did not use multivitamins, iron, and folic acid (odds ratio 0.69, 95% confidence interval 0.57 to 0.84). Similar estimates were found in propensity score matched (0.68, 0.54 to 0.86) and sibling control (0.77, 0.52 to 1.15) matched analyses, though the confidence interval for the latter association included 1.0 and was therefore not statistically significant. There was no consistent evidence that either iron or folic acid use were inversely associated with ASD prevalence. Conclusions Maternal multivitamin supplementation during pregnancy may be inversely associated with ASD with intellectual disability in offspring. Further scrutiny of maternal nutrition and its role in the cause of autism is recommended. </jats:sec

Overt Visual Attention as a Causal Factor of Perceptual Awareness

Our everyday conscious experience of the visual world is fundamentally shaped by the interaction of overt visual attention and object awareness. Although the principal impact of both components is undisputed, it is still unclear how they interact. Here we recorded eye-movements preceding and following conscious object recognition, collected during the free inspection of ambiguous and corresponding unambiguous stimuli. Using this paradigm, we demonstrate that fixations recorded prior to object awareness predict the later recognized object identity, and that subjects accumulate more evidence that is consistent with their later percept than for the alternative. The timing of reached awareness was verified by a reaction-time based correction method and also based on changes in pupil dilation. Control experiments, in which we manipulated the initial locus of visual attention, confirm a causal influence of overt attention on the subsequent result of object perception. The current study thus demonstrates that distinct patterns of overt attentional selection precede object awareness and thereby directly builds on recent electrophysiological findings suggesting two distinct neuronal mechanisms underlying the two phenomena. Our results emphasize the crucial importance of overt visual attention in the formation of our conscious experience of the visual world