Caroline Chambon

Visual and Visuospatial Short-Term Memory in Mild Cognitive Impairment and Alzheimer Disease: Role of Attention.

It has been proposed that visual recognition memory and certain attentional mechanisms are impaired early in Alzheimer disease (AD). Little is known about visuospatial recognition memory in AD. The crucial role of the hippocampus on spatial memory and its damage in AD suggest that visuospatial recognition memory may also be impaired early. The aim of the present study was to evaluate which modality, i.e. visual or visuospatial, is more implicated in the early memory impairment in AD. First, to determine onset of memory impairment, we compared the performances of patients with AD to those with amnestic mild cognitive impairment (MCI). Second, to determine the relative contribution of attentional impairment on the performance of MCI and AD patients, we tested the influence of a distractor in the interval between the memory image and recognition tests. Results showed that visuospatial short-term deficits appear earlier than visual short-term ones. In addition to mnemonic deficits, results showed attentional deficiency in both MCI and AD patients. Deficits of performances in visual modality seemed of attentional origin whereas those of visuospatial modality seemed of memory origin. The combination of attentional and mnemonic evaluation is likely to be a promising approach to finding predictive markers that distinguish MCI patients that convert to AD.

Positive effects of computer-based cognitive training in adults with mild cognitive impairment

Considering the high risk for individuals with amnestic Mild Cognitive Impairment (A-MCI) to progress towards Alzheimers disease (AD), we investigated the efficacy of a non-pharmacological intervention, that is, cognitive training that could reduce cognitive difficulties and delay the cognitive decline. For this, we evaluated the efficacy of a 12-week computer-based memory-attention training program based on recognition in subjects with A-MCI and compared their performances with those of A-MCI controls trained in cognitively stimulating activities. The effect of training was assessed by comparing outcome measures in pre- and post-tests 15 days before and after training. To evaluate the duration of training benefits, a follow-up test session was performed 6 months after memory and attention training or cognitively stimulating activities. Outcome measures showed that the trained group, compared to control group, improved episodic recall and recognition. Six months after training, scores remained at the level of the post-test. Since the training program was exclusively based on recognition, our results showed a generalization from recognition to recall processes, which are memory components that represent part of the core cognitive impairments in individuals at risk of converting to AD. Thus, cognitive training based on recognition holds promise as a preventive therapeutic method and could be proposed as a non-pharmacological early-intervention strategy. Future investigations need to focus on methodological constraints and delineating possible neuroplastic mechanisms of action.

Neuroanatomical, sensorimotor and cognitive deficits in adult rats with white matter injury following prenatal ischemia

Perinatal brain injury including white matter damage (WMD) is highly related to sensory, motor or cognitive impairments in humans born prematurely. Our aim was to examine the neuroanatomical, functional and behavioral changes in adult rats that experienced prenatal ischemia (PI), thereby inducing WMD. PI was induced by unilateral uterine artery ligation at E17 in pregnant rats. We assessed performances in gait, cognitive abilities and topographical organization of maps, and neuronal and glial density in primary motor and somatosensory cortices, the hippocampus and prefrontal cortex, as well as axonal degeneration and astrogliosis in white matter tracts. We found WMD in corpus callosum and brainstem, and associated with the hippocampus and somatosensory cortex, but not the motor cortex after PI. PI rats exhibited mild locomotor impairments associated with minor signs of spasticity. Motor map organization and neuronal density were normal in PI rats, contrasting with major somatosensory map disorganization, reduced neuronal density, and a marked reduction of inhibitory interneurons. PI rats exhibited spontaneous hyperactivity in open‐field test and short‐term memory deficits associated with abnormal neuronal density in related brain areas. Thus, this model reproduces in adult PI rats the main deficits observed in infants with a perinatal history of hypoxia‐ischemia and WMD.

Behavioral Effects of Basal Forebrain Cholinergic Lesions in Young Adult and Aging Rats

The interactive effects of age and cholinergic damage were assessed behaviorally in young and middle-aged rats. Rats were lesioned at either 3 or 17 months of age by injection of 192 IgG-saporin immunotoxin into the medial septum and the nucleus basalis magnocellularis, and they were then tested on a range of behavioral tasks: a nonmatching-to-position task in a T-maze, an object-recognition task, an object-location task, and an open-field activity test. Depending on the task used, only an age or a lesion effect was observed, but there was no Age X Lesion interaction. Middle-aged and young rats responded to the cholinergic lesions in the same manner. These results show that in the middle-aged rats in which cholinergic transmission was affected, additional injury to the system was not always accompanied by major cognitive dysfunctions.

Benefits of Computer-Based Memory and Attention Training in Healthy Older Adults

Multifactorial cognitive training programs have a positive effect on cognition in healthy older adults. Among the age-sensitive cognitive domains, episodic memory is the most affected. In the present study, we evaluated the benefits on episodic memory of a computer-based memory and attention training. We targeted consciously controlled processes at encoding and minimizing processing at retrieval, by using more familiarity than recollection during recognition. Such an approach emphasizes processing at encoding and prevents subjects from reinforcing their own errors. Results showed that the training improved recognition performances and induced near transfer to recall. The largest benefits, however, were for tasks with high mental load. Improvement in free recall depended on the modality to recall; semantic recall was improved but not spatial recall. In addition, a far transfer was also observed with better memory self-perception and self-esteem of the participants. Finally, at 6-month follow up, maintenance of benefits was observed only for semantic free recall. The challenge now is to corroborate far transfer by objective measures of everyday life executive functioning.

Pro-Brain-Derived Neurotrophic Factor (proBDNF)-Mediated p75NTR Activation Promotes Depolarizing Actions of GABA and Increases Susceptibility to Epileptic Seizures.

The brain-derived neurotrophic factor (BDNF) is synthesized as a precursor, namely proBDNF, which can be processed into mature BDNF (mBDNF). Evidences suggest that proBDNF signaling through p75NTR may account for the emergence of neurological disorders. These findings support the view that the relative availability of mBDNF and proBDNF forms is an important mechanism underlying brain circuit formation and cognitive functions. Here we describe novel insights into the proBDNF/p75NTR mechanisms and function in vivo in modulating neuronal circuit and synaptic plasticity during the first postnatal weeks in rats. Our results showed that increased proBDNF/p75NTR signaling during development maintains a depolarizing γ-aminobutyric acid (GABA) response in a KCC2-dependent manner in mature neuronal cells. This resulted in altered excitation/inhibition balance and enhanced neuronal network activity. The enhanced proBDNF/p75NTR signaling ultimately led to increased seizure susceptibility that was abolished by in vivo injection of function blocking p75NTR antibody. Altogether, our study shed new light on how proBDNF/p75NTR signaling can orchestrate the GABA excitatory/inhibitory developmental sequence leading to depolarizing and excitatory actions of GABA in adulthood and subsequent epileptic disorders.

Molecular gene expression following blunt and rotational models of traumatic brain injury parallel injuries associated with stroke and depression

Traumatic brain injury (TBI) is associated with a collection of physical, emotional and cognitive post complications. The background for such complex consequences may be due to a number of different factors, and the nature of these changes indicates that the frontal lobes may be implicated. In this study we have employed gene expression arrays and gene ontology databases to search for possible similarities between different forms of acquired brain injuries in order to test whether molecular relationships exist between the different pathologies. Two types of experimental models for traumatic brain injuries, lateral fluid percussion and rotational acceleration, were used. Their molecular signature was identified and compared with those related to other rodent models simulating stress, depression, alcohol dependence, stroke, and Alzheimer’s disease. The data show that the two TBI models share similar gene expression changes with the models with regard to depression and stroke, indicating a common molecular support between these pathologies. The data provided can contribute to the introduction of new treatment strategies related to TBI.

Neuronal and Glial Changes in Rat Hippocampal Formation afterCholinergic Deafferentation

The effects of cholinergic insult were studied in the hippocampal formation of cholinergic lesioned rats at metabolic and cellular levels by in vivo nuclear magnetic resonance spectrometry and immuno-histochemical approaches. Cholinergic deafferentation was induced by injection of the cholinergic immunotoxin 192 IgG-saporin into the medial septum. The immunotoxin effects were tested at 3, 7, and 30 days post-lesion. Rats with cholinergic deafferentation of the hippocampus showed a lack of NeuN immunoreactivity cells, indicating neuronal loss in hippocampal formation. This neuronal loss was more pronounced in the dentate gyrus, underlining the greater sensitivity of this region to the cholinergic insult. Interestingly, this neuronal loss was not associated with metabolic alteration. These data suggest that the remaining neurons upregulated their functional activity, which would contribute to maintaining the relatively stable level of metabolites and memory abilities. No alteration in GFAP and OX42 immunostaining and in glutamine and myoionositol metabolite concentration was observed in the deafferented regions.SIRT1 is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase which regulates many physiological and pathological processes. Over the past decade, increasing attention has been paid to the wide distribution of SIRT1 in the eye and its important role in eye development. The short review summarized the most recent research in the study of SIRT1 related to eye development and its distribution in eye.