Debora Cutuli

On whether the environmental enrichment may provide cognitive and brain reserves

The construct of brain and cognitive reserves holds that cognitive enrichment fosters the development of neuroplasticity properties, which permit normal cognitive functioning even in the presence of brain pathology. Interpreting the experience-dependent increase of neuronal connectivity and efficiency in the light of the reserve theory provides an interesting approach for explaining the maintenance of cognitive function observed in some subjects affected by neurodegenerative disorders. In fact, mental and physical engagement with complex environments strengthens synaptic connectivity and provides the means by which preexisting neuronal networks are efficiently utilized and alternative networks are recruited to meet environmental demands and to cope with brain damage. There is considerable interest in determining the biological factors that allow the development of these reserves. To investigate these factors, it is possible to model situations of environmental enrichment in animals that parallel human cognitive enrichment. Experimental findings indicate that early onset and extended housing in an environment with enhanced sensorimotor, cognitive, and social stimulations results in significant changes in brain biochemistry, synaptic connectivity, and neuronal function in enriched animals. These changes provide the groundwork for the improvement of behavioral performance and maintenance of performance following brain damage. As this is the fundamental assumption of the reserve hypothesis, it is possible that as human educational attainment and occupational status, environmental enrichment develops reserves to be spent in the case of a subsequent lesion.

A single intraperitoneal injection of endotoxin in rats induces long-lasting modifications in behavior and brain protein levels of TNF-α and IL-18

BackgroundSystemic inflammation might cause neuronal damage and sustain neurodegenerative diseases and behavior impairment, with the participation of pro-inflammatory cytokines, like tumor necrosis factor (TNF)-α and interleukin (IL)-18. However, the potential contribution of these cytokines to behavioral impairment in the long-term period has not been fully investigated.MethodsWistar rats were treated with a single intraperitoneal injection of LPS (5 mg/kg) or vehicle. After 7 days and 10 months, the animal behavior was evaluated by testing specific cognitive functions, as mnesic, discriminative, and attentional functions, as well as anxiety levels. Contextually, TNF-α and IL-18 protein levels were measured by ELISA in defined brain regions (that is, frontal cortex, hippocampus, striatum, cerebellum, and hypothalamus).ResultsBehavioral testing demonstrated a specific and persistent cognitive impairment characterized by marked deficits in reacting to environment modifications, possibly linked to reduced motivational or attentional deficits. Concomitantly, LPS induced a TNF-α increase in the hippocampus and frontal cortex (from 7 days onward) and cerebellum (only at 10 months). Interestingly, LPS treatment enhanced IL-18 expression in these same areas only at 10 months after injection.ConclusionsOverall, these results indicate that the chronic neuroinflammatory network elicited by systemic inflammation involves a persistent participation of TNF-α accompanied by a differently regulated contribution of IL-18. This leads to speculation that, though with still unclear mechanisms, both cytokines might take part in long-lasting modifications of brain functions, including behavioral alteration.

n-3 polyunsaturated fatty acids supplementation enhances hippocampal functionality in aged mice

As major components of neuronal membranes, omega-3 polyunsaturated acids (n-3 PUFA) exhibit a wide range of regulatory functions, modulating from synaptic plasticity to neuroinflammation, from oxidative stress to neuroprotection. Recent human and animal studies indicated the n-3 PUFA neuroprotective properties in aging, with a clear negative correlation between n-3 PUFA levels and hippocampal deficits. The present multidimensional study was aimed at associating cognition, hippocampal neurogenesis, volume, neurodegeneration and metabolic correlates to verify n-3 PUFA neuroprotective effects in aging. To this aim 19 month-old mice were given n-3 PUFA mixture, or olive oil or no dietary supplement for 8 weeks during which hippocampal-dependent mnesic functions were tested. At the end of behavioral testing morphological and metabolic correlates were analyzed. n-3 PUFA supplemented aged mice exhibited better object recognition memory, spatial and localizatory memory, and aversive response retention, without modifications in anxiety levels in comparison to controls. These improved hippocampal cognitive functions occurred in the context of an enhanced cellular plasticity and a reduced neurodegeneration. In fact, n-3 PUFA supplementation increased hippocampal neurogenesis and dendritic arborization of newborn neurons, volume, neuronal density and microglial cell number, while it decreased apoptosis, astrocytosis and lipofuscin accumulation in the hippocampus. The increased levels of some metabolic correlates (blood Acetyl-L-Carnitine and brain n-3 PUFA concentrations) found in n-3 PUFA supplemented mice also pointed toward an effective neuroprotection. On the basis of the present results n-3 PUFA supplementation appears to be a useful tool in health promotion and cognitive decline prevention during aging.

Dopamine neuronal loss contributes to memory and reward dysfunction in a model of Alzheimer’s disease

Alterations of the dopaminergic (DAergic) system are frequently reported in Alzheimers disease (AD) patients and are commonly linked to cognitive and non-cognitive symptoms. However, the cause of DAergic system dysfunction in AD remains to be elucidated. We investigated alterations of the midbrain DAergic system in the Tg2576 mouse model of AD, overexpressing a mutated human amyloid precursor protein (APPswe). Here, we found an age-dependent DAergic neuron loss in the ventral tegmental area (VTA) at pre-plaque stages, although substantia nigra pars compacta (SNpc) DAergic neurons were intact. The selective VTA DAergic neuron degeneration results in lower DA outflow in the hippocampus and nucleus accumbens (NAc) shell. The progression of DAergic cell death correlates with impairments in CA1 synaptic plasticity, memory performance and food reward processing. We conclude that in this mouse model of AD, degeneration of VTA DAergic neurons at pre-plaque stages contributes to memory deficits and dysfunction of reward processing.

Linking novelty seeking and harm avoidance personality traits to cerebellar volumes

Personality traits are multidimensional traits comprising cognitive, emotional, and behavioral characteristics, and a wide array of cerebral structures mediate individual variability. Differences in personality traits covary with brain morphometry in specific brain regions, and neuroimaging studies showed structural or functional abnormalities of cerebellum in subjects with personality disorders, suggesting a cerebellar role in affective processing and an effect on personality characteristics. To test the hypothesis that cerebellar [white matter (WM) and cortex] volumes are correlated with scores obtained in the four temperamental scales of the Temperament and Character Inventory (TCI) by Cloninger, a total of 125 healthy participants aged 18–67 years of both genders (males = 52) completed the TCI and underwent magnetic resonance imaging. The scores obtained in each temperamental scale were associated with the volumes of cerebellar WM and cortex of right and left hemispheres separately by using linear regression analyses. In line with our hypothesis, novelty seeking (NS) scores were positively associated with WM and cortex cerebellar volumes. Harm avoidance (HA) scores were negatively associated with WM and cortex cerebellar volumes. The range of individual differences in NS and HA scores reflects the range of variances of cerebellar volumes. The present data indicating a cerebellar substrate for some personality traits extend the relationship between personality and brain areas to a structure up to now thought to be involved mainly in motor and cognitive functions, much less in emotional processes and even less in personality individual differences. Hum Brain Mapp 35:285–296, 2014.

Enriched environment improves motor function and increases neurotrophins in hemicerebellar lesioned rats.

Background. Environmental enrichment (EE) defined as “a combination of complex inanimate and social stimulation” influences brain function and anatomy by enhancing sensory, cognitive, motor, and social stimulation. The beneficial effects of EE in the presence of brain damage have been partially attributed to upregulation of neurotrophins, proteins involved in neuronal survival and in activity-dependent plasticity. Objective. The authors tested the hypothesis that EE may have advantageous effects on recovery of motor function after cerebellar damage, associated with changes in local neurotrophin production. Methods. They performed a hemicerebellectomy in rats previously exposed to EE or reared in standard conditions. The time course of compensation of motor symptoms was analyzed in both lesioned groups. Then, the local production of the nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) in the spared hemicerebellum and other extracerebellar regions was evaluated. Results. Long-term exposure to EE accelerated the motor recovery in hemicerebellectomized rats and elicited an increase in NGF levels in the spared hemicerebellum, as compared with nonenriched lesioned and control rats. BDNF levels were higher in hemicerebellectomized rats but not influenced by EE. In the frontal cortex, both NGF and BDNF levels were upregulated in hemicerebellectomized enriched rats as compared with hemicerebellectomized nonenriched and control rats. Conclusions. This study suggests that the beneficial effects of EE on motor symptoms after cerebellar damage may be, at least partly, because of modulation of neurotrophic proteins involved in the regeneration processes.

Cognitive performances of cholinergically depleted rats following chronic donepezil administration

Since acute and chronic administration of the acetylcholinesterase inhibitors, namely donepezil, improves cognitive functions in patients afflicted by mild to moderate dementia and reverses memory deficits in experimental models of learning and memory, it seemed interesting to assess the effects of chronic donepezil treatment on cognitive functions in adult rats with forebrain cholinergic depletion. Lesions were performed by means of intracerebroventricular injections of the immunotoxin 192 IgG-saporin. The cognitive functions of lesioned animals treated or not treated with donepezil were compared with those of intact animals. Cholinergic depletion affected working memory functions, weakened procedural competencies, affected the acquisition of localizing knowledge, and evoked remarkable compulsive and perseverative behaviors. In lesioned animals, chronic donepezil treatment ameliorated localizatory capabilities, performances linked to cognitive flexibility and procedural abilities. Furthermore, it attenuated compulsive deficits. The present data indicate positive effects of chronic donepezil treatment on specific cognitive performances, suggesting that an aimed use of acetylcholinesterase inhibitors, targeting some symptoms more than others, may be beneficial in the case of cholinergic hypofunction. The animal model used in the present research may provide an efficient method for analyzing cognition-enhancing drugs before clinical trials.

New evidence for the cerebellar involvement in personality traits

Following the recognition of its role in sensory-motor coordination and learning, the cerebellum has been involved in cognitive, emotional, and even personality domains. This study investigated the relationships between cerebellar macro- and micro-structural variations and temperamental traits measured by Temperament and Character Inventory (TCI). High resolution T1-weighted, and Diffusion Tensor Images of 100 healthy subjects aged 18–59 years were acquired by 3 Tesla Magnetic Resonance scanner. In multiple regression analyses, cerebellar Gray Matter (GM) or White Matter (WM) volumes, GM Mean Diffusivity (MD), and WM Fractional Anisotropy (FA) were used as dependent variables, TCI scores as regressors, gender, age, and education years as covariates. Novelty Seeking scores were associated positively with the cerebellar GM volumes and FA, and negatively with MD. No significant association between Harm Avoidance, Reward Dependence or Persistence scores and cerebellar structural measures was found. The present data put toward a cerebellar involvement in the management of novelty.

Exposure to an Enriched Environment Accelerates Recovery from Cerebellar Lesion

The exposure to enriched environments allows the maintenance of normal cognitive functioning even in the presence of brain pathology. Up until now, clinical and experimental studies have investigated environmental effects mainly on the symptoms linked to the presence of neuro-degenerative diseases, and no study has yet analyzed whether prolonged exposure to complex environments allows modifying the clinical expression and compensation of deficits of cerebellar origin. In animals previously exposed to complex stimulations, the effects of cerebellar lesions have been analyzed to verify whether a prolonged and intense exposure to complex stimulations affected the compensation of motor and cognitive functions following a cerebellar lesion. Hemicerebellectomized or intact animals housed in enriched or standard conditions were administered spatial tests. Postural asymmetries and motor behavior were also assessed. Exposure to the enriched environment almost completely compensated the effects of the hemicerebellectomy. In fact, the motor and cognitive performances of the enriched hemicerebellectomized animals were similar to those of the intact animals. The plastic changes induced by enhanced mental and physical activity seem to provide the development of compensatory responses against the disrupting motor and cognitive consequences of the cerebellar damage.

Before or after does it matter? Different protocols of environmental enrichment differently influence motor, synaptic and structural deficits of cerebellar origin

Cerebellar compensation is a reliable model of lesion-induced plasticity occurring through profound synaptic and neurochemical modifications in cortical and sub-cortical regions. As the recovery from cerebellar deficits progresses, the firstly enhanced glutamate striatal transmission is then normalized. The time course of cerebellar compensation and the concomitant striatal modifications might be influenced by protocols of environmental enrichment (EE) differently timed in respect to cerebellar lesion. In the present study, we analyzed the effects of different EE protocols on postural and locomotor behaviors (by means of a neurological rating scale), and on striatal synaptic activity (by means of recordings of spontaneous glutamate-mediated excitatory postsynaptic currents (sEPSCs)) and on morphological correlates (by means of density and dendritic length of Fast Spiking (FS) interneurons) following hemicerebellectomy (HCb) in rats. Cerebellar motor deficits were reduced faster in the enriched animals in comparison to standard housed HCbed rats. The beneficial influence of EE was higher in the animals enriched before the HCb than in rats enriched only after the lesion. In parallel, the HCb-induced increase in striatal sEPSCs was not observed in rats enriched before HCb and attenuated in rats enriched after HCb. Furthermore, the EE prevented the shrinkage of dendritic arborization of FS striatal interneurons. Also this effect was more marked in animals enriched before than after the HCb. The exposure to EE exerted either neuro-protective or therapeutic actions on the cerebellar deficits. The experience-dependent changes of the synaptic and neuronal connectivity observed in the striatal neurons may represent one of the mechanisms through which the enrichment facilitates functional compensation following the cerebellar damage.