C. Zancada-Menendez

Effects of environmental enrichment on anxiety responses, spatial memory and cytochrome c oxidase activity in adult rats

We have studied the effect of an environmental enrichment (EE) protocol in adult Wistar rats on the activity in the elevated zero-maze (EZM), performance in the radial-arm water maze (RAWM) and we have also examined the changes in the neuronal metabolic activity of several brain regions related to anxiety response and spatial memory through cytochrome c oxidase histochemistry (COx). Our EE protocol had anxiolytic effect in the EZM; the animals spent more time and made more entries into the open quadrants, they had lower latency to enter into the open quadrant and lower levels of defecation. Also, the EE group showed fewer working memory and reference memory errors, as well as lesser distance travelled in the first day of the spatial training. In relation to the neuronal metabolic activity, EE reduced the COx activity in brain regions related to anxiety response, such as the infralimbic cortex, the paraventricular thalamic and hypothalamic nucleus, the basolateral amygdala, and the ventral hippocampus. Interestingly, there were no significant differences between groups in the dorsal hippocampus, more related to spatial cognition. These results suggest a beneficial effect of EE on spatial memory as a result of reducing anxiety levels and the COx activity in brain regions involved in anxiety response. We also found a differential pattern of activation inside the hippocampus, suggesting that the dorsal hippocampus has a preferential involvement in spatial learning and memory, whereas the ventral hippocampus has a role in anxiety response.

Effects of forced exercise on spatial memory and cytochrome c oxidase activity in aged rats

We have studied the effects of exercise in aged rats (18 months-old) on spatial learning and changes in neuronal metabolic activity associated with exercise program and the spatial learning process. The changes on neuronal oxidative metabolic activity was studied through cytochrome c oxidase histochemistry (COx) in brain regions related to spatial memory, reward, and motor activity after a forced exercise program on Rotarod. The spatial learning task was performed in the 4 arm-radial arm water maze (4-RAWM). Exercise program improved slightly the performance, with more percentage of entries into the correct arm along the days. Respect to COx activity, exercise increased the basal oxidative metabolism in frontal regions, such as motor, cingulate and retrosplenial cortex, and in central and basolateral amygdala. In the spatial memory task, the exercise group showed lower COx activity than the non-exercise group in prefrontal cortex, bed nucleus of the stria terminalis, amygdala, hippocampus, retrosplenial cortex, tegmental ventral area and supramammillary nucleus, but the neuronal activity increased in the motor cortex in exercised group. These results suggest that our exercise program produces a more accurate performance and it increased efficiency, because the exercise group had lower neuronal metabolic needs in the regions implicated in the spatial memory process. Also, the reduction of COx activity in brain regions traditionally related to stress and some behavioral parameters, such as the lower velocity or more time spent in the center of the maze, may indicate a possible reduction of anxiety in the exercise group during the spatial task.

Age-dependent effects of environmental enrichment on brain networks and spatial memory in Wistar rats

We assessed the effect of 3h of environmental enrichment (EE) exposure per day started at different ages (3 and 18months old) on the performance in a spatial memory task and on brain regions involved in the spatial learning (SPL) process using the principal component analysis (PCA). The animals were tested in the four-arm radial water maze (4-RAWM) for 4days, with six daily trials. We used cytochrome c oxidase (COx) histochemistry to determine the brain oxidative metabolic changes related to age, SPL and EE. Behavioural results showed that the enriched groups, regardless of their age, achieved better performance in the spatial task. Interestingly, in the case of the distance travelled in the 4-RAWM, the effect of the EE was dependent on the age, so the young enriched group travelled a shorter distance compared to the aged enriched group. Respect to COx histochemistry results, we found that different brain mechanisms are triggered in aged rats to solve the spatial task, compared to young rats. PCA revealed the same brain functional network in both age groups, but the contribution of the brain regions involved in this network was slightly different depending on the age of the rats. Thus, in the aged group, brain regions involved in anxiety-like behaviour, such as the amygdala or the bed nucleus of the stria terminalis had more relevance; whereas in the young enriched group the frontal and the hippocampal subregions had more contribution.

Environmental enrichment as a therapeutic avenue for anxiety in aged Wistar rats: Effect on cat odor exposition and GABAergic interneurons

The use of more ethological animal models to study the neurobiology of anxiety has increased in recent years. We assessed the effect of an environmental enrichment (EE) protocol (24h/day over a period of two months) on anxiety-related behaviors when aged Wistar rats (21months old) were confronted with cat odor stimuli. Owing to the relationship between GABAergic interneurons and the anxiety-related neuronal network, we examined changes in the expression of Parvalbumin (PV) and 67kDa form of glutamic acid decarboxylase (GAD-67) immunoreactive cells in different brain regions involved in stress response. Behavioral results revealed that enriched rats traveled further and made more grooming behaviors during the habituation session. In the cat odor session, they traveled longer distances and they showed more active interaction with the odor stimuli and less time in freezing behavior. Zone analysis revealed that the enriched group spent more time in the intermediate zone according to the proximity of the predator odor. Regarding the neurobiological data, the EE increased the expression of PV-positive cells in some medial prefrontal regions (cingulate (Cg) and prelimbic (PL) cortices), whereas the GAD-67 expression in the basolateral amygdala was reduced in the enriched group. Our results suggest that EE is able to reduce anxiety-like behaviors in aged animals even when ethologically relevant stimuli are used. Moreover, GABAergic interneurons could be involved in mediating this resilient behavior.

Housing condition-related changes involved in reversal learning and its c-Fos associated activity in the prefrontal cortex

Our study examined how different housing conditions modulated the acquisition of a spatial reference memory task and also, a reversal task in the 4-radial arm water maze (4-RAWM). The animals were randomly assigned to standard or enriched cages, and, as a type of complementary stimulation along with the environmental enrichment (EE), a group of rats also ran 15 min/day in a Rotarod. Elevated-zero maze results allowed us to discard that our exercise training increased anxiety-related behaviors. 4-RAWM results revealed that the non-enriched group had a worse performance during the acquisition and also, during the first trial of each session with respect to the enriched groups. Regarding the reversal task, this group made more perseverative errors in the previous platform position. Interestingly, we hardly found differences between the two enriched groups (with and without exercise). We also analyzed how the reversal learning, depending on the previous housing condition, modulated the expression of c-Fos-positive nuclei in different subdivisions of the medial prefrontal cortex (cingulate (Cg), prelimbic (PL) and infralimbic (IL) cortices) and in the orbitofrontal (OF) cortex. The enriched groups had higher c-Fos expression in the Cg and OF cortices and lower in the IL cortex respect to the non-enriched animals. In the PL cortex, we did not find significant differences between the groups that performed the reversal task. Therefore, our short EE protocol improved the performance in a spatial memory and a reversal task, whereas the exercise training, combined with the EE, did not produce a greater benefit. This better performance seemed to be related with the specific pattern of c-Fos expression in brain regions involved in cognitive flexibility.

Metabolic brain activity underlying behavioral performance and spatial strategy choice in sedentary and exercised Wistar rats.

We have studied the performance of a spatial reference memory task, the navigation strategy and the changes in the cytochrome c oxidase activity (COx) in different brain regions in exercised (forced exercise, 10 consecutive days, 15min/day) and non-exercised adult Wistar rats. The spatial learning task was carried out in the radial-arm water maze (RAWM) for four days with six daily trials, and on the fifth day, a probe session was run, in which we rotated the position of the distal cues 90° in a clockwise direction. During the four days of training, the exercised group showed shorter latency and distance traveled to find the platform, as well as fewer memory errors and reduced use of non-appropriate navigation strategies according to the protocol of the task (egocentric). Interestingly, the rotation of the cues did not affect the performance of the exercised group, in contrast to the non-exercised group, which spent more time in the center of the maze and traveled longer distance to find the platform. Finally, higher COx activity in the cingulate and the retrosplenial cortices, as well as in the dorsal CA1 and CA3 was found in the exercised group. All in all, it seems that the exercise favored the configuration of an efficient and accurate cognitive map of the environment, which was supported by our finding that the rotation of the cues, without altering their overall configuration, did not affect performance. The brain regions with higher COx activity in the exercised group seem to be involved in this function.

Attention and inhibition in Mild Cognitive Impairment and Alzheimer's Disease

Mild cognitive impairment is understood as a cognitive deficit of insufficient severity to fulfil the criteria for Alzheimer’s disease. Many studies have attempted to identify which cognitive functions are most affected by this type of impairment and which is the most sensitive neuropsychological test for early detection. This study investigated sustained and selective attention, processing speed, and the inhibition process using a sample of people divided into three groups mild cognitive impairment, Alzheimer disease and cognitively healthy controls selected and grouped based on their scores in the Mini Mental State Examination and Cambridge Cognitive Examination-revised. Three tests from the Cambridge Neuropsychological Test Automated Battery (Motor Screening Task, Stop Signal Task and Reaction time) were used as well as the d2 attention test. The results show that that participants with mild cognitive impairment and Alzheimer disease showed lower levels of concentration compared with the cognitively healthy controls group in the d2 test and longer reaction times in the Cambridge Neuropsychological Test Automated Battery, although the differences were not marked in the latter test. The impairments in basic cognitive processes, such as reaction time and sustained attention, indicate the need to take these functions into account in the test protocols when discriminating between normal aging and early and preclinical dementia processes.

Requiring collaboration: Hippocampal-prefrontal networks needed in spatial working memory and ageing. A multivariate analysis approach

&NA; Ageing is characterized by a decline in the processes of retention and storage of spatial information. We have examined the behavioural performance of adult rats (3 months old) and aged rats (18 months old) in a spatial complex task (delayed match to sample). The spatial task was performed in the Morris water maze and consisted of three sessions per day over a period of three consecutive days. Each session consisted of two trials (one sample and retention) and inter‐session intervals of 5 min. Behavioural results showed that the spatial task was difficult for middle aged group. This worse execution could be associated with impairments of processing speed and spatial information retention. We examined the changes in the neuronal metabolic activity of different brain regions through cytochrome C oxidase histochemistry. Then, we performed MANOVA and Discriminant Function Analyses to determine the functional profile of the brain networks that are involved in the spatial learning of the adult and middle‐aged groups. This multivariate analysis showed two principal functional networks that necessarily participate in this spatial learning. The first network was composed of the supramammillary nucleus, medial mammillary nucleus, CA3, and CA1. The second one included the anterior cingulate, prelimbic, and infralimbic areas of the prefrontal cortex, dentate gyrus, and amygdala complex (basolateral l and central subregions). There was a reduction in the hippocampal‐supramammilar network in both learning groups, whilst there was an overactivation in the executive network, especially in the aged group. This response could be due to a higher requirement of the executive control in a complex spatial memory task in older animals. HighlightsDiscriminant analysis is a useful multivariate tool in brain networks assessment.New spatial working memory task reflects age‐related difficulties in performance.Poor anticonsolidation response in ageing compensated with the executive network.