Monique Soffié

Behavioural and glial changes in old rats following environmental enrichment.

The effects of enriched environment on short-term memory for event durations and on astrocytes (cell density, cell area and % of GFAP immunoreactivity) in hippocampus (Hi), frontal cortex (FC) and corpus callosum (CC) were analysed in old rats housed from weaning to the end of behavioural testing (23 months) either in standard (SC) or in enriched (EC) conditions and in young adults (5 months) all housed in SC. Old SC and EC and young SC rats trained (for 2 months) or not, in a Symbolic Delayed Matching to Sample Task, had to discriminate and remember two (2- and 10-s) signals after short retention intervals. Results confirm the aging-related acquisition and memory deficit. EC reduced the slowness of acquisition, reversed the short-term memory deficit and promoted the retention of the short signal (choose short effect). Old SC naive rats had many hypertrophied astrocytes with long processes in Hi and CC while old EC rats had decreased astrocytes number and size. The behavioural testing resulted in young adult SC rats in Hi and CC, in increased astrocytes number, size and GFAP% and in their decrease in old SC rats. EC and testing have additive effects (very low astrocytes number, size and GFAP%) to compensate for the aging-induced gliosis, mostly in Hi.

Differential environmental modulations on locomotor activity, exploration and spatial behaviour in young and old rats.

The effects of environmental enrichment on motor activity, exploration and spatial performances were studied in young and old rats. Both young (4 mo old) and old (22 mo old) rats were housed from weaning to testing either in standard or in enriched conditions. All rats were submitted successively to spontaneous alternation test and to object exploration test. Results show that locomotion is decreased by age and enrichment but that the quality of exploration expressed by corrected alternation scores or by the response to spatial change is improved by enrichment sometimes in old, sometimes in young rats. Enrichment tends to accelerate the acquisition of spatial informations in young rats, but it does not succeed to restore the reactivity to spatial change of old rats in the object exploration test. These results, although they do not rule out a persistance of a continued behavioural plasticity during aging, also support the idea that the beneficial effects of environmental stimulations do not succeed to restore high cognitive function, such as the capacity to have a spatial representation, in old animals.

Effects of aluminum exposure on behavioral parameters in the rat.

Adult rats were treated by intraperitoneal injection of aluminum gluconate for 3 months. Rats were submitted to the radial maze test to determine the influence of chronic aluminum intoxication on cognitive and noncognitive behavioral processes. Both learning abilities (working memory and reference memory) and rapidity (time spent to respond and to master a trial) were analyzed. Aluminum concentration was evaluated in the brain, serum, and liver to assess aluminum body burden. While hippocampus and neocortex showed a significant increase in aluminum concentration, aluminum treatment did never affect the animals performance during cue learning or when the insert cues were removed. The only behavioral difference observed was a decrease in rapidity: both the total time to finish a trial and the latency to make the first choice were lengthened in aluminum-intoxicated rats.

Scopolamine effects on juvenile conspecific recognition in rats: Possible interaction with olfactory sensitivity

The social recognition of a juvenile conspecific by an adult male rat was evaluated as the decrease in investigation time when the same juvenile individual was reintroduced 30min after the first exposure period. The results showed that scopolamine impaired this transient individual recognition. A drop in investigation time was also observed in both tests (first and second exposure), with the same and with different juvenile individuals, in scopolamine treated animals. A second experiment showed that scopolamine disturbed the chemosensory preference for familiar odour observed in the control group. In the light of these two experiments, and according to the chemosensory mediation of social recognition in the rat, it is impossible to rule out a lack of odour discrimination in the absence of social recognition after scopolamine injection.

Scopolamine-induced deficits in acquisition of a complex spatial learning☆

The role of scopolamine was studied in a complex spatial orientation task. The procedure involved an increasing difficulty of the task: at the pretraining stage a cue (box) was placed at the reinforcement spot and the animal could give a correct response by adopting either a cue-strategy or an orientation response (i.e., go to the arm on the right of a visual landmark). In the subsequent spatial training, the box was removed, so that the orientation response was the only correct one. Results show that scopolamine-injected animals are able to use a cue-strategy but are unable to acquire a spatial orientation strategy: this more complex task asks for more time and for more sustained attention. When the response is already partly acquired, scopolamine has less effect. The cholinergic system would thus be involved in the quality or even the complexity of the response rather than in the retention itself. Though a state-dependent effect may not be excluded, it by itself cannot explain the observed differences. Finally, an impairment of the maintenance of attention could be responsible for the deficits observed in the acquisition of the complex task.

Cognitive and noncognitive processes involved in selective object exploration: comparison between young adult and old rats.

The age effects on locomotor activity, object-oriented exploration, habituation, and response to a spatial change were studied in young adult and old rats using an object exploration test. In this test the spatial response was evaluated by the renewal of exploration of a familiar object after its repositioning. The specificity of the spatial response was determined by comparison with control animals not submitted to a spatial change. Male Wistar rats 6 and 24 months old were used. Results showed a significant decrement in locomotor activity, object exploration, and spatial reactivity in old rats. The habituation curve and the reactivity to a new object were preserved. Detail analyses suggest that the spatial deficit of old rats is due to an incapacity to detect the spatial change and not to their poor locomotor or exploratory activity. These results corroborate those obtained in spatial orientation tasks and support the idea that the lack of spatial response observed in old animals is more related to cognitive impairments than to other factors such as sensory, motor, or motivational differences.

Scopolamine disrupts visual reversal without affecting the first discrimination

The effect of scopolamine (0.5 mg/kg) was determined in a brightness discrimination test (Y maze) motivated by electrical shocks (escape avoidance). Male adult Sprague Dawley rats were used. Results show that scopolamine impairs significantly the visual reversal without affecting the first brightness discrimination. The qualitative analysis reveals that the anticholinergic drug-induced deficit involves both perseveration, i.e. failure to suppress inappropriate response, and a tendency to adopt a position habit. A parallelism with hippocampal and frontal lobe damage symptoms is discussed and an interpretation in terms of disinhibition and incapacity to solve a more difficult problem is proposed.

Acquisition and long-term retention of a two-lever DRL schedule : comparison between mature and aged rats

The effects of ageing on temporal regulation, general activity and memory were analysed in a two-lever DRL schedule. The task consisted in pressing on lever A and then waiting a minimum of time before pressing lever B to get the reinforcer. Adult and senescent rats were submitted to preliminary training followed by 5 DRL 5-second training sessions and 3 retention testing sessions after a 21-day break. Results showed that, relative to adults, senescent rats were slower to reach the 5-second DRL criterion, emitted fewer temporally regulated A-B response sequences and an equivalent amount of repetitive superfluous A-A and B-B response sequences. The quality of temporal regulation was evaluated by the coefficient of variation (CV) and the median of the A-B interresponse-time distribution. In training, aged rats exhibited a higher CV only during the first 10-minute periods of the sessions, and emitted median IRTs similar to those of adults. The B-A intertrial-intervals were longer in aged than in adult rats. No age-related differences appeared for efficiency. Finally, long-term retention was not affected in either age group. The results favour an interpretation in terms of temporary recall memory deficit with a preservation of temporal regulation capacity, rather than age-related motor and motivational differences.

Age-related scopolamine effects on social and individual behaviour in rats.

The modulation of spontaneous (social and individual) behaviour as a function of the age of the rat (1, 3, 6, 12, 18 and 24 months) and of scopolamine dose (0.1, 0.2, 0.3 and 0.5 mg/kg) was studied. Observations were conducted during the dark phase of the reverse light/dark schedule using a reintroduction procedure. Results showed a marked effect of scopolamine on most of the behavioural patterns considered. Environmental interaction was enhanced whilst agonistic and social active interactions (social grooming) and play fighting were reduced by the drug. A slight hyposensitivity in the youngest rats and a marked hyposensitivity to the drug in the oldest ones were observed. The relationship to biochemical data and human sensitivity on the one hand and to learning and memory tasks and cholinergic specificity on the other hand, are discussed.

Relation between milking order and dominance value in a group of dairy cows

Abstract A group of Friesian Dutch dairy cows (varying between 34 to 50 individuals) in an open stall system was observed for a period of 1 year. The milking order and the dominance order of the group were determined. Results show that (1) the order of entrance of the herd to the milking parlor is systematic; (2) the same animal leads at the exit of the yard and at the entrance to the milking parlor; the order of the rest of the herd is not the same; (3) the leading animal occupies a high social position but is not the dominant of the whole group; (4) there is a low positive correlation between the order of entrance to the milking parlor and the dominance order; (5) high correlations between all periods were found for milking order and for dominance value; (6) there is no correlation between milk production and milking order or dominance rank.