Correlations among central serotonergic parameters and age-related emotional and cognitive changes assessed through the elevated T-maze and the Morris water maze

Abstract

Emotion and spatial cognitive aspects were assessed in adult and middle-aged rats using the elevated T-maze (ETM) and the Morris water maze (MWM) tasks. Both adult and middle-aged rats were able to acquire inhibitory avoidance behaviour, though the middle-aged subjects showed larger latencies along the trials, including the baseline, which was significantly longer than that showed by adult rats. Further, compared to adult rats, middle-aged rats had longer escape latency. In spite of the worse performance in the second session of the spatial cognitive task, the middle-aged rats were able to learn the task and remember the information along the whole probe trial test. Both thalamic serotonin (5-HT) concentration and amygdala serotonergic activity (5-HIAA/5-HT) are significantly correlated, respectively, to escape latency and behavioural extinction in the MWM only for middle-aged rats. A significant correlation between the 5-HIAA/5-HT ratio in the amygdala and behavioural extinction for middle-aged, but not for adult, rats was observed. This result suggests that serotonergic activity in the amygdala may regulate behavioural flexibility in aged animals. In addition, a significant negative correlation was found between hippocampal 5-HIAA/5-HT ratio and the path length at the second training session of the MWM task, although only for adult subjects. This was the only session where a significant difference between the performance of middle-aged and adult rats has occurred. Although the involvement of the hippocampus in learning and memory is well established, the present work shows, for the first time, a correlation between a serotonergic hippocampal parameter and performance of a spatial task, which is lost with ageing.

Ageing and spatial reversal learning in humans: Findings from a virtual water maze

“…As such, in the present task, participants showing high measured anxiety may perform poorly throughout testing. On the other hand, since anxiety and cognition can interact during task performance [10], in line with the data of Oliveira et al [6], we hypothesized that anxiety may have a progressively detrimental effect across trials especially in older participants. This would give rise to an interaction between age, anxiety and test block, older anxious participants showing a sharper decline in performance than those in younger groups.…”

“…Although the detrimental effects of ageing on spatial learning are well documented, in animals and in human participants, emotional factors may also play a role, and may in some cases mediate or contribute to age effects, particularly since anxiety and memory appear to share common molecular components [5]. Oliveira et al have found a moderator effect such that only older animals' serotonergic activity correlated significantly with reversal learning in the Morris water maze [6]. But this is only one possible explanation of the interrelations of emotional states, neurotransmitter systems, and water maze performance, derived from animal research.…”

“…While both procedures eliminated the spatial preference for the trained platform location, animals repeatedly exposed to random platform locations maintained an active random search pattern, while those repeatedly trained without any platform appeared to despair and "floated" [7,9,20]. Clearly, the water maze task can be considered more frustrating and aversive in the extinction than in the reversal learning condition [6]. Spatial reversal learning was also shown to depend on hippocampal longterm depression in CA1 cells [21], which lead us to the assumption that the reversal condition might be more sensitive to age-related hippocampal changes than a single place learning task.…”

Expression of Amyloid-Associated miRNAs in Both the Forebrain Cortex and Hippocampus of Middle-Aged Rat

“…The main characteristic of impaired cognitive ability in middle-aged rats is the decreased learning ability without marked memory decline as evaluated by MWM. This result is similar with previous study, which demonstrated that middle-aged rats (18 months old) showed significantly slower escape latency and longer swimming distance in cued trial than those in young rats, without significant difference in probe trial between two groups [46]. …”

Effect of Zhuang Jing Decoction on Learning and Memory Ability in Aging Rats

“…To the best of our knowledge, the neurotransmitters namely catecholamines (norepinephrine [NE], dopamine [DA]) and serotonin (5-hydroxytryptamine [(5-HT]) play critical role in emotions, sleep, arousal, and cognitive function. 5,6 Neurotrophic factors are critical for neuronal differentiation, maturation, and survival. However, as the aging, the balance of neurotrophic factors is disturbed.…”