Facilitation of shuttle-box avoidance by the platform method: temporal effects

Cognitive Impairments of Sleep-Deprived Ovariectomized (OVX) Female Rats by Voluntary Exercise

Introduction:

Previous studies demonstrated that forced and voluntary exercise had ameliorative effects on behavioral tasks followed by Sleep Deprivation (SD) in intact female rats. The main goal of this research was evaluating the impact of voluntary exercise on cognitive functions while SD and ovariectomization is induced in female wistar rats.

Methods:

The rats were anesthesized combining dosage of ketamine and xylazine. Then, both ovaries were eliminated and 3 weeks after surgery the animals entered the study. The exercise protocol took 4 weeks of voluntary exercise in a wheel which was connected to home cage. For inducing a 72 hours deprivation the multiple platforms was applied. The cognitive functions were studied by exploiting the Morris Water Maze (MWM) and Novel object recognition tests. Anxiety was evaluated by open field test and corticostrone measurement was carried out by ELISA method. One-way and two-way ANOVA and repeated measures were utilized for data analysis and P<0.05 was considered statistically significant.

Results:

We observed significant spatial and recognition learning and memory impairments in OVX sleep-deprived rats compared to the control group and voluntary exercise alleviated the SD-induced learning and memory defects.

Conclusion:

We concluded that voluntary exercise can improve cognitive impairments followed by SD in OVX female rats.

A time to remember: the role of circadian clocks in learning and memory

The circadian system has pronounced influence on learning and memory, manifesting as marked changes in memory acquisition and recall across the day. From a mechanistic perspective, the majority of studies have investigated mammalian hippocampal-dependent learning and memory, as this system is highly tractable. The hippocampus plays a major role in learning and memory, and has the potential to integrate circadian information in many ways, including information from local, independent oscillators, and through circadian modulation of neurogenesis, synaptic remodeling, intracellular cascades, and epigenetic regulation of gene expression. These local processes are combined with input from other oscillatory systems to synergistically augment hippocampal rhythmic function. This overview presents an account of the current state of knowledge on circadian interactions with learning and memory circuitry and provides a framework for those interested in further exploring these interactions.

Experimental sleep deprivation as a tool to test memory deficits in rodents

Paradigms of sleep deprivation (SD) and memory testing in rodents (laboratory rats and mice) are here reviewed. The vast majority of these studies have been aimed at understanding the contribution of sleep to cognition, and in particular to memory. Relatively little attention, instead, has been devoted to SD as a challenge to induce a transient memory impairment, and therefore as a tool to test cognitive enhancers in drug discovery. Studies that have accurately described methodological aspects of the SD protocol are first reviewed, followed by procedures to investigate SD-induced impairment of learning and memory consolidation in order to propose SD protocols that could be employed as cognitive challenge. Thus, a platform of knowledge is provided for laboratory protocols that could be used to assess the efficacy of drugs designed to improve memory performance in rodents, including rodent models of neurodegenerative diseases that cause cognitive deficits, and Alzheimer's disease in particular. Issues in the interpretation of such preclinical data and their predictive value for clinical translation are also discussed.

Muscarinic cholinergic receptor blockade in the rat prelimbic cortex impairs the social transmission of food preference

Previous findings demonstrate the involvement of the cholinergic NBM in the acquisition of the social transmission of food preference (STFP), a relational associative odor-guided learning task. There is also evidence that muscarinic receptors in the medial prefrontal cortex, an important NBM target area, may modulate olfactory associative memory. The present experiment determined the consequences of blocking muscarinic cholinergic receptors in a component of the medial prefrontal region (the prelimbic cortex) on the STFP task. Adult male Wistar rats were bilaterally infused with scopolamine (20 microg/site) prior to training and showed a severe impairment in the expression of the task measured in two retention sessions, both immediately and 24h after training. Local scopolamine injections in the prelimbic cortex did not affect other behavioral measures such as olfactory perception, social interaction, motivation to eat, neophobia, or exploration. Results suggest that muscarinic transmission in the prelimbic cortex is essential for the STFP, supporting the hypothesis that ACh in a specific prefrontal area is important for this naturalistic form of olfactory relational memory. Current data are discussed in the context of disruption of learning as a result of interferences in PLC functions such as behavioral flexibility, attention, and strategic planning.

Circadian modulation of learning and memory in fear-conditioned mice

Endogenous processes referred to as circadian oscillators generate many of the daily rhythms in physiology and behavior of a variety of animals including humans. We investigated the possible circadian regulation of acquisition, recall and extinction in two strains of mice (C-57/6J and C-3H). Mice were trained in either the day or night with a tone and context fear conditioning protocol. The mice were then tested over the course of several days for their ability to recall the training. When comparing the performance of animals in the day and night, the mice acquired the conditioning faster in the day than in the night. Furthermore, the recall for context and tone consistently peaked during the day for at least 3 days after training, irrespective of the time of training. Finally, the loss of this training (or extinction) exhibited a rhythm in that mice trained in night exhibited a greater degree of extinction than mice trained in the day. For all of these rhythms in acquisition, recall, and extinction the phase of the rhythm was controlled by the prior light-dark (LD) cycle. When we reversed the phase of the LD cycle, the phase of the rhythm also reversed. Importantly, all three of the rhythms also continued in constant darkness demonstrating the endogenous, and presumably circadian nature, of the rhythms.

Effects of habenular lesions upon two-way active avoidance conditioning in rats

To evaluate if habenular nuclei lesions improve, impair, or have no effects on two-way active avoidance acquisition and/or retention, rats in a Lesion group were subjected to bilateral electrolytical lesions of this complex, while control rats were sham-operated (Sham group). Once recovered from the stereotaxic procedures, rats were submitted to 5 training sessions (10 trials each, one session per day) of two-way active avoidance conditioning. Ten days after the last training session, another session was administered in order to test the long-term retention of the task. Results indicated that habenular lesions did not affect the overall performance of the rats during either the acquisition sessions or the retention session of two-way active avoidance. We suggest that habenular lesions can affect the acquisition of several learning tasks, probably through their role in modulating stress responses and/or arousal states. The nature of these effects (whether facilitative, detrimental, or neutral) might depend on the interaction between several factors such as the kind of task, the specific conditioning procedures (which may generate different stress levels), and the specific area destroyed by the lesion.

Facilitation of shuttle-box avoidance by the platform method: effects of conditioned stimulus duration

To evaluate whether the duration of the conditioned stimulus (CS) influences the facilitatory effect of posttraining platform treatment upon the acquisition and long-term retention (LTR) of a shuttle-box conditioning, rats were assigned to one of the four following treatments: P-3 group rats were subjected to a 5-h treatment on 16 cm diameter platforms immediately after each of 5 training sessions (10 trials each separated by 24-h intervals) in which the CS consisted of a tone lasting 3 s; control-3 rats were trained the same way but were not subjected to the platform treatment; P-10 rats did also receive the immediate 5-h treatment on platforms, but the CS was a tone lasting 10 s; finally, control-10 rats did not receive any treatment and were also trained with a 10-s tone. Ten days after training, all rats were also tested for LTR (1 session of 10 trials). When the CS duration was 3 s, the platform treatment improved both the acquisition and LTR of the task, compared to control subjects, but the same treatment had no effect when the CS lasted 10 s. With the use of a 10-s CS, the level of learning achieved by both treated and untreated subjects was similar to the final level of acquisition reached by treated subjects trained with a 3-s CS. We conclude that the facilitatory effects of the platform method treatment upon the acquisition and LTR of a distributed shuttle-box avoidance depend on the difficulty of the task.