Hippocampus-dependent and Associative Memory in Mice Subjected to Acute Predator Stress

Proceedings of the 9th International Multidisciplinary Conference «Stress and Behavior» Saint-Petersburg, Russia, 16–19 May 2005.A number of studies documented contradictory effects of acute stress on learning abilities. Here, we investigated effects of predator stress in mice on two distinct types of memory: a hippocampus-dependent contextual memory and a cortex-dependent conditioned taste aversion associative learning. Also, we related memory scores to individual copying strategies of social behavior. Employed stress paradigm was proposed earlier as a model of extreme environmental stress in humans.Methods. Male CD1 mice have been tested in a resident-intruder paradigm, in which animals display either dominant or subdominant types of social behavior. Type of social behavior in mice is considered to be a valuable parameter reflecting stress-responsiveness and general style of behavioral coping with various aversive situations. Two month after testing, animals were exposed to predator stress for a time period of 9 h. Therefore they were placed into a small container and introduced to a cage, which was containing a rat; mice were water and food deprived during entire period of stress. Non-stressed animals remained untreated and were kept in regular animal facility. 4 hours after termination of stress, stressed and non-stressed animals were split to two experimental groups and trained in two learning tasks. Half of animals were subjected to a conditioned taste aversion paradigm. Animals were previously trained to a special water drinking schedule, getting a 2-h access to water daily. For training, they received 2.5 % sucrose solution and 30 min later were injected with 0.18 M/kg LiCl that caused nausea in all mice. 24 h later, mice were tested for their preference to sucrose solution (a parameter of associative memory), in a two-bottle paradigm based on a choice between sucrose solution and plain water. Second half of stressed and control animals was trained in a step-down avoidance paradigm. Mice learned to refrain from stepping down onto a grid floor in order to avoid an electric shock. In this test, baseline latency of stepping down, a measure of anxiety-related behavior, as well as short-term and long-term memory was estimated.Results and discussion. Among control mice subjected to training in conditioned taste aversion paradigm, six out of nine animals showed decreased preference to sucrose (below 50 %) as compared to mice not treated with LiCl (mean preference to sucrose 90 %) and were considered as good learners. In the stress group, five out of ten animals acquired conditioned taste aversion task. The only difference between the groups was in water drinking: stressed mice showed reduced water consumption. Thus, predator stress does not impair associative learning in conditioned taste aversion paradigm. In a step-down avoidance paradigm, stressed mice showed normal learning scores both for short-term memory (during recall session 3 h after training) and long-term memory (during recall session 24 h after training). However, analysis of good learners from the stress group showed that 80 % of them were constituted from mice with subdominant type of behavior. Notably, preliminary experiments in naпve mice did not reveal any differences in acquisition of step-down avoidance between dominant and subdominant groups of mice. In a present experiment, parameters of anxiety were not statistically different between the groups; moreover, dominant mice had a tendency to have higher anxiety scores. These data suggest that differences in learning of passive avoidance task between dominant and subdominant mice cannot be explained by unspecific changes in anxiety-related behavior.Conclusion. Thus, the type of behavioral copying plays a significant role in stress-responsiveness and hippocampus-dependent learning in male mice subjected to acute stress

Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I

There is a strongly held opinion that one of the most important functions of sleep is its involvement in the formation of memories The standard test for studies of learning and memory processes in animals is the Morris water test Effects of Sleep Deprivation on Consolidation of Spatial Memory in Rats after 1032 Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 61, No. 3, pp. 322-331, May-June, 2011. Original article submitted December 24, 2009. Accepted October 18, 2010. The effects of sleep deprivation produced using a carousel method on the consolidation of spatial memory were studied in rats (male Wistar rats) after one-day training using the Frick et al. protocol (2000) in a Morris water maze. Data were obtained providing evidence that the memory trace after rapid 3-h training was retained for one day. Sleep deprivation for 24 h after training prevented reinforcement (consolidation) of spatial memory. The results led to the conclusion that a model based on one-day training can be used to study the neurophysiological and neurochemical mechanisms of the effects of sleep deprivation on consolidation of spatial memory

Sleep- and wake-like states in small networks in vivo and in vitro

Wakefulness and sleep are highly complex and heterogeneous processes, involving multiple neurotransmitter systems and a sophisticated interplay between global and local networks of neurons and non-neuronal cells. Macroscopic approaches applied at the level of the whole organism, view sleep as a global behaviour and allow for investigation into aspects such as the effects of insufficient or disrupted sleep on cognitive function, metabolism, thermoregulation and sensory processing. While significant progress has been achieved using such large-scale approaches, the inherent complexity of sleep-wake regulation has necessitated the development of methods which tackle specific aspects of sleep in isolation. One way this may be achieved is by investigating specific cellular or molecular phenomena in the whole organism in situ, either during spontaneous or induced sleep-wake states. This approach has greatly advanced our knowledge about the electrophysiology and pharmacology of ion channels, specific receptors, intracellular pathways and the small networks implicated in the control and regulation of the sleep-wake cycle. Importantly though, there are a variety of external and internal factors that influence global behavioural states which are difficult to control for using these approaches. For this reason, over the last few decades, ex vivo experimental models have become increasingly popular and have greatly advanced our understanding of many fundamental aspects of sleep, including the neuroanatomy and neurochemistry of sleep states, sleep regulation, the origin and dynamics of specific sleep oscillations, network homeostasis as well as the functional roles of sleep. This chapter will focus on the use of small neuronal networks as experimental models and will highlight the most significant and novel insights these approaches have provided