Retrieval of Inhibitory Avoidance Memory Induces Differential Transcription of arc in Striatum, Hippocampus, and Amygdala

The role of hippocampal 5-HT1D and 5-HT1F receptors on learning and memory in rats

Serotonin is a neurotransmitter, which is involved in memory via its receptors. The 5-HT_1D and 5-HT_1F receptors mainly exist in the hippocampus, which plays an important role in memory processing. However, few studies have assessed the effect of these serotonin receptors on memory. We evaluated the effect of a 5-HT_1D receptor agonist, PNU142633, 5-HT_1D receptor antagonist, BRL15572 hydrochloride, and 5-HT1F receptor agonist, LY344864, on the recognition and avoidance memory in the hippocampus area. Fifty adult male Wistar rats weighing 200-250 g were divided into the control, sham-operated, PNU, BRL, and LY groups (n=10 per group). Bilateral guide cannulas were implanted into the dentate gyrus area of the hippocampus. The drugs were administered at the dose of 1 μg/μl before the novel object recognition (NOR) and passive avoidance learning (PAL) tests. The results showed that in the NOR test, the administration of PNU and LY had no significant effect on recognition index; however, the recognition index was increased by BRL. In the PAL test, the administration of PNU had no significant effect on recognition index, but the administration of BRL and LY increased the time spent in the dark compartment of the apparatus and decreased the step-through latency into the dark compartment apparatus. It can be concluded that the inhibition of the hippocampal 5-HT_1D receptor improved cognition memory but impaired avoidance memory. Activation of the hippocampal 5-HT_1F receptor had no effect on cognitive memory but impaired avoidance memory.

Oxidative stress, the immune response, synaptic plasticity, and cognition in transgenic models of Alzheimer disease

INTRODUCTION

Worldwide, approximately 50 million people have dementia, with Alzheimer disease (AD) being the most common type, accounting for 60%-70% of cases. Given its high incidence, it is imperative to design studies to expand our knowledge about its onset and development, and to develop early diagnosis strategies and/or possible treatments. One methodological strategy is the use of transgenic mouse models for the study of the factors involved in AD aetiology, which include oxidative stress and the immune response.

DEVELOPMENT

We searched the PubMed, Scopus, and Google Scholar databases for original articles and reviews published between 2013 and 2019. In this review, we address two factors that have been studied independently, oxidative stress and the immune response, in transgenic models of AD, and discuss the relationship between these factors and their impact on the loss of synaptic and structural plasticity, resulting in cognitive impairment.

CONCLUSION

This review describes possible mechanisms by which oxidative stress and the immune response participate in the molecular, cellular, and behavioural effects of AD, observing a close relationship between these factors, which lead to cognitive impairment.

Measuring maladaptive avoidance: from animal models to clinical anxiety

Avoiding stimuli that predict danger is required for survival. However, avoidance can become maladaptive in individuals who overestimate threat and thus avoid safe situations as well as dangerous ones. Excessive avoidance is a core feature of anxiety disorders, post-traumatic stress disorder (PTSD), and obsessive-compulsive disorder (OCD). This avoidance prevents patients from confronting maladaptive threat beliefs, thereby maintaining disordered anxiety. Avoidance is associated with high levels of psychosocial impairment yet is poorly understood at a mechanistic level. Many objective laboratory assessments of avoidance measure adaptive avoidance, in which an individual learns to successfully avoid a truly noxious stimulus. However, anxiety disorders are characterized by maladaptive avoidance, for which there are fewer objective laboratory measures. We posit that maladaptive avoidance behavior depends on a combination of three altered neurobehavioral processes: (1) threat appraisal, (2) habitual avoidance, and (3) trait avoidance tendency. This heterogeneity in underlying processes presents challenges to the objective measurement of maladaptive avoidance behavior. Here we first review existing paradigms for measuring avoidance behavior and its underlying neural mechanisms in both human and animal models, and identify how existing paradigms relate to these neurobehavioral processes. We then propose a new framework to improve the translational understanding of maladaptive avoidance behavior by adapting paradigms to better differentiate underlying processes and mechanisms and applying these paradigms in clinical populations across diagnoses with the goal of developing novel interventions to engage specific identified neurobehavioral targets.

Oxidative stress, the immune response, synaptic plasticity, and cognition in transgenic models of Alzheimer disease

INTRODUCTION

Worldwide, approximately 50 million people have dementia, with Alzheimer disease (AD) being the most common type, accounting for 60%-70% of cases. Given its high incidence, it is imperative to design studies to expand our knowledge about its onset and development, and to develop early diagnosis strategies and/or possible treatments. One methodological strategy is the use of transgenic mouse models for the study of the factors involved in AD aetiology, which include oxidative stress and the immune response.

DEVELOPMENT

We searched the PubMed, Scopus, and Google Scholar databases for original articles and reviews published between 2013 and 2019. In this review, we address 2 factors that have been studied independently, oxidative stress and the immune response, in transgenic models of AD, and discuss the relationship between these factors and their impact on the loss of synaptic and structural plasticity, resulting in cognitive impairment.

CONCLUSION

This review describes possible mechanisms by which oxidative stress and the immune response participate in the molecular, cellular, and behavioural effects of AD, observing a close relationship between these factors, which lead to cognitive impairment.