Increased training compensates for OX1R blockage-impairment of spatial memory and c-Fos expression in different cortical and subcortical areas

Withdrawn: The altered dynamic community structure for adaptive adjustment in stroke patients with multidomain cognitive impairments: A multilayer network analysis

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Hypothalamic orexins as possible therapeutic agents in threat and spatial memory disorders

Orexin-A and orexin-B, neuropeptides produced exclusively in the lateral hypothalamus, have been implicated in various functions, including memory. Their levels are elevated in certain pathological states, such as PTSD, and lowered in other states, e.g., memory deficits. Recent developments have shown the possibilities of using orexins to modulate memory. Their administration can improve the results of test animals in paradigms such as passive avoidance (PA), cued fear conditioning (CFC), and the Morris water maze (MWM), with differences between the orexin used and the route of drug administration. Blocking orexin receptors in different brain structures produces opposing effects of memory impairments in given paradigms. Therefore, influencing the orexinergic balance of the brain becomes a viable way to ameliorate memory deficits, shift PTSD-induced recall of stressful memories to an extinction path, or regulate other memory processes.

Protocol to assess rewarding brain stimulation as a learning and memory modulating treatment: Comparison between self-administration and experimenter-administration

Intracranial electrical self-stimulation (ICSS) is a useful procedure in animal research. This form of administration ensures that areas of the brain reward system (BRS) are being functionally activated, since the animals must perform an operant response to self-administer an electrical stimulus. Rewarding post-training ICSS of the medial forebrain bundle (MFB), an important system of the BRS, has been shown to consistently improve rats' acquisition and retention in several learning tasks. In the clinical setting, deep brain stimulation (DBS) of different targets is currently being used to palliate the memory impairment that occurs in some neurodegenerative diseases. However, the stimulation of the MFB has only been used to treat emotional alterations, not memory disorders. Since DBS stimulation treatments in humans are exclusively administered by external sources, studies comparing the efficacy of that form of application to a self-administered stimulation are key to the translationality of ICSS. This protocol compares self-administered (ICSS) and experimenter-administered (EAS) stimulation of the MFB on the spatial Morris Water Maze task (MWM). c-Fos immunohistochemistry procedure was carried out to evaluate neural activation after retention. Results show that the stimulation of the MFB improves the MWM task regardless of the form of administration, although some differences in c-Fos expression were found. Present results suggest that MFB-ICSS is a valid animal model to study the effects of MFB electrical stimulation on memory, which could guide clinical applications of DBS. The present protocol is a useful guide for establishing ICSS behavior in rats, which could be used as a learning and memory-modulating treatment.

Intranasal insulin and orexins to treat age-related cognitive decline

The intranasal (IN) administration of neuropeptides, such as insulin and orexins, has been suggested as a treatment strategy for age-related cognitive decline (ARCD). Because dysfunctional neuropeptide signaling is an observed characteristic of ARCD, it has been suggested that IN delivery of insulin and/or orexins may restore endogenous peptide signaling and thereby preserve cognition. IN administration is particularly alluring as it is a relatively non-invasive method that directly targets peptides to the brain. Several laboratories have examined the behavioral effects of IN insulin in young, aged, and cognitively impaired rodents and humans. These studies demonstrated improved performance on various cognitive tasks following IN insulin administration. Fewer laboratories have assessed the effects of IN orexins; however, this peptide also holds promise as an effective treatment for ARCD through the activation of the cholinergic system and/or the reduction of neuroinflammation. Here, we provide a brief overview of the advantages of IN administration and the delivery pathway, then summarize the current literature on IN insulin and orexins. Additional preclinical studies will be useful to ultimately uncover the mechanisms underlying the pro-cognitive effects of IN insulin and orexins, whereas future clinical studies will aid in the determination of the most efficacious dose and dosing paradigm. Eventually, IN insulin and/or orexin administration may be a widely used treatment strategy in the clinic for ARCD.

Mechanisms of Memory Impairment Induced by Orexin-A via Orexin 1 and Orexin 2 Receptors in Post-traumatic Stress Disorder Rats

Post-traumatic stress disorder (PTSD) patients exhibit abnormal learning and memory. Axons from orexin neurons in the lateral hypothalamus innervate the hippocampus, modulating learning and memory via the orexin 1 and 2 receptors (OX1R and OX2R). However, the role of the orexin system in the learning and memory dysfunction observed in PTSD is unknown. This was investigated in the present study using PTSD animal model-single prolonged stress (SPS) rats. Spatial learning and memory in the rats were evaluated with the Morris water maze (MWM) test; changes in body weight and food intake were recorded to assess changes in appetite; and the expression of orexin-A and its receptors in the hypothalamus and hippocampus was examined and quantified by immunohistochemistry, western blotting and real-time PCR. The results showed that spatial memory was impaired and food intake was decreased in SPS rats; this was accompanied by downregulation of orexin-A in the hypothalamus and upregulation of OX1R and OX2R in the hippocampus and of OX1R in the hypothalamus. Intracerebroventricular administration of orexin-A improved spatial memory and enhanced appetite in SPS rats and partly reversed the increases in OX1R and OX2R levels in the hippocampus and hypothalamus. These results suggest that the orexin system plays a critical role in the memory and appetite dysfunction observed in PTSD.

Orexin-1 receptor blockade differentially affects spatial and visual discrimination memory facilitation by intracranial self-stimulation

Intracranial self-stimulation (ICSS) of the medial forebrain bundle is an effective treatment to facilitate memory. Performance in both explicit and implicit memory tasks has been improved by ICSS, and this treatment has even been capable of recovering loss of memory function due to lesions or old age. Several neurochemical systems have been studied in regard to their role in ICSS effects on memory, however the possible involvement of the orexinergic system in this facilitation has yet to be explored. The present study aims to examine the relationship between the OX1R and the facilitative effects of ICSS on two different types of memory tasks, both carried out in the Morris Water Maze: spatial and visual discrimination. Results show that the OX1R blockade, by intraventricular administration of SB-334867, partially negates the facilitating effect of ICSS on spatial memory, whereas it hinders ICSS facilitation of the discrimination task. However, ICSS treatment was capable of compensating for the severe detrimental effects of OX1R blockade on both memory paradigms. These results suggest different levels of involvement of the orexinergic system in the facilitation of memory by ICSS, depending on the memory task.