Using the conditioned fear stress (CFS) animal model to understand the neurobiological mechanisms and pharmacological treatment of anxiety

Comparative metabolic profiling of posterior parietal cortex, amygdala, and hippocampus in conditioned fear memory

Fear conditioning and retrieval are suitable models to investigate the biological basis of various mental disorders. Hippocampus and amygdala neurons consolidate conditioned stimulus (CS)-dependent fear memory. Posterior parietal cortex is considered important for the CS-dependent conditioning and retrieval of fear memory. Metabolomic screening among functionally related brain areas provides molecular signatures and biomarkers to improve the treatment of psychopathologies. Herein, we analyzed and compared changes of metabolites in the hippocampus, amygdala, and posterior parietal cortex under the fear retrieval condition. Metabolite profiles of posterior parietal cortex and amygdala were similarly changed after fear memory retrieval. While the retrieval of fear memory perturbed various metabolic pathways, most metabolic pathways that overlapped among the three brain regions had high ranks in the enrichment analysis of posterior parietal cortex. In posterior parietal cortex, the most perturbed pathways were pantothenate and CoA biosynthesis, purine metabolism, glutathione metabolism, and NAD+ dependent signaling. Metabolites of posterior parietal cortex including 4'-phosphopantetheine, xanthine, glutathione, ADP-ribose, ADP-ribose 2'-phosphate, and cyclic ADP-ribose were significantly regulated in these metabolic pathways. These results point to the importance of metabolites of posterior parietal cortex in conditioned fear memory retrieval and may provide potential biomarker candidates for traumatic memory-related mental disorders.

Leite L, da S. Tavares-Henriques M, Lopes LAF, Oliveira LGR, Silva-Filho SE, da Silveira APS, Cuman RKN, de S. Silva-Comar FM, Comar JF, do A. Brasileiro L, dos Santos JN, de Freitas WR, Leão KV, da Silva JG, Klein RC, Klein MHF, da S. Ramos BH, Fernandes CKC, de L. Ribas DG, Oesterreich SA. Modulation of the Serotonergic Receptosome in the Treatment of Anxiety and Depression: A Narrative Review of the Experimental Evidence

Serotonin (5-HT) receptors are found throughout central and peripheral nervous systems, mainly in brain regions involved in the neurobiology of anxiety and depression. 5-HT receptors are currently promising targets for discovering new drugs for treating disorders ranging from migraine to neuropsychiatric upsets, such as anxiety and depression. It is well described in the current literature that the brain expresses seven types of 5-HT receptors comprising eighteen distinct subtypes. In this article, we comprehensively reviewed 5-HT1-7 receptors. Of the eighteen 5-HT receptors known today, thirteen are G protein-coupled receptors (GPCRs) and represent targets for approximately 40% of drugs used in humans. Signaling pathways related to these receptors play a crucial role in neurodevelopment and can be modulated to develop effective therapies to treat anxiety and depression. This review presents the experimental evidence of the modulation of the “serotonergic receptosome” in the treatment of anxiety and depression, as well as demonstrating state-of-the-art research related to phytochemicals and these disorders. In addition, detailed aspects of the pharmacological mechanism of action of all currently known 5-HT receptor families were reviewed. From this review, it will be possible to direct the rational design of drugs towards new therapies that involve signaling via 5-HT receptors.

Therapeutic Potential of Exogenous Ketone Supplement Induced Ketosis in the Treatment of Psychiatric Disorders: Review of Current Literature

Globally, psychiatric disorders, such as anxiety disorder, bipolar disorder, schizophrenia, depression, autism spectrum disorder, and attention-deficit/hyperactivity disorder (ADHD) are becoming more prevalent. Although the exact pathological alterations are not yet clear, recent studies have demonstrated that widespread changes of very complex metabolic pathways may partially underlie the pathophysiology of many psychiatric diseases. Thus, more attention should be directed to metabolic-based therapeutic interventions in the treatment of psychiatric disorders. Emerging evidence from numerous studies suggests that administration of exogenous ketone supplements, such as ketone salts or ketone esters, generates rapid and sustained nutritional ketosis and metabolic changes, which may evoke potential therapeutic effects in cases of central nervous system (CNS) disorders, including psychiatric diseases. Therefore, the aim of this review is to summarize the current information on ketone supplementation as a potential therapeutic tool for psychiatric disorders. Ketone supplementation elevates blood levels of the ketone bodies: D-β-hydroxybutyrate (βHB), acetoacetate (AcAc), and acetone. These compounds, either directly or indirectly, beneficially affect the mitochondria, glycolysis, neurotransmitter levels, activity of free fatty acid receptor 3 (FFAR3), hydroxycarboxylic acid receptor 2 (HCAR2), and histone deacetylase, as well as functioning of NOD-like receptor pyrin domain 3 (NLRP3) inflammasome and mitochondrial uncoupling protein (UCP) expression. The result of downstream cellular and molecular changes is a reduction in the pathophysiology associated with various psychiatric disorders. We conclude that supplement-induced nutritional ketosis leads to metabolic changes and improvements, for example, in mitochondrial function and inflammatory processes, and suggest that development of specific adjunctive ketogenic protocols for psychiatric diseases should be actively pursued.

Anxiolytic Effect of Exogenous Ketone Supplementation Is Abolished by Adenosine A1 Receptor Inhibition in Wistar Albino Glaxo/Rijswijk Rats

Anxiety disorders are one of the most common mental health problems worldwide, but the exact pathophysiology remains largely unknown. It has been demonstrated previously that administration of exogenous ketone supplement KSMCT (ketone salt/KS + medium chain triglyceride/MCT oil) by intragastric gavage for 7 days decreased the anxiety level in genetically absence epileptic Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats. To investigate the potential role of the adenosinergic system in the pathomechanism of anxiety we tested whether the inhibition of adenosine A₁ receptors (A₁Rs) influence the anxiolytic effect of the exogenous ketone supplement. As A₁Rs may mediate such an effect, in the present study we used a specific A₁R antagonist, DPCPX (1,3-dipropyl-8-cyclopentylxanthine) to test whether it modulates the anxiolytic effect of sub-chronically (7 days) applied KSMCT in the previously tested animal model by using elevated plus maze (EPM) test. We administered KSMCT (2.5 g/kg/day) alone by intragastric gavage and in combination with intraperitoneally (i.p.) injected of DPCPX in two doses (lower: 0.15 mg/kg, higher: 0.25 mg/kg). Control groups represented i.p saline and water gavage with or without i.p. DPCPX administration (2.5 g/kg/day). After treatments, the level of blood glucose and beta-hydroxybutyrate (βHB), as well as body weight were recorded. KSMCT alone significantly increased the time spent in the open arms and decreased the time spent in the closed arms, supporting our previous results. Injection of lower dose of DPCPX decreased, while higher dose of DPCPX abolished the effect of KSMCT administration on EPM. Blood βHB levels were significantly increased after administration of KSMCT, while DPCPX did not change the KSMCT induced increase in blood βHB levels. These results demonstrate that A₁R inhibition modified (decreased) the anti-anxiety effect of KSMCT administration implying that the adenosinergic system, likely via A₁Rs, may modulate the exogenous ketone supplement induced anxiolytic influence.

Role of tandospirone, a 5-HT1A receptor partial agonist, in the treatment of central nervous system disorders and the underlying mechanisms

5-hydroxytryptamine (5-HT, serotonin) is an important neurotransmitter in the modulation of the cognitive, behavioral and psychological functions in animals and humans. Among the fourteen subtypes of 5-HT receptor, 5-HT1A receptor has been extensively studied. Tandospirone, an azapirone derivative with strong and selective agonist effect on 5-HT1A receptor, has been used for the treatment of anxiety disorders especially generalized anxiety disorder for decades. Recently, tandospirone showed the efficacy in relieving the syndromes of social anxiety disorder and post-traumatic stress disorder as well as in potentiating the effect of antidepressants in the treatment of depression in both preclinical and clinical studies. More impressively, the beneficial effect of tandospirone has been revealed on improvement of motor dysfunction of Parkinson's disease and cognitive deficits of schizophrenia either in monotherapy or in combination with other drugs. This review discusses the superiority of tandospirone in the treatment of the disorders and associated mechanisms in central nervous system from the literature.

Exogenous Ketone Supplements Reduce Anxiety-Related Behavior in Sprague-Dawley and Wistar Albino Glaxo/Rijswijk Rats

Nutritional ketosis has been proven effective for seizure disorders and other neurological disorders. The focus of this study was to determine the effects of ketone supplementation on anxiety-related behavior in Sprague-Dawley (SPD) and Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats. We tested exogenous ketone supplements added to food and fed chronically for 83 days in SPD rats and administered sub-chronically for 7 days in both rat models by daily intragastric gavage bolus followed by assessment of anxiety measures on elevated plus maze (EPM). The groups included standard diet (SD) or SD + ketone supplementation. Low-dose ketone ester (LKE; 1,3-butanediol-acetoacetate diester, ~10 g/kg/day, LKE), high dose ketone ester (HKE; ~25 g/kg/day, HKE), beta-hydroxybutyrate-mineral salt (βHB-S; ~25 g/kg/day, KS) and βHB-S + medium chain triglyceride (MCT; ~25 g/kg/day, KSMCT) were used as ketone supplementation for chronic administration. To extend our results, exogenous ketone supplements were also tested sub-chronically on SPD rats (KE, KS and KSMCT; 5 g/kg/day) and on WAG/Rij rats (KE, KS and KSMCT; 2.5 g/kg/day). At the end of treatments behavioral data collection was conducted manually by a blinded observer and with a video-tracking system, after which blood βHB and glucose levels were measured. Ketone supplementation reduced anxiety on EPM as measured by less entries to closed arms (sub-chronic KE and KS: SPD rats and KSMCT: WAG/Rij rats), more time spent in open arms (sub-chronic KE: SPD and KSMCT: WAG/Rij rats; chronic KSMCT: SPD rats), more distance traveled in open arms (chronic KS and KSMCT: SPD rats) and by delayed latency to entrance to closed arms (chronic KSMCT: SPD rats), when compared to control. Our data indicates that chronic and sub-chronic ketone supplementation not only elevated blood βHB levels in both animal models, but reduced anxiety-related behavior. We conclude that ketone supplementation may represent a promising anxiolytic strategy through a novel means of inducing nutritional ketosis.