Intranasal Administration of Rotenone Reduces GABAergic Inhibition in the Mouse Insular Cortex Leading to Impairment of LTD and Conditioned Taste Aversion Memory

Reduced menthol sensitivity in a prodromal Parkinson's disease model induced by intranasal rotenone treatment

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor symptoms, and it is associated with several prodromal non-motor symptoms, including an impaired sense of smell, taste and touch. We previously reported that bitter taste impairments occur independently of olfactory impairments in an early-stage PD animal model using short-term intranasal rotenone-treated mice. Cool temperatures also affect bitter taste perception, but it remains unclear whether or not bitter taste impairments result from an altered sensitivity for intraoral cool stimuli. We examined disturbances in the intraoral menthol sensitivity, such as coolness at low concentrations of menthol, using a brief-access test. Once a day, one solution from the 7-concentration series of (-)-menthol (0-2.3 mM) or the bitter taste quinine-HCl (0.3 mM) was randomly presented 20 times for 10 s to water-deprived mice before and 1 week after rotenone treatment. The total number of licks within 20 times was significantly decreased with the presentation of 2.3 mM menthol and quinine-HCl, compared to distilled water in untreated mice, but not in rotenone-treated mice. The correlation between the licks for quinine-HCl and that for menthol was increased after rotenone treatment. In contrast, the 2-bottle choice test for 48 h clarified that menthol sensitivity was increased after rotenone treatment. Furthermore, a thermal place preference test revealed that seeking behavior toward a cold-floored room was increased in the rotenone-treated mice despite the unchanged plantar cutaneous cold sensitivity. These results suggest that taste impairments in this model mice are at least partly due to intraoral somatosensory impairments, accompanied by peripheral/central malfunction.

Adjunct antiseizure effect of clotrimazole in a rotenone corneal kindling mouse model of mitochondrial drug-resistant epilepsy

This study aimed to investigate the therapeutic potential of clotrimazole, an inhibitor of the transient receptor potential cation channel, for treating mitochondrial drug-resistant epilepsy and to understand its underlying neurochemical mechanisms. Adult albino mice underwent rotenone-corneal kindling, receiving daily electric shocks (15 mA, 20 V, 6-Hz for 3 s) through a corneal electrode, to induce mitochondrial drug-resistant epilepsy. The onset of drug resistance was confirmed by the significant (p < 0.05) lack of seizure control with standard antiseizure medications including levetiracetam (40 mg/kg), valproate (250 mg/kg), phenytoin (35 mg/kg), lamotrigine (15 mg/kg), and carbamazepine (40 mg/kg). Drug-resistant mice were then classified into one vehicle-treated group and three groups treated with varying doses of clotrimazole (40, 80, and 160 mg/kg orally). Neurochemical analysis of the seizurogenic hippocampus and cerebral cortex was conducted using high-performance liquid chromatography with an electrochemical detector. Administration of clotrimazole alongside standard antiseizure medications led to a significant decrease (p < 0.05) in seizure scores suggesting the restoration of antiseizure effects. Neurochemicals, including tryptophan, serotonin, kynurenine, serine, taurine, gamma-aminobutyric acid, and glutamate, were significantly restored post-clotrimazole treatment. Overall, the present study underscores the adjunct antiseizure effect of clotrimazole in a rotenone corneal kindling mouse model of mitochondrial drug-resistant epilepsy, emphasising its role in neurochemical restoration.

Electroacupuncture alleviates the relapse of pain-related aversive memory by activating KOR and inhibiting GABAergic neurons in the insular cortex

Pain-related aversive memory is common in chronic pain patients. Electroacupuncture has been demonstrated to block pain-related aversive memory. The insular cortex is a key region closely related to aversive behaviors. In our study, a potential mechanism underlying the effect of electroacupuncture treatment on pain-related aversive memory behaviors relative to the insular cortex was investigated. Our study used the chemogenetic method, pharmacological method, electroacupuncture intervention, and behavioral detection. Our study showed that both inhibition of gamma-aminobutyric acidergic neurons and activation of the kappa opioid receptor in the insular cortex blocked the pain-related aversive memory behaviors induced by 2 crossover injections of carrageenan in mice; conversely, both the activation of gamma-aminobutyric acidergic neurons and inhibition of kappa opioid receptor in the insular cortex play similar roles in inducing pain-related aversive memory behaviors following 2 crossover injections of carrageenan. In addition, activation of gamma-aminobutyric acidergic neurons in the insular cortex reversed the effect of kappa opioid receptor activation in the insular cortex. Moreover, electroacupuncture effectively blocked pain-related aversive memory behaviors in model mice, which was reversed by both activation of gamma-aminobutyric acidergic neurons and inhibition of kappa opioid receptor in the insular cortex. The effect of electroacupuncture on blocking pain-related aversive memory behaviors may be related to the activation of the kappa opioid receptor and inhibition of gamma-aminobutyric acidergic neurons in the insular cortex.

IL-1β/IL-1R1 signaling is involved in the propagation of α-synuclein pathology of the gastrointestinal tract to the brain

The pathological hallmark of Parkinson's disease (PD) is the intraneuronal accumulation of misfolded alpha-synuclein (termed Lewy bodies) in dopaminergic neurons of substantia nigra par compacta (SNc). It is assumed that the α-syn pathology is induced by gastrointestinal inflammation and then transfers to the brain by the gut-brain axis. Therefore, the relationship between gastrointestinal inflammation and α-syn pathology leading to PD remains to be investigated. In our study, rotenone (ROT) oral administration induces gastrointestinal tract (GIT) inflammation in mice. In addition, we used pseudorabies virus (PRV) for tracing studies and performed behavioral testing. We observed that ROT treatments enhance macrophage activation, inflammatory mediator expression, and α-syn pathology in the GIT 6-week post-treatment (P6). Moreover, pathological α-syn was localized with IL-1R1 positive neural cells in GIT. In line with these findings, we also find pS129-α-syn signals in the dorsal motor nucleus of the vagus (DMV) and tyrosine hydroxylase in the nigral-striatum dynamically change from 3-week post-treatment (P3) to P6. Following that, pS129-α-syn was dominant in the enteric neural cell, DMV, and SNc, accompanied by microglial activation, and these phenotypes were absent in IL-1R1r/r mice. These data suggest that IL-1β/IL-1R1-dependent inflammation of GIT can induce α-syn pathology, which then propagates to the DMV and SNc, resulting in PD.

Taste Impairments in a Parkinson’s Disease Model Featuring Intranasal Rotenone Administration in Mice

Background: Taste impairments are often accompanied by olfactory impairments in the early stage of Parkinson’s disease (PD). The development of animal models is required to elucidate the mechanisms underlying taste impairments in PD. Objective: This study was conducted to clarify whether the intranasal administration of rotenone causes taste impairments prior to motor deficits in mice. Methods: Rotenone was administrated to the right nose of mice once a day for 1 or 4 week(s). In the 1-week group, taste, olfactory, and motor function was assessed before and after a 1-week recovery period following the rotenone administration. Motor function was also continuously examined in the 4-weeks group from 0 to 5 weeks. After a behavioral test, the number of catecholamine neurons (CA-Nos) was counted in the regions responsible for taste, olfactory, and motor function. Results: taste and olfactory impairments were simultaneously observed without locomotor impairments in the 1-week group. The CA-Nos was significantly reduced in the olfactory bulb and nucleus of the solitary tract. In the 4-week group, locomotor impairments were observed from the third week, and a significant reduction in the CA-Nos was observed in the substantia nigra (SN) and ventral tegmental area (VTA) at the fifth week along with the weight loss. Conclusion: The intranasal administration of rotenone caused chemosensory and motor impairments in an administration time-period dependent manner. Since chemosensory impairments were expressed prior to the locomotor impairments followed by SN/VTA CA neurons loss, this rotenone administration model may contribute to the clarification of the prodromal symptoms of PD.

The different effects of intramuscularly-injected lactate on white and brown adipose tissue in vivo

BACKGROUND

Lactate is an important product of glycolysis metabolism during exercise and has long been recognized as an important metabolic signaling molecule involved in inhibiting lipolysis and promoting lipogenesis, which consequently leads to regulated adipose tissue metabolism. However, recent studies have shown that lactate promotes the browning of white adipose tissue (WAT), which induces heat production and energy expenditure and ultimately causes weight loss. These studies assessing the effects of lactate on lipid metabolism in adipose tissue have revealed conflicting data, making it an important area worthy of further research.

METHODS

In this study, using intramuscular injection of lactate to the gastrocnemius, we identified the role of lactate treatment on lipid metabolism and mitochondrial biogenesis of white adipose tissue and brown adipose tissue (BAT).

RESULTS

Our results showed that lactate treatment activated the cAMP/PKA signaling pathway and promoted the expression of lipolysis-related proteins (AMPK, HSL, ATGL) and mitochondrial biomarkers (PGC-1α, COXIV) of WAT, while BAT showed an opposite trend after lactate treatment. Further studies showed that lactate treatment significantly increased serum epinephrine and promoted β3-AR protein expression in WAT and significantly decreased in BAT.

CONCLUSION

Our study shows that lactate seems to regulate β3-adrenergic receptors differently in WAT and BAT, thereby eliciting disparate responses in adipose tissue.

The Intriguing Contribution of Hippocampal Long-Term Depression to Spatial Learning and Long-Term Memory

Long-term potentiation (LTP) and long-term depression (LTD) comprise the principal cellular mechanisms that fulfill established criteria for the physiological correlates of learning and memory. Traditionally LTP, that increases synaptic weights, has been ascribed a prominent role in learning and memory whereas LTD, that decreases them, has often been relegated to the category of “counterpart to LTP” that serves to prevent saturation of synapses. In contradiction of these assumptions, studies over the last several years have provided functional evidence for distinct roles of LTD in specific aspects of hippocampus-dependent associative learning and information encoding. Furthermore, evidence of the experience-dependent “pruning” of excitatory synapses, the majority of which are located on dendritic spines, by means of LTD has been provided. In addition, reports exist of the temporal and physical restriction of LTP in dendritic compartments by means of LTD. Here, we discuss the role of LTD and LTP in experience-dependent information encoding based on empirical evidence derived from conjoint behavioral and electrophysiological studies conducted in behaving rodents. We pinpoint the close interrelation between structural modifications of dendritic spines and the occurrence of LTP and LTD. We report on findings that support that whereas LTP serves to acquire the general scheme of a spatial representation, LTD enables retention of content details. We argue that LTD contributes to learning by engaging in a functional interplay with LTP, rather than serving as its simple counterpart, or negator. We propose that similar spatial experiences that share elements of neuronal representations can be modified by means of LTD to enable pattern separation. Therewith, LTD plays a crucial role in the disambiguation of similar spatial representations and the prevention of generalization.

Advances and Challenges in Intranasal Delivery of Antipsychotic Agents Targeting the Central Nervous System

Treatment of central nervous system (CNS) disorders is challenging using conventional delivery strategies and routes of administration because of the presence of the blood–brain barrier (BBB). This BBB restricts the permeation of most of the therapeutics targeting the brain because of its impervious characteristics. Thus, the challenges of delivering the therapeutic agents across the BBB to the brain overcoming the issue of insufficient entry of neurotherapeutics require immediate attention for recovering from the issues by the use of modern platforms of drug delivery and novel routes of administration. Therefore, the advancement of drug delivery tools and delivering these tools using the intranasal route of drug administration have shown the potential of circumventing the BBB, thereby delivering the therapeutics to the brain at a significant concentration with minimal exposure to systemic circulation. These novel strategies could lead to improved efficacy of antipsychotic agents using several advanced drug delivery tools while delivered via the intranasal route. This review emphasized the present challenges of delivering the neurotherapeutics to the brain using conventional routes of administration and overcoming the issues by exploring the intranasal route of drug administration to deliver the therapeutics circumventing the biological barrier of the brain. An overview of different problems with corresponding solutions in administering therapeutics via the intranasal route with special emphasis on advanced drug delivery systems targeting to deliver CNS therapeutics has been focused. Furthermore, preclinical and clinical advancements on the delivery of antipsychotics using this intranasal route have also been emphasized.

Environmental triggers of Parkinson's disease - Implications of the Braak and dual-hit hypotheses

Idiopathic Parkinson's disease (PD) may take decades to develop, during which many risk or protective factors may come into play to initiate the pathogenesis or modify its progression to clinical PD. The lack of understanding of this prodromal phase of PD and the factors involved has been a major hurdle in the study of PD etiology and preventive strategies. Although still controversial, the Braak and dual-hit hypotheses that PD may start peripherally in the olfactory structures and/or the gut provides a theoretical platform to identify the triggers and modifiers of PD prodromal development and progression. This is particularly true for the search of environmental causes of PD as the olfactory structures and gut are the major human mucosal interfaces with the environment. In this review, we lay out our personal views about how the Braak and dual-hit hypotheses may help us search for the environmental triggers and modifiers for PD, summarize available experimental and epidemiological evidence, and discuss research gaps and strategies.

Association between IL-17A, IL-17F and IL-17RA gene polymorphisms and susceptibility to psoriasis and psoriatic arthritis: a meta-analysis

BACKGROUND

Psoriasis (Ps) is a chronic dermatosis characterized by erythematous-squamous plaques derived from an inflammatory response. The effect of polymorphisms in the genes that encode the members of the IL-17 family and their receptors has been studied to find an association with the susceptibility to Ps. However, the findings have not been conclusive.

OBJECTIVES

To describe the association between IL-17A, IL-17F and IL-17RA gene polymorphisms and susceptibility to Ps.

METHOD

A systematic review was conducted using the PubMed and Scopus databases to identify studies that evaluated the association between IL-17A, IL-17F, and IL-17RA gene polymorphisms and Ps susceptibility. This meta-analysis included reports published until June 2021. Heterogeneity was assessed using Cochran's Q-statistic test and I² statistics. The associations between polymorphisms and Ps susceptibility were determined by pooled OR with a 95% CI.

RESULTS

Fifteen studies were included. The frequency of the T allele of the IL-17F rs763780 polymorphism was significantly lower in patients with vulgar Ps (OR = 0.732, p = 0.026). The TT genotype of the IL-17F rs763780 polymorphism was significantly associated with a decreased frequency in individuals with Ps and psoriatic arthritis (PsA) (TT:TC + CC OR = 0.664, p = 0.046). Regarding IL-17RA polymorphisms, the AG genotype of the rs4819554 polymorphism showed a near-significant decrease in psoriasis risk compared to the GG genotype (AG:GG OR = 0.604, p = 0.050). Other polymorphisms in IL-17A, IL-17F and IL-17RA showed no association with Ps.

CONCLUSIONS

The T allele and TT genotype of the IL-17F rs763780 polymorphism may be associated with a decreased risk of psoriasis. Therefore, the implications of this variant on psoriasis pathogenesis and treatment require further investigation.