The effect of chronic neuropeptide-S treatment on non-motor parameters in experimental model of Parkinson's disease

Central treatment of neuropeptide-S attenuates cognitive dysfunction and hippocampal synaptic plasticity impairment by increasing CaMKII/GluR1 in hemiparkinsonian rats

Neuropeptide-S (NPS) has been demonstrated to mitigate learning and memory deficits in experimental models of Parkinson's Disease (PD). Despite this, the precise mechanisms through which NPS exerts its influence on cognitive functions remain to be fully unknown. This study aims to elucidate the effects of central administration of NPS on learning and memory deficits associated with an experimental rat hemiparkinsonian model, examining both electrophysiological and molecular parameters. The hemiparkinsonian model was established via stereotactic injection of 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle. Central NPS (1 nmol, icv) was administered into the lateral ventricle via a cannula for seven consecutive days following the 6-OHDA lesion. The Morris water maze and object recognition tests were used to evaluate the rat's learning and memory abilities. Long-term potentiation (LTP) recordings were conducted to assess hippocampal synaptic plasticity. Immunohistochemistry was employed to determine the expression levels of phosphorylated CaMKII (pCaMKII), GluR1, and GluR2 in the hippocampus. The 6-OHDA-induced decline in cognitive performance was significantly (p < 0.05) improved in rats that received central NPS. In 6-OHDA-lesioned rats, NPS treatment significantly (p < 0.05) enhanced the amplitude of LTP at the dentate gyrus/perforant path synapses. Furthermore, NPS significantly (p < 0.05) increased the number of pCaMKII and GluR1 immunoreactive cells in the hippocampus, which had been diminished due to 6-OHDA, except for GluR2 levels. These findings provide insight into the mechanisms by which central NPS administration enhances cognitive functions in an experimental model of PD, highlighting its potential therapeutic benefits for addressing cognitive deficits in PD.

Chronic Nasal Administration of Kisspeptin-54 Regulates Mood-Related Disorders Via Amygdaloid GABA in Hemi-Parkinsonian Rats

Background

Depression and anxiety, the most prevalent neuropsychiatric manifestations in Parkinson’s disease (PD), negatively impact their quality of life.

Aims

To determine whether the chronic nasal administration of kisspeptin-54 (KP-54) could. Alleviate symptoms of anxiety and depression in hemi-Parkinsonian rats.

Study Design

Experimental study.

Methods

This study included adult Sprague Dawley male rats who were administered either a vehicle (artificial cerebrospinal fluid) or 6-hydroxydopamine (6-OHDA) unilaterally into the medial forebrain bundle. The vehicle, or KP-54 (3 nmol/kg, applied topically to the rhinarium), was administered daily for a seven-day period. The sucrose preference test (SPT), elevated plus maze test (EPMT), and open field test (OFT) were implemented to evaluate depression- and anxiety-like behaviors, respectively, seven days following the lesion surgery. Gamma-aminobutyric acid (GABA) concentrations in the amygdala were quantified using mass spectrometry. Tyrosine hydroxylase in substantia nigra was analyzed using immunohistochemistry.

Results

The nasal delivery of KP-54 significantly reduced depressionand anxiety-like behaviors that were induced by 6-OHDA, as indicated by the results of the SPT, OFT, and EPMT. Moreover, it was observed that nasal KP-54 effectively mitigated 6-OHDA-induced motor deficits and the loss of nigral dopaminergic neurons. The nasal administration of KP-54 augmented the decline in GABA levels in the amygdala induced by 6-OHDA. Furthermore, effective correlations were established between GABA concentrations and behavioral parameters.

Conclusion

The nasal delivery of KP-54 could function as a viable therapeutic alternative for treating mood-related disorders in PD.

Pathophysiological and therapeutic implications of neuropeptide S system in neurological disorders

Neuropeptide S (NPS) is a 20 amino acids-containing neuroactive molecule discovered by the reverse pharmacology method. NPS is detected in specific brain regions like the brainstem, amygdala, and hypothalamus, while its receptor (NPSR) is ubiquitously expressed in the central nervous system (CNS). Besides CNS, NPS and NPSR are also expressed in the peripheral nervous system. NPSR is a G-protein coupled receptor that primarily uses Gq and Gs signaling pathways to mediate the actions of NPS. In animal models of Parkinsonism and Alzheimer's disease, NPS exerts neuroprotective effects. NPS suppresses oxidative stress, anxiety, food intake, and pain, and promotes arousal. NPSR facilitates reward, reinforcement, and addiction-related behaviors. Genetic variation and single nucleotide polymorphism in NPSR are associated with depression, schizophrenia, rheumatoid arthritis, and asthma. NPS interacts with several neurotransmitters including glutamate, noradrenaline, serotonin, corticotropin-releasing factor, and gamma-aminobutyric acid. It also modulates the immune system via augmenting pro-inflammatory cytokines and plays an important role in the pathogenesis of rheumatoid arthritis and asthma. In the present review, we discussed the distribution profile of NPS and NPSR, signaling pathways, and their importance in the pathophysiology of various neurological disorders. We have also proposed the areas where further investigations on the NPS system are warranted.

Investigation of non-invasive focused ultrasound efficacy on depressive-like behavior in hemiparkinsonian rats

Depression is a common non-motor symptom in Parkinson's disease (PD) that includes anhedonia and impacts quality of life but is not effectively treated with conventional antidepressants clinically. Vagus nerve stimulation improves treatment-resistant depression in the general population, but research about its antidepressant efficacy in PD is limited. Here, we administered peripheral non-invasive focused ultrasound to hemiparkinsonian ('PD') and non-parkinsonian (sham) rats to mimic vagus nerve stimulation and assessed its antidepressant-like efficacy. Following 6-hydroxydopamine (6-OHDA) lesion, akinesia-like immobility was assessed in the limb-use asymmetry test, and despair- and anhedonic-like behaviors were evaluated in the forced swim test and sucrose preference test, respectively. After, tyrosine hydroxylase immuno-staining was employed to visualize and quantify dopaminergic degeneration in the substantia nigra pars compacta, ventral tegmental area, and striatum. We found that PD rats exhibited akinesia-like immobility and > 90% reduction in tyrosine hydroxylase immuno-staining ipsilateral to the lesioned side. PD rats also demonstrated anhedonic-like behavior in the sucrose preference test compared to sham rats. No 6-OHDA lesion effect on immobility in the forced swim test limited conclusions about the efficacy of ultrasound on despair-like behavior. However, ultrasound improved anhedonic-like behavior in PD rats and this efficacy was sustained through the end of the 1-week recovery period. The greatest number of animals demonstrating increased sucrose preference was in the PD group receiving ultrasound. Our findings here are the first to posit that peripheral non-invasive focused ultrasound to the celiac plexus may improve anhedonia in PD with further investigation needed to reveal its potential for clinical applicability.

Investigating affective neuropsychiatric symptoms in rodent models of Parkinson's disease

Affective neuropsychiatric disorders such as depression, anxiety and apathy are among the most frequent non-motor symptoms observed in people with Parkinson's disease (PD). These conditions often emerge during the prodromal phase of the disease and are generally considered to result from neurodegenerative processes in meso-corticolimbic structures, occurring in parallel to the loss of nigrostriatal dopaminergic neurons. Depression, anxiety, and apathy are often treated with conventional medications, including selective serotonin reuptake inhibitors, tricyclic antidepressants, and dopaminergic agonists. The ability of these pharmacological interventions to consistently counteract such neuropsychiatric symptoms in PD is still relatively limited and the development of reliable experimental models represents an important tool to identify more effective treatments. This chapter provides information on rodent models of PD utilized to study these affective neuropsychiatric symptoms. Neurotoxin-based and genetic models are discussed, together with the main behavioral tests utilized to identify depression- and anxiety-like behaviors, anhedonia, and apathy. The ability of various therapeutic approaches to counteract the symptoms observed in the various models is also reviewed.

Therapeutic Approaches to Non-Motor Symptoms of Parkinson's Disease: A Current Update on Preclinical Evidence

Despite being classified as a movement disorder, Parkinson's disease (PD) is characterized by a wide range of non-motor symptoms that significantly affect the patients' quality of life. However, clear evidence-based therapy recommendations for non-motor symptoms of PD are uncommon. Animal models of PD have previously been shown to be useful for advancing the knowledge and treatment of motor symptoms. However, these models may provide insight into and assess therapies for non-motor symptoms in PD. This paper highlights non-motor symptoms in preclinical models of PD and the current position regarding preclinical therapeutic approaches for these non-motor symptoms. This information may be relevant for designing future preclinical investigations of therapies for nonmotor symptoms in PD.

Application of Neurotoxin-Induced Animal Models in the Study of Parkinson's Disease-Related Depression: Profile and Proposal

Depression can be a non-motor symptom, a risk factor, and even a co-morbidity of Parkinson's disease (PD). In either case, depression seriously affects the quality of life of PD patients. Unfortunately, at present, a large number of clinical and basic studies focused on the pathophysiological mechanism of PD and the prevention and treatment of motor symptoms. Although there has been increasing attention to PD-related depression, it is difficult to achieve early detection and early intervention, because the clinical guidelines mostly refer to depression developed after or accompanied by motor impairments. Why is there such a dilemma? This is because there has been no suitable preclinical animal model for studying the relationship between depression and PD, and the assessment of depressive behavior in PD preclinical models is as well a very challenging task since it is not free from the confounding from the motor impairment. As a common method to simulate PD symptoms, neurotoxin-induced PD models have been widely used. Studies have found that neurotoxin-induced PD model animals could exhibit depression-like behaviors, which sometimes manifested earlier than motor impairments. Therefore, there have been attempts to establish the PD-related depression model by neurotoxin induction. However, due to a lack of unified protocol, the reported results were diverse. For the purpose of further promoting the improvement and optimization of the animal models and the study of PD-related depression, we reviewed the establishment and evaluation strategies of the current animal models of PD-related depression based on both the existing literature and our own research experience, and discussed the possible mechanism and interventions, in order to provide a reference for future research in this area.

Neuropeptide S Receptor as an Innovative Therapeutic Target for Parkinson Disease

Parkinson disease (PD) is a neurodegenerative disease mainly characterized by the loss of nigral dopaminergic neurons in the substantia nigra pars compacta. Patients suffering from PD develop severe motor dysfunctions and a myriad of non-motor symptoms. The treatment mainly consists of increasing central dopaminergic neurotransmission and alleviating motor symptoms, thus promoting severe side effects without modifying the disease’s progress. A growing body of evidence suggests a close relationship between neuropeptide S (NPS) and its receptor (NPSR) system in PD: (i) double immunofluorescence labeling studies showed that NPSR is expressed in the nigral tyrosine hydroxylase (TH)-positive neurons; (ii) central administration of NPS increases spontaneous locomotion in naïve rodents; (iii) central administration of NPS ameliorates motor and nonmotor dysfunctions in animal models of PD; (iv) microdialysis studies showed that NPS stimulates dopamine release in naïve and parkinsonian rodents; (v) central injection of NPS decreases oxidative damage to proteins and lipids in the rodent brain; and, (vi) 7 days of central administration of NPS protects from the progressive loss of nigral TH-positive cells in parkinsonian rats. Taken together, the NPS/NPSR system seems to be an emerging therapeutic strategy for alleviating motor and non-motor dysfunctions of PD and, possibly, for slowing disease progress.

Sexual dimorphism in rats exposed to maternal high fat diet: alterations in medullary sympathetic network

Exposure to high fat diet during perinatal period (PHFD) leads to neuroplastic changes in autonomic circuits, however, the role of gender has been incompletely understood. This study aims to investigate (i) short, and (ii) long-term effects of PHFD on autonomic outflow, and (iii) sexual dimorphic variations emerge at adulthood. Male and female rats were fed a control diet (13.5 % kcal from fat) or PHFD (60 % kcal from fat) from embryonic day-14 to postnatal day-21. To assess changes in autonomic outflow, heart rate variability (HRV) was analyzed at 10- and 20-week-old ages. Expressions of tyrosine hydroxylase (TH), metabotropic glutamate_2/3 receptor (mGlu_2/3R), N-methyl-D-aspartate₁ receptor (NMDA₁R), and gamma aminobutyric acid_A receptor (GABA_AR) were evaluated by immunohistochemistry. PHFD did not affect the body weight of 4-, 10-or 20-week-old male or female offsprings. PHFD significantly increased the sympathetic marker low frequency (LF) component, and sympatho-vagal balance (LF:HF) only in 10-week-old PHFD males. Compared with control, the propranolol-induced (4 mg·kg^- 1, ip) decline in LF was observed more prominently in PHFD rats, however, these changes were found to be restored at the age of 20 weeks. In caudal ventrolateral medulla and nucleus tractus solitarius, expression of mGlu_2/3R was downregulated in PHFD males, whereas no change was detected in NMDA₁R. The number of GABA_AR-expressing TH-immunoreactive cells was decreased in rostral ventrolateral medulla of PHFD males. The findings of this study suggest that exposure to maternal high-fat diet could lead to autonomic imbalance with increased sympathetic tone in the early adulthood of male offspring rats without developing obesity.

Neuropeptide-S prevents 6-OHDA-induced gastric dysmotility in rats

This study aims to explore the effect of chronic central neuropeptide-S (NPS) treatment on gastrointestinal dysmotility and the changes of cholinergic neurons in the dorsal motor nucleus of the vagus (DMV) of a Parkinson's disease (PD) rat model. The PD model was induced through a unilateral medial forebrain bundle (MFB) administration of the 6-hydroxydopamine (6-OHDA). Locomotor activity (LMA), solid gastric emptying (GE), and gastrointestinal transit (GIT) were measured 7 days after the surgery. NPS was daily administered (1 nmol, icv, 7 days). In substantia nigra (SN), dorsal motor nucleus of the vagus (DMV), and gastric whole-mount samples, changes in tyrosine hydroxylase (TH), choline acetyltransferase (ChAT), neuronal nitric oxide synthase (nNOS), glial fibrillary acidic protein (GFAP), NPS receptor (NPSR), and alpha-synuclein (Ser129) were examined by immunohistochemistry. Cuprolinic blue staining was used to evaluate the number of neuronal cells in myenteric ganglia. The GIT rate, the total number of myenteric neurons, and the expressions of ChAT, nNOS, TH, and GFAP in the myenteric plexus were not changed in rats that received the 6-OHDA. Chronic NPS treatment reversed 6-OHDA-induced impairment of the motor performance, and GE, while preventing the loss of dopaminergic and cholinergic neurons in SN and DMV, respectively. NPS attenuated 6-OHDA-induced α-syn (Ser129) pathology both in SN and DMV. Additionally, expression of NPSR protein was detected in gastro-projecting cells in DMV. Taken together, centrally applied NPS seems to prevent 6-OHDA-induced gastric dysmotility through a neuroprotective action on central vagal circuitry.

The role of autonomic pathways in peripheral apelin-induced gastrointestinal dysmotility: involvement of the circumventricular organs

NEW FINDINGS

What is the central question of this study? Are central autonomic pathways and circumventricular organs involved in apelin-induced inhibition of gut motility? What is the main finding and its importance? Peripherally administered apelin-13 inhibits gastric and colonic motor functions through sympathetic and parasympathetic autonomic pathways, which seems to be partly mediated by the apelin receptor in circumventricular organs.

ABSTRACT

Peripheral administration of apelin-13 has been shown to inhibit gastrointestinal (GI) motility, but the relevant mechanisms are incompletely understood. This study aimed to investigate (i) whether the apelin receptor (APJ) is expressed in circumventricular structures involved in autonomic functions, (ii) whether they are activated by peripherally administered apelin, (iii) the role of autonomic pathways in peripheral exogenous apelin-induced GI dysmotility, and (iv) the changes in apelin levels in the extracellular environment of the brain following its peripheral application. Ninety minutes after apelin-13 administration (300 μg kg^-1 , i.p.), gastric emptying (GE) and colon transit (CT) were measured in rats that underwent parasympathectomy and/or sympathectomy. Plasma and cerebrospinal fluid (CSF) samples were also collected from another group of rats that received apelin-13 or vehicle injection. The immunoreactivities for APJ and c-Fos in circumventricular organs (CVOs) were evaluated by immunohistochemistry. Compared with vehicle-treated rats, GE and CT were inhibited significantly by apelin-13 treatment, and were completely restored in animals that underwent the combination of parasympathectomy and sympathectomy and sympathectomy alone, respectively. Apelin concentrations were elevated in both plasma and CSF following peripheral administration of apelin-13. APJ expression was detected in area postrema (AP), subfornical organ and organum vasculosum of lamina terminalis, and c-Fos expression was observed in response to apelin injection. Apelin-induced c-Fos expression in AP was partially attenuated by pretreatment with the cholecystokinin-1 receptor antagonist lorglumide, whereas it was completely abolished in vagotomized rats. The present data suggest that APJ in CVOs could indirectly contribute to the inhibitory action of peripheral apelin on GI motor functions.

Modeling Parkinson's Disease Neuropathology and Symptoms by Intranigral Inoculation of Preformed Human α-Synuclein Oligomers

The accumulation of aggregated α-synuclein (αSyn) is a hallmark of Parkinson's disease (PD). Current evidence indicates that small soluble αSyn oligomers (αSynOs) are the most toxic species among the forms of αSyn aggregates, and that size and topological structural properties are crucial factors for αSynOs-mediated toxicity, involving the interaction with either neurons or glial cells. We previously characterized a human αSynO (H-αSynO) with specific structural properties promoting toxicity against neuronal membranes. Here, we tested the neurotoxic potential of these H-αSynOs in vivo, in relation to the neuropathological and symptomatic features of PD. The H-αSynOs were unilaterally infused into the rat substantia nigra pars compacta (SNpc). Phosphorylated αSyn (p129-αSyn), reactive microglia, and cytokine levels were measured at progressive time points. Additionally, a phagocytosis assay in vitro was performed after microglia pre-exposure to αsynOs. Dopaminergic loss, motor, and cognitive performances were assessed. H-αSynOs triggered p129-αSyn deposition in SNpc neurons and microglia and spread to the striatum. Early and persistent neuroinflammatory responses were induced in the SNpc. In vitro, H-αSynOs inhibited the phagocytic function of microglia. H-αsynOs-infused rats displayed early mitochondrial loss and abnormalities in SNpc neurons, followed by a gradual nigrostriatal dopaminergic loss, associated with motor and cognitive impairment. The intracerebral inoculation of structurally characterized H-αSynOs provides a model of progressive PD neuropathology in rats, which will be helpful for testing neuroprotective therapies.