Self-Amplification of Nigral Degeneration in Parkinson's Disease: A Hypothesis

Obstructive sleep apnea in Parkinson's disease: A prevalent, clinically relevant and treatable feature

Parkinson's disease (PD) is a chronic neurodegenerative disease characterized by motor and non-motor symptoms, including obstructive sleep apnea (OSA), a common comorbid sleep disorder. The prevalence of OSA in PD is high, and its impact on quality of life, accident risk, and limited treatment options underscores the need for vigilant monitoring and effective interventions. OSA is observed in 20-70% of PD patients, whereas the general population exhibits a lower prevalence ranging from 2 to 14%. These discrepancies in prevalence may be attributed to differences in demographic characteristics, sample sizes with selection bias, and variations in scoring systems for apnea and hypopnea events used across different studies. This review highlights the potential pathogenesis of comorbid OSA in PD and provides an overview of ongoing clinical trials investigating interventions for this condition. Several mechanisms have been implicated in the development of OSA in PD, including intermittent hypoxemia, sleep fragmentation, alterations in the glymphatic system homeostasis, upper airway obstruction, and inflammation. Given the adverse effects of PD comorbid OSA, early intervention measures are crucial. It is imperative to conduct longitudinal studies and clinical trials to elucidate the pathogenesis and develop novel and effective interventions for OSA in PD patients. These efforts aim to delay the progression of PD, enhance patients' quality of life, and alleviate the burden on society and families.

A new experimental evidence that olfactory bulb lesion may be a causative factor for substantia nigra degeneration; preliminary study

Background: Anosmia has been considered as the first diagnostic criteria of Parkinson disease (PD), we investigated the effect of the olfactory bulbectomy (OBX) on histopathological features of the substantia nigra in an animal model.Methods: Twenty-seven male rats were used in this study. Animals were divided into three groups as five (control), six SHAM and sixteen study (OBL) groups. Nothing was done in the control group, the only burr hole was done in the SHAM group, OBL was not applied, and bilateral OBL was performed in the study group, and followed ten weeks, then animals were decapitated. Olfactory bulb volumes were measured by macro anatomically. The olfactory bulbs and substantia nigra sections were analyzed by a stereological method to evaluate olfactory glomerulus and neuron density of substantia nigra per cubic centimeter and compared with statistically.Results: The mean olfactory bulb volume, degenerated olfactory glomerulus density and degenerated neuron density of substantia nigra were measured as:(4.14 ± 0.20) mm³, (1 ± 1)/mm³ and (7 ± 2)/mm³ in control (Group I); (3.6 ± 0.16)/mm³, (4 ± 1)/mm³ and(32 ± 7)/mm³ in SHAM (Group II) and (2.2 ± 0.9)/mm³, (112 ± 18)/mm³ and (1543 ± 115)/mm³in study group (Group III). Diminished olfactory bulb volume was observed in Group III animals.Conclusions: We concluded that OBL may lead to the degeneration of substantia nigra.

Cyclosomatostatin- and haloperidol-induced catalepsy in Wistar rats: Differential responsiveness to sleep deprivation

Total sleep deprivation (SD) has been found to mitigate motor dysfunctions in Parkinson's disease. Apparently, the similar sensitivity of an animal model for parkinsonism would support the model's validity. Recently, we described catalepsy induced in Wistar rats by somatostatin antagonist, cyclosomatostatin (cSST); this model simulates such a disease-associated abnormality as a fall in brain somatostatin levels. To evaluate the similarity between the cSST model and Parkinson's disease, we assessed here the responsiveness of cSST-induced catalepsy to 1-h and 3-h SD. In parallel, the influence of SD on catalepsy induced by a dopamine receptor antagonist, haloperidol, was examined. It was found that the short-term SD failed to influence cataleptic responses of both types (sleep deprived rats and undisturbed ones displayed a similar duration of immobility, p > 0.05). By contrast, 3-h SD suppressed (p < 0.01) cSST-induced catalepsy, however, enhanced (p < 0.01) cataleptic response to haloperidol. Thus, the anti-cataleptic effect of SD appears to be cSST-specific. These findings support the validity of the cSST-induced catalepsy in Wistar rats as a model for parkinsonian motor dysfunctions.

Brain sites mediating cyclosomatostatin-induced catalepsy in Wistar rats: A specific role for the nigrostriatal system and locus coeruleus

A decrease in somatostatin activity is observed in the Parkinsonian brain. In recent experiments on rats, we simulated this abnormality by intracerebroventricular injections of a somatostatin antagonist, cyclosomatostatin. The treated animals displayed catalepsy, a state that resembles the extrapyramidal signs of Parkinson's disease. The neuroanatomical substrates mediating the catalepsy-inducing effect of cyclosomatostatin are unknown. To clarify this issue, we assessed here the action of cyclosomatostatin injected into the substantia nigra pars compacta (SNc), dorsal striatum (DS), locus coeruleus (LC), pedunculopontine tegmental nucleus (PPTg), and inferior colliculus (IC). The experiments were conducted with male Wistar rats of 270-290 g bw, catalepsy was evaluated by using the bar test. The injections into the PPTg and IC were without effect whereas the intra-SNc, intra-DS, and intra-LC administrations produced distinct cataleptic response. Thus, it was shown for the first time that the LC is a brain center capable of causing catalepsy. These data provide new insights into the neuroanatomical organization of the catalepsy-initiating mechanism and suggest the LC representing a potential target for therapeutic manipulations of extrapyramidal dysfunctions.

The Interaction between Obstructive Sleep Apnea and Parkinson's Disease: Possible Mechanisms and Implications for Cognitive Function

Parkinson's disease (PD) is a relentlessly progressive neurodegenerative disorder associated with hallmark motor and nonmotor symptoms (NMS) such as sleep disturbances and cognitive dysfunction. While dopaminergic treatments have improved the motor aspects of PD, progression remains inevitable. Research has recently increasingly focused on strategies to modify disease progression and on nonmotor manifestations of PD, given their impact on patients' quality of life. Obstructive sleep apnea (OSA) is a treatable sleep disorder, common in the general population, associated with excessive daytime sleepiness and neurocognitive deficits. Neuroimaging has demonstrated structural and functional changes in OSA patients; in animal models, OSA causes brain inflammation and oxidative injury, including in key areas involved in PD pathophysiology such as locus coeruleus. The prevalence of OSA in PD has been variable in studies to date, and potential consequences and interrelationship between the two disorders have not been well studied. There is however emerging evidence that OSA is associated with increased NMS in PD, particularly cognitive dysfunction. This review focuses on the possible interrelationship between OSA and PD. Mechanisms promoting OSA in PD will be reviewed, as well as mechanisms whereby OSA can affect the neurodegenerative process in PD.

Treatment with a substance P receptor antagonist is neuroprotective in the intrastriatal 6-hydroxydopamine model of early Parkinson's disease

Neuroinflammation and blood brain barrier (BBB) dysfunction have been implicated in the pathogenesis of Parkinson's disease (PD). The neuropeptide substance P (SP) is an important mediator of both neuroinflammation and BBB dysfunction through its NK1 receptor in a process known as neurogenic inflammation. Increased SP content has previously been reported following 6-OHDA treatment in vitro, with the levels of SP correlating with cell death. The present study used an in vivo 6-OHDA lesion model to determine if dopaminergic degeneration was associated with increased SP in the substantia nigra and whether this degeneration could be prevented by using a SP, NK1 receptor antagonist. Unilateral, intrastriatal 6-OHDA lesions were induced and SP (10 µg/2 µL) or the NK1 receptor antagonists, N-acetyl-L-tryptophan (2 µL at 50 nM) or L-333,060 (2 µL at 100 nM), administered immediately after the neurotoxin. Nigral SP content was then determined using immunohistochemical and ELISA methods, neuroinflammation and barrier integrity was assessed using Iba-1, ED-1, GFAP and albumin immunohistochemistry, while dopaminergic cell loss was assessed with tyrosine hydroxylase immunohistochemistry. Motor function in all animals was assessed using the rotarod task. Intrastriatal 6-OHDA lesioning produced an early and sustained increase in ipsilateral nigral SP content, along with a breakdown of the BBB and activation of microglia and astrocytes. Further exacerbation of SP levels accelerated disease progression, whereas NK1 receptor antagonist treatment protected dopaminergic neurons, preserved barrier integrity, reduced neuroinflammation and significantly improved motor function. We propose that neurogenic inflammation contributes to dopaminergic degeneration in early experimental PD and demonstrate that an NK1 receptor antagonist may represent a novel neuroprotective therapy.

The contributions of antioxidant activity of lipoic acid in reducing neurogenerative progression of Parkinson's disease: a review

ABSTRACT This work reviews the evidence of the mechanism of neuronal degeneration in Parkinson's disease (PD) and the neuroprotective effect of lipoic acid and its use in the treatment of PD. PD is characterized by slow and progressive degeneration of dopaminergic neurons of the substantia nigra pars compacta, leading to reduction of the striatal dopaminergic terminals. It is known that several factors influence neuronal damage. Among these factors, oxidative stress, immune system activity, microglial cells, and apoptotic mechanisms are of major importance. Currently, several antioxidants have been studied with the aim of reducing/slowing the progression of neurodegenerative processes. Lipoic acid is considered a universal antioxidant because it is an amphipathic substance. Lipoic acid and its reduced form, dihidrolipoic acid, act against reactive oxygen species, reducing oxidative stress. Therefore, this antioxidant has been used in the treatment of many diseases, including a new perspective for the treatment of Parkinson's disease.