Structure-activity studies of neurotensin on muscular rigidity and tremors induced by 6-hydroxydopamine lesions in the posterolateral hypothalamus of the rat

Demystifying the Neuroprotective Role of Neuropeptides in Parkinson's Disease: A Newfangled and Eloquent Therapeutic Perspective

Parkinson's disease (PD) refers to one of the eminently grievous, preponderant, tortuous nerve-cell-devastating ailments that markedly impacts the dopaminergic (DArgic) nerve cells of the midbrain region, namely the substantia nigra pars compacta (SN-PC). Even though the exact etiopathology of the ailment is yet indefinite, the existing corroborations have suggested that aging, genetic predisposition, and environmental toxins tremendously influence the PD advancement. Additionally, pathophysiological mechanisms entailed in PD advancement encompass the clumping of α-synuclein inside the lewy bodies (LBs) and lewy neurites, oxidative stress, apoptosis, neuronal-inflammation, and abnormalities in the operation of mitochondria, autophagy lysosomal pathway (ALP), and ubiquitin-proteasome system (UPS). The ongoing therapeutic approaches can merely mitigate the PD-associated manifestations, but until now, no therapeutic candidate has been depicted to fully arrest the disease advancement. Neuropeptides (NPs) are little, protein-comprehending additional messenger substances that are typically produced and liberated by nerve cells within the entire nervous system. Numerous NPs, for instance, substance P (SP), ghrelin, neuropeptide Y (NPY), neurotensin, pituitary adenylate cyclase-activating polypeptide (PACAP), nesfatin-1, and somatostatin, have been displayed to exhibit consequential neuroprotection in both in vivo and in vitro PD models via suppressing apoptosis, cytotoxicity, oxidative stress, inflammation, autophagy, neuronal toxicity, microglia stimulation, attenuating disease-associated manifestations, and stimulating chondriosomal bioenergetics. The current scrutiny is an effort to illuminate the neuroprotective action of NPs in various PD-experiencing models. The authors carried out a methodical inspection of the published work procured through reputable online portals like PubMed, MEDLINE, EMBASE, and Frontier, by employing specific keywords in the subject of our article. Additionally, the manuscript concentrates on representing the pathways concerned in bringing neuroprotective action of NPs in PD. In sum, NPs exert substantial neuroprotection through regulating paramount pathways indulged in PD advancement, and consequently, might be a newfangled and eloquent perspective in PD therapy.

The Emerging Role of Neuropeptides in Parkinson's Disease

Parkinson’s disease (PD), the second most common age-related neurodegenerative disease, results from the loss of dopamine neurons in the substantia nigra. This disease is characterized by cardinal non-motor and motor symptoms. Several studies have demonstrated that neuropeptides, such as ghrelin, neuropeptide Y, pituitary adenylate cyclase-activating polypeptide, substance P, and neurotensin, are related to the onset of PD. This review mainly describes the changes in these neuropeptides and their receptors in the substantia nigra-striatum system as well as the other PD-related brain regions. Based on several in vitro and in vivo studies, most neuropeptides play a significant neuroprotective role in PD by preventing caspase-3 activation, decreasing mitochondrial-related oxidative stress, increasing mitochondrial biogenesis, inhibiting microglial activation, and anti-autophagic activity. Thus, neuropeptides may provide a new strategy for PD therapy.

The role of neurotensin in physiologic and pathologic processes

PURPOSE OF REVIEW

Neurotensin is a 13-amino acid peptide found in the central nervous system central nervous system and the gastrointestinal tract. Since its initial discovery in 1973, neurotensin has been shown to play a role in a wide range of physiologic and pathologic processes throughout the body. Ongoing research efforts continue to clarify the role of neurotensin in various central nervous system and gastrointestinal processes, as well as how disruption of these normal mechanisms may lead to diseases ranging from schizophrenia to colorectal cancer. The goal of this review is to provide an overview of the most recent advances in the field of neurotensin research, in the context of what has been previously published.

RECENT FINDINGS

Because of the seemingly unrelated functions of neurotensin in the central nervous system and the periphery, the scope of the articles reviewed is rather broad. Contributions continue to be made to our understanding of the downstream effects of neurotensin signaling and the complex feedback loops between neurotensin and other signaling molecules. By selective targeting or blockade of specific neurotensin receptors, investigators have identified potential drugs for use in the treatment of schizophrenia, alcoholism, chronic pain, or cancer. Neurotensin-based pharmacologic agents are being used successfully in animal models for a number of these conditions.

SUMMARY

The review highlights the wide array of biological processes in which neurotensin has a role, and summarizes the most recent advances in various fields of neurotensin research. The knowledge gained through this research has led to the development of first-in-class drugs for the treatment of various medical conditions, and it is clear that in the coming years some of these agents will be ready to move from the bench to the bedside in clinical trials.

Neurotensin receptor mechanisms and its modulation of glutamate transmission in the brain: relevance for neurodegenerative diseases and their treatment

The extracellular accumulation of glutamate and the excessive activation of glutamate receptors, in particular N-methyl-D-aspartate (NMDA) receptors, have been postulated to contribute to the neuronal cell death associated with chronic neurodegenerative disorders such as Parkinson's disease. Findings are reviewed indicating that the tridecaptide neurotensin (NT) via activation of NT receptor subtype 1 (NTS1) promotes and reinforces endogenous glutamate signalling in discrete brain regions. The increase of striatal, nigral and cortical glutamate outflow by NT and the enhancement of NMDA receptor function by a NTS1/NMDA interaction that involves the activation of protein kinase C may favour the depolarization of NTS1 containing neurons and the entry of calcium. These results strengthen the hypothesis that NT may be involved in the amplification of glutamate-induced neurotoxicity in mesencephalic dopamine and cortical neurons. The mechanisms involved may include also antagonistic NTS1/D2 interactions in the cortico-striatal glutamate terminals and in the nigral DA cell bodies and dendrites as well as in the nigro-striatal DA terminals. The possible increase in NT levels in the basal ganglia under pathological conditions leading to the NTS1 enhancement of glutamate signalling may contribute to the neurodegeneration of the nigro-striatal dopaminergic neurons found in Parkinson's disease, especially in view of the high density of NTS1 receptors in these neurons. The use of selective NTS1 antagonists together with conventional drug treatments could provide a novel therapeutic approach for treatment of Parkinson's disease.

Neurotensin: role in psychiatric and neurological diseases

Neurotensin (NT), an endogenous brain-gut peptide, has a close anatomical and functional relationship with the mesocorticolimbic and neostriatal dopamine system. Dysregulation of NT neurotransmission in this system has been hypothesized to be involved in the pathogenesis of schizophrenia. Additionally, NT containing circuits have been demonstrated to mediate some of the mechanisms of action of antipsychotic drugs, as well as the rewarding and/or sensitizing properties of drugs of abuse. NT receptors have been suggested to be novel targets for the treatment of psychoses or drug addiction.

Antiparkinson-like effects of a novel neurotensin analog in unilaterally 6-hydroxydopamine lesioned rats

Parkinson's disease is a neuropathological disorder involving the degeneration of dopamine neurons in the substantia nigra, with the resultant loss of their terminals in the striatum. This dopamine loss causes most of the motor disturbances associated with the disease. One animal model of Parkinson's disease involves destruction of the nigrostriatal pathway with a neurotoxin (6-hydroxydopamine) injected into this pathway. In unilaterally lesioned animals, injection of D-amphetamine causes rotation towards the lesioned side, while injection of apomorphine acting upon supersensitive postsynaptic dopamine receptors causes rotation away from the lesioned side. In this study, we tested the effects of acute and subchronic injection of a neurotensin analog (NT69L) on the rotational behavior induced by D-amphetamine (5 mg/kg) or apomorphine (600 microg/kg) in unilaterally 6-hydroxydopamine lesioned rats. Pretreatment of animals with intraperitoneal injections of NT69L (1 mg/kg) resulted in a significant reduction of apomorphine-induced contralateral rotation and D-amphetamine-induced ipsilateral rotation in these lesioned rats with an ED(50) of 40 and 80 microg/kg, respectively. After three daily injections of NT69L, its effects on this rotational behavior were unchanged, suggesting that no tolerance develops to this effect of NT69L.

Characterization of neurotensin-like immunoreactivity in human basal ganglia: increased neurotensin levels in substantia nigra in Parkinson's disease

A method that combines high performance liquid chromatography with radioimmunoassay (HPLC/RIA) has been used to characterize neurotensin-like immunoreactivity (NT-IR) in the basal ganglia from control subjects and Parkinson's disease (PD) patients. In samples from the caudate nucleus and putamen, NT-IR eluted as two HPLC peaks. One was indistinguishable from the synthetic tridecapeptide, while the other peak corresponded to oxidized NT, as judged by its chromatographic behaviour and its reaction with the antiserum employed. There were marked discrepancies between the IR detected in crude extracts and that in HPLC purified samples. NT levels (HPLC/RIA) were unaltered in the caudate nucleus, putamen and both segments of the globus pallidus in the parkinsonian brain. In contrast, there was a two-fold increase in NT content in both zona compacta and zona reticulata of the substantia nigra in PD patients compared to controls. Degeneration of the nigrostriatal pathway and/or prolonged antiparkinsonian treatment in PD appears to alter neurotensin levels in an attempt to activate the dopaminergic nigrostriatal pathway.

Sex difference in the neurotensin-immunoreactive cell populations of the preoptic area in quail (Coturnix japonica)

The distribution of neurotensin-immunoreactive cells and fibers was analyzed by immunocytochemistry in the forebrain of male and female Japanese quail (Coturnix japonica) by using an antibody directed against the C-terminal part of the molecule. Immunoreactive perikarya were located almost exclusively in the medial preoptic area with small populations also being present in the nucleus paraventricularis and in the tuberal region. Immunoreactive fibers were observed not only throughout the preoptic area-hypothalamus, but also in the septal region, nucleus intercollicularis, substantia grisea centralis and the classical catecholaminergic areas of the mesencephalon, such as the area ventralis of Tsai and the nucleus tegmenti pedunculo-pontinus, pars compacta. The preoptic neurotensin-immunoreactive cells were exclusively located within the boundaries of the sexually dimorphic medial preoptic nucleus. They were significantly more numerous in females than in males. In females, the number of neurotensin cells varied during the ovulatory cycle: fewer cells were observed in birds that were about to lay an egg (they had a calcified egg in the oviduct) than in those that had already laid or were not going to lay on that day. These data indicate major variations in the expression of neurotensin in response to neurochemical or neuroendocrine changes associated with ovulation.