Striatal neuropeptide levels in Parkinson's disease patients

Brain-Biomarker Changes in Body Fluids of Patients with Parkinson's Disease

Parkinson's disease (PD) is an incurable neurodegenerative disease that is rarely diagnosed at an early stage. Although the understanding of PD-related mechanisms has greatly improved over the last decade, the diagnosis of PD is still based on neurological examination through the identification of motor symptoms, including bradykinesia, rigidity, postural instability, and resting tremor. The early phase of PD is characterized by subtle symptoms with a misdiagnosis rate of approximately 16-20%. The difficulty in recognizing early PD has implications for the potential use of novel therapeutic approaches. For this reason, it is important to discover PD brain biomarkers that can indicate early dopaminergic dysfunction through their changes in body fluids, such as saliva, urine, blood, or cerebrospinal fluid (CSF). For the CFS-based test, the invasiveness of sampling is a major limitation, whereas the other body fluids are easier to obtain and could also allow population screening. Following the identification of the crucial role of alpha-synuclein (α-syn) in the pathology of PD, a very large number of studies have summarized its changes in body fluids. However, methodological problems have led to the poor diagnostic/prognostic value of this protein and alternative biomarkers are currently being investigated. The aim of this paper is therefore to summarize studies on protein biomarkers that are alternatives to α-syn, particularly those that change in nigrostriatal areas and in biofluids, with a focus on blood, and, eventually, saliva and urine.

Cell–Cell Communication Alterations via Intercellular Signaling Pathways in Substantia Nigra of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative movement disorder characterized with dopaminergic neuron (DaN) loss within the substantia nigra (SN). Despite bulk studies focusing on intracellular mechanisms of PD inside DaNs, few studies have explored the pathogeneses outside DaNs, or between DaNs and other cells. Here, we set out to probe the implication of intercellular communication involving DaNs in the pathogeneses of PD at a systemic level with bioinformatics methods. We harvested three online published single-cell/single-nucleus transcriptomic sequencing (sc/snRNA-seq) datasets of human SN (GSE126838, GSE140231, and GSE157783) from the Gene Expression Omnibus (GEO) database, and integrated them with one of the latest integration algorithms called Harmony. We then applied CellChat, the latest cell–cell communication analytic algorithm, to our integrated dataset. We first found that the overall communication quantity was decreased while the overall communication strength was enhanced in PD sample compared with control sample. We then focused on the intercellular communication where DaNs are involved, and found that the communications between DaNs and other cell types via certain signaling pathways were selectively altered in PD, including some growth factors, neurotrophic factors, chemokines, etc. pathways. Our bioinformatics analysis showed that the alteration in intercellular communications involving DaNs might be a previously underestimated aspect of PD pathogeneses with novel translational potential.

What substance P might tell us about the prognosis and mechanism of Parkinson's disease?

The neuropeptide substance P (SP) plays an important role in neurodegenerative disorders, among which Parkinson's disease (PD). In the present work we have reviewed the involvement of SP and its preferred receptor (NK1-R) in motor and non-motor PD symptoms, in both PD animal models and patients. Despite PD is primarily a motor disorder, non-motor abnormalities, including olfactory deficits and gastrointestinal dysfunctions, can represent diagnostic PD predictors, according to the hypothesis that the olfactory and the enteric nervous system represent starting points of neurodegeneration, ascending to the brain via the sympathetic fibers and the vagus nerve. In PD patients, the α-synuclein aggregates in the olfactory bulb and the gastrointestinal tract, as well as in the dorsal motor nucleus of the vagus nerve often co-localize with SP, indicating SP-positive neurons as highly vulnerable sites of degeneration. Considering the involvement of the SP/NK1-R in both the periphery and specific brain areas, this system might represent a neuronal substrate for the symptom and disease progression, as well as a therapeutic target for PD.

Brain and Peripheral Atypical Inflammatory Mediators Potentiate Neuroinflammation and Neurodegeneration

Neuroinflammatory response is primarily a protective mechanism in the brain. However, excessive and chronic inflammatory responses can lead to deleterious effects involving immune cells, brain cells and signaling molecules. Neuroinflammation induces and accelerates pathogenesis of Parkinson’s disease (PD), Alzheimer’s disease (AD) and Multiple sclerosis (MS). Neuroinflammatory pathways are indicated as novel therapeutic targets for these diseases. Mast cells are immune cells of hematopoietic origin that regulate inflammation and upon activation release many proinflammatory mediators in systemic and central nervous system (CNS) inflammatory conditions. In addition, inflammatory mediators released from activated glial cells induce neurodegeneration in the brain. Systemic inflammation-derived proinflammatory cytokines/chemokines and other factors cause a breach in the blood brain-barrier (BBB) thereby allowing for the entry of immune/inflammatory cells including mast cell progenitors, mast cells and proinflammatory cytokines and chemokines into the brain. These peripheral-derived factors and intrinsically generated cytokines/chemokines, α-synuclein, corticotropin-releasing hormone (CRH), substance P (SP), beta amyloid 1–42 (Aβ1–42) peptide and amyloid precursor proteins can activate glial cells, T-cells and mast cells in the brain can induce additional release of inflammatory and neurotoxic molecules contributing to chronic neuroinflammation and neuronal death. The glia maturation factor (GMF), a proinflammatory protein discovered in our laboratory released from glia, activates mast cells to release inflammatory cytokines and chemokines. Chronic increase in the proinflammatory mediators induces neurotoxic Aβ and plaque formation in AD brains and neurodegeneration in PD brains. Glial cells, mast cells and T-cells can reactivate each other in neuroinflammatory conditions in the brain and augment neuroinflammation. Further, inflammatory mediators from the brain can also enter into the peripheral system through defective BBB, recruit immune cells into the brain, and exacerbate neuroinflammation. We suggest that mast cell-associated inflammatory mediators from systemic inflammation and brain could augment neuroinflammation and neurodegeneration in the brain. This review article addresses the role of some atypical inflammatory mediators that are associated with mast cell inflammation and their activation of glial cells to induce neurodegeneration.

Continuous infusion of substance P into rat striatum alleviates nociceptive behavior via phosphorylation of extracellular signal-regulated kinase 1/2

Intraplantar injection of 0.4% formalin into the rat hind paw leads to a biphasic nociceptive response; an 'acute' phase (0-15 min) and 'tonic' phase (16-120 min), which is accompanied by significant phosphorylation of extracellular signal-regulated kinase (ERK)1/2 in the contralateral striatum at 120 min post-formalin injection. To uncover a possible relationship between the slow-onset substance P (SP) release and increased ERK1/2 phosphorylation in the striatum, continuous infusion of SP into the striatum by reverse microdialysis (0.4 μg/mL in microdialysis fiber, 1 μL/min) was performed to mimic volume neurotransmission of SP. Continuous infusion for 3 h of SP reduced the duration of 'tonic' phase nociception, and this SP effect was mediated by neurokinin 1 (NK1) receptors since pre-treatment with NK1 receptor antagonist CP96345 (10 μM) blocked the effect of SP infusion. However, formalin-induced 'tonic' phase nociception was significantly prolonged following acute injection of the MAP/ERK kinase 1/2 inhibitor PD0325901 (100 pmol) by microinjection. The coinfusion of SP and PD0325901 significantly increased the 'tonic' phase of nociception. These data demonstrate that volume transmission of striatal SP triggered by peripheral nociceptive stimulation does not lead to pain facilitation but a significant decrease of tonic nociception by the activation of the SP-NK1 receptor-ERK1/2 system. Noxious stimulation induces a slow-onset substance P (SP) release as a volume transmitter, activating extra-synaptic NK1 receptors, and evokes phosphorylation of extracellular signal-regulated kinase (ERK) 1/2. The SP-NK1-ERK1/2 system in the striatum decreases tonic nociception.

Modulation of acetylcholine release by cholecystokinin in striatum: receptor specificity; role of dopaminergic neuronal activity

Cholecystokinin, a neuroactive peptide functioning as a neurotransmitter and neuromodulator in the central nervous system, mediates a number of processes and is implicated in neurological and psychiatric disorders such as Parkinson's disease, anxiety and schizophrenia. Striatum is one of the brain structures with the highest concentrations of CCK in the brain, rich in CCK receptors as well. The physiological effect of CCK on cholinergic interneurons, which are the major interneurons in striatum and the modulatory interactions which exist between dopamine, acetylcholine and cholecystokinin in this brain structure are still unclear. We studied the effect of cholecystokinin octapeptide (CCK-8) on the release of acetylcholine (ACh) from striatal slices of the rat brain. CCK-8 (0.01-0.1μM) showed no statistically significant effect on the basal but enhanced dose-dependently the electrically (2Hz)-evoked release of [(3)H]ACh. When slices were preperfused with 100μM sulpiride, a selective dopamine D(2) receptor antagonist, the CCK-8 (0.01μM) effect on electrically stimulated ACh release was increased nearly 2-fold. A similar increase was observed after depletion of endogenous dopamine (DA) from nigro-striatal dopaminergic neurons with 6-hydroxydopamine (6-OHDA) (2× 250μg/animal, i.c.v.). Furthermore in the presence of dopamine (100μM) or apomorphine (10μM), the prototypical DA receptor agonist, CCK-8 (0.01μM) failed to enhance the stimulation-evoked release of [(3)H]ACh. The D(2) receptor agonist quinpirol (1μM) abolished the CCK-8 effect on electrically stimulated ACh release as well. The increase in electrically induced [(3)H]ACh release produced by 0.01μM CCK-8 was antagonized by d,l loxiglumide (CR 1505), 10μM, a non-peptide CCK-A receptor antagonist and by Suc-Tyr-(OSO3)-Met-Gly-Trp-Met-Asp-β-phenethyl-amide (GE-410), 1μM, a peptide CCK-A receptor antagonist. The antagonistic effect of GE-410 on the CCK-8-potentiated, electrically induced release of [(3)H]ACh was studied in striatum for the first time. CAM 1028 (10μM), a CCK-B receptor antagonist, also prevented the potentiating effect of CCK-8 (0.01μM) on electrically stimulated release of [(3)H]ACh. The presented results indicate that (i) CCK-8 is capable of increasing ACh elicited by field electrical stimulation in striatum; (ii) CCK-8 is more effective in its ACh-stimulating effect when dopaminergic activity in striatum is blocked i.e. CCK-8-facilitated release of electrically induced ACh from cholinergic interneurons in the striatum is under the inhibitory control of the tonic activity of dopamine from the nigrostriatal pathway; (iii) the enhancing effect of CCK-8 on electrically evoked ACh release is mediated through both CCK-A and CCK-B cholecystokinin receptors located most likely on the cell bodies of cholinergic interneurons in striatum.

Animal models of Parkinson's disease: a source of novel treatments and clues to the cause of the disease

Animal models of Parkinson's disease (PD) have proved highly effective in the discovery of novel treatments for motor symptoms of PD and in the search for clues to the underlying cause of the illness. Models based on specific pathogenic mechanisms may subsequently lead to the development of neuroprotective agents for PD that stop or slow disease progression. The array of available rodent models is large and ranges from acute pharmacological models, such as the reserpine- or haloperidol-treated rats that display one or more parkinsonian signs, to models exhibiting destruction of the dopaminergic nigro-striatal pathway, such as the classical 6-hydroxydopamine (6-OHDA) rat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse models. All of these have provided test beds in which new molecules for treating the motor symptoms of PD can be assessed. In addition, the emergence of abnormal involuntary movements (AIMs) with repeated treatment of 6-OHDA-lesioned rats with L-DOPA has allowed for examination of the mechanisms responsible for treatment-related dyskinesia in PD, and the detection of molecules able to prevent or reverse their appearance. Other toxin-based models of nigro-striatal tract degeneration include the systemic administration of the pesticides rotenone and paraquat, but whilst providing clues to disease pathogenesis, these are not so commonly used for drug development. The MPTP-treated primate model of PD, which closely mimics the clinical features of PD and in which all currently used anti-parkinsonian medications have been shown to be effective, is undoubtedly the most clinically-relevant of all available models. The MPTP-treated primate develops clear dyskinesia when repeatedly exposed to L-DOPA, and these parkinsonian animals have shown responses to novel dopaminergic agents that are highly predictive of their effect in man. Whether non-dopaminergic drugs show the same degree of predictability of response is a matter of debate. As our understanding of the pathogenesis of PD has improved, so new rodent models produced by agents mimicking these mechanisms, including proteasome inhibitors such as PSI, lactacystin and epoximycin or inflammogens like lipopolysaccharide (LPS) have been developed. A further generation of models aimed at mimicking the genetic causes of PD has also sprung up. Whilst these newer models have provided further clues to the disease pathology, they have so far been less commonly used for drug development. There is little doubt that the availability of experimental animal models of PD has dramatically altered dopaminergic drug treatment of the illness and the prevention and reversal of drug-related side effects that emerge with disease progression and chronic medication. However, so far, we have made little progress in moving into other pharmacological areas for the treatment of PD, and we have not developed models that reflect the progressive nature of the illness and its complexity in terms of the extent of pathology and biochemical change. Only when this occurs are we likely to make progress in developing agents to stop or slow the disease progression. The overarching question that draws all of these models together in the quest for better drug treatments for PD is how well do they recapitulate the human condition and how predictive are they of successful translation of drugs into the clinic? This article aims to clarify the current position and highlight the strengths and weaknesses of available models.

Role of central dopaminergic circuitry in pain processing and nitroglycerin-induced hyperalgesia

Experimental evidence shows that dopaminergic transmission within the basal ganglia is involved in the modulation of nociceptive information. Epidemiological studies show that in some disease states inherent pathophysiological mechanisms that involve degenerative changes (Parkinson's disease; PD) can also impact negatively on other unrelated functional systems (i.e. nociception). Delayed Fos expression in response to nitroglycerin (NTG) administration is a procedure used to identify the neuroanatomical substrates of the migraine condition. In this study, we investigated the influence of dopaminergic nigrostriatal denervation, obtained by intrastriatal injection of 6-hydroxydopamine (6-OHDA), on this response in Sprague-Dawley rats. We also explored the effects on the NTG-induced hyperalgesic response to painful stimuli (formalin and tail-flick tests). Nigrostriatal lesion prevented the neuronal activation typically induced by NTG in sub-cortical areas involved in pain perception, autonomic control and neuroendocrine functions, such as hypothalamic nuclei, periaqueductal grey, parabrachial nucleus and the medullary nuclei. In addition, 6-OHDA-induced lesion inhibited NTG-induced hyperalgesia. Our data show that integrity of central dopaminergic neurotransmission is required for the NTG-induced activation of sub-cortical areas involved in the expression of migraine symptoms, as well as for the hyperalgesic response to painful stimuli elicited by the drug.

D1 receptor regulation of preprotachykinin-A gene by extracellular signal-regulated kinase pathway in striatal cultures

In animal models of Parkinson's disease, a supersensitive response to dopamine (DA) is associated with a switch in the coupling of striatal DA D1 receptors from a cyclic AMP/protein kinase A signaling pathway to one involving extracellular signal-regulated kinase/mitogen-associated protein kinase. In this study, we found that generation of organotypic striatal cultures, with concomitant loss of DA innervation, led to a downregulation in preprotachykinin-A gene expression, which was reinstated by D1 receptor activation in an extracellular signal-regulated kinase/mitogen-associated protein kinase-dependent manner. These data demonstrate that acute organotypic slice cultures recapitulate important changes in D1 receptor-mediated signal transduction seen in DA-denervated animals, providing a valuable model system to study denervation effects on DA signaling and striatal gene expression.

Phenotype of striatofugal medium spiny neurons in parkinsonian and dyskinetic nonhuman primates: a call for a reappraisal of the functional organization of the basal ganglia

The classic view of anatomofunctional organization of the basal ganglia is that striatopallidal neurons of the "indirect" pathway express D2 dopamine receptors and corelease enkephalin with GABA, whereas striatopallidal neurons of the "direct" pathway bear D1 dopamine receptors and corelease dynorphin and substance P with GABA. Although many studies have investigated the pathophysiology of the basal ganglia after dopamine denervation and subsequent chronic levodopa (L-dopa) treatment, none has ever considered the possibility of plastic changes leading to profound reorganization and/or biochemical phenotype modifications of medium spiny neurons. Therefore, we studied the phenotype of striatal neurons in four groups of nonhuman primates, including the following: normal, parkinsonian, parkinsonian chronically treated with L-dopa without exhibiting dyskinesia, and parkinsonian chronically treated with L-dopa exhibiting overt dyskinesia. To identify striatal cells projecting to external (indirect) or internal (direct) segments of the globus pallidus, the retrograde tracer cholera toxin subunit B (CTb) was injected stereotaxically into the terminal areas. Using immunohistochemistry techniques, brain sections were double labeled for CTb and dopamine receptors, opioid peptides, or the substance P receptor (NK1). We also used HPLC-RIA to assess opioid levels throughout structures of the basal ganglia. Our results suggest that medium spiny neurons retain their phenotype because no variations were observed in any experimental condition. Therefore, it appears unlikely that dyskinesia is related to a phenotype modification of the striatal neurons. However, this study supports the concept of axonal collateralization of striatofugal cells that project to both globus pallidus pars externa and globus pallidus pars interna. Striatofugal pathways are not as segregated in the primate as previously considered.

Effect of cholecystokinin on experimental neuronal aging

AIM: To observe the effect of cholecystokinin (CCK) on lipofusin value, neuronal dendrite and spine ultrastructure, and total cellular protein during the process of experimental neuronal aging.

METHODS: Experimental neuronal aging study model was established by NBA₂ cellular serum-free culture method. By using single intracellular lipofusin value from microspectrophotometry, morphology of neuronal dendrites and spines from the scanner electron microscopy, and total cellular protein as the indexes of experimental neuronal aging, we observed the effect of CCK₈ on the process of experimental neuronal aging.

RESULTS: Under the condition of serum-free culture, intracellular fluorescence value (%) increased with the extension of culture time (1 d 8.51±3.43; 5 d 10.12±3.03; 10 d 20.54±10.3; 15 d 36.88±10.49; ^bP<0.01). When CCK was added to serum-free culture medium, intracellular lipofusin value (%) decreased remarkably after consecutive CCK reaction for 10 and 15 d (control 36.88±10.49; 5 d 32.03±10.01; 10 d 14.37±5.55; 15 d 17.31±4.80; ^bP<0.01). As the time of serum-free culturing was prolonged, the number of neuronal dendrite and spine cells decreased. The later increased in number when CCK₈ was added. CCK₈ could improve the total cellular protein in the process of experimental neuronal aging.

CONCLUSION: CCK₈ may prolong the process of experimental neuronal aging by maintaining the structure and the number of neuronal dendrite and spine cells and changing the total cellular protein.

The immunocytochemical localization of substance P in the human striatum: A postmortem ultrastructural study

The striatum is a basal ganglia structure that is involved in motor, cognitive, and behavioral functions. In the striatum, the neuroactive peptide, substance P, is colocalized with GABA in the subset of medium spiny neurons that projects to the substantia nigra. Normal human striata (n = 5) obtained from the Maryland Brain Collection were processed for substance P immunoreactivity, prepared for electron microscopy, and analyzed using both stereology and simple profile counts. Most substance P-labeled neurons had a nonindented nucleus and a moderate amount of cytoplasm, typical of medium spiny projection neurons in other species. A small percentage (8%) of labeled neurons had indented nuclei, but otherwise had similar morphology. Synapses formed on labeled cell bodies were rare. Synapses formed by substance P-labeled axon terminals constituted 4.4% of the total synapses in the neuropil. Labeled terminals (1) formed synapses with both spines and dendrites with approximately equal frequency, (2) formed mostly symmetric synapses (76-85%), and (3) formed synapses predominantly with unlabeled (78%) profiles. Substance P-labeled spines varied in shape and comprised 37-42% of all spines forming synapses. In the caudate, the proportion of synapses with perforated postsynaptic densities was 55% on unlabeled vs. 45% on labeled spines, but in the putamen, this type of synapse was much more frequently present on unlabeled (73%) vs. labeled (27%) spines. These data describe substance P in the normal human striatum, which serve as comparative data to that of other species as well as normative data for further studies of brain disease that may involve striatal substance P neurons.

Increases in striatal preproenkephalin gene expression are associated with nigrostriatal damage but not L-DOPA-induced dyskinesias in the squirrel monkey

Changes in preproenkephalin expression in the caudate and putamen have been linked to the development of L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias in primate models of Parkinson's disease, although not all investigators have been able to confirm this association. Because nigrostriatal damage per se is associated with increases in striatal preproenkephalin mRNA levels, it is difficult to know if changes in transcript levels are a result of lesioning or concurrent L-DOPA treatment and resulting dyskinesias. To circumvent these difficulties, we measured striatal preproenkephalin mRNA levels in monkeys with L-DOPA-induced dyskinesias both with and without lesions of the nigrostriatal system. The latter model is not confounded by morphological and biochemical changes resulting from nigrostriatal damage. Monkeys were gavaged with L-DOPA (15 mg/kg) twice daily for a 2-week period and killed 3 days after treatment. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment alone resulted in an increase in preproenkephalin mRNA levels as previously shown. However, striatal transcript levels were similarly elevated in dyskinetic MPTP-lesioned animals treated with L-DOPA. In unlesioned animals, preproenkephalin mRNA levels were also similar in control and L-DOPA-treated dyskinetic monkeys. Because drug-induced changes in mRNA may not be sustained for a prolonged period after treatment, a second series of experiments were done in which animals were killed 3-4 h after the last dose of L-DOPA, but the results were similar to those obtained after 3 days. These data show that, while elevations in striatal preproenkephalin mRNA levels are associated with nigrostriatal damage, they are not linked to the development of L-DOPA-induced dyskinesias. These results thus question the importance of preproenkephalin mRNA in the pathogenesis of this disabling complication of L-DOPA therapy in Parkinson's disease.

Regional decreases in NK-3, but not NK-1 tachykinin receptor binding in dystonic hamster (dt(sz)) brains

Although the pathophysiology of primary dystonias is currently unknown, it is thought to involve changes in the basal ganglia-thalamus-cortex circuit, particularly activity imbalances between direct and indirect striatal pathways. Substance P, a member of the tachykinin family of neuropeptides, is a major component in the direct pathway from striatum to basal ganglia output nuclei. In the present study quantitative autoradiography was used to examine changes in neurokinin-1 (NK-1) and neurokinin-3 (NK-3) receptors in mutant dystonic hamsters (dt(sz)), a well characterized model of paroxysmal dystonia. NK-1 receptors were labeled in 10 dystonic brains and 10 age-matched controls with 3 nM [(3)H]-[Sar(9), Met(O(2))(11)]-SP. NK-3 binding sites were labeled in adjacent sections with 2.5 nM [(3)H]senktide. NK-1 binding was found to be unaltered in 27 brain areas examined. In contrast, NK-3 binding was significantly reduced in layers 4 and 5 of the prefrontal (-46%), anterior cingulate (-42%) and parietal (-45%) cortices, ventromedial thalamus (-42%) and substantia nigra pars compacta (-36%) in dystonic brains compared to controls. The latter effects may be particularly relevant in view of evidence that activation of NK-3 receptors on dopaminergic neurons in the substantia nigra pars compacta can increase nigrostriatal dopaminergic activity. Since previous studies indicated that a reduced basal ganglia output in mutant hamsters is based on an overactivity of the direct pathway which also innervates substantia nigra pars compacta neurons, the decreased NK-3 binding could be related to a receptor down-regulation. The present finding of decreased NK-3 receptor density in the substantia nigra pars compacta, thalamic and cortical areas substantiates the hypothesis that disturbances of the basal ganglia-thalamus-cortex circuit play a critical role in the pathogenesis of paroxysmal dystonia.

Increase of preproenkephalin mRNA levels in the putamen of Parkinson disease patients with levodopa-induced dyskinesias

The expression of preproenkephalin messenger RNA was studied in the brain of Parkinson disease (PD) patients using in situ hybridization. All these patients were treated with levodopa (LD) and the development of motor complications was recorded. Eleven normal controls and 14 PD patients were used, of which 4 developed dyskinesias, 3 developed wearing-off, 3 developed both dyskinesias and wearing-off, and 4 developed no adverse effect following dopaminomimetic therapy. Nigrostriatal denervation was similar between the subgroups of PD patients as assessed using 125I-RTI-specific binding to the dopamine transporter and measures of catecholamine concentrations by HPLC. A significant increase of preproenkephalin messenger RNA levels was observed in the lateral putamen of dyskinetic patients in comparison to controls (+210%; p < 0.01) and in comparison to nondyskinetic patients (+112%; p < 0.05). No change was observed in medial parts of the putamen or in the caudate nucleus. No relationship between preproenkephalin messenger RNA levels and other clinical variables such as development of wearing-off, age of death, duration of disease, or duration of LD therapy was found. These findings suggest that increase synthesis of preproenkephalin in the medium spiny output neurons of the striatopallidal pathway play a role in the development of dyskinesias following long-term LD therapy in Parkinson disease.

Intracerebroventricular administration of substance P increases dopamine content in the brain of 6-hydroxydopamine-lesioned rats

The interactions existing between substance P- and dopamine-positive neurons, notably in the basal ganglia, suggest that substance P may have therapeutic use in treatment of Parkinson's disease characterized by impaired dopaminergic transmission. The effects of intracerebroventricularly administered substance P were tested on the levels of dopamine and its metabolites in the striatum, nucleus accumbens and frontal cortex of 6-hydroxydopamine-lesioned rats. Intracerebroventricular injection of 6-hydroxydopamine decreased the levels of dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid in the brain structures under investigation. Administration of substance P in low dose (0.35 nmol/kg) had no effect on the 6-hydroxydopamine-induced reduction of the dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid contents in the brain. However, treatment with substance P in higher dose (3.5 nmol/kg) increased the concentrations of dopamine and its metabolites in the striatum, nucleus accumbens and frontal cortex relative to saline-treated group. Additionally, 6-hydroxydopamine lesions significantly increased 3,4-dihydroxyphenylacetic acid/dopamine and homovanillic acid/dopamine ratios in the striatum and nucleus accumbens. Substance P (3.5 nmol/kg) partially reversed lesion-induced increases in 3,4-dihydroxyphenylacetic acid/dopamine and homovanillic acid/dopamine ratios in the striatum, but did not alter these ratios in nucleus accumbens. To test whether substance P fragmentation is responsible for this phenomenon, substance P(5-11), which is one of the main substance P fragments in rat CNS, was administered in equimolar dose. Substance P(5-11) was found to have no effect on the content of dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid in the striatum and nucleus accumbens. In the frontal cortex, substance P(5-11) produced decreases in dopamine levels and increases in homovanillic acid/dopamine ratio. The results of this study suggest that substance P helps to restore dopamine deficit in the brain in an animal model of Parkinson's disease, with the positive effects being more prominent on the nigrostriatal than on the mesocorticolimbic dopaminergic system, but substance P(5-11) is not responsible for this effect.

Preprotachykinin-A mRNA expression in the human and monkey brain: An in situ hybridization study

The mRNA expression for preprotachykinin-A (PPT-A) was studied throughout the human and cynomolgus monkey brain to assess the neuroanatomical expression pattern of the PPT-A gene in primates. In situ hybridization showed that the PPT-A mRNA is expressed highly in specific regions of the postmortem human brain, including the striatum, islands of Calleja, hypothalamus (posterior, premammillary, medial mammillary, and ventromedial nuclei), superior and inferior colliculi, periaqueductal gray, and oculomotor nuclear complex. PPT-A mRNA-expressing neurons also were present in the paranigralis (ventral tegmental area) and were scattered in the bed nucleus stria terminalis throughout the sublenticular substantia innominata region, including the diagonal band of Broca and the nucleus basalis of Meynert. In the hippocampus, high PPT-A mRNA expression was localized predominantly to the polymorphic layer of the dentate gyrus; no labeled cells were present in the granular layer. Positively labeled cells also were found scattered in the CA regions as well as in the amygdaloid complex. Neocortical expression of PPT-A mRNA was localized mainly to the deep laminae (layers V/VI), except for the striate cortex (labeling was seen also in superficial layers). The subiculum, thalamus, globus pallidus, ventral pallidum, substantia nigra pars compacta, red nucleus, pontine nuclei, and cerebellum were characterized by very weak to undetectable expression of PPT-A mRNA. An expression pattern was evident in the monkey forebrain similar to that observed in the human, except for the absence of PPT mRNA-expressing cells in the medial mammillary nucleus despite intense expression in supramammillary, lateral mammillary, and premammillary nuclei. Overall, more similarities than differences are apparent between primate species in the expression pattern of the PPT-A gene. J. Comp. Neurol. 411;56-72, 1999.

Striatal preproenkephalin gene expression is upregulated in acute but not chronic parkinsonian monkeys: implications for the contribution of the indirect striatopallidal circuit to parkinsonian symptomatology

This study examined the extent of striatal dopamine (DA) denervation and coincident expression of preproenkephalin (PPE) mRNA in monkeys made parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. Some animals (n = 4) became moderately parkinsonian after receiving large doses of MPTP over short periods of time and were symptomatic for only a short period of time (1-3 months; acute parkinsonian group). Other animals became moderately parkinsonian after receiving either escalating doses of MPTP over long periods (4-6 months; n = 5) or a high dose of MPTP over a short period (<1 month; n = 1) and remained symptomatic for an extended period (>8 months; chronic parkinsonian group). Despite similar symptomatology and similar degrees of striatal DA denervation at the time of their deaths, only acute parkinsonian animals had significantly increased PPE expression in sensorimotor striatal regions. PPE expression in chronic parkinsonian animals was either not changed or significantly decreased in most striatal regions. These findings suggest that the duration and not the extent of striatal DA denervation is a critical factor in modulating changes in striatal PPE expression. Furthermore, these results question the role of increased activity in the enkephalin-containing indirect striatopallidal pathway in the expression of parkinsonian symptoms.

Subgroups of parkinsonian patients differentiated by peptidergic immunostaining of caudate nucleus biopsies

In this study, Met-enkephalin (Met-enk), substance P (SP) and tyrosine hydroxylase (TH) immunostaining was assessed in caudate nucleus biopsies from 15 Parkinson's disease patients who were treated surgically. According to the combination of changes in Met-enk, SP and TH immunostaining, several subgroups of parkinsonian patients were disclosed. Group I: Patients showing low SP and normal Met-enk immunostaining, and variably reduced TH immunoreactivity. Group II: both SP and Met-enk immunostaining were apparently of normal intensity in these PD patients, but they showed the greatest decrease in TH labeling. Group III: PD patients that showed normal SP, very low Met-enk and variably reduced TH immunostaining. Low Met-enk immunostaining tended to correlate with the severity of the disease as judged by higher Unified Parkinson's disease Rating Scale and gait scores. These results suggest that different neurochemical phenotypes may exist among Parkinson's disease patients. Peptidergic deficits should be taken into account for therapeutic intervention.

Electrochemical studies of the effects of substance P on dopamine terminals in the rat striatum

The purpose of this study was to investigate the regulation of dopamine (DA) release and clearance by Substance P (SP) in striatum. In vivo high speed chronoamperometric recording techniques, with Nafion-coated carbon-fiber electrodes, were used to evaluate extracellular DA concentrations in urethane-anesthetized Sprague-Dawley rats. SP was locally applied to striatum. Our data indicate that SP can induce DA release in striatum. However, only about half of the striatal sites respond to SP. Readministration of SP to the same site elicited a smaller DA release. These data suggest that SP-evoked release shows tachyphyllaxis and is heterogeneous in the striatum. Lesioning of DA neurons with 6-OHDA into the medial forebrain bundle abolished DA release induced by SP. It has been shown that SP interacts with three different tachykinin receptors. We found that application of the Neurokinin-1 (NK1) agonist [Sar9, Met (O2)11]SP, but not the NK3 agonist senktide, induced DA release, suggesting that SP-induced DA release may be mediated through NK1 receptors. We further examined SP effects on DA clearance in striatum. We found that pretreatment with SP significantly attenuated extracellular levels of DA after exogeneous application of DA, suggesting that DA clearance is augmented by SP. Taken together, our data demonstrate that substance P facilitates dopamine release and clearance in the striatum.

Glial cell line-derived neurotrophic factor attenuates behavioural deficits and regulates nigrostriatal dopaminergic and peptidergic markers in 6-hydroxydopamine-lesioned adult rats: comparison of intraventricular and intranigral delivery

The effects of intranigrally- or intraventricularly-administered glial cell line-derived neurotrophic factor were tested on low dose (0.05 mg/kg) apomorphine-induced rotations and tyrosine hydroxylase activity in the substantia nigra and striatum of stable 6-hydroxydopamine-lesioned rats. In addition, we determined if 6-hydroxydopamine lesions in the absence or presence of treatment affected neuropeptide (substance P, met-enkephalin, dynorphin) content in the striatum. Glial cell line-derived neurotrophic factor, when administered intranigrally, prevented apomorphine-induced rotational behaviour for 11 weeks following a single injection. In comparison, intraventricularly-administered glial cell line-derived neurotrophic factor produced a transient reduction in rotational behaviour that lasted for two to three weeks following a single injection. We also show that rotational behaviour is reduced following each subsequent intraventricular injection of glial cell line-derived neurotrophic factor given every six weeks, a time-point when baseline rotation deficits were re-established. Intranigrally- or intraventricularly-administered glial cell line-derived neurotrophic factor significantly reduced weight gain in all 6-hydroxydopamine-lesioned rats in this study. Following behavioural analysis where a confirmed improvement of behaviour was established, tissues were dissected for neurochemical analysis. In lesioned rats with intranigral injections of administered glial cell line-derived neurotrophic factor, significant increases of nigral, but not striatal tyrosine hydroxylase activity were measured. Additionally, 6-hydroxydopamine lesions significantly increased striatal dynorphin (61-139%) and met-enkephalin (81-139%), but not substance P levels. In these rats, intranigrally-administered glial cell line-derived neurotrophic factor injections reversed lesion-induced increases in nigral dynorphin A levels and increased nigral dopamine levels, but did not alter nigral met-enkephalin or substance P levels nor striatal dopamine levels. In lesioned rats with intraventricular injections of glial cell line-derived neurotrophic factor, tyrosine hydroxylase ispilateral to the lesion was increased in the substantia nigra, but not in the striatum. Intraventricularly-administered glial cell line-derived neurotrophic factor did not reverse lesion-induced increases in nigral dynorphin A or met-enkephalin levels nor did glial cell line-derived neurotrophic factor affect substance P levels in the striatum. These results suggest that in an animal model of Parkinson's disease, the neurotrophic factor glial cell line-derived neurotrophic factor reverses behavioural consequences of 6-hydroxydopamine administration, an effect that may involve both dopaminergic and peptidergic neurotransmission.

Bilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopamine pathway reproduces the effects of unilateral lesion on substance P but not on enkephalin expression in rat basal ganglia

This study compared the effects of unilateral and bilateral 6-hydroxydopamine-induced lesions of the nigrostriatal dopaminergic neurons on substance P and enkephalin expression in the rat striatum and its main target structures by means of quantitative in situ hybridization and immunocytochemistry. In animals with bilateral lesion, substance P mRNA levels were decreased in the striatum, and this was matched by parallel reductions in substance P immunoreactivity in the striatum and in the striatonigral terminals at substantia nigra level in both hemispheres. These changes were similar to those observed ipsilaterally to unilateral lesion. In contrast, whereas increased striatal enkephalin immunoreactivity and mRNA levels and decreased immunoreactivity in the globus pallidus were observed on the lesioned side after unilateral lesion, no significant change in these enkephalin markers occurred in animals with bilateral lesion. These data suggest that the effects of dopamine deafferentation on substance P expression in the striatonigral system may be due primarily to removal of direct dopamine influence, whereas the effects on enkephalin expression in the striatopallidal system may involve complex interhemispheric adaptive mechanisms. The present finding that bilateral dopamine lesion does not simply reproduce the effects of unilateral lesion but creates a new functional state may have a critical bearing on the understanding and treatment of Parkinson's disease.

Tachykinins, neurotrophism and neurodegenerative diseases: a critical review on the possible role of tachykinins in the aetiology of CNS diseases

The tachykinins are a family of undecapeptides that are widely distributed throughout the body, including the central nervous system (CNS). They have several well defined roles in non-CNS sites as well as in the dorsal horn, where they are involved in the transmission of nociceptive information. However their function(s) in other CNS sites is unclear, but there is some evidence that they function as neuromodulators rather than neurotransmitters. This neuromodulation includes a possible role in maintaining the integrity of neuronal populations, analogous to the functions of neurotrophic factors. This review critically evaluates the role of tachykinins as neurotrophic factors, with particular reference to the common neurodegenerative diseases of the CNS.

Striatal expression of substance P and methionin-enkephalin in genes in patients with Parkinson's disease

The striatal expression of substance P (SP) and methionin-enkephalin (met-enk) genes was studied post mortem by in situ hybridization in patients with Parkinson's disease and a group of control subjects. No significant difference in striatal expression of these two neuropeptide messenger RNAs (mRNAs) was found in the patients compared with control subjects. This contrasts with animal models of parkinsonism, where expression of SP mRNA is decreased and met-enk mRNA increased. Possible explanations include: (1) compensatory mechanisms, which may develop during the long term evolution of Parkinson's disease; (2) normalized expression of the two genes resulting from chronic L-DOPA therapy.

Induction of c-fos and zif/268 gene expression in rat striatal neurons, following stimulation of D1-like dopamine receptors, involves protein kinase A and protein kinase C

Changes in the level of dopaminergic activity in the rat striatum lead to the induction of a number of immediate-early genes, including c-fos and zif/268. These immediate-early genes are thought in turn to alter the rate of transcription of downstream genes. There is evidence that the dopaminergic activation of the c-fos and zif/268 genes in the striatum in vivo is linked to stimulation of D1-like dopamine receptors. We have used primary cultures of embryonic rat striatal neurons to identify the intracellular pathways involved in this response. Dopamine (10 nM-5 microM) caused a marked increase in the levels of c-fos mRNA and zif/268 mRNA in cultured striatal neurons, an effect that was reproduced by the D1-like dopamine receptor agonist SKF38393 (10 nM-5 microM). These actions were attenuated by the D1-like antagonist SCH23390 (1 microM) but not by the D2-like antagonist eticlopride (1 microM). The D2-like agonist quinpirole did not increase zif/268 mRNA above basal levels at concentrations up to 5 microM, but caused a slight increase in the levels of c-fos mRNA. The stimulation of c-fos mRNA levels caused by 1 microM SKF38393 was reduced by 45% following pretreatment with the selective protein kinase A inhibitor KT5720, and by 87% following pretreatment with the selective protein kinase C inhibitor calphostin C. The stimulation of zif/268 mRNA levels caused by 1 microM SKF38393 was reduced by 90% following pretreatment with KT5720, but was not significantly affected by pretreatment with calphostin C. In addition, the actions of SKF38393 to stimulate the expression of both immediate-early genes were attenuated by coadministration of quinpirole. These results suggest that SKF38393 acts on striatal neurons to stimulate c-fos expression predominantly through protein kinase C, but also partially through protein kinase A. Conversely, SKF38393 induces zif/268 expression through protein kinase A. The ability of quinpirole to antagonize the actions of SKF38393 on cultured neurons is consistent with the presence of both D1-like receptors on the same neuronal population.

Preproenkephalin and preprotachykinin messenger RNA expression in normal human basal ganglia and in Parkinson's disease

Striatal expression of preproenkephalin and preprotachykinin messenger RNA was studied in normal controls and in patients with Parkinson's disease using in situ hybridization histochemistry. In controls, preproenkephalin messenger RNA was expressed in a population of medium-sized neurons of mean cross-sectional area 165 microns 2, accounting for 66% of striatal medium-sized neurons, whereas preprotachykinin messenger RNA was expressed in a population of medium-sized neurons of mean cross-sectional area 204 microns 2 (23% larger than those expressing enkephalin, P < 0.05), accounting for 58% of medium-sized striatal neurons. Much lower levels of both preproenkephalin messenger RNA and preprotachykinin messenger RNA were expressed by large neurons in the globus pallidus and substantia nigra reticulata. In addition, preproenkephalin messenger RNA was expressed at low levels by neurons in the subthalamic nucleus. In Parkinson's disease cases, there was a statistically significant increase in preproenkephalin messenger RNA expression in the body of the caudate (109% increase, P < 0.05) and in the intermediolateral putamen (55% increase, P < 0.05) due to an increase in the level of gene expression per neuron rather than an increase in the number of neurons expressing preproenkephalin messenger RNA. Similar increases were observed in other putaminal subregions and in the putamen as a whole, but these did not reach statistical significance. No change in preprotachykinin messenger RNA expression was detected. These findings demonstrate selective up-regulation of a striatal neuropeptide system in Parkinson's disease compatible with increased activity of the "indirect" striatopallidal pathway, which is thought to play a crucial role in the pathophysiology of akinesia and rigidity in this condition.

Morphine and naltrexone modulate D2 but not D1 receptor induced motor behavior in MPTP-lesioned monkeys

Interactions at the behavioral level between dopamine (DA) and opioid receptors in the mammalian brain have been amply demonstrated. Considering the pivotal role for DA receptors in the pharmacotherapy of Parkinson's disease (PD), these interactions might be clinically relevant. Therefore, in the present study the effects of the opioid antagonist naltrexone and agonist morphine on D1 and D2 receptor induced stimulation of motor behavior in the unilateral MPTP monkey model (n = 5) of PD were investigated. The results show that both naltrexone and morphine [0.1-1.0 mg/kg; intramuscular injection (IM)] inhibited D2 receptor stimulated contralateral rotational behavior and hand use induced by administration of quinpirole (LY 171555; 0.01 mg/kg, IM) in a dose-related way. However, no effects of these opioid drugs were observed on D1 receptor stimulated contralateral rotational behavior and hand use induced by administration of SKF 81297 (0.3 mg/kg, IM). Interestingly, the action of the alleged preferential mu-receptor antagonist naltrexone was mimicked by the selective delta-opioid antagonist naltrindole (0.5 mg/kg, IM). From this study it is concluded that in a non-human primate model of PD, alteration of opioid tonus leads to modulation of D2 receptor but not D1 receptor controlled motor behavior. The possible underlying mechanisms and clinical relevance of these findings are discussed.

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.

Neurotensin, substance P, delta and mu opioid receptors are decreased in basal ganglia of Parkinson's disease patients

The specific binding of [3H]neurotensin, [3H]substance P, [3H]D-Ala2-D-Leu5-enkephalin (delta receptors) and [3H]-Tyr-D-Ala-Gly-(NMe)Phe-Gly-ol (mu receptors) were studied in membrane preparations of caudate nucleus, putamen, globus pallidus and substantia nigra from patients with Parkinson's disease and from age-matched controls. The density of neurotensin receptors was decreased in globus pallidus (lateral and medial segments) in parkinsonian brain. Substance P receptors were reduced in the putamen (anterior and posterior) and in lateral globus pallidus in Parkinson's disease. There was a reduction in the density of opioid receptors in posterior putamen and in mu receptors in caudate nucleus and putamen (anterior and posterior). No differences in neuropeptide receptor binding were observed in substantia nigra from parkinsonian brains compared with control subjects. The reductions in neuropeptide receptor density were less marked than the decrease in caudate and putamen content of dopamine and its metabolites. This suggests that neuropeptide receptors are only partially localized to striatal dopamine terminals.

Endogenous opiates: 1992

This paper is the fifteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1992 involving the behavioral, non-analgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.

Parallel alterations in Met-enkephalin and substance P levels in medial globus pallidus in Parkinson's disease patients

Met-enkephalin (Met-enk) and substance P (SP) were measured by a combined high-performance liquid chromatography/radioimmunoanalysis method in medial (GPM) and lateral globus pallidus (GPL) from controls and from Parkinson's disease (PD) patients. All patients showed a similar marked (> 90%) reduction in dopamine (DA) levels in putamen compared with controls. However, based on DA levels in the caudate nucleus, two subgroups of PD patients were differentiated. In patients with > 80% decrease in caudate nucleus DA content, there was a three-fold increase in both Met-enk and SP levels in GPM. In contrast, in patients showing an approximately 50% reduction in DA content in caudate, levels of both peptides were markedly reduced (approximately 80%). Met-enk and SP levels in GPL were unchanged in PD. These results suggest that neurons containing Met-enk and SP projecting to GPM adapt according to the extent of degeneration in the substantia nigra in PD.