Brain neuropeptides in progressive supranuclear palsy

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.

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.

Cholinergic and peptidergic systems in PSP

PSP is associated with a widespread cholinergic deficit likely corresponding to a loss in cholinergic neurons. The cholinergic damage dramatically affects the basal ganglia and specific cell groups of the mesencephalon and pons. This provides an anatomically defined basis for motor and supranuclear oculomotor syndromes characteristic of PSP. Unlike Alzheimer's disease and Parkinson's disease with dementia, the disease is not associated with a marked cholinergic deficiency in the cerebral cortex. Various peptides are present at normal concentrations in extrapyramidal and limbic subcortical areas in brains of patients with PSP. Of particular interest, is somatostatin, the levels of which are subnormal in cerebral cortex of patients with dementia of Alzheimer' or Parkinson's disease type.

Striatal neuropeptide levels in Parkinson's disease patients

Substance P (SP), Met-enkephalin (Met-enk) and cholecystokinin-8-S (CCK-8-S) were measured by a combined HPLC/RIA method in the caudate nucleus and anterior putamen from controls and from Parkinson's disease (PD) patients. SP levels were reduced in caudate in PD, but unchanged in putamen. No differences in Met-enk content were found in parkinsonians compared to controls. However, a significant correlation between DA and Met-enk levels in caudate nucleus from PD was observed. The concentration of CCK-8-S was unaltered in caudate nucleus or putamen in PD. The decrease in caudate nucleus SP levels might be related to the decrease in nigral SP levels in PD, while the reduction in Met-enk levels appears to be a feature of a subgroup of parkinsonian patients.

Effects of a unilateral 6-hydroxydopamine lesion and prolonged L-3,4-dihydroxyphenylalanine treatment on peptidergic systems in rat basal ganglia

The effect of a unilateral 6-hydroxydopamine (6-OHDA) lesion of the medial forebrain bundle or of a sham lesion on the neuropeptide content of the striatum and substantia nigra was investigated with or without 6 months L-3,4-dihydroxyphenylalanine (L-DOPA; 200 mg/kg per day) plus carbidopa (25 mg/kg per day) treatment. [Met5]- and [Leu5]enkephalin, substance P (SP), neurotensin (NT) and cholecystokinin (CCK) were measured by a combined HPLC/RIA method. Neurotensin levels were increased in the striatum, and [Leu5]enkephalin, and SP levels were reduced in the substantia nigra as a consequence of the lesion, while the levels of other peptides were unaltered. Administration of L-DOPA to sham-operated rats bilaterally increased SP levels in striatum and substantia nigra, and [Met5]enkephalin and CCK content in substantia nigra. L-DOPA treatment of 6-OHDA-lesioned rats increased [Met5]- and [Leu5]enkephalin and CCK levels in the striatum ipsilateral to the lesion but not on the intact side. In the substantia nigra, the lesion-induced decrease in [Leu5]enkephalin and SP was reversed by L-DOPA treatment, [Met5]enkephalin and CCK levels ipsilateral to the lesion were further enhanced, and there was an increase in NT ipsilateral to the lesion. Cryptic [Met5]- and [Leu5]enkephalin increased in the ipsilateral striatum following an 6-OHDA lesion. L-DOPA treatment did not alter cryptic enkephalin levels or the lesion-induced increase in cryptic [Met5]enkephalin, while cryptic [Leu5]enkephalin was further increased in lesioned animals given L-DOPA. These results suggest that the pattern of change in basal ganglia peptides in Parkinson's disease is not due solely to the destruction of the nigrostriatal pathway, the drug treatment of the disease or a combination of these factors.

Chronic MPTP treatment reduces substance P and met-enkephalin content in the basal ganglia of the marmoset

Common marmosets were treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 1.25-2.5 mg/kg s.c., twice a week) for 5-10 consecutive months. The initial doses of MPTP produced a severe parkinsonian syndrome but motor activity was partially recovered at the end of treatment. Fifteen days or 6 months after the last MPTP dose, monkeys were sacrificed. In addition to a strong decrease of dopamine in the striatum, there were significant reductions in substance P and Met-enkephalin content in the substantia nigra, caudate nucleus and putamen. In the globus pallidus, the reduction in peptide levels did not reach statistical significance as compared to controls. Neurotensin levels were also decreased in the caudate nucleus. The chronic administration of MPTP for 5-10 months induces changes in substance P and Met-enkephalin systems which resemble the degeneration found in brains from parkinsonian patients.

Neuropeptide levels in the basal ganglia of aged common marmosets following prolonged treatment with MPTP

Aged common marmosets were treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 0.5-2.0 mg/kg/week i.p.) for 16 or 24 weeks, observed for a total of 30 weeks and then killed for measurement of biochemical parameters in basal ganglia. The MPTP treatment induced a marked depletion in dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid levels in the caudate nucleus and putamen. In contrast, the concentrations of five neuropeptides: [Met5]-enkephalin, [Leu5]-enkephalin, cholecystokinin, substance P and neurotensin as measured by a combined HPLC/RIA method, remained unaltered in all basal ganglia regions examined. Enkephalin precursor levels, as reflected by cryptic [Met5]-enkephalin content, were increased in the putamen, but not in the caudate nucleus, as a consequence of MPTP administration. Cryptic [Leu5]-enkephalin content remained unchanged in the striatum of MPTP treated marmosets. Overall, these results suggest an increase in striatal [Met5]-enkephalin release following chronic MPTP treatment of aged marmosets. However, the chronic treatment of aged marmosets with MPTP does not reproduce the neuropeptide alterations characteristic of Parkinson's disease.

A comparative immunohistochemical study on striatal Met-enkephalin expression in Alzheimer's disease and in progressive supranuclear palsy

Using a sensitive immunoperoxidase technique we examined Met-enkephalin (MEnk) expression in the striatum and globus pallidus external segment (GPe) from patients with Alzheimer's disease (AD) and with progressive supranuclear palsy (PSP). In AD patients strong MEnk-like immunoreactivity was persistent in the striatum showing so-called "striosomes". In addition, a number of typical "woolly fibers" were observed in the GPe. MEnk-positive striosomes were also visible in the striatum of PSP patients and were similar to those of normal controls and of AD patients. However, the MEnk-positive "woolly fibers" appearance was less well recognizable in the GPe from all the PSP patients examined.

Decrease in a proenkephalin peptide in cerebrospinal fluid in Huntington's disease and progressive supranuclear palsy

The cerebrospinal fluid (CSF) content of Met5-enkephalin-Arg-Gly-Leu immunoreactivity was found to be significantly decreased in patients with Huntington's disease and progressive supranuclear palsy. This peptide is derived from the proenkephalin precursor protein and normally is found in high concentrations in the basal ganglia. The decrease in CSF from Huntington's disease patients likely reflects the loss of proenkephalin-containing neurons seen in postmortem analyses of basal ganglia tissue. The decrease in progressive supranuclear palsy, a disease in which dopamine neurons degenerate but enkephalin levels in the basal ganglia are reportedly not decreased, may reflect a functional decline in enkephalinergic neuronal activity secondary to a striatal cholinergic deficit. The results suggest that a substantial portion of the CSF Met5-enkephalin-Arg-Gly-Leu immunoreactivity is derived from the basal ganglia and that CSF levels of this peptide can serve as an index of functional or anatomical integrity of proenkephalin synthesizing neurons in the basal ganglia.

Levels of Met-enkephalin, Leu-enkephalin, substance P and cholecystokinin in the brain of the common marmoset following long term 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine treatment

Common marmosets were treated daily with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 7-9 mg/kg i.p.) for 25 days, and then kept out of drug for three months before biochemical measurements in various brain areas. This treatment induced a dramatic fall (-80%) in dopamine, homovanillic acid and dihydroxyphenylacetic acid levels in the putamen and caudate nucleus, and a significant but less pronounced reduction (less than or equal to 50%) in the levels of these compounds in the nucleus accumbens. In contrast, the concentrations of four neuropeptides: met-enkephalin, leu-enkephalin, substance P, and cholecystokinin, remained unaltered in all brain areas examined in MPTP-treated marmosets. Therefore the neuropeptide alterations previously reported in Parkinson's disease are probably not secondary to the severe lesion of dopaminergic neurones, but constitute another intrinsic feature of the disease.