Dynorphin levels in parkinsonian patients: Leu5-enkephalin production from either proenkephalin A or prodynorphin in human brain

L-DOPA-induced dyskinesia is associated with regional increase of striatal dynorphin peptides as elucidated by imaging mass spectrometry

Opioid peptides are involved in various pathophysiological processes, including algesia, epilepsy, and drug dependence. A strong association between L-DOPA-induced dyskinesia (LID) and elevated prodynorphin mRNA levels has been established in both patients and in animal models of Parkinson's disease, but to date the endogenous prodynorphin peptide products have not been determined. Here, matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) was used for characterization, localization, and relative quantification of striatal neuropeptides in a rat model of LID in Parkinson's disease. MALDI IMS has the unique advantage of high sensitivity and high molecular specificity, allowing comprehensive detection of multiple molecular species in a single tissue section. Indeed, several dynorphins and enkephalins could be detected in the present study, including dynorphin A(1-8), dynorphin B, α-neoendorphin, MetEnkRF, MetEnkRGL, PEnk (198-209, 219-229). IMS analysis revealed elevated levels of dynorphin B, α-neoendorphin, substance P, and PEnk (220-229) in the dorsolateral striatum of high-dyskinetic animals compared with low-dyskinetic and lesion-only control rats. Furthermore, the peak-intensities of the prodynorphin derived peptides, dynorphin B and α-neoendorphin, were strongly and positively correlated with LID severity. Interestingly, these LID associated dynorphin peptides are not those with high affinity to κ opioid receptors, but are known to bind and activate also μ- and Δ-opioid receptors. In addition, the peak intensities of a novel endogenous metabolite of α-neoendorphin lacking the N-terminal tyrosine correlated positively with dyskinesia severity. MALDI IMS of striatal sections from Pdyn knockout mice verified the identity of fully processed dynorphin peptides and the presence of endogenous des-tyrosine α-neoendorphin. Des-tyrosine dynorphins display reduced opioid receptor binding and this points to possible novel nonopioid receptor mediated changes in the striatum of dyskinetic rats. Because des-tyrosine dynorphins can only be detected by mass spectrometry, as no antibodies are available, these findings highlight the importance of MALDI IMS analysis for the study of molecular dynamics in neurological diseases.

Presynaptic modulation of synaptic transmission by opioid receptor in rat subthalamic nucleus in vitro

Presynaptic modulation of synaptic transmission in rat subthalamic nucleus (STN) neurons was investigated using whole-cell patch-clamp recordings in brain slices. Evoked GABAergic inhibitory postsynaptic currents (IPSCs) were reversibly reduced by methionine enkephalin (ME) with an IC(50) value of 1.1 +/- 0.3 microM. The action of ME was mimicked by the mu-selective agonist [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin (DAMGO), and was partially blocked by the mu-selective antagonists naloxonazine and D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP). Evoked GABA(A) IPSCs were also inhibited by the delta-selective agonist [D-Pen(2,5)]-enkephalin (DPDPE), but not by the kappa-selective agonist (+)-(5 alpha,7 alpha,8 beta)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4.5]dec-8-yl]-benzeneacetamide (U-69593) and the orphan receptor agonist orphanin FQ/nociceptin (OFQ). DPDPE-induced inhibition was completely blocked by the delta-selective antagonist N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH (ICI 174,864). ME, DAMGO and DPDPE increased the paired-pulse ratio of IPSCs. Evoked excitatory postsynaptic currents (EPSCs) were reversibly reduced by ME with an IC(50) value of 0.35 +/- 0.14 microM. Inhibition by ME was associated with an increase in the paired-pulse ratio of EPSCs. The action of ME was mimicked by DAMGO, and blocked by naloxonazine. DPDPE had little effect on evoked EPSCs. Neither U-69593 nor OFQ had any effect. ME significantly decreased the frequency of spontaneous miniature EPSCs (mEPSCs) without change in their amplitude. The action of ME was mimicked by DAMGO. DPDPE had no effect. The presynaptic voltage-dependent potassium conductance blocker 4-aminopyridine (4-AP, 100 microM) abolished the inhibitory effects of ME on evoked IPSCs and EPSCs. In contrast, 4-AP only partially blocked the actions of baclofen. These results suggest that opioids inhibit inhibitory synaptic transmission in the STN through the activation of presynaptic mu- and delta- receptors. In contrast, inhibition of excitatory synaptic inputs to the STN occurs through the activation of only mu-receptors. Both inhibitions may be mediated by blockade of voltage-dependent potassium conductance.

Dopaminergic regulation of postnatal development of dynorphin neurons in rat striatum

This study examined whether the postnatal development of the biosynthesis of an opioid peptide, dynorphin A (1-8) (DYN) is influenced by dopamine (DA) deficiency. The neurotoxin 6-hydroxydopamine (6-OHDA) was used as a tool to induce DA deficiency on the third day of the postnatal period in Sprague-Dawley rat pups. During the postnatal period, the levels of striatal DYN steadily increased in an age-dependent fashion and appeared to peak between 35 and 45 days. In neonatal 6-OHDA-lesioned animals, the category with 95% or more DA loss exhibited a reduction in the levels of DYN in the postnatal period whereas the category with less than 95% DA loss did not show significant changes in DYN levels. The results indicate that the normal development of striatal DYN is negatively affected only when there is a near-total loss of DA during early postnatal period.

Effects of unilateral 6-hydroxydopamine lesions on neuropeptide immunoreactivity in the basal ganglia of the common marmoset, Callithrix jacchus, a quantitative immunohistochemical analysis

Previous immunocytochemical studies in rats have indicated that striatal dopamine depletion leads to an increase in enkephalin-immunoreactivity and a decrease in substance P-immunoreactivity in the striatum. Similar studies in primates have lead to contradictory results. In the present study changes in tyrosine hydroxylase-, met-enkephalin- and substance P-immunoreactivity were determined in the basal ganglia of 6 common marmosets Callithrix jacchus following dopamine depletion by unilateral intracerebral 6-hydroxydopamine (6-OHDA) injections using three different survival times. The non-lesioned side served as an intra-individual control. Tyrosine hydroxylase immunoreactivity was strongly reduced in the entire ipsilateral striatum. Enkephalin-immunoreactivity was increased throughout the striatum. Substance P-immunoreactivity was significantly increased in only one case in the caudate nucleus and in two cases in the putamen, while in other cases either a non-significant increase or decrease was found. Therefore, the results of the present study indicate that in marmosets dopamine has a inhibiting effect on the levels of striatal enkephalin, while its effect on substance P (SP) appears to be absent.

Mesencephalic grafts partially restore normal nigral dynorphin levels in 6-hydroxydopamine-lesioned rats treated chronically with L-dihydroxyphenylalanine

An increase of dynorphin levels is commonly observed in the substantia nigra of 6-hydroxydopamine-lesioned rats chronically treated with daily injections of L-DOPA. This study investigates the potential of fetal mesencephalic grafts to restore normal levels of dynorphin in such cases. After 19 consecutive days of treatment with L-DOPA, lesioned rats with the most severe nigral cell loss showed increased levels of dynorphin in the substantia nigra ipsilateral to the lesion, as expected. The changes were assessed by standard immunohistochemical techniques combined with the use of an image analysis system. Such changes were not observed in the substantia nigra of rats that received fetal mesencephalic cells in the striatum six months prior to the beginning of the chronic treatment. However, only animals displaying heavy loss of dopaminergic neurons in the substantia nigra pars compacta showed significant changes of dynorphin levels in the substantia nigra following drug treatment. Our results show that fetal nigral cells transplanted into the striatum have the potential to prevent biochemical changes observed in the basal ganglia induced by the lesion of the nigrostriatal pathway and chronic treatment with L-DOPA. It is still hypothesized from studies in rodents that this peptide may play a role in the appearance of DOPA-induced dyskinesia, because dynorphin levels increase in the substantia nigra pars reticulata after L-DOPA treatment. If this happens to be the case, then the use of fetal nigral grafts could therefore be an important step to prevent the induction of dyskinesia after chronic L-DOPA treatment.

Naltrexone, an opiate antagonist, fails to modify motor symptoms in patients with Parkinson's disease

One month of adjunct treatment with naltrexone (100 mg/day) was compared with placebo in a double-blind, randomized, cross-over design in two groups of patients with Parkinson's disease. The first group was composed of 10 patients with a moderate motor impairment insufficiently controlled by monotherapy with bromocriptine. The second group was composed of eight patients with L-dopa-induced peak-dose dyskinesia. Naltrexone as compared with placebo did not demonstrate any significant change in motor function in either group. These negative clinical results do not support a significant role of endogenous opioid systems in the pathophysiology of motor impairment in Parkinson's disease.

Neuroendocrine and behavioral effects of the selective kappa agonist spiradoline in Tourette's syndrome: a pilot study

To evaluate the role of opioids in Tourette's syndrome (TS), we performed a dose-response study of the behavioral and neuroendocrine effects of the selective kappa agonist spiradoline mesylate (U-62066E) in five TS patients and five normal control subjects, aged 20 to 47. The intramuscularly administered doses of spiradoline were 0.0, 0.8, 1.6, and 3.2 micrograms/kg. Baseline and postdrug tic frequencies were determined from "blind" videotape tic counts and bedside clinician ratings. In comparison with placebo, the lowest dose of spiradoline was associated with significant decreases in cumulative postdrug counts of total tics and phonic tics, as well as in clinician ratings of postdrug motor tic frequencies. By contrast, there was a trend for tic frequencies to increase following the intermediate dose (1.6 micrograms/kg) of spiradoline. As a group, the TS subjects also secreted significantly more growth hormone following the 1.6 micrograms/kg dose of spiradoline than did the normal control subjects. These preliminary findings provide additional evidence for the involvement of opioids in TS and suggest (1) that opioids may exert dual modulatory effects on the expression of tic symptoms and (2) that some TS patients may be characterized by increased sensitivity of kappa receptors regulating growth hormone secretion.

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.

Opioid peptides in Parkinson's disease: effects of dopamine repletion

Neurotransmitters other than dopamine, including neuropeptides, could have important pathophysiologic and therapeutic roles in Parkinson's disease. Both Met-enkephalin, the main transmitter of the striatopallidal pathway, and dynorphin, one of the co-transmitters of the striatonigral pathway display complex anatomic and biochemical interactions with the basal ganglionic dopamine system. In this study, the cerebrospinal fluid content of a proenkephalin derivative, Met5 enkephalin-Arg6-Gly7-Leu8 (MERGL), was found in significantly low concentrations in parkinsonian patients following overnight withdrawal of all medications compared with control subjects, and failed to change after at least 16 h of steady-state, optimal doses of levodopa infusion intravenously. MERGL levels increased with advancing age among normal individuals but not among patients with Parkinson's disease. In contrast dynorphin A(1-8) levels were not different between the two study groups, did not change with levodopa therapy, and failed to correlate with age or any indices of disease progression. These observations, consistent with post-mortem studies on Parkinson brains and contrary to findings in animal models of Parkinsonism, suggest that abnormality of the enkephalin system in this disease is due to involvement of these striatal neurons in the primary pathologic process.

Pathology of Parkinson's disease. Changes other than the nigrostriatal pathway

In Parkinson's disease (PD), in addition to degeneration of the nigrostriatal dopaminergic pathway, a variety of neuronal systems are involved, causing multiple neuromediator dysfunctions that account for the complex patterns of functional deficits. Degeneration affects the dopaminergic mesocorticolimbic system, the noradrenergic locus ceruleus (oral parts) and motor vagal nucleus, the serotonergic raphe nuclei, the cholinergic nucleus basalis of Meynert, pedunculopontine nucleus pars compacta, Westphal-Edinger nucleus, and many peptidergic brainstem nuclei. Cell losses in subcortical projection nuclei range from 30 to 90% of controls; they are more severe in depressed and demented PD patients. Most of the lesions are region-specific, affecting not all neurons containing a specific transmitter or harboring Lewy bodies. In contrast to Alzheimer's disease (AD), subcortical system lesions in Parkinson's disease appear not to be related to cortical pathology, suggesting independent or concomitant degeneration. The pathogenesis of multiple-system changes contributing to chemical pathology and clinical course of Parkinson's disease are unknown.

Dopamine dependent decrease in enkephalin and substance P levels in basal ganglia regions of postmortem parkinsonian brains

This study examined whether a relationship exists between the degree of dopamine (DA) loss and the changes in opioid (Met5-enkephalin, ME; dynorphin A (1-8) (DYN)) or tachykinin (substance P, SP) peptidergic systems in basal ganglia (caudate and putamen) and limbic (frontal cortex) regions of postmortem tissue samples derived from patients who died of Parkinson's disease (PD). The levels of ME, SP and DYN were determined by radioimmunoassays. The levels of DA and 5-hydroxytryptamine (5-HT) and their metabolites were determined by HPLC with electrochemical detection. The degree of loss of DA in PD tissues was classified into two major categories, those with less than 80% and those with more than 80% loss as compared to control. The results reveals that only the category with greater than 80% DA loss exhibited lower levels of ME in caudate and SP in putamen whereas no differences were observed in the levels of DYN in these regions. The frontal cortical region exhibited no changes in the levels of peptides. In other studies, experimental DA deficiency in rodents induced by neurotoxin such as 6-hydroxydopamine (6-OHDA) produced an increase in ME and a decrease in SP in basal ganglia. However, the levels of both peptides were lower in postmortem Parkinsonian basal ganglia in the present study. It appears that there is a DA-dependent, secondary loss of enkephalin and tachykinin peptides in PD. In view of the involvement of these peptidergic systems in the regulation of behaviour, movement, memory and other functions, derangements in these systems should be considered as additional factors in the progression of symptoms of PD.

Evidence that the agonist action of dynorphin A(1-8) in the guinea-pig myenteric-plexus may be mediated partly through conversion to [Leu5]enkephalin

1. The agonist action of the opioid peptide dynorphin A(1-8) on the myenteric plexus-longitudinal muscle of the guinea-pig ileum has been characterized. 2. The endogenous opioid peptide dynorphin A(1-8) was rapidly degraded by slices of myenteric plexus-longitudinal muscle of the guinea-pig ileum. 3. A product of the degradation was the delta-receptor preferring [Leu5]enkephalin. Levels of [Leu5]enkephalin were markedly increased in the presence of the peptidase inhibitors bestatin, thiorphan and captopril. 4. In the myenteric plexus dynorphin A(1-8) acted as a kappa-receptor agonist. In the presence of bestatin, thiorphan and captopril a mu-receptor agonist effect was observed. This mu-agonist action was lost in the presence of N-[1-(RS)-carboxy-2-phenylethyl]Ala-Ala-Phe-p-aminobenzoate, an inhibitor of the endopeptidase enzyme EC 3.4.24.15. 5. The results suggest that formation of [Leu5]enkephalin from dynorphin A(1-8) may be an important conversion process. The enzyme responsible may be the Zn2(+)-metalloendopeptidase, EC 3.4.24.15.

Regional distribution of calcitonin gene-related peptide-, substance P-, cholecystokinin-, Met5-enkephalin-, and dynorphin A (1-8)-like materials in the spinal cord and dorsal root ganglia of adult rats: effects of dorsal rhizotomy and neonatal capsaicin

Biochemical mapping of five different peptide-like materials--calcitonin gene-related peptide (CGRP), substance P (SP), Met5-enkephalin (ME), cholecystokinin (CCK), and dynorphin A (1-8) (DYN)--was conducted in the dorsal and ventral zones of the spinal cord at the cervical, thoracic, and lumbar levels in 3-month-old rats 10 days after unilateral dorsal rhizotomy at the cervical level (C4-T2) or after neonatal administration of capsaicin (50 mg/kg s.c.). In control rats, all peptide-like materials were more abundant in the dorsal than in the ventral zone all along the spinal cord. However, in both zones, absolute concentrations of CGRP, SP, ME, and CCK were significantly higher at the lumbar than at the cervical level. Rhizotomy-induced CGRP depletion (-85%) within the ipsilateral dorsal zone of the cervical cord was more pronounced than that due to neonatal capsaicin (-60%), a finding suggesting that this peptide is contained in both capsaicin-sensitive (mostly unmyelinated) and -insensitive (myelinated) primary afferent fibers. In contrast, similar depletions of SP (-50%) were observed after dorsal rhizotomy and neonatal capsaicin treatment, as expected from the presence of SP only in the capsaicin-sensitive small-diameter primary afferent fibers. Although the other three peptides remained unaffected all along the cord by either intervention, evidence for the existence of capsaicin-insensitive CCKergic primary afferent fibers could be inferred from the increased accumulation of CCK (together with SP and CGRP) in dorsal root ganglia ipsilateral to dorsal root sections.

Two different types of dynorphin-A-immunoreactive terminals in rat substantia nigra

The opioid peptide dynorphin A (1-17) is the third transmitter identified in the striatonigral projection, the other two being gamma-aminobutyric acid (GABA) and substance P. The ultrastructural features of the dynorphinergic terminals in substantia nigra/pars reticulata were studied using pre-embedding immunocytochemistry with the classical peroxidase-antiperoxidase-diaminobenzidine-method; these features were compared with GABAergic boutons visualized with an immunogold method. Two distinct types of dynorphin-A-immunoreactive boutons could be identified: (1) type A (81%) possessing characteristics similar to the GABAergic nerve endings in this region, i.e., large pleomorphic vesicles and symmetric synaptic contacts; (2) type B (19%) displaying asymmetric synaptic zones and small, mostly round vesicles. These results are in agreement with physiological studies suggesting a dual action of dynorphin A in substantia nigra.

Formation of [Leu5]enkephalin from dynorphin A(1-8) by rat central nervous tissue in vitro

[3H]Dynorphin A(1-8) is readily metabolised by rat lumbosacral spinal cord tissue in vitro, affording a variety of products including a significant amount (20% recovered activity) of [3H][Leu5]enkephalin. In the presence of the peptidase inhibitors bestatin, captopril, thiorphan, and leucyl-leucine, [3H][Leu5]enkephalin was the major metabolic product, accounting for 60% of recovered activity. Production of [3H][Leu5]enkephalin was seen across all gross brain regions. The enzyme responsible for the cleavage has an optimal substrate length of 8-13 amino acids and is inhibited by N-[1-(RS)-carboxy-2-phenylethyl]-Ala-Ala-Phe-p-aminobenzoate, a site-directed inhibitor of the metalloendopeptidase EC 3.4.24.15. However the enzymic breakdown also has properties in common with involvement of endo-oligopeptidase A. Possible consequences of the formation of [Leu5]-enkephalin from the smaller dynorphins are discussed.

Localization of striatal opioid gene expression, and its modulation by the mesostriatal dopamine pathway: an in situ hybridization study

In situ hybridization was used to study the macroscopic distribution and regulatory control of proenkephalin mRNA and prodynorphin mRNA in rat striatum. While proenkephalin mRNA was widely distributed throughout the striatum, levels of prodynorphin mRNA were highest in the medial and ventral portions of the striatum. Furthermore, in contrast to the results for proenkephalin mRNA, the levels of prodynorphin mRNA appeared higher in the nucleus accumbens than in the striatum. The mesostriatal dopaminergic pathway was destroyed by discrete, unilateral injection of 6-hydroxy-dopamine (6-OHDA) into either the substantia nigra or the neighboring ventral tegmental area (VTA). Lesions of the substantia nigra caused a dramatic ipsilateral increase in the hybridization signal for proenkephalin mRNA, but no change was observed in the hybridization signal for prodynorphin mRNA. Similar effects were seen with VTA lesions. Since destruction of the mesostriatal dopamine system elevates the levels of proenkephalin mRNA, but not of prodynorphin mRNA, in the striatal target neurons, it appears that the mesostriatal pathway exerts a tonic and selective suppression of striatal proenkephalin gene expression at the mRNA level.

Biochemical mapping of cholecystokinin-, substance P-, [Met]enkephalin-, [Leu]enkephalin- and dynorphin A (1-8)-like immunoreactivities in the human cerebral cortex

The distribution of immunoreactive cholecystokinin, substance P, [Met]enkephalin, [Leu]-enkephalin and dynorphin was determined in the cerebral cortex of the human brain post mortem. Peptide radioimmunoassays in three selected zones of the cortical gray mantle (frontal, temporal, occipital) revealed significant regional differences, prompting to the development of a new dissection procedure for the complete mapping of peptide-like materials throughout the entire cerebral cortex. For this purpose, frozen cerebral hemispheres were cut rostrocaudally in 21 verticofrontal serial sections, from which the cortical gray matter was divided into 4-5 distinct zones. The peptides could be measured in each of the 93 dissected pieces of tissue, but their distribution was uneven. The most abundant was cholecystokinin, particularly in the anterior part of the frontal lobe and in the temporal cortex, where its levels reached 0.5 ng/mg of tissue. The regional distribution of cholecystokinin resembled that of substance P with a decreasing gradient from the frontal to the occipital pole, but absolute levels of substance P were hardly one tenth of cholecystokinin levels. The mean concentrations of the three opioid peptides were even less than those of substance P, and their regional distributions were markedly different. [Met]Enkephalin was concentrated in the occipital cortex, and [Leu]enkephalin in the temporal cortex. Dynorphin was the least abundant, even in the temporal cortex where the highest levels were found. The widespread and heterogeneous distribution of these peptides strongly suggests that each of them exerts specific functions in the human cerebral cortex.

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.

Immunocytochemical studies on the basal ganglia and substantia nigra in Parkinson's disease and Huntington's chorea

The basal ganglia and substantia nigra, taken from control human brain and from patients dying with a diagnosis of Parkinson's disease or Huntington's chorea, were analysed with histochemical and biochemical techniques. The pigmented neurons of the substantia nigra pars compacta possess tyrosine hydroxylase immunoreactivity and are disposed in three major layers, alpha, beta and gamma. This pattern became obscured in choreic brains by the severe shrinkage of the nigra, but total numbers of pigmented neurons were within the normal range. In contrast, pigmented neurons were lost from all layers of the substantia nigra in Parkinson's disease, although examination of cases with minimal cell loss suggested that an internal part of the lateral alpha sub-layer was most severely and consistently affected. A dopaminergic projection between this internal part of the alpha sub-layer and the putamen was suggested by the preferential loss of catecholamines from the putamen in Parkinson's disease. The distribution of the peptides, substance P, methionine-enkephalin and dynorphin 1-17 were mapped immunohistochemically within the substantia nigra. The different patterns of immunoreactive axons and terminals were found to be extensive, at least partially overlapping, and largely avoided the region of the pigmented perikarya of the alpha sub-layer and nucleus paranigralis. All peptides were depleted in choreic substantia nigra, reflecting the degeneration of the striatonigral pathway. However, concentrations of enkephalin-like immunoreactivity were increased within the interpeduncular nucleus. In Parkinson's disease there was a loss of enkephalin- and dynorphin-like immunoreactivity from the substantia nigra but a fall in substance P-like immunoreactivity was only detected by radioimmunoassay, not by immunocytochemistry. Peptide immunoreactivity was also reduced within choreic basal ganglia. However, no gross changes were found in peptide staining of the parkinsonian basal ganglia. In summary we have reported a number of changes in peptide-containing pathways in human degenerative disorders that may reflect the degeneration of neuronal pathways either as a primary event or secondary to initial lesion. We have also emphasized the sensitivity of the alpha sub-layer of nigral neurons to damage in Parkinson's disease. We suggest that the lower density of peptidergic fibres in the area of the perikarya may contribute to the susceptibility of these neurons to damage.

Elevated CSF dynorphin A [1-8] in Tourette's syndrome

A recent neuropathological study has reported decreased levels of dynorphin A immunoreactivity in striato-pallidal fibers in the brain of a patient with severe Gilles de la Tourette's syndrome (TS). This observation, taken with the neuroanatomic distribution of dynorphin and its broad range of motor and behavioral effects, has led to speculation concerning its role in the pathobiology of TS. We report on the presence of elevated concentrations of dynorphin A [1-8] in the CSF of 7 TS patients, aged 20 to 45 years. The increase in CSF dynorphin was found to be associated with the severity of the obsessive compulsive symptoms but not with tic severity in these patients. Although CSF studies lack the precision necessary to address questions of selective involvement of neuronal system in specific CNS locations, these findings suggest that endogenous opioids are involved in the pathobiology of TS and related disorders. Tourette's syndrome (TS) is a chronic neuropsychiatric disorder of childhood onset that is characterized by multiple motor and phonic tics that wax and wane in severity and an array of behavioral problems including some forms of obsessive compulsive disorder (OCD) (1). Once thought to be a rare condition, the prevalence of TS is now estimated to be one case per 1,000 boys and one case per 10,000 girls, and milder variants of the syndrome are likely to occur in a sizeable percentage of the population (2). Although the etiology of TS remains unknown, the vertical transmission of TS within families follows a pattern consistent with an autosomal dominant form of inheritance (3,4). Neurobiologic and pharmacological data have implicated central monoaminergic and neuropeptidergic systems in the pathophysiology of TS, and basal ganglia structures remain the prime candidates as the neuroanatomical origin for TS and related conditions (1). Endogenous opioids, including dynorphin and met-enkephalin are concentrated in structures of the basal ganglia (5), are known to interact with central dopaminergic neurons (6, 7), and may play an important role in the control of motor functions (8). Post-mortem brain studies have directly implicated opioids in the pathophysiology of Parkinson's disease (9), Huntington's disease (10), and most recently in TS (11). The neuropathological study of Haber et al. (11) reported decreased levels of dynorphin A [1-17] immunoreactivity in striatal fibers projecting to the globus pallidus in the brain of a patient with severe TS. This ovservation, taken with the neuroanatomic distribution of dynorphin and its broad range of motor and behavioral effects, has led to speculation concerning its role in the pathobiology of TS.(ABSTRACT TRUNCATED AT 400 WORDS)

An immunohistochemical study of the acute and long-term effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the marmoset

Administration of the drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine induces a parkinsonian syndrome in primates. Intraperitoneal injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the common marmoset (Callithrix jacchus) produced symptoms of rigidity, akinesia and tremor which persisted for at least one month. However, after this time, considerable behavioural recovery occurred, although animals were still severely bradykinetic compared with controls. Marmosets were allowed to survive for 1, 3 1/2 or 7 months prior to histological and immunocytochemical analysis. Detection of catecholaminergic neurons using antibodies directed against the enzyme tyrosine hydroxylase revealed a profound (80%) loss of dopaminergic cells from the substantia nigra one month after initiation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment. This was accompanied by a severe gliosis. Fewer cells were lost from the adjacent ventral tegmental area (45%), but dopamine-containing cells in other brain areas were not obviously affected. At longer survival times the substantia nigra was less damaged, with a proliferation of glia in the pars compacta and a loss of approximately 20% of the dopaminergic perikarya. Using immunohistochemical techniques, the distribution of neuropeptides substance P, [Met]enkephalin and dynorphin 1-17-like immunoreactivity were examined and found to exhibit distinctive patterns in the marmoset substantia nigra. The integrity of these systems appeared intact at all times after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment. These results support the hypothesis that the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine produces a clinical syndrome, indistinguishable from Parkinson's disease, via a selective destruction only of neurons with perikarya in the substantia nigra pars compacta and the ventral tegmental area. The findings that the peptidergic input to these cells together with most non-nigral dopaminergic cell groups are not damaged, indicate that the selectivity of the lesion produced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine appears greater than that seen in idiopathic Parkinson's disease. The neurotoxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the marmoset may not be permanent since both behavioural and biochemical recovery were observed after several months.

Opioid receptors inhibit the adenylate cyclase in guinea pig cochleas

The effects of mu- and delta-preferring agonists on adenylate cyclase activity have been investigated in vitro in homogenates of guinea pig cochleas. Morphine, Leu-enkephalin, D-Ala2, N-methyl-Phe4, Gly-ol5-enkephalin (DAGO) and D-Ser2-Leu-enkephalin-Thr (DSLET) each inhibited the synthesis of cyclic AMP. This effect was reversed by naloxone which had a greater affinity in blocking the effect of the mu-preferring agonists (morphine, DAGO) than in blocking the effect of the delta-preferring agonists (Leu-enkephalin, DSLET). Finally, no additive effects were observed when various combinations of two agonists were used. These results indicate that opioid receptors exist in the guinea pig cochlea and that they are negatively linked to adenylate cyclase. The different affinities shown by naloxone to reverse the inhibition induced by the mu- and delta-preferring agonists suggest that morphine and DAGO act through mu-receptors, whereas Leu-enkephalin and DSLET act through delta-receptors. Since no additive effects have been found when combining two different agonists, it can be hypothesized that the mu- and delta-receptors are coupled to the same pool of adenylate cyclase. It may be proposed from these findings that in vivo enkephalins inhibit the synthesis of cyclic AMP via mu- and delta-receptors. However, whether this effect occurs at a presynaptic level (within opioid-containing olivocochlear varicosities) or at the postsynaptic level (within dendrites of the primary auditory neurons) remains to be determined.

Opioid receptors and neuropeptides in the CNS in rats treated chronically with amoxapine or amitriptyline

The central mechanism responsible for the potentiation by antidepressant drugs of analgesia induced by morphine, was explored by measuring the levels of various neuropeptides (met-enkephalin, leu-enkephalin, dynorphin, substance P and cholecystokinin-like materials) and the density of delta and mu opioid binding sites in the spinal cord of rats treated for 14 days with amoxapine (10 mg/kg i.p., daily) or amitriptyline (10 mg/kg i.p., daily). Similar measurements were made in the hypothalamus and cerebral cortex for comparison. Chronic treatment with amoxapine or amitriptyline did not affect the levels of dynorphin, substance P and cholecystokinin, but markedly enhanced the levels of leu-enkephalin in the three structures examined. The levels of met-enkephalin were also increased after treatment with amitriptyline but only in the spinal cord and hypothalamus. No changes in opioid receptors were found in the cerebral cortex, but the densities of delta and mu opioid binding sites were increased in the spinal cord, and decreased in the hypothalamus of rats treated with amoxapine or amitriptyline. These changes induced by antidepressants in opioidergic markers at the spinal level might account for the potentiation of the action of morphine in amoxapine- or amitriptyline-treated rats. In addition, the observed alterations in the same markers in the hypothalamus could be associated with changes induced by antidepressants in neuroendocrine regulation.

Neuropeptides in neurological disease

Neuropeptides are widely distributed in the central nervous system, where they serve as neuroregulators. Recent interest has focused on their role in degenerative neurological diseases. We describe the normal anatomy of neuropeptides in both the cerebral cortex and basal ganglia as a framework for interpreting neuropeptide alterations in Alzheimer's disease (AD), Huntington's disease, and Parkinson's disease. Concentrations of cortical somatostatin are reduced in AD and in dementia associated with Parkinson's disease. Concentrations of neuropeptide Y and corticotropin-releasing factor are also reduced in AD cerebral cortex. The reduced cortical concentrations of somatostatin and neuropeptide Y in AD cerebral cortex may reflect a loss of neurons or terminals in which these two peptides are co-localized. In Huntington's disease, basal ganglia neurons in which somatostatin and neuropeptide Y are co-localized are selectively preserved. Cerebrospinal fluid concentrations of neuropeptides in AD reflect alterations in cortical concentrations. Improved understanding of neuropeptides in degenerative neurological illnesses will help define which neuronal populations are specifically vulnerable to the pathological processes, and this could lead to improved therapy.

Endogenous opiates: 1985

This paper is the eighth installment of our annual review of research involving the endogenous opiate peptides. It is restricted to the non-analgesic and behavioral studies of the opiate peptides published in 1985. The specific topics this year include stress, tolerance and dependence, eating, drinking and alcohol consumption, gastrointestinal and renal activity, mental illness, learning and memory, cardiovascular responses, respiration and thermoregulation, seizures and neurological disorders, activity, and some other selected topics.

Opioid peptides in Huntington's disease: alterations in prodynorphin and proenkephalin system

The concentrations of dynorphin A1-8 and Met-enkephalin-Arg6-Gly7-Leu8 were measured in the basal ganglia of postmortem brains from patients with Huntington's disease (HD) and from control subjects. A significant reduction of dynorphin A1-8 concentration was found in caudate nucleus, putamen, external globus pallidus and substantia nigra of HD brains. Levels of Met-enkephalin-Arg6-Gly7-Leu8 were reduced in HD caudate nucleus, putamen, internal and external globus pallidus. These data indicate that both the prodynorphin and proenkephalin opioid peptide system are affected in the basal ganglia in HD.