Action of calcitonin gene-related peptide upon bovine vascular endothelial and smooth muscle cells grown in isolation and co-culture.

1. Bovine aortic endothelial cells (BAE) and smooth muscle cells (BASM) were grown separately and in co-culture. 2. Calcitonin gene-related peptide (CGRP) caused dose-dependent activation of adenylate cyclase in each cell type when grown in isolation. The concentration of CGRP causing half-maximal activation in BAE and BASM was 200 nM and 310 nM, respectively. 3. In cells grown in co-culture exposure to bradykinin produced dose-dependent elevations in cyclic GMP content which were maximal 1 min after application of the agonist. 4. CGRP (1 nM-1 microM) did not stimulate a rise in cyclic GMP in co-cultures. 5. Displaceable CGRP binding was identified throughout the wall of the bovine aorta. 6. We conclude that CGRP receptors coupled to adenylate cyclase are present on BAE and BASM, but there is no coupling of these receptors to the release of any agent (such as endothelium-derived relaxing factor) that activates guanylate cyclase.     

Novel antiepileptic drug levetiracetam decreases dyskinesia elicited by L-dopa and ropinirole in the MPTP-lesioned marmoset.

Long-term dopamine replacement therapy of Parkinson's disease leads to the occurrence of dyskinesias. Altered firing patterns of neurons of the internal globus pallidus, involving a pathological synchronization/desynchronization process, may contribute significantly to the genesis of dyskinesia. Levetiracetam, an antiepileptic drug that counteracts neuronal (hyper)synchronization in animal models of epilepsy, was assessed in the MPTP-lesioned marmoset model of Parkinson's disease, after coadministration with (1) levodopa (L-dopa) or (2) ropinirole/L-dopa combination. Oral administration of levetiracetam (13-60 mg/kg) in combination with either L-dopa (12 mg/kg) alone or L-dopa (8 mg/kg)/ropinirole (1.25 mg/kg) treatments was associated with significantly less dyskinesia, in comparison to L-dopa monotherapy during the first hour after administration. Thus, new nondopaminergic treatment strategies targeting normalization of abnormal firing patterns in basal ganglia structures may prove useful as an adjunct to reduce dyskinesia induced by dopamine replacement therapy without affecting its antiparkinsonian action.     

Fipamezole (JP-1730) is a potent alpha2 adrenergic receptor antagonist that reduces levodopa-induced dyskinesia in the MPTP-lesioned primate model of Parkinson's disease.

Previous studies in the MPTP-lesioned primate model of Parkinson's disease have demonstrated that alpha(2) adrenergic receptor antagonists such as idazoxan, rauwolscine, and yohimbine can alleviate L-dopa-induced dyskinesia and, in the case of idazoxan, enhance the duration of anti-parkinsonian action of L-dopa. Here we describe a novel alpha(2) antagonist, fipamezole (JP-1730), which has high affinity at human alpha(2A) (K(i), 9.2 nM), alpha(2B) (17 nM), and alpha(2C) (55 nM) receptors. In functional assays, the potent antagonist properties of JP-1730 were demonstrated by its ability to reduce adrenaline-induced (35)S-GTPgammaS binding with K(B) values of 8.4 nM, 16 nM, 4.7 nM at human alpha(2A), alpha(2B), and alpha(2C) receptors, respectively. Assessment of the ability of JP-1730 to bind to a range of 30 other binding sites showed that JP-1730 also had moderate affinity at histamine H1 and H3 receptors and the serotonin (5-HT) transporter (IC(50) 100 nM to 1 microM). In the MPTP-lesioned marmoset, JP-1730 (10 mg/kg) significantly reduced L-dopa-induced dyskinesia without compromising the anti-parkinsonian action of L-dopa. The duration of action of the combination of L-dopa and JP-1730 (10 mg/kg) was 66% greater than that of L-dopa alone. These data suggest that JP-1730 is a potent alpha(2) adrenergic receptor antagonist with potential as an anti-dyskinetic agent in the treatment of Parkinson's disease.     

Subthalamic projection to nucleus tegmenti pedunculopontinus in the rat

A projection from the subthalamic nucleus to the nucleus tegmenti pedunculopontinus has been demonstrated in the rat using retrograde and anterograde transport of horseradish peroxidase. Small, well-localized injections of peroxidase in nucleus pedunculopontinus gave rise to retrogradely labelled cell bodies in the subthalamic nucleus. Injections of peroxidase restricted to the subthalamic nucleus gave terminal labelling in nucleus pedunculopontinus.     

Reduction of [125I]Bolton Hunter CCK8 and [3H]MK-329 (devazepide) binding to CCK receptors in the substantia nigra/VTA complex and its forebrain projection areas following MPTP-induced hemi-parkinsonism in the monkey.

Cholecystokinin (CCK) receptors were visualized autoradiographically using [125I]Bolton Hunter CCK8 ([125I]BHCCK8) in the fore- and midbrain of 3 monkeys rendered hemi-parkinsonian by unilateral intra-carotid infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). More specifically, CCK-A receptors were detected using [3H]MK-329 (devazepide), a peripheral-type (CCK-A) receptor antagonist. In the substantia nigra pars compacta, ipsilateral to the toxin infusion, where dopamine D2 receptors (labelled with [3H]sulpiride) were lost, there was a decrease in the binding of both [125I]BHCCK8 and [3H]MK-329. Binding of the two CCK ligands was also reduced in the ipsilateral nucleus accumbens and most medial part of the caudate nucleus, whereas 3H-sulpiride binding was increased in the lateral caudate nucleus and putamen. These results indicate that CCK-A receptors may be located on dopaminergic cells within the substantia nigra, which are lost in the parkinsonian brain, and may also be present on dopaminergic terminals within restricted regions of nigral/ventral tegmental area projection sites.     

Induction of chorea and dystonia in parkinsonian primates

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in primates induced a parkinsonian syndrome that could be reversed by levodopa treatment. Animals quickly developed an apparent restlessness ("akathisia") of the lower limbs after as little as five doses. After 4-10 weeks of regular levodopa therapy, animals developed "peak dose" choreiform movements in the lower limbs that spread, with time, to involve the upper limbs and orofacial musculature. With further treatment (5-21 months), animals developed "peak dose" dystonia that variably involved the limbs and orofacial musculature. These conditions represent novel models of levodopa-induced chorea and dystonia in humans. They depend on the same underlying neuropathology and treatment regimen as their human counterparts. It is to be anticipated that these models of dyskinesia will be useful in determining the mechanisms underlying chorea and dystonia in humans and are ideally suited for experimental evaluation of new treatment strategies.     

Antiparkinsonian actions of ifenprodil in the MPTP-lesioned marmoset model of Parkinson's disease

Dopamine-replacement strategies form the basis of most symptomatic treatments for Parkinson's disease. However, since long-term dopamine-replacement therapies are characterized by many side effects, most notably dyskinesia, the concept of a nondopaminergic therapy for Parkinson's disease has attracted great interest. To date, it has proved difficult to devise a nondopaminergic therapy with efficacy comparable to that of dopamine replacement. In animal models of Parkinson's disease, loss of striatal dopamine leads to enhanced excitation of striatal NR2B-containing NMDA receptors. This is responsible, in part at least, for generating parkinsonian symptoms. Here we demonstrate that, in the MPTP-lesioned marmoset, monotherapy with the NR2B-selective NMDA receptor antagonist, ifenprodil, administered de novo, has antiparkinsonian effects equivalent to those of l-DOPA (administered as its methyl ester form). In MPTP-lesioned marmosets, median mobility scores, following vehicle-treatment were 12.5/h (range 6-21), compared to 61/h (range 26-121) in normal, non-MPTP-lesioned animals. Following ifenprodil (10 mg/kg) treatment in MPTP-lesioned marmosets, the median mobility score was 66/h (range 34-93), and following l-DOPA (10 mg/kg i.p.) treatment 89/h (range 82-92). The data support the proposal that NR2B-selective NMDA receptor antagonists have potential as a nondopaminergic monotherapy for the treatment of parkinsonian symptoms when given de novo.     

Drug eluting stents: maximising benefit and minimising cost

A policy of selective implantation of drug eluting stents, in a minority of lesions most likely to benefit, seems to be a rational way to employ this new and currently costly technology.