Chronic high dose L-dopa treatment does not alter the levels of dopamine D-1, D-2 or D-3 receptor in the striatum of normal monkeys: an autoradiographic study

To assess the role of dopamine receptors in the genesis of dyskinesia, we have used quantitative autoradiography to determine the effect of chronic L-dopa administration on dopamine D-1 (using [3H]SCH 23390), D-2 (using [3H]spiperone) and D-3 (using [3H]7-OH-DPAT) receptor binding levels in the striatum of dyskinetic or non-dyskinetic monkeys. Total and subregional striatal analysis showed no difference in D-1, D-2 or D-3 receptor binding in the caudate and putamen between monkeys receiving high dose L-dopa treatment with marked dyskinesia and those without dyskinesia compared to untreated animals. It thus appears unlikely that changes in dopamine receptor expression are a primary cause of L-dopa induced dyskinesia. Rather, a functional dissociation of D-2 receptor coupling to co-expressed enkephalin/adenosine-2a receptor activity in the striato-GPe indirect pathway may be more important in the development or expression of L-dopa-induced involuntary movements.

Up-regulation of secretoneurin immunoreactivity and secretogranin II mRNA in rat striatum following 6-hydroxydopamine lesioning and chronic L-DOPA treatment

Destruction of the nigro-striatal pathway in Parkinson's disease and treatment with L-DOPA lead to persistent alterations in basal ganglia output pathways that are poorly characterised. Differential display mRNA analysis was used to study the effects of 6-hydroxydopamine-induced lesions of the medial forebrain bundle on gene expression in the rat striatum. One up-regulated cDNA identified in two independent groups of 6-hydroxydopamine-lesioned animals was cloned and sequence analysis showed 97% homology to secretogranin II. Differential up-regulation of secretogranin II following 6-hydroxydopamine lesioning was confirmed in a further group of 6-hydroxydopamine-lesioned rats using TaqMan real time quantitative reverse transcription-polymerase chain reaction. Following chronic L-DOPA treatment of 6-hydroxydopamine-lesioned rats, secretogranin II mRNA was further up-regulated to a similar degree to that observed for preproenkephalin A mRNA expression. Immunohistochemical analysis confirmed the increase in secretogranin II peptide levels in striatal neurones in 6-hydroxydopamine-lesioned rats following chronic L-DOPA treatment. The increase in secretogranin II mRNA occurring following destruction of the nigro-striatal pathway and chronic L-DOPA treatment may result in an increase in secretoneurin levels, which could be important for the regulation of striatal output pathways.

Increased cannabinoid CB1 receptor binding and activation of GTP-binding proteins in the basal ganglia of patients with Parkinson's syndrome and of MPTP-treated marmosets

Recent evidence obtained in rat models of Parkinson's disease showed that the density of cannabinoid CB1 receptors and their endogenous ligands increase in basal ganglia. However, no data exists from post-mortem brain of humans affected by Parkinson's disease or from primate models of the disorder. In the present study, we examined CB1 receptor binding and the magnitude of the stimulation by WIN55,212-2, a specific CB1 receptor agonist, of [35S]GTPgammaS binding to membrane fractions from the basal ganglia of patients affected by Parkinson's disease. In Parkinson's disease, WIN55,212-2-stimulated [35S]GTPgammaS binding in the caudate nucleus, putamen, lateral globus pallidus and substantia nigra was increased, thus indicating a more effective activation of GTP-binding protein-coupled signalling mechanisms via CB1 receptors. This was accompanied by an increase in CB1 receptor binding in the caudate nucleus and the putamen, although no changes were observed in the lateral globus pallidus and the substantia nigra. Because Parkinson's disease patients had been chronically treated with l-DOPA, brains were studied from normal common marmosets and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated animals with and without chronic L-DOPA treatment. MPTP-lesioned marmosets had increased CB1 receptor binding in the caudate nucleus and the putamen compared to control marmosets, as well as increased stimulation of [35S]GTPgammaS binding by WIN55,212-2. However, following l-DOPA treatment these parameters returned towards control values. The results indicate that a nigro-striatal lesion is associated with an increase in CB1 receptors in the basal ganglia in humans and nonhuman primates and that this increase could be reversed by chronic l-DOPA therapy. The data suggest that CB1 receptor blockade might be useful as an adjuvant for the treatment of parkinsonian motor symptoms.

Antiparkinsonian and neuroprotective effects of modafinil in the mptp-treated common marmoset

The psychostimulant drug, modafinil, protects rodents against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity, striatal ischemia and partial transection of the nigro-striatal pathway. We now report on the ability of modafinil to reverse motor disability in MPTP-treated common marmosets and to prevent MPTP-induced nigral cell death in this species. In the initial experiments, adult common marmosets were treated with MPTP to produce stable motor deficits. The subsequent administration of modafinil (10, 30 or 100 mg/kg/day, p.o.) produced a dose-dependent reversal of motor disability. In a subsequent experiment, normal common marmosets were concurrently treated with 10, 30 or 100 mg/kg of modafinil once daily by gavage during acute MPTP administration (daily for 5 days), continuing for 2 weeks after the last dose of MPTP. Modafinil dose-dependently prevented the decline in motor activity normally produced by MPTP treatment. MPTP treatment caused a 76% loss of nigral tyrosine-hydroxylase-immunoreactive cells in placebo-treated animals, and this was dose-dependently prevented by modafinil. At the highest dose (100 mg/kg/day) of modafinil, there was no significant loss of tyrosine-hydroxylase-immunoreactive cells in the substantia nigra compared with normal animals. MPTP treatment also reduced striatal dopamine uptake sites by 95%, as measured by specific [3H]-mazindol binding, compared with normal controls. Modafinil treatment dose-dependently reduced the loss of specific [3H]-mazindol binding. Behavioural and morphological evidence in the present study indicate a potential antiparkinsonian and neuroprotective role for modafinil, which may form a new pharmacological approach to the treatment of Parkinson's disease.

Alterations in preproenkephalin and adenosine-2a receptor mRNA, but not preprotachykinin mRNA correlate with occurrence of dyskinesia in normal monkeys chronically treated with L-DOPA

Chronic treatment with L-DOPA induces dyskinesia in patients with Parkinson's disease (PD) and 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-treated monkeys, but is not thought to do so in normal humans or primates. However, we have shown that chronic oral high dose L-DOPA administration, with the peripheral decarboxylase inhibitor, carbidopa and with or without the peripherally acting catechol-O-methyl transferase (COMT) inhibitor, entacapone, to normal macaque monkeys for 13 weeks induced dyskinesia in a proportion of animals. In the present study, in situ hybridization histochemistry was used to investigate the effect of chronic L-DOPA administration on the activity of the direct and indirect striatal output pathways by measuring striatal preprotachykinin (PPT), preproenkephalin-A (PPE-A) and adenosine-2a (A2a) receptor gene expression in these monkeys. Overall there was no significant difference in striatal PPT, PPE-A and A2a receptor mRNA levels between normal animals and all L-DOPA (plus carbidopa and/or entacapone)-treated animals irrespective of whether or not dyskinesia occurred. However, when the level of PPE-A and A2a receptor mRNA was analysed in eight monkeys displaying marked dyskinesias as a result of L-DOPA (plus carbidopa with or without entacapone) treatment, there was a significant increase in PPE-A and A2a receptor mRNA message levels in the striatum compared with animals receiving identical treatment, but displaying few or no involuntary movements, and compared with normal controls. There was no difference in striatal PPT mRNA levels in monkeys exhibiting severe dyskinesia compared with those showing little or no dyskinesia after L-DOPA treatment or to normal controls. These results suggest that prolonged L-DOPA treatment alone has no consistent effect on either the direct or indirect pathways, as judged by striatal PPT, PPE-A or A2a receptor mRNA levels in normal monkeys. However, in monkeys exhibiting marked dyskinesia resulting from chronic L-DOPA treatment, abnormal activity is detected in the indirect striato-pallidal output pathway, as judged by striatal PPE-A and A2a receptor mRNA levels, indicating an imbalance between the direct and indirect striatal pathway which may explain the emergence of dyskinesia in these animals.

Chronic L-DOPA treatment increases striatal cannabinoid CB1 receptor mRNA expression in 6-hydroxydopamine-lesioned rats

The effect of a unilateral 6-hydroxydopamine (6-OHDA) lesion of the left medial forebrain bundle and 3 weeks treatment with L-DOPA of normal and 6-OHDA lesioned rats on CB1r mRNA expression was investigated by in situ hybridization. A 6-OHDA lesion of nigrostriatal pathway alone, confirmed by the loss of nigral tyrosine hydroxylase mRNA, did not alter CB1r mRNA levels in the dopamine depleted striatum. Similarly, chronic L-DOPA treatment of normal rats had no effect on striatal CB1r mRNA expression. In contrast, chronic L-DOPA treatment of 6-OHDA-lesioned rats significantly increased CB1r mRNA expression in the denervated striatum. These results suggest that the CB1r activity may be altered by L-DOPA's action and this may be related to the treatment of Parkinson's disease.

High efficiency gene transfer to the central nervous system of rodents and primates using herpes virus vectors lacking functional ICP27 and ICP34.5

The safe and efficient use of herpes simplex virus (HSV)-based vectors to deliver genes of potentially therapeutic benefit to the central nervous system will require their effective disablement by the inactivation of viral genes required for lytic growth. Here we report that viruses lacking functional genes for ICP27 (which is required for growth in all cell types) and ICP34.5 (which is required for growth in nondividing cell types) can deliver a marker gene to both the rodent and primate CNS with high efficiency whilst producing relatively minimal damage and having no effect on sodium currents in dorsal root ganglion neurons. Such viruses paradoxically deliver genes at much higher efficiency than the less disabled single mutant lacking ICP34.5 alone and also, as expected, produce less damage in vivo. Moreover, unlike the single mutant lacking ICP27 the double mutant viruses cannot revert to wild-type by acquistion of complimenting gene sequences during growth of virus stocks in vitro on dividing cells expressing ICP27 since artificial expression of ICP34.5 in these cells is not required. Such ICP27-; ICP34.5- viruses thus offer a platform for the development of vectors which are sufficiently safe for ultimate use in human gene therapy.

Glutathione depletion in rat brain does not cause nigrostriatal pathway degeneration

Nigral cell death in Parkinson's disease (PD) may involve oxidative stress and mitochondrial dysfunction initiated by a decrease in reduced glutathione (GSH) levels in substantia nigra. L-buthionine-(S,R)-sulphoximine (BSO; 4.8 and 9.6 mg/kg/day), an irreversible inhibitor of gamma-glutamyl cysteine synthetase, was chronically infused into the left lateral ventricle of rats over a period of 28 days and markedly reduced GSH concentrations in substantia nigra (approx. 59% and 65% in 4.8 and 9.6 mg/kg/d BSO respectively) and the striatum (approx. 63% and 80% in 4.8 and 9.6 mg/kg/d BSO respectively). However, the number of tyrosine hydroxylase (TH)-positive cells in substantia nigra was not altered by BSO-treatment compared to control animals. Similarly, there was no difference in specific [3H]-mazindol binding in the striatum and nucleus accumbens of BSO-treated rats compared to control rats. In conclusion, depletion of GSH following chronic administration of BSO in the rat brain does not cause damage to the nigrostriatal pathway and suggests that loss of GSH alone is not responsible for nigrostriatal damage in PD. Rather, GSH depletion may enhance the susceptibility of substantia nigra to destruction by endogenous or exogenous toxins.

Altered motor function and graft survival produced by basic fibroblast growth factor in rats with 6-OHDA lesions and fetal ventral mesencephalic grafts are associated with glial proliferation

Basic fibroblast growth factor (bFGF) promotes the survival and growth of dopaminergic neurons. We have investigated the effect of treating fetal ventral mesencephalon with bFGF or nerve growth factor (NGF) on the subsequent survival and function of grafted dopaminergic neurons implanted into the striatum of rats with a unilateral 6-hydroxydopamine lesion. Animals implanted with fetal ventral mesencephalon mixed with bFGF, but not with NGF, displayed more rapid compensation in motor behavior up to 9 weeks after graft implantation. bFGF, but not NGF, produced an increase in the number of tyrosine hydroxylase (TH)-positive neurons, a larger graft volume, and longer neurite outgrowth in comparison to control grafts. bFGF also increased the number of glial fibrillary acidic protein (GFAP)-positive astrocytes within the grafts. The increased number of GFAP-positive astrocytes induced by bFGF correlated with the increase in the number of TR-positive neurons, with graft volume and with neurite outgrowth. These findings support the use of bFGF to promote the functional integration of fetal ventral mesencephalon grafts into the denervated host brain and and suggest that its action may be indirectly mediated through glial cells.

Partial reversal of increased preproenkephalin messenger ribonucleic acid (mRNA) and decreased preprotachykinin mRNA by foetal dopamine cells in unilateral 6-hydroxydopamine-lesioned rat striatum parallels functional recovery

In situ hybridization histochemistry was used to investigate the expression of striatal preproenkephalin and preprotachykinin messenger ribonucleic acid (mRNA) in rats with 6-hydroxydopamine lesions of the nigrostriatal pathway followed 4 weeks later by implantation of foetal dopamine cells into the denervated striatum. Striatal dopamine deafferentation caused an (+)-amphetamine-induced rotational asymmetry, an increase in striatal preproenkephalin mRNA message, and a decrease in striatal preprotachykinin mRNA message relative to control animals. Two months after grafting a foetal ventral mesencephalon suspension, there was reversal of the rotational asymmetry to (+)-amphetamine. At this time the increase in striatal preproenkephalin mRNA was significantly attenuated and the decrease in preprotachykinin mRNA was partially reversed compared to animals with a 6-hydroxydopamine lesion alone. Subregional analysis showed the attenuation of the increase in preproenkephalin mRNA to occur in dorsolateral, dorsomedial and ventromedial, but not ventrolateral, striatal subdivisions. The partial reversal of the decreased preprotachykinin mRNA density after grafting was only statistically significant in the DM and VM subdivisions. These results demonstrate graft-induced partial recovery of striatal function, as judged by preproenkephalin and preprotachykinin mRNA levels, within 2 months of transplantation.

Regenerative and other responses to injury in the retinal stump of the optic nerve in adult albino rats: transection of the intracranial optic nerve

The response to injury of the proximal (retinal) stump of the intracranially transected optic nerve in adult rats has been studied by electron microscopy. The central part of the retinal stump of the optic nerve underwent severe ischaemic damage resulting in the formation by 3 days postoperation (dpo) of a cone-shaped region of necrotic tissue which extended from a base occupying most of the cross-sectional area of the nerve at the cut end to an apex within the intraorbital part of the nerve and only 2-3 mm from the eyeball. A mixture of apparently viable and dead or dying cells and axons was present in an intermediate zone surrounding the ischaemic core. Apparently intact nerve fibres occupied most of the periphery of the optic nerve. Small bundles of sprout-like axons were seen in the intermediate zone at 3 dpo, and by 5 dpo such sprouts were present at the periphery of the degenerative core. By 7 dpo, the sprouts were also found in the centre of the degenerative core, accompanied by astrocyte processes. The number of axonal sprouts present in the degenerative core and intermediate zone was much higher at 2 and 4 wk postoperation (wpo) than at 7 dpo, then declined gradually by 6 and 8 wpo. These results show that intracranial transection of the rat optic nerve produces extensive degeneration in the proximal stump and effectively produces an intraorbital axotomy of many retinal ganglion cells. Nevertheless, surviving axons display the ability to produce regenerative sprouts which persist for considerably longer than those produced after intraorbital injury.

Chronic L-DOPA treatment differentially regulates gene expression of glutamate decarboxylase, preproenkephalin and preprotachykinin in the striatum of 6-hydroxydopamine-lesioned rat

The effect of a unilateral 6-hydroxydopamine lesion of the medial forebrain bundle in rats and subsequent L-DOPA treatment for eight weeks on preproenkephalin, preprotachykinin and glutamate decarboxylase (M(r) 67,000) gene expression in the striatum was investigated by in situ hybridization. A 6-hydroxydopamine lesion of the medial forebrain bundle markedly increased the level of preproenkephalin messenger RNA (+66%) and modestly elevated the level of glutamate decarboxylase (M(r) 67,000) messenger RNA (+36%) in the denervated striatum, but caused a decrease in the level of preprotachykinin messenger RNA (-54%) relative to the intact striatum and to sham-lesioned control animals. Treatment with L-DOPA (200 mg/kg/24 h) for eight weeks reduced but did not abolish the 6-hydroxydopamine lesion-induced elevation of preproenkephalin messenger RNA and slightly reduced the elevation of glutamate decarboxylase (M(r) 67,000) messenger RNA in denervated striatum relative to intact side and control groups. However, L-DOPA treatment almost completely reversed the decrease in preprotachykinin messenger RNA caused by 6-hydroxydopamine lesioning when compared to intact side and control groups. The effect of L-DOPA on the gene expression of preproenkephalin and glutamate decarboxylase (M(r) 67,000) differs from the increase in striatal enkephalin content and glutamate decarboxylase activity previously found following L-DOPA treatment. In contrast, L-DOPA reversed the changes in preprotachykinin messenger RNA, reflecting previously reported increases in substance P content. The findings provide new evidence that chronic L-DOPA treatment differentially affects direct striatonigral and indirect striatopallidal pathways at the molecular level.

Regenerative and other responses to injury in the retinal stump of the optic nerve in adult albino rats: transection of the intraorbital optic nerve

The proximal stump of the optic nerve was examined by electron microscopy from 1 d to 8 wk (dpo/wpo) after intraorbital transection. At 1 dpo a layer of axonal, cytoplasmic and myelin debris approximately 15 microns thick was present at the cut end. A zone approximately 25 microns thick of abnormal and partly degenerate tissue composed of many swollen axons filled with organelles of predominantly abnormal appearance lay between the zone of debris and more proximal levels of the optic nerve, which retained a normal appearance. The earliest putative axonal sprouts were seen at 1 dpo in this zone. By 2 dpo, bundles of small nonmyelinated axons containing microtubules, almost certainly axonal sprouts, had grown out from more proximal regions of the proximal stump and extended as far as its cut end. By 3 dpo, large numbers of axonal sprouts, as well as large numbers of macrophages and newly formed blood vessels, were seen close to the cut end of the proximal stump. Glial cells were not seen to accompany these early outgrowing bundles of axonal sprouts. By 5 dpo, the number of sprouts and macrophages had increased; many bundles of sprouts were now in contact with the surface of astrocytes, which were partly covered by basal lamina. At 7 dpo most of the macrophages had disappeared from the most distal part of proximal stump and bundles of axonal sprouts, associated with astrocytes, which in some cases had penetrated and were fasciculating such bundles, were present at the cut end. The regenerating axonal sprouts in the scar-like tissue at the distal end of the proximal stump of the optic nerve declined in numbers sharply at 2 wpo and only a few sprout-like axonal profiles were present by 8 wpo. Thus while ultimately abortive the early regenerative response is vigorous and involves the outgrowth of a large number of axonal sprouts in the first week after injury.