The unilateral 6-hydroxydopamine lesion model in behavioral brain research. Analysis of functional deficits, recovery and treatments.

Rats sustaining unilateral near-complete 6-hydroxydopamine lesions of the mesostriatal dopamine pathway received daily injections of 3, 4 dihydroxyphenyl-l-alanine (L-DOPA, 8 mg/kg plus 15 mg/kg benserazide) for 3 weeks. During this period, about 50% of the rats gradually developed abnormal involuntary movements, lasting for 2-3 h following each L-DOPA dose. Rats were killed 3 days after the last L-DOPA injection, and sections through the striatum were processed for in situ hybridization histochemistry. Within the L-DOPA-treated group, levels of preproenkephalin (PPE) mRNA, glutamic acid decarboxylase (GAD67) mRNA, and prodynorphin (PDyn) mRNA in the dopamine-denervated caudate-putamen, as well as GAD67 mRNA expression in the globus pallidus ipsilateral to the 6-hydroxydopamine (6-OHDA) lesion, were higher in dyskinetic than non-dyskinetic animals, and positively correlated with the rats' dyskinesia scores. By contrast, striatal preprotachykinin mRNA expression and D2 receptor-radioligand binding were not significantly associated with dyskinesia. Among all these markers, PDyn mRNA levels showed the most pronounced treatment-dependence (three times higher in the L-DOPA-treated group than in saline-injected lesion-only controls), and the strongest correlation with the rats' dyskinesia scores (r2 = 0.82). However, a multiple regression equation including the three factors, GAD67 mRNA levels in the GP, GAD67 mRNA in the lateral CPu, and striatal PDyn mRNA, gave a better fit for dyskinesia scores than PDyn mRNA alone (r2 = 0.92). The results show that L-DOPA-induced dyskinesia is associated with overexpression of PDyn and GAD67 mRNA in the striatal projection neurons, and GAD67 mRNA levels in the globus pallidus. Due to its treatment-dependent expression, and strong correlation with the associated dyskinetic symptoms, striatal PDyn mRNA, in particular, may play a role in the mechanisms of behavioural sensitization brought about by the drug.

L-DOPA-induced dyskinesia in the rat is associated with striatal overexpression of prodynorphin- and glutamic acid decarboxylase mRNA.

L-DOPA-induced dyskinesia in the rat is associated with striatal overexpression of prodynorphin- and glutamic acid decarboxylase mRNA: Striatal gene expression and dyskinesia in the rat

This review will consider the classification and phenomenology, the acute pharmacology, and the etiology of levodopa-induced dyskinesias

Levodopa-induced dyskinesia: review, observations, and speculations.

Drugs acting on brain dopamine receptors: a conceptual re-evaluation five years after the first selective D-1 antagonist.

Differential effect of repeated treatment with L-dopa on dopamine-D1 or -D2 receptors.

Unilateral lesions of the nigro-striatal dopamine (DA) pathway induced contralateral rotations to apomorphine, increased (3H)-spiroperidol binding and enhanced the sensitivity of striatal adenylate cyclase to DA stimulation. Prolonged L-dopa administration counteracted the increased density of (3H)-spiroperidol binding sites but further enhanced the hypersensitivity of adenylate cyclase to DA and decreased the inhibitory effect of opiates on this enzyme. The apomorphine-induced contralateral rotations were also strongly potentiated. On the contrary the binding of (3H)-SCH-23390 was affected neither by DA nerve degeneration nor by chronic L-dopa treatment. These results suggest that DA-D1 and DA-D2 receptors are differently affected by prolonged L-dopa treatment. The biochemical changes of DA-D1 receptors associated with adenylate cyclase seem to be correlated with the enhanced behavioural responses to apomorphine and could be a consequence of a decreased opiate inhibitory tone on the enzyme. The increased supersensitivity of the DA-D1 receptors may play a role in the clinical changes seen in parkinsonian patients following chronic use of L-dopa.

Dopamine receptor changes in response to prolonged treatment with L-dopa.

In this study, a dynamic TV pupillometric system has been used to record the effects of the anticholinergic drug biperidene (Akineton) on pupil responsiveness to various types of stimuli. Plasma levels of the drug were evaluated by means of the radioreceptor binding technique at the same times of pupillometric monitoring. An excellent correlation was found between the effects of biperidene on pupil diameter after light and dark adaptation, light reflex and near vision reaction and the plasma levels of the drug. Radioreceptor binding and dynamic TV pupillometry represent useful tools to evaluate the possible alterations induced by drug therapy on the cholinergic system in man.

Pupillometry and radioreceptor binding. Semeiologic suggestions in the evaluation of the treatment with anticholinergic drugs.

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Differential effect of repeated treatment with L-dopa on dopamine-D1 or -D2 receptors.

Dopamine receptor changes in response to prolonged treatment with L-dopa.

Pupillometry and radioreceptor binding. Semeiologic suggestions in the evaluation of the treatment with anticholinergic drugs.