Addiction to apomorphine: a clinical case-centred discussion

Memantine increases NMDA receptor level in the prefrontal cortex but fails to reverse apomorphine-induced conditioned place preference in rats

Studies have shown that inflammation and neurodegeneration may accompany the development of addiction to apomorphine and that the glutamate NMDA receptor antagonist, memantine, may be neuroprotective. The similarity between apomorphine and dopamine with regard to their chemical, pharmacological and toxicological properties provided a basis for investigating the mechanism of action of the former agent. In this study, we investigated whether memantine would suppress apomorphine-seeking behavior in rats subjected to apomorphine-induced place preference conditioning, through modulation of NMDA receptors in the prefrontal cortex. Repeated apomorphine (1 mg/kg) treatment induced conditioned place preference (CPP) and had no significant effect on NMDA receptor levels in the prefrontal cortex. Prior treatment with memantine (5 mg/kg or 10 mg/kg) increased the levels of NMDA receptors in the prefrontal cortex but did not suppress CPP induced by apomorphine. These data give further support to the addictive effect of apomorphine and demonstrate that blockade of NMDA receptors by memantine is unable to suppress apomorphine-seeking behavior.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

Clinical insights into use of apomorphine in Parkinson's disease: tools for clinicians

SUMMARY 

Apomorphine was introduced before the era of levodopa as a treatment for idiopathic Parkinson's disease (iPD). A number of practical obstacles were to be solved before a wider use of the drug was possible. Today, however, the drug is probably still underutilized. Apomorphine is a strong nonergoline D1 and D2 receptor agonist with a dopaminergic effect comparable with levodopa. In this review motor and non-motor indications for intermittent injections and subcutaneous apomorphine infusions are listed. The reduction of 'off' periods is more than 50% on infusion therapy and if monotherapy is achieved a significant reduction of pre-existing levodopainduced dyskinesias is seen. The aim of this review is to give practical insight into apomorphine treatment, highlighting side effects, and complications and device-related problems are discussed with advice on how to prevent or handle these, should they occur. A number of practical points including the apomorphine test, requirements of the clinical setting, how to increase adherence and troubleshooting are added.

Compulsive use of dopamine replacement therapy: a model for stimulant drug addiction?

The compulsive use of dopamine replacement therapy (DRT) or dopamine dysregulation syndrome (DDS) is one of the behavioural disturbances reported in some patients with Parkinson's disease (PD) and other disorders who are receiving DRT. We draw this phenomenon to the attention of the addiction field as a topic deserving of more systematic study. We outline: the clinical features, epidemiology and clinical correlates of the disorder; the unresolved issues in its definition and diagnosis; and its potential relevance to neurobiological models of psychostimulant addiction. We argue that compulsive DRT use may provide a useful model for drug addiction, while advancing our understanding of the neurobiology of addiction and improving the management of PD patients with the disorder.