Amantadine in Parkinson's disease

Targeting the N-methyl-D-aspartate receptor for chronic pain management. Preclinical animal studies, recent clinical experience and future research directions

A 1967-1999 MEDLINE search of published reports evaluating the role of the glutamate N-methyl-D-aspartate (NMDA) receptor in pain identified 378 animal studies and 132 human studies. There is convincing evidence in these studies that the NMDA receptor mediates prolonged nociceptive behaviors in animal models and various chronic pain symptoms in the clinical population. Administration of older compounds, such as ketamine, dextromethorphan, and amantadine, which are now known to act as NMDA receptor antagonists, have recently been shown to alleviate chronic pain. For years, the pharmaceutical industry has been attempting to produce novel compounds that modulate NMDA receptor activity; however, the adverse effects associated with this class of drugs have prevented their widespread clinical use. Collaborative studies between basic researchers, clinical scientists, and clinicians are needed to delineate characteristics of NMDA receptor antagonism that predict optimal analgesic activity and an acceptable toxicity profile in patients with chronic pain.

Speech dysfunction in early Parkinson's disease

The purpose of this study is to determine if subjects in the early stages of untreated Parkinson's disease (PD) or PD treated with deprenyl alone suffer from motor speech abnormalities. Speech defects are common in advanced PD, including disturbances of respiration, phonation, and articulation. We studied 12 subjects with early PD (Hoehn and Yahr stage < or = 2, mean duration disease 3.2 years) who were not taking symptomatic therapy and tested them under two conditions: on and off deprenyl. None of the subjects was depressed or demented (Mini Mental Status mean 29.9/30; Hamilton Depression Rating mean 2.7/52). All functioned independently (Schwab and England Activities of Daily Living mean 93.1/100). Acoustic and speech productions were assessed using the DSP Sona-Graph 5500 and an evaluation of dysarthria. All 12 had at least two characteristics of dysarthria on examination, although 8 were not aware of it. Vocal tremor was identified on narrow band spectrogram for four subjects. Deprenyl did not have a consistent effect on speech. Ten subjects had no detectable change in speech on deprenyl, one was worse, and one was improved.

Inhibition of plasma prolactin in the rat by amantadine

A single iv injection of 15 or 30 but not 7.5 mg/kg BW of an antiviral drug, amantadine, significantly (P less than 0.05) decreased plasma prolactin (PRL) concentrations in male rats. This effect was dose-dependent, with the highest dose producing a longer-lasting decrease in plasma PRL. The amantadine-induced decrease was unaffected by a simultaneous injection of 5-hydroxytryptophan (30 mg/kg BW) but was completely blocked by a simultaneous injection of haloperidol (0.05 mg/kg BW). It is concluded that this novel effect of amantadine on PRL is produced by an interaction with the dopaminergic system.

Speech disorders of Parkinsonism: a review

Study of the speech disorders of Parkinsonism provides a paradigm of the integration of phonation, articulation and language in the production of speech. The initial defect in the untreated patient is a failure to control respiration for the purpose of speech and there follows a forward progression of articulatory symptoms involving larynx, pharynx, tongue and finally lips. There is evidence that the integration of speech production is organised asymmetrically at thalamic level. Experimental or therapeutic lesions in the region of the inferior medial portion of ventro-lateral thalamus may influence the initiation, respiratory control, rate and prosody of speech. Higher language functions may also be involved in thalamic integration: different forms of anomia are reported with pulvinar and ventrolateral thalamic lesions and transient aphasia may follow stereotaxis. The results of treatment with levodopa indicates that neurotransmitter substances enhance the clarity, volume and persistence of phonation and the latency and smoothness of articulation. The improvement of speech performance is not necessarily in phase with locomotor changes. The dose-related dyskinetic effects of levodopa, which appear to have a physiological basis in observations previously made in post-encephalitic Parkinsonism, not only influence the prosody of speech with near-mutism, hesitancy and dysfluency but may affect work-finding ability and in instances of excitement (erethism) even involve the association of long-term memory with speech. In future, neurologists will need to examine more closely the role of neurotransmitters in speech production and formulation.

Adverse psychiatric reactions to modern medication

From this survey it will be apparent that many psychiatric reactions to drugs are largely caused by their direct toxic actions or from combinations of drugs. As such, they are often dose related, although age and slow speed of detoxification will increase the risk of patients developing delirium, hallucinations, sleep disturbances, anxiety etc. Similar toxic reactions can also occur when drugs to which a patient has developed some measure of tolerance are abruptly withdrawn. In this context the effects of drugs upon patterns of sleep may be important determinants of adverse withdrawal symptoms. In contrast are the reactions which resemble one or other of the functional psychoses. In these patients it appears that a past history of an affective or schizophrenic psychosis is the best predictor of a similar illness being precipitated by a particular drug. Nonetheless, with substances like reserpine and cycloserine there is good reason for thinking that, given a sufficient quantity, practically any patient can develop an adverse psychiatric reaction.