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It has been reported that 50% to 80% of patients with Parkinson's disease have abnormal glucose tolerance which may be further exacerbated by levodopa therapy. Little is known about the impact of chronic hyperglycemia on the severity of the motor manifestations and the course of the disease as well as its impact on the efficacy of levodopa or other dopaminergic drugs. This issue, which has been largely ignored, is of clinical relevance since animal studies indicate that chronic hyperglycemia decreases striatal dopaminergic transmission and increases the sensitivity of postsynaptic dopamine receptors. In addition, evidence from experimental animal studies indicates that diabetic rats are resistant to the locomotor and behavioral effects of the dopamine agonist amphetamine. The resistance to the central effects of amphetamine is largely restored with chronic insulin therapy. In the present communication, I propose that in Parkinson's disease diabetes may exacerbate the severity of the motor disability and attenuate the therapeutic efficacy of levodopa or other dopaminergic agents as well as increase the risk of levodopa-induced motor dyskinesias. Thus, it is advocated that Parkinsonian patients should be routinely screened for evidence of glucose intolerance and that if found aggressive treatment of the hyperglycemia may improve the response to levodopa and potentially diminish the risk of levodopa-induced motor dyskinesias.

Cannabidiol (CBD), a nonpsychoactive cannabinoid of Cannabis, was given to 5 patients with dystonic movement disorders in a preliminary open pilot study. Oral doses of CBD rising from 100 to 600 mg/day over a 6 week period were administered along with standard medication. Dose-related improvement in dystonia was observed in all patients and ranged from 20 to 50%. Side-effects of CBD were mild and included hypotension, dry mouth, psychomotor slowing, lightheadedness, and sedation. In 2 patients with coexisting Parkinsonian features, CBD at doses over 300 mg/day exacerbated the hypokinesia and resting tremor. CBD appears to have antidystonic and Parkinsonism-aggravating effects in humans.

No abstract

Serotonin (5-HT) has been intimately linked with global regulation of motor behavior, local control of motoneuron excitability, functional recovery of spinal motoneurons as well as neuronal maturation and aging. Selective degeneration of motoneurons is the pathological hallmark of amyotrophic lateral sclerosis (ALS). Motoneurons that are preferentially affected in ALS are also densely innervated by 5-HT neurons (e.g., trigeminal, facial, ambiguus, and hypoglossal brainstem nuclei as well as ventral horn and motor cortex). Conversely, motoneuron groups that appear more resistant to the process of neurodegeneration in ALS (e.g., oculomotor, trochlear, and abducens nuclei) as well as the cerebellum receive only sparse 5-HT input. The glutamate excitotoxicity theory maintains that in ALS degeneration of motoneurons is caused by excessive glutamate neurotransmission, which is neurotoxic. Because of its facilitatory effects on glutaminergic motoneuron excitation, 5-HT may be pivotal to the pathogenesis and therapy of ALS. 5-HT levels as well as the concentrations 5-hydroxyindole acetic acid (5-HIAA), the major metabolite of 5-HT, are reduced in postmortem spinal cord tissue of ALS patients indicating decreased 5-HT release. Furthermore, cerebrospinal fluid levels of tryptophan, a precursor of 5-HT, are decreased in patients with ALS and plasma concentrations of tryptophan are also decreased with the lowest levels found in the most severely affected patients. In ALS progressive degeneration of 5-HT neurons would result in a compensatory increase in glutamate excitation of motoneurons. Additionally, because 5-HT, acting through presynaptic 5-HT1B receptors, inhibits glutamatergic synaptic transmission, lowered 5-HT activity would lead to increased synaptic glutamate release. Furthermore, 5-HT is a precursor of melatonin, which inhibits glutamate release and glutamate-induced neurotoxicity. Thus, progressive degeneration of 5-HT neurons affecting motoneuron activity constitutes the prime mover of the disease and its progression and treatment of ALS needs to be focused primarily on boosting 5-HT functions (e.g., pharmacologically via its precursors, reuptake inhibitors, selective 5-HT1A receptor agonists/5-HT2 receptor antagonists, and electrically through transcranial administration of AC pulsed picotesla electromagnetic fields) to prevent excessive glutamate activity in the motoneurons. In fact, 5HT1A and 5HT2 receptor agonists have been shown to prevent glutamate-induced neurotoxicity in primary cortical cell cultures and the 5-HT precursor 5-hydroxytryptophan (5-HTP) improved locomotor function and survival of transgenic SOD1 G93A mice, an animal model of ALS.