Positron emission tomography of dopamine pathways in familial Parkinsonian syndromes

Dopamine, vocalization, and astrocytes

Dopamine, the main catecholamine neurotransmitter in the brain, is predominately produced in the basal ganglia and released to various brain regions including the frontal cortex, midbrain and brainstem. Dopamine's effects are widespread and include modulation of a number of voluntary and innate behaviors. Vigilant regulation and modulation of dopamine levels throughout the brain is imperative for proper execution of motor behaviors, in particular speech and other types of vocalizations. While dopamine's role in motor circuitry is widely accepted, its unique function in normal and abnormal speech production is not fully understood. In this perspective, we first review the role of dopaminergic circuits in vocal production. We then discuss and propose the conceivable involvement of astrocytes, the numerous star-shaped glia cells of the brain, in the dopaminergic network modulating normal and abnormal vocal productions.

Marked Reduction in the Striatal Dopamine Transporter Uptake During the Early Stage of Motor Symptoms in Patients with the MAPT N279K Mutation

We herein report two patients harboring the mutation N279K in microtubule-associated protein tau (MAPT), who showed parkinsonism with a disease duration within three years from the onset, evaluated by dopamine transporter (DAT) [¹²³I]N-ω-fluoroprophyl-2β-carbomethoxy-3β-(4-iodophenyl) tropane single-photon emission computed tomography. We performed a quantification analysis, comparing five age- and severity-matched PD patients and six normal controls. The patients with the N279K mutation showed a more marked reduction in their DAT densities, especially in the caudate nucleus and anterior putamen, than the others. An early marked reduction in the DAT densities in the caudate nucleus and anterior putamen may be an early biomarker of patients with MAPT mutations.

Frontotemporal dementia and parkinsonism linked to chromosome 17--the first Polish family

BACKGROUND

Frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) is a neurodegenerative disorder with various clinical phenotypes. We present the first Central-Eastern European family (Gdansk Family) with FTDP-17 because of a P301L mutation in microtubule-associated protein tau (MAPT).

METHODS

We have studied a family consisting of 82 family members, 39 of whom were genetically evaluated. The proband and her affected brother underwent detailed clinical and neuropsychological examinations.

RESULTS

P301L mutation in MAPT was identified in two affected and five asymptomatic family members. New features included hemispatial neglect and unilateral resting tremor not previously reported for P301L MAPT mutation. Low blood folic acid levels were also detected.

CONCLUSIONS

Our report suggests that FTDP-17 affects patients worldwide, but because of its heterogenous clinical presentation remains underrecognized.

Clinical-pathologic study of biomarkers in FTDP-17 (PPND family with N279K tau mutation)

The objective of this clinical-pathologic study was to identify biomarkers for a pallidopontonigral degeneration (PPND) kindred of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) harboring the N279K tau mutation. Five affected subjects, one at-risk who later became symptomatic, and one at-risk asymptomatic mutation carrier, had abnormal (18)fluorodeoxyglucose PET demonstrating asymmetric temporal lobe hypometabolism. All except the asymptomatic mutation carrier had abnormal brain MRI. Parkinsonism, myoclonus, anosmia, insomnia, speech, and autonomic dysfunction were identified. Autopsy of six affected subjects showed frontotemporal degeneration with extensive tauopathy. Further studies of FTDP-17 patients are needed to replicate these findings.

Brain sites of movement disorder: genetic and environmental agents in neurodevelopmental perturbations

In assessing and assimilating the neurodevelopmental basis of the so-called movement disorders it is probably useful to establish certain concepts that will modulate both the variation and selection of affliction, mechanisms-processes and diversity of disease states. Both genetic, developmental and degenerative aberrations are to be encompassed within such an approach, as well as all deviations from the necessary components of behaviour that are generally understood to incorporate "normal" functioning. In the present treatise, both conditions of hyperactivity/hypoactivity, akinesia and bradykinesia together with a constellation of other symptoms and syndromes are considered in conjunction with the neuropharmacological and brain morphological alterations that may or may not accompany them, e.g. following neonatal denervation. As a case in point, the neuroanatomical and neurochemical points of interaction in Attention Deficit and Hyperactivity disorder (ADHD) are examined with reference to both the perinatal metallic and organic environment and genetic backgrounds. The role of apoptosis, as opposed to necrosis, in cell death during brain development necessitates careful considerations of the current explosion of evidence for brain nerve growth factors, neurotrophins and cytokines, and the processes regulating their appearance, release and fate. Some of these processes may possess putative inherited characteristics, like alpha-synuclein, others may to greater or lesser extents be endogenous or semi-endogenous (in food), like the tetrahydroisoquinolines, others exogenous until inhaled or injested through environmental accident, like heavy metals, e.g. mercury. Another central concept of neurodevelopment is cellular plasticity, thereby underlining the essential involvement of glutamate systems and N-methyl-D-aspartate receptor configurations. Finally, an essential assimilation of brain development in disease must delineate the relative merits of inherited as opposed to environmental risks not only for the commonly-regarded movement disorders, like Parkinson's disease, Huntington's disease and epilepsy, but also for afflictions bearing strong elements of psychosocial tragedy, like ADHD, autism and Savantism.

Parkinson's disease: imaging update

PURPOSE OF REVIEW

We aim to review recent neuroimaging contributions to our understanding of the cause and pathogenesis of Parkinson's disease, as well as treatment-related complications of disease, with a focus on functional anatomy and neurochemistry.

RECENT FINDINGS

Recent reports describe altered dopaminergic activity in extrastriatal regions, as well as changes in other monoaminergic systems, such as serotonin. Attempts to correlate altered dopaminergic function with personality traits have also been described in the last year. The role of different markers of presynaptic dopaminergic integrity in the assessment of disease progression is discussed, as is the role of biomarkers in detection of preclinical disease. Cerebral activation studies not only confirm altered function of cortico-striatal-thalamo-cortical loops in Parkinson's, but also emphasize the importance of networks involving the cerebellum. The ability to detect changes in synaptic availability of dopamine using positron emission tomography with [(11)C]raclopride is reviewed, including the application to detect altered levels of dopamine in response to pharmacological, mechanical and behavioral stimuli. Such studies have been used to identify altered patterns associated with the development of motor fluctuations, as well as a biochemical substrate underlying the placebo effect in Parkinson's.

SUMMARY

Functional imaging studies can provide novel insights into the etiopathogenesis of Parkinson's disease, as well as the mechanisms that contribute to complications of long-term therapy. They also shed light on the mechanisms that may underly behavioral changes and benefit derived from surgical interventions.