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1.  Serotonergic mechanisms responsible for levodopa-induced dyskinesias in Parkinson’s disease patients 
The Journal of Clinical Investigation  2014;124(3):1340-1349.
Levodopa-induced dyskinesias (LIDs) are the most common and disabling adverse motor effect of therapy in Parkinson’s disease (PD) patients. In this study, we investigated serotonergic mechanisms in LIDs development in PD patients using 11C-DASB PET to evaluate serotonin terminal function and 11C-raclopride PET to evaluate dopamine release. PD patients with LIDs showed relative preservation of serotonergic terminals throughout their disease. Identical levodopa doses induced markedly higher striatal synaptic dopamine concentrations in PD patients with LIDs compared with PD patients with stable responses to levodopa. Oral administration of the serotonin receptor type 1A agonist buspirone prior to levodopa reduced levodopa-evoked striatal synaptic dopamine increases and attenuated LIDs. PD patients with LIDs that exhibited greater decreases in synaptic dopamine after buspirone pretreatment had higher levels of serotonergic terminal functional integrity. Buspirone-associated modulation of dopamine levels was greater in PD patients with mild LIDs compared with those with more severe LIDs. These findings indicate that striatal serotonergic terminals contribute to LIDs pathophysiology via aberrant processing of exogenous levodopa and release of dopamine as false neurotransmitter in the denervated striatum of PD patients with LIDs. Our results also support the development of selective serotonin receptor type 1A agonists for use as antidyskinetic agents in PD.
PMCID: PMC3934188  PMID: 24531549
2.  Serotonergic loss in motor circuitries correlates with severity of action-postural tremor in PD 
Neurology  2013;80(20):1850-1855.
The underlying pathophysiology of tremor in Parkinson disease (PD) is unclear; however, it is known that tremor does not appear to be as responsive to dopaminergic medication as bradykinesia or rigidity. It is suggested that serotonergic dysfunction could have a role in tremor development.
Using 11C-DASB PET, a marker of serotonin transporter binding, and clinical observations, we have investigated function of serotonergic terminals in 12 patients with tremor-predominant and 12 with akinetic-rigid PD. Findings were compared with those of 12 healthy controls.
Reductions of 11C-DASB in caudate, putamen, and raphe nuclei significantly correlated with tremor severity on posture and action, but not with resting tremor. The tremor-predominant group also showed reductions of 11C-DASB in other regions involved in motor circuitry, including the thalamus and Brodmann areas 4 and 10.
Our findings support a role for serotonergic dysfunction in motor circuitries in the generation of postural tremor in PD.
PMCID: PMC3908354  PMID: 23596065
3.  Increased PK11195 PET binding in the cortex of patients with MS correlates with disability 
Neurology  2012;79(6):523-530.
Activated microglia are thought to play a major role in cortical gray matter (GM) demyelination in multiple sclerosis (MS). Our objective was to evaluate microglial activation in cortical GM of patients with MS in vivo and to explore its relationship to measures of disability.
Using PET and optimized modeling and segmentation procedures, we investigated cortical 11C-PK11195 (PK11195) binding in patients with relapsing-remitting MS (RRMS), patients with secondary progressive MS (SPMS), and healthy controls. Disability was assessed with the Expanded Disability Status Scale (EDSS) and Multiple Sclerosis Impact Scale (MSIS-29).
Patients with MS showed increased cortical GM PK11195 binding relative to controls, which was multifocal and highest in the postcentral, middle frontal, anterior orbital, fusiform, and parahippocampal gyri. Patients with SPMS also showed additional increases in precentral, superior parietal, lingual and anterior superior, medial and inferior temporal gyri. Total cortical GM PK11195 binding correlated with EDSS scores, with a stronger correlation for the subgroup of patients with SPMS. In patients with SPMS, PK11195 binding also correlated with MSIS-29 scores. No correlation with disability measures was seen for PK11195 binding in white matter. Higher EDSS scores correlated with higher levels of GM PK11195 binding in the postcentral gyrus for patients with RRMS and in precentral gyrus for those with SPMS.
Microglial activation in cortical GM of patients with MS can be assessed in vivo. The distribution is not uniform and shows a relationship to clinical disability. We speculate that the increased PK11195 binding corresponds to enhanced microglial activation described in postmortem SPMS cortical GM.
PMCID: PMC3413767  PMID: 22764258
4.  Striatal dopamine D2/D3 receptor binding in pathological gambling is correlated with mood-related impulsivity 
Neuroimage  2012;63(1):40-46.
Pathological gambling (PG) is a behavioural addiction associated with elevated impulsivity and suspected dopamine dysregulation. Reduced striatal dopamine D2/D3 receptor availability has been reported in drug addiction, and may constitute a premorbid vulnerability marker for addictive disorders. The aim of the present study was to assess striatal dopamine D2/D3 receptor availability in PG, and its association with trait impulsivity. Males with PG (n = 9) and male healthy controls (n = 9) underwent [11C]-raclopride positron emission tomography imaging and completed the UPPS-P impulsivity scale. There was no significant difference between groups in striatal dopamine D2/D3 receptor availability, in contrast to previous reports in drug addiction. However, mood-related impulsivity (‘Urgency’) was negatively correlated with [11C]-raclopride binding potentials in the PG group. The absence of a group difference in striatal dopamine binding implies a distinction between behavioural addictions and drug addictions. Nevertheless, our data indicate heterogeneity in dopamine receptor availability in disordered gambling, such that individuals with high mood-related impulsivity may show differential benefits from dopamine-based medications.
► Assessed 11C-raclopride binding in pathological gambling, a putative behavioral addiction. ► No group difference in striatal dopamine binding from healthy controls. ► Dopamine binding negatively correlated with mood-related impulsivity (‘Urgency’).
PMCID: PMC3438449  PMID: 22776462
Gambling; Impulsivity; Dopamine; Neuroimaging; Addiction; Striatum

Results 1-4 (4)