Objective: Using resting-state (RS) fMRI, we investigated the functional integrity of the default-mode network (DMN) in cognitively unimpaired patients with Parkinson disease (PD). Methods: RS fMRI at 3 T was collected in 16 cognitively unimpaired patients with PD and 16 age- and gender-matched healthy controls. Single-subject and group-level independent component analysis was used to investigate differences in functional connectivity within the DMN in patients with PD and healthy controls. Statistical analysis was performed using BrainVoyager QX. In addition, we used voxel-based morphometry to test whether between-group differences in RS functional connectivity were related to structural abnormalities. Results: Patients with PD compared with controls showed a decreased functional connectivity of the right medial temporal lobe and bilateral inferior parietal cortex within the DMN. Although patients with PD were cognitively unimpaired, the decreased DMN connectivity significantly correlated with cognitive parameters but not with disease duration, motor impairment, or levodopa therapy. The analysis of regional volume differences did not reveal any differences in local gray matter between patients and controls. Conclusions: Our findings revealed a functional disruption of the DMN in cognitively unimpaired patients with PD, in the absence of significant structural differences between patients and controls. We hypothesize that a dysfunction of the DMN connectivity may have a role in the development of cognitive decline in PD.

BACKGROUND AND PURPOSE: FOG is a troublesome symptom of PD. Despite growing evidence suggesting that FOG in PD may be associated with cognitive dysfunction, the relationship between regional brain atrophy and FOG has been poorly investigated. MATERIALS AND METHODS: Optimized VBM was applied to 3T brain MR images of 24 patients with PD and 12 HC. Patients were classified as either FOG− or FOG+ (n = 12) based on their responses to a validated FOG Questionnaire and clinical observation. All patients with PD also underwent a detailed neuropsychological evaluation. RESULTS: The VBM analysis in patients with FOG+ showed a reduced GM volume in the left cuneus, precuneus, lingual gyrus, and posterior cingulate cortex compared with both patients with FOG− and HC. We did not detect any significant change of GM volume when comparing HC versus all patients with PD (FOG− and FOG+). FOG clinical severity was significantly correlated with GM loss in posterior cortical regions. Finally, patients with FOG+ scored lower on tests of frontal lobe function. CONCLUSIONS: Our findings provide the first evidence that the development of FOG in patients with PD is associated with posterior GM atrophy, which may play a role in the complex pathophysiology of this disabling symptom.

Analysis of the structure of nerve growth factor (NGF)-tyrosine kinase receptor A (TrkA) complex, site-directed mutagenesis studies and results from chemical modification of amino acid residues have identified loop 1, loop 4, and the N-terminal region of the NGF molecule as the most relevant for its biological activity. We synthesized several peptides mimicking the two loops (1 and 4) linked together with an appropriate spacer, with or without the N-terminal region. Two peptides named NL1L4 and L1L4 demonstrated good NGF agonist activity at a concentration as low as 3 μm. They induced differentiation of chick dorsal root ganglia and stimulated tyrosine phosphorylation of TrkA, but not TrkB, receptor. In addition L1L4 was able to induce differentiation of PC12 cells. More interestingly, the peptide with the highest “in vitro” activity (L1L4) was shown to reduce neuropathic behavior and restore neuronal function in a rat model of peripheral neuropathic pain, thereby suggesting a potential therapeutic role for this NGF-mimetic peptide.

Non-invasive low-intensity transcranial electrical stimulation (tES) of the brain is an evolving field that has brought remarkable attention in the past few decades for its ability to directly modulate specific brain functions. Neurobiological after-effects of tES seems to be related to changes in neuronal and synaptic excitability and plasticity, however mechanisms are still far from being elucidated. We aim to review recent results from in vitro and in vivo studies that highlight molecular and cellular mechanisms of transcranial direct (tDCS) and alternating (tACS) current stimulation. Changes in membrane potential and neural synchronization explain the ongoing and short-lasting effects of tES, while changes induced in existing proteins and new protein synthesis is required for long-lasting plastic changes (LTP/LTD). Glial cells, for decades supporting elements, are now considered constitutive part of the synapse and might contribute to the mechanisms of synaptic plasticity. This review brings into focus the neurobiological mechanisms and after-effects of tDCS and tACS from in vitro and in vivo studies, in both animals and humans, highlighting possible pathways for the development of targeted therapeutic applications.