Altered parabrachial nucleus nociceptive processing may underlie central pain in Parkinson's disease.

The presence of central neuropathic pain in Parkinson's disease suggests that the brain circuits that allow us to process pain could be dysfunctional in the disorder. However, there is to date no clear pathophysiological mechanism to explain these symptoms. In this work, we present evidence that the dysfunction of the subthalamic nucleus and/or substantia nigra pars reticulata may impact nociceptive processing in the parabrachial nucleus (PBN), a low level primary nociceptive structure in the brainstem, and induce a cellular and molecular neuro-adaptation in this structure. In rat models of Parkinson's disease with a partial dopaminergic lesion in the substantia nigra compacta, we found that the substantia nigra reticulata showed enhanced nociceptive responses. Such responses were less impacted in the subthalamic nucleus. A total dopaminergic lesion produced an increase in the nociceptive responses as well as an increase of the firing rate in both structures. In the PBN, inhibited nociceptive responses and increased expression of GABAA receptors were found following a total dopaminergic lesion. However, neuro-adaptations at the level of dendritic spine density and post-synaptic density were found in both dopaminergic lesion groups. These results suggest that the molecular changes within the PBN following a larger dopaminergic lesion, such as increased GABAA expression, is a key mechanism to produce nociceptive processing impairment, whilst other changes may protect function after smaller dopaminergic lesions. We also propose that these neuro-adaptations follow increased inhibitory tone from the substantia nigra pars reticulata and may represent the mechanism generating central neuropathic pain in Parkinson's disease.

The Subthalamic Nucleus: A Hub for Sensory Control via Short Three- Lateral Loop Connections with the Brainstem?

The subthalamic nucleus (STN) is classically subdivided into sensori-motor, associative and limbic regions, which is consistent with the involvement of this structure in not only motor control, but also in cognitive and emotional tasks. However, the function of the sensory inputs to the STN's sensori-motor territory is comparatively less well explored, although sensory responses have been reported in this structure. There is still a paucity of information regarding the characteristics of that subdivision and its potential functional role in basal ganglia processing and more widely in associated networks. In this perspective paper, we summarize the type of sensory stimuli that have been reported to activate the STN, and describe the complex sensory properties of the STN and its anatomical link to a sensory network involving the brainstem, characterized in our recent work. Analyzing the sensory input to the STN led us to suggest the existence of previously unreported threelateral subcortical loops between the basal ganglia and the brainstem which do not involve the cortex. Anatomically, these loops closely link the STN, the substantia nigra pars reticulata and various structures from the brainstem such as the superior colliculus and the parabrachial nucleus. We also discuss the potential role of the STN in the control of sensory activity in the brainstem and its possible contribution to favoring sensory habituation or sensitization over brainstem structures to optimize the best selection of action at a given time.

Gene replacement therapy provides benefit in an adult mouse model of Leigh syndrome.

Mutations in nuclear-encoded mitochondrial genes are responsible for a broad spectrum of disorders among which Leigh syndrome is the most common in infancy. No effective therapies are available for this severe disease mainly because of the limited capabilities of the standard adeno-associated viral (AAV) vectors to transduce both peripheral organs and the CNS when injected systemically in adults. Here, we used the brain-penetrating AAV-PHP.B vector to reinstate gene expression in the Ndufs4 knockout mouse model of Leigh syndrome. Intravenous delivery of an AAV.PHP.B-Ndufs4 vector in 1-month-old knockout mice restored mitochondrial complex I activity in several organs including the CNS. This gene replacement strategy extended lifespan, rescued metabolic parameters, provided behavioural improvement, and corrected the pathological phenotype in the brain, retina, and heart of Ndufs4 knockout mice. These results provide a robust proof that gene therapy strategies targeting multiple organs can rescue fatal neurometabolic disorders with CNS involvement.