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Abstract: Since the early 90s, the subthalamic nucleus (STN) has started to be the subject of an increasing interest not only in the community of the basal ganglia scientists but also for neurosurgeons and neurologists, thanks to the development of the surgical treatment for Parkinson''s disease. The involvement of the STN in cognitive and motivational processes has been demonstrated since, and psychiatrists are now considering this small structure as a possible target for the treatment of various disorders. In this review, we will address six questions to highlight (1) How increased knowledge has led us from a strictly motor model to an integrative one. (2) How knowledge acquired in animal models can be similar or (3) different from the effects observed in human patients. (4) How clinical trials are sometimes ahead of fundamental research carried out in animals, showing effects that could not be predicted on the basis of animal studies, thus questioning the relevance of some animal models, especially for psychiatric disorders. We will also address the possible future orientations (5) and how the use, or precaution not to use, certain key words in animal research dedicated to STN functions can lead to the omission of a certain amount of available data in the literature (6). This article is part of a Special Issue entitled: Function and Dysfunction of the Basal Ganglia. [Copyright &y& Elsevier]

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Abstract Cellular expression of cytochrome oxidase subunit I (COI) mRNA has recently been used as a metabolic marker for neuronal activity to study the functional changes in the subthalamic nucleus (STN) in parkinsonism. The previous experimental studies have been performed when the pathological state was stabilized at a maximal level. In order to determine the evolution of changes in neuronal activity in the STN after nigrostriatal denervation, we analysed by in situ hybridization the cellular expression of COI mRNA in the subthalamic neurons at different times, from 6 h to 14 days, after unilateral intranigral microinjection of 6-hydroxydopamine (6-OHDA) in rats. In parallel, the time-dependent changes of the unit neuronal activity of subthalamic neurons have been recorded. Levels of COI mRNA increased by 41% in subthalamic neurons from 24 h after 6-OHDA intoxication, to 14 days (+26%). Similarly, electrical activity started to increase slightly 24 h after lesion (+20%) and remained significantly higher at 14 days after the lesion (+189%). Changes in neuronal mean discharge rate were associated with changes in the pattern of spiking activity, from a regular firing pattern to an irregular one with a high bursting activity. These results show that: (i) the hyperactivity of the STN represents a very early phenomenon in the physiopathology of parkinsonian syndromes; and (ii) that changes in COI mRNA expression slightly precede changes in electrical neuronal activity. [ABSTRACT FROM AUTHOR]

Abstract: In animals, the pedunculopontine (PPN) and the sub-cuneiform (SCU) nuclei located in the upper brainstem are involved during the processing of gait. Similar functional nuclei are suspected in humans but their role in gait is unclear. Here we show that, using extra-cellular recordings of the PPN/SCU region obtained in two parkinsonian patients, the SCU neurons increased their firing rate without modifying their firing pattern during mimicked steps. We conclude that SCU neurons are activated during gait processes. [Copyright &y& Elsevier]