The European journal of neuroscience
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The subthalamic nucleus (STN) receives dopamine inputs from the substantia nigra but their implication in the pathophysiology of parkinsonism is still debated. Extracellular microrecordings were used to study the effect of microiontophoretic injection of dopamine and the D1 receptor agonist SKF 38393 on the activity of STN neurons in normal and 6-hydroxydopamine-lesioned rats under urethane anaesthesia. Dopamine and SKF induced an increase in the firing rate of the majority of STN neurons in both normal and 6-OHDA rats. ⋯ Systemic administration of apomorphine provoked a decrease in the firing rate of STN neurons in rats with 6-OHDA lesions. These results show that dopamine exerts an excitatory influence on STN neurons, suggesting that the inhibitory effect induced by the systemic injection of apomorphine is due to the GABAergic inputs from the globus pallidus as predicted by the current model of basal ganglia organization. In addition, we show that dopamine, GABA and glutamate can act on the same STN neuron and that GABA can reverse the excitatory effect of dopamine and glutamate, suggesting the predominant influence of GABAergic inputs to the subthalamic nucleus.
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The cloned vanilloid receptor VR1 can be activated by capsaicin and by thermal stimuli. The pattern of nerve terminals that contain VR1 in adult rat spinal cord does not correspond to axons that arise from a single subset of dorsal root ganglion neurons. Thus, we postulated that the basis underlying this complexity might be better understood from a developmental perspective. ⋯ In peripheral processes, the number of VR1-positive nerve fibres and terminals in cutaneous structures in postnatal day 10 was half of that in adults. We also show that the association of VR1 with Ret is the reciprocal of the association of VR1 with Trk A. These results suggest that neurotrophins may regulate the extent to which populations of dorsal root ganglion neurons express VR1.