SYNCHRONIZED RHYTHMIC ACTIVITY OF THE PALLIDUM

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A loss of midbrain dopaminergic cells results in parkinsonism. It has been hypothesized that parkinsonian rigidity and tremor are associated with abnormal, wide spread synchronized, rhythmic firing of the pallidum. The goal of this proposal is to reveal the mechanisms responsible for the synchronized rhythmic activity of the pallidum. Our basic hypothesis is that the synchronized rhythmic activity is generated because dopamine (DA) depletion has altered the intrinsic membrane properties and synaptic inputs of the pallidum. We hypothesize that pallidal neurons have intrinsic mechanisms for membrane oscillation, and that the membrane oscillatory mechanism is controlled by the DAergic innervation from the midbrain and peptidergic innervations from the neostriatum (Str). To test these hypothesis, physiological and pharmacological studies will be performed using a whole cell recording method in slice preparations. Our study will focus on the potassium and calcium currents involved in the membrane oscillations and effects of DNA and striatal peptides on these currents. Calcium imaging will aid in analyzing the distribution of calcium currents along the dendrites. We hypothesize that the wide synchronization of activity seen in the pallidum of parkinsonian subjects is due to changes in synaptic transmission. Evaluation of this hypothesis should begin with physiological and anatomical studies. To reveal the properties of unitary post-synaptic responses of pallidal neurons to striatal, intra-pallidal, and subthalamic stimulation, and to reveal the effects of DA and striatal peptides on the strength and duration of unitary post-synaptic responses, physiological and pharmacological studies will be performed using a whole cells recording method in slice preparations. All neurons record in the slice experiments will be further characterized for parvalbumin immunoreactivity, somato-dendritic morphology, and at the molecular level for ion channels, receptors, and calcium binding proteins using single cell RT-PCR techniques. To reveal the structural bases for the pallidal synchronizations, intracellular staining of striatal, pallidal, and subthalamic neurons will be performed in anesthetized rats, and the axons of stained neurons will then be analyzed, using computer assisted 3-dimensional reconstruction systems, at both the light and electron microscopic levels. The light microscopic analysis will reveal the number and distribution of synaptic boutons of single axons in the pallidum, and the electron microscopic analysis will reveal the ultrastructure of the synapses, the synaptic pattern, and the structure post-synaptic to the synapses.