Network properties of the globus pallidus pars externa
The external globus pallidus (GPe) is usually considered simply a relay in the indirect pathway between the striatum and the basal ganglia output neurons in the internal pallidal segment and substantia nigra. This view has been disrupted by recent findings that the GPe contains several different cell types. with different striatal afferents that include the direct pathway. and different downstream targets. and which are interconnected in the GPe by their axon collateral arborizations. The network interactions in the GPe may fundamentally transform the signals from both the direct and indirect pathway and may include crosstalk between those signals. Neurons in the GPe exhibit intrinsic oscillations and fire continuously. even in slices and in the absence of inputs. Two superclasses of neurons with distinct patterns of axonal projections dominate the GPe and are identifiable by non-overlapping expression of either parvalbumin (PV) or neuronal PAS domain protein 1 (Npas1). Inhibitory input from the direct pathway is primarily directed at the Npas1 neuronal population. whereas indirect pathway inhibition targets the PV group of neurons. PV neurons target the traditional basal ganglia output neurons in the internal pallidal segment and substantia nigra. whereas the Npas1 neurons target the cerebral cortex. striatal output neurons. the thalamic reticular nucleus. and midbrain dopaminergic neurons. Our previous work established that ongoing synaptic interactions are intact and detectable in slice. presenting an opportunity to use this preparation to uncover the function of the local collateral network in the GPe. My proposed work addresses how the local collateral network in the GPe (1) shapes the spontaneous pattern of GPe cell activity in the absence of striatal input. and (2) controls the responses to both direct pathway and indirect pathway striato-pallidal input. I hypothesize the local collaterals dampen and deregularize neuronal firing. decorrelate network firing. and modulate the size and duration of inhibitory responses in both cell groups to striato-pallidal signals.