Subthalamic nucleus globus pallidus input

Figure 15.9 Peptide modulation of striatal input to the globus pollidus. Enkephalin released from axon terminals of neurons of the indirect pathway (see Fig. 15.2 for details) is thought to inhibit GABA release from the same terminals so that feedback (auto) inhibition is reduced. This will free the neurons to inhibit the subthalamic nucleus (SThN) and its drive to GPint and SNr which in turn will have less inhibitory effect on cortico-thalamic traffic and possibly reduce akinesia. Dynorphin released from terminals of neurons of the direct pathway may also reduce glutamate release and excitation in the internal globus pallidus and further depress its inhibition of the cortico-thalamic pathway. High concentrations of these peptides may, however, result in dyskinesias. (See Henry and Brotchie 1996 and Maneuf et al. 1995)...

Fig. 13. A) Diagram showing an example of inputs to the globus pallidus (GP) from striatal spiny projection neurons. Typically there are two major sites of axonal arborization, one in the region immediately adjacent to the striatum and a second in the central region of the GP. B) Stylized drawing of two pallidal neurons showing how the dendrites of neurons are confined within the two regions of the GP that conform to the pattern of striatal inputs. C) The axonal projection of a globus pallidus neuron of the type with discoid dendrites, which provides collaterals to the striatum (CP), to the entopeduncular nucleus (EP), subthalamic nucleus (stn) and substantia nigra (SN). Adapted from Kita and Kitai 1994.

Neurons in the subthalamic nucleus project axons that target neurons in the globus pallidus and in the entopeduncular nucleus and substantia nigra, as well as a sparse projection to the striatum (Kita and Kitai 1987). These inputs provide an excitatory input to each of the target structures (Kita and Kitai 1991 Nakanishi et al. 1987b Robeldo and Feger 1990). 

There are two other distinctive features of striatal output organization. The first is the segregation of the projections of the patch-matrix compartments of the striatum. This will be discussed in a later section. The second, which has been mentioned, is the dual projection zones of striatal inputs in both the globus pallidus and substantia nigra. As will be described these dual projection systems appear also in the organization of other components of the basal ganglia, including the projection of the subthalamic nucleus. 

Fig. 33. A diagram of the model of Parkinson s disease that suggests that dopamine (DA) depletion in the disease results in an elevated output of the indirect pathway (enkephalin, ENK, D2 containing neurons), which results in increased excitatory input from the subthalamic nucleus (stn) to the internal globus pallidus (GPi) and substantia nigra and a decreased output of the direct pathway (substance P SP, D1 containing neurons). See text for further details.

---