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. Author manuscript; available in PMC: 2009 Nov 26.
Published in final edited form as: Neuron. 2008 Nov 26;60(4):543–554. doi: 10.1016/j.neuron.2008.11.005

Figure 1. Direct and indirect pathway basal ganglia circuits.

Figure 1

Sagittal view of a mouse brain (A), depicting cortex-basal ganglia-thalamus-cortex circuits. Axons from the thalamus and striatum form excitatory synapses onto striatonigral/direct-pathway MSNs (blue) and striatopallidal/indirect-pathway MSNs (red). Direct pathway MSNs send axons directly to basal ganglia output nuclei (medial globus pallidus, GPm, and substantia nigra, pars reticulata, SNr), where they form inhibitory synapses. Indirect-pathway MSNs inhibit neurons in the globus pallidus (GP), which in turn make inhibitory connections with the subthalamic nucleus (STN). STN projections target the GPm and SNr, where they form excitatory synapses onto GABAergic basal ganglia output neurons. These inhibitory output neurons send axons to ventroposterior thalamic motor nuclei. Finally, glutamatergic neurons in the thalamus project back to cortex, completing the circuit. A sagittal slice from a BAC-transgenic mouse expressing GFP under the control of genomic regulatory elements for the dopamine D2 receptor (D2-GFP) (B), or the muscarinic M4 receptor (M4-GFP) (C), which labels indirect- and direct-pathway MSNs, respectively. Figure inspired by (Gerfen, 2006).