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. 2010 Jun 7;4:30. doi: 10.3389/fnbeh.2010.00030

Figure 3.

Figure 3

Summary of neural circuits underlying tonic inhibition of tadpole swimming and motor pattern selection by the vertebrate basal ganglia (adapted from Lambert et al., 2004a (A) and Grillner et al., 2005 (B), with permission from Springer and Elsevier, respectively). (A) Tension in the mucus secreted by the head cement gland during attachment of the tadpole to a substrate like the edge of a dish, activates cement gland mechanosensory neurons (SN). The sensory neurons directly excite rostral hind brain (RH) neurons and mid hind brain reticulospinal neurons (MHR). The RH neurons excite the MHRs and provide an indirect route for effects on spinal cord circuitry. The MHR neurons provide GABAergic inhibition of the spinal swim circuits. During the more-or-less continuous attachment of the tadpole during the first post-hatch day sustained tonic activity in the cement gland sensory neuron leads to corresponding tonic activity in the MHR followed by suppression of swim behavior. (B) Cortical and thalamic areas provide excitatory synaptic connections to the striatal input area of the basal ganglia that is involved in movement induction and selection. Striatal neurons activate brain stem command centers by inhibiting the firing of pallidal neurons. In the absence of striatal activity, pallidal neurons fire at high rates and provide tonic inhibition to brain stem command centers that are responsible for the activation of motor programs for saccadic eye movements, locomotion and posture. The striatum thus provides a disinhibitory mechanism for the generation of basic movements. Striatal and pallidal control pathways are functionally organized to allow the selective disinhibition of particular motor programs. This is indicated by the division of motor programs into boxed compartments with a corresponding segregation of the inhibitory connecting pathways. All the inhibitory connections in these circuits are GABAergic. A stick indicates an excitatory synaptic connection between neurons or nuclei, and a ball an inhibitory synaptic connection.