ABSTRACT

The sets of non-cortical cerebral neurons known as the basal ganglia (BG) help to regulate the motor functions. Motor functions are commanded by the neural activity of the motor and premotor cortices (Cx). Cortical commands are sent to the spinal chord where motoneurons in charge of activating the muscles involved in movement are located. The BG regulate these commands and "programs" of motor activation while they are going on. In order to do that, the BG receive inputs from the sensory Cx that help to correct and tune the motor commands and programs. As most brain circuits, the BG use fast neurotransmission associated with postsynaptic ligand-gated receptor-channels, and the transmitters glutamate (excitatory) and g-amminobutyric acid (GABA) (inhibitory), to build its circuits. However, fast neurotransmission is regulated by the so-called slow or modulatory neurotransmission, associated with receptors coupled to intracellular signaling cascades (e.g., G proteins). Perhaps, the most important modulatory neurotransmitter of the BG is dopamine (DA). Without DA, the BG circuit suffers a total collapse and stops functioning. This constitutes a dramatic example of the importance of neuromodulation. This is what happens in Parkinson's disease, which might be the first pathological entity recognized as a neuromodulatory disorder. The treatment of this disease is based on restitution therapy using analogues or precursors of the neuromodulator DA. Similarly, various motor diseases are now conceived as neuromodulatory unbalances in the BG circuit (choreas, distonias, etc). In the present work, both the BG circuit and the neuromodulatory actions of DA are reviewed.