The Involvement of Dopamine in Strengthening Cortical Signals Activating NMDA Receptors in the Striatum (a hypothetical mechanism)

A possible mechanism is proposed for the enhancement/weakening of those cortical signals in the cortex-basal ganglia-thalamus-cortex neural network which induce/do not induce opening of NMDA channels in the spiny neurons of the striatum and which can be regarded as strong/weak in terms of this measure. The mechanism is based on the modulatory influences of dopamine on changes in the efficiency of corticostriatal inputs. In the absence of dopamine, relative increases in the intensity of strong (weak) cortical signals can lead to the induction of long-term potentiation (depression) of corticostriatal synapses. In this case, because of the differently directed influences on thalamic cells of signals passing via strionigral and striopallidal cells, strong signals at the output of the thalamus are weakened, while weak signals are strengthened. Activation of dopamine D₁ (D₂) receptors on strionigral (striopallidal) neurons may facilitate increases in the extent of long-term potentiation/depression (decreases in the extent of long-term potentiation/depression or induction of long-term potentiation/depression). The consequence of this is that strong signals at the output of the thalamus can be strengthened synergistically, while weak signals cab be weakened synergistically. Background cortical signals evoking tonic release of dopamine in the striatum can decrease strengthening because of weakening of the modulatory influence of dopamine on the modification of corticostriatal synapses.