Catecholamine sensitivities of motor cortical neurons of the monkey

The effects of noradrenaline (NA) and dopamine (DA) were examined in 139 neurons of the motor cortex (area 4) of the monkey, using multibarreled micropipettes. Sampled neurons were those spontaneously active and sensitive to iontophoretically applied glutamate (30-50 nA). Iontophoretically applied NA and DA induced excitatory and inhibitory responses in 91 neurons (NA: excitatory, n = 17; inhibitory, n = 53; DA: excitatory, n = 16; inhibitory, n = 37). Cortical depth was determined in 121 neurons tested. Neurons sensitive to NA (excitatory, n = 13; inhibitory, n = 46) were distributed uniformly across the cortical layers, while neurons sensitive to DA (excitatory, n = 14; inhibitory, n = 30) were numerous in layers V and VI. This suggests that NA may influence various neuronal activities, and that DA may predominantly influence neuronal activities of layers V and VI in the monkey motor cortex.