VTA in horizontal brain slices was recognized as an area medial to the substantia nigra compacta and medial to the terminal nucleus of the accessory optic tract. The neuron was identified as dopaminergic, if there was a clear hyperpolarization-activated cation-current (I h-current) seen after hyperpolarizing the cell in 10-mV steps to −130 mV [18]–[20].
