The Neurobiology of Dopamine Signaling
Nerve cells communicate with each other through two mechanisms, referred to as fast and slow synaptic transmission. Fast-acting neurotransmitters, e.g., glutamate (excitatory) and GABA (inhibitory), achieve their effects on their target cells, within one thousandth of a second, by virtue of opening ligand-operated ion channels. Slow-acting neurotransmitters, which include dopamine and serotonin, all peptide neurotransmitters, as well as glutamate and GABA, achieve their effects over seconds to minutes, by an enormously more complicated sequence of biochemical steps involving second messengers, protein kinases, and protein phosphatases. Slow-acting neurotransmitters control the efficacy of synaptic transmission, both by regulating the efficiency of neurotransmitter release from presynaptic terminals and by regulating the efficiency with which both fast- and slow-acting neurotransmitters produce their effects on postsynaptic receptors. Fast synaptic transmission can be considered to represent the hardware of the brain, and slow synaptic transmission its software (see Figure 1).