Six types exist in humans and rodents (type I, II and III NRG1 are expressed in excitatory and inhibitory neurons, as well as astrocytes), and some types (I and IV) can be regulated by neuronal activity.
NRG1 has different forms that appear in human and rodent brains (types I, II, and III are present in excitatory and inhibitory nerve cells, along with astrocytes), and some of these types (I and IV) can be modulated by neuronal function.