NRG1 and psychiatric disorder: NRG1/erb-b2 receptor tyrosine kinase 4 (ERBB4) signaling in DA-ergic axonal projections modulates DA homeostasis, whereas NRG1/ERBB4 signaling in both GABA-ergic interneurons and DA neurons in the midbrain contribute to the modulation of animal behaviors relevant to psychiatric disorders [24,25].