Corticotropin releasing factor (CRF) and related peptides play a role in mediating neuronal effects of stress. These peptides mediate stress responses by their interactions with the CRF receptors and the CRF-binding protein (CRF-BP). Since the CRF-BP is implicated in neurotransmission within the ventral tegmental area (VTA), we investigated whether the CRF-BP is expressed in VTA neurons. By in situ hybridization we detected cellular expression of CRF-BP mRNA in the VTA; no such expression was seen in neighboring substantia nigra pars compacta (SNC) or substantia nigra pars reticulata. By double in situ hybridization we determined that VTA neurons with CRF-BP mRNA co-expressed transcripts encoding either tyrosine hydroxylase (TH, a marker for dopamine, DA, neurons) or glutamic acid decarboxylase (GAD, synthesizing enzyme of γ-amino butyric acid, GABA). Neurons with CRF-BP mRNA represented 25% of the total population of TH-expressing neurons and 28% of the total population of GAD-expressing neurons, indicating that discrete subpopulations of dopaminergic and GABAergic neurons are present in the VTA. Within the total population of neurons containing CRF-BP mRNA, 70% co-expressed TH mRNA, and only 27% co-expressed GAD mRNA. ? As far as we are aware, we provide the first anatomical evidence that a molecule, CRF-BP, is encoded by DAergic neurons of the VTA, but not by those of the SNC. Based on the observation that the majority of VTA neurons expressing CRF-BP mRNA are DAergic, we propose that in the VTA interactions of CRF-BP with CRF, or with CRF-related peptides, are likely to be predominately mediated by DAergic neurons.
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