Neuronal phenotypic charcaterization

National Institute On Drug Abuse

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Abstract

Corticotropin releasing factor (CRF) and CRF-related peptides mediate stress responses, in part, by their interactions with the CRF-binding protein (CRF-BP). The CRF-BP plays a role in dopamine (DA) and glutamate neurotransmission within the ventral tegmental area (VTA). Here we investigated whether specific local neurons could be a source of CRF-BP in the VTA. By in situ hybridization we detected cellular expression of CRF-BP mRNA in the VTA, but not in neighboring substantia nigra compacta (SNC) or substantia nigra reticulata. The selective expression of CRF-BP mRNA proved to be useful in demarcating boundaries between the SNC and the VTA. By double in situ hybridization we determined that VTA neurons with CRF-BP mRNA co-expressed transcripts encoding either tyrosine hydroxylase (TH, a maker for DAergic neurons) or glutamic acid decarboxylase (GAD, synthesizing enzyme of ?-amino butyric acid, GABA). We found that 25% of the total population of TH expressing neurons contained CRF-BP mRNA, providing support to the notion that discrete subpopulations of dopamine neurons are present in the VTA. We determined that within the total population of neurons expressing CRF-BP mRNA 70% co-expressed CRF-BP mRNA TH mRNA, and only 25% co-expressed GAD mRNA. [unreadable] 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.