Faculty Bibliography

Levels of mRNA for the major subunits of the GABAA receptor were assayed in the rat pituitary anterior and neurointermediate lobes by ribonuclease protection assay. alpha 1, beta 1, beta 2, beta 3, and gamma 2s were found to be the predominant subunits in the anterior lobe, whereas alpha 2, alpha 3, beta 1, beta 3, gamma 2s, and gamma 1 were the predominant subunits expressed in the neurointermediate lobe. alpha 5, alpha 6, and delta subunits were not detectable. Hill and Scatchard analysis of [3H] muscimol binding to anterior and neurointermediate lobe membranes showed high-affinity binding sites with dissociation constants of 5.6 and 4.5 nM, respectively, and Hill coefficients near 1. Muscimol sites were present at a maximum of 126 fmol/mg in the anterior lobe and 138 fmol/mg in the neurointermediate lobe. The central-type benzodiazepine antagonist [3H]Ro 15-1788 bound to a high-affinity site with a dissociation constant of 1.5 nM in both tissues, at a maximum of 60 fmol/mg in anterior pituitary and 72 fmol/mg in neurointermediate lobe. A Hill coefficient of 1 was measured for this site in both tissues. Assays of CL 218,872 displacement of Ro 15-1788 were consistent with a pure type I benzodiazepine site in the anterior lobe and a pure type II site in the intermediate lobe. These results are consistent with both tissue-specific expression of particular GABAA receptor subunits and receptor heterogeneity within individual cells in the pituitary.

An improved methodology has been developed which allows resolution, identification, and quantitation of hundreds of proteins and neuropeptides from a single rat brain nucleus (5 mg wet wt.). After metabolic labelling, proteins (greater than about 15 kDa) are separated from peptides (less than about 10 kDa) by sonicating the tissue in an acidic peptide extraction buffer; after centrifugation, proteins are in the pellet, peptides in the supernatant. To quantitate peptide synthesis, peptides are resolved to purity by reverse-phase HPLC followed by ion exchange HPLC. Proteins are resolved with a two-dimensional (2-D) gel protocol optimized for neural tissue. To identify specific proteins by immunoanalysis, proteins are transferred to polyvinyl difluoride (Immobilon) and immunostained in the presence of Tween blocking buffer. After visualization with an avidin-biotin alkaline phosphatase procedure, the blot is post-stained with India ink to visualize the protein pattern context. To sequence spots, proteins are transferred to Immobilon, stained with Coomassie, and directly subjected to automated gas phase sequencing. The immunoblot procedure can detect less than 0.1 pmol protein, and the sequencing procedure can detect less than 10 pmol protein. After transfer enough material remains on the gels to allow subsequent autoradiography or silver stain. Quantitative analysis of 2-D gels is examined in a companion paper. These procedures should enhance the utility of 2-D gels in neurochemical studies.