CART receptor binding in primary cell cultures of the rat nucleus accumbens

Specific cocaine-amphetamine regulated transcript (CART) receptor binding has been reported in AtT20 and PC12 cells. In this study, receptor binding has been examined in primary cell cultures of several rat brain regions. Utilizing (125)I-CART 61-102 as a ligand and CART 55-102 as a displacer, significant levels of specific binding compared with nonspecific binding were found in the nucleus accumbens. Specific CART binding was substantially lower in hippocampal, hypothalamic, and pituitary cells. The specific binding was saturable with a K(d) of 1.43 +/- 0.25 nM and a B(max) of 49.03 +/- 2.33 fmol/mg protein. The binding was also highly specific for CART 55-102 as other inactive CART peptide fragments, unrelated peptides, gamma-aminobutyric acid, or cocaine showed no affinity for the receptor at 10 muM concentrations. Furthermore, addition of the GTP analog, Gpp(NH)p, significantly decreased specific binding but addition of an ATP analog did not, suggesting that the receptor is a g-protein coupled receptor. This is the first demonstration of CART peptide receptor binding in primary cell cultures of the rat brain.