GABA AND ENKEPHALIN PROJECTION FROM THE NUCLEUS-ACCUMBENS AND VENTRALPALLIDUM TO THE VENTRAL TEGMENTAL AREA

GABAergic and enkephalinergic afferents to the ventral tegmental area were investigated in the rat using retrograde tracing techniques combi ned with in situ hybridization. Following iontophoretic deposit of Flu oro-Gold in the ventral tegmental area labeling in the forebrain was m ost dense in the shell of the nucleus accumbens, rostral ventromedial ventral pallidum and diagonal band of Broca. A smaller density was als o observed in the lateral septum. In these forebrain regions, the port ion of retrogradely labeled cells that contained mRNA for glutamate de carboxylase ranged from 25% to 50%, whereas only 5% to 15% were double -labeled for preproenkephalin mRNA. Cells double-labeled with either g lutamate decarboxylase or preproenkephalin mRNA were most numerous in the lateral septum, shell of the nucleus accumbens, rostral ventral pa llidum and diagonal band of Broca. Large Fluoro-Gold deposits which in vaded the medial substantia nigra resulted in a significant number of retrogradely labeled cells in the core of the nucleus accumbens, and a portion of these neurons also contained mRNA for glutamate decarboxyl ase or preproenkephalin. These data demonstrate the presence of GABAer gic and enkephalinergic neurons projecting from the nucleus accumbens, ventral pallidum and diagonal band of Broca to the ventral tegmental area.