The present application relates to 1,2,3,4,4a,5,6,7-octahydropyrazino[1,2 -a][1,4]benzodiazepine, 1,2,3,4,4a,5,6,7-octahydropyrazino[1,2-a][1,5]benzodiazepine, 2,3,4,4a,5,6,7,11b-octahydro-1H-pyrido[3,4-d][2]benzazepine, 1,2,3,4,4a,5,6,7 -octahydropyrazino[1,2-a][1]benzazepine, 1,2,3,4,4a,5-hexahydro-7H-pyrazino[1,2 -a][4,1]benzoxazepine, and 2,3,4,4a,5,6-hexahydro-1H-pyrazino[2,1-d][1,5]benzoxazepine, and 5,6,7,7a,8,9,10,11-octahydropyrazino[1,2-d]pyrido[3,2-b][1,4]diazepine derivatives of formula (I) wherein R1, R2, R3, R4, R5, R6, X1, X2, X3, X4, Y1, Y2, and Y3 are as defined in the specification. The present application also relates to compositions comprising such compounds, and methods of treating disease conditions using such compounds and compositions, and methods for identifying such compounds.