Several fused bicyclic systems have been investigated to serve as the core structure of potent and selective 5-HT1F receptor agonists. Replacement of the indole nucleus in 2 with indazole and 'inverted'indazole provided more potent and selective 5-HT1F receptor ligands. Indoline and 1, 2-benzisoxazole systems also provided potent 5-HT1F receptor agonists, and the 5-HT1A receptor selectivity of the indoline-and 1, 2-benzisoxazole- ...