A number of [(3-chlorophenyl) piperazinylpropyl] pyridazinones and the corresponding isoxazolopyridazinones, showing the arylpiperazinyl substructure present in very potent antinociceptive agents reported in the literature, were synthesized and tested for their analgesic activity. The investigated compounds showed antinociceptive properties in the mouse hot-plate test (thermal nociceptive stimulus) after systemic administration with an ...