A phosphodiesterase 10A inhibitor serving as an effective prophylactic or therapeutic agent for Parkinson's disease, Huntington's disease, Alzheimer's disease, and schizophrenia. The PDE10A inhibitor contains as an active ingredient a pyrazoloÄ1,5-aÜpyridine derivative represented by the following general formula: <CHEM> wherein R<1> and R<2> are each independently a hydrogen atom or a lower alkyl group having 1 to 4 carbons; and R<3> is a hydrogen atom, a lower alkyl group having 1 to 4 carbons, or a lower alkoxyl group having 1 to 3 carbons.
PHOSPHODIESTERASE 10A INHIBITORS FOR USE IN THE TREATMENT OF PARKINSON'S DISEASE, HUNTINGTON'S DISEASE AND SCHIZOPHRENIA