Remedial agent for neural degeneration

A therapeutic agent for neurodegenerative disorders comprising, as an active ingredient, a xanthine derivative represented by formula (I):

• 14
• wherein R1, R2 and R3 independently represent hydrogen, lower alkyl, lower alkenyl or lower alkynyl;
• R4represents cycloalkyl, —(CH2)n—R5 (wherein R5 represents substituted or unsubstituted aryl, or a substituted or unsubstituted heterocyclic group, and n is an integer of 0 to 4), or the following group:
• 15
• wherein Y1 and Y2 independently represent hydrogen, halogen or lower alkyl, and Z represents substituted or unsubstituted aryl or the following group:
• 16
• (wherein R6 represents hydrogen, hydroxy, lower alkyl, lower alkoxy, halogen, nitro or amino, and m is an integer of 1 to 3), or a substituted or unsubstituted heterocyclic group;
• and
• X1 and X2 independently represent O or S, or a pharmaceutically acceptable salt thereof.