Methods for increasing D-Serine concentration and reducing concentration of the toxic products of D-Serine oxidation, for enhancing learning, memory and/or cognition, or for treating schizophrenia, Alzheimer's disease, ataxia, or neuropathic pain, or preventing loss in neuronal function characteristic of neurodegenerative diseases involve administering to a subject in need of treatment a therapeutic amount of a compound of formula I, or a pharmaceutically acceptable salt or solvate thereof: I wherein Z1 is N or CR3; Z2 is N or CR4; Z3 is O or S; A is hydrogen, alkyl or M+; M is aluminum, calcium, lithium, magnesium, potassium, sodium, zinc or a mixture thereof; R1, R2, R3 and R4 are independently selected from hydrogen, alkyl, hydroxy alkoxy, aryl, acyl, halo, cyano, haloalkyl, NHCOOR5 and SO2NH2; R5 is aryl, arylalkyl, heteroaryl or heteroarylalkyl; at least one of R1, R2, R3 and R4 is other than hydrogen; and at least one of Z1 and Z2 is other than N.