The invention provides a vector, preferably a herpes simplex virus (HSV) vector, comprising a polynucleotide sequence encoding a glutamic acid decarboxylase (GAD) protein. The invention also provides a stock of such vectors and a pharmaceutical composition comprising such vectors. The invention further provides a method of treating pain, such as spinal cord injury pain, in a mammal comprising administering to a mammal a vector comprising a nucleotide sequence encoding a glutamic acid decarboxylase (GAD) protein in an amount effective to treat spinal cord injury pain.