Three Classes of Antidepressant Drugs Used in Human Beings Have $\gamma$

Three classes of antidepressant drugs used in human beings have also found use in veterinary medicine include all except:

A) monoamine oxidase inhibitors (MAOI)
B) tricyclic antidepressants (TCA's)
C) selective serotonin reuptake inhibitors (SSRI's)
D) gamma ( $\gamma$ ) aminobutyric acid (GABA)