This invention relates to the functional characterization of myo-inositol monophosphatase 2 (IMPA2), one of the enzymes acting in the phosphatidyl inositol signaling pathway. In particular, the present invention provides evidence that IMPA2 is associated with depression- and anxiety inducing conditions, in particular anxiety and affective disorders. In a first aspect the present invention provides the use of an IMPA2 enzyme in an assay to identify anti-anxiety or an anti-depression compounds. In particular to the use of an isolated polynucleotide encoding said IMPA2 protein, wherein said IMPA2 protein is preferably being selected from polynucleotides encoding the mouse, rat or human IMPA2 enzyme. It is thus an object of the present invention to provide a method for identifying anti-anxiety or anti-depression compounds wherein said compounds are capable of enhancing neuronal plasticity, said method comprising the steps of: a) providing a composition comprising an IMPA2 protein; b) contacting the IMPA2 protein with the test compound; and c) measuring the activity of the IMPA2 protein wherein a decrease in the IMPA2 activity in the presence of the test compound is an indicator of an anti-anxiety or anti-depression compound. In these assays the activity of the IMPA2 protein is assessed by measuring the hydrolysis of myo-inositol 1-phosphate to generate inositol and inorganic phosphate, in particular by measuring the accumulation of either myo-inositol monophosphate product in the form of radiolabeled inositol or inorganic phosphate (Pi) in the form of radiolabeled 32Pi or in a colorimetric assay. The compositions comprising the IMPA2 protein could either be cellular extracts, whole cells or organisms expressing the IMPA2 proteins according to the invention.