Acts in different tissues through interaction to nicotinic acetylcholine receptors (nAChRs). In brain, isoform 2 modulates functional properties of nAChRs to prevent excessive excitation, and hence neurodegeneration. Enhances desensitization by increasing both the rate and extent of desensitization of alpha(4)beta(2) nAChRs and slowing recovery from desensitization. Promotes large amplitude ACh-evoked currents through alpha(4)beta(2) nAChRs (By similarity). Prevents plasticity in the primary visual cortex late in life (By similarity). In keratinocytes, isoform 3 delays differentiation and prevents apoptosis.