SNAP25 and coloboma: Furthermore, mRNA expression of Tyrosine Hydroxylase (a rate limiting enzyme in the synthesis of dopamine and noradrenaline) was significantly increased in the cells of the noradrenergic locus coeruleus, indicating that a perturbed level of noradrenaline (presumably caused by the lack of SNAP25 copy) may contribute to the hyperactive behavior of the coloboma. Similarly, NA depletion using DSP-4(N-(2-chloroethyl)-N-ethyl-2 bromobenzylamine hydrochloride) significantly reduced hyperactivity in the Coloboma mouse, supporting the noradrenaline hypothesis [8].