Signaling adapter that couples activated growth factor receptors to signaling pathway in neurons. Involved in the signal transduction pathways of neurotrophin-activated Trk receptors in cortical neurons. Interacts with the Trk receptors in a phosphotyrosine-dependent manner. Once activated, binds to GRB2. Interacts with activated EGF receptors. Mainly expressed in brain. Hardly detectable in other tissues, except in pancreas. Highly expressed in the cerebral cortex, frontal and temporal lobes, occipital pole, hippocampus, caudate nucleus and amygdala. Expressed at low level in the cerebellum, medulla and spinal cord. Tyrosine phosphorylated.