Recently, Renko et al. [99] developed a small molecule named BT44 which mimics the GDNF molecular signal (activation of receptor tyrosine kinase RET and its signaling cascade): BT44 displays protective effects on cultured midbrain DA neurons from the MPP–induced toxicity and promote functional recovery in rats modelling an advanced stage of PD. Here, GDNF is linked to Parkinson disease.