The JAK-STAT (Janus kinase-signal transducer and activator of transcription
) signalling pathway that is stimulated by cytokines has been much investig
ated in haematopoietic cells, but recent data indicate that this pathway is
also present and active during neuronal and glial differentiation. Further
more, it is now clear that growth factors other than the classical cytokine
s can act through this pathway and that physiological inhibitors of this si
gnalling cascade exist. Thus, the JAKs, the STATs and their specific inhibi
tors could be molecules with important roles in the CNS.