Resea R ch highlights fbr Addict ion Cocaine regulates MEF2 to control synaptic and behavioral plasticity Pulipparacharuvil, S. et al. Neuron 59, 621–633 (2008) Cocaine addiction results in behavioural changes and increased spine density on medium-sized spiny neurons in the nucleus accumbens. Here, cocaine increased spine density by reducing the activity of the transcription factor myocyte enhancer factor 2 (MEF2). Cocaine did not alter spine density in mice expressing a constitutively active form of MEF2; surprisingly, however, behavioural responses to cocaine were enhanced, suggesting that the increase in spine density is functionally uncoupled from behavioural responses. The identification of MEF2 as a key player in drug addiction could lead to novel treatments. n eurodegener Ation Sc Crossing the species barrier by PrP replication in vitro generates unique infectious prions Castilla, J. et al. Cell 134, 757–768 (2008) Sc Misfolded prion proteins (PrP ), which induce misfolding of cellular prion proteins (PrP ), are the infectious agents that cause Sc neurodegeneration in prion diseases. PrP can cross the species barrier between some species but not others. The requirements for crossing this barrier are unknown. The authors used protein misfolding cyclic amplification (PMCA) technology to demonstrate that, under certain conditions, misfolding of hamster PrP can be Sc induced by mouse PrP , resulting in new hamster prion strains, and vice versa. Therefore, at least in vitro, the species barrier for prions seems to be more penetrable than was previously thought. neurogene S i S Roles of continuous neurogenesis in the structural and...