Ras, part of the mitogen-activated protein kinase pathway, is a protein which plays a critical role in transmitting extracellular signals. It has been shown that expression of the active RasG12V mutation in glutamatergic forebrain neurons of mice results in enhanced hippocampal-dependent learning and LTP at Schaffer collateral synapses (SFN 2002 abstract # 779.9). In order to investigate potential morphological correlates of these behavioural and electrophysiological enhancements, serial electron microscopy was conducted on CA1 Schaffer collateral synapses in 5 H-RASG12V and 5 wild-type littermates, and the density of several synaptic types was quantified. No changes were observed in the density of the total population of synapses, or nonperforated synapses of any type. Perforated synapses, however, showed a significant increase in concave perforated synapses in H-RASG12V mice. As this synaptic type is highly implicated in synaptic efficacy, this data provides a potential morphological correlate of the enh...