A novel finding in this study was that third-trimester equivalent binge-like alcohol exposure affected the density of mature and immature spines through a predominance of mature spines while not affecting total spine density. Moreover, it is interesting to note that we saw a decrease in dendritic complexity accompanying the increase in mature spines. Spines function as biomechanical (Nimchinsky et al., 2002; Ethell & Pasquale, 2005) and electrical dendritic compartments (Tsay & Yuste, 2004). Spine densities fluctuate across brain region, neuronal type, and location on an individual dendritic tree (Nimchinsky et al., 2002; Spruston, 2008). Spines vary considerably in shape and size and are highly plastic (Spruston, 2008). In fact, certain phenotypes, or shapes, have been associated with either immature or mature synapses (Zhang & Benson, 2000; Irwin et al., 2001; Portera-Cailiau et al., 2003; Ethell and Pasquale, 2005). Previous work in our lab found that in the mPFC, postnatal alcohol exposure produced a decrease in apical spine density without producing changes in spine phenotypes (Whitcher & Klintsova, 2008). This raises the question of why there is a significant increase in mature spine phenotype without any change to spine density in the basilar dendrites.
