Finally, we analyzed dendritic spines and their postsynaptic densities in CA1. Like for thorny excrescences, 4 weeks of enrichment led to a marked and comparable increase in stratum radiatum spine densities in β-Adducin−/− click here and wild-type mice ( Figure 6A). In further analogy to AZ densities at thorny excrescences,

a detailed analysis of PSD95-positive postsynaptic densities revealed that frequencies of PSD95 puncta per spine decreased markedly upon enriched environment ( Figure 6B), leading to a suppression of CA1 excitatory synapse increases upon enrichment in β-Adducin−/− mice ( Figure 6B). Taken together, these results provide evidence that the presence of β-Adducin is specifically required to establish new synapses under conditions of enhanced plasticity in the adult. In the absence of β-Adducin, environmental enrichment still leads to an increase in dendritic spine numbers, but this increased density of spines is not matched by a corresponding increase in actual synapses, leading to a failure to increase the densities of excitatory synapses at

LMTs and in CA1. Does the failure to establish new synapses upon enrichment in β-Adducin−/− mice affect the beneficial effects of environmental enrichment on learning? To address this question, we focused on learning protocols involving a hippocampal mossy fiber requirement (e.g., Jessberger et al., 2009), where any learning defect may then be rescued by re-expressing GFP-β-Adducin in granule cells. In a first set of experiments, we compared freezing upon contextual fear conditioning in mice housed under control or enriched (4 weeks) conditions. DAPT datasheet As expected, and consistent with stronger learning, re-exposure to context 1 day after learning elicited stronger freezing in enriched wild-type mice ( Figure 7A). When housed under control conditions β-Adducin−/− mice were not noticeably different from wild-type controls in this associative learning task ( Figure 7A; as mentioned in Experimental Procedures, and in good agreement with a previous study [ Rabenstein et al., 2005], the mutant mice did exhibit Rolziracetam reduced freezing to context when subjected to a milder

conditioning method). However, instead of increasing freezing, enrichment reduced freezing in β-Adducin−/− mice ( Figure 7A). In control experiments the environmental enrichment protocol did enhance fear conditioning-induced freezing in Rab3a−/− mice that lack mossy fiber LTP ( Castillo et al., 1997), indicating that failure by environmental enrichment to increase fear conditioning learning in β-Adducin−/− mice was not just due to a deficit in LTP at this critical synapse ( Figure 7A). Environmental enrichment has been shown to increase neurogenesis in the dentate gyrus in the adult, and adult neurogenesis has been related to improved hippocampal learning ( Deng et al., 2010). Therefore, in a second set of control experiments, we compared adult dentate neurogenesis upon enrichment in wild-type and β-Adducin−/− mice.