Ampal CA1 subfield in individuals with MCI POR-8 site compared to NCI (Fig. 4), which correlated with the subject’s Mini-Mental State Exam score (MMSE), but not with NFT Braak stage or apolipoprotein E (ApoE) status, a genetic risk factor for AD (Scheff et al., 2006). Unlike the outer molecular layer, CA1 receives input from the Schaffer collaterals arising from CA3 and not from the glutamatergic neurons of the entorhinal cortex, suggesting differential responses to synapse loss within the hippocampus based upon afferent innervation or chemical phenotype, some of which precipitate BMS-214662 side effects synaptic reorganization. A recent report characterized changes in the dendritic branching of the basilar tree of hippocampal CA1 pyramidal neurons. In this study, formalin-fixed tissue autopsy obtained from University of Kentucky Alzheimer’s Disease Center who died with a clinical diagnosis of NCI, MCI or AD was prepared for Golgi impregnation (Fig. 5). Camera lucida drawings of the basilar tree of randomly selected CA1 neurons were analyzed for alterations in dendritic arbor amount, distribution and complexity (Mervis et al., 2013). Quantitation showed a significant increase in dendritic length (18 ) and complexity (23 ) in CA1 neurons in MCI compared to NCI. Conversely, there was a significant reduction in branch length (-39 ) and arbor complexity (-25 ) during the progression from MCI to AD (Fig. 5). These findings suggest that the observed increase in CA1 dendritic parameters from NCI to MCI may be another example of a neuroplastic compensatory response to a loss of afferent input early in the course of the disease, which is not maintained as the disease progresses. The role that the reported reduction in total synapse number plays in CA1 neuroplasticity remains unknown. However, these examples of early CA1 neural reorganization may represent a viable window for potential therapeutic strategies aimed at restoring or maintaining hippocampal function during the transition from MCI to AD. Future studies should determine whether alterations in specific synapse subtypes (i.e., perforated vs. non-perforated) are differentially affected and their relation to cognitive decline and brain pathology during the onset of AD. Interestingly, the size of the synaptic contacts was found to be substantially larger in AD cortex compared to non-demented aged controls (Scheff et al., 1990), which was suggested to be part of a compensatory mechanism found in regions of the neocortex and hippocampus (see review Scheff and Price, 2006). These investigators found that as the number of synapses declined in a given region, the size of the residualAuthor Manuscript Author Manuscript Author Manuscript Author ManuscriptNeuroscience. Author manuscript; available in PMC 2016 September 12.Mufson et al.Pagesynapses increased. This synaptic compensatory response was also observed early in the course of the AD (DeKosky and Scheff, 1990). Neuronal structural alterations may not be the only factor(s) contributing to cognitive decline and hippocampal plasticity in MCI. For example, studies have reported significant reductions in synaptic vesicle trafficking-related genes in the AD brain, which interrupt the efficacy of normal synaptic transmission (Yao et al., 2003; Murphy et al., 2003; Kennedy et al., 2005). Counts et al. (2014) examined progressive changes in the expression classes of synaptic gene within single CA1 neurons in subjects who died with a clinical diagnosis of NCI, MCI or moderate AD obtain.Ampal CA1 subfield in individuals with MCI compared to NCI (Fig. 4), which correlated with the subject’s Mini-Mental State Exam score (MMSE), but not with NFT Braak stage or apolipoprotein E (ApoE) status, a genetic risk factor for AD (Scheff et al., 2006). Unlike the outer molecular layer, CA1 receives input from the Schaffer collaterals arising from CA3 and not from the glutamatergic neurons of the entorhinal cortex, suggesting differential responses to synapse loss within the hippocampus based upon afferent innervation or chemical phenotype, some of which precipitate synaptic reorganization. A recent report characterized changes in the dendritic branching of the basilar tree of hippocampal CA1 pyramidal neurons. In this study, formalin-fixed tissue autopsy obtained from University of Kentucky Alzheimer’s Disease Center who died with a clinical diagnosis of NCI, MCI or AD was prepared for Golgi impregnation (Fig. 5). Camera lucida drawings of the basilar tree of randomly selected CA1 neurons were analyzed for alterations in dendritic arbor amount, distribution and complexity (Mervis et al., 2013). Quantitation showed a significant increase in dendritic length (18 ) and complexity (23 ) in CA1 neurons in MCI compared to NCI. Conversely, there was a significant reduction in branch length (-39 ) and arbor complexity (-25 ) during the progression from MCI to AD (Fig. 5). These findings suggest that the observed increase in CA1 dendritic parameters from NCI to MCI may be another example of a neuroplastic compensatory response to a loss of afferent input early in the course of the disease, which is not maintained as the disease progresses. The role that the reported reduction in total synapse number plays in CA1 neuroplasticity remains unknown. However, these examples of early CA1 neural reorganization may represent a viable window for potential therapeutic strategies aimed at restoring or maintaining hippocampal function during the transition from MCI to AD. Future studies should determine whether alterations in specific synapse subtypes (i.e., perforated vs. non-perforated) are differentially affected and their relation to cognitive decline and brain pathology during the onset of AD. Interestingly, the size of the synaptic contacts was found to be substantially larger in AD cortex compared to non-demented aged controls (Scheff et al., 1990), which was suggested to be part of a compensatory mechanism found in regions of the neocortex and hippocampus (see review Scheff and Price, 2006). These investigators found that as the number of synapses declined in a given region, the size of the residualAuthor Manuscript Author Manuscript Author Manuscript Author ManuscriptNeuroscience. Author manuscript; available in PMC 2016 September 12.Mufson et al.Pagesynapses increased. This synaptic compensatory response was also observed early in the course of the AD (DeKosky and Scheff, 1990). Neuronal structural alterations may not be the only factor(s) contributing to cognitive decline and hippocampal plasticity in MCI. For example, studies have reported significant reductions in synaptic vesicle trafficking-related genes in the AD brain, which interrupt the efficacy of normal synaptic transmission (Yao et al., 2003; Murphy et al., 2003; Kennedy et al., 2005). Counts et al. (2014) examined progressive changes in the expression classes of synaptic gene within single CA1 neurons in subjects who died with a clinical diagnosis of NCI, MCI or moderate AD obtain.
