Faculty Bibliography

Epilepsy affects approximately 1% of children under the age of 15, making it a very common neurological disorder in the pediatric population (Russ et al., 2012). In addition, ~0.4-0.8% of all pregnant women have some form of epilepsy (Hauser et al., 1996a,b; Borthen et al., 2009; Krishnamurthy, 2012). Despite the potential deleterious effects of antiepileptic drugs (AEDs) on the developing brain, their use is still required for seizure control in pregnant women (Krishnamurthy, 2012), and they represent the standard approach for treating children with epilepsy (Chu-Shore and Thiele, 2010; Quach et al., 2010; Verrotti et al., 2011). Even when AEDs are effective, there are potential side effects, including cognitive and affective changes or altered sleep and appetite. The consequences of AED exposure in development have been studied extensively (Canger et al., 1999; Modi et al., 2011a,b; Oguni, 2011). Despite intensive study, there is still debate about the long-term consequences of early life AED exposure. Here, we consider the evidence to date that AED exposure, either prenatally or in early postnatal life, has significant adverse effects on the developing brain and incorporate studies of laboratory animals as well as those of patients. We also note the areas of research where greater clarity seems critical in order to make significant advances. A greater understanding of the impact of AEDs on somatic, cognitive and behavioral development has substantial value because it has the potential to inform clinical practice and guide studies aimed at understanding the genetic and molecular bases of comorbid pathologies associated with common treatment regimens. Understanding these effects has the potential to lead to AEDs with fewer side effects. Such advances would expand treatment options, diminish the risk associated with AED exposure in susceptible populations, and improve the quality of life and health outcomes of children with epilepsy and children born to women who took AEDs during pregnancy.

Seizures in patients with Alzheimer's disease (AD) have been examined by many investigators over the last several decades, and there are diverse opinions about their potential relevance to AD pathophysiology. Some studies suggest that seizures appear to be a fairly uncommon co-morbidity, whereas other studies report a higher incidence of seizures in patients with AD. It was previously thought that seizures play a minor role in AD pathophysiology because of their low frequency, and also because they may only be noticed during late stages of AD, suggesting that seizures are likely to be a consequence of neurodegeneration rather than a contributing factor. However, clinical reports indicate that seizures can occur early in the emergence of AD symptoms, particularly in familial AD. In this case, seizures may be an integral part of the emerging pathophysiology. This view has been supported by evidence of recurrent spontaneous seizures in transgenic mouse models of AD in which familial AD is simulated. Additional data from transgenic animals suggest that there may be a much closer relationship between seizures and AD than previously considered. There is also evidence that seizures facilitate production of amyloid beta (Abeta) and can cause impairments in cognition and behavior in both animals and humans. However, whether seizures play a role in the early stages of AD pathogenesis is still debated. Therefore, it is timely to review the similarities and differences between AD and epilepsy, as well as data suggesting that seizures may contribute to cognitive and behavioral dysfunction in AD. Here we focus on AD and temporal lobe epilepsy (TLE), a particular type of epilepsy that involves the temporal lobe, a region that influences behavior and is critical to memory. We also consider potential neurobiological mechanisms that support the view that the causes of seizures in TLE may be related to the causes of cognitive dysfunction in AD. We suggest that similar underlying mechanisms may exist for at least some of the aspects of AD that are also found in TLE.

Androgens have dramatic effects on neuronal structure and function in hippocampus. However, androgen depletion does not always lead to hippocampal impairment. To address this apparent paradox, we evaluated the hippocampus of adult male rats after gonadectomy (Gdx) or sham surgery. Surprisingly, Gdx rats showed increased synaptic transmission and long-term potentiation of the mossy fiber (MF) pathway. Gdx rats also exhibited increased excitability and MF sprouting. We then addressed the possible underlying mechanisms and found that Gdx induced a long-lasting upregulation of MF BDNF immunoreactivity. Antagonism of Trk receptors, which bind neurotrophins, such as BDNF, reversed the increase in MF transmission, excitability, and long-term potentiation in Gdx rats, but there were no effects of Trk antagonism in sham controls. To determine which androgens were responsible, the effects of testosterone metabolites DHT and 5alpha-androstane-3alpha,17beta-diol were examined. Exposure of slices to 50 nm DHT decreased the effects of Gdx on MF transmission, but 50 nm 5alpha-androstane-3alpha,17beta-diol had no effect. Remarkably, there was no effect of DHT in control males. The data suggest that a Trk- and androgen receptor-sensitive form of MF transmission and synaptic plasticity emerges after Gdx. We suggest that androgens may normally be important in area CA3 to prevent hyperexcitability and aberrant axon outgrowth but limit MF synaptic transmission and some forms of plasticity. The results also suggest a potential explanation for the maintenance of hippocampal-dependent cognitive function after androgen depletion: a reduction in androgens may lead to compensatory upregulation of MF transmission and plasticity.

The histopathological hallmarks of Alzheimer disease (AD) include intraneuronal neurofibrillary tangles composed of abnormally hyperphosphorylated tau protein. Insulin dysfunction might influence AD pathology, as population-based and cohort studies have detected higher AD incidence rates in diabetic patients. But how diabetes affects tau pathology is not fully understood. In this study, we investigated the impact of insulin dysfunction on tau phosphorylation in a genetic model of spontaneous type 1 diabetes: the nonobese diabetic (NOD) mouse. Brains of young and adult female NOD mice were examined, but young NOD mice did not display tau hyperphosphorylation. tau phosphorylation at tau-1 and pS422 epitopes was slightly increased in nondiabetic adult NOD mice. At the onset of diabetes, tau was hyperphosphorylated at the tau-1, AT8, CP13, pS262, and pS422. A subpopulation of diabetic NOD mice became hypothermic, and tau hyperphosphorylation further extended to paired helical filament-1 and TG3 epitopes. Furthermore, elevated tau phosphorylation correlated with an inhibition of protein phosphatase 2A (PP2A) activity. Our data indicate that insulin dysfunction in NOD mice leads to AD-like tau hyperphosphorylation in the brain, with molecular mechanisms likely involving a deregulation of PP2A. This model may be a useful tool to address further mechanistic association between insulin dysfunction and AD pathology.

Olfaction is often impaired in Alzheimer's disease (AD) and is also dysfunctional in mouse models of the disease. We recently demonstrated that short-term passive anti-murine-Abeta immunization can rescue olfactory behavior in the Tg2576 mouse model overexpressing a human mutation of the amyloid precursor protein (APP) after beta-amyloid deposition. Here we tested the ability to preserve normal olfactory behaviors by means of long-term passive anti-murine-Abeta immunization. Seven-month-old Tg2576 and non-transgenic littermate (NTg) mice were IP-injected biweekly with the m3.2 murine-Abeta-specific antibody until 16mo of age when mice were tested in the odor habituation test. While Tg2576 mice treated with a control antibody showed elevations in odor investigation times and impaired odor habituation compared to NTg, olfactory behavior was preserved to NTg levels in m3.2-immunized Tg2576 mice. Immunized Tg2576 mice had significantly less beta-amyloid immunolabeling in the olfactory bulb and entorhinal cortex, yet showed elevations in Thioflavin-S labeled plaques in the piriform cortex. No detectable changes in APP metabolite levels other than Abeta were found following m3.2 immunization. These results demonstrate efficacy of chronic, long-term anti-murine-Abeta m3.2 immunization in preserving normal odor-guided behaviors in a human APP Tg model. Further, these results provide mechanistic insights into olfactory dysfunction as a biomarker for AD by yielding evidence that focal reductions of Abeta may be sufficient to preserve olfaction.

Although anti-human beta-amyloid (Abeta) immunotherapy clears brain beta-amyloid plaques in Alzheimer's disease (AD), targeting additional brain plaque constituents to promote clearance has not been attempted. Endogenous murine Abeta is a minor Abeta plaque component in amyloid precursor protein (APP) transgenic AD models, which we show is approximately 3%-8% of the total accumulated Abeta in various human APP transgenic mice. Murine Abeta codeposits and colocalizes with human Abeta in amyloid plaques, and the two Abeta species coimmunoprecipitate together from brain extracts. In the human APP transgenic mouse model Tg2576, passive immunization for 8 weeks with a murine-Abeta-specific antibody reduced beta-amyloid plaque pathology, robustly decreasing both murine and human Abeta levels. The immunized mice additionally showed improvements in two behavioral assays, odor habituation and nesting behavior. We conclude that passive anti-murine Abeta immunization clears Abeta plaque pathology-including the major human Abeta component-and decreases behavioral deficits, arguing that targeting minor endogenous brain plaque constituents can be beneficial, broadening the range of plaque-associated targets for AD therapeutics.

Emerging evidence suggests that dysregulated translation through phosphorylation of eukaryotic initiation factor-2alpha (eIF2alpha) may contribute to Alzheimer's disease (AD) and related memory impairments. However, the underlying mechanisms remain unclear. Here, we crossed knockout mice for an eIF2alpha kinase (GCN2: general control nonderepressible-2 kinase) with 5XFAD transgenic mice, and investigated whether GCN2 deletion affects AD-like traits in this model. As observed in AD brains, 5XFAD mice recapitulated significant elevations in the beta-secretase enzyme BACE1 and the CREB repressor ATF4 concomitant with a dramatic increase of eIF2alpha phosphorylation. Contrary to expectation, we found that GCN2(-/-) and GCN2(+/-) deficiencies aggravate rather than suppress hippocampal BACE1 and ATF4 elevations in 5XFAD mice, failing to rescue memory deficits as tested by the contextual fear conditioning. The facilitation of these deleterious events resulted in exacerbated beta-amyloid accumulation, plaque pathology and CREB dysfunction in 5XFAD mice with GCN2 mutations. Notably, GCN2 deletion caused overactivation of the PKR-endoplasmic reticulum-related kinase (PERK)-dependent eIF2alpha phosphorylation pathway in 5XFAD mice in the absence of changes in the PKR pathway. Moreover, PERK activation in response to GCN2 deficiency was specific to 5XFAD mice, since phosphorylated PERK levels were equivalent between GCN2(-/-) and wild-type control mice. Our findings suggest that GCN2 may be an important eIF2alpha kinase under the physiological condition, whereas blocking the GCN2 pathway under exposure to significant beta-amyloidosis rather aggravates eIF2alpha phosphorylation leading to BACE1 and ATF4 elevations in AD.

Early endosomal changes, a prominent pathology in neurons early in Alzheimer's disease, also occur in neurons and peripheral tissues in Down syndrome. While in Down syndrome models increased amyloid-beta protein precursor (AbetaPP) expression is known to be a necessary contributor on the trisomic background to this early endosomal pathology, increased AbetaPP alone has yet to be shown to be sufficient to drive early endosomal alterations in neurons. Comparing two AbetaPP transgenic mouse models, one that contains the AbetaPP Swedish K670N/M671L double mutation at the beta-cleavage site (APP23) and one that has the AbetaPP London V717I mutation near the gamma-cleavage site (APPLd2), we show significantly altered early endosome morphology in fronto-parietal neurons as well as enlargement of early endosomes in basal forebrain cholinergic neurons of the medial septal nucleus in the APP23 model, which has the higher levels of AbetaPP beta-C-terminal fragment (betaCTF) accumulation. Early endosomal changes correlate with a marked loss of the cholinergic population, which is consistent with the known dependence of the large projection cholinergic cells on endosome-mediated retrograde neurotrophic transport. Our findings support the idea that increased expression of AbetaPP and AbetaPP metabolites in neurons is sufficient to drive early endosomal abnormalities in vivo, and that disruption of the endocytic system is likely to contribute to basal forebrain cholinergic vulnerability.