Dissociable effects of 5-HT2C receptor antagonism and genetic inactivation on perseverance and learned non-reward in an egocentric spatial reversal task

Cognitive flexibility can be assessed in reversal learning tests, which are sensitive to modulation of 5-HT2C receptor (5-HT2CR) function. Successful performance in these tests depends on at least two dissociable cognitive mechanisms which may separately dissipate associations of previous positive and negative valence. The first is opposed by perseverance and the second by learned non-reward. The current experiments explored the effect of reducing function of the 5-HT2CR on the cognitive mechanisms underlying egocentric reversal learning in the mouse. Experiment 1 used the 5-HT2CR antagonist SB242084 (0.5 mg/kg) in a between-groups serial design and Experiment 2 used 5-HT2CR KO mice in a repeated measures design. Animals initially learned to discriminate between two egocentric turning directions, only one of which was food rewarded (denoted CS+, CS−), in a T- or Y-maze configuration. This was followed by three conditions; (1) Full reversal, where contingencies reversed; (2) Perseverance, where the previous CS+ became CS− and the previous CS− was replaced by a novel CS+; (3) Learned non-reward, where the previous CS− became CS+ and the previous CS+ was replaced by a novel CS-. SB242084 reduced perseverance, observed as a decrease in trials and incorrect responses to criterion, but increased learned non-reward, observed as an increase in trials to criterion. In contrast, 5-HT2CR KO mice showed increased perseverance. 5-HT2CR KO mice also showed retarded egocentric discrimination learning. Neither manipulation of 5-HT2CR function affected performance in the full reversal test. These results are unlikely to be accounted for by increased novelty attraction, as SB242084 failed to affect performance in an unrewarded novelty task. In conclusion, acute 5-HT2CR antagonism and constitutive loss of the 5-HT2CR have opposing effects on perseverance in egocentric reversal learning in mice. It is likely that this difference reflects the broader impact of 5HT2CR loss on the development and maintenance of cognitive function

Gene Expression Profiling in Cells with Enhanced γ-Secretase Activity

BACKGROUND: Processing by gamma-secretase of many type-I membrane protein substrates triggers signaling cascades by releasing intracellular domains (ICDs) that, following nuclear translocation, modulate the transcription of different genes regulating a diverse array of cellular and biological processes. Because the list of gamma-secretase substrates is growing quickly and this enzyme is a cancer and Alzheimer's disease therapeutic target, the mapping of gamma-secretase activity susceptible gene transcription is important for sharpening our view of specific affected genes, molecular functions and biological pathways. METHODOLOGY/PRINCIPAL FINDINGS: To identify genes and molecular functions transcriptionally affected by gamma-secretase activity, the cellular transcriptomes of Chinese hamster ovary (CHO) cells with enhanced and inhibited gamma-secretase activity were analyzed and compared by cDNA microarray. The functional clustering by FatiGO of the 1,981 identified genes revealed over- and under-represented groups with multiple activities and functions. Single genes with the most pronounced transcriptional susceptibility to gamma-secretase activity were evaluated by real-time PCR. Among the 21 validated genes, the strikingly decreased transcription of PTPRG and AMN1 and increased transcription of UPP1 potentially support data on cell cycle disturbances relevant to cancer, stem cell and neurodegenerative diseases' research. The mapping of interactions of proteins encoded by the validated genes exclusively relied on evidence-based data and revealed broad effects on Wnt pathway members, including WNT3A and DVL3. Intriguingly, the transcription of TERA, a gene of unknown function, is affected by gamma-secretase activity and was significantly altered in the analyzed human Alzheimer's disease brain cortices. CONCLUSIONS/SIGNIFICANCE: Investigating the effects of gamma-secretase activity on gene transcription has revealed several affected clusters of molecular functions and, more specifically, 21 genes that hold significant potential for a better understanding of the biology of gamma-secretase and its roles in cancer and Alzheimer's disease pathology

Expression of signaling molecules associated with apoptosis in human ischemic stroke tissue

There is growing evidence that, because of the highly significant differences in gene activation/protein expression between animal models of stroke and stroke patients, the current treatment strategies based on animal stroke models have been unsuccessful. Therefore, it is imperative that the pathobiology of human stroke be studied. As a first step here, Western blotting and immunohistochemistry were employed to examine expression and tissue localization of key apoptotic proteins in infarct and peri-infarcted (penumbra) from grey and white matter in human postmortem tissue of 18 patients who died between 2 and 37 d after stroke caused by large vessel disease. The contralateral hemisphere was used as a control. JNK1, JNK2, and p53 were upregulated in the majority of samples, whereas Bcl-2, caspase-3, active caspase-3, phosphorylated p53 (p-p53), phosphorylated JNK1 (p-JNK1), and phosphorylated JNK2 (p-JNK2) were upregulated in approximately half of the samples. JNK1 expression was positively correlated with JNK2 expression in grey and white matter infarct and penumbra, whereas active caspase-3 levels were positively correlated with p-JNK2 levels in grey and white matter infarct. Using indirect immunoperoxidase staining of paraffin-embedded sections, active caspase-3 was found in infarcted neurons that co-localized with TUNEL-positive cells. p-JNK localization in the nuclei of TUNELpositive cells with the morphological appearance of neurons from infarct and penumbra was also demonstrated. The use of Kaplan Meier survival data demonstrated that the presence of Bcl-2 in penumbra of grey matter correlated significantly with shorter survival (p = 0.006). In conclusion, the present study has identified significantly altered expression of apoptotic proteins in human stroke tissue and shown that the presence of Bcl-2 in penumbra of grey matter has prognostic value. It is tempting to suggest that further studies of apoptotic proteins in human stroke may lead to identification of novel targets for drug discovery