Biology subjects

Sidiropoulou, K.

Publications and source records attributed to Sidiropoulou, K..

7 recordsLinked to original sources

bioRxiv2026

GAT1508, a selective neuronal GIRK1/2 activator, exhibits superior antiepileptic efficacy and synergizes with cannabidiol

G protein-gated inwardly rectifying potassium (GIRK; Kir3) channels are key regulators of neuronal excitability and represent promising therapeutic targets for epilepsy. Here, we characterize GAT1508, a urea-based small-molecule activator selectively targeting neuronal GIRK1/2 heterotetramers, and compare its efficacy with previously described urea compounds ML297 and GiGA1. In a pentylenetetrazole (PTZ)-induced seizure model, GAT1508 demonstrated robust antiseizure activity, outperforming both ML297 and GiGA1 and achieving efficacy comparable to valproic acid. Electrophysiological studies using two-electrode voltage clamp in Xenopus oocytes revealed that GAT1508, unlike ML297 and GiGA1, selectively activates GIRK1/2 channels without significant activation of cardiac GIRK1/4 channels, suggesting reduced risk of cardiovascular side effects. Structural and computational analyses indicate that enhanced stabilization of GAT1508 compared to ML297 within the GIRK1/2 binding pocket promotes both ion permeation and channel gating through coordinated interactions with key residues. Furthermore, GAT1508, like the two other urea drugs, exhibited synergistic activation of GIRK channels when combined with G{beta}{gamma}-mediated pathways and significantly potentiated the antiseizure effects of cannabidiol (CBD) in both hippocampal slice recordings and in vivo seizure models. These findings establish GAT1508 as a potent and selective GIRK1/2 activator and support a novel combination therapeutic strategy for epilepsy based on convergent GIRK channel modulation.

pharmacology and toxicology↗

bioRxiv2024

Properties and predictive potential of the pre-ictal oscillatory dynamics in an ex vivo model of epileptiform activity in the different hippocampal subregions

The hippocampus, including the cornu ammonis (CA) and dentate gyrus (DG) subregions, is a brain area highly susceptible to seizure-like activity (SLA). Most studies conducted in vivo have been performed in a single hippocampal subregion. In our study, we used the high [K+] (HK+) model of SLA to investigate the role of oscillatory activity in predicting SLA and in its modulation by anti-epileptic drugs in the three hippocampal subregions (CA1, CA3 and DG). For this, we recorded spontaneous local field potentials (LFPs) in CA1, CA3 and DG subregions from mouse hippocampal slices. We find that the oscillatory activity in the 20 second pre-ictal period is significantly different compared to the oscillatory activity in the absence of SLA or to a more distant period from the ictal event. A classification algorithm revealed that the oscillatory dynamics, particularly in the CA1 subregion, can predict the emergence of an ictal event with high accuracy. Furthermore, oscillatory activity is differentially modulated by anti-epileptic drugs in the different hippocampal subregions. We found that diazepam and carbamazepine modulated the oscillatory activity significantly greater in the CA3 and DG subregions, compared to CA1. Imaging of neuronal activation in the ex vivo model of seizure-like activity, using the Fos protein as an activity marker, revealed a similar subregion-dependent differential modulation following diazepam and carbamazepine perfusion. Therefore, while oscillatory activity in the pre-ictal period in the CA1 subregion can better predict the emergence of ictal events, anti-convulsant drugs have a stronger effect in oscillatory activity in the CA3 and DG subregions.

neuroscience↗

bioRxiv2024

Effects of working memory training on cognitive flexibility, dendritic spine density and long-term potentiation in female mice

Working memory (WM) is a cognitive function that refers to the ability of short-term storage and manipulation of information necessary for the accomplishment of a task. Two brain regions involved in WM are the prefrontal cortex (PFC) and the hippocampus (HPC). Several studies have suggested that training in WM (WMT) can improve performance in other cognitive tasks. However, our understanding of the neurobiological changes induced by WMT is very limited. Previous work from our lab has shown that WMT enhances synaptic and structural plasticity in the PFC and HPC in male mice. In this study, we investigate the effect of WMT on cognitive flexibility and synaptic properties in PFC and HPC in adult female mice. To this end, female adult mice were split into 3 groups: a) naive which remained in their home cage, b) non-adaptive which learned to alternate the arms in the T-maze but without any delays and c) adaptive which were trained in the delayed alternation task for 9 days. The delayed alternation task was used for WMT. In one cohort, following the delayed alternation task, all mice were tested in the attention set-shifting (AST) task in order to measure cognitive flexibility, and then, the brains were harvested for Golgi-Cox staining to study dendritic spine density. Our results showed that in female mice, there were no differences in performance in the AST among the three groups tested, however, the latency to make a choice was reduced. With regards to dendritic spine density, no significant differences were identified in PFC while increased dendritic spine density was found in the hippocampus of the adaptive group, compared to the naive group. In a second cohort, acute brain slices were prepared following the delayed alternation task to investigate the synaptic properties in the PFC and the HPC. Evoked field excitatory post-synaptic potential (fEPSP) recordings were performed in either PFC or HPC brain slices. Our results show that tetanic-induced long-term potentiation (LTP) in the PFC was not different among the three training groups. In the HPC, theta-burst induced LTP was significantly increased in the adaptive group also compared to the other two groups. These results reveal both similarities and differences of WMT on cognitive flexibility, dendritic spine density and LTP in females, compared to males.

neuroscience↗

bioRxiv2020

Long-term synaptic depression triggers local biogenesis of autophagic vesicles in dendrites and requires autophagic degradation

In neurons, biogenesis of autophagic vesicles (AVs) is spatially confined to the axon tip under baseline conditions. However, it remains unknown whether their biogenesis can be induced in other neuronal compartments following synaptic activity in order to serve local functions. Here, we show that both major types of long-term synaptic depression (LTD), a form of plasticity expressed by the shrinkage and elimination of dendritic spines, trigger the rapid and local biogenesis of AVs in post-synaptic dendrites. In return, autophagy is indispensable for LTD, as either genetic ablation of atg5 in pyramidal neurons or acute pharmacological inhibition of AV biogenesis totally prevents LTD induction. Using quantitative proteomic profiling of purified AVs, we reveal that upon LTD the autophagic cargo is significantly enriched for synaptic proteins, as well as modulators of the actin cytoskeleton and autism-implicated proteins. In line with these findings, a mild autophagy deficit is sufficient to impair behavioral flexibility, a cognitive function that requires efficient LTD. Therefore, local synthesis and assembly of the autophagic machinery in dendrites ensure the elimination of synaptic structures via degradation of their components, facilitating plasticity and associated behaviors. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=165 HEIGHT=200 SRC="FIGDIR/small/983965v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@1a7bc14org.highwire.dtl.DTLVardef@12cece0org.highwire.dtl.DTLVardef@738687org.highwire.dtl.DTLVardef@8518af_HPS_FORMAT_FIGEXP M_FIG C_FIG In briefKallergi, Daskalaki and colleagues demonstrate that autophagy is cell autonomously required in pyramidal excitatory neurons for the induction of long-term synaptic depression (LTD). They uncover the novel and local biogenesis of autophagic vesicles (AVs) in dendrites upon LTD, by which post-synaptic components are rapidly accessible on-site for autophagic degradation. Using quantitative proteomics on purified AVs, they reveal that upon LTD the autophagic cargo is enriched in synaptic, cytoskeletal and autism-implicated proteins. HighlightsO_LIAutophagy is required cell-autonomously in pyramidal neurons for LTD. C_LIO_LINMDAR- and mGluR-mediated LTD trigger the local biogenesis of autophagic vesicles in dendrites. C_LIO_LIAutophagic vesicles sequester primarily synaptic and cytoskeletal cargo upon LTD. C_LIO_LIMild impairment in autophagy leads to deficits in cognitive flexibility. C_LI

neuroscience↗

bioRxiv2020

Early postnatal inhibitory circuit development in the mouse medial prefrontal and primary somatosensory cortex

The prefrontal cortex (PFC) is characterized by protracted maturation. The cellular mechanisms controlling the early development of prefrontal circuits are still largely unknown. Our study delineates the developmental cellular processes in the mouse medial PFC (mPFC) during the second and third postnatal weeks and characterizes their contribution to the changes in network activity. We show that spontaneous inhibitory postsynaptic currents (sIPSC) are increased while spontaneous excitatory postsynaptic currents (sEPSC) are reduced from the second to the third postnatal week. Drug application suggested that the increased sEPSC frequency in mPFC at P10 is due to depolarizing GABAA receptor (GABAAR) function. To further validate this, perforated patch-clamp recordings were obtained and the expression levels of K-Cl co-transporter 2 (KCC2) protein were examined. The reversal potential of IPSCs in response to current stimulation was significantly more depolarized at P10 compared to P20 while KCC2 expression is decreased. Moreover, the number of parvalbumin-expressing GABAergic interneurons increase from P10 to P20 in the mPFC and their intrinsic electrophysiological properties significantly mature. Using computational modeling, we show that the developmental changes in synaptic and intrinsic properties of mPFC neurons contribute to the enhanced network activity in the juvenile compared to neonatal mPFC.

neuroscience↗

bioRxiv2018

Effects of working memory training on reference memory, reversal learning and synaptic plasticity in middle-aged male mice

Working memory (WM) is the ability to hold on-line and manipulate information. The prefrontal cortex (PFC) is a key brain region involved in WM, while the hippocampus is also involved, particularly, in spatial WM. Although several studies have investigated the neuronal substrates of WM in trained animals, the effects and the mechanisms underlying learning WM tasks have not been explored. In our study, we investigated the effects of learning WM tasks in mice on the function of PFC and hippocampus, by training mice in the delayed alternation task for 9 days (adaptive group). This group was compared to naive mice that stayed in their homecage (naive) and mice trained in the alternation procedure only (non-adaptive). Following training, a cohort of mice (Experiment A) was tested in the left-right discrimination task and the reversal learning task, while another cohort (Experiment B) was tested in the attention set- shifting task (AST). The adaptive group performed significantly better in the reversal learning task (Experiment A) and AST (Experiment B), compared to non-adaptive and naive groups. At the end of the behavioral experiments in Experiment A, field excitatory post-synaptic potential (fEPSP) recordings were performed in PFC and hippocampal brain slices. The adaptive group had enhanced the long-term potentiation (LTP) in the PFC, compared to the other groups. In the hippocampus, both the adaptive and the non-adaptive groups exhibited increased fEPSP compared to the naive group, but no differences in LTP. In Experiment B, the dendritic spine density was measured, which, in the PFC, was found increased in the adaptive group, compared to the non-adaptive and naive groups. In the hippocampus, there was an increase in mature dendritic spine density in the adaptive group, compared to the other two groups. Our results indicate a role for long-term potentiation and dendritic spine density in learning WM tasks. Significance statementWorking memory (WM) allows for transient storage and manipulation of information and has a central role in cognition. While a great number of research studies have investigated the mechanisms underlying the memory part of WM in well-trained animals, the mechanisms that underlie learning WM tasks are not known. Studies have indicated that learning a WM tasks alters and enhances neuronal firing during the delay period, suggesting that long-term plasticity mechanisms could be involved. Our results in this study suggest that learning a working memory task primarily increases long-term potentiation and dendritic spine density in the prefrontal cortex, providing evidence for a role of long-term plasticity processes in learning working memory tasks. Furthermore, learning working memory tasks enhances cognitive flexibility.

neuroscience↗

bioRxiv2018

Development of the MAM model of schizophrenia in mice: Sex similarities and differences of prefrontal cortical and hippocampal function

Schizophrenia is a debilitating disorder with complex and unclarified etiological factors. Sex differences have been observed in humans but animal models have only focused on male subjects. In this study, we report the establishment of the neurodevelopmental MAM model of schizophrenia in mice and compare the schizotypic-like characteristics and cognitive function in both sexes. Pregnant mice were injected with 26mg/kg(i.p.) of Methylazoxy-methanol acetate (MAM) or saline (5ml/kg) on gestational day (GD) 16 (MAM-16) or 17 (MAM-17). Behavioral, histological and electrophysiological and mass spectrometry-based comparative proteomic techniques were employed to assess the schizotypic-like characteristics and cognitive function of adult male and female offspring (MAM- or saline-treated). Female MAM-16, but not MAM-17 treated mice exhibited enhanced hyperlocomotion after acute administration of the NMDA receptor antagonist, MK-801, compared to saline treated mice. Male MAM-16, but not MAM-17 treated mice showed decreased pre-pulse inhibition of the acoustic startle reflex. Both male and female MAM-16 and MAM-17 treated mice exhibited reduced hippocampal (HPC) size and thinning of the prefrontal cortex (PFC), but only male MAM-16 treated mice showed decreased parvalbumin expression in HPC and PFC. Similarly, both male and female MAM-16 treated mice displayed impaired contextual fear memory, while only male MAM-16 treated mice exhibited deficits in the delayed alternation task. The neurophysiological mechanisms that underlie these cognitive functions were further investigated. Both male and female MAM-16 treated mice had significantly reduced long-term potentiation (LTP) in the HPC CA1 synapses, while only male MAM-16 treated mice exhibited decreased LTP in the PFC. Proteomic analyses of PFC lysates further showed significant MAM- and sex-dependent differences in regulation of protein expression. Our results demonstrate that while both male and female mice, prenatally exposed to MAM on GD16, display several core schizophrenia-like deficits and impairments in the hippocampus, only male MAM-treated mice have PFC-dependent cognitive deficits.

neuroscience↗