Therapeutic irradiation of the brain is commonly used to treat brain tumors but can induce cognitive impairments that can severely affect quality of life. The underlying mechanisms responsible for radiation-induced cognitive deficits are unknown but likely involve alterations in neuronal activity. To gain some mechanistic insight into how irradiation may affect hippocampal neurons known to be associated with cognitive function, we quantitatively assessed the molecular distribution of the behaviorally induced immediate-early gene Arc (activity-regulated cytoskeleton-associated protein) at the level of mRNA and the protein. Young adult C57BL/6J mice received whole-brain irradiation with 0 or 10 Gy, and 1 week or 2 months later, exploration of a novel environment was used to induce Arc expression. The fractions of neurons expressing Arc mRNA and Arc protein were detected using fluorescence in situ hybridization and immunocytochemistry, respectively. Our results showed that there was a significant reduction in the percentage of neurons expressing Arc protein 1 week after irradiation, whereas 2 months after irradiation, there was a reduction in the percentage of neurons expressing both Arc mRNA and Arc protein. Importantly, radiationinduced changes in Arc expression were not a result of neuronal cell loss. The changes observed at 2 months were associated with a significant increase in the number of activated microglia, supporting the idea that inflammation may contribute to neuronal dysfunction. These findings are the first to show that local brain irradiation initiates changes in hippocampal neurons that disrupt the activity patterns (Arc expression) associated with neuroplasticity and memory.

The library of 27 new 1-(4-phenylpiperazin-1-yl)- or 1-(morpholin-4-yl)-(2,5-dioxopyrrolidin-1-yl)propanamides and (2,5-dioxopyrrolidin-1-yl)butanamides as potential new hybrid anticonvulsant agents was synthesized. These hybrid molecules join the chemical fragments of well-known antiepileptic drugs (AEDs) such as ethosuximide, levetiracetam, and lacosamide. Compounds 5, 10, 11, and 24 displayed the broad spectra of activity across the preclinical seizure models, namely, the maximal electroshock (MES) test, the subcutaneous pentylenetetrazole (scPTZ) test, and the six-hertz (6 Hz) model of pharmacoresistant limbic seizures. The highest protection was demonstrated by 11 (ED50 MES = 88.4 mg/kg, ED50 scPTZ = 59.9 mg/kg, ED50 6 Hz = 21.0 mg/kg). This molecule did not impair the motor coordination of animals in the chimney test even at high doses (TD50 > 1500 mg/kg), yielding superb protective indexes (PI MES > 16.97, PI PTZ > 25.04, PI 6 Hz > 71.43). As a result, 11 displayed distinctly better safety profile than clinically relevant AEDs ethosuximide, lacosamide, or valproic acid.

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The focused set of new pyrrolidine-2,5-diones as potential broad-spectrum hybrid anticonvulsants was described. These derivatives integrate on the common structural scaffold the chemical fragments of well-known antiepileptic drugs such as ethosuximide, levetiracetam, and lacosamide. Such hybrids demonstrated effectiveness in two of the most widely used animal seizure models, namely, the maximal electroshock (MES) test and the psychomotor 6 Hz (32 mA) seizure models. Compound 33 showed the highest anticonvulsant activity in these models (ED MES = 79.5 mg/kg, ED 6 Hz = 22.4 mg/kg). Compound 33 was also found to be effective in pentylenetetrazole-induced seizure model (ED PTZ = 123.2 mg/kg). In addition, 33 demonstrated effectiveness by decreasing pain responses in formalin-induced tonic pain, in capsaicin-induced neurogenic pain, and notably in oxaliplatin-induced neuropathic pain in mice. The pharmacological data of stereoisomers of compound 33 revealed greater anticonvulsant activity by R(+)-33 enantiomer in both MES and 6 Hz seizure models.

Ionizing irradiation significantly affects hippocampal neurogenesis and is associated with cognitive impairments; these effects may be influenced by an altered microenvironment. Oxidative stress is a factor that has been shown to affect neurogenesis, and one of the protective pathways to deal with such stress involves the antioxidant enzyme superoxide dismutase (SOD). This study addressed how the deficiency of cytoplasmic (SOD1) or mitochondrial (SOD2) SOD impacts radiation effects on hippocampal neurogenesis. Wild type (WT), SOD 1 and SOD2 knock out (KO) mice received a single x-ray dose of 5 Gy, and quantification of the survival and phenotypic fate of newly generated cells in the dentate subgranular zone was performed 2 months later. Radiation exposure reduced neurogenesis in WT mice but had no apparent effect in KO mice, although baseline levels of neurogenesis were reduced in both SOD KO strains prior to irradiation. Additionally, there were marked and significant differences between WT and both KO strains in how irradiation affected newly generated astrocytes and activated microglia. The mechanism(s) responsible for these effects are not yet known, but a pilot in vitro study suggests a 'protective' effect of elevated levels of superoxide. Overall, these data suggest that under conditions of SOD deficiency, there is a common pathway dictating how neurogenesis is affected by ionizing irradiation.

Ionizing irradiation is an effective treatment for intracranial tumors but is limited by the potential adverse effects induced in surrounding normal brain. These effects can include cognitive impairments, and whereas the pathogenesis of such injury has not yet been definitively established, it may involve injury to the neurogenic cell population that exists in the dentate subgranular zone (SGZ) of the hippocampus. Understanding the issues surrounding this topic could have a major impact in the management of specific sequelae associated with cranial irradiation. Although radiation is now becoming a useful tool in investigations into the biology of neurogenesis, the perspective of this review is directed more toward the potential relevance of studying radiation and the stem/precursor cell response.

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In our recent studies, we identified compound N-benzyl-2-(2,5-dioxopyrrolidin-1-yl)propanamide (AS-1) as a broad-spectrum hybrid anticonvulsant which showed potent protection across the most important animal acute seizure models such as the maximal electroshock (MES) test, the subcutaneous pentylenetetrazole (s.c. PTZ) test, and the 6-Hz (32 mA) test in mice. Therefore, AS-1 may be recognized as a candidate for new anticonvulsant effective in different types of human epilepsy with a favorable safety margin profile determined in the rotarod test in mice. In the aim of further pharmacological evaluation of AS-1, in the current study, we examined its activity in the 6-Hz (44 mA) test, which is known as the model of drug-resistant epilepsy. Furthermore, we determined also the antiseizure activity in the kindling model of epilepsy induced by repeated injection of pentylenetetrazole (PTZ) in mice. As a result, AS-1 revealed relatively potent protection in the 6-Hz (44 mA) test, as well as delayed the progression of kindling induced by repeated injection of PTZ in mice at doses of 15 mg/kg, 30 mg/kg, and 60 mg/kg. Importantly, the isobolographic analysis showed that a combination of AS-1 and valproic acid (VPA) at the fixed ratio of 1:1 displayed a supra-additive (synergistic) interaction against PTZinduced seizures in mice. Thus, AS-1 may be potentially used in an add-on therapy with VPA. Moreover, incubation of zebrafish larvae with AS-1 substantially decreased the number, cumulative but not the mean duration of epileptiform-like events in electroencephalographic assay. Finally, the in vitro ADME-Tox studies revealed that AS-1 is characterized by a very good permeability in the parallel artificial membrane permeability assay test, excellent metabolic stability on human liver microsomes (HLMs), no significant influence on CYP3A4/CYP2D6 activity, and moderate inhibition of CYP2C9 in a concentration of 10 μM, as well as no hepatotoxic properties in HepG2 cells (concentration of 10 μM).