Nigel C. Jones

Working memory relies on synchronised network oscillations involving complex interplay between pyramidal cells and GABAergic interneurons. NMDA receptor (NMDAR) antagonists influence both network oscillations and working memory, but the relationship between these two consequences has not been elucidated. This study aimed to determine the effect of NMDAR antagonists on network oscillations during a working memory task in mice, and the contribution of the GluN2D receptor subunit. After training wildtype (WT) and GluN2D-knockout (KO) mice on the Trial-Unique-Non-match to Location (TUNL) touchscreen task of working memory, recording electrodes were implanted into the prefrontal cortex (PFC) and hippocampus. Mice were challenged with either (S)-ketamine (30 mg/kg), (R)-ketamine (30 mg/kg), phencyclidine (PCP, 1 mg/kg), MK-801 (0.3 mg/kg) or saline prior to TUNL testing while simultaneous local field potential recordings were acquired. PCP disrupted working memory accuracy in WT (p = 0.001) but not GluN2D-KO mice (p = 0.79). MK-801 (p < 0.0001), (S)-ketamine (p < 0.0001) and (R)-ketamine (p = 0.007) disrupted working memory accuracy in both genotypes. PCP increased baseline hippocampal gamma (30-80 Hz) power in WT (p = 0.0015) but not GluN2D-KO mice (p = 0.92). All drugs increased baseline gamma power in the PFC in both genotypes (p < 0.05). Low gamma was induced during the maintenance phase of the TUNL task and increased when mice correctly completed the task (p = 0.024). This response-dependent increase in low gamma was disrupted by all drugs. In summary, PCP action involves the GluN2D subunit of the NMDA receptor in the hippocampus to alter baseline gamma power and working memory. Task-induced low gamma activity during maintenance aligns with task performance, and is disrupted by all NMDAR antagonists.

Objective: There is initial evidence that the common neurotropic parasite Toxoplasma gondii is a risk factor for the development of epilepsy; however, whether it influences epileptogenesis is unknown. This study investigated whether a pre-existing chronic T. gondii infection alters epileptogenesis and neuropathology in a mouse model of mesial temporal lobe epilepsy. Methods: Male and female C57BL/6Jax mice were intraperitoneally administered T. gondii tachyzoites or vehicle control. After 6 weeks, mice underwent self-sustained electrical status epilepticus (SSSE) through an implanted bipolar electrode, or a sham procedure. Continuous video-EEG recordings were taken 0-4- and 12-16-weeks post-SSSE to detect spontaneous seizures. Neuroinflammatory markers were assessed within 1-week post-SSSE, behavior testing was done at 8-12 weeks post-SSSE, and ex vivo MRI was conducted at 16 weeks post-SSSE. Results: Male T. gondii + SSSE mice had an increased incidence of epilepsy compared to Vehicle + SSSE, while female T. gondii + SSSE mice had worse seizure severity compared to non-infected SSSE mice. There was amplified neuroinflammation in both male and female T. gondii + SSSE mice compared to Vehicle + SSSE mice. T. gondii infection in the absence of SSSE also resulted in epilepsy and neuroinflammation. MRI revealed abnormalities in brain morphology in T. gondii + SSSE male and female mice and changes in white matter integrity in male T. gondii + SSSE mice, compared to both non-infected SSSE and T. gondii control mice. SSSE and T. gondii infection impacted anxiety and spatial memory in males, and anxiety and social behavior in females. Conclusions: These findings demonstrate that a chronic T. gondii infection can result in epilepsy, and that a pre-existing T. gondii infection exacerbates epileptogenesis following a brain insult, in mice.

Epilepsy continues to pose significant social and economic challenges on a global scale. Existing therapeutic approaches predominantly revolve around neurocentric mechanisms, and fail to control seizures in approximately one-third of patients. This underscores the pressing need for novel and complementary treatment approaches to address this gap. An increasing body of literature points to a role for glial cells, including microglia and astrocytes, in the pathogenesis of epilepsy. Notably, microglial cells, which serve as pivotal inflammatory mediators within the epileptic brain, have received increasing attention over recent years. These immune cells react to epileptogenic insults, regulate neuronal processes, and play diverse roles during the process of epilepsy development. Additionally, astrocytes, another integral non-neuronal brain cells, have garnered increasing recognition for their dynamic contributions to the pathophysiology of epilepsy. Their complex interactions with neurons and other glial cells involve modulating synaptic activity and neuronal excitability, thereby influencing the aberrant networks formed during epileptogenesis. This review explores the alterations in microglial and astrocytic function and their mechanisms of communication following an epileptogenic insult, examining their contribution to epilepsy development. By comprehensively studying these mechanisms, potential avenues could emerge for refining therapeutic strategies and ameliorating the impact of this complex neurological disease.

Objective: To test a hypothesis that acutely regulated plasma microRNAs (miRNAs) can serve as prognostic biomarkers for the development of post-traumatic epilepsy (PTE). Methods: Adult male Sprague-Dawley rats (n = 245) were randomized to lateral fluid-percussion-induced traumatic brain injury (TBI) or sham operation at three study sites (Finland, Australia, United States). Video-electroencephalography (vEEG) was performed on the seventh post-injury month to detect spontaneous seizures. Tail vein plasma collected 48 h after TBI for miRNA analysis was available from 209 vEEG monitored animals (45 sham, 164 TBI [32 with epilepsy]). Based on small RNA sequencing and previous data, the seven most promising brain enriched miRNAs (miR-183-5p, miR-323-3p, miR-434-3p, miR-9a-3p, miR-124-3p, miR-132-3p, and miR-212-3p) were validated by droplet digital polymerase chain reaction (ddPCR). Results: All seven plasma miRNAs differentiated between TBI and sham-operated rats. None of the seven miRNAs differentiated TBI rats that did and did not develop epilepsy (p > .05), or rats with ≥3 vs <3 seizures in a month (p > .05). However, miR-212-3p differentiated rats that developed epilepsy with seizure clusters (i.e., ≥3 seizures within 24 h) from those without seizure clusters (.34 ± .14 vs .60 ± .34, adj. p < .05) with an area under the curve (AUC) of .81 (95% confidence interval [CI] .65-.97, p < .01, 64% sensitivity, 95% specificity). Lack of elevation in miR-212-3p also differentiated rats that developed epilepsy with seizure clusters from all other TBI rats (n = 146, .34 ± .14 vs .55 ± .31, p < .01) with an AUC of .74 (95% CI .61-.87, p < .01, 82% sensitivity, 62% specificity). Glmnet analysis identified a combination of miR-212-3p and miR-132-3p as an optimal set to differentiate TBI rats with vs without seizure clusters (cross-validated AUC .75, 95% CI .47-.92, p < .05). Conclusions: miR-212-3p alone or in combination with miR-132-3p shows promise as a translational prognostic biomarker for the development of severe PTE with seizure clusters.