Ascorbic acid (AA; a.k.a. vitamin C) is well known for its cellular protection in environments of high oxidative stress. Even though physiological concentrations of AA in the brain are significant (0.2–10 mM), surprisingly little is known concerning the role of AA in synaptic neurotransmission under normal, non-disease state conditions. Here, we examined AA effects on neurotransmission, plasticity and spontaneous network activity (i.e., sharp waves and high frequency oscillations; SPW-HFOs), at the synapse between area 3 and 1 of the hippocampal cornu ammonis region (CA3 and CA1) using an extracellular multi-electrode array in in vitro mouse hippocampal slices. We found that AA decreased evoked field potentials (fEPSPs, IC₅₀ = 0.64 mM) without affecting V₅₀s or paired pulse facilitation indicating normal neurotransmitter release mechanisms. AA decreased presynaptic fiber volleys but did not change fiber volley-to-fEPSP coupling, suggesting reduced fEPSPs resulted from decreased fiber volleys. Inhibitory effects were also observed in CA1 stratum pyramidale where greater fEPSPs were required for population spikes in the presence of AA suggesting an impact on the intrinsic excitability of neurons. Other forms of synaptic plasticity and correlates of memory (i.e., short- and long-term potentiation) were also significantly reduced by AA as was the incidence of spontaneous SPW-HFOs. AA decreased SPW amplitude with a similar IC₅₀ as fEPSPs (0.65 mM). Overall, these results indicate that under normal conditions AA significantly regulates neurotransmission, plasticity, and network activity by limiting excitability. Thus, AA may participate in refinement of signal processing and memory formation, as well as protecting against pathologic excitability.

Higher therapeutic concentrations of the antiseizure medication carbamazepine (CBZ) are associated with cognitive side effects. Hippocampal sharp wave-ripple complexes (SPW-Rs) are proposed to participate in memory consolidation during periods of quiet and slow-wave sleep. SPW-Rs are generated in the CA3 region and are regulated by multiple synaptic inputs. Here, we used a multi-electrode array to determine the effects of CBZ on SPW-Rs and synaptic transmission at multiple hippocampal synapses. Our results demonstrate that CBZ reduced SPW-Rs at therapeutically relevant concentrations (IC₅₀ = 37 μM) and altered the core characteristics of ripples, important for information processing and consolidation. Moreover, CBZ inhibited neurotransmission in a synapse-specific manner. CBZ inhibition was most potent at the medial-perforant-path-to-CA3 and mossy-fiber-to-CA3 synapses (IC₅₀s ~ 30 and 60 μM, respectively) and least potent at medial-perforant-path-to-dentate granule cell synapses (IC₅₀ ~ 120 μM). These results suggest that the synapse-specific CBZ inhibition of neurotransmission reduces SPW-Rs and that the CBZ inhibition of SPW-Rs may underlie the cognitive impairments observed with therapeutic doses of CBZ.

Background/Objectives: Hyperexcitable neuronal activity associated with seizures may disrupt brain homeostasis resulting in abnormal glucose and nutrient management and metabolism. Specialized ependymal cells known as tanycytes line the third ventricle wall bridging communication between the brain, CSF, and blood. Despite their positional importance, whether tanycytes are impacted by epilepsy is unknown. Here, known protein markers of tanycytes were assessed in the Kcna1-null mouse model of genetic epilepsy with spontaneous recurrent seizures (SRS mice). Further, whether an anti-seizure metabolic ketogenic diet (KD), previously proven effective in SRS mice, restored protein levels was determined. Methods: Known tanycyte proteins, including glucose transporter 1 (GLUT1), glial fibrillary acidic protein (GFAP), and doublecortin (DCX, to determine potential neurogenic differences) were examined throughout the anterior–posterior axis of the third ventricle using immunofluorescent histochemistry. Results: Decreased GLUT1 immunoreactivity and elevated GFAP levels were found in the SRS cohorts. The number of neurogenic DCX-expressing cells did not differ. Two weeks of KD treatment reduced GFAP to WT levels. GLUT1 remained low in KD-treated SRS mice. Conclusions: These data suggest that the expression of proteins important for the structure and function of tanycytes is altered in preclinical epilepsy and is differentially restored with KD treatment. Whether tanycytes actively participate in the pathophysiology of epilepsy or associated comorbidities is an intriguing possibility given their integral role in brain homeostasis.

Cognitive impairment is a major comorbidity in temporal lobe epilepsy (TLE), yet its underlying pathophysiology remains poorly understood and current therapies provide minimal benefit. While oxidative stress has traditionally been viewed as a precursor to cell death-mediated cognitive decline, cell death is absent in many patients and preclinical models with memory impairment. Here, we tested whether excessive mitochondrial reactive oxygen species (ROS) actively contribute to memory impairment through mechanisms distinct from cell death. Using Kv1.1 knockout (KO) mice, a TLE model with mitochondrial respiratory chain complex I (MRCI) impairment, we found elevated hippocampal mitochondrial superoxide, impaired recognition memory, deficits in synaptic plasticity, and abnormal sharp wave–ripple oscillations. Applying the MRCI inhibitor rotenone to wild-type hippocampal slices caused increased superoxide and mirrored electrophysiology deficits. Both acute and sub-chronic treatment with the mitochondria-targeted antioxidant mitoquinone (MitoQ) reduced superoxide levels, rescued synaptic plasticity, restored network activity, and normalized memory performance in KO mice—without altering seizure frequency, severity, or neuronal excitability. Our results identify mitochondrial superoxide as a reversible driver of hippocampal dysfunction in epilepsy and demonstrate that mitochondria-targeted antioxidant therapy can restore cognition despite persistent seizures. This study provides proof-of-concept for novel treatments improving cognitive comorbidities in TLE beyond seizure control.

Background: Sudden unexpected death in epilepsy (SUDEP) causes significant mortality, affecting approximately 1 in 1000 people with epilepsy. Clinical and preclinical studies have identified severe seizures, bradycardia, apnea, severe postictal hypoxia, and sleep deficiency that emerge prior to SUDEP and thus may represent temporal biomarkers. The metabolic ketogenic diet (KD) therapy increases longevity in preclinical SUDEP models. Here, the hypothesis that KD therapy would determine whether the emergent sleep deficiency, bradycardia, apnea and/or hypoxemia persist as temporal biomarkers in preclinical SUDEP was tested. Methods: Kv1.1 knockout (KO) mice, a preclinical SUDEP model, and wild-type littermates were weaned onto a standard diet (SD) or treated with KD. In separate cohorts, approximately every 10 days, seizures and sleep architecture were recorded with electroencephalography–electromyography (EEG-EMG), heart rate was measured with noninvasive ECGenie, apnea was assessed with noninvasive airway mechanics, and blood O₂ saturation was measured with pulse oximetry. Data were aligned from the day of sudden death and analyzed retrospectively. Results: KD treatment significantly increased longevity and reduced seizures, reproducing previous studies. Using retrospective analyses from the day of death, KD treatment attenuated the emergence of (i) interictal intermittent bradycardia in the last 20 days of life, (ii) apnea, and (iii) intermittent hypoxemia in the last 10 days of life. In contrast, (iv) KD treatment did not rescue REM and NREM sleep deficiencies during the last 10 days of life. Conclusions: Our findings provide novel preclinical support for KD as a candidate therapy to attenuate seizure frequency and burden, bradycardia, apnea, and hypoxemia in SUDEP. In addition, sleep deficiency persisted as a potential temporal biomarker of preclinical SUDEP; however, causality will need to be tested in future studies.