Effect of the closed-loop hippocampal low-frequency stimulation on seizure severity, learning, and memory in pilocarpine epilepsy rat model

Long-term hippocampal low-frequency stimulation alleviates focal seizures, memory deficits and synaptic pathology in epileptic mice

BACKGROUND

Mesial temporal lobe epilepsy (MTLE) is a prevalent form of focal epilepsy characterized by seizures originating from the hippocampus and adjacent regions. Neurostimulation presents an alternative for surgery-ineligible patients with intractable seizures. However, conventional approaches have limited efficacy and require refinement for better seizure control. While hippocampal low-frequency stimulation (LFS) has shown promising seizure reduction in animal studies and small clinical cohorts, its mechanisms, sex-specific outcomes, and long-term effects remain unknown.

OBJECTIVES

We aimed to identify the antiepileptic and cognitive outcomes and potential underlying mechanisms of long-term hippocampal LFS in chronically epileptic male and female mice.

METHODS

We used the intrahippocampal kainate mouse model replicating the features of MTLE: spontaneous seizures, hippocampal sclerosis, and memory deficits. During the chronic phase of epilepsy, we applied 1 Hz electrical LFS in the sclerotic hippocampus 6 h/day, four times/week for 5 weeks and examined its effects on epileptiform activity, spatial memory, and kainate-induced pathological features at cellular and synaptic levels.

RESULTS

Long-term hippocampal LFS consistently diminished focal seizures in epileptic male and female mice, with seizure reduction extending beyond the stimulation period. Additionally, long-term LFS relieved spatial memory deficits and reversed pathological modifications at perforant path-dentate granule cell synapses shortly after stimulation. LFS had no significant effect on secondarily generalized seizures, anxiety-like behaviour, neurogenesis, hippocampal sclerosis, or presynaptic vesicles in perforant path fibres.

CONCLUSION

These findings provide clinically relevant insights into the seizure type-specific effects of hippocampal LFS, which, alongside synaptic and behavioural improvements, could contribute to enhanced seizure control and quality of life in MTLE patients.

Modelling Epilepsy Associated Alzheimer's Disease Through Mitochondrial Complex-I Inhibition: Neurochemical and Therapeutic Perspectives

Alzheimer's disease (AD) is comorbid condition in epilepsy. Mitochondrial dysfunction serves as a common disease mechanism. This study aimed to develop a new mouse of epilepsy-associated AD by inhibiting mitochondrial complex-I and exploring neurochemistry to identify therapeutic targets. Swiss albino mice were divided into naïve, corneal kindled (CK), and rotenone corneal kindled (RCK) groups. CK underwent epileptogenesis by using 6 Hz corneal kindling model (15 mA, 20 V, 6-Hz, 3 s for 15 days), while RCK underwent both epileptogenesis and mitochondrial dysfunction via rotenone administration (2.5 mg/kg, i.p daily). RCK mice exhibited generalised tonic-clonic seizures, cognitive deficits, oxidative stress, and Aβ/tau deposition. Neurochemical analysis showed increased glutamate, kynurenine, and reduced GABA, taurine, monoamines, antioxidants, and acetylcholinesterase activity. The RCK model replicates construct and face validity of both epilepsy and AD, may serve as a new model to investigate shared disease mechanisms and associated altered neurotransmitter as therapeutic approach.

Photopharmacological activation of adenosine A1 receptor signaling suppresses seizures in a mouse model for temporal lobe epilepsy

Up to 30 % of epilepsy patients suffer from drug-resistant epilepsy (DRE). The search for innovative therapies is therefore important to close the existing treatment gap in these patients. The adenosinergic system possesses potent anticonvulsive effects, mainly through the adenosine A1 receptor (A1R). However, clinical application of A1R agonists is hindered by severe systemic side effects. To achieve local modulation of A1Rs, we employed a photopharmacological approach using a caged version of the A1R agonist N6-cyclopentyladenosine, termed cCPA. We performed the first in vivo study with intracerebroventricularly (ICV) administered cCPA to investigate the potential to photo-uncage and release sufficient amounts of cCPA in the hippocampus by local illumination in order to suppress hippocampal excitability and seizures in mice. We validated the presence of cCPA in the hippocampus after ICV injection and explored its pharmacokinetic profile and in vivo stability. Using hippocampal evoked potential recordings, we showed a reduction in hippocampal neurotransmission after photo-releasing CPA, similar to that obtained with ICV injection of CPA. Furthermore, in the intrahippocampal kainic acid mouse model for DRE, photo-release of CPA in the epileptic hippocampus resulted in a strong suppression of seizures. Finally, we demonstrated that intrahippocampal photo-release of CPA resulted in less impairment of motor performance in the rotarod test compared to ICV administration of CPA. These results provide a proof of concept for photopharmacological A1R modulation as an effective precision treatment for DRE.

Ultrasound-Induced Synchronized Neural Activities at 40 Hz and 200 Hz Entrained Corresponded Oscillations and Improve Alzheimer's Disease Memory

AIMS

Neurological diseases like Alzheimer's disease (AD) with cognitive deficits show impaired theta, gamma, and ripple bands. Restoring these oscillations may be crucial for rescuing cognitive functions. Low-intensity transcranial ultrasound stimulation (TUS), a noninvasive neuromodulation method, offers high spatial resolution and deep penetration. However, it remains unclear how 40 Hz and 200 Hz TUS may improve memory in AD by regulating hippocampal oscillations.

METHODS

We applied 40 Hz and 200 Hz TUS to the CA1 region of AD mice, performing memory assessments and CA1 electrophysiology recordings simultaneously.

RESULTS

Our results showed that both 40 Hz and 200 Hz TUS significantly improved memory performance in AD mice by targeting the dorsal hippocampus and increasing power in corresponding frequency bands. Specifically, 40 Hz TUS enhanced gamma and ripple bands, while 200 Hz TUS strongly affected both. This enhancement increased during stimulation and persisted 5 days poststimulation. Improved coupling between theta and gamma oscillations indicated better hippocampal coordination with other brain regions. Additionally, 40 Hz TUS raised sharp wave ripple (SPW-Rs) incidence, and 200 Hz TUS increased both SPW-R incidence and duration, contributing to memory improvement. Behavioral performance significantly improved with TUS at both frequencies.

CONCLUSION

Ultrasound-induced synchronized neural activities at 40 Hz and 200 Hz entrained corresponding oscillations and improved memory in Alzheimer's disease.

The role of neuromodulation in the management of drug-resistant epilepsy

Drug-resistant epilepsy (DRE) poses significant challenges in terms of effective management and seizure control. Neuromodulation techniques have emerged as promising solutions for individuals who are unresponsive to pharmacological treatments, especially for those who are not good surgical candidates for surgical resection or laser interstitial therapy (LiTT). Currently, there are three neuromodulation techniques that are FDA-approved for the management of DRE. These include vagus nerve stimulation (VNS), deep brain stimulation (DBS), and responsive neurostimulation (RNS). Device selection, optimal time, and DBS and RNS target selection can also be challenging. In general, the number and localizability of the epileptic foci, alongside the comorbidities manifested by the patients, substantially influence the selection process. In the past, the general axiom was that DBS and VNS can be used for generalized and localized focal seizures, while RNS is typically reserved for patients with one or two highly localized epileptic foci, especially if they are in eloquent areas of the brain. Nowadays, with the advance in our understanding of thalamic involvement in DRE, RNS is also very effective for general non-focal epilepsy. In this review, we will discuss the underlying mechanisms of action, patient selection criteria, and the evidence supporting the use of each technique. Additionally, we explore emerging technologies and novel approaches in neuromodulation, such as closed-loop systems. Moreover, we examine the challenges and limitations associated with neuromodulation therapies, including adverse effects, complications, and the need for further long-term studies. This comprehensive review aims to provide valuable insights on present and future use of neuromodulation.

Closed-loop Low-frequency stimulation: seizure reduction and more

Effect of the Closed-Loop Hippocampal Low-Frequency Stimulation on Seizure Severity, Learning, and Memory in Pilocarpine Epilepsy Rat Model Zare M, Rezaei M, Nazari M, Kosarmadar N, Faraz M, Barkley V, Shojaei A, Raoufy MR, Mirnajafi-Zadeh J. Effect of the closed-loop hippocampal low-frequency stimulation on seizure severity, learning, and memory in pilocarpine epilepsy rat model. CNS Neurosci Ther. 2024;30(3):e14656. doi:10.1111/cns.14656 Aims: In this study, the anticonvulsant action of closed-loop, low-frequency deep brain stimulation (DBS) was investigated. In addition, the changes in brain rhythms and functional connectivity of the hippocampus and prefrontal cortex were evaluated. Methods: Epilepsy was induced by pilocarpine in male Wistar rats. After the chronic phase, a tripolar electrode was implanted in the right ventral hippocampus and a monopolar electrode in medial prefrontal cortex (mPFC). Subjects’ spontaneous seizure behaviors were observed in continuous video recording, while the local field potentials (LFPs) were recorded simultaneously. In addition, spatial memory was evaluated by the Barnes maze test. Results: Applying hippocampal DBS, immediately after seizure detection in epileptic animals, reduced their seizure severity and duration, and improved their performance in Barnes maze test. DBS reduced the increment in power of delta, theta, and gamma waves in pre-ictal, ictal, and post-ictal periods. Meanwhile, DBS increased the post-ictal-to-pre-ictal ratio of theta band. DBS decreased delta and increased theta coherences, and also increased the post-ictal-to-pre-ictal ratio of coherence. In addition, DBS increased the hippocampal-mPFC coupling in pre-ictal period and decreased the coupling in the ictal and post-ictal periods. Conclusion: Applying closed-loop, low-frequency DBS at seizure onset reduced seizure severity and improved memory. In addition, the changes in power, coherence, and coupling of the LFP oscillations in the hippocampus and mPFC demonstrate low-frequency DBS efficacy as an antiepileptic treatment, returning LFPs to a seemingly non-seizure state in subjects that received DBS.