The effect of intracerebroventricular administration of orexin receptor type 2 antagonist on pentylenetetrazol-induced kindled seizures and anxiety in rats

Transient targeting of hypothalamic orexin neurons alleviates seizures in a mouse model of epilepsy

Lateral hypothalamic (LH) hypocretin/orexin neurons (HONs) control brain-wide electrical excitation. Abnormally high excitation produces epileptic seizures, which affect millions of people and need better treatments. HON population activity spikes from minute to minute, but the role of this in seizures is unknown. Here, we describe correlative and causal links between HON activity spikes and seizures. Applying temporally-targeted HON recordings and optogenetic silencing to a male mouse model of acute epilepsy, we found that pre-seizure HON activity predicts and controls the electrophysiology and behavioral pathology of subsequent seizures. No such links were detected for HON activity during seizures. Having thus defined the time window where HONs influence seizures, we targeted it with LH deep brain stimulation (DBS), which inhibited HON population activity, and produced seizure protection. Collectively, these results uncover a feature of brain activity linked to seizures, and demonstrate a proof-of-concept treatment that controls this feature and alleviates epilepsy.

Orexin receptor antagonists in the pathophysiology and treatment of sleep disorders and epilepsy

The correlation between sleep and epilepsy has been argued over the past decades among scientists. Although the similarities and contrasts between sleep and epilepsy had been considered, their intertwined nature was not revealed until the nineteenth century. Sleep is recognized as a recurring state of mind and body through alternating brain electrical activities. It is documented that sleep disorders are associated with epilepsy. The origin, suppression, and spread of seizures are affected by sleep. As such, in patients with epilepsy, sleep disorders are a frequent comorbidity. Meanwhile, orexin, a wake-promoting neuropeptide, provides a bidirectional effect on both sleep and epilepsy. Orexin and its cognate receptors, orexin receptor type 1 (OX1R) and type 2 (OX2R), orchestrate their effects by activating various downstream signaling pathways. Although orexin was considered a therapeutic target in insomnia shortly after its discovery, its potential usefulness for psychiatric disorders and epileptic seizures has been suggested in the pre-clinical studies. This review aimed to discuss whether the relationship between sleep, epilepsy, and orexin is clearly reciprocal.

Self-Assembled Lecithin-Chitosan Nanoparticles Improved Rotigotine Nose-to-Brain Delivery and Brain Targeting Efficiency

Rotigotine (RTG) is a non-ergoline dopamine agonist and an approved drug for treating Parkinson’s disease. However, its clinical use is limited due to various problems, viz. poor oral bioavailability (<1%), low aqueous solubility, and extensive first-pass metabolism. In this study, rotigotine-loaded lecithin-chitosan nanoparticles (RTG-LCNP) were formulated to enhance its nose-to-brain delivery. RTG-LCNP was prepared by self-assembly of chitosan and lecithin due to ionic interactions. The optimized RTG-LCNP had an average diameter of 108 nm with 14.43 ± 2.77% drug loading. RTG-LCNP exhibited spherical morphology and good storage stability. Intranasal RTG-LCNP improved the brain availability of RTG by 7.86 fold with a 3.84-fold increase in the peak brain drug concentration (Cmax(brain)) compared to intranasal drug suspensions. Further, the intranasal RTG-LCNP significantly reduced the peak plasma drug concentration (Cmax(plasma)) compared to intranasal RTG suspensions. The direct drug transport percentage (DTP (%)) of optimized RTG-LCNP was found to be 97.3%, which shows effective direct nose-to-brain drug uptake and good targeting efficiency. In conclusion, RTG-LCNP enhanced drug brain availability, showing the potential for clinical application.

The blockade of transient receptor potential ankyrin 1 (TRPA1) protects against PTZ-induced seizure

Treatment of epilepsy remains a major problem as some epileptic patients do not respond to the current therapeutics. Transient receptor potential ankyrin 1 (TRPA1) belongs to the TRP channels and has diverse physiological functions in the body. Considering its physiological properties, we aimed to evaluate its role in two experimental models of epilepsy, including pentylenetetrazol (PTZ)-induced acute seizure and PTZ-evoked kindling. Furthermore, the TRPA1 protein levels were assessed in the cerebral cortex, hippocampus, and cerebellum after seizure induction. Three groups of Wistar rats received acute intraperitoneal injection of pentylenetetrazol (PTZ, 85 mg/kg). The groups received intraventricular injections of vehicle (dimethyl sulfoxide, Tween 80, and sterile 0.9% saline), valproate (30 µg/rat), or HC030031 (TRPA1 antagonist, 14 µg/rat) before PTZ injection. In the PTZ-induced kindling model, PTZ was administrated 35 mg/kg every other day for 24 days. PTZ gradually provoked seizure-related behaviors. After experiments, the TRPA1 levels in the brain were assessed using western blot. The results showed that HC030031 reduced the median of seizure scores and S5 duration while increasing S2 and S5 latencies in acute and kindling models. The anticonvulsant effect of HC030031 was comparable with valproate as a standard anticonvulsant drug. Furthermore, induction of seizure, either acute or kindling, enhanced TRPA1 levels in the cerebral cortex, hippocampus, and cerebellum that were prevented by HC030031 or valproate administration. The results of this study showed that HC030031 as a TRPA1 receptor antagonist promoted a significant anticonvulsant effect comparable with valproate. Both drugs prevented TRPA1 upregulation during seizures. These findings imply that TRPA1 is a potential target in treating epilepsy.

Dual orexin antagonist normalized sleep homeostatic drive, enhanced GABAergic inhibition, and suppressed seizures after traumatic brain injury

STUDY OBJECTIVES

Traumatic brain injury (TBI) can result in posttraumatic epilepsy (PTE) and sleep disturbances. We hypothesized that treatment with sleep aids after TBI can ameliorate PTE.

METHODS

CD-1 mice underwent controlled cortical impact (CCI), sham injury, or no craniotomy. Sham and CCI groups underwent a monthlong daily treatment with sleep aids including a dual orexin antagonist (DORA-22) or THIP (gaboxadol) or a respective vehicle starting on the day of CCI. We performed continuous EEG (electroencephalography) recordings at week 1 and months 1, 2, and 3 for ~1 week each time. Seizure analysis occurred at all-time points and sleep analysis occurred in week 1 and month-1/2 in all groups. Subsets of CCI and sham groups were subjected to voltageclamp experiments in hippocampal slices to evaluate GABAergic synaptic inhibition.

RESULTS

DORA-22 treatment suppressed seizures in month 1-3 recordings. TBI reduced the amplitude and frequency of miniature inhibitory synaptic currents (mIPSCs) in dentate granule cells and these changes were rescued by DORA-22 treatment. Sleep analysis showed that DORA-22 increased nonrapid eye movement (NREM) sleep during lights-off whereas THIP increased REM sleep during lights-on in week 1. Both treatments displayed subtle changes in time spent in NREM or REM at month-1/2 as well. TBI not only increased normalized EEG delta power (NΔ) at week-1 and month-1 but also resulted in the loss of the homeostatic diurnal oscillation of NΔ, which was restored by DORA-22 but not THIP treatment.

CONCLUSIONS

Dual orexin antagonists may have a therapeutic potential in suppressing PTE potentially by enhancing GABAergic inhibition and impacting sleep homeostatic drive.

The Interaction Between Sleep and Epilepsy

PURPOSE OF REVIEW

To review the mutual interactions between sleep and epilepsy, including mechanisms of epileptogenesis, the relationship between sleep apnea and epilepsy, and potential strategies to treat seizures.

RECENT FINDINGS

Recent studies have highlighted the role of functional network systems underlying epileptiform activation in sleep in several epilepsy syndromes, including absence epilepsy, benign focal childhood epilepsy, and epileptic encephalopathy with spike-wave activation in sleep. Sleep disorders are common in epilepsy, and early recognition and treatment can improve seizure frequency and potentially reduce SUDEP risk. Additionally, epilepsy is associated with cyclical patterns, which has led to new treatment approaches including chronotherapy, seizure monitoring devices, and seizure forecasting. Adenosine kinase and orexin receptor antagonists are also promising new potential drug targets that could be used to treat seizures. Sleep and epilepsy have a bidirectional relationship that intersects with many aspects of clinical management. In this article, we identify new areas of research involving future therapeutic opportunities in the field of epilepsy.

Suvorexant, a Dual Orexin Receptor Antagonist, Protected Seizure through Interaction with GABAA and Glutamate Receptors

Orexin can increase neuronal excitability and induce epileptic activity. In this study, the effects of suvorexant (orexin receptor antagonist) on pentylenetetrazol (PTZ) and maximal electroshock (MES)-induced seizure were investigated. Mice were divided into 5 groups of six animals each including normal saline (10 mL/kg), diazepam (2 mg/kg), and suvorexant (50, 100 and 200 mg/kg) groups. In PTZ test, the latency to first minimal clonic seizure (MCS), latency to the first generalized tonic–clonic seizures (GTCS), total duration of seizure and also protection against mortality were evaluated. In MES, the hind limb tonic extension (HLTE) and the protection against mortality were recorded. In order to evaluate the role of GABA_A in anticonvulsant effect of suvorexant, flumazenil was used and to investigate the role of glutamate, the protein levels of AMPAR and NMDAR were measured in hippocampus by western blotting.  In PTZ model, suvorexant (200mg/kg) increased MCS and GTCS latencies. Suvorexant (100 and 200 mg/kg) decreased total duration of seizure compared to control group. In PTZ model, flumazenil inhibited the prolongation of seizure latency induced by suvorexant. In MES, the HLTE was decreased by suvorexant (100 and 200 mg/kg) and suvorexant was protected against mortality by 83.3%. Moreover, the protein levels of NMDAR and AMPAR were decreased by suvorexant.

Suvorexant exerted anticonvulsant activity and in addition to its inhibitory effect on orexin receptors, this effect may be mediated, at least partly, through interaction with GABA_A and glutamate receptors.

Bypassing the Blood-Brain Barrier: Direct Intracranial Drug Delivery in Epilepsies

Epilepsies are common chronic neurological diseases characterized by recurrent unprovoked seizures of central origin. The mainstay of treatment involves symptomatic suppression of seizures with systemically applied antiseizure drugs (ASDs). Systemic pharmacotherapies for epilepsies are facing two main challenges. First, adverse effects from (often life-long) systemic drug treatment are common, and second, about one-third of patients with epilepsy have seizures refractory to systemic pharmacotherapy. Especially the drug resistance in epilepsies remains an unmet clinical need despite the recent introduction of new ASDs. Apart from other hypotheses, epilepsy-induced alterations of the blood-brain barrier (BBB) are thought to prevent ASDs from entering the brain parenchyma in necessary amounts, thereby being involved in causing drug-resistant epilepsy. Although an invasive procedure, bypassing the BBB by targeted intracranial drug delivery is an attractive approach to circumvent BBB-associated drug resistance mechanisms and to lower the risk of systemic and neurologic adverse effects. Additionally, it offers the possibility of reaching higher local drug concentrations in appropriate target regions while minimizing them in other brain or peripheral areas, as well as using otherwise toxic drugs not suitable for systemic administration. In our review, we give an overview of experimental and clinical studies conducted on direct intracranial drug delivery in epilepsies. We also discuss challenges associated with intracranial pharmacotherapy for epilepsies.

Intrathecal and intracerebroventricular dopamine for Parkinson's disease

While CDD directly to the CSF can provide a constant delivery of the dopaminergic drug resulting in a more stable treatment effect without the limitations of traditional oral therapy without peripheral effects, it is still young and longitudinal data is lacking. These experimental therapies show promise and further investigation into their efficacy and safety could extend the frontiers for management of PD.

Decreased Cerebrospinal Fluid Orexin-A (Hypocretin-1) Concentrations in Patients after Generalized Convulsive Status Epilepticus

The effects of status epilepticus on the orexin/hypocretin system have yet to be investigated. The present study aimed to assay orexin-A/hypocretin-1 in the cerebrospinal fluid (CSF) of patients after generalized convulsive status epilepticus (GCSE). The study groups included 20 GCSE patients, 24 patients diagnosed with epilepsy but remaining in remission (ER), and 25 normal controls (CTR). Diagnostic lumbar puncture was performed in GCSE patients within 3–10 days of seizure cessation, as well as in the ER and to CTR subjects. Among all GCSE patients, the outcome was graded according to the modified Rankin Scale (mRS) at 1-month follow-up. Orexin-A levels were measured in unextracted CSF samples, using a commercial radioimmunoassay. There was a significant overall difference in median CSF orexin-A concentrations between GCSE, RE, and CTR patients (p < 0.001). The lowest concentrations were noted in the GCSE group compared to ER (p < 0.001) or CTR (p < 0.001). CSF orexin-A levels in GCSE patients inversely correlated with clinical outcome as assessed on the mRS at 1-month follow-up (r = −0.55; p = 0.1). In conclusion, CSF orexin-A levels may serve as a biomarker of increased turn-over of the peptide or post-SE neuronal damage, and implicates the orexin system in the pathogenesis of SE.

Revisiting the role of anxiety in the initial acquisition of two-way active avoidance: pharmacological, behavioural and neuroanatomical convergence

Two-way active avoidance (TWAA) acquisition constitutes a particular case of approach -avoidance conflict for laboratory rodents. The present article reviews behavioural, psychopharmacological and neuroanatomical evidence accumulated along more than fifty years that provides strong support to the contention that anxiety is critical in the transition from CS (conditioned stimulus)-induced freezing to escape/avoidance responses during the initial stages of TWAA acquisition. Thus, anxiolytic drugs of different types accelerate avoidance acquisition, anxiogenic drugs impair it, and avoidance during these initial acquisition stages is negatively associated with other typical measures of anxiety. In addition behavioural and developmental treatments that reduce or increase anxiety/stress respectively facilitate or impair TWAA acquisition. Finally, evidence for the regulation of TWAA acquisition by septo-hippocampal and amygdala-related mechanisms is discussed. Collectively, the reviewed evidence gives support to the initial acquisition of TWAA as a paradigm with considerable predictive and (in particular) construct validity as an approach-avoidance conflict-based rodent anxiety model.

The Effect of Orexin Receptor Antagonism on Quinpirole-Induced Compulsive-Like Checking Behavior in Rats

The orexinergic system supposedly plays a role in stress circuits for arousing behaviors during anxiety, suggesting that it may play a role also in neural circuits mediating the compulsive behavior characteristic of obsessive-compulsive disorder (OCD). This study aims to investigate the roles of the orexinergic system in the development of OCD behaviors, using as preparation the induction of compulsive checking by chronic treatment with the D2/D3 agonist, quinpirole. Repeated injections of quinpirole (0.5 mg/kg, twice per week for a total of 10 injections) were used to induce compulsive checking. In separate groups of rats, OX1R (SB334867-A; 10 μg i.c.v) and OX2R (TCS-OX2-29; 10 μg i.c.v) receptor antagonists were co-administered together with quinpirole. Checking behavior in a large open field was measured after the first, fifth, and tenth injections of the drugs. SB334867-A attenuated checking behavior and the level of anxiety. TCS-OX2-29 administration ameliorated anxiety but did not block the development of compulsive checking. Orexin 1 receptors seem to play a more critical role than orexin 2 receptors in the induction of compulsive checking. Considering that the quinpirole sensitization model of OCD involves activation of dopamine systems and sensitization to quinpirole, it is suggested that neural interaction between orexigenic and dopamine systems may be important in the pathogenesis of OCD.

Progressive cardiorespiratory dysfunction in Kv1.1 knockout mice may provide temporal biomarkers of pending sudden unexpected death in epilepsy (SUDEP): The contribution of orexin

OBJECTIVE

Immediately preceding sudden unexpected death in epilepsy (SUDEP), patients experienced a final generalized tonic-clonic seizure (GTCS), rapid ventilation, apnea, bradycardia, terminal apnea, and asystole. Whether a progressive pathophysiology develops and increases risk of SUDEP remains unknown. Here, we determined (a) heart rate, respiratory rate, and blood oxygen saturation (SaO₂ ) in low-risk and high-risk knockout (KO) mice; and (b) whether blocking receptors for orexin, a cardiorespiratory neuromodulator, influences cardiorespiratory function mice or longevity in high-risk KO mice.

METHODS

Heart rate and SaO₂ were determined noninvasively with ECGenie and pulse oximetry. Respiration was determined with noninvasive airway mechanics technology. The role of orexin was determined within subject following acute treatment with a dual orexin receptor antagonist (DORA, 100 mg/kg). The number of orexin neurons in the lateral hypothalamus was determined with immunohistochemistry.

RESULTS

Intermittent bradycardia was more prevalent in high-risk KO mice, an effect that may be the result of increased parasympathetic drive. High-risk KO mice had more orexin neurons in the lateral hypothalamus. Blocking of orexin receptors differentially influenced heart rate in KO, but not wild-type (WT) mice. When DORA administration increased heart rate, it also decreased heart rate variability, breathing frequency, and/or hypopnea-apnea. Blocking orexin receptors prevented the methacholine (MCh)-induced increase in breathing frequency in KO mice and reduced MCh-induced seizures, via a direct or indirect mechanism. DORA improved oxygen saturation in KO mice with intermittent hypoxia. Daily administration of DORA to high-risk KO mice increased longevity.

SIGNIFICANCE

High-risk KO mice have a unique cardiorespiratory phenotype that is characterized by progressive changes in five interdependent endpoints. Blocking of orexin receptors attenuates some of these endpoints and increases longevity, supporting the notion that windows of opportunity for intervention exist in this preclinical SUDEP model.