Anticonvulsant effects of focal and intracerebroventricular adenosine on penicillin-induced epileptiform activity in rats

Putative Role of Adenosine A1 Receptors in Exogenous Ketone Supplements-Evoked Anti-Epileptic Effect

Approximately 30% of patients with epilepsy are drug-refractory. There is an urgent need to elucidate the exact pathophysiology of different types of epilepsies and the mechanisms of action of both antiseizure medication and metabolic therapies to treat patients more effectively and safely. For example, it has been demonstrated that exogenous ketone supplement (EKS)-generated therapeutic ketosis, as a metabolic therapy, may decrease epileptic activity in both animal models and humans, but its exact mechanism of action is unknown. However, it was demonstrated that therapeutic ketosis, among others, can increase adenosine level, which may enhance activity of A1 adenosine receptors (A1Rs) in the brain. It has also been demonstrated previously that adenosine has anti-epileptic effect through A1Rs in different models of epilepsies. Thus, it is possible that (i) therapeutic ketosis generated by the administration of EKSs may exert its anti-epileptic effect through, among other mechanisms, increased adenosine level and A1R activity and that (ii) the enhanced activity of A1Rs may be a necessary anti-epileptic mechanism evoked by EKS administration-generated ketosis. Moreover, EKSs can evoke and maintain ketosis without severe side effects. These results also suggest that the therapeutic application of EKS-generated ketosis may be a promising opportunity to treat different types of epilepsies. In this literature review, we specifically focus on the putative role of A1Rs in the anti-epileptic effect of EKS-induced ketosis.

Ultraflexible endovascular probes for brain recording through micrometer-scale vasculature

Implantable neuroelectronic interfaces have enabled advances in both fundamental research and treatment of neurological diseases but traditional intracranial depth electrodes require invasive surgery to place and can disrupt neural networks during implantation. We developed an ultrasmall and flexible endovascular neural probe that can be implanted into sub-100-micrometer-scale blood vessels in the brains of rodents without damaging the brain or vasculature. In vivo electrophysiology recording of local field potentials and single-unit spikes have been selectively achieved in the cortex and olfactory bulb. Histology analysis of the tissue interface showed minimal immune response and long-term stability. This platform technology can be readily extended as both research tools and medical devices for the detection and intervention of neurological diseases.

Ultra-flexible endovascular probes for brain recording through micron-scale vasculature

Implantable neuroelectronic interfaces have enabled significant advances in both fundamental research and treatment of neurological diseases, yet traditional intracranial depth electrodes require invasive surgery to place and can disrupt the neural networks during implantation. To address these limitations, we have developed an ultra-small and flexible endovascular neural probe that can be implanted into small 100-micron scale blood vessels in the brains of rodents without damaging the brain or vasculature. The structure and mechanical properties of the flexible probes were designed to meet the key constraints for implantation into tortuous blood vessels inaccessible with existing techniques. In vivo electrophysiology recording of local field potentials and single-unit spikes has been selectively achieved in the cortex and the olfactory bulb. Histology analysis of the tissue interface showed minimal immune response and long-term stability. This platform technology can be readily extended as both research tools and medical devices for the detection and intervention of neurological diseases.

Recent advancements to enhance the therapeutic efficacy of antiepileptic drugs

Epilepsy is a multifactorial neurological disorder characterized by recurrent or unprovoked seizures. Over the past two decades, many new antiepileptic drugs (AEDs) were developed and are in use for the treatment of epilepsy. However, drug resistance, drug-drug interaction and adverse events are common problems associated with AEDs. Antiepileptic drugs must be used only if the ratio of efficacy, safety, and tolerability of treatment are favorable and outweigh the disadvantages including treatment costs. The application of novel drug delivery techniques could enhance the efficacy and reduce the toxicity of AEDs. These novel techniques aim to deliver an optimal concentration of the drug more specifically to the seizure focus or foci in the CNS without numerous side-effects. The purpose of this article is to review the recent advancements in antiepileptic treatment and summarize the novel modalities in the route of administration and drug delivery, including gene therapy, for effective treatment of epilepsy.

Attenuation of pentylenetrazole-induced acute status epilepticus in rats by adenosine involves inhibition of the mammalian target of rapamycin pathway

Adenosine (ADO) has been characterized as an endogenous anticonvulsant and alternative therapeutic drug, but its mechanism is not entirely clear. This study aimed to examine the relationship of ADO with the mammalian target of rapamycin (mTOR) in a Wistar rat model of pentylenetetrazole (PTZ)-induced acute status epilepticus. ADO (200 mg/kg) was administered intraperitoneally 30 min before PTZ (55-65 mg/kg) treatment, and Western blot assays and immunohistochemistry were performed 3 h after the onset of acute status epilepticus to detect phospho-TOR and the downstream target of mTOR, phospho-S6. The expression of these phosphoproteins in the hippocampus was significantly increased in PTZ-treated rats, but this increase was attenuated by the addition of ADO. To further verify a role for ADO in attenuating mTOR activity, we also evaluated its ability to suppress mTOR activity in normal rats that were not treated with PTZ. Our results suggest that ADO suppresses mTOR and S6 phosphorylation in normal rats and that this suppression can be reversed by the application of Compound C, an inhibitor of AMP-activated protein kinase, which functions as an upstream suppressor of the mTOR pathway. Thus, our results provide a novel antiepileptic mechanism for ADO in suppressing mTOR pathway activation upon PTZ-induced acute status epilepticus.

Increased cortical extracellular adenosine correlates with seizure termination

OBJECTIVE

Seizures are currently defined by their electrographic features. However, neuronal networks are intrinsically dependent on neurotransmitters of which little is known regarding their periictal dynamics. Evidence supports adenosine as having a prominent role in seizure termination, as its administration can terminate and reduce seizures in animal models. Furthermore, microdialysis studies in humans suggest that adenosine is elevated periictally, but the relationship to the seizure is obscured by its temporal measurement limitations. Because electrochemical techniques can provide vastly superior temporal resolution, we test the hypothesis that extracellular adenosine concentrations rise during seizure termination in an animal model and humans using electrochemistry.

METHODS

White farm swine (n = 45) were used in an acute cortical model of epilepsy, and 10 human epilepsy patients were studied during intraoperative electrocorticography (ECoG). Wireless Instantaneous Neurotransmitter Concentration Sensor (WINCS)-based fast scan cyclic voltammetry (FSCV) and fixed potential amperometry were obtained utilizing an adenosine-specific triangular waveform or biosensors, respectively.

RESULTS

Simultaneous ECoG and electrochemistry demonstrated an average adenosine increase of 260% compared to baseline, at 7.5 ± 16.9 s with amperometry (n = 75 events) and 2.6 ± 11.2 s with FSCV (n = 15 events) prior to electrographic seizure termination. In agreement with these animal data, adenosine elevation prior to seizure termination in a human patient utilizing FSCV was also seen.

SIGNIFICANCE

Simultaneous ECoG and electrochemical recording supports the hypothesis that adenosine rises prior to seizure termination, suggesting that adenosine itself may be responsible for seizure termination. Future work using intraoperative WINCS-based FSCV recording may help to elucidate the precise relationship between adenosine and seizure termination.

Purinergic signalling: from normal behaviour to pathological brain function

Purinergic neurotransmission, involving release of ATP as an efferent neurotransmitter was first proposed in 1972. Later, ATP was recognised as a cotransmitter in peripheral nerves and more recently as a cotransmitter with glutamate, noradrenaline, GABA, acetylcholine and dopamine in the CNS. Both ATP, together with some of its enzymatic breakdown products (ADP and adenosine) and uracil nucleotides are now recognised to act via P2X ion channels and P1 and P2Y G protein-coupled receptors, which are widely expressed in the brain. They mediate both fast signalling in neurotransmission and neuromodulation and long-term (trophic) signalling in cell proliferation, differentiation and death. Purinergic signalling is prominent in neurone-glial cell interactions. In this review we discuss first the evidence implicating purinergic signalling in normal behaviour, including learning and memory, sleep and arousal, locomotor activity and exploration, feeding behaviour and mood and motivation. Then we turn to the involvement of P1 and P2 receptors in pathological brain function; firstly in trauma, ischemia and stroke, then in neurodegenerative diseases, including Alzheimer's, Parkinson's and Huntington's, as well as multiple sclerosis and amyotrophic lateral sclerosis. Finally, the role of purinergic signalling in neuropsychiatric diseases (including schizophrenia), epilepsy, migraine, cognitive impairment and neuropathic pain will be considered.

Role of adenosine A2A receptor signaling in the nicotine-evoked attenuation of reflex cardiac sympathetic control

Baroreflex dysfunction contributes to increased cardiovascular risk in cigarette smokers. Given the importance of adenosinergic pathways in baroreflex control, the hypothesis was tested that defective central adenosinergic modulation of cardiac autonomic activity mediates the nicotine-baroreflex interaction. Baroreflex curves relating changes in heart rate (HR) to increases or decreases in blood pressure (BP) evoked by i.v. doses (1-16μg/kg) of phenylephrine (PE) and sodium nitroprusside (SNP), respectively, were constructed in conscious rats; slopes of the curves were taken as measures of baroreflex sensitivity (BRS). Nicotine (25 and 100μg/kg i.v.) dose-dependently reduced BRS(SNP) in contrast to no effect on BRS(PE). BRS(SNP) was also attenuated after intracisternal (i.c.) administration of nicotine. Similar reductions in BRS(SNP) were observed in rats pretreated with atropine or propranolol. The combined treatment with nicotine and atropine produced additive inhibitory effects on BRS, an effect that was not demonstrated upon concurrent exposure to nicotine and propranolol. BRS(SNP) was reduced in preparations treated with i.c. 8-phenyltheophylline (8-PT, nonselective adenosine receptor antagonist), 8-(3-Chlorostyryl) caffeine (CSC, A(2A) antagonist), or VUF5574 (A(3) antagonist). In contrast, BRS(SNP) was preserved after blockade of A(1) (DPCPX) or A(2B) (alloxazine) receptors or inhibition of adenosine uptake by dipyridamole. CSC or 8-PT abrogated the BRS(SNP) depressant effect of nicotine whereas other adenosinergic antagonists were without effect. Together, nicotine preferentially impairs reflex tachycardia via disruption of adenosine A(2A) receptor-mediated facilitation of reflex cardiac sympathoexcitation. Clinically, the attenuation by nicotine of compensatory sympathoexcitation may be detrimental in conditions such as hypothalamic defense response, posture changes, and ventricular rhythms.

Nanotechnology for delivery of drugs to the brain for epilepsy

Epilepsy results from aberrant electrical activity that can affect either a focal area or the entire brain. In treating epilepsy with drugs, the aim is to decrease seizure frequency and severity while minimizing toxicity to the brain and other tissues. Antiepileptic drugs (AEDs) are usually administered by oral and intravenous routes, but these drug treatments are not always effective. Drug access to the brain is severely limited by a number of biological factors, particularly the blood-brain barrier, which impedes the ability of AEDs to enter and remain in the brain. To improve the efficacy of AEDs, new drug delivery strategies are being developed; these methods fall into the three main categories: drug modification, blood-brain barrier modification, and direct drug delivery. Recently, all three methods have been improved through the use of drug-loaded nanoparticles.

Detailed spectral profile analysis of penicillin-induced epileptiform activity in anesthetized rats

Penicillin model is a widely used experimental model for epilepsy research. In the present study we aimed to portray a detailed spectral analysis of penicillin-induced epileptiform activity in comparison with basal brain activity in anesthetized Wistar rats. Male Wistar rats were anesthetized with i.p. urethane and connected to an electrocorticogram setup. After a short period of basal activity recording, epileptic focus was induced by injecting 400IU/2 microl penicillin-G potassium into the left lateral ventricle while the cortical activity was continuously recorded. Basal activity, latent period and the penicillin-induced epileptiform activity periods were then analyzed using both conventional methods and spectral analysis. Spectral analyses were conducted by dividing the whole spectrum into different frequency bands including delta, theta (slow and fast), alpha-sigma, beta (1 and 2) and gamma (1 and 2) bands. Our results show that the most affected frequency bands were delta, theta, beta-2 and gamma-2 bands during the epileptiform activity and there were marked differences in terms of spectral densities between three investigated episodes (basal activity, latent period and epileptiform activity). Our results may help to analyze novel data obtained using similar experimental models and the simple analysis method described here can be used in similar studies to investigate the basic neuronal mechanism of this or other types of experimental epilepsies.

Nitric oxide signaling pathway in the anti-convulsant effect of adenosine against pentylenetetrazol-induced seizure threshold in mice

The present study was performed to examine the involvement of nitric oxide (NO) signaling pathway in the anti-convulsant effect of adenosine against pentylenetetrazol seizure threshold in mice. Minimal dose of pentylenetetrazol (i.v., mg/kg) needed to induce different phases (myoclonic jerks, generalized clonus and tonic extension) of convulsions was recorded as an index of seizure threshold. Adenosine (100 or 200 mg/kg i.p.) produced a significant increase in the seizure threshold for convulsions induced by pentylenetetrazol i.v. infusion. The anti-convulsant effect of adenosine (100 mg/kg i.p.) was prevented by either L-arginine (50 mg/kg i.p.) [substrate for nitric oxide synthase (NOS)] or sodium nitroprusside (3 mg/kg i.p.) [a NO donor]. On the other hand, N(G)-nitro-L-arginine methyl ester (L-NAME, 2.5 mg/kg i.p.) [a non-selective NOS inhibitor] or 7-nitroindazole (7-NI) (25 mg/kg i.p.) [a specific neuronal nitric oxide synthase (nNOS) inhibitor] potentiated the anti-convulsant action of sub-effective dose of adenosine (50 mg/kg i.p.). Aminoguanidine (100 mg/kg i.p.) [a specific inducible NOS (iNOS) inhibitor] pre-treatment was not effective in inducing anti-convulsant effect with sub-effective dose of adenosine (50 mg/kg i.p.). Furthermore, the increase in seizure threshold elicited by adenosine (100 mg/kg i.p.) was also inhibited by concomitant administration with sildenafil (5 mg/kg i.p.) [phosphodiesterase 5 inhibitor]. In contrast, treatment of mice with methylene blue (1 mg/kg i.p.) [a direct inhibitor of both nitric oxide synthase (NOS) and soluble guanylate cyclase (sGC)] failed to induce anti-convulsant action with adenosine (50 mg/kg i.p.) against pentylenetetrazol i.v. infusion. The results demonstrated that the anti-convulsant action of adenosine in the pentylenetetrazol i.v. seizure threshold paradigm may possibly involve an interaction with the L-arginine-NO-cGMP pathway which may be secondary to the activation of adenosine receptors.

Effect of systemic administration of adenosine on brain adenosine levels in pentylenetetrazol-induced seizure threshold in mice

Adenosine is one of the inhibitory neuromodulators in the brain. The present study was carried out to elucidate the effect of adenosine on the pentylenetetrazol (PTZ)-induced seizure threshold in mice. Further, the study also correlated the brain adenosine levels in PTZ-induced seizure threshold. PTZ (0.5%, w/v) was infused through lateral tail vein of mouse at a constant rate of 0.3 ml/min until various stages of convulsions were observed. Minimal dose of PTZ (mg/kg) needed to induce different phases (myoclonic jerks, generalized clonus and tonic extensor) of PTZ convulsions were noted as an index of seizure threshold. Intravenous infusion of PTZ resulted in a significant decrease in brain adenosine levels. Systemic administration of adenosine (100 and 200 mg/kg, i.p.), 30 min before PTZ infusion, produced a dose-dependent elevation of PTZ-seizure threshold and also enhanced brain adenosine levels as compared to vehicle treated group. The behavioral and neurochemical observations demonstrated a relationship between adenosine levels in the brain and the PTZ seizure threshold in mice.