Endocannabinoid CB1 receptors are involved in antiepileptogenic effect of low frequency electrical stimulation during perforant path kindling in rats

Involvement of dopamine D2 -like receptors in the antiepileptogenic effects of deep brain stimulation during kindling in rats

AIMS

Deep brain electrical stimulation (DBS), as a potential therapy for drug resistive epileptic patients, has inhibitory action on epileptogenesis. In the present investigation, the role of dopamine D₂ -like receptors in the antiepileptogenic action of DBS was studied.

METHODS

Seizures were induced in adult rats by stimulating the perforant path in a semi-rapid kindling method. Five minutes after the last kindling stimulation, daily DBS was applied to the perforant path at the pattern of low frequency stimulation (LFS; 1 Hz; pulse duration: 0.1 ms; intensity: 50-150 μA; 4 trains of 200 pulses at 5 min intervals). Sulpiride (10 μg/1 μl, i.c.v.), a selective dopamine D₂ -like receptor antagonist, was administered prior to the daily LFS application.

RESULTS

Kindling stimulations increased cumulative daily behavioral seizure stages, daily afterdischarge duration (dADD), and population spike amplitude (PS) in dentate gyrus following perforant path stimulation, while applying LFS decreased the kindled seizures' parameters. In addition, kindling potentiated the early (at 10-50 ms inter-pulse interval) and late (at 150-1000 ms inter-pulse interval) paired-pulse inhibition and decreased the paired-pulse facilitation (at 70-100 ms inter-pulse interval). These effects were also inhibited by applying LFS. All inhibitory effects of LFS on kindling procedure were prevented by sulpiride administration.

CONCLUSION

These data may suggest that LFS exerts its preventive effect on kindling development, at least partly, through the receptors on which sulpiride acts which are mainly dopamine D₂ -like (including D₂ , D₃ , and D₄ ) receptors.

Neuroplastic alterations in cannabinoid receptors type 1 (CB1) in animal models of epileptic seizures

Currently, there is an urgent need to better comprehend neuroplastic alterations in cannabinoid receptors type 1 (CB1) and to understand the biological meaning of these alterations in epileptic disorders. The present study reviewed neuroplastic changes in CB1 distribution, expression, and functionality in animal models of epileptic seizures. Neuroplastic alterations in CB1 were consistently observed in chemical, genetic, electrical, and febrile seizure models. Most studies assessed changes in hippocampal and cortical CB1, while thalamic, hypothalamic, and brainstem nuclei were rarely investigated. Additionally, the relationship between CB1 alteration and the control of brain excitability through modulation of specific neuronal networks, such as striatonigral, nigrotectal and thalamocortical pathways, and inhibitory projections to hippocampal pyramidal neurons, were all presented and discussed in the present review. Neuroplastic alterations in CB1 detected in animal models of epilepsy may reflect two different scenarios: (1) endogenous adaptations aimed to control neuronal hyperexcitability in epilepsy or (2) pathological alterations that facilitate neuronal hyperexcitability. Additionally, a better comprehension of neuroplastic and functional alterations in CB1 can improve pharmacological therapies for epilepsies and their comorbidities.

Group I metabotropic glutamate receptors contribute to the antiepileptic effect of electrical stimulation in hippocampal CA1 pyramidal neurons

Low-frequency deep brain stimulation (LFS) inhibits neuronal hyperexcitability during epilepsy. Accordingly, the use of LFS as a treatment method for patients with drug-resistant epilepsy has been proposed. However, the LFS antiepileptic mechanisms are not fully understood. Here, the role of metabotropic glutamate receptors group I (mGluR I) in LFS inhibitory action on epileptiform activity (EA) was investigated. EA was induced by increasing the K⁺ concentration in artificial cerebrospinal fluid (ACSF) up to 12 mM in hippocampal slices of male Wistar rats. LFS (1 Hz, 900 pulses) was delivered to the bundles of Schaffer collaterals at the beginning of EA. The excitability of CA1 pyramidal neurons was assayed by intracellular whole-cell recording. Applying LFS reduced the firing frequency during EA and substantially moved the membrane potential toward repolarization after a high-K⁺ ACSF washout. In addition, LFS attenuated the EA-generated neuronal hyperexcitability. A blockade of both mGluR 1 and mGluR 5 prevented the inhibitory action of LFS on EA-generated neuronal hyperexcitability. Activation of mGluR I mimicked the LFS effects and had similar inhibitory action on excitability of CA1 pyramidal neurons following EA. However, mGluR I agonist's antiepileptic action was not as strong as LFS. The observed LFS effects were significantly attenuated in the presence of a PKC inhibitor. Altogether, the LFS' inhibitory action on neuronal hyperexcitability following EA relies, in part, on the activity of mGluR I and a PKC-related signaling pathway.

Low-Frequency Stimulation Prevents Kindling-Induced Impairment through the Activation of the Endocannabinoid System

Background

Cannabinoid system affects memory and has anticonvulsant effects in epileptic models. In the current study, the role of cannabinoid 1 (CB1) receptors was investigated in amelioration of the effects of low-frequency stimulation (LFS) on learning and memory impairments in kindled rats.

Methods

Electrical stimulation of the hippocampal CA1 area was employed to kindle the animals. LFS was applied to the CA1 area in four trials following the last kindling stimulation. One group of animals received intraperitoneal injection of AM251 (0.1 μg/rat), a CB1 receptor antagonist, before the LFS application. Similarly, CB1 agonist WIN55-212-2 (WIN) was administrated to another group prior to LFS. The Morris water maze (MWM) and the novel object recognition (NOR) tests were executed 48 h after the last kindling stimulation to assess learning and memory.

Results

Applying LFS in the kindled+LFS group restored learning and memory impairments in the kindled rats. There was a significant difference between the kindled and the kindled+LFS groups in learning and memory. The application of AM251 reduced the LFS effects significantly. Adversely, WIN acted similarly to LFS and alleviated learning and memory deficits in the kindled+WIN group. In addition, WIN did not counteract the LFS enhancing effects in the KLFS+WIN group.

Conclusions

Improving effects of LFS on learning and memory impairments are mediated through the activation of the endocannabinoid (ECB) system.

The role of α adrenergic receptors in mediating the inhibitory effect of electrical brain stimulation on epileptiform activity in rat hippocampal slices

The Inhibitory effect of electrical low-frequency stimulation (LFS) on neuronal excitability and seizure occurrence has been indicated in experimental models, but the precise mechanism has not established. This investigation was intended to figure out the role of α₁ and α₂ adrenergic receptors in LFS' inhibitory effect on neuronal excitability. Epileptiform activity induced in an in vitro rat hippocampal slice preparation by high K⁺ ACSF and LFS (900 square wave pulses at 1 Hz) was administered at the beginning of epileptiform activity to the Schaffer collaterals. In CA1 pyramidal neurons, the electrophysiological properties were measured at the baseline, before high K⁺ ACSF washout, and at 15 min after high K⁺ ACSF washout using whole-cell, patch-clamp recording. Results indicated that after high K⁺ ACSF washout, prazosine (10 µM; α₁ adrenergic receptor antagonist) and yohimbine (5 µM; α₂ adrenergic receptor antagonist) suppressed the LFS' effect of reducing rheobase current and utilization time following depolarizing ramp current, the latency to the first spike following a depolarizing current and latency to the first rebound action potential following hyperpolarizing current pulses. Thus, it may be proposed that LFS' inhibitory action on the neuronal hyperexcitability, in some way, is mediated by α₁ and α₂ adrenergic receptors.

Long-Term Effects of Hippocampal Low-Frequency Stimulation on Pro-Inflammatory Factors and Astrocytes Activity in Kindled Rats

Objective

Epilepsy is accompanied by inflammation, and the anti-inflammatory agents may have anti-seizure effects. In this investigation, the effect of deep brain stimulation, as a potential therapeutic approach in epileptic patients, was investigated on seizure-induced inflammatory factors.

Materials and Methods

In the present experimental study, rats were kindled by chronic administration of pentylenetetrazol (PTZ; 34 mg/Kg). The animals were divided into intact, sham, low-frequency deep brain stimulation (LFS), kindled, and kindled +LFS groups. In kindled+LFS and LFS groups, animals received four trains of intra-hippocampal low-frequency deep brain stimulation (LFS) at 20 minutes, 6, 24, and 30 hours after the last PTZ injection. Each train of LFS contained 200 pulses at 1 Hz, 200 µA, and 0.1 ms pulse width. One week after the last PTZ injection, the Y-maze test was run, and then the rats’ brains were removed, and hippocampal samples were extracted for molecular assessments. The gene expression of two pro-inflammatory factors [interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α)], and glial fibrillary acidic protein (GFAP) immunoreactivity (as a biological marker of astrocytes reactivation) were evaluated.

Results

Obtained results showed a significant increase in the expression of of interleukin-6 (IL-6), tumor necrosis factor (TNF)-α, and GFAP at one-week post kindling seizures. The application of LFS had a long-lasting effect and restored all of the measured changes toward normal values. These effects were gone along with the LFS improving the effect on working memory in kindled animals.

Conclusion

The anti-inflammatory action of LFS may have a role in its long-lasting improving effects on seizure-induced cognitive disorders.

The role of dopamine D2-like receptors in a "depotentiation-like effect" of deep brain stimulation in kindled rats

The mechanisms involved in the anti-seizure effects of low-frequency stimulation (LFS) have not been completely determined. However, G_i-protein-coupled receptors, including D₂-like receptors, may have a role in mediating these effects. In the present study, the role of D₂-like receptors in LFS' anti-seizure action was investigated. Rats were kindled with semi-rapid (6 stimulations per day), electrical stimulation of the hippocampal CA1 area. In LFS-treated groups, subjects received four trials of LFS at 5 min, 6 h, 24 h, and 30 h following the last kindling stimulation. Each LFS set occurred at 5 min intervals, and consisted of 4 trains. Each train contained 200, 0/1 ms long, monophasic square wave pulses at 1 Hz. Haloperidol (D₂-like receptors antagonist, 2 µm) and/or bromocriptine (D₂-like receptors agonist 2 µg/µlit) were microinjected into the lateral ventricle immediately after the last kindling, before applying LFS. Obtained results showed that applying LFS in fully-kindled subjects led to a depotentiation-like decrease in kindling-induced potentiation and reduced the amplitude and rise slope of excitatory and inhibitory post-synaptic currents in whole-cell recordings from CA1 pyramidal neurons. In addition, LFS restored the kindling-induced, spatial learning and memory impairments in the Barnes maze test. A D₂-like receptor antagonist inhibited these effects of LFS, while a D₂-like receptor agonist mimicked these effects. In conclusion, a depotentiation-like mechanism may be involved in restoring LFS' effects on learning and memory, and synaptic plasticity. These effects depend on D₂-like receptors activity.

Intrahippocampal 5-HT1A receptor antagonist inhibits the improving effect of low-frequency stimulation on memory impairment in kindled rats

In addition to its anticonvulsant effect, low frequency stimulation (LFS) improves learning and memory in kindled animals. In the present study, the role of 5-HT_1A receptors in mediating LFS' improving effect on spatial learning and memory was investigated in amygdala-kindled rats. Amygdala kindling was conducted in a semi-rapid kindling stimulations (12 stimulations per day) in male Wistar rats. LFS (4 trains of 0.1 ms pulse duration at 1 Hz, 200 pulses, 50-150 μA, at 5 min intervals) was applied after termination of kindling stimulations. NAD-299 (a selective 5-HT_1A receptor antagonist; 2.5 and 5 μg/μl) was microinjected into the hippocampal CA1 before applying LFS. The Morris water maze, and novel object recognition tests were conducted after the last kindling stimulation. Hippocampal samples were also prepared, and 5-HT_1A receptor gene expression levels were assessed using quantitative RT-PCR. In kindled animals, LFS reduced impairments in spatial learning and memory in the Morris water maze and novel object recognition tests. Microinjection of NAD doses of 5 μg/μl reduced the effects of LFS on learning and memory. The gene expression level of 5-HT_1A receptors increased significantly in the hippocampus of amygdala-kindled rats. However, LFS applied after kindling stimulations inhibited this effect. It seems that activation of 5-HT_1A receptors in the CA1 field is necessary for LFS' improving effects on spatial learning and memory in kindled animals; although surprisingly, LFS application prevented the elevation in gene expression of 5-HT_1A receptors in kindled animals.