Electrical Stimulation Of Perforant Path Research Articles

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

IntroductionAdministration of low-frequency electrical stimulation (LFS) at the kindling site has an antiepileptogenic effect. In the present study, we investigated the role of cannabinoid receptors type 1 (CB1) in mediating the inhibitory effects of LFS on the development of perforant path kindled seizures. MethodsFor seizure generation, rats were kindled by electrical stimulation of perforant path in semi-rapid kindling manner (12 stimulations per day at 10 min intervals at afterdischarge threshold intensity).To determine the effect of LFS (0.1 ms pulse duration at 1 Hz, 800 pulses) on seizure generation, LFS was applied to the perforant path 5 min after the last kindling stimulation daily. AM281, a CB1 receptor antagonist, was microinjected into the lateral ventricle immediately after the last kindling stimulation (before LFS application) at the doses of 0.5 and 2 μg/μl during kindling procedure. The expression of cannabinoid receptors in the dentate gyrus was also investigated using immunohistochemistry. ResultsApplication of LFS had inhibitory effect on development of kindled seizures (kindling rate). Microinjection of AM281 (0.5 μg/μl) immediately after the last kindling stimulation (before LFS application) reduced the inhibitory effect of LFS on the kindling rate and suppressed the effects of LFS on potentiation (increasing the magnitude) of both population spike amplitude and population excitatory postsynaptic potential slope during kindling acquisition. AM281 pretreatment also prevented the effects of LFS on kindling-induced increase in early and late paired pulse depression. The higher dose of AM281 (2 μg/μl) failed to exert the effects observed with its lower dose (0.5 μg/μl). In addition, there was a decreased CB1 receptors immunostaining in kindled animals compared to control. However, application of LFS following kindling stimulations led to overexpression of CB1 receptors in the dentate gyrus. ConclusionObtained results showed that activation of overexpressed cannabinoid CB1 receptors by endogenous cannabinoids may have a role in mediating the inhibitory effect of LFS on perforant path kindled seizures.

Field potential recording from rat hippocampus provides a functional evaluation method for assessing demyelination and myelin repair

Objectives: In multiple sclerosis (MS) demyelination occurs in both white and gray matter. Here we introduce an electrophysiological approach for studying functional demyelination and myelin repair in rat hippocampus, a gray matter structure, which is frequently affected in patients suffering from MS.Methods: Using a stereotaxic approach, bipolar stimulating and monopolar recording electrodes were respectively implanted into the perforant path and the dentate gyrus of the hippocampus of the adult male Sprague-Dawley rats weighing 280–320 g. Animals received intra-hippocampal injections of saline or lysolecithin (LPC) and afterward, changes in the parameters of field potentials recorded from the dentate gyrus granular cells in response to electrical stimulation of perforant path were investigated on days 7, 14, and 28, post-lesion. Changes in the electrophysiological parameters were compared with changes in the molecular markers of myelination (myelin basic protein, MBP) and repairing cells (Olig2).Results: On day 2, a significant decrease in the slope of the population excitatory postsynaptic potential (pEPSP) and the amplitude of population spike (PS) was observed. However, during days 7–28, these parameters were increased toward control. Decreased expression of MBP and increased expression of Olig2 were observed on days 2 and 7 while the expression levels were partially reversed toward control on day 28.Discussion: Our data showed the efficacy of field potential recording for studying demyelination and endogenous myelin repair in hippocampus. Changes in electrophysiological parameters were concomitant with the level of molecular markers. This recording method provides an opportunity for functional evaluation of myelin loss and repair and the effect of potential therapies.

Regulation of limbic status epilepticus by hippocampal galanin type 1 and type 2 receptors

It has been well established that galanin is a potent endogenous anticonvulsant peptide. However, the role of galanin receptor subtypes in mediating anticonvulsant effects of the peptide is poorly understood. Using pharmacological, transgenic and antisense approaches, we examined the involvement of galanin receptors GalR1 and GalR2 in regulating seizures and associated neuronal degenerative changes. In the rat model of status epilepticus (SE) induced by electrical stimulation of perforant path, in vivo uncoupling of G protein coupled receptors (GPCR) through intrahippocampal administration of pertussis toxin (PTX) facilitated the initiation of SE, and increased the severity of the established SE. Injection of a non-selective GalR1/GalR2 agonist galanin (1-29) and a preferential GalR2 agonist galanin (2-11) into the hippocampus of PTX-pretreated rats revealed that while during early phase of SE galanin inhibited seizures predominantly through GalR1, GalR2 mediated anticonvulsant effects of the peptide during advanced stage of SE. GalR1 knockout mice showed increased severity of both pilocarpine- and perforant path stimulation -induced SE, compared to wild type (WT) littermates. In GalR1 knockout animals SE led to more severe and wider-spread hippocampal injury, than in WT. Focal downregulation of GalR2, which had been achieved in rats by intrahippocampal infusion of anti-GalR2 peptide nucleic acid (PNA) antisense, significantly increased the severity of perforant path stimulation- induced SE. Downregulation of GalR2 led to mild injury to hilar interneurons and potentiated seizure-induced hippocampal damage. In conclusion, both GalR1 and GalR2 mediate anticonvulsant effects of galanin. GalR1 and GalR2 exhibit differential effects on the initiation and the maintenance phases of SE. Activation of both galanin receptor subtypes exerts neuroprotective effects under conditions of excitotoxic injury.

Kindling induced mossy fiber sprouting has no functional significance in developing seizure discharges in rats

It is reported that chronic electrical stimulation of perforant path (PP) produces mossy fiber sprouting in dentate granule cells and as a result new recurrent excitatory circuits are formed. It has been assumed that the circuits are responsible for the well-known lowering in the threshold required to generate seizure discharges by the electrical stimulation. The assumption was tested in the present investigation. Current source density analysis of the field potential in the dentate gyrus was carried out in control (n = 8) and kindled (n = 10) rats under pentobarbital anesthesia during seizure discharges. The field potential was produced by stimulating the PP and recorded simultaneously from 10 sites which were 50 microns apart from each other. The field potential consisted of a monosynaptic excitatory postsynaptic field current (EPSC) in the middle molecular layer followed by a population spike current (PSC). In the kindled rats, following the EPSC and PSC, a late sink appeared in the supragranular layer (SGL). The amplitude of the SGL late-sink showed a positive correlation with the density of Timm granules (r = 0.76). The latency difference between the onset of PSC and that of the SGL late-sink ranged from 0.5 to 1.5 ms. This suggested the possibility that the SGL late-sink is produced via the recurrent excitatory circuit newly formed by mossy fiber sprouting. The SGL late-sink, however, evoked no further firing in dentate granule cells. During 5 Hz PP stimulation for 10 s, the amplitude of SGL late-sink increased gradually at first, but later it decreased gradually and disappeared before seizure discharges produced. Accordingly, there was no evidence suggesting that the new recurrent excitatory circuit played any role in producing seizure discharges. During seizure discharges, the EPSC resembling the SGL late-sink appeared spontaneously only in the SGL and seemed to initiate repetitive synchronized-firing of granule cells in one of four kindled rats. The number of burst discharges and the duration of seizure discharges with the late sink, however, were not significantly different from those of seizure discharges without such a late skin. These results suggest that the newly formed recurrent circuit plays no essential role in decreasing the threshold required to generate seizure discharges or in developing them.