A new rapid kindling variant for induction of cortical epileptogenesis in freely moving rats

Abstract

Kindling, one of the most used models of experimental epilepsy is based on daily electrical stimulation in several brain structures. Unlike the classic or slow kindling protocols (SK), the rapid kindling types (RK) described until now require continuous stimulation at suprathreshold intensities applied directly to the same brain structure used for subsequent electrophysiological and immunohistochemical studies, usually the hippocampus. However, the cellular changes observed in these rapid protocols, such as astrogliosis and neuronal loss, could be due to experimental manipulation more than to epileptogenesis-related alterations. Here, we developed a new RK protocol in order to generate an improved model of temporal lobe epilepsy (TLE) which allows gradual progression of the epilepsy as well as obtaining an epileptic hippocampus, thus avoiding direct surgical manipulation and electric stimulation over this structure. This new protocol consists of basolateral amygdala (BLA) stimulation with 10 trains of biphasic pulses (10 s; 50 Hz) per day with 20 min-intervals, during 3 consecutive days, using a subconvulsive and subthreshold intensity, which guarantees tissue integrity. The progression of epileptic activity was evaluated in freely moving rats through electroencephalographic (EEG) recordings from cortex and amygdala, accompanied with synchronized video recordings. Moreover, we assessed the effectiveness of RK protocol and the establishment of epilepsy by evaluating cellular alterations of hippocampal slices from kindled rats. RK protocol induced convulsive states similar to SK protocols but in 3 days, with persistently lowered threshold to seizure induction and epileptogenic-dependent cellular changes in amygdala projection areas. We concluded that this novel RK protocol introduces a new variant of the chronic epileptogenesis models in freely moving rats, which is faster, highly reproducible and causes minimum cell damage with respect to that observed in other experimental models of epilepsy.

Cortical epileptogenesis of slowly kindled freely moving rats

“…The current intensity for obtaining ADT in our animals is consistent with previous findings [7,22]. The gradual reduction of ADT was described earlier [23] and it may be related to histological [24], neurochemical [25] changes or to microhemorrhages and the deposition of iron [26].…”

“…The gradual reduction of the level of ADT can actually be observed as a consequence of the electrode implantation, but this was observed only after longer periods [23,27]. As such in our case the reduction of ADT was a consequence of repetitive stimulation [22].…”

Enhanced astroglial Ca2+ signaling increases excitatory synaptic strength in the epileptic brain

“…To induce epileptogenesis we used a rapid kindling protocol (RK) developed in our laboratory, as described previously (Morales et al, ). Briefly explained, male Sprague‐Dawley rats (35 postnatal days) were anesthetized and subjected to stereotactic surgery procedures for electrode implantation.…”

Vitamin C Transporter (SVCT2) Distribution in Developing and Adult Brains

“…Moreover, our group has recently defined that SVCT2 protein is induced in reactive astrocytes in various in vivo pathological models that generate severe reactive astrogliosis. Specifically, such events involve neuroinflammation generated by intracerebroventricular injection of adenovirus-GFP or the bacterial enzyme, neuraminidase, mechanical damage of the brain cortex evaluated at 5 and 10 days post-injury, and astrogliosis observed in the brain cortex and hippocampus from "Kindled" rats, a widely used model of epilepsy at the mesial temporal lobe [16,17]. In vitro studies support these findings by showing that SVCT2 is induced in astrocytes that have been cultured for long periods and express markers of astrocytic activation [3].…”