**1. Introduction**

Cannabidiol (CBD), the second most important component of *Cannabis sativa*, has no psychotropic effects and holds low toxicity in both humans and experimental animals. Thus, it has been studied in a wide dose range for potential use in various neurological and psychiatric diseases [1–5]. CBD has a weak affinity for cannabinoid receptors CB1 and CB2, acting as a negative allosteric modulator and inverse agonist, respectively [6]. Besides, it

**Citation:** Gáll, Z.; Kelemen, K.; Tolokán, A.; Zolcseak, I.; Sável, I.; Bod, R.; Ferencz, E.; Vancea, S.; Urkon, M.; Kolcsár, M. Anticonvulsant Action and Long-Term Effects of Chronic Cannabidiol Treatment in the Rat Pentylenetetrazole-Kindling Model of Epilepsy. *Biomedicines* **2022**, *10*, 1811. https://doi.org/10.3390/ biomedicines10081811

Academic Editor: Wesley M. Raup-Konsavage

Received: 20 June 2022 Accepted: 26 July 2022 Published: 28 July 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

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also has an antagonistic effect on GPR55 receptors, partial agonist action on 5-HT1A, and a negative allosteric modulatory effect on opioid receptors (μ and δ) [7]. Ion channels are also important targets for CBD, the most-studied being the transient receptor potential vanilloid type 1 (TRPV1) and ankyrin type 1 (TRPA1), and T-type voltage-gated calcium channels, which are involved in the regulation of Ca2+ signaling in the brain [3,8,9]. Therefore, CBD treatment could have numerous beneficial outcomes in neuropsychiatric illnesses; however, at present, the only approved indication for CBD is to treat seizures associated with childhood epilepsy syndromes like Lennox–Gastaut and Dravet syndromes [10,11].

CBD has a well-described anticonvulsant effect based on in vitro and in vivo models of epilepsy. In vitro, CBD reduced the amplitude and duration of epileptiform activities induced by low concentrations of magnesium and 4-aminopyridine but did not influence signal propagation [12]. CBD administered in a dose range of 40–360 mg/kg body weight ameliorated the seizures induced by electric currents or convulsive agents such as pilocarpine, penicillin, and pentylenetetrazole (PTZ) in rodents [12–17]. It should be noted that, when CBD is administered before seizure induction, in the acute phase, it reduces seizure severity, but there is little information about how CBD affects the processes that take place during the chronic phase or how it might modify the course of the disease [18,19]. It is important to consider that CBD has anti-inflammatory, antiapoptotic, and neuroprotective effects, possibly due to the existence of cannabinoid receptors both in glial cells and on the surface of B, NK, and T lymphocytes, as all of these cells are involved in neuroinflammation. Several studies confirmed that neuroinflammatory processes may play an important role in epileptogenesis, seizure worsening, or developing epilepsy-associated neuropsychiatric comorbidities (e.g., anxiety, depression, cognitive impairment) [20–26].

Epileptogenesis can be triggered by lesions of varying duration and intensity that, after a certain period of time, will cause spontaneous and recurrent seizures [27]. Between the initial insult and the emergence of spontaneous seizures, some adaptive changes occur at both the cellular and molecular levels, but these have not ye<sup>t</sup> been fully elucidated [28,29]. It is known that pentylenetetrazole (PTZ) can cause acute seizures in rats at higher doses, but when used at lower, subconvulsive doses, it can produce a chronic epileptic state characterized by a progressive decrease in the seizure threshold and a continuous increase in seizure severity [30]. Behavioral, biochemical, and structural changes in neural development can all be induced by PTZ kindling. Despite lacking spontaneous seizures, a seizure threshold decrease in kindled animals mimics epilepsy phenotypes through an imbalance between the excitatory and inhibitory neurotransmission systems. [31–33]. In addition, the PTZ-kindling model has been shown to reflect the cognitive impairments [34,35] and the characteristic cellular changes related to epilepsy in rats, such as astrogliosis [18] and microglia activation [36].

This study aimed to evaluate the effects of chronic CBD administration in the PTZkindling model of epilepsy in rats using behavioral tests, bioanalytical assay for brain exposure quantification, and immunohistochemistry to assess cellular alterations, and finally, to evaluate the role CBD plays in cognitive performance change.

#### **2. Materials and Methods**
