6 Hz corneal kindling in mice triggers neurobehavioral comorbidities accompanied by relevant changes in c‐Fos immunoreactivity throughout the brain

Abstract

SummaryObjective: Besides seizures, patients with epilepsy are affected by a variety of cognitive and psychiatric comorbidities that further impair their quality of life. The present study provides an in-depth characterization of the behavioral alterations induced by 6 Hz corneal kindling. Furthermore, we correlate these behavioral changes to alterations in c-Fos protein expression throughout the brain following kindling. Methods: Adolescent male Naval Medical Research Institute (NMRI) mice were kindled via repetitive subconvulsive 6 Hz corneal stimulations until they reached the fully kindled state (defined as 10 consecutive generalized seizures). Afterwards we performed an elaborate battery of behavioral tests and we evaluated cFos expression throughout the brain using immunohistochemistry. Results: Fully kindled mice display an abnormal behavioral phenotype, characterized by basal and amphetamine-induced hyperlocomotion, anhedonia, social withdrawal, and deficits in short-and long-term memory. Moreover, 6 Hz corneal kindling enhances c-Fos immunoreactivity in the visual, parahippocampal, and motor cortices and the limbic system, whereas c-Fos + cells are decreased in the orbital cortex of fully kindled mice. Significance: The behavioral outcomes of 6 Hz corneal kindling cluster into 3 main categories: positive symptoms, negative symptoms, and cognitive impairment. These symptoms are accompanied by c-Fos activation in relevant brain regions once the fully kindled state is established. Based on the face validity of this model, we speculate that 6 Hz corneal kindling can be used to model not only pharmacoresistant limbic seizures, but also several neurobehavioral comorbidities that affect patients with epilepsy.

Lamotrigine‐resistant corneal‐kindled mice: A model of pharmacoresistant partial epilepsy for moderate‐throughput drug discovery

“…A history of chronic seizures, regardless of LTG sensitivity, also promoted increased anxiety‐like behavior as measured by the extent of time a mouse spent in the center of an OF (Figure D). Although the small group size of the sham‐kindled mice is a limitation of the present behavioral study, these data support the further detailed evaluation of behavioral phenotypes in VEH‐ and LTG‐kindled mice relative to sham‐kindled animals in more sensitive behavioral assays of anxiety‐like behavior (eg, elevated plus maze). Nonetheless, these data are consistent with findings from Albertini and colleagues in the 6 Hz CKM and support the conclusion that kindled rodents are a clinically useful model of epilepsy for ASD identification.…”

“…8,12 Indeed, CKM do exhibit pathophysiology consistent with human epilepsy, 25 including cognitive deficits, 23 neuroinflammation, 24 and behavioral disturbances. 39 Both kindling treatment groups (VEH-and LTG-kindled mice) presently demonstrated behavioral hyperexcitability ( Figure 4A,B) regardless of ASD sensitivity, an effect that was not observed in sham-kindled mice. A history of chronic seizures, regardless of LTG sensitivity, also promoted increased anxiety-like behavior as measured by the extent of time a mouse spent in the center of an OF (Figure 4D).…”

“…Nonetheless, in 2015, the NINDS‐sponsored ETSP placed a prominent emphasis on the 60 Hz CKM and LTG‐resistant amygdala‐kindled rat for ASD identification and differentiation, respectively . Indeed, CKM do exhibit pathophysiology consistent with human epilepsy, including cognitive deficits, neuroinflammation, and behavioral disturbances . Both kindling treatment groups (VEH‐ and LTG‐kindled mice) presently demonstrated behavioral hyperexcitability (Figure A,B) regardless of ASD sensitivity, an effect that was not observed in sham‐kindled mice.…”

A companion to the preclinical common data elements for pharmacologic studies in animal models of seizures and epilepsy. A Report of the TASK3 Pharmacology Working Group of the ILAE/AES Joint Translational Task Force

“…In addition to spontaneous seizures, kindled rodents exhibit a number of behavioral comorbidities of epilepsy, 60,63,69-72 a finding consistent with clinical reports that seizures in humans are just one symptom of epilepsy diagnosis. 73 It is important to note that kindled rodents consistently demonstrate increased anxiety-like behaviors and cognitive deficits in a diversity of approaches performed by numerous independent investigators, 60,63,67,68 further supporting the utility of kindling for studies of disease-modification and/or epileptogenesis and demonstrating that these behavioral comorbidities are relevant biomarkers in kindling models, as well as models with spontaneous recurrent seizures (SRS). Kindled models offer the capability to tightly control the epileptogenesis process in a manner that is distinct from other models of epilepsy.…”

How do we choose the appropriate animal model for antiseizure therapy development?

“…However, much like the amygdala-kindled rat, CKM are not innately pharmacoresistant [9]. Modifications have produced a 6 Hz corneal kindling protocol that may be more pharmacoresistant [13], albeit the published pharmacological profile of this model is quite limited ( Table 1). More recently, a lamotrigine-resistant CKM has demonstrated a broad and highly pharmacoresistant profile, including resistance to retigabine and carbamazepine (Table 1 [11]).…”