Effect of repeated seizures on spatial exploration and immediate early gene expression in the hippocampus and dentate gyrus

Abstract

Immediate early genes (IEGs) are coordinately activated in response to neuronal activity and can cause activation of secondary response genes that modulate synaptic plasticity and mediate long-lasting changes in behaviour. Excessive neuronal stimulation induced by epileptic seizures induce rapid and dramatic changes in IEG expression. Although the impact of acute seizure activity on IEG expression has been well studied, less is known about the long-term effects of chronic seizures on IEG induction during seizure free periods where behavioural and cognitive impairments are frequently observed in people with epilepsy and in animal models of epilepsy. The present study sought out to examine the impact of chronic pentylenetetrazole evoked seizures (PTZ kindling) on spatial exploration induced in IEG expression (c-Fos, ΔFosB, Homer1a, Egr1, Npas4, Nr4a1) in the hippocampus (CA1 and CA3 subfields) and dentate gyrus of rats. Male rats underwent two weeks of PTZ kindling (every 2 days) or received vehicle injections and were placed into a novel open field arena for 30 min either 24 hrs or 4 weeks after the last treatment. Although exploratory activity was similar between PTZ kindled and vehicle controls when examined 24 hrs after the last treatment, we observed a significant reduction in spatial exploration induced expression of c-Fos, Egr1, and ΔFosB in the hippocampus and dentate gyrus, and reduced expression of Nr4a1 in the dentate gyrus and Homer1a in the hippocampus only. When testing was conducted after a 4-week recovery period, only c-Fos continued to show reduced expression after exposure a novel environment in previously PTZ kindled animals. Interestingly, these animals also showed reduced activity in the center region of the open field suggestive of heightened anxiety-like behaviour. Collectively, these results suggest that repeated seizures may lead to longterm downregulation in hippocampal IEG expression that can extend into seizure free periods thereby providing a critical mechanism for the development of cognitive and behavioural deficits that arise during chronic epilepsy

Complement C4-deficient mice have a high mortality rate during PTZ-induced epileptic seizures, which correlates with cognitive problems and the deficiency in the expression of Egr1 and other immediate early genes

“…In the CNS, c-Fos, Egr1, and Arc are used as a markers of neuronal activity in the context of memory formation and development of multiple psychiatric disorders such as SZ and ASD ( Minatohara et al, 2016 ; Gallo et al, 2018 ). It was previously shown that multiple IEGs, including Egr1, Egr4, c-Fos, c-Jun, Naps4, Nur77, and Arc were upregulated in in vivo animal (from rodents to primates) and in in vitro models of epilepsy, as was confirmed in our study ( Kiessling and Gass, 1993 ; Barros et al, 2015 ; Kalinina et al, 2022 ; Rienecker et al, 2022 ). However, in contrast to earlier studies that used in situ hybridization, repetitive stimulations with PTZ, or using the earliest time-point at 30 min, we used more sensitive quantitative real-time PCR, which allowed us to detect upregulation of ten IEGs within a 9 ± 1 min period post-PTZ injections to ensure that all tested animals are alive.…”

“…It is well known that during epileptic seizures neuronal cells upregulate IEGs within minutes ( Kalinina et al, 2022 ). IEGs are responsible for many neuronal functions including their activation, long-term potentiation (LTP), memory, and CNS repair ( Kiessling and Gass, 1993 ; Dragunow, 1996 ; Gallo et al, 2018 ).…”

Zebrafish models of candidate human epilepsy-associated genes provide evidence of hyperexcitability

“…Dysregulation of npas4a, npas4b, erg1, fosab, and nr4a1 was seen in mutant wnt8b (Figure 4D.ii) fish and fosab, erg1, and npas4b in kcnd2 (Figure 4D.ii) mutants. All IEG expression was significantly downregulated, consistent with chronic epilepsy as opposed to the upregulation observed after acute seizure induction [24][25][26]. Models with no significant findings from LFP also showed no significant IEG DEGs (Figure 4C, D,E.ii).…”

Blocking salt‐inducible kinases with YKL‐06‐061 prevents PTZ‐induced seizures in mice

“…Hippocampal and cortical hyperexcitability are the defining features of most epilepsies (Zhang et al., 2010 ), but the molecular mechanisms regulating excitability in these brain regions are not fully understood. Excessive neuronal stimulation induced by epileptic seizures results in rapid and dramatic changes in the expression of IEGs (Kalinina et al., 2022 ), which can mediate direct effects on neuronal excitability and function. Inhibition of IEG induction by antisense oligonucleotides can disrupt seizure development in several animal models of epilepsy (Chiasson et al., 1998 ; Panegyres & Hughes, 1997 ; Rocha & Kaufman, 1998 ; Rocha et al., 1999 ; Suzukawa et al., 2003 ).…”