C-Fos immunohistochemical mapping of the audiogenic seizure network and tonotopic neuronal hyperexcitability in the inferior colliculus of the Frings mouse
Department of Pharmacology and Toxicology, University of Utah, Salt Lake City, Utah, United States Epilepsy Research
(Impact Factor: 2.02).
12/2004; 62(1):13-25. DOI: 10.1016/j.eplepsyres.2004.06.007
The Frings mouse is a model of audiogenic seizure (AGS) susceptibility. The genetic locus responsible for the AGS phenotype in the Frings mouse has been named monogenic audiogenic seizure-susceptible (MASS1). MASS1 is unique in that it is one of only two identified seizure loci that are not associated with an ion channel mutation. Furthermore, Frings mice display a robust AGS phenotype demonstrating very high and prolonged susceptibility to sound-induced tonic extension seizures. The purpose of this investigation was to use c-Fos immunohistochemistry to map the brain structures involved in the Frings AGS and to examine neuronal hyperexcitability in the inferior colliculus, the brain structure that is recognized as the site of AGS initiation. AGS mapping revealed that intense seizure-induced neuronal activation was mostly limited to structures involved in a brainstem seizure network, including the external and dorsal nuclei of the inferior colliculus, as observed in other AGS rodents. Acoustically induced c-Fos expression in the central nucleus of the inferior colliculus to sub-AGS threshold tone stimulations displayed a greater level of neuronal activation in AGS-susceptible Frings, DBA/2J and noise-primed C57BL/6J mice compared to AGS-resistant C57BL/6J and CF1 mice. The AGS-susceptible mice also displayed c-Fos immunoreactivity that was more focused within the tonotopic response domain of the inferior colliculus compared to AGS-resistant mice. Furthermore, Frings mice displayed significantly greater tonotopic hyper-responsiveness compared to other AGS-susceptible mice.
Available from: Senthilvelan Manohar
- " and a faster decay of their inhibitory postsynaptic po - tentials ( IPSP ) in dentate gyrus ( Spigelman et al . , 2002 ) , sug - gesting that GABA tonic inhibition is critical towards the prevention of seizures . The reduction of GABR - d and GABR - a6 subunits in the IC may be related to hyperactivity in the IC when responding to sound stimuli ( Klein et al . , 2004 ; Kwon and Pierson , 1997 ) . Our study found that early age hearing loss di - minishes the expression of GABR - d and GABR - a6 subunits , thus promoting hyperactivity in the IC and ultimately inducing AGS at a later age ."
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ABSTRACT: Tinnitus and hyperacusis, commonly seen in adults, are also reported in children. Although clinical studies found children with tinnitus and hyperacusis often suffered from recurrent otitis media, there is no direct study on how temporary hearing loss in the early age affects the sound loudness perception. In this study, sound loudness changes in rats affected by perforation of the tympanic membranes (TM) have been studied using an operant conditioning based behavioral task. We detected significant increases of sound loudness and susceptibility to audiogenic seizures (AGS) in rats with bilateral TM damage at postnatal 16 days. As increase to sound sensitivity is commonly seen in hyperacusis and tinnitus patients, these results suggest that early age hearing loss is a high risk factor to induce tinnitus and hyperacusis in children. In the TM damaged rats, we also detected a reduced expression of GABA receptor δ and α6 subunits in the inferior colliculus (IC) compared to the controls. Treatment of vigabatrin (60 mg/kg/day, 7-14 days), an anti-seizure drug that inhibits the catabolism of GABA, not only blocked AGS, but also significantly attenuated the loudness response. Administration of vigabatrin following the early age TM damage could even prevent rats from developing AGS. These results suggest that TM damage at an early age may cause a permanent reduction of GABA tonic inhibition which is critical towards the maintenance of normal loudness processing of the IC. Increasing GABA concentration during the critical period may alleviate the impairment in the brain induced by early age hearing loss.
- "We also identified a strong c-Fos staining in the IC in the TM damaged rats after AGS, suggesting the AGS may be related to the hyperactivity in the IC responding to sound stimuli. These results are consistent with previous studies on AGS using mice which are genetically prone to AGS (Klein et al., 2004; Kwon and Pierson, 1997). In addition, we found the AGS can be reversibly suppressed by vigabatrin treatments (i.p. injection or oral take), suggesting that the AGS caused by the TM damage may be related to a deficiency of GABA inhibition. "
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ABSTRACT: Recent clinical reports found a high incidence of recurrent otitis media in children suffering hyperacusis, a marked intolerance to an otherwise ordinary environmental sound. However, it is unclear whether the conductive hearing loss caused by otitis media in early age will affect sound tolerance later in life. Thus, we have tested the effects of tympanic membrane (TM) damage at an early age on sound perception development in rats. Two weeks after the TM perforation, more than 80% of the rats showed audiogenic seizure (AGS) when exposed to loud sound (120 dB SPL white noise, < 1 min). The susceptibility of AGS lasted at least sixteen weeks after the TM damage, even the hearing loss recovered. The TM damaged rats also showed significantly enhanced acoustic startle responses compared to the rats without TM damage. These results suggest that early age conductive hearing loss may cause an impaired sound tolerance during development. In addition, the AGS can be suppressed by the treatment of vigabatrin, acute injections (250 mg/kg) or oral intakes (60 mg/kg/day for 7 days), an antiepileptic drug that inhibits the catabolism of GABA. c-Fos staining showed a strong staining in the inferior colliculus (IC) in the TM damaged rats, not in the control rats, after exposed to loud sound, indicating a hyper-excitability in the IC during AGS. These results indicate that early age conductive hearing loss can impair sound tolerance by reducing GABA inhibition in the IC, which may be related to hyperacusis seen in children with otitis media.
Available from: Melanie Leussis
- "Expression of messenger cfos is a plausible mechanism for inducing abnormal neural plasticity by directing protein synthesis in the nucleus. Immunoreactivity for the immediate-early gene product, cFos, has also been examined in several animal seizure models in order to reveal brain regions recruited as a result of seizure activity (Fabene et al., 2004; Klein et al., 2004; Simler et al., 1999), and is thought to reflect non-specifically heightened neuronal excitability in these regions (Zhang et al., 2002). For example, cFos is upregulated in the dentate gyrus of EL mice following vestibular stimulation (tossing-up) and/or seizures (Nakagawa et al., 1999). "
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ABSTRACT: The present studies employed behavioral and neural markers of seizure-related plasticity to examine the relative contributions of genetic predisposition versus rearing environment in generating adult phenotypes in EL mice, a stress-induced animal model of epilepsy. Early environment was manipulated by cross-fostering pups of the EL strain to a seizure-resistant CD-1 control strain of mouse. The impact of changes in rearing quality on growth, exploratory and stress-reactivity phenotypes were examined, with a focus on the role of maternal care in shaping seizure susceptibility and neural cFos activation. Improvement in maternal care imposed by replacing biological EL dams with foster CD-1 mothers was sufficient to decrease pup mortality, to increase body weight gain (+ 0.1 g/day) and to delay the onset of seizure susceptibility in EL offspring beyond post-natal day 80–90. Moreover, hypoactivity in hippocampus and cortex among EL offspring cross-fostered to EL, but not CD-1 control, dams suggests that changes in rearing environment were accompanied by enduring changes in brain plasticity. Thus, neural and behavioral phenotypes of EL mice are dependent upon post-partum maternal care which if systematically enhanced can postpone seizure expression.
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