Development of Epileptic Activity in Embryos and Newly Hatched Chicks of the Fayoumi Mutant Chicken

Abstract

The homozygous Fayoumi strain of epileptic chickens (Fepi) is affected by generalized convulsions consistently induced by intermittent light stimulation (ILS) and by intense sound. Although interictal EEG recordings show continuous spikes and spike and wave activity, desynchronization and flattening (DF) of the EEG are observed during seizures. We have studied development of the epileptic phenotype in embryonic (E) and posthatching (P) Fepi. As compared with those of chicken embryos of a normal strain, no differences were observed in the EEG before embryonic day (E) 16. Clearly differentiated spikes and spike and waves appeared at E17 in Fepi. Metrazol-induced EEG seizures were observed at E16 in normal embryos and at E17 in Fepi. The Fepi showed some characteristics: Spontaneous EEG seizure-like discharges also appeared at E17 but decreased toward hatching; visual or acoustic hyperexcitability developed at E20 together with evoked responses in normal chickens; desynchronization of the EEG, typical of the epileptic seizure of the adult, could be induced by ILS at B20, but ILS- or sound-induced generalized motor seizures appeared at P1, a few hours after hatching. Results show that Fepi phenotype reaches full expression at P1, but the electric paroxysms are expressed earlier, paralleling synaptic maturation.

The generation of theta rhythm in hippocampal formation maintainedin vitro

“…This specific pattern of in vitro and in vivo theta appearance is controlled by gating cells, which have just recently been discovered (Konopacki et al ., ; Kowalczyk et al ., ). Although some brain regions are recognized as epileptogenic, generally epileptiform activity is not restricted to specific regions of the brain (except cerebellum). In contrast, in vitro theta rhythm was observed only in the neocortex (Lukatch & MacIver, ), hippocampal formation (Konopacki, ; Konopacki et al ., ; D'antuono et al ., ), enthorinal cortex (Konopacki & Gołębiewski, ; Goutagny et al ., ) and posterior hypothalamus (Kowalczyk et al ., ), regions known to produce physiological in vivo theta. In contrast to in vivo and in vitro theta, which developed usually 8–12 days postnatally (Leblanc & Bland, ; Konopacki et al ., ), in vivo and in vitro recorded epileptiform discharges can be induced in all stages of postnatal brain development and even prenatally (Guy et al ., ). It is known that orthodromic stimulation of CA1 afferent fibres in vitro normally gives one population spike when recorded extracellularly from the pyramidal cell body layer. The bath perfusion of HPC slices with CCH at a concentration sufficient to induce theta‐like activity does not change this pattern of evoked field potential.…”

EEG as a measure of developmental changes in the chicken brain

“…Thus, the first signs of recognizable forebrain EEG activity are observed around embryonic Day 13, EEG rhythms can be detected at embryonic Day 17, and a pattern that begins to look like posthatch EEG appears at embryonic Day 19 or 20 in preparation for hatching at Day 21 (Bakhuis & Bour, 1980;Corner & Bakhuis, 1969;Rogers, 1995). These descriptive data have provided a foundation for recent work which has used the EEG more specifically, for example, to monitor the development of epileptic activity in embryonic and newly hatched chicks (Guy et al, 1992;Guy, Fadlallah, Naquet, & Batini, 1995). We know of no EEG studies that have looked quantitatively at the development of the post-hatch chicken brain and yet major structural and functional changes have been demonstrated to occur during the period of maturation in the weeks following hatching (Rostas, Brent, & Guldner, 1984;Rostas, Kavanagh, Dodd, Heath, & Powis, 1992;Weinberger & Rostas, 1988).…”

Cracking the Egg: Potential of the Developing Chicken as a Model System for Nonclinical Safety Studies of Pharmaceuticals

“…A homozygous strain of epileptic chickens, the Fayoumi strain, has been used in epilepsy research for over 30 years (Nunoya et al, 1983). Epileptic chickens show differences in electroencephalography compared with normal chickens from E17 (Guy et al, 1995). They have been used for magnetic resonance imaging (Fabene and Sbarbati, 2004) and evaluation of anticonvulsant drugs (Loscher, 1984;Johnson et al, 1985) and N-methyl-D-aspartate receptor (NMDA)…”