Epileptiform seizures in domestic fowl. IV. The effects of anticonvulsant drugs

Learning impairment in 1-2-day-old epileptic chicks

The cause of learning impairment in children with seizure disorders is obscure, in part because of the lack of adequate animal models of learning deficiencies that can be used for study. The discriminating passive avoidance test has been used extensively to study learning behavior in chicks. In the present study, we applied the passive avoidance test to epileptic chicks to determine if learning deficiencies could be demonstrated in this epileptic model. Epileptic fowl have a hereditary form of primary generalized epilepsy characterized by tonic-clonic seizures. The seizures occur spontaneously and can also be induced by photic stimulation. The epileptic phenotype is the result of an autosomal recessive mutation. Heterozygotes do not have seizures and were used as age-matched controls. The discriminating passive avoidance test used in the present study was based on the observation that chicks readily peck at bright shiny beads. Once chicks taste a colored bead coated with a bitter chemical (methylanthranilate), they refuse to peck the bead on subsequent presentations. In addition, chicks can discriminate between colored beads and will continue to peck at a bead of different color than the methylanthranilate (MeA)-coated bead. compared to carriers, epileptic chicks demonstrated significantly less ability to discriminate between colored beads. Furthermore, this learning impairment was observed in epileptic chicks treated with phenobarbital (PB), indicating that the learning impairment in epileptic chicks is an inherent neurological problem and not a consequence of seizure activity.

Development of epileptic activity in embryos and newly hatched chicks of the Fayoumi mutant chicken

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.

Megalencephaly in the epileptic chicken: a morphometric study of the adult brain

The epileptic chicken is a genetic model of generalized epilepsy in which epilepsy is combined with megalencephaly. We have performed a morphometric study of the brains of adult epileptic hens, using heterozygous carrier hens as controls. There is no obvious disorder of cell form or of architectural arrangement in the megalencephalic brains. We have found that the enlargement of the epileptic brain is not uniform: it is most marked in the telencephalon, and is present to a lesser degree in the cerebellum, but neither the optic tectum nor the diencephalic nucleus rotundus shows a significant increase in size. The enlarged regions are characterized by a decrease in the packing density of neurons. There is an increase in the total neuron population in some of the enlarged areas (archistriatum), despite the lower density per unit volume, but in other enlarged areas (hippocampus) there is no difference in total neuron numbers. The glial cells, by contrast, show no significant alteration in packing density. These findings suggest that the megalencephaly of the epileptic chicken is due to an increase in neuron size, with a contribution from increased numbers of neurons and glial cells. The epileptic chicken may provide a valuable model for further dynamic studies of aberrant neuronal development, and of structural-functional relationships in epilepsy.

Behavioral and electroencephalographic manifestations of avian epilepsy: a review of the literature

Recently, electrophysiological studies on sleep and wakefulness in birds have yielded useful results. Furthermore, recent evidence obtained in behavioral and electroencephalographical investigations of epileptic birds, induced neuropharmacologically or genetically, have led to recognition of the fact that epileptic seizures are present in aves, and that these seizures reveal many similarities between mammalian and avian epilepsy. While the investigation of birds is of obvrious value for demonstrating the neuropharmacological interrelationship with the brain, comparison of the correlation between abnormal behavior and the electroencephalogram in birds and higher vertebrates requires further research. In the present paper, normal and abnormal electroencephalographic activity associated with behavior of birds is reviewed. It was concluded that birds provide a useful preparation for studying experimental epilepsy.