Application of Bicuculline to the Gerbil Somatosensory Cortex Induces Repetitive Ear Movements Accompanied by Induction of c-Fos Immunoreactivity in the Thalamus.

Abstract

We previously established a seizuresensitive strain of Mongolian gerbil, MGS/ Idr, in which seizure-inducing stimuli often elicit repetitive backward jerks of the ears at the beginning of seizures, and found that unilateral application of (-)-bicuculline methiodide (BMI) to an area of the somatosensory cortex in this strain induced similar, but long-lasting, repetitive movements of the contralateral ear. In the present study, we have extended this observation by using immunohistochemistry to look for areas of the brain in which c-Fos protein, an immediate early gene product, appeared unilaterally following BMI application. At 4 hr after BMI application, the cerebral cortex under the application site showed intense c-Fos immunostaining. In addition, c-Fos immunoreactivity appeared in restricted areas of the ipsilateral thalamus, including the ventroposterior nucleus, posterior nucleus, and reticular nucleus. Control saline-treated gerbils did not show unilateral staining in the corresponding thalamic areas. These areas may form a network with the somatosensory cortex that is involved in the recurrent phenomena, as proposed for other areas of the cerebral cortex.