Seizure-induced c-fos expression in rat medulla oblongata is not dependent on associated elevation of blood pressure

This study was performed to determine whether c-fos immunoreactivity (IR) induced in medulla oblongata by pentylenetetrazole seizures is a consequence of seizure-associated blood pressure elevation and activation of baroreceptor afferent pathways, or occurs independently of hypertension. Immunohistochemical study of sections of medulla oblongata revealed that seizures are followed by induction of c-fos IR in nucleus tractus solitarius (NTS), dorsal motor nucleus of the vagus (DMN 10), and ventrolateral medulla (VLM), while there is negligible c-fos IR after saline sham injections. Seizures were associated with blood pressure elevation peaking at 31 +/- 17% (+/- SD) above baseline. Experimental hypertension at a similar level induced by i.p. phenylephrine also resulted in induction of c-fos IR in NTS. When seizures were preceded by antihypertensive treatment with the alpha-adrenergic antagonist, phentolamine, peak blood pressure tended to remain near the baseline level and lower than sham-injected controls. Normotensive seizures were associated with c-fos IR in NTS, DMN 10, and VLM similar to the pattern following hypertensive seizures. Seizure-induced activation of c-fos IR occurred despite normal blood pressure, and thus can be attributed to a direct effect of the seizure, and not to an indirect effect mediated by hypertension.