EXPRESSION OF FOS IN THE SUPERIOR LATERAL SUBDIVISION OF THE LATERAL PARABRACHIAL (LPBSL) AREA AFTER GENERALIZED TONIC SEIZURES IN RATS

Generalized tonic-clonic seizures of brain stem origin in rats are ass ociated with acute induction of neuronal Fos in several discrete regio ns of the brain. One particular site in the dorsal pans shows remarkab le Fos induction following generalized tonic seizures induced by maxim al electroshock in normal rats or by audiogenic stimulation in genetic ally epilepsy-prone rats (GEPRs). Although this area shows the most in tense Fos induction of any brain area following generalized tonic seiz ures, its identity has been uncertain. Based an its general location, we hypothesized that this nucleus was either 1) a component of the ped unculopontine tegmentum nucleus-pars compacta (PPTn-pc) or 2) the supe rior lateral subnucleus of lateral parabrachial area (LPBsl). The pres ent study used Fos-protein immunocytochemistry in combination with the reduced form of nicotinamide-adenine dinucleotide phosphate (NADPH)-d iaphorase histochemistry, cholecystokinin (CCK) immunocytochemistry, a nd neuronal tract-tracing to determine the identity of this cluster of Fos-immunoreactive neurons in the dorsal pens. Following maximal elec troshock seizure (MES), Fos labeling was compared to NADPH diaphorase staining (a marker for cholinergic neurons of the PPTn-pc); retrograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) i njected into the ventromedial nucleus of the hypothalamus (VMH; to ide ntify the LPBsl) or CCK immunoreactivity (also a marker for LPBsl neur ons). Results showed this cluster of Fos immunoreactive (FI) neurons t o be closely associated, but not overlapping, with the lateral and mos t caudal aspect of the PPTn-pc. Alternatively, WGA-HRP retrograde-labe led neurons corresponded precisely with the seizure-induced FI neurons . Additionally, the location of CCK immunoreactive neurons directly ov erlapped with the FI neurons, although they were not nearly as prevale nt. These results demonstrate that the seizure-induced FI neurons in t his area are neurons of the LPBsl and not cholinergic neurons of the P PTn-pc. This is the first report of seizure-induced Fos expression spe cifically localized to the superior lateral subnucleus of the lateral parabrachial area. (C) 1998 Elsevier Science Inc.