UC Irvine

Biochemical studies have indicated that norepinephrine is present in lower levels in certain brain regions of genetically epilepsy-prone rats (GEPR-9s) as compared to non-epileptic Sprague-Dawley (SD) rats. In this study, the immunocytochemical localization of dopamine beta-hydroxylase (DBH), the synthesizing enzyme for norepinephrine, was compared between GEPR-9s and SD rats. Brain regions caudal to the inferior colliculus, such as the cerebellum and locus coeruleus, showed no differences in the distribution of DBH-like immunoreactive (DBH-I) neurons and fibers. In contrast, differences in the distribution of DBH-I fibers were observed in more rostral brain regions including the central nucleus of the inferior colliculus, thalamus, piriform, orbital and somatosensory cortices and hippocampus. In these areas, the number, and often the staining intensity, of DBH-I processes was lower in GEPR-9s as compared to SD rats. It was interesting to note that other cortical regions displayed no differences in DBH immunoreactivity between GEPR-9s and SD rats. These results provide anatomical data that support previously described biochemical results. Furthermore, the reduced number of fibers and their decreased staining intensity in specific brain regions provide greater details to resolve the localization of deficiencies in the noradrenergic fiber plexus of GEPR-9s.