| Presentation |
Kevin Muenzer
Appalachian State University
Subject Listing - Neuroscience
Advisor: Dr. Mark Zrull
Friday, Oral Session 6, Presentation 3, Karpen Hall 034
TONOTOPIC ORGANIZATION OF CENTRAL NUCLEUS OF INFERIOR COLLICULUS AFTER ONE OR SIX AUDIOGENIC SEIZURES.
In a model of reflex epilepsy, rats become susceptible to sound-induced seizures by exposure to loud (120 dB), 10 kHz tone pips (8/s, 8 min) on postnatal day (pnd) 18 and to loud (120 dB) noise on pnd 32. The single audiogenic seizure (AGS) causes disorganization of sound processing in auditory brain stem structures. In this study, an understanding of the relationship between seizure frequency and neural plasticity was sought by comparing the effect of one and multiple seizures on the tonotopic organization of the central nucleus of inferior colliculus (CNIC), which is an auditory brain stem relay center. Long Evans rats were primed and tested for seizure activity on pnd 32 (n=10, P1T) or on pnds 32, 46, 53, 60, 153 and 160 (n=8, P6T). A normal, age-matched control group (n=8) was also available. Between pnds 120 and 220 rats were stimulated in a sound attenuating chamber with 4, 10 or 20 kHz pure tone pulses (70 dB, 120 min). The pure tones produced c-fos protein in sound activated neurons and provided a reliable tool for mapping tonotopic organization of the CNIC. Rats were sacrificed after stimulation, perfused, and brains were removed, sectioned and processed using immunohistochemistry for neurons expressing the c-fos protein (fos+ cells). Using microscopy, fos+cells were counted and expressed as ratios of activated cells within to outside the tonotopic area for a pure tone stimulus. Within:outside ratios for normal control animals were 2.2:1 indicating increased neural activity in frequency specific areas for a pure tone. In P1T and P6T rats, within:outside ratios were about 1:1 indicating an absence of tonotopic organization (p<.05). There was no significant difference in CNIC organization between P1T and P6T groups. The results suggest priming and having at least one seizure, rather than multiple AGSs, are responsible for disorganized pure tone processing observed in rats prone to sound-induced seizures.
Advisor: Dr. Mark Zrull, Associate professor, Psychology, Appalachian State University, Boone, NC