Physiol. Res. 51 (Suppl. 1): S95-S104, 2002

 


Changes in Extracellular Space Volume and Geometry Induced by Cortical Spreading Depression in Immature and Adult Rats

F. C. NWABUEZE-OGBO, J. POPELÁŘ, J. SYKA

Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague,
Czech Republic


Summary
The role of the cortico-tectal pathways in the processing of auditory signals was investigated by recording the click-evoked responses and extracellular multiple unit activity in the inferior colliculus (IC) after functional ablation of the auditory cortex (AC) by local intracortical application of a sodium channel blocker, tetrodotoxin (TTX). Click-evoked IC responses (IC-ER) and multiple unit activity in response to tone bursts were recorded with implanted electrodes in the IC of rats lightly anaesthetized with xylazine. Neural activity was recorded before and after the application of TTX into the ipsilateral auditory cortex (AC) through three implanted cannulas in a total dose of 30 ng. The functional status of the AC was monitored by recording click-evoked middle latency responses from a ball electrode implanted on the AC. During inactivation of the AC, IC-ER amplitudes were either increased (48 % of the cases), decreased (32 % of the cases) or not evidently changed (20 % of the cases). Corresponding effects were observed in the firing rate of IC neurons. Functional ablation of the AC also resulted in a significant prolongation of the latencies of individual waves of the IC-ER. However, the discharge pattern of the multiple unit responses, response thresholds and tuning were not altered during AC inactivation. IC neural activity recovered within several hours, and maximally during 2 days. The results reveal principles of the interaction of cortico-tectal pathways with IC neuronal activity.


Key words
Auditory cortex • Inferior colliculus • Corticotectal pathways • Functional ablation • Rat
 


Reprint requests
Fidel C. Nwabueze-Ogbo, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Vídeňská 1083, 142 20 Prague 4, Czech Republic. Tel.: 02/ 475 2128. FAX: 02/475 2787. e-mail: ncfidel@biomed.cas.cz


PHYSIOLOGICAL RESEARCH
© 2002 by the Institute of Physiology, Czech Academy of Sciences

ISSN 0862 - 8408

Suppl 1