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
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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
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