Corticofugal modulation of acoustically induced Fos expression in the rat auditory pathway.
To investigate the corticofugal modulation of acoustic information ascending through the auditory pathway of the rat, immunohistochemical techniques were used to study the functional expression of Fos protein in neurons. With auditory stimulation at different frequencies, Fos expression in the medial geniculate body (MGB), inferior colliculus (IC), superior olivary complex, and cochlear nucleus was examined, and the extent of Fos expression on the two sides was compared. Strikingly, we found densely Fos-labeled neurons in all divisions of the MGB after both presentation of an auditory stimulus and administration of a gamma-aminobutyric acid type A (GABA(A)) antagonist (bicuculline methobromide; BIM) to the auditory cortex. The location of Fos-labeled neurons in the ventral division (MGv) after acoustic stimulation at different frequencies was in agreement with the known tonotopic organization. That no Fos-labeled neurons were found in the MGv with acoustic stimuli alone suggests that the transmission of ascending thalamocortical information is critically governed by corticofugal modulation. The dorsal (DCIC) and external cortices (ECIC) of the IC ipsilateral to the BIM-injected cortex showed a significantly higher number of Fos-labeled neurons than the contralateral IC. However, no difference in the number of Fos-labeled neurons was found between the central nucleus of the IC on either side, indicating that direct corticofugal modulation occurs only in the ECIC and DCIC. Further investigations are needed to assess the functional implications of the morphological differences observed between the descending corticofugal projections to the thalamus and the IC.
Sun
Xia
X
Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
Xia
Qiang
Q
Lai
Chun-Hong
CH
Shum
Daisy Kwok-Yan
DK
Chan
Ying-Shing
YS
He
Jufang
J
D000161:Acoustic Stimulation / Q000379:methods*; D000818:Animals; D001303:Auditory Cortex / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D001306:Auditory Pathways / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects*; D001640:Bicuculline / Q000494:pharmacology; D001931:Brain Mapping; D002452:Cell Count / Q000379:methods; D004307:Dose-Response Relationship, Radiation; D007839:Functional Laterality; D018756:GABA Antagonists / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D007150:Immunohistochemistry / Q000379:methods; D007245:Inferior Colliculi / Q000378:metabolism; D008297:Male; D009474:Neurons / Q000378:metabolism; D009716:Numerical Analysis, Computer-Assisted; D016761:Oncogene Proteins v-fos / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D018756:GABA Antagonists; D016761:Oncogene Proteins v-fos; D001640:Bicuculline