The spatial expression of the immediate-early gene c-fos in central au
ditory nuclei of the anaesthetised guinea pig was investigated followi
ng exposure of the animal to acoustic stimulation. Accurate control of
both the spectra and the level of the stimulus was designed so that t
he presumed excitation of central auditory nuclei was similar across a
nimals. For unstimulated anaesthetised control animals, levels of labe
lling were significantly higher when compared with unanaesthetised con
trols. This appeared to be a result of the combination of the experime
ntal manipulations and also the use of the anaesthetic. A surprising f
inding was that unstimulated control animals placed in an anechoic cha
mber demonstrated the highest levels of fos-like immunoreactivity (Fos
-LIR). When anaesthetised animals were exposed to acoustic stimuli the
total number of cells showing Fos-LIR was elevated when compared to a
naesthetised, but unstimulated animals. There was no evidence at any l
evel of the auditory pathway that these animals demonstrated spatially
restricted Fos-LIR which may have suggested place-frequency mapping.
In contrast, spatially restricted labelling was found in awake animals
exposed to an identical stimulus.