A survey of the auditory midbrain, thalamus and forebrain in the chicken (Gallus domesticus) with cytochrome oxidase histochemistry.

The chicken's central auditory nuclei from the inferior colliculus to field L in the forebrain were studied with cytochrome oxidase histochemistry. All stations of the ascending pathway displayed high activity levels, including the inferior colliculus, the nucleus ovoidalis of the thalamus, and field L1 to L3 and the hyperstriatum ventrale caudale which correspond to primary and secondary auditory cortex. In the inferior colliculus a moderately active external nucleus could be distinguished from a more intensely stained central and superficial nucleus. In the central nucleus there was a lateral shell displaying stronger neuropil reactivity than a central core. Unilateral cochlea removal caused no remarkable effect in tectum and thalamus. The auditory forebrain contralateral to the lesion displayed reduced CO reactivity compared with the ipsilateral side. After bilateral cochlea extirpation auditory structures still displayed higher enzyme levels than most other nuclei.