C-FOS IMMUNOCYTOCHEMICAL EVIDENCE FOR ACOUSTIC PATHWAY MAPPING IN RATS

Principles of the functional organization of brain structures are mani fested in the response characteristics of the composing neuronal eleme nts. In order to visualize and map some of the fundamental organizatio n principles in the mammalian auditory system, namely tonotopy, ipsila teral versus contralateral inputs, and excitatory and inhibitory inter actions, the present study employed the c-fos immunocytochemistry tech nique for imaging changes in acoustically evoked synaptic activity. Yo ung rats were either monaurally or binaurally stimulated with pure ton e pulses, and the distribution of immunoreactive neurons was analyzed in auditory brainstem nuclei. In a quantitative approach, i.e. by coun ting the number of labeled neurons in a given nucleus, monaural nuclei could be distinguished from binaural nuclei. Moreover, by relating ar eas with increased or decreased labeling to the stimulus conditions, f urther information was obtained on the nature of the inputs, i.e. whet her ipsilateral and contralateral stimuli elicit predominantly excitat ory and/or inhibitory responses. Taken together, the present data demo nstrate the suitability of the c-fos immunocytochemistry technique to identify tone-evoked excitation (and inhibition) in auditory brainstem neurons and to visualize fundamental principles of organization.