ELECTRICALLY-INDUCED FOS-LIKE IMMUNOREACTIVITY IN THE AUDITORY PATHWAY OF THE RAT - EFFECTS OF SURVIVAL-TIME, DURATION, AND INTENSITY OF STIMULATION

The goal of the present study was to establish how Fos-like immunoreac tivity (FLI) elicited in the rat auditory pathway by unilateral electr ic stimulation of the cochlea is affected by the following experimenta l parameters: duration and intensity of stimulation, duration of survi val time after offset of stimulation. The dense FLI found in the ipsil ateral dorsal cochlear nucleus, as well as the moderate FLI found in t he contralateral dorsal cochlear nucleus and in the posteroventral coc hlear nucleus on both sides, were consistent after survival times rang ing from 0 to 2-3 h, but they significantly decreased after longer sur vival times (5 and 6 h). In the same nuclei, FLI was increased even by short durations of stimulation (5 and 10 min) as compared to control rats, although FLI progressively increased for longer stimulation (20 and 45 min). In the auditory thalamus, FLI was found mainly in the per ipeduncular nucleus, the dorsal and medial divisions of the medial gen iculate body, whereas its ventral division was virtually devoid of imm unoreactive neurons. This pattern of FLI distribution in the auditory thalamus persisted even after relatively long survival times (5 and 6 h). In both the cochlear nucleus and auditory thalamus, the density of FLI slightly increased in parallel with the intensity of stimulation. In other auditory nuclei, such as the inferior colliculus and the nuc leus of the lateral lemniscus, there was no simple relation between th e density of FLI and the three tested experimental parameters. Thus, t he distribution and density of FLI did not vary in parallel in the var ious nuclei of the auditory pathway as a function of the tested experi mental parameters; different patterns of FLI changes were instead obse rved in different auditory nuclei.