Long-term regulation in calretinin staining in the rat inferior colliculus after unilateral auditory cortical ablation

In this study we analyzed the effects in the inferior colliculus of a unilateral ablation of the auditory cortex in rats. Variations in both calretinin immunoreactivity and protein levels determined by Western blot suggest that such lesions induce changes in the regulation of this calcium-binding protein. Stereological counts of calretinin-immunoreactive neurons in the inferior colliculus 15, 90, and 180 days after the lesion showed a progressive increase in the number of immunoreactive neurons, with a parallel increase in the intensity of staining. Two hundred forty days after the cortical lesion, both the number of immunoreactive neurons and the staining intensity had returned to control values. The effects of the cortical lesion on calretinin regulation are more intense in those inferior colliculus subdivisions more densely innervated by the corticocollicular projection. This finding, along with the time course of calretinin regulation suggests that degeneration of the descending projection is linked to calretinin regulation in the inferior colliculus. We hypothesize, based on the role of calretinin, that the observed increase in immunoreactivity levels seen in the inferior colliculus after lesioning of the auditory cortex may be related to altered excitability in deafferented neurons. Our finding, may reflect adaptive mechanisms to changes in calcium influx and excitability in inferior colliculus neurons induced by lesions of the descending projection from the cortex to the inferior colliculus.