SPATIAL-ORGANIZATION AND PLASTICITY OF THE PRIMARY AND SECONDARY OLFACTORY PROJECTIONS IN GOLDFISH

Crystals of the lipophilic tracer Dil were applied to discrete regions of the olfactory epithelium of goldfish to trace the primary sensory projection to the olfactory bulb. Receptors from the anterior half of the sensory sheet project primarily to glomeruli in the medial half of the bulb and receptors in the posterior half terminate mainly within the lateral half of the bulb. This pattern disappeared following ablat ion of selected, discrete epithelial regions. In order to investigate reorganization of secondary olfactory projections, unoperated control and unilaterally bulbectomized animals received injections of [H-3]pro line into the right olfactory bulb. Densities of silver grains per uni t area were determined within six different forebrain nuclei in both t he right and left hemispheres of each animal. Of the six areas examine d, three demonstrated a significantly greater density of afferent inne rvation from the ipsilateral versus contralateral bulb; a difference w hich disappeared in two of these three regions after bulbectomy. Thus, for at least two forebrain nuclei, bulb removal caused a change in th e afferent input from the spared olfactory bulb to those regions. We c onclude that both primary and secondary olfactory projections in goldf ish are capable of some degree of reorganization following insult.