Developmental changes in olfactory bulb projections revealed by degeneration argyrophilia.

The maturation of the main and accessory olfactory bulb projections to the ventral forebrain of the golden hamster has been traced by using the Fink-Heimer silver technique to stain degenerating axons and terminal arborizations after bulbectomy at different ages between birth and 33 days. In the youngest pups, long-lasting degeneration argyrophilia (LLDA) is found in two regions of prepiriform cortex: at the level of the rostral tubercle and rostral amygdala. By five days of age the caudal region exhibiting a long-lasting degeneration reaction extends from the middle of the olfactory tubercle to the middle of the amygdala. The olfactory tubercle, medial and cortical amygdala and entorhinal cortex subsequently develop substantial LLDA at ages varying between 9 and 13 days. In a previous study (Leonard, '74b) the onset of LLDA in optic tract terminals in the superior colliculus was found to coincide with the age of eye opening and the onset of a stage of rapid snyapse formation. Since different olfactory responses appear at different times during the golden hamster pup's first two weeks of postnatal life, it seems possible that the onset of LLDA in different regions of the olfactory projection at different ages may be related to the onset of different specific olfactory functions.