Olfaction in Olfactory Bulbectomized Rats

American University, Washington DC

Investigators

Abstract

Sensory cells in the nose respond to odors and send signals back to the olfactory bulb of the brain. These cells live for only a few weeks and, when they die, they are replaced by maturing cells from a germinal cell layer in the olfactory tissue. The maturing cells extend their axons into the olfactory bulb where they replace the contacts made by the axons of the dying neuron. The ability of the olfactory receptor epithelium to reconstitute itself in this fashion is unique because neurons in other sensory systems are not replaced if they die. Of particular interest is the fact that if the olfactory bulb is removed, the axons of maturing sensory neurons will continue to grow until they reach brain tissue. They will then make synaptic contact with neurons that do not normally receive inputs from olfactory receptor cells. While this remarkable example of neural plasticity has been demonstrated in anatomical studies, it remains unclear whether these new synaptic contacts can be used by the brain to support the sense of smell. We propose to examine this issue by removing the olfactory bulb in neonatal rats and testing their ability to detect and discriminate odors when they are adults. Operated rats will be trained in a precision olfactometer device to determine their odor sensitivity and whether they can discriminate among odors. Behavioral results will be correlated with an anatomical analysis of forebrain connections originating from the olfactory bulb. A positive outcome would provide evidence for a hitherto unrecognized ability of the brain to utilize novel information and translate it into conscious sensory signal