THE EFFECTS OF VARIABLE PERIODS OF FUNCTIONAL DEPRIVATION ON OLFACTORY-BULB DEVELOPMENT IN RATS

Dramatic alterations occur in the developing olfactory bulb when air f low is reduced through one-half of the nasal cavity. Naris closure on the day after the day of birth (P1) in rats, for example, results in r educed cell survival in the ipsilateral bulb by P20 and a substantial (25%) decrease in bulb size by P30. Almost immediate changes in protei n synthesis and cell metabolism are also observed, and one prevalent t heory suggests that these changes may be important in specifying which cells are subsequently eliminated. In the present study we used a rev ersible technique for unilateral naris closure to examine the sensitiv e period for the effects of olfactory deprivation on bulb size and cel l survival. This technique involves the insertion of removable plugs i nto a rat pup's external naris. We occluded the naris for increasing p eriods of time (P1-P10, P1-P15, or P1-P20), reared all animals to P30, and measured volumes of bulb laminae. In addition, we examined the du ration of naris closure needed to affect cell survival by injecting an imals with the thymidine analogue bromodeoxyuridine to label cells bor n soon after the onset of olfactory deprivation. Results indicate that relatively long periods of naris occlusion (P1-P15 or longer) are req uired to produce a substantial reduction in experimental bulb size. Ce ll survival was decreased following olfactory deprivation from P1 to P 10, but not after deprivation from P1 to P3. These data support the hy pothesis that changes that occur within 48 h of naris closure are not sufficient to affect cell survival. (C) 1997 Academic Press.