Volumetric changes in the anterior olfactory nucleus of the rat after neonatal olfactory deprivation

The effect of olfactory deprivation in the postnatal development of the ant erior olfactory nucleus (AON) was studied in 60-day-old rats which underwen t unilateral naris closure after birth (postnatal day 1). Volumetric and mo rphometric analyses of the AON ipsilateral and contralateral to the closed naris were performed and data were statistically compared among them and wi th those of control animals. The volumes of the AONs and those of their sub divisions were calculated by the Cavalieri method and the area of the subdi visions was measured at seven established rostrocaudal levels. Whereas no s tatistically significant differences were detected between the ipsilateral and the contralateral. AONs, comparison of these with controls revealed sig nificant reductions in the volumes and dimensions of most AON subdivisions. The reduction was larger in the ipsilateral than in the contralateral AON and more pronounced in the rostralmost subdivisions (external and lateral) than in the caudal ones, the dorsal subdivision not being affected. These d ata demonstrate that the disruption of the normal afferent activity to one olfactory bulb has effects on the postnatal development of both the ipsilat eral and the contralateral AONs. In addition, the most affected subdivision s were those that develop later and that receive the bulk of projections fr om the olfactory bulb, suggesting that the degree of maturity is an importa nt factor in susceptibility to changes induced by reduced afferent activity . Finally, the results indicate that, contrary to the olfactory bulb, the c ontralateral AON cannot be used as a control structure in deprivation studi es. (C) 2001 Academic Press.