Functional consequences of unilateral olfactory deprivation: time-course and age sensitivity

Unilateral olfactory deprivation in the rat profoundly modifies olfactory bulb anatomy, chemistry and function. The present report examined the time-course of the functional effects of unilateral deprivation on inhibition in the olfactory bulb using paired-pulse stimulation of the lateral olfactory tract and olfactory nerve. In addition, an attempt was made to correlate these physiological measures with olfactory bulb dopamine and norepinephrine levels and tyrosine hydroxylase immunoreactivity. Deprivation from postnatal day 1 to postnatal day 20 or postnatal day 40 significantly enhanced lateral olfactory tract paired-pulse depression, while late onset deprivation (postnatal day 20) had no effect. Olfactory nerve paired-pulse depression was enhanced by 40 days of deprivation regardless of the age at onset. The time-course of these deprivation-induced physiological changes did not correlate well with reductions in dopamine. Dopamine levels were reduced in all deprivation conditions by 70-80% compared with control bulbs. Norepinephrine content was slightly elevated in deprived bulbs. These results suggest that early olfactory deprivation modifies olfactory bulb synaptic activity and further, as with other sensory systems, these effects are age and duration dependent.