Heterogeneous effects of noradrenaline on spontaneous and stimulus-driven activity in the male accessory olfactory bulb

Noradrenaline (NA) release has been linked to experience-dependent plasticity in many model systems and brain regions. Among these is the rodent accessory olfactory system (AOS), which is crucial for detecting and processing socially relevant environmental cues. The accessory olfactory bulb (AOB), the first site of chemosensory information processing in the AOS, receives dense centrifugal innervation by noradrenergic (NAergic) fibers originating in the locus coeruleus. Though NA release has been linked to behavioral plasticity through its actions in the AOB, the impacts of NAergic modulation on AOB information processing have not been thoroughly studied. We made extracellular single-unit recordings of AOB principal neurons in ex vivo preparations of the early AOS taken from adult male mice. We analyzed the impacts of bath-applied NA (10 μM) on spontaneous and stimulus-driven activity. In the presence of NA, we observed overall suppression of stimulus-driven neuronal activity with limited impact on spontaneous activity. NA-associated response suppression in the AOB came in two forms: one that was strong and immediate (21%), and the other which involved gradual, stimulus-dependent monotonic response suppression (47%). NA-associated changes in spontaneous activity were more modest, with an overall increase in spontaneous spike frequency observed in 25% of neurons. Neurons with increased spontaneous activity demonstrated a net decrease in chemosensory discriminability. These results reveal that NAergic signaling in the AOB causes cell-specific changes in chemosensory tuning, even among similar projection neurons.

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