Main olfactory bulb reconfiguration by prolonged passive olfactory experience correlates with increased brain-derived neurotrophic factor and improved innate olfaction.

The main olfactory bulb (MOB) is highly plastic and constantly reconfiguring its function and structure depending on sensory experience. Despite the extensive evidence of anatomical, functional and behavioural changes in the olfactory system induced by highly variable olfactory experiences, it is still unknown whether prolonged passive odour experience could reconfigure the MOB at its input and network activity levels and whether these changes impact innate olfaction. Here, by measuring odour-induced glomerular activation, MOB network activity and innate olfactory behaviours, we described a profound MOB reconfiguration induced by prolonged passive olfactory experience in adult animals that impacts MOB input integration at the glomerular layer including an increase in the activated glomerular area and signal intensity, which is combined with a refinement in the number of activated glomeruli and less-overlapped glomerular maps. We also found that prolonged passive olfactory experience dramatically changes MOB population activity in the presence and absence of odours, which is reflected as a decrease in slow oscillations (<12 Hz) and an increase in fast oscillations (>12 Hz). All these functional changes in awake and anaesthetized mice correlate with an increase in brain-derived neurotrophic factor (BDNF) and with improved innate olfactory responses such as habituation/dishabituation and innate preference/avoidance. Our study shows that prolonged passive olfactory experience in adult animals produces a dramatic reconfiguration of the MOB network, possibly driven by BDNF, that improves innate olfactory responses.

Altered Sensory Representations in Parkinsonian Cortical and Basal Ganglia Networks.

In parkinsonian conditions, network dynamics in the cortical and basal ganglia circuits present abnormal oscillations and periods of high synchrony, affecting the functionality of multiple striatal regions including the sensorimotor striatum. However, it is still unclear how these altered dynamics impact on sensory processing, a key feature for motor control that is severely impaired in parkinsonian patients. A major confound is that pathological dynamics in sensorimotor networks may elicit unspecific motor responses that may alter sensory representations through sensory feedback, making it difficult to disentangle motor and sensory components. To address this issue, we studied sensory processing using an anesthetized model with robust sensory representations throughout cortical and basal ganglia sensory regions and limited motor confounds in control and hemiparkinsonian rats. A general screening of sensory-evoked activity in large populations of neurons recorded in the primary sensory cortex (S1), dorsolateral striatum (DLS) and substantia nigra pars reticulata (SNr) revealed increased excitability and altered sensory representations in the three regions. Further analysis revealed uncoordinated population dynamics between DLS and S1/SNr. Finally, DLS lesions in hemiparkinsonian animals partially recovered population dynamics and execution in the rotarod.