Speaker
Description
Social insects possess voluminous mushroom bodies (MBs), high-order sensory integration centers for multisensory integration, learning, and memory. In the honeybee Apis mellifera, the MBs receive olfactory input in the MB-calyx lip region. Within the lip, olfactory projection neurons (PNs) form discrete modular synaptic complexes (microglomeruli, MG), mainly with dendritic specializations from MB intrinsic neurons, the Kenyon cells (KCs). Besides excitatory olfactory input, MG in the MB-calyx lip also receive inhibitory signaling from γ-aminobutyric acid (GABA)-ergic feedback neurons from the MB lobes (type A3v). These were shown to play an important role in maintaining sparse olfactory coding by the KCs and olfactory learning and memory performances.
Our earlier studies using a combination of immunolabeling and serial section electron microscopy demonstrated a remarkable structural plasticity in olfactory MG densities and numbers associated with thermal experience mediated by brood care, adult age, task, as well as non-associative and associative sensory experience. During natural behavioral maturation from nursing to foraging, an overall reduction in MG numbers (pruning) goes along with an increase of the numbers of postsynaptic profiles per MG, resulting in an increase in the PN-KC synaptic divergence ratio by >30%. This raises the question: How do changes in innervation by GABAergic feedback neurons contribute to the plasticity in MG microcircuits?
Given the functional importance of inhibitory signaling for olfactory processing and complex learning tasks, we analyze the maturation of GABAergic innervation patterns in the MB calyx. Using consecutive age cohorts, we address quantitative aspects like the density of GABAergic terminal profiles in the calyx lip at different ages after adult eclosion. Our results show that the olfactory lip is densely innervated by profiles from GABAergic feedback neurons. Preliminary results suggest that GABAergic innervation densities remain stable during adult maturation, while the number of PN boutons decreases, thus indicating a shift in the GABAergic innervation ratio in the calyx lip. This suggests that resulting changes in GABAergic signaling may play an important role in the maturation of odor discrimination and learning abilities.
Supported by DFG (project # 430253184 to CG and project # 272768235).
