Figure 4.

Circuitry of consolidation.

(A) Output from DPM neurons after training is required for memory consolidation. DPM neurons ramify throughout the mushroom body, except the calyx. Innervation of the α′β′ and γ lobe appears more dense than in the αβ lobe, and the αβ_c in particular, but the functional significance is not known. Expression of the GFP-tagged presynaptic marker protein bruchpilot predominantly localized to the αβ lobes, implying plausible functional directionality of DPM from the α′β′ and γ lobes to the αβ lobe. (B) Output from APL neurons is required after training to maintain labile memory. Inhibitory APL neurons innervate the entire mushroom body neuropil and show no obvious regional preference. APL neurons are gap junction-coupled to DPM neurons. (C) Model for memory consolidation. Cholinergic (ACh) projection neurons transfer olfactory information to αβ, α′β′ and γ Kenyon cell dendrites in the mushroom body calyx (1). Within microcircuit domains (shaded yellow) the odor-activated and learning-potentiated Kenyon cells activate the APL neuron (2). The APL depolarizes the DPM neuron through gap junctions mainly in the α′β′ lobes (3). The serotonergic (5-HT) DPM closes a reverberant circuit loop by releasing transmitter onto Kenyon cells (4). APL neurons provide lateral inhibition within the mushroom body lobes and calyx, maintaining signal specificity within the recurrent network (5). Over time, DPM-released 5-HT consolidates memory in the αβ Kenyon cells through the d5HT1A receptor (6).