Neural coding of isopentyl acetate alarm pheromone signals in the honey bee brain

Alarm pheromone is a high-priority social signal in honey bees, yet direct evidence for how its major component, isopentyl acetate (IPA), is encoded in antennal lobe remains limited. Here, we combine intracellular recording, neuronal staining, and three-dimensional reconstruction to examine neural responses to IPA in the honey bee brain. Integrated analysis of antennal lobe neurons revealed clear but heterogeneous time-locked responses to IPA, which could be grouped into four temporal response motifs: fast transient, monophasic, biphasic excitation-inhibition, and delayed excitation-inhibition. A morphologically identified antennal lobe neuron exhibited a stable excitatory response characterized by short latency and prolonged elevated firing after stimulus onset. In a representative delayed-type antennal lobe neuron, response magnitude showed strong concentration dependence: peak amplitude and post-peak inhibition increased significantly with increasing IPA concentration, whereas peak latency remained largely unchanged. Repeated stimulation at an intermediate concentration produced comparatively modest effects, expressed mainly as attenuation of peak amplitude and a gradual delay in response timing. In addition to antennal lobe neurons, we identified two IPA-responsive protocerebral neurons. Together, these results provide direct single-neuron evidence that IPA is heterogeneously encoded in the honey bee antennal lobe.