**6. The male-specific macroglomerular complex**

In male *M. sexta*, the approximately 42,000 long trichoid sensilla commonly each contain two bipolar olfactory-sensory neurons that project to the macroglomerular complex (MGC) in the AL [9, 63–65]. Each of these two neurons is very sensitive

#### **Figure 3.**

*The figure shows the intracellularly recorded physiological responses of labeled projection neurons in the antennal lobes of the sphinx moth Manduca sexta during antennal stimulation with pheromone. (a) this C15-specialist neuron responded with membrane potential inhibition to a stimulus that contained C15. This was followed by strong depolarization and again inhibition (third and fourth trace). Likewise, antennal stimulation with the pheromone blend of C15 + BAL evoked a mixed response. In contrast, stimulation with bombykal (BAL) evoked an inhibitory response. The antenna was stimulated with five 50-ms stimulus pulses at 5 Hz. The stimulus markers are depicted as black boxes beneath the records. (b) the membrane potential of the neuron was depolarized by injecting current through the recording electrode. As a result, the nerve impulse firing frequency increased, whereas the first stimulus pulse of BAL induced a membrane hyperpolarization and reduction in firing (inhibition). (c) the laser scanning confocal micrograph shows the morphology of two projection neurons in the antennal lobe. The neuron labeled in red, stained with biocytin, is described in figure panels (a) and (b), whereas panels (d) and (e) show the responses of the green, uniglomerular projection neuron, which is in Lucifer yellow (frontal view). C15-specialist neuron, the red neuron, has dendritic branches in the cumulus glomerulus of the macroglomerular complex and not in the toroid-1 or any other glomerulus. The green neuron sent dendritic branches into only one ordinary glomerulus. (d) Electrophysiological recordings from an antennal lobe projection neuron that innervated one of the ordinary glomeruli. When the antenna was stimulated with bomybkal, C15, or a blend of both pheromone components, the neuron responded with a reduction of the firing rate. As in panels (a) and (b), five identical stimulus pulses were delivered to the ipsilateral antenna at a frequency of 5 Hz. (e) Antennal stimulation of the same neuron with the pheromone blend resulted in inhibition, even when the membrane potential of the neuron was depolarized through current injection. The first antennal pheromone stimulus resulted in membrane hyperpolarization. C - cumulus; do - dorsal; G - ordinary glomerulus; la - lateral; me - medial; T1 - toroid-1; T2 - toroid-2. Scale bar = 100 μm. From [66].*
