One of the goals of the lab is to identify the underlying neural mechanisms that cause the stereotypical zigzagging paths that we observe from plume tracking moths. We have been working to locate and identify the descending neurons, shown to be involved in the sex-pheromone tracking behavior of male silkworm moths, Bombyx mori, in the brain of Manduca sexta. In order to see groups of descending interneurons, we applied flourescent dye to stain axons of neurons running through the cervical connectives running between the brain and thoracic ganglia. These ganglia house the motor neurons which control the muscles that move the wings.
By using scanning confocal microscopy , we have identified two groups of descending interneurons that match in their location and anatomy those known from B mori, and are shown to be involved in their pheromone tracking behavior by Ryohei Kanzaki. Although the anatomy of the these cells in the M. sexta brain matches those of B. mori, we have not recorded their physiological responses to pheromone, so we can not yet say if they play the same role in the behavior of M. sexta that they do in B. mori.
In B. mori, the physiological activity of these neurons during pheromone stimulation has been termed "flip-flopping" and is characteristic of these cells. When the animals are stimulated by pheromone these neurons "flip" from a state of low (or high) firing to high (or low) firing. On the next pheromone stimulus the cell's firing state "flops" back into its previous firing state. When the cell on the right flips to the high firing state its mirror image cell in the left connective flops to a low firing state. These neurons connect to the motor neurons controlling the neck mucsles in B. mori, so the head turns back-and-forth as the firing rate in the flip-flop cells changes during pheromone stimulation. Previous studies by Ryohei Kanzaki, involving B. mori have shown that the body follows the head, creating a turn. Therefore it is thought that the result of flip-flopping activity in the descending interneurons of walking B. mori is a zigzagging track to the pheromone source. We plan to take recordings from these interneurons while the moth is odor tracking in our wind tunnel to see if the same mechanisms that B. mori uses holds true for M. sexta.
We have also observed neurons in the thoracic ganglia which appear to be cells carrying information from the flight motor centers to the brain. The presence of cell bodies in the thoracic ganglia with axons leading to the brain suggests that information flows from the thorax to the brain allowing feedback from locomotory structures.