A Novel Major Output Target for Pheromone-Sensitive Projection Neurons in Male Moths

Abstract

Even though insects have comparably small brains, they achieve astoundingly complex behaviors. One example is flying moths tracking minute amounts of pheromones using olfactory circuits. The tracking distance can be up to 1 km, which makes it essential that male moths respond efficiently and reliably to very few pheromone molecules. The male-specific macroglomerular complex (MGC) in the moth antennal lobe contains circuitry dedicated to pheromone processing. Output neurons from this region project along three parallel pathways, the medial, mediolateral, and lateral tracts. The MGC-neurons of the lateral tract are least described and their functional significance is mainly unknown. We used mass staining, calcium imaging, and intracellular recording/staining to characterize the morphological and physiological properties of these neurons in the noctuid moth, Helicoverpa armigera. All lateral-tract MGC neurons targeted the column, a small region within the superior intermediate neuropil. We identified this region as a unique converging site for MGC lateral-tract neurons responsive to pheromones, as well as a dense congregating site for plant odor information since a substantial number of lateral-tract neurons from ordinary glomeruli (OG) also terminates in this region. The lateral-tract MGC-neurons responded with a shorter peak latency than the well-described neurons in the medial tract. Different from the medial-tract MGC neurons encoding odor quality important for species-specific signal identification, those in the lateral tract convey a more robust and rapid signal-potentially important for fast control of hard-wired behavior.

Neuronal architecture of the second-order CO2 pathway in the brain of a noctuid moth

“…Although some of the LPOG PNs stained here, i.e. four neuron subtypes (Pt_a (LPOG) , Pt_d (LPOG) , Pm_e (LPOG) , and Pl_g (LPOG) ), had axonal terminals in the SLP, they targeted a distinct area localized more ventrally and lateral-posteriorly as compared to the MGC PNs 25,35,45 .…”

“…www.nature.com/scientificreports/ Iontophoretic staining of individual PNs originating from the LPOG. The procedure of iontophoretic staining of AL PNs was performed as previously described 25,27,35 . Sharp electrodes were made by pulling quartz capillaries (OD: 1 mm, ID: 0.5 mm, with filament; Sutter instrument) on a horizontal puller (P-2000, Sutter instruments, CA, United States).…”

“…Reconstruction and registration of neurons into the representative brain. The 3D reconstruction of relevant neuropil structures was based on the previously conducted confocal stacks for the representative brain 25 . We used the nomenclature established by Ito, et al 60 with the exceptions of the VLP.…”

“…To provide a framework for determining the target areas of the LPOG PNs, we reconstructed nine new protocerebral regions from the confocal image stack previously utilized for creating the representative brain model 25 , Image intensity processing and statistical analysis. As retrograded staining from the Ca labeled dendrites of all AL PNs linked with this neuropil, we could investigate putative differences in connection pattern between the LPOG and a typical ordinary glomerulus by measuring the glomerular fluorescence intensities.…”

Distinct protocerebral neuropils associated with attractive and aversive female-produced odorants in the male moth brain

“…CC-BY-NC-ND 4.0 International license perpetuity. It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in The copyright holder for this this version posted December 11, 2020. ; https://doi.org/10.1101/2020.12.11.421289 doi: bioRxiv preprint could potentially overlap in specific protocerebral regions (Chu et al, 2020a). To explore whether such PNs intersect, we next performed multi-staining experiments.…”