Antennal-lobe tracts in the noctuid moth, Heliothis virescens: new anatomical findings

Abstract

As in other insects, three main tracts in the moth brain form parallel connections between the antennal lobe and the protocerebrum. These tracts, which consist of the antennal-lobe projection-neuron axons, target two main areas in the protocerebrum, the calyces of the mushroom bodies and the lateral horn. In spite of the solid neuroanatomical knowledge already established, there are still unresolved issues regarding the antennal-lobe tracts of the moth. One is the proportion of lateral-tract neurons targeting the calyces. In the study presented here, we have performed both retrograde and anterograde labeling of the antennal-lobe projection neurons in the brain of the moth, Heliothis virescens. The results from the retrograde staining, obtained by applying dye in the calyces, demonstrated that the direct connection between the antennal lobe and this neuropil is maintained primarily by the medial antennal-lobe tract; only a few axons confined to the lateral tract were found to innervate the calyces. In addition, these staining experiments, which allowed us to explore the arborization pattern of labeled neurons within the antennal lobe, resulted in new findings regarding anatomical arrangement of roots and cell body clusters linked to the medial tract. The results from the anterograde staining, obtained by applying dye into the antennal lobe, visualized the total assembly of axons passing along the antennal-lobe tracts. In addition to the three classical tracts, we found a transverse antennal-lobe tract not previously described in the moth. Also, these staining experiments revealed an organized neuropil in the lateral horn formed by terminals of the four antennal-lobe tracts.

Olfactory Projection Neurons From the Moth Antennal Lobe Lateral Cluster exhibit Diverse Morphological and Neurophysiological Characteristics

“…The lALT has previously been identified as a major output pathway for lcPNs (Homberg et al, 1988;Berg et al, 2007;Ian et al, 2016a,b). The current study confirms that pheromone-responsive lcPNs contribute to the lALT but also reveals that this tract bifurcates around the GC giving rise to ventral and dorsal pathways (Rø et al 2007;Ian et al, 2016b). Physiologically these PNs responded to single odorants but were characterized as blend enhanced.…”

“…The morphology of the contralateral lcPN (Fig. 9E) is similar to ones previously reported in A. segetum (Wu et al 1996) and H. virescens (Ian et al 2016b). The axon of this PN followed the v-lALT ipsilaterally with no apparent synaptic contacts in the isthmus or along the ipsilateral process ( Fig.…”

“…8D). This part of the SIP was termed the column by Ian et al (2016b) although this is not a recognized structure in the consensus insect brain (Ito et al 2014).…”

The brain of a nocturnal migratory insect, the Australian Bogong moth

“…The second major target region for olfactory projections from the AL is the lateral horn ( Figure 6I). The neurons terminating in the lateral horn either originate in the medial antennal lobe tract and reach the lateral horn after providing input to the calyx, or they target this region directly via the lateral and mediolateral antennal lobe tracts (Ian, Berg, Lillevoll, & Berg, 2016). The lateral horn neuropil is located in the lateralmost part of the central brain and is medially completely fused with the surrounding protocerebral regions (inferior, superior and ventrolateral protocerebrum).…”

Coincidence of pheromone and plant odor leads to sensory plasticity in the heliothine olfactory system

“…In a recent study of the heliothine moth, we demonstrated that the calyces get input mainly from the uni-glomerular PNs belonging to the medial ALT [16]. This kind of arrangement allowed us to measure odor-evoked activity from the medial-tract PNs specifically by applying the calcium-sensitive dye fura2 into the calyx.…”