Individual Neurons Confined to Distinct Antennal-Lobe Tracts in the Heliothine Moth: Morphological Characteristics and Global Projection Patterns

Abstract

To explore fundamental principles characterizing chemosensory information processing, we have identified antennal-lobe projection neurons in the heliothine moth, including several neuron types not previously described. Generally, odor information is conveyed from the primary olfactory center of the moth brain, the antennal lobe, to higher brain centers via projection neuron axons passing along several parallel pathways, of which the medial, mediolateral, and lateral antennal-lobe tract are considered the classical ones. Recent data have revealed the projections of the individual tracts more in detail demonstrating three main target regions in the protocerebrum; the calyces are innervated mainly by the medial tract, the superior intermediate protocerebrum by the lateral tract exclusively, and the lateral horn by all tracts. In the present study, we have identified, via iontophoretic intracellular staining combined with confocal microscopy, individual projection neurons confined to the tracts mentioned above, plus two additional ones. Further, using the visualization software AMIRA, we reconstructed the stained neurons and registered the models into a standard brain atlas, which allowed us to compare the termination areas of individual projection neurons both across and within distinct tracts. The data demonstrate a morphological diversity of the projection neurons within distinct tracts. Comparison of the output areas of the neurons confined to the three main tracts in the lateral horn showed overlapping terminal regions for the medial and mediolateral tracts; the lateral tract neurons, on the contrary, targeted mostly other output areas in the protocerebrum.

Anatomical organization of the brain of a diurnal and a nocturnal dung beetle

“…While the mlALT in dung beetles seems to connect specifically to the LH, the tALT bifurcates and appears to make connections also to the protocerebrum. These connection patterns are similar to those in Drosophila (Tanaka, Suzuki, et al, 2012) and Heliothis Ian, Zhao, et al, 2016).…”

“…As in other species, the mALT was found to be the thickest ALT, and could be clearly distinguished from the rest by a strongly anti-5-HTimmunoreactive fiber. As in the noctuid moth H. virescens, the mALT in dung beetles seems to be the only ALT that directly connects the AL and the mushroom body calyx (CA) (Figure 9d-f; Ian, Zhao, Lande, & Berg, 2016). As in the noctuid moth H. virescens, the mALT in dung beetles seems to be the only ALT that directly connects the AL and the mushroom body calyx (CA) (Figure 9d-f; Ian, Zhao, Lande, & Berg, 2016).…”

“…Presumably, this fiber belongs to a 5-HTimmunoreactive neuron that is found across species and innervates most, if not all of the AL glomeruli and runs through the mALT into the CA (Dacks, Christensen, & Hildebrand, 2006;Kloppenburg & Mercer, 2008;Schachtner et al, 2005). As in the noctuid moth H. virescens, the mALT in dung beetles seems to be the only ALT that directly connects the AL and the mushroom body calyx (CA) (Figure 9d-f; Ian, Zhao, Lande, & Berg, 2016). While the mlALT in dung beetles seems to connect specifically to the LH, the tALT bifurcates and appears to make connections also to the protocerebrum.…”

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

“…Contralateral neurons of the type reported here (Fig. 9E) have only been noted occasionally in Manduca sexta (Homberg et al, 1988), H. virescens (Ian et al, 2016a) and another noctuid species, Agrotis segetum (Wu et al, 1996). Our results indicate that the contralateral neuron follows the v-lALT before sending a branch toward the margin of PED with the main axon turning toward the midline.…”

“…Rø et al (2007) reported a similar l-lcPN with sparse dendritic arborizations in several glomeruli from a female H. virescens indicating that the d-lALT pathway is not restricted to pheromone processing in males. Another such l-lcPN was reported by Ian et al (2016a) although it was not clear if this neuron was stained in a female or male H. virescens.…”