Projection patterns of different types of antennal sensilla in the antennal glomeruli of Drosophila melanogaster

Abstract

Cobalt fills from small, defined regions of the antenna in D. melanogaster show that the three types of sensilla on the third segment, the flagellum, and a fourth sensillum located in the arista, project into the glomeruli of the antennal lobe. We have identified 19 glomeruli in each lobe, according to their location, shape, and size. At least ten of these represent major projection areas of flagellar or aristal sensilla. The large majority of glomeruli is innervated from both antennae, but a small group of five receive exclusively ipsilateral input. A particular sensory fiber appears to terminate only in one specific glomerulus, either in the ipsilateral or in both lobes. Fills from flagellar regions bearing a single type of sensillum, yield a specific pattern of glomeruli containing stained terminals. Aristal projections remain strictly ipsilateral, whereas those from the other sensilla consist of an ipsilateral and a bilateral component. When filling from different points in an area bearing one type of sensillum, similar projections are produced, suggesting that projection patterns observed reflect predominantly the type of sensillum rather than its location on the flagellum. Accordingly, individual glomeruli might represent functional units, each receiving antennal input in a characteristic combination.

Complementary Function and Integrated Wiring of the Evolutionarily DistinctDrosophilaOlfactory Subsystems

“…3E). These include IR75d (VL1), consistent with previous cobalt backfill analyses (Stocker et al, 1983), and the IR40a axons innervating the column but not most of the arm (Fig. 3E).…”

“…Similarly, our attempts to construct a functional reporter for IR21a, which is expressed in neurons in the arista and sacculus (Benton et al, 2009), were unsuccessful (data not shown). However, these cells may correspond to those labeled by an enhancer trap near the brivido1 gene [encoding a transient receptor potential (TRP) channel] that-consistent with previous backfill studies (Stocker et al, 1983)-project to the VP3 glomerulus at the posterior of the antennal lobe (also referred to as the proximal antennal protocerebrum) (Gallio et al, 2011). Finally, the neurons expressing two IR coreceptors, IR8a and IR25a, as well as IR76b, which is expressed in one cell in each coeloconic sensillum class (Fig.…”

“…3G). Glomeruli receiving exclusively ipsilateral input, including the V glomerulus innervated by GR21a/GR63a neurons (Stocker et al, 1983;Scott et al, 2001;Couto et al, 2005;Jones et al, 2007;Kwon et al, 2007), are also grouped together in a posterior-ventral portion of the lobe (Fig. 3H ).…”

“…The coreceptor IR25a, but not IR8a, is robustly expressed in these populations of neurons (Benton et al, 2009), suggesting that it may act as a coreceptor for these sacculus and aristal IRs. j VP1 was originally described, through cobalt backfill analysis, as one of the five glomeruli receiving unilateral input located between VP2 and VP3 (Stocker et al, 1983). The complete morphology of this glomerulus has not been reported, however, and the inability to visualize this neuropil with nc82 staining has led to subsequent antennal lobe maps either excluding VP1 (Laissue et al, 1999;Couto et al, 2005) or presenting different representations of its position (Chou et al, 2010a;Yu et al, 2010a).…”

Sensory determinants of behavioral dynamics in Drosophila thermotaxis

“…Substantial progress has been made in understanding circuits for thermotaxis in the adult fly (3). Distinct peripheral sensory pathways for warm and cold avoidance that start in the fly antenna and project to the adult central brain, also to a region ventral to the antennal lobe, have now been identified (9,37), as well as a distinct internal sensory pathway involving the anterior cell warmth sensors in the fly brain (10). The molecules, cells, and circuits for negative thermotaxis in Drosophila larva remain poorly understood, except at noxious temperatures (18,38), and we have not yet identified circuits for negative thermotaxis (warm avoidance).…”