A fly pheromone receptor
Tal Soo Ha and Dean P. Smith
Insects use pheromone signaling for all sorts of interesting behaviors, yet only a single volatile pheromone has been identified in Drosophila, the lipid 11-cis-vaccenyl acetate (VA). Upon release by males, VA induces aggregation behavior in both sexes. This week, Ha and Smith identify VA's molecular target on trichoid sensilla, located on the ventral-lateral surface of the antenna. VA activates olfactory neurons on T1-type sensilla. The authors screened the Drosophila odorant receptor (Or) gene family in flies lacking functional T1 sensilla. One gene, Or67d was reduced or absent in the mutants. Misexpression of Or67d in olfactory neurons of non-T1 sensilla conferred sensitivity to VA. LUSH, an extracellular protein expressed by sensillar lymph cells, is required for T1 sensitivity to VA and is also expressed in non-T1 sensilla. The lush1 mutation eradicated VA sensitivity in transgenic flies misexpressing Or67d. Thus, VA sensitivity requires both Or67d and LUSH.
Visualizing a netrin gradient
Timothy E. Kennedy, Hao Wang, Wallace Marshall, and Marc Tessier-Lavigne
Chemotropic guidance cues can act through gradients formed by graded expression levels or graded distribution. This week, Kennedy et al. visualized the netrin-1 gradient that guides commissural axons within the developing spinal cord. The authors generated antibodies to visualize netrin-1 and netrin-2 in the developing chick spinal cord. At the time when commissural axons began to extend, netrin-1 immunoreactivity was found not only in the floor plate where it is expressed by floor plate cells, but also in the ventral neural epithelium and dorsal spinal cord. Netrin-2 in contrast had a much more restricted pattern limited to neural epithelial cells that express it in the ventral spinal cord, and it was expressed at much lower levels. In mice, netrin-1, which performs the function of both proteins, was expressed in a pattern similar to that of netrin-1 and netrin-2 in chicks. Thus for commissural neuron guidance, the netrin-1 gradient is consistent with its long-range actions.
Contextual modulation in human visual areas
Hiroshi Ban, Hiroki Yamamoto, Masaki Fukunaga, Asuka Nakagoshi, Masahiro Umeda, Chuzo Tanaka, and Yoshimichi Ejima
When it comes to visual processing, a complex scene, once viewed, is broken into pieces, sent to the contralateral hemisphere, and put back together by higher processing centers. This week, Ban et al. explore the role that the early stage of processing in the primary visual area (V1) has in putting a complex visual scene back together again. The authors presented subjects with quarter arc patterns located in one quadrant of the visual field. Using functional magnetic resonance imaging, regions of interest (ROI) in contralateral V1 were activated by quarter arcs in each quadrant. Activity in the ROI for one quadrant was enhanced when a complete circle was presented compared to the arc alone. Interestingly, the response was strongest when two arcs were presented in diagonal (interfield) rather than adjacent (intrafield) quadrants, perhaps best suggesting a complete circle. The authors argue that this phenomenon, called contextual modulation, involves feedback to V1 from higher centers.
Revisiting the direct and indirect striatal pathways
Agnes Nadjar, Jonathan M. Brotchie, Celine Guigoni, Qin Li, Shao-Bo Zhou, Gui-Jie Wang, Paula Ravenscroft, François Georges, Alan R. Crossman, and Erwan Bezard
Striatal neurons are often grouped by their projection targets. Neurons of the "direct" pathway innervate the internal segment of the globus pallidus (GPi), express the D1 dopamine receptor, and corelease dynorphin and substance P with GABA, whereas "indirect" pathway neurons target the external GP (GPe), express D2 receptors, and corelease enkephalin with GABA. This week, Nadjar et al. asked how these projection neurons might change with the loss of dopaminergic inputs. The authors studied four groups of monkeys: normal, parkinsonian, and parkinsonian chronically treated with L-dopa, with and without dyskinesia. The authors injected the GP with the retrograde tracer cholera toxin subunit b (CTb), and then co-immunostained the striatum for CTb and dopamine receptors or opioid peptides. Surprisingly, they found evidence of all four proteins in both pallidal areas. This pattern was not affected by the presence of parkinsonism. The results suggest that striatofugal pathways are not completely segregated in the primate.