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The Journal of Neuroscience, September 14, 2005, 25(37)
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This Week in the Journal
Cellular/Molecular
The Smallest Sensilla of the Drosophila Antenna
C. Andrea Yao, Rickard Ignell, and John R. Carlson
(see pages 8359–8367)
The fruit fly "nose" consists of arrays of sensilla in the third antennal segment. Drosophila olfactory receptor neurons (ORNs) are housed in morphologically distinct sensilla, including the tiny, and therefore previously uncharted, coeloconic sensilla. Using extracellular recordings, Yao et al. identified four types of coeloconic sensilla (ac1–ac4) containing seven classes of ORNs and a broad range of functional characteristics. These sensilla typically contained two ORNs, A and B cells, distinguishable based on their spike amplitudes. Some cells responded strongly to a particular odor, whereas the ac3B ORN was very broadly responsive to the odors tested. Ammonia, a component of human sweat, was one notable trigger, something to remember the next time you share space with mosquitoes. Cells of the ac1 and ac2 sensilla were hygrosensors, responding to changes in humidity. The properties of the evolutionarily ancient coeloconic sensilla may provide a clue to the basic needs of insects of long ago.
Development/Plasticity/Repair
Pluripotency and Juvenile Cortical Neurons
Tomoharu Osada, Nobuaki Tamamaki, Si-Young Song, Naoki Kakazu, Yukiko Yamazaki, Hatsune Makino, Ayako Sasaki, Teruyoshi Hirayama, Shun Hamada, Klaus-Armin Nave, Ryuzo Yanagimachi, and Takeshi Yagi
(see pages 8368–8374)
Some neurons can retain developmental pluripotency, as shown by the cloning of mice from olfactory receptor neurons by tetraploid complementation. This week, Osada et al. produced fertile offspring from cortical neurons of juvenile mice. The authors isolated green fluorescent protein (GFP)-tagged pyramidal or GABAergic neurons from juvenile mice and injected the neuronal nuclei into enucleated oocytes. From the resulting blastocysts, they established six embryonic stem (ES) cell lines. In tetraploid complementation, ES cells are transferred into the blastocoele of a tetraploid blastocyst; the ES cells produce the embryo, whereas extraembryonic tissues such as the placenta are derived from the tetraploid cells. This method produced 19 (of 992 attempts) mouse pups with GFP-labeled bodies, but not placenta. Nuclear transfer (injection of an ES cell nucleus into an enucleated oocyte) yielded four pups. Of these pups, three showed GFP in body and placenta and one reached adulthood. Thus some of these central neurons had developmental pluripotency, and perhaps rarely totipotency.
Behavioral/Systems/Cognitive
Recording Single Neurons in the Human ACC
Karen D. Davis, Keri S. Taylor, William D. Hutchison, Jonathan O. Dostrovsky, Mary P. McAndrews, Erich O. Richter, and Andres M. Lozano
(see pages 8402–8406)
This week, Davis et al. had the rare opportunity to study single neuron activity in humans. The authors recorded from caudal anterior cingulate cortex (cACC) neurons in patients undergoing cingulotomy for severe obsessive–compulsive disorder (OCD). The cACC has been implicated in several cognitive processes, including salience and attention. During the recordings, subjects performed cognitive Stroop tasks; they were asked how many times a word appeared within lists of neutral or conflicting words. Cognitively conflicting words were numbers (e.g., one) that differed from the correct answer for the task (e.g., 3). Emotionally conflicting words (e.g., murder) included some that were upsetting to OCD patients (e.g., filthy). The cell responses fell into four categories, perhaps indicating that ACC cells are involved in salience detection. High-conflict-specific cells responded specifically to high-conflict words, whereas graded cells responded slightly more to high-conflict words. There were also nonspecific cells and nonresponsive cells. Some cACC cells were affected preferentially by emotionally laden high-conflict tasks.
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Representative example showing the electrode trajectory (white line) and area of recorded cells (rectangle) in a human subject, as reconstructed from magnetic resonance imaging and cell microdrive recording depths. See the article by Davis et al. for details.
Neurobiology of Disease
Cdk4, E2F, myb, Bim: You're Dead
Subhas C. Biswas, David X. Liu, and Lloyd A. Greene
(see pages 8349–8358)
Cell-cycle regulatory molecules contribute to apoptotic neuron death, but the signaling pathways have yet to be fully explored. This week, Biswas et al. link the pro-apoptotic BH3-domain molecule, Bim, in this process. They traced an apoptotic cascade triggered by NGF withdrawal in pheochromocytoma 12 cells or cultured sympathetic neurons. Inhibitors of the cell-cycle-related molecule cdk4 blocked Bim upregulation, placing cdk4 in the pathway. A complex of E2F and retinoblastoma (Rb) usually silences genes with E2F binding sites, but cdk4 activation results in de-repression of E2F-regulated genes, including the myb family of transcription factors. The Bim promoter contains two binding sites for the myb family transcription factors. B-myb and C-myb were de-repressed by apoptotic stimuli and mediated Bim induction. Thus, one pathway linking the cell cycle to apoptosis includes cdk4, E2F–Rb, myb, and Bim.
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