1. Mapping the Tectum onto the Hindbrain in Zebrafish
Tomomi Sato, Takanori Hamaoka, Hidenori Aizawa, Toshihiko Hosoya, and Hitoshi Okamoto.
Retinotopic inputs to the optic tectum have been thoroughly mapped, but now Sato et al. map tectal efferents that project to the premotor reticulospinal system of the hindbrain. Stimulation of these efferents trigger eye and tail movements, often as escape behavior. The authors began with a transgenic zebrafish that expressed green fluorescent protein (GFP), driven by the brn3 promoter. GFP labeled the ipsilateral (uncrossed) but not contralateral (crossed) tectobulbar tracts. By combining the cre/loxP and Gal4/UAS systems under the control of brn3a-hsp70, the authors zeroed in on the somatic origin and final projection sites of individual tectal neurons. Within the hindbrain, rhombomeres (r) 2 and 6 received inputs in distinct anterior-posterior patterns, potentially indicative of their role in visuomotor transformations. Reticulospinal neurons in r2 are activated during visually evoked escape behavior. Ectopic expression of ephrinB2a increased the probability that neurons projected to r2.
2. Aggrecan and Perineuronal Nets in Barrel Cortex
Paulette A. McRae, Mary M. Rocco, Gail
Kelly, Joshua C. Brumberg, and Russell
The component of the extracellular matrix called the perineuronal net (PN), as its name implies, surrounds the cell body and proximal dendrites of selected cortical neurons. This week, McRae et al. report that the PN in somatosensory barrel cortex is affected by sensory experience. The authors identified the PN by staining with Cat-315, an antibody for the proteoglycan, aggrecan. Neurons ensheathed by lattice-likePNwere enriched in layer IV of mouse barrel cortex. Sensory deprivation, imposed by continuous trimming of right-side whiskers for the first 30 d of postnatal life, reduced the number of neurons expressing Cat-315-positive PN. Sensory deprivation of adult mice had no effect on Cat-315 staining. When whiskers were allowed to regrow after the initial 30 d deprivation, PNs did not recover but instead continued to decline, highlighting the importance of sensory activity during the first postnatal month. Inside the Cat- 315-reactive nets, the main catch was parvalbumin-expressing interneurons.
3. Dendritic Spines Take Shape during LTP
Lulu Y. Chen, Christopher S. Rex,
Malcolm S. Casale, Christine M. Gall,
and Gary Lynch.
Synaptic plasticity often affects the shape of synaptic structures. This week, Chen et al. take this question to the level of single dendritic spines by investigating actin network dynamics following theta burst stimulation (TBS). In rat hippocampal slices, TBS induced phosphorylation of p21-activated kinase (PAK) and its downstream effecter cofilin, signaling proteins that enable actin filament growth. Immunolabeling for phosphorylated (p) cofilin (pCofilin) and pPAK was robust in a small number of synapses, and was transient, beginning about 30-120 s post-TBS. PAK/cofilin-positive synapses were larger, apparently because of a simple rounding up of spines. Occasional enlarged and rounded spines were also seen in control slices. Block ofAMPAreceptors reduced pCofilin immunoreactivity. The authors estimate that the increase in spines with PAK/cofilin activation was in line with the number of synapses in which long-term potentiation (LTP) occurred.
4. Parkinsonian Mice on Treadmills
Giselle M. Petzinger, John P. Walsh,
Garnik Akopian, Elizabeth Hogg, Avery
Abernathy, Pablo Arevalo, Patty
Turnquist, Marta Vuckovic, Beth E.
Fisher, Daniel Togasaki, and Michael
Exercise can result in symptomatic improvement in patients with Parkinson's disease (PD). In this week's Journal, Petzinger et al. report on exercise-induced changes in dopamine transmission in control C57Bl6/J mice and in PD mice that had been treated with 1-methyl- 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Mice will run spontaneously on running wheels, but these mice got the health club treatment: 28 d of 2-30 min sessions on a 6 lane treadmill, 5 d/week (weekends off apparently). By the end of training, both groups were moving at about 1.8 km/h. The treadmill experience improved balance in control and MPTPlesioned mice. Although there was no difference in striatal dopamine (DA) levels between exercised and nonexercised MPTP-lesioned mice, exercise increased striatal DA levels in control mice. In MPTP-lesioned mice, exercise increased evoked vesicular DA release in striatal slices, particularly in dorsal striatum. Exercise also decreased striatal DA transporter and tyrosine hydroxylase immunoreactivity in MPTP-lesioned mice.