Characterization of the deg-3/des-2 receptor: a nicotinic acetylcholine receptor that mutates to cause neuronal degeneration.

The nicotinic acetylcholine receptor family (nAChR) is a large family of acetylcholine-gated cation channels. Here we characterize the Caenorhabditis elegans DEG-3/DES-2 nAChR, a receptor identified due to its involvement in neuronal degeneration. Pharmacological analysis of a DEG-3/DES-2 receptor expressed in Xenopus oocytes shows that this receptor is preferentially activated by choline. This choline sensitivity of the DEG-3/DES-2 channel can explain its role in neuronal degeneration, as shown by the toxic effects of choline on oocytes expressing the mutant DEG-3/DES-2 channel. We also show that in C. elegans the DEG-3/DES-2 receptor is localized to nonsynaptic regions, including the sensory endings of chemosensory neurons. This localization is in agreement with a role for this receptor in chemosensation of choline, as inferred from a defect in chemotaxis for choline seen in deg-3 mutants. Thus, this work also provides evidence for the diversity of nonsynaptic activities associated with nAChRs.

Polynuclear chromium(III) carboxylates. 1. Synthesis, structure, and magnetic properties of an octanuclear complex with a ring structure.

A novel cyclic octanuclear chromium(III) complex with hydroxo and acetato bridging ligands was isolated and its structure determined by X-ray crystallography. The complex [Cr8(OH)12(OAc)12] (1) (OAc- = CH3CO2-), as found in crystals of 1.34H2O, is obtained by refluxing an aqueous solution of the trinuclear "basic" chromium acetate. 1.34H2O crystallizes in the tetragonal space group I42d with the following unit cell dimensions: a = 16.592(2) A, c = 31.557(4) A, V = 8687(1) A3, and Z = 2. A total of 2000 unique data with I > 3 sigma (I) were used to solve and refine the structure to R(Fo) = 0.066 and Rw(Fo) = 0.085. The structure consists of eight Cr(III) ions that form a ring structure and are bridged by hydroxo and acetato ligands. Each of the two neighboring metal atoms in 1 is bridged either by two OH- ligands and one OAc- ligand, with a Cr...Cr distance of 2.949(2) A, or by two OAc- ligands and one OH- ligand, with a Cr...Cr distance of 3.383(2) A in an alternating fashion. The complex resides on a crystallographic 4 center, and the overall symmetry of 1 is S4. The magnetic susceptibility of 1.34H2O was measured in the temperature range of 5-240 K. Our theoretical modeling of the susceptibility data indicates alternating antiferromagnetic exchange interactions between adjacent spin 3/2 Cr3+ ions around the ring, of magnitude J/kB = 13.7 and 8.9 K, respectively.

Relation of cell division to the acquisition of responsiveness to cortisol in the neural retina of the chick embryo.

Responsiveness of the neural retina to cortisol, as measured by cortisol-induced glutamine synthetase activity, is acquired in the chick embryo during the second week of embryogenesis. The magnitude of the response is inversely related to the growth rate of the neural retina. This developmental event is also acquired by the 8-d-old neural retina under organ culture conditions. The acquisition of competence to respond to the hormonal stimulation can be reversibly abolished by inhibition of DNA synthesis with 0.01 mM cytosine arabinoside; the magnitude of response that resumes after withdrawal of the drug, is characterized by the stage of growth of the neural retina. Responsiveness to cortisol in the embryonic neural retina is apparently coupled to the number of Muller cells (the targets for cortisol action) that have withdrawn from the cell cycle.

Interaction of cortisol with the neural retina of the chick embryo in culture.

The uptake of cortisol and the kinetics of hormone-receptor interaction in the cytosol and cell nucleus were investigated in the intact tissue in organ culture. Cortisol is concentrated by the neural retina. The accumulation of the free steroid is temperature dependent but the effect of temperature decreases with the increase of cortisol in medium. Cortisol binding to specific receptors in the cytosol shows a sigmoidal type of kinetics which correlates well with the kinetics of glutamine-synthetase induction by cortisol. The temperature dependent translocation of the receptor-hormone complexes to the nuclei and the effect of detergents on the binding to nuclei are presented.