A new substrate for cultures of dissociated primary rat brain

Different substrates were used to coat plastic petri dishes for the cultivation of dissociated fetal rat brain cells. Only on surfaces which were coated with a mixture of serum and non-reconstituted collagen, did the majority of the inoculated cells attach singly or as aggregates within 24 h. The attachment of the cells was followed by the outgrowth of cellular processes either from single cells or from aggregates in the same time period. This did not occur on collagen or serum treated or on regular plastic dishes. Under the latter conditions a similar outgrowth was observed only after 3–5 days.     

Activity of orotate metabolizing enzyme complex and various urea-cycle enzymes in mutant mice with ornithine transcarbamylase deficiency

Summary The overall activity of the enzyme complex consisting of orotate phosphoribosyl transferase and orotidine monophosphate decarboxylase, and of various enzymes of the urea cycle, has been studied in sparse-fur (spf) mutant mice with ornithine transcarbamylase deficiency. The enzyme complex has a lower overall activity, which could be caused by disturbed pyrimidine metabolism due to hyperammonemia. Other enzymes of the urea cycle do not show any significant change.Acknowledgments. The research was supported by a grant from the Conseil des Clubs Sociaux and Fondation Justine Lacoste Beaubien, Montréal. The authors wish to thank Ms Louise Poulin and Ms Francine Poisson for technical assistance.     

A voltage-gated ion channel model inferred from the crystal structure of alamethicin at 1.5-A resolution

The crystal structure of alamethicin in nonaqueous solvent has been determined, and refined at 1.5-A resolution. The molecular conformation of the three crystallographically independent molecules is largely alpha-helical with a bend in the helix axis at an internal proline residue. The helix structure is highly amphipathic as most of the solvent-accessible polar atoms lie on a narrow strip of surface parallel to the helix axis. Molecular models for the voltage-gated ion channel, with n-fold symmetry and based on the molecular conformations observed in the crystal, are characterized by strong surface complementarity, a hydrophilic interior and a hydrophobic exterior. The channel structures are stabilized by a hydrated annulus of hydrogen-bonded glutamine residues which produce the greatest restriction in the channel diameter.     

Different postsynaptic events in two types of retinal bipolar cell

The first synapse in the vertebrate visual system is made between the photoreceptors and the biopolar cells. Bioplar cells fall into two distinct classes according to whether the cell hyperpolarizes or depolarizes to small centred spots of light. Most evidence indicates that the light-induced hyperpolarization of the photoreceptprs suppresses transmitter release from the synaptic terminals, and it is probable that the differences between the two bipolar cell classes results from the different actions of the photoreceptor transmitter. In analysing the membrane potential fluctuations in both types of bipolar cell we find that the voltage noise spectra differ. It is to be expected that postsynaptic noise would be composed of the sum of noise generated in and transmitted from the cones and the noise arising from the statistical nature of synaptic transmission. We report here evidence for two such components in the voltage noise spectra recorded from each type of bipolar cell. The differences in the frequency distribution of the presumed transmitter-related components indicates that the transmitter generates events of longer duration in the depolarizing biopolar cells.     

Adaptation of the pituitary gland to prolonged LRH stimulation

Summary With prolonged constant rate infusion of luteinizing hormone-releasing hormone (LRH), the LH secretion rate of the rat pituitary gland changes continuously until a steady state of relative desensitization has developed. Recovery from this state can occur independently from changes in the pituitary's LH content.