Indole metabolism in the pineal organ of the pigeon with special reference to melatonin-synthesizing cells

By means of radioimmunoassay a clear-cut peak of melatonin concentration was found in the pineal organ of the pigeon at the middle of the scotophase (Coisin et al. 1982a). The aim of the present study was to identify the cell type responsible for the nocturnal indole metabolism, including melatonin synthesis, in the pineal of this avian species. After a short-term incubation or organ culture in the presence of [3H]-indolic precursors, [3H]-5-hydroxytryptophan or [3H]-5-hydroxytryptamine, the relative amounts of deaminated and acetylated products occurring in the pineal organ were measured by the use of thin layer chromatography and liquid-scintillation counting. It was possible to modify the relative amounts of deaminated and acetylated indoles by the application of some inhibitors of monoamine oxidase and cyclic nucleotide phosphodiesterase. Irrespective of the experimental conditions, high-resolution autoradiography combined with the above-mentioned radiochemical experiments showed that the cells of the receptor line (modified photoreceptor cells) are responsible for indole storage and metabolism, and very probably also for melatonin biosynthesis. The other cell types of the pineal parenchyma did not display significant labeling.     

Isolation and characterization of a 40-kDa cyclophilin-related protein.

Major and minor isoforms of cyclophilin (CyP-18), a 17.8-kDa protein with peptidyl-prolyl cis-trans isomerase activity, comprise the primary intracellular binding proteins for cyclosporin A. Additional CyP-like proteins with approximate molecular masses of 22 (CyP-22) and 40 kDa (CyP-40) have been recovered from the soluble fraction of calf brain along with CyP-18 by adsorption onto a cyclosporin A affinity column and elution with cyclosporin A. Based on a limited number of peptide sequences from CyP-22, it appears that we have isolated from tissue CyPB, a protein whose sequence was deduced previously from cloned cDNA. The 40-kDa protein was separated from CyP-18 and CyP-22 on a molecular sieving column. Isoelectric focusing of CyP-40 yielded two bands at pI 5.3 and 5.5, in contrast to the basic pI values of CyP-18. Some tryptic peptides from CyP-40 were found to be highly homologous but not identical to bovine CyP-18; others were not significantly homologous to CyP-18 or any other protein in the data base. Unlike the major and minor isoforms of Cyp-18, monospecific polyclonal anti-CyP-18 antibodies did not cross-react with CyP-22 and CyP-40. Likewise, anti-CyP-40 serum minimally cross-reacts with CyP-18 and CyP-22. Cyp-40 possesses peptidyl-prolyl cis-trans isomerase activity which is less sensitive to inhibition by cyclosporin A (IC50 = 300 nM) than is CyP-18 (IC50 = 20 nM).     

Selenocysteine confers the biochemical properties characteristic of the type I iodothyronine deiodinase.

The conversion of thyroxine to 3,5,3'-triiodothyronine (T3) is the first step in thyroid hormone action, and the Type I iodothyronine deiodinase supplies most of this extrathyroidal T3 in the rat. We found that the cDNA coding for this enzyme contains an in-frame UGA encoding the rare amino acid selenocysteine. Using site-directed mutagenesis, we have converted selenocysteine to cysteine and expressed the wild-type and cysteine mutant enzymes in JEG-3 cells by transient transfection. The kinetic properties of the transiently expressed wild-type enzyme are nearly identical to those reported for rat liver Type I deiodinase. Substitution of sulfur for selenium causes a 10-fold increase in the Km of the enzyme for the favored substrate 3,3',5'-triiodothyronine (rT3), a 100-fold decrease in the sensitivity of rT3 deiodination to competitive inhibition by gold and a 300-fold increase in the apparent Ki for uncompetitive inhibition by 6-n-propylthiouracil. These results demonstrate that selenium is responsible for the biochemical properties which characterize Type I iodothyronine monodeiodination.     

Differences in learning by foraging juvenile pumpkinseed and bluegill sunfish in a structured habitat

Synopsis We investigated the ability of two congeneric species of sunfish to learn to forage on a novel prey item in feeding arenas containing structured habitats. Eight bluegill sunfish and eight pumpkinseed sunfish were given the opportunity to forage on whiteworms daily for 10 days. Each day, several behavioural measures were recorded for each fish. Both species of sunfish learned to feed over the 10-day period but the bluegill sunfish learned to feed more quickly than the pumpkinseed sunfish. Pumpkinseeds, however, attained a higher level of foraging efficiency. The differences in learning and foraging efficiency were related to body morphology.     

Regulation of chicken pineal arylalkylamine-N-acetyl transferase by postsynaptic alpha 2-adrenergic receptors

The present investigation sought to characterize the adrenergic inhibition of arylalkylamine-N-acetyltransferase in cultured chicken pineal glands. Arylalkylamine-N-acetyltransferase, the melatonin rhythm generating enzyme, displays daily oscillations of activity that are driven by a circadian oscillator. Norepinephrine released at sympathetic nerve endings inhibits the enzyme and appears to play a role in maintaining a circadian rhythm of melatonin release. Chicken pineal glands were isolated in organ culture and the effects of adrenergic agents on the night time peak of N-acetyltransferase activity were studied. Norepinephrine and clonidine prevented 50 to 65% of the nocturnal rise of N-acetyltransferase activity. When applied at middark, norepinephrine and clonidine caused a 50 to 65% inhibition of N-acetyltransferase activity in 2 hours. Dose-response studies indicated clonidine was 100 times more potent than norepinephrine or cirazoline at inhibiting N-acetyltransferase activity. Inhibition of N-acetyltransferase activity was also observed, at micromolar concentration with epinephrine, UK 14,304 and alpha-methylnorepinephrine but not with phenylephrine, isoproterenol or dopamine. Epinephrine and clonidine actions were antagonized by yohimbine but not by prazosin. Destruction of the presynaptic compartment by bilateral superior cervical ganglionectomy did not affect the clonidine-induced inhibition of N-acetyltransferase and its reversal by yohimbine. It is concluded that the adrenergic inhibition of N-acetyltransferase activity in chicken pineal gland probably occurs via stimulation of postsynaptic alpha 2-adrenergic receptors.     

A note on dipole sources in conducting biological tissues

The study of current flow fields in biologicaltissue requires finding the potential field from dipole sources such that the normal gradient vanishes at the exterior surface. A convenient way to determine the dipole field is by taking the gradient of the potential field set up by a point source. However, the point source problem is ill-posed when the normal gradient is required to vanish at the outer surface. In the paper the nature of this problem is discussed and several methods for overcoming the difficulty are presented.     

Secondary product formation in plant tissue cultures

The formation of secondary products in plant tissue culturesis reviewed. The conditions for the enhanced production of secondaryproducts, which include alkaloids, terpenoids, steroids andphenolics, can be regulated in a number of ways. For example,manipulation of secondary product formation is possible by varyingthe nutrient composition of the growth medium, light, temperatureand pH, and by the use of elicitors, permeabilisation and two-stagesystems. Molecular engineering and the use of biomass and large-scaleculture are described along with future prospects for the commercialproduction of secondary products from cell suspension cultures.