Melanocortin‐1 receptor structure and functional regulation

The melanogenic actions of the melanocortins are mediated by the melanocortin‐1 receptor (MC1R). MC1R is a member of the G‐protein‐coupled receptors (GPCR) superfamily expressed in cutaneous and hair follicle melanocytes. Activation of MC1R by adrenocorticotrophin or α‐melanocyte stimulating hormone is positively coupled to the cAMP signaling pathway and leads to a stimulation of melanogenesis and a switch from the synthesis of pheomelanins to the production of eumelanic pigments. The functional behavior of the MC1R agrees with emerging concepts in GPCR signaling including dimerization, coupling to more than one signaling pathway and a high agonist‐independent constitutive activity accounting for inverse agonism phenomena. In addition, MC1R displays unique properties such as an unusually high number of natural variants often associated with clearly visible phenotypes and the occurrence of endogenous peptide antagonists. Therefore MC1R is an ideal model to study GPCR function. Here we review our current knowledge of MC1R structure and function, with emphasis on information gathered from the analysis of natural variants. We also discuss recent data on the regulation of MC1R function by paracrine and endocrine factors and by external stimuli such as ultraviolet light.     

Changes in the Activity of the Maturation-Promoting Factor Are Correlated with Those of a Major Cyclic AMP and Calcium-Independent Protein Kinase During the First Mitotic Cell Cycles in the Early Starfish Embryo

Many studies suggest that MPF activation depends on protein phosphorylation or that MPF is itself a protein kinase. In the present report, cyclic variations of MPF activity have been correlated in vivo with changes in the extent of protein phosphorylation or in vitro with changes of a major protein kinase during the first cell cycles of fertilized starfish eggs. This cycling protein kinase neither requires cAMP nor Ca²⁺. Neither colchicine nor aphidicoline, which inhibits cleavage and chromosome replication respectively, was found to suppress the synchronous and cyclic variations of both MPF and protein kinase activities. Protein synthesis was found to be required for both MPF and protein kinase activities to reappear after their simultaneous drop at the time of mitotic or meiotic cleavages. Production of either MPF or protein kinase activities is not the immediate result of protein synthesis since there is a delay at each cell cycle between the time when protein synthesis is required and the time when both MPF and protein kinase activities are produced. This suggests that both MPF and protein kinase activities might involve some post-translational modification of a precursor protein synthesized during the preceeding cell cycle.     

Brain injury following cardiorespiratory arrest in cats. Effects of alphaxalone-alphadolone

The effects of alphaxalone-alphadolone acetate (27.07 microM/kg-7.68 microM/kg) on neurologic injury following acute cerebral ischemia induced by an 8 min cardiorespiratory arrest (CRA) were investigated in cats through the analysis of neurological deficit scores and brain electrical activity; i.e., electroencephalogram (EEG) from parieto-occipital cortices and EEG and multiunit activity (MUA) from mesencephalic reticular formation (MRF). The CRA resulted from electrically induced cardiac arrest and stopping of mechanical ventilation in paralyzed cats which were successfully resuscitated within the immediate 4 min after the end of CRA. Two groups of cats were studied: I. Untreated, which received saline iv; II. Treated, which received alphaxalone-alphadolone acetate iv, 7-9 min after the end of CRA. Neuromuscular blockade and mechanical ventilation were maintained until 8 h following the CRA; then the cats were allowed to recover spontaneous respiratory activity. EEG phenomena were different in untreated and treated cats during this immediate post-arrest period. The former showed rhythmic bursts of fast (12-20 Hz) EEG activity at 1-2 sec intervals from 15-20 min until 3-4 h after the CRA, abundant spikes and delta-like waves. By contrast, administration of alphaxalone-alphadolone acetate resulted in burst suppression EEG pattern during 1 h. Progressive recovery of background EEG activity occurred afterwards. MUA from MRF disappeared during the CRA, however 6 h later the mean MUA frequency in untreated cats ranged between 32-46% and in treated cats 18-27% of their control mean frequencies during paradoxical sleep (100%). Daily electrographic records were performed in all the cats during quiet attentive behavior at each of the five days following the CRA. Significant differences were found in the frequency distributions of MUA from MRF (1st day, p less than 0.01; 5th day, p less than 0.01) as well as in the cortical EEG waves (1st day, p less than 0.01; 5th day, p less than 0.05) before and after the CRA in the untreated group. A wide dispersion of MUA values, and increased proportions of delta and theta-like waves and spindle bursts, besides a significantly high (p less than 0.001) number of spikes occurred in these EEG records the days following the CRA. The frequency distributions of MUA and EEG did not significantly differ before and after the CRA in the treated group; however, a significantly high (p less than 0.05) number of spikes was found in treated cats following the CRA.(ABSTRACT TRUNCATED AT 400 WORDS)     

中国平脉树螽属五新种记述：直翅目：螽斯科：树螽亚科

本文报道中国平脉树螽属5个新种。每个新种皆有详细的形态描述和形态特征图。所有模式标本存于北京农业大学昆虫标本室。     

Changes in Abscisic Acid Content in Axis and Cotyledons of Developing Phaseolus vulgaris Embryos and their Physiological Consequences

Prevost, I. and Le Page–Degivry, M. Th. 1985. Changesin absicisic acid content in axis and cotyledons of developingPhaseolus vulgaris embryos and their physiological consequences.—J.exp. Bot. 36: 1900–1905.Changes in abscisic acid (ABA)content with time were measured in embryonic axes and in cotyledonsof Phaseolus vulgaris embryos using a radio–immunoassay.During embryogenesis, a similar pattern was observed in bothtissues: ABA increased to a maximum 29 d after an thesis, followedby a decrease as the seed matured. The level of ABA in the cotyledonswas always much higher than that in the axes. In in vitro cultures,the duration of the lag phase before germination of isolatedembryonic axes increased with ABA content. The presence of cotyledonsalways lengthened the lag phase; longer lag phases were associatedwith greater concentrations of ABA in the cotyledons. Moreoverthe presence of cotyledons stimulated the growth of seedlings. Key words: ABA distribution, embryo maturation, axis and embryo germinability     

Plasmid-determined resistance to arsenic and antimony inPseudomonas aeruginosa

Resistance to arsenic salts in aPseudomonas aeruginosa clinical isolate was shown to be determined by a 100 kb transferable plasmid. The resistance pattern included arsenate, arsenite, and antimonate ions. Arsenate and arsenite resistances were inducible by previous exposure of cultures to subinhibitory amounts of either of the two ions. Phosphate ions protectedP. aeruginosa cells from the toxic effects of arsenate but did not alter arsenite toxicity.