Electro-olfactogram and multiunit olfactory receptor responses to binary and trinary mixtures of amino acids in the channel catfish, Ictalurus punctatus

In vivo electrophysiological recordings from populations of olfactory receptor neurons in the channel catfish, Ictalurus punctatus, clearly showed that responses to binary and trinary mixtures of amino acids were predictable with knowledge obtained from previous cross-adaptation studies of the relative independence of the respective binding sites of the component stimuli. All component stimuli, from which equal aliquots were drawn to form the mixtures, were adjusted in concentration to provide for approximately equal response magnitudes. The magnitude of the response to a mixture whose component amino acids showed significant cross-reactivity was equivalent to the response to any single component used to form that mixture. A mixture whose component amino acids showed minimal cross-adaptation produced a significantly larger relative response than a mixture whose components exhibited considerable cross-reactivity. This larger response approached the sum of the responses to the individual component amino acids tested at the resulting concentrations in the mixture, even though olfactory receptor dose-response functions for amino acids in this species are characterized by extreme sensory compression (i.e., successive concentration increments produce progressively smaller physiological responses). Thus, the present study indicates that the response to sensory stimulation of olfactory receptor sites is more enhanced by the activation of different receptor site types than by stimulus interaction at a single site type.     

Phosphorylation of the GABAA receptor by cAMP-dependent protein kinase and by protein kinase C: Analysis of the substrate domain

Previous work has shown that the GABA_A-receptor (GABA_A-R) could be phosphorylated by cAMP-dependent protein kinase (PKA), protein kinase C (PKC), and a receptor associated kinase. However, no clear picture has yet emerged concerning the particular subunit subtypes of the GABA_A-R that were phosphorylated by PKA and PKC. In the present report we show that an antibody raised against a 23 amino acid polypeptide corresponding to a sequence in the putative intracellular loop of the 1 subunit of the receptor blocks the in vitro phosphorylation of the purified receptor by PKA and PKC. Moreover, N-terminal sequence analysis of the principal phosphopeptide fragment obtained after proteolysis of the receptor yielded a sequence that corresponds to the 3 subunit of the receptor. Such data provide additional support for our hypothesis (Browning et al., 1990, Proc. Natl. Acad. Sci. USA 87:1315–1317) that both PKA and PKC phosphorylate the -subunit of the GABA_A-R.Special issue dedicated to Dr. Paul Greengard.     

Comparison of ccd of F, parDE of RP4, and parD of R1 using a novel conditional replication control system of plasmid R1

A number of plasmid-encoded gene systems are thought to stabilize plasmids by killing plasmid-free cells (also termed post-segregational killing or plasmid addiction). Here we analyse the mechanisms of plasmid stabilization by ccd of F, parDE of RP4 and parD of R1, and compare them to hok/sok of R1. To induce synchronous plasmid loss we constructed a novel plasmid replication-arrest system, which possesses the advantage that plasmid replication can be completely arrested by the addition of IPTG, a non-metabolizable inducer. Using isogenic plasmid constructions we have found, for the first time, consistent correlation between the effect on steady-state loss rates and the effect on cell proliferation in the plasmid replication-arrest assay for all three systems. The parDE system had the most pronounced effect both on plasmid stabilization and on plasmid retention after replication arrest. In contrast, ccd and parD both exhibited weaker effects than anticipated from previously published results. Thus, our results indicate that the function and efficiencies of some of the systems should be reconsidered. Our results are consistent with the previously postulated hypothesis that ccd and parDE act by killing plasmid-free segregants, whereas parD seems to act by inhibiting cell division of plasmid-free segregants.     

Prostatic ductal system in rats: regional variation in morphological and functional activities

The rat prostate is a complex ductal system with branches and subbranches extending from one end to another. Owing to the relative distance of various regions of the duct from the urethra, the entire length of the ductal system can be arbitrarily divided into three segments, i.e., the proximal, intermediate, and distal segments. The present study was carried out to assess the regional variation in cellular activities in this ductal system. Ventral prostates from adult Sprague-Dawley rats were dissected so that an individual ductal system was mechanically isolated and longitudinally sectioned to reveal various segments. Epithelial cells lining distal segments were tall-columnar type and were actively engaging in mitotic activity. Cells in intermediate segments were also tall-columnar type. However, they were mitotically quiescent, but able to produce secretory proteins. Evidence of programmed cell death was not observed in either of these two segments. Cells in proximal segments, on the other hand, were low-columnar or cuboidal in shape and were stained heavily for cathepsin D, a marker associated with late manifestation of cell death. Following castration in adult rats, there was a reversal in the site of programmed death in cells lining the ductal system. By Day 4 post-castration, distal segments contained many epithelial cells with intense cytoplasmic staining for cathepsin D while proximal segments showed a reduction in number of positively stained cells. By Day 7 post-castration, cells in proximal segments, though atrophied, were devoid of staining for cathepsin D.(ABSTRACT TRUNCATED AT 250 WORDS)     

Absence of acetohydroxy acid synthetase in a clinical isolate of Neisseria gonorrhoeae requiring isoleucine and valine

A clinical isolate of Neisseria gonorrhoeae with an unusual growth requirement for isoleucine and valine lacked the activity of acetohydroxy acid synthetase, one of the enzymes required for the biosynthesis of these amino acids. A spontaneous mutant which no longer required isoleucine and valine had acquired this enzymatic activity.     

Prokaryotic toxin-antitoxin stress response loci

Although toxin-antitoxin gene cassettes were first found in plasmids, recent database mining has shown that these loci are abundant in free-living prokaryotes, including many pathogenic bacteria. For example, Mycobacterium tuberculosis has 38 chromosomal toxin-antitoxin loci, including 3 relBE and 9 mazEF loci. RelE and MazF are toxins that cleave mRNA in response to nutritional stress. RelE cleaves mRNAs that are positioned at the ribosomal A-site, between the second and third nucleotides of the A-site codon. It has been proposed that toxin-antitoxin loci function in bacterial programmed cell death, but evidence now indicates that these loci provide a control mechanism that helps free-living prokaryotes cope with nutritional stress.     

Human placental trophoblast in regions of high and low environmental pollution. A histochemical and morphological study

The authors demonstrate the dependence of development of a uniform layer of syncytiotrophoblast with good cytochrome oxidase activity in placental villi on the absence of noxious industrial by-products in the environment of the pregnant woman. The degree of deviation from the developmental norm observed in regions free from industrial pollution can serve as measure of the degree of that pollution in urban-industrial regions.