The origin of postembryonic neuroblasts in the ventral nerve cord of Drosophila melanogaster

Embryonic and postembryonic neuroblasts in the thoracic ventral nerve cord of Drosophila melanogaster have the same origin. We have traced the development of threefold-labelled single precursor cells from the early gastrula stage to late larval stages. The technique allows in the same individual monitoring of progeny cells at embryonic stages (in vivo) and differentially staining embryonic and postembryonic progeny within the resulting neural clone at late postembryonic stages. The analysis reveals that postembryonic cells always appear together with embryonic cells in one clone. Furthermore, BrdU labelling suggests that the embryonic neuroblast itself rather than one of its progeny resumes proliferation as a postembryonic neuroblast. A second type of clone consists of embryonic progeny only.     

Oviposition by screwworm flies (Diptera: Calliphoridae) on contact with host fluids

Factor affecting oviposition by screwworm flies, Cochliomyia hominivorax (Coquerel), contacting different host fluids were examined in a laboratory bioassay. Fresh bovine blood, which does not release the attractive odors involved in host finding, nevertheless stimulated as many or more females to oviposit than did the other fluids tested. These other fluids included attractive fluid from screwworm-infected wounds (a favored oviposition site in nature) and cultures of Providencia rettgeri (a bacterium implicated in attractant production). Oviposition did not vary with batch of fresh blood or frozen storage, making blood a useful standard for comparing oviposition rates among studies. Oviposition did vary with the substrate to which the blood was applied, suggesting that an interaction between tactile and chemical stimuli is important for host recognition. Both insemination and darkness during bioassay increased oviposition rates, but the magnitude of these effects was small compared with that due to substrate. Age had no effect for at least 1 wk after females became gravid.     

Translation and ribosome assembly in extremely thermophilic archaebacteria.

Several features of translation and ribosome structure in extremely thermophilic, sulfur-dependent archaebacteria are described, including: i) a peculiar mechanism of transfer RNA-mediated 70S ribosome formation from free subunits; ii) poly(U)translation by hybrid ribosomes composed by one archaebacterial and one eucaryotic subunit; iii) ribosome assembly and homologous and heterologous RNA/protein recognition.     

Structure and biological activity of crustacean gastrointestinal peptides identified with antibodies to gastrin/cholecystokinin.

Four gastrin/cholecystokinin-like peptides (G/CCK) which cross-react with a specific C-terminal gastrin/CCK antiserum have been isolated from the stomach of the marine crustacean Nephrops norvegicus. The molecular weight of the four peptides was estimated between 1000 and 2000 Da by molecular sieving. By radioimmunoassay, the cross-reactivity of these peptides with human gastrin 17-I was found to be around 0.03%. Pure peptidic fractions were recovered after four successive steps of HPLC. Amino-acid analysis suggested a similarity between the four peptides identified which may belong to a new family. A limited homology between the C-terminus of one Nephrops peptide and vertebrate G/CCK was found after sequencing. Two of the peptides exhibited secretagogue effects on crustacean isolated midgut glands. The Nephrops peptides, although structurally distinct from the vertebrate G/CCKs, appear to serve similar biological functions in crustaceans.     

Pyridostigmine enhances even if it does not normalize the growth hormone responses to growth hormone-releasing hormone in patients with Cushing's disease.

Subjects with Cushing's disease have diminished growth hormone (GH) response to growth hormone-releasing hormone (GHRH). The aim of our study was to investigate the underlying mechanism of this diminished GH response in these patients using pyridostigmine (PD), an acetylcholinesterase inhibitor, which is reported to increase GH secretion by reducing somatostatin tone. Eight subjects with untreated Cushing's disease (caused by a pituitary adenoma) and 6 control subjects received GHRH 100 micrograms in 1 ml of saline, as intravenous bolus injection 60 min after (1) placebo (2 tablets, p.o.) or (2) PD (120 mg, p.o.). After GHRH plus placebo, the GH peak (mean +/- SEM) was significantly lower in subjects with Cushing's disease (2.4 +/- 0.5 micrograms/l) compared to control subjects (25.1 +/- 1.8 micrograms/l, p less than 0.05). After GHRH plus PD, the GH peak was significantly enhanced both in subjects with Cushing's disease (7.1 +/- 2.3 micrograms/l, p less than 0.05) and in control subjects (42.3 +/- 4.3 micrograms/l, p less than 0.05). In patients with Cushing's disease, the GH response to GHRH plus PD was lower with respect to the GH response to GHRH alone in normal subjects. We conclude that hypercortisolism may cause a decrease in central cholinergic tone which is in turn hypothesized to be responsible of an enhanced somatostatin release from the hypothalamus. However, other metabolic or central nervous system alterations may act synergistically with hypercortisolism in causing GH inhibition in patients with Cushing's disease.