Interactions of piperidine derivatives with the nicotinic cholinergic receptor complex from Torpedo electric organ

The interactions of eight piperidine derivatives with nicotinic receptor complexes fromTorpedo californica electric organ were studied using [¹²⁵I]alpha-bungarotoxin ([¹²⁵I]BGT) as a probe for the acetylcholine binding site and [³H]perhydrohistrionicotoxin ([³H]H₁₂-HTX) as a probe for a site associated with the receptor-gated ion channel.Cis- andtrans-2-methyl-6-n-undecanyl piperidines (MUP), major constituents of fire ant venom, had a high-affinity for [³H]H₁₂-HTX binding sites (K_i=0.08–0.24 M), but had no affect on receptor binding. MUP affinity for [³H]H₁₂-HTX binding sites was approximately doubled in the presence of 1 M carbamylcholine. Introduction of a 2-hydroxyl group to the undecanyl side channel had little effect on activity of the alkaloid. The analog 2,6- (but not 3,5-) dimethylpiperidine was a moderately active inhibitor of [³H]H₁₂-HTX binding (K _i-8.8 M). 2-Methylpiperidine was considerably less active (K _i=600 M), although it was more potent than either 3- or 4-methylpiperidine. The affinities of 2,6-dimethylpiperidine and 2-methylpiperidine for [³H]H₁₂-HTX binding sites were decreased in the presence of 1 M carbamylcholine. Carbamylcholine affinity for the receptor was increased by up to 7 fold in the presence of 10 and 32 M MUP, but was decreased in the presence of 2,6-dimethylpiperidine and 2-methylpiperidine. Thecis- andtrans-isomers of MUP were equipotent in producing each of its effects. In these actions, MUP resembles a variety of other compounds derived from 2,6-disubstituted piperidines, including histrionicotoxins, gephyrotoxins and pumiliotoxins. These studies establish the importance of alkyl substitutions in theortho position of the piperidine ring in conferring ion channel specificity, and the importance of substantial alkyl side chains in conferring the ability of channel blockers to stabilize the nicotinic receptor complex in high affinity, desensitized conformations.     

Nitrogen mineralization ofSesbania sesban used as green manure for lowland rice in Sri Lanka

Sesbania sesban was evaluated as green manure crop for lowland rice in the Dry Zone of Sri Lanka. The legume was grown during a fallow period before lowland rice (Oryza sativa) and ploughed under just before transplanting. Weight loss and nitrogen content in litterbags containing leaves, stems and roots of the legume were monitored. Comparisons were made between rice yields from 20 m² plots after green manuring in combination with different nitrogen fertilizer levels (0, 2.4, 4.8 and 7.2 gm⁻²) and nitrogen fertilizer (9.6 gm⁻²) alone. Above-ground biomass ofS. sesban was 440 gm⁻² (dry wt) when ploughed under after 84 days growth. N-content in leaves, stems and roots was 3.76%, 0.41% and 0.73%, respectively. This gave a N-input fromS. sesban of 9.2 gm⁻² (8.3 g from above-ground parts and 0.9 g from roots). The corresponding K and P inputs were 7.3 and 0.6 gm⁻² respectively. The nitrogen rich leaves, which contained 88% of the nitrogen in the above-ground parts, decomposed and released its nitrogen much more rapidly than the stems and roots. After only four days the leaves had released 5.3 g Nm⁻² and after 14 days they had released 6.4 g Nm⁻². The highest rice yield (505 gm⁻²) was obtained usingS. sesban and 4.8 gm⁻² of N-fertilizer. The yields with only N-fertilizer or onlyS. sesban were 442 gm⁻² and 396 gm⁻², respectively. Due to the rapid decomposition of the nitrogen rich leaves,S. sesban did not behave as a slow release fertilizer. Thus, it is not necessary to apply nitrogen fertilizers as a basal dose.     

Compensatory payments and vasectomy acceptance in urban Sri Lanka

The effects of different levels of compensatory payment for vasectomy on sterilization acceptance were examined in 496 vasectomized men in urban Sri Lanka. The results indicate that compensatory payments significantly enhanced the participation of economically poor men in vasectomy programs, especially those who had already achieved a large family size. The proportion of poor acceptors (those with a monthly income of Rs 1000 or less) increased with higher levels of payment; the acceptor's level of education was negatively correlated with the compensation amount, and the mean age of the youngest child was higher among those who received higher payments. 60% of vasectomy acceptors reported using contraception immediately before the vasectomy, suggesting a high level of motivation not to have another child. Respondents cited high effectiveness, no extra expense, and no side effects for their wives as the main reasons for selecting vasectomy over other means of contraception, regardless of the amount of payment received. Only 5% said cash payment was an important reason for choosing vasectomy, and this response did not vary significantly by level of payment. There was no influence of payment level on postoperative complications or satisfaction. While compensatory payments significantly enhanced the participation of poor men in vasectomy programs, they were not effective in attracting poorer men with few children or those whose last child was relatively young. Overall, this study's findings suggest that the decision to provide compensatory payments and how much to provide should be based on economic and political factors, not on the grounds that higher compensatory payments have led to the recruitment of ineligible men or that the promotion of vasectomy has been at the expense of a loss in the quality of services provided.     

Label-fracture of cell surfaces by replica staining

We introduce replica-staining label-fracture, a method for the cytochemical mapping of membrane surfaces. This method is a corollary of the rationale of label-fracture (Pinto da Silva and Kan, 1984: J Cell Biol 99:1156). After freeze-fracture the exoplasmic halves of the membrane remain attached to the replica. We show that cytochemical labeling of cell surfaces can be performed by direct post-fracture staining of freeze-fracture replicas. This new variant of label-fracture leads to miniaturization of labeling procedures and allows standardization of labeling conditions and simultaneous processing of different specimens.     

Decline in measles mortality: nutrition,age at infection,or exposure?

The mortality from measles was studied in an urban area of Guinea-Bissau one year before and five years after the introduction of a vaccination programme. The years after the introduction of immunisation saw a decline in mortality among unvaccinated children with measles. This decline occurred despite a lower age at infection and an increasing prevalence of malnourished children. State of nutrition (weight for age) did not affect the outcome of measles infection. The incidence of isolated cases, however, increased in the period after the introduction of measles vaccination. As mortality was lower among these cases, diminished clustering explained some of the reduction in mortality. Comparison between the urban district and a rural area inhabited by the same ethnic group showed a lower age at infection, less clustering of cases, and lower case fatality ratios in the urban area.Endemic transmission of measles in urban districts leads to less clustering of cases, which may help explain the usually lower case fatality ratios in these areas. As measles vaccination increases herd immunity and diminishes clustering of cases, it may reduce mortality even among unvaccinated children who contract the disease.     

Comparative chromatography of Brazilian coral snake (Micrurus) venoms.

1. Elution profiles of 11 coral snake venoms, including those of Micrurus albicinctus, M. corallinus, M. frontalis altirostris, M. f. brasiliensis, M. f. frontalis, M. fulvius fulvius, M. ibiboboca, M. lemniscatus ssp., M. rondonianus, M. spixii spixii and M. surinamensis surinamensis, were compared using high performance gel filtration and reverse phase media. 2. Micrurus venom profiles were compared with those of "outgroup" taxa Bothrops moojeni, Naja naja kaouthia and Bungarus multicinctus. 3. Purified elapid venom constituents were also chromatographed under identical conditions in order to suggest possible identities of Micrurus venom constituents. 4. Masses of various components were confirmed by mass spectrometry. 5. Phospholipase constituents in three venoms were positively identified based on their reverse phase chromatograms. 6. Venoms of M. rondonianus and M. s. surinamensis are shown to be significantly different in their peptide composition from other Micrurus venoms.     

Taxonomic status of the species of the green algal genusNeochloris

Komárek has recently reviewed the various species assigned to the green algal genusNeochloris Starr (Chlorococcales, Chlorococcaceae) and removed those with uninucleate vegetative cells to a new genus,Ettlia. Watanabe & Floyd, unaware ofKomárek's work, also reviewed the species ofNeochloris and distributed them among three genera—Neochloris, Chlorococcopsis gen. nov., andParietochloris gen. nov.—on the basis of details of the covering of the zoospore and the arrangement of the basal bodies of the flagellar apparatus. This paper reconciles these two treatments and makes additional recommendations at the ranks of genus, family, order, and class.     

Application of flow karyotyping in prenatal detection of chromosome aberrations

This paper describes the application of bivariate flow karyotyping to (1) classification of chromosomes isolated from cultures of cells taken by amniocentesis and (2) detection of numerical and structural aberrations. Chromosomes were isolated from primary cultures 2-5 wk after amniocentesis, stained with Hoechst 33258 and chromomycin A3, and analyzed using dual beam flow cytometry. Information about chromosome DNA content and DNA base composition was derived from the locations of the peaks in the flow karyotypes, each peak being produced by one or more chromosome types with similar DNA content and DNA base composition. Information about the relative frequency of each chromosome type was determined on the basis of the relative volume of the peak for that chromosome type. Cytogenetic information determined on the basis of flow karyotypes was compared with that obtained by visual analysis following G-banding. Variability among the peak means and volumes in flow karyotypes was determined from analyses of 50 normal amniocyte cultures. Numerical aberrations involving chromosomes 21, 18, and Y were detected correctly in all of 28 analyses, including eight in a blind study. Structural aberrations involving chromosomes 1, 2, 3, 6, 9-12, 13, 14, 15, 21, and 22 were detected in all of seven cultures in a blind study. Flow karyotypes proved to be insensitive to small, normally occurring chromosome polymorphisms detected by banding analysis. In addition, a few samples were erroneously scored as having numerical aberrations.     

Movements of some indigenous riverine fish in Sri Lanka

The migratory movements of reproductive potamodromus fish established in man-made tropical lakes in the dry zone of Sri Lanka were determined. It was shown that the nine indigenous riverine species do not spawn in these lakes but move into the upstream channels when sexually mature. The pattern of upstream movement was found to be species-specific although most species showed a diurnal periodicity. It is suggested that the development of totally lacustrine forms of riverine species is very unlikely to occur in the man-made lakes of Sri Lanka because of their relatively short duration time.