Intercellular structure in a many-celled magnetotactic prokaryote

A many-called magnetotactic prokaryote obtained from brackish water was observed to possess intercellular connections at points of contact between the outer membranes of constituent cells. Each aggregate organism consisted of 10 to 30 individual Gram-negative cells containing material with the appearance of poly--hydroxybutyrate and magnetosomes of unusual arrangement, structure and composition. The aggregate, which possessed prokaryotic-type flagella arranged at the outwards surfaces of each cell, showed motility indicative of co-ordination between individual component cells. These results suggest that this organism could be a multicellular prokaryote.     

Studies on new,centrally active and reversible acetylcholinesterase inhibitors

We have synthesized the tertiary amines of pyridostigmine and neostigmine, 3-pyridinol dimethylcarbamate (norpyridostigmine) and 3-dimethylaminophenol dimethylcarbamate (norneostigmine) respectively, and we have tested their abilities to cross the blood-brain barrier and inhibit mouse brainAChE activity. The in vivo inhibition of AChE activity by norpyridostigmine reaches 72% at 10 minutes which is comparable to that seen with physostigmine (73% at 10 minutes). Inhibition by norneostigmine is less effective (50% at 10 minutes) and approaches that obtained with tetrahydroaminoacridine (57% at 10 minutes). These data show that both norpyridostigmine and norneostigmine cross the blood-brain barrier and that they are effective inhibitors of mouse brain AChE activity. These drugs could be useful in the treatment of memory, impairment associated with Alzheimer's disease, and other memory disorders.     

Conformations of the central transforming region (Ile 55-Met 67) of the p21 protein and their relationship to activation of the protein

The GTP-binding p21 protein, encoded by the ras-oncogene, becomes transforming if amino acid substitutions are made at critical positions in the polypeptide chain, e.g., at Gly 12, Gly 13, Ala 59, Gln 61 and Glu 63. Most of these substitutions occur in two phosphate-binding loop regions, Tyr 4-Thr 20, herein designated as segment 1, and Ile 55-Met 67, herein designated, as segment 2. These two segments are homologous to two corresponding regions in the two purine nucleotide binding proteins, bacterial elongation factor (EF-tu) (Val 12-Thr 28 corresponds to segment 1; His 78-Ile 92 corresponds to segment 2) and adenylate kinase (ADK) (Lys 9-Cys 25 corresponds to segment 1 and Tyr 95-Arg 107 corresponds to segment 2). We find that the conformations of the segment 1 region in the p21 protein, EF-tu and ADK are similar to one another and that the conformation of the segment 2 region of EF-tu is superimposable on that of segment 2 of ADK. Furthermore, the relative position of the two segments in EF-tu is strikingly similar to that of the two segments in ADK. In the originally proposed X-ray structure for the p21 protein, the conformation of segment 2 in the p21 protein is not similar to that found for the other two proteins, and its disposition relative to segment 1 and the remainder of the protein is also different from that observed for the other two proteins.(ABSTRACT TRUNCATED AT 250 WORDS)     

Histamine-like immunoreactivity in photoreceptors of the compound eyes and ocelli of the flies Calliphora erythrocephala and Musca domestica

Summary Antibodies to histamine were used for immunocytochemical studies of the visual system in the flies Calliphora erythrocephala and Musca domestica. Specific immunolabeling of photoreceptors was found both in the compound eyes and ocelli of both species. In the compound eyes histamine-like immunoreactivity (HA-IR) was found in all the short visual fibers (photoreceptors R1–6) and one type of long visual fiber (photoreceptor R8). In addition, the ocellar photoreceptors also show HA-IR. In view of earlier biochemical and pharmacological/physiological findings by Elias and Evans (1983) and Hardie (1987) it thus seems likely that histamine is a neurotransmitter in insect photoreceptors. Interestingly, the second type of long visual fiber (photoreceptor R7) has recently been found to be GABA-immunoreactive (Datum et al. 1986). The two types of long visual fibers may hence use different transmitters which act on different receptors of the postsynaptic neurons in the second visual neuropil, the medulla. In addition to the photoreceptors in the retina and ocelli, we found processes of HA-IR neurons in one of the optic lobe neuropils, the lobula. This finding indicates that histamine may also be a transmitter in certain interneurons in the visual system.Abbreviations HA histamine - GABA -amino butyric acid - GAD glutamic acid decarboxylase - 5-HT 5-hydroxytryptamine (serotonin) - HA-IR histamine-like immunoreactivity - R1-R6 class of short-axoned photoreceptors - R7 and R8 long-axoned photoreceptors - LMC large monopolar neuron of lamina - HSA human serum albumin - PBS phosphate-buffered saline - DEPC diethylpyrocarbonate     

Visual optics in toads (Bufo americanus)

Aspects of visual optics were investigated in the American toad (Bufo americanus). The development of the refractive state of the eye during metamorphosis was followed with IR photoretinoscopy. Frozen sections documented the changes in optical parameters before and after metamorphosis. There is a difference in light sensitivity between juvenile and adult toads. Binocular accommodation in adult toads was observed. 1. IR photoretinoscopic measurements showed that the refractive state of the eye changed very rapidly during metamorphosis, about 10 D/h while the animal entered the terrestrial habitat. 2. Frozen sections showed that the almost spherical lens in a tadpole eye had flattened in a just metamorphosed toad's eye while at the same time the distance of the lens to the retina had decreased. However, the morphological measurements were not sufficiently sensitive to record the relatively small changes in ocular dimensions that were responsible for the rapid changes in refractive state during metamorphosis. 3. Schematic eyes, with homogeneous and non homogeneous lenses, were constructed for tadpoles, juvenile toads, and adult toads. 4. Nonparaxial raytracing studies in schematic eyes suggested that the lenses of animals of the three developmental stages tadpole, juvenile toad, and adult are not homogeneous but have a refractive index gradient. The raytracing studies indicated that the refractive index gradient is different for the different developmental stages, being highest in the tadpole lens. 5. The observations of toads during feeding behavior at different light levels showed an increased light sensitivity in the adult nocturnal toads in contrast to the juvenile animals, which are diurnal. The increased light sensitivity could partly be explained with an increase in aperture and an increase in red rod outer segments. To fully explain the higher light sensitivity in adult toads, changes in neuronal parameters had to be assumed. 6. Retinoscopic measurements of the resting refractive state in the adult toad showed a hyperopic defocus of about +8 D. By subtracting the measurement artefact for retinoscopy, the true resting focus was found to be nearly emmetropic. 7. The amount of natural accommodation in adult toads during normal feeding behavior was investigated with IR photoretinoscopy. Binocular accommodation of about 8 D was observed.     

A new species of Crepidostomum (Allocreadiidae: Digenea) from northeastern Finland,with comments on its possible origin

Crepidostomum wikgreni n. sp. is described from the gall-bladder and intestine of the whitefish Coregonus acronius in Lake Yli-Kitka in NE Finland. It is morphologically similar to Crepidostomum farionis, with which it occurs sympatrically and sometimes concurrently; but it differs in that the eggs are much larger, i.e. 96±6.5 m mean-length, as opposed to 71±4.7 m mean-length for C. farionis in the same host and locality.It is suggested that the new species has arisen from C. farionis after deglaciation and since c. 8,400 BP, at which time the waters of the Lake Kitka System were isolated from those in the rest of Finland and flowed eastwards into the White Sea Basin. The isolation of the White Sea Basin appears to have been maintained by watersheds running north-south close to the Fenno-Soviet border and east-west through central Karelia. It is further suggested that C. farionis currently occurring in Lake Yli-Kitka is a recent re-introduction brought about by the translocation of fish-stocks.     

Effects of lignin on the anaerobic degradation of (ligno) cellulosic wastes by rumen microorganisms

Summary There appeared to be a clear correlation between the lignin content (% of TS) of several waste and natural materials and their degradability by rumen microorganisms. Materials with lignin contents higher than 25% were not degraded within 72 h. The effects of Kraft pine lignin and some lignin monomers on filter paper degradation, methane production and CMCase activity were tested. Testing these compounds in concentrations comparable to natural conditions showed minor effects. At higher concentrations p-coumaric acid strongly inhibited cellulose degradation and methane production in batch cultures. Influence of lignin compounds on degradation is discussed in relation to structural effects and enzyme or growth inhibition.     

Alterations in Retinal Tyrosine and Dopamine Levels in Rats Consuming Protein or Tyrosine-Supplemented Diets

The ad libitum ingestion of casein diets varying in protein content altered serum and retinal levels of tyrosine. The serum tyrosine level rose when protein ingestion was increased from 6 to 24% casein. In rats consuming high-protein diets (40% casein), no further increase in serum tyrosine level occurred, although the levels of other large neutral amino acids, which compete with tyrosine for retinal uptake, continued to rise. The activity of the liver enzyme tyrosine aminotransferase varied directly with the percentage of protein in the diet and may partially explain the failure of chronic high-protein feeding to increase serum tyrosine levels. The retinal tyrosine concentration was significantly correlated with the serum tyrosine level and with the serum tyrosine ratio at all levels of protein intake. Retinal 3,4-dihydroxyphenylalanine synthesis and dopamine (DA) level varied in parallel with the level of the precursor, tyrosine. Addition of pure L-tyrosine (1, 2, or 4%) to normal protein diets resulted in a stepwise increase in serum and retinal tyrosine levels and retinal DA turnover. Alterations of retinal tyrosine level as a result of change in amount of dietary protein or by its addition to the normal diet can influence retinal DA synthesis and release.