Postinhibitory unit response of crustacean stretch receptors after direct and recurrent inhibition

The postinhibitory response of a slowly adapting neuron was investigated in experiments on an isolated preparation of crustacean stretch receptor and abdominal nerve chain. The structural features of this preparation are such that this response can be regarded as the response of the postsynaptic membrane to synaptic inhibition and not the action of synaptic excitation. IPSPs arise in the slowly adapting neuron in response to stimulation of the abdominal nerve chain (direct inhibition) or to excitation of the neuron itself (recurrent inhibition). The postinhibitory response consists of the development of action potentials or an increase in their amplitude and frequency. The magnitude of the response is determined by the duration of the inhibition and the state of the neuron membrane. The postinhibitory response was strongest when IPSPs were superposed on cathodal depression. IPSPs and an intracellular hyperpolarizing current evoke similar postinhibitory responses. Repetitive excitation of an inhibitory neuron may result in the appearance of a regular spike discharge from a previously inactive neuron through the mechanism of the postinhibitory response. Activation of a chain of recurrent inhibition increases the duration of the postinhibitory response evoked by direct inhibition or by a hyperpolarizing current. The existence of a chain of recurrent inhibition prevents the cessation of firing by a neuron during increasing cathodal depression. A mechanism of postinhibitory rebound lies at the basis of this phenomenon.     

Analysis of theta-rhythms recorded in an isolated strip of rabbit sensomotor cortex

To test the possibility that the theta-rhythm may spread passively from the hippocampus into the neocortex in rabbits and to analyze the properties of these rhythms recorded from the surface of the neocortex, an investigation was made of activity recorded simultaneously from the hippocampus and various points of the neocortex, including from a strip of the sensomotor cortex isolated completely with respect to its nervous connections. The use of special correlation methods showed that an appreciable contribution to the potentials recorded from the isolated strip can be made by the passive conduction of hippocampal activity (provided that it generates a regular high-amplitude theta-rhythm). At the same time, potentials in a theta-rhythm may be generated in the isolated strip itself. The theta-rhythm recorded in the intact rabbit cortex may thus be of combined genesis: generated in the neocortex itself and spreading passively from the hippocampus through the brain tissues as through a volume conductor.     

The copolymeric structure of pig skin dermatan sulphate. Isolation and characterization of l-idurono-sulphate-containing oligosaccharides from copolymeric chains

Dermatan sulphate was degraded by testicular hyaluronidase and an oversulphated fraction was isolated by ion-exchange chromatography. This preparation, which contained fairly long segments derived from the non-reducing terminal portion of the molecule, was subjected to periodate oxidation under acidic conditions. The oxidized iduronic acid residues were cleaved by reduction-hydrolysis (Smith-degradation) (Fransson & Carlstedt, 1974) or by alkaline elimination. The oligosaccharides so obtained contained both GlcUA (glucuronic acid) and IdUA-SO(4) (sulphated iduronic acid) residues. Copolymeric oligosaccharides obtained after alkaline elimination were cleaved by chondroitinase-AC into disaccharide and higher oligosaccharides. Since the corresponding oligosaccharides obtained by Smith-degradation were unaffected by this enzyme, it was concluded that the carbohydrate sequences were GalNAc-(IdUA-GalNAc)(n)-GlcUA-GalNAc. The iduronic acid-containing sequences were resistant to digestion with chondroitinase-ABC. It was demonstrated that the presence of unsulphated N-acetylgalactosamine residues in these sequences could be responsible for the observed effect. This information was obtained in an indirect way. Chemically desulphated dermatan sulphate was found to be a poor substrate for the chondroitinase-ABC enzyme. Moreover, digestion with chondroitinase-ABC of chondroitinase-AC-degraded dermatan sulphate released periodate-resistant iduronic acid-containing oligosaccharides. It is concluded that copolymeric sequences of the following structure are present in pig skin dermatan sulphate: [Formula: see text] N-acetylgalactosamine moieties surrounding IdUA-SO(4) residues are unsulphated to a large extent.     

Preparation of anti-inhibitor serum and its effect on the multiplication of influenza virus

Antiserum был подготовлен противингибитор вируса haemagglutination (IVH)одна из эмбриона chorioallantoic мембр анныепутем иммун изации морских св инокЭто анти-инги битора в сыворотке заблокирован ингибирование IVH из chorioallantoicмембран в haemagglutination испытанияно ника кого влияния на ре цепторы эритроци товСыворотке кро] ви не влияет рост chorioallantoic мембраны клет ок инет нейтрализ овать воздействи е на вирус гриппа Она снизилась спо собность chorioallantoic мембр ан для adsorb вируса гри ппа, а также степен ь размножения вир усав такого рода тканиАвторы хоте ли бы поблагодари ть г-н Г. Ruttkay-Ne -палубе и для проведения эле ктрофореза меру ния.     

Trapping a local population of spruce bark beetles Ips typographus (L.): Population size and origin of trapped beetles

A method of trapping local populations of Ips typographus was investigated in the field. The size of a population emerging from a hibernation site in the forest litter was estimated using tent traps. This estimate was compared with another estimate where beetles from the population were marked and recaptured in pheromone traps. The estimate of population size with mark-recapture was much higher than the estimate with tent traps, indicating a high degree of immigration. According to calculations only a minor part (less than 20%) of the beetles caught in the pipe traps originated in the local population. Re-emerging parent-adults were marked and released during the second flight period. The recapture rate was 29.8%, almost the same as during the first flight. Immigration during the first and second flight periods was estimated to be of similar magnitude. The results show that it is difficult to suppress local populations of highly mobile bark beetles by trapping.     

Relative positions of some epitopes on carcinoembryonic antigen

Summary To investigate whether anti-(carcinoembryonic antigen) monoclonal antibodies (mAb) react with single or repeated epitopes, sandwich radioimmunoassays in homologous and heterologous combinations were performed. Four mAb (I-27, I-47, II-17 and to some degree II-16) gave homologous binding while two mAb (I-38S1 and II-10) did not. Taken together with previous immunoprecipitation studies we conclude that all these mAb except II-10 react with repeated epitopes. The relative positions of the epitopes recognized by these mAb and of three additional mAb (II-6, II-7 and CB-CEA-1) were investigated using a plate antibody competition test with enzyme-labelled carcinoembryonic antigen (CEA). mAb I-38S1, II-6, II-7, II-10, II-16 and CB-CEA-1 were mutually cross-reactive, and were classified as belonging to one epitope group. mAb I-27 and I-47 fell outside this group and did not interfere with the binding of CEA conjugate to mAb II-17 either. They therefore represent a second epitope group. mAb II-17 showed no interference with the binding of CEA to any of the other mAb and must therefore represent a third epitope group. The slopes of the plate antibody competition curves were used for calculation of a correlation matrix, which in turn was used to depict the relative positions of the epitopes recognized by the mAb in the large group.     

Zooplankton of Lake Peipsi-Pihkva in 1909–1987

164 taxa were identified in the net zooplankton of the pelagial of L. Peipsi-Pihkva in 1909–1987, including 3 species of protozoans, 74 species of rotifers, 58 species of cladocerans, 28 species of copepods and 1 mollusc. One rotifer species, Ploesoma peipsiense Mäemets et Kutikova, has been described as new for science here. The zooplankton of L. Peipsi-Pihkva is remarkably rich in species including rarities in Estonia: Limnosida frontosa, Drepanothrix dentata, Bythotrephes longimanus, B. cederstroemi etc. Due to its large surface area, L. Peipsi-Pihkva provides a large scale of biotopes of a diverse trophic state and humic content, which support species with different ecological requirements. Most of the aquatory of the lake has lately been mesotrophic, favouring the coexistence of indicators of oligo- and mesotrophic state and species preferring a higher trophic state. The occurrece of 10 species of the genus Bosmina including B. berolinensis, B. gibbera, B. lilljeborgi, B. thersites and B. crassicornis, sparse in Estonian lakes, is the most noteworthy feature of the zooplankton of L. Peipsi-Pihkva. The coexistence of B. coregoni and B. berolinensis, B. gibbera, B. lilljeborgi etc. which were earlier regarded as subspecies of B. c. coregoni proves that they are different species producing usually no hybrids. The species composition was subjected to certain changes during the years under consideration. Larvae of Dreissena were first found in zooplankton in 1962. The oligo-mesotrophic indicator Holopedium gibberum occurred in the lake in 1909–1964, but was lacking in later samples.     

Predation on artificial,solitary and aggregated wader nests on farmland

Predation rates on artificial wader nests, solitary curlew (Numenius arquata) and lapwing (Vanellus vanellus) nests and lapwing nests in colonies were studied on a farmland site in central Sweden. Predation rates were highest on artificial wader nests, intermediate on solitary curlew and lapwing nests and lowest on lapwing nests in colonies, probably because of active defence of adults at real nests and/or because of selection of nest sites with lower predation risk by breeding birds. A comparison of nests close to (50 m) and far away from (200 m) forest edges revealed no increased predation risk close to edges for any of the studied nest types. Predation risk changed during the season for artificial nests (highest in the middle of May), while predation rates on lapwing and curlew nests were more stable. Artificial nests seem to be inappropriate for measuring actual predation rates and temporal differences in predation rates on real nests, but they might be suitable for use as an index of spatial differences.