A. A. Ukhtomskiĭ and I. P. Pavlov: a controversy or a dialogue?

Pavlov's concept of conditioned reflexes and Ukhtomskii theory of dominanta fall within the biological line in physiology. They unravel the integral adaptive and active nature of the organism behavior in the environment. It is impossible to develop modern concepts about the determinants of goal-directed behavior of animals and voluntary activity of humans without in-depth study of the achievements of these Russian physiological schools which not only formed the methodological basis for the current studies but also directed the way for their further development.     

Distribution and ecological aspects of leptocephali collected 1979–1994 in North- and Central Atlantic. I. Congridae

This is the first report on the leptocephalus catches made during the last 15 years in North-and Central Atlantic during the course of 19 cruises of five different ships from Germany and one from Poland. This report comprises identification, geographical occurrence and abundance and in some cases depth preference, migratory routes and spawning area of Congridae in the North Atlantic. The largest part of this collection consists of 876Conger conger larvae. The likelihood that this species spawns in the Mediterranean is again confirmed. Decreasing density as well as increasing size from Gibraltar west-and north westward showed migration to be occurring in that direction. Age was determined by counting “daily rings” on the otoliths of up to 120-mm long larvae. It is suggested to be more than 300 days and is calculated to be 1 1/4 years for the largest larvae (TL=140–160 mm). Some 126 specimens of three otherConger species, i.e.C. oceanicus, C. triporiceps, C. esculentus, were identified in the collection. The major part originated from the western North Atlantic. The most numerous larvae, belonging to another genus of Congridae, wereAriosoma balearicum (n=265). They showed, also in consideration of other studies, quite a wide range in number of myomeres. Their systematic status is therefore uncertain, as is also the status of those known from the NW Indian Ocean and the NW Pacific. One larva, probably ofAriosoma selenops, of un-usually large size (TL=467 mm) and captured in the Iberian Basin is described and compared with specimens known from the literature. Two larvae of unknown identity were captured off NW Africa; they resembledA. balearicum but had too high a number of myomeres. The identity of most of theGnathophis larvae caught in the East Atlantic is uncertain. Leptocephali ofParaconger notialis in the East Atlantic, up to the area north of New Guinea, exhibited a higher number of myomeres than those known from the West Atlantic. Larvae ofXenomystax congroides (n-29), belonging to a population with a relatively high number of myomeres, were captured in the Sargasso Sea.     

β-Adrenoceptors in the Tree Shrew Brain. I. Distribution and Characterization of [125I]Iodocyanopindolol Binding Sites

1. The number and distribution pattern of -adrenergic receptors in the brain have been reported to be species specific. The aim of the present study was to describe binding of the -adrenoceptor ligand [¹²⁵I]iodocyanopindolol in the brain of the tree shrew (Tupaia belangeri), a species which provides an appropriate model for studies of psychosocial stress and its consequences on central nervous processes.2. ¹²⁵I-Iodocyanopindolol (¹²⁵ICYP) labeling revealed a high degree of nonspecific binding, which was due mainly to interactions of this ligand with serotonin binding sites. For a quantitative evaluation of ₁- and ₂-adrenoceptors, serotonin binding sites had to be blocked by 100 M 5HT.3. Binding of the radioligand to ₁- and ₂-adrenoceptors was characterized using the ₁-specific antagonist CGP20712A and the ₂-specific antagonist ICI118.551. ₁-adrenoceptor binding is present in the whole brain, revealing low receptor numbers in most brain regions (up to 1.5 to 2.7 fmol/mg). A slight enrichment was observed in cortical areas (lateral orbital cortex: 4.0±0.7 fmol/mg) and in the cerebellar molecular layer (8.7±1.0 fmol/mg).4. Competition experiments demonstrated high- and low-affinity binding sites with considerable variations in K _i values for CGP20712A, showing that various affinity states of ₁-adrenoceptors are present in the brain (K _i: 0.61 nM to 67.1 M). In the hippocampus, only low-affinity ₁-adrenoceptors were detected (K _i: 1.3±0.2 M). Since it is known that ¹²⁵ICYP labels not only membrane bound but also internalized -adrenoceptors, it can be assumed that the large population of the low-affinity sites represents internalized receptors which may be abundant due to a high sequestration rate.5. High numbers of ₂-adrenoceptors are present in only a few brain structures of tree shrews (external layer of the olfactory bulb, 15.8±2.0 fmol/mg; claustrum, 19.3±1.5 fmol/mg; anteroventral thalamic nucleus, 19.4±1.5 fmol/mg; cerebellar molecular layer, 55.0±4.3 fmol/mg). Also for this class of -adrenoceptors, high- and low-affinity binding sites for the ₂-selective antagonist ICI118.551 were observed, indicating that ¹²⁵ICYP labels membrane bound and internalized ₂-adrenoceptors. Only in the cerebellar molecular layer was a high percentage of high-affinity ₂-adrenoceptors detected (K _i for ICI118.551 was 1.8±0.3 nM for 90% of the receptors).6. In conclusion, ₁- and ₂-adrenoceptor binding can be localized and quantified by in vitro receptor autoradiography in the brains of tree shrews when serotonergic binding sites are blocked. Modulatory effects of long-term psychosocial conflict on the central nervous -adrenoceptor system in male tree shrews are described in the following paper.     

Phototoxicity of phenothiazine derivatives. I. Inactivating and mutagenic effects on bacteriophage φX174

Inactivation of φX174 bacteriophages as a function of the irradiation time in the near-UV and in the presence of triflupromazine (TFPZ), promazine (PZ), chlorpromazine (CPZ) or methoxypromazine (MTPZ) proceeds according to single hit kinetics. Acepromazine (ACPZ) has no significant activity. At low concentrations (0.1 mM) TFPZ and PZ are the most active compounds. Higher concentrations (up to 5 mM) result in a protective effect by these two compounds but cause increased inactivation rates in the case of MTPZ or CPZ. Photoinactivation mediated by TFPZ or CPZ increases the reversion frequency of a φXamber mutant. Neither MTPZ nor PZ sensitization induces mutagenesis. The effect of NaN₃ on the phage inactivation rate varies depending upon both the sensitizer and the concentration of the quencher. Phage inactivation in an N₂ atmosphere is measurable only in the presence of high concentrations of CPZ and MTPZ. The drugs do not show any selectivity for calf thymus DNA or bovine serum albumin, at least as measured by dialysis equilibrium experiments.     

Interaction of α-lactalbumin with dimyristoyl phosphatidylcholine vesicles. I. A microcalorimetric and fluorescence study

α-Lactalbumin and dimyristoyl phosphatidylcholine were used as a prototype to study the influence of a protein conformational change, induced by the pH, on the interaction between that protein and a phospholipid.The enthalpy changes associated with the interaction of α-lactalbumin with dimyristoyl phosphatidylcholine vesicles were measured as a function of the molar ratio of phospholipid to protein, pH and temperature. Gel-filtration, electron-microscopic and fluorescence data for the same experimental conditions were also obtained. At pH 4 and 5, the enthalphy changes (ΔH) are not only larger than at physiological pH, but also show a maximum at about 23°C in the ΔH vs. temperature graph. At pH 6 and 7, on the contrary, ΔH increases with decreasing temperature without a maximum in the curve. Gel-chromatographic and electron-microscopic data show that at pH 6 and 7, the morphological characteristics of the vesicles are unchanged upon addition of α-lactalbumin, while at pH 4 and 5 at 23°C an extra peak appears in the gel-filtration graphs between the pure vesicles and α-lactalbumin. The new fraction contains lipid-protein complexes. Electron micrographs show that bar-shaped entities are formed. A red shift at 23°C and a blue shift at 37°C, both to 336 nm, are observed for λ_max of the fluorescence emission spectra at pH 4 when α-lactalbumin is brought into contact with the phospholipid. At the same time, a strong increase in the fluorescence intensity is observed. The chromatographic and fluorescence data indicate that a lipid-protein complex with a molar ratio of approx. 80 is formed. At pH 7 and different temperatures, the emission maximum remains at the wavelength of pure α-lactalbumin, the change in the fluorescence intensity, however, indicates that interaction with the lipid occurs.The results can be explained on the basis of an electrostatic interaction at pH 6 and 7, and a hydrophobic interaction at pH 4 and 5.     

The α-glucosidases of Dictyostelium discoideum: I. Identification and characterization

We have identified four isozymes of α-glucosidase in the cellular slime mold, Dictyostelium discoideum. The isozymes can be distinguished by their physical and enzymatic properties. α-Glucosidase-1, α-glucosidase-2, and α-gluocosidase-3 are all present in vegetative cells, while α-glucosidase-4 is present only after the cells have proceeded through aggregation. Three of the four enzymes, α-glucosidase-1, α-glucosidase-3, and α-glucosidase-4, have acidic pH optima of 3.5, 2.2, and 4.0, respectively. In contrast, α-glucosidase-2 has a neutral pH optimum, 7.25. α-Glucosidase-1, α-glucosidase-2, and α-glucosidase-3 are distinguishable by electrophoresis in native polyacrylamide gels. α-Glucosidase-4 comigrates with α-glucosidase-2 on native gels but they can be resolved by isoelectric focusing. The isozymes also differ with respect to affinity for the substrates p-nitrophenyl-α-d-glucoside and 4-methyl-umbelliferyl-α-d-glucopyranoside and the relative maximal rates of hydrolysis of these substrates. α-Glucosidases-1, -2, and -4 have apparent K_m's in the millimolar range while the apparent K_m of α-glucosidase-3 for p-nitrophenyl-α-d-glucoside is much higher. This may suggest that isozyme 3 is an endoglycosidase or may have greater affinity for other sugar substrates. α-Glucosidase-1 is the major isozyme in vegetative cells.     

Is protein folding hierarchic? I. Local structure and peptide folding

The folding reactions of some small proteins show clear evidence of a hierarchic process, whereas others, lacking detectable intermediates, do not. Nevertheless, we argue that both classes fold hierarchically and that folding begins locally. If this is the case, then the secondary structure of a protein is determined largely by local sequence information. Experimental data and theoretical considerations support this argument. Part I of this article reviews the relationship between secondary structures in proteins and their counterparts in peptides.     

Cell-wall Polysaccharides of Immature Barley Plants. I. Isolation and Characterization of a β-d-Glucan

A β-d-glucan was isolated on fractionation of a 4% potassium hydroxide extract (hemi-celluloses) of immature barley plants (Hordeum distichum L.). Most of the glucose residues in the extract were found to be derived from the glucan. Methylation analysis and enzyme degradation studies showed that the glucan had (l-→3)-and (1-→4)-linked d-glucopyranosyl residues in an approximate molar ratio of 1.0:2.3. The molecular weight of the glucan was estimated to be 1.8 x 10⁵ by gel filtration on Sepharose CL-6B.     

Methoxyflurane and Nitrous Oxide as Obstetric Analgesics. I.—A Comparison by Continuous Administration

Methoxyflurane and nitrous oxide have been compared as obstetric analgesics. The inhaled concentrations of these agents, given continuously, were adjusted by an anaesthetist to maintain each patient at the optimum state between reaction to pain and consciousness. Assessments were made continuously.Though the anaesthetist''s assessment showed no difference between the mean results, a greater proportion of the methoxyflurane patients were “satisfactory” for 90–100% of the time than of the nitrous oxide patients, particularly in regard to objective pain relief. The midwives'' opinion of those who had “complete” pain relief supported this. Nausea was significantly less among methoxyflurane patients, and vomiting during labour occurred only in patients who had nitrous oxide. It is concluded that nitrous oxide and methoxyflurane given in a continuously adjusted concentration are almost equally effective as obstetric analgesics, though there are certain features which favour methoxyflurane.     

Pre- and post-zygotic reproductive isolation between co-occurring Mussaenda pubescens var. alba and A/I. shikokiana （Rubiaceae）

Reproductive isolation is a fundamental require- ment for speciation and includes several sequential stages. Few studies have determined the relative contributions of pre- and post-zygotic reproductive isolation in plants, especially between relative species with clear differentiation in flower form. To investigate the mechanisms responsible for repro- ductive isolation in sympatric A4ussaenda pubescens var. alba and Mussaenda shikokiana （Rubiaceae） in Guangxi Province, China, we made observations of flowering phenology, patterns of insect visitation, and conducted pollination experiments, including artificial hybridization. The two species had over- lapping flowering times and were pollinated by overlapping pollinators; however, their relative importance differed significantly with M. pubescens visited more commonly by bees and M. shikokiana more frequently by butterflies. Using vegetative and floral characters and molecular evidence based on nuclear ribosomal internal and external transcribed spacer regions we detected seven naturally occurring hybrids among a sample of approximately 125 individuals. Hybrids were characterized by morphologies that most closely resembled their maternal parents based on chloroplast evidence. Studies of artificially synthesized and natural hybrids demonstrated that hybrid seed had very low germination rates and naturally occurring hybrids exhibited pollen sterility. Post-zygotic reproductive isolating mechanisms play a primary role in limiting gene exchange between co-occurring species and maintaining species integrity in areas of sympatry.     

A cytochemical and ultrastructural study of the “S.I.F.” cells in cat sympathetic ganglia

Summary According to the hypothesis of Eccles and Libet, the small intensely fluorescent cells (S.I.F. cells) in the sympathetic ganglion would represent an essential element in the inhibition of the principal neuron. As a contribution to the study of this important problem, we have investigated serial sections in superior cervical (S.C.G.) and celiac (C.G.) ganglia of the cat, a species that has not been extensively studied up to now, both by fluorescence and electron microscopy. We have shown that the S.I.F. cells are three times fewer in the cat S.C.G. than in the rat S.C.G. There are five times more S.I.F. cells in the C.G. of the cat than in the S.C.G. of the same species. Moreover we have described two types of S.I.F. cells.Type I is composed of cells characterized by highly polymorphous large dense-cored vesicles. These cells lack processes and are grouped in clusters centered on fenestrated capillaries. They could be endocrine function cells. Type II is formed of isolated cells which exibit long processes and establish synaptic junctions with the dendrites of the principal neurons. In this case, the dense-cored vesicles are very regular and much smaller. These cells could be equivalent to interneurons. Type I very strongly predominates in the S.C.G. and C.G. of the cat where it represents more than 90% of the S.I.F. cell total observed by fluorescence microscopy. A priori such a quantitative and qualitative heterogeneity hardly consistent with Eccles and Libet's hypothesis based on the existence of dopaminergic interneurons only, allows the question to be raised as to the functional significance of the S.I.F. cells in ganglion physiology. The notion of modulation of ganglionic transmission does not seem to be quiered by these new data but could be founded on different forms of action embodied in the broader conception of the neuromodulation phenomenon.     

Computer simulation of the motoneuron pool–muscle complex. I. Input system and motoneuron pool

 The aim of the present study was to simulate the input system and the motoneuron (MN) pool of the MN pool–muscle complex (MNPMC). Input fibers, which can originate from command centers in the central nervous system or from sensory organs, activate the MN pool. They generate sequences of action potentials, the frequency of which is proportional to a time-dependent activation factor (which is an input to the model). Different connection patterns between the input fibers and motor units (MUs) are allowed. For simplicity and since no precise experimental data are available, 70 input fibers and 4 boutons per fiber and MN are simulated (this corresponds approximately to the monosynaptic group-Ia input of the cat medial gastrocnemius muscle). Each bouton generates the same conductance change in the postsynaptic membrane. The MNs are modeled with a single compartment and a homogenous membrane. According to experimental data, the membrane leakage conductance and capacitance are MU dependent. Since the precise relation is unknown: (a) the computed relation between MU contraction force and the MN leakage conductance was taken from a steady-state MNPMC model, and (b) the capacitance was assumed to be proportional to the leakage conductance. The MN membrane includes time- and voltage-dependent ionic channels (fast and slow K⁺ and low- and high-threshold Ca²⁺ channels). The density and time constant of the slow K⁺ channels and the density of the Ca²⁺ channels were fitted to approximate afterhyperpolarization characteristics and frequency-injected current relations of type-identified cat MNs. If the membrane reaches a voltage threshold the MNs generate action potentials, which were simulated by voltage pulses. The activation of the MN pool of the human first dorsal interosseus muscle was simulated with injected and synaptic currents in order to illustrate the size principle, synaptic noise, and other features of muscle activation. It is concluded that the present model reproduces the main properties of the input–output relations of different MN types within a muscle. Together with the simulation of the muscle force and the surface EMG, which will be published in subsequent papers, it will be a powerful tool for reproducing experiments on the motor system and investigating functional mechanisms of motor control. Received: 17 April 2001 / Accepted in revised form: 6 November 2001