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Biomedical subjects

J Johansen

Publications and source records attributed to J Johansen.

At least 127 records · Page 7Linked to original sources
PubMed1985

Properties of action potentials carried by divalent cations in identified leech neurons.

Properties of divalent cation potentials carried by either Sr2+ or Ca2+ ions in Na+-free, TEA-Ringer solution were characterized in identified neurons of two species of leeches (Macrobdella and Haementeria). In Macrobdella, the overshoot of the potentials varied logarithmically with [Sr2+]0 (28.5 mV per 10-fold change). The overshoot, Vmax, and duration of the potentials increased with increasing divalent cation concentration and saturated at about 20 to 30 mM [Sr2+]0. The Vmax, amplitude, and duration of the potentials were reversibly blocked by Co2+ and Mn2+. The block by Mn2+ could be well-fitted by a reverse Langmuir-curve with an apparent KI of 100 micromolar. The local anesthetic procaine also reversibly inhibited the Vmax and duration of the potentials. The inhibition was greater at alkaline pH suggesting that procaine blocks the calcium channel from inside the membrane. The identified leech neurons examined in Macrobdella varied considerably in their ability to sustain somatic divalent cation potentials. Stimulation of T cells and most motoneurons produced no or only weak potentials, whereas stimulation of Retzius, N, Nut, and AP cells evoked overshooting potentials of several seconds' duration. Stimulation of the ALG cell of Haementeria in normal Ringer solution evoked a slowly-rising, purely Ca2+-dependent potential of approximately 100 ms duration. This response was TTX-resistant, unaffected by complete removal of Na+ from the Ringer solution, and abolished by 1 mM Mn2+. The overshoot varied logarithmically with a slope of 28 mV/decade change in [Ca2+]0.

Action Potentials↗
PubMed1985

Inhibition of Ca2+ conductance in identified leech neurons by benzodiazepines.

Benzodiazepines (BZs) in micromolar concentrations inhibit Mn2+- and Co2+-sensitive regenerative divalent cation potentials, which are revealed in the presence of tetraethylammonium ion, in leech nociceptive neurons (N cells). This BZ effect is reversible and dose-dependent. The BZs, like Mn2+ and Co2+, inhibit the maximum rate of depolarization (Vmax) and duration of divalent cation potentials at concentrations that do not significantly affect resting membrane potential or Vmax of the Na+-dependent action potential. Ultraviolet-induced BZ binding to micromolar-affinity sites in ganglia and isolated cells irreversibly blocks Ca2+ conductance in neurons without significantly affecting resting membrane potentials. BZ binding studies with leech neuronal membrane show saturable, specific binding in the micromolar concentration range that was similar to BZ binding to synaptosomal membrane fractions. The apparent Kd obtained from the micromolar-affinity BZ binding curve for leech ganglionic membrane preparations agrees well with the apparent Ki estimated from the dose-response curve measuring BZ inhibition of Vmax of the divalent cation potentials. These findings indicate that BZs act like Ca2+-channel antagonists in intact neuronal preparations and are consistent with the hypothesis that BZ binding to micromolar-affinity receptors modulates voltage-gated Ca2+ channels.

Action Potentials↗
PubMed1984

Monoclonal antibody identifies a 63,000 dalton antigen found in all central neuronal cell bodies but in only a subset of axons in the leech.

The monoclonal antibody Lan3-8 binds to all the neuronal cell bodies in midbody, head, tail, and supraesophageal ganglia in the mud leech (Haemopis marmorata) and the medicinal leech (Hirudo medicinalis). In contrast to the general distribution of the antigen in cell bodies it is only found in a subset of axons, where electron microscopy suggests that it may be associated with a cytoskeletal filament system. Immunoblotting shows that the antibody binds to a 63,000 dalton band that is protease-sensitive. The same 63 kilodalton (kd)-antigen is found in all regions of the central nervous system, in proteins isolated from connectives (axons alone), and from hand-dissected identified cell types. The molecular weight and electron microscopic localization raised the possibility that this antigen is the core neurofilament protein, but the antigen does not comigrate with 67-kd intense coomassie blue band that binds another anti-intermediate filament antibody. The supraesophageal ganglia are known to have a different developmental or origin from the other structures in the leech central nervous system. Two-dimensional gel electrophoresis and silver staining show that, like the 63-kd antigen, many other proteins are very similar in these developmentally distinct neural structures.

Animals↗
PubMed1984

Axonal projections of mechanosensory neurons in the connectives and peripheral nerves of the leech, Haemopis marmorata.

The axonal projections of the seven mechanosensory neurons in the connectives and peripheral nerves were examined by horseradish peroxidase (HRP) injections. In the connective the closely functionally related mechanosensory neurons travel in two bilaterally symmetrical regions, which comprise less than 10% of the connective's cross-sectional area. This grouping may reflect the similar functional properties and synaptic connections of the cells. Serial sections through the neuropil-connective junction zone showed that the organization of the axons is independent of glial fasciculation. Fascicles are not rigid structures; they were found to part and fuse in a seemingly random manner. The glial cell seems therefore to have only a supportive structural function and not to play any role in axonal guidance or to define any specific nerve fascicles in the leech. The projections of the mechanosensory cells in the peripheral roots were not as stereotyped as in the connective. However, examination of the branching of the medial and lateral P cells in the posterior root showed that the roots are highly structured and that some axons may be confined to tracts which have specific positions related to the branching of the root. The possible role of the P cells in pioneering these tracts is discussed.

Animals↗
PubMed1984

Distribution and morphology of nociceptive cells in the CNS of three species of leeches.

The present study describes the segmental variation in the distribution and morphology of nociceptive neurons (N cells) in the central nervous system of the leech. N cells of midbody ganglia can be segregated into lateral and medial types. We show that monoclonal antibodies specific for N cells can distinguish between the two populations. The monoclonal antibodies were used to map the complete distribution of the cells along the nervous cord. There are two pairs of the medial and lateral nociceptive neurons in the midbody ganglia, one pair of the medial type in the sex ganglia (5 and 6), and a pair of the lateral type in ganglia 20 and 21. The caudal brain is without nociceptive neurons. This distribution was confirmed by electrophysiological means. The morphology of N cells in different parts of the nervous system was investigated by intracellular horseradish peroxidase (HRP) injections. In the terminal segmental ganglia the N cells showed extensive arborizations in the head and tail brains and, contrary to N cells in the midbody ganglia, their arborizations spanned more than three segments. N cells are absent in the tail brain, but the N cells of ganglia 20 and 21 were shown to innervate the entire caudal region. The basic morphology of all N-cell homologues was found to be very similar for three leech species. In the sex ganglia the pair of N-cell homologues were examined in Haemopis, Hirudo, and Macrobdella. The results showed a progressive modification in the three species of the cell's morphology, peripheral projections, and physiological responses, possibly correlated with the evolution and complexity of the sexual organs. HRP injections and monoclonal antibody staining revealed that a common feature of N-cell homologues is the presence of processes that tightly surround the cell soma of other cells. This suggests that N cells may have other functional properties in addition to being primary sensory neurons.

Animals↗
PubMed1984

Procaine actions on tetrodotoxin sensitive and insensitive leech neurons.

Procaine (0.1-10 mM) was applied to two kinds of identified neurons in segmental leech ganglia. Both Retzius (R) cells and nociceptive (N) cells responded by dose-dependent reduction of maximum rates of de- and repolarization during action potentials. However, the N cells, which are more sensitive to tetrodotoxin than R cells, were also 3 times more sensitive to procaine. The prolongation of action potentials produced by procaine in R cells was enhanced by low Ca but antagonized by high Ca. This implies that the drug interfered with repolarization by affecting a Ca-dependent mechanism. In alkaline solution (pH 8.5), sensitivity of the R cell to procaine approached that of the N cell at pH 7.4 suggesting that the drug acted at an intracellular site after passage through membrane lipids in its uncharged form. The combined effects of TTX and procaine, in concentrations which produced about 50% inhibition of dV/dTdep in N cells when given separately, were found to be intermediate between those predicted by two models which assume identical and independent sites of action, respectively. These data extend our earlier observations regarding the existence of two types of Na channels in mature leech neurons. They imply that the differential sensitivity to procaine among these cells may be a consequence of variable access to an otherwise identical 'receptor' and that TTX and procaine act on separate sites which may interact with each other.

Animals↗
PubMed1984

Actions of procaine on specific nociceptive cells in leech central nervous system.

The effects of the local anesthetic, procaine, on the electrophysiological properties of the leech neurons responding to nociceptive stimuli (N cells) were examined in isolated segmental ganglia in Macrobdella . In the N cell situated laterally in ganglia 7 to 19, procaine produced a depolarization; whereas in the N cell situated medially, it caused a hyperpolarization. These changes in membrane potential were accompanied by a decrease in input resistance, persisted in solutions containing 20 mM MgCl2, and were reversible after drug washout. The depolarization induced by procaine in the lateral N cell was abolished in Na-free solutions. The hyperpolarization produced by procaine in the medial N cell persisted in low chloride solutions and was enhanced by about 30% when the K concentration was reduced to one-tenth of its control value. Therefore, it seems likely that an increase in the resting K conductance was a contributing factor to this hyperpolarization. Procaine greatly prolonged the action potential of the lateral but not the medial N cell. This effect was not solely a consequence of the membrane potential change produced by the drug. Ganglia 5, 6, 20, and 21 contained two rather than four cells with N-like properties. These neurons were N-like by virtue of the shape of their action potential and their morphological similarities to the N cells found in ganglia 7 to 19, as well as by their selective sensitivities to nociceptive mechanical stimulation of the skin. The cells in ganglia 5 and 6 responded to gut stimulation, as did the medial N cells in ganglia 7 to 19.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Surface molecules identify groups of growing axons.

Studies on vertebrate and invertebrate species have established that, during development, axons have the ability to choose particular paths over others. The chemical basis of this pathfinding is not clear but biochemical differences between neurons have long been postulated to account for the specificity of neuronal connections. Such subtle molecular differences between different cells in a single tissue are difficult to study with standard biochemical techniques but hybridoma technology has offered a potential solution to this type of problem. This technique has made possible the production of monoclonal antibodies for identifying and characterizing a family of glycoproteins which are expressed on the surface of specific axon bundles during the development of the leech nervous system. The results show that groups of growing axons do indeed carry chemically distinct surface molecules.

Animals↗
PubMed1982

Morphological and electrophysiological mapping of giant neurons in the suboesophageal ganglia of Helix pomatia.

1. To reveal the morphology of the suboesophageal ganglia of Helix pomatia, the connective tissue was completely removed and the preparations stained whole-mount with methyl green-pyronin G to display the relative locations of the neurons. 2. Fifteen large cells which could be recognized as individuals in at least 75% of the preparations investigated, were morphologically identified by size, position and color. 3. The cells were electrophysiologically characterized with respect to spontaneous activity, synaptic input from peripheral nerves, and response to application of drugs (e.g. ACh, DA and 5-HT). 4. The peripheral axonal projections of eight of the major identified cells were investigated by intracellular CoCl2 injection and by cobalt backfilling of the peripheral nerves.

Animals↗
PubMed1979

A simple and rapid whole-mount staining method with methyl green-pyronin G applied to a molluscan brain preparation.

Subesophageal ganglia of molluscs have been stained as whole mounts with methyl green-pyronin G to display the relative location of individual neurons. Nuclei appear blue, perikarya red. Expose the ganglion cells by dissection of the connective tissue in snail Ringer. Transfer the ganglion to a fixative of 2.5% glutaraldehyde in 0.1 M Na cacodylate pH 7.1 at 4 C for 12--24 hours, and wash in distilled water for 1 1/2 hours. Stain with methyl green-pyronin G for 1/2--1 hour and differentiate in 96% ethanol using many rapid changes. Transfer the ganglion to absolute ethanol for 2 1/2 hours and clear in xylene for 3 hours before embedding in Depex in a suitable dish. When the Depex has hardened, the preparation can be stored, and is readily available for subsequent examination. The method may be applicable to other invertebrate tissues, and may be useful in preparing objects for teaching purposes.

Animals↗
PubMed1977

Middle third femoral fractures treated with medullary nailing or AO compression plates.

Fifty-eight medullary nailings and 46 internal fixations with AO plates were performed on fractures of the middle third of the femur. The complication rate was 21-2%, infections accounting for 7-7% and implant failures for another 7-7%. Critical descriptions of the failures are given, 6 of 8 implant failures being biomechanical. Follow-up results were excellent or satisfactory in 95% of cases in both groups. At follow-up after 3 1/2 years, there was no difference in results between the two methods of treatment.

Adolescent↗