Electroconvulsive therapy in South Carolina.
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Data Collection↗
Biomedical subjects
C H Keller
Publications and source records attributed to C H Keller.
Na+ channel accumulation on axolemma of afferent endings in nerve end neuromas in Apteronotus.
In mammals, cut sensory axons trapped in a nerve end neuroma have been shown to develop hyperexcitability, and to become a source of ectopic afferent discharge and abnormal sensation. We have explored cellular mechanisms underlying neuroma electrogenesis. First we confirmed that ectopic neuroma discharge develops in injured afferents in the electrosensory lateral line nerve of the weakly electric fish Apteronotus, as it does in mammals. Then, using previously characterized antibodies that specifically recognize Na+ channel proteins in this species, we obtained light and electron microscopic evidence of abnormally intense immunolabelling of axolemma at the injury site. Accumulation of excess Na+ channels in afferent endings in neuromas could account for their electrical hyperexcitability.
Animals↗
From distributed sensory processing to discrete motor representations in the diencephalon of the electric fish, Eigenmannia.
During their jamming avoidance response (JAR), weakly electric fish of the genus Eigenmannia shift their electric organ discharge (EOD) frequency away from a similar EOD frequency of a neighboring fish. The behavioral rules and neural substrates for stimulus recognition and motor control of the JAR have been extensively studied (see review by Heiligenberg 1986). The diencephalic nucleus electrosensorius (nE) links sensory processing within the torus semicircularis and optic tectum with the mesencephalic prepacemaker nucleus which, in turn, modulates the medullary pacemaker nucleus and hence the EOD frequency. Two separate areas within the nE responsible for JAR-related EOD frequency rises and frequency falls, respectively, were identified by iontophoresis of the excitatory amino acid L-glutamate. Bilateral lesion of the areas causing EOD frequency rises resulted in elimination of JAR-related frequency rises above a baseline frequency obtained in the absence of a jamming stimulus. Similarly, bilateral lesion of the areas causing frequency falls resulted in a loss of JAR-related frequency falls below the baseline frequency. Whether these areas are also responsible for non-JAR-related frequency shifts is not known. The strength of response and spatial extent of the areas causing frequency shifts varied among fish and also varied in individual fish, reflecting the strength of JAR-related frequency shifts and the balance of activities in frequency-rise and frequency-fall areas. Local application of bicuculline-methiodide or GABA demonstrated a tonic inhibitory input to each area and suggests a reciprocal inhibitory interaction between the two ipsilateral areas, possibly accounting for much of the individual plasticity. The nE thus is a site for neuronal transformation from distributed, topographically organized processing within the laminated structures of the torus and tectum to discrete cell clusters which control antagonistic motor responses.
Action Potentials↗
Different classes of glutamate receptors mediate distinct behaviors in a single brainstem nucleus.
We have taken advantage of the increasing understanding of glutamate neuropharmacology to probe mechanisms of well-defined vertebrate behaviors. Here we report a set of experiments that suggests distinct roles for two major classes of glutamate receptors in a discrete premotor nucleus of the brainstem. The medullary pacemaker nucleus of weakly electric fish is an endogenous oscillator that controls the electric organ discharge (EOD). Its regular frequency of firing is modulated during several distinct behaviors. The pacemaker nucleus continues firing regularly when isolated in vitro, and modulatory behaviors can be reproduced by stimulating the descending input pathway. Glutamate agonists applied to the pacemaker in vitro produced increases in frequency, while glutamate antagonists selectively blocked stimulus-induced modulations. Experiments with glutamate antagonists in the intact animal resulted in specific effects on two well-characterized behaviors. Our data indicate that these behaviors are separately mediated in the pacemaker by receptors displaying characteristics of the kainate/quisqualate and N-methyl-D-aspartate subtypes of glutamate receptor, respectively.
2-Amino-5-phosphonovalerate↗
Stimulus discrimination in the diencephalon of Eigenmannia: the emergence and sharpening of a sensory filter.
Neuronal reliability and sensitivity to behaviorally relevant stimulus patterns were investigated in a higher-order nucleus of the diencephalon believed to participate in the jamming avoidance response (JAR) of the weakly electric fish, Eigenmannia. The fish raises or lowers its frequency of electric organ discharge (EOD) to minimize interference from a neighboring fish's EOD. Proper JARs require determination of the sign of the difference frequency (Df) between the neighboring fish's EOD and the fish's own EOD. Bastian and Yuthas (1984) recently described diencephalic neurons within the nucleus electrosensorius that are able to make this determination. In the present study, response properties of such neurons were compared with those of lower-level 'sign-selective' cells found in the torus semicircularis and the optic tectum (Heiligenberg and Rose 1985) as well as with properties of the intact behavior. Most sign-selective cells within the nucleus electrosensorius show a high degree of selectivity for one sign of the difference frequency; cells with either sign preference were found in approximately equal numbers. The sign preference and the degree of sign selectivity is most often independent of the spatial orientation of the jamming stimulus. In contrast, the responses of toral and tectal cells are less robust and consistent and are often highly dependent on the geometry of the jamming stimulus. Determination of the sign of the difference frequency requires the analysis of amplitude modulations coupled with modulations in phase (timing) differences between pairs of areas of the body surface. The most sensitive cells recorded in the nucleus electrosensorius can determine the sign of the difference frequency with timing differences of 1 microsecond or less, roughly comparable to the behavioral threshold of 400 ns (Carr et al. 1986). The best toral/tectal response required at least a 16 microseconds modulation. Cells within the nucleus electrosensorius thus code the sign of Df with a high degree of reliability and sensitivity. Ambiguities persist, however, which suggest that single cells at this level cannot completely account for the behavioral discrimination. Additional processing may be necessary to transform a still primarily sensory code into a motor program for control of the JAR (Rose et al. 1988).
Animals↗
Hormone-induced and maturational changes in electric organ discharges and electroreceptor tuning in the weakly electric fish Apteronotus.
Plasticity in the frequency of the electric organ discharge (EOD) and electroreceptor tuning of weakly electric fish was studied in the genus Apteronotus. Both hormone-induced and maturational changes in EOD frequency and electroreceptor tuning were examined. Apteronotus is different from all other steroid-responsive weakly electric fish in that estradiol-17 beta, rather than androgens, induces discharge frequency decreases. This result can account for the 'reversed' discharge frequency dimorphism found in Apteronotus in which, counter to all other known sexually dimorphic electric fish, females have lower discharge frequencies than males. Studies of electroreceptor tuning in Apteronotus indicate that electroreceptors are closely tuned to the frequency of the EOD. This finding was noted not only in adult animals, but also in juvenile animals shortly after the onset of their EODs. Tuning plasticity in Apteronotus, as in other species studied, is associated with altered EOD frequencies and was noted in both maturational EOD changes and in estrogen-induced changes. Thus, tuning plasticity appears to be a general phenomenon which occurs concurrent with a variety of EOD changes.
Androgens↗
Evidence for a direct effect of androgens upon electroreceptor tuning.
Tuberous electroreceptors of individual wave type weakly electric fish are tuned to the fundamental frequency of that fish's electric organ discharge (EOD). EOD frequency and receptor best frequency (BF) are both lowered following systemic injection of 5-alpha-dihydrotestosterone (DHT). A previous study (Meyer et al. 1984) showed that the effect of DHT on the EOD generating circuitry was independent of an ongoing EOD and suggested that its effect on electroreceptor tuning was indirect, possibly mediated by the electric field. We have continued these studies to determine the factors which influence electroreceptor tuning. Baseline recordings of EOD frequency, receptor oscillations, and single afferent tuning curves were taken. After fish were electrically silenced by spinal cord transection they were injected daily with either DHT or saline or were implanted with either DHT-filled or empty silastic capsules. As previously reported, the EOD frequency (determined from pacemaker nucleus recordings) was lowered in DHT-treated, transected fish and increased in control fish. Similarly, receptor tuning was lowered in the DHT-treated, silenced fish. Oscillation frequencies decreased in both treated and control groups, but significantly more in the hormone group. Single afferent best frequencies were lowered in both DHT groups and raised in their respective control groups. In another series of experiments exogenous electric fields capable of driving receptors in a 1-to-1 phase-locked manner were placed around silenced fish. We were unable to elicit any shift in pacemaker frequency or electroreceptor tuning regardless of stimulus field geometry. Four transected fish were injected with DHT and placed in exogenous electric fields of higher frequency than their original EOD. Even in the presence of a higher frequency electric field, DHT lowered EOD frequency and afferent BF. We conclude that androgens produce effects both on the EOD generating circuitry, probably at the level of the pacemaker nucleus, and on electroreceptors, probably, ultimately, on receptor cell membrane conductances. These effects occur in parallel allowing the two parameters to remain well matched. In contrast to former predictions, exogenous electric fields alone appear unable to shift receptor tuning.
Animals↗
Reconstitution of calmodulin-sensitive adenylate cyclase from bovine brain with phosphatidylcholine liposomes.
A partially purified calmodulin (CaM)-sensitive adenylate cyclase from bovine cerebral cortex was reconstituted with a series of phosphatidylcholine liposomes having variable fatty acid composition. The enzyme was successfully associated with dimyristoyl, dipalmitoyl, distearoyl, and dioleoylphosphatidylcholine liposomes. The specific activity of the enzyme in the various liposomes varied over a 4.6-fold range indicating some degree of specificity for fatty acid composition. The adenylate cyclase-liposome preparation retained sensitivity to both CaM and 5'-guanylylimidodiphosphate (GppNHp). Arrhenius plots of enzyme activity in the four different liposome preparations all exhibited a pronounced discontinuity at 30 degrees C +/- 2, even though the bulk-phase thermal transition points for the liposomes varied from -20 to 54 degrees C. Fluorescence anisotropy studies of reconstituted liposome systems illustrated that incorporation of protein did not alter the normal-phase transition point of these lipids. Since Arrhenius plots of the enzyme in Lubrol PX, prior to reconstitution with lipids, were strictly linear, it is concluded that the breaks at 30 degrees C may be the effect of a local enzyme-phospholipid environment. It appears that this adenylate cyclase is not particularly sensitive to phase transitions of the bulk lipid phase. The phospholipid reconstituted enzyme system appears suitable for examination of the influence of lipids on the CaM-sensitive adenylate cyclase.
Adenylyl Cyclases↗
Calcium-dependent and calcium-independent affinities of calmodulin for calmodulin-binding proteins determined by fluorescence techniques.
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Animals↗
Interaction of a fluorescent N-dansylaziridine derivative of troponin I with calmodulin in the absence and presence of calcium.
Rabbit skeletal muscle troponin I was covalently labeled with N-dansylaziridine, resulting in a fluorescent labeled protein. This derivative (DANZTnI) and native troponin I (TnI) inhibited calmodulin (CaM) stimulation of bovine heart Ca2+-sensitive cyclic nucleodite phosphodiesterase with identical inhibition constants. Association of DANZTnI with calmodulin was monitored directly by changes in flourescence intensity in the presence of Ca2+ and by changes in fluorescence anisotropy in the absence of Ca2+. Quantitation of the affinity of calmodulin for calmodulin-binding proteins in both the presence and absence of Ca2+ is necessary for prediction of the extent of interaction of both Ca2+ and calmodulin-binding proteins with calmodulin in vivo. The dissociation constants for the DANZTnI-calmodulin-l4Ca2+ and DANZTnI-calmodulin complexes were 20 nM and 70 micrometers, respectively. These dissociation constants define a free energy coupling of-4.84 kcal/mol of troponin I for binding of Ca2+ and troponin I to calmodulin. The Ca2+ dependence for troponin I-calmodulin complex formation predicted from these experimentally determined parameters was closely approximated by the Ca2+ dependence for complex formation between troponin I and fluorescent 5-[[[(iodoacetyl)amino]ethyl]-amino]-1-napthalenesulfonic acid derivatized calmodulin as determined by fluorescence anisotropy. Complex formation occurred over a relatively narrow range of Ca2+ concentration, indicative of positive heterotropic cooperativity for Ca2+ and troponin I binding to calmodulin.
3',5'-Cyclic-AMP Phosphodiesterases↗
Determination of the free-energy coupling for binding of calcium ions and troponin I to calmodulin.
Regulation of a wide variety of biological systems by Ca2+ is now known to be mediated through calmodulin, a Ca2+-binding protein. Calmodulin forms Ca2+-dependent complexes with several proteins, including troponin I. We have determined the free-energy coupling (delta GoCT) for binding of Ca2+ and troponin I to calmodulin by measuring Ca2+ binding to calmodulin and to the 1:1 calmodulin-troponin I complex by equilibrium dialysis. The dissociation constant for the Ca2+4.calmodulin and troponin I complex was also determined directly by monitoring fluorescence intensity changes accompanying complex formation between Ca2+4.CaM and N-dansylaziridine-troponin I, a fluorescent derivative of troponin I. Calmodulin displayed four Ca2+-binding sites of similar affinity with a geometric mean dissociation constant of 14 microM. In the presence of saturating troponin I, the geometric mean dissociation constant for the four Ca2+-binding sites was shifted to 1.7 microM. delta GoCT was therefore -1.25 kcal/mol of Ca2+. Saturation of calmodulin with Ca2+ would therefore be expected to increase its affinity for troponin I about 4500-fold. A dissociation constant of 20 nM was determined for the Ca2+4.calmodulin.N-dansylaziridine-troponin I complex. The dissociation constant of the calmodulin.N-dansylaziridine-troponin I complex in the absence of Ca2+ should therefore be about 90 microM. A prediction of this data is that binding of Ca2+ to calmodulin will show strong positive cooperativity when Ca2+ binding to a substoichiometric number of sites is sufficient to promote calmodulin.troponin I complex formation.
Calcium↗
Preparation of a fluorescent-labeled derivative of calmodulin which retains its affinity for calmodulin binding proteins.
Calmodulin was derivatized with 5-[[[(iodoacetyl)amino]ethyl]amino]-1-naphthalenesulfonic acid to fluorescently label the protein. This derivative (AEDANS.CaM) stimulated the Ca2+-sensitive cyclic nucleotide phosphodiesterase and formed Ca2+-dependent complexes with troponin I and the phosphodiesterase. Association between AEDANS.CaM and these proteins was directly monitored by changes in fluorescence anisotropy. The dissociation constants for the AEDANS.CaM--troponin I and AEDANS.CaM--phosphodiesterase complexes were 60 nM and 4 nM, respectively. This fluorescent derivative of calmodulin appears suitable for direct monitoring of the complexes between calmodulin and calmodulin binding proteins. Rotational diffusion of AEDANS.CaM was also measured with fluorescence anisotropy. These measurements indicated that the shape of calmodulin in solution is best approximated by a prolate ellipsoid.
Animals↗
Preparation of azidocalmodulin: a photoaffinity label for calmodulin-binding proteins.
A photoaffinity label for calmodulin-binding proteins was prepared from 125I-labeled calmodulin (125I-calmodulin) and methyl-4-azidobenzimidate. Azidocalmodulin containing one azido group per calmodulin retained its ability to stimulate the CA2+-sensitive phosphodiesterase purified from bovine heart muscle. The concentrations of calmodulin and azidocalmodulin required for half-maximal stimulation of phosphodiesterase activity were 170 and 230 pM, respectively. Azido-125I-calmodulin was used to photoaffinity label troponin I, myosin light chain kinase, and the Ca2+-sensitive phosphodiesterase. Formation of crosslinked complexes required the presence of Ca2+ or Mn2+ and was inhibited by excess unmodified calmodulin. The calmodulin-binding subunits all formed 1:1 complexes with calmodulin, and the molecular weights of the crosslinked products obtained with troponin I, the phosphodiesterase, and myosin light chain kinase were 43,000, 79,000, and 116,000, respectively. Photolysis experiments using azido-125I-calmodulin and bovine cerebral cortex membranes or detergent-solubilized membranes resulted in formation of a limited number of specifically labeled polypeptides. Azido-calmodulin appears to be an appropriate photoaffinity label for the identification and characterization of calmodulin-binding subunits.
3',5'-Cyclic-AMP Phosphodiesterases↗
Ca2+ regulation of cyclic nucleotide metabolism.
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Adenylyl Cyclases↗
The treatment of hypercholesterolemia with beta-pyridylcarbinol. Part 5. Report on 16 cases with severe hypercholesterolemia treated for 12 years.
A group of 78 patients with severe hypercholesterolemia (-X = 464 mg/dl) and symptoms of vascular disease of the heart, the extremities, or the brain, started a beta-pyridylcarbinol treatment with an average daily dosage of 1.2 g in 1964. In 1976 we could re-examine 12 patients, still on the same therapy. No myocardial infarction has occurred in this group since 1973, only 2 patients have had more attacks of angina pectoris that 1964. In contrast patients discontinuing therapy or replacing beta-pyridylcarbinol by other hypolipidemic drugs had a higher mortality.
Adult↗