Theodore H. Bullock

Bio: Theodore H. Bullock is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Electric fish & Jamming avoidance response. The author has an hindex of 56, co-authored 185 publications receiving 9128 citations. Previous affiliations of Theodore H. Bullock include Scripps Institution of Oceanography & University of Missouri.

Compensation for temperature in the metabolism and activity of poikilotherms

Abstract: SUMMARY Many poikilothermal animals exhibit in their metabolism or activity some degree of independence of their temperature. In the general case this is regarded as reflecting a compensation rather than a fundamental insensitivity of metabolism or the rate functions measured. Illustrative cases are assembled including the following: (1) latitudinally separated populations of the same species and of different species which show adaptation in some rate function, often far from complete but sometimes apparently complete, those from higher latitudes having higher rates at given temperatures. (2) Micro-geographic adaptation has been discovered in intertidal molluscs, comparing low-tide level with mid-tide level individuals of the same species; heart rates at a given temperature are higher in those from the cooler habitat. (3) Seasonal shift of various rate processes in a homoeostatic direction is likewise documented, as is (4) experimental acclimation, regarded as evidence of normal, shorter term regulations accompanying periods of unseasonable weather. (5) A number of cases show the phenomenon of rapid compensation, completed in hours or minutes and often sensibly perfect. Even when not perfect, many organisms show in one way or another that they do not submit passively to different temperatures. A number of exceptions are listed which show that the ability to compensate is far from universal. However, the same species may sometimes compensate in other rate functions. The mechanism and properties of compensation are discussed. It is concluded that even in the same organism there are several simultaneous mechanisms with different time courses and at different levels, involving enzymes, cells, organs and behaviour. The activity of several enzymes alters, as tested in homogenates from acclimated animals, but other enzymes show no change. The limiting factor in the use of temperature-compensating mechanisms for overcoming temperature barriers to distribution is presumed to be such failure to balance the regulation of different processes. It is considered likely that at least in certain cases regulation may depend on specialized receptors for temperature. It is shown that non-adapting, absolute temperature sense organs, such as are necessary, occur in various groups of poikilo-therms, though it cannot be said that they function in acclimation. Acclimation is manifested by a change in the acutely* measured rate-temperature (R-T) curve in any of several ways. Commonly there is something more than a shift of the curve along the temperature axis; some upward shift as well, or a flattening of the slope, accompanies cold adaptation. The facts at hand do not permit a simple statement as to the relative importance among eurythermal species of genetically determined adaptability within a genotype and of temperature races. Both clearly exist. Some species are at first hyper-responsive to temperature change, settling down to a steady rate after some hours, others are initially under-responsive. Neglect of this short-term time factor vitiates many comparisons between R-T curves taken during dissimilar phases of response to changes. The wide distribution and demonstrated natural occurrence of acclimation and related rate compensations for temperature bespeak a large-scale role in ecology and evolution. It is a pleasure to acknowledge the inspiration and stimulus as well as much critical thinking due to my collaborators, in particular Drs John L. Roberts, K. Pampapathi Rao, Paul A. Dehnel and Earl Segal, who themselves have contributed the original work from this laboratory.

Induced Rhythms in the Brain

Abstract: to Induced Rhythms: A Widespread, Heterogeneous Class of Oscillations.- Oscillations in the Striate Cortex.- 1 Mechanisms Underlying the Generation of Neuronal Oscillations in Cat Visual Cortex.- 2 Stimulus-Specific Synchronizations in Cat Visual Cortex: Multiple Microelectrode and Correlation Studies from Several Cortical Areas.- Cortical Rhythms, Ongoing (EEG) and Induced (ERPs).- 3 The Rhythmic Slow Activity (Theta) of the Limbic Cortex: An Oscillation in Search of a Function.- 4 Is There any Message Hidden in the Human EEG?.- 5 Event-Related Synchronization and Desynchronization of Alpha and Beta Waves in a Cognitive Task.- 6 Magnetoencephalographic Evidence for Induced Rhythms.- 7 Rostrocaudal Scan in Human Brain: A Global Characteristic of the 40-Hz Response During Sensory Input.- 8 Evoked Potentials: Ensembles of Brain Induced Rhythmicities in the Alpha, Theta and Gamma Ranges.- 9 Predictions on Neocortical Dynamics Derived from Studies in Paleocortex.- 10 A Comparison of Certain Gamma Band (40-HZ) Brain Rhythms in Cat and Man.- 11 Human Visual Evoked Potentials: Induced Rhythms or Separable Components?.- Thalamic Oscillations.- 12 Network Properties of the Thalamic Clock: Role of Oscillatory Behavior in Mood Disorders.- 13 Mesopontine Cholinergic Systems Suppress Slow Rhythms and Induce Fast Oscillations in Thalamocortical Circuits.- 14 Oscillations in CNS Neurons: A Possible Role for Cortical Interneurons in the Generation of 40-Hz Oscillations.- Cellular and Subcellular Mechanisms Based on Invertebrate and Simple Systems.- 15 Modification of Oscillator Function by Electrical Coupling to Nonoscillatory Neurons.- 16 Biological Timing: Circadian Oscillations, Cell Division, and Pulsatile Secretion.- 17 Comparison of Electrical Oscillations in Neurons with Induced or Spontaneous Cellular Rhythms due to Biochemical Regulation.- 18 Signal Functions of Brain Electrical Rhythms and their Modulation by External Electromagnetic Fields.- Theories and Models.- 19 Inhibitory Interneurons can Rapidly Phase-Lock Neural Populations.- 20 The Problem of Neural Integration: Induced Rhythms and Short-Term Correlations.- 21 Flexible Linking of Visual Features by Stimulus-Related Synchronizations of Model Neurons.- 22 Synergetics of the Brain: An Outline of Some Basic Ideas.- Epilogue.- Brain Natural Frequencies are Causal Factors for Resonances and Induced Rhythms.

Pacemaker Neurons: Effects of Regularly Spaced Synaptic Input

Abstract: The consequences of inhibitory or excitatory synaptic input between pacemaker neurons were predicted mathematically and through digital-computer simulations, and the predicted behavior was found to occur in abdominal ganglia of Aplysia and in stretch receptors of Procambarus. Discharge patterns under conditions that do not involve interneuronal feedback are characteristic and self-stabilizing. Paradoxically, increased arrival rates of inhibitory input can increase firing rates, and increased excitatory input rates can decrease firing rates.

The jamming avoidance response of high frequency electric fish: I. General features

Abstract: Summary1.The J.A.R. is a reflex shift in the frequency of discharge of their electric organs by high frequency electric fish (Gymnotidae:Eigenmannia, Sternarchus) when stimulated by an alternating current in the water, with a frequency close to the fish's. The shift is in the direction of increasing the difference (ΔF) between its frequency (Ffish) and that of the stimulus (Fstim). The significance of this behavior is presumed to be the maintenance of a private frequency for the object-detection function of the electric system, when another fish of nearly the same frequency approaches.2.The pathway (Fig. 1) includes a high precision pacemaker unit in the medulla under the tonic influence of electroreceptors. The simplicity of the relevant parameters and the convergence on one command unit in a complete piece of quantifiable social behavior attracts attention to the J.A.R.3.The latency, time course, form, asymmetry, and variability, the effects of temperature, anesthesia, mechanical and electrical disturbance, light, salinity and spontaneous background changes, and the absence of effect of sound are described (Figs. 2, 3, 4, 5).4.Eigenmannia will usually shiftFfish up for a — ΔF and down for a +ΔF, rather symmetrically;Sternarchus will only shift upwards and gives no response to a +ΔF.5.Experimentally isolating parts of the system indicates that the fish does not compare the stimulus frequency with its pacemaker frequency directly but must receive both through the same set of electroreceptors.6.The stimuli of opposite effect, when given simultaneously cause an intermediate response, i.e. both stimuli are effective.7.The response survives section of the posterior branch of the anterior lateral line nerves bilaterally and, with slightly raised threshold and latency, of the supraorbital and maxillary branches as well, leaving only the mandibular. It survives partial lesions of the corpus cerebelli and valvula and complete transection in front of the mesencephalon. Lesions of the torus semicircularis of the mesencephalon cause loss or gross abnormality of the J.A.R.8.The ΔF sensitivity, dynamic range and other properties suggest that the biological significance of preserving a private frequency lies in the need of unknown brain mechanisms, that analyze the fish's own field for object detection, to function over a considerable range of distance from object to fish and therefore of voltage of a signal clearly the fish's own.9.Evidence from bringing two or more fish together, whose separate frequencies are close, suggests the J.A.R. is used in natural social situations.

Measurement of imposed voltage gradient adequate to modulate neuronal firing.

Abstract: Many authors1–31 have described the effects of polarization by imposed electric current upon nerve cells. We have not seen in the literature, however, a quantitative evaluation of the sensitivity of nerve cells to electric fields in terms of voltage gradient across some appropriate dimension of the neuron. We have undertaken to estimate the threshold value as being the unique value of greatest interest and have found this to be far lower for modulation of the frequency of an already active neuron than for the excitation of a silent one.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation.

Abstract: The approach taken in this study to produce localised changes of cerebral excitability in the intact human was modulation of neuronal excitability by weak electric currents applied transcranially. So far, this technique has mainly been used in animal research, primarily through modulation of the resting membrane potential (Terzuolo & Bullock, 1956; Creutzfeld et al. 1962; Eccles et al. 1962; Bindman et al. 1964; Purpura & McMurtry, 1965; Artola et al. 1990; Malenka & Nicoll, 1999). In general, cerebral excitability was diminished by cathodal stimulation, which hyperpolarises neurones. Anodal stimulation caused neuronal depolarisation, leading to an increase in excitability (Bindman et al. 1962; Purpura & McMurtry, 1965), as was shown by spontaneous neuronal discharges and the amplitudes of evoked potentials (Landau et al. 1964; Purpura & McMurtry, 1965; Gorman, 1966). However, in single cortical layers opposite effects were seen (Purpura & McMurtry, 1965), underlining the fact that the effects of DC stimulation depend on the interaction of electric flow direction and neuronal geometry. Enduring effects of 5 h and longer have been described if the stimulation itself lasts sufficiently long, about 10–30 min. These prolonged effects are not simply due to prolonged membrane potential shifts or recurrent excitation, because intermittent complete cancellation of electrical brain activity by hypothermia does not abolish them (Gartside, 1968a,b). Long-term potentiation (LTP) and long-term depression (LTD) have been proposed as the likely candidates for this phenomenon (Hattori et al. 1990; Moriwaki, 1991; Islam et al. 1995; Malenka & Nicoll, 1999). The concept described here was an attempt to induce neuronal excitability changes in man by application of weak DC stimulation through the intact skull. It has already been demonstrated within invasive presurgical epilepsy diagnostics that intracranial currents of sufficient strength can be achieved in humans by stimulation with surface electrodes at intensities of up to 1.5 mA (Dymond et al. 1975). A suitable candidate for evaluating cortical excitability changes is transcranial magnetic stimulation (TMS), because it allows the quantification of motor-cortical neurone responses in a painless and non-invasive manner. The amplitude of the resulting motor-evoked potential (MEP) represents the excitability of the motor system. In the following, we confirm the principal possibility of altering cortical excitability by applying weak DC. Furthermore we show that systematic DC stimulation with minimum stimulation duration and intensity is necessary for an effective application of weak current in humans. This is of particular importance for inducing effects which outlast the duration of stimulation.