Spatial spread of light-induced sensitization in rod photoreceptors exposed to low external calcium

Light sensitizes rods that have been desensitized by exposure to low external calcium. Yoshikami and Hagins [Biophys. Soc. Abstr. 15, 169a (1975)] suggested that desensitization in low external calcium results from exposure of intracellular calcium binding sites subsequent to depletion of internal calcium, and that background light sensitizes in this situation by releasing calcium to occupy those binding sites. In this view, it might be expected that light-induced sensitization would be spatially restricted to the illuminated region of the outer segment. However, in the present experiments, background illumination at one end of the outer segment potentiated responses to test flashes at the other end; resensitization was global rather than local. Patch-clamp recordings from the outer segment showed that the spread of internal transmitter was longitudinally restricted. Therefore, the sensitizing effect of background light is apparently not mediated via the internal transmitter, as required in the calcium-depletion explanation described above.

Application of automated REM and slow wave sleep analysis: I. Normal and depressed subjects

Computerized analysis of rapid eye movement (REM) and delta electroencephalographic (EEG) sleep patterns in normal and depressed subjects offers opportunities to examine sleep more precisely than previously possible. In the present study, automated REM analyses demonstrated good reliability with traditional manual procedures in both normal and depressed subjects. However, automated delta analyses correlated well with traditional scoring in normal subjects, but not in depressed patients. These findings suggest the use of automated delta techniques similar to those employed in this report or spectral analytic techniques in the following types of studies: specificity of delta sleep in various psychiatric syndromes, changes in delta sleep produced by the administration of psychotropic agents, relationships between delta sleep and sleep-related neuro-endocrine patterns, and, finally, relationships between delta sleep patterns and other biological rhythms such as activity and temperature.

Application of automated REM and slow wave sleep analysis: II. Testing the assumptions of the two-process model of sleep regulation in normal and depressed subjects

Abnormalities in a two-process model of sleep regulation (a sleep-dependent process, termed Process S, and a sleep-independent circadian process, termed Process C) have been proposed to account for sleep abnormalities in depressive states. The major tenets of the two-process model of sleep regulation as applied to depression are: the level of process S, as reflected by the electroencephalographic (EEG) slow-wave activity, corresponds to the sleep-dependent facet of sleep propensity; the pathognomonic changes of sleep in depressives are a consequence of a deficiency in the build-up of process S. The application of automated rapid eye movement (REM) and delta wave analyses in normal subjects and younger depressed patients supports the model to some extent: The time spent asleep is positively correlated with total delta waves (normals and depressives) and average delta waves (depressives); delta sleep is lower in depressives than in normals; the average delta wave count is significantly reduced in younger depressives over the total night and in non-REM period 1. The model also postulates that measures of phasic REM activity are inversely related to process S, suggesting that process S can be regarded as exerting an inhibitory influence on phasic REM activity.

Location and function of voltage-sensitive conductances in retinal rods of the salamander, Ambystoma tigrinum

The functional role and spatial location of voltage-sensitive conductances that modify the light-evoked electrical signals were studied in retinal rods of the tiger salamander. An isolated rod was drawn into a suction electrode for recording membrane current and impaled with an intracellular electrode for recording membrane potential and passing current. A bright flash gave a rapid initial hyperpolarization that relaxed to a smaller plateau. Simultaneously the dark current of the outer segment was shut off with the time course of a rounded step function. This characteristic difference between the wave forms demonstrates that the voltage relaxation does not result from reopening of light-sensitive channels. The voltage relaxation in (2) did not require light or interruption of the dark current, as the wave form was duplicated by suddenly switching off a depolarizing current injected during steady saturating light. This is explained if the relaxation depends purely on voltage-sensitive conductances. The voltage response to a dim flash reached its peak value before the current response. The voltage wave form was predicted assuming that the recorded photo-current drove a linear high-pass filter with parameters derived from analysis of the voltage response to injection of a current step. When the intracellular voltage was changed by current injection the slope resistance of the outer segment slowly declined to a lower level, indicating that the outer segment contains a voltage-sensitive conductance. When a current step was injected in bright steady light, the current recorded from the outer segment consisted of a capacity component proportional to dV/dt and a small extracellular leakage current but no detectable ionic current. This supports other evidence indicating that light-sensitive channels comprise the main or exclusive ionic conductance of the outer segment. The behaviour in (5) is explained if the light-sensitive channels themselves are slowly opened by hyperpolarization and closed by depolarization. Analysis of the current-injection experiments suggests that most of the high-pass filtering in a rod results from the action of voltage-sensitive conductances located in the inner segment. Addition of 10 mM-CsCl to the Ringer solution abolished the relaxation in the voltage response to a bright flash but left intact the high-pass filtering of small signals. This would be explained by a selective block of one of two sets of voltage-sensitive channels in the inner segment or by a voltage-sensitive block of one kind of channel.

All-night spectral analysis of the sleep EEG in untreated depressives and normal controls

Sleep was recorded in nine drug-free depressive patients and nine age- and sex-matched normal control subjects. All-night spectral analysis of the sleep electroencephalogram (EEG) showed a significantly reduced power density in the 0.25-2.50 Hz band in the depressive group. Power density values integrated over the entire frequency range (0.25-25.0 Hz) exhibited for both groups a decreasing trend over the first three non-REM/REM sleep cycles. In each cycle depressives had lower values than controls. The results are consistent with hypothesis that the build-up of a sleep-dependent process is deficient in the sleep regulation of depressive patients.

Dark noise in the outer segment membrane current of green rod photoreceptors from toad retina

The outer segment membrane current of single green rods from toad retina was recorded with a suction electrode, and the rate of spontaneous noise events similar to single-photon responses was measured at different temperatures. The activation energy, Gibbs free energy of activation, and entropy of activation for the process producing spontaneous events were similar to the values reported for thermal isomerization of free 11-cis-retinal (Hubbard, 1966), suggesting that thermal isomerization of the chromophore may be the trigger for the spontaneous events. The apparent rate constant for thermal activation of the green rod photopigment was about 4 times higher than in red rods but about 1000 times lower than for free 11-cis-retinal. Thus, both red and green rod opsin appear to stabilize 11-cis-retinal against thermal isomerization, but green rod opsin is somewhat less effective. The speed of the average dim-flash response increased as temperature was raised, as reported previously in both cone and rod photoreceptors. The reciprocal of the time-to-peak of the dim-flash response had an average Q10 of 3.3 between 20 and 30 degrees C. Changing temperature shifted the time scale of the response without altering response wave form, suggesting that all delay stages shaping the light response were approximately equally affected by temperature. At temperatures greater than 25 degrees C, flash responses were sometimes biphasic, i.e. inward dark current first decreased after a flash, then transiently increased beyond the resting dark level.

Photocurrents of single retinal rods from Rana pipiens tadpoles

Outer segment membrane current was recorded from single rod photoreceptors of Taylor-Kollros State III and Stage XXIII tadpoles. Response-intensity relations and kinetics of the photocurrent were similar to those of audit amphibian photoreceptors, suggesting that phototransduction is quantitatively similar in developing rods and adult rods. Maximum response amplitude was about 1/3 that of adult rods, probably because of the shorter length of the outer segment in tadpoles (20 vs 50 micrometers).

Relationship of antihypertensive effect of enalapril to serum MK-422 levels and angiotensin converting enzyme inhibition

In hypertensive patients the time courses for the rise in serum MK-422 level, and fall in both angiotensin converting enzyme (ACE) activity and blood pressure after 10 mg of enalapril were very similar. A close relationship between serum MK-422 levels and percentage ACE inhibition could be demonstrated and the acute fall in blood pressure showed a good correlation with either measurement. With chronic administration, serum MK-422 levels increased linearly with the dose of enalapril. As in the acute study, close relationships between the serum MK-422 level and ACE inhibition, and between either measurement and the fall in blood pressure, could be demonstrated after chronic enalapril administration. However, when compared to the acute response, the ACE inhibition dose-response line was shifted to the right after chronic enalapril therapy suggesting that enalapril may lead to ACE induction in humans. This did not appear to influence significantly the blood pressure lowering effect of enalapril or the relationship between ACE inhibition and the hypotensive effect.

Physiological characteristics of single green rod photoreceptors from toad retina

The outer segment membrane current of single isolated green and red rods from toad retina was recorded with a suction electrode, and characteristics of the response to light were examined. The maximum response amplitude of green rods was smaller than that of red rods, but the density of dark current along the green rod outer segment was similar to previously reported values for red rods. Thus, the smaller maximum response is explained by the shorter outer segment of green rods (45 vs. 60 microns). The intensity-response relation was fitted by a Michaelis equation with half-saturating photon density corresponding to about 55 isomerizations per flash. The form of the green rod light response was similar to that of red rods: in both cases the kinetics were consistent with four first-order delay stages shaping the light response. The time-to-peak of the dim-flash response was usually about 1 sec for both green and red rods in the present experiments. The spectral sensitivity curve of green rods was fitted by the nomogram for a vitamin A1-based pigment with lambda max = 433 nm. The relation between steady light intensity and flash sensitivity of green rods obeyed the Weber-Fechner relation, and the average background intensity necessary to reduce sensitivity to half of its dark level corresponded to about 4 isomerizations sec-1. This is slightly lower than the value of about 8 isomerizations sec-1 reported for toad red rods by Baylor, Matthews & Yau (1980). Green rods were similar to red rods in all respects except spectral sensitivity. Thus, no evidence was found to support the assertion that green rods are 'cone-like'.

Temperature effects on the membrane current of retinal rods of the toad

Thermal effects on the visual transduction mechanism of toad rods were examined by recording the membrane current of a single outer segment while changing the temperature within the range 15-30 degrees C. Warming increased the amplitude rmax of the saturating flash response. This effect had a Q10 of about 1.8 and may result from an increase in the light-sensitive conductance. The flash sensitivity decreased with increasing temperature, while the half-saturating flash intensity increased. There was no evidence of a temperature effect on the probability that an incident 500 nm photon triggered an electrical response. Together with the results in (2) and (3) this indicates that at higher temperature a successfully absorbed photon blocked a smaller fraction of the light-sensitive conductance. Upon warming, the time scale of the flash response shortened but the characteristic wave form was preserved. The speed of the dim flash response, measured by the reciprocal of its time-to-peak, had a Q10 of 2.7 and an apparent activation energy of 16.8 kcal mole-1. The power spectrum of the continuous component of the dark noise could be predicted at different temperatures by assuming that the underlying event was shaped by two of the four delays required to fit the light response. This behaviour is consistent with the notion that the continuous noise arises within the cascade of processes controlling the internal transmitter concentration of the outer segment.

Decreased uterine bradykinin receptors during captopril infusion in rats

To assess whether local tissue changes in bradykinin metabolism occur with captopril, the effect of intravenous infusion of bradykinin and captopril on bradykinin receptors in rat uterine smooth muscle was compared. Bradykinin and captopril decreased both the blood pressure and the number of bradykinin uterine receptors, estimated by direct radiolabeled binding techniques, without changing receptor affinity. These results demonstrate that bradykinin "down-regulates" its membrane receptor in rat myometrium. The similar change in receptor numbers induced by captopril could be explained by a local increase in bradykinin at receptor sites. The increase in local tissue level of bradykinin may contribute to the hypotensive action of captopril.

Two components of electrical dark noise in toad retinal rod outer segments

1. Physiological noise in the visual transduction mechanism was studied by recording membrane current from single rod outer segments in pieces of isolated toad retina. 2. The inward current in darkness showed spontaneous fluctuations which disappeared during the response to bright light. 3. The dark noise consisted of two components, a continuous fluctuation of rms amplitude about 0.2 pA and occasional discrete events about 1 pA in size. 4. Intervals between discrete events followed the exponential distribution expected of a Poisson process with a mean rate of about one event per 50 sec (20 degrees C). 5. The amplitude and power spectrum of the discrete events resembled those of single photon effects in the same rod, suggesting that discrete events may arise from spontaneous activation of single rhodopsin molecules. 6. The temperature dependence of the mean frequency of occurrence of discrete events gave an activation energy of 22 kcal mole-1, probably characteristic of thermal isomerization of rhodopsin. 7. The variance of the continuous component of the dark noise rose linearly with the length of the outer segment drawn into the suction electrode, indicating that this component is generated in the outer segment. 8. The power spectrum of a rod's continuous noise was usually fitted by the square of a Lorentzian with the same time constant as that of the four first-order delays in the cell's single photon response. The shot effects composing the continuous component thus appear to be shaped by two of four sequential processes in transduction. 9. The variance and spectrum of the continuous noise are interpreted to reflect shot effects about 1/400 the size of a single photon effect occurring at a frequency of 6 x 10(3) sec-1. 10. The rod's flash sensitivity was halved by a steady light to giving about 8 photoisomerizations sec-1. The much lower mean rate of discrete events indicates that Io in increment sensitivity experiments on individual receptors is not set by thermal activation of rhodopsin. 11. Values of sensitivity and time-to-peak flash response collected from many cells in darkness were correlated by the same power law relation obtaining in the presence of backgrounds. The correlation observed would be explained if a single variable controlled both the gain and time scale of several stages of the transduction mechanism in background light and in darkness.

Glutamate and synaptic excitation of reticulospinal neurones of lamprey

1. Intracellular recordings were made from the cell bodies and axons of giant reticulospinal neurones (Müller cells) of the lamprey, and responses to bath- and ionophoretically applied glutamate and aspartate were studied. 2. Bath-applied glutamate and aspartate depolarized both cell bodies and axons, but there appeared to be an associated conductance increase only in the cell bodies. The depolarization of Müller axons by the bath-applied drugs probably resulted from the passive flow of current into them from spinal cells to which the axons are coupled electrically. 3. The reversal potentials for responses to ionophoretically applied glutamate and for excitatory post-synaptic potentials (e.p.s.p.s) evoked by stimulation of the contralateral vestibular nerve were directly determined in Müller cell bodies which had been damaged by penetration with low-resistance electrodes. The glutamate and e.p.s.p. reversal potentials were identical, the average difference in eight cells being 0.31 mV. The absolute value of the e.p.s.p.--glutamate reversal potential varied from --16 to --35 mV in different cells, with the more negative values occurring in less damaged cells with higher resting potentials. 4. Injection of Cl into Müller cell bodies had no effect on the e.p.s.p.--glutamate reversal potential. Reduction of the extracellular Na concentration to 1 over 10 normal produced a negative shift in the glutamate reversal potential. 5. It is proposed that the natural excitatory transmitter and glutamate produce identical conductance changes in Müller cells, involving an increase in Na and K conductance.

Glycine, GABA and synaptic inhibition of reticulospinal neurones of lamprey

1. Intracellular recordings were made from the cell bodies and axons of giant reticulospinal neurones (Müller cells) of the lamprey and the effects of a variety of putative neurotransmitters tested. Bath-applied acetylcholine, carbamylcholine, norepinephrine, dopamine, histamine and serotonin were without effect. Glycine and gamma-aminobutyric acid (GABA) hyperpolarized and reduced the input resistance of cell bodies but had no effect on the membrane conductance of axons. 2. The threshold dose of bath-applied GABA or glycine for a conductance change in somata was about 0.5 mM and the maximum effect was reached at about 10 mM. The maximum conductance change produced by glycine was always greater than that produced by GABA. 3. Replacement of the sodium in the bathing saline with lithium or choline prolonged the conductance change produced by ionophoretically applied glycine or GABA, suggesting the presence of sodium-dependent uptake systems for glycine and GABA. 4. The reversal potentials for responses to ionophoretically applied glycine and GABA average about --83 mV, the same as that for the inhibitory post-synaptic potential (i.p.s.p.) produced in Müller cells by stimulation of the ipsilateral vestibular nerve. 5. The i.p.s.p. and drug responses appeared to involve an increase in chloride conductance, since their reversal potentials were shifted appropriately by changes in either internal or external chloride. 6. Changes in extracellular potassium concentration also changed i.p.s.p. and drug reversal potentials. However, these effects could be attributed to secondary changes in internal chloride. 7. The receptors for GABA and glycine appeared to be different because of the absence of cross-desensitization and because, at doses below 20 microM, picrotoxin and bicuculline selectively blocked GABA responses while strychnine selectively blocked glycine responses. 8. At concentrations of 20 microM, strychnine eliminated the i.p.s.p. while picrotoxin and bicuculline had no effect. Further, the i.p.s.p. and glycine response of Müller cells located in the isthmic region of the midbrain had the same threshold sensitivity to strychnine. However, the glycine response of other Müller cells was more sensitive to strychnine than was the i.p.s.p. 9. We conclude that glycine is a better candidate for the inhibitory transmitter onto Müller cells than is GABA.

An objective measure of physical activity for epidemiologic research

The development of a device is reported called the Large-scale integrated Motor Activity Monitor to examine physical activity during individuals' normal daily lives. The unit which is slightly larger than a wrist watch records body movement when worn at various body locations. Two population studies were conducted to evaluate the units. Experiment 1 examined 20 male graduate students for a two-day period. The data indicated that the units were sensitive to individual differences in physical activity and did not interfere with normal activities. Experiment 2 compared 10 Physical Education majors with 10 non-Physical Education majors by having individuals log activities and record movement counts for a two-day period. The movement data revealed that the monitors significantly discriminated between the two populations. The energy expenditure derived from the specific loggings was highly related (r = +.69) to the trunk movements, indicating that the movement counts are an accurate estimate of physical activity. The high relationship to energy analysis, the sensitivity of the units and the ease of implementation indicate that the units may be useful in relating normal activity to acute heart disease and to risk factors such as obesity and lipoproteins.

A simplified polyacrylamide gel electrophoresis apparatus for simultaneous application of multiple buffer systems or detergent combinations

A previous design of an apparatus for the simultaneous fractionation by polyacrylamide gel electrophoresis in 10 different buffer systems (1) was replaced by a greatly simplified new design, employing small, cylindrical buffer partitions within the lower buffer reservoir and/or upper buffer reservoir of a conventional, temperature-regulated polyacrylamide gel electrophoresis apparatus for cylindrical gels. The apparatus was tested in application to the problem of simultaneous polyacrylamide gel electrophoresis in different buffer systems with the purpose of optimizing the operative pH for a particular fractionation problem. It was also applied to fractionations in a single buffer system to which various combinations of ionic and nonionic detergents were admixed.

Properties of the membrane current of rod outer segments

The membrane current of single rod outer segments in pieces of isolated toad retina was recorded with a glass suction electrode. Light evoked a slow net outward photocurrent consisting of a reduction in the steady inward dark current. In very dim light, the photocurrent broke up into discrete shot effects with a rounded shape and an amplitude of about 1 pA. These events were shown to result from photoisomerization of single rhodopsin molecules. The current in darkness showed fluctuations consisting of (a) discrete events apparently resulting from thermal isomerization of rhodopsin molecules, and (b) smaller amplitude shot effects shaped by two of the four rate processes of the light response.

Evoked depolarizing and hyperpolarizing potentials in reticulospinal axons of lamprey

1. Intracellular recordings were made from reticulospinal axons (Müller axons) in the lamprey spinal cord. Electrical stimuli applied to the spinal cord surface elicited depolarizing and hyperpolarizing 'synaptic-like' potentials in Müller axons. The physiological basis of these evoked potentials was investigated. 2. The depolarizing response was not the result of increased extracellular K, as demonstrated by the constancy of the undershoot of the axonal action potential during the depolarization, by the failure of the response to summate during repetitive stimulation and by the failure of the response amplitude to vary as predicted when the [K] of the saline was varied. 3. When the membrane potential of the axon was varied by passing current through a micro-electrode, the amplitude of the depolarizing evoked potential decreased at membrane potentials positive to the resting potential and increased up to a maximum when the axon was hyperpolarized by about 10 mV. The extrapolated 'reversal potential' for the depolarizing response was about 15 mV positive to the normal -80 mV resting potential of the axon. However, the amplitude of the response did not continue to grow with hyperpolarizations greater than 10 mV, and, thus, the response did not behave as would a normal depolarizing synaptic potential. 4. Müller axons make numerous electrical synapses with spinal motoneurones and interneurones, and this suggested that the depolarizing response might be a coupling potential. In agreement with this idea, quantitative correspondence was found between changes in the input resistance of the axon produced by the depolarizing response and the variation in the depolarizing response amplitude. Thus, although the depolarizing response mimicked in some ways the behaviour of an excitatory synaptic potential, we conclude that it is a coupling potential. 5. The hyperpolarizing response also appeared to be a coupling potential. Its amplitude was not changed by hyperpolarizing the axon up to 30 mV and was decreased by depolarizing the axon sufficiently to decrease the axon's input resistance. 6. It is proposed that both depolarizing and hyperpolarizing evoked potentials in lamprey Müller axons are a result of passive flow of current from cells activated by the spinal cord stimulus and electrically coupled to Müller axons.

REM sleep in primary depression: a computerized analysis

REM sleep in 35 inpatients with primary depression was automatically analyzed for 7 consecutive nights during placebo administration. For the total night of sleep, as well as each individual REM period, the number of REMs, their total voltage integral over time, the sum of their durations and the average REM size were automatically calculated. Validity of these automated REM measures was established by significant correlations with manually scored REM measures. Changes in REM sleep across the night were also investigated. Similar to findings in normal subjects, REM time did not change from REM period to REM period. Average REM size increased significantly from REM period 2-3 and 3-4. Contrary to what is seen in normal subjects, REM frequency was high during the first REM period, significantly decreased from the first to second REM period and then remained constant. Finally, a significant inverse correlation between REM frequency for the first REM period and REM latency was noted. This pattern of REM sleep is interpreted as indicating a high pressure for phasic REM at the beginning of the night which is dissipated by the first REM period.

Sustained depolarizing potentials in reticulospinal axons during evoked seizure activity in lamprey spinal cord

1. Intracellular recordings were made from lamprey reticulospinal axons (Müller axons) during seizures evoked by electrical stimulation of the isolated spinal cord in saline containing either 0 Cl or 1 mM picrotoxin. The seizures had tonic and clonic-phases similar to ictal seizures in mammalian brain. 2. During seizures Müller axons were depolarized by 10-15 mV. These seizure-depolarizations were not due to any direct effect of the evoking stimulus on the Müller axons themselves nor were they initiated by an accumulation or extracellular potassium. 3. A decrease in axonal input resistance occurred during a seizure-depolarization. Also, the amplitude of a seizure-depolarization was decreased by depolarizing the axon 5-15 mV with injected current. Further, hyperpolarizing the axon increased the amplitude of the seizure-depolarization, but the growth flattened out beyond 30-40 mV of hyperpolarization. The decrease in input resistance during the seizure-depolarization and the dependence of the response amplitude on axonal membrane potential suggested that the seizure-depolarization was an excitatory synaptic potential. However, the failure of the seizure-depolarization amplitude to continue to grow at membrane potentials greater than 30 mV negative to the resting potential was not consistent with this interpretation. 4. A synaptic conductance change as the cause of the seizure-depolarization was ruled out by setting the axonal membrane potential at different levels with injected current and monitoring the input resistance of the axon before and during seizure-depolarizations. It was found that no change in input resistance occurred during the seizure-depolarization when the axon was hyperpolarized more than approximately 30 mV, the same potential at which the growth in the response amplitude ceased. From analysis of these data and the passive current-voltage properties of Müller axons it is concluded that the seizure-depolarization is not a chemical synaptic potential, but rather the result of the passive injection of depolarizing current into the axons. 5. The source of the depolarizing current which flows into Müller axons during seizures is probably paroxysmal action-potential activity in spinal motoneurons and interneurons, many of which are electrically coupled to Müller axons.

Strength-duration properties of single units driven by electrical stimulation of the lateral hypothalamus in rats

Cathodal strength-duration functions were measured for 27 single units which were driven by electrical stimulation of the lateral hypothalamus. The distribution of chronaxies of these units showed four clusters at about 0.1, 0.25, 0.4 and 0.5 msec. These chronaxies are not fundamentally different from those previously reported for peripheral nerve. Two units fired repetitively during a long-duration stimulation pulse. Anodal strengitation. The data are discussed with reference to behaviorally determith duration properties were obtained from 14 units. Four units were not excited by anodal pulses of any strength or duration, four were excited during an anodal pulse (anode-make excitation) but not at the termination of the pulse (anode-break excitation), and six showed both anode-make and anode-break excitation. The data are discussed with reference to behaviorally determined strength-duration functions for brain stimulation reward.

Neural substrate for brain stimulation reward in the rat: cathodal and anodal strength-duration properties

The trade-off between current strength and duration of a stimulating pulse was studied for the rewarding and priming effects of brain stimulation reward (BSR). With cathodal pulses, strenght-duration functions for BSR had chronaxies of .8-3 msec. No differences were observed between the results for rewarding and priming effects. With anodal pulses. strength-duration curves were parallel to the cathodal curves at pulse durations of .1-5 msec, but at pulse durations greater than 5 msec the anodal curves showed a greater drop in required current intensity than did the cathodal curves. The parallel portion of the anodal curves was interpreted as due to anode-make excitation, and the drop at longer pulse durations was interpreted as due to anode-break excitation. Cathodal strength-duration functions for the motor effect elicited through the BSR electrodes had chronaxies of .15-.48 msec. Measurements of the latency of the muscle twitch confirmed that anode-make and anode-break excitation occurred, the latter becoming evident at pulse durations as brief as .3-.4 msec. The results provide quantitative characterization of cathodal and anodal strength-duration properties of the neural substrate for BSR and are discussed in terms of their value in guiding electrophysiological investigation of that substrate.

Electrical stimulation of the rat diencephalon: differential effects of interrupted stimulation on on- and off-responding

Rats were trained to turn on and to turn off electrical stimulation of the hypothalamus. Breaking trains of stimulation into bursts of pulses separated by intervals of no-stimulation attenuated off-responding more than on-responding. Current intensity was raised in an attempt to maintain a constant level of performance when either burst duration was decreased or interburst interval was increased. Current increases necessary to maintain on-responding were consistently smaller than the increments required to maintain off-responding. At shorter burst durations, off-responding usually ceased while on-responding continued. Four interpretations of the results are discussed: (1) temporal integration characteristics of the underlying neural systems, (2) reward adaptation, (3) electrode location, and (4) procedural artifacts. Only the first explanation which holds that the buildup of activity in the rewarding system is more rapid than in the aversive system is consistent with all the results. If correct, this conclusion indicates that multiple effects of electrical stimulation at a single brain site can be differentiated by manipulating the temporal pattern of the stimulation.

On the effect of calcium on the frequency of miniature end-plate potentials at the frog neuromuscular junction

1. The effect of the extracellular Ca concentration on the frequency of miniature end-plate potentials (min. e.p.p.s) at the frog neuromuscular junction was studied. 2. In saline containing elevated K (5 or 11 mM), the frequency of min. e.p.p.s increased as Ca concentration was increased from 0-1 to 1-3 mM. However, with further increases of Ca concentration up to 10 mM, min. E.P.P. frequency declined. 3. In saline containing the normal concentration of K (2 mM), increasing Ca concentration from 0-1 to 10 mM produced a slight, monotonic increase in min. e.p.p. frequency. 4. The non-monotonic effect of Ca on min. e.p.p. frequency in preparations depolarized by elevated K is consistent with the existence of two opposing effects of Ca on transmitter release. Firstly, raising the external concentration of Ca increases the electrochemical potential for Ca entry, which tends to increase Ca influx and transmitter release. Secondly, increasing external Ca concentration increases electrostatic screening of fixed negative charges on the outer surface of the nerve terminal membrane. Such an increase in screening of charges near voltage-sensitive Ca gates would produce a hyperpolarization across the gates and they would tend to close, an effect which would tend to decrease Ca influx. The monotonic increase in min. e.p.p. frequency with increasing Ca concentration in 2 mM-K is consistent with the voltage insensitivity of the Ca gates at potentials close to the normal resting potential.

Effects of guanidine on transmitter release and neuronal excitability

1. Guanidine hydrochloride (CH5N3-HCl) was applied to frog neuromuscular junctions blocked by reduced external Ca2+, or increased external Mg2+ concentration, or by both. Guanidine produced a dose-dependent increase in the average number of quanta released by presynaptic action potentials, the threshold dose being 0-1-0-2 mM. No post-synaptic effects were observed. 2. Guanidine also increased the excitability of the motor nerve fibres, as evidenced by multiple firing to single electrical stimuli and finally by spontaneous action potentials. These effects were studied in greater detail in giant axons (Müller axons) in the spinal cord of lamprey. Exposure to guanidine produced in these axons a progressive increase in excitability, manifested by repetitive firing to a single electrical stimulus, spontaneous membrane potential oscillations and spontaneous bursts of action potentials. Guanidine had no effect on the resting potential. 3. The effect of guanidine on the excitability of Müller axons was mimicked in every detail simply by reducing the divalent cation concentration of the bathing solution. 4. Guanidine also produced dose-dependent increases in the duration of action potentials in Müller axons. This effect always preceded in time the appearance of the excitability effects and was not mimicked by reducing the divalent cation concentration. It is suggested that the broadening of the action potential is separate from the excitability effects and may reflect a decrease of delayed rectification. 5. Guanidine (0-3 mM) increased the frequency of miniature end-plate potentials (min. e.p.p.) in solutions containing 2-11 mM-K+ in such a way as to shift the relationship between min. e.p.p. frequency and extracellular K+ toward lower values of K+. This effect was interpreted to mean that guanidine produced a depolarization of the nerve terminal which summed with the depolarization produced by a given concentration of K+. The calculated depolarization produced by 0-3 mM guanidine was 5-7 mV. 6. The effects of guanidine on evoked transmitter release, excitability, and min. e.p.p. frequency are consistent with a hypothesis which states that guanidine binds at or near fixed negative changes on the outside of nerve membrane and reduces the screening effect of divalent cations.

Sodium restriction and thiazide diuretics in the treatment of hypertension

In a group of hypertensive patients it has been shown that moderate sodium chloride restriction has a hypotensive effect that is similar to that produced by thiazide diuretics. Blood pressure changed in relation to body weight in individual patients, and appeared to correlate with their sodium balance. The more a patient was depleted of sodium, the lower was the blood pressure. The serum potassium level fell with the use of thiazide diuretics, but in this group of patients there was little change in total body potassium content. The fall in serum potassium level appeared to relate to a shift into the cells due to the accompanying alkalosis. Potassium supplementation appeared to have had little effect and was unnecessary for most patients who were given diuretics for hypertension. Amiloride corrected the alkalosis and restored the serum potassium level to normal.

Cardiological changes and car driving

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Acute orthotopic transplantation of hearts stored for 72 hours

Using a storage method based on hypothermic (4° C) perfusion with a water-based asanguinous solution the dog heart has been preserved for up to 72 hours in a viable condition. The ultimate functional test of the viability of such hearts is orthotopic transplantation. Seven of eight dog hearts stored for 72 hours were able to support the recipient circulation in a stable manner after acute orthotopic transplantation. The donor hearts maintained a mean arterial pressure of 70-100 mmHg, left atrial pressure 5-12 cm H₂O, and maximum dp/dt of the left ventricular pressure was 1,200-2,400 mmHg/second. No myocardial stimulants were used. The results of 72 hours' hypothermic perfusion storage were superior to those of previously reported six hours' non-perfusion storage. A comment is made on the empirical nature of this field.

A simple method for short-term (6-hour) transport of the dog heart prior to orthotopic transplantation

A method of transporting the isolated dog heart for periods of up to 6 hours is described. It consists essentially of flush-cooling the heart with a suitable water-based solution at 4-6° C. followed by storage in a specially designed portable container which maintains the temperature of the heart at 4-6° C. The viability of the hearts was tested by orthotopic transplantation. Of nine hearts so stored (six for 6 hours), all supported the recipient circulation immediately after transplantation, with a mean systemic arterial pressure of 70 to 100 mm. Hg and a mean max. dp/dt of the left ventricular pressure of 1,050 mm. Hg/second without catecholamine stimulation. A comparable group of hearts flush-cooled in the same way but stored in ice after the manner of the method used for kidney transport was markedly inferior in performance to those stored at 4-6° C. Some of the limitations of non-perfusion methods of storing the heart are discussed.