bluuebunny/crossref_metadata_2025 huggingface dataset:
Receptor potentials of lizard hair cells with free‐standing stereocilia: responses to acoustic clicks.
Authors: Baden‐Kristensen K , Weiss T F
Published: December 2014

Receptor potentials of single hair cells in the free‐standing region of the basilar papilla of the anaesthetized alligator lizard were measured intracellularly with micropipettes. Stimuli were primarily acoustic pulses (clicks) delivered to the tympanic membrane. The receptor potential was independent of click repetition rate for the range 10‐150 clicks/s. This property is presumed to be the basis of the rate independence of the extracellular cochlear microphonic potential. The receptor potential wave‐form consisted of a fast oscillatory component (or oscillation) superimposed on a usually positive (depolarizing) slow component. Reversal of the stimulus polarity resulted in a reversal of the polarity of the oscillations; the polarity of the slow component remained unchanged. The relative magnitudes of the two components depended on click level. At the higher click levels the magnitudes of the slow and oscillatory components were comparable. The relation of the receptor potential to the stimulus was non‐linear; the peak‐to‐peak magnitude of the receptor potential increased less than proportionately with increasing sound‐pressure level, and reversal of the stimulus polarity did not result in a reversal of the receptor potential. The receptor‐potential magnitude for high‐level clicks ranged from 1‐13 mV peak‐to‐peak with an average value of 3.5 mV. At the lower click levels the magnitude of the slow component was much smaller than that of the oscillatory component. The relation of the receptor potential to the acoustic stimulus approached that of a linear system, the magnitude of the receptor potential became approximately proportional to the sound‐pressure level, and reversal of the stimulus polarity resulted in approximate reversal of the receptor potential. For low‐level stimuli the frequency of the oscillations of the receptor potential in response to clicks was approximately equal to the frequency of maximal a.c. response to tones. Apparently, both phenomena reflect the frequency selectivity of the processes generating the receptor potential. The frequency of oscillations in the click response varied from one cell to another (range of 1.0‐2.2 kHz in this study). The results are qualitatively consistent with a model (Weiss, Mulroy & Altmann, 1974) that contains a linear, band‐pass filter followed by a rectifier followed by a low‐pass filter.
A sign‐reversing pathway from rods to double and single cones in the retina of the tiger salamander.
Authors: Attwell D , Werblin F S , Wilson M , Wu S M
Published: December 2014

Signal transmission between rods and cones was studied by passing current into a rod and recording the voltage response in a nearby double or single cone and vice versa. Two types of rod‐cone interaction were found. Between immediately adjacent rods and cones, passage of current into either receptor elicited in the other receptor a sustained voltage response of the same sign as the injected current. These signals were still seen in the presence of Co2+, and are probably mediated by the electrical synapses which have been seen anatomically between adjacent rods and cones. In addition to this short‐range sign‐preserving interaction, passing current into a rod elicited a transient sign‐inverted signal in cones up to at least 80 micron from the injected rod. No such response was seen in rods for current injection into cones. This signal was greatly reduced by Co2+ ions. Hyperpolarization of the cone to about ‐65 mV, with about 0.1 nA current, reversed this signal, which is presumed to be mediated by a chemical synaptic input to cones. Light flashes suppressed the sign‐inverted signal for a period which was longer for brighter flashes. The time of reappearance of the signal was correlated with the return of the rod and horizontal cell potentials to their dark levels. This suppression could also be produced by an annulus of light which produced no light response in the receptors at the centre of the annulus, but which did polarize horizontal cells under the centre of the annulus. The wave form of the sign‐inverted signal was similar to that produced in horizontal cells by current injection into rods, but of opposite sign. If an electrode was left in a cone for some time, the normal hyperpolarizing light response diminished, leaving a depolarizing response produced, presumably, by feed‐back from horizontal cells. This signal was reversed when the cone was hyperpolarized with about 0.1 nA current. These data suggest that the sign‐inverted response is mediated by feed‐back from horizontal cells and, assuming that depolarization increases the rate of release of horizontal cell synaptic transmitter, then the feed‐back transmitter opens channels in the cone membrane whose currents have a reversal potential around ‐65 mV.
The role of the electrogenic sodium pump in the glutamate afterhyperpolarization of frog spinal cord.
Authors: Padjen A L , Smith P A
Published: December 2014

Drug responses of isolated hemisected frog spinal cords were examined by means of the sucrose‐gap technique. The glutamate‐induced depolarizations (glu‐d) of motoneurones (recorded from ventral roots), and primary afferents (recorded from dorsal roots), were followed by an afterhyperpolarization (glu‐a.h.). The depolarization induced by DL‐homocysteic acid (DLH) was only occasionally followed by an afterhyperpolarization (DLH‐a.h.). The glu‐a.h. on both roots persisted in the presence of tetrodotoxin (TTX, 0.1‐1 microM), or Ringer solution containing 10 mM‐Mg2+; 0.1 mM‐Ca2+ or 2 mM‐Mn2+; 0.2 mM‐Ca2+. This indicated that the response was neither due to the release of endogenous neurally active substances nor to the activation of a Ca2+‐sensitive K+ conductance. The glu‐a.h. was reduced or blocked by K+‐free Ringer solution, 3‐acetylstrophanthin (3‐Ac‐Str; 1 microM) or Li+ ions, and was therefore attributed to the activity of the electrogenic Na+ pump. The duration of depolarization induced by glu or DLH was increased in the presence of K+‐free Ringer solution, 1 microM 3‐Ac‐Str or Li ions. It is therefore suggested that the electrogenic Na+ pump may play a role in limiting the duration of depolarization induced by the action of excitatory amino acids. The re‐admission of K+ ions to preparations which had been incubated in K+‐free Ringer solution produced a transient hyperpolarization (K‐a.h.) of the membrane potential of ventral roots which is also attributable to the activation of the electrogenic Na+ pump. Both the K‐a.h. and the glu‐a.h. were enhanced in Ca2+‐free Ringer solution. It is therefore suggested that the Ca2+ ions may modulate the activity of the electrogenic pump in central nervous tissue.
Rat endometrial bioelectric activity in vivo and in vitro: effects of adrenaline.
Authors: Levin R J , Phillips J C
Published: December 2014

The transuterine potential difference (p.d.) generated by the endometrium was measured in vivo in anaesthetized, ovariectomized rats treated with 10 micrograms oestradiol‐17 beta each day for 3 days. Intravenous injection of adrenaline induced transient hyperpolarization of the p.d.; sigmoid dose‐dependency was observed over the range 2‐40 micrograms/kg. Pre‐treatment of the rats with syrosingopine shifted the dose‐response curve to the left (enhancement) while combined propranolol (800 micrograms/kg) and phentolamine (800 micrograms/kg) shifted the dose‐response curve to the right (depression). Isoprenaline gave similar quantitative changes in the p.d. in vivo which displayed a similar time course and sigmoid dose‐dependency. Propranolol alone (800 micrograms/kg) shifted this dose‐response curve significantly to the right. Addition of adrenaline or isoprenaline to the serosal solution bathing uteri incubated in vitro after removal from oestradiol‐treated rats induced changes in endometrial bioelectric activity that exhibited sigmoid dose‐response curves for the transuterine p.d. and short‐circuit current (Isc). Propranolol significantly shifted the dose‐response curves for adrenaline to the right. Only adrenaline caused small but significant decreases in the uterine resistance but these were not dose‐dependent. Acetylcholine, 5‐hydroxytryptamine, noradrenaline and phenylephrine had no effect on the transuterine p.d. in vivo or in vitro or on the Isc in vitro. No significant electrical changes could be induced by adrenaline or any of the other drugs across the uteri from untreated ovariectomized rats either in vivo or in vitro. The transluminal membrane p.d. of surface endometrial cells measured with micro‐electrodes was depolarized by an addition of serosal adrenaline but only 41% of the cells successfully impaled responded in this way. The results indicate that endometrial cells under oestrogen stimulation possess electrogenic processes that can be modulated specifically by adrenaline through the mediation of a serosally sited beta‐adrenoceptor. The physiological role of the mechanism has yet to be established.
Persistent slow inward calcium current in voltage‐clamped hippocampal neurones of the guinea‐pig.
Authors: Brown D A , Griffith W H
Published: December 2014

CA1 and CA3 neurones in transverse slices of guinea‐pig hippocampus were voltage clamped through a single micro‐electrode, and perfused with Krebs solution containing 0.5 microM‐tetrodotoxin and 10 mM‐tetraethylammonium at (normally) 24‐26 degrees C. Slow inward currents of less than or equal to 0.5 nA were recorded during depolarizing voltage commands to membrane potentials positive to between ‐40 and ‐30 mV. These currents peaked at 100‐300 msec after the onset of the depolarizing command, then subsequently declined during continuing depolarization. This decline could be ascribed to a developing outward current since repolarizing inward current tails showed no diminution up to 700 msec. No clear evidence for time‐dependent inactivation of the inward current could be obtained. A persistent component of inward current could be detected when the membrane potential was maintained above the inward current threshold, such that small hyperpolarizing commands induced an outward relaxation and large hyperpolarizations produced an inward tail current. The inward current was depressed by removing external Ca, or by adding 0.2‐0.5 mM‐Cd, or 0.1 mM‐verapamil, and was increased by adding 1 mM‐Ba. A possible role for this persistent inward current in generating the slow membrane depolarization underlying burst discharges in these neurones is discussed. In some neurones (primarily CA1), an additional fast spike‐like current was recorded, which was blocked by Cd or Mn and depressed by a depolarizing pre‐pulse. It is suggested that this was a manifestation of the previously‐reported dendritic Ca spike.
Effects of internal sodium and hydrogen ions and of external calcium ions and membrane potential on calcium entry in squid axons.
Authors: Mullins L J , Tiffert T , Vassort G , Whittembury J
Published: December 2014

Squid giant axons were impaled with electrodes to measure pNai, pHi, Em, and were injected with either aequorin or arsenazo III to measure [Ca]i or with phenol red to measure [H]i. Depolarization of such axons with elevated [K] in sea water leads to a Ca entry that is a function of [Ca]o, [Na]i, and [H]i. With saturating [Na]i half‐maximal Ca entry is produced by a [Ca]o of 0.58 mM. With saturating [Ca]o, depolarization produced by 450 mM‐K+ leads to half‐maximal Ca entry when [Na]i is 25 mM; entry is virtually undetectable if [Na]i is 18 mM. If [Ca]o is 50 mM, Ca entry upon depolarization as measured with aequorin is phasic with a rapid phase of light emission and a plateau; Ca entry as measured with arsenazo III shows no such phasic behaviour, absorbance vs. time is a square wave that closely follows the depolarization vs. time trace. Both detectors of [Ca]i show a square‐wave response if [Ca]o is 3 mM. The introduction of 2 mM‐CN into the sea water bathing the axon does not affect the response to depolarization nor does the destruction of most of the ATP in the axon following the injection of apyrase. If axons are microinjected with phenol red rather than arsenazo, the entry of Ca produces an acidification in the peripheral parts of the axoplasm. Other experiments measuring [Ca]i show that Ca entry is strongly inhibited by a decrease in pHi. Making sea water alkaline with pH buffers scarcely affects the Ca entry induced by depolarization; making axoplasm alkaline by adding NH4+ to sea water greatly enhances Ca entry by Na/Ca exchange and also enhances the ability of axoplasmic buffers to absorb Ca.
Localization of monosynaptic Ia excitatory post‐synaptic potentials in the motor nucleus of the cat biceps femoris muscle.
Authors: Botterman B R , Hamm T M , Reinking R M , Stuart D G
Published: December 2014

Evidence is presented for the existence of a localization of monosynaptic Ia excitatory post‐synaptic potentials (e.p.s.p.s) in the motor nucleus of a cat hind limb muscle. Intracellular recordings from biceps femoris motoneurones were made in anaesthetized low spinal cats of the effects of stimuli to the nerve branches supplying the anterior, middle, and posterior portions of the biceps femoris muscle. Recordings were also made during stimulation of nerves to semimembranosus and semitendinosus in order to provide a means of categorizing middle biceps cells as ‘extensors’ (middle biceps‐extensor; i.e. like anterior biceps cells) or as ‘flexors’ (middle biceps‐flexor; like posterior biceps). Homonymous nerve‐branch (i.e. from anterior, middle or posterior biceps) monosynaptic Ia e.p.s.p.s were compared within unifunctional (flexor or extensor) groups of motoneurones. In three of four comparisons (anterior biceps nerve branch onto anterior and middle biceps‐extensor cells, middle biceps onto middle biceps‐flexor and posterior biceps, posterior biceps onto middle biceps‐flexor and posterior biceps) the anterior, middle and posterior biceps nerve branches contributed larger e.p.s.p.s to their ‘own’ motoneurones than to motoneurones supplying other ‘compartments’ of the muscle. In the fourth case, middle biceps's input appeared to have similar effects onto anterior biceps and middle biceps‐extensor cells. A normalization was performed to eliminate the possibility that the differences in e.p.s.p. sizes were due to differences in cell type within the four cell groupings (i.e. differences in the number of cells supplying FF, F(int.), FR and S muscle units). This normalization confirmed that the localization in the first three comparisons was not a consequence of differences in motoneurone type and, in addition, suggested that middle biceps may indeed have greater effects on middle biceps‐extensor than anterior biceps cells. In addition to the asymmetrical effects of anterior and middle biceps nerve branches onto anterior biceps and middle biceps‐extensor motoneurones, it was shown that while semitendinosus and posterior biceps contributed larger e.p.s.p.s to middle biceps‐flexor than to middle biceps‐extensor cells, the anterior biceps nerve branch and semimembranosus nerve contributed equally to the two middle biceps groups. Analysis of cell location in the spinal cord and rostro‐caudal differences in group I volley sizes gave evidence of a topographic organization of the biceps femoris motor nucleus which could contribute to the observed localization. However, localization was also evident when comparing e.p.s.p. amplitudes in pairs of neighbouring cells of different category, indicating a role for neuronal recognition factors.
Tactile discrimination of textured surfaces: psychophysical performance measurements in humans.
Authors: Lamb G D
Published: December 2014

Psychophysical experiments were designed to assess the tactile discriminative abilities of human subjects when touching textured surfaces. Plastic strips were produced which had raised dots in a square arrangement (standard surface) or in one of a number of rectangular arrangements (modified surfaces) in which the spacing of the dots differed from the standard surface by some constant amount in one direction. Subjects were presented with pairs of surfaces and asked to discriminate whether each pair consisted of (a), two identical standard surfaces, or (b), a standard surface and a modified surface. Performance measurements were analysed using decision theory. When subjects moved their fingers over the surfaces (active touch) their responses were virtually unbiased, and there was a linear relationship between discriminative performance and the difference between the spacing of the dots on the two surfaces. At the 75% correct level, subjects could distinguish surfaces in which the period of the dots differed by only 2%. Performance was virtually independent of the method of movement used, despite large differences in the velocity profiles of the various movements. Experiments in which the surfaces were moved under the subject's stationary finger (passive touch) displayed the same linear relationship between performance and period difference as in the active‐touch experiments. Furthermore, the discriminative performance levels were very similar in the two types of experiments. In the passive‐touch experiments, subjects could distinguish smaller differences in period in the surface dimension parallel to (along) the direction of movement than they could distinguish in the dimension perpendicular to (across) the direction of movement. The hypothesis is advanced that normal active discrimination of surfaces is made possible by using similar movements in successive surface contacts and a relatively simple neural code.
Amino acid transport and cell volume regulation in Ehrlich ascites tumour cells.
Authors: Hoffmann E K , Lambert I H
Published: December 2014

Cellular and extracellular concentrations of amino acids were measured in Ehrlich ascites cells by amino acid analysis and by distribution of radioactive amino acids between cells and medium. Dilution of the medium results in a reduction in the cellular concentration of non‐essential amino acids and taurine and an equivalent increase in the extracellular content of these amino acids. The membrane potential and the electrochemical gradient of sodium were measured. The decrease in the cellular to extracellular gradient of taurine and glycine is not a consequence of a decrease in the sodium gradient but is caused by the changes in osmolarity and cell volume. The unidirectional influx and efflux of glycine and taurine were measured as the initial influx of [14C]glycine and [35S]taurine, using a rapid filter technique. For both amino acids the rate constants for influx are decreased and the rate constants for efflux increased following a reduction in osmolarity. The taurine and glycine fluxes were analysed as a simple pump and leak system. Reduction in osmolarity increases the leak permeability to both taurine and glycine. The results for glycine are also discussed in relation to a Na+‐glycine co‐transport model, where reduction in osmolarity increases the leak permeability to glycine. The cellular permeability to taurine and glycine increases as a function of increasing cell volume. The taurine permeability increases 7‐fold and the glycine permeability 1.5‐fold with an increase in cell volume of 30%. The absolute increase in permeability is equal for both taurine and glycine.
The saturation of monochromatic lights obliquely incident on the retina.
Authors: Alpern M , Tamaki R
Published: December 2014

Foveal dark‐adaptation undertaken to test the hypothesis that the excitation of rods causes the desaturation of ‘yellow’ lights in a 1 degree field traversing the margin of the pupil, fails to exclude that possibility. The desaturation is largest for a 1 degree outside diameter annular test, is still measurable with a 0.5 degree circular disk, but disappears for a 0.29 degree disk. The supersaturation of obliquely incident 501.2 nm test light follows the opposite pattern; it disappears with an annulus and is largest for a 0.29 degree circular field. It is unlikely that rods replace short‐wave sensitive cones in the trichromatic match of an obliquely incident test with normally incident primaries. If rods as well as all three cones species are involved, the matches might not be trichromatic in the strong sense. Grassmann's law of scalar multiplication was tested and shown not to hold for the match of an obliquely incident test with normally incident primaries, though it remains valid whenever, both primaries and test strike the retina at the same angle of incidence (independent of that angle). The result in section 3 (above) cannot be due to rod intrusion. It persists (and becomes more conspicuous) on backgrounds (4.0 log scotopic td) which saturate rods. Moreover obliquely incident ‘yellow’ lights remain desaturated in intervals in the dark after a full bleach, whilst the test field is below rod threshold. The amount of desaturation does not differ appreciably from that normally found. The assumption of the unified theory of Alpern, Kitahara & Tamaki (1983) that the outer segments of only a single set of three cone species (with acceptance angles wide enough to include the entire exit pupil) contain the visual pigments absorbing both the normally incident primaries and the obliquely incident test is disproved by these results. Failure of Grassmann's law is most conspicuous under the conditions for which the changes in saturation upon changing from normal to oblique incidence are greatest and least when the saturation changes are the smallest. Either all unified theories of the Stiles‐Crawford effects are wrong or all the effects of oblique incidence operate at a stage in the visual process at which the effects of radiation of different wave‐lengths are no longer compounded by the simple linear laws.
Convergence of trigeminal afferents on retractor bulbi motoneurones in the anaesthetized cat.
Authors: Grant K , Horcholle‐Bossavit G
Published: December 2014

Retractor bulbi motoneurones were identified by intracellular recording of their antidromic invasion following stimulation of the motor axons. Characteristics of excitatory post‐synaptic potentials (e.p.s.p.s) evoked by electrical stimulation of long ciliary nerves (corneal afferents), the supraorbital nerve and the ipsilateral or contralateral vibrissae were analysed. Comparison of the orthodromic responses induced by supra‐threshold stimulation of the four trigeminal inputs showed that the most powerful excitatory effect was due to corneal afferent stimulation. Excitatory synaptic potentials were followed in some cases by a period of hyperpolarization lasting 15‐20 msec. It is suggested that this is an inhibitory potential of post‐synaptic origin. Interaction between condition and test e.p.s.p.s evoked by long ciliary nerve and supraorbital nerve stimulation revealed a partial blocking of test e.p.s.p.s over a longer period (more than 30 msec), and it is suggested that inhibitory mechanisms within the trigeminal nucleus may be in part responsible for the absence of facilitation at the level of the motoneurone.
Statistics of the maintained discharge of cat retinal ganglion cells.
Authors: Frishman L J , Levine M W
Published: December 2014

Action potentials were recorded from single fibres in the optic tracts of anaesthetized cats. Continuous records were obtained at various levels of scotopic and mesopic retinal illumination. In some cases, the light intensity was modulated by a pseudorandom Gaussian white‐noise signal. The maintained discharge of on‐centre neurones increased while the maintained discharge of off‐centre neurons decreased with increased illumination of the receptive field centre. For both cell types, the coefficient of variation declined with increased rate of discharge. There was minimal short‐term dependency in the firing patterns, and it was unaffected by the level of retinal illumination. Virtually all of the structure revealed by the normalized autocovariance functions could be attributed to the shape of the interval distributions. The first few coefficients of the serial correlogram were slightly negative. The magnitude of this negativity was not related to illumination. Long‐term dependency in the firing pattern was also quite small; the standard deviations of the mean rate in samples of about 1 sec duration were only slightly less than would be predicted from the interval distributions. This dependency tended to increase at higher retinal illuminations. Neural discharges elicited by Gaussian modulation of the light were strikingly different from those elicited by steady light. Modulation caused the first coefficient of the serial correlogram to become more positive, while the next several coefficients became more negative. A corresponding pattern could be seen in the normalized autocovariance functions, and in the differences between the normalized autocovariance and normalized autoconvolution. Long‐term dependency also increased dramatically, such that the standard deviations of mean rate were about 60% of what would be expected given the interval distributions observed. These results place a number of constraints upon the ways in which intrinsic noise in the retina may enter the visual processing network. Two alternative models consistent with the data are presented.
Tonic and reflex synaptic activity recorded in ciliary ganglion cells of anaesthetized rabbits.
Authors: Johnson D A , Purves D
Published: December 2014

We have studied patterns of synaptic activity in rabbit ciliary ganglion cells by intracellular recording in vivo, and have examined the morphology of functionally characterized neurones by intracellular injection of horseradish peroxidase. Nearly all of the neurones studied (293 of 300) received tonic synaptic input from preganglionic neurones. This tonic activity was not decreased by darkness or by acute optic nerve section. The rate of tonic synaptic activity recorded in the vast majority of neurones (94%) changed in response to retinal illumination. Most ganglion cells showed an increased rate; some cells, however, showed decreased activity during illumination. The rate of synaptic activity recorded in ciliary neurones tended to be progressively higher in neurones with more complex geometries. Neurones with similar reflex properties included cells that lacked dendrites and cells with complex dendritic arborizations; conversely, neurones with similar geometries often had different reflex characteristics. The synaptic activity arising from different preganglionic axons innervating the same ganglion cell was not temporally linked in any obvious way. The relevance of these results to the regulation of the number of axons that innervate target neurones is discussed.
Permeation of divalent and monovalent cations through the ovarian oocyte membrane of the mouse.
Authors: Yoshida S
Published: December 2014

Ovarian oocytes were isolated from adult mice and intracellular recording was performed using single glass micro‐electrodes. The resting potential was ‐ 7.0 +/‐ 1.8 mV in standard solution, and the oocyte showed a regenerative response at the cessation of hyperpolarizing current pulse. Ca spikes were observed under Na+‐free conditions. The overshoot of the spike increased 28 mV for a 10‐fold increase in [Ca2+]o and showed saturation as [Ca2+]o was elevated. The spike was insensitive to tetrodotoxin (TTX) and was blocked by polyvalent cations such as Co2+, Cd2+, Mn2+ and La3+. Sr2+ or Ba2+ substituted for Ca2+ in generating action potentials. Na spikes were observed under Ca2+‐free conditions. The overshoot of the spike showed the slope of 39 mV for a 10‐fold increase in [Na+]o and a saturation was detected when [Na+]o was raised. The spike was resistant to TTX and was blocked by Ca antagonists such as Co2+, Cd2+, Mn2+ or La3+. Li+ substituted for Na+ in producing spikes, while Rb+ did not. The overshoot and maximum rate of rise of the Na spike became smaller when Ca2+ was present in the bathing solution, indicating a competition between Na+ and Ca2+. Mn2+ acted not only as a Ca blocker but also as a charge carrier during excitation. Mn spikes were detected in Na+‐, Ca2+‐free solutions and were blocked by Ca antagonists. The resting membrane is permeable to not only Na+ but also to some extent to K+. It is suggested that the ovarian oocyte membrane of the mouse has voltage‐dependent Ca channels, and both divalent (Ca2+, Sr2+, Ba2+, Mn2+) and monovalent (Na+, Li+) cations can pass through the Ca channels to generate action potentials.
Hyperglycaemia, a morphine‐like effect produced by naloxone in the cat.
Authors: Feldberg W , Pyke D A , Stubbs W A
Published: December 2014

In unanaesthetized cats the pronounced hyperglycaemia produced by intravenous morphine (5 mg/kg) was inhibited by naloxone. However, naloxone itself produced hyperglycaemia when given in doses slightly larger than those required to produce inhibition. These two effects of naloxone were obtained when it was injected intravenously, into a lateral cerebral ventricle, or into the cisterna magna. The hyperglycaemia produced when naloxone or morphine was injected into a lateral cerebral ventricle or into the cisterna magna was not inhibited by intravenous naloxone. Hyperglycaemia was not the only morphine‐like effect of naloxone. It also reproduced some of the behavioural effects of morphine.
Compensatory eye movements during active and passive head movements: fast adaptation to changes in visual magnification.
Authors: Collewijn H , Martins A J , Steinman R M
Published: December 2014

Rotational eye and head movements were recorded with great precision with scleral and cranial search coils in a rotating magnetic field. Compensatory eye movements were recorded in light and darkness during active as well as passive head movements in the frequency range 0.33‐1.33 Hz. From the recorded, nominal gaze movements the effective gaze was reconstructed taking into account magnification or reduction factors of corrective spectacles. Effective gain was calculated as the ratio between the velocities of the effective corrective eye movements and the head movements. In the light, effective gain of compensatory eye movements during active head motion was mostly between 0.97 and 1.03. It was never precisely unity and differed systematically between subjects and between the two eyes of each subject. During passive head motion in the light, gain was lower by about 3% than during active motion. During active head movement in the dark, gain was mostly between 0.92 and 1.00; values were about 5% lower than during active motion in the light. During passive head movement in the dark, gain was about 13% lower than during active motion, and the variability of the oculomotor response increased. Adaptation of these base‐line conditions was induced by fitting the subjects with magnifying or reducing spectacles for periods of 40 min to 24 h. The largest required change in amplitude of eye movements was 36%. When active head movements were made, the amplitude of compensatory eye movements in the light as well as in the dark adjusted rapidly. Most of the adaptation of the vestibulo‐ocular reflex in the dark was completed in about 30 min. This rate is much faster than that found in previous experiments requiring larger adaptive changes. Differential adaptation to unequal demands for the two eyes proved to be very hard or impossible. In a mild conflict situation the system adjusted to an intermediate level, distributing the error symmetrically between the eyes. When the discrepancy was large, the adaptive process of both eyes was controlled by the one eye which provided the most meaningful information. It is concluded that the system generating compensatory eye movements performs best during active rather than passive head movements, and that adaptation to moderate changes in optimal gain are made very rapidly.
The cation selectivity and voltage dependence of the light‐activated potassium conductance in scallop distal photoreceptor.
Authors: Cornwall M C , Gorman A L
Published: December 2014

Light‐dependent voltage and current responses were measured from the distal hyperpolarizing photoreceptors of the scallop (Pecten irradians) retina. In normal external solution, the hyperpolarizing receptor potential was caused by a light‐dependent K+ outward current. The magnitude of the hyperpolarizing receptor potential and the light‐dependent outward current, measured at the resting potential, was graded with light intensity. In normal external solution, during prolonged illumination the light‐dependent K+ outward current was characterized by an early peak and a subsequent plateau. Current responses to brief light flashes were reduced progressively during background illumination. In the absence of external Na+ ions, the reversal potential for the receptor potential changed 58 mV per 10‐fold change in the extracellular K+ concentration. The estimated internal K+ concentration was 385 mM. The hyperpolarizing receptor potential produced by prolonged bright illumination consists of an early peak which decays to a plateau. This decay was determined by a decrease in the light‐dependent K+ conductance during maintained illumination. The light‐dependent conductance pathway passed outward currents better than inward K+ currents. The light‐dependent K+ conductance was estimated to increase e‐fold per 23‐34 mV depolarization at the peak and during the plateau of the light response. The light‐dependent conductance pathway was highly selective for K+ ions. The selectivity sequence for monovalent cations was T1+, K+ greater than Rb+ greater than NH4 greater than Cs+, Li+, Na+. External caesium and tetraethylammonium blocked inward but not outward K+ currents through the light‐dependent K+ conductance pathway. The data suggest that K+ ions move through an aqueous pore which is controlled by light.
Potassium accumulation around individual purkinje cells in cerebellar slices from the guinea‐pig.
Authors: Hounsgaard J , Nicholson C
Published: December 2014

K+‐selective micropipettes were used to measure external K+ concentration [( K+]o) in the immediate vicinity of Purkinje cells in slices from guinea‐pig cerebellum. The cells were either spontaneously active or were polarized via a separate intracellular micro‐electrode. The level of [K+]o rose by 1‐3 mM around the soma and dendrites of Purkinje cells during spike activity. The increases in [K+]o were usually greater during Ca2+‐mediated spikes than during Na+‐mediated spikes. This was even true at the soma where the Ca2+ spike only invaded electrotonically from the dendrites, in contrast to the Na+ spikes which were generated at the soma. No [K+]o changes were seen in the vicinity of Purkinje cells when the cells were hyperpolarized with current passage nor was any [K+]o change seen during subthreshold depolarizations. In glial cells, however, a hyperpolarizing current reduced [K+]o while a depolarizing current increased [K+]o in a symmetrical manner. When Ba2+ was substituted for Ca2+ in the bathing Ringer solution, prolonged plateau‐potential spikes could be evoked from Purkinje cells. These spikes were accompanied by large [K+]o elevations but the plateau potentials outlasted the [K+]o elevations. These experiments suggest that large [K+]o increases can occur in the absence of Ca2+‐mediated K+ conductances. Substitution of Mn2+ for Ca2+ in the Ringer solution removed some of the [K+]o increases at the Purkinje cell soma. Addition of tetrodotoxin to normal Ringer solution also reduced, but did not abolish the [K+]o increases at the soma. These experiments confirmed that both Na+ and Ca2+ spikes were involved in the [K+]o change. The diffusion characteristics of the slices were determined by an ionophoretic method using tetramethylammonium and ion‐selective micropipettes. The extracellular volume fraction of the slice averaged 0.28 while the tortuosity averaged 1.84. These values were close to those found previously in the intact rat cerebellum. These data were used to make quantitative estimates of the expected [K+]o accumulation in the vicinity of a single cell (see Appendix). Such estimates showed reasonable agreement with the measured values. Our data show that quite large increases in [K+]o may occur around single Purkinje cells. Such increases have previously only been evident during the activation of cell populations in mammalian preparations. The present results are probably due to the superior recording conditions of the slice. Implications for intercellular communication are discussed.
Sustained and transient synaptic inputs to on‐off ganglion cells in the mudpuppy retina.
Authors: Belgum J H , Dvorak D R , McReynolds J S
Published: December 2014

Synaptic inputs to on‐off ganglion cells in mudpuppy retina were studied by measuring current‐voltage relations in darkness, during different phases of the response to light, and in the presence of 4 mM‐Co2+. The addition of Co2+ to the bathing medium usually caused a hyperpolarization of the membrane potential in darkness and an increase in input resistance, indicating that on‐off ganglion cells receive tonic excitatory synaptic input in darkness. Other results suggest that an additional synaptic input, with a reversal potential near the dark potential, may also be active in darkness. At the onset of a light stimulus in the receptive field centre all on‐off ganglion cells responded with transient excitatory and inhibitory synaptic events, both of which were due to increases in conductance. Similar transient excitatory and inhibitory events occurred at the termination of the light stimulus. In about one‐half of the on‐off ganglion cells studied the synaptic activity during steady illumination was the same as in darkness. In the remaining cells steady illumination caused an increase in sustained inhibition.
Effects of altered extracellular and intracellular calcium concentration on hyperpolarizing responses of the hamster egg.
Authors: Igusa Y , Miyazaki S
Published: December 2014

Upon fertilization the hamster egg shows transient, periodic hyperpolarizing responses (h.r.s) due to a Ca‐activated K conductance; these are superimposed on a gradual, hyperpolarizing shift of the resting potential (h.s.) (Miyazaki & Igusa, 1981a, 1982a). The h.r.s and h.s. were further analysed by changing external divalent cations or by injection of Ca2+ into the egg, to study the mechanisms of the increase in the intracellular Ca2+ concentration ([Ca2+]i). The series of h.r.s was abolished by the removal of external Ca2+. The frequency of the h.r. was decreased by lowering the [Ca2+]o or by adding Mn2+ or Co2+, and it was increased by raising the [Ca2+]o in a time‐ and concentration‐dependent manner. The h.r. frequency was decreased on sustained depolarization with steady current, and increased on hyperpolarization. In contrast to the h.r. frequency, the amplitude, conductance increase and reversal potential of each h.r. were little affected by [Ca2+]o, Mn2+ or Co2+. The h.s. was decreased by lowering the [Ca2+]o, by adding Mn2+ or Co2+, or by injection of EGTA. The h.s. may reflect continuous Ca influx stimulating a Ca‐activated K conductance (GK). In unfertilized eggs a regenerative h.r. was induced by Ca injection with an apparent threshold. The relationship between GK and the injected Ca2+ showed a steep jump at the critical current, associated with a four‐fold increase in GK. The regenerative h.r. was followed by a refractory period of 1‐2 min. In inseminated eggs the periodic sperm‐mediated h.r.s. (s.‐h.r.s) were interrupted by interposed h.r.(s) induced by Ca injection(s): the periodicity of s.‐h.r.s was reset by Ca‐induced h.r. In inseminated eggs the regenerative h.r. was induced by Ca injection with a much smaller pulse than necessary in unfertilized eggs. The refractory period was shortened to 40‐50 sec, comparable to the period of s.‐h.r.s. In inseminated eggs periodic h.r.s similar to s.‐h.r.s were produced by continuous, repetitive injections of Ca2+ with constant pulses. The frequency of these h.r.s was dependent on the injection current. It is concluded that each h.r. indicates an enhancement of the increase in [Ca2+]i, probably the result of Ca‐induced Ca release from intracellular stores. A possible mechanism for periodic increase in [Ca2+]i reflected in s.‐h.r.s is proposed, based on a linkage of the continuous Ca influx to Ca release.
Periodic hyperpolarizing responses in hamster and mouse eggs fertilized with mouse sperm
Authors: Igusa Yukio , Miyazaki Shun‐Ichi , Yamashita Naohide
Published: December 2014

1. The zona‐free hamster egg allows multiple entries of heterologous as well as homologous sperm. The hamster egg inseminated with mouse sperm (M × H egg) showed recurring, transient hyperpolarizing responses (h.r.s) with the peak of ‐70 to ‐80 mV. They were superimposed on a hyperpolarizing shift of the resting potential (h.s.) which gradually reached ‐60 mV in 50 min after insemination.

2. Unlike the hamster sperm, the cessation of flagellar motion of the first mouse sperm (‘1‐stop’) failed to induce the first h.r. but produced only a small hyperpolarizing ‘step’ of 3‐7 mV. Similar steps occurred for each of additional sperm with a one‐to‐one correspondence, 4‐50 sec ahead of the cessation of sperm motion.

3. In M × H eggs, the h.r. first appeared about 15 min after the ‘1‐stop’. The intervals of the h.r.s thereafter were in the range between 2‐10 min, in contrast to 30‐45 sec in hamster eggs inseminated with hamster sperm (H × H eggs).

4. The h.r.s in M × H eggs were abolished by intracellular injection of EGTA, suggesting that they were caused by periodic increase in the intracellular Ca2+ concentration ([Ca2+]i) as in H × H eggs.

5. The gradual h.s. in M × H eggs was considered to be due mainly to an increase in Ca‐independent K permeability, since the resting potential beyond ‐60 mV at 50‐70 min after insemination was changed by only 3‐5 mV on the removal of Cl ions and on EGTA injection.

6. Histological observations revealed that the resumption of the second meiosis, the indication of egg activation, is delayed in M × H eggs by about 15 min, compared with that in H × H eggs. There was a good correlation between the delay of activation and that of the occurrence of the first h.r.

7. In M × H eggs, the probability of egg activation within 70 min was dependent on the number of sperm penetrations: 90% for more than ten sperm while 20‐30% for less than five sperm. Eggs in which sperm penetration was not followed by activation showed no h.r.s.

8. The mouse egg inseminated with mouse sperm showed small h.r.s (3‐4 mV) superimposed on the h.s. from ‐35 to ‐55 mV in 50 min after insemination. Both h.r.s and h.s. were associated with an increase in the membrane conductance. The h.s. was considered to be due mainly to a Ca‐independent increase in K permeability.

9. Iontophoretic injection of Ca2+ into the unfertilized mouse egg could not increase the K conductance with injection currents up to 4 nA. However, the h.r.s were suggested to be resulted from a periodic increase in [Ca2+]i, since they were abolished by injection of EGTA.
Time domain spectroscopy of the membrane capacitance in frog skeletal muscle.
Authors: Huang C L
Published: December 2014

Dielectric spectra representing the frequency dependence of the complex permitivity at a range of depolarizations were obtained from voltage‐clamped frog skeletal muscle membranes. This employed an analysis that derived the Fourier coefficients defining the capacitative transients to 10 mV steps as continuous functions of frequency, and so could examine closely the relevant frequencies at which non‐linear components occurred. Non‐linear capacitative components were identified through their appearance at lower frequencies than those of the linear components as obtained at the ‐85 mV control voltage, from spectra representing a logarithmic scale of frequencies. Permitivities from small depolarizing steps between about ‐75 and ‐50 mV gave single q beta dielectric loss peaks; the real permitivities declined monotonically with increasing frequency. Simple arc loci were obtained in the complex plane. With further depolarization, an additional q gamma loss peak at low frequencies and a resonant frequency in the real spectra occurred over a narrow voltage range around ‐45 mV. The complex loci then showed features implying an increased movement of charge not explicable through the simple effect of an electric field on a dielectric species. Spectra from small hyperpolarizing steps possessed only single dielectric loss peaks and real permitivities that declined monotonically with increasing frequency. However, in the complex plane, the loss tangents at the higher frequencies implied a population of two or more dielectric relaxations. The potential dependence of the frequency at maximum dielectric loss obtained from depolarizing steps showed a discontinuity at the onset of q gamma. In contrast, in hyperpolarizing responses, this dependence was smooth. The q beta relaxations obtained after q gamma was abolished by 1 mM‐tetracaine gave dielectric spectra that were similar whether to depolarizing or hyperpolarizing potential steps. They gave single dielectric loss peaks and semicircular complex plane loci. The singularities in the dielectric spectra thus result from the q gamma charge movement component. They may reflect co‐operative mechanisms that might also produce its steep voltage dependence and kinetics, and consequently those of the physiological processes it may control. These are discussed in terms of the mechanisms expected in allosteric proteins.
Mechanism of action of noradrenaline on the sodium‐potassium pump in isolated rat liver cells.
Authors: Berthon B , Burgess G M , Capiod T , Claret M , Poggioli J
Published: December 2014

Noradrenaline, which mobilizes Ca from intracellular stores, stimulated the Na‐K pump in isolated rat liver cells. This resulted in transient decreases in internal Na content and external K concentration. The effect of the hormones was observed in the presence of the beta‐adrenergic antagonist propranolol and was blocked by the alpha‐antagonist phenoxybenzamine. Prazosin appeared to be 1000 times more potent than yohimbine in suppressing the cell response to the hormone, suggesting that the effect is mediated by an activation of alpha 1‐adrenergic receptors. Externally applied ATP and the Ca ionophore A23187 which, in common with alpha‐agonists, deplete internal Ca stores in this tissue, similarly stimulated the Na‐K pump and transiently decreased internal Na and external K. The effects of noradrenaline and ATP were not additive. Moreover, the cell response to ATP was observed in the presence of the alpha‐antagonist phenoxybenzamine, indicating that though acting via separate receptors, noradrenaline and ATP use a common mechanism to alter the carrier. The effect of noradrenaline and A23187 on the Na‐K pump was not dependent on the presence of extracellular Ca. In contrast, when the hepatocytes were incubated in Ca‐free medium for long periods (cell Ca depletion) the activity of the Na‐K pump was increased to a level corresponding to that induced by maximal doses of noradrenaline. In these conditions, noradrenaline and A23187 did not increase the pump activity further. In cells in which the Na content was raised, leading to a 3‐fold increase in the Na‐K pump activity, noradrenaline continued to be able to stimulate the pump. Again long‐term incubations in Ca‐free medium increased the pump activity and the effect of noradrenaline was greatly reduced. It is proposed that in isolated rat liver cells alpha‐agonists and applied ATP influence the Na‐K pump by releasing Ca bound to plasma membranes, thus removing the inhibitory effect of this ion on the Na pump.