bluuebunny/crossref_metadata_2025 huggingface dataset:
Neural respiratory and circulatory interaction during chemoreceptor stimulation and cooling of ventral medulla in cats.
Authors: Millhorn D E
Published: December 2014

The effects on respiratory and sympathetic neural activity, measured as integrated phrenic and cervical nerve activities respectively, during changing input from the central chemoreceptors was studied in anaesthetized, paralysed cats whose carotid sinus nerves and vagus nerves had been cut. Central respiratory drive was altered either by graded cold block of the intermediate areas, located bilaterally near the ventral surface of the medulla oblongata, or by step increases in end‐tidal PCO2. Cervical nerve activity showed both a tonic (or mean) level of activity and a prominent cyclic discharge that was in phase with phrenic nerve activity. Graded focal cooling of the intermediate areas to 20 degrees C when end‐tidal PCO2 was kept constant caused progressive decreases in phrenic activity, the amplitude of the inspiratory related discharge and mean arterial pressure, but only a small decrease in mean cervical nerve activity. Cooling the intermediate areas in the absence of the inspiratory related discharge (i.e. when phrenic activity was below the apnoeic threshold) led to a much smaller decrease in arterial pressure. Step increases of end‐tidal PCO2 caused progressive increases of both cervical and phrenic nerve activities. The increase in cervical activity was due primarily, if not wholly, to a progressive increase in the amplitude of the inspiratory related discharge. These findings show that the predominant effect on sympathetic activity during stimulation of the central chemoreceptor and graded cold block of the intermediate areas is a change in the amplitude of the inspiratory related discharge and suggest that the change in arterial pressure that accompanies central chemoreceptor stimulation and graded cold block of the intermediate areas is mediated by the inspiratory related discharge rather than by an increase in the mean level of sympathetic activity. When phrenic activity was lowered to below apnoeic threshold by cooling the intermediate areas, step increases in end‐tidal PCO2 caused inhibition rather than stimulation of cervical nerve activity. This finding indicates that sympathetic neurones are not activated by central chemoreceptor input directly, but rather indirectly via intracranial connexions with neuronal networks involved in regulation of respiration.
Blood pressure response evoked by ventral root afferent fibres in the cat.
Authors: Chung J M , Kim J , Shin H K
Published: December 2014

Systemic arterial blood pressure changes in response to stimulation of the distal stump of the cut spinal ventral root were investigated in anaesthetized, vagotomized, and carotid sinus‐denervated cats. Low intensity electrical stimulation (less than 20 T, where T is threshold intensity) of the ventral root caused a rise in blood pressure. This elevation was abolished by paralysing the muscles with gallamine. This pressor response has been reported previously, and it is likely to be evoked by afferents excited by the contracting muscle. High intensity electrical stimulation (500 T) of the ventral root caused a second and marked pressor response. This was not affected by muscular paralysis or by cutting the sciatic nerve, but it was abolished by cutting the dorsal root. Threshold intensity for the second component of the pressor response was within the same range as the intensity needed for activation of C fibres in the ventral root, ranging between 200 T and 300 T. This response was graded with increasing stimulus intensity, and it showed both spatial and temporal summation. From the above results, we conclude that non‐myelinated fibres in feline spinal ventral root course distally to the dorsal root ganglion and then enter the spinal cord via the dorsal root. Activation of these fibres results in a marked elevation of the systemic arterial blood pressure as in other somato‐sympathetic reflexes induced by peripheral C fibre activation.
Length‐related changes in activation threshold and wave form of motor units in human masseter muscle.
Authors: Miles T S , Nordstrom M A , Türker K S
Published: December 2014

Action potentials of single motor units in the human masseter muscle were recorded during isometric contractions at different muscle lengths over most of the working range of the temporomandibular articulation. The shape of the unit potential wave form changed progressively as the muscle length changed. This was considered to be due principally to a change in the geometric relationship of the electrode to the muscle fibres at various muscle lengths. The recruitment thresholds for all units increased sharply when the jaw opening approached the maximal gape. The pattern of change of unit thresholds with muscle length closely paralleled the curve of length versus passive tension for the combined jaw‐closing muscles, temporomandibular articulation and associated soft tissues. It was concluded that the change in unit recruitment thresholds with length is likely to be a consequence of the length‐passive tension relationship of the muscles, joint and soft tissues. The results of this study indicate that attempts to assign masseter motor units to one or other of the accepted functional categories on the basis of recruitment force or wave form only are unlikely to give reliable results.
Ventilation in intact and glossopharyngeal nerve sectioned anaesthetized rats exposed to oxygen at high pressure.
Authors: Cragg P A , Drysdale D B , Hamilton J H
Published: December 2014

The cause of the initial hyperventilation, which occurs on exposure to O2 at high pressure (o.h.p.), has been investigated by measuring tidal volume (VT), frequency of breathing (f) and hence ventilation (VE) in thirty‐six barbiturate‐anaesthetized rats, with or without their glossopharyngeal (IX) nerves sectioned, during 30‐60 min of exposure to o.h.p. at 4, 6 or 8 atm absolute. In intact rats the rates of rise of VT, f and VE with time during exposure to o.h.p. were smallest at 4 and greatest at 8 atm absolute. In IX‐sectioned rats the rates of rise of VT at 4, 6 and 8 atm absolute and of f at 4 atm absolute were similar to those of intact rats. At 6 atm absolute and even more so at 8 atm absolute, however, f decreased. Hence the slope of VE in IX‐sectioned compared with intact rats was similar at 4 atm absolute but smaller at 6 and 8 atm absolute. In fact at 8 atm absolute VE remained constant in IX‐sectioned rats. Since the slope of VE versus time in intact rats was steeper the greater the pressure and since the removal of carotid bodies in IX‐sectioned rats reduced the VE slope at 6 and 8 atm absolute, the stimulus to the hyperventilation induced by o.h.p. cannot be an accumulation of CO2 in the brain resulting from the lack of O2 desaturation of haemoglobin. This theory would predict that VE should be identical at all pressures above 3.5 atm absolute. The findings in the IX‐sectioned rats indicate a major contribution of the carotid bodies to the f increase in o.h.p. They may be stimulated by a histotoxic hypoxia induced by early O2 poisoning. Since the VT increase on exposure to o.h.p. was both large and fairly similar in intact and IX‐sectioned rats, it is suggested that a large part of the VT increase was caused by stimulation of the central chemoreceptors by lactic acidosis induced by an o.h.p.‐induced histotoxic hypoxia of the brain.
The release of histamine by parasympathetic stimulation in guinea‐pig auricle and rat ileum.
Authors: Bani-Sacchi T , Barattini M , Bianchi S , Blandina P , Brunelleschi S , Fantozzi R , Mannaioni P F , Masini E
Published: December 2014

Two preparations, a segment of rat ileum and the vagally innerved guinea‐pig auricles, have been used in an analysis of the responses to vagal or to electrical field stimulation. The responses to parasympathetic stimulation were depressed by atropine and by tetrodotoxin, and potentiated by eserine. Supramaximal stimulation (10‐20 Hz) resulted in increased release of acetylcholine and histamine, both in rat ileum and guinea‐pig auricles. The release of histamine after parasympathetic stimulation did not exhibit tachyphylaxis, and it was not reproduced by non‐parasympathetic stimuli. In both preparations, atropine produced a significant, dose‐related reduction of histamine measured in the bath fluid after stimulation, while eserine increased histamine output. A significant diminution of mast cell granules metachromasia was observed in guinea‐pig auricles and in rat intestine after parasympathetic stimulation. The possibility is discussed that acetylcholine released by parasympathetic stimulation would in turn evoke the secretion of histamine from tissue mast cells.
Facilitation of vergence changes by saccades: influences of misfocused images and of disparity stimuli in man.
Authors: Enright J T
Published: December 2014

When confronted with randomly presented targets demanding change in mean visual direction (version of 4.5‐7 deg) as well as a change in vergence (1.5‐2.5 deg) both naive and experienced subjects can make short‐latency saccades which differ markedly and appropriately in the excursion of the two eyes, and which thereby achieve a large fraction of the required change in vergence. Mean values for the portion of vergence change occurring during the saccades, over all target positions, ranged from 41 to 70% for the five subjects tested, but subject‐specific directional biases in performance were also conspicuous. When such targets were presented randomly during monocular viewing, so that only accommodation cues could induce vergence change, a consistent fraction (13‐48%) of the resulting vergence movement also occurred during the saccades. These data indicate that on average about one‐quarter of the intra‐saccadic vergence change achieved during binocular viewing could have been due to accommodation stimuli perceived by one eye. The monocular results indicate that the direction of image misfocus (nearer vs. farther), which guides accommodation‐vergence, can be correctly distinguished for targets which are about 6 deg from the centre of the fovea, and that this assessment can be made within the 200‐300 ms latency for saccadic eye movements, and hence without trial‐and‐error refocusing. The binocular inequality of saccades during monocular viewing involved conspicuous subject‐specific right‐left asymmetries, as well as consistently positive within‐subject correlations between intra‐saccadic vergence change and finally realized accommodation‐vergence movement, and consistent correlations between phoria before the saccade and intra‐saccadic vergence change.
Characterization of the acetylcholine‐induced potassium current in rabbit cardiac Purkinje fibres.
Authors: Carmeliet E , Mubagwa K
Published: December 2014

Acetylcholine (ACh) induces a K+ current in rabbit cardiac Purkinje fibres. The question was studied whether ACh produces this effect by modifying the properties of K+ channels pre‐existing in the absence of the neurotransmitter or whether it induces the formation of a different type of K+ channels. The relaxation properties of the ACh‐induced current and its blockade by Cs+ and Ba2+ have been investigated using voltage clamp. During hyperpolarizing or depolarizing voltage pulses of moderate amplitude, the ACh‐induced current is time independent. For large voltage pulses, time‐dependent changes of the ACh‐induced current are observed. These latter changes can be explained by intracellular K+ accumulation/depletion phenomena or by the effects of ACh on time‐dependent currents (e.g. the late outward current, ix). Cs+ and Ba2+ block the ACh‐induced current. The block produced by 20 mM‐Cs+ is instantaneous and increases with hyperpolarization, i.e. it is voltage dependent. The block produced by Ba2+ at high concentrations (greater than 1 mM) is also instantaneous but complete at all potentials studied, and thus voltage independent. At these concentrations, either ion also blocks the background inward rectifier (iK1) current in a similar way. Low [Ba2+] (less than 0.1 mM) cause a block of the ACh‐induced current which is instantaneous and little voltage dependent. The block of iK1 in contrast is time and voltage dependent for the same concentrations. These results indicate that the ACh‐induced K+ current is different from the background iK1 current.
Stimulation of pulmonary C fibres decreases coronary arterial resistance in dogs.
Authors: Ordway G A , Pitetti K H
Published: December 2014

A constant‐flow preparation was used to assess coronary arterial resistance while activating pulmonary C fibres in chloralose‐anaesthetized dogs. A Gregg cannula was passed through the left common carotid artery until the tip fitted snugly in the left circumflex coronary artery. The cannula was perfused with blood from the left femoral artery and blood flow through the cannula was maintained constant with a perfusion pump. Perfusion pressure in the coronary artery was measured from a side arm in the cannula, and resistance in that vessel was calculated as the ratio of pressure to blood flow. Capsaicin (10‐20 micrograms/kg), injected into the right jugular vein, produced significant (P less than 0.05) decreases in heart rate, systemic arterial pressure, coronary arterial pressure and coronary arterial resistance. These responses were abolished by bilateral vagotomy. Neither left atrial injections of capsaicin nor acutely decreasing the systemic arterial pressure by occluding the inferior vena cava had a significant effect on the coronary arterial pressure or resistance. Additionally, overdrive pacing of the heart had no effect on the reflex decreases in coronary arterial pressure and resistance that were evoked when capsaicin was injected into the jugular vein. alpha‐Adrenergic blockade reduced the reflex decrease in coronary arterial pressure and resistance evoked by capsaicin by 31 and 38%, respectively. Combined alpha‐adrenergic and cholinergic blockade reduced the reflex decreases in both coronary arterial pressure and resistance by approximately 89%. These results indicate that activation of pulmonary C fibres produces a reflex decrease in coronary arterial resistance, and that this response is due to the combined effects of increased parasympathetic cholinergic activity and withdrawal of alpha‐adrenergic tone.
Synaptic excitation in cultures of mouse spinal cord neurones: receptor pharmacology and behaviour of synaptic currents.
Authors: Nelson P G , Pun R Y , Westbrook G L
Published: December 2014

Fast monosynaptic excitatory post‐synaptic potentials between spinal cord neurones in cell culture (s.c.‐s.c. e.p.s.p.s) were studied with current‐clamp and two‐electrode voltage‐clamp methods. The reversal potential, response to acidic amino acid antagonists, and behaviour of the synaptic current were examined. The amplitude of the e.p.s.p. increased with membrane potential hyperpolarization and decreased with depolarization. The reversal potential of the e.p.s.p. was +3.8 +/‐ 2.5 mV (mean +/‐ S.E. of mean). The reversal potential for responses to ionophoretically applied L‐glutamate and L‐aspartate was also near 0 mV. The acidic amino acid antagonist, cis‐2,3‐piperidine dicarboxylic acid (PDA, 0.25‐1.0 mM) reversibly antagonized the monosynaptic e.p.s.p.s as well as responses to kainate (KA) or quisqualate (QA). The selective N‐methyl‐D‐aspartate antagonist, (+/‐) 2‐amino‐5‐phosphonovaleric acid (APV), had little effect on either the monosynaptic e.p.s.p.s or responses to QA or KA at concentrations that abolished responses to L‐aspartate. Under voltage clamp, the peak synaptic current (e.p.s.c.) was linearly related to the membrane potential, increasing in amplitude with hyperpolarization and decreasing with depolarization from the resting potential. The decay of a somatic e.p.s.c. was well fitted by a single exponential function with a time constant of 0.6 ms at 25 degrees C. E.p.s.c.s which had proximal dendritic locations had decay time constants of 1‐2 ms. The decay time constant was voltage‐insensitive between ‐80 and +10 mV. We suggest that an acidic amino acid receptor other than that for NMDA mediates excitatory transmission at the s.c.‐s.c. synapse; and that the underlying conductance mechanism is voltage insensitive with an estimated mean channel lifetime of less than 1 ms.
Cyclic adenosine 3',5'‐monophosphate mediates beta‐receptor actions of noradrenaline in rat hippocampal pyramidal cells.
Authors: Madison D V , Nicoll R A
Published: December 2014

Intracellular recordings were made from rat hippocampal CA1 pyramidal neurones in the in vitro slice preparation to study the actions of cyclic adenosine 3',5'‐monophosphate (cyclic AMP). Application of the membrane permeant analogue of cyclic AMP, 8‐Br cyclic AMP caused a small depolarization of the resting membrane potential accompanied by an increase in membrane input resistance and also reduced the amplitude of depolarization‐evoked calcium‐activated potassium after‐hyperpolarizations (a.h.p.s.). 8‐Br cyclic AMP reduced calcium‐activated a.h.p.s but did not reduce calcium action potentials in these cells. 8‐Br cyclic AMP also reduced action potential frequency accommodation. The effects of 8‐Br cyclic AMP were not mimicked by cyclic AMP applied extracellularly but were imitated by intracellular injections of cyclic AMP. Activation of the endogenous adenylate cyclase of pyramidal cells either by intracellular injection of the stable guanosine 5'‐triphosphate (GTP) analogue guanylyl‐imidodiphosphate, or by extracellular application of forskolin, reduced the a.h.p. and accommodation. Reducing phosphodiesterase activity with application of either 3‐isobutyl‐1‐methylxanthine or Ro20‐1724 reduced the amplitude of the a.h.p. and potentiated the a.h.p.‐blocking action of noradrenaline. Reducing adenylate cyclase activity by application of SQ22,536 slightly increased the amplitude of the (a.h.p.) and reduced the a.h.p.‐blocking action of noradrenaline. We conclude that the beta‐receptor actions of NA on hippocampal CA1 pyramidal cells are mediated by intracellularly produced cyclic AMP.
Voltage‐gated potassium conductance in human T lymphocytes stimulated with phorbol ester.
Authors: Deutsch C , Krause D , Lee S C
Published: December 2014

The whole‐cell patch‐clamp method was used to study the voltage‐gated K+ conductance of human peripheral blood T lymphocytes. After entry into whole‐cell recording mode, there are time‐dependent changes in some properties of the conductance. Over the first 10‐30 min, the threshold for activation shifts about 10 mV more negative, and the rates of activation and inactivation increase. Inactivation is less strongly voltage dependent than activation or deactivation. Lymphocytes were stimulated to proliferate in culture with the tumour promoter 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). No changes in K+ conductance were observed in the first few hours of TPA stimulation. At 24 h after mitogen addition, TPA‐treated cells were found to have 1.7‐fold greater average voltage‐gated K+ conductance than unstimulated control cells. At 48 h, TPA‐stimulated cells had the same average K+ conductance as at 24 h, even though the cells were now much increased in size, as measured by cell capacitance. DNA synthesis by cultures stimulated with TPA, phytohaemagglutinin or succinyl concanavalin A was depressed by the addition of 0.1 mM‐quinine at any point in the culture period. In the first 20 h after mitogen addition, DNA synthesis was more effectively inhibited by quinine than if the drug were added later. Cell proliferation was equally sensitive to quinine regardless of mitogen.
Electrophysiology of smooth muscle of the small intestine of some mammals.
Authors: Hara Y , Kubota M , Szurszewski J H
Published: December 2014

Intracellular recordings were made from cells located in the longitudinal, inner and outer circular muscle layers of the dog, cat, rabbit, opossum and human small intestine. In whole‐thickness preparations in all five species, longitudinal muscle cells generated slow waves and spikes. However, in isolated longitudinal muscle preparations, all cells tested were electrically silent. In whole‐thickness and in isolated preparations, cells in the inner circular muscle layer generated spontaneous spikes superimposed on slow potentials. However, the occurrence of spikes and slow potentials was more regular in whole‐thickness preparations. In whole‐thickness preparations, cells in the outer circular muscle layer generated slow waves which were coupled with phasic contractions. However, in isolated outer circular muscle preparations, all cells tested were electrically silent and spontaneous phasic contractions were absent. In whole‐thickness preparations, non‐neural cells located on the serosal side of the outer circular muscle layer generated slow waves. The data suggest that spontaneous slow waves of the small intestine of the dog, cat, rabbit, opossum and human are generated in non‐neural cells located between the longitudinal and outer circular muscle layer and by non‐neural cells located between the outer and inner circular muscle layers.
A study of intracellular calcium oscillations in sheep cardiac Purkinje fibres measured at the single cell level.
Authors: Eisner D A , Valdeolmillos M
Published: December 2014

Previous work has shown that an elevation of intracellular calcium concentration [( Ca2+]i) produces spontaneous oscillations of [Ca2+]i. However the fact that the oscillations are unsynchronized between different cells has made it difficult to study them. We have therefore injected only one cell in a Purkinje fibre with aequorin in order to avoid these problems. The addition of strophanthidin (10 microM) produced an increase of mean aequorin light over the course of several minutes. During this period spontaneous oscillations of light developed and, with time, their frequency and magnitude increased. The oscillations could first be seen at levels of [Ca2+]i of less than 1 microM. The amplitude of the oscillations of [Ca2+]i could be up to 10 microM and was modulated at a slow rate (about 0.3‐0.5 Hz). This suggests that, even within one cell, different regions may oscillate at different frequencies. Elevating [Ca+]o, removing extracellular Na+, or depolarization increased the magnitude of the aequorin light oscillations. Converting the records to [Ca2+]i showed that this increase in the magnitude of the aequorin oscillations was accompanied by a real increase of mean [Ca2+]i and of the magnitude of the oscillations [Ca2+]i. The frequency of the oscillations increased up to a point but saturated at a maximum value of 3‐4 Hz. Since previous experiments have used the mean aequorin light to estimate mean [Ca2+]i, we have calculated the error produced in this calculation by the presence of [Ca2+]i oscillations. We estimate that the error is greatest at low levels of Ca2+ loading when the frequency of the oscillations is low. However, at higher Ca2+ loads, when the frequency is above 2 Hz, the error is probably less than 10%. If oscillations were produced by removal of external Na+ after the application of strophanthidin, then either ryanodine or caffeine abolished the oscillations. Furthermore, in both cases, the resulting steady level of [Ca2+]i was similar to the mean level before the addition of the drugs. In another series of experiments we examined the effects of these drugs on oscillations produced by the application of strophanthidin. Caffeine produced a transient increase in both the frequency of the oscillations and mean [Ca2+]i before abolishing the oscillations and decreasing [Ca2+]i to below the level in the absence of caffeine. In contrast ryanodine gradually decreased both the mean [Ca2+]i and the frequency until the oscillations were abolished. During this period of slowing of the oscillations their magnitude was often increased.
Sodium‐calcium exchange in the outer segments of bovine rod photoreceptors.
Authors: Schnetkamp P P
Published: December 2014

Intact rod outer segments (r.o.s.) isolated from bovine retinas were used to measure net Ca2+ fluxes using the optical Ca2+ indicator Arsenazo III. Ca2+ fluxes were observed, which could change the internal Ca2+ content of isolated r.o.s. by as much as 0.5 mM s‐1. The Ca2+ content of isolated intact r.o.s. was strongly dependent on the Na/Ca ratio in the isolation medium, and could be made less than 0.1 mol Ca2+ mol‐1 rhodopsin (zero Ca2+ in isolation medium) or up to 7 mol Ca2+ mol‐1 rhodopsin (zero Na+ in isolation medium). Ca2+ efflux from r.o.s. rich in Ca2+ was observed only when Na+ was added to the external medium (as opposed to any other alkali cation); in Ca2+‐depleted r.o.s. Ca2+ uptake required the presence of internal Na+ and was inhibited selectively by external Na+. These results suggest that Na‐Ca exchange across the plasma membrane operated freely in both directions and controlled the internal Ca2+ concentration in r.o.s. Na+‐stimulated Ca2+ efflux depended on the external Na+ concentration in a sigmoidal way. This suggests that the simultaneous binding of two Na ions is rate limiting for transport. In Ca2+‐depleted r.o.s. and in the absence of external Na+, 1 mol Ca2+ mol‐1 rhodopsin (or 3 mM‐total Ca2+) could be taken up within 1 min by intact r.o.s. at a free external Ca2+ concentration of about 1 microM. Only part of the internal Ca2+ was available for Na‐Ca exchange. The external Na+ and K+ concentration as well as the temperature were factors controlling the accessibility of internal Ca2+ to participate in Na‐Ca exchange. Ca2+ fluxes in r.o.s. with a permeabilized plasma membrane but intact disk membranes were very similar to those observed in intact r.o.s.; Na‐Ca exchange could operate in both directions across the disk membrane. In addition to Na‐Ca exchange, leaky r.o.s. also showed a guanosine 3', 5'‐cyclic monophosphate (cyclic GMP)‐induced Ca2+ release that was about 1/20 of the rate of Na‐Ca exchange. Na‐Ca exchange could release 1.5 mol Ca2+ mol‐1 rhodopsin from disks as compared with a cyclic‐GMP‐induced release of 0.15 mol Ca2+ mol‐1 rhodopsin.
Calcium‐dependent currents in cultured rat dorsal root ganglion neurones are inhibited by an adenosine analogue.
Authors: Dolphin A C , Forda S R , Scott R H
Published: December 2014

Dorsal root ganglion neurones from 2‐day‐old rats were grown in dissociated culture. The effect of the adenosine analogue 2‐chloroadenosine (2‐CA) was investigated on action potential duration and on Ca2+ current (ICa) activation. 2‐CA (0.5 microM) shortened both control action potentials and those prolonged by tetraethylammonium (TEA), Ba2+, or intracellular Cs+. This effect was prevented by two adenosine antagonists isobutylmethylxanthine (IBMX, 1‐2 mM) and 8‐phenyltheophylline (8‐PT, 2.5 microM). The inward current, ICa, recorded using the 'whole‐cell' patch‐clamp technique in medium containing 2.5 microM‐tetrodotoxin, 25 mM‐TEA and 2.5 mM‐Ba2+ was reduced by 2‐CA (0.05 microM). The activation of ICa was decreased, but its reversal potential was unchanged. The effect of 2‐CA was antagonized by IBMX (1 mM) and 8‐PT (1 microM). 2‐CA also reduced the large inward tail currents which occurred at the termination of the depolarizing voltage step command in a proportion of neurones. Brief application of 2‐CA (0.05 microM) did not affect the inward holding current required to maintain the cells at ‐80 mV. In the presence of TTX (2.5 microM) and Ca2+ (5 mM), 2‐CA decreased the activation of outward K+ currents caused by 5 s depolarizing voltage commands from ‐80 mV or ‐40 mV. The GABAB agonist (‐)‐baclofen (50‐100 microM) also shortened the action potential duration and reduced ICa. 8‐PT (1 microM) did not prevent the effect of baclofen on ICa. It is concluded that in cultured rat dorsal root ganglion neurones 2‐CA reduces ICa activation by a direct effect on an A1 adenosine receptor.
Projection of pulmonary rapidly adapting receptors to the medulla of the cat: an antidromic mapping study.
Authors: Davies R O , Kubin L
Published: December 2014

The activity of pulmonary rapidly adapting receptor (r.a.r.) neurones was recorded extracellularly in the nodose ganglion of the decerebrate cat. The receptors were identified by their rapid adaptation to 'ramp and hold' hyperinflations of the lung. The antidromic mapping technique was used to determine the sites of projection and branching patterns within the nucleus of the tractus solitarius (n.t.s.) of eleven r.a.r.s. The medulla was explored with a stimulating electrode to activate the r.a.r.s. antidromically. In each penetration, depth‐threshold measurements were made for each antidromic response characterized by a distinct latency. Using the anatomical sites of the minimum threshold points, the locations of central branches of individual r.a.r.s. were determined. The main axons of all of them coursed within the tractus solitarius (t.s.) at levels from 2 mm rostral to 0.5 mm caudal to the obex. The axonal conduction velocities within the t.s. were 6.2‐9.7 m/s, where the peripheral conduction velocities were 11.2‐20.4 m/s (28 degrees C). Different latencies of response evoked in a single penetration were considered to indicate branching. The densest branching was found in the ipsilateral commissural subnucleus of the n.t.s. at levels 0.3‐1.3 mm caudal to the obex and, to a lesser degree, in the contralateral commissural subnucleus. All r.a.r.s. sent a few branches to the medial n.t.s. rostral to the obex. Four r.a.r.s. ramified in the ventrolateral n.t.s. where inspiratory cells are located. Depth‐threshold graphs were interpolated by best fitting parabolic equations: Ith = Ad2 + Bd + C; where Ith is the threshold current, d the corresponding depth of stimulation, and A, B and C are coefficients. Coefficient A is a measure of steepness of the parabola. The A coefficients were inversely related to the conduction velocity (v) of the stimulated branch. An analysis of the data from the present study (v = 5.0‐9.7 m/s) combined with data from the literature (v = 2.2‐85 m/s) led to a simple relationship between the A coefficient and the conduction velocity of the stimulated fibre: A = 6500/v, where A is expressed in microA/mm2 and v is expressed in m/s. Within the range 3‐35 m/s, the formula is useful in predicting the effective current spread when the conduction velocity is known, or to estimate the conduction velocity from the shape of a depth‐threshold curve. Two slowly adapting pulmonary stretch receptors (p.s.r.s) were studied.(ABSTRACT TRUNCATED AT 400 WORDS)
gamma‐Aminobutyric acid hyperpolarizes rat hippocampal pyramidal cells through a calcium‐dependent potassium conductance.
Authors: Blaxter T J , Carlen P L , Davies M F , Kujtan P W
Published: December 2014

Application of gamma‐aminobutyric acid (GABA) to the dendrites of CA1 pyramidal cells in hippocampal slices produced depolarizing and hyperpolarizing responses. Picrotoxin (50 microM) blocked the depolarizing response of the dendrites to GABA but not the hyperpolarizing responses of the dendrites. The hyperpolarizing response of the cell body to GABA was reduced but not blocked by picrotoxin, suggesting the presence of a complex response at the cell body. The depolarizing response of the dendrites and the hyperpolarizing response of the cell body appeared to be at least partly Cl‐ dependent as they were respectively increased and decreased in size in low‐Cl‐ artificial cerebrospinal fluid (ACSF), while the hyperpolarizing response of the dendrites was unaffected. The hyperpolarizing response of the dendrites was increased in amplitude in low‐K+ ACSF and the extrapolated reversal potential of the response became more negative, suggesting that the response was K+ dependent. The hyperpolarizing response of the dendrites was decreased in size in high‐K+ ACSF and could be readily inverted by current injection. The reversal potential became less negative in high‐K+ ACSF in a similar manner to that of the slow after‐hyperpolarization following a train of spikes, indicating that the response was a K+ conductance. Perfusion of the slice with normal or 0‐Ca2+ ACSF containing Cd2+ or Mn2+ blocked synaptic transmission, increased spike duration and blocked the slow phase of the spike after‐hyperpolarization (a.h.p.). This latter potential is thought to be mediated by a Ca2+‐dependent K+ conductance. Later, the hyperpolarizing response of the dendrites to GABA was blocked without an effect on the other GABA responses. Pressure application of Cd2+ (0.2‐2 mM) onto the surface of the slice rapidly reduced or blocked the slow a.h.p. and the dendritic hyperpolarizing response to GABA. Intracellular injection of EGTA rapidly blocked the slow phase of the a.h.p. and then later blocked or reduced the dendritic hyperpolarizing response to GABA. We conclude that the hyperpolarizing response of the dendrites to GABA is mediated by a Ca2+‐dependent K+ conductance.
The interrelation of neural discharge, intra‐articular pressure, and joint angle in the knee of the dog.
Authors: Ferrell W R , Nade S , Newbold P J
Published: December 2014

Single‐ and multi‐unit recordings were obtained from the medial articular nerve (m.a.n.) of knee joints in the anaesthetized dog. The single‐unit recordings were confined to low threshold (group I and II) articular mechanoreceptors. Multi‐unit recordings revealed that the m.a.n. discharge was maximal in extension, submaximal in flexion, and minimal at intermediate angles, i.e. a U‐shaped profile. Subatmospheric intra‐articular pressures do not appear to influence the m.a.n. discharge. Intra‐articular infusion of even small quantities of fluid, although not affecting the U‐shaped profile, reversed the m.a.n. discharge pattern with maximum neural activity occurring in flexion and being submaximal in extension. Recordings from single units indicated that the enhanced discharge after fluid infusion was a result of increased discharge frequency and 'recruitment' of individual afferents.
Effects of light reversal on the circadian pattern of motor activity and voltammetric signals recorded in rat forebrain.
Authors: Fillenz M , O'Neill R D
Published: December 2014

To investigate the functional relationships between the circadian changes in rat motor activity and changes in the extracellular concentration of ascorbic acid and homovanillic acid (HVA) monitored in the striatum and nucleus accumbens, reversal of the light/dark cycle was used to disturb the pattern of motor activity. Microcomputer‐controlled linear sweep voltammetry with carbon‐paste electrodes was used to continuously monitor circadian changes in the ascorbate signal and the HVA signal simultaneously in nucleus accumbens and striatum over a 13 day period in unrestrained rats; total motor activity for each animal was also recorded. Regression analyses were carried out on each day's data to investigate the relationships between motor activity and the two voltammetric signals. During days 1‐5, the lighting was on normal 12/12 light/dark cycle and high correlations were observed. Reversal of the light/dark cycle on day 6 caused an immediate change in the pattern of motor activity and electrochemical signals; by days 7‐8 after light reversal the relationships between lighting, ascorbate, HVA and motor activity were reestablished under the new lighting conditions. During the intervening period, however, there was a complete breakdown in some of the correlations. The findings are discussed in the light of the hypothesis that changes in brain extracellular ascorbate reflect changes in the release of excitatory amino acids, and in terms of a recent model of the role, in the control of motor activity, for cortical and mesencephalic inputs to forebrain subcortical regions.
Non‐cholinergic neurotransmission and the effects of peptides on the urinary bladder of guinea‐pigs and rabbits.
Authors: Callahan S M , Creed K E
Published: December 2014

Supramaximal repetitive field stimulation with pulses of 50 microseconds produced contraction of strips of bladder from rabbits and guinea‐pigs. Atropine reduced responses at all frequencies to about 60% and the contraction was poorly maintained. With the double sucrose‐gap technique large excitatory junction potentials (e.j.p.s) were recorded with superimposed action potentials. These were not reduced by atropine or phentolamine. Substance P (SP) produced contraction and increased the frequency of spontaneous action potentials recorded with micro‐electrodes from bladder strips. Vasoactive intestinal peptide (VIP) produced relaxation and slowed action potentials in rabbit but had no effect in guinea‐pig; neurotensin, somatostatin and leu‐enkephalin were without action in either species. When the tissue was kept in contact with SP, a second application after 10 min produced only a small contraction suggesting that SP receptors were desensitized. However, the electrical response to field stimulation was unchanged and the mechanical response was increased. Chymotrypsin reduced mechanical responses to SP but had no effect on responses to field stimulation. The SP analogue, D‐Pro2, D‐Phe7, D‐Trp9‐SP, had no effect on responses to SP or to field stimulation. It is concluded that the bladder receives excitatory non‐cholinergic innervation which is responsible for a large excitatory junction potential and contraction. Although SP can contract the detrusor muscle, it is unlikely that it is an excitatory transmitter or that any of the five peptides act as modulators of transmitter release.
Taurine transport associated with cell volume regulation in flounder erythrocytes under anisosmotic conditions.
Authors: Fugelli K , Thoroed S M
Published: December 2014

The taurine transport of flounder erythrocytes is associated with a cell volume regulation in anisosmotic media. An osmolality reduction leads to a cell volume increase, which is followed by a volume readajustment towards the original level. A 75 mosM reduction is accompanied by a 33 mumol g dry wt.‐1 reduction in the cellular taurine content. The reduction in osmolality activates the taurine release mechanism by transiently increasing the rate coefficient for taurine efflux. The rate coefficient for taurine influx is similarly stimulated. This influx is mediated by a Na+‐independent transport system. The concomitant activation of influx and efflux suggests a coupling between these two systems. Higher taurine efflux and influx rate coefficients which decayed more slowly with time were measured in cells suspended in Na+‐free (choline replacement) media than in the presence of Na+. This suggests that Na+ may play a role in the taurine release mechanism. Noradrenaline induced a cellular swelling at normal osmolality (330 mosM), but had only a minor effect on the taurine efflux and influx and the cellular taurine content. Urea‐induced cellular swelling at normal osmolality initiated a volume regulatory process and activated the taurine release mechanism, similarly to an osmolality reduction. These results show that osmolality reduction and cellular swelling are no prerequisites for the activation of the taurine release mechanism and the cell volume readajustment. It is suggested that the dimension of an intracellular solute compartment determines the activation level of this mechanism.
Action potentials, macroscopic and single channel currents recorded from growth cones of Aplysia neurones in culture.
Authors: Belardetti F , Schacher S , Siegelbaum S A
Published: December 2014

Action potentials, macroscopic ionic currents and single channel currents were recorded from growth cones of Aplysia right upper quadrant (r.u.q.) cells in culture, using the patch‐clamp technique. Recordings were obtained from both intact growth cones and from growth cones that had been mechanically isolated from the rest of the neurone. In current‐clamp mode, greater than half of the isolated growth cones display an all‐or‐none action potential when depolarized above 0 mV with outward current pulses. The remaining growth cones display only a graded depolarization that is unaffected by tetrodotoxin (TTX). In whole‐cell voltage clamp almost all isolated growth cones display a rapidly activating and inactivating inward current followed by a delayed outward current in response to depolarizations positive to ‐20 mV. The rapid inward current reverses direction at around +70 to +80 mV and is completely suppressed by 100 microM‐TTX, which suggests that this current is carried by the fast Hodgkin‐Huxley sodium current channels. The delayed outward current appears to result from the activation of both the delayed rectifier potassium current, IK, and the calcium‐activated potassium current, IC. The growth cones do not display any prominent early transient outward current, IA. The sodium current, INA, was studied in isolation by substituting caesium for potassium ions in the pipette solution. INa is half‐inactivated at a holding potential of ‐36 mV, reaches half‐maximal activation with a depolarization to 0 mV, and has a mean peak current density of 13 microA/cm2. The time course of inactivation is well described by a single exponential (tau = 3 ms at 0 mV). In cell‐attached patches, a rapidly activating and inactivating inward current channel was recorded with an average unit conductance of 6.9 pS. The activation and inactivation parameters of the ensemble averaged current closely match the measured values from the macroscopic sodium current. At very positive potentials we recorded a voltage‐dependent outward current channel with a conductance of around 35 pS. No significant inward calcium current was observed in whole‐cell measurements and few single calcium channel currents were measured in cell‐attached patches, suggesting a sparse distribution of calcium channels in the r.u.q. growth cones.
Comparative development of end‐plate currents in two muscles of Xenopus laevis.
Authors: Kullberg R , Owens J L
Published: December 2014

The development of miniature end‐plate currents (m.e.p.c.s) was studied in the superior oblique and interhyoideus muscles of Xenopus laevis. An analysis of m.e.p.c. decays shows that each muscle possesses its own characteristic programme of end‐plate current development. In the superior oblique, the exponential decay constants of m.e.p.c.s were initially about 3 ms; they declined within half a day to 1 ms and remained at that value for six weeks. They then gradually became longer, reaching a mean value of 1.7 ms at late metamorphosis. In the interhyoideus, m.e.p.c. decay constants were initially about 6 ms. They declined in less than one day to a mean value of 2.6 ms and remained there for the following seven weeks. Upon completion of metamorphosis, the decay constants underwent a further decrease to about 1 ms. In both muscles, the changes in m.e.p.c. decays were correlated with developmental changes in muscle contraction speeds, as measured by maximum twitch frequencies. The above changes in end‐plate currents in the superior oblique and interhyoideus muscles are discussed in terms of the development of acetylcholine receptor channel gating and acetylcholinesterase activity.
D‐galactose transport in rat intestinal brush border membrane vesicles studied with a molecular‐sieve technique.
Authors: Bronk J R , Hastewell J G
Published: December 2014

A technique using G‐50 Sephadex molecular‐sieve chromatography has been developed to study both the accumulation of transported solutes by rat intestinal brush border membrane vesicles and the wash‐out of these solutes from pre‐loaded vesicles. The extent to which D‐galactose was taken up into the brush border membrane vesicles was dependent on the medium osmolarity and this dependence was significantly reduced (P less than 0.01) by pre‐treating the vesicles with the non‐ionic detergent Triton X‐100. The transport of D‐galactose into the brush border membrane vesicles was sodium dependent, electrogenic and phloridzin sensitive. It is, therefore, qualitatively similar to D‐glucose transport into brush border membrane vesicles. The wash‐out of D‐galactose from pre‐loaded brush border membrane vesicles was inhibited by phloridzin and accelerated by the presence of an outwardly directed sodium gradient. D‐Galactose was released from the pre‐loaded brush border membrane vesicles more slowly than D‐glucose and this difference was consistent with the higher overshoot found for D‐galactose during the transport of the sugars into the vesicles.
Interaction between the soma and the axon terminal of retinal horizontal cells in Cyprinus carpio.
Authors: Yagi T
Published: December 2014

Intracellular recordings were made from the monophasic horizontal cells of the carp retina which are known to respond with a sustained hyperpolarization to all visible monochromatic light. The receptive field of each subcellular structure, the soma and the axon terminal, was determined using a long narrow slit of light. Somata and axon terminals showed receptive fields that encompassed almost the entire retina. This observation suggests that each aggregate of the subcellular parts forms a synctial structure. However, with increasing distance from the slit, the response peak decayed more steeply in somata than in axon terminals. The spatial decline of the peak consisted of two exponential functions in somata, while a single exponential function in axon terminals. The length constant of the axon terminal was similar to the larger length constant revealed in the soma. This finding suggests an electrical communication at work between the soma and the axon terminal. A quantitative account was made in light of a discrete resistive network model which consists of a pair of syncytia coupled through connecting axons; one represents the contiguous layer of somata and the other the contiguous layer of axon terminals. Relevant response properties computed from the model analysis were in satisfactory agreement with experimental data. It was concluded that the soma and the axon terminal of the horizontal cell are electrically connected in the cyprinid retina.