bluuebunny/crossref_metadata_2025 huggingface dataset:
Human smooth and saccadic eye movements during voluntary pursuit of different target motions on different backgrounds.
Authors: Collewijn H , Tamminga E P
Published: December 2014

Horizontal and vertical eye movements of ten human subjects were recorded with a scleral induction‐coil technique during voluntary pursuit of sinusoidal, triangular and pseudo‐random target motions of different frequency, amplitude and dimensionality upon a dark, diffuse or structured background. Data processing included separation of the composite eye movement into a cumulative smooth and saccadic displacement, computation of gain and phase of the composite and smooth eye movements with respect to the target movement and analysis of retinal position error. Pursuit eye movements were never completely smooth. Smooth pursuit gain was always lower than 0.95 and saccades were used to supplement the smooth eye movements in pursuing the target with the proper amplitude. The gain of composite eye movements was about unity for sinusoidal target motions and ramps; it exceeded unity for the highest frequency components in a pseudo‐random motion. The gain of the smooth eye movements decreased monotonously whenever target velocity increased. It was higher for single sine waves than for a pseudo‐random motion, however, with pseudo‐random motion it was relatively higher for the higher frequency components. Phase lags were in general smaller for single sine waves than for pseudo‐random motion, but for the latter a phase lead of the smooth component was consistently found for the lower frequency components. During pursuit of a rhomboid trajectory, the eye movements showed directional errors which are interpreted as anticipatory behaviour. The distribution of the retinal error was symmetrical around zero. Its standard deviation varied between about 0.2 and 1.3 degrees; it was about proportional to target velocity and inversely proportional to smooth pursuit gain. It was limited by the insertion of saccades which were in general corrective. The influence of a diffusely illuminated background was minimal. A structured background inhibited smooth pursuit in the horizontal direction by about 10% and in the vertical direction by about 20%. This deficit of smooth pursuit was fully compensated by the insertion of more saccades and had no consequences for the standard deviation of the retinal error. The type of structure of the background was only of marginal importance. Horizontal pursuit was in general slightly smoother and more precise than vertical pursuit.
Depolarization of feline primary afferent fibres by acidic amino acids.
Authors: Curtis D R , Headley P M , Lodge D
Published: December 2014

When administered micro‐electrophoretically into the spinal grey matter of cats anaesthetized with pentobarbitone, acidic amino acids known to be neuronal excitants lower the threshold of electrically stimulated muscle and cutaneous primary afferent fibres and terminations. This depolarizing effect was not observed with fibres stimulated in the white matter. Depolarization by micro‐electrophoretic potassium and excitant amino acids appeared not be be associated with an alteration in terminal membrane conductance since there was no change in synaptically evoked primary afferent depolarization. Excitant amino acid depolarization was not blocked by the gamma‐aminobutyric acid antagonist bicuculline methochloride, but was reduced by selective excitant amino acid antagonists. The results are discussed in relation to the probable absence of specific excitant amino acid receptors on afferent terminals, the depolarizing effect of the amino acids on myelinated fibres and non‐myelinated terminals being more likely a consequence of changes in the extracellular medium associated with the depolarization and firing of neurones.
Inhibition of gastric motility induced by hepatic portal injections of D‐glucose and its anomers.
Authors: Sakaguchi T , Shimojo E
Published: December 2014

Intragastric pressures were recorded in bilaterally adrenalectomized male rats with insulin hypoglycaemia. A significant depression in intragastric pressure was noted following the administration of D‐glucose injected into the hepatic portal vein but not after the administration of L‐glucose, D‐mannose, D‐fructose, D‐galactose, D‐xylose or D‐arabinose. The reduction in intragastric pressure induced by the portal administration of D‐glucose was not reproduced following selective division of the hepatic branch of the vagus nerve. Of the three anomeric forms of D‐glucose used (alpha‐D‐glucose, equilibrated D‐glucose and beta‐D‐glucose), beta‐D‐glucose was most potent in reducing the intragastric pressure. These results suggest that the vagal afferents may convey information concerning glucose concentration in the portal vein to the central nervous system, and that the activation of such afferents may modulate gastric motility which is dependent on the anomeric stereospecificity of D‐glucose.
Characterization of a slow cholinergic post‐synaptic potential recorded in vitro from rat hippocampal pyramidal cells.
Authors: Cole A E , Nicoll R A
Published: December 2014

Intracellular recording from CA1 pyramidal cells in the hippocampal slice preparation was used to compare the action of exogenously applied acetylcholine (ACh) and cholinomimetics to the effect of electrically stimulating sites in the slice known to contain cholinergic fibres. ACh depolarized pyramidal cells with an associated increase in input resistance, blocked a calcium‐activated potassium conductance (GK(Ca], and blocked accommodation of action potential discharge. All of these actions were blocked by the muscarinic antagonist, atropine. Repetitive electrical stimulation of stratum (s.) oriens evoked a series of fast excitatory post‐synaptic potentials (e.p.s.p.s) followed by an inhibitory post‐synaptic potential. These potentials were followed by a slow e.p.s.p. that lasted 20‐30 s. The slow e.p.s.p. was selectively enhanced by eserine and blocked by atropine. Ionophoretic application of ACh closely mimicked the time course of the slow e.p.s.p. The slow e.p.s.p. was blocked by tetrodotoxin and cadmium, indicating that it was dependent on propagated action potentials and on calcium. Considerably higher stimulus strengths were needed to elicit a slow e.p.s.p. than to elicit the earlier synaptic potentials. The size of the slow e.p.s.p. was markedly increased by repetitive stimulation. Stimulation of the alveus, s. oriens, s. pyramidale and fimbria all evoked a slow e.p.s.p., while stimulation of s. radiatum was relatively ineffective. The input resistance of the cell increased during the slow e.p.s.p. Hyperpolarizing the cell decreased the size of the slow e.p.s.p. and at membrane potentials of ‐70 mV or greater, little response was recorded. Stimulation of s. oriens blocked GK(Ca) and accommodation of action potential discharge. These effects, which could be seen in the absence of any change in membrane potential, were enhanced by eserine and blocked by atropine. The present electrophysiological results establish that CA1 pyramidal cells receive a cholinergic input and demonstrate that this input can dramatically alter the firing properties of these neurones for tens of seconds in the absence of any marked effect on membrane potential. Such an action contrasts with previously characterized synaptic potentials in this region of the brain.
A voltage‐gated hydrogen ion current in the oocyte membrane of the axolotl, Ambystoma.
Authors: Barish M E , Baud C
Published: December 2014

Membrane currents in the immature oocyte of the urodele amphibian Ambystoma were studied using the two‐micro‐electrode voltage‐clamp technique. A current carried by H ions (IH) constituted the major portion of outward current activated by depolarizations from the resting voltage (about ‐60 mV). Net inward current was not observed at this developmental stage. The reversal potential for IH measured from tail currents obtained in two step voltage‐clamp experiments shifted by 54 mV per unit change in external pH between pH 6.9 and 8.4. The reversal potential at pH 7.4 was not affected by changes in external K or Cl concentrations. A small change in reversal potential was observed with removal of external Na. The amplitude of IH was not affected by removal of external Ca (Mg or Sr substitution). Ca ionophore A23187 shifted the current‐voltage relation towards negative voltages. Activation of IH did not appear to depend on Ca influx. The instantaneous current‐voltage relation for IH, measured from tail currents at approximately equal internal and external H ion concentrations, was linear between ‐40 and +30 mV. The steady‐state conductance‐voltage relationship was sigmoidal with membrane voltage, and, at pH 7.4, was one‐half maximum at about +15 mV (V1/2). The time courses of activation and deactivation were proportional to 1‐exp (‐t/tau). A plot of time constant (tau) against voltage was bell‐shaped, with a maximum near V1/2. These results suggested that the activation of IH is voltage dependent. Increases in the external H ion concentration shifted the conductance‐voltage and time constant‐voltage relations in parallel towards positive voltages. The magnitude of these shifts showed a lower saturation near pH 9. Low concentrations of external Cd (10‐300 microM) reduced current amplitude by shifting the current‐voltage relation in the positive direction. Cd also reduced the limiting slope conductance. These effects were partially reversible.
Cyclic nucleotide‐dependent enzyme secretion in the rat lacrimal gland.
Authors: Dartt D A , Donowitz M , Joshi V J , Mathieu R S , Sharp G W
Published: December 2014

To characterize the role of cyclic nucleotides in secretion of enzymes by the lacrimal gland, pieces of rat exorbital glands were perfused with (1) 8‐bromoadenosine‐3',5'‐cyclic monophosphate (8 Br cyclic AMP), (2) 8‐bromoguanosine‐3',5'‐cyclic monophosphate (8 Br cyclic GMP), (3) forskolin, a stimulator of adenylate cyclase activity, (4) 3‐isobutyl‐1‐methylxanthine (IBMX), an inhibitor of phosphodiesterase activity, or (5) carbachol, a cholinergic agonist. As a measure of enzyme secretion, timed collections of the perifusate effluent were analysed for peroxidase, an enzyme secreted by the lacrimal gland. Control peroxidase secretion was 0.3‐0.9 (u./min per milligram protein). Peroxidase secretion was stimulated by 8 Br cyclic AMP (1 mM), but not by 8 Br cyclic GMP (1 mM). A 2‐fold increase was detected. Peroxidase secretion was also stimulated by forskolin (60 microM), IBMX (1 mM), and the cholinergic agonist carbachol, which all stimulated peroxidase secretion 2‐or 3‐fold. The effect of maximally effective concentrations of IBMX (1 mM) and carbachol (0.1 mM) on secretion was additive. Finally, Ca2+ depletion in the presence of EGTA (1 mM) inhibited both IBMX‐and carbachol‐induced secretion by 45% and 60% respectively. We conclude that cyclic AMP, but not cyclic GMP, can stimulate lacrimal gland enzyme secretion. Cyclic AMP appears to utilize a pathway separate from but convergent with cholinergic agonists.
Vago‐vagal reflexes to the colon of the anaesthetized ferret.
Authors: Collman P I , Grundy D , Scratcherd T , Wach R A
Published: December 2014

Electrical stimulation of the central end of the vagal communicating branch in the thorax at frequencies between 2 and 20 Hz elicited, after a latency of 7.2 +/‐ 0.8 s, large‐amplitude colonic contractions. 5 Hz stimulation gave near maximal contractions and, because vomiting was more likely to occur at higher stimulus frequencies, was used as the standard stimulus for subsequent experiments. At this frequency the peak colonic contraction was 6.5 +/‐ 0.9 kPa. Following atropine the characteristics of the response to central vagal stimulation differed from that seen before atropinization. The latency was longer (45.7 +/‐ 8.2 s) and the amplitude greatly attenuated (0.7 +/‐ 0.2 kPa). Cooling the vagus nerves to 2 degrees C at a level either above or below the site of stimulation completely abolished both the cholinergic and the atropine‐resistant colonic responses to central vagal stimulation. These results are consistent with the vagus containing two motor pathways to the colon which are reflexly stimulated by a vagal afferent input. The functional significance of these reflexes is discussed.
Discharges of Purkinje cells in the paravermal part of the cerebellar anterior lobe during locomotion in the cat.
Authors: Armstrong D M , Edgley S A
Published: December 2014

Extracellular recordings were made from 124 Purkinje cells in the paravermal part of lobule V of the cerebellum in cats walking steadily at a speed of 0.5 m/s on a moving belt. All cells tested had a tactile receptive field from which simple spikes could be evoked and 96% of these were on the ipsilateral forelimb. Seventy‐six of the cells were also studied whilst the animals sat or lay quietly without movement. Complex spikes were discharged at 1‐2/s and these were accompanied by simple spikes in fifty‐nine cells (78%); in the remaining cells there were no or few simple spikes. The over‐all mean discharge rate (including both types of spike) was 37.8 +/‐ 27 impulses/s (+/‐ S.D.). During locomotion all cells discharged both types of spike and the over‐all mean rate was 57.6 +/‐ 29 impulses/s (+/‐ S.D.). In all cells but one, the frequency of the simple spikes was modulated rhythmically in time with the stepping movements but the phasing relative to the step cycle varied widely between cells. Peak rates also varied widely, the average being 91.5 +/‐ 44 impulses/s (+/‐ S.D.). Most cells (63%) generated one period of accelerated discharge per step but others generated two (35%) or three (2%) such periods. Despite the individual variations in discharge timing the population as a whole was considerably more active during the swing than the stance phase of the step cycle in the ipsilateral forelimb (68 impulses/s as compared with 49 impulses/s on average). Thirty‐four cells were electrophysiologically identified as lying in the c1 zone of the cortex and twenty‐five as being in the c2 zone (nomenclature of Oscarsson, 1980). During locomotion, the population activity in the two zones differed slightly: activity in the c1 population was phase advanced by approximately one‐tenth of the step cycle. The results are discussed, with particular emphasis on the finding that population activity in the Purkinje cells of the c1 zone fluctuated during the step cycle in parallel with that in the part of nucleus interpositus to which they project.
Post‐tetanic depression of spinal reflexes in the rabbit and the possible involvement of opioid peptides.
Authors: Catley D M , Clarke R W , Pascoe J E
Published: December 2014

In spinally transected, decerebrated rabbits, the reflex evoked in the ankle extensor gastrocnemius medialis by stimulation of the ipsilateral sural nerve was depressed for periods of 12‐45 min following tetanic stimulation of the high‐threshold afferents of the ipsilateral tibial, common peroneal, gastrocnemius medialis and sural nerves. It was unaffected by similar tetanic stimulation of ipsilateral saphenous or semitendinosus nerves, or of any nerve in the contralateral limb. The extension reflex between saphenous nerve and vastus lateralis was depressed after tetanic stimulation of saphenous nerve. Post‐tetanic depression was partially reversed by the opioid antagonist (‐)‐naloxone in a dose of 50 micrograms/kg I.V., implicating the involvement of endogenous opioids. The sural‐semitendinosus flexion reflex was depressed only by stimulation of the homonymous muscle nerve. It was enhanced for up to 20 min after iterative stimulation of the high‐threshold fibres of the ipsilateral sural nerve. This reflex was unaffected by tetanic stimulation of any of the other ipsilateral or contralateral nerves tested. Tetanic stimulation of high‐threshold afferents of hind‐limb nerves apparently stimulates the release of endogenous opioids within the spinal cord. It is proposed that this is brought about by the activation of enkephalin‐containing neurones in the superficial laminae of the dorsal horn.
Changes in benzodiazepine receptor binding as seen autoradiographically in the central nervous system of the spastic mouse.
Authors: Biscoe T J , Fry J P , Rickets C
Published: December 2014

Quantitative light‐microscope autoradiography has been used to compare the specific, clonazepam‐displaceable binding of [3H]flunitrazepam, a photoaffinity label for the 1,4‐benzodiazepine receptor, in different regions of the brain and spinal cord of spastic mice and their unaffected littermates. Specific binding of [3H]flunitrazepam in the central nervous system of the spastic mouse showed significant increases in the anterior colliculus and pretectal area and in all laminae of the grey matter in the lumbar spinal cord. These results confirm homogenate binding assays suggesting an increased number of benzodiazepine receptors in the spinal cord of the spastic mouse. Possible sites are therefore provided at which disorders of function could arise, associated with changes seen at the gamma‐aminobutyric acid (GABA)‐benzodiazepine receptor complex in spinal cord homogenates from the mutant mouse spastic.
The kinetics of magnesium adenosine triphosphate cleavage in skinned muscle fibres of the rabbit.
Authors: Ferenczi M A , Homsher E , Trentham D R
Published: December 2014

The time course of magnesium adenosine triphosphate (Mg ATP) cleavage in chemically skinned muscle fibres of the rabbit was measured by a method in which Mg ATP cleavage was initiated by photolytic release of ATP from P3‐1‐(2‐nitro)phenylethyladenosine 5'‐triphosphate (caged ATP) and terminated by rapid freezing 50 ms to 8 s later. Up to 5 mM‐ATP was released following a single 50 ns laser pulse at 347 nm. Mg ATP cleavage was measured at 19 degrees C in the presence and absence of calcium ions, for fibres near rest length and stretched beyond overlap of the myofilaments. At full overlap and in the absence of calcium (less than 10(‐8) M) and nucleotide, the fibres developed rigor tension. Following the laser pulse the tension decreased to that of a relaxed fibre in two distinct phases. The first phase lasted about 40 ms and was followed by a second phase during which tension decreased to zero with an approximately exponential time course with a rate constant of 11 s‐1. In the presence of 2 X 10(‐5) M‐free calcium ions, the initial phase following the laser flash lasted approximately 13 ms, and was followed by an exponential rise of tension with a rate constant of 28 s‐1. The active tension reached by the muscle fibres was 54 kN/m2. For fibres stretched beyond overlap, no change in tension was observed following the release of Mg ATP. Under all conditions the time course of Mg ATP cleavage was biphasic, and consisted of a rapid initial burst of ADP formation, complete within 50 ms, followed by a slower steady‐state rate of Mg ATP cleavage. The number of molecules of Mg ATP cleaved during the burst was approximately equal to the number of myosin subfragment 1 heads for fibres at full myofilament overlap, and equal to 0.7 molecules per myosin subfragment 1 head for fibres stretched beyond overlap. At full overlap in the presence of calcium ions, the steady‐state rate equalled 1.8 mol Mg ATP cleaved per mole myosin subfragment 1 head per second. In all other cases the steady‐state rate of Mg ATP cleavage was at least 10‐fold less. When fibres at full overlap were pre‐incubated with 2 mM‐ADP, the initial phase of the tension response was somewhat prolonged, but the burst of ADP formation was also complete within 50 ms.(ABSTRACT TRUNCATED AT 400 WORDS)
Receptive fields of cricket giant interneurones are related to their dendritic structure.
Authors: Bacon J P , Murphey R K
Published: December 2014

The structural relationship between the afferent projection and the dendrites of the interneurones was examined in the cercal‐to‐giant interneurone system of the cricket using intracellular recording and dye injection techniques. The physiology of the sensory neurones beneath the cercal filiform hairs was investigated by placing a recording pipette over the end of a cut hair and using movements of the pipette to characterize the directionality of the receptor. Most of the filiform receptors could be classified as belonging to one of four major types. Each type is sensitive to a different wind direction and is confined to particular regions of the cercus. The location of the terminal arborizations of each type of sensory cell was revealed by staining with cobalt chloride. Single cells were stained reliably by placing a dye‐filled pipette over a cut hair. Each physiological receptor type arborizes in a different region of the central nervous system. Therefore the neuropile is functionally divided according to wind direction. The dendrites of three identified interneurones were examined in the context of this afferent projection. It was found that each of these neurones has dendrites in regions of neuropile corresponding to different wind directions. By searching for unitary synaptic potentials in identified interneurones, it was possible to show a strong correlation between anatomical overlap of primary afferent and interneurone and the existence of a synaptic connexion. Further, when there was no overlap, no synaptic potentials were seen. Therefore the over‐all excitatory receptive field of an interneurone could be predicted by examining its dendritic structure. Each of the three identified interneurones examined in this study was found to have a directional response that matched the response predicted on the basis of its anatomy.
Relationship between presynaptic membrane potential and acetylcholine release in synaptosomes from Torpedo electric organ.
Authors: Meunier F M
Published: December 2014

The membrane potential of purely cholinergic synaptosomes isolated from Torpedo electric organ was monitored with fluorescent carbocyanine dyes. An increased fluorescence was associated with depolarization and a quenching with hyperpolarization. Fluorescence data provided evidence that Torpedo synaptosomes have a membrane potential mainly driven by a K+ diffusion potential and a membrane potential of about ‐50 mV could be estimated after calibration of fluorescence signals with ionophore antibiotics. The release of acetylcholine (ACh) from Torpedo synaptosomes was monitored continuously by measuring the light emitted by a chemiluminescent method (Israël & Lesbats, 1981 a). Using fluorescence data, the release of ACh was expressed as a function of membrane potential. The relationship between presynaptic potential and transmitter release as determined by biochemical methods at cholinergic nerve endings showed striking similarities to that observed at the squid giant synapse. Several substances were also tested with regard to their depolarizing and releasing properties and it was found that the toxin isolated from the venom of the annelid Glycera convoluta, which induced a large increase in quantal release of transmitter (Manaranche, Thieffry, & Israël, 1980) promoted a depolarization of Torpedo synaptosomes in addition to ACh release.
Interneurones in the Xenopus embryo spinal cord: sensory excitation and activity during swimming.
Authors: Clarke J D , Roberts A
Published: December 2014

The dorsolateral spinal cord of embryonic Xenopus laevis has previously been shown to contain two anatomical classes of interneurones with dendrites in the dorsal tract where they could be contacted by the central axons of Rohon‐Beard cells (Roberts & Clarke, 1982). The activity of these neurones within the dorsolateral spinal cord has been examined using intracellular micro‐electrodes. Following electrical stimulation of Rohon‐Beard neurites within the ipsilateral skin, dorsolateral neurones receive a short‐latency, compound, excitatory post‐synaptic potential (e.p.s.p.). The amplitude of the e.p.s.p. depends upon the number of Rohon‐Beard cells stimulated. The e.p.s.p. consists of early and later components. The early components may result from monosynaptic connexions from Rohon‐Beard cells, the later components from some unidentified interposed neurones. During episodes of fictive swimming the dorsolateral neurones are inhibited by rhythmic inhibitory post‐synaptic potentials. Following Rohon‐Beard neurite stimulation, neurones in the contralateral spinal cord receive e.p.s.p.s. These contralateral e.p.s.p.s are probably one of the post‐synaptic effects of one of the dorsolateral neurone classes. The results suggest that the dorsolateral neurones are responsible for amplifying and distributing the primary afferent signals of Rohon‐Beard cells, and may be involved in the initiation of swimming and reflex movements.
Anaesthetic action of esters and ketones: evidence for an interaction with the sodium channel protein in squid axons.
Authors: Elliott J R , Haydon D A , Hendry B M
Published: December 2014

The effects of methyl butyl ketone, methyl heptyl ketone and methyl pentanoate on the sodium current of the squid giant axon have been examined. The peak inward current in intact axons was reduced reversibly by each substance. Sodium currents were recorded in intracellularly perfused axons before and during exposure to the test substances and the records were fitted with equations similar to those proposed by Hodgkin & Huxley (1952). Shifts in the voltage dependence of the steady‐state activation and inactivation parameters (m infinity and h infinity), reductions in the peak heights of the activation and inactivation time constants (tau m and tau h) and changes in the maximum sodium conductance (gNa) caused by these substances have been tabulated and compared with the effects of methyl octanoate (Haydon & Urban, 1983b). Each compound shifted the voltage dependence of the steady‐state inactivation parameter in the hyperpolarizing direction and that of the steady‐state activation parameter in the depolarizing direction. The shifts produced by the ketones are compared with those produced by methyl pentanoate and by methyl octanoate. The possible role of an interaction between the carbonyl oxygen of the test substance and the sodium channel protein in producing the h infinity shift is discussed. The peak time constants are reduced and the voltage dependences of tau m and tau h are shifted in a direction commensurate with the shifts in steady‐state properties. The maximum sodium conductance is not much affected either by the ketones or by methyl pentanoate. Large reductions in peak inward current coupled with little effect on gNa have been reported for the n‐alkanols and other surface‐active compounds (Haydon & Urban, 1983b). This lack of a large effect on gNa indicates that whatever direct interaction does take place between the test substance and the channel protein, it does not result in a blockage of the channel.
Source and concentration of extracellular adenosine triphosphate during haemostasis in rats, rabbits and man.
Authors: Born G V , Kratzer M A
Published: December 2014

A new technique was developed for the measurement of extracellular free ATP in very small samples of whole blood using the luciferin‐luciferase enzyme system. The method had a very low background corresponding to approximately 10(‐16) mol ATP. ATP was measured in blood as it emerged during haemostasis following precise puncture of rat and rabbit arteries and after standardized incisions of human skin by the Simplate device. The initial concentration of free ATP in blood emerging 2‐4 s after vascular injury was about 2 X 10(‐7) M in rats and rabbits and about 2 X 10(‐6) M in humans. The free‐ATP concentration increased to 2 X 10(‐5) M 3‐5 min after injury and these increases could be prevented by heparin (20 u./ml). The source of the initial free ATP was identified as damaged cells in the injured vessel wall. Sufficient ADP, both released as such with ATP and generated by enzymic dephosphorylation of ATP, would be present at the site of injury to initiate haemostatic aggregation of platelets.
Tension receptors with vagal afferent fibres in the proximal duodenum and pyloric sphincter of sheep.
Authors: Cottrell D F , Iggo A
Published: December 2014

Single‐unit afferent activity was recorded from the hepatic‐duodenal branch of the vagus nerve of chloralose‐anaesthetized sheep during acute electrophysiological experiments. The impulse activity of sixty‐seven slowly adapting mechanoreceptors situated in the muscularis externa of the proximal duodenum and pyloric sphincter was synchronous with alterations in electromyographic and tension records. Afferent units were excited during passive distension, compression and drug‐induced increases in muscle tension, thus satisfying the criteria for 'in series' tension receptors (Iggo, 1955). From the responses to compression some evidence was found for the existence of separate populations of tension receptors with different mechanical thresholds. Two fibre populations were found: non‐myelinated (0.70 +/‐ 0.26 S.D. ms‐1) and myelinated (7.6 +/‐ 1.6 S.D. m s‐1). Mucosal application of solutions of hydrochloric acid, volatile fatty acids, alkali and amino acids, and mucosal probing modified the activity of most units. These changes were reduced by anaesthesia of the mucosa. It is concluded that tension receptors in the sheep duodenum occupy a position 'in series' with longitudinal muscle, and that their activity can be modified by the particulate and chemical composition of chyme by a mechanism involving local nerve plexuses. The activity of tension receptors is compared with that of two other mechanoreceptor classes located serosally (five units) and in the lesser omentum (eleven units). Receptors in neither of these two classes were directly excited by active contraction of the duodenum.
Efferent control of cochlear inner hair cell responses in the guinea‐pig.
Authors: Brown M C , Nuttall A L
Published: December 2014

The efferent crossed olivocochlear bundle (c.o.c.b.) was electrically stimulated during intracellular recordings from cochlear inner hair cells in anaesthetized guinea‐pigs. The effect of c.o.c.b. stimulation was to decrease the magnitude of the inner hair cell depolarizing component (d.c.) and alternating component (a.c.) receptor potentials evoked by tone bursts at the characteristic frequency. At low sound pressure levels, the decrease in receptor potentials caused by c.o.c.b. stimulation was equivalent to decreasing the sound intensity by 9‐24 dB. C.o.c.b. stimulation usually had a similar effect on the compound action potential of the auditory nerve. The change in inner hair cell membrane resistance during moderate‐level sound was measured for sound alone and when sound was accompanied by c.o.c.b. stimulation. Sound alone produced a greater membrane resistance change than sound with c.o.c.b. stimulation, in proportion to the d.c. receptor potential during the same conditions. The time course of the c.o.c.b. effect was slow, with 50‐250 ms required for a full effect and for recovery. The effects of varying the frequency and voltage of electrical stimulation were similar for the d.c. receptor potential and for the compound action potential. For sounds of high level and for frequencies well below the characteristic frequency, c.o.c.b. stimulation was less effective in reducing receptor potentials. Frequency tuning curves for the d.c. receptor potential taken during intervals of continuous c.o.c.b. stimulation showed decreases in sensitivity primarily in the tip segment of the tuning curve. When no sound stimulus was present, the resting membrane potential was relatively unaltered during c.o.c.b. stimulation. The resting membrane resistance did not change during c.o.c.b. stimulation. Since the c.o.c.b. innervates mainly the outer hair cells, these results strongly suggest that changes in outer hair cell activity can influence the receptor potentials of inner hair cells and thus alter the transmission of acoustic responses to the central nervous system.
Facilitatory influence of noradrenergic afferents on the excitability of rat paraventricular nucleus neurosecretory cells.
Authors: Day T A , Ferguson A V , Renaud L P
Published: December 2014

The role of the A1 and A2 noradrenergic cell groups of the caudal medulla in regulating the activity of paraventricular nucleus neurosecretory cells was examined with electrophysiological methods in anaesthetized male Sprague‐Dawley rats. Antidromically identified neurosecretory cells were classified as vasopressin or oxytocin secreting on the basis of spontaneous firing patterns and responsivity to baroreceptor activation. The effect on cell firing of single pulses (25‐200 microA) delivered to either the A1 or A2 cell group areas was then examined using peri‐stimulus histograms. Stimulation of the A1 region enhanced the activity of 78% of putative vasopressin‐secreting neurones tested (n = 18), but failed to affect the activity of the majority (73%) of putative oxytocin‐secreting units (n = 15). A2 stimulation enhanced the firing rate of both putative vasopressin‐ (60%, total n = 14) and putative oxytocin‐secreting (70%, total n = 27) neurones. Destruction of the paraventricular nucleus catecholamine terminal plexus by pre‐treatment with the neurotoxin 6‐hydroxydopamine abolished the facilitatory effects of both A1 and A2 stimulation. These findings suggest that noradrenergic afferents of medullary origin facilitate the activity of paraventricular nucleus neurosecretory cells. The role of the projection from the A1 cell group appears to differ from that of the A2 group, however, in that its effects are specific to putative vasopressin‐secreting units.
Polyneuronal innervation and quantal transmitter release in formamide‐treated frog sartorius muscles.
Authors: Herrera A A
Published: December 2014

The incidence of focal polyneuronal innervation was measured at end‐plates in normal and reinnervated sartorius muscles from Rana pipiens either in the presence of curare to partially block neuromuscular transmission or in normal Ringer solution after pre‐treatment with formamide to block excitation‐contraction coupling. The incidence of polyneuronal innervation estimated with curare in normal muscles during the winter (19%) was significantly higher than the incidence in summer (9%). After formamide treatment, large end‐plate potentials (e.p.p.s) and miniature e.p.p.s (m.e.p.p.s) could be recorded in Ringer solution containing physiological levels of Ca2+. For both normal and reinnervated muscles, higher levels of polyneuronal innervation could be recorded in normal Ringer solution after formamide treatment compared with levels measured in the presence of curare. This was true whether randomly selected end‐plates or the same group of identified end‐plates were examined before and after formamide treatment. Quantal content in normal Ringer solution containing 1.8 mM‐Ca2+ was measured as the ratio of mean e.p.p. amplitude divided by mean m.e.p.p. amplitude. In randomly selected samples of normal end‐plates the range of quantal contents seen was 18‐112 (mean 50). For reinnervated end‐plates 60 days after nerve crush, quantal contents were 6‐181 (mean 54). It was concluded that formamide pre‐treatment is a more sensitive technique for estimating the incidence of focal polyneuronal innervation and that, with appropriate controls, it can be used to measure quantal transmitter release accurately without using synaptic blocking agents.
The role of motilin in periodic interdigestive pancreatic secretion in dogs.
Authors: Magee D F , Naruse S
Published: December 2014

The role of motilin in the periodic interdigestive secretion of the pancreas was studied in conscious dogs, each with a chronic gastric fistula, a Heidenhain pouch and a Thomas duodenal fistula. Motilin increased pancreatic water, bicarbonate and protein secretion and the motility of the stomach, duodenum and Heidenhain pouch in a manner which closely resembles the spontaneous changes which occur during interdigestive activity. Endogenous motilin released by duodenal alkalinization had the same effect as exogenous hormone. Continuous infusion of motilin did not cause continuous pancreatic secretion and gut motility but merely shortened the interval of the periodic interdigestive activity. Exogenous and endogenous motilin were ineffective following atropine. Hexamethonium abolished the pancreatic and duodenal peaks but not the changes in gastric and pouch motility induced by motilin or duodenal alkalinization.
Crossed actions of group I muscle afferents in the cat.
Authors: Harrison P J , Zytnicki D
Published: December 2014

Reflex actions evoked by electrical stimulation of contralateral quadriceps, hamstring and gastrocnemius‐soleus muscle afferents were investigated using intracellular recording from motoneurones, in chloralose‐anaesthetized, acute, low spinal cats. Contralateral group I afferents were found to evoke excitatory post‐synaptic potentials only occasionally. Contralateral group II afferents evoked post‐synaptic potentials (excitatory to extensor motoneurones and inhibitory to flexor motoneurones) from the quadriceps nerve, whereas contralateral group III afferents evoked post‐synaptic potentials (with the same pattern as quadriceps group II) from all muscles tested. Contralateral group I afferents were found to facilitate Ia reciprocal inhibition, and both the excitatory and inhibitory reflex actions from Ib afferents. This is taken to indicate an action of these afferents on interneurones interposed in ipsilateral reflex pathways.
Characteristics of secretin‐stimulated pancreatic secretion in dogs.
Authors: Maggee D F , Naruse S
Published: December 2014

The effect of the periodic interdigestive activity of the gut on secretin‐stimulated pancreatic secretion was studied in eight conscious dogs each with a Thomas duodenal fistula, a gastric fistula and a Heidenhain pouch. Pancreatic water and bicarbonate responses to a small dose of secretin were greatly augmented in phase with the spontaneous periodic activity of the gut. This augmentation was closely related to pancreatic protein secretion. As the dose of secretin was increased the interval between peaks was prolonged, the peaks became less sharp, the nadirs were raised, and finally the periodic activity was no longer seen. Bilateral cervical vagal blockade with local anaesthetics reduced the secretin‐stimulated bicarbonate secretion by 50% but the augmentation at the peak was not abolished. Atropine abolished the periodic augmentation completely and reduced the bicarbonate response by 80%. The peak response of volume and bicarbonate to secretin obeyed Michaelis‐Menten kinetics. The nadir secretin dose response, however, was a sigmoid curve with a Hill coefficient larger than one. The action of atropine or hexamethonium was to shift the peak response kinetics to the nadir kinetics. It is concluded that the pancreatic response to secretin is greatly modulated by the spontaneous periodic activity of nerves.
Effects of axotomy on the distribution of passive electrical properties of cat motoneurones.
Authors: Gustafsson B , Pinter M J
Published: December 2014

Previously obtained experimental results concerning the effect of axotomy on motoneurone passive electrical properties have been re‐analysed. As shown earlier, axotomy causes an average increase of motoneurone input resistance, membrane time constant and after‐hyperpolarization duration. The present analysis suggests that the increased input resistance is related to a higher specific membrane resistivity, a decreased cell size and an altered dendritic geometry. The results also suggest that the change takes place only in neurones projecting to fast‐twitch muscle units and produces in them passive electrical properties normally exhibited only by motoneurones projecting to slow‐twitch units. Based on the notion that axotomy causes a 'dedifferentiation' of motoneurone properties, the present results might be taken to indicate that undifferentiated motoneurones are slow in character. A possible scheme in which a post‐natal differentiation of motoneurone properties may lead to muscle differentiation is discussed.
Miniature end‐plate potentials in rat skeletal muscle poisoned with botulinum toxin.
Authors: Kim Y I , Lømo T , Lupa M T , Thesleff S
Published: December 2014

Spontaneous transmitter release, recorded as miniature end‐plate potentials (m.e.p.p.s), was studied in rat extensor digitorum longus (e.d.l.) and soleus muscles partially or completely paralysed by botulinum toxin type A (BoTx). Normal unpoisoned muscles were examined for comparison. Analysis of m.e.p.p.s in both normal and BoTx‐poisoned muscles confirmed the presence of two populations of potentials. One population, which comprised about 96% of the m.e.p.p.s recorded at non‐poisoned end‐plates, was characterized by a uniform time course and a mean time‐to‐peak of 0.5‐0.7 ms. These potentials had a shape and time‐to‐peak similar to that of quantal end‐plate potentials (e.p.p.s) evoked by nerve stimuli. These were designated 'fast m.e.p.p.s'. The other population of m.e.p.p.s was characterized by a slower, more variable rise‐time, the time‐to‐peak exceeding 1.1 ms, and generally a larger amplitude. These were designated 'slow m.e.p.p.s'. In both partial and complete paralysis by BoTx the frequency of fast m.e.p.p.s was reduced by more than 90% and the reduction lasted several weeks. After 6‐10 days of poisoning the frequency of slow m.e.p.p.s gradually increased. The highest frequency of slow m.e.p.p.s (0.4 Hz) was recorded in the partially paralysed soleus muscle, the frequency being about ten times that at unpoisoned end‐plates. In both partially paralysed muscles slow m.e.p.p. frequency returned towards normal 28 days after poisoning. A significant correlation (r = 0.67) was observed between the quantal content of e.p.p.s and the frequency of fast m.e.p.p.s in partially paralysed e.d.l. muscles. No significant correlation was observed between quantal content of e.p.p.s and the frequency of slow m.e.p.p.s. To further study if muscle activity influenced the appearance of slow m.e.p.p.s, partially paralysed soleus muscles were directly stimulated in vivo during the first 11‐13 days following BoTx poisoning, using a stimulation pattern which inhibits nerve terminal sprouting and the appearance of denervation changes. This procedure did not alter the frequency of slow m.e.p.p.s as compared to unstimulated poisoned controls. It is concluded that enhancement of slow m.e.p.p. frequency in muscles poisoned with BoTx is related to the blockade of evoked Ca2+‐dependent quantal transmitter release. However, additional factors influence this type of spontaneous and Ca2+‐insensitive release of acetylcholine since there is a great variability between fibres and a time lag between the disappearance of fast m.e.p.p.s and the activation of slow m.e.p.p. frequency.(ABSTRACT TRUNCATED AT 400 WORDS)
Dorsal root potentials are unchanged in adult rats treated at birth with capsaicin.
Authors: Cervero F , Plenderleith M B
Published: December 2014

The possible contribution of non‐myelinated afferent fibres (C fibres) to the mechanisms of primary afferent depolarization (p.a.d.) in the spinal cord of the rat has been investigated. Dorsal root potentials (d.r.p.s.) were recorded in the lumbar cord of normal adult rats, of adult rats which had been injected at birth with a solution of capsaicin (50 mgkg‐1 s.c.) and of adult rats which had been injected at birth with the drug vehicle only. D.r.p.s were recorded from the dorsal rootlet that entered the spinal cord in the main area of termination of the tibial nerve. The location of this area was assessed by mapping the spinal cord in the rostro‐caudal axis while recording cord dorsum potentials evoked by A‐fibre volleys from the tibial nerve. No differences in peak amplitude, area or time to peak amplitude were observed between the d.r.p.s evoked in control and capsaicin‐treated rats by stimulation of the tibial, sural or common peroneal nerves. The relation between the size of incoming A volleys to the spinal cord and the size of the d.r.p.s evoked by them was unaffected by the neonatal capsaicin treatment. Rats treated at birth with capsaicin showed a virtual absence of afferent C fibres as assessed from the lack of C waves in the compound action potentials evoked in each of the three nerves studied after antidromic stimulation of the dorsal roots. The presence of p.a.d. in control and in capsaicin‐treated animals was also established using the technique of excitability testing of primary afferent fibres (Wall, 1958). No differences were observed between the p.a.d. recorded in control and in capsaicin‐treated animals using this technique. D.r.p.s and p.a.d. (assessed by excitability testing of primary afferent fibres) were of similar magnitude in control and in capsaicin‐treated rats anaesthetized with either sodium pentobarbitone or urethane. It is concluded that p.a.d. of myelinated afferent fibres produced by incoming volleys in myelinated afferent fibres is not affected by a life‐long loss of non‐myelinated afferent fibres.
Ionic currents and charge movements in organ‐cultured rat skeletal muscle.
Authors: Hollingworth S , Marshall M W , Robson E
Published: December 2014

The middle of the fibre voltage‐clamp technique was used to measure ionic currents and non‐linear charge movements in intact, organ‐cultured (in vitro denervated) mammalian fast‐twitch (rat extensor digitorum longus) muscle fibres. Muscle fibres organ cultured for 4 days can be used as electrophysiological and morphological models for muscles in vivo denervated for the same length of time. Sodium currents in organ‐cultured muscle fibres are similar to innervated fibres except that in the temperature range 0‐20 degrees C (a) in the steady state, the voltage distribution of inactivation in cultured fibres is shifted negatively some 20 mV; (b) at the same temperature and membrane potential, the time constant of inactivation in cultured fibres is about twice that of innervated fibres. Potassium currents in innervated and cultured fibres at 15 degrees C can be fitted with the Hodgkin‐Huxley n variable raised to the second power. Despite the large range we would estimate that the maximum value of the steady‐state potassium conductance of cultured fibres is about one‐half that of innervated fibres. The estimated maximum amount of charge moved in cultured fibre is about one‐third that in innervated fibres. Compared to innervated fibres, culturing doubles the kinetics of the decay phase of charge movement. The possibility of a negative shift of the voltage distribution of charge movements in cultured fibres is discussed.