bluuebunny/crossref_metadata_2025 huggingface dataset:
Differentiation of vasodilator and sudomotor responses in the cat paw pad to preganglionic sympathetic stimulation.
Authors: Bell C , Jänig W , Kümmel H , Xu H
Published: December 2014

We monitored sweat secretion (using skin potential) and blood flow (using skin temperature) in the hind‐paw skin of chloralose‐anaesthetized cats pre‐treated with guanethidine, and studied the responses to electrical stimulation of the ipsilateral lumbar sympathetic trunk. Stimulation caused sweat secretion and an increase in skin blood flow which was almost entirely restricted to the paw pads and was completely ipsilateral. Stimulation of the tibial nerve trunk produced similar effects, except that the increase in blood flow was more prolonged. The vasodilator effect of sympathetic trunk stimulation was not affected by chronic deafferentation of the paw. Atropine methonitrate (0.5‐1 mg/kg I.V.) abolished the sudomotor response to sympathetic stimulation, but did not attenuate the blood flow response. Hexamethonium (1‐2 mg/kg I.V.) abolished the vasodilator response to sympathetic stimulation, but did not affect the sudomotor response. Larger doses of hexamethonium (10‐20 mg/kg) abolished both responses. The data suggest that the lumbar post‐ganglionic neurones mediating vasodilatation in the skin of the cat paw pad are distinct from those that mediate sudomotor secretion.
Influence of a change in stimulation rate on action potentials, currents and contractions in rat ventricular cells.
Authors: Mitchell M R , Powell T , Terrar D A , Twist V W
Published: December 2014

The effects of a change in stimulation rate on electrical activity and accompanying contraction were investigated in ventricular cells isolated from rat heart; the cells were stimulated to contract either by brief depolarization pulses which evoked action potentials, or, under voltage‐clamp conditions, by step depolarizations. An increase in stimulation rate from 0.3 to 3 Hz resulted in a gradual reduction in the amplitude of contraction and attenuation of the late phase of the action potential. These changes were less marked at more depolarized potentials. The ventricular cells were voltage clamped at ‐40 mV and initially stimulated at 0.3 Hz by step depolarizations to 0 mV for 10 or 100 ms, which activated the second inward current (Isi) and an accompanying contraction. The amplitude and time course of contraction were similar with the two pulse durations. When the duration of the depolarization was 100 ms, an increase in stimulation rate to 3 Hz caused a gradual decline in the amplitude of Isi and of the evoked contraction; at the same time extra contractions and small, transient inward currents appeared in addition to the evoked contractions and Isis. There was a reduction in the early component of decay of Isi at 3 Hz. With a depolarizing pulse duration of 10 ms, an increase in stimulation rate to 3 or to 4.2 Hz did not change the amplitude of the evoked Isi or contraction and no extra contractions or currents appeared. Intracellular EGTA abolished all contractions in the cells and an increase in the rate of stimulation with 100 ms pulses did not then induce transient inward currents. There was some decrease in the Isi amplitude but this was not as marked as in the absence of EGTA and the time course of current decay was similar at the two rates. Ryanodine prevented the appearance of extra contractions and currents when the stimulation rate was increased to 3 Hz and, as in the presence of intracellular EGTA, there was a small decrease in Isi amplitude while the time course of decay was similar at the two stimulation rates. The time course of recovery of Isi from inactivation, as shown by a double‐pulse procedure, was altered when the duration of the first pulse was reduced from 100 to 10 ms, an extra inactivation of Isi being seen at pulse intervals of 20‐100 ms. This extra component of inactivation was not seen with intracellular EGTA or in the presence of ryanodine.(ABSTRACT TRUNCATED AT 400 WORDS)
Pancreatic neuroendocrine responses to butyrate in conscious sheep.
Authors: Bloom S R , Edwards A V
Published: December 2014

The role of the autonomic innervation in the control of pancreatic endocrine responses to I.V. infusions of butyrate (0.02 mmol kg‐1 min‐1 for 10 min) has been investigated in conscious 4‐6 month old weaned lambs. Intravenous butyrate produced a small rise in mean arterial plasma pancreatic glucagon concentration which was unlikely to have had any physiological effect and produced no consistent or statistically significant changes in mean plasma pancreatic polypeptide concentration in any of the groups studied. In contrast, butyrate produced an abrupt and substantial rise in mean plasma insulin concentration, which rose to a peak incremental value of about 300 pmol l‐1 in normal control lambs. This response was unaffected by pre‐treatment with either phentolamine or propranolol alone, but was significantly reduced by simultaneous administration of these drugs, as it was either by pre‐treatment with atropine or prior section of the splanchnic nerves. The rise in mean plasma insulin concentration was inhibited most effectively by combined treatment with propranolol, phentolamine and atropine, which was significantly more effective than administration of atropine to lambs with cut splanchnic nerves (P less than 0.01). It is concluded that both divisions of the autonomic nervous system are likely to be involved in mediating the release of insulin from the pancreas, in response to butyrate, in this species under these experimental conditions and also in the resting state.
Responses of muscle receptors in the kitten.
Authors: Gregory J E , Proske U
Published: December 2014

Responses have been recorded in single functional afferents supplying muscle receptors of the soleus muscle in kittens aged between 1 and 23 days. Recordings of nerve volleys in whole dorsal or ventral roots in response to muscle nerve stimulation showed that conduction velocity for afferent and motor fibres was similar and increased from 9 m s‐1 in a 2‐day‐old animal to 33 m s‐1 in a 23‐day‐old animal. Of a total of 215 single functional axons isolated from 28 animals, 82 showed responses typical of tendon organs and 103 resembled muscle spindles, leaving 30 unidentified units. Both muscle spindles and tendon organs were characterized by having an over‐all low firing rate compared with responses of adult receptors. The most immature receptors also lacked a maintained response to the hold phase of a ramp‐and‐hold stretch. Spindles in animals over the whole range of ages, including the youngest animals could be shown to be supplied with a fusimotor innervation. On a few occasions it was possible to isolate single fusimotor axons to a spindle; such axons were sometimes found to conduct impulses at a speed characteristic of non‐myelinated fibres. Evidence was obtained for the existence of a beta‐(skeletofusimotor) innervation of spindles. On four occasions it was possible to isolate single functional beta‐axons in the ventral root. The incidence of beta‐innervation appeared to be higher than in the adult.
Effect of excitatory amino acids and analogues on [3H]acetylcholine release from amacrine cells of the rabbit retina.
Authors: Cunningham J R , Neal M J
Published: December 2014

The pharmacology of cholinergic amacrine cells has been further studied by examining the effects of excitatory amino acids and antagonists on [3H]acetylcholine (ACh) release from the retinas of anaesthetized rabbits. Exposure of the retina to glutamate (5 mM), aspartate (5 mM), kainate (8 microM) and quisqualate (8 microM) abolished the light‐evoked release of [3H]ACh but increased the spontaneous resting release four‐ to fivefold. N‐methyl‐D‐aspartate (NMDA) (5 mM) in normal Krebs bicarbonate medium abolished the light‐evoked release of [3H]ACh but did not affect the resting release. However, in Mg‐free medium, NMDA (0.5 mM) abolished the light‐evoked release of [3H]ACh and increased the resting release fivefold. The effects of other agonists were not altered in Mg‐free medium. The amplitude of the electroretinogram (e.r.g.) b‐wave was not significantly reduced by glutamate, aspartate or NMDA (in normal or Mg‐free medium). Kainate and quisqualate reduced the b‐wave amplitude to approximately 50 and 30% of controls respectively. The general excitatory amino acid antagonist, cis‐2,3‐piperidine dicarboxylic acid (PDA) (2 mM) blocked the light‐evoked release of [3H]ACh, but had no significant effect on the e.r.g. b‐wave amplitude or on the resting release of [3H]ACh. L(+)‐2‐amino‐4‐phosphonobutyrate (L(+)‐APB) decreased the light‐evoked release of [3H]ACh and the amplitude of the e.r.g. b‐wave in parallel (correlation coefficient 0.995). D(‐)‐APB had similar effects but was fifteen times less potent. Since the L(+)‐compound is known to mimic the photoreceptor transmitter on the depolarizing, but not hyperpolarizing, bipolar cells, these results strongly suggest that the [3H]ACh released in response to light originates mainly from the 'on' (displaced) cholinergic amacrine cells. Our experiments give no information on the origin of the spontaneously released [3H]ACh. PDA (2‐5 mM) blocked the effects of glutamate, aspartate, kainate, quisqualate and NMDA on the resting release of [3H]ACh. In contrast, D(‐)‐APB (5 mM), which is a relatively non‐specific excitatory amino acid antagonist in the spinal cord, blocked only the actions of kainate and had no blocking effect on the actions of glutamate or aspartate (the putative bipolar cell transmitters) or NMDA. D(‐)‐2‐amino‐5‐phosphonovalerate (APV) which is a relatively selective NMDA antagonist in the spinal cord failed to discriminate between the effects of kainate and NMDA on the resting release of [3H]ACh. D‐alpha‐aminoadipate at concentrations up to 5 mM had no effect on any of the agonists.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrical excitability of motor nerve terminals in the mouse.
Authors: Konishi T
Published: December 2014

Electrical activity of motor nerve terminals was recorded with focal extracellular electrodes under visual location with Nomarski optics in the intercostal muscle of the mouse. Following ionophoretic applications of tetrodotoxin (TTX) to the last three nodes of Ranvier, a nerve impulse jumped across the three inexcitable nodes and excited the heminodal region. When excitation at the last node of Ranvier and the heminodal region was blocked by TTX, the distal terminal revealed a small inward current in response to nerve stimulation. This inward current disappeared when TTX was applied to the distal terminal, indicating the presence of active inward currents in this region under normal conditions. When excitation at the last node, heminode and distal terminals was blocked by TTX, the transmitter release was still observed by nerve stimulation, suggesting substantial passive depolarization of the terminal by excitation of up‐stream nodes of Ranvier. Local hyperpolarization of the distal terminal caused an increase in the amplitude of the TTX‐sensitive inward current at the terminal, and the reverse effects were exerted by depolarization of the terminal. It is concluded that the mouse motor terminal is electrically excitable and that the TTX‐sensitive inward current at the terminal is largely masked by passive depolarization due to excitation of up‐stream nodes of Ranvier and the heminode under normal conditions.
Synaptic transmission at N‐methyl‐D‐aspartate receptors in the proximal retina of the mudpuppy.
Authors: Lukasiewicz P D , McReynolds J S
Published: December 2014

The effects of excitatory amino acid analogues and antagonists on retinal ganglion cells were studied using intracellular recording in the superfused mudpuppy eyecup preparation. Aspartate, glutamate, quisqualate (QA), kainate (KA) and N‐methylaspartate (NMA) caused depolarization and decreased input resistance in all classes of ganglion cells. The order of sensitivity was QA greater than or equal to KA greater than NMA greater than aspartate greater than or equal to glutamate. All of these agonists were effective when transmitter release was blocked with 4 mM‐Co2+ or Mn2+, indicating that they acted at receptor sites on the ganglion cells. At a concentration of 250 microM, 2‐amino‐5‐phosphonovalerate (APV) blocked the responses of all ganglion cells to NMA, but not to QA or KA, indicating that NMA acts at different receptor sites from QA or KA. Responses to bath‐applied aspartate and glutamate were reduced slightly or not at all in the presence of APV, indicating that they were acting mainly at non‐NMDA (N‐methyl‐D‐aspartate) receptors. In all ganglion cells 250 microM‐APV strongly suppressed the sustained responses driven by the 'on'‐pathway but not those driven by the 'off'‐pathway. In most on‐off ganglion cells the transient excitatory responses at 'light on' and 'light off' were not reduced by 500 microM‐APV. APV‐resistant transient excitatory responses were also present in some on‐centre ganglion cells. APV did not block the transient inhibitory responses in any class of ganglion cells. At concentrations which blocked the sustained responses of ganglion cells, APV did not affect the sustained responses of bipolar cells, indicating that it acted at sites which were post‐synaptic to bipolar cells. The simplest interpretation of these results is that the transmitter released by depolarizing bipolar cells acts at NMDA receptors on sustained depolarizing amacrine and ganglion cells. It may act at non‐NMDA receptors at synapses which produce transient excitatory responses, but this could not be proved. The transmitter released by hyperpolarizing bipolar cells does not appear to act at NMDA receptors on any post‐synaptic cells.
Electromyographic responses evoked in muscles of the forelimb by intracortical stimulation in the cat.
Authors: Armstrong D M , Drew T
Published: December 2014

Chronically implanted microwires were used to deliver brief trains of electrical stimuli (11 cathodal pulses at 330 Hz and intensity 5‐35 microA) to sixty‐two locations in the grey matter of the pericruciate cortex in cats. Electromyographic (e.m.g.) responses in the contralateral forelimb were recorded from a total of ten muscles (four to eight in each animal) acting about the shoulder, elbow and wrist and on the digits. The animals were relaxed with little background e.m.g. in the muscles and as a result only excitatory effects could be described. Five muscles which are flexors in the locomotor context were excited from more electrodes, distributed more widely across the motor cortex, than another five muscles which are extensors during locomotion; this difference in 'accessibility' was present both at 35 microA stimulus intensity and at 15 microA. At a stimulus intensity of 15 microA, effective cortical electrodes tended to cluster either in the most lateral part of the anterior sigmoid gyrus (rostromedial focus) or in the coronal gyrus just caudal to a line prolonged beyond the lateral end of the cruciate sulcus (caudolateral focus). This is consistent with the existence of a double motor representation within the forelimb motor cortex (Pappas & Strick, 1981). The two foci were similar in that both gave rise to more flexor than extensor responses and to fewer responses in digit or wrist muscles than in muscles acting about more proximal joints (elbow and shoulder). At stimulus intensity 35 microA the latency of the earliest e.m.g. responses ranged from 11 to 14 ms in different muscles. For some muscles and electrodes the amplitude of the e.m.g. responses was substantially altered by a quite small postural change. After pyramidectomy the cortical thresholds and the e.m.g. latencies were both greatly increased.
Forelimb electromyographic responses to motor cortex stimulation during locomotion in the cat.
Authors: Armstrong D M , Drew T
Published: December 2014

The forelimb motor cortex was stimulated via chronically implanted microelectrodes whilst electromyographic (e.m.g.) responses were recorded from muscles in the contralateral forelimb in cats walking steadily at 0.5 m/s. The stimuli were brief trains of 0.2 ms pulses (11 pulses at 330 Hz), intensity 5‐20 microA and e.m.g.s were recorded from the following muscles: biceps brachii, brachialis, long and lateral heads of triceps brachii, latissimus dorsi, cleidobrachialis, extensor digitorum communis, palmaris longus and flexor and extensor carpi ulnaris. During locomotion, stimulation at 20 microA readily elicited brief, short‐latency changes in the normal locomotor patterns of activity in all muscles studied. The changes included production of e.m.g. at times in the step cycle when the muscles are normally inactive and brief augmentations or diminution of the normal locomotor e.m.g.s. Individual electrodes usually influenced several muscles, and muscles acting antagonistically about the same joint were sometimes co‐contracted. The first effect on locomotor flexor muscles (i.e. muscles active in relation to the swing phase of the step cycle) was almost always excitatory and such effects were often phase‐dependent, usually occurring when the muscle was normally active or about to become active. Extensor muscles were excited from some cortical loci but inhibited from others (inhibitions were necessarily detectable only when the muscles exhibited locomotor‐related e.m.g.s). Some micro‐electrodes elicited excitation during swing (when the extensors are inactive) but elicited inhibition during stance. In several muscles the latencies of the excitatory e.m.g. changes could be as short as 6 ms measured from the first pulse in the stimulus train. In flexors, but not in extensors, latencies fluctuated according to the timing of the stimuli relative to the step cycle. Reduction in stimulus intensity reduced the amplitude of the e.m.g. changes, the number of muscles influenced and often increased the latency. However, both excitations and inhibitions were sometimes evident at 5 microA and thresholds for excitatory responses were, over‐all, substantially lower than in the resting animal. Longer trains of stimuli were capable of resetting the step cycle. Response thresholds were greatly increased after pyramidectomy. These findings support the view that the natural bursts of impulses discharged by pyramidal tract neurones during steady locomotion are likely to contribute to regulating forelimb muscle activity on a step‐by‐step basis.
Force‐velocity properties of fast‐twitch and slow‐twitch muscles of the kitten.
Authors: Hatcher D D , Luff A R
Published: December 2014

The characteristics of the isometric and force‐velocity properties of the fast‐twitch flexor digitorum longus (f.d.l.) and the slow‐twitch soleus muscles of the developing kitten were determined at post‐natal ages of 2 days and 1,2,4 and 6 weeks. The contractile properties of the isometric twitch and tetanus were similar to those previously reported by other authors. The minimum stimulation frequency required for isotonic contractions to achieve the maximum speed of shortening at any given load was 200 Hz for f.d.l. and 150 Hz for soleus at all ages. The extrapolated maximum speed of sarcomere (sarc.) shortening (Vmax) was significantly different between the f.d.l. (22.3 microns s‐1 sarc.‐1) and soleus (13.1 microns s‐1 sarc.‐1) at 2 days of age. The f.d.l. Vmax achieved adult values by 4 weeks of age, while there was little or no change in the soleus Vmax. The force‐velocity properties are discussed and compared to the changes which have been observed in other contractile properties of the cat f.d.l. and soleus muscles.
Dinitrophenol effect on proximal tubular acidification in the rat.
Authors: Lopes A G , Malnic G , Rebouças N A
Published: December 2014

The effect of 10(‐3) M‐dinitrophenol (DNP) on renal tubular acidification was studied in proximal tubules of rat kidneys perfused with mammalian Ringer solution. Alkaline (pH 7.8) or acid (pH 5.8) phosphate‐buffered solutions were injected into the lumen, and pH changes recorded with antimony micro‐electrodes. Luminal perfusion with DNP caused complex acidification or alkalinization curves, an initial rapid shift toward a higher than control pH being followed by a slower acidification. Acidification half‐times of the initial phase (t1/2 = 1.6 s) were markedly shorter than controls (6.2 s). This response was probably due to transient action of DNP, since keeping constant peritubular DNP levels by capillary perfusion caused simple exponential pH curves. In such experiments luminal pH increased from pH 6.6‐6.8 to 7.1‐7.2, while acidification and alkalinization t1/2 decreased from about 7 s to 3‐5 s. Secretory H‐ion fluxes increased transiently and then fell below controls after a few minutes of perfusion, while H‐ion efflux from the lumen increased progressively. These data suggest that, besides its known effect on cell metabolism, DNP acts directly on proximal tubular cell membranes, increasing the rate of passive H‐ion equilibration, both mechanisms impairing the tubular capacity to maintain normal proximal pH gradients and fluxes.
Adaptation in the input‐output relation of the synapse made by the barnacle's photoreceptor.
Authors: Hayashi J H , Moore J W , Stuart A E
Published: December 2014

A study was made of synaptic transmission between the four median photoreceptors of the giant barnacle (Balanus nubilus) and their post‐synaptic cells (I‐cells). Simultaneous intracellular recordings were made from the presynaptic terminal region of a photoreceptor and from the soma of an I‐cell. The photoreceptor's membrane potential provided feed‐back to bath electrodes that passed current into the receptors' axons, permitting the voltage to be controlled at the point of arborization of their presynaptic terminals. Simultaneous recordings from a second photoreceptor showed that its voltage tracked the first. Step depolarizations of the receptors from their dark resting potential (about ‐60 mV) caused hyperpolarizations of the I‐cell that reached a peak, then decayed to a plateau value. The amplitude of the I‐cell's response grew with presynaptic depolarizations, saturating at presynaptic values 10‐20 mV depolarized from dark rest. Step hyperpolarizations of the receptors from dark rest evoked depolarizations of the I‐cell consisting of an initial peak, which varied greatly in amplitude and wave form from preparation to preparation, followed by a plateau. The presence of this post‐synaptic response indicates that transmitter is released continuously from the receptors at their dark resting potential. An input‐output relation of the synapse was obtained by presenting step depolarizations from a holding potential of ‐80 mV, where steady‐state transmitter release is shut off. The relation is sigmoidal; in the exponentially rising phase of the curve, a 5‐11 mV presynaptic change produces a 10‐fold change in post‐synaptic response. When the presynaptic holding potential was set at values ranging from ‐80 to ‐40 mV, the relation between the I‐cell's response and the absolute potential to which the receptor was stepped shifted along the presynaptic voltage axis. The slopes of the input‐output relations were roughly parallel or increased as the photoreceptors were held more depolarized. This observation limits the possible mechanisms of the shift.
Biochemical separation of delayed rectifier currents in frog short skeletal muscle fibres.
Authors: Lynch C
Published: December 2014

Frog short (1‐1.5 mm) skeletal muscle fibres in sucrose hypertonic Ringer at 5 degrees C were voltage clamped employing a two‐electrode technique. Decreasing pH from 7.0 to 5.0 dramatically increased the rate of turn on of the slow delayed rectifier (GK,s) current, so that it became similar to the rapidly activated form. The accelerating effects of decreased pH upon slow current kinetics had a pKa of 5.8. Decreased pH also appeared to shift the voltage dependence of fast and GK,s gating to more positive potentials. In addition, a decrease in pH from 7.0 to 5.0 shifted the reversal potential of GK,s by over 11 mV in the positive direction. GK,s was selectively and irreversibly abolished by applying 1 mM‐diethylpyrocarbonate (DEP), a histidine reagent. This effect occurred even after GK,s had been accelerated by low pH. DEP had no effect upon fast delayed rectifier current except for a small positive shift in voltage dependence. Application of 1 or 2 mM‐N‐ethylmaleimide, a sulphydryl reagent, depressed the fast delayed rectifier while sparing the GK,s currents. However, the muscle fibres also developed markedly increased leakage currents.
The effect of altered peripheral field on motoneurone function in developing rat soleus muscles.
Authors: Lowrie M B , O'Brien R A , Vrbová G
Published: December 2014

In soleus muscles of 4‐ to 5‐day‐old rats the quantum content of axon terminals from L4 spinal roots is less than half that from L5. With development the size of L4 motor units decreases and the quantum content of L4 nerves increases to become similar to that of L5 axons. During this time the overlap of territories of L4 and L5 axons is reduced from 46% at 4‐6 days to 2% at 18‐20 days. This reduction occurs entirely at the expense of L4 territory. Removal of the L5 ventral ramus (v.r.) at 4‐6 days prevents the reduction of L4 territory so that at 18 days L4 motor units are about 4 X normal size. In spite of this enlarged peripheral field of L4 axons the quantum content of their terminals increases to normal levels. When L5 v.r. was removed at 16‐18 days, i.e. when the reduction of the L4 peripheral field was complete, expansion of L4 motor units was also seen, but in this case the quantum content of L4 terminals was less than normal. Thus it appears that during early stages of development, before synaptic reorganization within the muscle is complete, motoneurones are able to adapt their function to increased peripheral demands more effectively than at later stages of post‐natal development. Retrograde labelling of soleus motor pool with horseradish peroxidase (HRP) showed that removal of L5 v.r. either at 4 or 15 days of age reduced the number of motoneurones supplying soleus muscle to less than 20%. No change in size of the remaining motoneurones was seen, indicating that the adjustment of transmitter output at the neuromuscular junctions in the younger group had no effect on the size of the cell.
A calcium‐activated potassium current in motor nerve terminals of the mouse.
Authors: Mallart A
Published: December 2014

Local circuit currents involving presynaptic terminals were recorded by micro‐electrodes inserted into the perineurium of nerves from the triangularis sterni muscle of the mouse. A transient outward current component was isolated by blocking the voltage‐activated (delayed rectifier) K current by 3,4‐diaminopyridine (3,4‐DAP). The amplitude of this component depended on external K concentration and fell to zero at [K]o = 15 mM. Since it also depended on [Ca]o, it was identified as a Ca‐activated K current (IK(Ca)). Tetraethylammonium (TEA) (2 mM), Ba (2 mM), Co (10 mM) and Mn (2.5 mM) blocked IK(Ca). IK(Ca) decayed to zero in approximately 12 ms and recovered from inactivation in about 100 ms. Ca current was enhanced in inverse proportion to the degree of IK(Ca) depression. The possible role of IK(Ca) in the process of neuromuscular facilitation is briefly discussed.
Characterization of miniature inhibitory post‐synaptic potentials in rat spinal motoneurones.
Authors: Kojima H , Takahashi T
Published: December 2014

Intracellular recordings were made from motoneurones in the isolated spinal cord of neonatal rats. After action potentials had been abolished by tetrodotoxin (TTX, 10(‐6) g/ml), small (approximately 0.4 mV) depolarizing potentials occurred spontaneously in motoneurones at low frequencies (approximately 1.5 Hz). These potentials were detectable only after the intracellular Cl‐ concentration of motoneurones was raised by using KCl electrodes and most of them were blocked by strychnine, suggesting that they are inhibitory post‐synaptic potentials (i.p.s.p.s). These spontaneous i.p.s.p.s under TTX are designated as 'miniature i.p.s.p.s' in order to distinguish them from i.p.s.p.s arising from spontaneous impulse activities of interneurones or afferent fibres. The miniature i.p.s.p.s were still observed after Ca2+ in saline was substituted by Mg2+ or Mn2+. In low Ca2+ and high Mg2+ saline, the amplitude distribution of miniature i.p.s.p.s was essentially the same as in normal saline. The frequency of miniature i.p.s.p.s increased when external Ca2+ concentration was raised. The frequency decreased to about 60% of the control when external Ca2+ was substituted by Mg2+ (2‐4 mM), whereas it increased to more than 20‐fold when substituted by Mn2+ (3‐5 mM). When the external K+ concentration was raised, the frequency of miniature i.p.s.p.s under TTX increased non‐linearly with the K+ concentration. The maximum slope in the relation between the log frequency and log K+ concentration was about 3.6. When the osmotic pressure was increased by adding sucrose, miniature i.p.s.p.s increased in frequency. The effect of osmotic pressure was relatively mild compared with that reported for the miniature end‐plate potentials (e.p.p.s) in the frog. When the temperature was raised, the frequency of miniature i.p.s.p.s increased. The relation between frequency and temperature fitted approximately to a straight line in Arrhenius plot with a Q10 of about 2.6. These characteristics of the miniature i.p.s.p.s closely resemble those of the miniature e.p.p.s. It is concluded that the miniature i.p.s.p.s recorded in motoneurones are equivalent in nature to the miniature e.p.p.s in neuromuscular junctions, thus reflecting the spontaneous release of quantal packages of the inhibitory transmitter.
Contractile effect of short‐chain fatty acids on the isolated colon of the rat.
Authors: Yajima T
Published: December 2014

The contractile effect of short‐chain fatty acids on proximal, middle and distal segments of the rat colon was studied in vitro. A single contraction of the longitudinal muscle of the everted preparation of the middle and distal but not the proximal colon was induced by mucosal application of propionate, butyrate or valerate. Sigmoid dose‐responses were observed between contraction and log dose of propionate, butyrate and valerate. The threshold concentration of short‐chain fatty acids was between 0.02 and 0.04 mM. A maximal contraction was induced with 0.1 mM‐propionate, butyrate and valerate. While acetate (up to 10 mM) and lactate (up to 30 mM) had no contractile effect at all. Serosal application of short‐chain fatty acids was without effect, while the contractile response with up to 10 mM‐propionate was abolished in both the middle and distal colon by scraping away the mucosa. Cumulative addition of short‐chain fatty acids to the organ bath (without wash‐out of the first dose) caused adaptation of the contractile response; thus, the effect of propionate (1 mM) was abolished by prior addition of acetate (10 mM) or lactate (30 mM) or propionate (1 mM) or butyrate (1 mM) or valerate (1 mM). The contractile effect of propionate was also inhibited by atropine (1 microM), procaine (0.4 mM) and tetrodotoxin (3 microM); was unaffected by hexamethonium (0.1 mM) and enhanced by eserine (10 nM). The results suggest that short‐chain fatty acids, which are normal constituents of the colon, have the ability to stimulate colonic contractions, probably via an enteric reflex involving local sensory and cholinergic nerves.
Inhibitors of calcium buffering depress evoked transmitter release at the squid giant synapse.
Authors: Adams D J , Takeda K , Umbach J A
Published: December 2014

Evoked release of transmitter at the squid giant synapse was examined under conditions where the calcium ion concentration in the presynaptic terminal was manipulated by inhibitors of calcium sequestration. Simultaneous intracellular recordings of presynaptic and post‐synaptic resting and action potentials were made during bath application of one of the following metabolic inhibitors: sodium cyanide (NaCN), carbonyl cyanide‐p‐trifluoromethoxyphenyl hydrazone (FCCP); ruthenium red (RuR) and sodium‐free (lithium) sea water. Cyanide and lithium sea water reversibly depressed the post‐synaptic potential (p.s.p.) whilst RuR and FCCP blocked the evoked post‐synaptic response irreversibly. The progressive reduction of p.s.p. amplitude was accompanied by a reversible increase in synaptic delay. The time course of block of the p.s.p. was similar for different agents and dependent on the rate of presynaptic activity (30‐40 min at 0.01 Hz). Recovery of the post‐synaptic action potential following block by cyanide and lithium sea water was obtained within 40 min and 5 min respectively. Synaptic depression by the metabolic inhibitors does not result from changes in presynaptic resting or action potentials, nor from a change in post‐synaptic receptor sensitivity. The post‐synaptic response to the local ionophoresis of L‐glutamate was unchanged following inhibition of evoked release of transmitter by cyanide. Injections of EGTA into presynaptic terminals poisoned by cyanide produced transient increases in p.s.p. amplitude, suggesting that cyanide is having its effect through raising intracellular calcium rather than lowering ATP. Control experiments injecting EGTA into unpoisoned nerve terminals showed no apparent effect on evoked transmitter release.
Synaptic block of a transmitter‐induced potassium conductance in Aplysia neurones.
Authors: Kehoe J
Published: December 2014

A voltage‐clamp study was made of a slow excitatory post‐synaptic potential (slow e.p.s.p.) that can be elicited in the medial cells of the left pleural ganglion of Aplysia californica by the firing of at least three different presynaptic neurones (labelled I, II and III). Each of these three neurones elicits other permeability changes in addition to the slow e.p.s.p., and all elements of these synaptic responses were shown to be mediated monosynaptically. The slow e.p.s.p., associated with an increase in membrane resistance, was shown to be due to a decrease in K permeability. When the slow e.p.s.p. was present spontaneously, it could be blocked by three compounds (tetraethylammonium (TEA), phenyltrimethylammonium (PTMA), or methylxylocholine (beta‐TM 10], all previously shown to block the cholinergic receptor that mediates an increase in K conductance in the medial cells (see Kehoe, 1972b). Furthermore, in ganglia in which no slow e.p.s.p. was seen in response to firing of the neurones I, II, and III, such a response became manifest when agonists capable of activating the cholinergic receptor were applied (e.g. acetylcholine (ACh), carbachol, arecoline, or F2268). The slow e.p.s.p. thus appears to result from the reduction, induced by any one of three 'blocking neurones', of a cholinergically controlled K conductance. Finally, when presynaptic neurone I (the only neurone tested) was fired shortly before or during the activation of presynaptic neurone IV, previously shown to be cholinergic (Kehoe, 1972b), the K component of the cholinergic post‐synaptic inhibitory potential was markedly reduced. The concentration at which a given agonist caused the manifestation of the synaptic diminution in K conductance (i.e. the slow e.p.s.p.) was found to be the same as that at which it caused a reduction in the synaptically activated, cholinergic, K‐dependent conductance elicited by presynaptic neurone IV. Intracellularly injected adenosine 3',5'‐cyclic monophosphate (cyclic AMP) imitated the effect of the 'blocking neurones' on the K conductance activated by bath‐applied cholinomimetics. This effect was superimposed on a cyclic‐AMP‐induced, voltage‐dependent inward current that disappeared when the cell was bathed in Na‐free sea water, or when the extracellular Ca concentration was increased to 60 mM. The effect of cyclic AMP on the cholinergic K conductance remained even after this cyclic‐AMP‐activated inward current was eliminated.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of calcium, barium and lanthanum on depolarization‐contraction coupling in skeletal muscle fibres of Rana pipiens.
Authors: Bolaños P , Caputo C , Velaz L
Published: December 2014

Voltage‐clamp experiments were carried out to study the effect of Ca, Ba and La on the contractile responses of short (approximately 1.5 mm) muscle fibres. In the absence of external Ca or when 1.8 mM‐Ca was substituted by 1.8 mM‐Ba the contractile responses to short depolarizing pulses (400 ms) were not modified and only a minor shift in the tension‐voltage relationship was observed. At high concentration (76 mM) of Ba or Ca, or in the presence of 2 mM‐La, shifts in the tension‐voltage relationship of 30, 41 and 25 mV respectively were observed. In addition the steepness of the activation curve was decreased in high Ba and Ca solutions. In the presence of 76 mM‐Ba, the rate of the relaxation phase which follows membrane repolarization after a short pulse was diminished, possibly due to an intracellular action of Ba. In the absence of Ca, or when Ca was substituted by 1.8 mM‐Ba the area under the prolonged contractile responses (contractures) was reduced considerably. In the presence of 76 mM‐Ba, the normal contracture time course was altered, showing a late slower relaxation phase, occasionally with a secondary tension development. In the presence of high Ca or La, the time course of the contractures was greatly prolonged. The steady‐state inactivation curve was shifted toward more negative potentials, in the absence of external Ca or when 1.8 mM‐Ca was substituted by 1.8 mM‐Ba. In the presence of 76 mM‐Ba the steady‐state inactivation curve was not affected. In the presence of 76 mM‐Ca or 2 mM‐La the curve was shifted toward less negative potential, with a marked decrease in its steepness. Ba at a concentration as high as 1 or 2 mM did not activate tension development in chemically skinned muscle fibres. Ba at 1 or 2 mM did not appreciably alter the Ca uptake capacity of isolated sarcoplasmic reticulum vesicles. At 5 mM a decrease in the Ca uptake capacity was observed. The results indicate that Ba at low (1.8 mM) concentration is not effective in substituting for Ca. The effects of divalent cations at high concentration, and of La, on the tension‐voltage relationship and on the steady‐state inactivation curve are most probably mediated by interaction with the external surface of the fibre membrane.(ABSTRACT TRUNCATED AT 400 WORDS)
The electrotonic location of low‐resistance intercellular junctions between a pair of giant neurones in the snail Lymnaea.
Authors: Benjamin P R , Pilkington J B
Published: December 2014

The passive electrotonic properties of neurones VD1 and RPD2 in the brain of the snail Lymnaea can be represented by a soma‐finite cable model with closed‐circuit axon termination. There is a considerable individual variation in input resistance, membrane time constant, electrotonic length and axon‐soma conductance ratio, but the average values for these parameters are similar in the two neurones. The cells are tightly coupled by an electrotonic synapse giving an average steady‐state coupling coefficient of 0.68 and an average resistance measured between recording sites in the cell bodies of 20 M omega. Calculations using a model consisting of a symmetrical pair of cells with standard values for the electrotonic parameters show that in this system, for a soma‐soma resistance of 20 M omega, the junction cannot be more than 0.16 length constants from the cell bodies. Reduction in coupling due to membrane current losses in such short proximal axon segments is insignificant. Intra‐axonal recordings indicate that most of the coupling resistance is located at the junction between VD1 and RPD2, which must therefore be closer to the cell bodies than the limiting value of 0.16 length constants assuming an electrical equivalent model which includes the standard electrotonic parameters. If all the soma‐soma resistance is located at the junction, then it could be physically a single array of gap‐junction particles. Despite its low conductance (1/20 M omega = 50 nS) and possibly small physical dimensions, the electrotonic synapse is more than sufficient to ensure spike synchrony in the two cells.
Excitatory and differential disinhibitory actions of acetylcholine in the lateral geniculate nucleus of the cat.
Authors: Eysel U T , Pape H C , Van Schayck R
Published: December 2014

Single neurones were recorded in the dorsal lateral geniculate nucleus (d.l.g.n.) of adult cats anaesthetized with a mixture of halothane, nitrous oxide and oxygen. The multibarrel‐glass micro‐electrodes were filled with sodium acetate, L‐glutamate, acetylcholine (ACh), gamma‐aminobutyric acid (GABA) and bicuculline. In normally innervated, spontaneously active d.l.g.n. cells, ACh and L‐glutamate elicited increased firing rates. After elimination of the excitatory input from the retina by retinal photocoagulation, the effects of ACh and L‐glutamate were similar. This proves that both drugs have direct excitatory effects on d.l.g.n. cells and that disinhibition is not the most prominent influence of ACh in the d.l.g.n. The excitatory action of ACh on relay cells in the d.l.g.n. was strongly influenced by barbiturates. Sub‐narcotic levels of sodium pentobarbitone completely abolished the excitation by ACh while the response to L‐glutamate remained unchanged. Excitation, centre‐surround antagonism and periphery effects were elicited by spots of light and by large field phase‐reversing gratings with and without central sparing of the receptive field area. Binocular inhibition was elicited with the phase‐reversing grating presented to the non‐dominant eye. After localized destruction of the retinal receptive field area, retinogeniculate excitation ceased and an isolated lateral inhibition was observed in the acutely deafferented d.l.g.n. cells. The time course and strength of this inhibition was disclosed by raising the background discharge with microiontophoretically applied L‐glutamate. With increasing size of retinal lesions the strength of isolated lateral inhibition decreased exponentially. A maximal intrageniculate range of more than 1000 microns was derived from computations of the lateral extent of deafferentation in the d.l.g.n. The inhibition acted beyond the classic surround inhibition of d.l.g.n. cells and thus was named long‐range lateral inhibition. Microiontophoretically applied GABA elicits a strong inhibitory effect at the d.l.g.n. cells which is antagonized by bicuculline. Centre‐surround antagonism, binocular inhibition and long‐range inhibition were blocked by bicuculline and thus proven to be GABAergic. Each class of inhibition was differentially influenced by microiontophoretically applied ACh. Long‐range inhibition was disinhibited, centre‐surround antagonism was enhanced, and binocular inhibition was not significantly changed. In contrast to ACh excitation, the disinhibitory action of ACh was not suppressed by pentobarbitone.(ABSTRACT TRUNCATED AT 400 WORDS)
The hypothalamo‐hypophyseal rat explant in vitro: endocrinological studies of the pars intermedia dopaminergic neural input.
Authors: Davis M D
Published: December 2014

Short‐term in vitro incubation of hypothalamo‐hypophyseal tissue from young rats was undertaken to discern more clearly the functional relationship between putative dopaminergic neural projections in the pars intermedia and the secretory activity of melanophore stimulating hormone (MSH). This explant consisted of a portion of the mediobasal hypothalamus containing the dopamine neurone cell bodies of interest, with the attached pituitary neuro‐intermediate lobe (n.i.l.). The n.i.l. was inserted into the end of a 1 mm diameter tube attached to a perfusion pump which allowed uninterrupted sampling of medium neighbouring the n.i.l. A 'real‐time' analysis of hormone secretion was obtained by immediately and continuously bioassaying for MSH. A bipolar stimulating electrode was placed on the ventral floor of the mediobasal hypothalamus either directly on the arcuate nucleus, median eminence or infundibular stalk. Electrical stimulation for 5 min (0.1‐20.0 Hz) caused a transient inhibition of basal MSH secretion, while continuous stimulation (0.1‐5.0 Hz) led to a much greater, long‐term, reversible inhibition. In the latter, the degree of inhibition was generally dependent on stimulation rate up to a maximum at 5 Hz. Application of the dopamine D2 receptor antagonist, 1‐sulpiride (0.001‐0.1 microM) to the perfusion medium not only completely and reversibly blocked the stimulus‐induced inhibition of MSH release but by itself, significantly increased the basal secretion rate. Applied to the isolated n.i.l., 1‐sulpiride did not alter release but did prevent the inhibitory response caused by exogenously applied dopamine (0.1 microM). The gamma‐aminobutyric acid receptor antagonist, bicuculline (0.01‐1.0 microM), had no effect on any of the parameters studied. In explants, cutting the infundibular stalk linking the mediobasal hypothalamus with the n.i.l., mimicked the effects of 1‐sulpiride by interrupting impulse flow to the gland. Thus, electrical stimulation of hypothalamic neurones in these explants apparently causes a release of dopamine from nerve terminals in the pars intermedia to inhibit MSH secretion and perhaps other pro‐opiomelanocortin‐derived peptides as well.
The non‐uniform character of expiratory synaptic activity in expiratory bulbospinal neurones of the cat.
Authors: Ballantyne D , Richter D W
Published: December 2014

Intracellular recordings were made from caudal medullary expiratory neurones in pentobarbitone‐anaesthetized, vagotomized and artificially ventilated cats. The sample consisted of thirty‐three bulbospinal neurones and seven neurones which were not antidromically excited from either the spinal cord (C2‐C3) or vagus nerve. Their rhythmic activity consisted of an alternating inspiratory hyperpolarization due to Cl(‐)‐dependent inhibitory post‐synaptic potentials (i.p.s.p.s) (Mitchell & Herbert, 1974) and an expiratory depolarization. The precise shape of the expiratory depolarizing wave varied within a given neurone depending on the over‐all pattern of respiration. This variation extended from a smoothly developing depolarization, continuous throughout its course, through an intermediate state in which depolarization proceeded in two stages with a definite transition between them, to a final state in which the early part of expiration was occupied by a distinct hyperpolarizing component to the membrane potential trajectory. Under conditions of a brisk phrenic nerve discharge, these variations in the shape of the membrane potential profile were related to the time course and intensity of post‐inspiratory discharge in the nerve. However, other factors (depth of anaesthesia and stimulation of laryngeal receptors) could influence the time course of the membrane potential profile of expiratory neurones independently of post‐inspiratory phrenic discharge. In five of fifteen neurones which were tested, early expiration was occupied by a rapidly developing, decrementing wave of Cl(‐)‐dependent i.p.s.p.s (post‐inspiratory i.p.s.p.s). These i.p.s.p.s were present only under conditions of a strong phrenic rhythm (large amplitude, fairly rapid phrenic discharge). They became weaker and ultimately disappeared when the level of anaesthesia was deepened and the phrenic rhythm became slower. Under these conditions, the post‐inspiratory wave of i.p.s.p.s could be restored by stimulation of the superior laryngeal nerve. Adequate stimulation of presumed 'irritant' laryngeal receptors elicited post‐inspiratory i.p.s.p.s in seven of ten neurones tested which initially showed either no post‐inspiratory i.p.s.p.s or possibly just a weak pattern. In ten of fifteen neurones tested, the responses to current injection revealed clear differences in membrane potential behaviour in early and late expiration, which became intensified following stimulation of the superior laryngeal nerve.(ABSTRACT TRUNCATED AT 400 WORDS)