bluuebunny/crossref_metadata_2025 huggingface dataset:
cAMP‐dependent reversal of opioid‐ and prostaglandin‐mediated depression of the isolated respiratory network in newborn rats
Authors: Ballanyi K. , Lalley P. M. , Hoch B. , Richter D. W.
Published: September 2004

Membrane potential (Vm) and resistance (Rm) of ventral respiratory group (VRG) neurons were measured in the isolated brainstem–spinal cord from newborn rats during bath application of the opioid receptor agonists fentanyl or [D‐Ala2, D‐Leu5]‐enkephalin (Ala‐Leu‐Enk) and of the prostaglandin Et (PGE1).

PGE1 (0.1–3 μm) and fentanyl or Ala‐Leu‐Enk (1–50 μm) produced depression and, at higher doses, block of inspiratory nerve activity and respiration‐related postsynaptic potentials. This apnoea was associated with hyperpolarization and Rm fall in 25% of thirty‐two VRG neurons tested, whereas resting Vm and Rm were not changed in the other cells.

The selective μ‐ and δ‐receptor blockers naloxonazine (10–20 μm) and naltrindole (50–100 μM) antagonized the effects of 5 μm fentanyl and 50 μM Ala‐Leu‐Enk, respectively.

Opioid‐ and PGE1‐evoked respiratory depression was reversed upon elevation of endogenous cAMP levels by stimulating adenylyl cyclase with 100 μM forskolin, activating dopamine D1 receptors with 50–100 μm 6‐chloro‐7,8‐dihydroxy‐3‐allyl‐1‐phenyl‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepine (6‐chloro‐APB) or preventing cAMP breakdown with 50–100 μm isobutylmethylxanthine.

The results indicate that opioid‐ or prostaglandin‐induced respiratory depression is due to a fall in cAMP levels in cells responsible for generation of rhythm or providing a tonic drive to the respiratory network.

We suggest that elevation of cAMP levels is an effective antidote in neonates against such forms of respiratory depression.
Activity‐dependent properties of synaptic transmission at two classes of connections made by rat neocortical pyramidal axons in vitro
Authors: Thomson Alex M.
Published: September 2004

To compare the dynamics of synaptic transmission at different types of connection, dual intracellular recordings were made from pairs of neurones in slices of adult rat neocortex. Excitatory postsynaptic potentials (EPSPs) were elicited by single spikes, spike pairs and brief spike trains in presynaptic pyramidal cells and responses recorded in postsynaptic pyramidal cells and in inter neurones.

Pyramid–pyramid EPSPs were strongly voltage dependent and this resulted in a range of paired pulse effects. At thirty‐two of sixty‐nine pyramid–pyramid connections, the 2nd EPSP was the same shape as the 1st, indicating minimal interaction between active synapses. In these thirty‐two connections, paired pulse depression (PPD) was apparent (2nd EPSP integral 46 ± 21% of the 1st, at 5–20 ms), which recovered within 60–70 ms.

In eleven additional pyramid–pyramid pairs, the 2nd EPSP was also the same shape as the 1st, but paired pulse facilitation (PPF, 149 ± 32%) decaying within 50–60 ms was apparent. Even these connections displayed frequency‐dependent depression, however, as 3rd EPSPs were smaller than 1st EPSPs at intervals < 100 ms.

At twenty‐five pyramid–pyramid connections, 2nd EPSPs were broader than 1st EPSPs and in sixteen of these, voltage‐ and NMDA receptor‐dependent enhancement was large enough to obscure the underlying PPD. PPD was revealed by postsynaptic hyperpolarization (4 pairs), N‐methyl‐D‐aspartate (NMDA) receptor blockade (3 pairs), or if Mg2+ was removed (in the one case studied). If synapse location allowed significant depolarization of one active site by another, voltage‐dependent enhancement could produce supralinear EPSP summation and overcome PPD. Third EPSPs were, however, consistently smaller than 1st EPSPs.

In striking contrast, profound frequency‐dependent facilitation, independent of voltage or NMDA receptors was seen at fifteen connections involving two classes of postsynaptic inter neurones.

At these pyramid–interneurone connections, facilitation of the 2nd EPSP (655 ± 380% at 5–20 ms) decayed rapidly, within 50–60 ms. Third and fourth EPSPs showed additional facilitation which decayed more slowly, within 90 ms and 2 s, respectively. Facilitation due to five to six spike trains was still apparent at 3 s. Therefore, once initiated by a brief high frequency spike train, facilitation was maintained at lower frequencies.
Fusimotor Influence on Jaw Muscle Spindle Activity during Swallowing‐Related Movements in the Cat
Authors: Taylor A. , Hidaka O. , Durbaba R. , Ellaway P. H.
Published: September 2004

The activity patterns of muscle spindle afferents in jaw‐closer muscles were studied during reflex swallowing movements in anaesthetized cats. Simultaneous records were made of the electromyogram (EMG) in masseter and anterior digastric muscles and of the unloaded jaw movements. The underlying patterns of fusimotor activity were deduced by comparing afferent discharges occurring during active swallowing with those occurring when exactly the same movements were imposed passively. The interpretation of spindle behaviour was greatly facilitated by characterizing the afferents according to the evidence for their contact with the various intrafusal muscle fibres, derived from testing with succinylcholine. It was also valuable to have two different types of afferent recorded simultaneously.

There was clear evidence of fusimotor activity occurring during active jaw closing so as to oppose the spindle silencing. This effect was most marked in b2c‐type afferents (probably secondaries) and was therefore attributed to a modulation of static fusimotor discharge approximately in parallel with α‐activity.

Afferents with evidence of bag1 fibre contacts (primaries) showed much greater sensitivity to muscle lengthening during active movement than when the movement was imposed. This difference was exaggerated when anaesthesia was deepened for the passive movements. This was interpreted as evidence for a higher level of dynamic fusimotor activity maintained during active movements than at rest.

The results support the view that for a variety of active jaw movements, static fusimotor neurone firing is modulated roughly in parallel with α‐activity but leading it so as to counteract spindle unloading. Dynamic fusimotor neurone firing appears to be set at a raised level during active movements. Anaesthesia appears to depress activity in the α‐motoneurones more than in γ‐motoneurones.
Mechanism of oxidative stress‐induced intracellular acidosis in rat cerebellar astrocytes and C6 glioma cells
Authors: Tsai Ke‐Li , Wang Seu‐Mei , Chen Ching‐Chow , Fong Tsorng‐Harn , Wu Mei‐Lin
Published: September 2004

Following ischaemic reperfusion, large amounts of superoxide anion (.O2−), hydroxyl radical (.OH) and H2O2 are produced, resulting in brain oedema and changes in cerebral vascular permeability. We have found that H2O2 (100 μm) induces a significant intracellular acidosis in both cultured rat cerebellar astrocytes (0.37 ± 0.04 pH units) and C6 glioma cells (0.33 ± 0.07 pH units).

Two membrane‐crossing ferrous iron chelators, phenanthroline and deferoxamine, almost completely inhibited H2O2‐induced intracellular acidosis, while the non‐membrane‐crossing iron chelator apo‐transferrin had no effect. Furthermore, the acidosis was completely inhibited by two potent membrane‐crossing .OH scavengers, N‐(2‐mercaptopropionyl)‐grycine (N‐MPG) and dimethyl thiourea (DMTU). Since .OH can be produced during iron‐catalysed H2O2 breakdown (Fenton reaction), we have shown that a large reduction in pH1 in glial cells can result from the production of intracellular .OH via H2O2 oxidation.

We have ruled out the possible involvement of: (i) an increase in intracellular Ca2+ levels; and (ii) inhibition of oxidative phosphorylation.

Our results suggest that .OH inhibits glycolysis, leading to ATP hydrolysis and intracellular acidosis. This conclusion is based on the following observations: (i) in glucose‐free medium, or in the presence of iodoacetate or 2‐deoxy‐D‐glucose, H2O2‐induced acidosis is completely suppressed; (ii) H2O2 and iodoacetate both produce an increase in levels of intracellular free Mg2+, an indicator of ATP breakdown; and (iii) direct measurement of intracellular ATP levels and lactate production show 50 and 55% reductions in ATP content and lactate production, respectively, following treatment with 100 μm H2O2.

Inhibition of the pH1 regulators (i.e. the Na+–H+ exchange and possibly the Na+–HCO3−–dependent pH1 transporters) resulting from H2O2‐induced intracellular ATP reduction may also be involved in the H2O2‐evoked intracellular acidosis in glial cells.
The removal of acetylcholine by diffusion at nicotinic synapses in the rat otic ganglion
Authors: Callister Robert J. , Sah Pankaj
Published: September 2004

We have examined the clearance of synaptically released acetylcholine in the otic ganglion when acetylcholinesterase was blocked with eserine.

Intracellular recordings were made from otic ganglion neurones, in vitro. The decay of the excitatory postsynaptic potential (EPSP), in response to stimulation of afferent fibres, was greatly prolonged in the presence of eserine. Low frequency (0.05–4 Hz) repetitive synaptic stimulation led to a slow depolarization of the postsynaptic cell that persisted throughout the period of stimulation. This slow depolarization was blocked by the nicotinic antagonists mecamylamine (100 μm) or (+)tubocurarine (100 μm), but was unaffected by atropine (1 μm), indicating that the response was due to the activation of nicotinic receptors.

Following 2 Hz synaptic stimulation (30 s), the rate of rise of the slow depolarization had a time constant of 3.1 ± 0.4 s and a peak amplitude of 12 ± 1 mV. Upon cessation of stimulation, the depolarization decayed to resting levels with a time constant of 18.3 ± 1.5 s (n= 23). At increasing stimulation frequencies the rate of rise of the depolarization increased. Lowering the probability of release, by adding cadmium to the perfusing solution or by lowering extracellular calcium, slowed the rise time of the response.

Both the onset and decay kinetics of the slow depolarization had a low temperature sensitivity, indicating that they reflect diffusional processes.

Repetitive stimulation (2 Hz) of the afferent nerve supplying the ganglion, in the presence of eserine, also caused a slow depolarization in cells in which we could not demonstrate a synaptic input. This indicates that synaptically released acetylcholine can spill over onto nearby neurones.

We conclude that at parasympathetic synapses, under physiological conditions, transmitter action is terminated by the enzymatic degradation of acetylcholine. When acetylcholinesterase is blocked, acetylcholine accumulates because its removal by diffusion is slow.
On‐going and reflex synaptic events in rat superior cervical ganglion cells
Authors: McLachlan Elspeth M. , Davies Philip J. , Häbler H.‐Joachim , Jamieson John
Published: September 2004

Synaptic events evoked by brief noxious cutaneous stimuli were recorded in sympathetic neurones in the superior cervical ganglion of anaesthetized rats.

On‐going excitatory synaptic potentials (ESPs) and/or action potentials (APs) were recorded in 69% of neurones at mean frequencies that varied from 0.01 to 6.3 Hz in different cells. From histograms of ESP amplitude during membrane hyper polarization, it appears that most cells received one (52%), or two or more (36%), suprathreshold inputs and several subthreshold inputs with overlapping amplitudes.

Pinching the skin for 1–3 s evoked either a brief burst of synaptic events (lasting about 300 ms) preceding a few seconds of inhibition (burst–inhibitory (BI) neurones), or simply an excitation (excitatory (E) neurones), or no response (O neurones). In 60% of BI neurones, a second burst occurred after the end of the pinch.

BI neurones had a higher frequency of on‐going synaptic activity (2.9 ± 0.5 Hz, n= 15) than E neurones (0.2 ± 0.1 Hz, n= 5) or O (0.2 ± 0.1 Hz, n= 5) neurones. Most neurones with two or more suprathreshold inputs were BI neurones. In 20% of neurones (all BI with high rates of synaptic activity), several other inputs had ESPs with amplitudes close to threshold.

Subthreshold and suprathreshold inputs responded in the same way in only 45% of neurones, but suprathreshold inputs were excited in 73% of BI and all E neurones. The order of recruitment of different inputs varied from trial to trial. If classification was based only on suprathreshold responses, there were 36% BI, 32% E and 32% O neurones.

In the majority of neurones, postganglionic discharge was initiated exclusively by supra‐threshold inputs, even during reflex excitation.

Qualitatively similar, but smaller, responses were evoked by a puff of air on the abdomen in 71% of cells tested.

The data suggest that the natural discharge of SCG neurones is largely determined by the activity of one or two preganglionic inputs with high quantal contents. BI neurones may include vasoconstrictor neurones, whereas the other types include secretomotor, pilomotor and other neurones projecting to targets in the head.
Increased Sensitivity of Gastrin Cells to Gastric Distension following Antral Denervation in the Rat
Authors: Higham A. , Noble P. , Thompson D. G. , Dockray G. J.
Published: September 2004

Secretion of the antral hormone gastrin is increased by protein in the gastric lumen and by nervous reflexes. We have examined the relative importance of luminal and neuronal mechanisms, by lesioning the antral innervation using benzalkonium chloride.

Benzalkonium chloride was applied to the serosa of the antrum in anaesthetized rats. In some animals, a stainless‐steel cannula was also implanted in the corpus. Animals were allowed 10 days to recover. Plasma gastrin was measured by radioimmunoassay and mRNAs encoding gastrin, somatostatin and histidine decarboxylase were measured by Northern blot.

Antral denervation was associated with gastric retention after fasting, and elevated plasma gastrin (28.4 ± 7 pM compared with 7.6 ± 1.0 pM in controls). When fasted control or denervated rats were refed, plasma gastrin increased 3‐fold in both cases. A gastrin‐releasing peptide antagonist inhibited the post‐prandial rise in plasma gastrin in control rats, but had no effect in antrally denervated rats.

In fasted, antrally denervated rats with a gastric fistula, basal gastric acid secretion was depressed 3‐fold, and plasma gastrin concentrations were similar to controls.

Distension of the stomach with peptone via a barostat attached to the gastric cannula (5 cmH2O, 30 min), produced 3‐fold increases in plasma gastrin in both control and denervated rats. However, distension with a non‐nutrient solution at pH 6.0 had no effect in controls, but increased gastrin to a similar extent to peptone in denervated rats; distension with 50 mM HCl had no effect in either control or denervated rats.

Somatostatin and gastrin mRNA abundances in the antrum were depressed by about 35% by antral denervation, but somatostatin mRNA in the corpus was unchanged; GAPDH mRNA abundance was unaffected by antral denervation.

The data suggest that luminal nutrient releases gastrin in the rat, in vivo, via activation of antral neurons secreting gastrin‐releasing peptide, and that the antral innervation normally inhibits G‐cell responses to non‐nutrient distension of the stomach. After antral denervation, gastric distension with a non‐nutrient solution is an adequate stimulus for gastrin release.
Hypoxia‐induced catecholamine secretion in isolated newborn rat adrenal chromaffin cells is mimicked by inhibition of mitochondrial respiration
Authors: Mojet Mart H. , Mills Elliott , Duchen Michael R.
Published: September 2004

In newborn mammals, systemic hypoxia provokes catecholamine secretion from the adrenal medulla. In contrast to adults, this release is independent of sympathetic innervation. We have studied the cellular processes involved in hypoxia‐induced catecholamine secretion, employing fluorimetric techniques to measure changes in [Ca2+]i, NADH and mitochondrial potential, and voltammetric techniques to record changes inPO2and catecholamine secretion.

In adrenal chromaffin cells freshly dissociated from newborn rats, severe hypoxia increased [Ca2+]iand secretion of catecholamines, indicating that the response of the newborn adrenal medulla to hypoxia is an intrinsic property of these cells. Discrete quantal secretory events were identifiable, suggesting an exocytotic mechanism of secretion.

Hypoxia‐induced secretion was only seen whenPO2fell below 5 mmHg, similar to the threshold arterialPO2reported to stimulate releasein vivo.Such oxygen tensions also inhibited mitochondrial metabolism, shown by an increase in NADH autofluorescence. We therefore explored the involvement of mitochondria in oxygen sensing. Inhibition of mitochondrial respiration either by CN−at complex IV or by rotenone at complex I mimicked severe hypoxia, reversibly increasing both [Ca2+]iand catecholamine secretion. The CN−‐induced depolarization of the mitochondrial inner membrane potential preceded the increase in [Ca2]iby ∼6 s.

The effects of severe hypoxia and CN−on [Ca2+]iand catecholamine secretion were not additive, suggesting a common mechanism.

Chemical anoxia failed to increase [Ca2+]iin a significant proportion of cells dissociated from 2‐ to 4‐week‐old rats. Thus, the sensitivity to hypoxia is specific to adrenal chromaffin cells dissociated from newborn rats.

These data indicate that hypoxia‐induced catecholamine secretion in the newborn adrenal medulla is mediated by reversible inhibition of mitochondrial respiration, leading to an increase in [Ca2+]iand catecholamine secretion.
Modulation of endogenous firing patterns by osmolarity in rat hippocampal neurones
Authors: Azouz Rony , Alroy Gil , Yaari Yoel
Published: September 2004

Intracellular recordings in adult rat hippocampal slices were used to investigate the modulation of endogenous neuronal firing patterns by moderate changes (± 13%) in the extracellular osmotic pressure (πo). The responses of CA1 pyramidal cells to graded depolarizing current pulses were used to differentiate between regular and burst‐firing patterns and to characterize the stimulus requirements for evoking endogenous burst discharge.

Decreasing or increasing πo had no significant effects on resting membrane potential and input resistance, spike threshold and amplitude, and the amplitudes of the fast, medium and slow spike after‐hyperpolarizations (AHPs). The apparent membrane time constant (τm) increased in low πo and decreased in high πo.

Reducing πo converted non‐bursting neurones (non‐bursters) to bursting neurones (bursters) and decreased the stimulus requirements for evoking burst firing in native bursters. Increasing πo suppressed endogenous burst firing.

Lowering πo increased the size of the ‘active’ (i.e. re‐depolarizing) component of the spike after‐depolarization (ADP). Conversely, increasing πo suppressed the active ADP component.

The sensitivity of spike ADPs and firing patterns of pyramidal cells to the changes in πo persisted also in Ca2+‐free saline, indicating that the osmotic effects are not imparted by modulation of Ca2+ and/or Ca2+‐activated K+ currents.

Blocking most K+ currents with Ca2+‐free, TEA‐containing saline induced large and prolonged (up to 1 s), TTX‐sensitive plateau potentials following the primary fast spikes. These potentials were augmented by low πo and abated by high πo.

When injected with subthreshold depolarizing current pulses in Ca2+‐free saline, pyramidal cells displayed a distinct TTX‐sensitive inward rectification. This rectification was augmented by low πo and reduced by high πo.

The various effects of low‐πo and high‐πo saline solutions were reversible upon washing with normosmotic saline.

We conclude that πo is a critical determinant of the endogenous firing patterns of CA1 pyramidal cells. The data suggest that the osmotic effects are most likely to be mediated by changes in the persistent Na+ current, which underlies the active spike ADP and the burst potential in CA1 pyramidal neurones. The possible contribution of these effects to changes in brain excitability in various abnormal osmotic states is discussed.
Effect of Midbrain Stimulations on Thermoregulatory Vasomotor Responses in Rats
Authors: Zhang Yi‐Hong , Hosono Takayoshi , Yanase‐Fujiwara Motoko , Chen Xiao‐Ming , Kanosue Kazuyuki
Published: September 2004

Efferent projections eliciting vasodilatation when the preoptic area is warmed were investigated by monitoring tail vasomotor responses of ketamine‐anaesthetized rats when brain areas were stimulated electrically (0.2 mA, 200 μs, 0 Hz) or with the excitatory amino acid D,L‐homocysteic acid (1 mM, 0.3 μM).

Both stimulations elicited vasodilatation when applied within a region extending from the most caudal part of the lateral hypothalamus to the ventrolateral periaqueductal grey matter (PAG) and the reticular formation ventrolateral to the PAG.

Vasodilatation elicited by preoptic warming was suppressed when either stimulation was applied within the rostral part of the ventral tegmental area (VTA).

Sustained vasodilatation was elicited by knife cuts caudal to the VTA, and vasodilatation elicited by preoptic warming was suppressed by cuts either rostral to the VTA or in the region including the PAG and the reticular formation ventrolateral to it.

These results, together with the results of earlier physiological and histological studies, suggest that warm‐sensitive neurones in the preoptic area send excitatory signals to vasodilatative neurones in the caudal part of the lateral hypothalamus, ventrolateral PAG and reticular formation, and send inhibitory signals to vasoconstrictive neurones in the rostral part of the VTA.
Development of Carotid Chemoreceptor Dynamic and Steady‐State Sensitivity to CO2 in the Newborn Lamb
Authors: Calder N. A. , Kumar P. , Hanson M. A.
Published: September 2004

The maturation of carotid chemoreceptor steady‐state and dynamic responses to CO2 in newborn lambs was measured. In total, sixteen fibres (13 lambs) were studied at 3–4 days, nineteen fibres (13 lambs) at 5–9 days and twenty‐one fibres (17 lambs) at 10–24 days after birth.

Steady‐state CO2 sensitivity was measured over a range of arterial CO2 pressures (Pa,CO2) at four levels of arterial O2 pressure (Pa,O2): hyperoxia (Hyp), 115–150 mmHg; normoxia (Nx), 90–105 mmHg; moderate hypoxia (ModHx), 40–60 mmHg; and severe hypoxia (SvHx), 20–35 mmHg.

Steady‐state CO2 sensitivity was present at all ages, and a significant effect of age (P < 0.001) and Pa,O2 (P < 0.025) (ANOVA) was observed. Older lambs were unable to sustain an increase in chemoreceptor discharge during SvHx as CO2 was increased.

Dynamic CO2 sensitivity was measured by producing alternations in end‐tidal CO2 levels (etCO2) (alternation amplitude, 1.23 ± 0.07% (mean ±s.e.m.); etCO2, 7.56 ± 0.15%) over 2–8 s at two Pa,O2 levels only: 80–100 (Nx) and 40–60 mmHg (ModHx). Peak and trough values of the oscillation in chemoreceptor discharge were plotted against maximum and minimum etCO2 for the control and CO2‐loaded breaths. Dynamic CO2 sensitivity was calculated as the slope between these points.

Dynamic CO2 sensitivity was greater than steady‐state sensitivity in Nx (P < 0.05) and ModHx (P < 0.01, Student's paired t test). Unlike steady‐state CO2 sensitivity, there was no significant effect of age or Pa,O2 on dynamic sensitivity (P > 0.39 and P > 0.68, respectively, ANOVA).

Our results show that the neonatal lamb possesses a carotid body steady‐state CO2 sensitivity within a few days of birth, an age when hypoxia sensitivity is low. This CO2 sensitivity increases with age, perhaps due to the increasing interaction between CO2 and O2. Dynamic sensitivity of the carotid body to CO2 is mature at birth and does not increase with age, as predicted if the response of the carotid body to rapid changes in CO2 is independent of the sensitivity to the partial pressure of O2 (PO2).
Bilateral disruption of conditioned responses after unilateral blockade of cerebellar output in the decerebrate ferret
Authors: Ivarsson M. , Svensson P. , Hesslow G.
Published: September 2004

Lesions of the cerebellar cortex can abolish classically conditioned eyeblink responses, but some recovery with retraining has been observed. It has been suggested that the recovered responses are generated by the intact contralateral cerebellar hemisphere. In order to investigate this suggestion, bilaterally acquired conditioned responses were studied after the unilateral blockade of cerebellar output.

Decerebrate ferrets were trained with ipsilateral electrical forelimb stimulation (300 ms, 50 Hz, 1 mA) as the conditioned stimulus and bilaterally applied peri‐orbital stimulation (40 ms, 50 Hz, 3 mA) as the unconditioned stimulus. The conditioned and unconditioned eyeblink responses were monitored by EMG recordings from the orbicularis oculi muscle. The output from one cerebellar hemisphere was blocked either by injecting small amounts of lignocaine (lidocaine; 0.5‐1.0μl)) into the brachium conjunctivum, or by a restricted mechanical lesion of the brainstem rostral to the cerebellum.

As described by previous investigators, the unilateral blockade of cerebellar output abolished ipsilateral conditioned responses.

More importantly, such blockade also abolished or strongly depressed contralateral conditioned responses. When mechanical lesions of the brachium conjunctivum were made, contralateral responses, in contrast to ipsilateral responses, recovered within 1–2.5 h.

When the unconditioned stimulus was removed on one side, causing extinction of conditioned responses on this side, conditioned responses were temporarily depressed on the trained side as well.

Unilateral interruption of cerebellar output had no clear effect on contralateral unconditioned reflex responses.

The results demonstrate that one cerebellar hemisphere in ferrets exerts a marked control of contralateral conditioned eyeblink responses, probably via premotor neurones involved specifically in conditioned, and not in unconditioned, responses.
Excitatory and inhibitory motor reflexes in the isolated guinea‐pig stomach
Authors: Hennig G.W. , Brookes S.J.H. , Costa M.
Published: September 2004

We have described and analysed the movements of the isolated stomach during distension by correlating intragastric pressure with video recordings, and investigated the presence of intrinsic inhibitory and excitatory reflexes.

Isolated guinea‐pig stomachs, placed in an organ bath, were slowly distended with Krebs solution using a syringe pump via a cannula through the pylorus. The changes in intragastric pressure during cycles of distension were monitored by pressure transducers connected to both oesophageal and pyloric cannulae. The resistivity of the gastric wall (change in pressure with volume, δP/δV) and the amplitude and frequency of phasic pressure events were calculated from pressure recordings.

The movements of the stomach were also recorded onto videotape. The motion of the gastric wall during distension cycles was analysed to establish the patterns of contractions, their propagation and the distribution of fluid in the stomach. During filling, fluid was preferentially accommodated in the fundus. Propagating (peristaltic) contractions, often starting in the fundus, moved aborally towards the pylorus. The peak of the phasic pressure event was observed when a contraction reached the orad antrum. As it reached the pylorus, intragastric pressure was at its minimum.

During the initial phase of distension, intragastric pressure increased steeply. Tetrodotoxin and hyoscine reduced both the resistivity and amplitude of phasic pressure events. Hexamethonium had a similar effect. Thus distension appears to activate an excitatory reflex pathway, involving nicotinic ganglionic transmission. This reflex increases wall tension and enhances myogenic peristaltic contractions.

In control preparations, with larger distension volumes, the intragastric pressure decreased, despite the continued infusion of Krebs solution. l‐NAME and apamin abolished this drop in pressure, indicating that gastric enteric inhibitory mechanisms prevail at larger distension volumes. After blockade of the excitatory reflex, hexamethonium antagonized the inhibitory response, indicating that activation of inhibitory mechanisms involves nicotinic transmission, probably on enteric inhibitory motoneurons.

Both the excitatory and inhibitory reflexes in the isolated stomach operate within a physiological range of gastric volumes. The excitatory reflex predominates at small distension volumes, leading to large phasic propagated contractions that mix the contents and may lead to emptying of the stomach. The inhibitory reflex, described previously as adaptive relaxation, can maximally relax the stomach and is activated preferentially at higher distension volumes to accommodate the contents. The interplay of these reflex pathways in the isolated stomach produces a rich repertoire of gastric movements.

The isolated stomach preparation, used with a combination of kinematic, kinetic and pharmacological methods, provides a highly suitable means of investigating the mechanisms of gastric motility.
Gating of cutaneous input to cerebellar climbing fibres during a reaching task in the cat
Authors: Apps Richard , Atkins Melanie J. , Garwicz Martin
Published: September 2004

Task‐dependent modulation of cutaneous input to climbing fibres projecting to the C1, C2 and C3 zones in the cerebellar paravermal lobule V was investigated in awake cats during performance of a reaching task.

Climbing fibre responses resulting from low intensity (non‐noxious) electrical stimulation of the ipsilateral superficial radial nerve were recorded as extracellular field potentials in the cerebellar cortex using chronically implanted microwires.

Response size, measured as the time–voltage integral of the evoked field potential, was assessed during three phases of the reaching movement, reaction, reach and grasp, and compared with the response size at rest.

At C1 and C3 zone recording sites response size was usually reduced during the task (7/10 sites). The reduction was most pronounced in the grasp phase, occasionally accompanied by a smaller reduction in the reach and reaction phases. In one case an enhancement was found in the reach phase.

Response size was also modulated during the task at four of six C2 zone recording sites. However, the results were mixed. In three cases the modulation resembled the pattern at C1/C3 sites with the responses being reduced in the grasp phase accompanied on occasion by a lesser reduction in the reach phase. In the remaining case there was an enhancement during grasp. In this case and one other there was also an enhancement during the reaction phase.

The findings indicate significant gating of cutaneous input to climbing fibres projecting to the C1, C2 and C3 zones during reaching movements, while the variability between recording sites suggests functional differences, both between and within zones.
Forearm sympathetic withdrawal and vasodilatation during mental stress in humans
Authors: Halliwill John R. , Lawler Lori A. , Eickhoff Tamara J. , Dietz Niki M. , Nauss Lee A. , Joyner Michael J.
Published: September 2004

In humans, mental stress elicits vasodilatation in the muscle vascular beds of the forearm that may be neurally mediated. We sought to determine the extent to which this vasodilatation is due to sympathetic withdrawal, active neurogenic vasodilatation, or β‐adrenergically mediated vasodilatation.

We simultaneously measured forearm blood flow and muscle sympathetic nerve traffic to the forearm during mental stress in humans. In a second study, we measured forearm blood flow responses to mental stress after selective blockade of α‐adrenergic neurotransmission in one forearm. In a final study, we measured forearm blood flow responses to mental stress after unilateral anaesthetic blockade of the stellate ganglion, alone or in combination with selective β‐adrenergic receptor blockade of the forearm.

During mental stress, muscle sympathetic nerve activity decreased from 5113 ± 788 to 1509 ± 494 total integrated activity min− (P < 0.05) and forearm vascular resistance decreased from 96 ± 29 to 33 ± 7 mmHg (dl of tissue) min ml− (P < 0.05). Considerable vasodilatation was still elicited by mental stress after selective blockade of α‐adrenergic neurotransmission. Vasodilatation also occurred during mental stress after stellate ganglion blockade. This dilatation was reduced by selective blockade of β‐adrenergic receptors in the forearm.

Our results support a role for both sympathetic withdrawal and β‐adrenergic vasodilatation as the major causes of the forearm vasodilatation during mental stress in humans.
The contribution of otoliths and semicircular canals to the perception of two‐dimensional passive whole‐body motion in humans
Authors: Ivanenko Y. P. , Grasso R. , Israël I. , Berthoz A.
Published: September 2004

Perception of two‐dimensional (2–D) whole‐body passive motion in the horizontal plane was studied in twelve blindfolded healthy volunteers: pure rotation in place (180 deg), linear motion (4.5 m) and a semicircular trajectory (radius, 1.5 m; angular acceleration, 0.2 rad s−2) were applied in random sequence by means of a remote‐controlled robot equipped with a racing‐car seat. The seat orientation in the horizontal plane was controlled by the experimenter, independent of the robot trajectory. Thus different degrees of otolith–canal interaction were obtained. The maximal linear acceleration during the semicircular trajectory was 0.1 g; however, the linear acceleration vector was complex as it rotated relative to the subject's head.

In the first of two sessions, subjects were instructed to maintain an angular pointer oriented towards a remote (15 m) previously seen target during the passive movements. In the second session they had to make a drawing of the path of the perceived trajectory, after the movement was finished.

The results showed that, on average, the movement of the pointer matched the dynamics of the rotatory component of the 2‐D motion well. This suggests that, in the range of linear accelerations used in this study, no appreciable influence of otolith input on canal‐mediated perception of angular motion occurred.

The curvature of the drawn paths was mostly explained by the input to the semicircular canals. Subjects’ reconstruction of motion did not account for the directional dynamics of the input to the otoliths occurring during passive motion.

This finding proves that reconstructing trajectory in space does not imply a mathematically perfect transformation of the linear and angular motion‐related inputs into a Cartesian or polar 2‐D representation. Physiological constraints on the interaction between motion direction and change of heading play an important role in motion perception.
Coherent oscillations in monkey motor cortex and hand muscle EMG show task‐dependent modulation
Authors: Baker S. N. , Olivier E. , Lemon R. N.
Published: September 2004

Recordings were made of local field potential (slow waves) and pyramidal tract neurone (PTN) discharge from pairs of sites separated by a horizontal distance of up to 1.5 mm in the primary motor cortex of two conscious macaque monkeys performing a precision grip task.

In both monkeys, the slow wave recordings showed bursts of oscillations in the 20–30 Hz range. Spectral analysis revealed that the oscillations were coherent between the two simultaneously recorded cortical sites. In the monkey from which most data were recorded, the mean frequency of peak coherence was 23.4 Hz.

Coherence in this frequency range was also seen between cortical slow wave recordings and rectified EMG of hand and forearm muscles active during the task, and between pairs of rectified EMGs.

The dynamics of the coherence were investigated by analysing short, quasi‐stationary data segments aligned relative to task performance. This revealed that the 20–30 Hz coherent oscillations were present mainly during the hold phase of the precision grip task.

The spikes of identified PTNs were used to compile spike‐triggered averages of the slow wave recordings. Oscillations were seen in 11/17 averages of the slow wave recorded on the same electrode as the triggering spike, and 11/17 averages of the slow wave recorded on the distant electrode. The mean period of these oscillations was 45.8 ms.

It is concluded that oscillations in the range 20–30 Hz are present in monkey motor cortex, are coherent between spatially separated cortical sites, and encompass the pyramidal tract output neurones. They are discernable in the EMG of active muscles, and show a consistent task‐dependent modulation.
Consequences of metabolic inhibition in smooth muscle isolated from guinea‐pig stomach
Authors: Nakayama S. , Chihara S. , Clark J. F. , Huang S.‐M. , Horrachi T. , Tomita T.
Published: September 2004

In smooth muscle isolated from the guinea‐pig stomach, cyanide (CN) and iodoacetic acid (IAA) were applied to block oxidative phosphorylation and glycolysis, respectively. Effects of IAA on generation of spontaneous mechanical and electrical activities were systematically investigated by comparing those of CN. Spontaneous activity ceased in 10–20 min during applications of 1 mm IAA. On the other hand, application of 1 mm CN also reduced the spontaneous activity, but never terminated it. In the presence of CN the negativity of the resting membrane potential was slightly reduced.

When spontaneous activity ceased with IAA, the resting membrane potential was not significantly affected. Also, before ceasing, the amplitude and duration of the spontaneous electrical activity were significantly reduced. The amplitude of the electrotonic potential was, however, not changed by IAA. Further, glibenclamide did not prevent the effects of IAA. These results suggest that, unlike cardiac muscle, activation of metabolism‐dependent K+ channels in stomach smooth muscle does not seem to play a major role in reducing and terminating spontaneous activity during metabolic inhibition.

Carbachol‐induced contraction transiently increased, and subsequently decreased gradually during application of IAA.

After 50 min application of IAA, when there was no spontaneous activity, the concentrations of phosphocreatine (PCr) and ATP measured with 31P nuclear magnetic resonance decreased to 60 and 80% of the control, respectively, while inorganic phosphate (Pi) concentration paradoxically fell to below detectable levels. During subsequent prolonged application of IAA, high‐energy phosphates steadily decreased. On the other hand, after 50 min CN application, [PCr] and [ATP] decreased to approximately 30 and 80% of the control, respectively, while [Pi] increased by 2.6‐fold.

In the presence of either CN or IAA, spontaneous mechanical and electrical activities were reduced or eliminated, although amounts of high‐energy phosphates sufficient to contract smooth muscle remained. It can be postulated that some mechanism(s) related to energy metabolism, but not including ATP‐sensitive K+ channels, plays an important role in generating spontaneous activity in guinea‐pig stomach smooth muscle. During metabolic inhibition the energy metabolism‐dependent mechanism(s) would preserve high‐energy phosphates, and consequently cell viability, by stopping spontaneous activity.
Development of electrical rhythmicity in the murine gastrointestinal tract is specifically encoded in the tunica muscularis
Authors: Ward Sean M. , Harney Sarah C. , Bayguinov Julia R. , McLaren Gerald J. , Sanders Kenton M.
Published: September 2004

Interstitial cells of Cajal (ICCs) have been identified as pacemaker cells in the gastrointestinal (GI) tracts of vertebrates. We have studied the development of ICCs in pacemaker regions and the onset of electrical rhythmicity in the gastric antrum, small bowel and proximal colon of the mouse.

ICCs, as detected by c‐Kit immunofluorescence, were found during embryogenesis in regions of the GI tract that eventually become pacemaker areas. Prior to birth, these cells were organized into well‐structured networks, and by the end of the embryonic period the morphology of ICC networks in pacemaker regions appeared very similar to that observed in adult animals.

Electrical rhythmicity was recorded prior to birth (by E18) in the proximal GI tract (stomach and jejunum), and this activity developed to adult‐like behaviour within a week after birth. In the ileum and proximal colon rhythmicity developed after birth, and adult‐like characteristics were apparent within the first week.

Post‐junctional responses of smooth muscles to neural inputs could be recorded at birth, and stimulation of intrinsic nerves often led to oscillatory activity resembling slow waves for up to several minutes following brief stimuli. Nerve stimulation augmented spontaneous activity in the proximal portions of the GI tract and elicited rhythmic activity temporarily in quiescent tissues of the distal GI tract.

ICCs and rhythmicity developed in an apparently normal manner in tissues isolated at birth and placed in organ culture. These data suggest that the tunica muscularis provides a suitable microenvironment for the development of ICCs and rhythmicity without the need for extrinsic stimuli.

Treatment of small intestinal tissues taken from embryos at E15 with neutralizing c‐Kit antibodies abolished ICC development and the organization of ICCs into networks that typically occurs during the late embryonic period. Treatment of muscles taken from newborn animals with c‐Kit antibodies blocked postnatal development of ICCs, disrupted already established and functional ICC networks, and rendered muscles electrically quiescent.

In summary, ICC networks develop in the pacemaker regions of the murine GI tract before birth. Development and organization of ICCs of the myenteric plexus region into networks precedes the development of electrical rhythmicity. Post‐natal development of electrical rhythmicity is mainly characterized by enhancement of the amplitude and frequency of slow waves. The development of ICCs and electrical rhythmicity persists in vitro. ICCs appear to be necessary for the initiation of electrical rhythmicity. These findings provide further evidence for the pacemaker role of ICCs.
The effects of chronic hypoxia on renal function in the rat
Authors: Neylon Marie , Marshall Janice M. , Johns Edward J.
Published: September 2004

Studies were performed on rats that had been made chronically hypoxic (CH rats) in a normoxic chamber at 12% O2 for 3–5 weeks. Under Saffan anaesthesia, respiratory and cardiovascular variables, renal haemodynamics and renal function were recorded while the rats spontaneously breathed 12% O2 followed by a switch to air breathing for 20 min. Plasma renin activity was assessed by radioimmunoassay of angiotensin I. Plasma atrial natiruetic peptide (ANP) was indirectly assessed by measurement of cyclic GMP in urine.

When breathing 12% O2, CH rats showed hyperventilation and raised haematocrit (52%) relative to normoxic (N) rats. But arterial pressure (ABP), renal blood flow (RBF), renal vascular conductance (RVC), mean right atrial pressure (mRAtP), urine flow, glomerular filtration rate (GFR) and absolute sodium excretion (UNaV) were comparable to those recorded in N rats breathing air. Urinary cGMP was 40% greater than in N rats, but plasma renin activity was not significantly greater in CH than in N rats.

Air breathing in CH rats induced hypoventilation, a 12% increase in ABP, no change in mRAtP, RBF or GFR, but increases of 75 and 100% in urine flow and UNaV, respectively. Neither urinary cGMP nor plasma renin activity changed. Such increases in urine flow and UNaV were absent when renal perfusion pressure (RPP) was prevented from rising during air breathing by using an occluder on the dorsal aorta.

We propose that by 3–5 weeks of chronic hypoxia renal function was normalized, principally because arterial O2 content was normalized by the increase in haematocrit and because ABP and renal haemodynamics were normalized: acute hypoxia in N rats produces a fall in ABP. We suggest that plasma ANP was raised by the actions of hypoxia or erythropoietin on the atrium, rather than by atrial distension, but suggest that ANP had little direct influence on renal function and tended to limit the influence of the renin–angotensin system. We further propose that the diuresis and natriuresis seen during air breathing were mediated by the increase in RPP; neither plasma ANP nor renin activity change in the immediate short term.
P‐glycoprotein is not a swelling‐activated Cl− channel; possible role as a Cl− channel regulator
Authors: Vanoye Carlos G. , Altenberg Guillermo A. , Reuss Luis
Published: September 2004

The whole‐cell configuration of the patch‐clamp technique was used to determine if P‐glycoprotein (Pgp) is a swelling‐activated Cl− channel.

Hamster pgp1 cDNA was transfected into a mouse fibroblast cell line resulting in expression of functional Pgp in the plasma membrane. This cell line was obtained without exposure to chemotherapeutic agents.

Swelling‐activated whole‐cell Cl− current (Icl,swell) was elicited by lowering the bath osmolality. Icl,swell, was characterized in detail in the pgp1‐transfected mouse cell line and compared with that of its parental cell line. Expression of Pgp did not modify the magnitude or properties of Icl,swell, except that addition of the anti‐Pgp antibody C219 to the pipette solution inhibited this current by 75% only in the Pgp‐expressing cells.

I
Cl,swell in the mouse Pgp‐expressing cell line was compared with that in a Pgp‐expressing hamster fibroblast cell line. The characteristics of ICl,swell (voltage dependence, blocker sensitivity, anion selectivity sequence, requirement for hydrolysable ATP) in Pgp‐expressing cells were different between the two cell lines. These results suggest that the channel(s) responsible for ICl,swell are different between the two cell lines. In addition, C219 inhibited ICl,swell in both Pgp‐expressing cell lines, even though they seem to express different swelling‐activated Cl− channels.

We conclude that firstly, Pgp is not a swelling‐activated Cl− channel; secondly, it possibly functions as a Cl− channel regulator; and thirdly, ICl,swell is underlined by different Cl− channels in different cells.
Inwardly rectifying, volt age‐dependent and resting potassium currents in rat pancreatic acinar cells in primary culture
Authors: Schmid Andreas , Feick Peter , Schulz Irene
Published: September 2004

In exocrine pancreatic acinar cells in primary culture an inwardly rectifying, a voltage‐dependent and a permanent resting K+ current were characterized.

Inwardly rectifying K+ currents could be elicited by elevation of the extracellular K+ concentration. The K+ inward currents were almost completely blocked by 5 mm Ba2+, whereas 10 mm TEA+ had only a partial effect.

Depolarizing voltage steps from negative clamp potentials evoked transient activation of a voltage‐dependent K+ current. This voltage‐dependent current could be blocked by 10 mm TEA+ and 1 mm 4‐aminopyridine, but not by 5 mm Ba2+.

Neither the K+ inward rectifier nor the voltage‐dependent K+ conductance produced a significant negative cell potential. Stable membrane potentials (–38.7 ± 2.3mV, n= 38) could only be recorded on cell clusters (≥ 5 cells).

Cell clusters, in contrast to single cells, had a permanent resting K+ conductance in addition to the inward rectifier and the voltage‐dependent current. This resting K+ conductance was not blocked by TEA+, Ba2+, 4‐aminopyridine or by the chromanol 293B.

Cytosolic alkalization by addition of NH4Cl to the bath solution decreased the resting K+ current. In parallel, electrical uncoupling of the cells and breakdown of the resting potential could be observed. The same effects could be produced when the cells were uncoupled by 0.2–1.0 mm n‐octanol. It can be concluded that cell coupling is essential for maintenance of stable resting membrane potentials in pancreatic acinar cells.