bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple ionic mechanisms mediate inhibition of rat motoneurones by inhalation anaesthetics
Authors: Sirois Jay E. , Pancrazio Joseph J. , Lynch Carl , Bayliss Douglas A.
Published: September 2004

We studied the effects of inhalation anaesthetics on the membrane properties of hypoglossal motoneurones in a neonatal rat brainstem slice preparation.

In current clamp, halothane caused a membrane hyperpolarization that was invariably associated with decreased input resistance; in voltage clamp, halothane induced an outward current and increased input conductance. Qualitatively similar results were obtained with isoflurane and sevoflurane.

The halothane current reversed near the predicted K+ equilibrium potential (EK) and was reduced in elevated extracellular K+ and in the presence of Ba2+ (2 mm). Moreover, the Ba2+‐sensitive component of halothane current was linear and reversed near EK. The halothane current was not sensitive to glibenclamide or thyrotropin‐releasing hormone (TRH). Therefore, the halothane current was mediated, in part, by activation of a Ba2+‐sensitive K+ current distinct from the ATP‐ and neurotransmitter‐sensitive K+ currents in hypoglossal motoneurones.

Halothane also inhibited Ih, a hyperpolarization‐activated cationic current; this was primarily due to a decrease in the absolute amount of current, although halothane also caused a small, but statistically significant, shift in the voltage dependence of Ih activation. Extracellular Cs+ (3 mm) blocked Ih and a component of halothane‐sensitive current with properties reminiscent of Ih.

A small component of halothane current, resistant to Ba2+ and Cs+, was observed in TTX‐containing solutions at potentials depolarized to ∼−70 mV. Partial Na+ substitution by N‐methyl‐D‐glucamine completely abolished this residual current, indicating that halothane also inhibited a TTX‐resistant Na+ current active near rest potentials.

Thus, halothane activates a Ba2+‐sensitive, relatively voltage‐independent K+ current and inhibits both Ih and a TTX‐insensitive persistent Na+ current in hypoglossal motoneurones. These effects of halothane decrease motoneuronal excitability and may contribute to the immobilization that accompanies inhalation anaesthesia.
Modulation of the unitary exocytic event amplitude by cAMP in rat melanotrophs
Authors: Sikdar Sujit K. , Kreft Marko , Zorec Robert
Published: September 2004

Secretory responses were measured in single rat pituitary melanotrophs as the relative increase in membrane capacitance (Cm) 8 min after the start of dialysis with solutions containing 0.45 μm Ca2+. In the added presence of cAMP (0.2 mM) in the patch pipette solution, capacitance responses increased 2‐ to 3‐fold in comparison with controls.

To study whether cAMP‐dependent mechanisms affect cytosolic calcium activity ([Ca2+]i), dibutyryl cyclic AMP (dbcAMP, 10 mM) was added to intact melanotrophs and [Ca2+]i was measured using fura‐2 AM. Addition of dbcAMP caused a transient reduction in [Ca2+]i to 82 ± 21 nM from a resting value of 100 ± 19 nM (mean ± s.e.m., n= 32, P < 0.002), indicating that the cAMP‐induced increase in secretory activity was not the result of cAMP acting to increase [Ca2+]i, which then increased secretory activity.

To investigate whether cAMP affects the secretory apparatus directly, the interaction of a single secretory granule with the plasmalemma was monitored by measuring discrete femtofarad steps in Cm. The signal‐to‐noise ratio of recordings was increased by pre‐incubating the cells with a hydrophobic anion, dipicrylamine.

Recordings of unitary exocytic events (discrete ‘on’ steps in Cm) showed that the amplitude of ‘on’ steps ‐ a parameter correlated to the size of exocytosing secretory granules ‐ increased from 4.2 ± 0.2 fF (n= 356) in controls to 7.9 ± 0.2 fF in the presence of cAMP (n= 329, P < 0.001), while the frequency of unitary exocytic events was similar in controls and in the presence of cAMP.

The results suggest that a cAMP‐dependent mechanism mediates the fusion of larger granules with the plasmalemma.
The role of GABAergic inputs for coincidence detection in the neurones of nucleus laminaris of the chick
Authors: Funabiki Kazuo , Koyano Konomi , Ohmori Harunori
Published: September 2004

Synaptic inputs to nucleus laminaris (NL) neurones were studied in a brainstem slice preparation of chick embryos (E15‐20) using the whole‐cell patch clamp technique. NL neurones are third order auditory neurones and are proposed to behave as coincidence detectors concerned with interaural timing discrimination.

Under voltage clamp conditions, electrical stimuli applied to either ventral or dorsal dendritic layers evoked EPSCs. These fast currents decayed with a time constant of 1.1 ms near the resting potential, reversed close to 0 mV, and were blocked by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, 20 μM) or 6,7‐dinitro‐quinoxaline‐2,3‐dione (DNQX, 20 μM). Coincident or near coincident stimulation of the ventral and the dorsal dendritic layers increased the probability of action potential generation (response probability).

In the presence of CNQX (40 μM) other postsynaptic currents (PSCs) were observed, which reversed close to the equilibrium potential for chloride (ECl), and were reversibly blocked by bicuculline (20 μM) and, therefore, were mediated by GABAA receptors. Spontaneous GABAergic PSCs were inward going near the resting membrane potential immediately after starting whole‐cell recording with a low Cl− (5 mM, ECl= ‐90 mV) pipette medium, but became outward‐going with time. This indicates that GABAergic inputs may generate depolarizing potentials in intact NL neurones.

Local GABA (10 μM) application reduced both the EPSP and EPSC amplitude and shortened the EPSP decay time constant (from 5.3 to 2.1 ms), while the EPSC decay time constant was not affected (from 1.3 to 1.2 ms). These GABA effects were mostly due to the shunting conductance of the postsynaptic GABAA receptors.

Depolarizing current injections combined with electrical stimuli to a unilateral axon bundle simulated bilateral synaptic inputs. Response probability increased with decreased interstimulus intervals, while local GABA (10 μM) application to the soma narrowed the time dependence of the response probability.

These results suggest that GABAergic inputs to NL neurones may serve to improve coincidence detection of the bilateral excitatory inputs through an increase in membrane conductance.
Association of somatic action potential shape with sensory receptive properties in guinea‐pig dorsal root ganglion neurones
Authors: Djouhri L. , Bleazard L. , Lawson S. N.
Published: September 2004

Intracellular voltage recordings were made from the somata of L6 and S1 dorsal root ganglion (DRG) neurones at 28.5–31 °C in young guinea‐pigs (150–300 g) anaesthetized with sodium pentobarbitone. Action potentials (APs) evoked by dorsal root stimulation were used to classify conduction velocities (CVs) as C, Aδ or Aα/β. Units with overshooting APs and membrane potentials (Vm) more negative than −40 mV were analysed: 40 C‐, 45 Aδ‐ and 94 Aα/β‐fibre units.

Sensory receptive properties were characterized as: (a) low‐threshold mechanoreceptive (LTM) units (5 C‐, 10 Aδ‐ and 57 Aα/β‐fibre units); (b) nociceptive units, responding to noxious mechanical stimuli, some also to noxious heat (40 C‐, 27 Aδ‐ and 27 Aα/β‐fibre units); (c) unresponsive units that failed to respond to a variety of tests; and (d) C‐fibre cooling‐sensitive units (n= 4). LTM units made up about 8 % of identified C‐fibre units, 36 % of identified Aδ‐fibre units and > 73 % of identified Aα/β‐fibre units. Compared with LTM units, the nociceptive units had APs that were longer on average by 3 times (C‐fibre units), 1.7 times (Aδ‐fibre units) and 1.4 times (Aα/β‐fibre units). They also had significantly longer rise times (RTs) and fall times (FTs) in all CV ranges. Between Aα/β‐nociceptors and Aα/β‐LTMs there was a proportionately greater difference in RT than in FT. The duration of the afterhyperpolarization measured to 80 % recovery (AHP80) was also significantly longer in nociceptive than LTM neurones in all CV ranges: by 3 times (C‐fibre units), 6.3 times (Aδ‐fibre units) and 3.6 times (Aα/β‐fibre units). The mean values of these variables in unresponsive units were similar to those of nociceptive units in each CV range; in C‐ and Aδ‐fibre groups their mean AHP duration was even longer than in nociceptive units.

A‐fibre LTM neurones were divided into Aδ‐ (D hair units, n= 8), and Aα/β‐ (G hair/field units, n= 22; T (tylotrich) hair units, n= 6; rapidly adapting (RA) glabrous units, n= 6; slowly adapting (SA) hairy and glabrous units, n= 2; and muscle spindle (MS) units n= 17). MS and SA units had the shortest duration APs, FTs and AHP80s of all these groups. The mean RT in D hair units was significantly longer than in all Aα/β LTM units combined. T hair units had the longest mean FT and AHP of all the A‐LTM groups. The mean AHP was about 10 times longer in T hair units than in all other A‐LTM units combined (significant), and was similar to that of A‐fibre nociceptive neurones.

These differences in somatic AP shape may aid in distinguishing between LTM and nociceptive or unresponsive C‐ and Aδ‐fibre units but probably not between nociceptive and unresponsive units. The differences seen may reflect differences in expression or activation of different types of ion channel.
Sensorimotor modulation of human cortical swallowing pathways
Authors: Hamdy Shaheen , Aziz Qasim , Rothwell John C. , Hobson Anthony , Thompson David G.
Published: September 2004

Transcranial magnetic stimulation over motor areas of cerebral cortex in man can activate short latency bilateral cortical projections to the pharynx and oesophagus. In the present paper we investigate the interaction between pathways from each hemisphere and explore how activity in these pathways is modulated by afferent feedback from the face, pharynx and oesophagus.

Comparison of unilateral and bilateral stimulation (using interstimulus intervals (ISIs) of 1, 5 or 10 ms between shocks) showed spatial summation of responses from each hemisphere at an ISI of 1 ms, indicating that cortical efferents project onto a shared population of target neurones. Such summation was not evident at ISIs of 5 or 10 ms. There was little evidence for transcallosal inhibition of responses from each hemisphere, as described for limb muscles.

Single stimuli applied to the vagus nerve in the neck or the supraorbital nerve, which alone produce intermediate (onset 20‐30 ms) and long (50‐70 ms) latency reflex responses in the pharynx and oesophagus, were used to condition the cortical responses. Compared with rest, responses evoked by cortical stimulation were facilitated when they were timed to coincide with the late part of the reflex. The onset latency was reduced during both parts of the reflex response. No facilitation was observed with subthreshold reflex stimuli.

Single electrical stimuli applied to the pharynx or oesophagus had no effect on the response to cortical stimulation. However, trains of stimuli at frequencies varying from 0.2 to 10 Hz decreased the latency of the cortically evoked responses without consistently influencing their amplitudes. The effect was site specific: pharyngeal stimulation shortened both pharyngeal and oesophageal response latencies, whereas oesophageal stimulation shortened only the oesophageal response latencies.

Cortical swallowing motor pathways from each hemisphere interact and their excitability is modulated in a site‐specific manner by sensory input. The latter may produce a mixture of excitation and inhibition at both brainstem and cortical levels.
Postnatal changes in responses of rat dorsal horn cells to afferent stimulation: a fibre‐induced sensitization
Authors: Jennings Ernest , Fitzgerald Maria
Published: September 2004

In vivo extracellular recordings were made of 171 dorsal horn cells in both superficial and deep laminae in urethane‐anaesthetized newborn rats aged 3, 6, 10 and 21 days, and their response to single and repeated stimuli to primary afferent fibres investigated.

No long‐latency spike responses were evoked in response to C fibre stimulation in pups at postnatal day 3 (P3) or P6, while by P10, 35 % of cells had a C fibre response. Latencies of response to A fibre skin stimulation were very long and varied widely in the youngest animals, particularly in superficial cells, but mean latencies decreased with postnatal age, from 33.1 ± 2.78 ms at P3 to 7.3 ± 0.3 ms at P21. The mean number of spikes evoked by a single A fibre skin stimulus was remarkably consistent between cells and not significantly different in superficial and deep laminae at each age. The mean value of 5.1 ± 0.6 at P3 increased to 7.0 ± 1.4 at P10.

Repeated stimulation of cutaneous A fibres at 0.5 Hz at twice the threshold level did not significantly alter the magnitude of the evoked response but led to shifts in latency, or ‘latency jitter’, which decreased with age. Deeper cells displayed more latency jitter than superficial cells.

Repeated stimulation of cutaneous A fibres at 0.5 Hz at twice the threshold level produced considerable sensitization in a population of dorsal horn cells in the neonate. This sensitization was unlike the classic C fibre‐evoked ‘wind‐up’ observed in adult dorsal horn. The direct A fibre‐evoked activity did not increase, but the background activity increased during repetitive stimulation leading to a prolonged after‐discharge beyond the stimulation period. At P6, 33 % of cells were sensitized, displaying a mean after‐discharge of 70.6 ± 18 s. At P10, only 6 % were sensitized, with a mean after‐discharge of 63 s, and by P21, sensitization was no longer observed.

The present study demonstrates that the postsynaptic activity evoked in neonatal dorsal horn cells by cutaneous afferents differs considerably from that in adults. The results may account for the known behavioural reflex sensitization to low‐intensity cutaneous stimulation observed in neonatal rats and man.
Medullary raphe neurones and baroreceptor modulation of the respiratory motor pattern in the cat
Authors: Lindsey B. G. , Arata A. , Morris K. F. , Hernandez Y. M. , Shannon R.
Published: September 2004

Perturbations of arterial blood pressure change medullary raphe neurone activity and the respiratory motor pattern. This study sought evidence for actions of baroresponsive raphe neurones on the medullary respiratory network.

Blood pressure was perturbed by intravenous injection of an α1‐adrenergic receptor agonist, unilateral pressure changes in the carotid sinus, or occlusion of the descending aorta in thirty‐six Dial‐urethane‐anaesthetized, vagotomized, paralysed, artificially ventilated cats. Neurones were monitored with microelectrode arrays in two or three of the following domains: nucleus raphe obscurus‐nucleus raphe pallidus, nucleus raphe magnus, and rostral and caudal ventrolateral medulla. Data were analysed with cycle‐triggered histograms, peristimulus time and cumulative sum histograms, cross‐correlograms and spike‐triggered averages of efferent phrenic nerve activity.

Prolongation of the expiratory phase and decreased peak integrated phrenic amplitude were most frequently observed. Of 707 neurones studied, 310 had altered firing rates during stimulation; changes in opposite directions were monitored simultaneously in fifty‐six of eighty‐seven data sets with at least two baroresponsive neurones.

Short time scale correlations were detected between neurones in 347 of 3388 pairs. Seventeen pairs of baroresponsive raphe neurones exhibited significant offset correlogram features indicative of paucisynaptic interactions. In correlated raphe‐ventrolateral medullary neurone pairs with at least one baroresponsive neurone, six of seven ventrolateral medullary decrementing expiratory (E‐Decr) neurones increased their firing rate during baroreceptor stimulation. Thirteen of fifteen ventrolateral medullary inspiratory neurones correlated with raphe cells decreased their firing rate during baroreceptor stimulation.

The results support the hypothesis that raphe neuronal assemblies transform and transmit information from baroreceptors to neurones in the ventral respiratory group. The inferred actions both limit and promote responses to sensory perturbations and match predictions from simulations of the respiratory network.
A slow calcium‐dependent component of charge movement in Rana temporaria cut twitch fibres
Authors: Hui Chiu Shuen
Published: September 2004

Charge movement was studied in highly stretched frog cut twitch fibres in a double Vaseline‐gap voltage‐clamp chamber, with the internal solution containing either 0.1 mM EGTA or 20 mM EGTA plus 1.8 mM total Ca2+.

Fibres were stimulated with TEST pulses lasting 100‐400 ms. Replacement of the external Cl− with an ‘impermeant’ anion, such as SO42‐, CH3SO3−, gluconate or glutamate, greatly reduced the calcium‐dependent Cl− current in the ON segment and generated a slowly decaying inward OFF current in charge movement traces.

Application of 20 mM EGTA to the internal solution abolished the slow inward OFF current, implying that the activation of the current depended on the presence of Ca2+ in the myoplasm. The possibility that the slow inward OFF current was carried by cations flowing inwards or anions flowing outwards was studied and determined to be unlikely.

During a long (2000 ms) TEST pulse, a slowly decaying ON current was also observed. When the slow ON and OFF currents were included as parts of the total charge movement, ON‐OFF charge equality was preserved. This slow capacitive current is named Iδ.

When Cl− was the major anion in the external solution, the OFF Iδ was mostly cancelled by a slow outward current carried by the inflow of Cl−.

The OFF Iδ component showed a rising phase. The average values of the rising time constants in CH3SO3− and SO42‐ were similar and about half of that in gluconate.

The OFF Iδ component in CH3SO3− had a larger magnitude and longer time course than that in SO42‐. The maximum amount of Qδ in CH3SO3− was about three times as much as that in SO42‐, whereas the voltage dependence of Qδ was similar in the two solutions.

Since the existence of Qδ depends on the presence of Ca2+ in the myoplasm, it is speculated that Qδ could be a function of intracellular calcium release.
Activity of C fibre cardiac vagal efferents in anaesthetized cats and rats
Authors: Jones James F. X. , Wang Yun , Jordan David
Published: September 2004

Bradycardia can be evoked by stimulation of both myelinated and non‐myelinated vagal efferent fibres. The on‐going activity and synaptic inputs to cardiac vagal preganglionic neurones with myelinated axons have been studied in detail, but there is little information regarding cardiac preganglionic neurones with non‐myelinated axons. In the present study, the on‐going discharge and afferent inputs to cardiac vagal efferents with non‐myelinated axons were studied in anaesthetized rats and cats.

Extracellular recordings were made from vagal preganglionic neurones in the dorsal vagal motor nucleus (DVMN) of anaesthetized rats following electrical stimulation of the cervical vagus nerve. Based on calculated axonal conduction velocities, fifty‐six neurones had non‐myelinated axons. Sixteen of these C fibre neurones had on‐going activity but this showed no relationship to central respiratory drive, lung inflation or the cardiac cycle. Activity of twenty‐one of these fifty‐six neurones was increased at short latency following right atrial injections of phenylbiguanide (PBG).

Eight presumed cardiac vagal preganglionic neurones were also recorded in the DVMN. Five of these were activated by PBG administration, and the one neurone with resting activity showed no indication of respiratory‐related activity.

Finally, twenty‐one single C fibres were recorded in peripheral branches of the cardiac vagus. They had a low rate of on‐going activity, and in twelve fibres this on‐going discharge was analysed in detail. On‐going activity in seven of these fibres showed no relationship to central respiratory drive, lung inflation or the cardiac cycle, whereas the other five had prominent relationships with both central respiratory drive and lung inflation, and two of these also showed a relationship to heart period. PBG administration evoked an increased activity in fourteen of the fifteen fibres tested, and the latencies of nine of these responses (1.3 ± 0.5 s) were within the pulmonary circulation time.

In anaesthetized cats, extracellular recordings were made in the DVMN from thirty‐three cardiac vagal preganglionic neurones with C fibre axons. The on‐going activity of these neurones, when present, never exhibited an on‐going‐ or reflexly induced respiratory rhythm, nor any indication of an input from the arterial baroreceptors. Right atrial injection of PBG evoked a short‐latency response in four of the five spontaneously active neurones but was without effect on the eight neurones tested which did not exhibit on‐going activity.

In conclusion, the majority of cardiac vagal preganglionic neurones located in the DVMN have C fibre axons, show no obvious input from central or peripheral respiratory‐ or cardiac‐related inputs, but are activated by stimulation of pulmonary C fibre afferent fibres.
Non‐linear summation of excitatory synaptic inputs to small neurones: a case study in spinal motoneurones of the young Xenopus tadpole
Authors: Wolf Ervin , Zhao Fei‐Yue , Roberts Alan
Published: September 2004

We examined the steady‐state summation of postsynaptic potentials (PSPs) in small, electrotonically compact neurones with short dendrites, using a one‐compartment electrical equivalent model of the passive membrane with conductances to represent chemical synapses and electrotonic junctional connections to neighbouring neurones.

Our model shows that PSP summation is non‐linear and for small depolarizations is mainly determined by the increase in total neurone conductance due to the opening of synaptic channels. At bigger depolarizations the change in synaptic driving force becomes an equally important cause of non‐linearity.

Non‐linear summation of AMPA‐mediated PSPs was measured experimentally when two monosynaptic pathways to motoneurones were stimulated. The conductances underlying these PSPs were calculated relative to the resting neurone conductance using our model. These conductance ratios were hardly affected by the size of electrotonic coupling conductances. The non‐linearity in PSP summation could be predicted by the model provided that the depolarizations remained negative to potentials at which voltage‐dependent channels open.

The model was used to estimate the relative contributions of glutamatergic, cholinergic and electrotonic excitation to EPSPs measured in Xenopus tadpole spinal motoneurones during swimming. Estimates of synaptic conductances and electrotonic coupling to other motoneurones suggest that ligand‐gated conductance mediated by glutamate may be twice that due to acetylcholine.

We conclude that in small electrotonically compact motoneurones of the Xenopus tadpole, our simple model can predict the non‐linearity in PSP summation and may allow the conductances of different synaptic inputs to be compared. Furthermore, excitatory synaptic conductances can increase the resting neurone conductance significantly and limit depolarization. Our general model may also be applicable to other small neurones.
Postural after‐contractions in man attributed to muscle spindle thixotropy
Authors: Hagbarth Karl‐Erik , Nordin Magnus
Published: September 2004

It is an old observation that non‐volitional arm abduction movements accompanied by a sensation of arm lightness often occur as an after‐effect following forceful voluntary arm abductor contractions against a restraint. In the present study we have tested the hypothesis that such non‐volitional, so‐called ‘postural after‐contractions’ are tonic reflex responses to an enhanced resting discharge in primary muscle spindle afferents which in turn is a consequence of thixotropy‐dependent enhanced stiffness of intrafusal muscle fibres.

Results obtained in ten volunteers show that the arm abductor after‐contraction phenomenon in man is most readily evoked by a type of conditioning procedure which in various respects mimics the procedure proven in animal experiments to be particularly effective in producing thixotropy‐dependent excitation of primary spindle endings.

It is also shown that changes in arm abductor intramuscular temperature affect the strength of the after‐contractions in a direction predicted by the thixotropy hypothesis.

Attention is drawn to several similarities between the after‐contraction phenomenon with accompanying sensory illusions and the tonic reflex responses and illusions that can be induced when primary spindle endings are excited by muscle vibration.

The results support our hypothesis that postural after‐contractions are induced by activity in primary muscle spindle afferents as a consequence of thixotropic properties of intrafusal muscle fibres. Central excitability changes following the conditioning voluntary effort may contribute to the phenomenon.
Electrophysiological characterization of spinal neuronal response properties in anaesthetized rats after ligation of spinal nerves L5‐L6
Authors: Chapman Victoria , Suzuki Rie , Dickenson Anthony H.
Published: September 2004

Despite a number of models of nerve injury, few studies have examined how peripheral nerve injury influences spinal somatosensory processing.

Ligation of two (L5‐L6) of the three spinal nerves that form the sciatic nerve produces a partial denervation of the hindlimb. Following ligation, rats exhibited withdrawal responses to normally innocuous punctate mechanical and cooling stimuli (acetone) applied to the lesioned hindpaw. Such mechanical and cooling allodynia was not observed in sham‐operated rats.

A significantly greater proportion of spinal neurones of ligated rats exhibited spontaneous activity at post‐operative (PO) days 7–10 (P= 0.03) and 14–17 (P= 0.0001), compared with sham controls. The frequency of the spontaneous activity was significantly higher than that of the sham controls (P= 0.03 and P= 0.02 for days 7–10 and days 14–17, respectively).

At the earlier PO period, significantly (P= 0.02) more neurones of spinal nerve‐ligated (SNL) rats responded to brush compared with the sham controls; at the later PO period the proportion of neurones of SNL rats responsive to prod was significantly (P= 0.007) reduced compared with the sham controls. The magnitude of the evoked neuronal response of SNL rats at PO days 7–10 was comparable to that of the sham controls. The magnitudes of brush‐ and prod‐evoked neuronal responses of SNL rats were significantly smaller (P= 0.05 and P= 0.002, respectively) than the sham controls at PO days 14–17. In addition, neuronal responses of SNL rats to mechanical punctate stimuli and the C fibre‐evoked neuronal responses were significantly reduced at the later PO period, compared with sham controls. Aβ‐fibre‐induced wind‐up was not observed under any conditions.

These complex changes in neuronal responses are both time and modality dependent. The plasticity of some of the neuronal and behavioural responses following nerve injury was difficult to reconcile. We suggest that an interplay between pathological peripheral and central mechanisms may account for some of the changes that could contribute to allodynia and hyperalgesia.
Efferent projection from the preoptic area for the control of non‐shivering thermogenesis in rats
Authors: Chen Xiao‐Ming , Hosono Takayoshi , Yoda Tamae , Fukuda Yutaka , Kanosue Kazuyuki
Published: September 2004

To investigate the characteristics of efferent projections from the preoptic area for the control of non‐shivering thermogenesis, we tested the effects of thermal or chemical stimulation, and transections of the preoptic area on the activity of interscapular brown adipose tissue in cold‐acclimated and non‐acclimated anaesthetized rats.

Electrical stimulation of the ventromedial hypothalamic nucleus (VMH) elicited non‐shivering thermogenesis in the brown adipose tissue (BAT); warming the preoptic area to 41.5 °C completely suppressed the thermogenic response.

Injections of d,l‐homocysteic acid (DLH; 0.5 mm, 0.3 μl) into the preoptic area also significantly attenuated BAT thermogenesis, whereas injections of control vehicle had no effect.

Transections of the whole hypothalamus in the coronal plane at the level of the paraventricular nucleus induced rapid and large rises in BAT and rectal temperatures. This response was not blocked by pretreatment with indomethacin. The high rectal and BAT temperatures were sustained more than 1 h, till the end of the experiment. Bilateral knife cuts that included the medial forebrain bundle but not the paraventricular nuclei elicited similar rises in BAT and rectal temperatures. Medial knife cuts had no effect.

These results suggest that warm‐sensitive neurones in the preoptic area contribute a larger efferent signal for non‐shivering thermogenesis than do cold‐sensitive neurones, and that the preoptic area contributes a tonic inhibitory input to loci involved with non‐shivering thermogenesis. This efferent inhibitory signal passes via lateral, but not medial, hypothalamic pathways.
Endogenous pacemaker activity of rat tumour somatotrophs
Authors: Kwiecien Renata , Robert Christophe , Cannon Robert , Vigues Stephan , Arnoux Annie , Kordon Claude , Hammond Constance
Published: September 2004

Cells derived from a rat pituitary tumour (GC cell line) that continuously release growth hormone behave as endogenous pacemakers. In simultaneous patch clamp recordings and cytosolic Ca2+ concentration ([Ca2+]i) imaging, they displayed rhythmic action potentials (44.7 ± 2.7 mV, 178 ± 40 ms, 0.30 ± 0.04 Hz) and concomitant [Ca2+]i transients (374 ± 57 nM, 1.0 ± 0.2 s, 0.27 ± 0.03 Hz).

Action potentials and [Ca2+]i transients were reversibly blocked by removal of external Ca2+, addition of nifedipine (1 μM) or Ni2+ (40 μM), but were insensitive to TTX (1 μM). An L‐type Ca2+ current activated at ‐33.6 ± 0.4 mV (holding potential (Vh), ‐40 mV), peaked at ‐1.8 ± 1.3 mV, was reduced by nifedipine and enhanced by S‐(+)‐SDZ 202 791. A T/R‐type Ca2+ current activated at ‐41.7 ± 2.7 mV (Vh, ‐80 or ‐60 mV), peaked at ‐9.2 ± 3.0 mV, was reduced by low concentrations of Ni2+ (40 μM) or Cd2+ (10 μM) and was toxin resistant. Parallel experiments revealed the expression of the class E calcium channel α1‐subunit mRNA.

The K+ channel blockers TEA (25 mM) and charybdotoxin (10‐100 nM) enhanced spike amplitude and/or duration. Apamin (100 nM) also strongly reduced the after‐spike hyperpolarization. The outward K+ tail current evoked by a depolarizing step that mimicked an action potential reversed at ‐69.8 ± 0.3 mV, presented two components, lasted 2‐3 s and was totally blocked by Cd2+ (400 μM).

The slow pacemaker depolarization (3.5 ± 0.4 s) that separated consecutive spikes corresponded to a 2‐ to 3‐fold increase in membrane resistance, was strongly Na+ sensitive but TTX insensitive.

Computer simulations showed that pacemaker activity can be reproduced by a minimum of six currents: an L‐type Ca2+ current underlies the rising phase of action potentials that are repolarized by a delayed rectifier and Ca2+‐activated K+ currents. In between spikes, the decay of Ca2+‐activated K+ currents and a persistent inward cationic current depolarize the membrane, activate the T/R‐type Ca2+ current and initiate a new cycle.
Muscle blood flow is reduced with dehydration during prolonged exercise in humans
Authors: González‐Alonso José , Calbet José A. L. , Nielsen Bodil
Published: September 2004

The present study examined whether the blood flow to exercising muscles becomes reduced when cardiac output and systemic vascular conductance decline with dehydration during prolonged exercise in the heat. A secondary aim was to determine whether the upward drift in oxygen consumption (V̇O2) during prolonged exercise is confined to the active muscles.

Seven euhydrated, endurance‐trained cyclists performed two bicycle exercise trials in the heat (35 °C; 40–50% relative humidity; 61 ± 2% of maximal V̇O2), separated by 1 week. During the first trial (dehydration trial, DE), they bicycled until volitional exhaustion (135 ± 4 min, mean ± s.e.m.), while developing progressive dehydration and hyperthermia (3.9 ± 0.3% body weight loss; 39.7 ± 0.2 °C oesophageal temperature, Toes). In the second trial (control trial), they bicycled for the same period of time while maintaining euhydration by ingesting fluids and stabilizing Toes at 38.2 ± 0.1 °C after 30 min exercise.

In both trials, cardiac output, leg blood flow (LBF), vascular conductance and V̇O2 were similar after 20 min exercise. During the 20 min‐exhaustion period of DE, cardiac output, LBF and systemic vascular conductance declined significantly (8–14%; P < 0.05) yet muscle vascular conductance was unaltered. In contrast, during the same period of control, all these cardiovascular variables tended to increase. After 135 ± 4 min of DE, the 2.0 ± 0.6 l min−1 lower blood flow to the exercising legs accounted for approximately two‐thirds of the reduction in cardiac output. Blood flow to the skin also declined markedly as forearm blood flow was 39 ± 8% (P < 0.05) lower in DE vs. control after 135 ± 4 min.

In both trials, whole body V̇O2 and leg V̇O2 increased in parallel and were similar throughout exercise. The reduced leg blood flow in DE was accompanied by an even greater increase in femoral arterial‐venous O2 (a‐vO2) difference.

It is concluded that blood flow to the exercising muscles declines significantly with dehydration, due to a lowering in perfusion pressure and systemic blood flow rather than increased vasoconstriction. Furthermore, the progressive increase in oxygen consumption during exercise is confined to the exercising skeletal muscles.
Respiratory modulation of carotid and aortic body reflex left ventricular inotropic responses in the cat
Authors: de Burgh Daly M. , Jones James F. X.
Published: September 2004

The reflex changes in the inotropic state of the left ventricle, measured as the dP/dtmax(maximum rate of change of pressure), occurring in response to selective stimulation of the carotid and aortic body chemoreceptors by sodium cyanide, were studied in the cat anaesthetized with a mixture of chloralose and urethane.

The animals were artificially ventilated with an open pneumothorax. The heart rate and mean arterial blood pressure were maintained constant.

With on‐going central respiratory activity, stimulation of the carotid bodies caused an increase in respiratory movements. Variable changes in left ventricular dP/dtmaxoccurred, the predominant response being an increase. The mean change was 8.3 ± 2.9 % from a control value of 6850 ± 450 mmHg s−1. Stimulation of the aortic bodies resulted in a smaller increase in respiration or no effect, but a significant increase occurred in left ventricular dP/dtmaxof 19.6 ± 2.9 % from a control value of 6136 ± 228 mmHg s−1. No significant changes in left ventricular end‐diastolic pressure occurred in response to stimulation of either group of chemoreceptors.

Tests of chemoreceptor stimulations were repeated during temporary suppression of the secondary respiratory mechanisms: the central respiratory drive was suppressed reflexly by electrical stimulation of the central cut ends of both superior laryngeal nerves and lung stretch afferent activity was minimized by stopping artificial respiration. Carotid body stimulation again evoked variable responses, the predominant now being a reduction in left ventricular dP/dtmaxof 3.1 % from a control value of 5720 ± 320 mmHg s−1, which was significantly different to that occurring during on‐going spontaneous respiration. Aortic body stimulation caused an increase in left ventricular dP/dtmaxsimilar to the response during on‐going spontaneous respiration.

The positive inotropic responses were mediated via the sympathetic nervous system, as indicated by their abolition as a result of intravenous injections of the β‐adrenoceptor blocking agent, propranolol.

It is concluded that the carotid bodies exert a small variable effect on left ventricular dP/dtmax, the predominant positive inotropic response being due to the concomitant neurogenic effects of the increase in respiration. In contrast, the positive inotropic response to excitation of the aortic chemoreceptors is not respiratory modulated.
Selective lesioning of the cat pre‐Bötzinger complex in vivo eliminates breathing but not gasping
Authors: Ramirez J. M. , Schwarzacher S. W. , Pierrefiche O. , Olivera B. M. , Richter D. W.
Published: September 2004

To examine the functional importance of the pre‐Bötzinger complex for breathing we micro‐injected, under in vivo conditions, the calcium channel blocker ω‐conotoxin GVIA and the sodium channel blocker tetrodotoxin (TTX) into the ventrolateral medulla of adult cats, while monitoring respiratory rhythmic motor output in the phrenic nerve.

ω‐Conotoxin GVIA caused a highly localized synaptic ablation by blocking presynaptic N‐type calcium channels. When injecting 5–60 fmol ω‐conotoxin GVIA unilaterally, the amplitude of phrenic nerve activity decreased bilaterally and sometimes disappeared, indicating central apnoea. These effects were reversible and could only be induced in a very localized area of the pre‐Bötzinger complex. By injecting ω‐conotoxin GVIA several times during an experiment and analysing the areas where injections affected respiratory activity, it was possible to map exactly the anatomical extent of the area critical for respiratory rhythm generation.

Following the precise localization of the pre‐Bötzinger complex with ω‐conotoxin GVIA, we injected TTX to induce an irreversible inactivation of this region. TTX injected unilaterally into the pre‐Bötzinger complex irreversibly reduced the amplitude of phrenic nerve activity. Bilateral TTX injections eliminated respiratory rhythmic activity, causing a persistent central apnoea.

After bilateral lesioning of the pre‐Bötzinger complex, it was still possible to induce gasping during hypoxia or asphyxia, indicating that respiration and gasping are generated by two different neuronal networks.

We propose that ω‐conotoxin GVIA as employed in this study to investigate the functional role of the pre‐Bötzinger complex can also be used as a general pharmacological approach to map other neuronal networks. We call this the ‘ω‐conotoxin GVIA tracing’ method.
Mesenteric, coeliac and splanchnic blood flow in humans during exercise
Authors: Perko M. J. , Nielsen H. B. , Skak C. , Clemmesen J. O. , Schroeder T. V. , Secher N. H.
Published: September 2004

Exercise reduces splanchnic blood flow, but the mesenteric contribution to this response is uncertain.

In nineteen humans, superior mesenteric and coeliac artery flows were determined by duplex ultrasonography during fasting and postprandial submaximal cycling and compared with the splanchnic blood flow as assessed by the Indocyanine Green dye‐elimination technique.

Cycling increased arterial pressure, heart rate and cardiac output, while it reduced total vascular resistance. These responses were not altered in the postprandial state. During fasting, cycling increased mesenteric, coeliac and splanchnic resistances by 76, 165 and 126%, respectively, and it reduced corresponding blood flows by 32, 50 and 43% (by 0.18 ± 0.04, 0.42 ± 0.03 and 0.60 ± 0.04 l min−1). Postprandially, mesenteric and splanchnic vascular resistances decreased, thereby elevating regional blood flow, while the coeliac circulation was not influenced. Postprandial cycling did not influence the mesenteric resistance significantly, but its blood flow decreased by 22% (0.46 ± 0.28 l min−1). Coeliac and splanchnic resistance increased by 150 and 63%, respectively, and the corresponding regional blood flow decreased by 51 and 31% (0.49 ± 0.07 and 0.96 ± 0.28 l min−1). Splanchnic blood flow values assessed by duplex ultrasound and by dye‐elimination techniques were correlated (r= 0.70; P < 0.01).

During submaximal exercise in humans, splanchnic resistance increases and blood flow is reduced following a 50% reduction in the hepato‐splenic and a 25% reduction in the mesenteric blood flow.
Coupling of sympathetic and somatic motor outflows from the spinal cord in a perfused preparation of adult mouse in vitro
Authors: Chizh Boris A. , Headley P. Max , Paton Julian F. R.
Published: September 2004

The relationship between sympathetic and somatic motor outflows from thoraco‐lumbar spinal cord was investigated in a novel arterially perfused trunk‐hindquarters preparation of adult mouse.

Ongoing activity was present in both somatic motor (obturator, sciatic or femoral nerves) and sympathetic outflows (either renal nerve or abdominal sympathetic chain). Sympathetic activity was rhythmic with bursts frequencies of 0.6‐2.2 Hz. No obvious rhythmic activity was found in the somatic motor outflow. There were periods during which sympathetic and somatic motor activity were correlated.

Addition of NMDA (20‐80 μM) to the perfusate elicited repetitive burst discharges in the somatic motor outflow which were sometimes rhythmic. The frequency of these burst discharges/rhythmic activity varied between preparations but in all cases increased with increasing NMDA concentration.

NMDA induced burst discharges in the sympathetic outflow. This bursting activity was of the same frequency as the somatic motor outflow and the two were coupled as revealed by correlation analysis. Periods of coupling persisted for up to 3 min.

Administration of hexamethonium (300 μM), to block sympathetic ganglionic transmission, had no effect on the somatic motor activity but severely attenuated sympathetic nerve discharge.

The thoraco‐sacral cord therefore has the neuronal machinery necessary for generating and coupling activity in somatic motor and sympathetic outflows. Our findings indicate a dynamic control over the degree of coupling. We discuss that the synchronization of these neural outflows reflects either coupling between two independent mechanisms or the presence of a common synaptic driver impinging on both somatic motor and sympathetic neurones.
Regulation of cerebral microvascular permeability by histamine in the anaesthetized rat
Authors: Sarker M. H. , Easton A. S. , Fraser P. A.
Published: September 2004

The permeability response of slightly leaky pial venular capillaries to histamine was investigated using the single microvessel occlusion technique.

Histamine dose‐response curves showed that concentrations between 5 nm and 5 μM increased permeability, while concentrations from 50 μM to 5 mM reduced it.

The H2 receptor antagonist cimetidine (2 μM) blocked the effects of lower concentrations of histamine, while the H1 receptor antagonist mepyramine (3 nM) blocked those of higher concentrations of histamine.

The effects of lower doses of histamine were mimicked by the H2 receptor agonist dimaprit, and the effects of higher doses of histamine were mimicked by the H1 receptor agonist α‐2‐(2‐aminoethyl)pyridine (AEP).

Low concentrations of histamine, which normally increase the permeability of Lucifer Yellow (PLY), reduced it when co‐applied with the phosphodiesterase 4 (PDE4) inhibitor rolipram. Rolipram also potentiated the response to AEP, but had no effect on that to dimaprit.

The effects of dimaprit were blocked by reducing extracellular Ca2+ from 2.5 mM to nominally Ca2+ free, or by applying the calcium entry blocker SKF 96365.
Mechanical advantage of the human parasternal intercostal and triangularis sterni muscles
Authors: De Troyer André , Legrand Alexandre , Gevenois Pierre‐Alain , Wilson Theodore A.
Published: September 2004

Previous studies in dogs have demonstrated that the maximum change in airway pressure (ΔPao) produced by a particular respiratory muscle is the product of three factors, namely the mass of the muscle, the maximal active muscle tension per unit cross‐sectional area (∼3.0 kg cm−2), and the fractional change in muscle length per unit volume increase of the relaxed chest wall (i.e. the muscle's mechanical advantage). In the present studies, we have used this principle to infer the ΔPao values generated by the parasternal intercostal and triangularis sterni muscles in man.

The mass of the muscles and the direction of the muscle fibres relative to the sternum were first assessed in six cadavers. Seven healthy individuals were then placed in a computed tomographic scanner to determine the orientation of the costal cartilages relative to the sternum and their rotation during passive inflation to total lung capacity. The fractional changes in length of the muscles during inflation, their mechanical advantages, and their ΔPao values were then calculated.

Passive inflation induced shortening of the parasternal intercostals in all interspaces and lengthening of the triangularis sterni. The fractional shortening of the parasternal intercostals decreased gradually from 7.7% in the second interspace to 2.0% in the fifth, whereas the fractional lengthening of the triangularis sterni increased progressively from 5.9 to 13.8%. These rostrocaudal gradients were well accounted for by the more caudal orientation of the cartilages of the lower ribs.

Since these fractional changes in length corresponded to a maximal inflation, the inspiratory mechanical advantage of the parasternal intercostals was only 2.2–0.6% l−1, and the expiratory mechanical advantage of the triangularis sterni was only 1.6–3.8% l−1. In addition, whatever the interspace, parasternal and triangularis muscle mass was 3–5 and 1–3 g, respectively. As a result, the magnitude of the ΔPao values generated by a maximal contraction of the parasternal intercostals or triangularis sterni in all interspaces would be only 1–3 cmH2O.

These studies therefore confirm that the parasternal intercostals in man have an inspiratory action on the lung whereas the triangularis sterni has an expiratory action. However, these studies also establish the important fact that the pressure‐generating ability of both muscles is substantially smaller than in the dog.
InsP3, but not novel Ca2+ releasers, contributes to agonist‐initiated contraction in rabbit airway smooth muscle
Authors: Iizuka Kunihiko , Yoshii Akihiro , Dobashi Kunio , Horie Takeo , Mori Masatomo , Nakazawa Tsugio
Published: September 2004

To examine the contributions of the putative Ca2+ releasers, inositol 1,4,5‐trisphosphate (InsP3), cyclic ADP ribose (cADPR), and nicotinate adenine dinucleotide phosphate (NAADP), to carbachol (CCh)‐induced contraction in airway smooth muscle, we measured force development of permeabilized rabbit tracheal smooth muscle, human bronchial smooth muscle and guinea‐pig ileum longitudinal smooth muscle.

In the presence of 50 μm GTP, CCh and InsP3 contracted α‐toxin‐permeabilized tracheal smooth muscle dose dependently; the EC50 values for CCh and InsP3 were 1.84 μm and 363 μm, and the maximum responses (normalized to the 30 mM caffeine response) to 100 μm CCh and to 800 μm InsP3 were 206 ± 13.4 % (mean ± s.e.m.) and 84.4 ± 5.3 %, respectively.

However, cADPR (10‐300 μm), β‐NAD+ (2.5 mM), FK506 (30 μm) and NAADP (100 μm) neither contracted the strip by themselves nor affected the subsequent CCh (1 μm) response. α‐Toxin‐permeabilized bronchial smooth muscle and ileum smooth muscle also responded to caffeine, InsP3 and CCh but not to cADPR.

Both 100 μm 8‐amino‐cADPR, a selective cADPR antagonist, and 100 μm thionicotinamide‐NADP, a selective NAADP antagonist, failed to inhibit the CCh response, although procaine abolished the caffeine, InsP3 and CCh responses in the permeabilized tracheal smooth muscle.

Although inhibition of the caffeine response by 30 μm ryanodine was nearly complete, approximately 30 % of the InsP3 (300 μm) plus GTP (50 μm) response was retained, and the resultant response disappeared after the caffeine response was evoked in the presence of ryanodine.

Heparin (300 μg ml−1) blocked InsP3 (300 μm) and CCh (3 μm) responses in β‐escin‐permeabilized tracheal smooth muscle, while Ruthenium Red (100 μm) partially inhibited the CCh response.

Collectively, InsP3 but not cADPR or NAADP plays a key role in CCh‐initiated contraction, and InsP3 utilizes a single compartment of the caffeine/ryanodine‐sensitive stored Ca2+ in airway smooth muscle.