bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.