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Unit Activity (unit + activity)
Selected AbstractsBehaviours of pulmonary sensory receptors during development of acute lung injury in the rabbitEXPERIMENTAL PHYSIOLOGY, Issue 4 2007Shuxin Lin We tested the hypothesis that oleic acid-induced acute lung injury activates pulmonary nociceptors, that is, C fibre receptors (CFRs) and high-threshold A, fibre receptors (HTARs). Single-unit activity was recorded in the cervical vagus nerve and assessed before and after injecting oleic acid (75 ,l kg,1i.v.) into anaesthetized, open-chest, mechanically ventilated rabbits. Unit activities increased within seconds and peaked within a few minutes (from 0.3 ± 0.1 to 1.4 ± 0.9 impulses s,1 for CFRs and from 0.5 ± 0.1 to 1.7 ± 0.3 impulses s,1 for HTARs, both n= 8 and P < 0.05). These activities were sustained while pulmonary oedema developed and dynamic lung compliance decreased over the 90 min observation period. Activities in slowly adapting receptors and rapidly adapting receptors were also increased; however, their responsiveness to airway pressure stimulation decreased progressively. We conclude that pulmonary nociceptors are stimulated during acute lung injury. The dual nociceptor system, consisting of both non-myelinated CFRs and myelinated HTARs, may play an important role in the pathophysiological process of acute lung injury-induced respiratory responses. [source] Inhibitory Effects Of Angiotensin Ii On Barosensitive Rostral Ventrolateral Medulla Neurons Of The RatCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 12 2001Delphine Bertram SUMMARY 1. The brain renin,angiotensin system can influence arterial baroreceptor reflex control of blood pressure (BP) through both direct and indirect effects on sympathetic premotor neurons of the rostral ventrolateral medulla (RVLM). The present study examined the direct effect of angiotensin (Ang) II applied by microiontophoresis on the ongoing activity of single RVLM neurons. 2. In 26 urethane-anaesthetized Wistar rats, recordings of single unit activities of barosensitive RVLM neurons were made from one barrel of a six-barrel micropipette assembly. The other five barrels were filled with either L -glutamate, AngII, valsartan (an AT1 receptor antagonist), PD 123177 (an AT2 receptor antagonist) and saline. All drugs were applied by microiontophoresis. 3. Mean BP was 83 ± 3 mmHg. Application of AngII inhibited the ongoing activity of RVLM neurons, identified as barosensitive because their activity was inhibited by a phenylephrine- induced increase in BP, from 12.6 ± 1.5 to 5.4 ± 1.1 Hz (n = 24; P < 0.001). Angiotensin II also inhibited the glutamate-evoked excitation of barosensitive RVLM neurons from 15 ± 3 to 5.8 ± 2.0 Hz (n = 6; P < 0.001). Valsartan significantly increased neuronal activity from 9.5 ± 2.3 to 13.5 ± 3.2 Hz (n = 7, P < 0.01), whereas PD 123177 significantly decreased neuronal activity from 13.5 ± 3.5 to 9.9 ± 2.8 Hz (n = 13; P < 0.01). 4. The results suggest that AngII exerts a tonic inhibitory effect on barosensitive RVLM neurons, which is presumably mediated through AT1 receptor stimulation. [source] Effects of Potassium Concentration on Firing Patterns of Low-Calcium Epileptiform Activity in Anesthetized Rat Hippocampus: Inducing of Persistent Spike ActivityEPILEPSIA, Issue 4 2006Zhouyan Feng Summary:,Purpose: It has been shown that a low-calcium high-potassium solution can generate ictal-like epileptiform activity in vitro and in vivo. Moreover, during status epileptiform activity, the concentration of [K+]o increases, and the concentration of [Ca2+]o decreases in brain tissue. Therefore we tested the hypothesis that long-lasting persistent spike activity, similar to one of the patterns of status epilepticus, could be generated by a high-potassium, low-calcium solution in the hippocampus in vivo. Methods: Artificial cerebrospinal fluid was perfused over the surface of the exposed left dorsal hippocampus of anesthetized rats. A stimulating electrode and a recording probe were placed in the CA1 region. Results: By elevating K+ concentration from 6 to 12 mM in the perfusate solution, the typical firing pattern of low-calcium ictal bursts was transformed into persistent spike activity in the CA1 region with synaptic transmission being suppressed by calcium chelator EGTA. The activity was characterized by double spikes repeated at a frequency ,4 Hz that could last for >1 h. The analysis of multiple unit activity showed that both elevating [K+]o and lowering [Ca2+]o decreased the inhibition period after the response of paired-pulse stimulation, indicating a suppression of the after-hyperpolarization (AHP) activity. Conclusions: These results suggest that persistent status epilepticus,like spike activity can be induced by nonsynaptic mechanisms when synaptic transmission is blocked. The unique double-spike pattern of this activity is presumably caused by higher K+ concentration augmenting the frequency of typical low-calcium nonsynaptic burst activity. [source] Morphine modulation of temporomandibular joint-responsive units in superficial laminae at the spinomedullary junction in female rats depends on estrogen statusEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2008A. Tashiro Abstract The influence of analgesic agents on neurons activated by stimulation of the temporomandibular joint (TMJ) region is not well defined. The spinomedullary junction [trigeminal subnucleus caudalis (Vc)/C1,2] is a major site of termination for TMJ sensory afferents. To determine whether estrogen status influences opioid-induced modulation of TMJ units, the classical opioid analgesic, morphine, was given to ovariectomized (OvX) rats and OvX rats treated for 2 days with low-dose (LE2) or high-dose (HE2) 17,-estradiol-3-benzoate. Under thiopental anesthesia, TMJ units in superficial and deep laminae at the Vc/C1,2 junction were activated by injection of ATP (1 mm) directly into the joint space. In superficial laminae, morphine inhibited evoked activity in units from OvX and LE2 rats in a dose-related and naloxone-reversible manner, whereas units from HE2 rats were not inhibited. By contrast, in deep laminae, morphine reduced TMJ-evoked unit activity similarly in all groups. Morphine reduced the background activity of units in superficial and deep laminae and resting arterial pressure similarly in all groups. Morphine applied to the dorsal surface of the Vc/C1,2 junction inhibited all units independently of E2 treatment. Quantitative polymerase chain reaction and immunoblots revealed a similar level of expression for ,-opioid receptors at the Vc/C1,2 junction in LE2 and HE2 rats. These results indicated that estrogen status differentially affected morphine modulation of TMJ unit activity in superficial, but not deep, laminae at the Vc/C1,2 junction in female rats. The site(s) for estrogen influence on morphine-induced modulation of TMJ unit activity was probably outside the medullary dorsal horn. [source] Episodic memory,From brain to mindHIPPOCAMPUS, Issue 9 2006Janina Ferbinteanu Abstract Neuronal mechanisms of episodic memory, the conscious recollection of autobiographical events, are largely unknown because electrophysiological studies in humans are conducted only in exceptional circumstances. Unit recording studies in animals are thus crucial for understanding the neurophysiological substrate that enables people to remember their individual past. Two features of episodic memory,autonoetic consciousness, the self-aware ability to "travel through time", and one-trial learning, the acquisition of information in one occurrence of the event,raise important questions about the validity of animal models and the ability of unit recording studies to capture essential aspects of memory for episodes. We argue that autonoetic experience is a feature of human consciousness rather than an obligatory aspect of memory for episodes, and that episodic memory is reconstructive and thus its key features can be modeled in animal behavioral tasks that do not involve either autonoetic consciousness or one-trial learning. We propose that the most powerful strategy for investigating neurophysiological mechanisms of episodic memory entails recording unit activity in brain areas homologous to those required for episodic memory in humans (e.g., hippocampus and prefrontal cortex) as animals perform tasks with explicitly defined episodic-like aspects. Within this framework, empirical data suggest that the basic structure of episodic memory is a temporally extended representation that distinguishes the beginning from the end of an event. Future research is needed to fully understand how neural encodings of context, sequences of items/events, and goals are integrated within mnemonic representations of autobiographical events. © 2006 Wiley-Liss, Inc. [source] Gonadotrophin-Releasing Hormone Pulse Generator Activity in the Hypothalamus of the GoatJOURNAL OF NEUROENDOCRINOLOGY, Issue 10 2009S. Ohkura Pulsatile release of gonadotrophin-releasing hormone (GnRH) is indispensable to maintain normal gonadotrophin secretion. The pulsatile secretion of GnRH is associated with synchronised electrical activity in the mediobasal hypothalamus (i.e. multiple unit activity; MUA), which is considered to reflect the rhythmic oscillations in the activity of the neuronal network that drives pulsatile GnRH secretion. However, the cellular source of this ultradian rhythm in GnRH activity is unknown. Direct input from kisspeptin neurones in the arcuate nucleus (ARC) to GnRH cell bodies in the medial preoptic area or their terminals in the median eminence could be the intrinsic source for driving the GnRH pulse generator. To determine whether kisspeptin signalling could be responsible for producing pulsatile GnRH secretion, we studied goats, measured plasma levels of luteinising hormone (LH) and recorded MUA in the posterior ARC, where the majority of kisspeptin neuronal cell bodies are located. Rhythmic volleys of MUA were found to be accompanied by LH pulses with regular intervals in the ARC, where kisspeptin neuronal cell bodies were found. Exogenous administration of kisspeptin stimulated a sustained increase in LH secretion, without influencing MUA, suggesting that the GnRH pulse generator, as reflected by MUA, originated from outside of the network of GnRH neurones, and could plausibly reflect the pacemaker activity of kisspeptin neurones, whose projections reach the median eminence where GnRH fibres project. These observations suggest that the kisspeptin neurones in the ARC may be the intrinsic source of the GnRH pulse generator. [source] Motor unit recruitment during lengthening contractions of human wrist flexorsMUSCLE AND NERVE, Issue 11 2001Paula J. Stotz MSc Abstract The purpose of this study was to revisit the question of recruitment of motor units during lengthening contractions because of conflicting views in the literature on this subject. Motor unit activity was recorded from the flexor carpi radialis muscle of four human subjects to compare the patterns of recruitment during lengthening and isometric contractions. Lengthening contractions were produced either when the subject voluntarily stopped opposing a background load or when an additional load was imposed on the already contracting muscle. In both cases, lengthening of the active muscle was produced at a variety of speeds, from quite slow to "as fast as possible." No differences in recruitment order were observed between isometric and lengthening contractions at any speed of lengthening contraction. It is concluded that all contractions in normal humans recruit motor units in an orderly fashion from small to large, according to the size principle of motor unit recruitment. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 1535,1541, 2001 [source] 5-Hydroxytryptamine selectively activates the vagal nodose C-fibre subtype in the guinea-pig oesophagusNEUROGASTROENTEROLOGY & MOTILITY, Issue 9 2008S. Yu Abstract, The afferent neurons innervating the oesophagus originate from two embryonic sources: neurons located in vagal nodose ganglia originate from embryonic placodes and neurons located in vagal jugular and spinal dorsal root ganglia (DRG) originate from the neural crest. Here, we address the hypothesis that 5-hydroxytryptamine (5-HT) differentially stimulates afferent nerve subtypes in the oesophagus. Extracellular recordings of single unit activity originating from nerve terminals were made in the isolated innervated guinea-pig oesophagus. Whole cell patch clamp recordings (35 °C) were made from the primary afferent neurons retrogradely labelled from the oesophagus. 5-Hydroxytryptamine (10 ,mol L,1) activated vagal nodose C-fibres (70%) in the oesophagus but failed to activate overtly vagal jugular nerve fibres and oesophagus-specific spinal DRG neurons. The response to 5-HT in nodose C-fibre nerve terminals was mimicked by the selective 5-HT3 receptor agonist 2-methyl-5-HT (10 ,mol L,1) and nearly abolished by the 5-HT3 receptor antagonists ondansetron (10 ,mol L,1) and Y-25130 (10 ,mol L,1). In patch clamp studies, 2-methyl-5-HT (10 ,mol L,1) activated a proportion of isolated oesophagus-specific nodose capsaicin-sensitive neurons (putative cell bodies of nodose C-fibres). We conclude that the responsiveness to 5-HT discriminates placode-derived (vagal nodose) C-fibres from the neural crest-derived (vagal jugular and spinal DRG) afferent nerves in the oesophagus. The response to 5-HT in nodose C-fibres is mediated by the 5-HT3 receptor in their neuronal membrane. [source] Motor unit recruitment and derecruitment induced by brief increase in contraction amplitude of the human trapezius muscleTHE JOURNAL OF PHYSIOLOGY, Issue 2 2003C. Westad The activity pattern of low-threshold human trapezius motor units was examined in response to brief, voluntary increases in contraction amplitude (,EMG pulse') superimposed on a constant contraction at 4,7% of the surface electromyographic (EMG) response at maximal voluntary contraction (4,7% EMGmax). EMG pulses at 15,20% EMGmax were superimposed every minute on contractions of 5, 10, or 30 min duration. A quadrifilar fine-wire electrode recorded single motor unit activity and a surface electrode recorded simultaneously the surface EMG signal. Low-threshold motor units recruited at the start of the contraction were observed to stop firing while motor units of higher recruitment threshold stayed active. Derecruitment of a motor unit coincided with the end of an EMG pulse. The lowest-threshold motor units showed only brief silent periods. Some motor units with recruitment threshold up to 5% EMGmax higher than the constant contraction level were recruited during an EMG pulse and kept firing throughout the contraction. Following an EMG pulse, there was a marked reduction in motor unit firing rates upon return of the surface EMG signal to the constant contraction level, outlasting the EMG pulse by 4 s on average. The reduction in firing rates may serve as a trigger to induce derecruitment. We speculate that the silent periods following derecruitment may be due to deactivation of non-inactivating inward current (,plateau potentials'). The firing behaviour of trapezius motor units in these experiments may thus illustrate a mechanism and a control strategy to reduce fatigue of motor units with sustained activity patterns. [source] Comparative effects of resistance training on peak isometric torque, muscle hypertrophy, voluntary activation and surface EMG between young and elderly womenCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 2 2007Jack Cannon Summary We compared the effect of a 10-week resistance training program on peak isometric torque, muscle hypertrophy, voluntary activation and electromyogram signal amplitude (EMG) of the knee extensors between young and elderly women. Nine young women (YW; range 20,30 years) and eight elderly women (EW; 64,78 years) performed three sets of ten repetitions at 75% 1 repetition maximum for the bilateral leg extension and bilateral leg curl 3 days per week for 10 weeks. Peak isometric torque, EMG and voluntary activation were assessed before, during, and after the training period, while knee extensor lean muscle cross-sectional area (LCSA) and lean muscle volume (LMV) were assessed before and after the training period only. Similar increases in peak isometric torque (16% and 18%), LCSA (13% and 12%), LMV (10% and 9%) and EMG (19% and 21%) were observed between YW and EW, respectively, at the completion of training (P<0·05), while the increase in voluntary activation in YW (1·9%) and EW (2·1%) was not significant (P>0·05). These findings provide evidence to indicate that participation in regular resistance exercise can have significant neuromuscular benefits in women independent of age. The lack of change in voluntary activation following resistance training in both age groups despite the increase in EMG may be related to differences between measurements in their ability to detect resistance training-induced changes in motor unit activity. However, it is possible that neural adaptation did not occur and that the increase in EMG was due to peripheral adaptations. [source] | |||||||||||||