Relationship between magnitude estimation of resistive loads, inspiratory pressures, and the RREP P(1) peak.
(25/1361)
This study investigated the relationship among resistive load magnitude (DeltaR), the cortical evoked potential P(1) peak amplitude of the respiratory-related evoked potential (RREP), mouth pressure (Pm), esophageal pressure (Pes), transdiaphragmatic pressure (Pdi), and resistive load magnitude estimation (ME) in human subjects. The RREP, Pdi, Pes, Pm, and ME were recorded in response to three DeltaR values. The RREP was recorded from C(3) and C(4), referenced to the vertex C(Z). The group means of the Pdi, Pm, ME, and RREP P(1) amplitude increased with increases in the DeltaR. A log-log plot of the P(1) amplitudes showed a relationship with ME as did Pes, Pdi, and Pm. There were linear log-log relationships between C(Z)-C(3) P(1) amplitude, C(Z)-C(4) P(1) amplitude, and Pdi to ME. Pdi had a linear log-log relationship with C(Z)-C(3) and C(Z)-C(4). These results support the hypothesis that the estimated magnitude of the respiratory load is related to the P(1) amplitude of the RREP. Pm, Pes, and Pdi are mechanically related and correlated with the P(1) peak amplitude, suggesting that the mechanoreceptors mediating the P(1) peak of the RREP are activated by changes in mechanical forces related to the inspiratory pump. (+info)
Neurobiological and psychophysical mechanisms underlying the oral sensation produced by carbonated water.
(26/1361)
Carbonated drinks elicit a sensation that is highly sought after, yet the underlying neural mechanisms are ill-defined. We hypothesize that CO(2) is converted via carbonic anhydrase into carbonic acid, which excites lingual nociceptors that project to the trigeminal nuclei. We investigated this hypothesis using three methodological approaches. Electrophysiological methods were used to record responses of single units located in superficial laminae of the dorsomedial aspect of trigeminal subnucleus caudalis (Vc) evoked by lingual application of carbonated water in anesthetized rats. After pretreatment of the tongue with the carbonic anhydrase inhibitor dorzolamide, neuronal responses to carbonated water were significantly attenuated, followed by recovery. Using c-Fos immunohistochemistry, we investigated the distribution of brainstem neurons activated by intraoral carbonated water. Fos-like immunoreactivity (FLI) was significantly higher in the superficial laminae of dorsomedial and ventrolateral Vc in animals treated with carbonated water versus controls. Dorzolamide pretreatment significantly reduced FLI in dorsomedial Vc. We also examined the sensation elicited by carbonated water in human psychophysical studies. When one side of the tongue was pretreated with dorzolamide, followed by bilateral application of carbonated water, a significant majority of subjects chose the untreated side as having a stronger sensation and assigned significantly higher intensity ratings to that side. Dorzolamide did not reduce irritation elicited by pentanoic acid. The present data support the hypothesis that carbonated water excites lingual nociceptors via a carbonic anhydrase-dependent process, in turn exciting neurons in Vc that are presumably involved in signaling oral irritant sensations. (+info)
Cerebral topography of rectal stimulation using single photon emission computed tomography.
(27/1361)
Central processing of visceral information in humans is incompletely understood. We aimed to demonstrate the feasibility of single photon emission computed tomography (SPECT) and to quantitate the changes in regional cerebral blood flow during rectal distension. Ten healthy volunteers underwent randomized sham and active rectal distensions on separate days, during which cerebral blood flow was assessed by intravenous technetium-99m ethyl cysteinate dimer ((99m)Tc-ECD) SPECT. Three-dimensional coregistration of brain images was used to quantitate activation in four preselected cerebral foci and two control regions. Paired analysis compared blood flow during sham and active distensions. There was increased right anterior cingulate gyrus activity (6.5 +/- 2.9%, P = 0.03) with active rectal distension. A 5.4 +/- 2.4% reduction in blood flow in the superior parieto-occipital control region (P = 0.04) suggested blood "redistribution" during stimulation. Marked variability in activation of the frontal cortex, thalamus/basal ganglia complex, and mesiotemporal lobe was noted. Thus rectal distension increases activity in the right anterior cingulate gyrus on average; other foci of cerebral activation are quite variable, suggesting a lack of specific cerebral projections during rectal stimulation. (+info)
Sensory loss by selected whisker removal produces immediate disinhibition in the somatosensory cortex of behaving rats.
(28/1361)
This study used extracellular unit recordings in behaving animals to evaluate thalamocortical response transformations in the rat whisker-barrel system. Based on previous acute studies using controlled whisker stimulation, we hypothesized that in a cortical barrel adjacent (non-principal) whiskers exert a net inhibitory effect. In contrast, in thalamic barreloid neurons, the effects of neighboring whiskers should be net facilitatory. We evaluated these hypotheses by recording unit activity at 21 sites in 17 animals trained to explore a wire mesh screen with their whiskers. In the middle of the recording session, selected vibrissae were clipped close to the skin surface. The absence of whiskers surrounding the principal whisker was associated with a mean 20% increase in cortical activity and, conversely, a 37% decrease in the thalamic activity. Removal of the principal whisker resulted in a 50% decrease in cortical unit firing. Findings are consistent with the idea that, in the behaving animal, each barrel uses multi-whisker thalamic inputs and local inhibitory circuitry to sharpen the receptive field properties of its constituent neurons. Cortical disinhibition as a consequence of selective whisker removal is likely to be an important factor underlying altered receptive field properties in sensory-deprived animals. (+info)
Caudal block in children: ropivacaine compared with bupivacaine.
(29/1361)
BACKGROUND: Bupivacaine provides reliable, long-lasting anesthesia and analgesia when given via the caudal route. Ropivacaine is a newer, long-acting local anesthetic that (at a concentration providing similar pain relief) has less motor nerve blockade and may have less cardiotoxicity than bupivacaine. METHODS: In a double-blind trial, 81 healthy children, undergoing ambulatory surgical procedures, were randomly allocated to receive caudal analgesia with either bupivacaine or ropivacaine, 0.25%, 1 mVkg. All blocks were placed by an attending anesthesiologist or an anesthesia fellow after induction of general anesthesia. RESULTS: Data were available for 75 children. There were no significant differences between the two groups in baseline characteristics or in anesthesia, surgery, recovery room, or day surgery unit durations. The quality and duration of postoperative pain relief did not differ. Motor and sensory effects were similar. Time to first micturition did not differ. CONCLUSION: Ropivacaine (0.25%, 1 ml/kg) provided adequate postoperative analgesia with no difference from bupivacaine (0.25%, 1 ml/kg) in quality and duration of pain relief, motor and sensory effects, or time to first micturition in our study children. (+info)
Serial force plate analyses of dogs with unilateral knee instability, with or without interruption of the sensory input from the ipsilateral limb.
(30/1361)
OBJECTIVE AND DESIGN: We characterized the mean peak vertical forces (MFz) in five groups of dogs which underwent transection of the left anterior cruciate ligament (ACLT) or sham ACLT and ipsilateral dorsal root ganglionectomy or sham-ganglionectomy, and the relationship of these forces to the severity of osteoarthritis (previously reported) 72 weeks after arthrotomy. Group I (N=7) underwent ACLT; Group II (N=8) underwent ACLT followed 52 weeks later by ganglionectomy; Group III (N=7) underwent ganglionectomy followed 2 weeks later by ACLT; Group IV (N=7) underwent sham-ganglionectomy followed 2 weeks later by ACLT; Group V (N=8) underwent ganglionectomy followed 2 weeks later by sham-ACLT. The dogs were evaluated 2, 6, 12, 24, 52 and 72 weeks after arthrotomy. RESULTS: From 6 weeks after arthrotomy until death, the left hindlimb MFz in Group V was significantly greater (P< 0.05) than that in the other four groups. The MFz of all groups which underwent ACLT decreased after arthrotomy. While the MFz of Group III (very severe OA) was about 10-20% greater than that of Groups I, II and IV (mild OA) 6 and 12 weeks after ACLT, and generally about 5-10% greater subsequently, this difference was not statistically significant. The MFz of Group II returned to pre-ganglionectomy levels, rather than to baseline levels, following ganglionectomy. CONCLUSIONS: (1) since the ipsilateral limb of dogs with ganglionectomy+sham ACLT bore normal amounts of weight throughout most of the postsurgical period, and its knee did not develop OA, one cannot argue that the knee was protected from OA because the limb was not used; (2) the fact that the MFz of dogs which underwent ACLT+ganglionectomy returned to pre-ganglionectomy levels, rather than baseline, is consistent with the hypothesis that the unstable joint was protected from accelerated breakdown by a central nervous system that was reprogrammed by sensation from the unstable limb; (3) the slightly-but consistently-greater MFz of dogs which underwent ganglionectomy+ ACLT may contribute to the acceleration of OA in this model. (+info)
Neuronal control of locomotion in C. elegans is modified by a dominant mutation in the GLR-1 ionotropic glutamate receptor.
(31/1361)
How simple neuronal circuits control behavior is not well understood at the molecular or genetic level. In Caenorhabditis elegans, foraging behavior consists of long, forward movements interrupted by brief reversals. To determine how this pattern is generated and regulated, we have developed novel perturbation techniques that allow us to depolarize selected neurons in vivo using the dominant glutamate receptor mutation identified in the Lurcher mouse. Transgenic worms that expressed a mutated C. elegans glutamate receptor in interneurons that control locomotion displayed a remarkable and unexpected change in their behavior-they rapidly alternated between forward and backward coordinated movement. Our findings suggest that the gating of movement reversals is controlled in a partially distributed fashion by a small subset of interneurons and that this gating is modified by sensory input. (+info)
Sensations induced by medium and long chain triglycerides: role of gastric tone and hormones.
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BACKGROUND: The relative roles of gastric relaxation and the neuroendocrine signals released by the small intestine in the perception of nutrient induced sensations are controversial. The different effects of long chain (LCT) and medium chain (MCT) triglyceride ingestion on perception, gastric relaxation, and hormonal release may help to elucidate the mechanisms underlying nutrient induced sensations. AIMS: To compare the effects of intraduodenal LCT and MCT infusions on perception, gastric tone, and plasma gut hormone levels in healthy subjects. SUBJECTS: Nine fasting healthy volunteers. METHODS: The subjects received duodenal infusions of saline followed by LCTs and MCTs in a randomised order on two different days. The sensations were rated on a visual analogue scale. Gastric tone was measured using a barostat, and plasma gut hormone levels by radioimmunoassay. RESULTS: LCT infusion increased satiation scores, reduced gastric tone, and increased the levels of plasma cholecystokinin, gastric inhibitory polypeptide, neurotensin, and pancreatic polypeptide. MCT infusion reduced gastric tone but did not significantly affect perception or plasma gut hormone levels. LCTs produced greater gastric relaxation than MCTs. CONCLUSIONS: The satiation induced by intraduodenal LCT infusion seems to involve changes in gastric tone and plasma gut hormone levels. The gastric relaxation induced by MCT infusion, together with the absence of any significant change in satiation scores and plasma hormone levels, suggests that, at least up to a certain level, gastric relaxation is not sufficient to induce satiation and that nutrient induced gastric relaxation may occur through cholecystokinin independent mechanisms. (+info)