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PubMed2006

The dynamic range and domain-specific signals of intracellular calcium in photoreceptors.

Vertebrate photoreceptors consist of strictly delimited subcellular domains: the outer segment, ellipsoid, cell body and synaptic terminal, each hosting crucial cellular functions, including phototransduction, oxidative metabolism, gene expression and transmitter release. We used optical imaging to explore the spatiotemporal dynamics of Ca(2+) signaling in non-outer segment regions of rods and cones. Sustained depolarization, designed to emulate photoreceptor activation in the darkness, evoked a standing Ca(2+) gradient in tiger salamander photoreceptors with spatially-averaged intracellular Ca(2+) concentration within synaptic terminals of approximately 2 microM and lower (approximately 750 nM) intracellular calcium concentration in the ellipsoid. Measurements from axotomized cell bodies and isolated ellipsoids showed that Ca(2+) enters the two compartments via both local L-type Ca(2+) channels and diffusion. The results from optical imaging studies were supported by immunostaining analysis. L-type voltage-operated Ca(2+) channels and plasma membrane Ca(2+) ATPases were highly expressed in synaptic terminals with progressively lower expression levels in the cell body and ellipsoid. These results show photoreceptor Ca(2+) homeostasis is controlled in a region-specific manner by direct Ca(2+) entry and diffusion as well as Ca(2+) extrusion. Moreover, quantitative measurement of intracellular calcium concentration levels in different photoreceptor compartments indicates that the dynamic range of Ca(2+) signaling in photoreceptors is approximately 40-fold, from approximately 50 nM in the light to approximately 2 microM in darkness.

Animals↗
PubMed2000

Rapid spectrophotometric determination of oxygen consumption using hemoglobin, in vitro: light scatter correction and expanded dynamic range.

The method of using absorbance in conjunction with hemoglobin (Hb) to monitor rapid changes in oxygen consumption in vitro was improved by using a non-linear calibration technique and multiwavelength spectroscopy. The O(2) dependence of Hb absorbance was effectively linearized using the current technique (R(2) = 0.990+/-0.002, n = 3), and extended the dynamic range of [O(2)] determinations by 1.6-fold over previous approaches. The association/dissociation rates of O(2) and Hb were evaluated using the current approach and were not significant on the 100-ms time domain. A method was also developed for compensating for large amplitude light scattering changes in turbid media using multiwavelength analysis. Both the nonlinear calibration curve and light scattering corrections were validated in isolated porcine heart mitochondrial preparations.

Animals↗
PubMed2001

Induction of long-term potentiation of single wide dynamic range neurones in the dorsal horn is inhibited by descending pathways.

Previous studies have shown that long-term potentiation (LTP) in the dorsal horn may be induced by noxious stimuli. In this study it is investigated whether induction of LTP in the dorsal horn may be affected by the descending pathways. Extracellular recordings of wide dynamic range (WDR) neurones in the lumbar dorsal horn in intact urethane-anaesthetized Sprague--Dawley rats were performed, and the electrically evoked neuronal responses in these neurones were defined as A-fibre and C-fibre responses according to latencies. Using a short-term cold block of the thoracic spinal cord, which produced a completely reversible increase of the A-fibre and C-fibre responses, the influence of the descending inhibitory system on the induction of LTP by electrical high-frequency conditioning applied to the sciatic nerve was examined. As previously shown the A-fibre responses were almost unchanged following the conditioning. In contrast, the C-fibre responses following the same conditioning were strongly increased. Thus, a clear LTP of the nociceptive transmission in the dorsal horn was observed following electrical high-frequency conditioning. Interestingly, we found that the LTP was more powerful when the effects of the descending pathways were temporarily eliminated during conditioning. It is concluded that induction of LTP by electrical high-frequency conditioning stimulation, which may be part of the wider term central sensitization, is inhibited by descending pathways.

Animals↗
PubMed2006

Overcoming the dynamic range problem in mass spectrometry-based shotgun proteomics.

Protein profiling using mass spectrometry technology has emerged as a powerful method for analyzing large-scale protein-expression patterns in cells and tissues. However, a number of challenges are present in proteomics research, one of the greatest being the high degree of protein complexity and huge dynamic range of proteins expressed in the complex biological mixtures, which exceeds six orders of magnitude in cells and ten orders of magnitude in body fluids. Since many important signaling proteins have low expression levels, methods to detect the low-abundance proteins in a complex sample are required. This review will focus on the fundamental fractionation and mass spectrometry techniques currently used for large-scale shotgun proteomics research.

Animals↗
PubMed2005

Nociceptive spinal withdrawal reflexes but not spinal dorsal horn wide-dynamic range neuron activities are specifically inhibited by halothane anaesthesia in spinalized rats.

The aim of the present study was to investigate the spinal cord effects and sites of action of different inhaled concentrations (0.5-2%) of the anaesthetic, halothane. Simultaneous recordings were made of 3 Hz, suprathreshold (1.5 x T) electrically evoked spinal dorsal horn (DH) wide-dynamic range (WDR) neuron responses and of single motor unit (SMU) electromyographic (EMG) responses underlying the spinal withdrawal reflex in spinalized Wistar rats. Compared with the baseline responses obtained with 0.5% halothane, the electrically evoked early responses of the DH WDR neurons as well as the SMUs were only depressed by the highest, 2% concentration of halothane. In contrast, 1.5% halothane markedly inhibited the late responses of the DH WDR neurons, whereas 1% halothane started to significantly depress the late responses of the SMUs. Likewise, wind-up of the WDR neuron late responses was inhibited by 1.5-2% halothane, whereas 1-2% halothane significantly depressed wind-up of the SMU EMG late responses. The inhibitory effects of 2% halothane on the early and the late responses of the DH WDR neurons, but not of the SMUs, were completely reversed by opioid micro-receptor antagonist naloxone (0.04 mg/kg). However, no significant effects of naloxone were found on different responses of the DH WDR neurons as well as the SMUs at 0.5-1% halothane, suggesting that different concentrations of halothane may modulate different spinal receptors. We conclude that halothane at high concentrations (1.5-2%) seems to play a predominant inhibitory role via spinal multireceptors on ventral horn (VH) motor neurons, and less on DH sensory WDR neurons, of the spinal cord.

Anesthetics, Inhalation↗
PubMed2000

Effect of a single-channel wide dynamic range compression circuit on perception of stop consonant place of articulation.

Previous studies have shown that altering the amplitude of a consonant in a specific frequency region relative to an adjacent vowel's amplitude in the same frequency region will affect listeners' perception of the consonant place of articulation. Hearing aids with single-channel, fast-acting wide dynamic range compression (WDRC) alter the overall consonant-vowel (CV) intensity ratio by increasing consonant energy. Perhaps one reason WDRC has had limited success in improving speech recognition performance is that the natural amplitude balances between consonant and vowel are altered in crucial frequency regions, thus disturbing the aforementioned amplitude cue for determining place of articulation. The current study investigated the effect of a WDRC circuit on listeners' perception of place of articulation when the relative amplitude of consonant and vowel was manipulated. The stimuli were a continuum of synthetic CV syllables stripped of all place cues except relative consonant amplitudes. Acoustic analysis of the CVs before and after hearing aid processing showed a predictable increase in high-frequency energy, particularly for the burst of the consonant. Alveolar bursts had more high-frequency energy than labial bursts. Twenty-five listeners with normal hearing and 5 listeners with sensorineural hearing loss labeled the consonant sound of the CV syllables in unaided form and after the syllables were recorded through a hearing aid with single-channel WDRC. There were significantly more listeners who were unable to produce a category boundary when labeling the aided stimuli. Of those listeners who did yield a category boundary for both aided and unaided stimuli, there were significantly more alveolar responses for the aided condition. These results can be explained by the acoustic analyses of the aided stimuli.

Adult↗
PubMed2003

Spinal cord stimulation inhibits long-term potentiation of spinal wide dynamic range neurons.

It has been suggested that long-term potentiation (LTP) of dorsal horn neurons is a phenomenon that contributes to the development of chronic neuropathic pain. Spinal cord stimulation (SCS) may be an effective tool in alleviating such pain. The aim of this electrophysiological study in rats was to examine if SCS suppresses LTP of dorsal horn wide dynamic range (WDR) neurons. Increased knowledge of the mechanisms behind the effects of SCS may facilitate its further advancement and improve clinical efficacy. As previously shown, intensive, high-frequency electrical stimulation of the sciatic nerve in the rat induces an increased firing response of WDR neurons. Here we report that SCS gradually reduced this increased C-fiber response back to the baseline level. However, A-fiber responses were neither potentiated by the conditioning stimulus used nor were they affected by SCS. These data suggest that SCS affects the C-fiber component of dorsal horn central sensitization which is noteworthy since SCS, based on previous studies, is believed to primarily influence A-fiber functions.

Animals↗
PubMed2005

Spinal cord injury triggers sensitization of wide dynamic range dorsal horn neurons in segments rostral to the injury.

A spinal cord injury (SCI) was produced in adult rats by complete spinal cord transection at L6-S1. Neuropathic pain behaviors similar to the chronic central pain (CCP) syndrome in human, such as thermal hyperalgesia, mechanical allodynia and autotomy, were present in these rats after spinal cord injury. Meanwhile, wide dynamic range (WDR) neurons recorded in the spinal dorsal horn rostral to the lesion responded as high frequency of spontaneous activities, long duration of after-discharges to noxious electrical stimuli and an augmented wind-up to 0.5 Hz stimuli. By using bupivacaine powder, a sodium channel blocker, at the locus of transection immediate after nerve injury, the chronic pain behaviors were prevented; the hyperexcitability of WDR neurons was also substantially reduced. It is suggested that spinal cord transection induces the CCP syndromes, which may be evoked and maintained by the hyperexcitability in WDR neurons rostrally. Reducing the neuronal activity at the site of lesion following injury may prevent the development of CCP after SCI.

Animals↗
PubMed2004

ZP8, a neuronal zinc sensor with improved dynamic range; imaging zinc in hippocampal slices with two-photon microscopy.

The synthesis of a difluorofluorescein monocarboxaldehyde platform and its use for preparing ZP8, a new member of the Zinpyr family of neuronal Zn(2+) sensors, are described. By combining an aniline photoinduced electron transfer (PET) switch and an electron-withdrawing fluorescein scaffold, ZP8 displays reduced background fluorescence and improved dynamic range compared to previous ZP probes. The bright sensor undergoes an 11-fold increase in fluorescence intensity upon Zn(2+) complexation (Phi = 0.03-0.35) with high selectivity over cellular concentrations of Ca(2+) and Mg(2+). In addition, sensors in the ZP family have been utilized for optical imaging in biological samples using two-photon microscopy (TPM). The cell-permeable ZP3 probe is capable of identifying natural pools of labile Zn(2+) within the mossy fiber synapses of live hippocampal slices using TPM, establishing the application of this technique for monitoring endogenous Zn(2+) stores.

Animals↗
PubMed1988

Spinal recordings suggest that wide-dynamic-range neurons mediate sympathetically maintained pain.

In order to determine which classes of spinal neurons are capable of mediating sympathetically maintained pain, recordings were made from single somatosensory neurons in spinal cords of anesthetized cats. Each neuron was functionally identified with mechanical stimuli, and its responses to electrical stimulation of the sympathetic trunk were recorded. Nearly half (45%) of the wide-dynamic-range (WDR) neurons tested were activated by sympathetic stimulation, but none of the high threshold (nociceptor-specific) neurons and only 17% of the low threshold neurons were activated. Sympathetic activation was most common for WDR neurons that had the following: receptive fields proximal to the toes, low thresholds for mechanical activation, and both rapidly and slowly adapting responses to pressure. The predominant WDR response to sympathetic stimulation was long latency (greater than 1 sec) excitation. Sympathetic activation of WDR neurons was abolished by each of the following procedures: subcutaneous injection of local anesthetic, cooling of the receptive field with ice, and intravenous injection of the alpha-adrenergic blocker, phentolamine. The axons of some sympathetically activated WDR were shown to project to higher centers. These results indicate that WDR neurons are the only spinal nociceptive neurons activated by sympathetic efferent activity in this preparation. Therefore, WDR neurons, rather than high threshold neurons, are most likely to mediate the spinal component of sympathetically maintained pain. These results provide supporting evidence for our previous hypothesis that sympathetically maintained pain is mediated by myelinated mechanoreceptors acting on sensitized WDR neurons. Our results also demonstrate that sympathetic activation of WDR neurons is mediated by an alpha-adrenergic mechanism in the skin.

Adaptation, Physiological↗
PubMed1995

The dominant class of somatosensory neurone recorded in the spinal dorsal horn of awake sheep has wide dynamic range properties.

In order to investigate the properties of dorsal horn neurones in the absence of the distorting influences of anaesthesia, preparative surgery, prior training or excessive restraint, recordings have been made in sheep chronically prepared for single-cell recording. Within the limitations of sampling error of dorsal horn neurones with cutaneous receptive fields, the cell type most frequently encountered had wide dynamic range (WDR; convergent; multireceptive) properties; these accounted for 59% of the 46 neurones that were examined in detail. High-threshold mechanoreceptive (nocispecific) and low-threshold mechanoreceptive neurones formed 11% and 30% of the sample, respectively. These and other data indicate that under normal physiological conditions in the awake state, many spinal neurones do indeed have WDR properties, implying that these cells have an important function in nociceptive processing.

Animals↗
PubMed1997

Application of capillary electrophoresis to the measurement of oligonucleotide concentration and purity over a wide dynamic range.

Synthetic oligonucleotides rarely contain 100% of the full-length sequence due, in part, to the failure sequences produced during synthesis. In this paper, a method is described for the determination of both the concentration and the purity of oligonucleotides, utilizing capillary electrophoresis with a deoxyribo-nucleoside triphosphate as an internal standard. This method is advantageous for several reasons: (a) the wide dynamic range allows for the analysis of samples without the need for dilutions; (b) a small sample size is used for analysis; (c) capillary electrophoresis is automatable which allows for high throughput; and (d) all of the samples are analyzed at the same run temperature which aids in reproducibility and consistency between runs performed at different times.

Deoxyadenine Nucleotides↗
PubMed2000

Effect of compression ratio on speech recognition and speech-quality ratings with wide dynamic range compression amplification.

This project examined the effect of varying compression ratio on speech recognition and quality. Both listeners with mild-to-moderate sensorineural hearing loss and a control group of listeners with normal hearing participated. Test materials were sentences from the Connected Speech Test (R. M. Cox, G. C. Alexander, & C. Gilmore, 1987) which were digitally processed with linear amplification and wide dynamic range compression amplification with 3 compression ratios. Speech-recognition scores were obtained with sentences in quiet and in noise at a 10-dB signal-to-noise ratio for each amplification condition. Additionally, the participants rated each amplification condition in terms of clarity, pleasantness, ease of understanding, and overall impression. Results indicated that, for speech in quiet, compression ratio had no effect on speech-recognition scores; however, speech-quality ratings decreased as compression ratio increased. For speech in noise, both speech-recognition scores and ratings decreased with increasing compression ratio for the listeners with hearing loss. These results suggest that selection of compression ratio on the basis of speech-quality judgments does not compromise speech recognition.

Adult↗
PubMed1999

Expression of long-term potentiation in single wide dynamic range neurons in the rat is sensitive to blockade of glutamate receptors.

Plasticity in pain control systems may play an important role in clinical pain and some mechanisms of plasticity may be similar to those involved in learning. In this study we investigate the importance of alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors for the maintenance of long-term potentiation (LTP) in wide dynamic range (WDR) neurons. Doses of 6-nitro-7-sulphomoylbenzoylquinoxaline-2,3-dione disodium (NBQX) and D-Q-amino-5-phosphonopentanoic acid (D-AP5) equipotent in reducing C-fiber mediated responses in controls, reduced the established LTP by about 50 and 80%, respectively. The drug effect lasted less than 1 h in controls. After induction of LTP, NBQX caused a reversible reduction of the potentiation. D-AP5, however, caused a stronger attenuation of the LTP, outlasting the effect of the drug in controls. We suggest that both pre-emptive analgesia preventing LTP induction and an early reduction of the excitation of neurons is important for the inhibition of LTP and central sensitization. Thus, it is possible that an early antinociceptive treatment preventing an excessive excitation of neurons in the dorsal horn may be of importance in preventing longlasting and pathological pain states.

2-Amino-5-phosphonovalerate↗
PubMed1996

Miniature sodium-selective ion-exchange optode with fluorescent pH chromoionophores and tunable dynamic range.

An extension into the fluorescence mode of ion-exchange optodes is described, allowing miniaturization and its concomitant benefits. A micrometer-size, fluorescent fiber-optic sodium sensor is described, based on a highly sodium-selective, crown ether-capped calix[4]arene ionophore, capable of ratiometric operation. Three sensor configurations are given, employing different lipophilic, fluorescent pH chromoionophores (Nile Blue derivatives), demonstrating the ability to improve the detection limit and tune the dynamic range to the desired region of interest. Two of the sensors are of special interest in that their working ranges lie within those desired for measuring intracellular cytosolic or blood levels of sodium at the respective physiological pH. These optodes have excellent sodium selectivity, with other physiologically relevant cations (e.g., potassium, calcium, and magnesium) being highly discriminated. Three simple mathematical relationships are given for the three experimentally used fluorescent signal mechanisms (intensity, intensity ratios, and inner-filter or energy transfer effects), permitting visualization on a single graph and enabling direct comparison of the different sensors' optical responses on a common platform. Finally, these optodes measure the sample's sodium activity, rather than the concentration, provided that the sample's pH is measured simultaneously by another sensor, such as a glass electrode.

Fiber Optic Technology↗
PubMed2003

A novel urea sensitive biosensor with extended dynamic range based on recombinant urease and ISFETs.

A novel urea biosensor based on immobilised recombinant urease as sensitive element and ion sensitive field effect transistor as transducer was developed. Recombinant urease from E. coli with an increased Km was photoimmobilised in PVA/SbQ (poly(vinyl alcohol) containing styrylpyridinium) membrane and has demonstrated quite good performance as biosensitive element. Enzymatic field effect transistors based on such a bioselective element were studied in model buffer solutions. This biosensor demonstrated an extended dynamic range up to 80 mM, a quite good reproducibility (standard deviation of the sensor responses was approximately 2.5%, n= 20 for urea concentration 10 mM) and a high stability. Such characteristics fit with the analytical requirements needed for urea control in plasma and liquids used during renal dialysis.

Biosensing Techniques↗
PubMed2005

Systemic and site-specific effects of A-425619, a selective TRPV1 receptor antagonist, on wide dynamic range neurons in CFA-treated and uninjured rats.

Systemic administration of A-425619, a potent and selective TRPV1 receptor antagonist that does not readily enter the CNS, produces antinociception in several rat models of pathological nociception, including complete Freund's adjuvant (CFA)-induced thermal hyperalgesia. To further understand the peripheral mechanisms of TRPV1-related antinociception, we examined the effects of systemic and site-specific injections of A-425619 on evoked and spontaneous firing of spinal wide dynamic range (WDR) neurons in uninjured rats and rats with peripheral inflammation (CFA; 48 h). In uninjured rats, capsaicin-evoked (1 microg) WDR activity was completely blocked by intraplantar administration of A-425619 (3-100 nmol). Systemic injection of A-425619 (3-30 micromol/kg, iv) reduced WDR responses to thermal stimulation in both CFA-inflamed (47 degrees C) and uninjured (52 degrees C) rats. However, the efficacy of A-425619 to attenuate thermal-evoked WDR activity was significantly greater (P < 0.01) in CFA-treated rats. Both intradorsal root ganglion (DRG; L5; 20 nmol) and intraplantar (30-300 nmol) injection of A-425619 reduced WDR responses to thermal stimulation. While the effectiveness of A-425619 was similar between CFA-inflamed and uninjured rats after intraplantar injection, the effects of A-425619 after intra-DRG injection were enhanced in the inflamed rats (compared with the uninjured rats). Spontaneous WDR discharges were unaltered by systemic or site-specific injections of A-425619. Thus noxious thermal stimulation triggers the transmission of TRPV1-related signals to spinal WDR neurons in both inflamed and uninjured animals. The apparent increase in TRPV1 signaling to WDR neurons after injury may be the result of changes to the distribution/sensitization of peripheral TRPV1 receptors.

Action Potentials↗