Biomedical subjects

Chen-Tung Yen

Publications and source records attributed to Chen-Tung Yen.

10 recordsLinked to original sources

PubMed2006

Frequency response characteristic of sympathetic mediated low-frequency blood pressure fluctuations in conscious rats.

A quantitative relationship between power densities of blood pressure (PBP) and sympathetic nerve activity (PSNA) in a low-frequency range (LF, 0.016-0.85 Hz), expressed as PSNA=PBPxax10bx(frequency) was proposed in pentobarbital-anesthetized rats. For evaluating the general applicability of this equation, the quantitative relationship of power density ratio Hf=PBP/PSNA across frequency was tested in a conscious state. Wistar rats were chronically instrumented with a femoral artery catheter and recording electrode around the renal sympathetic nerve. The blood pressure and renal sympathetic nerve activity were monitored both under pentobarbital anesthesia and in a conscious state. Linear regression analysis of the relationship between the frequency and logarithmic magnitude of the power density ratio in the LF range revealed excellent fit in both conditions (r=-0.96+/-0.01 and -0.93+/-0.01 for anesthetized and conscious rats, respectively). Comparing the regression lines, rats under pentobarbital anesthesia had significantly larger values for the y-intercept and slope compared to rats in a conscious state (y-intercepts: 0.80+/-0.09>0.53+/-0.08; slopes: -2.86+/-0.26>-1.62+/-0.21). Our results demonstrate that it is also feasible to use the weighted PBP in LF as a quantitative index of sympathetic variability in conscious rats, but the evaluation of possible complications controlling the regression parameters is called for.

Action Potentials↗

PubMed2005

BOLD signals correlate with ensemble unit activities in rat's somatosensory cortex.

Evoked neural activity (ensemble single-unit activity and evoked field potential) and functional magnetic resonance imaging (fMRI) changes of the primary somatosensory cortex in response to electrical stimulation of the hind paw were studied in rats under anesthesia. The effects of stimulation frequency (ranging from 0.3 to 10 Hz) and types of anesthetics (alpha-chloralose and sodium pentobarbital) on blood oxygen level dependent (BOLD) activation and neural activation were compared. Both ensemble single-unit activity and BOLD signal changes achieved maximal activation at 3 Hz of stimulation and responses were significantly stronger under alpha-chloralose anesthesia. The maximal activation of the integral evoked potential (sigmaEP), in contrast, was the highest at 10 Hz; and the values were similar for alpha-chloralose and pentobarbital. These analyses revealed that fMRI image changes were better correlated with ensemble single-unit activity than with sigmaEP during somatosensory stimulations.

Anesthesia↗

PubMed2005

Inhibitory avoidance learning altered ensemble activity of amygdaloid neurons in rats.

In this study, we examined single-unit activity in the amygdala before and after a rat had acquired an inhibitory avoidance task. Long-Evans rats with microwires chronically implanted into the central nucleus (CeA) or basolateral complex (BLC) of the amygdala were acclimatized to the apparatus of a step-through inhibitory avoidance task for three sessions. On the fourth session, rats in the experimental group received an inescapable footshock (3 mA, 1 s) as they stepped from the lit side into the dark side of the task apparatus, whereas rats in the control group received the same amount of shock on a different apparatus. All rats were tested for retention in the task apparatus 1 day after shock training. The experimental rats showed better retention than the controls as they stayed longer in the lit side. Ensemble unit activities were recorded in the amygdala nuclei from the indwelling wire bundles during the acclimation and test sessions. The data collected from well-isolated amygdala units showed that neuronal discharge habituated from the first to the third acclimation session. In the test session, the experimental group, but not the control group, showed elevated firing rates in the CeA or BLC neurons located on either side of the brain. These findings provide the first piece of evidence showing that learning of an inhibitory avoidance task leads to an increase in amygdala neuronal discharges during a retention test.

Action Potentials↗

PubMed2005

Comparison of anterior cingulate and primary somatosensory neuronal responses to noxious laser-heat stimuli in conscious, behaving rats.

In this study, we investigated single-unit responses of the primary sensorimotor cortex (SmI) and anterior cingulate cortex (ACC) to noxious stimulation of the tail of the rat. The influences of morphine on these nociceptive responses were also compared. Multiple single-unit activities were recorded from two eight-channel microwire arrays chronically implanted in the tail region of the SmI and ACC, respectively. CO2 laser-heat irradiation of the middle part of the tail at an intensity slightly higher than that causing a maximal tail flick response was used as a specific noxious stimulus. Examined individually, ACC neurons were less responsive than SmI neurons to laser-heat stimulus, in that only 51% of the ACC units (n = 125) responded compared with 88% of the SmI units (n = 74). Among these responsive ACC units, many had a very long latency and long-lasting excitatory type of response that was seldom found in the SmI. When ensemble activities were examined, laser heat evoked both short- (60 approximately 150 ms) and long-latency (151 approximately 600 ms) responses in the SmI and ACC. Latencies of both responses were longer in the ACC. Furthermore, a single dose of 2.5-10 mg/kg morphine intraperitoneally suppressed only the long latency response in the SmI, but significantly attenuated both responses in the ACC. These effects of morphine were completely blocked by prior treatment with the opiate receptor blocker, naloxone. These results provide further evidence suggesting that the SmI and ACC may play different roles in processing noxious information.

Action Potentials↗

PubMed2004

Wavelet-based analysis of low-frequency fluctuations of blood pressure and sympathetic nerve activity in rats.

Biorthogonal wavelets were employed to quantify the relationship of fluctuations between blood pressure (BP) and sympathetic nerve activity (SNA). We forced the SNA to fluctuate by electrical stimulation the medulla in anesthetized, paralyzed, vagotomized, cardiac sympathetic-blocked, baroreceptor-denervated, and angiotensin II-converting enzyme-inhibited rats. Although spectral analysis showed a close coupling between fluctuations of BP and SNA at the stimulating frequencies, only the fluctuations of SNA in frequencies of 0.25 to approximately 0.4 Hz were proportional to BP fluctuations over the course of time. The results suggest that fluctuations transmitted from SNA to BP were uniform without shifting due to the nature of vasculature or the lagging of sympathetic action in frequencies of 0.25 to approximately 0.4 Hz, and support the possibility of using low-frequency variabilities of BP to quantitatively estimate fluctuations of SNA at time domain.

Action Potentials↗

PubMed2004

Differential morphine effects on short- and long-latency laser-evoked cortical responses in the rat.

Evoked potential and ensemble neuronal activities were used to study the responses of the primary sensorimotor cortex (SmI) to noxious CO(2) laser irradiation of the middle part of the tail in conscious behaving rats. The hypothesis that systemic morphine treatment preferentially attenuates the longer-latency laser-evoked cortical responses was also tested. Laser-evoked potentials (LEPs) and multiple single-unit (SU) activities were, respectively, recorded from chronically implanted stainless-steel screws and microwire electrodes. When examined individually, many SmI neurons showed either short-latency (<100 ms) or long-latency (300-500 ms) responses to laser irradiation. These neurons are widely dispersed in the tail region and hind limb region of the SmI, and also in the forelimb and head regions of the primary motor cortex (MI). Quantitatively, a higher percentage of neurons in the SmI tail region responded with shorter latencies compared to those in the SmI hind limb region or in the MI. When responses of many simultaneously recorded SU were examined together, short-latency and long-latency SmI ensemble activities matched the LEP1 and LEP2, respectively. Systemic morphine significantly attenuated the long-latency but not the short-latency component in both LEPs as well as ensemble neuronal activity in the tail region of the SmI. These effects were blocked by naloxone pretreatment.

Action Potentials↗

PubMed2003

A simple method for fabricating horizontal and vertical microwire arrays.

Microwire array electrodes are important in multi-site, multiple single-unit recording experiments. A simple method is described herein for the construction of microwire arrays consisting of evenly spaced insulated microwires in either horizontal or vertical orientations. Several key steps in the fabrication of a good microwire array electrode are made easier with this method. These steps include (1) arranging microwires into a desirable configuration, (2) keeping track of microwire sequences, and (3) soldering microwires to closely packed slots. This method needs only general mechanical tools and is relatively simple even for inexperienced workers.

Action Potentials↗

PubMed2003

Reticular thalamic responses to nociceptive inputs in anesthetized rats.

The present study compares nociceptive responses of neurons in the reticular thalamic nucleus (RT) to those of the ventroposterior lateral nucleus (VPL). Extracellular single-unit activities of cells in the RT and VPL were recorded in anesthetized rats. Only units with identified tactile receptive fields in the forepaw or hindpaw were studied. In the first series of experiments, RT and VPL responses to pinching with a small artery clamp were tested with the rats under pentobarbital, urethane, ketamine, or halothane anesthesia. Under all types of anesthesia, many RT units were inhibited. Second, the specificity of the nociceptive response was tested by pinching and noxious heating of the unit's tactile receptive field. Of the 39 VPL units tested, 20 were excited by both types of noxious stimuli. In sharp contrast, of the 30 RT units tested, none were excited and 17 were inhibited. In a third series of experiments, low-intensity and beam-diffused CO(2) laser irradiation was used to activate peripheral nociceptive afferents. Wide-dynamic-range VPL units responded with short- and long-latency excitations. In contrast, RT units had short-latency excitation followed by long-latency inhibition. Nociceptive input inhibited RT units in less than 500 ms. We conclude that a significant portion of RT neurons were polysynaptically inhibited by nociceptive inputs. Since all the cells tested were excited by light tactile inputs, the somatosensory RT may serve in the role of a modality gate, which modifies (i.e. inhibits) tactile inputs while letting noxious inputs pass.

Action Potentials↗

PubMed2003

Identification of active thoracic spinal segments responsible for tonic and bursting sympathetic discharge in neonatal rats.

The isolated thoracic cord of a neonatal rat in vitro generates tonic sympathetic activities in the splanchnic nerves. This tonic sympathetic nerve discharge (SND) has a prominent quasi-periodic oscillation at approximately 1-2 Hz. Bath application of bicuculline and strychnine, which removes endogenous GABA(A) and glycine receptor activities, transforms the quasi-periodic tonic SND into synchronized bursts (bSND). Picrotoxin, another GABA(A) receptor antagonist, also induces bSND. Serial transections of the thoracic cord (T1-12) were performed to identify the cord segments responsible for these tonic and bursting SNDs. Removal of T1-5 did not affect tonic SND. Nerve-cord preparation with either T6-8 or T10-12 segments could generate a substantial amount of tonic SND that retained comparable oscillating patterns. On the other hand, removal of T1-5 significantly reduced bSND amplitude without affecting its rhythmicity. Either T6-8 or T10-12 segments alone could generate bSND. Mid-point transection of T6-12 at T9 might split bSND rhythmogenesis, leading to the occurrence of bSND that could be attributed to two independent oscillators. Our results demonstrated that three segments within the T6-12 cord were sufficient to generate a rudimentary tonic and bursting SNDs. The thoracic cord segments, however, are dynamically interacting so that a full size bSND could only be produced with the intact thoracic cord.

Action Potentials↗

PubMed2002

Neural and cardiac activities are altered by injection of picomoles of glutamate into the nucleus ambiguus of the rat.

A quantitative evaluation of the thresholds of changes in the firing rate/pattern and depolarizing block of the neuron and the bradycardiac response by pressure microinjection of 10 mM glutamate (Glu) into the region of the nucleus ambiguus (NA) of the ventral medulla was performed in anesthetized rats. A change in neuronal activity was shown with injection of about 2 pmol of Glu. A depolarizing block of single-unit activity could be observed at 2.9 +/- 0.3 nl (approximately 30 pmol, n = 22). Maximal bradycardiac response (-50 +/- 5%) was elicited with 4.4 +/- 0.7 nl (approximately 50 pmol, n = 10), which is significantly smaller than the ranges used in previous studies. Based on these results, a safe and effective use of 10 mM Glu to induce neuronal or physiological response should be in the range of a few nanoliters and less than 100 pmol, especially for the NA.

Animals↗