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S M Lu

Publications and source records attributed to S M Lu.

At least 37 records · Page 2Linked to original sources
PubMed1992

Relative contributions of burst and tonic responses to the receptive field properties of lateral geniculate neurons in the cat.

1. In an anesthetized, paralyzed in vivo preparation, we recorded extracellular responses of 61 geniculate neurons (2 W, 25 X, 33 Y, and 1 mixed) to drifting sine-wave gratings of various spatial frequency, temporal frequency, and contrast. Our goal was to study the differential contributions to these visual responses of bursting caused by voltage dependent, low-threshold (LT) Ca2+ spikes and of purely tonic responses unrelated to LT spikes. Cells responding with LT spikes are said to be in the burst firing mode and those responding in a purely tonic fashion to be in the relay or tonic firing mode. We separated the total visual response into LT burst and tonic components by use of the empirical criteria set forth in our intracellular study described in the previous paper (Lu et al. 1992). A response component was considered to be an LT burst if its action potentials displayed interspike intervals < or = 4 ms and if the first spike in the burst episode occurred after a silent period of > or = 100 ms (or > or = 50 ms when the neuron responds to visual stimuli at temporal rates > or = 8 Hz). All other activity is considered to be part of the tonic response. 2. In addition to LT bursts, we recognized another type of burst response, the high-threshold (HT) burst. These also have clusters of action potentials with interspike intervals < or = 4 ms. However, HT bursts, unlike LT bursts, lack a preburst silent period. HT bursts are part of the tonic response component and merely reflect the gradual decrease in interspike intervals that occurs as the cell becomes more depolarized and thus more responsive. Thus interspike interval is a necessary but insufficient criterion to identify LT bursts. 3. Visually evoked LT bursts were recorded among W, X, and Y cells. When evoked, LT bursts occurred in phase with drifting sine-wave grating stimuli at a rate never exceeding one per stimulus cycle. In response to individual cycles of the visual stimulus, LT bursts could comprise the total response, a tonic component could comprise the total response, or an LT burst and tonic component could be mixed. When a stimulus evoked a mixture of LT bursts and tonic response components, LT bursts were always the first response. 4. Of the 61 cells tested with grating stimuli, 47 exhibited LT bursts and 14 did not. Those that did exhibited varying amounts of burstiness.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1992

[Effects of combination chemotherapy of ovarian cancer in vitro].

To investigate the effects of combination chemotherapy on ovarian cancer in vitro, we observed the sensitivity of tumors to different drugs by incorporation assay of tritium thymidine (3H-TdR). The results revealed that the drugs and their sensitive degrees varied from tumor to tumor. Whether the combination of the drugs is synergism or sometimes only enhances toxicity depends on the difference of individuals. We suggest that in vitro anti-cancer drug sensitivity test could be applied in selection or determination of chemotherapy protocol.

Antibiotics, Antineoplastic↗
PubMed1991

Intracellular and extracellular in vivo recording of different response modes for relay cells of the cat's lateral geniculate nucleus.

Prior studies of thalamic neurons have demonstrated that they exhibit at least two response modes: a relay mode and a burst mode. During the relay mode, sensory information is faithfully relayed to cortex; during the burst mode, which is caused by a voltage-dependent Ca2+ conductance, this relay of sensory information is interrupted. We began in vivo studies of these response modes in neurons from the lateral geniculate nucleus of anesthetized, paralyzed cats. Each of the 9 X and 10 Y cells we recorded intracellularly displayed voltage-dependent, low threshold spikes that were presumably the Ca2+ spikes described from in vitro recording. These spikes were triangular in waveform and typically had 2-7 fast action potentials (interspike intervals of 1.2-4 ms) riding its crest. Furthermore, the cell's membrane had to be hyperpolarized to de-inactivate the low threshold spike before a depolarization could then activate it. We could activate these low threshold spikes in Y cells from EPSPs, whether spontaneous or evoked from activation of the optic chiasm. However, in only one of the X cells could we activate low threshold spikes from chiasm shock; in the remainder, we could activate low threshold spikes only via depolarizing current pulses, possibly because the EPSPs of these X cells were too small to activate these spikes. We also used extracellular recording to study spontaneous activity and responses to chiasm shock from 114 geniculate neurons and, as a control, 57 optic tract axons. We concentrated on periods of bursty responsiveness signifying the burst mode. We define a burst as 2-7 action potentials with interspike intervals less than or equal to 4 ms, and the bursts are separated by greater than 100 ms; from our intracellular recording, we know that such bursts signify low threshold spikes. We found that, during extracellular recording, 20 of the 39 X cells and each of the 75 Y cells displayed evidence of the burst response mode, although burst periods were rare in X cells. Electrical activation of the optic chiasm greatly enhanced the burstiness of Y cells for periods of 500 ms or more. We also electrically stimulated the parabrachial region of the midbrain, which provides a mostly cholinergic innervation to the lateral geniculate nucleus. Although parabrachial activation by itself had no detectable effect on Y cell response modes, prior parabrachial activation prevented the enhanced burstiness caused by chiasm stimulation. This parabrachial effect lasted for roughly 500 ms after stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

[Effect of levonorgestrel intrauterine device on human endometrial estrogen and progesterone receptors].

Estrogen and progesterone cytoplasmic receptors (ER, PgR) were determined by radiochemical DCC technique in the endometria of 16 normal women at before child bearing age and 6 to 9 months after LNG IUD insertion. The study showed that both ER and PgR were reduced significantly after LNG IUD insertion (P less than 0.01). The decrease of ER and PgR might play an important role in gland reduction and endometrial atrophy. It may be one mechanism of the contraceptive effect and the cause of anemia or spotting between menstruation during the course of LNG IUD insertion.

Adult↗
PubMed1990

N-methyl-D-aspartate receptors contribute to excitatory postsynaptic potentials of cat lateral geniculate neurons recorded in thalamic slices.

Neurons of the cat's dorsal lateral geniculate nucleus were recorded intracellularly to study the contribution of N-methyl-D-aspartate (NMDA) receptors to excitatory postsynaptic potentials (EPSPs) and low-threshold calcium spikes. EPSPs were evoked by stimulation of retinogeniculate axons in the optic tract and/or corticogeniculate axons in the optic radiations; EPSPs from both sources were similar. These EPSPs had one or two components, and the second component had several characteristics of NMDA receptor-mediated events. For example, EPSP amplitude decreased when neurons were hyperpolarized and increased when stimulus frequency was increased; these EPSPs could also be blocked reversibly by application of the selective NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV). We also studied the influence of NMDA receptors on low-threshold calcium spikes, which are large, voltage- and calcium-dependent depolarizations that are often accompanied by high-frequency action potential discharge. APV blocked synaptically activated low-threshold calcium spikes, but APV had no effect on low-threshold calcium spikes that were elicited by current injection. Therefore, APV does not appear to have a direct effect on the T-type calcium channel that is involved in generation of low-threshold calcium spikes. The voltage and frequency dependence of the NMDA receptor-mediated component of the EPSPs, as well as its ability to trigger low-threshold calcium spikes, provide for complex signal processing in the lateral geniculate nucleus.

2-Amino-5-phosphonovalerate↗
PubMed1990

The acceptable load while marching at a speed of 5 km h-1 for young Chinese males.

Ninety-three young Chinese men selected at random were involved in the load carrying experiments. They marched at 5 km h-1 carrying loads of 0, 15, 20, 25 and 31 kg for 7 h per day. At this speed the acceptable load to be carried was 20 kg. Under this load 95% of the men had heart rates below 120 bt min-1 while marching and energy metabolism was in balance. Nevertheless, 10-15% of the men were fatigued and felt tired.

Adult↗
PubMed1990

[In vitro drug-resistance decrease of ovarian cancer cells].

A chemosensitivity test for ovarian cancer using tritiated thymidine incorporation assay was carried out. A dose-response relationship was observed for cis-platinum and an 5-fold increase of concentration converted the drug resistant tumor into a drug-sensitive one. Verapamil was found to enhance the cytotoxic effect of vincristine against ovarian cancer cells. It is suggested that combination of vincristine with verapamil may be helpful in treating some vincristine-resistant cases.

Cisplatin↗
PubMed1987

Immunoreactivity to calcitonin gene-related peptide in the superior olivary complex and cochlea of cat and rat.

In both cat and rat, the cells of origin, axons, and terminals of the lateral olivocochlear system exhibit immunoreactivity to antisera to calcitonin gene-related peptide (CGRP). In the cat, immunoreactive neurons in the brainstem are located in the hilus of the lateral superior olivary nucleus and around its margins. In the rat, immunoreactive neurons are located within the lateral superior olivary nucleus proper. In both species, immunoreactivity in the cochlear duct is limited to the region beneath the inner hair cells. Immunoreactive axons in the cochlear nucleus could not be traced to their source but may arise as collaterals of the lateral olivocochlear system. No other components of the brainstem auditory system react to any extent with the antisera.

Animals↗
PubMed1986

Glutamic acid decarboxylase and somatostatin immunoreactivities in rat visual cortex.

Antibodies to glutamic acid decarboxylase (GAD) and somatostatin (SS) were used to determine the laminar distribution and morphology of GAD- and SS-immunoreactive neurons and terminals in rat visual cortex. The present study demonstrates that GAD-immunoreactive neurons constitute several morphologically distinct subclasses of neurons in rat visual cortex. These subclasses of neurons can be distinguished by differences in soma size, soma shape, dendritic branching patterns, axonal arborizations, and location in the neuropil. GAD-immunoreactive neurons are found throughout all layers of visual cortex. They have nonpyramidal morphology and constitute roughly 15% of the total neuronal population. The laminar pattern of GAD-immunoreactive puncta is uneven, with a prominent band of terminals in layer IV. Numerous large GAD-positive puncta surround the somata and proximal dendrites of pyramidal cells in layers II, III, and V. SS-immunoreactive neurons constitute a less numerous and more restricted population of nonpyramidal neurons. Their somata are located mainly in layers II, III, V, and VI. Very few, if any, SS-immunoreactive neurons are found in layers I and IV. SS-immunoreactive terminals are arranged along vertical and diagonal collateral branches that have a beaded appearance. Finally, many neurons in the supra- and infragranular layers and in the white matter are immunoreactive to both glutamic acid decarboxylase and somatostatin. This coexistence of immunoreactivity to both GAD and SS may characterize a broad subclass of cortical nonpyramidal neurons.

Animals↗
PubMed1985

Glutamate decarboxylase immunoreactivity in the intermediate grey layer of the superior colliculus in the cat.

Recent evidence suggests that gamma-aminobutyrate has a profound influence on the activity of premotor neurons in the intermediate grey layer of the superior colliculus. In the present study an antibody to glutamate decarboxylase, the synthesizing enzyme for gamma-aminobutyrate, was used to identify and characterize the structures in the intermediate grey layer of the cat that use gamma-aminobutyrate as a transmitter. The material was examined with both the light and electron microscope. Glutamate decarboxylase immunoreactivity was confined, for the most part, to axon terminals. Glutamate decarboxylase positive terminals almost completely cover the soma and proximal dendrites of the large neurons that are characteristic of this layer. Other glutamate decarboxylase positive terminals contact smaller, presumably more distal dendrites. By combining the glutamate decarboxylase immunocytochemistry with the retrograde transport of horseradish peroxidase in single animals, it was demonstrated that the cells of origin of the major descending efferent pathway from the intermediate grey layer, the predorsal bundle, are heavily contacted by glutamate decarboxylase immunoreactive terminals.

Animals↗
PubMed1985

Glutamic acid decarboxylase immunoreactivity in layer IV of barrel cortex of rat and mouse.

The morphology and distribution of neurons and terminals that are immunoreactive to glutamic acid decarboxylase (GAD) were investigated in barrel cortex of the rat and mouse. The morphology of the GAD-immunoreactive neurons located in layer IV of the barrel field resembles that of the large, smooth stellate neurons described previously in Golgi studies. Most of the somas of GAD-positive neurons are located along the sides of the barrels. They constitute about 13 to 15% of the total neuronal population in layer IV. The spatial distribution of GAD-positive terminals in layer IV is similar to the distribution of GAD-positive somas. Very few GAD-positive neurons and terminals are found in the septal regions. This unique distribution of GAD immunoreactivity in the barrel cortex may serve as a model to study cortical inhibitory mechanisms.

Animals↗
PubMed1984

Excitability of auditory neurons in the dorsal and ventral cochlear nuclei of DBA/2 and C57BL/6 mice.

Extracellular response properties were studied in neurons of the dorsal and ventral divisions of the cochlear nucleus (DCN and VCN, respectively) of DBA/2 (DBA) and C57BL/6 (C57) mice. Mice of the former inbred strain show susceptibility to audiogenic seizures and have severe high frequency hearing loss when young; mice of the latter strain do not. Whereas afterdischarges had been readily observed in the inferior colliculus of DBA mice in a previous study, they were never observed in the cochlear nucleus. The incidence of nonmonotonic intensity functions, the slopes of intensity functions, and the incidence of inhibition in response areas indicated that inhibition was diminished in the DCN of DBA mice. However, in the VCN, these response properties did not differ between the two strains. There appeared to be an "amplification" of excitability (i.e., attenuation of inhibition) from VCN to DCN to inferior colliculus in DBA mice.

Acoustic Stimulation↗
PubMed1982

Abnormal tonotopic organization in the ventral cochlear nucleus of the hearing-impaired DBA/2 mouse.

The representation of sound frequency by auditory neurons (tonotopic organization) was evaluated in the ventral cochlear nucleus (VCN) of DBA/2 mice, a strain with impaired sensitivity to the highest and lowest frequencies heard by normal mice. Tuning curves were obtained from multiple-unit activity (MUA) and compared with those of C57 mice, which do not have severe hearing loss. Tuning curves in the C57 VCN displayed the dorsoventral progression from high- to low-frequency sensitivity that is typical of mammals. By contrast, tuning curves of DBA mice varied little as a function of dorsoventral location, and most MUA thresholds were lowest for frequencies within a narrow range (about 12-16 kHz). Thus, normal tonotopic organization is absent in the DBA mouse's VCN. In addition, because of the consistently low thresholds for 12-16 kHz tones in DBA MUA, mean thresholds for these frequencies are lower than those of C57 MUA in the dorsal and ventral portions of the VCN.

Animals↗
PubMed1982

Noise-induced hearing loss can alter neural coding and increase excitability in the central nervous system.

Responses of auditory neurons in the inferior colliculi of mice were studied longitudinally before and shortly after each animal was exposed to intense noise. Noise exposure caused expected losses in auditory sensitivity, but in 31 percent of the neurons studied, unexpected alterations of temporal patterns of action potentials were observed: certain suprathreshold stimuli that had evoked only transient "onset" responses or inhibition of spontaneous discharges prior to noise exposure came to elicit sustained excitation after exposure. Thus, noise-induced hearing loss can be associated with increases in neural responsivity and alterations of normal neural coding processes.

Acoustic Stimulation↗