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Biomedical subjects

X Pei

Publications and source records attributed to X Pei.

At least 55 records · Page 3Linked to original sources
PubMed1996

Light enhances hydrodynamic signaling in the multimodal caudal photoreceptor interneurons of the crayfish.

1. The caudal photoreceptor (CPR) interneurons in the sixth abdominal ganglion of the crayfish are complex, multi-modal interneurons. These cells respond directly to light with tonic spike discharges, and they integrate synaptic input from an array of fili-form mechanoreceptors on the tailfan. They also provide input to rostral command centers, inducing backward walking at high firing frequencies, and thus directly influence behavior. 2. We recorded CPR activity in response to weak hydrodynamic stimulation of the tailfan mechanoreceptors while under varying intensities of light shined on the sixth ganglion. Spike trains were characterized according to the mean discharge rate (MDR) and the power spectrum from which the signal-to-noise ratio (SNR) was calculated. 3. Illumination of the CPR enhances the efficiency of transmitting mechanosensory signals. It does so by increasing the SNR of mechanosensory input received from tailfan receptors. A sevenfold, nonlinear increase in the SNRs was observed with increasing light intensity, an effect especially pronounced for weak hydrodynamic stimuli. In comparison with the dark, illumination of the ganglion lowered the hydrodynamic threshold and heightened the response to suprathreshold stimulation. Unlike the SNR, the MDR is little affected by mechanosensory input. 4. These results are compared with simulated electronic activity from an analogue threshold model and are discussed with respect to the mechanism of stochastic resonance.

Animals↗
PubMed1996

A study on detection of serum fasting total bile acid and choloyglycin in neonate for cholestasis.

Enzyme-linked colorimetric analysis and radioimmunoassay were employed to detect serum fasting total bile acids (FBA) and choloyglycin (CG) respectively in cases of 32 neonatal hepatitis, 33 cases of neonatal unconjugated hyperbilirubinemia and 34 cases of breast milk jaundice (BMJ). FBA and CG in acute period of neonatal hepatitis were obviously elevated and decreased gradually in convalescent and recovered period. The difference was significant for each stage as compared with controls. Acute FBA correlated strongly with the course. Both neonatal unconjugated hyperbilirubinemia and BMJ differed significantly from controls in FBA and CG. The results suggested that serum FBA and CG were helpful in judging the course and state of neonatal hepatitis, and cholestasis might existed in neonatal unconjugated hyperbilirubinemia.

Bile Acids and Salts↗
PubMed1995

Comparison of purity and enrichment of CD34+ cells from bone marrow, umbilical cord and peripheral blood (primed for apheresis) using five separation systems.

Interest in the isolation and characterization of primitive hemopoietic cells in both the clinical and research fields has rapidly increased. In parallel, different purification systems have been developed to isolate these cells. We have compared five different methods for separation of CD34+ cells from human umbilical cord blood, normal bone marrow and apheresis harvests and analyzed purity, recovery, yield and enrichment of colony forming cells (CFC) for each individual system. Our results indicate that the most reliable methods of purification for all samples were fluorescence activated cell sorting (FACS) and magnetic activated cell sorting (MACS) which consistently yielded high purities (> 70%) and enrichment of CFC. In this respect the enrichment of CFC from the MACS was superior to all the other systems including FACS. Similar results (> 70%) for purity were obtained using avidin affinity columns and a biotinylated antibody but neither yield nor CFC enrichment approached the values achieved with MACS. On average CFC enrichment using these affinity columns was greater than that observed for FACS while the purity was comparable. Both CELLector flasks and immunomagnetic beads coated with CD34 antibodies were less effective in our hands in separating purified populations of progenitor cells. Both purity and CFC enrichment of CD34+ cells using these methods were at least 50% lower than obtained with either FACS, MACS or affinity columns.

Antigens, CD↗
PubMed1995

Bone marrow purging with dibutyl phthalate--experimental basis and a preliminary clinical application.

It has been found recently that di-n-butyl phthalate (DBP) possesses a new pharmacological activity in the selective elimination of tumor cells from marrow. In combination with long-term liquid culture of marrow cells in vitro, DBP purged autologous bone marrow transplantation has first been applied to a case of acute myeloid leukemia at the first complete remission with successful reconstitution of hematopoiesis.

Adult↗
PubMed1995

[Mesenteric vein thrombosis after devasculation for portal hypertension].

Six patients with mesenteric vein thrombosis (MVT) after devasculation for portal hypertension were treated by intestinal resection. Two patients had recurrence of thrombosis after the initial operations. Among 6 patients 2 survived and 4 (66.7%) died. MVT is an underappreciated, patentially lethal complication after revasculation. Three pathogenic factors after the operation may lead to thrombus formation of the portal vein, portal congestion, hypercoaguble state, and extensive ligation of portal branches. The complication commonly occurs in the recent period after devasculation. It is a characteristic manifestation of MVT that abdominal pain is out of proportion to physical findings. The most effective method is resection of infarcted bowel with sufficient length of normal bowel and its mesentery. In order to avoid a recurrence of thrombosis, postoperative anticoagulation treatment should be given.

Adult↗
PubMed1994

Receptive field analysis and orientation selectivity of postsynaptic potentials of simple cells in cat visual cortex.

Postsynaptic potentials (PSPs) were recorded from cat striate cortical cells by the whole-cell in vivo recording technique using patch-clamp electrodes. EPSPs and IPSPs evoked by flashing bars on the receptive field at different positions and orientations revealed the spatial structure of the excitatory and inhibitory inputs. The elongation of the excitatory input field (length:width ratio) was found to be minimal (mean ratio of 1.7) and much lower than those reported for spike discharges. Two-dimensional receptive field response profiles of early PSPs were recorded by flashing a small spot of light over a square matrix covering the receptive field. These recordings also showed only mild degrees of elongations of the receptive field. Such elongations could be the result of either an excitatory input from the geniculate that is already biased for orientation or an excitatory convergence from a limited number of LGN fields arranged in a row. In most first-order cells, we found that inhibition was contributing significantly to orientation selectivity. Often prominent IPSPs could be evoked by stimuli of nonoptimum orientations. Presence of inhibition could also be inferred by the way that EPSPs were sharply cut off by inhibition. When the amplitude of an EPSP was measured at different latencies after its onset, the EPSP was found to be very broadly tuned to orientation at the beginning, but showing increasing orientation selectivity with time. It is proposed that this progressive development of orientation selectivity is due to (1) inhibitory inputs arriving after the first wave of excitation, (2) intracortical excitatory inputs from other cells tuned to similar orientations, and (3) voltage-sensitive mechanisms such as NMDA channels.

Animals↗
PubMed1994

Development of pattern ERG and pattern VEP spatial resolution in kittens with unilateral esotropia.

PURPOSE: To follow the development of strabismic amblyopia longitudinally by comparing mean amplitudes and the visual spatial resolving ability of retinal and cortical pattern responses at various stages of postnatal development in unilateral iatrogenic convergent strabismic kittens. METHODS: Surgery to produce iatrogenic convergent strabismus was performed on 20 kittens at 3 weeks of age; three kittens were used for controls. The monocular transient pattern electroretinogram (PERG) and pattern visual evoked potential (PVEP) were recorded simultaneously on the 23 kittens throughout development. RESULTS: The PVEPs of the strabismic eyes were very reduced at 4 to 5 postnatal weeks (P < 0.01). The reduction increased at 6 to 16 weeks but was even worse at 17 to 30 weeks. The PERG of the squinting eye showed only a slight reduction in the first 4 to 5 weeks of age (P > 0.05), the decrease of responses was significant (P < 0.01) at 6 to 16 weeks and 17 to 30 weeks. At 4 to 8 weeks of age, the PVEP evoked through the unoperated eye in kittens consisted mainly of two positive components of similar amplitude. During development, the slow component decreased in comparison to the fast one, and its peak shifted forward until it merged into the fast (P100) component. CONCLUSIONS: Esotropic amblyopia did affect the PERG and the PVEP in the amblyopic eye, but the effect on the PERG was less severe, had slower onset, and did not continue as long as for the PVEP.

Amblyopia↗
PubMed1992

Extensive disinhibitory region beyond the classical receptive field of cat retinal ganglion cells.

Forty-three single fibres were recorded from cat optic tract. They were tested with flashing lines of different lengths and/or spots of different dimensions. The area of centre excitation and of surround inhibition were represented in the length (or dimension)-response functions by the steep rising and falling phases, respectively. For most of the cells, a secondary gentle rise was seen when the stimulus extended beyond the inhibitory surround, indicating an extensive disinhibitory region (DIR) outside the classical receptive field (RF). Disinhibition appeared and developed concurrently with surround inhibition at stimulus intensities between 3 and 30 cd/m2, being represented in the phasic or the tonic component of responses depending on the cell type recorded.

Animals↗
PubMed1992

Postsynaptic potentials in cat visual cortex: dependence on polarization.

During the investigation of visually evoked postsynaptic potentials (PSPs) of visual cortical neurons, we recorded cell activity under different levels of membrane potential. In some cases, however, dependence of these PSPs on the level of membrane polarization appears to be inconsistent with the conventional scheme. One disagreement was the reduction, instead of an increase, of excitatory potentials during hyperpolarization of the cell. The other point was that depolarization of the cell often leads to increase of the amplitude of both excitatory and inhibitory postsynaptic potentials. This inconsistency may suggest the involvement of voltage-dependent ion channels in generating PSPs to visual stimuli. A possible way of separating the excitatory and inhibitory components of the response by polarization of the cell in spite of the presence of voltage-dependent channels and possible implications of this mechanism in the visual cortex are discussed.

Animals↗