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Biomedical subjects

Z Cheng

Publications and source records attributed to Z Cheng.

At least 127 records · Page 7Linked to original sources
PubMed1996

Receiver operating characteristic (ROC) analysis of neural code efficacies. I. Graded photoreceptor potentials and data quality.

Nerve cell signals are different in form from the stimuli that evoke them and they exhibit complex spatio-temporal characteristics. This defines a neural coding problem which is addressed by two current theories: Multiple Meaning Theory holds that neural signals contain patterns that make statements about combinations of stimulus properties; the Task Dependence Hypothesis suggests that different features of identical neural signals mediate performance in different behavioral tasks. These coding issues were addressed by investigating the representation of sensory information in the distal nervous system after transduction of visual stimuli into bio-electric signals. The objects of study were light-evoked neural responses which had been intracellularly recorded from single retinula (photoreceptor) cells in Limulus lateral eyes. The efficacies with which sensory information was represented by various candidate neural codes were calculated using receiver operating characteristic (ROC) analyses to provide objective indices. The specific visual problem under investigation was discrimination between light flashes whose intensities differed by a very small amount. A wide range of light adaptation states and relative stimulus intensities were explored. Extremely stringent data quality standards were applied which restricted the investigation to cells whose potentials did not exhibit any statistically significant drift during the hours required for data collection. Seven cellular characterizations were simultaneously monitored to detect drift in a given cell's potentials; these characterizations included the value of the membrane potential and the values of six candidate codes. These codes were: the area under the light-evoked receptor potential (RP), the mean value of the RP, the peak height of the RP, the slope of the onset of the RP, the duration required for the RP to drop from its peak by a given amount, and the duration required for the RP to end. The results were: (1) Light adaptation increases efficacy. (2) Thus, light adaptation trades sensitivity for acuity (as characterized by ROC discriminations). (3) Increasing relative light flash intensity also increases efficacy. (4) The efficacies of the various codes are significantly different and fall in the following order: area > or = peak = mean > or = duration-end = slope = duration-drop. These findings further demonstrate that arbitrary characterizations of stimulus-response relationships are very likely to be incomplete. They particularly indicate that many commonly used and quite conventional neural analysis strategies may substantially under-estimate system performance.

Adaptation, Ocular↗
PubMed1996

Receiver operating characteristic (ROC) analysis of neural code efficacies. II. Optic nerve action potentials and neural transmission.

Action potentials (APs) were intracellularly recorded from eccentric cells (which give rise to optic nerve fibers) in Limulus lateral eyes and their neural coding efficacies were determined over a wide range of light adaptation states and relative stimulus intensities. Extremely stringent data quality procedures were followed to ensure that the results are based on stable preparations. Waveforms which could be compared with those of comparable receptor potentials (RPs) were obtained by constructing plots of the reciprocals of successive interspike intervals, creating instantaneous spike frequency waveforms (ISFWs). Six candidate codes were then measured. They were: the area under the light-evoked ISFW, the mean value of the ISFW, the peak height of the ISFW, the slope of the onset of the ISFW, the duration required for the ISFW to drop from its peak by a given amount, and the duration required for the ISFW to end. Receiver operating characteristic (ROC) analyses were then applied to these coded ISFW values to provide objective indices of AP efficacies in the form of detectability (d') measurements. Several reliable findings were obtained: (1) Both adaptation state and relative intensity affect efficacy. More specifically, the d' values of all codes approach zero, representing chance detectability, when relatively weak flashes are presented in dark-adapted states. (2) Light adaptation produces a sensitivity-acuity tradeoff: as sensitivity decreases in more light-adapted states, detectabilities increase, indicating that ROC-characterized discrimination acuity increases. (3) The AP code efficacy order is similar to but not identical with the efficacy order previously found in photoreceptors: area = peak > or = mean > or = slope = duration-end = duration-drop. The previously measured photoreceptor RP efficacies were quantitatively compared with the present AP data from the optic nerve fiber level, with the following results: (1) All efficacies tend to decline at the more proximal neural level. (2) The decline is code dependent and transmission efficacy falls in this order: peak > area > mean > slope = duration-end = duration-drop. (3) The code which transmits best between photoreceptors and optic nerve fibers (i.e., the peak) differs from the code which has the highest efficacy at the photoreceptor level (i.e., the area); at the more proximal level, these two codes have indistinguishable efficacies. These findings support two conclusions: (1) They further demonstrate that arbitrary characterizations of stimulus-response relationships are very likely to be incomplete. This would be particularly important when, as is often the case in brain research, the mean code alone (i.e., the average firing rate) is used to characterize spike potentials. The present data show that the use of that code would have substantially underestimated detectability had it been used alone. (2) The fact that the code which most completely transmits information between cells is not the code which most completely represents information within a cell leads directly to a possible physiological basis for the existence of multiple neural codes. It particularly leads to the following extension of the Task Dependence Hypothesis of neural coding: Different codes may mediate performance in different behavioral tasks because different codes best serve different neural functions.

Action Potentials↗
PubMed1996

Comparative pharmacokinetics of paracetamol (acetaminophen) and its sulphate and glucuronide metabolites in desert camels and goats.

Paracetamol was administered at dosages of 5 mg/kg to camels and 10 mg/kg to goats by the intravenous and intramuscular routes. Parent paracetamol had a significantly slower clearance (21.9 +/- 1.4 mL/min.kg. vs. 52.8 +/- 7.3 mL/min.kg) (P < 0.01) in camels than in goats. In camels the predominant metabolite in plasma was the sulphate, although the ratios of glucuronide:paracetamol and sulphate:paracetamol were similar (5.20 +/- 0.50 vs. 6.59 +/- 0.51) following intravenous administration. In goats the glucuronide metabolite was the predominant moiety in plasma, and the area under the curve (AUC) of the sulphate was only 3.89% of that of the glucuronide conjugate. The apparent AUC for paracetamol in the camel following intramuscular administration was larger than that following intravenous administration, however, when the bioavailability (F) was determined, with correction for altered half-life, within the animal and between study phases it was 71 +/- 17% in goats and 105 +/- 26% in camels.

Acetaminophen↗
PubMed1996

Dependence of agonist activation on an aromatic moiety in the DPLIY motif of the gonadotropin-releasing hormone receptor.

In the GnRH receptor, the NPX2-3Y motif that is present in the seventh transmembrane helix of most G protein-coupled receptors is unusual in containing Asp instead of Asn but retains the highly conserved Tyr residue. The importance of this aromatic residue in the DPLIY sequence of the GnRH receptor function was analyzed by replacing Tyr322 with Ala or Phe residues. The Y322A mutant receptor expressed in COS-7 cells had high agonist binding affinity, but its ability to interact with G protein(s) and to activate inositol phosphate production in response to GnRH was abolished. Although functionally inactive, the Y322A mutant receptor was internalized at about 50% of the rate of the wild type receptor in agonist-treated cells. When Tyr322 was replaced with Phe to preserve its aromatic nature, the Y322F mutant receptor displayed normal G protein activation and inositol phosphate responses to GnRH and was internalized in the same manner as the wild type receptor. These findings demonstrate that the aromatic moiety of the Tyr322 component of the DPLIY motif in the GnRH receptor is a critical determinant of agonist-induced receptor activation and signal transduction.

Amino Acid Sequence↗
PubMed1996

[Observation of inner ear injury after landing impact in sitting position in Rhesus monkeys].

Tolerance limits of different tissues to landing impact were studied by doing experiment in Rhesus monkeys. 10 Rhesus monkeys were divided into three groups, each suffered a different landing load. The monkeys were killed lh after the experiment, and heart, liver, spleen, lung, and temporal bone were fixed, sliced, and then observed under microscope. Injuries of inner-ear were also observed. The results showed that when acceleration measured at the impact platform was less than 25 G, only slight injuries were found in the various organs and no injury was found in the inner ear; when platform acceleration was 25-35 G intermediate injuries were found in the various internal organs, and slight injury was found in the inner ear, such as detachment of otolith from macula of saccule and separation of epithelium in the ampulla.

Acceleration↗
PubMed1996

[Study on history of cosmopolitan medicine in China].

Roughly, three stages may be differentiated in the studies on the history of cosmopolitan medicine in China. The first stage (1907-1949) is mainly focussed on the translation of articles on medical history from abroad, mostly for popularization of the knowledge on medical history. The second stage (1950-1979), like the first stage, is a stage of translation of papers on medical history from foreign countries, mainly the USSR and Eastern European countries. The third stage (1980-1995) deals with, in addition to translation, studies on special topics with increasing coverage for investigation.

China↗