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Biomedical subjects

Z F Cheng

Publications and source records attributed to Z F Cheng.

18 recordsLinked to original sources
PubMed1998

The vacB gene required for virulence in Shigella flexneri and Escherichia coli encodes the exoribonuclease RNase R.

vacB, a gene previously shown to be required for expression of virulence in Shigella and enteroinvasive Escherichia coli, has been found to encode the 3'-5' exoribonuclease, RNase R. Thus, cloning of E. coli vacB led to overexpression of RNase R activity, and partial deletion or interruption of the cloned gene abolished this overexpression. Interruption of the chromosomal copy of vacB eliminated endogenous RNase R activity; however, the absence of RNase R by itself had no effect on cell growth. In contrast, cells lacking both RNase R and polynucleotide phosphorylase were found to be inviable. These data indicate that RNase R participates in an essential cell function in addition to its role in virulence. The identification of the vacB gene product as RNase R should aid in understanding how the virulence phenotype in enterobacteria is expressed and regulated. On the basis of this information we propose that vacB be renamed rnr.

Bacterial Proteins↗
PubMed1998

Involvement of medullary tail-flick related neurons in descending facilitation evoked by chemical stimulation of rat lateral habenular nucleus.

AIM: To study effects of sodium L-glutamate microinjection into lateral habenular nucleus (LHN) of rats on the firing of medullary tail-flick related neurons and tail-flick reflex (TF). METHODS: Using synchronous recording of unitary neuronal discharges and TF induced by noxious heat. RESULTS: Chemical stimulation of LHN induced an excitement of the on-cell spontaneous activity, an inhibition of the off-cell spontaneous activity with an enhancement of their TF related responses. The spontaneous firing rate of on-cells increased from 5.8 +/- 2.2 Hz to 10.9 +/- 3.4 Hz while the spontaneous firing rate of off-cells decreased from 11.8 +/- 2.2 Hz to 6.1 +/- 2.2 Hz. Meanwhile the TFL was shortened from 4.04 +/- 0.17 s to 2.97 +/- 0.13 s. CONCLUSION: The chemical stimulation of LHN produced a facilitating action on nociceptive spinal defensive reflex. This effect is brought out by the cooperation of on- and off-cells.

Animals↗
PubMed1996

[Involvement of medullary tail-flick related neurons in the descending facilitating effects evoked by stimulation of lateral habenular nucleus].

In lightly anesthetized rats 3 classes of neurons in the rostral ventromedial medulla (RVM) were in relation to tail-flick reflex (TF) recorded, i. e. the TF triggired on-cells, the TF triggered off-cells and the non-responsive or neutral cells. When lateral habenular nucleus (LHb) was stimulated the on-cells were excited, the off-cells inhibited while the neutral cells unaffected. The fact that stimulation of LHb facilitated tail-flick reflex appears to be quite well explained by its enhancement effect on the tail-flick related response of both the on- and the off-cells. These results indicate that the facilitating action of LHb on spinal defensive reflex is probably brought out by participation of the medullary tail-flick related cell activity.

Animals↗
PubMed1994

[Effects of lateral habenular stimulation on nociceptive response of neurons in rat spinal dorsal horn].

Ipsilateral stimulation of the LHb produced a significant attenuation of nociceptive response of wide dynamic range (WDR) neurons in the rat spinal dorsal horn. The inhibitory effect produced by LHb stimulation was partially blocked by systemic cyproheptadine and phentolamine but not naloxone. No significant change was observed in the activity of WDR neurons after ipsilateral electrolytical lesions of the LHb. These results suggest that the LHb participates in the supraspinal descending control on nociceptive response of WDR neurons in the spinal dorsal horn. However, tonic inhibitory mechanism seems not to be involved.

Animals↗
PubMed1993

[The action of medullary tail-flick related neurons in electroacupuncture analgesia].

Three types of cells, i.e., off-neurons, on-neurons and neutral neurons, could be recorded in the rostral ventromedial medulla (RVM) in light anesthetized rats. Just prior to the occurrence of tail flick elicited by noxious heat, the on-cells showed a burst of activity while the off-cells exhibited a cessation of discharge. No change of neutral cell activity related to tail flick was observed. Electroacupuncture at two "Ci Liao" points which resulted in inhibition of tail-flick reflex affected the spontaneous activity of off- and on-cells in a different way, i.e, the discharge of most off-cells was significantly increased (P < 0.001), while that of on-cells showed no obvious change (P > 0.05). Tail-flick related responses of the both cells were inhibited. These results provide the evidence that the off-cells may be the main efferent neurons in RVM involving in electroacupuncture analgesia.

Acupuncture Analgesia↗
PubMed1993

[Descending cord dorsum potentials evoked by stimulation at "Yong Quan" acupoint].

Segmental spinal cord potential (Y-sCDP) evoked by stimulation at "Yong Quan" acupoint of Sprague-Dawley rat vanished gradually when the recording electrode was moved rostrally along the dorsal surface of the spinal cord. When the recording electrode was placed more rostrally, for example at C6, another positive slow potential, Y-dCDP, could be recorded. Y-dCDP disappeared completely when the spinal cord had been sectioned at a higher cervical level. Electrolytic lesions of ventral periaqueductal gray (PAG) could also decrease remarkably the amplitude of Y-dCDP. This facet suggests that the PAG, an analgesia related nucleus, is involved in the generation of Y-dCDP induced by stimulation at "Yong Quan" acupoint.

Acupuncture Points↗
PubMed1990

[Dorsal root potential evoked by stimulation of periaqueductal gray and its efferent pathway analysis in rats].

When periaqueductal gray (PAG) was stimulated with concentric electrodes, a steady negative potential called PAG-DRP was recorded from L5 dorsal root. PAG-DRP with properties of spatial and temporal summation propagates decrementally along the dorsal root and is inhibited by picrotoxin. Lesions of NRM had no effect on the PAG-DRP evoked by stimulation of dorsal PAG, but showed obvious reduction up to about 40% on the PAG-DRP evoked by stimulation of ventral PAG. It is suggested that the descending inhibition of PAG includes some presynaptic inhibition and that the ventral PAG-DRP is relayed partly via NRM while the dorsal PAG-DRP is not associated with NRM.

Animals↗
PubMed1990

[Field potentials evoked by stimulation of DLF in the rat spinal cord].

When stimulation of DLF at cervical cord, a train of evoked potentials are recorded with a microelectrode at lumber level in rat. The longer slow positive potential wave, latency 7.22 +/- 1.41 ms, peak time 15 +/ 12 +/- 5.58 ms, duration 93 +/ 92 +/- 9.06 ms, is called DLF-FP. The negative center of the isopotential map of DLF-FP is located at 1.0-1.3 mm below the dorsal surface nearly in coincidence with that of the P1-FP evoked by the sural nerve stimulation. The amplitude of DLF-FP was decreased by picrotoxin and increased by strychnine. Both summation and inhibition can be observed between the potentials evoked by stimulation of the sural nerve and DLF. The results mentioned above show that DLF-FP is the reflection of primary afferent depolarization probably by the same spinal circuit underlying P1-FP.

Animals↗
PubMed1987

Evidence for two classes of nociceptive modulating neurons in the periaqueductal gray.

The midbrain periaqueductal gray (PAG) and the rostral ventromedial medulla (RVM) are important links in a neuronal network that modulates nociceptive transmission. In the RVM, 2 classes of cells have been identified that show changes in activity at the time of the tail-flick response (TF) elicited by noxious heat (Fields et al., 1983a). We now report that neurons in the PAG region also show changes in activity related to TF. Extracellular recordings were made from the PAG and the ventrally adjacent tegmentum at sites from which it was possible to inhibit TF using stimulating currents of 10 microA or less. Cell activity, time of TF occurrence, and tail temperature were recorded during 5 repetitions of the heat stimulus. Periresponse and peristimulus histograms were plotted with reference to the TF and tail temperature, respectively. A significant number of neurons in the PAG region showed changes in activity that preceded the TF. "Midbrain On-cells" (13.6% of the sample) displayed an abrupt increase in firing just prior to the TF. "Midbrain Off-cells" (4.4%) paused just prior to the TF. The remaining neurons (241 of 294, or 82%) did not exhibit changes in firing prior to the TF. Thus, cells with changes in activity related to the TF are present in the PAG region as well as in the RVM. The PAG has a large projection to the RVM, and microinjection of morphine in the PAG increases activity of RVM Off-cells and decreases that of RVM On-cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1986

Morphine microinjected into the periaqueductal gray has differential effects on 3 classes of medullary neurons.

The effects of microinjection of 5-10 micrograms of morphine into the midbrain periaqueductal gray (PAG) on the activity of neurons in the rostral ventral medulla (RVM) were studied in lightly anesthetized rats. Based on the relationship between changes in neuronal activity and the occurrence of the tail-flick reflex (TF), RVM neurons were divided into 3 groups: off-cells, on-cells and neutral cells. The off-cells exhibited an abrupt pause and the on-cells an acceleration beginning just prior to the occurrence of the TF. Neutral cell firing did not change at the time of the TF. Microinjections of morphine into the PAG which inhibited the TF had differential effects on the spontaneous activity of the 3 groups of neurons in RVM. Off-cells showed an increase and on-cells a decrease in spontaneous activity which preceded the inhibition of the TF. These microinjections also reduced the TF-related responses of off- and on-cells. The effects on cell activity were reversed by systemically administered naloxone and were not seen following microinjections which failed to block the TF. Neutral cell activity was unchanged following microinjection of morphine into the PAG. These results support the hypothesis that off- and on-cells in the RVM mediate the effects of microinjection of morphine into the PAG on spinal nociceptive reflexes.

Action Potentials↗