Search PubMed⌕ Search

Biomedical subjects

J G Collins

Publications and source records attributed to J G Collins.

At least 109 records · Page 6Linked to original sources
PubMed1988

Rapid methods for the high yield synthesis of carbon-13 enriched intermediates of the pentose-phosphate pathway.

Methods for the synthesis of carbon-13 enriched substrates, intermediates and products of the pentose-phosphate pathway, viz. ribose, arabinose, xylulose and ribulose 5-phosphates, sedoheptulose mono- and bisphosphates, octulose (both the ido- and altro-epimers) mono- and bisphosphates, are described. The procedure of the classical Kiliani synthesis was adopted for the preparation of the two starting compounds, [1-13C]ribose and [1-13C]arabinose 5-phosphates. Using these initial reactants and enzymic methods involving the group-transferring enzymes, transketolase, aldolase and transaldolase, a variety of specifically 13C-labelled five-, six-, seven- and eight-carbon sugar phosphates were synthesized in high yield and purity. The isolation and authenticity of each of the 13C-labelled sugars were established by column, paper and thin layer chromatographic methods and specific enzymic assays. The purity and positional isotopic analysis of these sugar-P's were confirmed by 13C-NMR spectroscopy. These specifically 13C-enriched compounds are required for enzymatic, mechanistic and quantitative investigations of pentose-pathway reactions in animal, plant and tumour tissues in vitro and in vivo.

Carbon Isotopes↗
PubMed1988

Assignment of the non-exchangeable proton resonances and solution conformation of the dodecanucleotide-d(CAATCCGGATTG).

The non-exchangeable base and sugar protons of the dodecanucleotide d(CAATCCGGATTG) have been assigned by the combined use of one and two-dimensional NMR spectroscopy. The sequential assignments of the base and sugar protons have been obtained using two dimensional nuclear Overhauser effect and homonuclear shift correlated spectra. By analysis of the nuclear Overhauser effect data it was determined that the dodecanucleotide assumes a right handed B-type helix in the aqueous medium used in this study.

Base Sequence↗
PubMed1987

A descriptive study of spinal dorsal horn neurons in the physiologically intact, awake, drug-free cat.

The extracellular recording of single neuron activity from the spinal dorsal horn of physiologically intact, awake, drug-free cats (n = 14) revealed two potentially important differences between the intact preparation and data obtained from acute preparations. The first of the differences, as previously reported in intact rat and monkey, is that low-threshold (LT) neurons had very low rates of spontaneous activity. Of 127 LT neurons that were studied in the intact animal, 82% had spontaneous rates less than 1 impulse/s (IPS). The second difference was the low number (n = 13) of wide dynamic range (WDR, multireceptive, convergent) neurons that were encountered in the intact animal. Three chronic intact animals were also recorded from during light barbiturate anesthesia. The presence of barbiturate anesthesia significantly increased both the number of LT neurons with spontaneous rates greater than 1 IPS and the likelihood of encountering dorsal horn neurons with WDR response profiles. In spite of these two differences, many similarities between the chronic preparations and previous acute studies were observed. For example, receptive field size and response properties to natural stimulation for LT, WDR, and proprioceptive neurons were found to be similar to those reported in acute preparations. The results of this study suggest that, although there are many similarities in dorsal horn neurophysiology in acute and chronic cats, important differences that may be attributed to the preparation itself may also exist.

Action Potentials↗
PubMed1987

Inhibition of spontaneous activity of spinal dorsal horn neurons in the intact cat is naloxone-insensitive.

Low-threshold neurons in the dorsal horn of the spinal cord of physiologically intact, awake, drug-free cats demonstrate minimal rates of spontaneous activity. Studies in acute animals suggest that the lack of spontaneous activity is due to descending inhibitory control mechanisms. The present study suggests that the inhibition of spontaneous activity is naloxone-insensitive. Intravenously administered naloxone in doses of up to 0.4 mg/kg failed to have any effect on the spontaneous activity of the 34 low-threshold neurons recorded from the dorsal horn of the spinal cord of physiologically intact, awake animals. Stimulus-evoked activity was also not significantly influenced by the doses of naloxone used in this study. These results confirm data previously obtained by others using acute preparations. This confirmation is important in that it demonstrates that, for this system, differences between acute and chronic preparations do not appear to alter neuronal sensitivity to specific drug manipulations. They also verify that, for this system, acute experiments accurately reflect conditions that exist in the intact animal.

Animals↗
PubMed1987

Lack of spontaneous activity of cutaneous spinal dorsal horn neurons in awake, drug-free, spinally transected cats.

Extracellular single-unit activity was recorded from neurons with cutaneous input in the dorsal horn of the spinal cord (L4-L6) of awake, drug-free cats before (for several weeks) and after (day 1 through day 7) cord transection (T12). The spontaneous activity of the neurons was minimal or nonexistent in both recording conditions. The lack of spontaneous activity following spinal cord transection contrasts sharply with activity recorded in acute spinal-cord transected preparations in which high rates of spontaneous activity have been reported. This discrepancy may reflect an important difference between the chronic, awake, drug-free and acute preparations.

Action Potentials↗
PubMed1987

WDR response profiles of spinal dorsal horn neurons may be unmasked by barbiturate anesthesia.

The number of WDR (convergent, multireceptive) neurons encountered in the spinal dorsal horn of physiologically intact, awake, drug-free cats has been much smaller than expected (9% in intact, drug-free animals). Control studies in barbiturate-anesthetized or spinal cord transected animals indicate that the dearth of WDR neurons was not just an artifact of the chronic recording technique. In those preparations WDR neurons represented 34% and 61% of the sample, respectively. Initial studies in which the effects of light barbiturate anesthesia on spinal dorsal horn neurons (n = 12) have been examined revealed that a 20 mg/kg dose of pentobarbital can, in some neurons (n = 4), unmask thermally evoked activity that was not present in the intact, drug-free animal. Responses to noxious mechanical stimuli were also enhanced following barbiturate administration. These changes resulted in a reclassification of neural type from low threshold in the intact, awake, drug-free animal to WDR in the anesthetized animal.

Anesthetics↗
PubMed1987

Effects of halothane on medullary inspiratory neurons of the cat.

The effect of halothane on the electrical activity of inspiratory neurons of the nucleus tractus solitarius (NTS) was studied in decerebrate, paralyzed, mechanically ventilated cats. Simultaneous recording of the activity of the neurons of the NTS and the phrenic nerve was done to identify the inspiratory neurons. Cells whose firing activity was synchronous with that of the phrenic nerve were considered inspiratory neurons. Administration of 1% and 1.5% halothane in oxygen induced a dose-dependent depression of the cell activity (spikes/s) with the cervical vagi intact or severed. Five and ten minutes after inhalation of 1% halothane, the cell activity (mean +/- SE) expressed as per cent of the control was 55.3 +/- 9 and 27 +/- 7, respectively (P less than 0.001), before bilateral cervical vagotomy. The corresponding values for 1.5% halothane were 25 +/- 10.1 and 5.6 +/- 3, respectively. Upon termination of halothane administration, the cell activity gradually returned toward the control level. The cell response to halothane was not affected by bilateral cervical vagotomy. Hypercapnia produced by inhalation of 5% CO2 increased the cell activity, but halothane caused profound depression of the cells even in the presence of hypercapnia. Based on these results, it may be concluded that: halothane has inhibitory effects on the activity of the inspiratory neurons of the NTS; and halothane-induced respiratory depression has a central component and that the NTS may serve as a site of action of halothane for its respiratory depressant effect.

Animals↗
PubMed1986

Lack of opiate effects on cat C polymodal nociceptive fibers.

The direct application of preservative-free morphine sulfate (1.5%, 1 ml, 19.8 mumol) or fentanyl (0.06%, 1 ml, 1.07 mumol) on the superficial radial or saphenous nerve of cats did not alter the response of single C polymodal nociceptive fibers (PMNs) to noxious radiant heat stimulation of their peripheral receptive fields. Intravenous administration of fentanyl (100 or 200 micrograms/kg, 0.179 or 0.358 mumol/kg) also showed a similar lack of effect on the radiant heat evoked responses of single PMNs. Slight changes in the mean latencies following drug administration were recognized, which were not statistically significant. The use of morphine (1.5%, 1 ml, 19.8 mumol) with preservatives (chlorbutanol 0.5% and sodium bisulfite less than 0.1%) caused conduction block of PMNs within 6-15 min. Subsequent washout of the drug resulted in the return of the unitary discharges within 8 min. Lidocaine (0.25 and 0.5%, 10.7 mumol and 21.4 mumol) caused conduction block within 5-18 min. These data support the classically held concept that opiates, in clinically useful concentrations, do not alter peripheral nerve function.

Action Potentials↗
PubMed1986

Spinal sufentanil effects on spinal pain-transmission neurons in cats.

The ability of sufentanil to suppress noxiously evoked activity of wide dynamic range (WDR) neurons was studied in decerebrate, spinal-cord-transected cats. Sufentanil, 2.5 micrograms (n = 7) or 5.0 micrograms (n = 7), when administered spinally, produced a significant, dose-dependent suppression of noxiously evoked (51 degrees C radiant heat stimulus) activity of WDR neurons in the dorsal horn of the spinal cord. Spontaneous recovery from sufentanil suppression was not seen for up to 2 h. Reversal following intravenous naloxone, 0.12 mg, although present, was not as complete as that seen following other spinal opiates. Intravenous sufentanil, 5.0 micrograms/kg (n = 4), produced significant but short-lasting depression of noxiously evoked WDR neuron activity. A comparison of the results of this study with data from a previous fentanyl study suggests that sufentanil may be more appropriate than fentanyl for spinal or epidural administration because of a possible longer duration of action. However, the lesser degree of naloxone reversal seen in this study may suggest that, clinically, reversal of sufentanil effects may be more difficult.

Animals↗
PubMed1986

A comparison of the effects of alfentanil applied to the spinal cord and intravenous alfentanil on noxiously evoked activity of dorsal horn neurons in the cat spinal cord.

The purpose of this study was to examine the effects of alfentanil applied to the surface of the spinal cord and the effects of intravenously administered alfentanil on noxiously evoked activity of dorsal horn neurons. Extracellular single neuron recordings were obtained from wide dynamic range neurons in 26 decerebrate cats with transected spinal cords. Spinally administered alfentanil, 25 micrograms or 50 micrograms, caused 36 and 86% suppression of noxiously evoked activity, respectively. Maximum mean suppression was achieved at 24 and 21 min after 25 micrograms, and 50 micrograms, respectively. Intravenous naloxone, 0.1 mg, when tested, completely reversed the suppression. Spontaneous recovery to control values occurred within 2 hr. Intravenously administered alfentanil, 12.5 micrograms/kg or 25 micrograms/kg, produced suppression of 43 and 89%, respectively, with maximum mean suppression observed at the 6- and 3-min time points, respectively. Complete recovery after intravenous administration was seen within 30 min. This study, using a sensitive neurophysiologic assay, demonstrates the important differences in onset and duration of drug effects that must be considered when comparing the responses of spinal cord neurons to intravenously administered narcotics and narcotics applied directly to the surface of the spinal cord.

Alfentanil↗
PubMed1986

Effects of ketamine on low intensity tactile sensory input are not dependent upon a spinal site of action.

The development of a technique for studying spinal dorsal horn electrophysiology in intact, awake, drug-free cats enables the study of spinal sites and mechanisms of action of anesthetic and analgesic agents in a system that more closely reflects normal physiology. Using this technique, we reevaluated the effect of ketamine on spinal dorsal horn sensory transmission. The results of our study confirm previous work done in acute preparations. Ketamine (maximum dose 20 mg/kg) did not significantly reduce the response of low threshold (n = 11) dorsal horn neurons to low intensity sensory stimulation. However, that same dose of ketamine did suppress noxiously evoked activity of the two wide dynamic range neurons encountered in the study, while having a varied effect on neurons responsive to proprioceptive input (n = 7). These findings confirm that, in the intact animal with all modulatory systems intact, ketamine "dissociation" of low intensity tactile stimuli does not appear to involve a spinal mechanism of action. The results also support the importance of spinal sites of action for the analgesia produced by ketamine, as well as the importance of distinguishing between the anesthetic and analgesic effects of that drug.

Analgesia↗
PubMed1985

A technique for chronic extracellular recording of neuronal activity in the dorsal horn of the lumbar spinal cord in drug-free, physiologically intact, cats.

A technique has been developed which allows extracellular recording from single neurons in the spinal cord of physiologically intact, awake, drug-free, restrained cats. The technique involves the surgical placement, under general anesthesia, of a stainless steel recording chamber which has a rectangular opening in its center that is 6 mm wide by 12 mm long. The recording chamber is attached to the vertebral column so that the opening is positioned over a similar opening that has been made in the bone of the vertebral column overlying the lumbar enlargement. Following a two week recovery period, the cats, which have been trained to accept restraint, are placed in a plexiglass restraining box, and a microdrive assembly is attached to the recording chamber. Tungsten microelectrodes (Frederick Haer & Co.) are then advanced through the dura into the dorsal horn of the spinal cord while receptive fields are stimulated. The chamber, when properly positioned, provides access to neurons with receptive fields on both hindlimbs. The stability of the system makes it possible to maintain single cell recordings from neurons in the dorsal horn of the spinal cord in the presence of either experimenter-induced or spontaneous movement of hindlimbs, tail or back musculature or during and after intramuscular, intravenous, spinal and epidural drug injections. Of greatest importance is the fact that the animals remain healthy and normal throughout the period of neuronal recordings.

Action Potentials↗
PubMed1985

Fentanyl and alfentanil suppress brainstem pain transmission.

The effects of intravenously administered fentanyl (25 micrograms/kg, n = 9; 50 micrograms/kg, n = 5) and alfentanil (12.5 micrograms/kg, n = 5; 25 micrograms/kg, n = 7) on the noxiously evoked, single-unit activity of cells in the nucleus reticularis gigantocellularis (NRGC) were studied in decerebrate cats. Only cells of the NRGC excited exclusively by supramaximal electrical stimulation of A delta fibers (noxious stimulation) of the superficial radial nerve were studied. The noxiously evoked activity of all cells in the NRGC was suppressed by the administration of opioids (by 58 and 88% for fentanyl, 25 micrograms/kg and 50 micrograms/kg, respectively; by 35 and 78% for alfentanil 12.5 micrograms/kg and 25 micrograms/kg, respectively). Fentanyl and alfentanil effects were antagonized by the intravenous administration of naloxone. These results indicate that opioid suppression of noxiously evoked activity is seen in neurons located in the brainstem, and thus suppression of brainstem neurons may be important in the production of fentanyl and alfentanil analgesia.

Alfentanil↗
PubMed1985

Direct opioid application to peripheral nerves does not alter compound action potentials.

The identification of opiate receptors on primary afferent fibers near the dorsal root ganglia suggests that opiates may be able to affect conduction in primary afferent nerve fibers. We examined the effect of directly applied, preservative-free morphine sulfate (0.1 mg/kg) and fentanyl citrate (25 micrograms/kg) on the A beta, A delta, and C components of the compound action potential of the superficial radial nerve in decerebrate cats (n = 18). Neither drug caused any significant change in the area under the curve of any of the compound action potentials studied. These data indicate that systemically administered opiates are unlikely to cause changes in primary afferent nerve conduction.

Action Potentials↗
PubMed1984

Neuronal activity recorded from the spinal dorsal horn of physiologically intact, awake, drug-free, restrained cats: a preliminary report.

A newly developed technique was used to record extracellular single unit activity in the dorsal horn of the spinal cord of physiologically intact, awake, drug-free, restrained cats. Activity of low threshold neurons in the intact animal differs from activity in spinal cord-transected animals in that there is little or no spontaneous activity present in the intact preparation. These data suggest important differences between the intact and spinal cord-transected preparations.

Animals↗
PubMed1984

The structure of a novel polysaccharide isolated from Zymomonas mobilis determined by nuclear magnetic resonance spectroscopy.

A novel polysaccharide has been observed in vivo by 13C nuclear magnetic resonance (NMR) spectroscopy of the gram-negative bacterium, Zymomonas mobilis. The polysaccharide, which was not removed from the Z. mobilis cell by washing with 0.86% saline, was extracted by mild acid treatment. The structure was elucidated by a combination of NMR techniques, including proton and proton-carbon two-dimensional methods. The structure was determined to be -alpha-fructofuranosyl-(2-1)-beta-fructofuranosyl-(2-6)-. The polysaccharide is unlike levan, a beta-(2-6)-fructose polymer which is produced by many bacteria, including Z.mobilis, when grown on sucrose. The polysaccharide isolated here is produced by cells cultured on glucose, fructose or sucrose.

Cell Fractionation↗
PubMed1984

31P nuclear magnetic resonance studies of the fermentation of glucose to ethanol by Zymomonas mobilis.

High resolution 31P nuclear magnetic resonance spectroscopy has been employed to study the fermentation of glucose to ethanol by Zymomonas mobilis, strain ZM4, a bacterium which uses the Entner-Doudoroff pathway. The levels of nucleoside triphosphates, sugar phosphates, UDP-sugars and Pi in intact fermenting cells have been studied with a time resolution of 1 min. It is suggested that a pH gradient is established across the cell membrane during fermentation and that the intracellular pH does not rise above approximately 6.4. 31P resonances from most phosphorus-containing intermediates in the Entner-Doudoroff pathway, as well as adenosine and uridine nucleotides and a number of other intracellular metabolites, have been assigned in perchloric extracts of fermenting cells by means of a number of techniques, including two-dimensional homonuclear J-resolved and two-dimensional homonuclear shift-correlated spectroscopy. Quantification of these metabolites in spectra of extracts of fermenting cells indicates that the rate-limiting steps in the Entner-Doudoroff pathway in Z. mobilis are the conversions of glucose 6-phosphate to 6-phosphogluconate and of 3-phosphoglycerate to 2-phosphoglycerate.

Ethanol↗