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P D Morrison

Publications and source records attributed to P D Morrison.

9 recordsLinked to original sources
PubMed2000

Time-resolved cryogenic modulation for targeted multidimensional capillary gas chromatography analysis.

Multidimensional gas chromatography (MDGC) is performed in a new manner, described in this paper. The method incorporates two directly coupled columns and employs a longitudinally modulated cryogenic trap located between the columns. No heartcutting process is used, but rather a method better termed selected zone compression pulsing is used. Compared with normal MDGC, where primary column effluent has to be temporarily diverted either to a monitor detector or to the second dimension column, the new procedure in its simplest mode passes all of the first column effluent to the second column. It is simply the times at which the modulation of the trap is performed that determines which target solutes will be selected for enhanced separation. This approach allows almost instantaneous separation of selected zones on the second column, and has the potential to significantly simplify the MDGC method. Since data are presented in a time-response format, and do not require transformation as previously described for comprehensive GC when using the longitudinal modulator, quantitation and report generation are essentially the same as in any GC method and data system. Advantages also include significant sensitivity improvement. By using cryofocussing, and benefiting from the zone compression effects along with fast GC conditions on the second dimension, new possibilities for MDGC can be realised. The method is demonstrated by using a mixture of semi-volatile aromatic hydrocarbons.

Chromatography, Gas↗
PubMed1995

Frequency dependent activation of a slow N-methyl-D-aspartate-dependent excitatory postsynaptic potential in turtle cerebellum by mossy fibre afferents.

The synaptic responses of turtle cerebellar Purkinje cells to stimulation of localized mossy fibre systems have been studied by use of intrasomatic and intradendritic recordings in a brainstem-cerebellum preparation in vitro. Activation of mossy fibre inputs from the spinocerebellar pathway evoked fast, disynaptic postsynaptic potentials which were graded in amplitude with stimulus intensity and elicited at latencies consistent with those reported for peripheral nerve stimulation. Repetitive activation (50-100 Hz, 2-10 stimuli) of both spinocerebellar and trigeminocerebellar pathways evoked a slow, long-lasting excitatory postsynaptic potential regardless of whether single stimuli resulted in excitatory, inhibitory, or no postsynaptic responses. This slow potential was capable of triggering dendritic pacemaker discharges in recorded Purkinje cells in addition to volleys of simple spikes when activated at or near resting membrane potential. The fast excitatory synaptic potentials evoked by spinocerebellar stimulation were blocked by the glutamate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione, consistent with the hypothesis that they are mediated by activation of ionotropic glutamate receptors of the alpha-amino-3-hydroxy-5-methylisox-azole-4-proprionic acid subtype at the mossy fibre-granule cell synapse and the subsequent parallel fibre-Purkinje cell synapse. The slow excitatory synaptic potential evoked by repetitive stimulation of either the spinocerebellar tract or trigeminal nerve was blocked by DL-2-amino-5-phosphonvalerate, indicating that this potential is primarily dependent upon N-methyl-D-aspartate receptors at the mossy fibre-granule cell synapse for its expression. This slow potential was reversibly potentiated by L-2-amino-4-phosphonobutyrate and bicuculline; the metabotropic glutamate antagonist (+)-alpha-methyl-4-carboxyphenylglycine did not block this potentiation. The ability of mossy fibre inputs to drive long, slow excitatory events in Purkinje cells adds another dimension to the mechanisms by which various sensory modalities can be processed interactively in the cerebellar cortex. The ability of incoming systems to access a second, longer duration response of the cerebellar output neuron may be of significant consequence to our understanding of the manner in which this neural centre integrates sensory information from multiple sources.

2-Amino-5-phosphonovalerate↗
PubMed1992

Changes in adenosine sensitivity in the hippocampus of rats with streptozotocin-induced diabetes.

1. Hippocampal slices have been used to assess the sensitivity of the CNS to adenosine and gamma-aminobutyric acid (GABA) in diabetes. The effects of adenosine, 2-chloroadenosine, GABA, muscimol and baclofen were studied on orthodromic synaptic potentials recorded in the CA1 region of slices taken from normal rats or animals made diabetic by the injection of streptozotocin. 2. In diabetic animals the sensitivity to adenosine was increased 4 fold compared with normal rats. The potency of 2-chloroadenosine was unchanged. 3. The nucleoside transport inhibitor, hydroxynitrobenzylthioinosine (HNBTI), increased the potency of adenosine in slices from normal rats but not in slices from diabetic rats. 4. No change was observed in the potency of GABA or muscimol, although a small but significant decrease was detected in the EC50 value for baclofen. 5. Treatment of diabetic animals with insulin restored the potency of adenosine to control levels. 6. It is concluded that the diabetic state is accompanied by substantial changes of adenosine sensitivity due to the loss of nucleoside uptake processes. Secondary neurochemical changes following from this in human diabetic patients may contribute to the reported behavioural changes.

2-Chloroadenosine↗
PubMed1987

Influence of a jejunal fistula on gastric emptying.

The aim was to determine whether a proximal jejunal fistula would speed gastric emptying after truncal vagotomy and Roux distal gastrectomy. Eight vagotomy-gastrectomy dogs were studied; 4 had a jejunal fistula, and 4 other dogs without a fistula served as controls. The rate of gastric emptying of 100 ml 25% dextrose in the fistula dogs with the fistula open (95 +/- 3 ml/20 min) was faster than in the same dogs with the fistula closed (62 +/- 10 ml/20 min; p less than 0.05) and faster than in dogs without a fistula (77 +/- 5 ml/20 min; p less than 0.05). The rate of emptying in dogs with the fistula closed, however, was similar to the rate in dogs without a fistula (p greater than 0.05). We concluded that diversion of the enteric content to the exterior through a proximal jejunal fistula increases the rate of gastric emptying of 25% dextrose solutions in dogs with truncal vagotomy and Roux gastrectomy.

Animals↗
PubMed1986

Increasing antidumping effect of intestinal pacing with motor-active agents.

The aim was to determine whether cholecystokinin-octapeptide (CCK-OP), bethanechol Cl, or metoclopramide HCl would increase the antidumping effect of intestinal pacing in five dogs with truncal vagotomy and Roux gastrectomy. While recording electrical activity from the conscious animals, the amount of a 100-ml, 25% dextrose gastric instillate emptied in 20 min was determined during control tests, during tests with CCK-OP (500 ng/kg/hr), bethanechol (80 micrograms/kg/hr), or metoclopramide alone (600 micrograms/kg/hr) given intravenously or during tests using combinations of pacing and drugs. In other tests, intraluminal gastrointestinal pressure was measured during control and drug infusions. CCK-OP, which relaxed the proximal stomach, slowed emptying of the dextrose instillates (mean +/- SEM emptied, no pacing, no drug = 74 +/- 5 ml; CCK-OP alone = 34 +/- 5 ml; P less than 0.05). CCK-OP also enhanced the slowing effect produced by pacing (pacing alone = 41 +/- 7 ml; pacing plus CCK-OP = 19 +/- 8 ml; P less than 0.05). In contrast, bethanechol and metoclopramide, which did not alter proximal gastric motility, did not alter emptying or augment or diminish the effect of pacing. The conclusion was that the combination of pacing and CCK-OP slowed gastric emptying of the dextrose more than pacing alone and thus had a greater antidumping effect. In contrast, neither bethanechol nor metoclopramide enhanced the pacing effect.

Action Potentials↗
PubMed1984

A case of metastasizing benign pleomorphic adenoma of the parotid.

A 69-year-old man who had a 50-year history of recurrent benign pleomorphic adenomas of the parotid presented with a further recurrence and a skull nodule. Biopsy of the skull nodule was consistent with a metastasis of a benign pleomorphic adenoma.

Adenoma, Pleomorphic↗
PubMed1983

A study of colovesical fistulae in a district hospital.

A retrospective study of 32 patients with colovesical fistula was carried out. The most frequent presenting symptoms were urinary; an abdominal mass was found in 40% of patients. Urine culture grew bowel organisms in 93% of patients and the diagnosis was most accurately confirmed by barium enema which showed evidence of a fistula in 55% of patients examined. Surgical treatment varied from staged resection to primary resection and anastomosis, disconnection of the fistulous tract or colostomy alone. The results are compared and suggest a higher success rate with a multi-staged procedure. Different methods of diagnosis are discussed as well as possible causes for varying success rates among the surgical procedures.

Adult↗