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Biomedical subjects

G Morris

Publications and source records attributed to G Morris.

121 records · Page 7Linked to original sources
PubMed1968

A comparison of escape and avoidance conditioning in wild and domesticated rats.

In the first of two experiments, three cotton rats (Sigmodon hispidus) and three albino rats were exposed to instrumental escape, unsignaled avoidance, and signaled avoidance, in that order. All subjects learned the escape procedure quickly, with the albino rats having generally shorter latencies, higher response rates, and requiring fewer sessions to reach the criterion. When the avoidance contingency was introduced, the cotton rats continued to respond almost entirely in the presence of the shock, whereas the albino rats responded in its absence, thus displaying effective avoidance behavior. Introduction of a pre-aversive stimulus did not improve the performance of the cotton rats. In the second experiment, five cotton rats and four albino rats were exposed to a free-operant (Sidman) avoidance procedure with a shock-shock interval of 3 sec and a response-shock interval of 20 sec. The cotton rats initiated responding at lower shock intensities than the albino rats, but their asymptotic avoidance responding was far less effective.

Animals↗
PubMedDate not supplied

Hereditary hyperlipidemia in the rabbit due to overproduction of lipoproteins. I. Biochemical studies.

An inherited metabolic disorder in a strain of New Zealand White rabbits, characterized by marked hypercholesterolemia (394 +/- 100 mg/dl), with moderately elevated or normal triglyceride levels is described. Low density lipoprotein (LDL), intermediate density lipoprotein (IDL) and very low density lipoprotein (VLDL) cholesterol levels were increased. VLDL and IDL, and to a lesser extent LDL, had increased free cholesterol and esterified cholesterol content, and triglyceride content was reduced. Kinetic studies with 131I and 125I-labelled rabbit lipoproteins showed a marked increase in production rates of VLDL apo B and LDL apo B. LDL cholesterol levels were directly related to LDL apo B production rate (r = 0.938, p less than 0.001). Both in hypercholesterolemic and normal rabbits injected with labelled VLDL, the specific activity-time curves of VLDL apo B and LDL apo B did not intersect, indicating that LDL apo B was in part derived from sources other than VLDL. No defect was demonstrated in receptor-mediated catabolism of LDL by cultured skin fibroblasts from hyperlipidemic animals. The fractional catabolic rate of LDL apo B was subnormal, but increased when the expanded LDL apo B pool size was reduced by exchange transfusion; the low fractional catabolism may therefore be attributable, at least in part, to saturation of LDL receptors consequent upon the increased pool size of LDL. The hyperlipidemia in this strain of rabbits may be unique in that the underlying mechanism appears to be overproduction of VLDL and LDL.

Animals↗
PubMedDate not supplied

Effects of resistive exercise on skeletal muscle in marrow transplant recipients receiving total parenteral nutrition.

Skeletal muscle protein loss occurs during marrow transplantation despite total parenteral nutrition. To determine if muscle atrophy could be minimized with exercise therapy, 30 patients undergoing marrow transplantation for acute leukemia completed a prospective randomized trial to receive: (1) no therapy (controls), (2) physical therapy thrice weekly (PT3), or (3) physical therapy five times weekly (PT5). Patients were studied through 35 days posttransplant. Muscle protein status and turnover was assessed by weekly nitrogen balance, and creatinine and 3-methylhistidine excretion. Results favored a muscle protein-sparing effect of exercise, as a significant decrease in creatinine excretion in controls only suggested muscle protein loss associated with inactivity. Changes in arm muscle area correlated with energy, but not protein intake. Large individual variation, inadequate nutritional support and differences in admission arm muscle area may have clouded these results.

Acute Disease↗
PubMedDate not supplied

In vivo detection of postictal perturbations of cerebral metabolism by use of proton MR spectroscopy: preliminary results in a canine model of prolonged generalized seizures.

BACKGROUND AND PURPOSE: Biochemical studies of seizures in patients and laboratory animals have monitored postictal perturbations in cerebral metabolism with either invasive techniques or with such noninvasive techniques as nuclear medicine, MR imaging, in vivo phosphorus MR spectroscopy (MRS), and in vivo proton MRS at field strengths of 1.5 T or above. We investigated postictal metabolic changes in a generalized seizure model with in vivo proton MRS at 0.5 T, in which the combination of glutamate and glutamine resonances (denoted glx) can be modeled as a singlet. METHODS: Five adult mongrel dogs underwent control and postictal experiments in which single-voxel proton MR spectra were obtained from the right frontal lobe cortex with a point-resolved spectroscopy technique approximately every 20 minutes for 3 hours. N-acetylaspartate (NAA), glx, and creatine (Cr) were quantified in absolute millimolar units with a cerebral water-referenced algorithm. Inter- and intrasubject differences in mean metabolite concentrations collected throughout the 3-hour period were compared using an unpaired, two-tailed Student's t test at a.05 level of significance. RESULTS: We found a significant increase (15.4%) in the postictal intersubject mean glx concentration, as well as a 23.7% postictal decrease in the intersubject mean Cr concentration. A trend toward a subtle decrease in postictal intersubject mean NAA concentration was not statistically significant. We also observed a substantial qualitative increase in the combination of postictal lactate and free fatty acid peaks. CONCLUSIONS: The glx, NAA, lactate, and free fatty acid results are in general agreement with previous studies of postictal perturbations in cerebral metabolism measured with invasive biochemical or noninvasive high-field-strength in vivo MRS detection assays. Given a high sensitivity for glx at 0.5 T relative to 1.5 T, further studies of postictal mesial temporal lobe structures are warranted in chronic animal preparations that model temporal lobe epilepsy.

Animals↗
PubMedDate not supplied

Functional MR of frontal lobe activation: comparison with Wada language results.

PURPOSE: Our purpose was to determine the utility of functional MR imaging in conjunction with a word-generation paradigm in the assessment of language lateralization. METHODS: Functional MR imaging and Wada testing for language lateralization was performed in patients with complex partial seizures during the performance of word-generation tasks. A language lateralization quotient was calculated from the number of activated pixels in the right and left hemispheres. A language laterality score was derived from the Wada results as the percentage of correct responses during right internal carotid artery injection minus the percentage of correct responses during left internal carotid injection. A correlation coefficient between the functional MR imaging results and the Wada language laterality scores was calculated. RESULTS: In 13 patients, hemispheric dominance based on Wada testing was confirmed by functional MR imaging during silent word generation. The Wada laterality scores varied from 100 to -100 and the functional MR imaging scores varied from 100 to -10. The language lateralization scores determined by functional MR imaging correlated significantly with the language lateralization scores derived from Wada testing. CONCLUSION: Functional MR imaging performed during word generation is an accurate method for lateralizing language function in patients with complex partial epilepsy.

Adult↗