Biomedical subjects

J D Allison

Publications and source records attributed to J D Allison.

40 records · Page 3Linked to original sources

PubMedDate not supplied

Temporal-frequency tuning of cross-orientation suppression in the cat striate cortex.

A sinusoidal mask grating oriented orthogonally to and superimposed onto an optimally oriented base grating reduces a cortical neuron's response amplitude. The spatial selectivity of cross-orientation suppression (XOR) has been described, so for this paper we investigated the temporal properties of XOR. We recorded from single striate cortical neurons (n = 72) in anesthetized and paralyzed cats. After quantifying the spatial and temporal characteristics of each cell's excitatory response to a base grating, we measured the temporal-frequency tuning of XOR by systematically varying the temporal frequency of a mask grating placed at a null orientation outside of the cell's excitatory orientation domain. The average preferred temporal frequency of the excitatory response of the neurons in our sample was 3.8 (+/- 1.5 S.D.) Hz. The average cutoff frequency for the sample was 16.3 (+/- 1.7) Hz. The average preferred temporal frequency (7.0 +/- 2.6 Hz) and cutoff frequency (20.4 +/- 6.9 Hz) of the XOR were significantly higher. The differences averaged 1.1 (+/- 0.6) octaves for the peaks and 0.3 (+/- 0.4) octaves for the cutoffs. The XOR mechanism's preference for high temporal frequencies suggests a possible extrastriate origin for the effect and could help explain the low-pass temporal-frequency response profile displayed by most striate cortical neurons.

Animals↗

PubMedDate not supplied

Frequency and variation of the posterior pituitary bright signal on MR images.

Sagittal T1-weighted series with 3-mm sections have routinely been used for all cranial MR studies at our institution. It was apparent from examining these studies that the rate of occurrence of a normal posterior pituitary bright signal was lower than has been previously reported, particularly in older patients. This prompted both a retrospective and a prospective review and analysis of the posterior lobe bright signal in three patient categories. The overall frequency of posterior pituitary bright signal and the influence of sex and age were evaluated in one category. An age-related statistically significant decline in the frequency of posterior pituitary bright signal was found, with a decline rate of approximately 1% per year. An evaluation of the occurrence of anatomic variation in the location of posterior lobe bright signal was made in a second group of 1500 patients. Aberrant location of the posterior lobe was found to be uncommon and was seen most frequently in patients with a sellar fossula. Temporal variation in the presence or absence and size of the posterior lobe bright signal was evaluated in a third group of 36 patients who had at least two MR examinations available for review. Follow-up MR study showed an obvious posterior lobe bright signal in 8% of these patients for whom no bright signal was apparent at the time of initial examination. Loss of the posterior lobe bright signal was apparent in another 25% of patients. A significant change in size of the bright signal was apparent in 19% of patients within this category. Our results indicate that variation in the bright signal of the posterior pituitary lobe should be expected as a normal physiological occurrence.

Adolescent↗

PubMedDate not supplied

In vitro cytotoxicity against human cancer cell lines during pulsed magnetic field exposure.

In an in vitro cell growth assay, carboplatin potency against A-431 cells increased after a 1 hour PMF (pulsed magnetic field) exposure (calculated peak field 5.2 mTesla, with an average field strength of 0.525 mTeslarms; pulses rose for 120 microseconds and then abruptly fell to neutral, and were repeated at a rate of 100 or 250 pulses per second). This potentiating effect was not observed with cisplatin or daunomycin. When cytotoxicity against HT-29 cells was measured, PMF exposure potentiated both carboplatin and daunomycin, but again, not cisplatin. Both cell types exhibited increased growth when exposed only to PMF. Exposure to PMF consistently increased the cell growth of these cancer cell lines, while only some in vitro antineoplastic agents were potentiated by PMFs.

Carboplatin↗

PubMedDate not supplied

Chemotherapy of human carcinoma xenografts during pulsed magnetic field exposure.

Immune deficient mice growing xenografts of HT-29 or A-431 cell lines were treated with cisplatin, carboplatin or doxorubicin in combination with one hour of wholebody pulsed magnetic field (PMF) exposure (calculated peak field 5.2 mTesla, with an average field strength of 0.525 mTeslarms; pulses rose for 120 microseconds and then abruptly fell to neutral, and were repeated at a rate of 250 pulses per second). At 24 days, the mice in each experiment were found to have significantly (p < 0.05, ANOVA) different tumor sizes among groups. The smallest mean tumor volume was consistently found in the drug+PMF group. With A-431 tumors, the cisplatin+PMF group (T) was significantly smaller, 52% [1-(100T/C)], than the cisplatin alone group (C). In HT-29 tumors, those treated with carboplatin+PMF had the smallest tumor volume at just 34% of the carboplatin-alone group. In HT-29 tumors, the doxorubicin+PMF group was 35% of the doxorubicin alone group.

Animals↗