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Biomedical subjects

R T Brown

Publications and source records attributed to R T Brown.

At least 127 records · Page 7Linked to original sources
PubMed1980

Time course of peripheral heterothermy in a homeotherm.

The integrity of the peripheral heterothermic response was monitored in adult Sprague-Dawley rats during cold acclimation. Subcutaneous peripheral temperature gradients were simultaneously recorded in the hindlimbs. One limb was exposed to room temperature (22 +/- 2 degrees C) while the contralateral limb was gradually cooled to 0 +/- 1 degrees C. Noncontrols were acclimated at 5 +/- 1 degrees C for periods up to 35 days. Controls responded to the cooling regimen (25 to 0 degrees C at 0.5 degrees C . min-1) in a "poikilothermic" manner indicating local cold-induced vasoconstriction (CIVC). CIVC was not released until tissue temperatures reached 22,3 +/- 2.5 degrees C whereupon nonpatterned limb temperature fluctuations, Lewis' hunting response, were often initiated. The hunting response occurred synchronously in the contralateral warmed limb despite its elevated temperature. The experiments revealed a progressive decrease in the intensity of heterothermy indicative of an earlier onset of cold-induced vasodilation as well as increased resistance to tissue cooling with increasing acclimation time. Following 21 days at 5 degrees C, limb exposure to 0 degrees C resulted in a 2-4 degrees C drop in tissue temperature. The time course of the diminution in peripheral heterothermy is discussed. In addition, evidence supporting the hypothesis of a central component in the regulation of the hunting response is presented.

Adaptation, Physiological↗
PubMed1979

Quantitative relationships of the ototoxic interaction of kanamycin and ethacrynic acid.

We determined the range of doses of kanamycin sulfate and ethacrynic acid that results in an ototoxic interaction in guinea pigs. In addition, we determined the time interval between the administration of the two drugs that is needed to produce this interaction. In all cases, the magnitude of the ototoxic lesion was determined by measuring the cochlea's ability to generate both the sensitivity and intensity functions of the ac cochlear potential. In addition, the cochlear pathologic conditions, as determined by counting the number of missing hair cells in the organ of Corti, was found to correlate highly with the ac cochlear potential data. The dosage range of ethacrynic acid during which the interaction occurs is very narrow, while the dose range of kanamycin is very large.

Animals↗
PubMed1979

Methylphenidate in hyperkinetic children: differences in dose effects on impulsive behavior.

This research tested the hypothesis that in hyperactive children a low dose of methylphenidate (0.3 mg/kg) would produce scores superior to those with a high dose (1.0 mg/kg) or placebo on the matching familiar figures test (MFF), a primary index of impulsivity. The hypothesis was based on an earlier finding that the highest percentage of correct responses on a short-term memory task were found in hyperactive subjects who were receiving 0.3 mg/kg of methylphenidate whereas at 1.0 mg/kg the percentage correct returned to the placebo level. The hypothesis was verified in that the low dose reduced the number of errors on the MFF significantly more than did placebo or the high dose. This work demonstrates that, for both learning and impulsivity in hyperactive children, the lower dose of the two doses of methylphenidate studied produced the preferable effect.

Adolescent↗
PubMed1978

Comparative ototoxic liability of netilmicin and gentamicin.

Netilmicin sulfate is a new aminoglycoside antibiotic currently undergoing clinical investigation. All of the aminoglycoside antibiotics now in clinical use are ototoxic. This study was done to determine the ototoxic liability of netilmicin when it is compared directly with gentamicin sulfate. Groups of ten guinea pigs each were given doses of 0, 50, 100, or 150 mg/kg of either gentamicin or netilmicin daily for four weeks. After a two-week stabilization period, the Preyer pinna reflex, the cochlea's ability to generate the ac cochlear potential, and the missing hair cells from the cochleas were determined. Additionally, the pharmacokinetics of both drugs in the plasma and perilymph were determined. Little or no cochlear damage was detected with netilmicin, even at the highest dose, while even the smallest dose of gentamicin produced measurable changes in cochlear function.

Acoustic Stimulation↗
PubMed1977

Reflection-impulsivity in normal and behavior-disordered children.

The primary index of reflection-impulsivity is Kagan's Matching Familiar Figures Test (MFF), which yields both a latency and an error score. To evaluate further the construct validity of these measures, both the latency and error scores of 9- and 15-year-old normal and "acting-out" behavior-disordered children were compared. Young behavior-disordered children were found to be more impulsive than the other groups on the MFF error measure. No differences occurred on the MFF latency measure. This result is consistent with previous findings with normal children in supporting the construct validity of the MFF error score and raising questions about the construct validity of the MFF latency score. Findings were inconsistent with Kagan's assertion that normal children become more reflective with age. The older behavior-disordered children were more reflective on the error measure than the younger behavior-disordered children and had equivalent error scores to both age groups of normals. This finding suggested a lag in the development of reflection in behavior-disordered children.

Adolescent↗
PubMed1975

Tobramycin ototoxicity: a second look.

Tobramycin was administered intravenously to guinea pigs and was shown to produce an impairment of the alternating current cochlear potential. This effect is temporary and occurs only when the blood pressure has been severely lowered. We conclude that these data do not represent the onset of ototoxicity of tobramycin as reported by others, but only represents the cochlear effect of the pronounced fall in blood pressure that is produced by the tobramycin.

Action Potentials↗
PubMed1975

Following and visual imprinting in ducklings across a wide age range.

Ducklings ranging in age from 20-125 hr were exposed to a moving silent object in an open circular apparatus until a criterion of 300 sec of following was met. All ducklings met the criterion, and age did not correlate with the time required. In subsequent choice tests most ducklings approached the imprinting object over a novel object, and age did not correlate with choice behavior. Results indicate that imprinting can occur over a fairly wide age range, and that the traditional critical period for imprinting may, in part, be an artifact of laboratory methods.

Age Factors↗
PubMed1975

Discrepancy from rearing conditions affects chicks' behavior in a novel situation.

Chicks raised in small or large cages were exposed to a relatively large novel situation at 12 or 24 hr of age. At both ages, chicks from small cages had longer latencies to begin moving and lower activity scores. Age itself had no effect. Apparently, chicks learn the characteristics of their home cage shortly after hatching, and discrepancy from the home affects their response to novel situations.

Animals↗