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P G MacRae

Publications and source records attributed to P G MacRae.

5 recordsLinked to original sources
PubMed1991

Adjusting for recall bias with the proportional hazards model.

In studying falling frequency in the elderly, we observed that having subjects keep a diary led to a larger number of falls reported than had been noted in a previous study in the same population. The previous study asked subjects to report any falls in the previous three months. We considered two related explanations for the observation of lower incidence reports with a 3-month recall survey. First, there may have been under-reporting of falls due to recall bias. Second, the less severe falls (which did not result in injuries) may not be reported. We suggest that the proportional hazards model may be used to adjust studies in which recall is used to determine incidence and time to falls.

Accidental Falls↗
PubMed1988

Reaction time and nigrostriatal dopamine function: the effects of age and practice.

Normal aged and Parkinsonian individuals lose the ability to initiate movements rapidly (increased reaction time) in parallel with changes in the nigrostriatal dopamine (DA) system. However, the ability of these individuals to improve their reaction time with practice has not been adequately assessed. We have developed a rodent model of human reaction time in which reaction time performance correlates highly with neurochemical measures of nigrostriatal DA integrity. In the present report, 15 young and 10 old male Sprague-Dawley rats were conditioned in a reaction time task to release a lever quickly in response to external stimuli in order to avoid a mild footshock. In order to examine the effects of practice on this reaction time task, the young animals were tested for 5 days at 3, 6 and 9 months of age and the old animals were tested for 5 days at 18, 21, and 24 months of age. From this well-practiced task, reaction time response latencies were measured and compared to measures of nigrostriatal DA function (steady-state levels of DA and its metabolites, D2DA receptor affinity and density). The old animals were slower in response latencies than the young animals. These age differences in response latencies, however, disappeared after several days of testing at each of the 3 test sessions, so that the old animals were not significantly slower than the young animals on days 4 and 5 of each session. As expected, the old animals showed reduced striatal D2DA receptor density with no age differences in DA receptor affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1987

Endurance training effects on striatal D2 dopamine receptor binding and striatal dopamine metabolite levels.

We have previously shown that endurance training is associated with higher binding of [3H]spiperone to striatal D2 dopamine (DA) receptors of presenescent (21 months old) rats. In the present study we investigated the effects of 6 months of endurance training of young adults on the relationship between steady-state levels of DA and its metabolites in striatum and the affinity and density of striatal D2 DA receptors. The extent of training was confirmed by evaluating the maximal oxygen consumption (VO2 max) in the subjects. D2 DA binding was significantly increased at each of 3 [3H]spiperone concentrations in the young runners. A 'synaptic coupling ratio' calculated as the specific DA binding/DOPAC concentration was significantly increased in runners for the 0.1 and 0.4 nM radioligand concentrations. Across experimental groups levels of DA were highly and positively correlated with specific DA binding at the 0.1, 0.2 and 0.4 nM [3H]spiperone concentrations. Together, these results suggest that exercise can alter the number of DA binding sites and the metabolism of DA in young adult animals.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1987

Endurance training effects on striatal D2 dopamine receptor binding and striatal dopamine metabolites in presenescent older rats.

Endurance training is associated with higher binding of 3H-spiperone to striatal D2 dopamine receptors of rats sacrificed 48 h following the last exercise bout (Gilliam et al. 1984). In the present study we investigated the effects of endurance training in presenescent older rats on the relationship between steady-state levels of DA and its metabolites in striatum versus the affinity and density of striatal D2 DA receptors. Citrate synthase activity of the gastrocnemius-plantaris muscle was 29.06 +/- 2.27 mumole/g wet wt in 21-month-old trained rats versus 22.88 +/- 1.13 mumole/g wet wt in 21-month-old untrained animals. DOPAC levels and DOPAC/DA ratios were greater in the old controls. Endurance training was associated with lower DOPAC levels in the 21-month-old animals. Thus, endurance training may postpone selectively changes in DA metabolism over a portion of the lifespan. As expected, the number of D2 DA binding sites was reduced with age (6 months Bmax:429 +/- 21 fmoles/mg protein; 21 months:355 +/- 20) with no change in affinity. The Bmax of old runners was significantly higher (457 +/- 38 fmoles/mg protein) than that of old controls. Thus, endurance training appears to exert a protective effect on D2 dopamine receptors during the lifespan. Taken together, the present results suggest that there may be a possible reciprocal relationship between changes in DA metabolites and DA binding as a function of exercise in presenescent older rats, and that endurance training may decelerate the effects of age both on nigrostriatal dopamine neurons and on striatal D2 dopamine receptors during a portion of the lifespan.

3,4-Dihydroxyphenylacetic Acid↗