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Biomedical subjects

M A Reynolds

Publications and source records attributed to M A Reynolds.

At least 73 records · Page 4Linked to original sources
PubMed1985

Relationship of body temperature stability to mortality in aging mice.

An age-related decline in the capacity for thermoregulation among homeothermic animals has been observed frequently under conditions of extreme ambient temperatures. We investigated the temporal stability of the internal body temperature of 69 C57BL/6J mice from 25 months of age until death in a controlled, neutral thermal environment. Estimates of temporal variability were calculated over consecutive 1-month intervals using (colonic) body temperature data collected weekly. The results of this longitudinal analysis indicated that the regulation of body temperature, as measured by its temporal stability, became increasingly less precise with advancing age. Body temperature exhibited a significant decline as the animal approached death. Individual differences in body temperature and the temporal regulation of body temperature were significantly correlated with lifespan, although the direction of the relations were opposite. Body temperature correlated positively with lifespan, whereas the temporal stability of body temperature correlated negatively with lifespan. Thus, animals exhibiting higher body temperatures and greater temporal stability also tended to live longer than their cohorts.

Aging↗
PubMed1985

Radial maze performance in young and aged mice: neurochemical correlates.

Young (8 month) and aged (27-28 month) male C57BL/6J mice were trained in a spatial discrimination task requiring working memory. The mice were tested during three trials daily in an eight-arm radial maze for 36 test days. Correct choices were reinforced with isotonic saline. In contrast to past reports, young mice learned the task. Old mice also learned the task, and no significant age-related differences in performance were observed. Following maze training, the mice were killed, the brains removed, and the specific activities of choline acetyltransferase (E.C.2.3.1.6., ChAT) and L-glutamic acid decarboxylase (E.C.4.1.1.15., GAD) were assayed in the hippocampus, and in frontal, sensorimotor, and cingulate areas of the cerebral cortex. The activities of these neurotransmitter synthetic enzymes did not differ significantly between young and old mice. Correct responding in the radial maze was positively correlated to ChAT activity in the cingulate cortex and negatively correlated to ChAT activity in the sensorimotor cortex. There was a similar pattern of correlation between performance and regional GAD activity, although none of the correlations involving GAD reached statistical significance.

Aging↗
PubMed1985

Morphology of embryonic neostriatal cell suspensions transplanted into adult neostriata.

Embryonic neostriatal cell suspensions were transplanted into intact or kainic acid-lesioned neostriata of adult host rats. These transplants survived and were sacrificed at 34-78 days posttransplantation. Nissl and Golgi preparations revealed neurons present within the transplants. Neurons with abundant dendritic spines (Spiny type I) were most frequent, but those with fewer spines (Spiny type II) and smooth dendrites (Aspiny II and III) were also present. These results indicate that neostriatal transplants are populated by the major output and internuncial neurons of the neostriatum.

Animals↗
PubMed1985

Discrimination learning requiring different memory components in rats: age and neurochemical comparisons.

The performances of young (8-9 months) and aged (22-24 months) male ACI rats were compared in a T-maze requiring two discriminations, each of which placed different demands on memory processing. A spatial discrimination in the stem of the T-maze required long-term reference memory; a discrete-trial, alternation discrimination in the arms of the T-maze required working memory. Following acquisition training in one maze, rats were also trained in a second maze at a different location in the room. The correct response in the stem of this maze was opposite to that in the first maze. In two experiments with slightly different pretraining procedures, similar results demonstrated that aged rats made more errors in all phases of maze training than did their young counterparts. The results suggest that all components of memory processing were affected equivalently because the age-related impairment was not selectively greater in any component of the task. In a third experiment, aged rats were unimpaired in the ability to perform in a T-maze task involving a brightness discrimination with intramaze cues. This result suggests that the age-related impairment in the two-component T-maze task was restricted to the cognitive demands of the task. Neurochemical analyses were performed to determine whether regional neurotransmitter synthetic enzyme activities could be used to identify neurochemical systems associated with performance in these tasks and with any age-related impairments observed. Choline acetyltransferase and glutamic acid decarboxylase were assayed as markers for cholinergic and GABAergic systems, respectively, in the hippocampi and the following cortical regions: frontal, sensorimotor, auditory, cingulate, occipital, and pyriform-perirhinal. A slight (8%) but significant age-related decline was observed in the activity of glutamic acid decarboxylase but not of choline acetyltransferase. Although the correlation between maze performance and regional enzyme activities generally supported several previous observations, the only significant correlation to emerge was between working memory performance and glutamic acid decarboxylase activity in the cingulate cortex.

Aging↗
PubMed1985

Benign intracranial hypertension following severe hyponatremic dehydration in congenital adrenal hyperplasia.

A case of salt-losing congenital adrenal hyperplasia with severe hyponatremic dehydration is presented. Clinical signs and symptoms of cerebral edema with elevated intracranial pressure were present. Conventional treatment was started, and after initial concern regarding future head growth and development, there was a good outcome with normal development at 1 year of age. This course is suggestive of benign intracranial hypertension. Possible mechanisms are discussed with a review of the relevant literature.

Adrenal Hyperplasia, Congenital↗
PubMed1983

Speaking without seeing, or the effect of interviewer absence on interviewee disclosure time.

The results of the present study confirmed earlier findings that the elimination of the usual face-to-face confrontation between interviewer and interviewee enhances disclosure time in relation to intimate questions. By unconfounding speaking time and pausing time, the present research demonstrated that the facilitating effect of an interviewer's absence is not simply an artifact of increased latencies and silent pauses within responses. The earlier findings were extended by manipulating the intimacy level of questions asked of subjects in the context of a gender-balanced design.

Female↗
PubMed1983

Effects of mutual invisibility and topical intimacy on verbal fluency in dyadic communication.

The mutual reduction of visual feedback, which in this study did not interfere with the synchronization of turns, reduced the productivity levels and increased the silent pauses of female speakers, even though it had no effect on their subjective discomfort, anxiety, and ease of communication self-ratings. The same reduction of visual feedback, which was achieved by seating the participants back-to-back rather than face-to-face, caused male speakers to feel anxious and uncomfortable and reduced the duration of their silent pauses, but only in same-gender dyads. These findings are explained in terms of previously noted gender differences in the need for visual feedback and in the anxiety-arousing effects of back-to-back interactions. Intimate communications, on the part of both male and female speakers, were associated with a slow pacing of speech but not with a decrease in productivity level, independently of the seating arrangement. These findings are interpreted in terms of the self-monitoring and self-censoring that is usually associated with the communication of intimate messages.

Adult↗
PubMed1983

Methadone effects on locomotor activity of young and aged mice.

The effect of age on the behavioral response to methadone hydrochloride was examined in male C57BL/6J mice. After 1 hr habituation to an oval runway, locomotor activity of young (6-8 months) and aged (30-32 months) mice was monitored for 3 hr following injections of saline or methadone hydrochloride (2.5, 7.5, 15.0 or 22.5 mg/kg). The three highest doses initially elevated activity which then declined over the next 1 1/2 to 2 1/2 hr. Compared to young mice, activity of aged mice was elevated less extensively, but remained elevated for a longer period of time. The attenuated elevation could be interpreted in terms of reduced physical capacity of aged mice; however, the more prolonged elevation was clearly an age-related difference in reaction to the drug. Although the mechanism accountable for this effect is unknown, it is not likely related to age differences in drug absorption or distribution to active sites.

Age Factors↗
PubMed1983

Age-dependent correlation of motor performance with neurotransmitter synthetic enzyme activities in mice.

The performance of male C57BL/6J mice (Mus musculus) was assessed in a battery of tests designed to detect age-related losses in motor abilities and also to examine individual differences within age groups. Studied were 4-, 18-, and 24-month-old mice. Within 5 days following the completion of the behavioral battery, the mice were killed, and brain tissue was taken for determinations of choline acetyltransferase (EC 2.3.1.6), L-glutamic acid decarboxylase (EC 4.1.1.15) and tyrosine hydroxylase (EC 1.14.16.2) activities in the frontoparietal + temporal + occipital cortex, hippocampus, striatum, and cerebellum. Two composite test scores were derived for each animal. The first composite score comprised measurements of locomotor activity, and the second reflected strength and coordination abilities. Test scores included in each composite correlated highly with that composite score, but not with the other composite. This observation suggests that there is a high degree of internal consistency for the composite scores and that the composite scores represent independent behavioral factors. Significant correlations between the composite scores and regional enzyme activities were detected; these correlations varied with age. In most cases, the sign (+, -) of the correlation was reversed at 24 months as compared with 4 months of age. These results suggest that the relations between performance and enzyme activities vary with age, and may reflect altered neurotransmitter function during senescence. This work serves as an example of how direct correlational analyses may help to elucidate behavioral-neurochemical interactions in aging.

Aging↗
PubMed1983

Effects of intermittent feeding upon growth, activity, and lifespan in rats allowed voluntary exercise.

From weaning until death, male Wistar rats were housed in activity-wheel cages with one group maintained on an ad libitum (AL) diet and another provided the diet every-other-day (EOD). EOD-fed rats had a mean lifespan of 124 weeks compared to 103 weeks for AL-fed rats. While post-weaning body weight and growth rates were reduced among the EOD-fed animals compared to AL-fed animals, there was no significant difference in growth duration. Positive correlations were observed between lifespan and estimates of growth rate and duration in the AL group but not in the EOD group; thus, little evidence was produced to support the hypothesis that growth rate is inversely related to longevity. While the EOD feeding regimen resulted in higher activity levels later in life, wheel activity levels were actually lower in this group in early life compared to the AL group. The observation of reduced wheel activity among young rats fed EOD was replicated in a second experiment. Thus, little support was obtained for the hypothesis that increased activity mediates the beneficial effects of dietary restriction on longevity, unless this mechanism is active late in the lifespan.

Animals↗
PubMed1983

Differential effects of intermittent feeding and voluntary exercise on body weight and lifespan in adult rats.

Male wistar rats were housed in laboratory cages or activity-wheel cages at eight 10.5 or 18 months of age. Part of each cage group continued to be fed ad libitum, whereas the remaining animals were fed every other day. Compared with the ad libitum condition, intermittent feeding decreased body weight and increased lifespan at both ages in both caging conditions. Compared with the caged condition, voluntary exercise in activity wheels reduced body weight only in the 10.5-month-old group fed ad libitum but produced no effect on survival of either age group. The results suggest that intermittent feeding can enhance survival in mature rats even beyond ages at which body weight growth usually ceases, whereas voluntary exercise appears to have an early threshold beyond which increases in longevity are not observed.

Animals↗
PubMed1983

Influence of dietary carbohydrate on the induction of diabetes in C57BL/KsJ-db/db diabetes mice.

Genetically diabetic C57BL/KsJ-db/db and normal littermate mice of both sexes were fed one of nine defined diets from weaning. The objective was to study dietary carbohydrate interaction with the diabetogenic genes through isocaloric substitution of protein for carbohydrate (either sucrose or dextrin starch) at concentrations of 0, 8, 24, and 60%. In addition, at 60% concentration, the effect of type of carbohydrate (e.g., glucose, fructose, sucrose or dextrin starch) on the deterioration of endocrine pancreatic structure and function was analyzed. The carbohydrate-free diet produced the greatest survival to 1 year of age and allowed the expression of an obesity syndrome uncomplicated by severe hyperglycemia or by extensive necrosis of pancreatic beta cells and islet atrophy. Those diets containing intermediate levels of carbohydrate (8 or 24% of sucrose or dextrin), or 60% dextrin starch, in comparison to diets containing 60% refined carbohydrates, extended life span and produced a more protracted pathogenesis, but were unable to circumvent eventual severe hyperglycemia and islet destruction. The diets containing 60% glucose, fructose, or sucrose all led to the rapid induction of diabetes. Thus, pathogenesis entails an interaction between dietary carbohydrate, the db gene, and other diabetes-predisposing genes in the genome.

Animals↗
PubMed1983

Age and strain comparisons of neurotransmitter synthetic enzyme activities in the mouse.

Activities of the neurotransmitter synthetic enzymes, choline acetyltransferase (EC 2.3.1.6; ChAT), glutamic acid decarboxylase (EC 4.1.1.15; GAD), and tyrosine hydroxylase (EC 1.14.3.2; TH), were assayed in four brain regions of A/J and C57BL/6J mice at three ages (4, 18, and 24 months). The brain regions assayed were the fronto-parietal cortex, hippocampus, striatum, and cerebellum. Strain effects: In some brain regions, at several ages, ChAT activity did not differ among the two strains. However, ChAT was higher in the C57BL/6J strain in the cortex at 18 months, the hippocampus at 18 and 24 months, the striatum at 24 months, and the cerebellum at 4 months. The reverse was true in the cerebellum at 24 months, where ChAT was higher in A/J mice. GAD activity in C57BL/6J mice compared to that of A/J mice was higher in the striatum and cortex, and lower in the hippocampus and cerebellum. TH activities in all four regions were generally higher in C57BL/6J mice than in A/J mice. Age effects: Age differences in enzyme activities varied with the genetic strain. ChAT activity generally was higher in brain regions of older mice of both strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1982

Decreased resistance to extinction in ob/ob mice following operant training.

Inconsistent results have emerged from past studies in which operant conditioning paradigms were used to assess the hunger motivation of genetically obese mice relative to that of normal mice. Methodological considerations indicated the need to examine operant performance to a criterion, rather than performance during time-based sessions, and then to focus upon response differences in resistance to extinction. Therefore, genetically obese (ob/ob) mice and normal littermates were trained successfully to bar-press for 100 food rewards on either a CRF or a FR-10 schedule of reinforcement. Extinction behavior was then examined over 9 daily 1-hr sessions. While obese and normal mice evidenced similar patterns of learning, or response discrimination for food rewards, they evidenced different levels of hunger motivation during extinction conditions. Obese mice displayed a greater reduction in responding across extinction sessions, or less resistance to extinction, than normal mice following training on both schedules of reinforcement. These findings suggest that ob/ob mice exhibit lower levels of hunger motivation than normal littermates.

Animals↗
PubMed1982

The relationship of genotype, sex, body weight, and growth parameters to lifespan in inbred and hybrid mice.

Data from nine inbred and six hybrid mouse strains of both sexes were used in a correlational analysis to examine the relationships between lifespan and several growth parameters, including body weight at weaning, at 6 weeks after weaning, and at 1 year, and estimates of growth rate, food consumption, and feeding efficiency during early life. The analysis revealed strong relationships of genotype to all variables. Hybridization was associated with longer lifespan, but sex was not related to lifespan. Several growth parameters were significantly related to lifespan, but the directions of the correlations were sex-dependent. Several body weight and growth parameters were positively correlated to lifespan in males, while negatively correlated to lifespan in females. Genotype accounted for most of the variance in these relationships with the exception of hybrid males, where the correlation between growth rate and lifespan was attributable largely to environmental factors. In demonstrating significant correlations between lifespan and constitutional variables within a species, the results supported a morphogenetically based hypothesis of lifespan inheritance; however, the sex differential in the direction of the relationship between growth and lifespan further demonstrated the difficulty of making predictions deduced from the hypothesis.

Animals↗