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M C McNamara

Publications and source records attributed to M C McNamara.

At least 19 recordsLinked to original sources
PubMed1996

Developmental characteristics in the daily rhythm of norepinephrine concentration within rabbit brainstem regions.

To examine the development of daily variations in norepinephrine levels, norepinephrine concentrations were measured within five distinct brainstem regions in 3-day-old, 21-day-old, and adult rabbits at 6-h intervals throughout the day. Norepinephrine was measured by radioenzymatic assay, and norepinephrine concentration was expressed relative to wet tissue weight. The data suggest that daily variations for norepinephrine concentrations are established by the third day of life. In the brainstem as a whole, there was an early nocturnal peak (2130 hours) for 3-day-old animals in contrast to a late nocturnal peak (0330 hours) for 21-day-old animals. Adult animals showed a late diurnal (1530 hours) peak. These gross daily variations constitute the sum of distinct region-specific patterns in the development of daily variations in norepinephrine concentration. Norepinephrine is involved in cardiorespiratory regulation and in the regulation of sleep/wake cycles. The observed developmental patterns may relate to the maturation and integration of these physiologic processes.

Animals↗
PubMed1995

Ontogeny of dopamine daily rhythms within rabbit brainstem regions.

To examine the development of daily variations in dopamine levels, we measured dopamine concentrations within five distinct brainstem regions in 3- and 21-day-old, and adult rabbits at 09.30, 15.30, 21.30 and 03.30 h. Dopamine was measured by radioenzymatic assay and the dopamine concentration was expressed relative to wet tissue weight. In addition to defining the presence of a daily variation in the dopamine concentration in the whole brainstem, we were interested in identifying brainstem region-specific differences in this daily variation. Our data suggest that daily variations in dopamine concentrations are established by 3 days of life. Analysis of gross brainstem daily variation data suggest a peak in the dopamine concentration during the early light phase (09.30 h) for 3-day-old animals in contrast to a late light phase peak (15.30 h) for 21-day-old animals. Adult animals showed a peak in the early dark phase (21.30 h). These gross daily variations reflect the net sum of distinct region-specific patterns in the dopamine concentration. Analysis by region reflects a region-specific ontogeny in the development of daily variations for dopamine. Dopamine is involved in cardiorespiratory regulation. The observed developmental patterns may relate to the maturation and integration of these physiologic processes.

Aging↗
PubMed1994

Immunocytochemical detection of serotonin content in raphe neurons of newborn and young adult rabbits before and after acute hypoxia.

The present immunocytochemical study demonstrates serotonin (5-HT) depletion in the dorsal raphe nucleus (DRN) of 3- and 21-day-old rabbits following exposure to mild (10% ambient partial pressure of oxygen) and severe hypoxia (5% ambient oxygen). Under the mild hypoxic condition, 5-HT immunoreactivity in cells and fibers of the DRN was decreased in 3-day-old as well as 21-day-old rabbits, as indicated by decreased intensity of the staining compared to age-matched controls. Although this decrease was more pronounced in the younger animals, recovery from mild hypoxia was seen in both age groups. Hypoxic effects were more striking in 3-day-old animals under the severe hypoxic condition, indicating a greater depletion of 5-HT than in the mildly hypoxic condition. However, little additional effect on the older age group was seen. Further, a decreased ability of the 3-day-old rabbits to recover following severe hypoxia suggests that protracted effects on the developing serotonergic system occur following severe hypoxia during the neonatal period. This was demonstrated by the long-lasting decrease in the number of stained cells and fibers of the DRN 4-hr after return to normal conditions (21% O2). We conclude that newborns have a decreased rate of 5-HT synthesis and/or metabolic turnover that results in rapid depletion of intracellular stores and protracted time to recover from a hypoxic challenge. Similar effects could occur in human fetuses, newborns or infants following birth trauma, apnea or other events associated with severe hypoxia.

Acute Disease↗
PubMed1990

Developmental characteristics in the daily rhythm of serotonin concentration within rabbit brainstem regions.

To examine the development of daily rhythms in serotonin levels, we measured serotonin concentration within five distinct brainstem regions in 3-day-old, 21-day-old and adult rabbits at 09.30, 15.30, 21.30 and 03.30. Serotonin was measured by radioenzymatic assay in the superior and inferior colliculi, rostral pons, caudal pons and medulla, and serotonin concentration was expressed relative to wet tissue weight. In addition to defining the presence of a daily rhythm in serotonin concentration in whole brainstem, we were interested in identifying brainstem region-specific differences in this rhythm. Our data suggest that daily rhythms for serotonin are established by 3 days of life. Analysis of gross brainstem rhythm data suggests a nocturnal peak in serotonin concentration in 3-day-old and adult animals in contrast to a diurnal peak for 21-day-old animals. These gross rhythms reflect the net sum of distinct region-specific patterns in serotonin concentration. Analysis by region reflects a region-specific ontogeny in the development of daily rhythms in serotonin concentration. Serotonin is involved in the initiation of sleep. The observed developmental patterns may relate to the maturation and integration of sleep/wake states.

Aging↗
PubMed1989

Development of daily variations in methionine enkephalin within rabbit brainstem regions.

To examine the development of daily variations in methionine enkephalin, we measured methionine enkephalin concentration within five distinct brainstem regions in 3-day-old, 21-day-old, and adult rabbits at 09.30, 15.30, 21.30 and 03.30 h. Methionine enkephalin was measured by radioimmunoassay and methionine enkephalin concentration was expressed relative to wet tissue weight. In addition to defining the presence of a daily variation in methionine enkephalin concentration in the whole brainstem, we were interested in identifying brainstem region specific differences in this daily variation. Our data suggest that daily variations for methionine enkephalin are established by three days of life. Analysis of gross brainstem daily variation data suggests a nocturnal peak in methionine enkephalin concentration for 3-day-old animals in contrast to a diurnal peak for 21-day-old animals. Adult animals, showed a biphasic pattern. These gross daily variations reflect the net sum of distinct region specific patterns in methionine enkephalin concentration. Analysis by region reflects a region specific ontogeny in the development of daily variations for methionine enkephalin. Our data also suggest a caudal-rostral progression in the establishment of daily rhythms. Methionine enkephalin is involved in nociception and cardiorespiratory regulation. The observed developmental patterns may relate to the maturation and integration of these physiologic processes.

Aging↗
PubMed1988

Developmental characteristics of substance P immunoreactivity within specific rabbit brainstem nuclei.

Microdissected areas of the rabbit brainstem were isolated at prenatal day E28, postnatal days P3, 7, 14, 21, at 2 months and adults. Substance P immunoreactivity (SPI) was assayed by RIA and SPI was expressed relative to the protein content of the extracted brain tissues. The developmental characteristics of SPI within specific brainstem nuclei are reported. In general, SPI was highest in the NTS (nucleus tractus solitarii) at all ages. The pattern of distribution of SPI, however, was age-specific. The development of SPI within select nuclei demonstrated marked variability and showed both age- and nucleus-specificity.

Aging↗
PubMed1986

Effect of hypoxia on brainstem concentration of biogenic amines in postnatal rabbits.

The effects of hypoxia FiO2 = 0.10 on concentration of biogenic amines in specific brainstem nuclear groups were investigated in 3-and 21-day-old rabbits. The rabbit pups were confined to temperature-controlled water-jacketed chambers and exposed to 6h of 21% O2 or to one of 3 combinations of 21% O2 and 10% O2. These 3 combinations were either intermittent hypoxia, or 4 h of normoxia followed by 2 h constant hypoxia, or 2 h of hypoxia followed by recovery for 4 h in normoxia. Radioenzymatic assays were used to determine the concentration of dopamine, norepinephrine and serotonin in the following brainstem nuclei: substantia nigra, locus coeruleus, dorsal raphe and the nucleus reticularis pontis oralis. Compared with control, hypoxia did not affect dopamine levels at either age. The concentration of norepinephrine was inconsistently affected by hypoxia at either age. In contrast, in the 3-day-old rabbits serotonin was consistently reduced in each of the nuclei. In the 21-day-old rabbits, serotonin was either unchanged or increased following hypoxia. Our results show that hypoxia alters the concentration of serotonin in an age-specific manner. This change in serotonin concentration may reflect altered serotonin metabolism and suggests a possible mechanism by which hypoxia disrupts physiologic homeostasis in newborns.

Acute Disease↗
PubMed1986

Age-dependent influence of hypoxia on methionine-enkephalin concentration within rabbit brainstem nuclei.

We examined the effect of hypoxia (FIO2 = 0.10) on methionine-enkephalin concentrations in brainstem nuclei involved in the integration of cardiopulmonary control in 3- and 21-day-old rabbits. Rabbit pups were confined in environmental chambers for 6 h and exposed to one of four conditions. Control, 21% O2 for 6 h; intermittent hypoxia, 12 cycles of 20 min 21% O2 followed by 10 min of 10% O2; acute hypoxia, 4 h of 21% O2 followed by 2 h of 10% O2; recovery, 2 h of 10% O2 followed by 4 h of 21% O2. Methionine-enkephalin was measured by radioimmunoassay in the nucleus tractus solitarius, nucleus ambiguus, nucleus parabrachialismedialis, and nucleus reticulogigantocellularis. In 3-day-old rabbits, exposure to 10% O2 did not affect methionine-enkephalin concentrations in any brainstem nuclei studied. In contrast, 21-day-old pups demonstrated a decrease in methionine-enkephalin concentration in three of the four nuclei studied when exposed to intermittent hypoxia, as well as an apparent ability to recover from an acute hypoxic exposure (p less than 0.05). These data support an age-, nucleus-, and stimulus-specific effect of hypoxia on methionine-enkephalin concentration within specific brainstem nuclei and suggest a possible mechanism for the newborn's increased cardiopulmonary instability under hypoxia.

Age Factors↗
PubMed1985

Development of methionine-enkephalin in microdissected areas of the rabbit brain.

Microdissected areas of the rabbit brain were isolated at prenatal day E-29, postnatal days P-3, 7, 14, 21, 2 months and adults. Methionine-enkephalin (ME) was assayed by RIA and ME concentration [ME] was expressed relative to the protein content of the extracted brain tissues. In brain nuclei with important roles in respiratory control [ME] was higher in prenatal and early postnatal life than in adults. In contrast, the prenatal and early postnatal [ME] levels in other nuclei were lower than or equal to adult values. These data suggest an important and changing role for ME in respiratory control throughout development. Early high [ME] levels within brainstem respiratory control nuclei may contribute to the newborn's increased susceptibility to respiratory depression.

Age Factors↗
PubMed1984

Turnover and synthesis of biogenic amines in discrete brainstem nuclei of the rabbit.

By use of a microtechnique and sensitive enzymatic isotopic assays norepinephrine (NE), dopamine (DA) and serotonin (5-HT) turnover rates were measured in 6 discrete brainstem regions. The results from young (3 days) and adult (1 year) rabbits were compared. In the dorsal raphe nucleus (dr) of the younger animals the slopes of disappearance of NE and 5-HT were significantly higher than in the adults. Whereas, in the dr the slope of the decline of DA was found to be significantly lower in younger animals. In the dr turnover rates of NE and 5-HT were higher in the young animals. However, higher turnover rates for DA were seen only in the LC-A6 region. The young animals had significantly lower turnover times for NE and 5-HT in the dr. The nts was the only nuclear group to reach significance for DA, and the young animals had longer turnover times when compared to adults. These results are indicative of the different roles the neurotransmitter systems play in maintaining homeostasis. The delicate balances in these systems in the brains of younger animals may contribute to their increased susceptibility to perturbations.

Age Factors↗
PubMed1984

Biogenic amine turnover in newborn and adult rabbit brainstem nuclei after pargyline administration.

Following the administration of the monoamine oxidase inhibitor, pargyline, turnover rates of the biogenic amines norepinephrine (NE), dopamine (DA) and serotonin (5HT) were determined in discrete brainstem nuclei: substantia nigra (SN-A9), dorsal raphe (dr), nucleus gigantocellularis (rgi), locus coeruleus (LC-A6), nucleus ambiguus (n amb) and nucleus tractus solitarius (nts) of young and adult rabbits. The initial concentration of the amines varied markedly among the various nuclei studied, with higher values predominating in the older animals. The turnover rates for NE and DA in the rgi and LC were lower in young animals. The turnover rates for DA in the dr and nts were greater in the young animals. In addition, young rabbits had higher turnover rates for 5HT in the nts. The average turnover times for NE and 5HT were longer for the young animals (17.5 h vs 4.1 h) and (8.3 h vs 3.5 h) respectively. These data point to maturational differences in neurochemistry which may aid in elucidating possible mechanisms of respiratory instability in newborns.

Aging↗
PubMed1983

Ontogeny of biogenic amines in respiratory nuclei of the rabbit brainstem.

The concentrations of the biogenic amines, norepinephrine, dopamine and serotonin, were determined in 5 respiratory-related brainstem regions by use of a micropunch technique and a sensitive enzymatic isotopic assay. Samples were taken from rabbits at different ages (term fetuses, 3, 7, 14, 21 days and 2-year-old adults). All brain regions contained norepinephrine, dopamine, and serotonin in measurable amounts, but the distribution was not uniform. Norepinephrine and dopamine remained relatively low (less than 5 ng/mg) in the fetus and during the first weeks of life. Norepinephrine achieved its highest levels in the nucleus tractus solitarius and the locus coeruleus of adult animals. Dopamine concentrations did not change significantly in any nuclear groups over the ages tested. Compared with the newborn values, high concentrations of serotonin were seen in all brainstem nuclei in the term fetus. Adult serotonin levels were not achieved during the neonatal period. These data demonstrate pre- and postnatal changes in neurotransmitter levels in brainstem nuclei which regulate respiratory control. The susceptibility of the newborn to abnormalities in respiratory control may be related to low serotonin levels observed during the postnatal period.

Animals↗
PubMed1982

Scanning electron microscopic study of age-related surface changes in rat femoral head articular cartilage.

The articular surface of the femoral heads of young (5 month-old) and old (21 month-old) female rats were examined with the use of the scanning electron microscope using an especially sensitive preparative technique in which the femoral heads were fixed in a glutaraldehyde-paraformaldehyde fixative, post-fixed in OsO4, dehydrated in ethanol and critical point dried. The articular surfaces of the young group were relatively smooth with only small ridges, which may represent superficial collagen fibrils embedded in a proteoglycan matrix. The old group's articular surfaces differed in 2 ways from the surfaces obtained from the young group. First, circumscribed depressions (roughly 20-25 micrometers in diameter) were found, which may represent the empty lacunae of superficial-layer chondrocytes. Secondly, the articular surface was 'roughened', apparently by numerous exposed collagen fibrils that may have been exposed as a result of a loss of superficial proteoglycans. It is concluded that our methodology of tissue preparations for observation with the scanning electron microscope is a sensitive and practical technique that could be useful for characterizing early morphological manifestations of articular cartilage degenerative changes.

Aging↗
PubMed1980

Vasopressin and conditioned flavor aversion in aged rats.

The effect of lysine vasopressin on the performance of young-adult and old rats subjected to a conditioned flavor aversion procedure was studied. Young rats maintained an aversion to a 0.1% saccharin solution significantly longer than did older rats. Treatment with lysine vasopressin ( 1 microgram/kg) during the recovery period prolonged the aversion in both age groups. A single injection of lysine vasopressin prior to the aversion procedure significantly reduced the age difference in extinction. These observations support the hypothesis that age-dependent changes in endogenous vasopressin synthesis or secretion underlie some of the behavioral deficits observed in old animals.

Aging↗
PubMed1978

Restitution of ATP and creatine phosphate after experimental depletion in young, adult, and old rats.

The rates of restitution of skeletal muscle, heart, and brain creatine phosphate and brain ATP, following experimental depletion, were compared in young (3-5 month), adult (12 month) and old (24 month) rats. In skeletal muscle, restitution of creatine phosphate after 3 min of recovery was greatest in the young rats, minimal in the adult animals, and absent in the old animals. In heart muscle, on the other hand, restitution was rapid in all three age groups, and was essentially complete after 60 sec recovery. In brain, restitution of creatine phosphate was rapid and was complete after 10 min recovery in the young and adult rats; restitution was slower and less complete in the old rats. In the old rats there was no restitution of brain ATP during the first 2 min of recovery, after which the rate of restitution paralleled that of the young and adult rats.

Adenosine Triphosphate↗
PubMed1977

Age related changes in the effect of electroconvulsive shock (ECS) on the in vivo hydroxylation of tyrosine and tryptophan in rat brain.

A single electroconvulsive shock (ECS) was applied to 40 young (9 months) and 40 old (24 months) male rats. The effect on brain catecholamine synthesis was determined at intervals after ECS by measuring the accumulation of dihydroxyphenylalamine (DOPA) and 5-hydroxytryptophan (5-HTP) in rats pretreated with a central decarboxylase inhibitor (M-hydroxybenzyl hydrazine, NSD 1015). This accumulation permitted an estimation of the in vivo rates of hydroxylation of tyrosine and tryptophan. Control brain DOPA and 5-HTP concentrations were both lower in the older animals. Following ECS there was an increase in brain DOPA concentration (maximal at 60 min after ECS) in both young and old rats, but the increase was much smaller in the older animals. There were no changes in brain 5-HTP at any time after ECS, in either age group. It appears that aging selectively affects the response of the brain dopaminergic neurotransmitter system to stress, and we suggest that this may be a factor in the decreased resistance to stress in older subjects.

5-Hydroxytryptophan↗
PubMed1977

Active and passive avoidance in rats as a function of age.

Rats of four age groups: young (30 days of age), adolescent (180 days of age), adult (365 days of age), and old (547 days of age) were trained on active and passive avoidance tasks. There was impaired acquisition and 30-day rentention of passive-avoidance learning in both young and old rats, compared to the intermediate age groups, and marked impairment of acquisition and retention of active-avoidance learning in the old rats. Learning impairment is thus associated with immaturity as well as senescence.

Aging↗