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Biomedical subjects

D A Blizard

Publications and source records attributed to D A Blizard.

At least 55 records · Page 3Linked to original sources
PubMed1981

The Maudsley reactive and nonreactive strains: a North American perspective.

The Maudsley experiment involving bidirectional selection for differences in open-field defecation (OFD) is briefly reviewed. Attention is focused on the North American stocks of these strains since problems have been encountered with regard to the open-field behavior and continued viability of the British stocks. The open-field behavior of the colonies of the Maudsley strains at the National Institutes of Health and at the University of Northern Iowa closely resembles that originally exhibited by the British strains, provided they are compared under standard conditions. On more complex behaviors, such as escape-avoidance conditioning, serious discrepancies have emerged between the British and North American findings. These may be resolved when attempts are made to replicate more closely the procedures used in the British studies. Particular emphasis has been placed on the potential of a second nonreactive strain, the MNRA/HAR strain, to serve as a replicate of selection for decreased emotionality. The value of the RXNRA group of recombinant-inbred strains, developed and maintained by the author, for examining the reliability of associations between traits is also stressed. A correlation between OFD and biochemical aspects of sympathetic function has been found in the Maudsley strains. This finding lends credibility to Hall's claim that the expression of emotionality is linked to autonomic arousal.

Animals↗
PubMed1978

The effect of neonatal oil administration on brain weight of inbred and heterogeneous mice.

A single injection of sesame oil on postnatal Day 4 reduced adult bain weight in male and female mice of the C3H/HeJ strain. The same neonatal treatment had no effect on brain weight of heterogeneous mice derived from a cross of 8 inbred strains. In agreement with previous findings in inbred strains, C3H/HeJ females were found to have larger brains than males. This difference between the genders was not seen in heterogeneous mice. The effect of neonatal oil administration on adult brain weight provides an additional example of the effect of neonatal manipulations on the adult organism and underscores the importance of adherence to appropriate control procedures in studies involving administration of hormones in early life, particularly when infant strains are used as experimental subjects.

Animals↗
PubMed1978

Central and peripheral norepinephrine concentrations in rat strains selectively bred for differences in response to stress: confirmation and extension.

Inbred rats from the Maudsley Reactive (MR) strain had lower concentrations of norepinephrine in hypothalamus, heart, and spleen, and lower total catecholamines in adrenal than inbred Maudsley Non-Reactive rats (MNRA line). In contrast, they had a higher concentration of telencephalic NE than MNRA rats. These results confirmed previous findings obtained on rats maintained by non-systematic breeding within the two lines. Comparisons were also made between MR and a second Maudsley Non-Reactive strain (MNR). Rats of the two Non-Reactive lines (MNRA, MNR) have been bred from the same foundation population and selected for the same behavioral characteristics, but have been genetically isolated from each other for many generations. It was found that MR rats showed differences from MNR rats in hypothalamic and peripheral (but not telencephalic) NE concentrations similar to those seen in MR/MNRA comparisons. Since rats of the two Non-Reactive lines differ appreciably from MR rats in open-field defecation (the criterion on which they were selected), their differences from MR rats in a neurochemical system involved in sympathetic function suggests that this system may be functionally related to well established behavioral and physiological differences between the lines.

Adrenal Glands↗
PubMed1977

Central and peripheral norepinephrine metabolism in rat strains selectively bred for differences in response to stress.

Rats of the Maudsley nonreactive (MNRA) strain were found to contain higher levels of norepinephrine in heart, spleen, and hypothalamus than animals of the Maudsley reactive (MR) strain. Total adrenal catecholamines were also greater in nonreactive animals. There was a trend toward higher endogenous norepinephrine concentration in MR rats in brainstem and telencephalon, but this was not statistically significant. Turnover measurements calculated from the fall of norepinephrine at 1 and 4 hours after a single dose of levo-alpha-methylparatyrosine showed no significant strain differences in telencephalon or brainstem, but MNRA animals had a faster rate of norepinephrine decline in heart than had MR rats. Possibly indicative of a higher rate of norepinephrine metabolism, the percentage of 3H-non-catechol metabolites relative to total counts was higher in brainstem of MNRA rats 90 min after intraventricular injection of 3H-norepinephrine. However, the disagreement between this estimate of norepinephrine metabolism and that provided by the alpha-methyl-paratyrosine technique prevents a conclusive statement about norepinephrine metabolism in the two strains. The results are discussed in the light of the established differences in behavior between the strains as well as other work exploring relationships between catecholamine metabolism and emotionality.

Adrenal Glands↗
PubMed1977

Serum prolactin and hypothalamic dopamine in rat strains selectively bred for differences in susceptibility to stress.

Rat strains selectively bred for behavioral differences in susceptibility to mild stress exhibited differences in serum prolactin (Prl) and hypothalamic dopamine (DA). Male rats from the Maudsley Reactive (MR) strain had higher levels of serum Prl and hypothalamic DA than rats from the Maudsley Non-Reactive (MNRA) strain. MR rats also showed a greater percentage increase in serum Prl 1 h after blockade of catecholamine synthesis by administration of alpha-methylparatyrosine (alphaMpT). The correlation of basal serum Prl levels with individual susceptibility to stress constitutes further evidence that Prl may play a functional role in the organism's response to stress. Strain differences in hypothalamic DA function may play a role in the etiology of strain differences in serum Prl.

Animals↗
PubMed1976

A reevaluation of the relation between estrogen and emotionality in female rats.

It has been hypothesized that the emotionality of the female rat is reduced at estrus. In confirmation of previous research, it was found that administration of estradiol benzoate (EB;20 mug/kg) to female rats of the Maudsley Reactive (MR) strain increased open-field activity and decreased open-field defecation. In addition, ovariectomy increased open-field defecation in MR females. Supporting the generality of these findings, hormone administration reduced open-field defecation and increased open-field activity in intact females of a genetically heterogeneous background. Additional studies suggested that the decrease in open-field defecation at estrus is dependent on estrogenic suppression of food intake. Hormone replacement decreased food intake in the period preceding the open-field test, and colonic contents were also lower in rats treated with EB+P (progesterone) immediately after the completion of the open-field test. These changes were seen in both MR and genetically heterogeneous females. It was concluded that the decrease in open-field defecation at estrus may be mediated by a reduction in food intake and a consequent decrease in colonic contents and that the validity of the defecation response as a measure of emotionality may be seriously questioned under these circumstances.

Animals↗
PubMed1975

Early life undernutrition and aggression in two mouse strains.

Early undernutrition was shown to be correlated with increased aggression in adult mice after isolation. This was significant in numbers of fights and shorter latency to fight in the DBA/2J strain. Lower 5HIAA in the brain after pretreatment with a monoamine oxidase inhibitor was found in the undernourished group.

Aggression↗
PubMed1975

Head mount for the control of infusion in freely moving animals.

The construction of a light weight head mount for the control of infusion in small laboratory animals is described. The head mount reduces restraint of the animal and includes a valve to seal the cannula so that the animal may be disconnected from the infusion system.

Animals↗
PubMed1975

Visceral responses to opposite types of autogenic-training imagery.

The purpose of this experiment was to test whether suggestions of imagery of the type used in autogenic training have specific effects on autonomic responses. In order to control for the effort involved in imagery and to determine the specificity of the effect, opposite types of imagery were used: (a) hands warm and heavy, and (b) hands cool and light. Nine subjects were trained for six daily sessions. Within each day 16 stimulus presentations were made, equally balanced between the two types of imagery. Heart rate, respiration rate, and EEG in the alpha frequency were recorded throughout all sessions. The 'cool' instruction reliably increased heart rate and respiration above pre-stimulus baselines; the 'warm' instruction resulted in statistically insignificant changes in the opposite direction. Large, consistent individual differences in autonomic response were found.

Adolescent↗