Rats exposed chronically (5–9 weeks) to a variety of mild unpredictable stressors showed a reduced consumption of and preference for saccharin or sucrose solutions. Preference deficits took at least 2 weeks to develop and were maintained for more than 2 weeks after termination of the stress regime. Sucrose preference was unaffected by 1 week of treatment with the tricyclic antidepressant DMI but returned to normal after 2–4 weeks of DMI treatment. DMI did not alter sucrose preference in unstressed animals. No significant changes were seen in saline preference either during stress or following drug treatment. DMI reduced blood corticosterone and glucose levels, but stress did not significantly alter either measure. The results are discussed in terms of an animal model of endogenous depression.

Reduction of sucrose preference by chronic unpredictable mild stress, and its restoration by a tricyclic antidepressant.

Falls in older people: risk factors and strategies for prevention.

Neuropsychopharmacological mechanisms of stimulant drug action in attention-deficit hyperactivity disorder: a review and integration

The concept of dominance is used in the behavioral and biological sciences to describe outcomes in a variety of competitive interactions. In some taxa, a history of agonistic encounters among individuals modifies the course of future agonistic encounters such that the existence of a certain type of relationship can be inferred. If one is to characterize such relationships as dominance, however, then they must be distinguished from other kinds of interaction patterns for which the term tends to be used, as well as from factors such as territoriality and "trained" winners and losers, which may also influence the expression of agonistic behavior. Operational definitions based on causal, functional, evolutionary, and ontogenetic considerations have been proposed. Reliability and validity problems have been discussed, but the dominance concept has proved useful despite methodological difficulties. The confusion of dominance relationships (which involve two or more individuals) with dominance ranks (which are assigned to a single individual) has obscured the possible evolutionary basis of dominance relationships. If benefits accrue to dominant members of pairs, then those attributes which allow an animal to establish dominance can be selected. Dominance per se and dominance ranks, on the other hand, cannot be genetically transmitted since they constitute relationships with other individuals rather than absolute attributes. Dominance rankings in particular may be useful for describing behavioral patterns within a group, but they may reflect our own ability to count rather than any important variable in social organization.

Dominance: The baby and the bathwater

Animal models of depression: an overview.

Technique for producing and measuring territorial aggression using laboratory mice.

Using a chronic stress model of depression, the biochemical, hormonal, and neurochemical effects of chronic stress were determined in male CD-1 mice. The effects of chronic administration of three tricyclic antidepressants (TCA): chlorimipramine, amitriptyline and desmethylimipramine, as well as fluoxetine, a specific serotonin uptake inhibitor, were also evaluated. Exposure to acute noise/light stress dramatically increased motor activity (behavioral activation) in comparison with basal (unstressed) activity. However, animals with a history of chronic stress exhibited reduced basal activity levels as well as a decreased behavioral activation response to acute stress. There was also exaggerated corticosterone (CS) responding in both of these behavioral test situations attributable to prior chronic stress exposure. Chronic treatment with any of the TCAs significantly restored the behavioral activation response to acute stress and normalized CS responding in chronically stressed animals. Chronic fluoxetine treatment was ineffective. In chronically stressed, but behaviorally untested (quiescent) mice, there were no changes in CS levels, but norepinephrine (NE) and 5-hydroxyindoleacetic acid (5-HIAA) levels were increased. However, chronically stressed mice tested for basal motor activity showed large NE decreases, while those receiving acute stress exposure prior to testing showed large NE decreases and further 5-HIAA increases. There were no alterations on neurochemical parameters due to any drug treatment which could be correlated with a possible mechanism for their efficacy, although evidence suggested NE involvement. It was further proposed that the chronic stress paradigm induced conditioned neuroendocrine and neurochemical responses.

Biochemical and behavioral correlates of chronic stress: effects of tricyclic antidepressants.

The effects of dietary supplements of L-tyrosine on aggressive behavior, locomotor activity, and brain neurochemical changes were assessed in young and aged mice following cold-swim stress. Male CF-1 mice, ages 3 months and 21 months, were maintained on a semi-synthetic basal diet for one week, pretested for aggressive behavior and locomotor activity, then switched to diets modified by the addition of tyrosine or casein (control). After one week on the diet supplements, half of the mice were stressed by cold water swim and all were again subjected to behavioral testing. Members of each group were sacrificed for analysis of amino acids and monoamines in brain tissue and corticosterones in blood. It was found that tyrosine supplementation induced a marked increase in aggressive behavior in young, nonstressed mice but not in aged mice. Stress decreased the aggressiveness of both young and aged mice, and tyrosine prevented this stress-induced decrease in both groups. Young mice exhibited no changes in locomotion as a function of stress or diet. However, tyrosine prevented decreases in locomotion observed on second testing of both stressed and nonstressed older mice. The effect of stress was to lower levels of brain norepinephrine (NE) and dopamine (DA) in both young and aged mice. Tyrosine supplementation increased brain tyrosine and DA in both groups. Brain serotonin levels were lower in the aged mice compared to the younger ones, and this was associated with relatively higher concentrations of 5-hydroxyindoleacetic acid. It appears that tyrosine supplementation was effective in reducing the effects of stress in the aged animals, possibly by virtue of its relationship to catecholamine metabolism.

Behavioral and neurochemical effects of dietary tyrosine in young and aged mice following cold-swim stress.

Maternal aggression in mice: Effects of treatments with PCPA, 5-HTP and 5-HT receptor antagonists

Dietary amino acid regimens designed to enhance catecholaminergic and serotonergic functioning were found to differentially affect territorial-induced attacks in mice. Male albino mice were maintained on a semi-synthetic 12% casein protein diet for 2 weeks, then switched to diets modified by the addition of a 4% L-amino acid supplement, or 4% casein (control). Measures of aggressive behavior and open-field locomotor activity were obtained before and after the dietary supplements were administered. Resident mice fed supplements of L-tyrosine displayed a marked increase in the number of attacks on intruders and shorter attack latencies, but their locomotor activity was unaffected. L-phenylalanine supplements alone or in combination with L-tyrosine reduced the latency to attack and increased motility but did not affect the number of attacks. As a whole, the group of animals fed L-tryptophan showed no changes in aggression or motility.

John B. Thurmond

Papers

Technique for producing and measuring territorial aggression using laboratory mice.

Biochemical and behavioral correlates of chronic stress: effects of tricyclic antidepressants.

Behavioral and neurochemical effects of dietary tyrosine in young and aged mice following cold-swim stress.

Maternal aggression in mice: Effects of treatments with PCPA, 5-HTP and 5-HT receptor antagonists

Effects of dietary tyrosine, phenylalanine, and tryptophan on aggression in mice.