Cholesterol, serotonin, and behavior in young monkeys

High-fiber diet promotes weight loss and affects maternal behavior in vervet monkeys

The dramatic increase in obesity in western societies has shifted the emphasis in nutrition research from the problems of undernutrition to the adverse consequences of being overweight. As with humans, Old World monkeys are at increased risk for type II diabetes and other chronic diseases when they gain excessive weight. To prevent overweight and obesity, promote animal health, and provide a more natural level of fiber in the diet, the standard commercial monkey chow diet at a vervet monkey breeding colony was changed to a higher fiber formulation in 2004. The new diet was also higher in protein and lower in carbohydrate and energy density than the standard diet. Because maternal behavior is known to be sensitive to differences in resource availability, data on weight and mother-infant interactions for 147 mothers with 279 infants born from 2000 through 2006 were assessed for effects of the diet change. The results showed that, even though food was provided ad libitum, the mean body weight of breeding females was 10% lower after the transition to the high-fiber diet. Behaviorally, mothers on the high-fiber diet were significantly more rejecting to their infants, and their infants had to play a greater role in maintaining ventral contact in the first few months of their lives. The effects of the diet change on maternal rejection were significantly related to the mother's body weight, with lower-weight mothers scoring higher in maternal rejection. These results demonstrate that maternal behavior is responsive to changes in maternal condition, and that beneficial changes in the diet may have unintended consequences on behavior.

Serum lipid levels in seasonal affective disorder

Previous research has assessed the relationship between blood lipid levels and depression with contradictory results. Several studies have linked low cholesterol levels with impulsive, aggressive and suicidal behaviours. The aim of this pilot study was to examine serum lipids in a sample of patients suffering from seasonal affective disorder (SAD). We conducted a retrospective analysis of data on total serum cholesterol and serum triglycerides in 39 SAD patients and 40 non-seasonally depressed or schizophrenic control subjects. Study subjects had to be free of psychotropic drugs for at least 2 weeks. Analysis of covariance (ANCOVA) was performed to assess group differences. After adjustment for significant covariates SAD patients had significantly lower total cholesterol levels (5.21 +/- 1.14 mmol/l) than control subjects (5.94 +/- 1.11 mmol/l; p = 0.013). Moreover, hypercholesterolemia (total cholesterol > 5.20 mmol/l) was significantly less frequent in the SAD group (46.2%) than in the control group (75.0%; p = 0.012). Total serum triglycerides did not differ significantly between SAD patients (1.54 +/- 1.07 mmol/l) and controls (1.56 +/- 0.96 mmol/l; p = 0.126). The results of this study support the idea that low cholesterol levels may be of pathogenetic importance in SAD. Further study in larger clinical samples is warranted to clarify our findings.

Serum cholesterol concentrations and non-physical aggression in healthy adults

Although physical aggression in humans and other primates appears to be negatively associated with total serum cholesterol (TSC) concentrations, the relationship between other forms of aggression and TSC is less clear. A plurality of studies have reported a positive association, some have reported no association, and a minority have reported a negative association. Some authors have speculated that the variability in findings is attributable to inconsistencies in the definitions and measurement of what has often been termed "verbal" aggression. Buss and Perry have developed the Aggression Questionnaire, a theoretically-derived and empirically validated self-report measure of aggression that breaks aggression into subcomponents. One hundred and seventy-one college students and university personnel were recruited to participate in a cholesterol screening health initiative and then invited to participate in a study of mood and cholesterol. They completed a Demographic Questionnaire, and the Aggression Questionnaire. Regression analyses with age and Body Mass Index (BMI) as covariates revealed that anger, hostility, and verbal aggression significantly predicted TSC. Physical aggression did not. This finding suggests that non-physical forms of aggression may constitute a risk factor for coronary artery disease and one that may be worthy of targeting through behavioral interventions such as anger management training.

Tamoxifen fails to affect central serotonergic tone but increases indices of anxiety in female rhesus macaques

The selective estrogen receptor modulator (SERM), tamoxifen, effectively slows the progression of estrogen-positive breast cancer and aids in the prevention of cancer in at-risk women. Tamoxifen is well characterized with regards to its effects on breast cancer, but its effects on other estrogen-related systems, particularly neural circuits regulating brain function and mood, are poorly understood. Using ovariectomized rhesus monkeys, we examined the effects of tamoxifen, with and without estrogen replacement therapy (ERT), on social behavior and central serotonin (5HT) systems thought to influence these behaviors. Relative to placebo treatments, estrogen treatment increased serotonergic tone, based on response in prolactin and cortisol to fenfluramine, a 5HT releasing agent. Tamoxifen neither blocked nor enhanced this effect, indicating it to be neither an antagonist nor an agonist on serotonergic activity. In contrast, CSF measures of the 5HT metabolite, 5HIAA, were not significantly affected by treatment. Tamoxifen-treated animals showed increases in measures of anxiety, compared with ERT-treated animals, suggesting that this SERM may be anxiogenic. Co-treatment with estrogen attenuated the anxiogenic properties of tamoxifen. These data show that tamoxifen administration increased anxiety levels, but the affect was not associated with differences in central levels of the serotonin tone.

Hypocholesterolaemia in Dogs with Dominance Aggression

Serum lipids and lipoprotein concentrations have been associated with dominance aggression in humans. The aim of this study was to investigate the link between serum lipids, including cholesterol, triglyceride, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC) to HDL-C ratio and dominance aggression in dogs. Levels of serum TC, triglyceride and HDL-C were significantly lower in dogs with dominance aggression compared with non-aggressive dogs (P < 0.001). These results suggest that a relationship exists between serum lipid profile and dominance aggression in dogs, and hypocholesterolaemia exists in dogs with dominance aggression.

Understanding the neurobiology of suicidal behavior

Our current knowledge about the neurobiology of suicide is still limited. Technical limitations and the complexity of the CNS are major obstacles. However, there is evidence for a hereditary disposition to suicide, which appears to be independent of diagnosis. Clinical, postmortem, genetic, and animal studies suggest that serotonin has a central role. The main regions of interest in the CNS have been the dorsal and median raphe nuclei in the midbrain that host the main serotonergic cell bodies and the prefrontal cortex, particularly the ventral PFC, innervated by the serotonergic system. In vivo and postmortem studies indicate serotonergic hypofunction in suicide and serious suicide attempts. This deficiency in turn can lead to a predisposition to impulsive and aggressive behavior, probably due to a breakdown in the inhibitory function of the ventral prefrontal cortex as a result of less serotonin input. In the context of this predisposition and the development of mental illness or other life stressors, the individual is at risk of acting on suicidal thoughts. Such deficient serotonin input into the PFC may arise as a result of genetic, parenting, head injury, and other effects. Identifying psychiatric, social, and environmental predictors of suicide are studied to improve prediction and prevention of suicide. A better understanding of the neurobiology of suicide can help detect at risk populations and help develop better treatment interventions.

Major trauma in elderly adults receiving lipid-lowering medications

BACKGROUND

Some clinical trials, laboratory experiments, and in vitro studies suggest that lipid-lowering medications predispose a person to traumatic injury.

METHODS

We used population-based administrative database analysis to study adults age 65 years or more over a 5-year interval (n = 1,348,259).

RESULTS

About 12% of the cohort received a prescription for a lipid-lowering medication and about 88% did not. The two groups had similar distributions of age, gender, and income. Overall, 2,557 (0.2%) were hospitalized for major trauma. Those who received a lipid-lowering medication were 39% less likely to sustain a major trauma than those who did not receive such medication (95% confidence interval, 29 to 47). Similar results were observed after adjustment for age, gender, and income; cardiac and neurologic medications; and lethality. No other cardiac or neurologic medication was associated with an apparent safety advantage.

CONCLUSION

Lipid-lowering medications do not lead to a clinically important increase in the absolute risk of major trauma for elderly patients in the community.

Serum cholesterol concentrations and mood states in violent psychiatric patients: an experience sampling study

The well-documented negative association between serum cholesterol and aggressive behavior has led Kaplan to propose a cholesterol-serotonin hypothesis of aggression. According to this hypothesis, low dietary cholesterol intake leads to depressed central serotonergic activity, which itself has been reported in numerous studies of violent individuals. In the present study, 25 violent psychiatric patients participated in a microbehavioral experience sampling procedure to examine differences in self-reports of affective and cognitive experiences as a function of serum cholesterol concentrations. For 7 days, they wore signaling devices that emitted an average of seven signals a day. Following each signal, patients filled out a mood questionnaire. Total serum cholesterol (TSC) concentration was positively associated with measures of affect, cognitive efficiency, activation, and sociability, suggesting a link between low TSC and dysphoria. These findings are consistent with the cholesterol-serotonin hypothesis and with the substantive literature linking both aggression and depression to depressed central serotonergic activity.

Higher prevalence of depressive symptoms in middle-aged men with low serum cholesterol levels

OBJECTIVE

Investigators from several studies have reported a positive relationship between low cholesterol levels and death due to violent causes (eg, suicide and accidents), possibly mediated by depressive symptoms, aggression or hostility, or impulsivity. We set out to establish whether middle-aged men with chronically low cholesterol levels (< or =4.5 mmol/liter) have a higher risk of having depressive symptoms, according to scores on the Beck Depression Inventory, compared with a reference group of men with cholesterol levels between 6 and 7 mmol/liter. A similar comparison was also made for measures of anger, hostility, and impulsivity.

METHODS

Cholesterol measurements were obtained as part of a population-based cholesterol screening study in 1990-1991. These levels were remeasured in 1993-1994. Only those whose cholesterol level remained in the same range were included in the study. Depressive symptoms were assessed by using the Beck Depression Inventory; anger, by questionnaires based on the Spielberger Anger Expression Scale and State-Trait Anger Scale; hostility, by the Buss-Durkee Hostility Inventory; and impulsivity, by the Eysenck and Eysenck Impulsivity Questionnaire.

RESULTS

Men with chronically low cholesterol levels showed a consistently higher risk of having depressive symptoms (Beck Depression Inventory score > or =15 or > or =17) than the reference group, even after adjusting for age, energy intake, alcohol use, and presence of chronic diseases. No differences in anger, hostility, and impulsivity were observed between the two groups.

CONCLUSIONS

Men with a lower cholesterol level (< or =4.5 mmol/liter) have a higher prevalence of depressive symptoms than those with a cholesterol level between 6 and 7 mmol/liter. These data may be important in the ongoing debate on the putative association between low cholesterol levels and violent death.