Regulation of 5-HT receptors and the hypothalamic-pituitary-adrenal axis. Implications for the neurobiology of suicide

The molecular neurobiology of stress--evidence from genetic and epigenetic models

Knowledge of the genetic and molecular events underlying the neuroendocrine and behavioural sequelae of the response to stress has advanced rapidly over recent years. The response of an individual to a stressful experience is a polygenic trait, but also involves non-genetic sources of variance. Using a combination of top-down (quantitative trait locus [QTL] and microarray analysis) and bottom-up (gene targeting, transgenesis, antisense technology and random mutagenesis) strategies, we are beginning to dissect the molecular players in the mediation of the stress response. Given the wealth of the data obtained from mouse mutants, this review will primarily focus on the contributions made by transgenesis and knockout studies, but the relative contribution of QTL studies and microarray studies will also be briefly addressed. From these studies it is evident that several neuroendocrine and behavioural alterations induced by stress can be modelled in mouse mutants with alterations in hypothalamic-pituitary-adrenal axis activity or other, extrahypothalamic, neurotransmitter systems known to be involved in the stress response. The relative contribution of these models to understanding the stress response and their limitations will be discussed.

Ketanserin attenuates the behavioural effects of corticosterone: implications for 5-HT(2A) receptor regulation

The effects of chronic corticosterone treatment on sexual behaviour and wet-dog shakes were investigated in both female and male rats. The serotonergic type 2A (5-HT(2A)) receptor antagonist ketanserin was administered to test the hypothesis that the behavioural effects of corticosterone were mediated by increased 5-HT(2A) receptor activity. Rats were randomly assigned to one of four chronic treatment groups: control, ketanserin alone, corticosterone alone, or ketanserin and corticosterone. Ketanserin attenuated the corticosterone-induced changes in both sexual behaviour and wet-dog shakes. Ketanserin alone had no effect on these behaviours. Results suggest that increased 5-HT(2A) receptor activity mediates the effects of corticosterone on sexual behaviour and wet-dog shakes.

Altered response to meta-chlorophenylpiperazine in anorexia nervosa: support for a persistent alteration of serotonin activity after short-term weight restoration

OBJECTIVE

Patients with anorexia nervosa (AN) have disturbances of appetite and behaviors, such as dysphoria, inhibition, and obsessions, that could be related to altered serotonin activity. To investigate such relationships, we administered meta-chlorophenylpiperazine (m-CPP), a relatively serotonin-specific drug.

METHODS

To avoid the confounding effects of malnutrition or weight loss, we studied 12 patients with restricting-type AN between 5 and 17 days after a return to a normal weight and while on a stable dietary intake. We compared them to 12 healthy control women (CW). m-CPP was administered double blind and placebo controlled.

RESULTS

Although weight restored, AN women had lower body weight and increased ratings for depression and obsessionality compared with CW. After m-CPP, AN women had an elevation in mood and a reduction in body image distortion when compared with placebo. After m-CPP, groups had similar cortisol, adrenocorticotropin (ACTH), and growth hormone responses whereas AN women had an uncertain reduction in prolactin response.

DISCUSSION

These data support other studies that suggest that altered serotonin activity persists after weight restoration in AN patients. The finding that m-CPP temporarily improved mood and reduced body image distortions supports the hypothesis that altered serotonin activity may contribute to the pathophysiology of AN.

Immediate and longterm effects of immune stimulation: hypothesis linking the immune response to subsequent physical and psychological wellbeing

We hypothesize that antigenic stimuli in susceptible persons during key developmental life stages alters neuroendocrine-immune organization and leads to the development of aberrant immune and neuroendocrine responses to subsequent environmental stressors, with longterm physical and psychological consequences. The release of interleukin-1beta (IL-1beta) and other proinflammatory cytokines associated with the immune response during times when individuals are most vulnerable to the effects of environmental influences activates the hypothalamic-pituitary-adrenal (HPA) axis and leads to maladaptive responses to subsequent stressors. The primed HPA axis is reactivated by proinflammatory cytokines, resulting in the secretion of corticotropin-releasing hormone (CRH) and cortisol, followed by physical and psychological effects that feedback on the HPA axis to produce an array of outcomes affecting general wellbeing. Through the release of histamine and other mediators and their effects on the mast cell-leukocyte cytokine cascade, immune stimuli in susceptible persons increase allergic inflammation and magnify stressors' effects through the release of HPA-axis-activating cytokines, such as IL-1beta, that drive the axis and reinforce the physiological and behavioral effects. Thus, specific proinflammatory cytokines and allergic reactions initiate, promote, and maintain immune-stimulus-associated HPA axis activity, and with CRH and cortisol, participate in a positive feedback loop, resulting in aberrant, maladaptive responses to physical or psychological stressors, with outcomes such as depression, hyperalgesia, and pain-related behavior.

Maternal deprivation regulates serotonin 1A and 2A receptors in the infant rat

Several studies have demonstrated that 5-HT1A and 5-HT2A receptors are altered in rat brain following chronic stress. While this is true in the adult animal, this may be different in the developing animal, which has a limited corticosterone response to acute challenges between days 3 and 14 of life.

METHODS

We investigated the effect of maternal deprivation on 5-HT2A and 5-HT1A receptor mRNA levels in the developing brain. In situ hybridization was used to quantify gene expression in rat pups at three ages: 6, 9, and 12 days old. In each age group, half were maternally deprived for 24 h and half were kept with their mothers. Maternally deprived animals showed elevated ACTH and corticosterone plasma levels when compared to NDEP animals, significantly elevated 5-HT1A mRNA levels in the CA1 hippocampal region and, significantly elevated 5-HT2A mRNA levels in the parietal cortex. No changes were observed in 5-HT1A or 5-HT-transporter mRNA levels in the dorsal raphe. Our results indicate that post-synaptic 5-HT receptors in the developing hippocampus and cortex are sensitive to maternal deprivation. Because hippocampal 5-HT1A gene expressions are known to decrease in the adult animal after chronic glucocorticoid elevation, this data also suggests that other mechanisms, perhaps central, predominate during development.

Cholesterol and triglyceride levels in the serum of muricidal male Wistar rats: indices of mitochondrial benzodiazepine receptors?

Cholesterol and triglyceride levels were studied in the serum of aggressive muricidal and non-muricidal male Wistar rats. The muricidal behavior was either spontaneous or induced by a long-term isolation or by adrenalectomy. Cholesterol levels were slightly higher in the whole population of muricidal rats; this was mainly observed in spontaneously and in adrenalectomized muricidal rats, as compared to non-muricidal rats of the same series. As regards triglyceride levels, they were significantly higher in the whole population of muricidal rats, mainly in isolation- and adrenalectomy-induced muricidal rats; the ratio of triglycerides to body weight was higher in the serum of muricidal rats of all series. The possible significance of these results is discussed in light of the data of the literature and related to the functional role of either mitochondrial benzodiazepine receptors or serotonin.

Neural circuits mediating stress

Stress has been linked to the pathophysiology and pathogenesis of mood and anxiety disorders. Over the past few years, our understanding of the brain and neuroendocrine circuits that are linked to the stress response have increased dramatically. This article reviews a series of animal and human studies aimed at understanding what are the pathways by which stress is perceived, processed, and transduced into a neuroendocrine response. We focus on the classic stress circuit: the limbic-hypothalamic-pituitary-adrenal (LHPA) axis. These studies indicate that the LHPA stress circuit is a complex system with multiple control mechanisms and that these mechanisms are altered in pathological states, such as chronic stress and depression. These studies also suggest that the interactions between the LHPA and other neurotransmitters, such as serotonin, may provide the neurobiological substrate by which stress may affect mood.

Seasonality in suicides: the influence of suicide method, gender and age on suicide distribution in Italy

In order to ascertain if and how age, gender and choice of lethal means influence the seasonal distribution of suicide in Italy, data concerning all suicides registered in Italy from 1984 to 1995 have been analyzed, taking these variables into account. In the age group 14-65 years and over a total of 31771 male suicides (mean yearly rate, 12.6 per 100000) and 11984 female suicides (mean yearly rate, 4.4 per 100000) have been identified in Italy during the study period. Suicides in the younger age ranges, both among males and females, show a less marked asymmetrical seasonal distribution than those in the older age groups. Only suicides committed by violent methods (ICD 953-958) show clear evidence of seasonality, with a peak in spring and a low in late autumn. Suicides committed by non-violent methods (950-952) follow no seasonal trend in either sex. Spectral analysis reveals a circannual rhythm for violent suicides (ICD 953-958) in both genders. For male non-violent suicides (ICD 950-952), a period with a frequency of 0.0833 (12 months) has been identified, but with a polarity opposite to that of male violent suicides. For female non-violent suicides, no period of frequency of 0.0833 could be identified, but, as for female violent suicides, a period with frequency close to 0.2500 (4 months) has been found. Changes in climate, then, correlate with the monthly distribution of violent and non-violent suicides in opposite ways: male violent suicides show a significant positive relationship with indicators of temperature and exposure to the sun, and a significant negative relationship with indicators of humidity and rainfall. Female suicides show less significant relationships with climate indicators. Work aimed at suicide prevention should therefore take into account the complex influence of seasonal climate both on human biological rhythms (particularly on 5-HT related functions and their actions on mood and impulsivity) and on sociorelational habits.