Stress control and human nutrition

Caffeine drinking potentiates cannabinoid transmission in the striatum: interaction with stress effects

Caffeine, the psychoactive ingredient of coffee and of many soft drinks, is frequently abused by humans especially during stressful live events. The endocannabinoid system is involved in the central effects of many psychoactive compounds and of stress. Whether caffeine alters the cannabinoid system and interferes with stress-induced synaptic alterations is however unknown. We have studied electrophysiologically the sensitivity of cannabinoid receptors modulating synaptic transmission in the striatum of mice exposed to caffeine in their drinking solution. Chronic caffeine assumption sensitized GABAergic synapses to the presynaptic effect of cannabinoid CB1 receptor stimulation by exo- and endocannabinoids. Caffeine was conversely unable to affect the sensitivity of cannabinoid receptors modulating glutamate transmission. The synaptic effects of caffeine were slowly reversible after its removal from the drinking solution. Furthermore, although exposure to caffeine for only 24h did not produce measurable changes of the sensitivity of cannabinoid CB1 receptors, it was able to contrast the down-regulation of CB1 receptor-mediated responses after social defeat stress. Our data suggest that the cannabinoid system is implicated in the psychoactive properties of caffeine and in the ability of caffeine to reduce the pathological consequences of stress.

Relationship between stress, eating behavior, and obesity

Stress is thought to influence human eating behavior and has been examined in animal and human studies. Our understanding of the stress-eating relation is confounded by limitations inherent in the study designs; however, we can make some tentative conclusions that support the notion that stress can influence eating patterns in humans. Stress appears to alter overall food intake in two ways, resulting in under- or overeating, which may be influenced by stressor severity. Chronic life stress seems to be associated with a greater preference for energy- and nutrient-dense foods, namely those that are high in sugar and fat. Evidence from longitudinal studies suggests that chronic life stress may be causally linked to weight gain, with a greater effect seen in men. Stress-induced eating may be one factor contributing to the development of obesity. Future studies that measure biological markers of stress will assist our understanding of the physiologic mechanism underlying the stress-eating relation and how stress might be linked to neurotransmitters and hormones that control appetite.

Efferent projection from the bed nucleus of the stria terminalis suppresses activity of taste-responsive neurons in the hamster parabrachial nuclei

Although the reciprocal projections between the bed nucleus of the stria terminalis (BNST) and the gustatory parabrachial nuclei (PbN) have been demonstrated neuroanatomically, there is no direct evidence showing that the projections from the PbN to the BNST carry taste information or that descending inputs from the BNST to the PbN modulate the activity of PbN gustatory neurons. A recent electrophysiological study has demonstrated that the BNST exerts modulatory influence on taste neurons in the nucleus of the solitary tract (NST), suggesting that the BNST may also modulate the activity of taste neurons in the PbN. In the present study, we recorded from 117 taste-responsive neurons in the PbN and examined their responsiveness to electrical stimulation of the BNST bilaterally. Thirteen neurons (11.1%) were antidromically invaded from the BNST, mostly from the ipsilateral side (12 cells), indicating that a subset of taste neurons in the PbN project their axons to the BNST. The BNST stimulation induced orthodromic responses on most of the PbN neurons: 115 out of 117 (98.3%), including all BNST projection units. This descending modulation on the PbN gustatory neurons was exclusively inhibitory. We also confirmed that activation of this efferent inhibitory projection from the BNST reduces taste responses of PbN neurons in all units tested. The BNST is part of the neural circuits that involve stress-associated feeding behavior. It is also known that brain stem gustatory nuclei, including the PbN, are associated with feeding behavior. Therefore, this neural substrate may be important in the stress-elicited alteration in ingestive behavior.

Aging, stress and the hippocampus

Functional loss often occurs in many body systems (e.g., endocrine, cognitive, motor) with the passage of years, but there is great individual variation in the degree of compromise shown. The current focus on brain aging will continue because demographic trends indicate that the average lifespan will show a continued increase. There is increasing emphasis on understanding how aging contributes to a decline in brain functions, cognition being a prime example. This is due in part to the fact that dementias and other losses in brain function that sometimes accompany aging cause an obvious decline in the quality of life and these deficits are of more concern as the number of elderly increase. Stress also is a ubiquitous aspect of life and there is now a greater interest in understanding the role of stress and the stress response in brain aging. The key role of the hippocampus and its related brain structures in cognition, as well as in the feedback control of the response to stress, have made this brain area a logical focus of investigation for those interested in the impact of stress on brain aging. Here, we describe how the hippocampus changes with age and we examine the idea that age-related changes in the secretion patterns of the hypothalamic-pituitary adrenal (HPA) axis can contribute to aging of this structure. We also examine the proposal that stress, perhaps due to compromised HPA axis function, can contribute to hippocampal aging through exposure to excessive levels of glucocorticoids. The aging hippocampus does not appear to suffer a generalized loss of cells or synapses, although atrophy of the structure may occur in humans. Thus, age-related cognitive impairments are likely related to other neurobiological alterations that could include changes in the signaling, information encoding, plasticity, electrophysiological or neurochemical properties of neurons or glia. Although excessive levels of glucocorticoids are able to interfere with cognition, as well as hippocampal neuronal integrity, and aging is sometimes accompanied by an increase in these steroids because of inadequate feedback control of the HPA axis, none of these are a foregone consequence of aging. The general preservation of cells and the plastic potential of the hippocampus provide a focus for the development of pharmacological, nutritive or lifestyle strategies to combat age-related declines in the hippocampus as well as other brain areas.