Sex differences in the regulation of brain IL-1ß in response to chronic stress.

Elevations in brain interleukin-1 beta (IL-1ß) during chronic stress exposure have been implicated in behavioral and cognitive impairments associated with depression and anxiety. Two critical regulators of brain IL-1ß production during times of stress are glucocorticoids and catecholamines. These hormones work in opposition to one another to inhibit (via glucocorticoid receptors) or stimulate (via beta-adrenergic receptors: ß-AR) IL-1ß production. While chronic stress often heightens both corticosterone and catecholamine levels, it remains unknown as to how chronic stress may affect the "yin-yang" balance between adrenergic stimulation and glucocorticoid suppression of brain IL-1ß. To investigate this further, male and female rats underwent 4 days of stress exposure or served as non-stressed controls. On day 5, animals were administered propranolol (ß-AR antagonist), metyrapone (a glucocorticoid synthesis inhibitor), vehicle, or both drugs and brain IL-1ß mRNA was measured by rtPCR in limbic brain areas. In males, administration of propranolol had no effect on IL-1ß expression in non-stressed controls but significantly reduced IL-1ß in the hippocampus and amygdala of chronically stressed animals. In females, propranolol significantly reduced IL-1ß in the amygdala and hypothalamus of both control and stressed rats. In male rats, metyrapone treatment significantly increased IL-1ß mRNA regardless of stress treatment in all brain areas, while in female rats metyrapone only increased IL-1ß in the hypothalamus. Interestingly, propranolol treatment blocked the metyrapone-induced increase in brain IL-1ß indicating the increase in brain IL-1ß following metyrapone treatment was due to increase ß-AR activation. Additional studies revealed that metyrapone significantly increases norepinephrine turnover in the hypothalamus and medial prefrontal cortex in male rats and that microglia appear to be the cell type contributing to the production of IL-1ß. Overall, data reveal that stress exposure in male rats affects the regulation of brain IL-1ß by the norepinephrine-ß-AR pathway, while stress had no effect in the regulation of brain IL-1ß in female rats.

The endocannabinoid system modulates stress, emotionality, and inflammation.

The physiological and behavioral effects of stress are well characterized. Endocannabinoids are produced on demand and function to attenuate many of the physiological effects of the stress response. The endocannabinoid system is made up of cannabinoid receptors, the fatty acid signaling molecules that bind to and activate these receptors, and the enzymes that synthesize and catabolize these endocannabinoid signaling molecules. Cannabinoid research has recently grown substantially, due in no small part to the development of genetic research models as well as highly selective pharmaceutical tools. The purpose of this minireview is to discuss a subset of the many parallels between cannabinoid and behavioral neuroimmunology research, with specific discussion of interactions between the endocannabinoid system and psychological stress, emotionality, and inflammation.

Repeated stressor exposure regionally enhances beta-adrenergic receptor-mediated brain IL-1ß production.

It has been proposed that increased brain cytokines during repeated stressor exposure can contribute to neuropathological changes that lead to the onset of depression. Previous studies demonstrate that norepinephrine acting via beta-adrenergic receptors (ß-ARs) mediate brain IL-1 production during acute stressor exposure. The aim of the current studies was to examine how the regulation of brain cytokines by adrenergic signaling might change following repeated stressor exposure. Fischer rats were exposed to four days of chronic mild stress and 24h after the last stressors ß-AR expression, norepinephrine turnover, and ß-AR-mediated induction of brain IL-1 were measured in limbic areas (e.g. hypothalamus, hippocampus, amygdala, and prefrontal cortex) and brainstem. Repeated stressor exposure resulted in decreases in ß-AR expression (B(max)) measured by saturation binding curves in many limbic brain areas, while an increase was observed in the brainstem. This coincided with significant increases in norepinephrine turnover in the prefrontal cortex, hypothalamus, and amygdala, a significant increase in norepinephrine turnover was not observed in the hippocampus or brainstem. Stress increased overall IL-1 production in the amygdala (both basal and stimulated). While stress did not affect basal IL-1 levels in any other brain area, central administration of isoproterenol (a ß-AR agonist) augmented IL-1 production in the hypothalamus of stressed animals. These data indicate that repeated stressor exposure results in brain area specific enhancements in ß-AR-mediated IL-1 production and extends current knowledge of stress-induced enhancement of brain cytokine beyond sensitized response to immunological stimuli.