David M. Knight

Identification of an immune-responsive mesolimbocortical serotonergic system: Potential role in regulation of emotional behavior

Peripheral immune activation can have profound physiological and behavioral effects including induction of fever and sickness behavior. One mechanism through which immune activation or immunomodulation may affect physiology and behavior is via actions on brainstem neuromodulatory systems, such as serotonergic systems. We have found that peripheral immune activation with antigens derived from the nonpathogenic, saprophytic bacterium, Mycobacterium vaccae, activated a specific subset of serotonergic neurons in the interfascicular part of the dorsal raphe nucleus (DRI) of mice, as measured by quantification of c-Fos expression following intratracheal (12 h) or s.c. (6 h) administration of heat-killed, ultrasonically disrupted M. vaccae, or heat-killed, intact M. vaccae, respectively. These effects were apparent after immune activation by M. vaccae or its components but not by ovalbumin, which induces a qualitatively different immune response. The effects of immune activation were associated with increases in serotonin metabolism within the ventromedial prefrontal cortex, consistent with an effect of immune activation on mesolimbocortical serotonergic systems. The effects of M. vaccae administration on serotonergic systems were temporally associated with reductions in immobility in the forced swim test, consistent with the hypothesis that the stimulation of mesolimbocortical serotonergic systems by peripheral immune activation alters stress-related emotional behavior. These findings suggest that the immune-responsive subpopulation of serotonergic neurons in the DRI is likely to play an important role in the neural mechanisms underlying regulation of the physiological and pathophysiological responses to both acute and chronic immune activation, including regulation of mood during health and disease states. Together with previous studies, these findings also raise the possibility that immune stimulation activates a functionally and anatomically distinct subset of serotonergic neurons, different from the subset of serotonergic neurons activated by anxiogenic stimuli or uncontrollable stressors. Consequently, selective activation of specific subsets of serotonergic neurons may have distinct behavioral outcomes.

The HSP90 molecular chaperone cycle regulates cyclical transcriptional dynamics of the glucocorticoid receptor and its coregulatory molecules CBP/p300 during ultradian ligand treatment.

HSP90 regulates cyclical glucocorticoid receptor activity, cofactor recruitment, histone acetylation and transcriptional pulsing at the Period 1 promoter in response to ultradian glucocorticoid exposure.

Blockade of the V1b receptor reduces ACTH, but not corticosterone secretion induced by stress without affecting basal hypothalamic–pituitary–adrenal axis activity

Vasopressin (AVP), produced in parvocellular neurons of the hypothalamic paraventricular nucleus, regulates, together with CRH, pituitary ACTH secretion. The pituitary actions of AVP are mediated through the G protein receptor V(1b) (V(1b)|R). In man, hyperactivity of the hypothalamic-pituitary-adrenal axis has been associated with depression and other stress-related conditions. There are also clinical data suggesting a role for AVP in the dysfunctional HPA axis described in some depressed patients. In this study, we have investigated the effect of a recently synthesised selective antagonist of the V(1b)R both on exogenous AVP-induced ACTH and corticosterone secretion, and on basal and stress-induced pituitary-adrenal activity. Adult male Sprague-Dawley rats treated with the V(1b)R antagonist (Org, 30 mg/kg, s.c.) or vehicle (5% mulgofen in 0.9% saline, 2 ml/kg, s.c.). We found that blockade of the V(1b)R reduced the increase in both ACTH and corticosterone secretion induced by AVP (100 ng, i.v.). The same treatment had no effect either on basal ACTH and corticosterone levels or on the ultradian or diurnal rhythms of corticosterone secretion. Acute administration of the V(1b)R antagonist reduced ACTH secretion following both restraint and lipopolysaccharide, but did not antagonise the ACTH response to noise. The same treatment did not reduce corticosterone secretion in response to any of the three stressors used in this study. Our results confirm that this compound is an antagonist of the V(1b)R in the rat, and that its ability to reduce stress-induced ACTH responses is stressor dependent with differential modulation of pituitary and adrenal responses.

Hormonal Control of Adipocyte Differentiation and Adipocyte Gene Expression

Publisher Summary This chapter presents a summarization of a large number of studies aimed at elucidating the signaling system by which determined cells decide to activate a terminal differentiation program. Using adipogenic cells in culture, it can be documented that the hormonal milieu plays a major role in dictating the decision to trigger differentiation. The effects of indomethacin suggest that the products of arachidonic acid may play a key role in the regulation of cell differentiation. Inhibition of protein kinase C activity is important for triggering differentiation as its activation by phorbol esters or certain growth factors inhibit expression of the differentiated phenotype. The phorbol ester and the growth factor repressible clone 5 gene play an important role in defining the biochemical state associated with the potential for differentiation; in particular, suppression of clone 5 gene expression appears to correlate with entry of cells into a nonproliferative state within the G1 portion of the cell cycle in which cells are incapable of differentiating.

Reduced prostacyclin and increased leukotriene B4 synthesis in porcine venous-arterial grafts

BACKGROUND Migration and proliferation of vascular smooth muscle cells in the intima and superimposed atheroma are the main changes underlying late failure of saphenous vein bypass grafts. There is evidence that these events are partly modulated by complex interactions between inhibitors of vascular smooth muscle cell proliferation, such as prostacyclin (PGI2), and mitogens, such as leukotriene B4 (LTB4). Because the relative balance between these eicosanoids may play a role in vein graft failure, the synthesis of PGI2 and LTB4 was measured in porcine saphenous vein-carotid artery grafts 4 weeks after implantation and compared with ungrafted vein and common carotid artery from the same animal. METHODS Vessels were cut into 2-mm squares and preincubated in Dulbeccos minimum essential medium for 4 hours at 37 degrees C. Tissues were then further incubated with Dulbeccos minimum essential medium containing a range of concentrations of noradrenaline, arachidonate, and calcium ionophore A23187. Release of PGI2 and LTB4 into the supernatant was then assessed by radioimmunoassay. RESULTS In response to all stimulators, PGI2 release was markedly diminished in vein grafts compared with ungrafted saphenous veins and carotid arteries. The patterns of responses were similar in each vessel type. In contrast, LTB4 release was significantly enhanced in vein grafts compared to ungrafted saphenous veins and carotid arteries. CONCLUSIONS These data indicate that there is a down-regulation of cyclooxygenase or PGI2 synthase in porcine vein grafts, which may constitute a further phenotypic change that would augment the hyperplastic process. Local increases in LTB4 synthesis in the vein graft, which indicates an induction of lipoxygenase and LTB4 synthase enzymes (and possibly reflects release from leukocytes which have infiltrated the graft), may contribute to increased intimal proliferation by direct promitogenic effects on smooth muscle cells.

The anxiogenic drug FG-7142 increases serotonin metabolism in the rat medial prefrontal cortex

The neural mechanisms underlying anxiety states are believed to involve interactions among forebrain limbic circuits and brainstem serotonergic systems. Consistent with this hypothesis, FG-7142, a partial inverse agonist at the benzodiazepine allosteric site of the GABAA receptor, increases c-Fos expression within a subpopulation of brainstem serotonergic neurons. Paradoxically, FG-7142 has no effect on extracellular serotonin concentrations, as measured using in vivo microdialysis, in certain anxiety-related brain structures. This study tested the hypothesis that FG-7142 alters serotonin metabolism within one or more nodes of a defined anxiety-related forebrain circuit. Rats received one of four treatments (vehicle, 1.9, 3.8, or 7.5 mg/kg FG-7142, i.p.) and brains were collected 1 h following treatment. Thirteen forebrain regions were microdissected and analyzed for l-tryptophan, serotonin, and 5-hydroxyindoleacetic acid concentrations using high pressure liquid chromatography with electrochemical detection. FG-7142 (7.5 mg/kg) increased l-tryptophan, serotonin, and 5-hydroxyindoleacetic acid concentrations in the prelimbic cortex but not in several other regions studied including subdivisions of the amygdala and bed nucleus of the stria terminalis. These data demonstrate that FG-7142 alters brain tryptophan concentrations and serotonin metabolism in specific components of an anxiety-related forebrain circuit including the medial prefrontal cortex, an important structure involved in executive function and the regulation of emotional behavior.

Differential effect of glucocorticoid receptor antagonists on glucocorticoid receptor nuclear translocation and DNA binding

The effects of RU486 and S-P, a more selective glucocorticoid receptor antagonist from Schering-Plough, were investigated on glucocorticoid receptor nuclear translocation and DNA binding. In the in vitro study, AtT20 cells were treated with vehicle or with RU486, S-P or corticosterone (3–300 nM) or co-treated with vehicle or glucocorticoid receptor antagonists (3–300 nM) and 30 nM corticosterone. Both glucocorticoid receptor antagonists induced glucocorticoid receptor nuclear translocation but only RU486 induced DNA binding. RU486 potentiated the effect of corticosterone on glucocorticoid receptor nuclear translocation and DNA binding, S-P inhibited corticosterone-induced glucocorticoid receptor nuclear translocation, but not glucocorticoid receptor-DNA binding. In the in vivo study, adrenalectomized rats were treated with vehicle, RU486 (20 mg/kg) and S-P (50 mg/kg) alone or in combination with corticosterone (3 mg/kg). RU486 induced glucocorticoid receptor nuclear translocation in the pituitary, hippocampus and prefrontal cortex and glucocorticoid receptor-DNA binding in the hippocampus, whereas no effect of S-P on glucocorticoid receptor nuclear translocation or DNA binding was observed in any of the areas analysed. These findings reveal differential effects of RU486 and S-P on areas involved in regulation of hypothalamic–pituitary–adrenal axis activity in vivo and they are important in light of the potential use of this class of compounds in the treatment of disorders associated with hyperactivity of the hypothalamic–pituitary–adrenal axis.