Carsten Riether

Acute amygdaloid response to systemic inflammation

The amygdala, a group of nuclei located in the medial temporal lobe, is a key limbic structure involved in mood regulation, associative learning, and modulation of cognitive functions. Functional neuroanatomical studies suggest that this brain region plays also an important role in the central integration of afferent signals from the peripheral immune system. In the present study, intracerebral electroencephalography and microdialysis were employed to investigate the electrophysiological and neurochemical consequences of systemic immune activation in the amygdala of freely moving rats. Intraperitoneal administration of bacterial lipopolysaccharide (100 μg/kg) induced with a latency of about 2 h a significant increase in amygdaloid neuronal activity and a substantial rise in extracellular noradrenaline levels. Activated neurons in the amygdaloid complex, identified by c-Fos immunohistochemistry, were mainly located in the central nucleus and, to a lesser extent, in the basolateral nucleus of the amygdala. Gene expression analysis in micropunches of the amygdala revealed that endotoxin administration induced a strong time-dependent increase in IL-1β, IL-6, and TNF-α mRNA levels indicating that these cytokines are de novo synthesized in the amygdala in response to peripheral immune activation. The changes in amygdaloid activity were timely related to an increase in anxiety-like behavior and decreased locomotor activity and exploration in the open-field. Taken together, these data give novel insights into different features of the acute amygdaloid response during experimental inflammation and provides further evidence that the amygdala integrates immune-derived information to coordinate behavioral and autonomic responses.

No Retrieval-Induced Forgetting Under Stress

Stress affects memory, yet no study has investigated the effects of stress on memory inhibition: Remembering not only facilitates later recall, but also inhibits retrieval of related material, a phenomenon known as retrieval-induced forgetting. We investigated the effects of stress on this mechanism, which is thought to adaptively guide memory selection. Participants learned categorized lists and were then exposed to either a psychosocial laboratory stressor or a cognitively challenging control treatment. They then actively retrieved parts of the previously learned material. Finally, memory for all initially learned items was tested. In the stress group, unlike in the control group, intervening retrieval practice did not impair final recall. Moreover, salivary Cortisol levels increased and psychological well-being decreased in the stress group only. Thus, psychosocial stress abolishes retrieval-induced forgetting. This effect may result from stress-induced hormone release from the hypothalamic-pituitary-adrenal (HPA) axis and may have implications for educational, legal, and clinical issues.

Time-dependent alterations of peripheral immune parameters after nigrostriatal dopamine depletion in a rat model of Parkinson's disease.

Dysfunction of the central dopaminergic system is associated with neurodegenerative disorders and mental illnesses such as Parkinsons disease and schizophrenia. Patients suffering from these diseases were reported to exhibit altered immune functions compared to healthy subjects and imbalance of the central dopaminergic system has been suggested as one causative factor for the immune disturbances. However, it is unclear whether the observed immune changes are primary or secondary to the disease. Here we demonstrate that central dopamine (DA) depletion in a rat model of Parkinsons disease induced transient changes in blood leukocyte distribution and cytokine production that were apparent until four weeks after bilateral intrastriatal administration of the neurotoxin 6-hydroxydopamine (6-OHDA). Eight weeks after treatment, no differences in blood immune parameters were anymore evident between neurotoxin-treated and control animals. Nevertheless, animals with a widespread damage of dopaminergic neurons in the nigrostriatal system showed an exacerbated pro-inflammatory response following in vivo challenge with bacterial lipopolysaccharide. Our data indicate that peripheral immune perturbations in the early phase after intrastriatal 6-OHDA administration might have been related to the neurodegenerative process itself whereas the increased sensitivity to the inflammatory stimulus seems to have resulted from an impaired dopaminergic control of prolactin (PRL) and corticosterone (CORT) secretion. The findings demonstrate that the brain dopaminergic system is involved in peripheral immune regulation and suggest that central dopaminergic hypoactivity bears the risk of excessive inflammation, e.g., during infection or tissue injury.

Victims of rape show increased cortisol responses to trauma reminders : a study in individuals with war- and torture-related PTSD

Studies investigating cortisol responses to trauma-related stressors in patients with posttraumatic stress disorder (PTSD) have yielded inconsistent results, demonstrating that cortisol responses were enhanced or unaffected when confronted with trauma reminders. This study investigated the effect of the type of trauma experienced on both salivary and plasma cortisol responses during confrontation with trauma-related material. Participants were 30 survivors of war and torture, with and without rape among the traumatic events experienced. Participants of both groups (raped vs. non-raped) fulfilled DSM-IV criteria of PTSD. Plasma and salivary cortisol levels were measured at three time points during a standardized clinical interview: once before and twice after assessing individual traumatic experiences. Results show that groups did not differ in basal plasma and salivary cortisol levels. However, differential salivary cortisol responses were observed in PTSD patients who had been raped compared to those who had not been raped (p<.05) but had experienced an equal number of traumatic events and showed equally high PTSD symptom severity. Whereas salivary cortisol levels decreased in the course of the interview for the group with no past experience of rape (p<.05), those PTSD patients who had been raped showed a significant cortisol increase when reminded of their traumatic events (p<.001). This effect was not found in plasma cortisol. Our results indicate that the type of traumatic stress experienced contributes to cortisol responses during the confrontation with trauma-related material. We hypothesize, that the nearness of the perpetrator during the traumatic event might shape later psychophysiological responding to trauma reminders.

Stimulation of β2-adrenergic receptors inhibits calcineurin activity in CD4+ T cells via PKA–AKAP interaction

The sympathetic nervous system (SNS) is able to modulate immune functions via adrenoceptor-dependent mechanisms. Activation of β₂-adrenergic receptors (AR) on CD4(+) T lymphocytes has been shown to inhibit Th1-cytokine production and cell proliferation. Here, we investigated the role of the calcium/calmodulin-dependent protein phosphatase calcineurin (CaN), a key element of the T cell receptor (TCR)-signaling pathway, in β₂-AR-mediated suppression of T cell function. Purified rat splenic CD4(+) T cells were stimulated with anti-CD3/anti-CD28 in presence or absence of the β₂-AR agonist terbutaline (TERB). Treatment with TERB induced a dose-dependent inhibition of cellular CaN activity, along with a reduction in IL-2 and IFN-γ production, and T cell proliferation. Co-administration of the β-AR antagonist nadolol abolished these effects. Blockade of the cAMP-dependent protein kinase A (PKA) with the inhibitor H-89 completely prevented TERB-induced CaN inhibition. However, a receptor-independent rise in the second messenger cAMP was not sufficient to suppress CaN activity. Disruption of the interaction between PKA and A-kinase anchoring protein (AKAP) by the inhibitor peptide St-Ht31 fully blocked TERB-induced CaN inhibition, demonstrating that PKA-AKAP interaction is essential for the β₂-AR-mediated CaN inhibition. Taken together, this study provides evidence for a link between the β₂-AR and TCR signaling pathways since expression of IL-2 and IFN-γ in activated T cells largely depends on dephosphorylation of the transcription factor NFAT by CaN, and identifies a novel intracellular mechanism that can lead to downregulation of T cell function after SNS activation.

Calcineurin inhibition in splenocytes induced by pavlovian conditioning

Pavlovian conditioning is one of the major neurobiological mechanisms of placebo effects, potentially influencing the course of specific diseases and the response to a pharmacological therapy, such as immunosuppression. In our study with behaviorally conditioned rats, a relevant taste (0.2% saccharin) preceded the application of the immunosuppressive drug cyclosporin A (CsA), a specific calcineurin (CaN) inhibitor. Our results demonstrate that through pavlovian conditioning the particular pharmacological properties of CsA can be transferred to a neutral taste, i.e., CaN activity was inhibited in splenocytes from conditioned rats after reexposure to the gustatory stimulus. Concomitant immune consequences were observed on ex vivo mitogenic challenge (anti‐CD3). Particularly, Th1‐cytokine, but not Th2‐cytokine, production and cell proliferation were impeded. Appropriate pharmacological and behavioral controls certify that all these changes in T‐lymphocyte reactivity are attributable to mere taste reexposure. Furthermore, the underlying sympathetic‐lymphocyte interaction was revealed modeling the conditioned response in vitro. CaN activity in CD4+ T lymphocytes is reduced by β‐adrenergic stimulation (terbutaline), with these effects antagonized by the β ‐adrenoreceptor antagonist nadolol. In summary, CaN was identified as the intracellular target for inducing conditioned immunosuppression by CsA, contributing to our understanding of the intracellular mechanisms behind “learned placebo effects.”—Pacheco‐López, G., Riether, C., Doenlen, R., Engler, H., Niemi, M.‐B., Engler, A., Kavelaars, A., Heijnen, C. J., Schedlowski, M. Calcineurin inhibition in splenocytes induced by pavlovian conditioning. FASEB J. 23, 1161–1167 (2009)

Electrical activity in rat cortico-limbic structures after single or repeated administration of lipopolysaccharide or staphylococcal enterotoxin B.

Immune-to-brain communication is essential for an individual to aptly respond to challenging internal and external environments. However, the specificity by which the central nervous system detects or ‘senses’ peripheral immune challenges is still poorly understood. In contrast to post-mortem c-Fos mapping, we recorded neural activity in vivo in two specific cortico-limbic regions relevant for processing visceral inputs and associating it with other sensory signalling, the amygdala (Am) and the insular cortex (IC). Adult rats were implanted with deep-brain monopolar electrodes and electrical activity was monitored unilaterally before and after administration of two different immunogens, the T-cell-independent antigen lipopolysaccharide (LPS) or the T-cell-dependent antigen staphylococcal enterotoxin B (SEB). In addition, the neural activity of the same individuals was analysed after single as well as repeated antigen administration, the latter inducing attenuation of the immune response. Body temperature and circulating cytokine levels confirmed the biological activity of the antigens and the success of immunization and desensitization protocols. More importantly, the present data demonstrate that neural activity of the Am and IC is not only specific for the type of immune challenge (LPS versus SEB) but seems to be also sensitive to the different immune state (naive versus desensitization). This indicates that the forebrain expresses specific patterns of electrical activity related to the type of peripheral immune activation as well as to the intensity of the stimulation, substantiating associative learning paradigms employing antigens as unconditioned stimuli. Overall, our data support the view of an intensive immune-to-brain communication, which may have evolved to achieve the complex energetic balance necessary for mounting effective immunity and improved individual adaptability by cognitive functions.

Attenuation of the cytotoxic T lymphocyte response to lymphocytic choriomeningitis virus in mice subjected to chronic social stress.

Chronic stress is suspected to increase the susceptibility to infections but experimental evidence from physiological stress models is scarce. We examined the effects of chronic social stress on virus-specific CTL responses in mice after infection with lymphocytic choriomeningitis virus (LCMV). Mice subjected to social stress on six consecutive days prior to infection showed a significant reduction of IFN-γ producing T(CD8+) splenocytes and markedly lowered plasma concentrations of IFN-γ. In contrast, the generation of LCMV-specific CTL responses was not altered in mice undergoing the same stress procedure concurrently with infection. Furthermore, stress exposure 6 days before and additional 3 days after LCMV infection profoundly reduced the expansion of T(CD8+) cells in the spleen, due to diminished in vivo proliferation. Pharmacological blockade of glucocorticoid receptors completely abrogated the stress-associated decline of T(CD8+) expansion. Stressed mice showed a significantly reduced expression of the early T-cell activation marker CD69 as well as impaired in vitro cytokine secretion of IFN-γ and IL-2. Additionally, social stress led to an altered migration capacity of T(CD8+) cells as demonstrated by adoptive T cell transfer experiments. Taken together, this study shows that chronic social stress fundamentally suppresses the functional capacities of T cells during a viral infection.

Weaken taste-LPS association during endotoxin tolerance

In naive individuals, the administration of bacterial lipopolysaccharide (LPS) provokes a rapid systemic increase in pro-inflammatory cytokines such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-6, inducing an acute phase response including sickness behavior. Strong associative learning occurs when relevant gustatory/olfactory stimuli precede the activation of the immune system, affecting long-term individual food selection and nutritional strategies. Repeated LPS administration results in the development of an endotoxin tolerance status, characterized by a drastic reduction in the LPS-induced cytokine response. Here we investigated how the postprandial categorization of a relevant taste (0.2% saccharin) changed after administration of a high dose of LPS (0.5 mg/kg i.p.) in LPS-tolerant animals. Determination of the consummatory fluid intake revealed that, in contrast to LPS-naive rats, taste-LPS association did not occur during endotoxin tolerance. Ninety minutes after the single association trial, the plasma responses of TNF-alpha, IL-1beta and IL-6 were completely blunted in LPS-tolerant animals, which also resulted in low LPS-adipsogenic and LPS-anorexic effects. These findings indicate that an identical immune challenge can result in completely different neuro-behavioral consequences depending on the immune history of the individual, thus revealing part of the complex interconnection between the immune and neuro-endocrine systems in regulating food selection and consumption during the infectious process.

34. Beta-adrenoceptor stimulation inhibits calcineurin in CD4+ T lymphocytes via a PKA-dependent pathway

and has the potential to cause complicating side effects such as severe infection. To avoid this problem it is important to understand how B cells might be regulated to influence the course of disease more specifically. A known regulator of B cell function is the sympathetic nervous system (SNS), but recent studies also showed a clear influence of the SNS on the experimental arthritis. Therefore, it was hypothesized that the SNS acts via regulating B cell function to modulate the development and severity of arthritis. We show that the SNS has the potential to support the generation of B cells that possess regulatory potential in collagen induced arthritis (CIA): (1) We activated B cells with anti-CD40 (1 mg/ml)/IL-4 (1 ng/ml) in the presence or absence of norepinephrine (10-6 M), and adoptively transferred 3 Mio. of these cells in arthritic DBA1J mice. Compared to arthritic mice that received PBS, mice that received B cells developed a less severe arthritis per se, however, this effect was significantly more pronounced when B cells activated in the presence of norepinephrine were used for treatment. (2) We induced arthritis in sympathectomized mice and control mice. At day 28 after induction of arthritis, we exchanged splenic B cells between the groups by adoptive transfer. Per se, sympathectomized mice developed more severe arthritis after splenectomy than control mice. However, transferring B cells from the sympathectomized mice into control mice, and vice versa, also changed the course of disease, respectively. Both findings support a role of the SNS in generating B cells that possess regulatory potential in arthritis.