Johannes Wildmann

K-ATP channels promote the differential degeneration of dopaminergic midbrain neurons

The selective degeneration of dopaminergic (DA) midbrain neurons in the substantia nigra (SN) is a hallmark of Parkinson disease. DA neurons in the neighboring ventral tegmental area (VTA) are significantly less affected. The mechanisms for this differential vulnerability of DA neurons are unknown. We identified selective activation of ATP-sensitive potassium (K-ATP) channels as a potential mechanism. We show that in response to parkinsonism-inducing toxins, electrophysiological activity of SN DA neurons, but not VTA DA neurons, is lost owing to activation of K-ATP channels. This selective K-ATP channel activation is controlled by differences in mitochondrial uncoupling between SN and VTA DA neurons. Genetic inactivation of the K-ATP channel pore-forming subunit Kir6.2 resulted in a selective rescue of SN but not VTA DA neurons in two mechanistically distinct mouse models of dopaminergic degeneration, the neurotoxicological 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model and the mutant weaver mouse. Thus, K-ATP channel activation has an unexpected role in promoting death of DA neurons in chronic disease.

Chronic neuropathic pain-like behavior correlates with IL-1β expression and disrupts cytokine interactions in the hippocampus.

Summary IL‐1β expression in the contralateral hippocampus coincides with neuropathic pain behavior in rats, and the correlations between hippocampal IL‐1β and IL‐1ra or IL‐6 are lost. ABSTRACT We have proposed that neuropathic pain engages emotional learning, suggesting the involvement of the hippocampus. Because cytokines in the periphery contribute to induction and maintenance of neuropathic pain but might also participate centrally, we used 2 neuropathic pain models, chronic constriction injury (CCI) and spared nerve injury (SNI), to investigate the temporal profile of hippocampal cytokine gene expression in 2 rat strains that show different postinjury behavioral threshold sensitivities. SNI induced long‐lasting allodynia in both strains, while CCI induced allodynia with time‐dependent recovery in Sprague Dawley (SD) and no allodynia in Wistar Kyoto (WK) rats. In WK rats, only SNI induced sustained upregulation of hippocampal interleukin (IL)‐1β, while IL‐6 expression was transiently increased and no significant changes in IL‐1ra expression were detected. Conversely, in SD rats, SNI resulted in sustained and robust increased hippocampal IL‐1β expression, which was only transient in rats with CCI. In this strain, IL‐6 expression was not affected in any of the 2 injury models and IL‐1ra expression was significantly increased in rats with SNI or CCI at late phases. We found that the degree and development of neuropathic pain depend on the specific nerve injury model and rat strain; that hippocampal IL‐1β mRNA levels correlate with neuropathic pain behavior; that, in contrast to sham‐operated animals, there are no correlations between hippocampal IL‐1β and IL‐1ra or IL‐6 in neuropathic rats; and that alterations in cytokine expression are restricted to the hippocampus contralateral to the injury side, again implying that the observed changes reflect nociception.

Disrupted brain-immune system-joint communication during experimental arthritis.

OBJECTIVE To explore the hypothesis that, in parallel with alterations in the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system, hypothalamic cytokine expression and monoaminergic neurotransmitter concentrations are affected during the course of arthritis development induced by type II collagen. This hypothesis was based on evidence that acute inflammatory processes induce cytokine expression in the brain and affect neuronal activity. We also studied whether depletion of hypothalamic noradrenaline can affect peripheral joint disease. METHODS Hypothalamic cytokine gene expression and neurotransmitter concentration, parameters of inflammation, and joint innervation were evaluated during arthritis development in rats induced by injection of type II collagen in Freunds incomplete adjuvant. Noradrenergic neurons in the brain were depleted with 6-hydroxydopamine. RESULTS Transiently increased corticosterone levels, followed by increased adrenaline levels and hypothalamic interleukin-1beta (IL-1beta) and IL-6 overexpression were observed only during the induction phase of the disease. Hypothalamic noradrenaline content was increased during the symptomatic phase and was paralleled by a gradual loss of noradrenergic fibers in the joints. The positive correlation between hypothalamic IL-1beta expression and noradrenaline content in control groups was not observed in rats in which arthritis developed. Depletion of hypothalamic noradrenergic neurons when arthritis was established did not affect the course of the disease. CONCLUSION The dissociation between hypothalamic cytokine gene expression and noradrenergic neuronal activity, the lack of sustained stimulation of the stress axes, and the loss of sympathetic signals in the joints indicate a disruption in communication between afferent immune messages to the central nervous system and 2 main efferent antiinflammatory pathways under control of the brain during collagen-induced arthritis.

The sympathetic nervous system modulates CD4(+)Foxp3(+) regulatory T cells via noradrenaline-dependent apoptosis in a murine model of lymphoproliferative disease.

The sympathetic nervous system (SNS) plays a crucial role in the course and development of autoimmune disease in Fas-deficient lpr/lpr mice. As regulatory T cells (Tregs) are considered important modulators of autoimmune processes, we analyzed the interaction between the SNS and Tregs in this murine model of lymphoproliferative disease. We found that the percentage of Tregs among CD4(+) T cells is increased in the spleen, lymph nodes, and thymus of lpr/lpr mice as compared to age-matched C57Bl/6J (B6) mice. Furthermore, noradrenaline (NA), the main sympathetic neurotransmitter, induced apoptosis in B6- and lpr/lpr-derived Tregs. NA also reduced the frequency of Foxp3(+) cells and Foxp3 mRNA expression via β2-adrenoceptor (β2-AR)-mediated mechanisms in a concentration and time-dependent manner. Destruction of peripheral sympathetic nerves by 6-hydroxydopamine significantly increased the percentage of Tregs in B6 control mice to an extent comparable to aged-matched lpr/lpr mice. The concentration of splenic NA negatively correlated with the frequency of CD4(+)Foxp3(+) Tregs. Additionally, 60days after sympathectomy, a partial recovery of NA concentrations led to Treg percentages comparable to those of intact, vehicle-treated controls. Immunohistochemical analysis of the spleen revealed localization of single Foxp3(+) Tregs in proximity to NA-producing nerve fibers, providing an interface between Tregs and the SNS. Taken together, our data suggest a relation between the degree of splenic sympathetic innervation and the size of the Treg compartment. While there are few examples of endogenous substances capable of affecting Tregs, our results provide a possible explanation of how the magnitude of the Treg compartment in the spleen can be regulated by the SNS.

Re-exposure to endotoxin induces differential cytokine gene expression in the rat hypothalamus and spleen

This study was designed to investigate whether the pattern of hypothalamic and splenic cytokine expression induced by peripheral administration of a bacterial lipopolysaccharide (LPS) is affected by prior exposure to LPS derived from another bacterial strain. Injection of LPS from Salmonella enteritidis (LPS2) alone resulted in increased hypothalamic gene expression of IL-1β, IL-6, TNFα, IL-1ra and IL-10. However, pre-exposure to LPS derived from Escherichia coli (LPS1) 3 weeks before, significantly attenuated hypothalamic IL-1ra, IL-6 and IL-10 expression. IL-1β expression also tended to be lower. This pattern contrasted with the robust cytokine expression in the spleen of LPS2-treated rats previously exposed to LPS1, since pre-treatment with endotoxin resulted in a significantly greater response of IL-1β and IL-1ra to LPS2. Expression of TNFα and IL-10 also tended to be higher. Pre-treatment with LPS1 did not significantly affect the marked increase in corticosterone and adrenaline blood levels induced by LPS2. Thus, while endotoxin pre-exposure seemed not to induce a “tolerant” state in the periphery as judged by the immune and endocrine parameters evaluated upon re-stimulation, expression of four of the six cytokines measured was decreased in the hypothalamus. This is the first demonstration that endotoxin priming can differentially affect cytokine expression in the central nervous system and peripheral tissues when a host is confronted with a second, acute, pro-inflammatory stimulus. These results may provide new evidence for the involvement of cytokine pathways in the central nervous system in modulating peripheral inflammation and mediating cognitive and behavioural alterations during inflammatory diseases.

When Immune-Neuro-Endocrine Interactions Are Disrupted: Experimentally Induced Arthritis as an Example

We studied whether, in parallel to the activity of the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system, hypothalamic cytokine expression and monoaminergic neurotransmitter concentrations are affected during the development and chronification of arthritis induced by immunization of rats with type II collagen. Corticosterone levels were increased only transiently, and were even below the normal range as the disease progressed. Increased adrenaline blood levels and hypothalamic IL-1β and IL-6 overexpression were observed only during the induction phase of the disease. The increase in hypothalamic noradrenaline content during the symptomatic phase was paralleled by a gradual loss of sympathetic fibers in the joints. Depletion of hypothalamic noradrenergic neurons at this time did not affect the symptomatology. Contrary to observations in healthy animals, no correlation between hypothalamic IL-1β expression and noradrenaline content was observed in rats with arthritis. The dissociation between hypothalamic cytokine gene expression and noradrenergic neuronal activity, the lack of sustained stimulation of the stress axes, and the loss of sympathetic signals in the joints indicate that the communication between afferent immune messages to the central nervous system and two main efferent anti-inflammatory pathways under control of the brain are disrupted during experimental arthritis.

Interleukin‐1β and Insulin Elicit Different Neuroendocrine Responses to Hypoglycemia

Interleukin (IL)‐1β induces a prolonged hypoglycemia in mice that is not caused by a reduction in food intake and is dissociable from insulin effects. There is a peripheral component in the hypoglycemia that the cytokine induces resulting from an increased glucose uptake, an effect that can be exerted in a paracrine fashion at the site where IL‐1 is locally produced. However, the maintenance of hypoglycemia is controlled at brain levels because the blockade of IL‐1 receptors in the central nervous system inhibits this effect to a large extent. Furthermore, there is evidence that the cytokine interferes with counter regulation to hypoglycemia. Here we report that administration of IL‐1 or long‐lasting insulin results in different changes in food intake and in neuroendocrine mechanisms 8 h following induction of the same degree of hypoglycemia (40–45% decrease in glucose blood levels). Insulin, but not IL‐1, caused an increase in food intake and an endocrine response that tends to reestablish euglycemia. Conversely, a decrease in noradrenergic and an increase in serotonergic activity in the hypothalamus occur in parallel with a reduction of glucose blood levels only in IL‐1‐treated mice, effects that can contribute to the maintenance of hypoglycemia. These results are compatible with the proposal that IL‐1 acting in the brain can reset glucose homeostasis at a lower level. The biologic significance of this effect is discussed.

T cells affect central and peripheral noradrenergic mechanisms and neurotrophin concentration in the spleen and hypothalamus

Interactions between T cells and noradrenergic pathways were investigated using athymic nude mice as a model. Higher noradrenaline (NA) concentrations and increased density of noradrenergic fibers were found in the spleen and hypothalamus, but not in the kidney, of 21‐day‐old Foxn1n (athymic) mice, compared with Foxn1n/Foxn1+ (heterozygous) littermates. Although no differences in nerve growth factor concentrations were detected, significantly higher brain‐derived neurotrophic factor concentrations were found in the spleen and hypothalamus of athymic mice compared with the controls. All of these alterations were abrogated in Foxn1n mice reconstituted by thymus transplantation at birth. These results suggest that T lymphocytes or their products can induce (1) a decrease in the number and activity in splenic sympathetic nerve fibers; (2) a decrease in NA content in the hypothalamus, which, in turn, may influence the pituitary–adrenal axis and the descending neural pathways associated with the autonomic nervous system; and (3) changes in neurotrophin concentration in the spleen and hypothalamus.

Deletion of muscarinic type 1 acetylcholine receptors alters splenic lymphocyte functions and splenic noradrenaline concentration

The existence of interactions between the immune and the sympathetic nervous systems is well established. Noradrenaline can promote or inhibit the immune response, and conversely, the immune response itself can affect noradrenaline concentration in lymphoid organs, such as the spleen. It is also well known that acetylcholine released by pre-ganglionic neurons can modulate noradrenaline release by the postsynaptic neuron. The spleen does not receive cholinergic innervation, but it has been reported that lymphocytes themselves can produce acetylcholine, and express acetylcholine receptors and acetylcholinesterase. We found that the spleen of not overtly immunized mice in which muscarinic type 1 acetylcholine receptors have been knocked out (M1KO) has higher noradrenaline concentrations than that of the wildtype mice, without comparable alterations in the heart, in parallel to a decreased number of IgG-producing B cells. Splenic lymphocytes from M1KO mice displayed increased in vitro-induced cytotoxicity, and this was observed only when CD4(+) T cells were present. In contrast, heterozygous acetylcholinesterase (AChE+/-) mice, had no alterations in splenic noradrenaline concentration, but the in vitro proliferation of AChE+/- CD4(+) T cells was increased. It is theoretically conceivable that reciprocal effects between neuronally and non-neuronally derived acetylcholine and noradrenaline might contribute to the results reported. Our results emphasize the need to consider the balance between the effects of these mediators for the final immunoregulatory outcome.

47. Regulatory T cells and the sympathetic nervous system in a murine model of autoimmune disease

The incidence of chronic diseases such as inflammatory bowel diseases, diabetes or asthma is continuously increasing over the past 5 decades. Fetal programming as a cause for these diseases has been hypothesized, since a genetic predisposition does not suffice to explain such incidence. A wealth of environmental challenges may affect the maturation of the fetus, causing permanent developmental changes of the offspring. High stress perception is known to affect the endocrine-immune homeostasis. The aim of this study was to identify if prenatal exposure to stress challenge compromises the immune equilibrium at the feto-maternal interface as well as maternal progesterone levels. Experiments were performed in BABL/c x BALB/c and DBA/2J-mated BALB/c female mice, pregnant mice were exposed to stress challenge (sound) on gestation day (gd) 12.5 and 14.5, analyses were performed on gd 16.5. No differences of total number of implantations could be found between the groups. Employing flow cytometry, we observed an increased frequency of uterine Natural Killer (uNK) and CD4+ cells and a decreased number of CD4+CD25+CD103+ cells, which was particularly profound in the allogenic mating combination. Further, levels of progesterone were significantly decreased upon stress challenge. These data suggest that a stress-triggered uterine disequilibrium, accompanied by insufficient progesterone levels, may impair placental function or directly harm, the developing fetus, hereby causing irreversible changes rendering the offspring more susceptible to develop diseases in later life.