Laura Lückemann

Memory-updating abrogates extinction of learned immunosuppression

When memories are recalled, they enter a transient labile phase in which they can be impaired or enhanced followed by a new stabilization process termed reconsolidation. It is unknown, however, whether reconsolidation is restricted to neurocognitive processes such as fear memories or can be extended to peripheral physiological functions as well. Here, we show in a paradigm of behaviorally conditioned taste aversion in rats memory-updating in learned immunosuppression. The administration of sub-therapeutic doses of the immunosuppressant cyclosporin A together with the conditioned stimulus (CS/saccharin) during retrieval blocked extinction of conditioned taste aversion and learned suppression of T cell cytokine (interleukin-2; interferon-γ) production. This conditioned immunosuppression is of clinical relevance since it significantly prolonged the survival time of heterotopically transplanted heart allografts in rats. Collectively, these findings demonstrate that memories can be updated on both neural and behavioral levels as well as on the level of peripheral physiological systems such as immune functioning.

Exogenous oxytocin reduces signs of sickness behavior and modifies heart rate fluctuations of endotoxemic rats

Besides the well-known roles of oxytocin on birth, maternal bonding, and lactation, recent evidence shows that this hypothalamic hormone possesses cardioprotective, anti-inflammatory and parasympathetic neuromodulation properties. In this study, we explore the heart rate fluctuations (HRF) in an endotoxemic rodent model that was accompanied by the administration of exogenous oxytocin. The assessment of HRF has been widely used as an indirect measure of the cardiac autonomic function. In this context, adult male Dark Agouti rats were equipped with a telemetric transmitter to continuously and remotely measure the electrocardiogram, temperature, and locomotion. In a between-subjects experimental design, rats received the following peripheral treatment: saline solution as a vehicle (V); lipopolysaccharide (LPS); oxytocin (Ox); lipopolysaccharide + oxytocin (LPS+Ox). Linear and non-linear parameters of HRF were estimated starting 3h before to 24h after treatments. Our results showed that exogenous oxytocin does not modify by itself the HRF of oxytocin-treated rats in comparison to vehicle-treated rats. However, in animals undergoing endotoxemia it: a) provokes a less anticorrelated pattern in HRF, b) decreased mean heart rate, c) moderated the magnitude and duration of the LPS-induced hyperthermia, and d) increased locomotion, up to 6h after the LPS injection. The less anticorrelated pattern in the HRF and decreased mean heart rate may reflect a cardiac pacemaker coupling with cholinergic influences mediated by oxytocin during LPS-induced endotoxemia. Finally, the anti-lethargic and long-term temperature moderating effects of the administration of oxytocin during endotoxemia could be a consequence of the systemic anti-inflammatory properties of oxytocin.

Applications and limitations of behaviorally conditioned immunopharmacological responses

The importance of placebo responses for the treatment of various medical conditions has increasingly been recognized, whereas knowledge and systematic application in clinical settings are still sparse. One possible application for placebo responses in pharmacotherapy is given by learning paradigms, such as behaviorally conditioned immunosuppression, aiming at drug dose reduction while maintaining therapeutic efficacy of drug treatment. In an established learning paradigm of conditioned taste aversion/avoidance (CTA) in both, rats and humans, respectively, a novel-tasting drinking solution (conditioned stimulus, CS) is paired with an injection of the immunosuppressive drug cyclosporine A (CsA) as unconditioned stimulus (US). The conditioned response, evoked by re-presenting the CS alone at a later time, is reflected by avoidance behavior of consuming the solution (conditioned taste aversion; CTA) and a diminished interleukin (IL)-2 and interferon (IFN)-γ cytokine production as well as mRNA expression of rat splenic T cells or human peripheral T lymphocytes, closely mimicking the immunosuppressive effects of CsA. However, due to unreinforced CS-re-exposure conditioned responses progressively decreases over time (extinction), reflecting a considerable challenge for potential clinical applications of this learned immunosuppression. The present article discusses and critically reviews actual approaches, applications but also limitations of learning paradigms in immune pharmacotherapy.

Rats taste-aversive learning with cyclosporine a is not affected by contextual changes.

In conditioned taste aversion (CTA) rats associate a novel taste (conditioned stimulus; CS) with a treatment (unconditioned stimulus; US) that induces symptoms of malaise. During retrieval, animals learn that the CS no longer predicts the US, with the consequence that the behavior elicited by the CS extinguishes. Importantly, CTA data with lithium chloride (LiCl) as US indicate that extinction learning is affected by changing the physical context. However, if this is also the case in different taste-aversion paradigms employing compounds other than LiCL as US is unknown. Against this background the present study investigated in a CTA paradigm with saccharin as CS and the immunosuppressant cyclosporine A (CsA) as US the influence of contextual changes on CTA extinction. Our results show, that extinction of a learned CS-US association with CsA is not prone to contextual changes. Due to the direct effects of CsA on CNS functioning, CTA with this immunosuppressant apparently operates under different mechanisms compared to other drugs, such as LiCl. These data indicate that taste aversive learning and its extinction are not necessarily specific to the context in which it is learned but also depends, at least in part, on the physiological and neuropharmacological effects of the drug employed as US.

Repeated Systemic Treatment with Rapamycin Affects Behavior and Amygdala Protein Expression in Rats

Abstract Background Clinical data indicate that therapy with small-molecule immunosuppressive drugs is frequently accompanied by an incidence rate of neuropsychiatric symptoms. In the current approach, we investigated in rats whether repeated administration of rapamycin, reflecting clinical conditions of patients undergoing therapy with this mammalian target of rapamycin inhibitor, precipitates changes in neurobehavioral functioning. Methods Male adult Dark Agouti rats were daily treated with i.p. injections of rapamycin (1, 3 mg/kg) or vehicle for 8 days. On days 6 and 7, respectively, behavioral performance in the Elevated Plus-Maze and the Open-Field Test was evaluated. One day later, amygdala tissue and blood samples were taken to analyze protein expression ex vivo. Results The results show that animals treated with rapamycin displayed alterations in Elevated Plus-Maze performance with more pronounced effects in the higher dose group. Besides, an increase in glucocorticoid receptor density in the amygdala was seen in both treatment groups even though p-p70 ribosomal S6 kinase alpha, a marker for mammalian target of rapamycin functioning, was not affected. Protein level of the neuronal activity marker c-Fos was again only elevated in the higher dose group. Importantly, effects occurred in the absence of acute peripheral neuroendocrine changes. Conclusions Our findings indicate that anxiety-related behavior following rapamycin treatment was not directly attributed to mTOR-dependent mechanisms or stress but rather due to hyperexcitability of the amygdala together with glucocorticoid receptor-regulated mechanism(s) in this brain region. Together, the present results support the contention that subchronic treatment with rapamycin may induce neurobehavioral alterations in healthy, naive subjects. We here provide novel insights in central effects of systemic rapamycin in otherwise healthy subjects but also raise the question whether therapy with this drug may have detrimental effects on patients’ neuropsychological functioning during immune therapy.

Oxytocin’s role on the cardiorespiratory activity of endotoxemic rats

BACKGROUND Recent findings concerning oxytocin indicate its anti-inflammatory, cardioprotective and parasympathetic modulating properties. In this study, we investigated the effects of systemically applied oxytocin on the cardiorespiratory activity in a rodent model of moderate endotoxemia. METHODS Telemetrically recorded electrocardiogram (ECGs) from animals which received lipopolysaccharide (LPS); oxytocin (Ox); lipopolysaccharide+oxytocin (LPS+Ox), or vehicle (V) were analyzed using the ECG-derived respiration (EDR) technique to estimate the respiratory rate. The mean R-R interval and the spectral parameters of heart rate variability (HRV), such as the natural logarithm of the high frequency (lnHF) and low frequency (lnLF) components were also estimated up to 24h after treatment. RESULTS The endotoxemic animals (LPS) showed an elevated respiratory rate as well as a reduced mean R-R interval, lnHF and lnLF components compared to controls (V) from +5 to +12h after the treatment. The administration of oxytocin significantly attenuated the hyperventilation produced by the LPS-induced endotoxemia (LPS+Ox) and restored the values of the mean R-R interval and such spectral parameters at different time points. CONCLUSIONS Our results support the existence of a link among the respiratory, cardiovascular, and immune systems in which oxytocin seems to act as a potential cardioprotective peptide by favoring cardiac cholinergic autonomic coupling. As a result, oxytocin diminished animals endotoxemic tachypnea and restored the cardiorespiratory interactions, which was indicated by the spectral components of HRV.

Behaviorally conditioned immunosuppression: Effects of pre-exposure to the unconditioned (US) and conditioned (CS) stimulus

We established a model of behaviorally conditioned immunosuppression employing a conditioned taste aversion (CTA) paradigm in rats, pairing a novel taste (saccharin) as a conditioned stimulus (CS) with the immunosuppressive drug cyclosporine A (CsA) as unconditioned stimulus (US). By re-presenting the CS during evocation, rats avoid drinking the saccharin and concomitantly displaying immunosuppression reflected by an reduction in splenic T cell IL-2 production. However, for a possible application of this specific learning protocol in clinical conditions, it is essential to know, whether conditioned immunosuppression could be induced in patients who are already on immunosuppressive therapy or have had previous contact to the gustatory stimulus used as CS. Thus, prior to acquisition rats were exposed three times either to the CS (saccharin) or to the US (CsA). Pre-exposure to both, the US as well as the CS accelerated extinction of the conditioned response on the behavioral level (CTA). Importantly, the conditioned suppression of peripheral immune functioning, reflected as diminished anti-CD3 stimulated IL-2 production, was neither affected by pre-exposure to the US (CsA) nor by the CS (saccharin). These results indicate that learning protocols, such as behaviorally conditioned immunosuppression with CsA, may be employed in clinical situations as supportive therapy together with standard pharmacological regimes, with the goal to reduce the amount of drugs and toxic side effects, maximizing the therapeutic outcome for the patient’s benefit.

Neuroprotective effects of hypothermia and levetiracetam after hypoxia-ischemia in the neonatal mouse brain

Aims Hypoxic-ischemic injury (HI) to the developing brain remains a major cause of morbidity. Hypothermia is currently the only established neuroprotective treatment available for term borns with hypoxic-ischemic encephalopathy, saving one in eight infants from developing severe neurological deficits. Therefore, additional treatments with clinically applicable drugs are indispensable. Furthermore, the pathophysiological mechanisms of hypothermia-induced recovery are not clearly understood. This study examines a potential additive neuroprotective effect of hypothermia combined with levetiracetam in neonatal mouse HI.

Teach the T cells: How learning can shape immunity

mouse skin which was reversed by additional noise stress. We observed a similar pattern of mRNA expression by rtPCR. We tested several Chrna7 antibodies but only one (Abcam, ab110851) gave reliable staining. All these data infer that in mast cells and in cutaneous neuro-immune network, NNCS mediators play a key role in the regulation of stress-sensitive inflammatory responses. Further studies are needed to elucidate the underlying mechanisms and the potential of pharmacological intervention.

Pre-exposure to the unconditioned or the conditioned stimulus differentially affect learned immunosuppression in rats

addition, immunohistochemical staining for CD68 was performed to visualize activated microglial cells in serial sections. Results: The DVR of [11C]PK11195 was significantly increased in the NAWM (p b 0.001) and thalamic ROIs (p = 0.027) of SPMS patients compared to the control group. Increased perilesional TSPO-uptake was present in 57% of the chronic T1-lesions in MRI, giving thus in vivo proof of a significant proportion of chronic active lesions among SPMS patients. Autoradiography performed with autopsy samples of MS brain revealed specific TSPO-ligand binding at the plaque edge. Finally, immunohistochemical staining confirmed co-localization of TSPO-ligand binding with activated, CD68-positive microglial cells/ macrophages. Conclusions: PET imaging enables the detection of microglial activation in brains of SPMS patients in vivo. It thus helps to visualize the diffuse pathology associated with activated microglial cells, and the presence of chronic active lesions.