Christina Weide Fischer

Pharmacological effects of Lu AA21004: a novel multimodal compound for the treatment of major depressive disorder.

1-[2-(2,4-Dimethylphenyl-sulfanyl)-phenyl]-piperazine (Lu AA21004) is a human (h) serotonin (5-HT)3A receptor antagonist (Ki = 3.7 nM), h5-HT7 receptor antagonist (Ki = 19 nM), h5-HT1B receptor partial agonist (Ki = 33 nM), h5-HT1A receptor agonist (Ki = 15 nM), and a human 5-HT transporter (SERT) inhibitor (Ki = 1.6 nM) (J Med Chem 54:3206–3221, 2011). Here, we confirm that Lu AA21004 is a partial h5-HT1B receptor agonist [EC50 = 460 nM, intrinsic activity = 22%] using a whole-cell cAMP-based assay and demonstrate that Lu AA21004 is a rat (r) 5-HT7 receptor antagonist (Ki = 200 nM and IC50 = 2080 nM). In vivo, Lu AA21004 occupies the r5-HT1B receptor and rSERT (ED50 = 3.2 and 0.4 mg/kg, respectively) after subcutaneous administration and is a 5-HT3 receptor antagonist in the Bezold-Jarisch reflex assay (ED50 = 0.11 mg/kg s.c.). In rat microdialysis experiments, Lu AA21004 (2.5–10.0 mg/kg s.c.) increased extracellular 5-HT, dopamine, and noradrenaline in the medial prefrontal cortex and ventral hippocampus. Lu AA21004 (5 mg/kg per day for 3 days; minipump subcutaneously), corresponding to 41% rSERT occupancy, significantly increased extracellular 5-HT in the ventral hippocampus. Furthermore, the 5-HT3 receptor antagonist, ondansetron, potentiated the increase in extracellular levels of 5-HT induced by citalopram. Lu AA21004 has antidepressant- and anxiolytic-like effects in the rat forced swim (Flinders Sensitive Line) and social interaction and conditioned fear tests (minimal effective doses: 7.8, 2.0, and 3.9 mg/kg). In conclusion, Lu AA21004 mediates its pharmacological effects via two pharmacological modalities: SERT inhibition and 5-HT receptor modulation. In vivo, this results in enhanced release of several neurotransmitters and antidepressant- and anxiolytic-like profiles at doses for which targets in addition to the SERT are occupied. The multimodal activity profile of Lu AA21004 is distinct from that of current antidepressants.

Neuropeptide S alters anxiety, but not depression-like behaviour in Flinders Sensitive Line rats: a genetic animal model of depression

Neuropeptide S (NPS) and its receptor (NPSR) have been implicated in the mediation of anxiolytic-like behaviour in rodents. However, little knowledge is available regarding the NPS system in depression-related behaviours, and whether NPS also exerts anxiolytic effects in an animal model of psychopathology. Therefore, the aim of this work was to characterize the effects of NPS on depression- and anxiety-related parameters, using male and female rats in a well-validated animal model of depression: the Flinders Sensitive Line (FSL), their controls, the Flinders Resistant Line (FRL), and Sprague-Dawley (SD) rats. We found that FSL showed greater immobility in the forced swim test (FST) than FRL, confirming their phenotype. However, NPS did not affect depression-related behaviour in any rat line. No significant differences in baseline anxiety levels between the FSL and FRL strains were observed, but FSL and FRL rats displayed less anxiety-like behaviour compared to SD rats. NPS decreased anxiety-like behaviour on the elevated plus-maze in all strains. The expression of the NPSR in the amygdala, periventricular hypothalamic nucleus, and hippocampus was equal in all male strains, although a trend towards reduced expression within the amygdala was observed in FSL rats compared to SD rats. In conclusion, NPS had a marked anxiolytic effect in FSL, FRL and SD rats, but did not modify the depression-related behaviour in any strain, in spite of the significant differences in innate level between the strains. These findings suggest that NPS specifically modifies anxiety behaviour but cannot overcome/reverse a genetically mediated depression phenotype.

Behavioral and systemic consequences of long-term inflammatory challenge

Inflammatory reactions are involved in a diversity of diseases, including major depressive disorder. Cytokines act as intercellular signaling molecules and mediators of inflammation between the periphery and the brain. Within the brain, evidence from animal studies of acute inflammation has shown that elevated cytokine levels are linked to behavioral responses of sickness and depression-like behavior. Although chronic inflammation is more translational to human depression than acute studies, little is known on central cytokine expression and associated behavioral responses following chronic immune challenges. The present study assessed behavioral changes and a selection of cytokines in the brain and in the blood in rats randomized to receive a single or 8week administration with either lipopolysaccharide (LPS, 600μg/kg, i.p.) or saline. Acute and long-term LPS treatments caused similar sickness and depression-like behavior. Chronic LPS administration did not have an effect on blood cytokine levels, indicating endotoxin tolerance, whereas increased fasting blood glucose was observed, indicating insulin resistance, a metabolic consequence of chronic inflammation. While a single LPS injection produced a generalized cytokine response in the brain, long-term LPS administration produced a specific central cytokine response with increased interleukin (IL)-1β and interferon (IFN)-γ. These cytokines can explain the behavioral changes observed, and could indicate microglia activation, although future studies are needed to uncover this assumption. Taken together, although the behavioral outcome was similar between acute and chronic LPS administration, the central cytokine response was distinct. As the long-term LPS paradigm also posed a metabolic demand, this setting may reflect a more translational insight into inflammatory reactions in human depression, and could prove useful for assessing cytokine down-stream effects and experimental antidepressant drug products.

Interferon-alpha treatment induces depression-like behaviour accompanied by elevated hippocampal quinolinic acid levels in rats.

Immunotherapy with the cytokine interferon-alpha (IFN-α) can induce symptoms of depression, and it is likely that the tryptophan-kynurenine pathway may be involved in this regard. In this study we investigated the effects of IFN-α on depression-like behaviour and central metabolites of the tryptophan-kynurenine pathway in rats. Secondly, we explored the modulating effects of an antidepressant (imipramine) and anti-inflammatory drug (celecoxib) on IFN-α-induced behavioural and pathophysiological changes in the brain. The following treatment groups were used: Control (saline), IFN-α (6×10(4)IU/kg s.c.), IFN-α+imipramine or IFN-α+celecoxib. Drugs were administered daily for 1 week. IFN-α treatment induced depression-like behaviour by increasing immobility in the forced swim test (FST), and decreased tryptophan levels in the brain. There was a trend for an increased kynurenine/tryptophan ratio, indicative of indoleamine 2,3-dioxygenase (IDO) activation, and increased quinolinic acid in the hippocampus. Imipramine decreased immobility in the FST, but did not reverse the IFN-α-induced changes in the tryptophan-kynurenine pathway. There was a trend for celecoxib to decrease immobility and to reverse the IFN-α-induced increase in the kynurenine/tryptophan ratio. Thus, our study provides further evidence for IFN-α-induced depression-like behaviour through central changes of the tryptophan-kynurenine pathway.

Isolation-induced behavioural changes in a genetic animal model of depression

Depression is a heterogeneous disorder displaying a range of symptoms including feelings of despair and social withdrawal. Social isolation may complicate the progression of depression and have effects on both behaviour and physiology. The aim of this study was to investigate the effects of social isolation on behavioural and metabolic parameters in a genetic rat model of depression, the Flinders Sensitive and Resistant Line (FSL/FRL) rats. Rats were housed either individually (social isolation) or pair-housed for 5weeks, and subjected to behavioural testing and metabolic evaluation. We found that social isolation erased the characteristic difference in depressive-like behaviour, measured as immobility in the forced swim test, between the FSL and FRL rats. Social isolation affected both strains equally in impairing object recognition memory, while leading to an increased explorative behaviour in the elevated plus maze test. Surprisingly, single-housed FRL rats showed an increased food intake compared to pair-housed FRL rats, whereas no difference in food intake or body weight was evident in FSL rats. Our results indicate that social isolation for 5weeks causes behavioural alterations, independent of strain. As the changes in appetite were only observed in the FRL rats, this may suggest that this strain responds to the stress of isolation by a change in feeding behaviour.

Expression of inflammatory markers in a genetic rodent model of depression

The complex bidirectional communication between the central nervous system and the peripheral immune system is of possible relevance for both normal brain functions and the development of psychiatric disorders. The aim of this investigation was to study central expression of inflammatory markers in a genetic rat model of depression (the Flinders sensitive line (FSL) and its control, the Flinders resistant line (FRL)). A peripheral immune activation was induced by lipopolysaccharide (LPS) in order to investigate possible differences in immune reactions between the two rat lines. To confirm behavioural differences between the rat lines the forced swim test was performed, a test to assess depressive-like behaviour. Expression of candidate inflammatory genes was measured in amygdala, hippocampus, hypothalamus, prefrontal cortex and striatum using quantitative real time PCR. Our results show, for the first time, significantly lower central expression of the glial-specific protein S100B and complement factor C3 in several brain regions of the FSL rats compared to controls, both at baseline and after peripheral immune stimulation. No significant differences in immune responses to LPS were observed between the rats lines. Both S100B and C3 have been suggested to be of relevance for brain development and plasticity as well as brain disorders. These proteins may be of importance for the behavioural differences between the FSL and FRL rats, and this model may be useful in studies exploring the influence of the immune system on brain functions.

An inhibitor of cAMP-dependent protein kinase induces behavioural and neurological antidepressant-like effects in rats

Although it is well established that cyclic adenosine monophosphate (cAMP) signalling via cAMP-dependent protein kinase (PKA)within neurons plays an important role in depression and antidepressant treatment, the importance of several newly discovered targets that function independently from PKA, such as exchange protein activated by cAMP (Epac), remains unexplored in this regard. In this study we used a cAMP analogue that inhibits PKA but not Epac (Rp-8-Br-cAMP), to explore the modifying actions of these two targets on immobility in the forced swim test (FST) and cerebellar cAMP response element binding protein (CREB) phosphorylation in rats. In addition, we assessed central cAMP and cGMP levels and investigated the involvement of cGMP-dependent protein kinase (PKG) on any observed effects by using a selective PKG inhibitor (Rp-8-Br-PET-cGMPS).Interestingly, Rp-8-Br-cAMPS strongly reduced immobility in the FST and induced an increase in the phosphorylation of CREB in the cerebellum, effects that were unaltered by the co-administration of Rp-8-Br-PET-cGMPS. Furthermore, Rp-8-Br-cAMPS increased the accumulation of cAMP and cGMP in the hippocampus, frontal cortex and cerebellum of these rats. Together, these results suggest that in addition to activating PKA, elevated cAMP may also stimulate other targets that mediate antidepressant activity. According to the pharmacodynamic profile of Rp-8-Br-cAMPS and taking into consideration what has recently been discovered regarding the cAMP signalling system, a likely candidate is the guanine nucleotide exchange factor, Epac.

Chronic exposure to low doses of lipopolysaccharide and high‐fat feeding increases body mass without affecting glucose tolerance in female rats

Obesity‐related inflammation may have a causal role in the development of diabetes and insulin resistance, and studies using animal models of chronic experimental endotoxemia have shown the link. However, many studies use only males, and much less is known about the role of obesity‐related inflammation in females. Therefore, we addressed how experimentally induced chronic inflammation affects body mass, energy intake, and glucose metabolism in female rats. Adult female Sprague Dawley rats were instrumented with slow release pellets that delivered a constant daily dose of 53 or 207 μg of lipopolysaccharide (LPS) per rat for 60 days. Control rats were instrumented with vehicle pellets. Due to inflammatory nature of high‐fat diet (HFD) half of the rats received HFD (60% of calories from lard), while the other half remained on control diet to detect possible interactions between two modes of induced inflammation. Our results showed that chronic LPS administration increased female rat body mass and calorie intake in a dose‐dependent manner, and that HFD further exacerbated these effects. Despite these effects, no effects of LPS and HFD were evident on female rat glucose metabolism. Only LPS elevated expression of inflammatory markers in the hypothalamus. To conclude, female rats respond to experimentally induced chronic inflammation by increasing body mass, but do not develop glucose intolerance in the given period of time.

Chronic lipopolysaccharide infusion fails to induce depressive-like behaviour in adult male rats.

Background Chronic inflammation is implicated in numerous diseases, including major depression and type 2 diabetes mellitus (T2DM). Since depression and T2DM often co-exist, inflammatory pathways are suggested as a possible link. Hence, the establishment of an immune-mediated animal model would shed light on mechanisms possibly linking depression and metabolic alterations. Objective In this study we investigated a behavioural and metabolic paradigm following chronic infusion with low doses of lipopolysaccharide (LPS) using osmotic minipumps in male rats. Methods Behavioural testing consisted of evaluating activity level in the open field and depressive-like behaviour in the forced swim test. Metabolic assessment included measurement of body weight, food and water intake, and glucose and insulin levels during an oral glucose tolerance test. Results LPS-infused rats showed acute signs of sickness behaviour, but chronic LPS infusion did not induce behavioural or metabolic changes. Conclusion These results suggest that although inflammation is immediately induced as indicated by acute sickness, 4 weeks of chronic LPS administration via osmotic minipumps did not result in behavioural changes. Therefore, this paradigm may not be a suitable model for studying the underlying mechanisms that link depression and T2DM.

A Preclinical Study of Casein Glycomacropeptide as a Dietary Intervention for Acute Mania

Abstract Background Casein glycomacropeptide is a peptide that lacks phenylalanine, tyrosine, and tryptophan. This profile may enable it to deplete phenylalanine, tyrosine, and tryptophan, and subsequently the synthesis of dopamine and serotonin in the brain. Dopamine- and serotonin-depleting amino acid mixtures have shown promise as acute antimanic treatments. In this study, we explore the depleting effects on amino acids, dopamine and serotonin as well as its actions on manic-like and other behavior in rats. Methods Casein glycomacropeptide and a selection of amino acid mixtures were administered orally at 2, 4, or 8 h or for 1 week chronically. Amino acid and monoamine levels were measured in plasma and brain and behavior was assessed in the amphetamine-hyperlocomotion, forced swim, prepulse inhibition, and elevated plus maze tests. Results Casein glycomacropeptide induced a time-dependent reduction in tyrosine, tryptophan, and phenylalanine in brain and plasma which was augmented by supplementing with leucine. Casein glycomacropeptide +leucine reduced dopamine in the frontal cortex and serotonin in the hippocampus, frontal cortex, and striatum after 2 and 4 h. Casein glycomacropeptide+leucine also had antimanic activity in the amphetamine-induced hyperlocomotion test at 2 h after a single acute treatment and after 1 week of chronic treatment. Conclusions Casein glycomacropeptide-based treatments and a branched-chain amino acid mixture affected total tissue levels of dopamine in the frontal cortex and striatum and serotonin in the frontal cortex, striatum, and hippocampus of rats in a time-dependent fashion and displayed antimanic efficacy in a behavioral assay of mania.