Modulation of fear behavior and neuroimmune alterations in house dust mite exposed A/J mice, a model of severe asthma.

Fear-associated conditions such as posttraumatic stress disorder (PTSD) and panic disorder (PD) are highly prevalent. There is considerable interest in understanding contributory risk and vulnerability factors. Accumulating evidence suggests that chronically elevated inflammatory load may be a potential risk factor for these disorders. In this regard, an association of asthma, a chronic inflammatory condition, with PTSD and PD has been reported. Symptoms of PD and PTSD are more prevalent in severe asthmatics, compared to those with mild or moderate asthma suggesting that factors that influence the severity of asthma, may also influence susceptibility to the development of fear-related disorders. There has been relatively little progress in identifying contributory factors and underlying mechanisms, particularly, the translation of severe asthma-associated lung inflammation to central neuroimmune alterations and behavioral manifestations remains unclear. The current study investigated the expression of behaviors relevant to PD and PTSD (CO2 inhalation and fear conditioning/extinction) in A/J mice using a model of severe allergic asthma associated with a mixed T helper 2 (Th2) and Th17 immune response. We also investigated the accumulation of Th2- and Th17-cytokine expressing cells in lung and brain tissue, microglial alterations, as well as neuronal activation marker, delta FosB (ΔFosB)) in fear and panic regulatory brain areas. HDM-exposed mice elicited higher freezing during fear extinction. CO2-associated spontaneous and conditioned freezing, as well as anxiety or depression-relevant exploratory and coping behaviors were not altered by HDM treatment. A significant increase in brain Th17-associated inflammatory mediators was observed prior to behavioral testing, accompanied by microglial alterations in specialized blood brain barrier-compromised circumventricular area, subfornical organ. Post extinction measurements revealed increased ΔFosB staining within the medial prefrontal cortex and basolateral amygdala in HDM-treated mice. Collectively, our data show modulation of brain immune mechanisms and fear circuits by peripheral airway inflammation, and is relevant to understanding the risk and comorbidity of asthma with fear-associated disorders such as PTSD.

Altered Fear Behavior in Aeroallergen House Dust Mite Exposed C57Bl/6 Mice: A Model of Th2-skewed Airway Inflammation.

There is a growing interest for studying the impact of chronic inflammation, particularly lung inflammation, on the brain and behavior. This includes asthma, a chronic inflammatory condition, that has been associated with psychiatric conditions such as posttraumatic stress disorder (PTSD). Although asthma is driven by elevated production of Th2 cytokines (IL-4, IL-5 and IL-13), which drive asthma symptomology, recent work demonstrates that concomitant Th1 or Th17 cytokine production can worsen asthma severity. We previously demonstrated a detrimental link between PTSD-relevant fear behavior and allergen-induced lung inflammation associated with a mixed Th2/Th17-inflammatory profile in mice. However, the behavioral effects of Th2-skewed airway inflammation, typical to mild/moderate asthma, are unknown. Therefore, we investigated fear conditioning/extinction in allergen house dust mite (HDM)-exposed C57Bl/6 mice, a model of Th2-skewed allergic asthma. Behaviors relevant to panic, anxiety, and depression were also assessed. Furthermore, we investigated the accumulation of Th2/Th17-cytokine-expressing cells in lung and brain, and the neuronal activation marker, ΔFosB, in fear regulatory brain areas. HDM-exposed mice elicited lower freezing during fear extinction with no effects on acquisition and conditioned fear. No HDM effect on panic, anxiety or depression-relevant behaviors was observed. While HDM evoked a Th2-skewed immune response in lung tissue, no significant alterations in brain Th cell subsets were observed. Significantly reduced ΔFosB+ cells in the basolateral amygdala of HDM mice were observed post extinction. Our data indicate that allergen-driven Th2-skewed responses may induce fear extinction promoting effects, highlighting beneficial interactions of Th2-associated immune mediators with fear regulatory circuits.

C57BL/6J mice exhibit reduced dopamine D3 receptor-mediated locomotor-inhibitory function relative to DBA/2J mice.

Previous reports have identified greater sensitivity to the locomotor-stimulating, sensitizing, and reinforcing effects of amphetamine in inbred C57BL/6J mice relative to inbred DBA/2J mice. The dopamine D3 receptor (D3R) plays an inhibitory role in the regulation of rodent locomotor activity, and exerts inhibitory opposition to D1 receptor (D1R)-mediated signaling. Based on these observations, we investigated D3R expression and D3R-mediated locomotor-inhibitory function, as well as D1R binding and D1R-mediated locomotor-stimulating function, in C57BL/6J and DBA/2J mice. C57BL/6J mice exhibited lower D3R binding density (-32%) in the ventral striatum (nucleus accumbens/islands of Calleja), lower D3R mRNA expression (-26%) in the substantia nigra/ventral tegmentum, and greater D3R mRNA expression (+40%) in the hippocampus, relative to DBA/2J mice. There were no strain differences in DR3 mRNA expression in the ventral striatum or prefrontal cortex, nor were there differences in D1R binding in the ventral striatum. Behaviorally, C57BL/6J mice were less sensitive to the locomotor-inhibitory effect of the D3R agonist PD128907 (10 microg/kg), and more sensitive to the locomotor-stimulating effects of novelty, amphetamine (1 mg/kg), and the D1R-like agonist +/- -1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8,-diol hydrochloride (SKF38393) (5-20 mg/kg) than DBA/2J mice. While the selective D3R antagonist N-(4-[4-{2,3-dichlorphenyl}-1 piperazinyl]butyl)-2-fluorenylcarboxamide (NGB 2904) (0.01-1.0 mg/kg) augmented novelty-, amphetamine-, and SKF38393-induced locomotor activity in DBA/2J mice, it reduced novelty-induced locomotor activity in C57BL/6J mice. Collectively, these results demonstrate that C57BL/6J mice exhibit less D3R-mediated inhibitory function relative to DBA/2J mice, and suggest that reduced D3R-mediated inhibitory function may contribute to heightened sensitivity to the locomotor-stimulating effects of amphetamine in the C57BL/6J mouse strain. Furthermore, these data demonstrate that comparisons between C57BL/6J and DBA/2J mouse strains provide a model for elucidating the molecular determinants of genetic influence on D3R function.

Cloning, expression, and regulation of a glucocorticoid-induced receptor in rat brain: effect of repetitive amphetamine.

Behavioral sensitization to psychostimulants involves neuroadaptation of stress-responsive systems. We have identified and sequenced a glucocorticoid-induced receptor (GIR) cDNA from rat prefrontal cortex. The full-length GIR cDNA encodes a 422 amino acid protein belonging to G-protein-coupled receptor superfamily. Although the ligand for GIR is still unknown, the dendrogram construction indicates that GIR may belong to peptide receptor subfamily (e.g., substance P receptor), with more distant relationship to subfamilies of glycoprotein hormone receptors (e.g., thyrotropin receptor) and biogenic amine receptors (e.g., dopamine receptor). GIR shares 31-34% amino acid identity to the tachykinin receptors (substance P receptor, neurokinin A receptor, and neurokinin B receptor). GIR mRNA is expressed preferentially in brain, and its neuronal expression is relegated to limbic brain regions, particularly in forebrain. GIR transcript levels are increased significantly and persistently in prefrontal cortex for 7 d after discontinuation of chronic amphetamine exposure. The induction of GIR expression by amphetamine is associated with augmented behavioral activation. These findings suggest that modulation of GIR expression may be involved in behavioral sensitization, and GIR may play a role at the interface between stress and neuroadaptation to psychostimulants.

Expression of the glucocorticoid-induced receptor mRNA in rat brain.

The glucocorticoid-induced receptor (GIR) is an orphan G-protein-coupled receptor awaiting pharmacological characterization. GIR was originally identified in murine thymoma cells, and shows a widespread, yet not completely complementary distribution in mouse and human brain. Expression of the mouse GIR gene is modulated by dexamethasone in the brain and periphery, suggesting that GIR function is directly responsive to glucocorticoid signals. The rat GIR was cloned from rat prefrontal cortex by our group and was shown to be up-regulated following chronic amphetamine. The physiological role of GIR in the rat is not known at present. In order to gain a clearer understanding of the potential functions of GIR in the rat, we performed a detailed mapping of GIR mRNA expression in the rat brain. GIR mRNA showed widespread distribution in forebrain limbic and thalamic structures, and a more restricted distribution in hindbrain areas such as the spinal trigeminal nucleus and the median raphe nucleus. Areas with moderate to high levels of GIR include olfactory regions such as the nucleus of olfactory tract, hippocampus, various thalamic nuclei, cortical layers, and some hypothalamic nuclei. In comparison with previous studies, significant regional differences exist in GIR distribution in mouse and rat brain, particularly in the thalamus, striatum and in hippocampus at a cellular level. Overall, the expression of GIR in rat brain more closely approaches that seen previously in human than mouse, suggesting that rat models may be more informative for understanding the role of GIR in glucocorticoid physiology and glucocorticoid-related disease states. GIR mRNA distribution in the rat indicates a potential role of this receptor in the control of feeding and ingestive behavior, regulation of stress and emotional behavior, learning and memory, and, drug reinforcement and reward.