Cognitive dysfunction in depression is a prevalent and debilitating symptom that is poorly treated by the currently available pharmacotherapies. Research over the past decade has provided evidence for proinflammatory involvement in the neurobiology of depressive disorders and symptoms associated with these disorders, including aspects of memory dysfunction. Recent clinical studies implicate inflammation-related changes in kynurenine metabolism as a potential pathogenic factor in the development of a range of depressive symptoms, including deficits in cognition and memory. Additionally, preclinical work has demonstrated a number of mood-related depressive-like behaviors to be dependent on indoleamine 2,3-dioxygenase-1 (IDO1), the inflammation-induced rate-limiting enzyme of the kynurenine pathway. Here, we demonstrate in a mouse model, that peripheral administration of endotoxin induced a deficit in recognition memory. Mice deficient in IDO were protected from cognitive impairment. Furthermore, endotoxin-induced inflammation increased kynurenine metabolism within the perirhinal/entorhinal cortices, brain regions which have been implicated in recognition memory. A single peripheral injection of kynurenine, the metabolic product of IDO1, was sufficient to induce a deficit in recognition memory in both control and IDO null mice. Finally, kynurenine monooxygenase (KMO) deficient mice were also protected from inflammation-induced deficits on novel object recognition. These data implicate IDO-dependent neurotoxic kynurenine metabolism as a pathogenic factor for cognitive dysfunction in inflammation-induced depressive disorders and a potential novel target for the treatment of these disorders.

Cognitive impairment, particularly involving dysfunction of circuitry within the prefrontal cortex (PFC), represents a core feature of many neuropsychiatric and neurodevelopmental disorders, including depression, post-traumatic stress disorder, schizophrenia and autism spectrum disorder. Deficits in cognitive function also represent the most difficult symptom domain to successfully treat, as serotonin reuptake inhibitors and tricyclic antidepressants have only modest effects. Functional neuroimaging studies and postmortem analysis of human brain tissue implicate the PFC as being a primary region of dysregulation in patients with these disorders. However, preclinical behavioral assays used to assess these deficits in mouse models which can be readily manipulated genetically and could provide the basis for studies of new treatment avenues have been underutilized. Here we describe the adaptation of a behavioral assay, the attentional set shifting task (AST), to be performed in mice to assess prefrontal cortex mediated cognitive deficits. The neural circuits underlying behavior during the AST are highly conserved across humans, nonhuman primates and rodents, providing excellent face, construct and predictive validity.

Objective-To determine whether impairment of endothelial connexin40 (Cx40), an effect that can occur in hypertension and aging, contributes to the arterial dysfunction and stiffening in these conditions. Approach and Results-A new transgenic mouse strain, expressing a mutant Cx40, (Cx40T202S), specifically in the vascular endothelium, has been developed and characterized. This mutation produces nonfunctional hemichannels, whereas gap junctions containing the mutant are electrically, but not chemically, patent. Mesenteric resistance arteries from Cx40T202S mice showed increased sensitivity of the myogenic response to intraluminal pressure in vitro, compared with wildtype mice, whereas transgenic mice overexpressing native Cx40 (Cx40Tg) showed reduced sensitivity. In control and Cx40Tg mice, the sensitivity to pressure of myogenic constriction was modulated by both NO and endothelium-derived hyperpolarization; however, the endothelium-derived hyperpolarization component was absent in Cx40T202S arteries. Analysis of passive mechanical properties revealed that arterial stiffness was enhanced in vessels from Cx40T202S mice, but not in wild-type or Cx40Tg mice. Conclusions-Introduction of a mutant form of Cx40 in the endogenous endothelial Cx40 population prevents endotheliumderived hyperpolarization activation during myogenic constriction, enhancing sensitivity to intraluminal pressure and increasing arterial stiffness. We conclude that genetic polymorphisms in endothelial Cx40 can contribute to the pathogenesis of arterial disease.

Morton et al Endothelial Cx40 and Activity-Dependent Hypertension 663over distance. 5,6 Although both connexin (Cx)37 and Cx40 are highly expressed in gap junctions within the endothelium, it is Cx40 which is essential for ascending vasodilation. 5 Because the resulting vasodilation reduces peripheral resistance and opposes the increase in blood pressure which occurs during exercise, we hypothesized that functional Cx40 in the endothelium may also be necessary for adequate blood pressure regulation during exercise. Thus, disruption of endothelial Cx40 function may lead to exercise-induced hypertension and provide a model in which to study this condition.Unfortunately, the current mouse models are not suitable to address this hypothesis. Global deletion of Cx40 (Cx40ko) or replacement of the endogenous Cx40 gene coding sequence with either Cx45 or a nonfunctional mutant Cx40A96S produces hypertension that is predominantly renal in origin. [7][8][9][10] Loss of functional Cx40 from the cardiac conduction system also results in arrhythmia.11,12 Interestingly, mice carrying an endothelial-specific deletion of Cx40 are reportedly normotensive 13 ; however, the effect of activity was not investigated. Our laboratory recently developed the Cx40T202STg mouse, which expresses an endothelial Cx40 mutant that permits electric, but not chemical transfer through gap junctions.14 As ascending vasodilation relies on electrotonic transmission of EDH, these mice were also not suitable for investigating the role of Cx40 in exercise-dependent blood pressure regulation.We have therefore developed a novel transgenic mouse expressing a mutant form of Cx40, Cx40T152A, alongside endogenous wtCx40, specifically within the vascular endothelium, a situation analogous to the heterozygous expression of mutant genes in the human population. Substitution of this highly conserved threonine has been described in Cx26, Cx37, Cx43, and Cx50, where it produces structurally sound, yet electrically impaired gap junctions that act as a dominantnegative toward their respective endogenous Cx isoforms. 15,16 The functional importance of this region is underscored by x-ray crystallography, which shows that the conserved threonine contributes to hemichannel stability by likely forming a hydrogen bond with a similarly conserved histidine, H95, in the second transmembrane domain ( Figure S1 in the online-only Data Supplement).17 Interestingly, atrial fibrillation is associated with mutation of the neighboring residue, Cx40A96S, in humans, 18,19 while mice globally expressing Cx40A96S exhibit atrial fibrillation, renal hypertension, and attenuation in ascending vasodilation without change in Cx37 expression. 10,20,21 When expressed in vitro, the Cx40A96S mutant forms electrically impaired gap junctions that act as a dominant-negative toward wtCx40. 18 We hypothesized that endothelial-specific expression of Cx40T152A would interfere with endogenous wtCx40, leading to impairment of ascending vasodilation and onset of exercise-induced hypertension, making t...

No abstract

No abstract

No abstract

Mutant forms of connexin40 (Cx40) are known to exist in the human population and increase the risk of cardiovascular diseases such as atrial fibrillation. We hypothesised that the existence of dysfunctional Cx40 proteins amongst the native Cx40 population in the vascular endothelium may also impair arterial function. To this end, we created a new transgenic mouse strain expressing a mutant Cx40 (Cx40T202S) specifically in the endothelium; leaving native Cx40 expression intact. The ability of this mutation to impair gap junction function was tested in Xenopus Oocytes and mouse coronary endothelial cells while its effect on arterial function was tested in isolated small mesenteric arteries using pressure myography. Cell coupling studies found that Cx40T202S could form electrically but not chemically patent gap junctions. Analysis of the myogenic response of arteries from Cx40T202S mice revealed increased sensitivity to intraluminal pressure compared to wild type (P<0.05). This effect coincided with a loss of basally activated endothelium dependent hyperpolarisation (EDH) while nitric oxide remained intact. Examination of passive arterial properties showed Cx40T202S arteries were significantly stiffer than wild type (P<0.05). We conclude that the presence of a mutant Cx40 in the vascular endothelium is sufficient to prevent basal EDH, and increase both myogenic sensitivity and arterial stiffness.