No abstract

Blood pressure is controlled by endocrine, autonomic, and behavioral responses that maintain blood volume and perfusion pressure at levels optimal for survival. Although it is clear that central angiotensin type 1a receptors (AT1aR; encoded by the Agtr1a gene) influence these processes, the neuronal circuits mediating these effects are incompletely understood. The present studies characterize the structure and function of AT1aR neurons in the lamina terminalis (containing the median preoptic nucleus and organum vasculosum of the lamina terminalis), thereby evaluating their roles in blood pressure control. Using male Agtr1a-Cre mice, neuroanatomical studies reveal that AT1aR neurons in the area are largely glutamatergic and send projections to the paraventricular nucleus of the hypothalamus (PVN) that appear to synapse onto vasopressin-synthesizing neurons. To evaluate the functionality of these lamina terminalis AT1aR neurons, we virally delivered light-sensitive opsins and then optogenetically excited or inhibited the neurons while evaluating cardiovascular parameters or fluid intake. Optogenetic excitation robustly elevated blood pressure, water intake, and sodium intake, while optogenetic inhibition produced the opposite effects. Intriguingly, optogenetic excitation of these AT1aR neurons of the lamina terminalis also resulted in Fos induction in vasopressin neurons within the PVN and supraoptic nucleus. Further, within the PVN, selective optogenetic stimulation of afferents that arise from these lamina terminalis AT1aR neurons induced glutamate release onto magnocellular neurons and was sufficient to increase blood pressure. These cardiovascular effects were attenuated by systemic pretreatment with a vasopressin-1a-receptor antagonist. Collectively, these data indicate that excitation of lamina terminalis AT1aR neurons induces neuroendocrine and behavioral responses that increase blood pressure.

Sigma receptors modulate nociception, offering a potential therapeutic target to treat pain, but relatively little is known regarding the role of sigma-2 receptors (S2R) in nociception. The purpose of this study was to investigate the in vivo analgesic and anti-allodynic activity and liabilities of a novel S2R selective ligand, 1-[4-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin-2-yl)butyl]-3-methyl-1,3-dihydro-1,3-benzimidazol-2-one (CM-398). The inhibition of thermal, induced chemical, or inflammatory pain as well as the allodynia resulting from chronic nerve constriction injury (CCI) model of neuropathic pain were assessed in male mice. CM-398 dose-dependently (10–45 mg/kg i.p.) reduced mechanical allodynia in the CCI neuropathic pain model, equivalent at the higher dose to the effect of the control analgesic gabapentin (50 mg/kg i.p.). Likewise, pretreatment (i.p.) with CM-398 dose-dependently produced antinociception in the acetic acid writhing test (ED50 (and 95% C.I.) = 14.7 (10.6–20) mg/kg, i.p.) and the formalin assay (ED50 (and 95% C.I.) = 0.86 (0.44–1.81) mg/kg, i.p.) but was without effect in the 55 °C warm-water tail-withdrawal assay. A high dose of CM-398 (45 mg/kg, i.p.) exhibited modest locomotor impairment in a rotarod assay and conditioned place aversion, potentially complicating the interpretation of nociceptive testing. However, in an operant pain model resistant to these confounds, mice experiencing CCI and treated with CM-398 demonstrated robust conditioned place preference. Overall, these results demonstrate the S2R selective antagonist CM-398 produces antinociception and anti-allodynia with fewer liabilities than established therapeutics, adding to emerging data suggesting possible mediation of nociception by S2R, and the development of S2R ligands as potential treatments for chronic pain.

No abstract

Considerable evidence has implicated the renin‐angiotensin system (RAS) as an important target for the therapeutic alleviation of stress‐related mood disorders. Along these lines, the ‘pro‐stress’ actions of Angiotensin‐II are largely thought to be mediated by the angiotensin type‐1 receptor (AT1R). On the other hand, the protective limb of the RAS that depends on the conversion of angiotensin‐II to angiotensin‐(1–7) by angiotensin‐converting enzyme 2 (ACE2) has been postulated to dampen stress and relieve anxiety. We have previously found that augmenting ACE2 activity has potent anxiolytic and hypothalamic‐pituitary‐adrenal (HPA) axis‐dampening effects in male mice. Relative to males, females are more susceptible to stress‐related mood disorders; however, whether increasing ACE2 activity in females also blunts stress responses has not been determined. This study tests the hypothesis that ACE2 overexpression decreases anxiety‐like behavior and attenuates stress‐induced HPA axis activation in female mice. We used the Cre/Lox system to generate female mice that ubiquitously overexpress ACE2. Female ACE2 knock‐in (ACEKI) mice and their wild‐type littermate controls were tested in the elevated‐plus maze (EPM), Light‐Dark Box (LDB), and Graham Cracker Test to evaluate the impact that augmenting ACE2 expression has on anxiety‐like behavior. Female mice were also subjected to an acute 30 min restraint stress challenge and blood samples were collected in order to evaluate HPA (i.e., corticosterone) reactivity. As expected, Cre‐Lox mediated overexpression of ACE2 resulted in elevated ACE2 mRNA and enzymatic activity in all tissues examined (i.e., hypothalamus, pituitary, blood, and brain). Relative to controls, ACE2KI mice spent significantly (p < 0.05) more time in the open arms of the EPM and in the light side of the LDB. When placed in a novel environment, ACEKI mice exhibited a significantly (p<0.05) decreased latency to consume graham crackers relative to controls. Importantly, total distance traveled in the EPM was not different between the groups, indicating that the locomotor activity of the female mice is unchanged by ACE2 overexpression. Interestingly, basal and acute stress‐induced corticosterone levels did not differ between ACE2KI and WT female mice. These results suggest that although neuroendocrine response to acute restraint was unaffected in females, ACE2 overexpression has anxiolytic effects on both male and female ACE2KI mice. Furthermore, our findings support the idea that the RAS may be a worthy target in the search for novel therapeutic interventions for stress‐related disorders.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.