SUMMARY Psychosocial stress accelerates myelopoietic production of monocytes and neutrophils that contributes to a variety of health complications ranging from atherosclerosis to anxiety. Here, we show that social stress in mice mobilizes hematopoietic stem progenitor cells (HSPCs) from the bone marrow that enter circulation, engraft into the spleen, and establish a persistent extramedullary hematopoietic depot. These splenic progenitors actively proliferate and differentiate into multiple cell types, including monocytes, neutrophils, and erythrocytes. Splenic erythropoiesis partially abrogates stress-induced anemia. Repeated injection with isoprenaline induces progenitor mobilization to the spleen, identifying a key role for β-adrenergic signaling. Moreover, protracted splenic production of CD11b+ cells persists for at least 24 days after the cessation of social stress. Thus, chronic stress establishes a persistent extramedullary hematopoietic depot that can modify a wide range of chronic disease processes and alter homeostasis of the bi-directional regulatory axis between the nervous and immune systems.

Background: Stress is associated with an increased prevalence of anxiety and depression. Repeated social defeat (RSD) stress in mice increases the release of monocytes from the bone marrow that are recruited to the brain by microglia. These monocytes enhance inflammatory signaling and augment anxiety. Moreover, RSD promotes "stress-sensitization", in which exposure to acute stress 24 days after cessation of RSD causes anxiety recurrence. The purpose of this study was to determine if microglia were critical to stress-sensitization and exhibited increased reactivity to subsequent acute stress or immune challenge.Methods: Mice were exposed to RSD, microglia were eliminated by CSF1R-antagonism (PLX5622), allowed to repopulate, and responses to acute stress or immune challenge (lipopolysaccharide) were determined 24 days after RSD-sensitization.Results: Microglia maintained a unique mRNA signature 24 d after RSD. Moreover, elimination of RSD-sensitized microglia prevented monocyte accumulation in the brain and blocked anxiety recurrence following acute stress (24 d). When microglia were eliminated prior to RSD, repopulated and mice were subjected to acute stress, there was monocyte accumulation in the brain and anxiety in RSD-sensitized mice. These responses were unaffected by microglial elimination/repopulation. This may be related to neuronal sensitization that persisted 24 d after RSD. Following immune challenge, there was robust microglial reactivity in RSD-sensitized mice associated with prolonged sickness behavior. Here, microglial elimination/repopulation prevented the amplified immune reactivity ex vivo and in vivo in RSD-sensitized mice.

It has been hypothesized that alcohol addiction is mediated, at least in part, by specific gamma-aminobutyric acid(A) (GABA(A)) receptors within the ventral pallidum (VP). Among the potential GABA(A) receptor isoforms regulating alcohol-seeking behaviors within the VP, the GABA(A) alpha1 receptor subtype (GABA(A1)) appears pre-eminent. In the present study, we developed beta-carboline-3-carboxylate-t-butyl ester (betaCCt), a mixed agonist-antagonist benzodiazepine (BDZ) site ligand, with binding selectivity at the A1 receptor to explore the functional role of VP(A1) receptors in the euphoric properties of alcohol. The in vivo actions of betaCCt were then determined following microinfusion into the VP, a novel alcohol reward substrate that primarily expresses the A1 receptor. In two selectively bred rodent models of chronic alcohol drinking (HAD-1, P rats), bilateral microinfusion of betaCCt (0.5-40 microg) produced marked reductions in alcohol-reinforced behaviors. Further, VP infusions of betaCCt exhibited both neuroanatomical and reinforcer specificity. Thus, no effects on alcohol-reinforced behaviors were observed following infusion in the nucleus accumbens (NACC)/caudate putamen (CPu), or on response maintained by saccharin. Parenteral-administered betaCCt (1-40 mg/kg) was equally effective and selective in reducing alcohol-reinforced behaviors in P and HAD-1 rats. Additional tests of locomotor activity revealed that betaCCt reversed the locomotor sedation produced by both chlordiazepoxide (10 mg/kg) and EtOH (1.25 g/kg), but was devoid of intrinsic effects when given alone. Studies in recombinant receptors expressed in Xenopus oocytes revealed that betaCCt acted as a low-efficacy partial agonist at alpha3beta3gamma2 and alpha4beta3gamma2 receptors and as a low-efficacy inverse agonist at alpha1beta3gamma2, alpha2beta3gamma2, and alpha5beta3gamma2 receptors. The present study indicates that betaCCt is capable of antagonizing the reinforcing and the sedative properties of alcohol. These anti-alcohol properties of betaCCt are primarily mediated via the GABA(A1) receptor. betaCCt may represent a prototype of a pharmacotherapeutic agent to effectively reduce alcohol drinking behavior in human alcoholics.

The present study tested the hypothesis that GABA A and opioid receptors within the central nucleus of the amygdala (CeA) regulate ethanol (EtOH), but not sucrose-maintained responding. To accomplish this, bCCt, a mixed benzodiazepine (BDZ) agonist-antagonist with binding selectivity at the a1 subunit-containing GABA A receptor, and the nonselective opioid antagonist, naltrexone, were bilaterally infused directly into the CeA of alcohol-preferring rats. The results demonstrated that in HAD-1 and P rat lines, bCCt (5-60 mg) reduced EtOH-maintained responding by 56-89% of control levels. On day 2, bCCt (10-40 mg) continued to suppress EtOH maintained responding in HAD-1 rats by as much as 60-85% of control levels. Similarly, naltrexone (0.5-30 mg) reduced EtOH-maintained responding by 56-75% of control levels in P rats. bCCt and naltrexone exhibited neuroanatomical and reinforcer specificity within the CeA. Specifically, no effects on EtOH-maintained responding were observed following infusion into the caudate putamen (CPu), a locus several millimeters dorsal to the CeA. Additionally, responding maintained by sucrose, when presented concurrently with ethanol (EtOH) or presented alone, was not altered by bCCt. Naltrexone reduced sucrose-maintained responding only under the 5 mg dose condition when sucrose was presented alone, however, it did not alter sucrose responding when given concurrently with EtOH. These results support the hypothesis that GABA A and opioid receptors within the CeA can selectively regulate EtOH-maintained responding. The CeA may represent a novel target site in the development of prototypical GABA A and opioidergic receptor ligands, which selectively reduce alcohol abuse in humans.