Alveolar liquid clearance in lung injury: Evaluation of the impairment of the ß2-adrenergic agonist response in an ischemia-reperfusion lung injury model.

While alveolar liquid clearance (ALC) mediated by the ß2-adrenergic receptor (ß2-AR) plays an important role in lung edema resolution in certain models of lung injury, in more severe lung injury models, this response might disappear. Indeed, we have shown that in an ischemia-reperfusion-induced lung injury model, ß2-agonists do not enhance ALC. The objective of this study was to determine if downregulation of the ß2-AR could explain the lack of response to ß2-agonists in this lung injury model. In an in vivo canine model of lung transplantation, we observed no change in ß2-AR concentration or affinity in the injured transplanted lungs compared to the native lungs. Furthermore, we could not enhance ALC in transplanted lungs with dcAMP + aminophylline, a treatment that bypasses the ß2-adrenergic receptor and is known to stimulate ALC in normal lungs. However, transplantation decreased αENaC expression in the lungs by 50%. We conclude that the lack of response to ß2-agonists in ischemia-reperfusion-induced lung injury is not associated with significant downregulation of the ß2-adrenergic receptors but is attributable to decreased expression of the ENaC channel, which is essential for sodium transport and alveolar liquid clearance in the lung.

Essential role for orbitofrontal serotonin 1B receptors in obsessive-compulsive disorder-like behavior and serotonin reuptake inhibitor response in mice.

BACKGROUND: Perseveration and sensorimotor gating deficits are core features of obsessive-compulsive disorder (OCD). Serotonin 1B receptor (5-HT1BR) agonists exacerbate OCD symptoms in patients and induce perseveration and sensorimotor gating deficits in mice. Serotonin reuptake inhibitors (SRIs), but not noradrenaline reuptake inhibitors (NRIs), reduce OCD symptoms following 4 to 8 weeks of treatment. Using mice, we compared the effects of chronic SRI versus NRI treatment on 5-HT1BR-induced OCD-like behavior and 5-HT1BR sensitivity in orbitofrontal-subcortical OCD circuits. Furthermore, we localized the 5-HT1BR population that mediates OCD-like behavior. METHODS: Mice chronically received the SRI clomipramine or the NRI desipramine and were examined for 5-HT1BR-induced OCD-like behavior or 5-HT1BR binding and G-protein coupling in caudate putamen, nucleus accumbens, and orbitofrontal cortex. Separate mice were tested for OCD- or depression-like behavior following 4, 14, 21, 28, or 56 days of SRI treatment. Finally, OCD-like behavior was assessed following intra-orbitofrontal 5-HT1BR agonist infusion or intra-orbitofrontal 5-HT1BR antagonist infusion coupled with systemic 5-HT1BR agonist treatment. RESULTS: Effective, but not ineffective, OCD treatments reduced OCD-like behavior in mice with a time course that parallels the delayed therapeutic onset in OCD patients and downregulated 5-HT1BR expression in the orbitofrontal cortex. Intra-orbitofrontal 5-HT1BR agonist infusion induced OCD-like behavior, and intra-orbitofrontal 5-HT1BR antagonist infusion blocked OCD-like effects of systemic 5-HT1BR agonist treatment. CONCLUSIONS: These results indicate that orbitofrontal 5-HT1BRs are necessary and sufficient to induce OCD-like behavior in mice and that SRI pharmacotherapy reduces OCD-like behavior by desensitizing orbitofrontal 5-HT1BRs. Our findings suggest an essential role for orbitofrontal 5-HT1BRs in OCD pathophysiology and treatment.

Reduced cortical noradrenergic neurotransmission is associated with increased neophobia and impaired spatial memory in aged rats.

In the present study, young (5-month-old (mo)) and aged (24 mo) adult male Fischer-344 (F344) rats were assigned to experimental groups based upon their performance of a reference memory task in the Morris water maze and reactivity to a novel palatable taste in a gustatory neophobia task. Levels of norepinephrine (NE) and its metabolite 3-methoxy-4-hydroxy-phenylglycol (MHPG) were assayed via high performance liquid chromatography (HPLC) in brain regions associated with the locus coeruleus (LC)-hippocampus-cortex system and A1/A2-hypothalamic system. Binding of ligands specific for alpha-1, alpha-2, beta-1, and beta-2 receptors was assessed in hippocampus and cortex with receptor autoradiography. Impaired acquisition and retention of the water maze task and gustatory neophobia in aged rats was primarily associated with decreased NE activity in cingulate cortex (CC) as indicated by a significant reduction in the MHPG/NE ratio coupled with increased NE content. No significant changes in adrenergic receptor binding were detected in any region sampled. The results suggest that an aging-related reduction in cortical NE neurotransmission is associated with the expression of increased neophobia and deficits in spatial learning and memory performance occurring with advanced age in rats.

Genotype-dependent time course of lymphocyte beta 2-adrenergic receptor down-regulation.

BACKGROUND: Volunteers homozygous for Glu27 beta(2)-adrenergic receptor (beta(2)AR) polymorphism have delayed onset of agonist-induced desensitization of cardiac beta(2)AR responses. METHODS AND RESULTS: To determine whether this can also be demonstrated for Glu27Glu beta(2)AR natively expressed in circulating lymphocytes, we assessed the effects of 2 weeks of oral treatment with 3 x 5 mg/d terbutaline on lymphocyte beta(2)AR density (determined by [-]-[iodine 125]iodocyanopindolol binding) and responsiveness (assessed as [-]-isoproterenol hydrochloride [INN, isoprenaline] [1 nmol/L to 1 micromol/L]-induced lymphocyte cyclic adenosine monophosphate increases) in 23 healthy volunteers (13 with wild-type beta(2)AR [group A], 5 homozygous for Glu27 with Gly16Gly or Arg16Gly [group B], and 5 homozygous for Gly16 with Gln27Gln or Gln27Glu [group C]). Before terbutaline treatment, lymphocyte beta(2)AR density and isoproterenol-induced lymphocyte cyclic adenosine monophosphate accumulation were not significantly different in the genotype groups; 2 weeks of terbutaline treatment significantly decreased lymphocyte beta(2)AR density and responsiveness in the 3 genotype groups to a nearly identical extent, and no differences were observed. In time-course studies, however, in groups A and C lymphocyte beta(2)AR showed significant (P <.05, repeated-measures ANOVA) down-regulation as early as 24 hours after the first terbutaline intake, whereas in group B significant (P <.05, repeated-measures ANOVA) beta(2)AR decreases were observed only 72 hours after the first terbutaline intake. Thus the time course of lymphocyte beta(2)AR down-regulation in group B was significantly (P <.01, 2-way ANOVA) different from that in groups A and C. CONCLUSION: The extent of lymphocyte beta(2)AR down-regulation after long-term terbutaline treatment in volunteers homozygous for the Gly16 or Glu27 beta(2)AR polymorphism was genotype-independent and was nearly identical to that in wild-type beta(2)AR volunteers. However, the onset of beta(2)AR down-regulation was delayed in volunteers homozygous for the Glu27 beta(2)AR polymorphism.

The anabolic-androgenic steroid nandrolone induces alterations in the density of serotonergic 5HT1B and 5HT2 receptors in the male rat brain.

Anabolic-androgenic steroids (AAS) are partly misused by males in order to become brave and intoxicated and these agents are highly associated with psychosis, disinhibition, aggression and acts of violence. Since such behavioral states have been related to an imbalanced serotonergic system and the involvement of the serotonergic 5HT(1B) and the 5HT(2) receptors, it was important to discern the impact of AAS on these receptors. The objective of our study was to investigate the effects of 2 weeks of treatment with the AAS nandrolone decanoate at three different doses (1, 5, 15 mg/kg/day) on the total specific binding of the radioligands [(125)I]-(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (5HT(2) receptors) by autoradiography. All doses caused a significant down-regulation of the 5HT(1B) receptor density in the hippocampal CA(1) and in the medial globus pallidus and a significant up-regulation of the 5HT(2) receptor density in the nucleus accumbens shell. Alterations in receptor density were also observed in the lateral globus pallidus, ventromedial hypothalamus, the amygdala and in the intermediate layers of various cortex regions. In conclusion, serotonergic 5HT(1B) or 5HT(2) receptors are likely to play important roles in mediating observed emotional states and behavioral changes among AAS abusers.

Relative uptake, metabolism, and beta-receptor binding of (1R,2S)-4-(18)F-fluorometaraminol and (123)I-MIBG in normotensive and spontaneously hypertensive rats.

UNLABELLED: The objective of the study was to compare relative uptake, metabolism, and beta-receptor affinity of the new positron-emitting uptake-1 tracer (1R,2S)-4-(18)F-fluorometaraminol (4-FM) with those of the SPECT pharmaceutical meta-(123)I-iodobenzylguanidine (MIBG) in Wistar Kyoto (WKY) rats and spontaneously hypertensive (SHR) rats. METHODS: No-carrier-added 4-(18)F-FM was applied to SHR and WKY rats in vivo and to retrogradely perfused hearts in vitro. Cardiac and extracardiac distribution was assessed, and metabolite formation was determined by thin-layer chromatography. The in vivo experiments were repeated with no-carrier-added (123)I-MIBG. By means of autoradiography, the beta-receptor affinity of 4-FM was compared with that of MIBG and propranolol (10 micromol/L) through displacement of (125)I-iodocyanopindolol (1.5 pmol/L) in slices of heart and spleen. RESULTS: Cardiomyopathic hearts showed heterogeneous 4-(18)F-FM uptake with gradients up to 3.6 in vivo and in vitro between different regions of the heart. Control hearts showed such gradients in 4-(18)F-FM uptake only in vitro. (123)I-MIBG exhibited a less heterogeneous in vivo distribution in SHR hearts. Extracardiac differences between WKY and SHR were found for uptake of 4-(18)F-FM in the spleen (63.3% plus minus 4% vs. 38.8% plus minus 5.7% of cardiac activity) and for renal uptake of (123)I-MIBG (373% plus minus 27% vs. 81.4% plus minus 17% of cardiac activity). Metabolites of 4-(18)F-FM were found only in the liver and those of (123)I-MIBG were found in the liver and kidney with a nearly equal relative fraction in both types of animals of about 20%, 60%, and 30%, respectively. 4-FM suppressed cardiac-specific beta-receptor binding of (125)I-iodocyanopindolol in heart and spleen of both types of animals significantly, whereas MIBG had almost no effect. CONCLUSION: The more heterogeneous cardiac distribution of 4-(18)F-FM suggests that it reflects alterations in uptake-1 better than (123)I-MIBG in addition to the possibility of quantification and higher spatial resolution by PET compared with SPECT. Altered biotransformation in cardiomyopathic diseases may also impair the evaluation of (123)I-MIBG-SPECT data. The beta-receptor binding of 4-(18)F-FM must be further elucidated.

Heterogeneous cardiac sympathetic innervation in heart failure after myocardial infarction of rats.

We examined cardiac neuronal function and beta-receptor with a dual-tracer method of [(131)I]meta-iodobenzylguanidine (MIBG) and [(125)I]iodocyanopindolol (ICYP) in rat heart failure after myocardial infarction (MI). In rats with MI, left ventricular (LV) systolic function decreased, and LV dimension and right ventricular (RV) mass increased gradually. MIBG accumulations of the noninfarcted LV (remote region) and RV decreased by 15% at 1 wk compared with sham-operated rats, and these accumulations were restored by 71% and 56%, respectively, at 24 wk compared with age-matched sham rats despite sustained depletion of myocardial norepinephrine contents in these regions. ICYP accumulation of the remote region and of the RV did not decrease at any stages. Myocardial MIBG distribution was heterogeneous at 1 wk when it was lower in the peri-infarcted region than in the remote region, associated with reduced ICYP accumulation in the peri-infarcted region. The heterogeneous distribution of both isotopes disappeared at 12 wk. Thus cardiac sympathetic neuronal alteration was coupled with downregulation of beta-receptors in rat heart failure after MI. The abnormal adrenergic signaling occurred heterogeneously in terms of ventricular distribution and time course after MI.

Aging regulates 5-HT(1B) receptors and serotonin reuptake sites in the SCN.

Middle age is associated with changes in circadian rhythms (e.g., alterations in the timing of the circadian wheel running rhythm) which resemble changes induced by selective destruction of the serotonergic input to the suprachiasmatic nucleus (SCN), the principal mammalian circadian pacemaker. We hypothesized that serotonergic neurotransmission in the SCN is decreased in middle-aged hamsters, as compared to young adults. This hypothesis was tested indirectly by investigating the effect of aging on two markers of serotonin neurotransmission, 5-HT(1B) receptors and serotonin reuptake sites, which are regulated by serotonin. Previous studies have shown that experimentally induced decreases in serotonergic neurotransmission increase 5-HT(1B) receptors but decrease serotonin reuptake sites. Quantitative autoradiography was conducted using [125I]iodocyanopindolol ([125I]ICYP) and [3H]paroxetine, selective radioligands for the 5-HT(1B) receptors and the serotonin reuptake sites, respectively. Consistent with the hypothesis, specific ([125I]ICYP binding was significantly elevated in the SCN of middle-aged hamsters, as compared to young hamsters. The results also showed that serotonin reuptake sites in the SCN were significantly increased in both middle-aged and old hamsters, as compared to young controls. This result could not have been caused by decreased serotonin release. Alternatively, increased serotonin reuptake, which would reduce serotonin levels in the synaptic cleft, may cause or contribute to the increase in 5-HT(1B) receptor binding in the SCN in middle aged animals. These results show that the SCN exhibits changes in serotonergic function during middle age, which has been characterized by changes in the expression of circadian rhythms. Because these changes occur during middle age, they probably reflect the aging process, rather than senescence or disease.

Differential addressing of 5-HT1A and 5-HT1B receptors in epithelial cells and neurons.

The 5-HT1A and 5-HT1B serotonin receptors are expressed in a variety of neurons in the central nervous system. While the 5-HT1A receptor is found on somas and dendrites, the 5-HT1B receptor has been suggested to be localized predominantly on axon terminals. To study the intracellular addressing of these receptors, we have used in vitro systems including Madin-Darby canine kidney (MDCK II) epithelial cells and primary neuronal cultures. Furthermore, we have extended these studies to examine addressing in vivo in transgenic mice. In epithelial cells, 5-HT1A receptors are found on both apical and basolateral membranes while 5-HT1B receptors are found exclusively in intracellular vesicles. In hippocampal neuronal cultures, 5-HT1A receptors are expressed on somatodendritic membranes but are absent from axons. In contrast, 5-HT1B receptors are found on both dendritic and axonal membranes, including growth cones where they accumulate. Using 5-HT1A and 5-HT1B knockout mice and the binary tTA/tetO system, we generated mice expressing these receptors in striatal neurons. These in vivo experiments demonstrate that, in striatal medium spiny neurons, the 5-HT1A receptor is restricted to the somatodendritic level, while 5-HT1B receptors are shipped exclusively toward axon terminals. Therefore, in all systems we have examined, there is a differential sorting of the 5-HT1A and 5-HT1B receptors. Furthermore, we conclude that our in vivo transgenic system is the only model that reconstitutes proper sorting of these receptors.