Signal transduction by the platelet Fc receptor

We have evaluated the mechanism by which crosslinking human platelet Fc receptor (FcR) for IgG triggers platelet aggregation and the platelet release reaction. Platelet FcR was crosslinked by incubating purified human platelets with anti-FcRII monoclonal antibody and F(ab')2 anti- mouse Ig. The resultant [Ca2+]i increase, monitored by Fura-2 and measured in the absence of extracellular Ca2+, reached a peak of 750 +/- 50 nmol/L. The effects of cyclooxygenase inhibitors, aspirin and indomethacin, and a phospholipase A2 inhibitor, dibromoacetophenone, were examined. Regardless of the inhibitor, at least 25% of the [Ca2+]i increase remained. Thrombin (0.2 U/mL) stimulated an immediate [Ca2+]i increase that reached 1.95 +/- 0.8 mumol/L. The [Ca2+]i increase generated by thrombin was only slightly reduced by these inhibitors. Crosslinking the FcRII of platelets resulted in a fivefold increase in the production of [3H]inositol phosphates, (IP) which, in the absence of extracellular Ca2+ was insensitive to aspirin. The activation of a [Ca2+]i increase along with the measured increases in IP indicate that FcRII crosslinking leads to the activation of phospholipase C (PLC). In contrast to thrombin, platelet activation via FcRII depends to a large extent on arachidonic acid metabolites. However, neither cyclooxygenase nor phospholipase A2 inhibitors completely blocked FcRII-stimulated [Ca2+]i increase. These observations led us to propose that crosslinking of platelet FcRII initially activates PLC.     

The Role of Serotonin (5-HT) in Behavioral Control: Findings from Animal Research and Clinical Implications

The neurotransmitters serotonin and dopamine both have a critical role in the underlying neurobiology of different behaviors. With focus on the interplay between dopamine and serotonin, it has been proposed that dopamine biases behavior towards habitual responding, and with serotonin offsetting this phenomenon and directing the balance toward more flexible, goal-directed responding. The present focus paper stands in close relationship to the publication by Worbe et al. (2015), which deals with the effects of acute tryptophan depletion, a neurodietary physiological method to decrease central nervous serotonin synthesis in humans for a short period of time, on the balance between hypothetical goal-directed and habitual systems. In that research, acute tryptophan depletion challenge administration and a following short-term reduction in central nervous serotonin synthesis were associated with a shift of behavioral performance towards habitual responding, providing further evidence that central nervous serotonin function modulates the balance between goal-directed and stimulus-response habitual systems of behavioral control. In the present focus paper, we discuss the findings by Worbe and colleagues in light of animal experiments as well as clinical implications and discuss potential future avenues for related research.     

Hyposomatomedinemia in men with post-poliomyelitis syndrome

The age of onset of the post-poliomyelitis syndrome (PPS) coincides with the tendency for declining activity of the growth hormone/somatomedin C (GH/SmC) axis. The normal plasma SmC range in men before the age of 40 is 0.50 to 1.50 units/mL. After age 40 about 30% of men have a plasma SmC level below 0.35 units/mL, signifying no detectable spontaneous GH secretory pulses. Because the GH/SmC axis stimulates DNA, RNA, and protein synthesis in muscle cells and increases their size and number, a deficiency of the GH/SmC axis could theoretically contribute as a secondary factor to the occurrence or severity of the PPS. Accordingly, the authors measured the plasma SmC level in 10 men with PPS, ages 35 to 63, and in 94 healthy men of similar age. In the PPS men, 100% of the values were less than or equal to 0.40 units/mL, and 90% were less than or equal to 0.35 units/mL. The corresponding proportions in the healthy men were 40% and 27%. Analysis of variance including age as a factor showed SmC to be significantly lower in the PPS men than in the healthy men. In an additional comparison, totally immobile nursing home men did not have lowered SmC values. In fact their SmC values were slightly higher than those of healthy men of similar age. The data revealed a new biochemical feature of PPS, hyposomatomedinemia, which might play a contributory role in the pathogenesis of the syndrome.     

Plasma dehydroepiandrosterone sulfate in nursing home men

Previous studies have shown the normal range of plasma dehydroepiandrosterone sulfate (DHEAS) for independent community men over 60 years old to be 30-200 micrograms/dL. In human adults, low levels of plasma DHEAS have been correlated with a high mortality rate. In rodents, dehydroepiandrosterone, the precursor of DHEAS, has exhibited antidiabetic, anticarcinogenic, neurotropic, and memory-enhancing effects. We have now measured plasma DHEAS in 50 independent community men age 55-94 and in 61 nursing home men age 57-104. Mean DHEAS was significantly lower in the nursing home men than in the community men. Plasma DHEAS was subnormal (less than 30 micrograms/dL) in 40% of the nursing home residents and in only 6% of the community subjects. In both groups, DHEAS was inversely related to age. In the nursing home men, additionally, plasma DHEAS was inversely related to the presence of an organic brain syndrome and to the degree of dependence in activities of daily living. Plasma DHEAS was subnormal in 80% of the nursing home men who required total care. There was no significant correlation between the plasma concentrations of DHEAS and testosterone, or between plasma DHEAS and one-year mortality rate.     

Regulation of crab Y-organ steroidogenesis in vitro: evidence that ecdysteroid production increases through activation of cAMP-phosphodiesterase by calcium-calmodulin

In decapod crustaceans steroidogenic glands (Y-organs) produce the molting hormone, ecdysone. A putative neuropeptide, molt-inhibiting hormone (MIH), released from eyestalk neurosecretory cells, directly regulates Y-organs by suppressing steroidogenesis; the effect is mediated by an increase in cAMP. We explored calcium-cAMP interactions in the regulation of Y-organs in vitro of the crab, Cancer antennarius. Basal ecdysteroid production was enhanced by extracellular calcium (EC). MIH suppression did not require EC but its action was blocked by high EC. The inhibitors of Ca2+ flux, lanthanum and ruthenium red, mimicked and enhanced MIH action. Calcium ionophore A23187 raised basal steroidogenesis dose-dependently (10(-6) to 10(-4) M) and with time course (effect evident after 2 h) similar to that of suppression by MIH. Low EC enhanced the suppressive effects on steroidogenesis of forskolin and dibutyryl cyclic AMP ((Bu)2cAMP) but not of MIH, lysine vasopressin (LVP), or 3-isobutyl-1-methyl-xanthine (IBMX); basal Y-organ cAMP levels were elevated by low EC and reduced by A23187. A23187 reduced the steroidogenic-suppressive effects of MIH, LVP, forskolin and (Bu)2cAMP but not of IBMX; rises in cAMP induced by MIH, LVP, and forskolin but not by IBMX were blunted by A23187. These findings suggested a stimulatory action of calcium on phosphodiesterase (PDE). The calmodulin (CM) inhibitor trifluoperazine (TFP; 10(-5) to 10(-4) M) reduced basal and A23187-stimulated steroidogenesis, enhanced the inhibitory effects of MIH and (Bu)2cAMP on ecdysteroid production, enhanced the stimulatory effects of MIH and forskolin on cAMP, and blocked the inhibition of cAMP by A23187. Y-organ PDE activity was enhanced by increasing free Ca2+ (10(-7) to 10(-5) M) and inhibited by TFP (10(-5) to 10(-4) M). Adenylate cyclase activity of Y-organ cell particulate fraction was unaffected by Ca2+ or TFP. Calcium stimulates steroidogenesis, apparently by activating a calcium-CM-dependent cAMP-PDE: the action is counter to the cAMP-mediated MIH-inhibitory system. Ca2+ fluxes were measured with dispersed Y-organ cells, in the presence and absence of agents that alter cAMP levels. The ionophore A23187, but not MIH or forskolin, increased 45Ca2+ entry by 45% over untreated control cells. Efflux from 45Ca2+-preloaded cells was increased 30% by MIH and forskolin, but not A23187. These data, together with those further above, suggest that MIH suppresses steroidogenesis in part by fostering Ca2+ depletion, and that the effect is mediated by cAMP.     

Comparison of Social Abilities of Children with Fetal Alcohol Syndrome to Those of Children with Similar IQ Scores and Normal Controls

Children diagnosed with fetal alcohol syndrome (FAS) were assessed with items from the social skills domain of the Vineland Adaptive Behavior Scales (VABS) via interviews with their caregivers. Their scores were compared with scores from children in two control groups. The control groups included children matched for IQ to the FAS group (specifically on verbal IQ, henceforth, the VIQ group) and children with IQ scores in the average to above-average range (normal control group). Forty-five children (age range, 5 years 7 months to 12 years 11 months) were assessed ( n /group = 15). All groups differed with regard to social ability, as measured by the VABS (NC > VIQ > FAS), even when the effects of socioeconomic status were held constant. The three subdomains of the VABS social scale (interpersonal relationship skills, use of play and leisure time, and coping skills) were assessed, and results showed that the children with FAS were most impaired on the subdomain that assessed interpersonal relationship skills. An additional measure was constructed by obtaining an age-equivalent score for the VABS social scale and calculating a difference score by subtracting the child's chronological age from his/her age-equivalent score. There was a significant correlation between chronological age and difference scores for children in the FAS group but not for children in the two control groups. Specifically, in older children with FAS, there was an increased discrepancy between their ages and their age-equivalent scores, a discrepancy that was not present in children in the control groups. These results suggest that social deficits in children with FAS are beyond what can be explained by low IQ scores and indicate that there may be arrested, and not simply delayed, development of social abilities in children with FAS.     

Age-related impairment of cerebral blood flow response to KATP channel opener in Alzheimer’s disease mice with presenilin-1 mutation

Local cerebral blood flow (CBF) responses to neuronal activity are essential for cognition and impaired CBF responses occur in Alzheimer’s disease (AD). In this study, regional CBF (rCBF) responses to the K_ATP channel opener diazoxide were investigated in 3xTgAD, WT and mutant Presenilin 1(PS1_M146V) mice from three age groups using Laser-Doppler flowmetry. The rCBF response was reduced early in young 3xTgAD mice and almost absent in old 3xTgAD mice, up to 30%–40% reduction with altered CBF velocity and mean arterial pressure versus WT mice. The impaired rCBF response in 3xTgAD mice was associated with progression of AD pathology, characterized by deposition of intracellular and vascular amyloid-β (Aβ) oligomers, senile plaques and tau pathology. The nitric oxide synthase (NOS) inhibitor N^ω-nitro-L-arginine abolished rCBF response to diazoxide suggesting NO was involved in the mediation of vasorelaxation. Levels of phosphor-eNOS (Ser1177) diminished in 3xTgAD brains with age, while the rCBF response to the NO donor sodium nitroprusside remained. In PS1_M146V mice, the rCBF response to dizoxide reduced and high molecular weight Abeta oligomers were increased indicating PS1_M146V contributed to the dysregulation of rCBF response in AD mice. Our study revealed an Aβ oligomer-associated compromise of cerebrovascular function in rCBF response to diazoxide in AD mice with PS1_M146V mutation.     

Activated natural killer cells and interleukin-2 promote granulocytic and megakaryocytic reconstitution after syngeneic bone marrow transplantation in mice

Purified populations of natural killer (NK) cells were obtained from mice with severe combined immune deficiency (SCID). SCID spleen cells were cultured and activated with recombinant human interleukin-2 (rhIL- 2) in vitro. The activated NK cells were then transferred with syngeneic BALB/c bone marrow cells (BMC) and rhIL-2 into lethally irradiated syngeneic recipients to determine their effect on long-term hematopoietic reconstitution. On analysis, the transfer of rhIL-2- activated NK cells along with BMC resulted in significant increases in splenic and BM hematopoietic progenitor cells when compared with those for mice not receiving NK cells. Histologic and flow cytometric analysis showed a marked increase in granulocytic and megakaryocytic lineage cells present in the spleens of the mice receiving activated NK cells. Analysis of the peripheral blood indicated that the transfer of activated NK cells with BMC also significantly improved platelet and total white blood cell counts, with increases in segmented neutrophils. Erythroid recovery was not affected. Finally, lethally irradiated mice receiving activated NK cells and rhIL-2 along with limiting numbers of syngeneic BMC showed a marked increase in survival rate. These results show that the use of populations enriched for activated NK cells after syngeneic BM transplantation (BMT) has a profound enhancing effect on engraftment primarily affecting megakaryocytic and granulocytic cell reconstitution. Therefore, the transfer of activated NK cells and rhIL- 2 may be of clinical use to promote hematopoietic reconstitution after BMT.