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Biomedical subjects

P Skolnick

Publications and source records attributed to P Skolnick.

At least 145 records · Page 8Linked to original sources
PubMed1991

Inhibition of calcium mobilization is an early event in opiate-induced immunosuppression.

Morphine administered as a subcutaneous implant inhibits the initial increase in cytoplasmic free-calcium [Ca2+]i induced by mitogens in mouse splenocytes. This effect was not reproduced by incubation of splenocytes with morphine (10(-8)-10(-4) M). Analysis of splenocyte subpopulations demonstrates that this effect was manifest in both B and T cells. However, within T cell subpopulations, CD4+ but not CD8+ cells were affected. Adrenalectomy abolished this effect of morphine in CD4+ T but not CD4-, CD8- spleen cells (most likely Thy 1.2- B cells). Moreover, simultaneous administration of the opiate antagonist naltrexone blocked the effect of morphine in CD4-, CD8- spleen cells, but not in CD4+ T cells. These data indicate that the effects of morphine on mitogen-stimulated increase in [Ca2+]i may be mediated through distinct glucocorticoid-dependent and -independent mechanisms. The morphine-induced inhibition of an increase in [Ca2+]i in immune cells reported here may be an early event mediating opiate-induced immunosuppression.

Animals↗
PubMed1991

t-[35S]butylbicyclophosphorothionate binding under equilibrium and nonequilibrium conditions: differential effects of barbiturates and gamma-aminobutyric acid in the long-sleep and short-sleep selected mouse lines.

Significant differences were demonstrated between the long-sleep (LS) and short-sleep (SS) selected mouse lines in the abilities of barbiturates and gamma-aminobutyric acid (GABA) to inhibit t-[35S]butylbicyclophosphorothionate [( 35S]TBPS) binding to well-washed cerebral cortical membranes. Thus, using phenobarbital to initiate the dissociation of [35S]TBPS, the extent of inhibition was significantly greater in LS mice (but not SS mice) than would be predicted using equilibrium conditions. Pentobarbital had the opposite effect, causing [35S]TBPS to dissociate to a greater extent in SS than LS membranes. [35S]TBPS binding was dissociated from LS and SS membranes by GABA to a greater and lesser extent, respectively, than would be predicted from equilibrium studies. Because no line differences in the potencies of these drugs to inhibit [35S]TBPS binding were found using equilibrium conditions, these results indicate that the association rates of barbiturates and GABA may be different between these lines. These findings are consistent with neurochemical studies indicating differences in the benzodiazepine/GABA receptor-chloride channel complex in these selected lines and may explain their differential sensitivities to certain agents acting through this supramolecular complex.

Animals↗
PubMed1990

Characterization of benzodiazepine receptors with a fluorescence-quenching ligand.

A conjugate of the high affinity benzodiazepine receptor ligand Ro 15-1788 and the fluorescent 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) moiety was synthesized. This novel compound (BD 623) exhibited excitation and emission maxima at 486 and 542 nm, respectively, and possessed fluorescent properties that are dependent upon the polarity of its environment. BD 623 bound reversibly to benzodiazepine receptors in the central nervous system with an apparent affinity (K(i) 5.7 nM) comparable to the parent imidazobenzodiazepine (K(d) 2.8 nM). Addition of BD 623 to a suspension of brain membranes resulted in a time-dependent quenching of its fluorescence. Fluorescence quenching of this compound was readily reversed by specific benzodiazepine receptor ligands but not by a variety of other substances. Moreover, inactivation of benzodiazepine receptors by photoaffinity labeling with Ro 15-4513 resulted in a reduction in the fluorescence quenching of BD 623 consistent with the reduction in density of benzodiazepine receptors measured using a radioreceptor assay. Monitoring of fluorescence/dequenching of BD 623 in real time permitted a quantitative characterization of the ligand-receptor interaction, with both the K(d) of BD 623 (13.9 nM) and K(i) of Ro 15-1788 (5.7 nM) comparable with the estimates obtained using radioreceptor techniques. These results indicate that application of fluorescence quenching techniques with BD 623 could prove a useful adjunct for the study of benzodiazepine receptors. BD 623 may serve as a prototype for the development of other fluorescent ligands to study ligand-receptor interactions.

4-Chloro-7-nitrobenzofurazan↗
PubMed1990

Rat pup isolation calls are reduced by functional antagonists of the NMDA receptor complex.

Compounds that reduce ion flux through N-methyl-D-aspartate (NMDA) coupled cation channels were evaluated for their effects on rat pup ultrasonic vocalizations (USV). Previous studies have demonstrated that rat pups emit ultrasonic calls during social isolation and that several classes of anxiolytics decrease, while putative anxiogenics increase, the number of these calls. The competitive NMDA antagonists 2-amino-7-phosphonoheptanoic acid (AP-7) and (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid [+/-)-CPP) as well as a partial agonist at the strychnine-insensitive glycine receptor, 1-aminocyclopropanecarboxylic acid (ACPC), reduced USV at doses that did not affect either motor activity or core temperature. A dose of glycine sufficient to elevate hippocampal glycine concentrations by 85% antagonized the effects of ACPC, but not AP-7. Glycine alone did not alter USV, but NMDA when given by itself increased USV by almost 50% at subconvulsant doses. Moreover, a dose of NMDA that did not affect USV antagonized the effects of AP-7 but not ACPC. Taken together, these findings are consistent with previous studies using conflict procedures which indicate that agents which reduce activity at NMDA receptor coupled cation channels may constitute a new class of anxiolytic agents.

2-Amino-5-phosphonovalerate↗
PubMed1990

Functional antagonists at the NMDA receptor complex exhibit antidepressant actions.

Inescapable, but not escapable, stress inhibits the induction of Long Term Potentiation (LTP) in the CA1 region of hippocampus, a process that is dependent upon activation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. Since inescapable stress also produces a syndrome of behavioral depression sensitive to clinically effective antidepressants, we examined the actions of functional antagonists at the NMDA receptor complex in animal models commonly used to evaluate potential antidepressants. A competitive NMDA antagonist (2-amino-7-phosphonoheptanoic acid [AP-7]), a non-competitive NMDA antagonist (Dizolcipine [MK-801]), and a partial agonist at strychnine-insensitive glycine receptors (1-aminocylopropanecarboxylic acid [ACPC]) mimicked the effects of clinically effective antidepressants in these models. These findings indicate that the NMDA receptor complex may be involved in the behavioral deficits induced by inescapable stress, and that substances capable of reducing neurotransmission at the NMDA receptor complex may represent a new class of antidepressants. Based on these findings, the hypothesis that pathways subserved by the NMDA subtype of glutamate receptors are involved in the pathophysiology of affective disorders may have heuristic value.

2-Amino-5-phosphonovalerate↗
PubMed1990

Strain-dependent association between immune function and paw preference in mice.

The relationship between immune function and the preferred direction of behavioral asymmetry was examined in several mouse strains. Mixed leukocyte reaction, natural killer cell activity, cytotoxic T lymphocyte response and lymphoproliferation in response to mitogens were investigated in animals with left or right paw preference. From the 7 strains and substrains examined, it appeared that differences in immune function between left and right pawed mice, when present, vary in directionality. Thus, in C3H/HeJ and 129/J, left pawed mice had higher immune responses than right pawed mice, whereas in C3H/HeNCr MTV- and BALB/cJ animals, the reverse was found. In C3H/HeNCr MTV+, C57BL/6J and Collin's heterogenous control population for the high/low asymmetry lines, no differences between animals with left or right paw preference were found. The statistical significance of these differences were not uniform for all the immune parameters studied. These data indicate that the association between immune function and preference for using the left versus right paw is a strain-dependent phenomenon and may suggest that the inconsistent evidence for an association between immune deficiency and left-handedness could be due to genetic heterogeneity among subpopulations.

Animals↗
PubMed1990

Morphine-induced immune alterations in vivo.

The high incidence of human immunodeficiency virus (HIV) seropositivity among drug abusers prompted us to examine in an animal model the effects of morphine on aspects of the immune system that may be specifically related to HIV infection. We now report a robust, sustained elevation in the ratio of CD4+/CD8+ cells in the spleen and thymus of mice chronically treated with morphine. Since CD4+ cells have been reported to be target cells for HIV, these alterations, in concert with a marked cellular atrophy that appears to be restricted to organs of the immune system, suggest that opiates may serve as cofactors in altering the immune status of the host and thus contribute to the increased susceptibility to HIV infection and eventual development of AIDS in opiate abusers.

Animals↗
PubMed1990

An endogenous modulator of N-methyl-D-aspartate receptor-coupled glycine receptors.

Extensive washing of a membrane preparation from rat brain resulted in a progressive enhancement of strychnine-insensitive [3H]glycine binding, which was due to an increase in the number of binding sites with no changes in the apparent affinity of this radioligand, precluding an explanation based solely on the elimination of endogenous glycine. Moreover, after extensive washing a population of [3H]glycine binding sites with very high affinity for L-serine was observed in addition to the sites with low affinity for L-serine present in less extensively washed tissue. The observed changes in [3H]glycine binding were attributable to the elimination of a low molecular weight, heat-stable compound which was readily detected in the wash supernatant. Extensive washing also altered [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohept-5,10-i min e maleate ([3H]MK-801) binding to N-methyl-D-aspartate (NMDA) receptor-associated channels, decreasing basal binding at equilibrium and producing slower association rates in the presence of either glycine or L-glutamate. Moreover, in well-washed membranes both glycine and glutamate enhanced [3H]MK-801 binding acting at high- and low-affinity sites. These findings suggest that the NMDA receptor complex can assume interconverting conformational states regulated by an endogenous substance(s).

Animals↗
PubMed1990

Reversal of the behavioral and electrophysiological abnormalities of an animal model of hepatic encephalopathy by benzodiazepine receptor ligands.

Behavioral and electrophysiological evidence implicating the GABA-benzodiazepine receptor complex in the pathogenesis of hepatic encephalopathy was obtained using an improved rat model of hepatic encephalopathy caused by thioacetamide-induced fulminant hepatic failure. After the administration of thioacetamide together with supportive therapy, acute hepatocellular failure developed in rats as a result of massive hepatocellular necrosis without evidence of renal failure or hypoglycemia. The evolution of hepatic encephalopathy in this model was sufficiently slow to readily permit the staging of the syndrome. Prominent features of the encephalopathy include a marked reduction in open field activity and an abnormal visual evoked response. Both the deficits in spontaneous motor function and visual evoked response abnormalities of rats in stages III to IV hepatic encephalopathy were significantly improved after the administration of the benzodiazepine receptor ligands flumazenil or Ro 15-4513. Doses of flumazenil or Ro 15-4513 that produced these effects in rats with hepatic encephalopathy had no detectable action on either the behavior or the visual evoked responses of normal rats. The ability of benzodiazepine receptor ligands to ameliorate both the behavioral depression and the visual evoked response abnormalities associated with hepatic encephalopathy in the thioacetamide-induced rat model suggest an involvement of the GABA/benzodiazepine receptor complex in the pathogenesis of hepatic encephalopathy. In addition, the similarity of these observations to those in rabbits with hepatic encephalopathy caused by galactosamine-induced fulminant hepatic failure is compatible with the hypothesis that the mechanisms of hepatic encephalopathy in these two distinct models share a common final pathway, the allosteric enhancement of GABAergic tone through the benzodiazepine receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Hepatic encephalopathy, GABA-ergic neurotransmission and benzodiazepine receptor ligands.

Evidence compatible with increased GABAergic tone contributing to the manifestations of hepatic encephalopathy (HE) in animal models of fulminant hepatic failure (FHF) includes: (i) increased resistance to drugs which induce seizures by reducing GABAergic tone; (ii) abnormalities of visual evoked responses (VERs) which resemble those induced by drugs which augment GABAergic tone; (iii) increased sensitivity of CNS neurons to a GABA agonist; and (iv) ameliorations of the encephalopathy induced by a GABA receptor antagonist. Evidence compatible with a benzodiazepine (BZ) receptor ligand with agonist properties contributing to increased GABAergic tone in animal models of FHF includes: (i) abnormalities of VERs which resemble those in BZ agonist-induced coma; (ii) increased sensitivity of CNS neurons to a BZ receptor agonist; (iii) excitation of CNS neurons induced by BZ receptor antagonists; (iv) reversal of the increased sensitivity of CNS neurons to a GABA agonist by a BZ receptor antagonist; (v) presence of a ligand(s) in brain which displaces a radiolabeled ligand from BZ receptors; and (vi) increased affinity of this ligand(s) for BZ receptors in the presence of GABA ("positive GABA shift").

Animals↗
PubMed1990

Immunoenhancing effects of alprazolam in mice.

The GABA/benzodiazepine receptor chloride channel complex has been proposed to play a modulatory role in immune function. The effects of alprazolam, a triazolobenzodiazepine with high affinity for "central" benzodiazepine receptors, were examined on several parameters of immune function in mice. Natural killer cell activity, mixed leukocyte reactivity and mitogen-induced lymphocyte proliferation were all significantly increased two hr after administration of low doses (0.02-1.0 mg/kg) of alprazolam. Twenty four hr later, similar but less robust immunoenhancing effects were observed. Higher doses of alprazolam (5-10 mg/kg) did not affect these measures of immune function. The immunoenhancing effects of alprazolam did not appear related to corticosterone levels. In contrast, vehicle injection caused a profound suppression of these immune parameters two hr later, which was no longer apparent 24 hr later. This immunosuppression appeared to correlate with a concurrent rise in serum corticosterone levels. These data support the hypothesis that the GABA/benzodiazepine receptor chloride channel complex modulates immune function. Use of low doses of alprazolam may be of potential clinical importance when immunoenhancement is required.

Adjuvants, Immunologic↗
PubMed1990

Differential immune responsiveness in mouse lines selectively bred for high and low sensitivity to ethanol.

Natural killer cell activity was compared in the Long-Sleep and Short-Sleep mouse lines. These mice, initially selected for their sensitivities to a hypnotic dose of ethanol, are also differentially sensitive to other agents which act through the benzodiazepine/GABA receptor chloride ionophore complex. Natural killer cell activity was 40-59% lower in Short-Sleep when compared to Long-Sleep mice. Flow cytofluorometric analysis demonstrated that the number of Nk-1+ cells was also lower in the spleens of Short-Sleep than Long-Sleep mice. In addition, the incidence of 3-methylcholanthrene-induced tumors was significantly greater in Short-Sleep (85.7%) than in Long-Sleep (14.3%) mice. These results suggest that the Long-Sleep and Short-Sleep mouse lines may represent a unique model to assess the physiological role of the benzodiazepine/GABA receptor chloride ionophore complex in the neural modulation of immune function.

Animals↗
PubMed1990

Immune function in lines of mice selected for high or low degrees of behavioral asymmetry.

Cerebral lateralization has been suggested to play a regulatory role in immune function. In this study, several measures of immune function were evaluated in mice selectively bred for either a strong (HI) or weak (LO) degree of behavioral asymmetry (paw preference) and compared to an unselected control population (HET). Both HI and LO animals had fewer spleen cells but higher degrees of [3H]thymidine incorporation into DNA (on a per cell basis) than HET mice. However, only HI mice had lower immune functions compared to HET controls manifest as reduced mixed leukocyte reaction (MLR), cytotoxic T lymphocyte (CTL) activity, and natural killer (NK) cell activity. These findings indicate that although both extremes in the degree of paw preference may be associated with deviations from the norm, a high degree of behavioral lateralization is associated with decreased immune responsiveness in this animal model.

Animals↗
PubMed1990

Structural requirements for agonist actions at the benzodiazepine receptor: studies with analogues of 6-(benzyloxy)-4-(methoxymethyl)-beta-carboline-3-carboxylic acid ethyl ester.

The analogues 2, 3, 8a-c, 9, 13, and 14 of the beta-carboline 6-(benzyloxy)-4-(methoxymethyl)-beta-carboline-3-carboxylic acid ethyl ester (ZK-93423, 1) were synthesized in order to determine which functional groups are required for agonist activity exhibited by the parent compound 1 at the benzodiazepine receptor (BzR). The potencies of these compounds were evaluated in vitro and in vivo; the beta-carbolines 2, 8a-c, and 13 were found to exhibit high affinity (0.5-22 nM) for BzR, but in vivo studies demonstrated they were not anticonvulsant while analogues 8a and 8b antagonized the effects of diazepam. These results are in agreement with the model proposed for the pharmacophore of the agonist site (domain) of the BzR, which requires the interaction of two sites of electron density [N(2) and C(4)], a third at E+ (electrostatic or steric), and two of lipophilicity [C(3) and C(6)] of the ligand with the BzR protein (see Figure 1). The pharmacophore for the agonist site is derived from the structure-activity relationships of the benzodiazepines, pyrazoloquinolines, and the beta-carboline 1, and compared to interactions required for ligand inverse agonist activity.

Animals↗
PubMed1990

Synthesis of substituted 7,12-dihydropyrido[3,2-b:5,4-b']diindoles: rigid planar benzodiazepine receptor ligands with inverse agonist/antagonist properties.

A series of 1-, 2-, 3-, 4-, 5-, 6-, 7-, 10-, and 12-substituted pyridodiindoles were synthesized and screened in vitro against [3H]diazepam for activity at the benzodiazepine receptor (BzR). In vitro, the 2-substituted pyridodiindoles were found to be the most potent (IC50 less than 10 nM) of this new class of BzR ligands. In vivo, 2-methoxypyridodiindole 19a (IC50 = 8 nM) was found to be the most potent partial inverse agonist (proconvulsant) of the series. The parent compound 2 (IC50 = 4 nM) was only slightly less potent. In addition, 2-hydroxypyridodiindole 21a (IC50 = 6 nM) was found to exhibit potent proconvulsant activity when administered as a prodrug derivative, pivaloyl ester 22. 2-Chloropyridodiindole 16a (IC50 = 10 nM) was devoid of preconvulsant activity; however, 16a was found to be the most potent antagonist of the anticonvulsant effects of diazepam in this class of BzR ligands. From the in vivo data available, substitution on ring E of 2 with electron-withdrawing groups results in antagonists at BzR, while replacement of hydrogen at C-2 with electron-releasing groups provides enhanced inverse agonist activity. The pyridodiindoles were used as "templates" for the formulation of a model of the inverse agonist/antagonist active site of the BzR. The proposed model consists of a hydrogen bond acceptor site (A1) and a hydrogen bond donor site (D2) disposed 6.0-8.5 A from each other on the receptor protein. The hydrogen-bonding sites are believed to be located at the base of a narrow cleft. A large lipophilic pocket at the mouth of the narrow cleft serves to direct molecules into the binding site, while the presence of a small lipophilic pocket permits substitution only at position 2 of the pyridodiindole nucleus for maximum binding potency.

Animals↗