Biomedical subjects

A M Montgomery

Publications and source records attributed to A M Montgomery.

At least 37 records · Page 2Linked to original sources

PubMed1996

Potentiation of the effects of raclopride on sucrose consumption by the 5-HT2 antagonist ritanserin.

We examined the effects on sucrose consumption of a dopamine (DA) D2/D3 antagonist (raclopride, 0-0.3 mg/kg), a serotonin 5-HT2/2c antagonist (ritanserin, 0-0.4 mg/kg), and raclopride (0.15 mg/kg) combined with ritanserin (0-0.4 mg/kg). Three different concentrations of sucrose solution (0.7%, 7.0% and 34%) were tested. The concentration-intake function in drug-free rats was an inverted-U, with 7.0% sucrose supporting the highest intake. Raclopride (0.3 mg/kg) inhibited intake of 7.0% sucrose, but its effect on 0.7% sucrose fell short of significance (P < 0.06) and intake of 34% sucrose was unchanged. Ritanserin did not affect sucrose intake when given on its own, but synergized with a previously ineffective dose of raclopride (0.15 mg/kg) so as to cause a significant inhibition of 7.0% sucrose intake and increase in 34% sucrose intake. These data indicate that 5-HT2 antagonism potentiated the behavioural effects of raclopride and we speculate that this interaction might contribute to the efficacy of atypical neuroleptic drugs.

Animals↗

PubMed1996

Human neural cell adhesion molecule L1 and rat homologue NILE are ligands for integrin alpha v beta 3.

Integrin alpha v beta 3 is distinct in its capacity to recognize the sequence Arg-Gly-Asp (RGD) in many extra-cellular matrix (ECM) components. Here, we demonstrate that in addition to the recognition of ECM components, alpha v beta 3 can interact with the neural cell adhesion molecule L1-CAM; a member of the immunoglobulin superfamily (IgSF). M21 melanoma cells displayed significant Ca(++)-dependent adhesion and spreading on immunopurified rat L1 (NILE). This adhesion was found to be dependent on the expression of the alpha v-integrin subunit and could be significantly inhibited by an antibody to the alpha v beta 3 heterodimer. M21 cells also displayed some alpha v beta 3-dependent adhesion and spreading on immunopurified human L1. Ligation between this ligand and alpha v beta 3 was also observed to promote significant haptotactic cell migration. To map the site of alpha v beta 3 ligation we used recombinant L1 fragments comprising the entire extracellular domain of human L1. Significant alpha v beta 3-dependent adhesion and spreading was evident on a L1 fragment containing Ig-like domains 4, 5, and 6. Importantly, mutation of an RGD sequence present in the sixth Ig-like domain of L1 abrogated M21 cell adhesion. We conclude that alpha v beta 3-dependent recognition of human L1 is dependent on ligation of this RGD site. Despite high levels of L1 expression the M21 melanoma cells did not display significant adhesion via a homophilic L1-L1 interaction. These data suggest that M21 melanoma cells recognize and adhere to L1 through a mechanism that is primarily heterophilic and integrin dependent. Finally, we present evidence that melanoma cells can shed and deposit L1 in occluding ECM. In this regard, alpha v beta 3 may recognize L1 in a cell-cell or cell-substrate interaction.

Amino Acid Sequence↗

PubMed1996

Eating attitudes in young females with diabetes: insulin omission identifies a vulnerable subgroup.

Eating attitudes were investigated in young females with diabetes (YFDs) and healthy age-matched female controls. Results from the Eating Disorder Inventory confirmed that YFDs had higher scores for drive for thinness, body dissatisfaction and bulimia. In addition, YFDs who omitted insulin injections had high scores for ineffectiveness and interoceptive awareness and had increased sensitivity to external eating cues (as measured by the Dutch Eating Behaviour Questionnaire). It is suggested that dieting and weight gain associated with diabetes treatment precipitate a deterioration in eating attitudes. Furthermore, omission of insulin and increased sensitivity to external eating cues serve as markers for a group of YFDs who are at increased risk of developing an eating disorder. The present results provide support for the spiral model of eating disorders (Heatherton & Polivy, 1992) and its emphasis on the importance of self-esteem and self-awareness.

Adolescent↗

PubMed1994

Integrin alpha v beta 3 antagonists promote tumor regression by inducing apoptosis of angiogenic blood vessels.

A single intravascular injection of a cyclic peptide or monoclonal antibody antagonist of integrin alpha v beta 3 disrupts ongoing angiogenesis on the chick chorioallantoic membrane (CAM). This leads to the rapid regression of histologically distinct human tumors transplanted onto the CAM. Induction of angiogenesis by a tumor or cytokine promotes vascular cell entry into the cell cycle and expression of integrin alpha v beta 3. After angiogenesis is initiated, antagonists of this integrin induce apoptosis of the proliferative angiogenic vascular cells, leaving preexisting quiescent blood vessels unaffected. We demonstrate therefore that ligation of integrin alpha v beta 3 is required for the survival and maturation of newly forming blood vessels, an event essential for the proliferation of tumors.

Allantois↗

PubMed1994

Effect of tissue inhibitor of the matrix metalloproteinases-2 expression on the growth and spontaneous metastasis of a human melanoma cell line.

In this study, we examined the effect of expression of tissue inhibitor of metalloproteinases-2 (TIMP-2) on the growth and dissemination of a highly metastatic human melanoma cell line (M24net). M24net melanoma cells express a number of matrix metalloproteinases (MMPs), including gelatinase A and B (MMP-2 and MMP-9) and interstitial collagenase (MMP-1) (A. M. P. Montgomery et al., Cancer Res., 53: 693-700, 1993). The activity of these proteases was effectively down-regulated by transfecting M24net cells with complementary DNA-encoding human TIMP-2. Overexpression of TIMP-2 markedly reduced melanoma growth in the skin of immunodeficient mice but did not prevent these highly malignant cells from spontaneously metastasizing to the lungs and lymph nodes of inoculated mice. We provide a mechanism to account for the growth inhibitory property of TIMP-2 based on its ability to regulate M24net cell growth in three-dimensional interstitial collagen. In the presence of this matrix, M24net cells assume a differentiated morphology and have a reduced growth rate. We present evidence that overexpression of TIMP-2 increases the susceptibility of M24net cells to growth inhibition and morphological differentiation by occluding interstitial collagen.

Animals↗

PubMed1994

Integrin alpha v beta 3 rescues melanoma cells from apoptosis in three-dimensional dermal collagen.

Human melanoma cells required ligation of the integrin alpha v beta 3 to sustain viability and growth in three-dimensional dermal collagen. Variant melanoma cells, lacking the alpha v subunit, progressed rapidly to apoptosis within this matrix, whereas transfection of these cells with an alpha v cDNA restored alpha v beta 3 expression and prevented apoptosis. Furthermore, inhibition of alpha v beta 3 ligation with a monoclonal antibody promoted cell death. Apoptosis of alpha v(-) cells within this matrix could be overcome by the addition of insulin or serum. However, alpha v(+) melanoma cells had a significant growth advantage in the presence of these growth factors. Initial adhesion of the melanoma cells to type I collagen depended on ligation of alpha 2 beta 1, but these cells can degrade this collagen to expose cryptic alpha v beta 3 binding sites. These findings provide evidence that the survival and growth of transformed cells may be regulated by collagen degradation and integrin-dependent anchorage to this proteolysed matrix.

Apoptosis↗

PubMed1993

Production and regulation of gelatinase B by human T-cells.

Here we describe for the first time the production of gelatinase B (MMP 9; 92-kDa type IV collagenase) by human peripheral blood T-lymphocytes. Expression of this enzyme was found to be dependent on the activation status of these T-cells and to be regulated by Interleukin-2.

Cell Separation↗

PubMed1993

Melanoma-mediated dissolution of extracellular matrix: contribution of urokinase-dependent and metalloproteinase-dependent proteolytic pathways.

Constitutive overexpression of both urokinase and matrix metalloproteinase (MMP) activity is frequently observed in individual malignant tumors. In this study we describe the combined contribution of these distinct enzyme systems to the invasive phenotype of a highly metastatic human melanoma cell line (M24met). M24met cells were found to secrete a spectrum of MMPs, including interstitial collagenase, type IV collagenases (M(r) 92,000 and 72,000 progelatinases), and stromelysin. Urokinase, but not tissue-type plasminogen activator, was detected in M24met-conditioned media and on cell surfaces. The contribution of these enzymes to extracellular matrix dissolution was determined by exploiting specific inhibitors, namely tissue inhibitor of the metalloproteinases-2 and plasminogen activator inhibitor-2. Due to the coexpression of urokinase and MMP-dependent activity, M24met cells were observed to degrade multiple components of the extracellular matrix and to significantly degrade both interstitial and basement membrane matrices. Urokinase-dependent removal of matrix glycoprotein was observed to precede MMP-dependent collagenolysis as a prerequisite rate-limiting step. We present evidence which suggests that this temporal relationship is imposed by the structural architecture of the matrix such that matrix glycoprotein serves to protect associated collagen from MMP-dependent degradation. In addition to mediating significant collagenolysis, MMP activity was further implicated in the dissolution of matrix tropoelastin. Urokinase/plasmin activity was not found to be required for MMP-zymogen activation.

Amino Acid Sequence↗

PubMed1993

The effect of a 5-HT3 receptor antagonist, ondansetron, on brain stimulation reward, and its interaction with direct and indirect stimulants of central dopaminergic transmission.

5-HT3 receptors are abundant in central dopamine (DA) terminal areas. They do not affect basal DA turnover but appear to modulate DA release by e.g. morphine and nicotine. The interpretation of these findings is uncertain, and it is unclear whether 5-HT3 receptors also influence the activity of compounds such as amphetamine and cocaine, which act more directly on the DA synapse. Variable-interval (VI), threshold-current hypothalamic self-stimulation can provide a continuous index of central dopaminergic activity, but is relatively insensitive to changes in 5-HT and thus offers a means of investigating this question. In the present study, a selective 5-HT3 receptor antagonist, ondansetron (GR 38032F) (1.0 to 1000 micrograms/kg sc), had no effect on VI self-stimulation, nor did a 100 micrograms/kg dose affect facilitation of responding by d-amphetamine (500 micrograms/kg ip). Ondansetron (100 micrograms/kg) reduced the initial depression of self-stimulation by high-dose nicotine (400 micrograms/kg), but not the ensuing facilitation. Similar results were obtained in rats "sensitized" to nicotine by prior chronic exposure. These results support the proposal that 5-HT3 receptors, normally quiescent under basal conditions, mediate the excitatory effect of compounds acting upstream from the DA neuron, such as nicotine, but do not affect the dopaminergic synapse directly.

Animals↗

PubMed1992

Effect of the 5-HT3 receptor antagonist ondansetron on hypothalamic self-stimulation in rats and its interaction with the CCK analogue caerulein.

It is unclear whether behavioral depression and suppression of food intake by cholecystokinin (CCK) is contributed to by aversive gastrointestinal effects such as nausea. In the present study we examined the effect of a new antiemetic agent, ondansetron, a specific antagonist of 5-HT3 receptors, on suppression of variable-interval self-stimulation by the CCK analogue caerulein. Responding by rats for brain-stimulation reward is especially sensitive to CCK, and provides a convenient means of investigating this question. Caerulein (30 micrograms/kg, s.c.), injected alone, was followed by a profound (ca. 80%) reduction in the rate of self-stimulation, lasting about 30 min. Ondansetron (1.0-1000 micrograms/kg, s.c.) injected on its own had no effect on self-stimulation rate, and a 100-micrograms/kg dose did not lessen the depressant action of caerulein. The behavioural depressant effects of CCK are thus unlikely to depend on brain mechanisms for nausea and vomiting involving 5-HT3 receptors.

Animals↗

PubMed1992

The targeting of T-helper cells and tumourcidal macrophages to a B-cell lymphoma using a PPD-monoclonal antibody heteroconjugate.

This paper describes a T-cell targeting strategy based on the use of an antigen-monoclonal antibody heteroconjugate. A rat anti-idiotypic monoclonal antibody specific for a murine B-cell lymphoma was conjugated to the purified protein derivative (PPD) of tuberculin. This construct selectively delivered up to 4.5 x 10(4) molecules of PPD onto each tumour cell. Targeted PPD was internalized for endosomal processing and was presented in association with the I-A class II restriction element to PPD-reactive T-helper (Th) cells. Activated Th cells were demonstrated to proliferate and secrete significant levels of tumour necrosis factor (TNF). Such lymphokine secretion was observed at a PPD concentration as low as 1 ng/ml. Despite the secretion of TNF, the B-cell lymphoma was found to be resistant to autonomous Th-mediated cytotoxicity. Targeted Th cells did, however, activate tumourcidal macrophages that subsequently mediated significant tumour cytostasis. Based on this observation, it is proposed that the targeting system described may be exploited as the basis for a future immunotherapeutic strategy.

Animals↗

PubMed1991

5-HT1A agonists and dopamine: the effects of 8-OH-DPAT and buspirone on brain-stimulation reward.

Two specific 5-HT1A agonists, 8-OH-DPAT (0-300 micrograms/kg), and buspirone (0-3.0 mg/kg), were tested on variable-interval, threshold-current self-stimulation of rat lateral hypothalamus. Buspirone produced a prolonged monotonic depression of responding, whereas the effects of 8-OH-DPAT were biphasic: 3.0 micrograms/kg produced a sustained enhancement of responding while higher doses (100-300 micrograms/kg) produced a relatively short-lasting depression. This biphasic pattern parallels previously reported effects of 8-OH-DPAT on food intake and on various other behaviours. Threshold-current self-stimulation is highly sensitive to alterations in dopaminergic transmission but relatively insensitive to changes in 5-HT. Thus the facilitatory effect of low-dose 8-OH-DPAT seems most plausibly interpreted in terms of enhanced dopaminergic transmission. This could be brought about by 5HT1A autoreceptor-mediated inhibiton of 5-HT release and consequent disinhibition of dopaminergic transmission. Depression of self-stimulation by higher doses of 8-OH-DPAT may reflect the activity of 8-OH-DPAT at postsynaptic 5-HT receptors, with consequent inhibition of DA transmission. Suppression of responding after buspirone at all doses tested may reflect the action of this compound as a partial agonist at postsynaptic 5-HT receptors, and/or its effects on other systems.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1990

An improved method for the detection of cell surface antigens in samples of low viability using flow cytometry.

A high non-specific background fluorescence signal was observed when cell surface antigen analysis was carried out using flow cytometry on a cell sample which contained a high proportion of dead and dying cells. To overcome this problem it was necessary to analyse the cells in three stages. First the intact cells were identified by their forward (FWD) and 90 degree scatter profile. These cells were gated-on, then analysed on the basis of their FWD scatter and propidium iodide (PI) signal, allowing the dead PI positive cells to be gated out. The PI negative cells were then displayed using their 90 degree scatter and fluorescence signals following staining with the irrelevant antibody control. This revealed a population of dead cells, which despite being PI negative, were non-specifically binding antibody molecules. Such multiparameter analysis permitted the successful analysis of cell surface antigens in preparations of low viability by gating out the high background fluorescence associated with dead PI positive and negative cells.

Animals↗

PubMed1990

A novel strategy for targeting CD4+ PPD-reactive T cells against tumour cells using PPD monoclonal antibody heteroconjugates.

We have constructed PPD monoclonal antibody heteroconjugates specific for a tumour-associated antigen of C57BL/6 melanomas or for human complement component C3d fixed de novo to murine fibrosarcoma cells (MC6A). The ability of our heteroconjugates to target CD4+ PPD-reactive T cells against the appropriate tumour targets was then determined in vitro. Heteroconjugate-treated B16-F10 and MC6A tumour targets were both able to present PPD to the specific T cells, resulting in activation and concomitant lymphokine secretion. Secreted lymphokines were then demonstrated to cause significant tumour cytolysis and cytostasis in vitro. Preliminary experiments in vivo suggest that this targeting system may provide the basis for a future immunotherapeutic strategy.

Animals↗

PubMed1990

Cytostasis of different tumours by a murine PPD-reactive CD4+ T lymphocyte clone is mediated by interferon-gamma and tumour necrosis factor alone or synergistically.

We have shown that a murine CD4+ PPD-reactive T lymphocyte clone was weakly cytotoxic towards the syngeneic tumour B16 melanoma and MC6A fibrosarcoma which had been coated with PPD using a monoclonal antibody-PPD heteroconjugate. Cell-free supernatants produced by PPD-stimulated T lymphocyte clones were however highly cytostatic for the two tumour targets when assayed over 48-72 h. In this study we have demonstrated good titres of tumour necrosis factor (TNF) and interferon-gamma (IFN-gamma) in the supernatants, which accounted for their observed cytostatic activity on the tumour targets. The high level of cytostasis seen with the B16 melanoma using the supernatants could be attributed to their sensitivity to the cytostatic activity of IFN-gamma; the lower levels of cytostasis seen with the IFN-gamma-resistant MC6A target was the result of IFN-gamma increasing the sensitivity of this target to TNF. Antibodies to IFN-gamma were able to neutralize the majority of the cytostatic activity of the supernatants on both targets, consistent with the role demonstrated for this lymphokine.

Animals↗

PubMed1989

Blockade of 8-OH-DPAT-induced feeding by dopamine antagonists.

Feeding elicited by the 5HT1A agonist 8-OH-DPAT was blocked by pretreatment with the DA antagonists SCH-23390 and sulpiride, in two experiments conducted in non-deprived rats and in three experiments conducted after 4 h food deprivation. In deprived animals, 8-OH-DPAT prolonged the initial period of feeding. However, in non-deprived animals, 8-OH-DPAT delayed the onset of eating, and suppressed post-prandial resting; both SCH-23390 and sulpiride restored the normal pattern of behaviour. All three drugs suppressed grooming. The results suggest that 8-OH-DPAT elicits feeding by a secondary disinhibition of activity postsynaptic to DA neurons. The consequences of this mechanism for the interpretation of 8-OH-DPAT-induced feeding are discussed.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1988

Fenfluramine disrupts the behavioural satiety sequence in rats.

Previous studies have shown that when hungry rats are fed to satiety, the offset of eating is followed by a short period of activity superseded by resting behaviour. Observations of rats consuming wet mash or sucrose confirmed this "behavioural satiety sequence" and showed that the duration of resting was related to the intake of calories rather than of bulk. Fenfluramine reduced the consumption of sucrose and wet mash, but at anorectic and subanorectic doses, fenfluramine also suppressed resting behaviour; the effects of dl- and d-fenfluramine were qualitatively similar. It is argued that the suppression of resting behaviour by fenfluramine is incompatible with an enhancement of satiety.

Animals↗

PubMed1988

Behavioural specificity of 8-OH-DPAT-induced feeding.

8-Hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) has been reported to increase food intake. This effect was confirmed in rats consuming plain or sweetened wet mash. However, the consumption of a 35% sucrose solution or of a range of other flavoured liquids was enhanced marginally if at all by a single low dose of 8-OH-DPAT, and the drug actually decreased the consumption of a high protein liquid diet. 8-OH-DPAT did, however, increase gnawing on a wooden block. These results suggest that 8-OH-DPAT-induced "hyperphagia" may to some extent be secondary to the elicitation of chewing behaviour. 8-OH-DPAT also caused certain other behavioural changes, including a suppression of grooming.

8-Hydroxy-2-(di-n-propylamino)tetralin↗