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R J Miller

Publications and source records attributed to R J Miller.

At least 181 records · Page 10Linked to original sources
PubMed1992

Investigations into neuropeptide Y-mediated presynaptic inhibition in cultured hippocampal neurones of the rat.

1. We have examined the effects of neuropeptide Y (NPY) on synaptic transmission and [Ca2+]i signals in rat hippocampal neurones grown in culture. [Ca2+]i in individual neurones displayed frequent spontaneous fluctuations often resulting in an elevated plateau [Ca2+]i. These fluctuations were reduced by tetrodotoxin (1 microM) or combinations of the excitatory amino acid antagonists 6-cyano-7-dinitro-quinoxaline (CNQX) (10 microM) and aminophosphonovalerate (APV) (50 microM), indicating that they were the result of glutamatergic transmission occurring between hippocampal neurones. 2. [Ca2+]i fluctuations were also prevented by Ni2+ (200 microM), by the GABAB receptor agonist, baclofen (10 microM) and by NPY (100 nM) or Y2 receptor-selective NPY agonists. Following treatment of cells with pertussis toxin, NPY produced only a brief decrease in [Ca2+]i fluctuations which rapidly recovered. 3. Perfusion of hippocampal neurones with 50 mM K+ produced a large rapid increase in [Ca2+]i. This increase was slightly reduced by NPY or by a combination of CNQX and APV. The effects of CNQX/APV occluded those of NPY. NPY had no effect on Ba2+ currents measured in hippocampal neurones under whole cell voltage-clamp even in the presence of intracellular GTP-gamma-S. On the other hand, Ba2+ currents were reduced by both Cd2+ (200 microM) and baclofen (10 microM). 4. Current clamp recordings from hippocampal neurones demonstrated the occurrence of spontaneous e.p.s.ps and action potential firing which were accompanied by increases in [Ca2+]i. This spontaneous activity and the accompanying [Ca2+]i signals were prevented by application of NPY (100 nM). When hippocampal neurones were induced to fire trains of action potentials in the absence of synaptic transmission, these were accompanied by an increase in cell soma [Ca2+]j. NPY (100 nM) had no effect on these cell soma [Ca2+], signals. NPY (100 nM) also had no effect on inward currents generated in hippocampal neurones by micropipette application of glutamate (50 microM).5. Thus, NPY is able to abolish excitatory neurotransmission in hippocampal cultures through a pertussis toxin-sensitive mechanism. However, no effect of NPY on Ca2+ influx into the cell soma of these hippocampal neurones could be discerned. These results are consistent with a localized presynaptic inhibitory effect of NPY on glutamate release in hippocampal neurones in culture.

2-Amino-5-phosphonovalerate↗
PubMed1992

The actions of baclofen on neurones and synaptic transmission in the nucleus tractus solitarii of the rat in vitro.

1. Intracellular and whole-cell patch recordings were made from sixty-seven neurones located in the nucleus tractus solitarii (NTS) in transverse slices of rat brainstem. 2. Baclofen at concentrations of 2-20 microM caused hyperpolarization from normal resting membrane potentials (Vm). This response was associated with a decrease in input resistance (Rm) tested by current pulses in discontinuous current clamp mode when membrane potential was restored to control level by current injection. In single electrode discontinuous voltage clamp mode, baclofen at these concentrations caused a small (< 50 pA) outward current associated with increased membrane conductance measured by voltage steps from holding potentials (Vh) of -50 or -60 mV. Current-voltage relations at these Vhs and the results of varying Vh between -50 and -110 mV during responses to baclofen gave a reversal potential of -73 mV. The amplitudes of baclofen responses were related to K+ concentration tested by comparing responses in media containing 1-24 mM extracellular K+, indicating that postsynaptically baclofen acts via a K+ conductance. 3. These effects were still apparent in the presence of tetrodotoxin (which did not abolish all spontaneous synaptic activity) and also in medium containing a combination of Co2+, the excitatory amino acid antagonist 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX) and the GABAA antagonist bicuculline which blocked synaptic activity. 4. The amplitude and frequency of spontaneous postsynaptic potentials (spPSPs) and spontaneous postsynaptic currents (spPSCs) were reduced by baclofen at concentrations (1 microM or less) which had no effect on membrane potential or holding current in current or voltage clamp recordings respectively. 5. The amplitude of evoked excitatory (evEPSPs/evEPSCs) and inhibitory (evIPSPs/evIPSCs) synaptic events elicited by electrical stimulation in the vicinity of the tractus solitarius (TS) was reduced by low concentrations of baclofen (250 nM-1 microM) which did not produce discernible postsynaptic responses. 6. In order to examine the effects of baclofen on excitatory synaptic events without contamination with inhibitory events, stimulation of the TS was carried out in the presence of bicuculline. Conversely to investigate actions on purely inhibitory synaptic responses experiments were carried out with CNQX in the bathing solution. Inhibitory synaptic responses could still be evoked, presumably by stimulation of interneurones in the vicinity of the TS. IPSPs/IPSCs were more sensitive to baclofen than EPSPs/EPSCs. 7. The effects of baclofen on membrane potential or holding current and PSP/PSCs were antagonized by 2-hydroxysaclofen (400 microM) confirming that baclofen was acting at gamma-aminobutyric acid (GABA)B receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1992

Role of metabotropic glutamate (ACPD) receptors at the parallel fiber-Purkinje cell synapse.

1. The role of metabotropic glutamate receptors at the parallel fiber (PF)-Purkinje cell synapse in cerebellum was studied by examining the actions of the active stereoisomer (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [1S,3R-ACPD (25-50 microM)] on fura-2-loaded, patch-clamped rat Purkinje cells in thin slices. 2. The bath application of 1S,3R-ACPD evoked a direct post-synaptic depolarization that readily desensitized during prolonged (> 1 min) applications of the drug. This depolarizing response to 1S,3R-ACPD differed from the slow depolarization to 1S,3R-ACPD observed in cortical neurons mediated via closure of potassium channels in that it was not associated with an obvious change in membrane conductance and was not blocked by external barium. Similarly, slow inward rectifier currents were not affected during the 1S,3R-ACPD-induced depolarization. 3. The direct depolarization induced by 1S,3R-ACPD was not mediated by N-methyl-D-aspartate (NMDA) or (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid kainate (AMPA)-KA excitatory amino acid (EAA) receptor subtypes, because the response was not blocked in the presence of antagonists of these receptors. 4. The EAA antagonist L-2-amino-3-phosphonopropionic acid, which blocks 1S,3R-ACPD-induced inositide synthesis in other cell types, had no effect on the depolarizing response. 5. Fura-2 measurements of somatic [Ca2+]i revealed that [Ca2+]i was not elevated during the 1S,3R-ACPD-induced depolarization unless the cell fired calcium-dependent action potentials. 6. In addition to the direct depolarization induced by 1S,3R-ACPD, the amplitude of PF-evoked excitatory postsynaptic potentials (EPSPs) was profoundly and reversibly reduced. This effect was observed in all cells regardless of whether a direct depolarization was produced by 1S,3R-ACPD. This reduction of the PF EPSP generally preceded the onset of depolarizing responses, did not desensitize during prolonged applications of 1S,3R-ACPD, and was reversible. 7. The reversible reduction of the PF EPSP by 1S,3R-ACPD was not related to a postsynaptic blocking action of the drug, because responses of Purkinje cells to AMPA, an agonist of the EAA receptor subtype mediating the EPSP, were reversibly potentiated in the presence of 1S,3R-ACPD. 8. The nitric oxide synthesis promoter sodium nitroprusside (1-3 nM) had no effect on the amplitude of PF EPSP or the membrane properties of Purkinje cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1992

Calcium signalling in single growth hormone-releasing factor-responsive pituitary cells.

The release of pituitary GH appears to be critically dependent on alterations in the free intracellular Ca2+ concentration ([Ca2+]i). However, little is known about the nature of Ca2+ signalling within normal pituitary cells. We, therefore, examined [Ca2+]i patterns in individual cultured pituicytes of adult male rats under basal conditions and in response to GH regulatory agents, using the calcium-sensitive dye fura-2 together with digital imaging microscopy. Perfusion of cultured anterior pituitary cells with GH-releasing factor (GHRF) resulted in a marked increase in [Ca2+]i in specific pituitary cells. These cells did not respond to other hypothalamic secretagogues (GnRH, TRH, or CRF), and there was no evidence of desensitization on repetitive administration of GHRF. Somatotrophs (n = 134) exhibited spontaneous oscillations of [Ca2+]i in the basal state, with considerable heterogeneity of oscillatory patterns among cells. After application of a near-maximal stimulatory dose of GHRF (1 nM), there was a striking 2.2-fold increase in the amplitude of [Ca2+]i oscillations and only a modest increase in their frequency. Forskolin (1 microM) augmented somatotroph [Ca2+]i in patterns similar to those of GHRF. Somatostatin (10 nM) abolished the [Ca2+]i response to GHRF (n = 26); this reflected a marked reduction in the amplitude of [Ca2+]i oscillations and a slight reduction in their frequency. Ca(2+)-free medium or the Ca2+ channel antagonist nimodipine (0.1-1 microM) suppressed the Ca2+ stimulatory effect of GHRF. Conversely, the Ca2+ channel agonist BAY K8644 (1 microM) strikingly augmented the GHRF-induced rise in [Ca2+]i, with a major stimulatory effect on the amplitude of [Ca2+]i oscillations and no observed effect on their frequency. In summary, GHRF and other hypothalamic secretagogues increase [Ca2+]i in pituitary cells in a highly specific manner, consistent with the known specificity of their effects on hormone release. Somatotrophs exhibit spontaneous rhythmic oscillation of [Ca2+]i in the basal state. Known regulators of GH release markedly alter the [Ca2+]i oscillatory pattern in characteristic manners, exerting predominant effects on the amplitude of [Ca2+]i pulses and lesser effects on their frequency. These striking effects of GH regulatory agents on pituitary Ca2+ signalling are consistent with the concept that modulation of [Ca2+]i is a critical mediator of somatotroph function.

Animals↗
PubMed1992

Interwoven threads: occupational therapy, feminism, and holistic health.

Occupational therapy is a predominantly female profession; 93% to 95% of occupational therapists are women. The implications and ramifications of this reality have seldom been directly addressed. In this article, beliefs about balance, activity, environment, and autonomy are explored from the perspectives of occupational therapy, feminism, holistic health, and medicine. The assertion that occupational therapy has more in common philosophically with feminism and holistic health than it does with medicine is supported. This awareness provides a new framework for examining current issues of concern to the profession, such as support for purposeful activity, existence outside the mainstream of power holders, and problems and powers inherent in being seen as a women's profession. Recommendations are made that occupational therapists commit more money and energy to encourage, facilitate, and support female leadership; develop innovative strategies for keeping members who take time out to raise families informed; support more holistic and feminist reorganization of work settings; instill awareness of these issues in our students; and address our strengths as a women's profession. All occupational therapists must also confront their own anti-women prejudice.

Curriculum↗
PubMed1992

Metabotropic glutamate receptors mediate excitatory transmission in the nucleus of the solitary tract.

Following microinjection into the nucleus tractus solitarius (NTS), the effects of glutamate on the baroreceptor reflex are poorly antagonized by kynurenic acid and DL-2-amino-5-phosphonovaleric acid, suggesting the possible involvement of metabotropic glutamate receptors in this response. The metabotropic glutamate receptor agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) depolarized neurons located medial to the tractus solitarius (TS) at the level of the area postrema in coronal sections of the rat NTS. This effect was mimicked by glutamate and was not blocked by antagonists at alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA)/kainate or NMDA receptors. 1S,3R-ACPD also produced an inward current under voltage clamp that was not accompanied by a rise in [Ca2+]i, monitored with the Ca(2+)-sensitive dye fura-2. Conversely, the muscarinic agonist carbachol produced an outward current and a rise in [Ca2+]i. 1S,3R-ACPD reduced both the excitatory and the inhibitory postsynaptic current resulting from single electrical stimuli in the region of the TS. High-frequency stimulation of the TS produced an inward current in the presence of AMPA/kainate and NMDA receptor blockers. This current had similar properties to that produced by 1S,3R-ACPD. Thus, metabotropic glutamate receptors may mediate a component of excitatory transmission in the NTS.

2-Amino-5-phosphonovalerate↗
PubMed1992

Calcium directly permeates kainate/alpha-amino-3-hydroxy-5-methyl-4- isoxazolepropionic acid receptors in cultured cerebellar Purkinje neurons.

In cultures of rat cerebellar neurons that were enriched in Purkinje cells, the non-N-methyl-D-aspartate glutamate receptor agonist kainate (KA) stimulated Ca2+ influx into all neurons in Na(+)-containing solutions. A large Ca2+ influx was also observed in most neurons when KA was applied in Na(+)-free solutions, even when the cells were voltage-clamped at negative potentials. KA also stimulated Co2+ uptake into both Purkinje and non-Purkinje neurons. The KA-induced Ca2+ influx was insensitive to pharmacological antagonists of voltage-sensitive Ca2+ channels and antagonists of N-methyl-D-aspartate receptors. Thus, different types of cerebellar neurons possess KA-gated ionophores that are permeable to Ca2+. This Ca2+ conductance may play an important role in glutamate-mediated physiological and pathological events in the cerebellum.

Animals↗
PubMed1992

Metabotropic glutamate receptors potentiate ionotropic glutamate responses in the rat dorsal horn.

The effects of the metabotropic glutamate receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD] were examined on responses mediated by the ionotropic glutamate receptor agonists N-methyl D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA), and kainic acid (KA), in neurons acutely isolated from the dorsal horn of the rat spinal cord. (1S,3R)-ACPD produced an increase in the intracellular Ca2+ concentration in 50% of acutely isolated dorsal horn neurons, which could be prevented by blockers of voltage-sensitive Ca2+ channels. (1S,3R)-ACPD markedly potentiated increases in the intracellular Ca2+ concentration induced by NMDA, AMPA, and KA but not by 10-50 mM KCl. This potentiation occurred in all cells, required the simultaneous presence of both agonists, and was rapidly reversible. In the spinal cord slice preparation, (1S,3R)-ACPD potentiated the inward currents evoked by pressure application of AMPA, NMDA, and KA, an effect that was also rapidly reversible. These short term effects of (1S,3R)-ACPD may play an important role in the regulation of ionotropic responses mediated by glutamate in the spinal cord.

Animals↗
PubMed1991

Inhibition of tumor implantation at sites of trauma by plasminogen activators.

The authors report on the influence of plasminogen activators (PA) on implantation of TA3Ha mammary tumor cells in the healing hepatic wounds of syngeneic strain A mice. Intravenously injected TA3Ha cells, although they rarely metastasize to the liver, formed tumors in the hepatic wounds of a significant percent (42%, P less than 0.0001) of mice. The frequency of tumor formation declined as the interval between surgery and tumor cell inoculation was increased. Furthermore, preexposure of cells to fibrinogen, fibronectin, laminin, or peptides containing the arginine-glycine-aspartic acid-serine residues dramatically reduced the frequency of tumor formation in the hepatic wounds. These results indicate that TA3Ha cells interact with fibrinogen-related proteins in the wound to aid their attachment and growth. Because these proteins are susceptible to digestion by plasmin, PA were used in this study to examine whether administration of these drugs to the mice would modulate tumor formation in the liver wounds. Among the PA tested, human plasmin B-chain-streptokinase complex (B-SK) and recombinant tissue plasminogen activator (t-PA) inhibited tumor implantation in a dose-related manner. Administration of 900 units (U) of B-SK or 3300 U of t-PA per mouse reduced the frequency of tumor formation from 42% to 0% (P = 0.02) and 11% (P = 0.02), respectively. The B-SK was complexed with p-nitrophenyl-p-guanidinobenzoate; it did not activate the plasminogen or inhibit tumor formation in the hepatic wounds. Although urokinase activated the plasminogen, it did not inhibit tumor implantation in the hepatic wound. Heparin, an anticoagulant that prevents conversion of fibrinogen to fibrin without being fibrinolytic, had no influence on tumor formation in the hepatic wounds. The PA can generate plasmin that digests the cell attachment proteins in wounds and consequently inhibits tumor cell attachment.

Adenocarcinoma↗
PubMed1991

Direct observation of global protein motion in hemoglobin and myoglobin on picosecond time scales.

Picosecond phase-grating spectroscopy is highly sensitive to density changes and provides a new holographic approach to the study of protein dynamics. Photodissociation of carbon monoxide from heme proteins induces a well-defined transition from a ligated to a deoxy structure that is important to hemoglobin and myoglobin functionality. Grating spectroscopy was used to observe protein-driven density waves on a picosecond time scale after carbon monoxide dissociation. This result demonstrates that global tertiary structure changes of proteins occur on an extremely fast time scale and provides new insight into the biomechanics of deterministic protein motion.

Animals↗
PubMed1991

Medical visits and psychological disturbance in chronic low back pain. A study of a back education class.

Associations between the frequency of medical visits and psychological disturbance were explored using chronic low back pain patients from a back education class. Psychometric measures included the illness Behaviour Questionnaire (IBQ), somatic problems, and current mood. Males and females responded similarly on all psychological measures. Pain duration and IBQ disease affirmation significantly predicted visits to both general practitioners and specialists. Additional predictors for specialist visits included a self-rated pain/mood association, sex, age, and IBQ denial. Patients' expectations and attitudes about illness and treatment appeared most central to medical visits and several different forms of psychological disturbance accompanied increased visits.

Activities of Daily Living↗