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Biomedical subjects

J A Strong

Publications and source records attributed to J A Strong.

At least 19 recordsLinked to original sources
PubMed2006

Robust increase of cutaneous sensitivity, cytokine production and sympathetic sprouting in rats with localized inflammatory irritation of the spinal ganglia.

We investigated the role and mechanisms of inflammatory responses within the dorsal root ganglion (DRG) in the development of chemogenic pathological pain. DRG inflammation was induced by a single deposit of the immune activator zymosan in incomplete Freund's adjuvant in the epidural space near the L5 DRG via a small hole drilled through the transverse process. After a single zymosan injection, rats developed bilateral mechanical hyperalgesia and allodynia which began by day 1 after surgery, peaked at days 3-7, and lasted up to 28 days. The number of macrophages in ipsilateral and contralateral DRGs increased significantly, lasting over 14 days. Robust glial activation was observed in inflamed ganglia. Cytokine profile analysis using a multiplexing protein array system showed that, in normal DRG, all but interleukin (IL)-5, IL-10 and granulocyte-macrophage colony stimulating factor (GM-CSF) were detectable with concentrations of up to 180 pg/mg protein. Local inflammatory irritation selectively increased IL-1beta, IL-6, IL-18, monocyte chemoattractant protein-1 (MCP-1), and growth-related oncogene (GRO/KC) up to 17-fold, and decreased IL-2 and IL-12 (p70) up to threefold. Inflaming the DRG also remarkably increased the incidence of spontaneous activity of A- and C-fibers recorded in the dorsal root. Many of the spontaneously active A-fibers exhibited a short-bursting discharge pattern. Changes in cytokines and spontaneous activity correlated with the time course of pain behaviors, especially light stroke-evoked tactile allodynia. Finally, local inflammation induced extensive sprouting of sympathetic fibers, extending from vascular processes within the inflamed DRG. These results demonstrate the feasibility of inducing chronic localized inflammatory responses in the DRG in the absence of traumatic nerve damage, and highlight the possible contribution of several inflammatory cytokines/chemokines to the generation of spontaneous activity and development and persistence of chemogenic pathologic pain.

Action Potentials↗
PubMed1999

Modulatory effects of myomodulin on the excitability and membrane currents in Retzius cells of the leech.

Ion channel modulation by the peptide myomodulin (MM) has been demonstrated in a wide variety of organisms including Aplysia, Lymnaea, and Pleurobranchaea. This neural and muscular modulation has been shown to be important for shaping and modifying behavior. In this paper, we report that MM modulates several distinct ionic channels in another species, the medicinal leech Hirudo medicinalis. Experiments have focused on the Retzius cell (R) because the R cell is a multifunction neuron that has been implicated in a number of behaviors including feeding, swimming, secretion, thermal sensing, and the touch elicited shortening reflex and its plasticity. Previous work had identified a MM-like peptide in the leech and demonstrated that this peptide modulated the excitability of the R cell. Using combined current- and voltage-clamp techniques to examine the effects of MM on the R cell, we found that in response to a step pulse, MM increased the excitability of the R cell such that the cell fires more action potentials with a shorter latency to the first action potential. We found that this effect was mediated by the activation of a Na+-mediated inward current near the cell resting membrane potential. Second, we found that MM differentially modulated the potassium currents IA and IK. No effect of MM was found on IA, whereas MM significantly reduced both the peak and steady-state amplitudes of IK by 49 +/- 2.9% and 43 +/- 7.2%, respectively (means +/- SE). Finally we found that MM reduced the amplitude of the Ca2+ current by approximately 20%. The ionic currents modulated by MM are consistent with the overall effect of MM on the cellular activity of the R cell. An understanding of the cellular mechanisms by which MM modulates the activity of the R cell should help us to better understand the roles of both MM and the R cell in a variety of behaviors in the leech.

Animals↗
PubMed1998

Endomorphins fully activate a cloned human mu opioid receptor.

Endomorphins were recently identified as endogenous ligands with high selectivity for mu opioid receptors. We have characterized the ability of endomorphins to bind to and functionally activate the cloned human mu opioid receptor. Both endomorphin-1 and endomorphin-2 exhibited binding selectivity for the mu opioid receptor over the delta and kappa opioid receptors. Both agonists inhibited forskolin-stimulated increase of cAMP in a dose-dependent fashion. When the mu opioid receptor was coexpressed in Xenopus oocytes with G protein-activated K+ channels, application of either endomorphin activated an inward K+ current. This activation was dose-dependent and blocked by naloxone. Both endomorphins acted as full agonists with efficacy similar to that of [D-Ala2,N-Me-Phe4,Gly-ol5]enkephalin (DAMGO). These data indicate that endomorphins act as full agonists at the human mu opioid receptor, capable of stimulating the receptor to inhibit the cAMP/adenylyl cyclase pathway and activate G-protein-activated inwardly rectifying potassium (GIRK) channels.

Analgesics, Opioid↗
PubMed1998

Single-nucleotide polymorphism in the human mu opioid receptor gene alters beta-endorphin binding and activity: possible implications for opiate addiction.

Opioid drugs play important roles in the clinical management of pain, as well as in the development and treatment of drug abuse. The mu opioid receptor is the primary site of action for the most commonly used opioids, including morphine, heroin, fentanyl, and methadone. By sequencing DNA from 113 former heroin addicts in methadone maintenance and 39 individuals with no history of drug or alcohol abuse or dependence, we have identified five different single-nucleotide polymorphisms (SNPs) in the coding region of the mu opioid receptor gene. The most prevalent SNP is a nucleotide substitution at position 118 (A118G), predicting an amino acid change at a putative N-glycosylation site. This SNP displays an allelic frequency of approximately 10% in our study population. Significant differences in allele distribution were observed among ethnic groups studied. The variant receptor resulting from the A118G SNP did not show altered binding affinities for most opioid peptides and alkaloids tested. However, the A118G variant receptor binds beta-endorphin, an endogenous opioid that activates the mu opioid receptor, approximately three times more tightly than the most common allelic form of the receptor. Furthermore, beta-endorphin is approximately three times more potent at the A118G variant receptor than at the most common allelic form in agonist-induced activation of G protein-coupled potassium channels. These results show that SNPs in the mu opioid receptor gene can alter binding and signal transduction in the resulting receptor and may have implications for normal physiology, therapeutics, and vulnerability to develop or protection from diverse diseases including the addictive diseases.

Base Sequence↗
PubMed1997

Luteinizing hormone activates chloride currents in hen ovarian granulosa cells.

Luteinizing hormone (LH) induces progesterone production in hen ovarian granulosa cells, and this induction is inhibited when chloride ions are removed from the culture medium. This suggests that chloride channels may be involved in the signal transduction pathway responsible for the LH-induced progesterone production. In this report, we examined effects of LH on plasma membrane ion currents in single granulosa cells isolated from the largest preovulatory follicle (Fl) of the hen (Gallus domesticus). Using the perforated patch whole cell voltage clamp technique, we found that addition of LH rapidly activated a chloride current in these cells. This chloride current was present at all voltages tested (-90 to +50 mV), showed outward rectification and showed no obvious time or voltage dependence. Its magnitude was 3.5-fold that of the total resting membrane current measured before LH treatment. LH is known to elevate cyclic AMP in these cells. We found that addition of the cAMP analog Sp-cAMPS mimicked LH in inducing chloride currents in these cells. We conclude that LH can activate a chloride conductance in granulosa cells, and that this action may be mediated by cAMP.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1996

The weaver mutation changes the ion selectivity of the affected inwardly rectifying potassium channel GIRK2.

The weaver mutation in mice has recently been identified as a single base-pair mutation in the Girk2 gene, which encodes a G-protein-activated inwardly rectifying potassium channel, GIRK2. The mutation results in a Gly to Ser substitution at residue 156, in the putative pore-forming region of the potassium channel. In the present study, we used Xenopus oocytes to express mutant GIRK2, and to characterize the effects of the mutation on the channel. The mutation results in a loss of the normal high selectivity for K+ over Na+, with little effect on other channel properties such as activation by the mu opioid receptor. The resulting increase in basal Na+ permeability causes a marked depolarization of oocytes expressing the mutant GIRK2 protein. This result was observed even when the mutant GIRK2 was coexpressed with GIRK1, a situation more analogous to that seen in vivo. Thus, the increased Na+ permeability and resulting depolarization may contribute to the pathology of cerebellar granule cells and substantia nigra dopaminergic neurons observed in the weaver mice.

Analgesics↗
PubMed1995

Effects of the protein tyrosine phosphatase inhibitor phenylarsine oxide on excision-activated calcium channels in Lymnaea neurons.

Most calcium channels are tightly regulated, closed in the resting cell, and open only in response to specific physiological signals such as depolarization or binding of a particular ligand. In addition, calcium permeable channels which can be activated experimentally by excising a small patch of plasma membrane from the cell have been described in several preparations, including neurons and cardiac muscle. Little is known about possible physiological regulators of these channels. We examined an excision-activated calcium channel from neurons of the pond snail Lymnaea stagnalis. This channel, the 'HP channel', is divalent selective and voltage-independent. In this report, we show that excision activation can occur very rapidly (within 200-400 ms after patch excision), and that this activity can be at least partially inhibited by 'cramming' the isolated membrane patch back into the cell's cytoplasm. We also show that excision activation is inhibited in cells which have been pretreated with inhibitors of protein tyrosine phosphatases, either pervanadate (0.5 mM) or phenylarsine oxide (1-7 microM). The effect of phenylarsine oxide is not seen in cells which have been pretreated with tyrosine kinase inhibitors (genistein or herbimycin A). The results suggest that tyrosine phosphorylation signalling pathways may play a role in the physiological regulation of these channels.

Animals↗
PubMed1995

The evaluation of pelvic injury in the female athlete.

The differential diagnosis of pelvic pain and possible injury in the female athlete is quite broad and must include gastrointestinal and genitourinary aetiologies, as well as musculoskeletal injuries. These considerations reflect the anatomical complexity of the female pelvis. The pelvic bones house the lower gastrointestinal and genitourinary viscera and transmit stress from the lower extremities to the upper body. The innervation of the pelvic structures also complicates evaluation and diagnosis when somatic and visceral afferent information affects the athlete's interpretation of pain. An algorithmic approach can facilitate evaluation and rehabilitation of pelvic injuries in the female athlete in the contest of previously described mechanisms of musculoskeletal injury.

Adolescent↗
PubMed1993

FMRF-amide modulates the electrical activity of the leech Retzius cell.

The effect of the peptide FMRF-amide on the electrical activity of the leech Retzius (R) cell was investigated using electrophysiological techniques. FMRF-amide and six structurally related analogs increased the excitability of the R cell in several distinct ways that could act in concert to modulate transmitter release. 'Puffs' of FMRF-amide transiently depolarized the cell leading to a barrage of action potentials. This depolarization was followed by a phase of rhythmical bursting that appeared intrinsic to the neuron. FMRF-amide also broadened the plateau of the Ca(2+)-dependent action potential. The results suggest that the terminal Phe and Arg as well as the C-terminal amide are critical for the activity of these peptides.

Action Potentials↗
PubMed1993

Bovine serum albumin enhances calcium currents in chicken granulosa cells.

The effect of bovine serum albumin (BSA) on Ca2+ currents in chicken granulosa cells was examined using both the nystatin-perforated and the conventional whole cell patch clamp techniques. Under voltage-clamp conditions, depolarizing voltage steps evoked inward Ca2+ currents with both methods. The time- and voltage-dependence of Ca2+ currents measured with the perforated patch technique was similar to those obtained with conventional whole cell recording. Commercially prepared BSA and essentially fatty acid free BSA both rapidly enhanced the amplitude of Ca2+ currents. However, the fatty acid free BSA was more potent, and its potency was greatly reduced by incubation with saturating concentrations of oleic acid. These data show that BSA, a common constituent of incubation media, can influence ion channels in the plasma membrane of granulosa cells.

Animals↗
PubMed1993

Pilocytic astrocytoma: correlation between the initial imaging features and clinical aggressiveness.

OBJECTIVE: Astrocytomas are classified as either fibrillary or pilocytic on the basis of their histologic appearance. The imaging features of the fibrillary astrocytoma correlate closely with the tumor's clinical aggressiveness and are, therefore, useful in predicting prognosis. Correlation between the imaging features and the clinical aggressiveness of the pilocytic astrocytoma, however, is not well established. Accordingly, we compared the initial MR and CT appearances of the lesion with tumor aggressiveness as seen clinically to determine if a correlation exists. MATERIALS AND METHODS: We retrospectively evaluated the initial MR images or CT scans of 32 consecutive patients who had a histologic diagnosis of pilocytic astrocytoma. The lesions were evaluated with regard to location, size, calcification, morphology, and degree of contrast enhancement. These initial imaging features were correlated with the aggressiveness of the tumor as seen clinically. Tumors were classified as aggressive or nonaggressive on the basis of their clinical manifestations. Patients with clinically aggressive lesions had progressive symptoms and radiologic evidence of tumor progression or recurrence within an unusually short period. Patients with clinically nonaggressive lesions had a more indolent course, either improving or remaining stable, on both clinical and radiologic evaluations. In 12 patients, the tumor was classified as aggressive clinically, either progressing or recurring within a median time of 7.5 months (range, 2.5-118 months) from the initial diagnosis. The remaining 20 patients had a clinically nonaggressive course. RESULTS: In our series of patients, lesion size and location were not significantly different between the nonaggressive and aggressive tumors, as noted clinically. Furthermore, the aggressive and nonaggressive tumors were similar with regard to the presence or absence of calcium. Most tumors in both groups showed either moderate or marked enhancement and were multilobular. CONCLUSION: The initial CT and MR features of pilocytic astrocytoma are unreliable for predicting which lesions will behave in a more aggressive manner clinically and have a poor prognosis.

Adolescent↗
PubMed1992

Divalent-selective voltage-independent calcium channels in Lymnaea neurons: permeation properties and inhibition by intracellular magnesium.

Calcium channels are tightly regulated. Voltage-gated calcium channels open only in response to depolarization, while voltage-independent calcium channels usually open only in response to specific intracellular or extracellular ligands. Voltage-independent calcium channels have been described in several invertebrate neurons. One difficulty in understanding the function of the neuronal channels is that their regulators are unknown. They open rarely in intact cells but are activated by formation of a cell-free patch, suggesting that some intracellular inhibitor usually keeps them closed. This article provides evidence that intracellular Mg2+ is one important regulator of the voltage-independent calcium channel (HP channel) in neurons of the pond snail Lymnaea stagnalis. Mg2+ (1 mM) rapidly and reversibly inhibited activity of this calcium channel when applied to the intracellular side of cell-free membrane patches. The primary effect of the Mg2+ was to promote long closings of the channel. The mechanism of the intracellular Mg2+ inhibition is distinct from open channel block, a phenomenon seen in a variety of cation channels. Open channel block can also be seen in the HP channels, but only at very positive membrane potentials. Some of the permeability and selectivity characteristics of these channels were also examined. The channels are permeable to Mg2+ and Ca2+ as well as Ba2+. Outward currents carried by monovalent cations can be observed only at very positive membrane potentials, indicating high selectivity for divalent over monovalent cations. The single channel current-voltage relationship is markedly nonlinear, becoming quite shallow near the reversal potential, and hence is qualitatively similar to that seen in many voltage-activated calcium channels.

Animals↗
PubMed1989

Effect of enprostil on glucose and lipid metabolism in type 2 diabetes.

Enprostil, a dehydro-prostaglandin E2 analogue, has been tested as treatment for peptic ulcer. Its effect on blood glucose and lipid metabolism in Type 2 diabetes was assessed in a randomized, double-blind trial. Fifteen patients on sulphonylurea therapy received, in addition, enprostil 35 micrograms or placebo thrice daily for two weeks, with a 2-week wash-out before crossover. Data from 12 patients were analysed. After a 530 Cal test breakfast at the end of active treatment, plasma glucose rose from a fasting concentration similar to that after the last placebo dose (10.5 +/- 0.8 (+/- SE) and 10.6 +/- 1.1 mmol l-1 respectively) to 1, 2 and 3 h concentrations which were 1.5 to 2.1 mmol l-1 lower than on placebo (2 h concentration 14.6 +/- 0.9 vs 16.4 +/- 1.3 mmol l-1, p less than 0.05). Serum fructosamine concentrations at the end of active treatment and placebo were 3.66 +/- 0.22 and 3.78 +/- 0.24 respectively (p = 0.051). No changes in fasting or post-prandial insulin concentrations were observed. After 2 weeks of enprostil, fasting serum triglyceride (1.76 +/- 0.18 mmol l-1) and total cholesterol (6.27 +/- 0.29 mmol l-1) concentrations were lower than after placebo (2.14 +/- 0.25 and 7.35 +/- 0.46 mmol l-1, p = 0.031 and p = 0.002, respectively), the latter effect being primarily due to reduced LDL-cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Protein kinase inhibitors selectively block phorbol ester- or forskolin-induced changes in excitability of Aplysia neurons.

Exposure of the bag cell neurons of Aplysia to activators of protein kinase C, such as phorbol esters, enhances electrically evoked action potentials by increasing the voltage-dependent calcium current. We have hypothesized that this effect is mediated by the activation of protein kinase C (PKC). An important prediction of this hypothesis is that inhibitors of PKC should inhibit these phorbol ester-induced changes in bag cell neuronal excitability. We have now found that treatment of bag cell neurons with the protein kinase inhibitor 1-[5-isoquinolinesulfonyl]-2-methyl piperazine (H-7) inhibits the phorbol ester-induced enhancement of bag cell action potentials and prevents the enhancement of calcium current by phorbol esters. The height and width of electrically evoked action potentials in bag cell neurons can also be enhanced by cAMP analogs or agents that elevate cAMP. These agents do not influence the major voltage-dependent calcium current in the bag cell neurons but may act by modulating potassium currents and other voltage-dependent currents. We have found that microinjection of a protein inhibitor of cAMP-PK (PKA-I) into isolated bag cell neurons prevents and reverses the effect of the adenylate cyclase activator forskolin on action potentials of these cells. In contrast, H-7 does not inhibit the effects of forskolin on a variety of responses in these cells, including its effects on action potentials, granule movement, and 32P incorporation into phosphoproteins. This suggests that H-7 is selective for PKC relative to cAMP-PK in intact bag cell neurons.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1989

Inhibitors of protein kinase C prevent enhancement of calcium current and action potentials in peptidergic neurons of Aplysia.

Following brief stimulation of an afferent pathway, the bag cell neurons of Aplysia undergo a dramatic change in excitability, resulting in a prolonged discharge of spontaneous action potentials. During the discharge, the action potentials of the bag cell neurons become enhanced in height and width. The afterdischarge triggers release of neuroactive peptides that initiate egg-laying behavior in this animal. Evidence suggests that changes in excitability of the bag cell neurons may be mediated by activation of protein kinase C (PKC) and cAMP-dependent protein kinase (cAMP-PK). PKC activators, such as the phorbol ester TPA (12-O-tetradecanoyl-13-phorbol acetate), enhance the amplitude of action potentials in isolated bag cell neurons in cell culture. These agents act by unmasking a previously covert species of voltage-dependent calcium channel resulting in an increase in calcium current. In the accompanying paper (Conn et al., 1989), we showed that H-7, a protein kinase inhibitor, inhibits the effect of TPA, and is a selective inhibitor of PKC relative to cAMP-PK in these cells. We now report that another PKC inhibitor, sphinganine, also inhibits the effect of TPA on action potential height and calcium current in cultured bag cell neurons, and that N-acetylsphinganine, an inactive sphinganine analog, fails to inhibit the effects of PKC activators. Although both H-7 and sphinganine prevent the effects of TPA when added prior to TPA addition, neither compound reverses the effects of TPA when added after the action potentials have already become enhanced by TPA.(ABSTRACT TRUNCATED AT 250 WORDS)

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗