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PubMed2004

The Kaposi's sarcoma-associated herpesvirus latency-associated nuclear antigen 1 N terminus is essential for chromosome association, DNA replication, and episome persistence.

To persist in latently infected, proliferating cells, Kaposi's sarcoma-associated herpesvirus (KSHV) episomes must replicate and efficiently segregate to progeny nuclei. Episome persistence in uninfected cells requires latency-associated nuclear antigen 1 (LANA1) in trans and cis-acting KSHV terminal repeat (TR) DNA. The LANA1 C terminus binds TR DNA, and LANA1 mediates TR-associated DNA replication in transient assays. LANA1 also concentrates at sites of KSHV TR DNA episomes along mitotic chromosomes, consistent with a tethering role to efficiently segregate episomes to progeny nuclei. LANA1 amino acids 5 to 22 constitute a chromosome association region (Piolot et al., J. Virol. 75:3948-3959, 2001). We now investigate LANA1 residues 5 to 22 with scanning alanine substitutions. Mutations targeting LANA1 5GMR7, 8LRS10, and 11GRS13 eliminated chromosome association, DNA replication, and episome persistence. LANA1 mutated at 14TG15 retained the ability to associate with chromosomes but was partially deficient in DNA replication and episome persistence. These results provide genetic support for a key role of the LANA1 N terminus in chromosome association, LANA1-mediated DNA replication, and episome persistence.

Antigens, Viral↗
PubMed2004

In vivo analysis of the 3' untranslated region of GB virus B after in vitro mutagenesis of an infectious cDNA clone: persistent infection in a transfected tamarin.

GB virus B (GBV-B), the virus most closely related to hepatitis C virus (HCV), infects tamarins and causes acute hepatitis. The 3' untranslated region (UTR) of an infectious GBV-B clone (pGBB) has a proximal short sequence followed by a poly(U) tract and a 3' terminal sequence. Our investigators previously demonstrated that the 3' terminal sequence was critical for in vivo infectivity. Here, we tested the effect of deleting the short sequence and/or the poly(U) tract from pGBB; infectivity of each mutant was tested by intrahepatic transfection of two tamarins with transcribed RNA. A mutant lacking both regions was not viable. However, mutants lacking either the short sequence or the poly(U) tract were viable. All four tamarins had a wild-type-like acute infection and developed acute hepatitis. Whereas we found that five tamarins transfected with the wild-type clone pGBB had acute resolving infection, one tamarin transfected with the poly(U) deletion mutant became persistently infected. This animal had viremia and hepatitis until its death at week 90. The genomes recovered at weeks 2, 7, 15, 20, 60, and 90 lacked the poly(U) stretch. Eight amino acid changes were identified at week 90. One change, in the putative p7 protein, was dominant at week 15. Thus, persistence of GBV-B, like persistence of HCV, was associated with the emergence of virus variants. Four tamarins inoculated with serum collected at weeks 2 and 90 from the tamarin with persistent infection had an acute resolving infection. Nonetheless, the demonstration that GBV-B can persist in tamarins strengthens its relevance as a surrogate model for the study of HCV.

3' Untranslated Regions↗
PubMed2024

Transcriptional profiles of Microcystis reveal gene expression shifts that promote bloom persistence in in situ mesocosms.

Harmful algal blooms caused by cyanobacteria threaten aquatic ecosystems, the economy, and human health. Previous work has tried to identify the mechanisms that allow blooms to form, focusing on the role of nutrients. However, little is known about how introduced nutrients influence gene expression in situ. To address this knowledge gap, we used in situ mesocosms initiated with water experiencing a Microcystis bloom. We added pulses of nutrients that are commonly associated with anthropogenic sources to the mesocosms for 72 hours and collected samples for metatranscriptomics to examine how the physiological function of Microcystis and bloom status changed. The addition of nitrogen (N) as urea, but not the addition of PO4, resulted in conspicuous bloom persistence for at least 9 days after the final introduction of nutrients. The addition of urea initially resulted in the upregulation of photosynthesis machinery, as well as phosphate, carbon, and N transport and metabolism. Once Microcystis presumably became N-replete, upregulation of amino acid metabolism, microcystin biosynthesis, and other processes associated with biomass generation occurred. These capacities coincided with the upregulation of toxin-antitoxin systems, CRISPR-cas genes, and transposases suggesting that phage defense and genome rearrangement are critical in bloom persistence. Overall, our results show the stepwise transcriptional response of a Microcystis bloom to the introduction of nutrients, specifically urea, as it is sustained in a natural setting. The transcriptomic shifts observed herein may serve as markers of the longevity of blooms while providing insight into why Microcystis blooms over other cyanobacteria.IMPORTANCEHarmful algal blooms represent a threat to human health and ecosystems. Understanding why blooms persist may help us develop warning indicators of bloom persistence and create novel mitigation strategies. Using mesocosm experiments initiated with water with an active bloom, we measured the stepwise transcription changes of the toxin-producing cyanobacterium Microcystis in response to the addition of nutrients that are important in causing blooms. We found that nitrogen (N), but not phosphorus, promoted bloom longevity. The initial introduction of N resulted in the upregulation of genes involved in photosynthesis and N import. At later times in the bloom, upregulation of genes involved in biomass generation, phage protection, genomic rearrangement, and toxin production was observed. Our results suggest that Microcystis first fulfills nutritional requirements before investing energy in pathways associated with growth and protection against competitors, which allowed bloom persistence more than a week after the final addition of nutrients.

Microcystis↗
PubMed2005

Risk factors for persisting neurological and cognitive impairments following cerebral malaria.

BACKGROUND: Persisting neurological and cognitive impairments are common after cerebral malaria. Although risk factors for gross deficits on discharge have been described, few studies have examined those associated with persistent impairments. METHODS: The risk factors for impairments following cerebral malaria were determined by examining hospital records of 143 children aged 6-9 years, previously admitted with cerebral malaria, who were assessed at least 20 months after discharge to detect motor, speech and language, and other cognitive (memory, attention, and non-verbal functioning) impairments. RESULTS: The median age on admission was 30 months (IQR 19-42) and the median time from discharge to assessment was 64 months (IQR 40-78). Thirty four children (23.8%) were defined as having impairments: 14 (9.8%) in motor, 16 (11.2%) in speech and language, and 20 (14.0%) in other cognitive functions. Previous seizures (OR 5.6, 95% CI 2.0 to 16.0), deep coma on admission (OR 28.8, 95% CI 3.0 to 280), focal neurological signs observed during admission (OR 4.6, 95% CI 1.1 to 19.6), and neurological deficits on discharge (OR 4.5, 95% CI 1.4 to 13.8) were independently associated with persisting impairments. In addition, multiple seizures were associated with motor impairment, age <3 years, severe malnutrition, features of intracranial hypertension, and hypoglycaemia with language impairments, while prolonged coma, severe malnutrition, and hypoglycaemia were associated with impairments in other cognitive functions. CONCLUSIONS: Risk factors for persisting neurological and cognitive impairments following cerebral malaria include multiple seizures, deep/prolonged coma, hypoglycaemia, and clinical features of intracranial hypertension. Although there are overlaps in impaired functions and risk factors, the differences in risk factors for specific functions may suggest separate mechanisms for neuronal damage. These factors could form the basis of future preventive strategies for persisting impairments.

Child↗
PubMed1995

Liver histology in hepatitis C infection: a comparison between patients with persistently normal or abnormal transaminases.

Forty two cases of confirmed hepatitis C virus (HCV) infection with available liver histology were studied. Most patients, 23 of 42 (55%) had abnormal liver function tests but 19 of 42 (45%) had persistently normal liver transaminases (mean aspartate transaminase (AST) 24.1 IU/l, mean follow up 10 months). Histological examinations in the group with normal AST activities were normal in two of 19 (11%), showed non-specific reactive hepatitis in eight of 19 (42%), chronic persistent hepatitis in six of 19 (31%), and chronic active hepatitis in three of 19 (16%). Twenty three of 42 (55%) had either persistently or temporary raised liver transaminases (mean AST 96.2 IU/l, mean follow up 16 months). Histological examinations in this second group with abnormal liver biochemistry showed reactive hepatitis in five of 23 (22%), chronic persistent hepatitis in six of 23 (26%), chronic active hepatitis in 10 of 23 (43%), and cirrhosis in two (9%). Average alcohol intake was significantly higher in the group within abnormal liver function (17.8 v 6.4 units, p = 0.01). Although serious pathology was more frequent in the abnormal transaminase group, significant liver pathology (chronic persistent hepatitis or chronic active hepatitis) was found in nine of 19 (47%) of cases with repeatedly normal transaminases. Liver biopsy is advised in all cases of chronic hepatitis C infection to accurately assess both the degree of fibrosis and the current activity of the disease.

Adult↗
PubMed1996

Incidence of persistent symptoms after laparoscopic cholecystectomy: a prospective study.

BACKGROUND AND AIMS: Laparoscopic cholecystectomy is the standard treatment for symptomatic gall stone disease. This study aimed to assess the effect of the operation on patients' symptoms. METHODS: One hundred consecutive patients undergoing laparoscopic cholecystectomy between June 1994 and June 1995 were evaluated using standard questionnaires examining demographic details, indication for laparoscopic cholecystectomy, characteristics of pain, and other associated dyspeptic and colonic symptoms. A history of psychiatric disturbances and of hysterectomy were also recorded. The same questionnaires were administered again six months after the operation. Operation notes and histological reports were reviewed. RESULTS: Three patients were converted to open surgery and were excluded from analysis. The median age of the remaining 97 patients was 50.9 (19-85) years; 19 were men. There was one complication each of bleeding and biliary leak. Indications for laparoscopic cholecystectomy were biliary type pain (66 patients) and complicated gall stone disease (acute cholecystitis 21, cholestatic jaundice six, and pancreatitis four). Thirteen patients (13%) had persistent pain and two (3%) developed diarrhoea at follow up. Only one patient with persistent pain after laparoscopic cholecystectomy originated from the complicated gall stone disease group. Logistic discriminant analysis showed that bloating (p < 0.001), constipation (p < 0.05), and previous and current use of psychotrophic drugs (p < 0.001) were significantly more common among those with a poor outcome after laparoscopic cholecystectomy. Heartburn was unaffected. Of patients with persistent symptoms after cholecystectomy 77% had no or mild histological changes of cholecystitis as compared with 30% in the pain free group. CONCLUSIONS: The incidence of persistent pain after laparoscopic cholecystectomy was 13%. Abdominal bloating and psychiatric medications were predictive for persistence of pain after laparoscopic cholecystectomy.

Adult↗
PubMed2005

Determinants of persistent negative T waves and early versus late T wave normalisation after acute myocardial infarction.

OBJECTIVE: To determine whether persistent versus early or delayed T wave normalisation of negative T waves after acute myocardial infarction is determined by the myocardial state, the treatment strategy, or both. DESIGN: 127 consecutive patients with a first acute myocardial infarction and > or = 2 negative T waves on the 24-36 hour ECG were studied. They underwent dobutamine stress echocardiography and coronary angiography during the first week. ECG was recorded at hospital discharge and at a mean (SD) of 4 (1) months. SETTING: University hospital. RESULTS: T wave normalisation was observed in 88 patients (early at discharge in 19 and delayed at four months in 69). Early T wave normalisation was associated with sustained contractile reserve during dobutamine stress (13 of 19 (68%)), whereas delayed T wave normalisation was observed mainly in patients with an ischaemic response (49 of 69 (71%)). The persistence of negative T waves was associated with an ischaemic response (21 of 39 (54%)) or persistent akinesis (17 of 39 (44%)). Among patients with an ischaemic response to dobutamine, in-hospital elective angioplasty was an independent determinant of delayed T wave normalisation (39 of 49 v 4 of 21 patients with persistent negative T waves at four months, p < 0.0001). CONCLUSIONS: Early T wave normalisation is associated with dobutamine induced, sustained improvement indicating myocardial stunning. Delayed normalisation is observed mainly in patients with ischaemic myocardium who have undergone revascularisation. Persistent negative T waves correspond to either extensive necrosis or non-revascularised, jeopardised myocardium.

Arrhythmias, Cardiac↗
PubMed2006

Troponin T measurement can predict persistent left ventricular dysfunction in peripartum cardiomyopathy.

OBJECTIVE: To determine whether measurement of cardiac troponin T (cTnT) concentration in newly diagnosed peripartum cardiomyopathy (PPCM) can be used to predict persistent left ventricular dysfunction after a 6-month follow-up. PATIENTS AND METHODS: This was a prospective, multiple-centre clinical trial that studied 106 patients with newly diagnosed PPCM surviving over 6 months. cTnT concentration was measured within 2 weeks of the onset of PPCM. RESULTS: Serum cTnT concentration was negatively correlated with left ventricular ejection fraction (LVEF) at follow-up (LVEF, r = -0.518, p = 0.0001). Analysis by receiver operator characteristic curve yielded an area under the curve of 0.764 (95% CI 0.669 to 0.860, p = 0.0001, vs null hypothesis value 0.5) for cTnT, and a cTnT concentration cut off of >0.04 ng/ml, predicting persistent left ventricular dysfunction with a sensitivity of 54.9% and a specificity of 90.9%. Among 106 recruited patients, there were 33 patients with cTnT concentrations >0.04 ng/ml and 73 patients with cTnT concentrations < or =0.04 ng/ml. After a 6-month follow-up, there was significantly smaller LVEF (35.42% (13.04% vs 50.16% (10.48%, p = 0.0001) and more persistent left ventricular dysfunction (84.8% vs 31.5%, OR = 12.17 (95% CI 4.17 to 35.57), p = 0.001) in patients with cTnT >0.04 ng/ml than in patients with cTnT < or =0.04 ng/ml. CONCLUSION: Serum cTnT concentration measured within 2 weeks of the onset of PPCM was correlated negatively with LVEF at follow-up. This marker offers a simple, quick, inexpensive, non-invasive method for predicting a persistent LVEF of < or =50%. A cTnT concentration of >0.04 ng/ml predicted persistent left ventricular dysfunction with a sensitivity of 54.9% and a specificity of 90.9%.

Adult↗
PubMed1993

Use of a second transcatheter Rashkind arterial duct occluder for persistent flow after implantation of the first device: indications and results.

OBJECTIVE: To assess the efficacy, feasibility, and most appropriate timing of the implantation of a second Rashkind arterial duct occluder because of persistent flow after the first device. DESIGN: A prospective serial Doppler study of patients after the insertion of a Rashkind arterial duct occluder including a subgroup in whom a second device was implanted. SETTING: A tertiary referral centre for congenital heart disease. PATIENTS: 144 patients aged 7 months to 67 years (median 3.38 years) who underwent transcatheter occlusion of patent arterial duct, 20 of whom had attempted implantation of a second device. INTERVENTIONS: Implantation of a second device alongside the first was attempted in 20 of the patients with persistent residual flow. MAIN OUTCOME MEASURES: Successful implantation of a second device, the incidence of complications, and the achievement of complete occlusion on follow up Doppler echocardiography. The time to complete occlusion in the whole group and factors predictive of persistent leak were also analysed. RESULTS: Second devices were successfully implanted in 19 of 20 first attempts and in the remaining patient at the second attempt. Complete occlusion was found in 19 patients at a mean follow up of eight months. The complications included fracture of a guidewire requiring femoral arteriotomy for its removal in one patient and embolisation of a device in another. With a single device, persistence of residual flow six months after implantation and malposition of the device on the aortogram after implantation were predictive of continuing residual patency. CONCLUSIONS: Implantation of a second device is safe, feasible, and effective and should be considered when residual flow persists beyond six months, or if malposition of the first device causes complications such as haemolysis.

Adolescent↗
PubMed1994

Umbrella occlusion of persistent arterial duct in children under two years.

OBJECTIVE: To assess the use of trans-catheter occlusion of a persistent arterial duct in symptomatic children < 2 years of age. DESIGN: Descriptive study of selected, non-randomised infants with persistent arterial duct who underwent attempted umbrella occlusion. SETTING: Tertiary referral centre. PATIENTS: Between June 1990 and April 1993, 29 young children with a symptomatic persistent arterial duct underwent attempted transcatheter occlusion. Their age ranged from 1.5 to 23 months, with the youngest infant weighing 2.9 kg. The diagnosis was established before operation in all patients by cross sectional echocardiography. INTERVENTION: Transcatheter occlusion of a haemodynamically important persistent arterial duct was performed with the Rashkind ductal umbrella. In the past year the front loading technique has been used to place the 12 mm umbrella through a 6 F (French) sheath and the 17 mm device through a 8 F sheath so extending the indications for their use. RESULTS: Umbrellas were successfully placed in 25 (86.2%) infants and there was symptomatic improvement in all. There were no deaths or severe complications. The four failures occurred early in the series. They were caused by kinking of the 11 F sheath in two cases and embolisation into the left pulmonary artery in one case. The procedure was abandoned in the fourth case because of a large duct. Only three of the 25 patients had small residual shunts at one year follow up (all with 17 mm devices) but no stenosis or turbulence was noted in any of the patients. CONCLUSION: The transcatheter occlusion of persistent arterial duct in young children with symptoms is a safe alternative to surgery. The new front loading umbrella technique enables successful ductal closure in even smaller infants than earlier devices.

Cardiac Catheterization↗
PubMed2003

A variant of multifocal motor neuropathy with acute, generalised presentation and persistent conduction blocks.

OBJECTIVE: Multifocal motor neuropathy with persistent conduction blocks is classically described as a chronic neuropathy with progressive onset, and acute forms have not previously been characterised. We report four cases of severe motor impairment with acute and generalised onset and with persistent motor conduction blocks. PATIENTS AND RESULTS: An acute tetraparesis with diffuse areflexia but little or no sensory disturbance was the clinical picture. Serial electrophysiological tests showed persistent multifocal motor conduction blocks with absent F waves in most tested motor nerves. No or minor abnormalities of the sensory nerve action potentials were observed. Cerebrospinal fluid contained normal or mildly increased protein levels (<1 g/l) without cells. Campylobacter jejuni serology was negative in three patients and consistent with past infection in one patient. Anti-ganglioside antibodies were positive in three patients. A five day course of intravenous immunoglobulins produced nearly complete symptom resolution in three patients and was ineffective in one patient. CONCLUSION: Because of the persistence of multifocal motor conduction blocks for several weeks or months as the isolated electrophysiological feature, these cases could not be consistent with Guillain-Barré syndrome or chronic inflammatory demyelinating polyneuropathy. They suggest an original variant of multifocal motor neuropathy with an acute and generalised initial presentation and persistent motor conduction blocks affecting all four limbs.

Acute Disease↗
PubMed1988

Response of cattle persistently infected with bovine virus diarrhoea virus to bovine leukosis virus.

Six cattle persistently infected with bovine virus diarrhoea virus (BVDV) and seronegative, and two control, virus negative seropositive cattle were inoculated with lymphocytes infected with bovine leukosis virus (BLV). The two controls produced a normal immune response to BLV, developing antibodies at four and five weeks after inoculation. Two of the six cattle persistently infected with BVDV developed a strong antibody response by six weeks after inoculation with BLV. Four developed a depressed response to BLV, characterised in three by a 'hooking' reaction in the immunodiffusion test which persisted in successive bleedings but was interspersed occasionally by a weak positive reaction. In one of these animals, a series of 'hooking' reactions was followed by a number of negative results. The fourth animal remained serologically negative until 16 weeks after inoculation when a 'hooking' reaction was observed followed by a series of negative results. BLV was isolated from all the cattle persistently infected with BVDV at 42 or 58 weeks after inoculation regardless of whether the serum samples gave negative, 'hooking', weak positive or positive reactions in the immunodiffusion test. BLV was consistently isolated from the nasal secretions of a steer which was BVDV negative but seropositive. The possibility of decreased immune responsiveness to BLV in animals persistently infected with BVDV should be considered when formulating regulations governing the testing of animals for freedom from BLV.

Animals↗
PubMed1987

Persistence of the electrophysiologic effects of mexiletine in canine Purkinje fibers alters the response to subsequent hypoxia.

The persistence of cellular electropharmacologic effects of mexiletine on canine Purkinje fibers was studied utilizing standard microelectrode techniques and two different protocols. In the first, the tissue was exposed to hypoxic perfusion before and 30 min after perfusion with one of the following: mexiletine hydrochloride 6.25 microM solution, mexiletine hydrochloride 12.5 microM solution, or drug-free Tyrode's solution. With the higher concentration of mexiletine, depression of the maximal upstroke velocity (Vmax) persisted 30 min after drug washout and subsequent exposure to hypoxia did not result in the anticipated shortening of action potential duration but did prevent the restoration of normal Vmax. After perfusion with the lower concentration of mexiletine, Vmax was not depressed and hypoxic action potential duration shortening was not prevented. In the second protocol, Purkinje fibers were perfused with 12.5 microM mexiletine hydrochloride solution and then exposed to hypoxia after 15, 30, 45, or 60 min of perfusion with drug-free solution. Depression of maximal upstroke velocity and shortening of action potential duration persisted during washout, returning to control values by 45 min, although mexiletine was not detectable in the tissue bath after 10 min of washout. Hypoxia initiated at 15 or 30 min of washout failed to produce the anticipated shortening of action potential duration. At 45 and 60 min, action potential duration was shortened by hypoxia. We concluded that mexiletine depression of Vmax and shortening of action potential duration may persist in the absence of drug. Further shortening of action potential duration in response to hypoxia is prevented during this period. The persistence of Vmax depression is prolonged by hypoxia.

Action Potentials↗
PubMed1982

Critical evaluation of the persistent loop sign in necrotizing enterocolitis.

A review of the records and radiographs of 21 newborn infants with necrotizing enterocolitis and 10 control infants was performed to test the significance of the persistent loop sign in necrotizing enterocolitis. Twelve clinical and laboratory variables were compared with the persistent loop sign. None of the control infants and seven of the 21 study infants had a persistent loop sign. Four of the seven infants were proven to have necrotic bowel. All four died. Four of the 14 study patients without the persistent loop sign had necrotic bowel. Two of these four infants died. The findings of this study do not support the use of a persistent segmental loop of bowel as a single criterion for surgical intervention.

Enterocolitis, Pseudomembranous↗
PubMed2003

Persistent sodium and calcium currents cause plateau potentials in motoneurons of chronic spinal rats.

After chronic spinal cord injury motoneurons exhibit large plateau potentials (sustained depolarizations triggered by brief inputs) that play a primary role in the development of muscle spasms and spasticity (Bennett et al. 2001a,b). The present study examined the voltage-gated persistent inward currents (PICs) underlying these plateaus. Adult rats were spinalized at the S2 sacral spinal level and after 2 mo, when spasticity developed, intracellular recordings were made from motoneurons below the injury. For recording, the whole sacrocaudal spinal cord was removed and maintained in vitro in normal artificial cerebral spinal fluid (nACSF), without application of neuromodulators. During a slow triangular voltage-clamp command (ramp) a PIC was activated with a threshold of -54.2 +/- 4.8 mV (similar to plateau threshold), with a peak current of 2.88 +/- 0.95 nA and produced a pronounced negative-slope region in the V-I relation. This PIC was in part mediated by Cav1.3 L-type calcium channels because it was low threshold and significantly reduced by 10 to 20 microM nimodipine or 400 microM Cd2+. The PIC that remained during a calcium channel blockade (in Cd2+) was completely and rapidly blocked by tetrodotoxin (TTX; 0.5 to 2 microM), and thus was a TTX-sensitive persistent sodium current. This persistent sodium current was activated rapidly about 7 mV below the spike threshold (spike threshold -46.1 +/- 4.5 mV), contributed approximately 1/2 of the initial peak of the total PIC, inactivated partly to contribute only approximately 1/3 of the sustained PIC (at 5 to 10 s), and deactivated rapidly with hyperpolarization (<50 ms). When TTX was added to the bath first, the nimodipine-sensitive persistent calcium current (L-type) was seen in isolation; it was slowly activated (>250 ms), had a low but variable threshold (either slightly above or below the spike threshold), contributed the other approximately 1/2 of the initial peak of the total PIC (before TTX), did not usually inactivate with time (contributed approximately two-thirds of the sustained PIC), and deactivated slowly with hyperpolarization to rest (in >300 ms). In summary, low-threshold persistent calcium (Cav1.3) and sodium currents spontaneously develop in motoneurons of chronic spinal rats and these enable large, rapidly activated plateaus that ultimately lead to spasticity.

Animals↗
PubMed1998

Kinetic and stochastic properties of a persistent sodium current in mature guinea pig cerebellar Purkinje cells.

Whole cell voltage-clamp techniques were employed to characterize the sodium (Na) conductances in acutely dissociated, mature guinea-pig cerebellar Purkinje cells. Three phenomenological components were noted: two inactivating and a persistent component (I(P)(Na). All exhibited similar sensitivities to tetrodotoxin (TTX; IC50 approximately 3 nM). The inactivating Na current demonstrates two components with different rates of inactivation. The persistent component activates at a more negative membrane potential than the inactivating components and shows little inactivation during a 5-s pulse. The amplitude of the persistent Na conductance had a higher Q10 than the inactivating Na conductance (2.7 vs. 1.3). (I(P)(Na) rapidly activates (approximately 1 ms) and deactivates (< 0.2 ms) and like the fast component appears to be exclusively Na permeable. (I(P)(Na) is not a "window" current because its range of activation exceeds the small overlap between the steady-state activation and inactivation characteristics of the inactivating current. Anomalous tail currents were observed during voltage pulses above -40 mV after a prepulse above -30 mV. The tails rose to a maximum inward current with a time constant of 1.5 ms and decayed to a persistent inward current with a time constant of 20 ms. The tails probably arose as a result of recovery from inactivation through the open state. The noise characteristics of (I(P)(Na) were anomalous in that the measured variance was lower at threshold voltages than would be predicted by a binomial model. The form of the variance could be partially accounted for by postulating that the maximum probability of activation of the persistent current was less than unity. The noise characteristics of (I(P)(Na) are such as to minimize noise near spike activation threshold and sharpen the threshold.

Animals↗
PubMed1999

Medullary dorsal horn neuronal activity in rats with persistent temporomandibular joint and perioral inflammation.

Studies at spinal levels indicate that peripheral tissue or nerve injury induces a state of hyperexcitability of spinal dorsal horn neurons that participates in the development of persistent pain and hyperalgesia. It has not been demonstrated that persistent injury in the orofacial region leads to a similar state of central hyperexcitability in the trigeminal system. The purpose of the present study was to conduct a parametric analysis of the response properties of nociceptive and nonnociceptive neurons in trigeminal nucleus caudalis (medullary dorsal horn, MDH) in a rat model of persistent orofacial inflammation. Neurons were recorded extracellularly and classified as low-threshold mechanoreceptive (LTM, n = 49), wide dynamic range (WDR, n = 82), and nociceptive-specific (NS, n = 11) neurons according to their response properties to mechanical stimuli applied to their cutaneous receptive fields (RFs). The inflammation was induced 24 h before the recordings by injecting complete Freund's adjuvant (CFA) into the temporomandibular joint (TMJ) capsule or the perioral (PO) skin. The mean areas of the high-threshold RFs of WDR neurons in TMJ (8.66 +/- 0.61 cm(2), n = 25) and PO (5.61 +/- 2.07 cm(2), n = 25) inflamed rats were significantly larger than those in naive rats (1.10 +/- 0. 16 cm(2), n = 32). The mean RF size in TMJ-inflamed rats also was significantly larger than that in PO-inflamed rats (P < 0.01). Furthermore the mean area of the RFs of NS neurons (3.74 +/- 1.44 cm(2), n = 5) was significantly larger in TMJ inflamed rats as compared with naive rats (0.4 +/- 0.09 cm(2), n = 3) (P < 0.05). The background activity in the TMJ- and PO-inflamed rats was generally greater in WDR and NS neurons, but less in LTM neurons, when compared with naive rats. The responses of WDR neurons to noxious mechanical stimuli were increased significantly in TMJ-inflamed rats (P < 0.05) as compared with naive rats. WDR neuronal responses to mechanical stimulation also were increased in PO-inflamed rats but to a lesser extent than in TMJ-inflamed rats. The injection of CFA into the TMJ or PO skin resulted in reduced responses of LTM neurons to mechanical stimuli. The responses of MDH nociceptive neurons to 48-55 degrees C heating were greater in inflamed rats as compared with naive rats. A subpopulation of WDR neurons recorded from TMJ (n = 4 of 10)- or PO (n = 3 of 13)-injected rats responded to cooling in addition to heating of the RFs but did not grade their responses with changes in stimulus intensity. These results indicate that persistent orofacial inflammation produced hyperexcitability of MDH nociceptive neurons. TMJ inflammation resulted in more robust changes in MDH nociceptive neurons as compared with PO inflammation, consistent with previous studies of increased inflammation, increased MDH Fos-protein expression, and increased MDH preprodynorphin mRNA expression in this deep tissue orofacial model of pain and hyperalgesia. The inflammation-induced MDH hyperexcitability may contribute to mechanisms of persistent pain associated with orofacial deep tissue painful conditions.

Animals↗
PubMed2000

Adenosine receptor antagonists induce persistent bursting in the rat hippocampal CA3 region via an NMDA receptor-dependent mechanism.

Adenosine receptor antagonists initiate repetitive bursting activity in the CA3 region of hippocampal slices. Although some studies have suggested that this effect is irreversible, this has been difficult to establish because many adenosine antagonists wash out of brain slices extremely slowly. Furthermore the cellular mechanism that underlies persistent bursting is unknown. To resolve these issues, we studied the effects of nonselective (8-p-sulfophenyltheophylline, 8SPT, 50-100 microM), A(l)-selective (8-cyclopentyl-1, 3-dipropylxanthine, 100 nM; xanthine carboxylic acid congener, 200 nM), and A(2A)-selective (chlorostyryl-caffeine; 200 nM) adenosine antagonists in the CA3 region of rat hippocampal slices using extracellular recording. Superfusion with all of the adenosine antagonists except chlorostyryl-caffeine induced bursting, and the burst frequency after 30 min drug superfusion did not differ for the different antagonists. Most slices showed a period of rapid initial bursting, followed either by stable bursting at a lower frequency or a pattern of oscillating burst frequency. In either case, the bursting continued after drug washout. Virtually identical patterns of long-term bursting activity were observed when 8SPT was washed out or applied continuously. Control experiments using exogenous adenosine to characterize the persistence of 8SPT in tissue demonstrated >95% washout at 60 min, a time when nearly all slices still showed regular bursting activity. When the N-methyl-D-aspartate (NMDA) antagonists DL-2-amino-5-phosphonovaleric acid (AP5; 50 microM) or dizocilpine (10 microM) were applied before and during 8SPT superfusion, bursting occurred in the presence of the NMDA antagonists but did not persist once the 8SPT was washed out. AP5 had no effect on persistent bursting when applied after the initiation of spiking. The selective calcium/calmodulin-dependent protein kinase inhibitor 1-[N, O-bis-(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN-62; 3 microM), which has been shown to block NMDA receptor-dependent synaptic plasticity in the CA1 region, also significantly decreased the long-term effect of 8SPT. Thus adenosine antagonists initiate persistent spiking in the CA3 region; this activity does not depend on continued occupation of adenosine receptors by antagonists, and can be blocked by treatments that prevent NMDA receptor-dependent plasticity.

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