Enhanced forebrain nitric oxide synthase activity in epileptic fowl.

Nitric oxide synthase (NOS) activity was examined in forebrain, cerebellum and optic lobes of adult domestic fowl, having a hereditary primary generalized convulsive disorder. NOS was approximately 2-fold higher in only the forebrain of adult epileptic fowl compared to non-epileptic (carrier) hatchmates. A significant increase in NOS was also evident in forebrains of 1-day-old epileptic chicks. Ca(2+)-dependency experiments confirmed that these increments were principally due to type I NOS (NOS-I). Induction of convulsions by intermittent photic stimulation did not affect pre-existing forebrain NOS-I activity. The present data suggest that an enhanced NO signaling may ensue in selected regions of the brain as an adaptive response to hereditary epileptogenesis.

Seizure control: how to use the new antiepileptic drugs in older patients.

Three new antiepileptic drugs--vigabatrin, gabapentin, and lamotrigine--provide alternatives in the management of older patients with refractory partial seizures. Each appears to have a unique mechanism of action. Clinical trials indicate that routine lab monitoring is not necessary for the safe and effective use of these drugs. They also do not induce liver enzymes or alter the metabolism of other antiepileptic drugs, thus minimizing the risk of interactions. Potential side effects of these agents include dizziness, somnolence, and other signs of CNS depression.

Learning impairment in 1-2-day-old epileptic chicks.

The cause of learning impairment in children with seizure disorders is obscure, in part because of the lack of adequate animal models of learning deficiencies that can be used for study. The discriminating passive avoidance test has been used extensively to study learning behavior in chicks. In the present study, we applied the passive avoidance test to epileptic chicks to determine if learning deficiencies could be demonstrated in this epileptic model. Epileptic fowl have a hereditary form of primary generalized epilepsy characterized by tonic-clonic seizures. The seizures occur spontaneously and can also be induced by photic stimulation. The epileptic phenotype is the result of an autosomal recessive mutation. Heterozygotes do not have seizures and were used as age-matched controls. The discriminating passive avoidance test used in the present study was based on the observation that chicks readily peck at bright shiny beads. Once chicks taste a colored bead coated with a bitter chemical (methylanthranilate), they refuse to peck the bead on subsequent presentations. In addition, chicks can discriminate between colored beads and will continue to peck at a bead of different color than the methylanthranilate (MeA)-coated bead. compared to carriers, epileptic chicks demonstrated significantly less ability to discriminate between colored beads. Furthermore, this learning impairment was observed in epileptic chicks treated with phenobarbital (PB), indicating that the learning impairment in epileptic chicks is an inherent neurological problem and not a consequence of seizure activity.

Early pulmonary homograft failure from dilatation due to distal pulmonary artery stenosis.

Early progressive pulmonary homograft insufficiency developed in an 11-month-old infant after repair of truncus arteriosus because of dilatation secondary to the presence of residual distal pulmonary artery stenosis and hypoplasia. Before repair, the pulmonary artery branches were discontinuous, with the right pulmonary artery being somewhat hypoplastic and originating from the trunk, and the left pulmonary artery supplied by a modified Blalock-Taussig shunt created in the newborn period. At repair, a pulmonary homograft was used to connect the branches. Progressive cardiomegaly and oxygen dependance occurred 3 weeks postoperatively. Cardiac catheterization showed systemic right ventricular pressure, severe homograft insufficiency, and residual distal pulmonary artery stenosis and hypoplasia. On reoperation at 3 months postoperatively, the homograft annulus diameter increased from 14 mm to 16 mm. Dilatation and insufficiency probably occurred because the right ventricle and homograft distal to the obstruction functioned as a unit during systole. The problem might have been minimized with the use of aortic homograft, which is thicker, or annular reinforcement with a synthetic material.

The biochemistry of learning and memory.

An overview of some of the biochemical and molecular events involved in the process of learning and memory are presented in a short review. Two invertebrate models of learning are considered: the gill-withdrawal reflex of Aplysia and avoidance learning in Drosophila melanogaster. Particular attention is paid to the biochemical mechanisms underlying both the development of long-term potentiation (LTP) and passive avoidance learning (PAL) in the young chick. The role of several biological molecules in learning and memory are considered, for example, protein kinase C (PKC), Ca(++)-Calmodulin kinase II (CaMKII), GAP-43, and glutamate receptors.

Diagnosis, surgical intervention, and prognosis of primary pancreatic lymphoma.

Primary pancreatic lymphoma is a rare but treatable malignancy that may present as an isolated pancreatic mass. Most of these patients are assumed to have ductal malignancies of the pancreas and are denied surgical intervention. Controversy exists concerning the method of diagnosis and the need for and extent of surgical intervention for these malignancies. Over the past 15 years, from 1976-1991, we have treated seven patients with pancreatic lymphoma who initially presented with a pancreatic mass. There were five females and two males ranging in age from 60-86 years (mean = 68). All patients were symptomatic and complained of epigastric pain, jaundice, anorexia, or early satiety. The interval between onset of symptoms and treatment averaged 6 weeks. Over half of these patients presented with an epigastric mass and/or jaundice. Abdominal CT scan was accurate in identifying and localizing the pancreatic mass in all patients. The diameter of the pancreatic mass ranged from 3-12 cm (mean = 8.1 cm) and the mass was located in the head of the pancreas in five patients. All attempted percutaneous needle biopsies of the pancreatic mass were non-diagnostic. Operative lymph node biopsy or transduodenal/wedge biopsy of the pancreatic mass was successful in demonstrating pancreatic lymphoma in all patients. Two of the seven patients underwent biliary bypass. One of the seven patients died in the postoperative period. Three of these seven patients received chemotherapy and survived an average of 6.3 years. One patient is alive 8 years after diagnosis and treatment and is currently asymptomatic. Patients who did not receive postoperative chemotherapy survived an average of 5 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Quisqualate receptors in epileptic fowl: the absence of coupling between quisqualate and N-methyl-D-aspartate receptors.

The ability of excitatory amino acid receptor agonists, AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and quisqualate to produce seizures was determined in 1-2 day old epileptic and non-epileptic (carrier) chicks. Both compounds produced prolonged clonic seizures in epileptic chicks at doses which were not convulsant in carrier chicks. Seizures produced in epileptics by AMPA were suppressed by the quisqualate antagonist CNQX (6-cyano-7-nitroquinoxaline-2,3-dione), but were not prevented by pretreatment with competitive (2-amino-7-phosphonoheptanoic acid, APH) or non-competitive (MK-801) NMDA (N-methyl-D-aspartate) receptor antagonists. These data do not support the hypothesis that NMDA receptors work in concert with quisqualate receptors. Binding sites for [3H]AMPA were characterized in cerebral hemispheres of both epileptic and carrier chicks. Analysis of the data revealed no significant alterations in the binding affinity (KD) or the number of binding sites (Bmax) of AMPA to tissue preparations from epileptic chickens when compared to carriers. The latter data does not explain the increased susceptibility of epileptic fowl to the convulsant effects of quisqualate and AMPA.

Attenuation of febrile seizures in epileptic chicks by N-methyl-D-aspartate receptor antagonists.

Experimental febrile seizures can be evoked in epileptic chicks by elevation of their body temperature. Both competitive N-methyl-D-aspartate (NMDA) receptor antagonists [(3-(+/- )2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), DL-2-amino-7-phosphosphonoheptanoic acid (APH), DL-2-amino-5-phosphonovaleric acid (APV), D-alpha-aminoadipic acid (AAA), and DL-alpha, epsilon-diaminopimelic acid (DAP)] and the noncompetitive NMDA antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5, 10-imine maleate (MK-801) produced dose-dependent increases in latency to the onset of seizures. Of the drugs tested, MK-801 had the highest potency followed in order by CPP = APH greater than APV much greater than AAA greater than DAP. There was a high correlation (r = 0.995) between the dose capable of doubling seizure latency and the affinity of the competitive NMDA antagonists for the NMDA receptor as determined by in vitro binding assays. These data suggest that NMDA receptor mediated mechanisms may be involved in the production of seizures in response to hyperthermia.

The relationship between anticonvulsant activity and receptor affinity of N-methyl-D-aspartate antagonists in epileptic fowl.

The N-methyl-D-aspartate (NMDA) receptor antagonists [(3-(+/-)2-carboxypiperazin-4-yl)-propyl-l-phosphonic acid (CPP), +/- 2-amino-7-phosphonoheptanoic acid (2AP7), +/- 2-amino-5-phosphonovaleric acid (2AP5), D-alpha-aminoadipic acid (alpha AA), and +/- alpha, epsilon-diaminopimelic acid (DAP)] were tested for anticonvulsant activity in epileptic chickens. There was a high correlation between anticonvulsant potencies (ED50) and the affinity for the NMDA receptor measured by displacement of L-[3H]glutamate from synaptosomal membranes. The high seizure susceptibility is not due to abnormalities in the NMDA receptor as comparison of KD, Bmax and Ki values in synaptosomal preparations from epileptic and non-epileptic chickens indicated no differences in NMDA receptor binding receptor characteristics.

Benzodiazepine antagonist Ro 15-1788 (flumazepil) attenuates the anticonvulsant activity of diazepam in epileptic fowl.

The ability of the imidazobenzodiazepine Ro 15-1788 to displace diazepam from brain membranes in vitro and to antagonize the anticonvulsant activity of diazepam in vivo was determined in epileptic fowl. At doses of 1.0 mg/kg and higher, Ro 15-1788 significantly attenuated the anticonvulsant action of diazepam (1.0 mg/kg) in epileptic chickens. Ro 15-1788 alone exerted no anticonvulsant activity even in doses as high as 10 mg/kg. Specific binding of 10 nM [3H]diazepam to whole homogenate fractions prepared from cerebral hemispheres of epileptic fowl was inhibited by Ro 15-1788 with an IC50 of 8.5 nM and the Ki was determined to be 4.25 nM. These results suggest that Ro 15-1788 competes directly with diazepam for a binding site involved in producing anticonvulsant activity.

A comparison of methods for removal of endogenous GABA from brain membranes prepared for binding assays.

Two commonly used procedures for removing endogenous GABA from brain homogenates were evaluated by measuring residual GABA using high performance liquid chromatography (HPLC). The effect of these treatments on [3H]muscimol binding to the GABA receptor was also determined. Membranes subjected to osmotic lysing and eight washes with Tris-citrate buffer contained significant quantities of residual GABA whereas lysing and incubation with Triton X-100 followed by three buffer washes resulted in GABA levels below the limits of detection. The apparent affinity for [3H]muscimol was significantly higher in the Triton X-100 treated membranes and this was probably a result of the lower amount of GABA present in these membranes. The effect of Triton treatment or buffer washing on residual levels of glutamate, glutamine, aspartate, and taurine were also determined.

Evidence for the pharmacological relevance of benzodiazepine receptors to anticonvulsant activity.

Each of a series of benzodiazepines was found to be effective in preventing convulsions evoked by intermittent photic stimulation of epileptic chickens. There was a high correlation between the anticonvulsant potencies (mean effective dosages) and the affinity of the agents for the putative benzodiazepine receptor as measured by displacement of [3H]diazepam from binding sites on chicken synaptosomal membranes. This correlation in a genetic model of epilepsy provides further evidence that benzodiazepines exert their anticonvulsant effects by interacting with the benzodiazepine receptor.

Experimental febrile convulsions in epileptic chickens: the anticonvulsant effect of elevated gamma-aminobutyric acid concentrations.

The high seizure susceptibility in epileptic chickens is due to an autosomal recessive mutation. In 3-day-old chicks homozygous for the epilepsy gene (epileptics), elevation of body temperature using microwave diathermy evoked an initial febrile seizure resembling the clonic seizures evoked in epileptic chicks by photic stimulation. After complete recovery, this was followed by a clonic-tonic seizure. In nonepileptic heterozygote hatchmates (carriers) of the same age, only the latter seizure pattern was observed. In 16- to 17-day-old chicks of either phenotype, both seizure patterns were observed during hyperthermia. In all cases, the temperature at which seizures occurred was significantly lower in epileptic than in nonepileptic chicks, indicating a lower threshold for febrile seizures when there is an inherited predisposition to convulse. The occurrence of seizures was dependent on the body temperature and not on the rate of rise of temperature. Elevation of the brain gamma-aminobutyric acid (GABA) concentrations by administration of the GABA transaminase inhibitor gamma-vinyl GABA reduced the incidence of the initial febrile seizures and increased the latency in those birds that were not fully protected.

Benzodiazepine receptors and seizure susceptibility in epileptic fowl.

Benzodiazepine binding to brain membrane preparations obtained from epileptic and nonepileptic carrier fowl was compared. [3H]Flunitrazepam binding to whole brain homogenates from 2-day-old chicks and [3H]diazepam binding to synaptosomal membranes and homogenates from adult chickens were determined. Scatchard analysis revealed no differences in either the number of receptors or their affinity for the ligands when the epileptics were sacrificed in the interictal state. Evoked seizures in adult epileptics had no effect on the number or affinity of binding sites using [3H]diazepam as the ligand. Moreover, the ability of gamma-aminobutyric acid to facilitate benzodiazepine binding was not different in epileptic fowl when compared with carriers.

Pharmacology of methyl- and propyl-beta-carbolines in a hereditary model of epilepsy.

Intravenous administration of beta-carboline-3-carboxylate methyl ester (beta-CCM) produced convulsions at small doses (0.03 mg/kg) in adult chickens, homozygous for the epileptic gene. Nonepileptic heterozygote hatchmates (carriers) did not undergo seizures at doses of 1 mg/kg, and doses of 3-5 mg/kg produced only brief myoclonic responses. The convulsant effect of beta-CCM could be prevented by pretreatment with large doses of beta-carboline-3-carboxylate propyl ester (beta-CCP). beta-Carboline-3-carboxylate methyl ester displayed a higher affinity than diazepam in displacement studies on synaptosomal membrane preparations from brains of epileptic and carrier chickens.

In vivo and in vitro studies of bacterial endotoxin-membrane interactions and the effects of membrane-active agents.

The characteristics of 51Cr-labelled E. coli endotoxin binding to human erythrocyte membranes in vitro have been investigated. A saturable component of binding was apparent at low endotoxin concentrations (less than 50 micrograms ml-1) relevant to its in vivo actions, while at higher concentrations binding was non-saturable and increased in linear fashion. Experiments examining the ability of unlabelled endotoxin to antagonize the binding of labelled toxin provided further evidence for these specific and non-specific modes of endotoxin-membrane interaction. Membrane-active agents previously shown to reduce endotoxin toxicity in vivo decreased endotoxin binding to erythrocyte membranes in vitro, with propranolol and pranolium being the most effective in this regard. Tissue distribution studies following administration of radiolabelled endotoxin to guinea-pigs showed a positive correlation between the accumulation of 51Cr-endotoxin in lung and elevations in plasma acid phosphatase activity, a measure of in vivo endotoxin toxicity. The in vivo accumulation of 51Cr-endotoxin in guinea-pig lung was reduced by prior treatment with (+)-propranolol or pranolium, paralleling the results of the in vitro binding studies. Our results suggest that membrane-active agents such as (+)-propranolol may be useful adjuncts to antimicrobial drugs in the therapy of gram-negative endotoxaemia.

Plasma acid phosphatase levels in endotoxaemia: modification by drugs and chemically detoxified endotoxins.

The ability of chemically detoxified E. coli endotoxins and membrane-active agents to modify the toxicity of native E. coli endotoxin in vivo was examined. The time- and dose-dependent increase in plasma acid phosphatase activity following toxin administration to rats provided a convenient quantitative measure of in vivo toxicity under various experimental conditions. Treatment of endotoxin with either sodium hydroxide or sodium periodate produced substances which, when injected alone, failed to cause an increase in plasma acid phosphatase activity. When given before native endotoxin, periodate-detoxified toxin produced a dose-dependent reduction in the elevation of plasma enzyme activity caused by unmodified toxin. Pretreatment with pranolium, hydrocortisone or (+)-propranolol also reduced the in vivo toxicity of endotoxin. Mortality studies in mice provided further independent support for the effectiveness of periodate-detoxified endotoxin and membrane-active drugs as endotoxin antagonists. Evidence has been found that under certain conditions gentamicin may act synergistically with bacterial endotoxins in vivo.

Plasma lysosomal enzymes in experimental and clinical endotoxemia.

Endotoxins, which are lipopolysaccharide complexes derived from the cell walls of gram-negative bacteria, have been implicated in the pathogenesis of gram-negative septic shock. One possible mechanism of endotoxin-induced damage may involve an action at cell surface membranes resulting in cell injury and lysosomal enzyme release. In our experiments, the administration of purified E. coli endotoxin (2 mg/kg intravenously) to guinea pigs produced elevations in the plasma activity of the lysosomal hydrolases glucosaminidase, acid phosphatase and Cathepsin D of approx. 2-, 3- and 4-fold, respectively, at 5 h following endotoxin injection. Animals haemorrhaged to produce sustained hypotension that was greater than the reduction in blood pressure seen with endotoxin treatment, exhibited an elevation only in plasma Cathepsin D activity that was, however, significantly lower than the increase associated with endotoxemia. The three lysosomal hydrolases were also measured in man, including a control group, patients with gram-negative septic shock, other shock, gram-positive and gram-negative septicaemia without shock. Plasma Cathepsin D activity was significantly elevated (26-fold above control) in the group with gram-negative septic shock as compared to all other groups. Patients in the gram-negative septic shock group and the other shock group both had significantly greater glucosaminidase activity than controls. Our results suggest that plasma Cathepsin D measurements may be of diagnostic and prognostic value in the clinical management of gram-negative septic shock.