Comprehensive Cardiovascular Management of Myotonic Dystrophy Type 1 Patients: A Report from the Italian Neuro-Cardiology Network

Myotonic dystrophy is a hereditary disorder with systemic involvement. The Italian Neuro-Cardiology Network-"Rete delle Neurocardiologie" (INCN-RNC) is a unique collaborative experience involving neurology units combined with cardio-arrhythmology units. The INCN facilitates the creation of integrated neuro-cardiac teams in Neuromuscular Disease Centers for the management of cardiovascular involvement in the treatment of myotonic dystrophy type 1 (MD1).

Cardiac implantable electronic devices (CIEDs) and allergy

Advances in cardiac implantable electronic devices (CIEDs) have prolonged life expectancy in various medical settings. However, the issue of hypersensitivity to components of CIEDs is still a concern. Since 1970, allergic reactions to metallic and nonmetallic components of CIEDs have been reported. Hypersensitivity reactions to medical devices are rare and not fully understood. In some cases, diagnosis and treatment are difficult. Cardiologists should always keep in mind pacemaker allergy when a patient appears with wound complications and no signs of infection. Patch testing should be tailored toward the specific biomaterials used in a device, in addition to testing with standard screening allergens in select cases.

Incidence of ventricular arrhythmias related to COVID infection and vaccination in patients with Brugada syndrome: Insights from a large Italian multicenter registry based on continuous rhythm monitoring

INTRODUCTION

Brugada syndrome (BrS) has a dynamic ECG pattern that might be revealed by certain conditions such as fever. We evaluated the incidence and management of ventricular arrhythmias (VAs) related to COVID-19 infection and vaccination among BrS patients carriers of an implantable loop recorder (ILR) or implantable cardioverter-defibrillator (ICD) and followed by remote monitoring.

METHODS

This was a multicenter retrospective study. Patients were carriers of devices with remote monitoring follow-up. We recorded VAs 6 months before COVID-19 infection or vaccination, during infection, at each vaccination, and up to 6-month post-COVID-19 or 1 month after the last vaccination. In ICD carriers, we documented any device intervention.

RESULTS

We included 326 patients, 202 with an ICD and 124 with an ILR. One hundred and nine patients (33.4%) had COVID-19, 55% of whom developed fever. Hospitalization rate due to COVID-19 infection was 2.76%. After infection, we recorded only two ventricular tachycardias (VTs). After the first, second, and third vaccines, the incidence of non-sustained ventricular tachycardia (NSVT) was 1.5%, 2%, and 1%, respectively. The incidence of VT was 1% after the second dose. Six-month post-COVID-19 healing or 1 month after the last vaccine, we documented NSVT in 3.4%, VT in 0.5%, and ventricular fibrillation in 0.5% of patients. Overall, one patient received anti-tachycardia pacing and one a shock. ILR carriers had no VAs. No differences were found in VT before and after infection and before and after each vaccination.

CONCLUSIONS

From this large multicenter study conducted in BrS patients, followed by remote monitoring, the overall incidence of sustained VAs after COVID-19 infection and vaccination is relatively low.

Tissue thickness measured with dielectric-based technology during radiofrequency catheter ablation

Radiofrequency catheter ablation of the cavotricuspid isthmus is the standard treatment for patients suffering from typical atrial flutter. The aim of this study was to test the feasibility of tissue thickness and lesion transmurality measurement by a novel dielectric system. This was a retrospective multicentric non-randomized open-label, single-arm study. The atrial wall thickness was significantly higher close to the tricuspid annulus than close to the inferior vena cava and a trend towards a progressive decrease of atrial wall thickness was observed moving the mapping catheter from the tricuspid valve to the inferior vena cava. The possibility to visualize the tissue thickness could modify the way to deliver radiofrequency energy, allowing a tailored approach in cardiac ablation procedures.

Arrhythmic CArdiac DEath in MYotonic dystrophy type 1 patients (ACADEMY 1) study: the predictive role of programmed ventricular stimulation

AIMS

Myotonic dystrophy type 1 (DM1) predisposes to the development of life-threatening arrhythmias and sudden cardiac death. Our study aimed to evaluate the prognostic value of programmed ventricular stimulation (PVS) in DM1 patients with conduction system disease.

METHODS AND RESULTS

Arrhythmic CArdiac DEath in MYotonic dystrophy type 1 patients (ACADEMY 1) is a double-arm non-randomized interventional prospective study. Myotonic dystrophy type 1 patients with permanent cardiac pacing indication were eligible for the inclusion. The study population underwent to pacemaker (PM) or implantable cardioverter-defibrillator (ICD) implantation according to the inducibility of ventricular tachyarrhythmias at PVS. Primary endpoint of the study was a composite of appropriate ICD therapy and cardiac arrhythmic death. The secondary study endpoint was all-cause mortality. Seventy-two adult-onset DM1 patients (51 ± 12 years; 39 male) were enrolled in the study. A ventricular tachyarrhythmia was induced in 25 patients (34.7%) at PVS (PVS+) who underwent dual chambers ICD implantation. The remaining 47 patients (65.3%) without inducible ventricular tachyarrhythmia (PVS-) were treated with dual-chamber PM. During an average observation period of 44.7 ± 10.2 months, nine patients (12.5%) met the primary endpoint, four in the ICD group (16%) and five (10.6%) in the PM group. Thirteen patients died (18.5%), 2 in the ICD group (8%) and 11 in PM group (23.4%). The Kaplan-Meier analysis did not show a significantly different risk of both primary and secondary endpoint event rates between the two groups.

CONCLUSIONS

The inducibility of ventricular tachyarrhythmias has shown a limited value in the arrhythmic risk stratification among DM1 patients.

Trends beyond the new normal: from remote monitoring to digital connectivity

COVID pandemic emergency has forced changes from traditional in-person visits to application of telemedicine in order to overcome the barriers and to deliver care. COVID-19 has accelerated adoption of digital health. During this time, the distance is itself a prevention tool and the use of technology to deliver healthcare services and information has driven the discovery of mobile and connected health services. Health services should to be prepared to integrate the old model of remote monitoring of CIEDs and adopt new digital tools such as mobile Apps and connected sensors.

P1133Impact of mid-septal versus apical pacing on the right ventricle performance of patients with right bundle branch block undergoing pacemaker implantation

Background

pacemaker induced cardiomyopathy or transient impairment of the left ventricle (LV) function could be common collateral effects of the prolonged right ventricle (RV) pacing in patients with a pacemaker (PM) and pre-existing intra-ventricular conduction disturbances. However, the impact of RV pacing-site on RV performance of patients with right bundle branch block(RBBB) is still under-investigated.

Purpose

to study the effects of RV pacing in the mid-septal versus apical site on the morpho-functional performance of RV in patients undergoing permanent PM implantation.

Methods

We prospectively enrolled consecutive patients with a pre-existent complete RBBB and undergoing dual-chamber PM implantation in our institution. We randomized the patients 1:1 to receive the RV catheter fixed either in the apex or in the mid-septal position. Patients with LV systolic dysfunction (LVEF <50%), severe valvulopathies, left bundle branch block (LBBB), or preserved intraventricular conduction were excluded. Patients who received PM implantation were evaluated both at baseline and after two months with a 12-lead ECG, 2D, and 3D echocardiogram with analysis focused on RV performance according to the guidelines of the European Association of Cardiovascular Imaging.

Results

a total of 22 patients were randomized in the study, 11 (50%) received RV catheter positioned in the apex and 11 (50%) in the mid-septum, respectively. No baseline differences were recorded between the two groups in clinical characteristics, ECG and echocardiographic parameters. At 2 months follow up, there were no statistically significant difference in the % of RV pacing between the two groups. Nonetheless, RV mid-septal group showed significantly shorter duration of the stimulated QRS (146 ± 12 msec vs. 161 ± 20 msec, p = 0.05), significantly reductions in the RV dimensions (pre: 42 ± 8 mm vs. post: 37 ± 7 mm, p = 0.05) telediastolic area (pre: 12 ± 3 cm2/m2 vs post: 9 ± 4 cm2/ m2, p = 0.02) telediastolic volume (pre: 55 ± 16 ml/m2 vs post: 50 ± 17 ml/m2, p = 0.02) and a significant improvement of RV ejection fraction (pre: 54 ± 9% vs post: 57 ± 11%, p = 0.02) than patients in the RV-apical group. Moreover, patients in the RV-apical group showed significant lowering in the GLS of the LV (pre: -16 ± 3% vs post: -11.7 ± 3%, p <0.001) and in the TAPSE (pre: 23 ± 5 mm vs post: 21 ± 2, p = 0.07) at follow up.

Conclusions

In this study, mid-septal pacing seems associated with a better morpho-functional RV performance than apical pacing in patients with pre-existent RBBB undergoing permanent PM implantation.

Impact of respiration on electroanatomical mapping of the right atrium: implication for cavotricuspid isthmus ablation

PURPOSE

Cavotricuspid isthmus (CTI) ablation for typical atrial flutter (AFL) has become the preferred treatment for this arrhythmia. The aims of this study were to assess the impact of respiratory gating (RG) on electroanatomical mapping of CTI and to assess the efficiency of CTI ablation guided by the Carto3® system equipped with the new respiration gating software.

METHODS

Forty-four consecutive patients (mean age, 60 ± 13 years; 25 male) undergoing cavotricuspid ablation for symptomatic common AFL were randomly assigned to CARTO™ mapping with or without enabling RG module (Group A, RG OFF, Group B, RG ON).

RESULTS

A significant reduction in mean RA volume, CTI central length and CS ostium maximum diameter has been observed in the RG maps. The mean total procedural, fluoroscopy and radiofrequency (RF) time were 102.9 ± 35.3, 10.6 ± 3.3, 22.9 ± 14.2 min in group A and 75.3 ± 21.7, 3.6 ± 4.5, 10.4 ± 5.7 min in group B, respectively (p < 0.05).

CONCLUSIONS

Electroanatomical mapping systems' accuracy may be strongly influenced by respiration movements. The current study showed that automatic respiratory gated acquisition resulted in a better visualization of CTI, and this determines a relevant reduction in fluoroscopy and RF times.

Allozyme variation and divergence in the phyllotine rodent Calomys hummelincki (Husson, 1960)

The aim of the present study was to assess the degree of genetic variation and divergence among six populations of Calomys hummelincki, a phyllotine rodent distributed in northern South America. With this information we will try to evaluate the two hypotheses of possible colonization and differentiation of this group of rodents postulated by Baskin and Reig. We studied 34 loci by electrophoretic analysis: 21 were monomorphic for all populations and 13 were polymorphic in at least one population, being P1% = 21.6% the mean value for all populations. The mean value of heterozygosity per locus was H = 0.075. Low values of genetic distance were observed among populations of the Llanos region (0.001 < D < 0.006). There was a larger genetic distance (D = 0.024) between the population from Isiro, in the northwestern semiarid region, and those from the Llanos region. The insular population of Aruba displayed the lowest value of genetic distance with the population from Isiro (D=0.014). The specimens from Sipao, on the right side of the Orinoco river, displayed the highest values of genetic distances in comparison with other populations of C. hummelincki (0.070 < D < 0.095). The relatively high differentiation was due to the fixation of new alleles, not found in other populations of C. hummelincki, at loci Idh-1 and Est-2. F-statistics and Nm values indicated reduced gene flow among the populations sampled. Despite the limited data, the results seem to support Reig's hypothesis about south to north colonization of genus Calomys in South America.

Occurrence of anti-thyroid autoantibodies in children vertically infected with HIV-1

Autoimmune phenomena, especially occurrence of non organ-specific autoantibodies, are common in congenitally acquired HIV infection, mostly in the symptomatic stages of the disease. Anti-thyroid autoantibodies detected in adult patients represent the only type of organ-specific autoantibodies reported in HIV infection. As far as we know, occurrence of these autoantibodies has not been observed in HIV infected children. In this study thyroid biochemical pattern and possible occurrence of anti-thyroid autoantibodies were investigated in 40 vertically HIV infected, 18 seroreverted and 22 healthy children. 34% of HIV infected symptomatic children showed anti-thyroglobulin antibodies. Asymptomatic patients, seroreverted and healthy controls did not show any anti-thyroid antibodies at the time of the study. High Tg levels were observed in 38% of the 40 HIV infected patients and high TSH concentrations were found in 27.5% of the HIV children. High TSH values were more frequently observed in the infected children with moderate or severe immunocompromised status. Thyroxine binding globulin levels were high in 68% of the HIV children and in 22% of the seroreverted. The finding of anti-thyroid autoantibodies in congenital HIV infected children confirms the thyroid's involvement in HIV infection and provides more information about the wide spectrum of autoimmune phenomena observed in the infection.

In search of a new ethic for treating patients with chronic pain: what can medical boards do?

Author argues that a complex "ethic of underprescribing" underlies the continued reluctance of physicians to use opioids to treat chronic pain. She contends that state medical boards are uniquely positioned to promote a new ethic for pain management, but stresses the difficulties for boards in attaining this goal. She thinks success may hinge on whether boards can change their approach to pain management and persuade a skeptical medical community that adopting a risk for underprescribing will serve the long-term interests of patients and the profession.

Characterization of superior sagittal sinus blood flow velocity using color flow Doppler in neonates and infants

The objective of the investigation was to determine what effect intracranial pathology has on alterations of superior sagittal sinus blood flow, and to determine the role of color flow Doppler imaging of the superior sagittal sinus in the diagnosis of intracranial pathology in the neonate and infant. One hundred examinations were performed prospectively in 96 patients. The velocity was determined with an angle correction at 30-60 degrees and was obtained with and without gentle transducer compression. Superior sagittal sinus thrombosis was identified in two patients by the absence of flow. Multiple t-tests for independent measures showed no clinically significant differences between flow velocities with regard to intracranial hemorrhage, ventriculomegaly, extracorporeal membrane oxygenation therapy or prematurity. The authors conclude that color flow Doppler can accurately diagnose superior sagittal sinus thrombosis and may be used to screen high risk neonates such as those with thrombosis elsewhere or those treated with extracorporeal membrane oxygenation. No clinically significant associations were found between superior sagittal sinus flow velocity and any of the parameters evaluated in this study.

[Neonatal abstinence syndrome and maternal toxicological profile]

Neonatal abstinence syndrome (NAS) is one of the most frequent manifestations in the neonates of drug-addicted mothers. It is caused by the abrupt interruption of the transplacentar passage of drugs from the mother to the fetus. The aim of this study was to evaluate the correlation between drugs taken during pregnancy and NAS. Data were examined relating to 223 neonates born during 1975-1992 to drug-addict mothers. Neonates were subdivided into four groups according to the maternal toxicological profile. It was thus possible to observe that there is a greater prevalence of NAS in cases of polypharmacomania and that it gradually diminishes in the children of heroin addicts and those receiving methadone treatment. Moreover, the intensity of the syndrome is correlated to the high doses of methadone and/or heroin. In the group of neonates whose mothers had complied with the methadone treatment protocol, the severity of NAS was proportional to the dose taken by the mother. In conclusion, the management of pregnant drug addicts following a controlled methadone treatment programme is accompanied by improved obstetric help and is the most suitable way of reducing perinatal complications and the prevalence of NAS.

Intracerebral hemorrhage after evacuation of a subdural hematoma in an infant

Intracerebral hematomas following evacuation of a subdural hematoma have been described in adults resulting from sudden decompression during the drainage of the hematoma. In infants an open fontanelle and patent sutures are expected to offer protection against sudden decompression. We report the occurrence of intracerebral hematoma in an infant following evacuation of a subdural hematoma. The multiplicity and centripetal spread of the postoperative hematomas suggested that they had resulted from sudden decompression.

[The effects of lactitol in the treatment of intestinal stasis in childhood]

Thirty-nine children (18 males, 21 females) suffering from intestinal stasis were treated with lactitol or a reference drug (lactulose in crystalline form), according to a balanced randomization, for 15 days. The first group of children included 19 subjects treated with lactitol, the second group included 20 subjects treated with lactulose. The dosages of lactitol and lactulose were, respectively, of 150-350 mg/kg and of 150-300 mg/kg daily per os with a single administration in the morning. During the trial, the children did not take any concomitant drug. For each patient the tested parameters were: number of intestinal evacuations, consistency of stool and adverse reactions (abdominal swelling, abdominal pain, nausea, vomiting, meteorism) daily; routine laboratory tests at the beginning and at the end of the trials. The results showed that the subjects treated with lactitol have manifested, besides a proved therapeutic efficacy, a better tolerability and compliance than the subjects treated with lactulose.

Salmonella osteomyelitis with epidural abscess. A case report with review of osteomyelitis in children with sickle cell anemia

Neurologic complications of sickle cell anemia are most commonly ischemic strokes secondary to sludging in cerebral arterioles. We, therefore, report a case of progressive paraparesis in a child with sickle cell anemia which was initially thought to be secondary to a spinal cord ischemic event. Further diagnostics demonstrated that the neurologic deficits were secondary to salmonella osteomyelitis and an epidural abscess, compressing the upper thoracic spinal cord at the T6 level. The diagnostic and radiological features which help to distinguish between bone infarct and osteomyelitis, both responsible for bone pain in sickle cell patients, are also presented. In particular, Tc-sulfur colloid bone marrow imaging is the most helpful test for distinguishing between these similarly presenting clinical entities, as early as 48 h after bone pain develops.

Reductions in acetylcholine and nicotine binding in several degenerative diseases

Alzheimer's disease, Parkinson's disease, and progressive supranuclear palsy are all characterized by loss of neurons in the basal forebrain cholinergic system and by associated reductions in cortical presynaptic cholinergic markers, such as choline acetyltransferase. In this report, we identify that a major cortical receptor alteration in these disorders is a reduction in nicotinic receptors measured using both tritiated acetylcholine and levorotatory tritiated nicotine binding.

Reductions in [3H]nicotinic acetylcholine binding in Alzheimer's disease and Parkinson's disease: an autoradiographic study

In Alzheimer's disease (AD) and Parkinson's disease (PD), dysfunction in the basal forebrain cholinergic system is accompanied by a consistent loss of presynaptic cholinergic markers in cortex, but changes in cholinergic receptor binding sites are poorly understood. In the present study, we used receptor autoradiography to map the distribution of nicotinic [3H]acetylcholine binding sites in cortices of individuals with AD and PD and matched control subjects. In both diseases, a profound loss of nicotinic receptors occurs in all cortical layers, particularly the deepest layers.

Corticospinal projections from the medial wall of the hemisphere

We injected wheat germ agglutinin conjugated to horseradish peroxidase into different segments of the spinal cord in order to examine the topographic organization of corticospinal projections from the medial wall of the hemisphere. We observed that substantial projections to the spinal cord originate not only from the supplementary motor area (SMA) in area 6, but also from 2 regions within the cingulate sulcus. The distribution of labeled neurons following tracer injections into different spinal cord segments indicates that corticospinal projections from the SMA and from the 2 cingulate regions are somatotopically organized. These findings together with other recent anatomical observations suggest that the corticospinal projections from the medial wall of the hemisphere provide the basal ganglia and limbic system with a somatotopically organized access to spinal cord mechanisms.

Corticospinal projections originate from the arcuate premotor area

We investigated the patterns of corticospinal projection to different segments of the cervical spinal cord using retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. We confirmed prior suggestions that the arcuate premotor area (APA) has a significant projection to the spinal cord. In addition, we observed that the corticospinal projection from the APA terminates in upper, but not lower segments of the cervical spinal cord. Furthermore, the region of the APA which projects to the cervical cord also projects to the arm area of the primary motor cortex on the crest of the precentral gyrus. Thus, we conclude that the APA projection to upper cervical segments is involved in the cortical control of arm movements.

Nicotinic acetylcholine binding sites in Alzheimer's disease

In Alzheimer's disease (AD), there is a loss of presynaptic cholinergic markers in the cerebral cortex, but the nature of cholinergic receptor changes is unclear. In this study, [3H]acetylcholine and [3H]nicotine were used to label nicotinic cholinergic binding sites in cerebral cortical tissues obtained at autopsy from patients with AD and from matched controls. A consistent and severe loss of nicotinic receptors was found in AD.

A strong influence of serotonin axons on beta-adrenergic receptors in rat brain

The role of serotonin axons in modulating the norepinephrine neurotransmission system in rat brain was investigated. Selective lesions of the forebrain serotonergic system were made by injecting 5,7-dihydroxytryptamine into the midbrain raphe nuclei. Four to six weeks after the lesion, the uptake of 3H-labeled serotonin in the frontal cortex and the hippocampus was reduced by more than 90 percent, while neither the uptake of 3H-labeled norepinephrine nor the content of norepinephrine was affected in either tissue. The number of beta-adrenergic receptors, as measured by radioligand binding with 3H-labeled dihydroalprenolol, was increased in the frontal cortex and hippocampus of rats with lesions. Similarly, specific lesions of central serotonin axons produced by systemically administered p-chloramphetamine resulted in an increase in the binding of 3H-labeled dihydroalprenolol to beta-adrenergic receptors and in the production of adenosine 3',5'-monophosphate in response to isoproterenol. These results indicate that serotonin axons may regulate beta-adrenergic receptor number and function in brain.

High-affinity binding of [3H]acetylcholine to muscarinic cholinergic receptors

High-affinity binding of [3H]acetylcholine to muscarinic cholinergic sites in rat CNS and peripheral tissues was measured in the presence of cytisin, which occupies nicotinic cholinergic receptors. The muscarinic sites were characterized with regard to binding kinetics, pharmacology, anatomical distribution, and regulation by guanyl nucleotides. These binding sites have characteristics of high-affinity muscarinic cholinergic receptors with a Kd of approximately 30 nM. Most of the muscarinic agonist and antagonist drugs tested have high affinity for the [3H]acetylcholine binding site, but pirenzepine, an antagonist which is selective for M-1 receptors, has relatively low affinity. The ratio of high-affinity [3H]acetylcholine binding sites to total muscarinic binding sites labeled by [3H]quinuclidinyl benzilate varies from 9 to 90% in different tissues, with the highest ratios in the pons, medulla, and heart atrium. In the presence of guanyl nucleotides, [3H] acetylcholine binding is decreased, but the extent of decrease varies from 40 to 90% in different tissues, with the largest decreases being found in the pons, medulla, cerebellum, and heart atrium. The results indicate that [3H]acetylcholine binds to high-affinity M-1 and M-2 muscarinic receptors, and they suggest that most M-2 sites have high affinity for acetylcholine but that only a small fraction of M-1 sites have such high affinity.

Differential binding properties of adenosine receptor agonists and antagonists in brain

The binding properties of N6-cyclohexyl [3H]adenosine ( [3H]CHA) and 1,3-diethyl-8-[3H]phenylxanthine ( [3H]DPX) in rat forebrain membrane are compared. The kinetic parameters of binding for each ligand are quite distinct, with [3H]CHA displaying two populations of binding sites (KD = 0.4 +/- 0.05 nM and 4.2 +/- 0.3 nM; Bmax = 159 +/- 17 and 326 +/- 21 fmol/mg protein), whereas [3H]DPX yielded monophasic Scatchard plots (KD = 13.9 +/- 1.1 nM; Bmax = 634 +/- 27 fmol/mg protein). The metals copper, zinc, and cadmium are potent inhibitors of [3H]CHA binding, with respective IC50 concentrations of 36 microM, 250 microM, and 70 microM. Copper is a much less potent inhibitor of [3H]DPX binding (IC50 = 350 microM). The inhibitory effect of copper on both [3H]CHA and [3H]DPX binding is apparently irreversible, as membranes pretreated with copper cannot be washed free of its inhibitory effect. The inhibitory effect of both copper and zinc on [3H]CHA binding was reversed by the guanine nucleotide Gpp(NH)p. [3H]DPX binding is only partially inhibited by zinc and cadmium (60% of specific binding remains unaffected), suggesting that this adenosine receptor ligand binds to two separate sites. Guanine nucleotides had no effect on the inhibition of [3H]DPX binding by either copper or zinc. Differential thermal and proteolytic denaturation profiles are also observed for [3H]CHA and [3H]DPX binding, with the former ligand binding site being more labile in both cases. Stereospecificity is observed in the inhibition of both [3H]CHA and [3H]DPX binding, with L-N-phenylisopropyladenosine (PIA) being 50-fold more potent than D-PIA in both cases. Evidence is therefore provided that adenosine receptor agonists and antagonists have markedly different binding properties to brain adenosine receptors.

Specific calcium antagonist binding sites in brain

The binding of the calcium antagonist [3H] nitrendipine ([3H] NDP) to brain and heart is described and the brain site is characterized. The binding is saturable, specific and of very high affinity with KD values of 0.16 nM in brain and 0.21 nM in heart. Our kinetic results are similar to those recently reported by two other groups (1, 2), indicating a saturable, high affinity binding site in brain. In brain the binding sites are enriched in crude nuclear and synaptosomal fractions. The highest levels of binding are seen in the hippocampus, caudate and cerebral cortex with much lower levels in the cerebellum and pons. Calcium has a marked stimulatory effect on [3H] NDP binding at 10(-4) M. Addition of 0.5 mM CaCl2 to EDTA treated membranes nearly doubles the number of binding sites. Of the many drugs and neurotransmitters tested only other calcium antagonists, i.e. verapamil, inhibit binding (IC50 = 250 nM). The inhibition of [3H] NDP binding by verapamil is apparently non-competitive and not complete, suggesting that [3H] NDP binds to several sites, only some of which are inhibited by verapamil. The [3H] NDP binding site is probably a protein since it is very sensitive to trypsin, heat and sulfhydryl reagents.

[3H]nitrobenzylthioinosine binding as a probe for the study of adenosine uptake sites in brain

The binding of the potent adenosine uptake inhibitor [3H]nitrobenzylthioinosine ([3H]NBI) to brain membrane fractions was investigated. Reversible, saturable, specific, high-affinity binding was demonstrated in both rat and human brain. The KD in both was 0.15 nM with Bmax values of 140-200 fmol/mg protein. Linear Scatchard plots were routinely obtained, indicating a homogeneous population of binding sites in brain. The highest density of binding sites was found in the caudate and hypothalamus in both species. The binding site was heat labile and trypsin sensitive. Binding was also decreased by incubation of the membranes in 0.05% Triton X-100 and by treatment with dithiothreitol and iodoacetamide. Of the numerous salt and metal ions tested, only copper and zinc had significant effects on [3H]NBI binding. The inhibitory potencies of copper and zinc were IC50 = 160 microM and 6 mM, respectively. Subcellular distribution studies revealed a high percentage of the [3H]NBI binding sites on synaptosomes, indicating that these sites were present in the synaptic region. A study of the tissue distribution of the [3H]NBI sites revealed very high densities of binding in erythrocyte, lung, and testis, with much lower binding densities in brain, kidney, liver, muscle, and heart. The binding affinity in the former group was approximately 1.5 nM, whereas that in the latter group was 0.15 nM, suggesting two types of binding sites. The pharmacologic profile of [3H]NBI binding was consistent with its function as the adenosine transport site, distinct from the adenosine receptor, since thiopurines were very potent inhibitors of binding whereas adenosine receptor ligands, such as cyclohexyladenosine and 2-chloroadenosine, were three to four orders of magnitude less potent. [3H]NBI binding in brain should provide a useful probe for the study of adenosine transport in the brain.

Benzodiazepines are weak inhibitors of [3H]nitrobenzylthioinosine binding to adenosine uptake sites in brain

Saturable, specific, high affinity binding of the potent adenosine uptake inhibitor [3H]nitrobenzylthioinosine ([3H]NBI) to brain membranes has been demonstrated. In an effort to test the hypothesis that benzodiazepine action may be due to the inhibition of adenosine uptake, the inhibition of [3H]NBI binding by diazepam, clonazepam and chlordiazepoxide was tested. The benzodiazepines are very weak inhibitors of [#H]NBI binding, having IC50 values several orders of magnitude above their therapeutic levels.

The benzodiazepines and inosine antagonize caffeine-induced seizures

The induction of generalized tonic-clinic seizures in mice by the methylxanthine stimulant caffeine is described. These seizures are indistinguishable in quality from those induced by pentylenetetrazol (PTZ), and pretreatment with low doses of caffeine potentiates PTZ-induced seizures. Benzodiazepines inhibit caffeine-induced seizures with a rank order potency that parallels their affinities for the central nervous system (CNS) benzodiazepine receptor in vitro. Inosine, a purine that has recently been shown to be a competitive inhibitor of [3H] diazepam binding in vitro, antagonizes caffeine-induced seizures, while 7-methyl-inosine, a purine that lacks receptor binding inhibitory activity, has no effect on seizures. Since the benzodiazepines, inosine, caffeine, and pentylenetetrazol all competitively inhibit [3H] diazepam binding and have marked effects on inducing or antagonizing seizures, further study of this receptor-ligand system may provide additional insights that concern possible biochemical mechanisms of seizures.

Demonstration of two new endogenous "benzodiazepine-like" compounds from brain

The recent report that purines are competitive inhibitors of specific [3H] diazepam binding to brain membranes has prompted further work concerning the characterization of possible endogenous ligands for the benzodiazepine receptor. In this report, two previously undescribed fractions capable of apparent competitive inhibition of [3H] diazepam binding are reported. Both factors are heat stable and resistant to proteolytic degradation. The larger factor (approximately 700 to 30,000 daltons) is present only in brain and pituitary. The smaller factor (500 to 600 daltons) is found in pituitary, liver, and muscle, but the highest levels are found in brain.