Genotype-phenotype correlations in RHOBTB2-associated neurodevelopmental disorders

PURPOSE

Missense variants clustering in the BTB domain region of RHOBTB2 cause a developmental and epileptic encephalopathy with early-onset seizures and severe intellectual disability.

METHODS

By international collaboration, we assembled individuals with pathogenic RHOBTB2 variants and a variable spectrum of neurodevelopmental disorders. By western blotting, we investigated the consequences of missense variants in vitro.

RESULTS

In accordance with previous observations, de novo heterozygous missense variants in the BTB domain region led to a severe developmental and epileptic encephalopathy in 16 individuals. Now, we also identified de novo missense variants in the GTPase domain in 6 individuals with apparently more variable neurodevelopmental phenotypes with or without epilepsy. In contrast to variants in the BTB domain region, variants in the GTPase domain do not impair proteasomal degradation of RHOBTB2 in vitro, indicating different functional consequences. Furthermore, we observed biallelic splice-site and truncating variants in 9 families with variable neurodevelopmental phenotypes, indicating that complete loss of RHOBTB2 is pathogenic as well.

CONCLUSION

By identifying genotype-phenotype correlations regarding location and consequences of de novo missense variants in RHOBTB2 and by identifying biallelic truncating variants, we further delineate and expand the molecular and clinical spectrum of RHOBTB2-related phenotypes, including both autosomal dominant and recessive neurodevelopmental disorders.

Project Baby Bear: Rapid precision care incorporating rWGS in 5 California children's hospitals demonstrates improved clinical outcomes and reduced costs of care

Genetic disorders are a leading contributor to mortality in neonatal and pediatric intensive care units (ICUs). Rapid whole-genome sequencing (rWGS)-based rapid precision medicine (RPM) is an intervention that has demonstrated improved clinical outcomes and reduced costs of care. However, the feasibility of broad clinical deployment has not been established. The objective of this study was to implement RPM based on rWGS and evaluate the clinical and economic impact of this implementation as a first line diagnostic test in the California Medicaid (Medi-Cal) program. Project Baby Bear was a payor funded, prospective, real-world quality improvement project in the regional ICUs of five tertiary care children's hospitals. Participation was limited to acutely ill Medi-Cal beneficiaries who were admitted November 2018 to May 2020, were <1 year old and within one week of hospitalization, or had just developed an abnormal response to therapy. The whole cohort received RPM. There were two prespecified primary outcomes-changes in medical care reported by physicians and changes in the cost of care. The majority of infants were from underserved populations. Of 184 infants enrolled, 74 (40%) received a diagnosis by rWGS that explained their admission in a median time of 3 days. In 58 (32%) affected individuals, rWGS led to changes in medical care. Testing and precision medicine cost $1.7 million and led to $2.2-2.9 million cost savings. rWGS-based RPM had clinical utility and reduced net health care expenditures for infants in regional ICUs. rWGS should be considered early in ICU admission when the underlying etiology is unclear.

Intranasal dexmedetomidine for attenuation of hemodynamic response to laryngoscopy and intubation in adults

Background : To evaluate effectiveness of intranasal dexmedetomidine for attenuation of hemo-dynamic response to laryngoscopy and intubation in adults. Design and setting : This prospective randomized study included 90 American Society of Anesthesiologists (ASA) status I, adult patients of either sex, aged between 18-60 years, and undergoing elective surgery under general anesthesia requiring endotracheal intubation. Methods : Patients were randomly assigned to one of three groups of 30 each, to receive either intranasal saline (Group C), intranasal dexmedetomidine 1µg/kg (Group D 1 ) or intranasal dexmedetomidine 2µg/kg (Group D 2) , administered 30 minutes before the induction of anesthesia. Anesthesia technique was standardized for all patients taking part in the study. Main outcome measures : Primary outcome studied was attenuation of hemodynamic response to laryngoscopy and intubation. Secondary parameters studied were sedation score and dose of propofol required at induction. Results : There was a statistically significant rise in heart rate and systolic, diastolic and mean arterial pressures at 1, 3, and 5 minutes of intubation in group C as compared to groups D 1 and D 2 . Sedation score was significantly higher in groups D 1 and D 2 (p<0.0001). Propofol requirement was significantly lower in groups D 1 and D 2 (p<0.0001). Intranasal dexmedetomidine 2µg/kg was associated with higher a incidence of bradycardia. Conclusion : Intranasal dexmedetomidine (1µg/kg and 2µg/kg) effectively diminishes hemodynamic changes associated with laryngoscopy and intubation in adult patients undergoing elective surgery. Intranasal dex-medetomidine 2µg/kg is associated with significant bradycardia. Intranasal dexmedetomidine also provides effective preoperative sedation and decreases the dose of propofol required for induction of anesthesia.

Clinical spectrum of individuals with pathogenic NF1 missense variants affecting p.Met1149, p.Arg1276, and p.Lys1423: genotype-phenotype study in neurofibromatosis type 1

We report 281 individuals carrying a pathogenic recurrent NF1 missense variant at p.Met1149, p.Arg1276, or p.Lys1423, representing three nontruncating NF1 hotspots in the University of Alabama at Birmingham (UAB) cohort, together identified in 1.8% of unrelated NF1 individuals. About 25% (95% confidence interval: 20.5-31.2%) of individuals heterozygous for a pathogenic NF1 p.Met1149, p.Arg1276, or p.Lys1423 missense variant had a Noonan-like phenotype, which is significantly more compared with the "classic" NF1-affected cohorts (all p < .0001). Furthermore, p.Arg1276 and p.Lys1423 pathogenic missense variants were associated with a high prevalence of cardiovascular abnormalities, including pulmonic stenosis (all p < .0001), while p.Arg1276 variants had a high prevalence of symptomatic spinal neurofibromas (p < .0001) compared with "classic" NF1-affected cohorts. However, p.Met1149-positive individuals had a mild phenotype, characterized mainly by pigmentary manifestations without externally visible plexiform neurofibromas, symptomatic spinal neurofibromas or symptomatic optic pathway gliomas. As up to 0.4% of unrelated individuals in the UAB cohort carries a p.Met1149 missense variant, this finding will contribute to more accurate stratification of a significant number of NF1 individuals. Although clinically relevant genotype-phenotype correlations are rare in NF1, each affecting only a small percentage of individuals, together they impact counseling and management of a significant number of the NF1 population.

Use of Flow Cytometry for Diagnosis of Epilepsy Associated With Homozygous PIGW Variants

BACKGROUND

Biallelic variants in PIGW have been suggested to cause infantile spasms and hyperphosphatasia. PIGW encodes for a protein involved in the third step of glycosylphosphatidylinositol (GPI) synthesis. GPI anchored proteins are increasingly recognized as important structures for cellular interactions and neuronal development.

METHODS

Molecular testing of PIGW was performed followed by fluorescence activating cell sorting analysis of granulocytes, lymphocytes, and monocytes, and compared to controls.

FINDINGS

An infant was homozygous for variants in PIGW (c.199C>G; p.Pro67Ala) with an associated phenotype of infantile spasms, myoclonic seizures, cortical visual impairment, developmental delay, and minor dysmorphic features. Alkaline phosphatase levels ranged from normal to mildly elevated. Flow cytometric studies showed significantly decreased expression of important GPIs, providing functional evidence of pathogenicity.

CONCLUSION

Our data provide further evidence of a novel autosomal recessive PIGW-related epilepsy disorder. Flow cytometry provided functional evidence of the pathogenicity of homozygous variants of uncertain significance in PIGW, and supports the use of flow cytometry as a functional tool to demonstrate decreased surface expression of GPI anchored proteins in individuals with variants of unknown significance.

Genotype-Phenotype Correlation in NF1: Evidence for a More Severe Phenotype Associated with Missense Mutations Affecting NF1 Codons 844-848

Neurofibromatosis type 1 (NF1), a common genetic disorder with a birth incidence of 1:2,000-3,000, is characterized by a highly variable clinical presentation. To date, only two clinically relevant intragenic genotype-phenotype correlations have been reported for NF1 missense mutations affecting p.Arg1809 and a single amino acid deletion p.Met922del. Both variants predispose to a distinct mild NF1 phenotype with neither externally visible cutaneous/plexiform neurofibromas nor other tumors. Here, we report 162 individuals (129 unrelated probands and 33 affected relatives) heterozygous for a constitutional missense mutation affecting one of five neighboring NF1 codons-Leu844, Cys845, Ala846, Leu847, and Gly848-located in the cysteine-serine-rich domain (CSRD). Collectively, these recurrent missense mutations affect ∼0.8% of unrelated NF1 mutation-positive probands in the University of Alabama at Birmingham (UAB) cohort. Major superficial plexiform neurofibromas and symptomatic spinal neurofibromas were more prevalent in these individuals compared with classic NF1-affected cohorts (both p < 0.0001). Nearly half of the individuals had symptomatic or asymptomatic optic pathway gliomas and/or skeletal abnormalities. Additionally, variants in this region seem to confer a high predisposition to develop malignancies compared with the general NF1-affected population (p = 0.0061). Our results demonstrate that these NF1 missense mutations, although located outside the GAP-related domain, may be an important risk factor for a severe presentation. A genotype-phenotype correlation at the NF1 region 844-848 exists and will be valuable in the management and genetic counseling of a significant number of individuals.

Community pharmacists' knowledge and dispensing recommendations for treatment of acute diarrhoea in Trinidad, West Indies

Using a hypothetical case presentation of a patient with acute diarrhoea, community pharmacists in Trinidad were asked about their knowledge and dispensing recommendations to manage acute diarrhoea. Oral rehydration salts (ORS) were recommended by 86% (79), but more pharmacists would recommend ORS as the first choice therapy alone, for children (70%) than adults (33%) (p < 0.01). Antimotility agents as a first choice therapy alone or with ORS would be given to more adults (60%) than children (10%) (p < 0.01), and more adults (59%) than children (33%) would receive cotrimoxazole. Pharmacists (93%) would counsel on preparation, storage and treatment schedule for ORS, but not on discontinuing (32%) or continuing ORS (4%). Despite 51 pharmacists knowing the WHO guidelines to treat acute diarrhoea, only 23 dispensed in accordance. Educational re-enforcement to manage acute diarrhoea and dispensing practices of medications are necessary for pharmacists who are the first patient contact in Trinidad.

Nucleotide sequence of psbQ gene for 16-kDa protein of oxygen-evolving complex from Arabidopsis thaliana and regulation of its expression

The psbQ gene encoding a 16-kDa polypeptide of the oxygen-evolving complex of photosystem II has been isolated from Arabidopsis thaliana and characterized. The gene consists of a 28 nucleotide long leader sequence, two introns and three exons encoding a 223-amino-acid precursor polypeptide. The first 75 amino acids act as a transit peptide for the translocation of the polypeptide into the thylakoid lumen. Expression studies show that the gene is light-inducible and expresses only in green tissues with high steady-state mRNA levels in leaves. Using this gene as a probe, restriction fragment length polymorphism between two ecotypes, Columbia and Estland, has also been detected.

The psbO gene for 33-kDa precursor polypeptide of the oxygen-evolving complex in Arabidopsis thaliana--nucleotide sequence and control of its expression

The 33-kDa polypeptide of the oxygen-evolving complex of photosystem II is nuclear-encoded. The single psbO gene of Arabidopsis thaliana, as suggested by Southern hybridization, has been isolated from the genomic library and sequenced. The sequence analysis has revealed that the psbO gene harbors two introns and encodes a precursor polypeptide of 332 amino acid residues; the first 85 amino acid residues represent the transit peptide and the following 247 amino acids constitute the mature polypeptide. The hydrophilic nature of the 33-kDa protein is confirmed by the presence of 27% charged residues. Northern analysis of the total RNA from Arabidopsis indicates that a 1.2-kb transcript represents the psbO gene. It is expressed in a tissue-specific manner -- the steady-state transcript levels being highest in the leaves and virtually undetectable in the roots. Also, expression of the psbO gene is development-dependent and regulated by light in young Arabidopsis seedlings. In a constitutively photomorphogenic mutant of Arabidopsis, pho2 (plumular hook open 2), the psbO gene is de-repressed in young, dark-grown seedlings, resulting in increased transcript abundance compared to the wild-type. These studies, thus, define the influence of at least one regulatory component for psbO expression.

Nucleotide sequence of the psbP gene encoding precursor of 23-kDa polypeptide of oxygen-evolving complex in Arabidopsis thaliana and its expression in the wild-type and a constitutively photomorphogenic mutant

The psbP gene encoding the precursor of 23-kDa polypeptide of the oxygen-evolving complex of photosystem II has been isolated from Arabidopsis thaliana genomic library and sequenced. The gene harbors three introns and encodes a mature polypeptide of 186 amino acid residues and a transit peptide of 77 amino acid residues. The deduced molecular mass of the mature polypeptide is 23.5-kDa and it contains 22.6% charged amino acid residues which may contribute to the hydrophilic nature of the protein. The transcript encoded by psbP gene of Arabidopsis is approximately 1.3-kb long. In wild-type Arabidopsis seedlings, its expression is organ-specific and is regulated by endogenous developmental cues, light and sucrose. In a constitutively photomorphogenic mutant of Arabidopsis, designated as pho1, the psbP gene is partly derepressed in young, dark-grown seedlings, resulting in a slightly higher level of the transcript. Additionally, the pho1 mutant shows slow accumulation of psbP transcript upon illumination of young, dark-grown seedlings. However, the derepression is not markedly displayed on dark-adaptation of pho1 plants grown in continuous light. These studies, therefore, define the activity of at least one cellular effector involved in regulation of psbP expression.

Presence of growth-stimulating fibrin degradation products containing fragment E in human atherosclerotic plaques

The key event in the formation of stenosing atherosclerotic lesions is widely thought to be smooth muscle cell proliferation, but the factors primarily responsible for initiating this remain uncertain. Previously we have shown that aqueous extracts of proliferative types of human atherosclerotic plaque stimulate cell proliferation in the chick chorioallantoic membrane (CAM). This has been attributed largely to the fibrin degradation products in the extracts, components removeable by affinity chromatography. We now demonstrate that the fibrinogen content of the extract, removeable by clotting out with thrombin, also makes a contribution to the activity by forming fibrin on the surface of the CAM. Affinity chromatography experiments using anti fragment D and E antisera indicate that activity resides in the E-containing fibrin fragments, consistent with previous work with FDP prepared in vitro.

Efficacy of LY233053, a competitive glutamate antagonist, in experimental central nervous system ischemia

Antagonists of excitatory amino acids appear to serve a neuroprotective role during ischemic conditions in a variety of in vivo and in vitro models. The usefulness of such agents in the clinical setting, however, may be limited by poor central nervous system (CNS) entry and intolerable side effects. The authors report high efficacy in reducing neurological damage and relatively limited side effects of LY233053, a novel competitive glutamate antagonist, in two models of experimental CNS ischemia in the rabbit.

Effect of protein kinase C modulation on outcome of experimental CNS ischemia

Protein kinase C (PKC) is an important intracellular regulator, and its activity may play a central role in the modulation of neuronal ischemic damage. Staurosporine and the compound H-7 are potent in vitro inhibitors of PKC, and 1,2-oleoylacetylglycerol (OAG) is an effective activator. We administered these compounds through a spinal subarachnoid catheter and demonstrated in vivo alteration of spinal cord PKC activity. We then tested the effects of altering PKC activity in a well-established rabbit model of reversible spinal cord ischemia. Animals within each experimental group were subjected to a range of spinal cord ischemic durations by temporary occlusion of the infrarenal abdominal aorta. Compared to control, both staurosporine and H-7 significantly shortened the duration of ischemia that the animals could tolerate, without developing permanent paraplegia. OAG resulted in an insignificant lengthening of the ischemic duration that the animals could withstand. The worsening of ischemic outcome by PKC inhibitors suggests that the enzyme is important for maintaining neurologic function under ischemic conditions, possibly secondary to modulation of intracellular calcium levels.

Spinal cord ischemia reduces calcium/calmodulin-dependent protein kinase activity

Calcium/calmodulin (Ca2+/CaM)-dependent protein phosphorylation was evaluated in a rabbit spinal cord ischemia model. One hour of ischemia reduced particulate (5% of control) and cytosolic (35% of control) Ca2+/CaM-dependent protein kinase activity significantly (p less than 0.01). In vitro phosphorylation of endogenous proteins by endogenous Ca2+/CaM-dependent protein kinase showed that phosphorylation of 14 particulate and 7 cytosolic proteins was stimulated in the presence of Ca2+/CaM in control tissue. However, after 1 hour of ischemia, Ca2+/CaM-dependent protein phosphorylation was virtually absent in the particulate fraction and significantly reduced in the cytosol. When equal amounts of control and ischemic tissue samples were combined and assayed, Ca2+/CaM-dependent protein kinase activity was 43% of control in particulate and 70% of control in cytosolic fractions. This suggests that reduced Ca2+/CaM-dependent protein phosphorylation is probably not due to the presence of an inhibitory activity in ischemic tissue. These results show that the Ca2+/CaM-dependent protein phosphorylation system is impaired after ischemia durations which cause irreversible damage. These altered phosphorylation reactions may play critical roles in mediating irreversible neurologic injury.

Pharmacologic studies of the neuroprotective actions of a glutamate antagonist in ischemia

Ischemia may increase glutamate release, which can lead to neuronal damage. The therapeutic value of drugs that antagonize glutamate's effects are being investigated in CNS ischemia. This study examined the efficacy of a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten- 5,10-imine hydrogen maleate], in reducing ischemic injury. We explored the limits of this therapy and different properties of MK-801 that might be involved in its neuroprotective actions. Two focal CNS ischemia models were used, a multiple cerebral embolic model (MCEM) and a rabbit spinal cord ischemia model (RSCIM). When animals were treated 5 minutes after the onset of injury, MK-801 was effective in reducing ischemic damage in both models. However, when treatment was delayed 10 minutes after the ischemic insult in the MCEM, no neuroprotection was observed even when the MK-801 dose was increased eightfold. We also did not find a beneficial effect of MK-801 pretreatment with a dose that was one tenth of the effective dose in the RSCIM. Studies using the (-) MK-801 isomer showed that MK-801 neuroprotection exhibited stereoselectivity. The contribution of anticonvulsant activity and sedation to MK-801's neuroprotective actions was examined indirectly using phenytoin and midazolam, respectively. Neither drug was effective in reducing ischemic injury in the MCEM. This suggests that MK-801's neuroprotective efficacy in ischemia is mediated through its NMDA receptor antagonist activity independent of its anticonvulsant or sedative properties. These results support the hypothesis that excessive NMDA receptor excitation may be involved in ischemic neuronal damage.

Protein phosphorylation during ischemia

Many investigations have shown that calcium and adenosine triphosphate are crucial to central nervous system functions. It is probable that alterations of these substances during central nervous system ischemia are involved in the processes that cause irreversible neural damage. Calcium regulates several protein kinases that are responsible for phosphorylation of proteins vital for many central nervous system functions. Using a rabbit spinal cord ischemia model, we found protein kinase C and calcium/calmodulin-dependent kinase were severely affected during the first hour of ischemia. Protein kinase A was not significantly affected. The time course of lost protein kinase C enzyme activity closely corresponded to irreversible loss of neurologic function, and there is evidence that protein kinase C inhibitor activity is generated. Also, drugs that inhibit protein kinase C increased neurologic damage when administered during the early phases of ischemia. These results suggest that protein phosphorylation, particularly by protein kinase C, is critical to maintenance of neurologic function.

Factors relevant to stimulatory activity of fibrin degradation products in vivo

Extracts of atherosclerotic lesions contain a range of fibrin degradation products (FbDP), similar fragments have been detected in extracts from human and mouse healing skin wounds and from the invasive edge of human breast carcinomas, which are all proliferating systems. We have previously shown that FbDP stimulate cell proliferation including angiogenesis in the chick chorioallantoic membrane (CAM), and sought to characterize further the active components. Fibrin prepared from platelet-rich and platelet-free plasma, and purified Kabi fibrinogen, was treated with plasmin, and the digests were all active. FbDP from platelet-rich plasma clots also increased vascularity of the CAM. Prior removal of fibronectin from plasma by gelatin-Sepharose affinity chromatography did not affect proliferative activity. Current studies showed that long digests of fibrin, in which the only major band detectable is fibrin fragment E are active. Commercial fibrinogen derived fragment E, itself inactive on the CAM, becomes active after exposure to thrombin cleavage of fibrinopeptides. Recently fragment E has been isolated from shorter digests, by simple filtration through a Millipore 0.2 microns centrifuge filter. It displayed similar activity to the fragment E obtained from long digests. Fragment E in plaque extracts has been shown consistently to lack fibrinopeptide A indicating it is of fibrin origin.

Atherosclerotic plaque growth: presence of stimulatory fibrin degradation products

Focal smooth muscle cell proliferation is widely perceived as a key event in the formation of stenosing atherosclerotic lesions, but the stimuli for this remain uncertain. Soluble extracts of human aortic intima from proliferative gelatinous and transitional lesions, as well as surface encrusted thrombi, have been shown by us to be mitogenic for the chick chorioallantoic membrane (CAM). They have also been shown to stimulate increase in vascularity of the CAM. When active samples were passed through anti-albumin and anti-whole-serum affinity columns, mitogenic activity in the unabsorbed, fibrin related antigen fraction remained close to the original whole extract level. In contrast, when the unabsorbed fractions from anti-whole-serum columns were passed through an antifibrinogen affinity columns, the activity was reduced to insignificant levels. Similarly, whole extracts lost activity after passing through an antifibrinogen column. This has been taken one stage further by dividing the unabsorbed fraction from an anti-whole-serum column into two equal volumes and passing one half through an antifibrinogen fragment D affinity column, and the other through an antifibrinogen fragment E affinity column. The activity of the unabsorbed fraction from the fragment D column remained the same, but that from the fragment E column was significantly reduced. Most of the fibrin degradation products (FbDP) in lesion extracts are derived from fibrin, not fibrinogen, and clotting out fibrinogen and fragment X with thrombin did not remove the activity. Whole extracts of atherosclerotic lesions clotted on the CAM surface as has previously been shown with plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced protein kinase C activity in ischemic spinal cord

Protein phosphorylation was evaluated in a rabbit spinal cord ischemia model under conditions where cyclic AMP-dependent protein kinase (PK-A) and calcium/phospholipid-dependent protein kinase (PK-C) were activated. One hour of ischemia did not affect PK-A activity significantly; however, PK-C activity was reduced by more than 60%. In vitro phosphorylation of endogenous proteins by endogenous PK-C revealed that eight particulate and five cytosolic proteins showed stimulated phosphorylation by PK-C activators in control tissue, although this stimulation was virtually absent in ischemic samples. When control and ischemic particulate fractions were combined, the endogenous protein phosphorylation pattern under PK-C-activating conditions was similar to the ischemic sample, which suggests that inhibitory molecules may be present in the ischemic particulate fraction. In vitro phosphorylation of endogenous proteins under PK-A-activating conditions in ischemic tissue was similar to that in control tissue. The results suggest that the PK-C phosphorylation system is selectively impaired in ischemic spinal cord. In addition to reduced PK-C-dependent phosphorylation, an Mr 64,000 protein was phosphorylated in ischemic cytosolic samples, but not in control samples. The phosphorylation of the Mr 64,000 protein was neither PK-C-dependent nor PK-A-dependent. These altered phosphorylation reactions may play critical roles in neuronal death during the course of ischemia.

Phenothiazines reduce ischemic damage to the central nervous system

We found substantial alterations in reactions catalyzed by calcium/phospholipid-dependent and calcium/calmodulin-dependent protein kinases during CNS ischemia which suggested that phenothiazines, drugs capable of inhibiting these reactions, might reduce neurologic damage. To test this hypothesis, we used chlorpromazine and trifluoperazine. Both drugs reduced neurologic function deficits relative to controls in a rabbit multiple cerebral embolism model and a rabbit spinal cord ischemia model. Chlorpromazine was effective despite reduction of blood pressure, and trifluoperazine did not alter blood pressure. These findings suggest that phenothiazines may be useful for preserving neurologic function when administered shortly after the onset of CNS ischemia.

Effects of calcium channel blockers on neurologic outcome after focal ischemia in rabbits

To determine the efficacy of calcium channel blockers in preserving neurologic function after central nervous system ischemia, we studied three such agents in two animal models. We treated rabbits after inducing ischemia in the brain with intra-arterial microspheres and in the spinal cord using a removable aortic occluding device. We found no benefit, in terms of neurologic functional outcome, from lidoflazine, nimodipine, or nicardipine. All three agents elevated regional blood flow in the spinal cord. We conclude that calcium antagonists are not likely to prove beneficial if used alone in the treatment of focal central nervous system ischemia.

Tissue plasminogen activator. Reduction of neurologic damage after experimental embolic stroke

Tissue plasminogen activator (tPA) has become available for pharmacologic use, and it appears to produce relatively fewer hemorrhagic complications than the previously available, less specific thrombolytic agents. We tested the effects of tPA in several models of embolic stroke and found that neurologic damage was reduced when the drug was administered as late as 45 minutes after cerebral embolic occlusion. The mechanism of therapeutic efficacy of tPA was probably thrombolysis. Drug-induced hemorrhages did not occur when therapy was started within four hours after the onset of vascular occlusion. These results suggest that tPA may be useful for thrombolytic therapy of embolic stroke if the drug is administered rapidly after the onset of vascular occlusion.

Glutamate antagonist therapy reduces neurologic deficits produced by focal central nervous system ischemia

Ischemia may increase synaptic concentrations of glutamate, which may cause neuronal damage. Drugs that antagonize glutamate's effects may reduce this type of damage. MK-801, an N-methyl-D-aspartate receptor antagonist that readily enters the central nervous system, was evaluated in two focal central nervous system ischemia models: a multiple cerebral embolic model and a rabbit spinal cord ischemia model. When animals were treated five minutes after the onset of injury, MK-801 was effective in reducing ischemic damage in both models. In the multiple cerebral embolic model, the average dose of microspheres trapped in the brain increased from 344.8 +/- 51.4 micrograms (n = 29) in controls to 534 +/- 41.4 micrograms (n = 17) in the MK-801-treated group. Similarly, in the rabbit spinal cord ischemia model, the average ischemia duration increased from 28.9 +/- 1.7 minutes (n = 52) in controls to 50.6 +/- 3.9 minutes (n = 12) in the MK-801-treated group. These results suggest that this glutamate antagonist should be useful for the treatment of stroke.

A model for quantitative evaluation of embolic stroke therapy

We developed a small animal embolic stroke model for pharmacological screening trials. Microspheres are injected into the carotid circulations and group embolus dose-response relationships are calculated. Emboli quantity is related to neurologic injury, and small changes in neurologic function are detectable. Rabbits tolerated twice as many microspheres when cyproheptadine-treated after embolization. This demonstrated both the sensitivity of the model and the value of serotonin antagonists in reducing neurological injury.

Members of a nicotinic acetylcholine receptor gene family are expressed in different regions of the mammalian central nervous system

Nicotinic acetylcholine receptors found in the peripheral and central nervous system differ from those found at the neuromuscular junction. Recently we isolated a cDNA clone encoding the alpha subunit of a neuronal acetylcholine receptor expressed in both the peripheral and central nervous system. In this paper we report the isolation of a cDNA encoding the alpha subunit of a second acetylcholine receptor expressed in the central nervous system. Thus it is clear that there is a family of genes coding for proteins with sequence and structural homology to the alpha subunit of the muscle nicotinic acetylcholine receptor. Members of this gene family are expressed in different regions of the central nervous system and, presumably, code for subtypes of the nicotinic acetylcholine receptor.

Central cholinergic correlates of low dose ethanol-induced locomotor stimulation

Brain area levels of acetycholine and choline plus the turnover rate of acetylcholine were measured in three strains of rats given low, locomotor-stimulating doses of ethanol. Maudsley reactive (MR/N), Sprague-Dawley, and randomly bred MR/N (MRrb) rats were killed by microwave irradiation and cholinergic function was measured by gas chromatography/mass spectroscopy methods. The results show that the MR/N strain (2 and 5 months old), which elicits enhanced locomotor stimulation after low doses of ethanol, also demonstrates significant increases in cholinergic function at the time of behavioral stimulation. However, after locomotor stimulation, cholinergic parameters returned to normal in these animals. Strains which do not show enhanced locomotor activity after ethanol did not demonstrate significant central cholinergic changes. We conclude that central cholinergic function is related to behavioral stimulation elicited by low doses of ethanol in the MR/N rat strain but not other strains.

An animal model for low dose ethanol-induced locomotor stimulation: behavioral characteristics

The present paper describes a rat strain, Maudsley reactive (MR/N), which dramatically and reliably shows enhanced locomotor stimulation in an openfield apparatus after low doses of ethanol. Other strains, Sprague-Dawley and Wistar inbred, do not show stimulation, whereas Maudsley nonreactive rats show a less dramatic and variable response to ethanol, compared to the MR/N strain. Female MR/N rats show greater stimulation than male MR/N rats, and the response is dose-, age-, and apparatus-related. We conclude that low dose ethanol-induced locomotor stimulation in the MR/N rat strain could be a valuable rodent model for studying central neurochemical correlates of alcohol intoxication.

Effects of different liquid diets and sustained ethanol release on alcohol metabolism

The effects of two liquid diets, Sustacal and Shorey-AIN, on liver alcohol dehydrogenase (ADH) activity and ethanol clearance were tested in rats under conditions of high ethanol exposure for nine days. High blood ethanol levels (BEL) were produced through a combination of an initial intubated dose of ethanol sustained ethanol release tube (SERT), and ethanol as 37% of total energy in the liquid diet. Under free-feeding conditions, rats consumed slightly more ethanol per unit body weight in the Shorey-AIN diet, a diet formulated for rodent nutrition, than in the Sustacal diet, a diet originally intended for human consumption. However, BEL were significantly higher in the Sustacal group than in the Shorey-AIN group. No differences in ethanol clearance rates were observed between the groups. On the other hand, total liver ADH activity was significantly reduced in both the Shorey AIN/ethanol and the Sustacal/ethanol groups, compared to lab chow controls. When the Sustacal diet was fortified with casein and methionine so that the protein content matched that of the Shorey AIN diet, the BEL were no longer significantly higher than those produced by the Shorey AIN/ethanol diet. The results demonstrate the effect of nutritional factors on BEL under conditions of high ethanol load. However, these factors do not appear to alter major characteristics of ethanol metabolism and clearance in our short-term experiments.