Psychiatric problems in chronic facial pain

Facial pain patients have been known to describe their life as "a living hell." By employing a biopsychosocial approach, the dental surgeon can often markedly reduce suffering and diminish the negative impact of chronic pain on the patient's day-to-day life, and enhance his or her capacity to deal long-term with this often complex clinical presentation.

Expression of a beta-adrenergic receptor kinase 1 inhibitor prevents the development of myocardial failure in gene-targeted mice

Heart failure is accompanied by severely impaired beta-adrenergic receptor (betaAR) function, which includes loss of betaAR density and functional uncoupling of remaining receptors. An important mechanism for the rapid desensitization of betaAR function is agonist-stimulated receptor phosphorylation by the betaAR kinase (betaARK1), an enzyme known to be elevated in failing human heart tissue. To investigate whether alterations in betaAR function contribute to the development of myocardial failure, transgenic mice with cardiac-restricted overexpression of either a peptide inhibitor of betaARK1 or the beta2AR were mated into a genetic model of murine heart failure (MLP-/-). In vivo cardiac function was assessed by echocardiography and cardiac catheterization. Both MLP-/- and MLP-/-/beta2AR mice had enlarged left ventricular (LV) chambers with significantly reduced fractional shortening and mean velocity of circumferential fiber shortening. In contrast, MLP-/-/betaARKct mice had normal LV chamber size and function. Basal LV contractility in the MLP-/-/betaARKct mice, as measured by LV dP/dtmax, was increased significantly compared with the MLP-/- mice but less than controls. Importantly, heightened betaAR desensitization in the MLP-/- mice, measured in vivo (responsiveness to isoproterenol) and in vitro (isoproterenol-stimulated membrane adenylyl cyclase activity), was completely reversed with overexpression of the betaARK1 inhibitor. We report here the striking finding that overexpression of this inhibitor prevents the development of cardiomyopathy in this murine model of heart failure. These findings implicate abnormal betaAR-G protein coupling in the pathogenesis of the failing heart and point the way toward development of agents to inhibit betaARK1 as a novel mode of therapy.

Loss of adrenergic control of the force-frequency relation in heart failure secondary to idiopathic or ischemic cardiomyopathy

This study was designed to determine whether the force-frequency effect on myocardial contractility, known to be importantly regulated by the adrenergic nervous system in experimental animals, can be enhanced by beta-adrenergic receptor stimulation in patients with heart failure. Animal experiments have demonstrated that the positive force-frequency relation in most mammals is subject to enhancement by beta-adrenergic receptor stimulation during exercise or infusion of a beta-receptor agonist. In animal models of heart failure, this regulatory mechanism generally is lost. The response to progressive increases in heart rate to 150 to 160 beats/min by right atrial pacing before and during dobutamine infusion was studied in 3 relatively normal subjects and in 5 patients with severe dilated cardiomyopathy. Left ventricular (LV) pressure and its first derivative (LV dP/dt(max)) were measured with a micromanometer, and the time constant of LV relaxation was assessed. The slopes of the relations between heart rate and LV dP/dt(max) in control subjects were positive at baseline and the mean slope increased substantially and significantly during dobutamine infusion. In patients with heart failure, the heart rate versus LV dP/dt(max) relations were depressed and flattened without a descending limb. Dobutamine infusion shifted this relation upward slightly, without increase in mean slope, indicating lack of amplification. The rate of isovolumic relaxation significantly decreased as heart rate increased at baseline and was further shortened by dobutamine. In patients with heart failure, a depressed and flattened relation between heart rate and LV dP/dt(max) (force-frequency effect) did not show the amplification of myocardial contractility by beta-adrenergic stimulation observed in the normal heart. This abnormality in control of the force-frequency relation undoubtedly plays an important role in the impairment of cardiac function during exercise in heart failure.

Mechanism of beta-adrenergic receptor desensitization in cardiac hypertrophy is increased beta-adrenergic receptor kinase

Pressure overload cardiac hypertrophy in the mouse was achieved following 7 days of transverse aortic constriction. This was associated with marked beta-adrenergic receptor (beta-AR) desensitization in vivo, as determined by a blunted inotropic response to dobutamine. Extracts from hypertrophied hearts had approximately 3-fold increase in cytosolic and membrane G protein-coupled receptor kinase (GRK) activity. Incubation with specific monoclonal antibodies to inhibit different GRK subtypes showed that the increase in activity could be attributed predominately to the beta-adrenergic receptor kinase (betaARK). Although overexpression of a betaARK inhibitor in hearts of transgenic mice did not alter the development of cardiac hypertrophy, the beta-AR desensitization associated with pressure overload hypertrophy was prevented. To determine whether the induction of betaARK occurred because of a generalized response to cellular hypertrophy, betaARK activity was measured in transgenic mice homozygous for oncogenic ras overexpression in the heart. Despite marked cardiac hypertrophy, no difference in betaARK activity was found in these mice overexpressing oncogenic ras compared with controls. Taken together, these data suggest that betaARK is a central molecule involved in alterations of beta-AR signaling in pressure overload hypertrophy. The mechanism for the increase in betaARK activity appears not to be related to the induction of cellular hypertrophy but to possibly be related to neurohumoral activation.

The MEKK-JNK pathway is stimulated by alpha1-adrenergic receptor and ras activation and is associated with in vitro and in vivo cardiac hypertrophy

In neonatal rat ventricular myocytes, stimulation of the alpha1-adrenergic receptor (alpha1-AdrR) activates a program of genetic and morphological changes characterized by transcriptional activation of the atrial natriuretic factor (ANF) gene and enlargement (hypertrophy) of the cells. The low molecular weight GTPase Ras has been established as an important regulator of hypertrophy both in vitro and in vivo. Ras activates a kinase cascade involving Raf, the mitogen-activated protein kinase kinase (MEK), and the extracellular signal-regulated protein kinase (ERK). However, the extent of involvement of this pathway in regulating hypertrophic responses is controversial. We demonstrate here that both alpha1-AdrR stimulation and Ras can also activate the c-Jun NH2-terminal kinase (JNK) in cardiomyocytes. The alpha1-AdrR effect on JNK occurs through a pathway requiring Ras and MEK kinase (MEKK). A constitutively activated mutant of MEKK that preferentially activates JNK, stimulates ANF reporter gene expression, while a dominant negative MEKK mutant inhibits ANF expression induced by PE. Furthermore, JNK activity is increased in the ventricles of mice overexpressing oncogenic Ras, whereas ERK activity is not. These results suggest that the alpha1-AdrR mediates ANF gene expression through a Ras-MEKK-JNK pathway and that activation of this pathway is associated with in vitro and in vivo hypertrophy.

Ras-dependent pathways induce obstructive hypertrophy in echo-selected transgenic mice

To overcome the genetic and interindividual variability frequently noted in complex phenotypes, we used echocardiographic selection to develop a substrain of myosin light chain (MLC)-Ras (RAS) transgenic mice with an enhanced ventricular hypertrophic phenotype. These echo-selected mice were then compared with wild-type (WT) animals and a pressure overload hypertrophy model (transverse aortic constriction; TAC). Echocardiography demonstrated increased wall thickness in RAS compared with the other groups. We developed novel miniaturized physiological technology to quantitatively identify in vivo intraventricular gradients; increased systolic Doppler velocity was seen in the left ventricle (LV) in 69% of RAS vs. none of WT or TAC. Intracavitary pressure gradients were present in 3 of 10 RAS vs. none of TAC or WT. Passive diastolic LV stiffness was not different among the three groups. Myofibrillar disarray was present in all RAS animals and was significantly more extensive (21.7% area fraction) than in TAC (1.5%) or WT (0.0%). RAS mice had selective induction of natriuretic peptide genes in the LV, a pattern distinct from that induced by pressure overload. Juvenile mortality was significantly increased in the offspring of echo-selected RAS parents. We conclude that adaptation of echocardiography to the mouse permits selection for cardiac phenotypes, and that selectively inbred MLC-Ras transgenic mice faithfully reproduce the molecular, physiological, and pathological features of human hypertrophic cardiomyopathy (HCM). Because previous studies support the concept that hypertrophy in human HCM is secondary to dysfunction created by sarcomeric protein mutations, the current studies suggest that Ras-dependent pathways might play a similar role in forms of human HCM.

MLP-deficient mice exhibit a disruption of cardiac cytoarchitectural organization, dilated cardiomyopathy, and heart failure

MLP is a LIM-only protein of terminally differentiated striated muscle cells, where it accumulates at actin-based structures involved in cytoarchitecture organization. To assess its role in muscle differentiation, we disrupted the MLP gene in mice. MLP (-/-) mice developed dilated cardiomyopathy with hypertrophy and heart failure after birth. Ultrastructural analysis revealed dramatic disruption of cardiomyocyte cytoarchitecture. At birth, these hearts were not hypertrophic, but already abnormally soft, with cell-autonomous and MLP-sensitive alterations in cytoarchitecture. Thus, MLP promotes proper cardiomyocyte cytoarchitecture, whose perturbation can lead to dilated cardiomyopathy. In vivo analysis revealed that MLP-deficient mice reproduce the morphological and clinical picture of dilated cardiomyopathy and heart failure in humans, providing the first model for this condition in a genetically manipulatable organism.

Elevated blood pressure and enhanced myocardial contractility in mice with severe IGF-1 deficiency

To circumvent the embryonic lethality of a complete deficiency in insulin-like growth factor 1 (IGF-1), we generated mice homozygous for a site-specific insertional event that created a mutant IGF-1 allele (igf1m). These mice have IGF-1 levels 30% of wild type yet survive to adulthood, thereby allowing physiological analysis of the phenotype. Miniaturized catheterization technology revealed elevated conscious blood pressure in IGF-1(m/m) mice, and measurements of left ventricular contractility were increased. Adenylyl cyclase activity was enhanced in IGF-1(m/m) hearts, without an increase in beta-adrenergic receptor density, suggesting that crosstalk between IGF-1 and beta-adrenergic signaling pathways may mediate the increased contractility. The hypertrophic response of the left ventricular myocardium in response to aortic constriction, however, was preserved in IGF-1(m/m) mice. We conclude that chronic alterations in IGF-1 levels can selectively modulate blood pressure and left ventricular function, while not affecting adaptive myocardial hypertrophy in vivo.

Evidence for alpha-helical conformation of an essential N-terminal region in the human Bcl2 protein

A region occupying approximately 24 amino acids near the N terminus of human Bcl2 is essential for this cytoplasmic membrane protein's ability to inhibit apoptosis. Systematic mutagenesis of this N-terminal region indicates that only five hydrophobic and aromatic residues within it are specifically required for function. Computerized secondary structure prediction, together with circular dichroism spectroscopy of synthetic peptides, indicates that the region encompassing these five residues has the propensity to take on an alpha-helical conformation in the presence of SDS micelles, which presumably mimic the hydrophobic surfaces of cellular membranes or polypeptides. The five critical residues are predicted to be clustered on one face of this putative helix, where they might serve to mediate protein-protein contacts involved in the multimerization of Bcl2 or in the interaction of Bcl2 with other, as yet unidentified components of the apoptotic pathway. Apparent structural homologues of this helical motif are also present in at least some other anti-apoptotic proteins from the Bcl2 family but not in those family members that tend to potentiate, rather than inhibit, apoptosis.

Characterization of the nuclear export signal of human T-cell lymphotropic virus type 1 Rex reveals that nuclear export is mediated by position-variable hydrophobic interactions

We previously determined that amino acids 64 to 120 of human T-cell lymphotropic virus type 1 (HTLV-1) Rex can restore the function of an effector domain mutant of human immunodeficiency virus type 1 (HIV-1) Rev (T. J. Hope, B. L. Bond, D. McDonald, N. P. Klein, and T. G. Parslow, J. Virol. 65:6001-6007, 1991). In this report, we (i) identify and characterize a position-independent 17-amino-acid region of HTLV-1 Rex that fully complements HIV-1 Rev effector domain mutants and (ii) show that this 17-amino-acid region and specific hydrophobic substitutions can serve as nuclear export signals. Mutagenesis studies revealed that four leucines within the minimal region were essential for function. Alignment of the minimal Rex region with the HIV-1 Rev effector domain suggested that the position of some of the conserved leucines is flexible. We found two of the leucines could each occupy one of two positions within the context of the full-length HTLV-1 Rex protein and maintain function. The idea of flexibility within the Rex effector domain was confirmed and extended by identifying functional substitutions by screening a library of effector domain mutants in which the two regions of flexibility were randomized. Secondly, the functional roles of the minimal Rex effector domain and hydrophobic substitutions were independently confirmed by demonstrating that these effector domains could serve as nuclear export signals when conjugated with bovine serum albumin. Nuclear export of the wild-type Rex conjugates was temperature dependent and sensitive to wheat germ agglutinin and was blocked by a 20-fold excess of unlabeled conjugates. Together, these studies reveal that position-variable hydrophobic interactions within the HTLV-1 Rex effector domain mediate nuclear export function.

Transthoracic echocardiography in models of cardiac disease in the mouse

BACKGROUND

Transthoracic echocardiography (M-mode and Doppler) offers a noninvasive approach for in vivo evaluation of the mouse heart. The present study examines its usefulness for assessing the morphological/functional phenotype of the left ventricle (LV) in several transgenic and surgical murine models of cardiac disease.

METHODS AND RESULTS

Observations were made in 83 intact, anesthetized mice. In mice with a surgical arteriovenous fistula, volume overload and LV dilation were detected. In normal mice, echocardiographic indexes of increased contractility (dobutamine) were confirmed by LV dP/dtmax. In transgenic mice with overexpression of the beta 2-adrenergic receptor, heart rate and mean velocity of circumferential fiber shortening were increased, indicating enhanced contractility. In colony screening of transgenic mice overexpressing the H-ras gene, 45% had increased LV wall thickness (> 0.9 mm), and those showing a striking increase were selected for breeding. In mice with LV hypertrophy (aortic constriction) and normal mice, the actual LV mass determined by echocardiography correlated well (r = .93), and 95% confidence limits were determined. The maximum intraobserver and interobserver coefficients of variation for M-mode data were 0.03 +/- 0.29 mm (+/- 2 SD), < 10% for LV internal dimensions but 27% to 30% for wall thickness.

CONCLUSIONS

These studies provide the first application of transthoracic echocardiography for morphological/functional characterization of the cardiac phenotype in transgenic and surgical murine models, including (1) high reliability for detecting LV chamber dilation and function; (2) reliability (and its limits) for determining abnormal LV wall thickness and LV mass; (3) identification of marked, sometimes asymmetrical, hypertrophy in a transgenic model of hypertrophic cardiomyopathy; and (4) usefulness for transgenic colony screening to identify markedly abnormal phenotypes.

A peptide sequence from Bax that converts Bcl-2 into an activator of apoptosis

Bcl-2 and Bax are members of a family of cytoplasmic proteins that regulate apoptosis. The two proteins have highly similar amino acid sequences but are functionally opposed: Bcl-2 acts to inhibit apoptosis, whereas Bax counteracts this effect. The antagonism appears to depend upon dimerization between Bcl-2 and Bax, but its mechanism is otherwise unknown. Here we report that overexpressing Bax induces apoptosis in a mammalian fibroblast cell line, and we identify a novel, short "suicide domain" in Bax that is required for this effect. Inserting this domain in place of the corresponding, divergent sequence in Bcl-2 converts Bcl-2 from an inhibitor into an activator of cell death. These findings imply that a specific region in Bax confers an active propensity for apoptosis in mammalian cells and support the view that Bcl-2 may block death primarily by suppressing Bax activity.

Functional dissection of the human Bcl2 protein: sequence requirements for inhibition of apoptosis

Overexpression of the cytoplasmic oncoprotein Bcl2 blocks programmed cell death (apoptosis) in many cellular systems. To map the sequences in Bcl2 that are necessary for its activity, we created a library of deletion-scanning mutants of this 239-amino-acid protein and tested their abilities to block staurosporine-induced fibroblast apoptosis, using a novel transient-transfection assay. Phenotypes of informative mutants were then confirmed by assaying for inhibition of steroid-induced apoptosis in stably transfected T-lymphoid cells. In accordance with earlier results, we found that Bcl2 activity was only partially reduced after deletion of the hydrophobic tail that normally anchors it in cytoplasmic membranes. Essential sequences were found in the remainder of the protein and appeared to be organized in at least two discrete functional domains. The larger, more C-terminal region (within residues 90 to 203) encompassed, but extended beyond, two oligopeptide motifs called BH1 and BH2, which are known to mediate dimerization of Bcl2 and related proteins. The second, more N-terminal regions (within residues 6 to 31) was not required for protein dimerization in vivo, but its deletion imparted a dominant negative phenotype, yielding mutants that promoted rather than inhibited apoptotic death. Residues 30 to 91 were not absolutely required for function; by deleting most of this region along with the hydrophobic tail, we derived a 155-residue mini-Bcl2 that retains significant ability to inhibit apoptosis.

Ventricular expression of a MLC-2v-ras fusion gene induces cardiac hypertrophy and selective diastolic dysfunction in transgenic mice

p21ras has been implicated in the hypertrophic response of cultured cardiac myocytes to defined growth stimuli. To determine if activation of ras-dependent intracellular signaling pathways is sufficient to induce in vivo hypertrophy, transgenic mice were created that express oncogenic ras in the cardiac ventricular chamber. Mice homozygous for the transgene displayed morphological, physiological, and genetic markers of marked cardiac muscle hypertrophy. Miniaturized catheterization technology documented a selective prolongation of cardiac relaxation, similar to that seen in early human hypertrophic heart disease. An increase in left atrial mass, in the absence of transgene expression in that chamber, further supported physiologically abnormal left ventricular diastolic function. Histological analysis revealed myofibrillar disarray, indistinguishable from that in hypertrophic cardiomyopathy in man. These studies establish a ras-dependent pathway for hypertrophic heart disease and document the feasibility of mapping in vivo signaling pathways for cardiac hypertrophy and dysfunction by applying in vivo microphysiological assays to genetically manipulated mice. ras-dependent pathways may also be a rational target for developing new approaches to inhibit the genesis of hypertrophy in certain pathological settings.

The U.K. Working Party's Diagnostic Criteria for Atopic Dermatitis. I. Derivation of a minimum set of discriminators for atopic dermatitis

A working party of 13 dermatologists, two family practitioners and a paediatrician was assembled, with the aim of developing a minimum list of reliable discriminators for atopic dermatitis. Each physician was asked to select 10 consecutive new cases of unequivocal mild to moderate atopic dermatitis and 10 controls with other inflammatory dermatoses. Each subject was examined by two independent observers, who were blind to the clinical diagnosis and study aim, with regard to 31 clinically useful diagnostic features for atopic dermatitis. Two hundred and twenty-four patients were studied (120 cases and 102 controls). Using the key physician's clinical diagnosis as a gold standard, the sensitivity and specificity of each of the 31 diagnostic criteria were tested. Using multiple logistic regression techniques, a minimum set of diagnostic criteria for atopic dermatitis was derived. These were: history of flexural involvement, history of a dry skin, onset under the age of 2, personal history of asthma, history of a pruritic skin condition, and visible flexural dermatitis. Adjustment for age, sex, region, social class and ethnic group did not alter the choice of final criteria. The discriminatory value of these criteria was also satisfactory when tested against a further sample of 150 patients drawn from the community, who did not have skin disease.

Gastric volvulus: two cases and a review of the literature

We report two cases of gastric volvulus. A discussion of the epidemiology, pathophysiology, clinical presentation, diagnosis, and treatment of this rare entity is presented.

Targeting gene expression to specific cardiovascular cell types in transgenic mice

Transgenic techniques, which allow the introduction of exogenous genes into the genome of experimental animals, promise to bridge the gap between the in vitro observations made by molecular and cellular biologists on cardiac and vascular cells in tissue culture and the physiology and pathology of the whole organ system. One such application of these techniques is tissue targeting: by genetic manipulation to direct expression of a protein--such as a signaling peptide, a growth factor receptor, or an oncogene involved in cell growth--to a tissue where it normally would not be expressed (or where expression is tightly controlled) by fusing it to the transcriptional control sequences of another gene normally expressed in that tissue. In the cardiovascular system, regulatory sequences for cardiomyocyte-specific proteins, vascular endothelium-specific proteins, and smooth muscle-specific proteins can be used to target heterologous genes to their respective tissues in transgenic animals. The effects that such perturbations have on organ physiology and intracellular and intercellular communication can be observed by applying established physiological and molecular approaches. In this review, we highlight some tissue-specific genes from cardiac and vascular cell types whose regulatory sequences may be used to target heterologous proteins; we discuss neutral "reporter" proteins and signal transduction components as paradigms for the application of this technique; and we briefly touch on the potentials and pitfalls of transgenic approaches to molecular physiology.

Detection of massive pulmonary embolus-in-transit by transesophageal echocardiography

Pulmonary embolus-in-transit represents an important cause of morbidity and mortality in the critically ill patient. Unexplained shock and acute pulmonary hypertension were evaluated with echocardiography. Standard transthoracic echocardiography failed to identify a large embolism-in-transit that was easily visualized by transesophageal imaging. A review of the literature involving emboli-in-transit suggests that early intervention in these patients may be beneficial.

cDNA cloning of mouse NKR-P1 and genetic linkage with LY-49. Identification of a natural killer cell gene complex on mouse chromosome 6

NK cells lyse tumor cells and virally infected cells, but the molecular basis for this phenomenon has not been defined. A mAb specific for the rat cell surface molecule, NKR-P1, stimulates rat NK cell lytic activity and is reactive with all rat NK cells, suggesting that this molecule may play a significant role in NK cell function. We have previously described another NK cell-specific Ag, Ly-49, that belongs to a family of cross-hybridizing genes on distal mouse chromosome 6. The rat NKR-P1 Ag shares several features with the mouse Ly-49 Ag, including selective cell surface expression on NK cells, homology to the C-type lectins, expression as a type II integral membrane protein, and disulfide-linked homodimeric structure. To further examine the relationship of NKR-P1 to Ly-49, we have cloned the cDNA encoding a mouse homologue of NKR-P1 (mNKR-P1). The mouse and rat NKR-P1-deduced polypeptide sequences are highly conserved, suggesting a similar tertiary structure. By examination of DNA from informative recombinant inbred mice with Southern blot analysis, we have determined that mNKR-P1 is encoded by a distinct gene that is genetically linked to the Ly-49 locus, lying within 0.5 centi-Morgan (cM) of Ly-49. Although the deduced amino acid sequences of mNKR-P1 and Ly-49 reveal that these proteins are structurally similar, they are only 24% identical at the amino acid level and the cDNA sequences do not demonstrate significant nucleotide homology. Our studies suggest that we have identified a region on mouse chromosome 6 that includes distinct NK-specific genes that encode structurally related proteins (type II integral membrane proteins, C-type lectin super-gene family) but which demonstrate considerable heterogeneity. We have termed this genetic region the NK complex.

cDNA cloning of mouse NKR-P1 and genetic linkage with LY-49. Identification of a natural killer cell gene complex on mouse chromosome 6

NK cells lyse tumor cells and virally infected cells, but the molecular basis for this phenomenon has not been defined. A mAb specific for the rat cell surface molecule, NKR-P1, stimulates rat NK cell lytic activity and is reactive with all rat NK cells, suggesting that this molecule may play a significant role in NK cell function. We have previously described another NK cell-specific Ag, Ly-49, that belongs to a family of cross-hybridizing genes on distal mouse chromosome 6. The rat NKR-P1 Ag shares several features with the mouse Ly-49 Ag, including selective cell surface expression on NK cells, homology to the C-type lectins, expression as a type II integral membrane protein, and disulfide-linked homodimeric structure. To further examine the relationship of NKR-P1 to Ly-49, we have cloned the cDNA encoding a mouse homologue of NKR-P1 (mNKR-P1). The mouse and rat NKR-P1-deduced polypeptide sequences are highly conserved, suggesting a similar tertiary structure. By examination of DNA from informative recombinant inbred mice with Southern blot analysis, we have determined that mNKR-P1 is encoded by a distinct gene that is genetically linked to the Ly-49 locus, lying within 0.5 centi-Morgan (cM) of Ly-49. Although the deduced amino acid sequences of mNKR-P1 and Ly-49 reveal that these proteins are structurally similar, they are only 24% identical at the amino acid level and the cDNA sequences do not demonstrate significant nucleotide homology. Our studies suggest that we have identified a region on mouse chromosome 6 that includes distinct NK-specific genes that encode structurally related proteins (type II integral membrane proteins, C-type lectin super-gene family) but which demonstrate considerable heterogeneity. We have termed this genetic region the NK complex.

Role of abortive retroviral infection of neurons in spongiform CNS degeneration

Retroviruses are involved in several human neurological diseases with varying pathological features. Whether these diseases are due to a direct effect of the virus on nervous system cells is unknown. To gain insight into the pathogenesis of one retroviral neurological disease, we are studying the murine neurotropic retrovirus, Cas-Br-E, which causes lower motor neuron disease associated with spongiform degenerative changes in brain and spinal cord. Central nervous system (CNS) injury seems to be due to direct viral action, but the precise target cells of the virus are uncertain. After blood-borne virus enters the CNS it is found in capillary endothelial cells. No microscopic evidence for virus within glia or neurons has been found in some studies, whereas virus or incomplete particles have been observed in CNS cells in other studies. Here we identify the neuron as a major target for Cas-Br-E in the CNS, suggesting that this disease may be a direct result of viral infection of neurons. We also show that envelope protein (Env, encoded by the env gene), a major determinant of neurovirulence, cannot be detected in neurons but is present in non-neuronal cells, although spliced env messenger RNA is synthesized in CNS tissue. This suggests that a post-transcriptional step in Cas-Br-E Env protein synthesis is impaired and that the neurological disease may be a consequence of abortive replication of virus in neurons. This may explain the failure to find neuronal infection in other neurological diseases by conventional methods of virus detection.

Maternal transmission of retroviral disease and strategies for preventing infection of the neonate

Moloney murine leukemia virus is efficiently transmitted from viremic mothers to offspring, primarily via virus-containing milk. To determine the level in the infectious process at which an antiviral agent can interfere most effectively with perinatal viral transmission, we examined the effect of the drug 3'-azido-3'-deoxythymidine (AZT) on transmission of Moloney murine leukemia virus from viremic mothers to offspring. Although AZT treatment did not affect the titer of virus in milk, it did suppress the development of viremia in all offspring. AZT, however, did not prevent transmission of virus from viremic mothers to 25% of the offspring, but did lead to a marked reduction in virus load in these infected mice. These results provide evidence for effective antiretroviral therapy during gestation and in the perinatal period and are of potential significance for the management of maternal transmission of human retroviruses.