Energy fuel utilization by fetal versus young rabbit brain: a 13C MRS isotopomer analysis of [U-(13)C]glucose metabolites

The principle substrate for brain metabolism is glucose, which provides both energy and the carbon skeletons of glutamate and glutamine, via the TCA cycle. The existence of two distinct cerebral metabolic compartments, neurons and glia, involved in glutamate and glutamine synthesis, respectively, is a widely accepted concept. In previous work, the relative glucose flux via pyruvate dehydrogenase (PDH) and pyruvate carboxylase (PC) in adult rabbit brain, using 13C NMR isotopomer analysis of glutamate and glutamine, was quantified. In this work, manifestation of cerebral compartmentation in the near-term fetal rabbit was investigated, using the above approach. Following infusion of [U-13C]glucose into maternal circulation (1 mg/kg per min) for 60-70 min, fetal brains were excised and brain extracts were studied by 13C NMR. The labelling patterns of fetal cerebral metabolites differed from those observed in the young adult brain. The most significant differences were found for glutamine labelling patterns. We suggested that these differences are a result of increased utilization of non-labeled fuels, mainly beta-hydroxybutyrate (beta-HBA) in the glia, the site of glutamine synthesis. In addition, we have shown that acute exposure to elevated beta-HBA levels leads to increased uptake, but not utilization, into the fetal rabbit brain; no increase in uptake is observed in the adult brain. We have also demonstrated that during short-term starvation, although no changes are detected in plasma and cerebral glucose levels in the fetal and young adult brain, amino acid levels and energy metabolism are altered in the young adult brain.

Effect of acute insulin-induced hypoglycemia on fetal versus adult brain fuel utilization, assessed by (13)C MRS isotopomer analysis of [U-(13)C]glucose metabolites

Tight glycemic control during diabetic pregnancy has been shown to significantly reduce the occurrence of congenital malformations and other effects of maternal diabetes on the offspring. However, intensive insulin therapy often causes recurring acute maternal hypoglycemia, which has been found to be harmful to the developing fetus, although the mechanisms involved are not clear. The aim of our work was to study the effect of acute insulin-induced maternal hypoglycemia on glucose metabolism in the fetal brain. To this end, near-term pregnant New Zealand rabbits were rendered hypoglycemic, and [U-(13)C]glucose was infused into maternal circulation. The metabolic fate of the (13)C-labeled glucose was then studied in fetal brain extracts by (13)C NMR isotopomer analysis, together with conventional biochemical assays of glucose and lactate levels in both plasma and brain. For comparison [U-(13)C]glucose was also administered to insulin-induced hypoglycemic young adult rabbits. Our results showed that while plasma glucose levels were significantly reduced (approximately 70%) relative to controls, no changes in cerebral glucose levels could be detected. Lactate levels were found to be significantly decreased in hypoglycemic fetal plasma and brain. No differences in lactate levels between control and hypoglycemic young rabbit plasma and brain were observed. These differences were attributed to the utilization of lactate as an energy substrate in the fetal brain, but not in the adult brain. Higher relative (13)C enrichments of most glucose metabolites, except lactate, in the hypoglycemic fetal and young rabbit brains, observed by (13)C NMR, stem from reduced endogenous plasma glucose pools, thereby diluting the labeled glucose to a lower extent. The relative glucose (or glucose-derived lactate) flux via the pyruvate carboxylase and pyruvate dehydrogenase pathways (PC/PDH ratio) was not altered under hypoglycemic conditions in the fetal brain for both glutamine and glutamate, but significantly increased in the adult brain for both glutamine and glutamate. The presented data indicate the ability of the fetal brain to maintain energy metabolism during acute hypoglycemia, via lactate utilization. The increase in the adult PC/PDH ratio was suggested by us to stem from increased PC activity, in order to replenish TCA cycle intermediates.

Characterization of a novel potyvirus isolated from maize in Israel

A potyvirus (proposed name of Zea mosaic virus [ZeMV]) isolated from maize in Israel was analyzed by serology, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of capsid proteins, symptomatology, and sequencing. Parts of the nuclear inclusion b, coat protein, and 3' regions were sequenced; the amino acid sequence of ZeMV capsid was determined by time-of-flight mass spectrometry (TOFMS). The results of these analyses were compared with those of similar analyses of the following potyviruses: Maize dwarf mosaic virus (MDMV), Sugarcane mosaic virus strain MDB (SCMV-MDB), Johnsongrass mosaic virus(JGMV), Sorghum mosaic virus (SrMV), and an isolate of MDMV from Israel. Indirect enzyme-linked immunosorbent assay using ZeMV antiserum detected only ZeMV, and reciprocal tests using MDMV, JGMV, or SrMV antisera failed to detect ZeMV. ZeMV cross-reacted weakly when SCMV-MDB antiserum was used. The mass of ZeMV capsid was determined to be 36,810 Da by SDS-PAGE and 34,216 Da by TOFMS. The ZeMV systemically infected johnsongrass (Sorghum halepense), but did not infect oat (Avena sativa), pearl millet (Pennisetum glaucum), barley (Hordeum vulgare), or rye (Secale cereale). Necrosis was caused in 19 sorghum lines by SrMV, in 15 by ZeMV, in 14 by MDMV, and in 5 by JGMV and SCMV-MDB. The nucleic acid and amino acid sequences of ZeMV clearly showed that it is not a strain of JGMV, MDMV, SCMV, or SrMV.

Immunocytochemical localization of the dopamine transporter in human brain

The dopamine transporter (DAT) was localized in normal human brain tissue by light microscopic immunocytochemistry by using highly specific monoclonal antibodies. Regional distribution of DAT was found in areas with established dopaminergic circuitry, e.g., mesostriatal, mesolimbic, and mesocortical pathways. Mesencephalic DAT-immunoreactivity was enriched in the dendrites and cell bodies of neurons in the substantia nigra pars compacta and ventral tegmental area. Staining in the striatum and nucleus accumbens was dense and heterogeneous. Mesocortical DAT immunoreactivity in motor, premotor, anterior cingulate, prefrontal, entorhinal/perirhinal, insular, and visual cortices was detected in scattered varicose and a few nonvaricose fibers. Varicose fibers were relatively enriched in the basolateral and central subnuclei of amygdala, with sparser fibers in lateral and basomedial subnuclei. Double-labeling studies combining DAT and tyrosine hydroxylase (TH) immunostaining in the ventral mesencephalon showed two subpopulations of dopaminergic neurons differentiated by the presence or absence of DAT-immunoreactivity in the A9 and A10 cell groups. In other dopaminergic cell groups (All, A13-A15), TH-positive hypothalamic neurons showed no detectable DAT-immunoreactivity. However, fine DAT-immunoreactive axons were scattered throughout the hypothalamus, particularly concentrated along the medial border, with more coarse axons present along the lateral border. These findings demonstrate that most mesotelencephalic dopamine neurons of human brain express high levels of DAT throughout their entire somatodendritic and axonal domains, whereas a smaller subpopulation of mesencephalic dopamine cells and all hypothalamic dopamine cell groups examined express little or no DAT. These data indicate that different subpopulations of dopaminergic neurons use different mechanisms to regulate their extracellular dopamine levels.

Pharmacotherapy of photorefractive keratectomy

PURPOSE

To compare the pharmacotherapeutic practices of high-volume photorefractive keratectomy (PRK) surgeons with suggested practices gleaned from the current literature.

SETTING

York Finch Eye Associates, Toronto, Canada.

METHODS

Seventy-five ophthalmic surgeons believed by the authors to do a high-volume of PRKs were surveyed over the summer of 1994 about their pharmacotherapeutic practices. The results were compared with suggested practices extracted from a review of the current literature.

RESULTS

Relatively consistent approaches to the management of post-PRK pain and prevention of acute post-PRK subepithelial infiltrative keratitis were reported. The administration of topical steroids after PRK was almost universally employed. Post-PRK analgesia was most commonly achieved with nonsteroidal anti-inflammatory drugs (NSAIDs) and a soft contact lens, but surgeons were not convinced of the benefits of long-term NSAID administration to control myopic regression and haze. There seemed to be no agreed-on solution to the infrequent problems of severe haze and regression and steroid-induced elevated intraocular pressure after PRK; however, many useful suggestions for the management of these problems were proposed.

CONCLUSION

In general, high-volume PRK surgeons use topical steroids, NSAIDs, and a soft contact lens in the immediate postoperative period, although they are uncertain about the long-term effectiveness of NSAIDs in controlling regression and haze.

Aerosol transport and deposition in the rhythmically expanding pulmonary acinus

Little is known about factors controlling the dynamics of aerosol dispersion and deposition in the lung periphery, though this knowledge becomes increasingly important in many fields such as environmental and occupational exposure, diagnostic applications, and therapeutic deliver of drugs via aerosols. For the last several years, we have been studying aerosol behavior in the pulmonary acinus, where the airway structure and the associated fluid mechanics are distinctly different from those in the conducting airways. Our major research efforts have been focused on the basic physics underlying acinar fluid mechanics and particle dynamics, which are likely to be conditioned by the two key geometric factors of acinar airways: structural alveolation and rhythmic expansion and contraction of the alveolar walls. A combination of computational and experimental analyses revealed that due to these unique geometric features acinar flow can be extremely complex despite the low Reynolds number, and can have substantial effects on particle dynamics. In particular, chaotic mixing can occur in the lung periphery. In the course of such a mixing process, the inhaled aerosol particles quickly mix with the residual alveolar gas in a manner that is radically different from the previously considered classical diffusion process. The objective of this paper is to briefly review our current understanding of these processes, to discuss existing deposition models, and to describe our ongoing research efforts toward a basic understanding of aerosol behavior in the pulmonary acinus.

Tracing intrinsic fiber connections in postmortem human brain with WGA-HRP

Modern methods for tracing central nervous system pathways depend largely on active axonal transport mechanisms and are carried out in in vivo animal experiments. This report describes the ability to trace axons and label cell bodies in postmortem human material, using injections of wheat germ agglutinin horseradish peroxidase. Furthermore, it demonstrates the compatibility of this method with immunocytochemical techniques for localizing neurotransmitters. Thus it is possible to study the intrinsic circuitry or short connections in brain regions such as cortex in both normal and pathological material, and, using double label methods, determine the transmitter systems involved. It also raises the issue of the mechanisms which are involved in the movement of the tracer molecule.

Anatomical relationship between the basal ganglia and the basal nucleus of Meynert in human and monkey forebrain

Previous immunohistochemical studies have provided evidence that the external segment of the globus pallidus extends ventrally beneath the transverse limb of the anterior commissure into the area of the substantia innominata. Enkephalin-positive staining in the form of "woolly fibers" has been used as a marker for the globus pallidus and its ventral extension. Acetylcholinesterase staining of both fibers and cell bodies, frequently used as a marker for the basal nucleus of Meynert, is also found in the area of the substantia innominata. This study describes the differential distribution of enkephalin-positive woolly fibers and acetylcholinesterase staining on adjacent sections in both the monkey and human basal forebrain area in an attempt to define the relationship between the basal ganglia and the basal nucleus of Meynert. The results show that while both occupy large regions of the basal forebrain, they overlap very little. In both species investigated, dense concentrations of acetylcholinesterase-positive neurons lie, for the most part, outside the boundaries of the pallidal fibers. However, some scattered acetylcholinesterase cells do lie within the confines of the dorsal pallidum, and a more prominent group is found in the subcommissural ventral pallidum. These cells may constitute a group separate from the more densely packed acetylcholinesterase-positive cells in woolly fiber-free regions in that they may receive direct striatal input.

Evaluation of Arizona Health Care Cost Containment System, 1984-85

In this article, we describe the evaluation of the Arizona Health Care Cost Containment System (AHCCCS), Arizona's alternative to the acute care portion of Medicaid. We provide an assessment of implementation of the program's innovative features during its second 18 months of operation, from April 1984 through September 1985. Included in the evaluation are assessments of the administration of the program, provider relations, eligibility, enrollment and marketing, information systems, quality assurance and member satisfaction activities, the relationship of the county governments to AHCCCS, the competitive bidding process, and the plans and their financial status.

Fetal neuronal grafts in monkeys given methylphenyltetrahydropyridine

Fetal substantia nigra cells of two different gestational ages were successfully transplanted into the brains of three methylphenyltetrahydropyridine-treated monkeys with severe parkinsonian motor and behavioural deficits. Functional improvement continued for 10 weeks after cell grafts into the striata of two monkeys with substantial numbers of tyrosine-hydroxylase-positive fetal neurons at necropsy. Behavioural improvement was correlated with increases in cerebrospinal fluid (CSF) homovanillic acid (HVA) concentrations after the transplants. A control monkey with inappropriately placed transplanted cells of an earlier gestational age remained severely parkinsonian and died during a similar period. CSF HVA fell slightly in this monkey from the low level seen before the transplants. Fetal dopamine neurons of two different gestational ages appear to survive transplantation in primates and have biochemical and functional effects.

Antigen presentation by hapten-specific B lymphocytes. II. Specificity and properties of antigen-presenting B lymphocytes, and function of immunoglobulin receptors

The studies described in this paper were designed to examine the ability of hapten-binding murine B lymphocytes to present hapten-protein conjugates to protein antigen-specific, Ia-restricted T cell hybridomas. BALB/c B cells specific for TNP or FITC presented hapten-modified proteins (TNP-G1 phi, TNP-OVA, or FITC-OVA) to the relevant T cell hybridomas at concentrations below 0.1 microgram/ml. Effective presentation of the same antigens by B lymphocyte-depleted splenocytes, and of unmodified proteins by either hapten-binding B cells or Ig spleen cells, required about 10(3)-to 10(4)-fold higher concentrations of antigen. The use of two different haptens and two carrier proteins showed that this extremely efficient presentation of antigen was highly specific, with hapten specificity being a property of the B cells and carrier specificity of the responding T cells. The presentation of hapten-proteins by hapten-binding B lymphocytes was radiosensitive and was not affected by the depletion of plastic-adherent cells, suggesting that conventional APCs (macrophages or dendritic cells) are not required in this phenomenon. Antigen-pulsing and antibody-blocking experiments showed that this hapten-specific antigen presentation required initial binding of antigen to surface Ig receptors. Moreover, linked recognition of hapten and carrier determinants was required, but these recognition events could be temporally separated. Finally, an antigen-processing step was found to be necessary, and this step was disrupted by ionizing radiation. These data suggest a role for B cell surface Ig in providing a specific high-affinity receptor to allow efficient uptake or focusing of antigen for its subsequent processing and presentation to T lymphocytes.

Antigen presentation by hapten-specific B lymphocytes. II. Specificity and properties of antigen-presenting B lymphocytes, and function of immunoglobulin receptors

The studies described in this paper were designed to examine the ability of hapten-binding murine B lymphocytes to present hapten-protein conjugates to protein antigen-specific, Ia-restricted T cell hybridomas. BALB/c B cells specific for TNP or FITC presented hapten-modified proteins (TNP-G1 phi, TNP-OVA, or FITC-OVA) to the relevant T cell hybridomas at concentrations below 0.1 microgram/ml. Effective presentation of the same antigens by B lymphocyte-depleted splenocytes, and of unmodified proteins by either hapten-binding B cells or Ig spleen cells, required about 10(3)-to 10(4)-fold higher concentrations of antigen. The use of two different haptens and two carrier proteins showed that this extremely efficient presentation of antigen was highly specific, with hapten specificity being a property of the B cells and carrier specificity of the responding T cells. The presentation of hapten-proteins by hapten-binding B lymphocytes was radiosensitive and was not affected by the depletion of plastic-adherent cells, suggesting that conventional APCs (macrophages or dendritic cells) are not required in this phenomenon. Antigen-pulsing and antibody-blocking experiments showed that this hapten-specific antigen presentation required initial binding of antigen to surface Ig receptors. Moreover, linked recognition of hapten and carrier determinants was required, but these recognition events could be temporally separated. Finally, an antigen-processing step was found to be necessary, and this step was disrupted by ionizing radiation. These data suggest a role for B cell surface Ig in providing a specific high-affinity receptor to allow efficient uptake or focusing of antigen for its subsequent processing and presentation to T lymphocytes.

Numerical analysis of the thermochemical tooth damage induced by laser radiation

A numerical model is developed to predict zones of thermochemical tooth damage induced by laser radiation. Particular attention is devoted to pulp denaturation, enamel fracture and caries sterilization treatment dependence on laser energy and other beam parameters.

Evaluation of the Arizona health care cost-containment system

This article evaluates Arizona's alternative to the acute portion of Medicaid, the Arizona Health Care Cost-Containment System (AHCCCS), during its first 18 months of operation from October 1982 through March 1984. It focuses on the program's implementation and describes and evaluates the program's innovative features. The features of the program outlined in the original AHCCCS legislation included: Competitive bidding, prepaid capitation of providers, capitation of the State by the Health Care Financing Administration, assignment of gatekeepers, beneficiary copayment, private administration, inclusion of private and public employees and county financed long-term care. An assessment of implementation during the second 18 months of the program reporting on more recent developments and is now being prepared by SRI International.

Epidemiology, health policy, and resource allocation: the Israeli perspective

Israel represents a developed country as far as demand and consumption of health services are concerned. The analysis of the Israeli health system reveals a significant trend of expansion in the intensity and the utilization of health services as well as an accelerated development of sophisticated technology, while the percentage of Gross National Product used for health expenditure remained constant and even decreased. Competing needs, reflecting population growth, a rapid aging process, new areas of treatment, and changes in use of health services, illustrate the aggravating issue of setting priorities. The permanent dilemma of the health system is oscillation between opposite trends: enlargement of public eligibility and technological capabilities and economic reduction and budget limitations. Is there a possibility that the insufficiencies of the system are built into patterns of thinking of those in the system, into its structure, and into its organization of health services delivery? Does the formulation of health policy influence, in terms of the outcomes of the system, priorities and allocation of resources? Does the process of decisionmaking reflect in an appropriate manner the epidemiologic data? Under the objective constraints, decisionmaking and health policy formulation become critical determinants of the ability to cope more efficiently and effectively with growing and changing needs. The authors suggest an alternative strategy of health decisionmaking that is more instrumental in order to prevent setbacks and to open new horizons for the future.

The distribution of enkephalin immunoreactive neuronal cell bodies in the monkey brain: preliminary observations

The distribution of enkephalin immunoreactive cell bodies was studied in the central nervous system of colchicine-treated monkeys. They followed a distribution pattern similar to enkephalin immunoreactive nerve fibers and terminal fields, and were found throughout much of the spinal cord and brain. Large numbers of enkephalin immunoreactive cell bodies were seen in the brainstem, hypothalamus and in telencephalic nuclear areas. In most regions, the distribution of enkephalin immunoreactive cell bodies in the monkey brain was similar to that reported for the rat.

The distribution of enkephalin immunoreactive fibers and terminals in the monkey central nervous system: an immunohistochemical study

Using immunohistochemical techniques, the distribution of met-enkephalin fibers and terminals was studied in the central nervous system of adult old-world monkeys. Areas which showed the greatest density of immunoreactivity included substantia gelatinosa, nucleus tractus solitarius, nucleus parabrachialis, substantia nigra, median eminence, globus pallidus (external segment), patches within the striatum and the region of nucleus accumbens and the olfactory area. Striking and discrete zones of enkephalin immunoreactive fibers and terminals which did not conform to known nuclear boundaries were observed in the latter areas. The distribution of enkephalin in the monkey is compared to what has been described in the rat central nervous system. In general, the two species are similar, however, differences were observed in some areas including the hypoglossal nucleus, substantia nigra and in the region of the nucleus accumbens and olfactory area. The results are discussed with regard to the possible functional significance of enkephalin localization in regions related to regulation of pain, mood, and autonomic function.