Developmental changes in NMDA-induced cell swelling and its transition to necrosis measured with 1H magnetic resonance imaging, impedance and histology

The vulnerability of the rat brain to intracerebrally injected N-methyl-D-aspartate (NMDA) drastically changes with age. We evaluated the developmental changes in the early and late responses to NMDA using 1H magnetic resonance imaging (MRI), cortical impedance and histology. NMDA, injected in the striatum of rats at postnatal days (P) 4, 7, 10, 14 and 21, induced a significant age-dependent reduction in the apparent diffusion coefficient (ADC) of tissue water in the striatum and the cerebral cortex monitored 1 h later using diffusion-weighted MRI. The reduction in ADC amounted 65% at P4 with lower values thereafter and was about 30% at P21. NMDA similarly induced a reduction in the cortical extracellular space (by 50% at P7 and 10% at P16) as measured with impedance recordings. The progressive decrease in the effect of NMDA with brain development was also indicated by a decrease in the volume of tissue in which the changes in ADC occurred (50 mm3 at P4 and 8 mm3 at P21). The diffusion of extracellular tracer molecules Mn2+ or [3H]-(R)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) injected in the striatum and monitored with T1-weighted MRI and autoradiography respectively showed a similar age dependence with the diffusion volume being twofold larger in P7 than in P21 brain. Thus restriction in diffusion during brain development may contribute to the decrease in NMDA-induced injury with age. The volume of tissue necrosis and gliosis, measured with T2-weighted MRI and histology 5 days after NMDA injection, was similar to that outlined by the ADC reduction detected soon after the insult at P4, P7 and P21. However, at P10 and P14 only 50% of the tissue showing a hyperintense signal in DW images displayed necrosis and gliosis 5 days later. This study shows that during development the early response to NMDA in terms of cytotoxic cell swelling (indicated both with impedance recordings and diffusion-weighted MRI) decreases with age. In addition, with maturation only part of the brain tissue acutely affected by NMDA does proceed into necrosis and gliosis, indicating an increased capacity of cells in the developing rat brain to survive NMDA-induced cell swelling.

Microwave-enhanced in situ end-labeling of fragmented DNA: parametric studies in relation to postmortem delay and fixation of rat and human brain

In situ end-labeling (ISEL) identifies DNA fragmentation in apoptotic or necrotic nuclei in tissue sections. However, application of ISEL on human brain requires conservation of DNA integrity during the postmortem delay (PMD) and good accessibility of fragmented DNA after (prolonged) tissue fixation. We therefore investigated ISEL in relation to PMD and fixation in rat and human brain. Application on a unilateral lesion model in perfused rat brain revealed that prolonged post-fixation strongly diminished ISEL results. However, microwave pre-treatment can counteract these masking effects without inducing nonspecific labeling contralaterally. On the other hand, in briefly post-fixed, perfused brain or immersion-fixed rat and human PMD brain, microwave pre-treatment was deleterious and induced strong nonspecific labeling. In young rat brain, PMD did not influence the low numbers of apoptotic nuclei until 24 hr PMD, when massive nuclear labeling occurred. In human cortex, DNA fragmentation patterns were independent of duration of fixation or PMD and were already present from 4.25 hr PMD onwards. Our data suggest that ISEL on human brain represents antemortem DNA damage rather than PMD artifacts. Furthermore, microwave pre-treatment appears beneficial only in particular fixation conditions.

Treatment with NMDA receptor antagonists does not affect developmental changes in NMDA receptor properties in vivo

Effects of acute and long-term treatment of neonatal rats with N-methyl-D-aspartate (NMDA) receptor antagonists on changes in NMDA receptor properties were examined. Animals received either on postnatal day 6 a single dose of the antagonists MK-801 (1 mg/kg), or D-CPPene (2 mg/kg) or during the period from postnatal day 5 to 14, two daily injections of MK-801 (0.25 mg/kg) or D-CPPene (0.75 mg/kg). Control littermates received saline injections. In both cases animals were sacrificed one day after the last injection. NMDA receptor properties were examined in membrane preparations derived from the cerebral cortex by studying the modulation of [3H]MK-801 binding by glutamate, Mg2+ and D-CPPene. The density of agonist- and antagonist-binding sites in the CA1 region of the hippocampus were determined by autoradiography, using [3H]CGP39653 or [3H]glutamate as ligands. A significant developmental increase in NMDA receptor binding sites was detected both in preparations of cerebral cortical membranes and in the CA1 area of the hippocampus. In addition, the Mg2+ sensitivity of [3H]MK-801 binding was significantly higher in membrane preparations from the cerebral cortex of postnatal day 15 compared to postnatal day 7 animals. Neither the single nor the subchronic treatment with NMDA receptor antagonists exerted a significant influence on the density of antagonist binding sites or on the modulation of [3H]MK-801 binding by glutamate, Mg2+ or D-CPPene. We conclude therefore that neonatal treatment with NMDA receptor antagonists in vivo does not involve significant alterations in the properties and the densities of NMDA receptors in the brain regions studies, i.e., during the period when expression of these receptors is subject to pronounced developmental regulation.

Restoration of the cAMP second messenger pathway enhances cardiac preservation for transplantation in a heterotopic rat model

Current organ preservation strategies subject graft vasculature to severe hypoxia (PO2 approximately 20 Torr), potentially compromising vascular function and limiting successful transplantation. Previous work has shown that cAMP modulates endothelial cell (EC) antithrombogenicity, barrier function, and leukocyte/EC interactions, and that hypoxia suppresses EC cAMP levels. To explore the possible benefits of cAMP analogs/agonists in organ preservation, we used a rat heterotopic cardiac transplant model; dibutyryl cAMP added to preservation solutions was associated with a time- and dose-dependent increase in the duration of cold storage associated with successful graft function. Preservation was also enhanced by 8-bromo-cAMP, the Sp isomer of adenosine 3',5'monophosphorothioate, and types III (indolidan) and IV (rolipram) phosphodiesterase inhibitors. Neither butyrate alone nor 8-bromoadenosine were effective, and the cAMP-dependent protein kinase antagonist Rp isomer of adenosine 3',5'monophosphorothioate prevented preservation enhancement induced by 8-bromo-cAMP. Grafts stored with dibutyryl cAMP demonstrated a 5.5-fold increase in blood flow and a 3.2-fold decreased neutrophil infiltration after transplantation. To explore the role of cAMP in another cell type critical for vascular homeostasis, vascular smooth muscle cells were subjected to hypoxia, causing a time-dependent decline in cAMP levels. Although adenylate cyclase activity was unchanged, diminished oxygen tensions were associated with enhanced phosphodiesterase activity (59 and 30% increase in soluble types III and IV activity, respectively). These data suggest that hypoxia or graft ischemia disrupt vascular homeostasis, at least in part, by perturbing the cAMP second messenger pathway. Supplementation of this pathway provides a new approach for enhancing cardiac preservation, promoting myocardial function, and maintaining vascular homeostatic properties.

B-50/GAP43 localization in polarized hippocampal neurons in vitro: an ultrastructural quantitative study

Hippocampal pyramidal neurons cultured in vitro gradually develop morphologically and biochemically distinct axons and dendrites, resulting in functional neuronal polarization [Dotti C. G. et al. (1988) J. Neurosci. 8, 1454-1468]. We have studied the distribution of the growth-associated protein B-50 in hippocampal neurons of the rat at stage 3 of development by means of light and electron microscopic immunocytochemistry. Hippocampal neurons grown for two to three days in vitro were aldehyde fixed and immunolabelled using polyclonal rabbit antibodies to B-50 and goat anti-rabbit immunoglobulins tagged with 1 nm gold particles. In order to permit visualization by both light and electron microscopy, the gold probes were silver intensified. Light microscopy demonstrated the absence of B-50 immunostaining in living neurons and the presence after permeabilization by fixation and subsequent treatment of the neurons with sodium borohydride, indicating that B-50 is located intracellularly. Both immunofluorescence and immunogold-silver labelling revealed that B-50 immunoreactivity outlined all neurites of the morphologically polarized neurons. For quantitative electron microscopy, six morphologically polarized neurons (developmental stage 3) were carefully selected from immunolabelled Epon-embedded neurons and processed completely to ultrathin sections. In this way the ultrastructural localization of B-50 has been studied in the cell body, the neurites and their growth cones. For each sectioned neuron, the relative distribution of the gold-silver deposits (representing B-50) over the plasma membrane of various cellular compartments was quantitated. B-50 is located at the plasma membrane of the neuronal cell body and all neurites including their growth cones. The density of B-50 on the plasma membrane of growth cones is not different from that of the neuritic shaft. In addition, B-50 is present on the cytosolic side of the membrane of small electron-lucent vesicles (average diameter 102.7 +/- 2.5 nm) resembling transport vesicles. These vesicles are present in the cell body and the neurites. A two-fold concentration is found in the central region of the growth cones, suggesting a role of these vesicles in axonal transport, membrane insertion and (or) recycling. Since, at the onset of neuronal polarization, B-50 is present at the plasma membrane in all compartments of the hippocampal neuron, we suggest that at this stage of development B-50 does not participate directly in the processes leading to morphological polarization.(ABSTRACT TRUNCATED AT 400 WORDS)

B-50/GAP43 localization on membranes of putative transport vesicles in the cell body, neurites and growth cones of cultured hippocampal neurons

We conducted an electron microscopic immunocytochemical study to locate B-50/GAP43 in various cellular elements of hippocampal neurons grown in dissociated cell culture. B-50 was detected with pre- and post-embedding immunoincubation, using affinity-purified B-50 antibodies and secondary antibodies coated on gold probes. For the first time ultrastructural evidence is presented for the location of B-50 on the membranes of electron-lucent transport vesicles with a diameter of 99.4 +/- 2.9 nm, present in the trans region of the Golgi apparatus, in neurites and in growth cones of cultured hippocampal neurons.

Ultrastructural localization of adrenocorticotrophic hormone and the phosphoprotein B-50/growth-associated protein 43 in freeze-substituted, Lowicryl HM20-embedded mesencephalic central gray substance of the rat

Previous studies have shown that the endogenous phosphorylation of the neuron-specific protein B-50 in isolated synaptic plasma membranes is inhibited by adrenocorticotrophic hormone(1-24). The aim of this study is to examine if there is a specific neuroanatomical interaction of adrenocorticotrophic hormone and B-50 in the mesencephalic central gray substance of the rat. With light microscopy, high B-50 immunoreactivity was detected throughout the mesencephalic central gray substance, overlapping with those areas where adrenocorticotrophic hormone-immunoreactive fibres were present. To study the ultrastructural localization of B-50 and adrenocorticotrophic hormone, we employed a method of immunogold labelling on ultrathin sections of freeze-substituted and Lowicryl HM20-embedded fixed brain tissue. This offered optimal morphological preservation together with high retention of antigenicity. At the electron microscopic level, adrenocorticotrophic hormone immunoreactivity was detected in dense-core secretory granules present in non-junctional regions of axoinal varicosities. This suggests a non-synaptic release of adrenocorticotrophic hormone from the axons. Using double immunolabelling techniques we showed that in adrenocorticotrophic hormone-innervated areas of the mesencephalic central gray substance B-50 immunoreactivity was present at plasma membranes of all unmyelinated axons and axonal varicosities and virtually absent in dendrites. The result on B-50 localization agrees well with previous studies in the hippocampus [Van Lookeren Campagne et al. 1990 J. Neurocytol. 19, 948-961] and in the pyramidal tract [Gorgels et al. 1989 J. Neurosci. 9, 3861-3869] of the rat and suggests that in the mature rat central nervous system, B-50 expression in axons is a general phenomenon. For the adrenocorticotrophic hormone-innervated areas, we discuss the proposal that non-synaptically released adrenocorticotrophic hormone modulates B-50 phosphorylation in axons and axon terminals.

Ultrastructural double localization of B-50/GAP43 and synaptophysin (p38) in the neonatal and adult rat hippocampus

B-50/GAP43, a neuron-specific phosphoprotein, is highly expressed in developing nervous tissue. Monospecific polyclonal affinity-purified B-50 antibodies were used to document the ultrastructural distribution of B-50 in the hippocampus of 90-day-old (P90) and 1-day-old (P1) rats. Double-labelling immunoprocedures were performed to compare the localization of B-50 and synaptophysin (p38), a protein specific for synaptic vesicles. By immunofluorescence light microscopy B-50 and p38 were similarly distributed in the CA1 neuropil of P90 rats. In contrast, in P1 rats B-50 was more widely distributed than p38. By electron microscopy of P90 hippocampus, B-50 was located at the plasma membranes of axon shafts and of p38-immunoreactive axon terminals. Some B-50 was found in the cytosol of axon terminals. B-50 was absent at the plasma membranes of apical dendrites and of pyramidal cells. In the P1 rat hippocampus, B-50 was detected at the plasma membrane of growth cones, axon terminals and axon shafts, but not in their cytosol. The plasma membranes of pyramidal cell bodies and their processes extending into the stratum radiatum were without B-50. B-50-immunoreactive organelles of the lysosomal family were found in the cytosol of pyramidal cells of the hippocampus of P1 and P90 rats. This ultrastructural study shows that during development of the stratum radium in the hippocampal field CA1, the localization of B-50 persist at the plasma membrane of axons and axon terminals in P1 and P90 rats. This localization of B-50 is consistent with the suggestion that B-50 acts as a regulator of neurotransmitter release and intracellular messengers.

B-50/GAP43 is localized at the cytoplasmic side of the plasma membrane in developing and adult rat pyramidal tract

The neuron-specific phosphoprotein B-50/GAP43 has been implicated in axonal outgrowth, since high levels of B-50/GAP43 are found in growth cones and during development of the nervous system. In adult brain, the B-50 levels are decreased. B-50 is primarily found in axons and presynaptic terminals. It is phosphorylated by protein kinase C, and this process has been implicated in the modulation of membrane signal transduction. During the outgrowth of the pyramidal tract, high levels of B-50 have been reported, whereas a low amount of B-50 persists into the adult stage. By immunoelectron microscopy, using immunogold labeling on cryosections and pre-embedding peroxidase labeling, we examined the distribution of B-50 in the pyramidal tract at the third cervical segment in developing 2-d-old and adult 90-d-old rats. B-50 immunoreactivity was found in axons and growth cones of the outgrowing tract. In the adult pyramidal tract, both unmyelinated and myelinated axons contained B-50 immunoreactivity. The immunogold label was predominantly located at the plasma membrane. Since the peroxidase reaction product was observed exclusively intracellularly, we conclude that the B-50 immunoreactivity is predominantly located at the cytoplasmic side of the plasma membrane of axons and growth cones. The high immunoreactivity in growth cones and axons of the outgrowing pyramidal tract further supports the hypothesis that B-50 plays a role in neurite outgrowth. The presence of B-50 in the adult pyramidal tract cannot merely be attributed to transport to the synapse. Therefore, it is suggested that B-50 plays, in addition, a local, growth-associated role in the adult tract.

Ultrastructural immunocytochemical localization of B-50/GAP43, a protein kinase C substrate, in isolated presynaptic nerve terminals and neuronal growth cones

Accumulating evidence indicates that the neuron-specific B-50/GAP43, a substrate for protein kinase C, plays a role in neuronal differentiation and neuritogenesis during nervous tissue development and axonal regeneration. An ultrastructural immunocytochemical study on the localization of B-50 in presynaptic terminals (synaptosomes) isolated from the frontal cortex of 6-week-old rats, and in neuronal growth cones, isolated from forebrains of 5-day-old rats, the majority of B-50 is detected at the surrounding neuronal plasma membrane. In both neuronal growth cones and synaptosomes, a relatively small fraction of B-50 in the cytoplasm was not evidently associated with internal membranes. Our results indicate that B-50 is mainly located at the cytoplasmic face of the synaptosomal and neuronal growth cone plasma membrane. The similar B-50 localization in neuronal growth cones and synaptosomes suggests that, both in extending axons and mature synaptic terminals, B-50 may exert identical functions as a protein kinase C substrate at the plasma membrane.

Effect of monodansylcadaverine on the synthesis of phosphatidylinositol by rabbit neutrophils

The present results show that the addition of monodansylcadaverine to rabbit neutrophils stimulates the incorporation of both [3H]inositol and [3H]glycerol into phosphatidylinositol. Monodansylcadaverine also induces the accumulation of phosphatidylinositol 4-phosphate, phosphatidic acid and diacylglycerol. These effects are all dose-dependent and occur at concentrations of monodansylcadaverine which are known to inhibit receptor-mediated endocytosis. Monodansylcadaverine has not effect on phosphatidylinositol hydrolysis or arachidonic acid release, indicating that it acts by increasing de novo synthesis of phosphatidylinositol but not its turnover. It is proposed that the effects of monodansylcadaverine on receptor-mediated endocytosis are mediated, at least in part, by its perturbing effect on lipid metabolism.