Morphological and biochemical changes in rat synaptosome fractions during neonatal development

Potential for Dependence on Lisdexamfetamine - In vivo and In vitro Aspects

Although lisdexamfetamine is used as a recreational drug, little research exists regarding its potential for dependence or its precise mechanisms of action. This study aims to evaluate the psychoactivity and dependence profile of lisdexamfetamine using conditioned place preference and self-administration paradigms in rodents. Additionally, biochemical techniques are used to assess alterations in the dopamine levels in striatal synaptosomes following administration of lisdexamfetamine. Lisdexamfetamine increased both conditioned place preference and self-administration. Moreover, after administration of the lisdexamfetamine, dopamine levels in the striatal synaptosomes were significantly increased. Although some modifications should be made to the analytical methods, performing high performance liquid chromatography studies on synaptosomes can aid in predicting dependence liability when studying new psychoactive substances in the future. Collectively, lisdexamfetamine has potential for dependence possible via dopaminergic pathway.

Local Gene Expression in Axons and Nerve Endings: The Glia-Neuron Unit

Neurons have complex and often extensively elongated processes. This unique cell morphology raises the problem of how remote neuronal territories are replenished with proteins. For a long time, axonal and presynaptic proteins were thought to be exclusively synthesized in the cell body, which delivered them to peripheral sites by axoplasmic transport. Despite this early belief, protein has been shown to be synthesized in axons and nerve terminals, substantially alleviating the trophic burden of the perikaryon. This observation raised the question of the cellular origin of the peripheral RNAs involved in protein synthesis. The synthesis of these RNAs was initially attributed to the neuron soma almost by default. However, experimental data and theoretical considerations support the alternative view that axonal and presynaptic RNAs are also transcribed in the flanking glial cells and transferred to the axon domain of mature neurons. Altogether, these data suggest that axons and nerve terminals are served by a distinct gene expression system largely independent of the neuron cell body. Such a local system would allow the neuron periphery to respond promptly to environmental stimuli. This view has the theoretical merit of extending to axons and nerve terminals the marginalized concept of a glial supply of RNA (and protein) to the neuron cell body. Most long-term plastic changes requiring de novo gene expression occur in these domains, notably in presynaptic endings, despite their intrinsic lack of transcriptional capacity. This review enlightens novel perspectives on the biology and pathobiology of the neuron by critically reviewing these issues.

Protein synthesis in axons and terminals: significance for maintenance, plasticity and regulation of phenotype. With a critique of slow transport theory

This article focuses on local protein synthesis as a basis for maintaining axoplasmic mass, and expression of plasticity in axons and terminals. Recent evidence of discrete ribosomal domains, subjacent to the axolemma, which are distributed at intermittent intervals along axons, are described. Studies of locally synthesized proteins, and proteins encoded by RNA transcripts in axons indicate that the latter comprise constituents of the so-called slow transport rate groups. A comprehensive review and analysis of published data on synaptosomes and identified presynaptic terminals warrants the conclusion that a cytoribosomal machinery is present, and that protein synthesis could play a role in long-term changes of modifiable synapses. The concept that all axonal proteins are supplied by slow transport after synthesis in the perikaryon is challenged because the underlying assumptions of the model are discordant with known metabolic principles. The flawed slow transport model is supplanted by a metabolic model that is supported by evidence of local synthesis and turnover of proteins in axons. A comparison of the relative strengths of the two models shows that, unlike the local synthesis model, the slow transport model fails as a credible theoretical construct to account for axons and terminals as we know them. Evidence for a dynamic anatomy of axons is presented. It is proposed that a distributed "sprouting program," which governs local plasticity of axons, is regulated by environmental cues, and ultimately depends on local synthesis. In this respect, nerve regeneration is treated as a special case of the sprouting program. The term merotrophism is proposed to denote a class of phenomena, in which regional phenotype changes are regulated locally without specific involvement of the neuronal nucleus.

A shift in protein S-palmitoylation, with persistence of growth-associated substrates, marks a critical period for synaptic plasticity in developing brain

In the mammalian cortex, the initial formation of synaptic connections is followed by a prolonged period during which synaptic circuits are functional, but retain an elevated capacity for activity-dependent remodeling and functional plasticity. During this period, synaptic terminals appear fully mature, morphologically and physiologically. We show here, however, that synaptic terminals during this period are distinguished by their simultaneous accumulation of multiple growth-associated proteins at levels characteristic of axonal growth cones, and proteins involved in synaptic transmitter release at levels characteristic of adult synapses. We show further that newly formed synapses undergo a switch in the dynamic S-palmitoylation of proteins early in the critical period, which includes a large and specific decrease in the palmitoylation of GAP-43 and other major substrates characteristic of growth cones. Previous studies have shown that a similar reduction in ongoing palmitoylation of growth cone proteins is sufficient to stop advancing axons in vitro, suggesting that a developmental switch in protein S-palmitoylation serves to disengage the molecular machinery for axon extension in the absence of local triggers for remodeling during the critical period. Only much later does a decline in the availability of major growth cone components mark the molecular maturation of cortical synapses at the close of the critical period.

Freeze-etched neuronal growth cones from rat cerebral cortex at birth: plasma membrane morphology in relation to synapse formation

Isolated growth cones from the cerebral cortex of newborn rats were studied using the freeze-etching technique. The intramembranous structure of their plasma membranes was examined in detail and synaptic sites were found. Their membrane morphology was compared with that of the synaptic sites in adult animals and several differences between them were established. The importance of the present results for understanding the formation and development of the synaptic sites in the cerebral cortex is outlined.

Identification of a 140 kDa protein of rat presynaptic terminal membranes encompassing the active zones

A polyclonal antiserum raised against the carboxy-terminal 17 amino acids of the rat p185c-neu (anct) reacted with a 140 kDa polypeptide in membranes of synaptosome fractions from neocortex and hippocampus of 11-day-old and adult rats. The same antiserum reacted with a 185 kDa polypeptide in microsome membranes from rat pheochromocytoma cells (PC12). By light microscopic immunocytochemistry, the anct antibodies against the 140 kDa protein were localized in the neuropile of brain, cerebellum and spinal cord of 11-day-old and adult rats. Especially prominent staining was obtained in the CA2-CA3 zones of the hippocampus, and in the substantia gelatinosa in the spinal cord. The finely granular and diffuse pattern of the immunostain was consistent with synaptic localizations. Interestingly, antibodies against the entire endodomain of p185c-neu (a-Bacneu) were localized in granular structures, probably representing axo-somatic and axo-dendritic synapses, on a subset of pyramidal neurons of the CA3 zone. By immunoelectron terminals in the giant mossy fiber type in the CA3 and CA4 regions. The immunolocalization of the anct antibodies was restricted in segments of the presynaptic membrane facing the synaptic cleft which include the active zone. The identify and function of the 140 kDa membrane protein of rat brain presynaptic terminals, detected by the anct antibodies, is unknown. The 140 kDa protein may be related to p185c-neu, a tyrosine kinase, or to other known or unknown kinases.

Na+ channel changes in the growth cone and developing nerve terminal

Previous saxitoxin binding studies indicated two forms of the sodium channel in the fetal rat brain; a low-affinity precursor located in an internal membrane compartment, present exclusively in growth cones and a high-affinity mature form present in the plasmalemma of growth cones and characteristic of synapses. This raises the questions (1) of the presence or absence of the beta2 subunit in these channel forms and (2) of the developmental regulation of the the beta2 subunit. Antibodies against the alpha and beta2 channel subunits were used to probe Western blots of subcellular fractions from rat brains at embryonic day 18 (E18), pups at postnatal (P) days 7-25, and adults, as well as purified sodium channels from adult brain. In both synaptosomes and the purified sodium channel the beta2 antibody recognized the expected band at 38 kDa under reducing conditions. However, in contrast to the alpha subunit, this band was absent at E18 and became apparent only from P7 onwards. At the earlier time intervals a very prominent immunoreactive band of unknown identity was evident at 260--300kDa, which declined in intensity concomitant with the appearance of the 38 kDa beta2 band. These data indicate that beta2 subunits are regulated independently from alpha subunits, are absent in differentiating neurons, and hence are not necessary for insertion of the sodium channel into the plasmalemma, at least during early development of the neuron.

Changes in synaptosomal glutamate release during postnatal development in the rat hippocampus and cortex

The effectiveness of K+ depolarisation in inducing the release of [3H]L-glutamate from preloaded hippocampal and cortical synaptosomes was examined in rats aged from postnatal day 4 (PND 4) to adult. In the lower age groups studied (PND 4-PND 15), the response to depolarisation was always smaller than that seen in the adult. From PND 15, the sensitivity of the release process increased steadily to a maximum level in the adult. The relatively small amounts of glutamate released in response to K(+)-depolarisation in the younger age groups may be a factor which contributes to the relative insensitivity of neonatal brain to ischaemic damage. Discrete variations in the sensitivity to K+ depolarisation observed in animals aged from PND 4 to PND 15 may be involved in plastic changes in neural activity which are known to occur during this important development period.

Norepinephrine increases angiotensin II binding in rat brain synaptosomes

Synaptosomes prepared from rat hypothalamus or brainstem contain specific binding sites for [125I]-angiotensin II (AII). Treatment of these synaptosomes with norepinephrine (NE) (10-500 microM) for 60 min results in a concentration-dependent increase in [125I]-AII specific binding which appears to be an increase in the number rather than the affinity of these binding sites. This effect of NE is qualitatively similar in synaptosomes prepared from neonate (one-day-old) or adult (140-day-old) rats. Furthermore, it is antagonized by prazosin (10 microM) but not by yohimbine (10 microM), indicating the involvement of alpha 1-adrenergic receptors. Finally, this effect of NE may involve activation of protein kinase C (PKC) because it is mimicked by a PKC agonist (TPA, 0.8 microM; 60 min) and is blocked by a PKC antagonist (H-7, 100 microM). These results match our previous findings on the regulation of AII receptors in neurons cultured from the hypothalamus and brainstem of neonate rats and provide strong evidence for a role of this catecholamine in the modulation of brain AII receptors.

Effects of phorbol esters and a calcium ionophore on angiotensin II binding in rat brain synaptosomes

In previous studies we determined that protein kinase C (PKC) and calcium are important intracellular regulators of neuronal angiotensin II (Ang II) binding sites. In the present study we investigated the effects of the protein kinase C (PKC) agonist phorbol esters (PE) and also a calcium ionophore (A23187) on the specific binding of [125I]Ang II to brain synaptosomes prepared from rats of different ages. The rationale was to determine whether the large changes in the level of brain Ang II specific binding observed in different age rats are due to changes in the regulation of these sites by PKC or by calcium. The present data indicate no qualitative differences in the effects of PE or A23187 on [125I]Ang II specific binding to hypothalamic or brain stem synaptosomes, from either 2-5 or 70-day-old rats, i.e. the active PE TPA increased while A23187 decreased Ang II binding in all situations. Thus, the dramatic differences in brain Ang II specific binding seen with age appear not to be due to changes in regulation by PKC or calcium.

Serotonin uptake in the central nervous system of rats fed a corn-diet

1. Endogenous serotonin (5-HT), 5-hydroxyindol acetic acid (5-HIAA) content and exogenous 5-HT uptake (Km and Vmax) were measured in different brain regions (cerebellum, diencephalon, brain stem and telencephalon) of rats fed with a corn diet and restricted protein (8%) diet during 6 weeks. 2. A reduction of 5-HT levels was found in all regions studied of animals fed a corn diet, whereas, 5-HIAA was only decreased in brain stem and diencephalon. 3. An important increase in Km and Vmax were registered in brain stem and diencephalon of protein restricted animals, whereas, an increase of 5-HT uptake affinity in cerebellum, brain stem and telencephalon (35, 42 and 33% respectively) was observed. Simultaneously, under corn diet conditions, the Vmax decreased 40, 30 and 34% respectively in those regions. 4. It is suggested that the brain stem was the more sensitive area under nutritional restricted conditions and the development of some possible compensatory mechanisms of the 5-HTergic system is discussed.

Subcellular fractionation and distribution of cholinergic binding sites in fetal human brain

Conventional subcellular fractionation techniques have been applied to human fetal brain (13-15 weeks gestation) and the fractions have been characterized by assaying for marker enzymes, cholinergic binding sites and electron microscopy. Fractionation of the homogenate resulted in a nuclear pellet (P1), a crude mitochondrial pellet (P2) and a supernatant (S2). Further resolution of the P2 fraction by density gradient centrifugation resulted in two bands at the gradient interfaces and a pellet. The P2 and subsequently the P2B fraction contained intact plasma membrane profiles as judged by the predominance of adenylate cyclase activity and the presence of occluded lactate dehydrogenase which constituted over 70% of the total activity in these fractions. Morphological examination of the gradient fractions revealed that the P2B fraction contains membrane bound structures which resemble synaptosomes prepared from neonatal rat brain. These structures have a granular matrix in which mitochondria and frequently, neurofilaments were observed. Very few synaptic vesicles were present and there was no evidence for post synaptic attachments. The cholinergic markers choline acetyltransferase, acetylcholinesterase and receptor sites defined by quinuclidinyl benzilate and alpha-bungarotoxin binding were enriched in fractions P2 and P2B which contained the bulk of nerve ending particles. This enriched preparation of fetal synaptosomes may be valuable for functional studies on pre-synaptic terminals in developing brain.

Protein profiles of sarcoplasmic reticulum from normal and dystrophic mouse muscle

Sarcoplasmic reticulum (SR) was isolated from skeletal muscle of dystrophic (C57BL/6J dy2J/dy2J) mice and the protein composition analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Densitometric analysis of dystrophic SR preparations indicated a decrease in the Ca2+-ATPase and calsequestrin, and the appearance of a protein with molecular weight 72 000. These differences in the protein profiles between normal and dystrophic SR became more apparent as the disease progressed. The observations are discussed in relation to secondary changes in the dystrophic process such as changes in fibre type and the presence of immature fibres.

Developmental changes in the activity of phosphatidylethanolamine N-methyltransferases in rat brain

The activity of phosphatidylethanolamine N-methyltransferase (PeMT), an enzymic system that catalyses the synthesis of phosphatidylcholine (PtdCho) via sequential methylation of phosphatidylethanolamine (PtdEtn) using S-adenosylmethionine (AdoMet) as a methyl donor, was examined in brain homogenates from rats of various ages. The data thus obtained were consistent with the existence of two distinct enzyme activities within this enzyme system, i.e. one catalysing the methylation of PtdEtn [to form phosphatidyl-N-monomethylethanolamine (PtdMeEtn)], and the other catalysing the methylations of PtdMeEtn and phosphatidyl-NN-dimethylethanolamine (PtdMe2Etn) (to form PtdMe2Etn and PtdCho, respectively). PeMT (PtdEtn-methylating) activity per g of brain was 4-fold higher in neonatal than in adult brains. The enzyme activity in adult brains exhibited Michaelis-Menten kinetics for AdoMet, and its affinity for AdoMet was high (apparent Km 1.6 microM). In neonatal brain the relationships between AdoMet concentrations and PtdMeEtn formation were more complex: a sigmoidal component (with a Hill coefficient of 2.7), requiring 90 microM-AdoMet for half-saturation predominated over the high-affinity component (similar to that of the adult brain). PeMT (PtdMe2Etn-methylating) activity per g of brain increased 2-fold between the 5th and the 20th postnatal days and remained constant thereafter; it was higher than that of PeMT (PtdEtn-methylating) activity at all ages studied, and its affinity for AdoMet was low (apparent Km 99 microM). No sexual dimorphism in brain PeMT activity was observed at any age. We conclude that PeMT (PtdEtn-methylating) catalyses the rate-limiting step in PtdCho synthesis in rat brain, and that PtdCho formation via this pathway may be greatest during the neonatal period.

The regional and subcellular development of cholecystokinin immunoreactivity in vertebrate brain

We have previously demonstrated that the development of CCK in rat brain occurs during the first postnatal month. In order to determine whether the appearance of CCK is associated with specific aspects of brain histogenesis, we examined the development of brain CCK immunoreactivity in both precocial and altricial mammals and birds. The two precocial species (guinea pig and chicken) were found to achieve adult CCK concentrations prenatally, while the altricial species (zebra finch and rat) manifested adult brain CCK concentrations only after several weeks of postnatal development. In adulthood, both mammals showed relatively high forebrain CCK concentrations, while the two species of birds manifested much lower forebrain levels. Brainstem levels of CCK were similar in all species studied. In each species, the development of CCK followed a common time course across all major brain areas, although adult brainstem levels of CCK were generally attained shortly before adult forebrain levels. Correlation of our comparative ontogenetic data with known patterns of brain histogenesis indicated that CCK development follows regional neuroblastic proliferation, migration and differentiation, and occurs during or soon after local synaptogenesis. In the rapidly developing precocial chicken brain, CCK production precedes the postnatal gliogenic and myelinogenic increases in brain weight, suggesting that neurogenic production of CCK occurs independently of these non-neuronal maturation events. Subcellular fractionation of developing chicken brain revealed that a substantial fraction of brain CCK is localized in synaptosomes relatively early in embryogenesis; this synaptosomal localization becomes even more pronounced with further brain maturation. This early appearance of CCK in synaptic terminals indicates a correspondingly precocial maturation for the intraneuronal mechanisms subserving peptide cleavage, axonal transport and vesicular insertion, and suggests that CCK may be available for neurotransmission quite early in development. In an analysis of the molecular forms of CCK, gel filtration disclosed no differences between species or different brain areas in the form of CCK present. CCK-8 always predominated in brain, with smaller void volume (pro-CCK) peaks, and negligible amounts of CCK-33. Finally, duodenal CCK (largely CCK-33) appeared much earlier than brain CCK in all species examined, suggesting that the gut and brain CCK systems develop independently of one another.

Isolation and partial characterisation of neuronal growth cones from neonatal rat forebrain

We have devised a method for the isolation of viable neuronal growth cones from neonatal rat forebrain. The method involves differential and density gradient centrifugation and exploits the relatively low buoyant density (approximately 1.018 g/cm3) of growth cones. There are no known biochemical markers for growth cones and it was necessary therefore to monitor for their presence during the isolation using transmission electron microscopy. Several criteria were used to identify isolated growth cones including the presence of filopodia, an extensive system of branching, tubular smooth endoplasmic reticulum and a region rich in microfilaments subjacent to the plasma membrane. These morphological features are similar to those of growth cones identified unequivocally in intact developing brain and in tissue culture. Electron microscopical analysis showed that greater than 90% of membrane-bound, identifiable objects in one fraction were growth cones by these criteria. The major contaminant consisted of membrane sacs and vesicles of unidentified origin. There were only small amounts of isolated rough endoplasmic reticulum and mitochondria. Isolated growth cones were roughly spherical in shape with a diameter of 1.9 +/- 0.5 micron (mean +/- 1 SD). They usually contained mitochondria, large granular vesicles and small vesicles, and occasionally contained coated vesicles, lysosomes, lamellar bodies and multivesicular bodies, and only very rarely, intermediate filaments. Occasionally, growth cones had rudimentary synapses on them. The viability of isolated growth cones was investigated by observing their behaviour in short-term culture. After a few hours in culture on poly-D-lysine-coated coverslips, growth cones flattened down and extended filopodia-like processes. This behaviour was inhibited by cytochalasin B and reversibly by cold (4 degrees C). We conclude that physiologically active growth cones can be isolated rapidly and in large numbers by the method described here.

Nerve growth cones isolated from fetal rat brain: subcellular fractionation and characterization

The biochemical and functional characterization of the nerve growth cone is of major interest for studies on mechanisms involved in nervous system development. We describe the isolation from fetal brain of membrane-bound fragments of nerve growth cones by density gradient fractionation. These so-called growth cone particles are highly uniform and identifiable on the basis of their organelle complement. Furthermore, they co-purify in mixing experiments with fragments of radiolabeled and light microscopically identified nerve growth cones from primary cultures. The possibility of isolating growth cone fragments in quantity renders feasible the analysis of molecular mechanisms involved in growth cone function.

A method for the dissection of the embryonic cerebral cortex into individual layers. An application to biochemical studies of glycan metabolism

A method is presented for the isolation of defined cerebral cortical layers from the prenatal rat brain. By this procedure cells at different stages of proliferation and/or differentiation can be obtained as relatively homogeneous populations. The principle of the proposed isolation procedure consists of freezing the isolated embryonic brain in a mould which flattens the two hemispheres. The different cortical layers are then isolated by carefully cutting serial cryostat sections. On embryonic day 16 (ED 16), 3 individual layers could be sampled from the cortex: the marginal zone, the zone of DNA synthesis and the mitotic region of the ventricular germinative zone. On ED 18 and ED 20, a further 3 layers could be isolated: the cortical plate, the sub-plate region, and the intermediate zone. As an example of an application of the isolation procedure for biochemical studies, maturation-dependent changes in the protein and Concanavalin A-binding glycoprotein patterns together with the activity of beta-N-acetylglucosaminidase in the different cortical layers of the embryonic brain are demonstrated at different stages of brain development.

Morphology of developing cerebral cortical synaptosomal fractions isolated from eu- and hypothyroid rats

Synaptosomal fractions isolated from the cerebrum of eu- and of hypothyroid rats during the neonatal period were analyzed by electron microscopy. This analysis revealed 3 main components: presynaptic endings, growth cones and unidentifiable structures that may be dendritic in origin. Since the size and the percentage of presynaptic endings were not altered by hypothyroidism but the size of the fraction in comparison to cerebrum weight was altered on postnatal day 14, it could be concluded that hypothyroidism results in a transient reduced synaptic density.

The maturation of cortical serotonin binding sites

Binding of serotonin to rat brain membranes increased linearly from birth to adulthood, but newborn receptor densities were already 39% of adult levels. These data suggest a postnatal development of serotonin receptors, coincident with synaptic maturation but do not preclude a non-transmitter function for serotonin during early maturation.

Ultrastructure of neurosecretosomes sedimented in the nuclear fraction from the posterior pituitary of the rat

Subcellular fractions of the posterior pituitary of the rat were isolated by differential and density gradient centrifugation, and microsamples prepared for electron miscroscopy by KMnO4 or glutaraldehyde-OsO4 fixation. The nuclear fraction, P1 (1000 g x 7 min), was the main neurosecretosome (NSS) fraction and contained nuclei and mitochondria in addition to NSS (60%). The crude mitochondrial fraction, P2 (10,000 g x 20 min), contained free mitochondria (70%), NSS, unidentified membrane particles, fat droplets derived from pituicytes, neurosecretory granules (NSG) and synaptosomes, identified by the presence of synaptic membrane thickenings. Fraction P3 (32,900 g x 20 min) contained mainly free NSG, while fraction P4 (118,000 g x 30 min) had a high microsome content.

Isolation of ribosome containing synaptosome subpopulation with active in vitro protein synthesis

Subpopulations of synaptosomes harvested from neonatal rat brain cortices revealed a differential ability to synthesize protein in vitro. Incubation of synaptosomes with radiolabeled leucine, followed by continuous sucrose gradient centrifugation produced an asymmetric shift in the radioactivity toward the higher density sucrose fractions. The bulk of the mitochondrial cytochrome c-oxidase activity was also found in these fractions, however, subfractionation studies of osmotically-lysed synaptosomes suggested that the newly-synthesized proteins reside in an osmotically sensitive, non-mitochondrial compartment. The ability of each subpopulation of synaptosomes to synthesize protein in vitro was assessed after their isolation from linear continuous sucrose gradients. There was an enrichment of highly active protein synthesizing particles in the "heavy" subpopulations of neonatal synaptosomes. The inhibitory effects of chloramphenicol and cycloheximide on the protein synthesis in these particles were similar to those of the original synaptosome fraction. Electron microscopic analysis revealed an increase in the numbers of ribosome-containing structures resembling dendritic and axonal growth cones.

Skeletal muscle calcium metabolism and contractile force in vitamin D-deficient chicks

The myopathy associated with vitamin D deficiency has not been well characterized, and it is not known if weakness is a result of a specific effect of vitamin D deficiency on skeletal muscle. Chicks were raised from hatching on a vitamin D-deficient diet, and by 3 wk of age were hypocalcemic and appeared weak. Tension generated by triceps surae during repetitive stimulation of posterior tibial nerve was significantly less than that developed by chicks given vitamin D(3) supplements (309 g tension/g wet weight of triceps surae, SD 60, for vitamin D-deficient chicks; 470, SD 77, for vitamin D(3)-treated chicks, P < 0.01). Histochemical and electron microscopic examination of skeletal muscles of these chicks showed no abnormalities, and there were no electrophysiologic evidences of motor nerve or neuromuscular junction dysfunction. The concentration of ATP in skeletal muscle of the vitamin D-deficient chicks (5.75 mumol/g wet weight, SD 0.17) was not significantly different from that in vitamin D-treated chicks (5.60, SD 0.50). There was no correlation between strength and serum calcium, serum inorganic phosphate, or skeletal muscle inorganic phosphate. Relaxation of tension after tetanic stimulation was slowed in the vitamin D-deficient chicks (20.6 ms, SD 1.7, vs. 15.4, SD 1.3, in vitamin D-treated chicks and 15.3, SD 1.0, in normal control chicks), and in vitro (45)Ca(++) transport by sarcoplasmic reticulum from the vitamin D-deficient chicks was reduced. Calcium content of mitochondria prepared from leg muscles of vitamin D-deficient chicks (24 nmol/mg mitochondrial protein, SD 6) was considerably lower than that of mitochondria from normal control chicks (45, SD 8) or from chicks treated with vitamin D for 2 wk or more (66-100, depending upon level and duration of therapy). Treatment of the vitamin D-deficient chicks from hatching with sufficient dietary calcium to produce hypercalcemia did not significantly raise skeletal muscle mitochondrial calcium content (31 nmol/mg mitochondrial protein, SD 7) and did not prevent weakness. These studies demonstrate objective weakness as a result of myopathy in vitamin D-deficient chicks, and provide evidence that vitamin D deficiency has effects on skeletal muscle calcium metabolism not secondary to altered plasma concentrations of calcium and phosphate.

Mitochondrial DNA, RNA, and protein synthesis in different regions of developing rat brain

In vivo and in vitro (tissue slices) incorporation of labeled precursors into DNA, RNA, and proteins was measured in mitochondria obtained from cerebral hemispheres, cerebellum, and brain stem of rats at different days of postnatal development. To compare the synthesis of macromolecules in mitochondria with that in other subcellular fractions, the incorporation of labeled precursors into DNA, RNA, and proteins extracted from nuclei and into RNA and proteins extracted from microsomes and cytoplasmic soluble fractions was also measured. The results obtained showed that the incorporation of [3H]thymidine into DNA and of [14C]leucine into proteins of nuclei and mitochondria from the various brain regions examined decreased during postnatal development; however, at 30 days of age the specific radioactivity of mitochondrial DNA was higher than that of nuclear DNA. [3H]Uridine incorporation into RNA decreased from 10 to 30 days of age in nuclei while in mitochondria it was quite similar at both ages. This result may be due to a faster turnover of mitochondrial RNA compared to that of mitochondrial DNA and proteins. The results obtained suggest an active biosynthesis of macromolecules in brain mitochondria and might indicate an intense biogenesis of these organelles in rat brain during postnatal development.

A regional study of electrophoretically separated proteins from the crude synaptosomal fractions of the developing rat brain

Albino rats of 1, 5, 9, 16, and 25 days of age were sacrificed, and six brain regions were dissected free. Crude synaptosomal preparations from each brain region and age were obtained by differential centrifugation. Protein content in these fractions from the six brain regions increased almost threefold between 1 and 25 days of age. The preparations were delipidated, solubilized, and subjected to polyacrylamide gel electrophoresis. The densitometric patterns of five samples from each age and brain region were analyzed for changes in the relative amount of stained protein bands. Of the polyacrylamide gel-separated protein bands, 16 regional differences at specific ages and 20 developmental changes in specific brain regions were found to be statistically significant. The hippocampal region showed the greatest number of statistical changes in the protein pattern as a function of age, whereas the cerebellum showed none. The results suggest the importance of considering regional differences in studies of biochemical developmental changes.

Myoinositol and phosphatidylinositol metabolism in synaptosomes from galactose-fed rats

The effects of experimental galactose toxicity on inositol and phosphatidylinositol (PtdIns) metabolism in synaptosomes from 0- to 30-day-old rats were investigated. Galactose toxicity was induced by feeding mothers a 40% galactose diet from the 12th day of pregnancy until 19 days postpartum when the offspring were weaned onto the maternal diet. There was no decrease in myoinositol concentrations and only a small decrease in PtdIns in synaptosomes from galactose-fed rats relative to glucose-fed controls. Synaptosomes from rats on the two diets converted equivalent amounts of [U-14C]glucose to inositol and PtdIns. Acetylcholine stimulated [2-3H]inositol incorporation into PtdIns while producing a net decrease in PtdIns concentration in synaptosomes from 22- to 30-day-old rats. However, the phospholipid response to acetylcholine in synaptosomes from galactose-fed rats was impaired. Thus, the acetylcholine-stimulated labeling of PtdIns was 40--50% lower in these synaptosomes while the effect on PtdIns concentration was reduced by a maximum of 55%. The data suggest that galactose-fed rats may have either a deficiency in the number of acetylcholine receptors or a defect in some step between receptor-neurotransmitter interaction and PtdIns breakdown.

Studies of fragmented sarcoplasmic reticulum from human skeletal muscle

Sarcoplasmic reticulum (SR) vesicles were isolated from muscle biopsies of 4 normal volunteers, a patient with McArdle disease (before and during contracture), and a patient with normokalemic periodic paralysis. Fractions were analyzed for purity by electron microscopy and biochemical analysis of specific marker enzymes. Adenosine triphosphate (ATP)-dependent calcium ion uptake was measured kinetically by the absorbence changes of murexide, a metallochromic indicator of ionized Ca++ concentrations, in the absence of oxalate or other calcium-complexing anions. In these experiments, time resolution of the Ca++ transport rate was limited by the manual mixing of reagents, which occurred in 1 to 3 seconds. In 1 case the "true" initial velocity of Ca++ uptake was measured by rapid mixing of ATP in a stopped-flow apparatus and by following the change in absorbence of murexide in a storage oscilloscope. In SR from normal human muscle the ATP-dependent Ca++ uptake was 3.5 nmoles per second per milligram of protein for the first 5 seconds after ATP mixing. Fast kinetic experiments showed that Ca++ uptake proceeded linearly for the first 500 msec at a rate of 9 nmoles per second per milligram of protein (at 25 degrees C) and then progressively declined to reach steady-state levels in 40 to 50 seconds. No abnormality of Ca++ transport was found in SR vesicles from the patient with McArdle disease and the patient with normokalemic periodic paralysis.

Ultrastructure of synaptosomes from fetal rat brain

The crude mitochondrial fraction P2 and subfractions of P2 were prepared from the brain stem, hemispheres and whole brain of 19-day-old fetal rats. Samples were fixed in glutaraldehyde-osmium, NaMnO4 or by Tranzer's triple fixation method (aldehydr-chromate-dichromate-osmium) and examined by electron microscopy. The C-fraction from whole brain was the main synaptosome fraction, containing 3.2% presynaptic terminals as counted from all membrane bound particles. The brain stem showed more presynaptic terminals than the hemisphere (2.8% versus 0.9%) suggesting a caudal-rostral maturation gradient for synaptogenesis. The maturity of the nerve endings obtained was very variable in contrast to the rather uniform synaptosomes derived from adult tissue. They varied from profiles without any substructures to mature synaptosomes displaying asymmetric synaptic junctions. Monoamine synaptosomes containing small granular vesicles were not detected in the present study, suggesting immaturity of the granular monoamine pool at this stage of development.

The buoyant density of synaptic plasma membranes from the cerebral cortex of neonatal rats

A fraction enriched in synaptic plasma membranes was prepared from neonatal (5-6 day old) rat cerebral cortex. The procedure was based on a method used to prepare synaptic plasma membranes from adult cerebral cortex. Critical steps were monitored by electron microscopy. Synaptic plasma membranes from neonatal cerebral cortex sedimented as a broad peak between 0.9 M and 1.1 M sucrose. In contrast, the majority of adult synaptic plasma membranes have been reported to sediment to 1.2 M sucorose. The activities of various enzyme markers were determined in subfractions of neonatal preparations in order to estimate contamination. The specific activities of these markers indicated substantial contamination of the neonatal synaptic plasma membrane fractions by microsomes and glia.

Ultrastructural identification of monoaminergic synaptosomes from one day old rat brain

Synaptosomes from one day old and adult rat brain were studied. Specific cytochemical methods for demonstrating monoaminergic (MA) nerve endings were used. Permanganate fixation after preincubation with 5-OHDA or alpha-methyl-NA demonstrated MA synaptosomes. Their number was small in the adult (less than 1 %) and still smaller in the one day old rat brain. The MA synaptosomes from developing rats were different from the adult ones. The large amount of endoplasmic reticulum in developing synaptosomes suggests that granular vesicles are formed from endoplasmic reticulum in nerve endings.

Luft's disease. Further biochemical and ultrastructural studies of skeletal muscle in the second case

In the second known case of non-thyroidal hypermetabolism (Luft's disease), there were large areas of mitochondrial aggregates in all fibers. Many mitochondria were abnormally large and contained packed cristae. In isolated mitochondrial fractions, studies of oxidative phosphorylation showed defective respiratory control and normal phosphorylation capacity ("loose coupling"). Spectra and content of cytochromes were normal. Basal ATPase activity was seven times greater than normal and poorly stimulated by 2,4-dinitrophenol. The rate of energy-dependent calcium uptake by isolated mitochondria was normal, but the amount of calcium accumulated was much decreased. Calcium could not be retained and was spontaneously released into the medium within 30 seconds. "Recycling" of calcium between mitochondria and cytosol may take place in vivo and result in sustained stimulation of respiration and loose coupling.

Effects of neonatal hypothyroidism on cerebral and cerebellar synaptosome development

The effect of hypothyroidism on cerebral and cerebellar synaptosome development has been studied. Neonatal hypothyroidism was induced following addition of 0.3% propylthiouracil to the diet of nursing mothers. Maturation profiles of total synaptosome fraction and specific activities of lactate dehydrogenase, Na+K ATPase, cytochrome c oxidase, and protein were obtained from days 6 to 32 on synaptosomes isolated from Ficoll-sucrose gradients. The greatest changes were found in the total activities of enzymes isolated from the cerebellum. Hypothyroidism induced a retardation of LDH and cytochrome c oxidase in cerebellar synaptosomes, but no change in corresponding specific activities. Maximum rates of 14C-leucine incorporation into cerebellar synaptosome protein was found at 16-20 days, after which a rapid decline occurred to adult levels at 32 days. In neonatal hypothyroidism, synthesis was significantly reduced at 8 and 14 days, but reached control levels or above at 21--32 days. In the cerebrum, maximum rates of 14C-leucine incorporation into synaptosome protein were identified at 8--12 days in normal with a rapid drop to adult levels at approximately 20 days. In neonatal hypothyroidism, peak activities were identified at 14 days and increased activities over control were noted at 14, 20 and 30 days. These observations demonstrate the sensitivity of the developing cerebellar synaptic apparatus to neonatal hypothyroidism, with a protraction in the peak levels of synaptosome protein synthesis in cerebrum and cerebellum.

Pathologic axons and synapses in human neuropsychiatric disorders

Ultrastructural studies of cerebral biopsy specimens from patients with various forms of psychomotor retardation and dementia have disclosed pathologic changes in axons and presynaptic or postsynaptic processes. The clinical disorders with lesions in axons and presynaptic terminals are reviewed. Three basic abnormalities have been detected: proliferation of tubulovesicular structures which probably originate from the smooth endoplasmic reticulum, "abnormal" mitochondria, and proliferation of 80 to 100 A filaments. Understanding of the pathogenesis of human disorders associated with axonic or "synaptic" lesions will probably depend on progress in areas of basic biomedical research concerned with the synthesis and turnover of biological membranes and the packaging and secretion of neurotransmitters, elucidation of mechanisms of cytoplasmic streaming and axoplasmic flow, and biophysical and biochemical characteristics and functions of "fibrous" proteins (neurotubules, neurofilaments, pathologic fibrous proteins). In several cases of mental retardation of unknown etiology, abnormal dendritic spines of cortical neurons have been observed with the use of the Golgi method. These dendritic (postsynaptic) disorders have been attributed to defective development ("dysgenesis"). The knowledge provided by ultrastructural analysis of brain tissue from the human disorders of mental retardation or dementia is "still formless, incomplete, lacking the essential threads of connection," and only future developments in lacking neurobiology will make possible the dissection of the primary phenomena from the secretory and probably irrelevant findings.