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P Morell

Publications and source records attributed to P Morell.

At least 91 records · Page 5Linked to original sources
PubMed1983

Differences in the kinetics of axonal transport for individual lipid classes in rat sciatic nerve.

Lipid precursors ([2-3H]glycerol for phospholipids and [3H]acetate for cholesterol) were injected into the L-5 dorsal root ganglion of adult rats. At various times, animals were killed, the ganglion and consecutive 5-mm segments of sciatic nerve were dissected, and lipids were extracted and analyzed by TLC. Individual lipid classes exhibited markedly different transport patterns. The crest of radioactive phosphatidylcholine moved as a sharply defined front at about 300 mm/day, with a relatively flat plateau behind the moving crest. Although some radioactive phosphatidylethanolamine also moved at the same rate, the crest was continually attenuated as it moved so that a gradient of radioactive phosphatidylethanolamine along the axon was maintained for several days. Transported diphosphatidylglycerol exhibited a defined crest, as did phosphatidylcholine, but moved at about half the rate. Labeled cholesterol was transported at a rapid rate similar to that for phosphatidylcholine and phosphatidylethanolamine, but like phosphatidylethanolamine, the initial moving crest of radioactivity was continually attenuated. Relative to the phospholipids, cholesterol showed a more prolonged period of accumulation in the axons and was more metabolically stable. We propose that most labeled phosphatidylcholine, phosphatidylethanolamine, and cholesterol is transported in similar (or the same) rapidly moving membranous particles. Once incorporated into these particles, molecules of phosphatidylcholine tend to maintain associated with them during transport. In contrast, molecules of phosphatidylethanolamine and cholesterol in these transported particles exchange extensively with unlabeled molecules in stationary axonal structures. Diphosphatidylglycerol, localized in a specialized organelle, the mitochondrion, is transported at a slower rate than other phospholipids, and does not exchange with other structures.

Acetates↗
PubMed1982

Sidedness of phospholipid synthesis on brain membranes.

We have investigated the localization of the site of incorporation and the subsequent equilibration of newly synthesized phospholipids in brain membranes. Rats were injected intracranially with [3H]glycerol; the animals were killed at varying times afterwards, and microsomal fractions were isolated from the brains. In some cases, microsomes were subfractionated on sucrose gradients. Initially, most of the radioactive phosphatidylethanolamine appeared in a pool that reacted with the impermeable reagent trinitrobenzene sulfonic acid (TNBS). This probe presumably modified only the lipid on the outer face of microsomal vesicles (which may, in large part, consist of pinched-off endoplasmic reticulum). At 5 min after injection, the specific radioactivity of the TNBS-modified phosphatidylethanolamine (cytoplasmic face) was four times that of the unmodified (luminal or inner face) phosphatidylethanolamine. With time, the ratio of the specific activities in the modified and unmodified pools of phosphatidylethanolamine approached 1.0, with kinetics that suggested a half-time on the order of 30 min for in vivo conversion of the TNBS-accessible to the -inaccessible pool. This equilibration in specific activities could be the result of either translocation of phospholipids across endoplasmic reticulum membranes or conversion with time of initially labeled endoplasmic reticulum to other membranous organelles which form randomly oriented vesicles upon homogenization. A similar experimental design, using phospholipase C to hydrolyze outer face phospholipids preferentially, verified this conclusion for phosphatidylethanolamine and yielded similar results for phosphatidylcholine. Control studies measuring radioactive sucrose permeability indicated that neither TNBS nor phospholipase C treatment significantly disrupted microsomal vesicles under the conditions used.

Animals↗
PubMed1981

Axonal transport of the mitochondria-specific lipid, diphosphatidylglycerol, in the rat visual system.

Rats 24 d old were injected intraocularly with [2-3H]glycerol and [35S]methionine and killed 1 h-60 d later. 35S label in protein and 3H label in total phospholipid and a mitochondria-specific lipid, diphosphatidylglycerol(DPG), were determined in optic pathway structures (retinas, optic nerves, optic tracts, lateral geniculate bodies, and superior colliculi). Incorporation of label into retinal protein and phospholipid was nearly maximal 1 h postinjection, after which the label appeared in successive optic pathway structures. Based on the time difference between the arrival of label in the optic tract and superior colliculus, it was calculated that protein and phospholipid were transported at a rate of about 400 mm/d, and DPG at about half this rate. Transported labeled phospholipid and DPG, which initially comprised 3-5% of the lipid label, continued to accumulate in the visual structures for 6-8 d postinjection. The distribution of transported material among the optic pathway structures as a function of time differed markedly for different labeled macromolecules. Rapidly transported proteins distributed preferentially to the nerve endings (superior colliculus and lateral geniculate). Total phospholipid quickly established a pattern of comparable labeling of axon (optic nerve and tract) and nerve endings. In contrast, the distribution of transported labeled DPG gradually shifted toward the nerve ending and stabilized by 2-4 d. A model is proposed in which apparent "transport" of mitochondria is actually the result of random bidirectional saltatory movements of individual mitochondria which equilibrate them among cell body, axon, and nerve ending pools.

Animals↗
PubMed1981

Effects of altered thyroid states on myelinogenesis.

Myelinogenesis was studied in controls and in rats treated since birth with Methimazole (hypothyroid) or thyroxine (hyperthyroid). The amount of myelin in forebrain and its protein composition were determined between 13 and 40 days of age, the period of most rapid myelin accumulation. Hypothyroid rats had reduced on both and brain weights relative to controls and the yield of myelin was reduced on both a per brain and a per milligram brain protein basis. Developmental changes in the protein composition of isolated myelin followed the pattern of control animals (the percentage of total myelin protein present as proteolipid protein, large basic protein, and small basic protein increased, as did the ratio of proteolipid/large basic protein) but were delayed temporally by 1-2 days. Hyperthyroid rats also had reduced body and brain weights. At 13 days myelin accumulation was greater than that of controls, corresponding to an earlier initiation of myelination. At later ages myelin yield was reduced on a per brain basis but not on a per milligram brain protein basis. The developmental pattern of myelin protein composition was accelerated temporally by 1-2 days. Myelination in optic nerve, assayed by proteolipid protein content, also was slightly delayed in hypothyroid animals and somewhat accelerated in hyperthyroid animals. The relative synthesis of myelin proteins (determined as incorporation of intracranially injected [(3)H]glycine into myelin protein relative to incorporation into whole brain protein), as well as distribution of radioactivity among individual myelin proteins, was determined. The results supported the conclusion of the myelin protein accumulation study; hypothyroidism retards the developmental program for myelinogenesis, whereas in the hyperthyroid state myelin synthesis is initiated earlier but is also terminated earlier.

Animals↗
PubMed1981

Effect of triethyl tin on myelination in the developing rat.

Myelinogenesis in developing rats was studied following chronic dosing with triethyl tin (TET), at a level of 1.0 mg TET/kg body wt/day. Experiments included starved controls with body weights depressed by 17 to 40% to equal those of the TET-treated groups. Rats at ages of 16, 21, and 30 days showed decreases relative to well-nourished controls in body weight, forebrain weight, myelin yield, cerebroside level, and specific activity of brain 2',3'-cyclic nucleotide-3'-phosphohydrolase when dosed with TET. At 30 days, myelin and cerebroside yields were reduced by approximately 55%, while CNP activity was reduced by less than 20%. No differences in the forebrain myelin protein composition between control, starved, and TET animals were noted. The rate of myelin protein synthesis relative to brain total protein (assayed by incorporation of intracranially injected [3H]glycine into brain homogenate and myelin proteins) was decreased in the TET rats in proportion to the decreased yield of myelin, but no particular myelin protein was preferentially affected. Matching starved controls exhibited similar body weight decreases, less pronounced forebrain weight decreases, and little or no decrease in myelin concentration. There was a relative increase in the myelin protein synthesis rate in the starved rats, indicating preferential utilization of limited protein precursors for myelin protein synthesis. Spinal cord myelin was also decreased in the TET rats, but less severely than in the forebrain. At all ages optic, but not sciatic, nerves showed decreases in myelin concentration with TET treatment. We conclude that TET inhibits forebrain growth and CNS myelination more severely than can be accounted for by a general metabolic insult.

Animals↗
PubMed1981

Turnover of axonally transported phospholipids in nerve endings of retinal ganglion cells.

We have investigated the metabolic turnover of axonally transported phospholipids in myelinated axons (optic tract) and nerve endings (superior colliculus) of retinal ganglion cells. One week following intraocular injection of [2-3H]glycerol, turnover rates for individual phospholipid classes in the retina (which contains a number of other cell types in addition to the ganglion cells) were all very similar to each other, with apparent half-lives of approximately 7 days. Apparent half-lives of labeled phospholipids in superior colliculus (presumably primarily in retinal ganglion cell nerve endings) were 10 days for both choline and inositol phosphoglycerides and 13 days for both serine and diacylethanolamine phosphoglycerides. Subcellular fractionation data obtained from superior colliculus at various times after injection suggested that apparent turnover rates determined for nerve ending phospholipids probably were not significantly affected by transfer of axonally transported 3H lipids into myelin. Apparent half-lives for phospholipids in optic tract were somewhat longer than in superior colliculus, ranging from 11 to 18 days. The slower turnover rates in optic tract may, in part, reflect the transfer of some axonal lipids to the more metabolically stable pool of lipids in the myelin ensheathing the retinal ganglion cell axons. In both optic tract and superior colliculus, apparent half-lives for axonally transported phospholipids labeled with [32P]phosphate were only slightly longer than for [2-3H]glycerol, while those for [14C]choline and [3H]acetate were markedly longer, indicating differing degrees of metabolic conservation or reutilization of these precursors relative to glycerol.

Acetates↗
PubMed1980

Axonal transport of proteins and glycoproteins in the rat nigro-striatal pathway and the effects of 6-hydroxydopamine.

Following stereotaxic injection of [35S]methionine into the substantia nigra of adult rats, there was rapid local incorporation of radioactivity into acid-insoluble material. Incorporation peaked by 4 h and then decreased. In contrast, acid-precipitable radioactivity in the corpus striatum (the major projection site of the substantia nigra) rose markedly between 1 and 8 h followed by a plateau period and another even more marked increase between 24 h and 6 days. Experiments involving injection of [3H]fucose gave similar results except that most of the acid-precipitable radioactivity in the striatum appeared in an early wave. In each case radioactivity in the contralateral striatum was less than 11% of that on the ipsilateral side. Stereotaxic injection of colchicine (20 microgram) into the nigrostriatal pathway (within the median forebrain bundle) blocked transport of [35S]protein and [3H]glycoprotein by 90% and 50%, respectively. In animals treated with 6-hydroxydopamine (6-OHDA; treated neonatally or as adults) the accumulation of striatal [35S]protein was reduced to 7 to 26% of control levels; striatal [3H]glycoprotein was also reduced, but not as much (29% to 73% of control). In control experiments, [3H]DOPA wa injected into the substantia nigra, and [3H]dopamine was measured in corpus striatum; 6-OHDA treatment reduced the amounts of striatal [3H]dopamine recovered to 3% of control values. The failure of colchicine or 6-OHDA to block transport of incorporated fucose as effectively as the transport of incorporated methionine is possible due to greater diffusion of fucose away from the injection site to non-dopaminergic nuclei projecting to the striatum. The molecular weight distribution of radioactive proteins at the substantia nigra and corpus striatum was analyzed by polyacrylamide gel electrophoresis. For both [35S]methionine and [3H]fucose, the gel electrophoretic pattern of radioactive proteins in the injection site (substantia nigra) was complex and did not change greatly between 2 h and 6 days. At the projection site (striatum) the electrophoretic distribution pattern was initially different from that of the substantia nigra, and changed markedly over the course of several days. In 6-OHDA-treated animals (treated neonatally or as adults), the bulk of proteins transported in nigro-striatal non-dopaminergic neurons appears to be very similar to that transported in the intact pathway in control rats. However, in striata of 6-OHDA-treated animals, a consistent reduction in striatal 35S- and 3H-radioactivitiy was observed in proteins with molecular weight from about 67,000 to 77,000. Assuming that the 6-OHDA treatment did not substantially affect the non-dopaminergic neurons, we interpret this to mean that some of the proteins in this molecular weight range are transported primarily by dopaminergic neurons.

Animals↗
PubMed1980

Developmental studies of the uptake of choline, GABA and dopamine by crude synaptosomal preparations after in vivo or in vitro lead treatment.

The kinetics of sodium dependent, high affinity uptake of choline and dopamine by striatal synaptosomal preparations and of GABA (gamma-aminobutyric acid) by cortical synaptosomal preparations have been examined during the development of Long-Evans control and lead-treated rats. Choline uptake was very low until 12 days postnatally, then the Vmax increased and approached adult values of 29 pmol/mg prot./min within a week. GABA uptake was somewhat elevated at birth and only after three weeks did it decrease to the adult value of 0.7 nmol/mg prot./min. Dopamine uptake was low at birth, developed linearly with age and by 30 days postnatally approached the adult value of 68 pmoles/mg prot./min. The high affinity uptake constants (choline, 0.66 microM; GABA, 4.4 muM; and dopamine, 0.31 muM) did not change markedly during development. Similar studies were conducted with rats treated at the highest lead dosage which did not result in weight loss (100 microgram lead as lead acetate/g body weight/day via intubation). Blood and brain lead determinations confirmed a substantial lead exposure. Such chronic exposure did not markedly affect the amount or developmental pattern of uptake of the putative neurotransmitters. The effect of 2.5 x 10(-5) M lead acetate in vitro on the kinetics of high affinity uptake of these compounds into preparations from 20-26-day-old rats was investigated. When uptake was assayed in the absence of calcium, lead caused a 20% increase in the Vmax for dopamine. This stimulation was reduced if samples were assayed in the presence of n mM CaCl2. The Km for high affinity uptake of these neurotransmitter-related compounds was not affected by lead. In other studies, crude synaptosomal preparations were preloaded with neurotransmitter by preincubation with radioactive choline, GABA, or dopamine. Release of radioactive neurotransmitter, either spontaneous or in response to potassium depolarization, was quantitated and correlated with the presence or absence of 2.5 x 10(-5) M lead and/or 10(-3) M calcium ions. Lead slightly inhibited calcium dependent spontaneous release of dopamine. Lead also appeared to partially substitute for calcium in the potassium depolarized release of dopamine and GABA, although subtraction of the spontaneous (potassium independent) component reduced the magnitude of the lead effect.

Aging↗
PubMed1980

Cholesterol is a component of the rapid phase of axonal transport.

Twenty-two-day-old rats were injected intraocularly with [3H]acetate and killed between 1 hr and 35 days later. Cholesterol was isolated from the retinas, optic tracts, lateral geniculate bodies, and superior colliculi. Within the retina, radioactivity was rapidly incorporated into cholesterol with maximal labeling present one hour after injection. Transported labeled cholesterol (contralaterally corrected for systemic background labeling) was present in the superior colliculus by three hours. Radioactive cholesterol accumulated in all visual structures throughout the 35-day period, but the rate of accumulation was maximal at about the time of arrival of the initial pulse of radioactivity. Colchicine treatment of the retina blocked transport of cholesterol but not its synthesis by the retina. The results indicate that cholesterol is rapidly transported in the visual system and also released from the retina for a prolonged period after its synthesis.

Age Factors↗
PubMed1980

Effect of inorganic lead exposure on myelination in the rat.

The effect of defined lead burdens on myelination of the central and peripheral nervous systems was studied in neonatal Long-Evans rats. Pups were exposed to inorganic lead (100 or 400 mg Pb as lead acetate/kg body wt/day by gastric intubation) from day 2 following birth to 30 days of age. Accumulation of myelin in forebrain was not affected by the 100-mg dosage, but at the 400mg/kg dosage level, myelin accumulation was reduced by approximately 42% on a per gram forebrain basis relative to vehicle-intubated animals. The deficit was over 50% on a per forebrain basis, since there was also a slight reduction in brain weight. This lead effect was observed at both 15 and 30 days of age. Accumulation of myelin in optic nerve (determined on the basis of proteolipid protein concentration) was also reduced by 30% relative to controls by this dosage level. However, myelination in sciatic nerve (determined on the basis of Po protein concentration) was not affected by this exposure regimen. Myelin deficits were greater than could be accounted for by undernutrition secondary to lead exposure and were not due to a developmental delay in the onset of myelination.

Animals↗
PubMed1980

Myelin.

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Animals↗