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Biomedical subjects

V H Gilad

Publications and source records attributed to V H Gilad.

At least 55 records · Page 3Linked to original sources
PubMed1987

Presynaptic effects of glucocorticoids on dopaminergic and cholinergic synaptosomes. Implications for rapid endocrine-neural interactions in stress.

Synaptosomal preparations from rat hippocampus were incubated with methylprednisolone or adrenocorticotropin. High affinity choline uptake was not affected by either hormones. Methylprednisolone however enhanced newly synthesized acetylcholine release in the presence of high potassium or acetylcholine concentrations, while adrenocorticotropin had no effect. Dopamine uptake was inhibited when synaptosomes from septum or striatum were incubated with methylprednisolone. We conclude: a) high glucocorticoid concentrations and not adrenocorticotropin can directly enhance acetylcholine release but only from stimulated cholinergic synaptosomes, and b) high glucocorticoids can reduce dopamine uptake by dopaminergic synaptosomes. The results imply that increased glucocorticoid levels during stress or disease, can directly modulate the neuronal activity of specific cholinergic and dopaminergic systems in the brain.

Acetylcholine↗
PubMed1987

Age-related reductions in brain cholinergic and dopaminergic indices in two rat strains differing in longevity.

We have recently reported that inbred Wistar-Kyoto rats which are highly reactive to stressful stimuli, have a much shorter mean life-span (21.5) compared to the less reactive Brown-Norway rats (31.0 +/- 4.5 months). In the present study we found a reduction in forebrain cholinergic neurotransmission indices in 24-month-old Wistar-Kyotos but not in Brown-Norways as compared to their respective young (3-month-old) counterparts. Also only in Wistar-Kyotos dopamine uptake was reduced in the aged striatum, but in the septum it remained unchanged in both strains. In Brown-Norways, age-related changes were observed only in choline acetyltransferase activity and only in brain regions known to contain mainly cholinergic nerve cell bodies. We conclude that at 24 months of age, reductions in brain cholinergic and dopaminergic neurotransmission are more prominent in the highly stress-reactive and shorter-lived Wistar-Kyoto strain, and may be genetically determined.

Acetylcholine↗
PubMed1987

Detachment of cultured neurons from substratum by astrocytic membrane-associated activity. Implications for CNS regeneration?

In primary cultures of dissociated cells from 6-day-old rat cerebellum, astrocytes proliferated and grew under the initially formed network of neurons. The growing astrocytes invaded the culture growth surface, while the neurons detached from the substratum and died. By 8 days after plating a confluent layer of astrocytes has taken over the entire growth surface area and neurons have disappeared. Membrane fractions prepared from astrocytes of 8-day-old cultures, have led to detachment of growing neurons. After 2 days in the presence of membrane fractions, about 70% of the neurons disappeared and many of the remaining ones had detached or retracted processes. The results indicate that the well-known phenomenon of disappearance of neurons from mixed primary CNS cultures, is probably caused by a membrane-associated activity of the proliferating astrocytes which can disturb neuron-substratum attachments. Our in vitro study implies that astrocytes may have a membrane-associated activity which is expressed under certain conditions and can disturb the contacts of growing or regenerating axons with their growth substrata.

Animals↗
PubMed1986

Dopaminergic modulation of the septo-hippocampal cholinergic system activity under stress.

The effects of the dopaminergic agonist apomorphine or the antagonist sulpiride on high affinity choline uptake and newly synthesized acetylcholine release by hippocampal synaptosomal preparations, were examined in rats subjected to immobilization stress. Increased dopamine uptake by septal synaptosomal preparations was taken as evidence for increased mesoseptal dopaminergic activity in response to stress. While apomorphine treatment failed to alter choline uptake or acetylcholine release in unhandled rats, it did however prevent the stress-induced increase in these cholinergic parameters. In contrast, after treatment with sulpiride both choline uptake and acetylcholine release were increased in unhandled rats, as they were after acute stress. Acute stress of sulpiride treated rats however resulted in changes similar to those produced by administration of either sulpiride or stress separately. We conclude that the mesoseptal dopaminergic system plays an important role in modulating the activity of the septo-hippocampal cholinergic system under stress.

Acetylcholine↗
PubMed1986

Early polyamine treatment accelerates regeneration of rat sympathetic neurons.

After injury of their axons, damaged neurons shift their metabolic activity into a reparative mode aimed at survival and regeneration or, alternatively, they undergo degeneration and die. Previous reports have shown that at the initial stages of the response to axonal injury, polyamines are essential for neuronal survival and can accelerate functional recovery. In this study we examined the ability of exogenous polyamines to accelerate regeneration following crush of the pre- or postganglionic sympathetic nerves of the superior cervical ganglion in adult rats. We found that early treatment with polyamines after pre- or postganglionic nerve crush, accelerated the reappearance of choline acetyltransferase activity in the superior cervical ganglion, and of [3H]norepinephrine uptake in the iris, respectively. Functional recovery from eyelid ptosis was also accelerated. We conclude that treatment with polyamines can enhance regeneration of peripheral sympathetic neurons.

Animals↗
PubMed1986

Increased number of sympathetic neurons with unchanged target organ innervation after postnatal polyamine treatment.

Treatment of newborn rats with polyamines from day 2 to day 9 after birth prevented the normal reduction in the number of sympathetic neurons in the superior cervical ganglion. About 40% more neurons prevailed in the ganglion after the polyamine treatment. This increase was paralleled by a comparable developmental increase in tyrosine hydroxylase activity and a small (17%) increase in choline acetyltransferase activity in the ganglion. However, in the iris, a target organ innervated by the sympathetic neurons, tyrosine hydroxylase activity and [3H]norepinephrine uptake remained unchanged. The results indicate that the polyamine-induced increase in the number of parent neurons is not accompanied by a change in the number of functional nerve terminals in the target organ.

Animals↗
PubMed1986

Cytotoxic effects of monodansylcadaverine and methylamine in primary cultures of rat cerebellar neurons.

The effects of dansylcadaverine and methylamine, competitive inhibitors of transglutaminase, were examined in primary cultures of dissociated rat cerebellar neurons. Addition of the drugs at plating time resulted 24 hr later in irreversible cytotoxic effects evidenced by failure of aggregation and neurite formation. Cytotoxicity was dose-dependent with methylamine being more potent (IC50 = 20 microM) than dansylcadaverine (IC50 = 30 microM). The cytotoxic effects were less potent when drugs were added 24 hr after plating, the time when neurons had already begun to extend neurites. Drugs were effective in the various sera and heat-inactivated sera tested. We concluded that low doses of methylamine and dansylcadaverine have potent toxic effects on primary neuronal cultures.

Animals↗
PubMed1986

Polyamines affect growth of cultured rat cerebellar neurons in different sera.

The study examines the effects of polyamines on growth of cultured neurons from 6-day-old rat cerebellar cortex, by means of: (a) irreversible inhibition of ornithine decarboxylase activity with alpha-difluoromethylornithine, and (b) treatment with the exogenous diamine putrescine and the polyamines spermidine and spermine, in the presence of sera from different sources. Inhibition of ornithine decarboxylase activity starting at plating time led after 24 hr to a partial inhibition of cell aggregation with a drastic (90%) inhibition of neurite formation. However, after 48 hr of enzyme inhibition aggregation and neurite formation increased to approach the 24 hr control values and eventually cultures fully recovered. Polyamines added at plating time in the presence of fetal calf serum led to a permanent dose-dependent inhibition of aggregation and neurite formation, spermine being effective at lower doses (spermine less than spermidine much less than putrescine). Adhesion of cells to polylysine coated surfaces was not affected by polyamines. Recovery from the cytostatic polyamine effect was observed after washing and addition of fresh medium. Prevention of the effect was achieved in the presence of aminoguanidine, an inhibitor of diamine and polyamine oxidases. The preventive effect of aminoguanidine was dose polyamine-dependent, with higher aminoguanidine concentrations needed to prevent the spermine effect (spermine much greater than spermidine greater than putrescine). The polyamine effects were observed in the presence of fetal calf, heat-inactivated fetal calf and human sera, but not with rat serum. Addition of polyamines to 24-hr-old cultured neurons, in the presence of fetal calf serum, led 12 hr later to cell death. This lethal effect could be inhibited by aminoguanidine. We conclude: (a) irreversible inhibition of ornithine decarboxylase activity delays but does not prevent neuronal growth in culture; (b) oxidation products of extracellular polyamines inhibit cell aggregation and neurite formation of cultured neuroblasts, and have lethal effects on growing neurons in culture, and (c) different pharmacological effects of polyamines can be expected in different species.

Animals↗
PubMed1985

Polyamine treatment in early development leads to increased numbers of rat sympathetic neurons.

Sympathetic and sensory neurons were counted in 35-day-old rats which were treated with polyamines from day 2 to day 9 after birth. The treatment led to an increase, averaging about 34%, in the number of sympathetic neurons in the superior cervical ganglion. The number of sensory neurons in the nodose ganglion was not changed. In sympathetic ganglia the activity of the neurotransmitter synthesizing enzyme tyrosine hydroxylase was also increased. The results demonstrate that increased polyamine supply during a limited developmental period can lead to an increased number of sympathetic neurons, possibly through enhanced neuron survival.

Aging↗
PubMed1985

Stress-induced activation of the hippocampal cholinergic system and the pituitary-adrenocortical axis.

The septo-hippocampal cholinergic system in rats undergoes rapid activation after acute stress. This is expressed by rapid increases both in high affinity choline uptake and newly synthesized acetylcholine release. Administration of ACTH or corticosterone at a high dose led 10 min later to changes comparable to those observed after acute stress. Choline uptake and acetylcholine release were also elevated 2 days after adrenalectomy. The effects of adrenalectomy could be attenuated by corticosterone, but not by ACTH treatment. The results demonstrate that (a) after short term stress the septo-hippocampal cholinergic system is activated secondary to activation of the pituitary-adrenocortical axis and (b) major changes in circulating corticosterone can modulate the activity of the hippocampal cholinergic synapse.

Acetylcholine↗
PubMed1985

Calcium-dependent transglutaminase of rat sympathetic ganglion in development and after nerve injury.

The activity of transglutaminase (TG) was examined in the rat superior cervical ganglion (SCG) during development and after postganglionic nerve crush. During postnatal development the enzyme activity is increased by sevenfold in parallel to protein content of the ganglion and reaches adult levels by day 35 after birth. The endogenous activity (enzyme activity assayed in the absence of the exogenous substrate) during development is transiently elevated with a peak at day 21 postnatal. In the adult ganglion the enzyme specific activity is evenly distributed in all subcellular compartments, but most of it is contained in the cytosol. Within the first hour after axotomy TG activity is rapidly and transiently elevated. The peak value, 80% above control levels, is attained by 30 min postoperative. At this time the activity is increased in all subcellular fractions, but the endogenous activity is selectively increased in the fraction containing nuclei. The enhanced TG activity after axotomy can be prevented by topical treatments with verapamil, an inhibitor of voltage-dependent calcium fluxes across excitable membranes, or with the calcium chelator EGTA. The results show that intracellular TG activity is present in the SCG and that it increases with postnatal growth of the ganglion. After axotomy the enzyme activity is rapidly and transiently increased in the ganglion and this elevation critically depends on calcium fluxes.

Acyltransferases↗
PubMed1985

Compensatory changes in contralateral sympathetic neurons of the superior cervical ganglion and in their terminals in the pineal gland following unilateral ganglionectomy.

The sympathetic noradrenergic neurons of the rat superior cervical ganglia (SCGs) provide the major source of innervation to the pineal gland. The present study sought to determine if this sympathetic innervation can undergo collateral sprouting following partial denervation of the pineal by unilateral removal of the SCG (ganglionectomy), and whether such growth of axon terminals is associated with biochemical changes in the contralateral SCG. In the pineal gland following partial denervation, residual noradrenergic terminals underwent compensatory changes indicative of collateral sprouting, as evidenced by: a rapid reduction in tyrosine hydroxylase (TH) activity and in [3H]norepinephrine (NE) uptake, to about 50% of control by 2 days, which was followed by a gradual but sustained increase to levels of approximately 80% of control by 10 days and a reduction in the intensity and density but not in the distribution of fibers containing NE-induced fluorescence by 2 days, which was followed by a sustained increase. In the contralateral SCG, choline acetyltransferase (CAT) activity, a marker of cholinergic preganglionic terminals, was transiently increased to about 115% of control by 4 days and returned to control levels by 14 days after unilateral ganglionectomy; later, TH activity in noradrenergic cell bodies was gradually increased to about 140% of control by 10 days where it remained for up to 52 days. Unilteral ganglionectomy combined with decentralization of the contralateral SCG by preganglionic nerve cut prevented the compensatory changes in noradrenergic nerve terminals within the pineal.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Inhibition of ornithine decarboxylase and glutamic acid decarboxylase activities by phosphorylethanolamine and phosphorylcholine.

Ornithine decarboxylase, which catalyzes the first step in polyamine biosynthesis, is rapidly and transiently increased in various tissues during growth and after various hormonal or noxious stimuli, prior to an elevation in choline kinase activity. Polyamines themselves have been demonstrated to activate choline kinase. The present study sought to determine the effect of phosphorylcholine, the product of the reaction catalyzed by choline kinase, on ornithine decarboxylase activity. The data demonstrate that ornithine decarboxylase activity. The data demonstrate that ornithine decarboxylase activity is inhibited by phosphorylcholine and more potently by the related compound phosphorylethanolamine. The inhibition by both compounds led to decreased affinity of partially purified ornithine decarboxylase for ornithine. The inhibition is not time dependent and reversible. Both compounds also inhibit glutamic acid decarboxylase activity. The results suggest that high intracellular levels of phosphorylethanolamine and phosphorylcholine can serve as natural inhibitors of decarboxylases.

Animals↗
PubMed1984

Reciprocal regulation of ornithine decarboxylase and choline kinase activities by their respective reaction products in the developing rat cerebellar cortex.

Changes in the activity of choline kinase were measured in the cerebellum during development. Early transient increase was found in the enzyme activity just prior to and during birth. This period of increase did not coincide with the periods of transient elevation in ornithine decarboxylase and choline acetyltransferase previously observed in the developing cerebellum. The effects of the naturally occurring polyamines (putrescine, spermidine, and spermine) on choline kinase and choline acetyltransferase activities, and of phosphorylcholine (the product of the reaction catalyzed by choline kinase) on ornithine decarboxylase and choline acetyltransferase activities, were also examined. Choline acetyltransferase activity was not influenced by either polyamines or phosphorylcholine. However, choline kinase activity from 7-day-old, but not from adult, cerebellum was increased 25% in the presence of 4 mM spermine. In contrast, low spermidine concentrations (less than 2 mM) inhibited choline kinase activity selectively in 7-day-old cerebellum. Ornithine decarboxylase activity from 7-day-old cerebellum was inhibited in a concentration-dependent manner by phosphorylcholine. The present data together with other previous reports suggest that: (a) polyamines may play a role in choline utilization during development via their regulation of choline kinase activity, on the one hand, and of acetylcholinesterase activity on the other; and (b) during development, a reciprocal regulation of choline kinase and ornithine decarboxylase activities by their respective reaction products may exist, whereby choline kinase activity is regulated in a complex manner by polyamines and, in turn, ornithine decarboxylase is inhibited by phosphorylcholine.

Animals↗
PubMed1983

Polyamine biosynthesis is required for survival of sympathetic neurons after axonal injury.

Treatment of adult rats with specific inhibitors of polyamine synthesizing enzymes prevented the early increase in ornithine decarboxylase activity and polyamine content in the superior cervical ganglion after the postganglionic nerve was cut. Moreover, after axotomy, this treatment led to a marked diminution of the chromatolytic response with a marked neuronal cell death. We conclude that after axonal injury an early increase in polyamine biosynthesis, probably within parent sympathetic neurons, is an obligatory step in the progression of the axon reaction.

Animals↗
PubMed1983

Early rapid and transient increase in ornithine decarboxylase activity within sympathetic neurons after axonal injury.

The activity of ornithine decarboxylase (ODC) was examined in the rat superior cervical ganglion during development and after postganglionic axotomy. During development the enzyme activity in the ganglion was transiently elevated at 19 days gestation (2 days before birth) and then declined to low adult activities by 5 days after birth. After axotomy the enzyme activity in the ganglion was rapidly increased. As early as 2 h after the injury the activity was increased to 200% and by 10 h it attained a peak of 453% above control values. The activity then rapidly declined to a lower value of about 200% above control by 24 h, where it remained as long as 5 days and then returned to control values by 10 days postoperative. The early increase in ODC activity was demonstrated by inhibitor cytochemistry to occur within neuronal cell bodies. The ODC activity was also increased after preganglionic nerve transection (denervation) (275%), end organ removal (60%), and 6-hydroxydopamine treatment (75%). We conclude that increased ODC activity is one of the earliest events in the reaction of the nerve cell body to axonal injury, and that increased ODC activity is a common feature of drastic metabolic alterations in neurons of the superior cervical ganglion.

Animals↗