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Biomedical subjects

G M Gilad

Publications and source records attributed to G M Gilad.

At least 55 records · Page 3Linked to original sources
PubMed1988

Retrograde changes in transglutaminase activity after peripheral nerve injuries.

It has been previously demonstrated that transglutaminase activity in rat superior cervical ganglion is rapidly and transiently increased minutes after nerve injury. The present series of experiments sought to determine: (1) whether or not similar changes are expressed by other peripheral neuronal systems, and (2) if injury-induced changes in the enzyme activity can be detected along the injured nerve, and if so do they occur in axons or in non-neuronal cells. In the nodose ganglion transglutaminase activity increased (approximately 40%) 48 h after the vagus nerve was crushed 25 mm from the ganglion. In the vagus nerve the activity was transiently increased (approximately 100%) within 1 h, followed by a second increase (approximately 140%) after 3 h. This occurred only in the proximal nerve stump close to the injury site and not in the section of nerve closer to the ganglion. Comparable enzyme activity was found in unoperated vagus nerve and in distal stumps of previously ligated vagus nerves. In dorsal root ganglia no changes were found for up to 24 h after the sciatic nerve was crushed 40 mm from the ganglion. In the facial nucleus a transient increase was observed after the facial nerve was crushed about 14 mm distally with a peak (approximately 300) at 3 days and a decline within 14 days. A second lesion of the facial nerve made 12 days following a conditioning lesion led to a rebound of enzyme activity in the facial nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Early polyamine treatment enhances survival of sympathetic neurons after postnatal axonal injury or immunosympathectomy.

We have recently demonstrated that following injury of their axon, sympathetic neurons of the rat superior cervical ganglion become dependent on polyamine synthesis for their survival. In addition we have observed that the treatment of newborn rats with biogenic polyamines can prevent the naturally occurring reduction in the number of neurons in the ganglion. In the present study groups of newborn rats were subjected to either postganglionic nerve crush (axotomy) or to treatment with antiserum to nerve growth factor (immunosympathectomy), two treatments which result in a massive loss of neurons in the ganglion. Daily injections of the polyamines putrescine, spermidine and spermine (10 mg/kg each), for 7 days after the operation to the axotomized group, and for 9 days starting with the first antiserum injection to the immunosympathectomized group, attenuated the nerve cell loss. The polyamine treatment also attenuated the reduction in the activity of the neurotransmitter-synthesizing enzyme tyrosine hydroxylase observed after both axotomy and immunosympathectomy in the ganglion. These results further indicate that polyamines are important for the survival of sympathetic neurons and, while their mechanism of action is unknown, an interaction with nerve growth factor regulation cannot be excluded. In the iris, the reduction observed in [3H]norepinephrine uptake after the two noxious treatments was unproportionately small when compared to the large drop in the number of parent neurons in the ganglion. This suggests that compensatory mechanisms exist which act to adjust the number of functional axon terminals per neuron so that the number of terminals innervating the target remains relatively constant.

Animals↗
PubMed1987

Age-dependent loss and compensatory changes of septohippocampal cholinergic neurons in two rat strains differing in longevity and response to stress.

Inbred Wistar-Kyoto rats which are behaviorally more reactive to stress have a shorter life span than Brown-Norway rats. This is paralleled by higher basal activity and more pronounced changes in the septohippocampal cholinergic system of Wistar-Kyotos after stress. Age- and strain-dependent differences were therefore characterized in the septohippocampal system of 3- and 24-month-old (aged) Wistar-Kyotos and Brown-Norways, and in 30-month-old Brown-Norways. High affinity [3H]choline uptake and newly synthesized [3H]acetylcholine release served as markers for cholinergic terminals in the hippocampus. [3H]Quinuclidinylbenzilate binding served as a marker of muscarinic receptors in the hippocampus. Choline acetyltransferase activity served as a marker for cholinergic neurons and their terminals in the septum and hippocampus respectively. Acetylcholinesterase histochemical staining served to localize cholinergic neurons and their terminals in the septum and hippocampus respectively. In the hippocampus of aged Wistar-Kyotos choline uptake and acetylcholine release were reduced by approximately 50% compared to their young counterparts, but remained unchanged in aged Brown-Norways. Hippocampal choline acetyltransferase activity, acetylcholinesterase staining and muscarinic binding were unchanged in aged rats of both strains. Pyramidal cell loss (observed in Cresyl violet stained sections) was detected in hippocampus of 24-month-old Wistar-Kyotos and 30-month-old, but not younger Brown-Norways. Numbers of acetylcholinesterase-stained cells in the septum were reduced by 45 and 25% in 24-month-old Wistar-Kyotos and Brown-Norways respectively, and by 50% in 30-month-old Brown-Norways. Mean diameter of these cells was increased only in aged Wistar-Kyotos (approximately 46%) and in 30-month-old Brown-Norways (40%). The results indicate: (1) there is an ongoing age-dependent degeneration of septohippocampal cholinergic neurons which is associated with two principal compensatory changes in remaining cholinergic neurons: (a) hypertrophy of perikarya and (b) relative increase in activity of presynaptic markers in terminals with unchanged regional distribution, suggesting possible collateral sprouting; (2) age-dependent loss of septal cholinergic neurons precedes loss of hippocampal pyramidal neurons and (3) loss of pyramidal neurons in the hippocampus is associated with a compensatory increased muscarinic binding by remaining target hippocampal neurons. The results imply that higher basal and stress-induced activity of septohippocampal cholinergic neurons may be correlated with an accelerated and more pronounced age-dependent degeneration of this cholinergic system.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
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

The stress-induced response of the septo-hippocampal cholinergic system. A vectorial outcome of psychoneuroendocrinological interactions.

Considerable data have emerged which strongly indicate that the septohippocampal cholinergic system is involved in the adaptive response to stress. Neurotransmitter regulatory mechanisms in cholinergic synaptic terminals of this part of the limbic system undergo adaptive changes in response to stress and recover slowly after stress. The initial stress-induced response is characterized by activation of hippocampal cholinergic terminals within minutes, as indicated by a rapid and transient elevation in high affinity choline uptake and increased newly synthesized acetylcholine release. The response of this cholinergic system to stress is influenced by both neuronal and hormonal stimuli. Among the several neuronal systems converging in the septum, terminals of the dopaminergic mesolimbic system have been found to be selectively involved in the early response to stress. Pharmacological interference with dopaminergic neurotransmission, with agonist and antagonist treatments, revealed that changes in the tonic inhibitory influence of septal dopaminergic terminals can modulate the response of hippocampal cholinergic terminals to stress. A similar activation of hippocampal cholinergic terminals as after short-term stress was observed after treatments with a large dose of either adrenocorticotropic hormone or corticosterone. Furthermore, glucocorticoids and not adrenocorticotropic hormone can directly enhance acetylcholine release, but only from excited terminals. This indicates that stress-induced activation of the septo-hippocampal system may occur secondary to, but not directly by, increased levels of pituitary-adrenocortical hormones. Yet, it is possible that under stressful conditions the increased glucocorticoid levels may modulate the activity of the stimulated hippocampal cholinergic terminals. Together the findings support the notion that the stress-induced response of the septo-hippocampal cholinergic system represents an integrated output of converging neuronal and hormonal stimuli which convey signals of stress to this limbic brain region.

Animals↗
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

Cholinergic muscarinic binding by rat lymphocytes: effects of antagonist treatment, strain and aging.

Cholinergic muscarinic binding by viable peripheral lymphocytes was assessed by measuring specific binding of the muscarinic antagonist [3H]quinuclidinyl benzylate. After atropine treatment maximal lymphocyte muscarinic binding was increased by about 30%, as it did in the hippocampus of the same rats. Strain-dependent differences in muscarinic binding by peripheral lymphocytes were correlated with similar differences in selective brain regions. Higher muscarinic binding was observed in lymphocytes derived from aged (24 months old) rats. We conclude: atropine treatment causes an increase in lymphocyte muscarinic binding as it does in the brain; strain differences in brain muscarinic binding are paralleled by similar differences in lymphocytes; and in aged rats muscarinic binding capacity by lymphocytes is elevated. The results indicate that circulating lymphocytes may serve as a useful peripheral marker reflecting induced alterations or inherent differences in muscarinic binding.

Aging↗
PubMed1986

Cholinergic muscarinic binding by human lymphocytes: changes with aging, antagonist treatment, and senile dementia of the Alzheimer type.

In peripheral blood lymphocytes (mixed lymphocytes isolated on a Ficoll-Hypaque density gradient) derived from normal human subjects, cholinergic muscarinic binding capacity was found to increase with age. In contrast, lymphocytes derived from patients with "probable" senile dementia of the Alzheimer type (SDAT) exhibited a marked reduction in binding capacity. Treatment of these patients with antimuscarinic drugs was associated with increased muscarinic binding by lymphocytes. These results indicate that cholinergic muscarinic binding by peripheral blood lymphocytes may be useful in the study of alterations associated with aging and SDAT, as well as in evaluating changes induced by certain cholinergic drug treatments.

Aging↗
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↗