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Biomedical subjects

G M Gilad

Publications and source records attributed to G M Gilad.

At least 73 records · Page 4Linked to original sources
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

Dynamics of cholinergic synaptic mechanisms in rat hippocampus after stress.

Changes in high affinity [3H]choline uptake, newly synthesized [3H]acetylcholine release and [3H]quinuclidinylbenzilate (QNB) binding were characterized in crude synaptosomal preparations from rat hippocampus immediately after different intervals of immobilization stress and at different times following chronic intermittent stress (2h once daily for 5 days). Choline uptake was increased to 125% of unhandled controls after 10 min of stress, after 2 h it returned to control levels and after chronic stress uptake was reduced to 75% of control. Acetylcholine release was enhanced after all stress intervals. Maximal muscarinic (QNB) binding capacity (Bmax) was increased to 135% of control only after chronic stress, with no change in Kd values. Following chronic stress the changes observed in cholinergic synaptic mechanisms all persist for up to 2 days. Recovery occurred only by the 7th post-stress day. We conclude: presynaptic hippocampal cholinergic terminals are rapidly activated by stressful stimuli and this is expressed by an increase in choline uptake and newly synthesized acetylcholine release; after prolonged periods of stress adaptive changes in the cholinergic terminals are expressed by a reduction in choline uptake and an elevation in the number of muscarinic binding sites; and the chronic stress-induced changes are slow to recover. The results demonstrate that the septo-hippocampal cholinergic system is an integral part of the adaptive response to stress.

Acetylcholine↗
PubMed1985

Transglutaminase activity in rat brain: characterization, distribution, and changes with age.

The activity of transglutaminase was characterized in the rat brain. In adults, comparable levels of transglutaminase activity are present in all brain regions examined. The activity is present in all subcellular fractions, as studied by differential centrifugation, but the soluble fraction contains the highest specific activity. The endogenous activity (enzyme activity assayed in the absence of the exogenous substrate casein) is very low in all subcellular fractions, except in the synaptosomal fraction where its highest levels are about 40-60% of the activity assayed in the presence of casein. Furthermore, enzyme activity is present on the external surface of synaptosomes. In the soluble fraction, maximal activity can be detected between pH values of 9 and 10 when assayed in the presence of 5 mM CaCl2 (with half-maximal activity requiring 0.75 mM CaCl2) and 0.4 mM putrescine (with an apparent Km for putrescine of 0.1 mM). The activity can be partially inhibited by ZnCl2 (with an IC50 of 4.5 mM) and by AlCl3 (with an IC50 of 5.1 mM). In the cerebellum, where the full span of neuronal development can be studied after birth, the highest specific activity is observed just after birth, thereafter the activity starts to decline and by 14 days, after a reduction of about 65%, it reaches levels observed throughout life.

Aging↗
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

Strain-dependent and stress-induced changes in rat hippocampal cholinergic system.

The study demonstrates that in the hippocampus of inbred Wistar-Kyoto (WKY) rats [3H]choline uptake is 38% higher than in Brown-Norway (BN) rats. In contrast, the maximum binding capacity of [3H]quinuclidinylbenzilate (QNB) is 28% lower in WKY than in BN rats. After immobilization stress there is a reduction in [3H]choline accumulation which is more pronounced in WKY rats. Furthermore, maximal QNB binding after stress is increased only in WKY rats. Choline acetyltransferase activity, which was 83.5% higher in WKY rats, was not altered after stress in both strains. We conclude that: (1) choline accumulation is directly related to choline acetyltransferase activity in hippocampal synaptosomes; (2) maximum cholinergic muscarinic binding capacity is inversely related to the above two presynaptic activities and (3) immobilization stress results in a decreased choline accumulation and may lead to an increased QNB binding. The results imply that reduction in choline accumulation may be a compensatory mechanism of cholinergic synapses during adaptation to lengthly periods of neuronal activity.

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↗
PubMed1981

Stain-dependent differences between the septo-hippocampal cholinergic system and hippocampal size.

The activity of choline acetyltransferase is over twice as high in the hippocampus of Wistar Kyoto (WKY) than in Brown Norway (BN) rats, and this is paralleled by a comparable difference in acetylcholinesterase staining intensity within the hippocampal formation. However, the size of the whole hippocampus is smaller in WKY than in BN rats. There are no strain differences in the activities of the neurotransmitter-synthesizing enzymes: tyrosine hydroxylase in the septum and glutamic acid decarboxylase in the hippocampus. The findings indicate the existence of strain-dependent inverse relationship between the septo-hippocampal cholinergic system and the size of the hippocampus.

Animals↗
PubMed1981

Increased choline kinase activity in the rat superior cervical ganglion after axonal injury.

The activity of choline kinase (CK) was examined in the rat superior cervical ganglion (SCG) during development and following postganglionic axotomy. The highest specific enzyme activity (nmol phosphorylcholine/mg protein/h) 52 +/- 8, is observed 5 d before birth, then it rapidly decreases by about 50%, reaching at the day of birth levels observed in the ganglion throughout life. During development the total enzyme activity per ganglion is increased steadily until it reaches a 5-fold increase which parallels the increase in protein content. Following axotomy the enzyme activity per ganglion is rapidly increased by about 2-fold between 1 and 5 d postoperative and then gradually decreases reaching control levels at 30 d. The transient increase in enzyme activity parallels the increase in protein content of the axotomized ganglia. The peak increase in enzyme activity coincides with the peak chromatolytic response of the axotomized ganglion. We conclude that choline kinase activity is transiently increased within neurons after axonal injury, and that this event represents an effort of the nerve cell body to enhance its phosphatidylcholine biosynthesis essential for new membrane synthesis during the regeneration of the cut axon.

Aging↗
PubMed1981

Modes of adaptation of peripheral neuroendocrine mechanisms of the sympatho-adrenal system to short-term stress as studied in two inbred rat strains.

Alterations in mechanisms involved in catecholamine (CA) and corticosterone (B) regulation following short periods of stress have been investigated in two inbred rat strains: a strain more reactive to stress, Wistar-Kyoto (WK), and a less reactive strain, Brown-Norway (BN). Measurements after decapitation stress alone and after decapitation following different periods of immobilization stress, indicate that: (a) plasma CA levels immediately after severe stress (i.e. decapitation) are directly related to the behavioral reactivity of the two rat strains to stress but inversely related to adrenal gland size, their content of CA and biosynthetic enzymes, and to plasma levels of MHPG; (b) levels of B in adrenal glands and in plasma after stress are similar in both strains, in spite of different gland sizes; (c) CAT activity in presynaptic sympathetic terminals is directly related to plasma CA after short-term stress; and (d) liver COMT activity is directly related to plasma CA levels after stress, but inversely plasma levels of MHPG. The implications of the findings are discussed further in the text and lead to the conclusion that the BN strain represents a mode of a slower response to stressful stimuli than WK.

Adaptation, Physiological↗
PubMed1981

Difference in choline acetyltransferase but similarities in catecholamine biosynthetic enzymes in brains of two rat strains differing in their response to stress.

Rats of the Wistar-Kyoto (WKY) strain are more reactive to stress than Brown-Norway (BN) rats as adjudged by their behavioral and plasma catecholamine (CA) responses to stress. Contrary to the strain differences existing in the periphery, brain CA and their biosynthetic enzyme activities were found to be similar in both strains before and after immobilization stress. However, as in the periphery, choline acetyltransferase (CAT) activity was higher in brains of WKY rats. The results suggest that: (1) peripheral and central CA systems may be under different genetic control mechanisms, and (2) strain differences in CAT activity may reflect differences in cholinergic systems both in the brain and periphery, which may be important in the behavioral differences observed.

Animals↗
PubMed1981

Cytochemical localization of ornithine decarboxylase with rhodamine or biotin-labeled alpha-difluoromethylornithine. An example for the use of labeled irreversible enzyme inhibitors as cytochemical markers.

The present work describes a new method for cytochemical localization of enzymes using ornithine decarboxylase (ODC) as an example. The method is based on the preservation of the characteristic-specific and irreversible binding of the inhibitor alpha-difluoromethylornithine (alpha-DFMO) following its conjugation to "label" molecules. The inhibitor has been conjugated to the fluorescent molecule rhodamine-B-isothiocyanate, and its localization in tissue sections was detected directly by fluorescence cytochemistry. Alternatively, alpha-DFMO has been conjugated to biotin and its cytochemical localization determined indirectly following its binding with avidin conjugated to horseradish peroxidase (HRP) and visualization of the HRP reaction product. Both labeled inhibitor molecules were successfully localized cytochemically within specific cells of the developing rat cerebellum and rat liver following thioacetamide injection where ODC activity is greatly enhanced. This novel technique should be of general application 1) in other tissues, 2) for other enzymes, and 3) in electron microscopic studies for ultrastructural localization of the enzyme.

Affinity Labels↗