Autoradiographic measurement of relative changes in ornithine decarboxylase in axotomized superior cervical ganglion neurons

Polyamines increase in sympathetic neurons and non-neuronal cells after axotomy and enhance neurite outgrowth in nerve growth factor-primed PC12 cells

Following axonal damage, sympathetic neurons are capable of regenerating and reinnervating their target tissues. Some years ago exogenous administration of polyamines was shown to enhance this regeneration. Recently, it was found that axonal injury leads to a dramatic up-regulation of the expression of arginase I in sympathetic neurons. This enzyme catalyzes the conversion of arginine to ornithine, which can subsequently be converted to the diamine putrescine and, ultimately, to the polyamines spermidine and spermine. In the present study, using an antiserum that reacts with both spermidine and spermine, we have found an increase in polyamine levels in both neurons and non-neuronal cells in the superior cervical ganglion 2 and 5 days following transection of the ganglion's postganglionic trunks. Using PC12 cells primed with nerve growth factor and then stripped off the culture dish and replated as a model system for axotomized sympathetic neurons, we found that spermidine treatment, with or without nerve growth factor, resulted in an increased percentage of cells with a neurite whose length was at least twice the diameter of the neuron's cell body. These increases could be seen within 48 h and were still evident after 8 days. Together, these data support the possibility that endogenous polyamines are involved in the normal regeneration which occurs following sympathetic axonal damage.

Polyamine metabolism in different pathological states of the brain

Biosynthesis of the polyamines spermidine and spermine and their precursor putrescine is controlled by the activity of the two key enzymes ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC). In the adult brain, polyamine synthesis is activated by a variety of physiological and pathological stimuli, resulting most prominently in an increase in ODC activity and putrescine levels. The sharp rise in putrescine levels observed following severe cellular stress is most probably the result of an increase in ODC activity and decrease in SAMDC activity or an activation of the interconversion of spermidine into putrescine via the enzymes spermidine N-acetyltransferase and polyamine oxidase. Spermidine and spermine levels are usually less affected by stress and are reduced in severely injured areas. Changes of polyamine synthesis and metabolism are most pronounced in those pathological conditions that induce cell injury, such as severe metabolic stress, exposure to neurotoxins or seizure. Putrescine levels correlate closely with the density of cell necrosis. Because of the close relationship between the extent of post-stress changes in polyamine metabolism and density of cellular injury, it has been suggested that polyamines play a role in the manifestation of structural defects. Four different mechanisms of polyamine-dependent cell injury are plausible: (1) an overactivation of calcium fluxes and neurotransmitter release in areas with an overshoot in putrescine formation; (2) disturbances of the calcium homeostasis resulting from an impairment of the calcium buffering capacity of mitochondria in regions in which spermine levels are reduced; (3) an overactivation of the NMDA receptor complex caused by a release of polyamines into the extracellular space during ischemia or after ischemia and prolonged recirculation in the tissue surrounding severely damaged areas; (4) an overproduction of hydrogen peroxide resulting from an activation of the interconversion of spermidine into putrescine via the enzymes spermidine N-acetyltransferase and polyamine oxidase. Insofar as a sharp activation of polyamine synthesis is a common response to a variety of physiological and pathological stimuli, studying stress-induced changes in polyamine synthesis and metabolism may help to elucidate the molecular mechanisms involved in the development of cell injury induced by severe stress.

Freund's complete adjuvant induces ornithine decarboxylase activity in the central nervous system of male rats and triggers the release of pituitary hormones

In male rats, inoculation of Freund's complete adjuvant (FCA, 0.5 mg/rat of Mycobacterium butyricum in paraffin oil) induced high levels of ornithine decarboxylase (ODC) in the hypothalamus and pituitary gland (285% and 245% of controls, respectively, within 12 h to 2 days). ODC activity also was altered in the cerebellum and left neocortex, but not in the right neocortex. This activity reflected a dynamic equilibrium which is influenced by ODC synthesis, degradation, activation, etc. The circadian rhythms of pituitary ODC activity and plasma prolactin level, 3-4 days after FCA, showed that enhancement of enzymatic activity during the dark phase correlated with a marked release of prolactin (Prl). During this early period after FCA, changes in plasma levels of other pituitary hormones were not significant or were less important. Pretreatment with bromocriptine microcapsules inhibited both basal and FCA-induced pituitary ODC activity, as well as Prl secretion. Further, significant increases in plasma luteinizing hormone and adrenocorticotropic hormone were noted from days 4 and 8, respectively, and onwards. Finally, a phase of reduced corticosterone secretion occurred during the latency period. This study shows that FCA influences central nervous system pathways and supports the idea that endogenous Prl is involved in some early events which lead to the development of adjuvant arthritis.

Effects of isolation and high helium pressure on the nucleolus of sympathetic neurons in the rat superior cervical ganglion

In prokaryotes, unicellular eukaryotes and cell-free systems, pressure is known to exert an inhibitory effect on protein synthesis and RNA metabolism, the mechanism(s) of which remain to be investigated in detail. The purpose of the present in vitro study was to compare ultrastructural and quantitative changes of the nucleolus, which is the site of ribosome biogenesis, in sympathetic neurons of rat superior cervical ganglia (SCG) maintained for 2, 3 and 5 h in NCTC 109 medium and subjected to pressure or not. In control SCG (left) the nucleolus greatly increased in volume (+ 33%) 2 h after excision, in comparison with SCG fixed immediately. This overall enlargement was found to reflect a marked increase in all nucleolar components (from 16 to 87%). After 5 h, volumes of nucleolus, fibrillar centers and vacuolar component returned to control values, whereas dense fibrillar and granular components remained affected. Such early and transient changes are regarded as reflecting basic metabolic changes associated with increased nucleolar RNA that should be of primary concern to experiments using SCG transplanted in culture media. Compression under helium up to 180 atmospheric pressure for 1 h of right SCG maintained for 2 h in culture medium, was shown to induce, on the contrary, a marked decrease in nucleolar volume (-39%) and in volumes of all nucleolar components (from -36 to -51%). When they were kept at constant high pressure for 1 and 3 h a progressive recovery of volumes of nucleoli and nucleolar components was observed. Consequently, compression was shown to exert opposite effects to those of isolation of SCG. Present data are interpreted as an inhibitory effect of pressure on ribosome biogenesis. Such observations on a vertebrate neuron might open a new field in the search for cellular mechanisms underlying the effects of pressure on living organisms and especially on the nervous system.

Effect of histamine on the development of astroglial cells in culture

The effect of histamine on different aspects of the growth of astrocytes was studied using primary cultures derived either from forebrain or from cerebellum of the rat. The influence on general growth and differentiation was monitored in terms of the activities of ornithine decarboxylase and glutamine synthetase enzymes, whereas [3H]thymidine incorporation into DNA was used as a specific index of cell proliferation. Treatment with 500 nM histamine of cells grown for 6 days in vitro, caused a time-dependent significant increase in ornithine decarboxylase activity of astrocytes from both sources. The maximum increase was observed at 4 h after histamine treatment, at that time the elevation in ornithine decarboxylase activity being about 80% and 300% over control values in the forebrain and the cerebellar astrocytes, respectively. Under similar experimental conditions, addition of histamine (500 nM) to medium resulted in a significant increase in [3H]thymidine incorporation into DNA in both types of cultures: in comparison with control, the elevation was about 45% at 48 h in forebrain astrocytes and at 24 h in cerebellar astrocytes. On the other hand, the specific activity of glutamine synthetase in cerebellar astrocytes was markedly enhanced (about 100%) by treatment with histamine (500 nM) for 4 days, but forebrain astrocytes were little affected. Addition of histamine to the culture medium produced no significant alteration in the activity of lactate dehydrogenase and protein content of either type of astroglial cells. The present findings, which support our earlier proposal that the biochemical properties of astrocytes differ between various brain regions, provide direct evidence for the involvement of histamine in the regulation of growth and development of astrocytes.

Ornithine decarboxylase in the inner ear of the guinea pig

L-Ornithine decarboxylase, the rate limiting enzyme of polyamine synthesis and a possible marker enzyme for tissue proliferation and maturation, has been found in the developing guinea pig cochlea using the unlabelled horseradish-peroxidase-antiperoxidase technique. Ornithine decarboxylase-like immunoreactive material was detected in the neurons of the Ganglion spirale and in their axonal and/or dendritic fibers. The location of the enzyme and the possible functional role of ornithine decarboxylase plays in the development and maturation of the auditory organ and of the hearing process are discussed.

Polyamines in cerebral ischemia

The present series of experiments was designed to study regional profiles of polyamines (putrescine, spermidine, and spermine) in reversible cerebral ischemia produced in rats and Mongolian gerbils. Polyamine profiles did not change during ischemia, but did following recirculation. The most prominent changes were a dramatic postischemic increase in putrescine and a marked decrease in spermine in severely damaged regions. Within a given brain structure, the postischemic putrescine levels correlated closely with the density of ischemic cell injury and the time period of cerebral ischemia. Furthermore, putrescine was already considerably increased in the CA1-subfield of the hippocampus of gerbils after 8 h recirculation, i.e., at a time when the cells are still intact. The results indicate that putrescine may be viewed as an excellent biochemical correlate of ischemic cell injury. The postischemic changes in putrescine levels are discussed in relation to the known activities of this compound.

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)

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.

Changes of ornithine decarboxylase activity in dorsal root ganglion cells after axon injury: possible relationship to alterations in neuronal chromatin

An autoradiographic technique was used to detect changes in ornithine decarboxylase in rat dorsal root ganglion neurons after sciatic nerve lesions. Binding of [3H]difluoromethylornithine ([3H]DFMO) to tissue sections of L5 ganglia was compared between axotomized and unoperated ganglia at 0.5, 1, 2, 3, 4, 5, 7, 8, 9, 11, 14, and 30 days after a crush lesion of the sciatic nerve. The [3H]DFMO binding to axotomized ganglion neurons was elevated compared with the unoperated side at 0.5, 1, 5, 7, 8, and 11 days postoperation. Enzymatic measurements of ornithine decarboxylase on ganglia at 1, 4, 8, and 9 days after sciatic nerve crush confirmed basic patterns of enzyme activity comparisons derived from autoradiography. Compared with patterns of [3H]actinomycin D binding to nuclei during the same periods after axotomy, [3H]DFMO binding increased prior to increases in [3H]actinomycin D binding within the first week. After that time, changes in both variables occurred in parallel. The data suggest that increased activities of ornithine decarboxylase or concentrations of polyamines may be linked to the induction of increased RNA synthesis in the early phases of the axon reaction.