The facilitating effect of gangliosides on the electrogenic (Na+/K+) pump and on the resistance of the membrane potential to hypoxia in neuromuscular preparation

From Frog Muscle to Brain Neurons: Joys and Sorrows in Neuroscience

One element, potassium, can be identified as the connecting link in the research of Czech neurophysiologist Prof. František Vyskočil. It accompanied him from the first student experiments on the frog muscle (Solandt effect) via sodium-potassium pump and quantum and non-quantum release of neurotransmitters (e.g. acetylcholine) to the most appreciated work on the reversible leakage of K+ from brain neurons during the Leao´s spreading cortical depression, often preceding migraine. He used a wide range of methods at the systemic, cellular and genetic levels. The electrophysiology and biochemistry of nerve-muscle contacts and synapses in the muscles and brain led to a range of interesting findings and discoveries on normal, denervated and hibernating laboratory mammals and in tissue cultures. Among others, he co-discovered the facilitating effects of catecholamines (adrenaline in particular) by end-plate synchronization of individual evoked quanta. This helps to understand the general effectiveness of nerve-muscle performance during actual stress. After the transition of the Czech Republic to capitalism, together with Dr. Josef Zicha from our Institute, he was an avid promoter of scientometry as an objective system of estimating a scientist´s success in basic research (journal Vesmír, 69: 644-645, 1990 in Czech).

ATP but not adenosine inhibits nonquantal acetylcholine release at the mouse neuromuscular junction

The postsynaptic membrane of the neuromuscular synapse treated with antiacetylcholinesterase is depolarized due to nonquantal release of acetylcholine (ACh) from the motor nerve ending. This can be demonstrated by the hyperpolarization produced by the application of curare (H-effect). ATP (1 x 10-5 M) decreased the magnitude of the H-effect from 5 to 1.5 mV. The membrane input resistance and the ACh sensitivity were unchanged, and so changes in these cannot explain the ATP effect. Adenosine alone was without effect on the nonquantal release. On the other hand, both ATP and adenosine depressed the frequency of spontaneous miniature endplate potentials, to 56% and 43% respectively. The protein kinase A inhibitor Rp-cAMP or the guanylyl cyclase inhibitor 1H-[1,2,4]oxidiazolo[4,3-a]quinoxalin-1-one did not affect the inhibitory influence of ATP on the H-effect, whereas staurosporine, an inhibitor of protein kinase C, completely abolished the action of ATP. Suramin, an ATP antagonist, enhanced the H-effect to 8.6 mV and, like staurosporine, prevented the inhibitory effect of ATP. ATP thus suppresses the nonquantal release via a direct action on presynaptic metabotropic P2 receptors coupled to protein kinase C, whilst adenosine exerts its action mainly by affecting the mechanisms underlying quantal release. These data, together with earlier evidence, show that nonquantal release of ACh can be modulated by several distinct regulatory pathways, in particular by endogenous substances which may or may not be present in the synaptic cleft at rest or during activity.

Glycosphingolipids of skeletal muscle: II. Modulation of Ca2(+)-flux in triad membranes by gangliosides

Membrane vesicles of rabbit skeletal muscle were prepared and separated by sucrose density gradient centrifugation. The fractions obtained (in the order of increasing density) were sarcolemma (SL), T-tubules (TT), sarcoplasmic reticulum (SR1 and SR2) and triads/mitochondria (Tr/M) as characterized by their specific marker enzymes, ligand binding, and ion flux activities. The distribution of neutral glycosphingolipids and gangliosides in these membrane preparations has been documented in the preceding paper (J. Müthing, U. Maurer, U. Neumann, B. Kniep, and S. Weber-Schürholz, Carbohydr, Res., (1988) 135-145). GM3(Neu5Ac) is the dominant ganglioside, neolacto-series gangliosides are moderately expressed and ganglio-series gangliosides were found in minor quantities, however, all showing different qualitative and quantitative membrane-type specific patterns. The voltage dependent Ca(2+)-channels of skeletal muscle reside prevalently in the triad enriched membrane fractions deduced from highest binding capacity of 1,4-dihydropyridines. Calcium channel complexes of triads were reconstituted into unilamellar phospholipid vesicles of 400 nm defined size and the active 45Ca(2+)-uptake into intravesicular space was measured after incorporation of muscle specific gangliosides into the outer vesicle lipid bilayer in parallel to control liposomes without gangliosides. GM3(Neu5Ac) strongly increased the uptake of 45Ca2+ (+285%) whereas GM3(Neu5Gc) severely inhibited the ion flux (-61%). Neolacto-series gangliosides evoked miscellaneous effects upon 45Ca(2+)-flux depending on isomeric sialic acid configuration, oligosaccharide size and fatty acid chain length of the ceramide portion. VI3Neu5Ac-nLcOse6Cer (C24-fatty acid), IV3Neu5Ac-nLcOse4Cer (C16-fatty acid) and IV6Neu5Ac-nLcOse4Cer (C16-fatty acid) strongly enhanced the 45Ca(2+)-flux (+208, +162, and +120%, respectively, whereas IV3Neu5Ac-nLcOse4Cer (C24-fatty acid), VI3Neu5Ac-nLcOse6Cer (C16-fatty acid) and IV6Neu5Ac-nLcOse4Cer (C24-fatty acid) slightly reduced 45Ca(2+)-flux (-3, -6, and -17%, respectively). Out of all gangliosides tested in this study, GM1 showed the strongest stimulatory effect (+327%). GD1a and GT1b gave rise to remarkable flux-stimulation of +283 and +255%, respectively, whereas GD1b exhibited only a slightly positive effect (+38%). This data suggest a functional role of gangliosides in subcellular muscle membranes giving strong evidence that gangliosides are capable of modulating the cytosolic calcium level of muscle, which regulates muscle contraction.

7-Oxo-prostacyclin affects the electrogenic Na+/K+ pump in mouse diaphragm fibers

The effect of a stable prostacyclin derivative, 7-oxo-prostacyclin, on the electrogenic Na+/K+ pump in mouse diaphragm muscle was investigated. Resting membrane potentials of muscle cells were measured with glass microelectrodes. In fresh diaphragm preparations from 7-oxo-prostacyclin-pretreated mice (50 micrograms.kg-1 7-oxo-prostacyclin i.p. 30-34 h prior to the experiment) resting membrane potentials were significantly higher (-83.86 +/- 1.40 mV, mean +/- S.E.M.) than in control preparations (-70.78 +/- 1.07 mV). Ouabain at a concentration of 10(-4) mol.l-1 abolished this hyperpolarization (P < 0.05). The electrogenic effect induced by addition of 5 mmol.l-1 K+ to Na(+)-loaded muscles from 7-oxo-prostacyclin-pretreated animals was also enhanced (delta resting membrane potential = 21.73 +/- 3.13 mV) compared with that of the controls (delta resting membrane potential = 18.36 +/- 1.29 mV). Ouabain antagonized the increase in electrogenicity of Na(+)-loaded diaphragms induced by 7-oxo-prostacyclin pretreatment (P < 0.05). In contrast to control preparations, no inhibition of the electrogenic effect induced by 10 mmol.l-1 Ca2+ ions in Na(+)-loaded muscles was observed in diaphragms from 7-oxo-prostacyclin-pretreated animals. In acute experiments with Na(+)-loaded muscles, where 10(-7) mol.l-1 7-oxo-prostacyclin was added to the bath, resting membrane potential reached up to -100 mV. The electrogenic pump-induced increase in resting membrane potential amounted to approximately 30 mV. This effect could be also abolished by 10(-4) mol.l-1 ouabain (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of calcium and calcium channel blockers on sodium pump

The effects of 10 mM Ca2+ and Ca2+ channel blockers verapamil, diltiazem and flunarizine on the ouabain-sensitive electrogenic Na+, K+ pump activity of mouse diaphragm muscle fibres enriched with Na+ were compared with the changes in cytosolic [Ca2+]. The electrogenic Na+ pump activity produced by adding K+ to muscles previously bathed for 4 h in a K(+)-free, 2-mM [Ca2+] solution increased the resting membrane potential by about 18 mV. This hyperpolarization was completely inhibited after 10 min incubation in 10 mM Ca2+. Verapamil 10(-5) M, 10(-5) M diltiazem and 10(-7) M flunarizine effectively prevented the effect of elevated [Ca2+]. At these concentrations, these drugs did not affect the K(+)-induced hyperpolarization. In mouse diaphragm, the basal cytosolic [Ca2+] measured by the fluorescent indicator 1-[2-(5-carboxyoxazol-2-yl)-6- aminobenzofuran-5-oxy]2-(2'-amino-5'-methylphenoxy)ethane-N,N,N',N '- tetraacetic acid acetoxymethyl ester (fura-2/AM) was 261 +/- 6 nM. After 4 h in a Liley K(+)-free, 2 mM [Ca2+] solution, the cytosolic [Ca2+] increased to 314 +/- 28 nM. Increase in [Ca2+] from 2 to 10 mM caused a twofold increase of cytosolic [Ca2+] to 637 +/- 26 nM. This rise was, like the Ca(2+)-induced inhibition of electrogenic pump, prevented by 10(-5) M verapamil, 10(-5) M diltiazem and 10(-7) M flunarizine. The results suggest that substances which block Ca2+ entry into the cell prevent the Ca(2+)-induced inhibition of the Na+ pump.

The effect of mixed bovine brain gangliosides on hypoxic conduction block in control and streptozotocin-diabetic rats

This study describes the electrophysiological responses of endoneurial preparations derived from rat sciatic nerve to acute hypoxia in vitro. Preparations from control rats exhibited a 40% decline in compound action potential (CAP) amplitude after 40 min exposure to medium gassed with 8% O2. In preparations from 4 week streptozotocin-diabetic rats CAP declined by only 29%, indicating a resistance to hypoxic conduction blockade. Treating diabetic rats with mixed bovine brain gangliosides (10 mg/kg/day i.p.) exaggerated this resistance to hypoxic conduction blockade as CAP amplitude fell to only 18% of initial values. In a separate experiment, treating non-diabetic rats with gangliosides (10 mg/kg/day i.p.) or adding gangliosides (400 micrograms/ml) directly to the medium in which control nerves were maintained during in vitro recording also significantly attenuated the decline in CAP amplitude after 40 min hypoxia, thus effectively inducing a resistance to hypoxic conduction blockade similar to that observed in nerves from diabetic rats. These studies demonstrate that the systemic or acute local administration of gangliosides induces a resistance to hypoxic conduction block in normal nerve and exaggerates the resistance to hypoxic conduction block of diabetic rats.

Failure of GM1 ganglioside to influence outcome in experimental focal ischemia

BACKGROUND AND PURPOSE

Reports of improved short-term (less than 72 hours) outcome in experimental models of mechanical and ischemic central nervous system injury suggest that exogenous ganglioside administration may confer a protective effect on neural tissue. We studied the effect of the monosialoganglioside GM1 on cerebral infarction and edema in spontaneously hypertensive rats subjected to permanent focal cerebral ischemia.

METHODS

GM1 or normal saline was injected intramuscularly once a day for 3 days before and 30 and 120 minutes after occlusion of the right middle and common carotid arteries. Following a 24-hour survival period, the volume of infarction was measured by computer-assisted image analysis, and the extent of edema was assessed by measurements of tissue water content and hemispheric volume.

RESULTS

Infarct volume was similar among the GM1-treated (n = 10) and saline-treated (n = 10) rats (212 +/- 10 versus 220 +/- 13 microliters, respectively). In a second series of experiments, the brain water content and edema volume of the ischemic right hemisphere in GM1-treated rats (n = 10) did not differ from saline-treated controls (n = 10).

CONCLUSIONS

GM1 ganglioside does not effectively reduce cerebral infarction caused by permanent focal ischemia.

Inhibition of sodium-potassium-ATPase: a potentially ubiquitous mechanism contributing to central nervous system neuropathology

Direct and indirect evidence suggests that Na+/K(+)-ATPase activity is reduced or insufficient to maintain ionic balances during and immediately after episodes of ischemia, hypoglycemia, epilepsy, and after administration of excitotoxins (glutamate agonists). Recent results show that inhibition of this enzyme results in neuronal death, and thus a hypothesis is proposed that a reduction and/or inhibition of this enzyme contributes to producing the central neuropathy found in the above disorders, and identifies potential mechanisms involved. While the extent of inhibition of Na+/K(+)-ATPase during ischemia, hypoglycemia and epilepsy may be insufficient to cause neuronal death by itself, unless the inhibition is severe and prolonged, there are a number of interactions which can lead to a potentiation of the neurotoxic actions of glutamate, a prime candidate for causing part of the damage following trauma. Presynaptically, inhibition of the Na+/K(+)-ATPase destroys the sodium gradient which drives the uptake of acidic amino acids and a number of other neurotransmitters. This results in both a block of reuptake and a stimulation of the release not only of glutamate but also of other neurotransmitters which modulate the neurotoxicity of glutamate. An exocytotic release of glutamate can also occur as inhibition of the enzyme causes depolarization of the membrane, but exocytosis is only possible when ATP levels are sufficiently high. Postsynaptically, the depolarization could alleviate the magnesium block of NMDA receptors, a major mechanism for glutamate-induced neurotoxicity, while massive depolarization results in seizure activity. With less severe inhibition, the retention of sodium results in osmotic swelling and possible cellular lysis. A build-up of intracellular calcium also occurs via voltage-gated calcium channels following depolarization and as a consequence of a failure of the sodium-calcium exchange system, maintained by the sodium gradient.

tGS ganglioside induces peculiar morphological features in grafted dopaminergic cells and promotes motor recovery in rats with unilateral lesions in the nigrostriatal dopamine pathway

A cell suspension of substantia nigra from fetal rats was introduced into the ipsilateral caudate nucleus of rats with unilateral lesions in the nigrostriatal dopamine pathway, and effects of bovine total ganglioside (tGS) and monosialoganglioside (GM1) treatment on the morphological features of the transplanted cells and recovery from motor imbalance (rotation induced by methamphetamine) were investigated. Gangliosides (30 mg/kg) were administered intraperitoneally once a day for 2 weeks after transplantation to test animals while control animals received saline alone. tGS animals showed definite motor recovery in the 2nd week (P less than 0.05) while control and GM1 animals exhibited slight recovery only. At 6 weeks after transplantation, motor imbalance disappeared in all 3 groups. Tyrosine hydroxylase (TH) immunocytochemical staining revealed that in the 2nd week TH-positive cells in tGS animals had more primary dendrites and more large neurites (meganeurites) than did controls. TH-positive cells of all 3 groups often had spiny processes at that time. In the 20th week, TH-positive cells became more multigonal and had wider dendritic fields in all groups, and had less meganeurites and spines. Motor recovery of each animal was dependent on the number of TH-positive cells and no significant difference was observed in the number of TH-positive cells among the three groups. tGS treatment for 2 weeks without grafting induced immunohistologically no axonal sprouting in the substantia nigra, medial forebrain bundle, accumbens and caudate nucleus when the chemical lesions were complete. Data suggest that tGS induces hypertrophy but not hyperplasia of the transplanted nigral cells, and increases the morphological plasticity. This might be the basis for promotion of recovery in motor function after transplantation.

Efficacy of ganglioside treatment in reducing functional alterations induced by vincristine in rabbit peripheral nerves

Vincristine (VCR) administration to rabbits resulted in severe electrophysiologic alterations of peripheral nerves. Sciatic nerve conduction velocity, compound action potential (CAP) amplitude, and area under the CAP waveform were all reduced in a dose-dependent fashion. In addition, the pattern of conduction velocity of both motor and sensory fibers was altered and shifted toward slow conduction classes. Simultaneous treatment with gangliosides limited significantly the changes in electrophysiologic parameters induced by VCR. It is suggested that gangliosides be given in the clinical setting as protection for the peripheral nerves against the side effects of antiblastic therapy.

Ganglioside function in the development and repair of the nervous system. From basic science to clinical application

Gangliosides play important roles in the normal physiological operations of the nervous system, in particular that of the brain. Changes in ganglioside composition occur in the mammalian brain not only during development, but also in aging and in several neuropathological situations. Gangliosides may modulate the ability of the brain to modify its response to cues or signals from the microenvironment. For example, cultured neurons are known to respond to exogenous ganglioside with changes characteristic of cell differentiation. Gangliosides can amplify the responses of neurons to extrinsic protein factors (neuronotrophic factors) that are normal constituents of the neuron's environment. The systemic administration of monosialoganglioside also potentiates trophic actions in vivo and improves neural responses following various types of injury to the adult mammalian central nervous system. The possible molecular mechanism(s) underlying the ganglioside effects may reflect an action in modulating ligand-receptor linked transfer of information across the plasma membrane of the cell.

Behavioural and morphological changes following treatment with GM-1 ganglioside of rats with an electrolytic lesion of the substantia nigra

The effects of daily treatment with GM-1 ganglioside (30 mg/kg i.p.) or saline (1 ml/kg i.p.) in rats with discrete unilateral electrolytic lesions of the dorsal substantia nigra were investigated. Treatment with GM-1 ganglioside, beginning 3 days prior to surgery and continuing for 33 days post-operatively, caused reductions in the total ipsilateral turns and peak turning rates induced by apomorphine (0.75 mg/kg s.c.) between 7 and 31 days post-operatively, without altering the time course of the effect of apomorphine. No effects of GM-1 on lesion-induced changes in synaptosomal uptake of [3H]dopamine, dopamine, serotonin in the striatum or corresponding levels of metabolites were found. Treatment with GM-1 ganglioside had no effect on the rostrocaudal extent of the electrolytic lesion, but caused morphological changes at the site of the lesion, including a reduction in the density of glial cells. Treatment with GM-1 ganglioside resulted in a relative preservation of cell bodies, staining immunocytochemically for tyrosine hydroxylase, in the substantia nigra pars compacta (expressed as a percentage of the intact side), when compared with saline-treated rats. The results showed that GM-1 ganglioside promoted a partial functional recovery from apomorphine-induced circling, which may be due in part to a reduction in the extent of damage at the lesion site.

GM1 ganglioside potentiates the effect of nerve growth factor in preventing vinblastine-induced sympathectomy in newborn rats

The effects of vinblastine (VNB) and nerve growth factor (NGF) administrations were assessed on sympathetic nerve terminals by measuring the noradrenaline (NA) content in the heart, spleen and kidneys of developing animals. Six-day-old rats, treated with 0.15 mg/kg VNB on postnatal day 3 (P3) showed a dramatic decrease of NA content in all these organs. This reduction was prevented by daily administrations of NGF on P3, P4 and P5. The effectiveness of NGF in inhibiting the VNB-induced sympathectomy was related to the dose administered and to the time interval between the VNB administration and the first NGF injection given on P3. Dose-response curves to NGF (ranging from 0.01 to 0.5 mg/kg) were obtained in both heart and spleen of VNB-treated animals. Thus, this experimental paradigm provides a quantitative assessment of the NGF activity in vivo. The systemic administration of GM1 (30 mg/kg) on P3, P4 and P5, was able to potentiate the NGF activity in preventing the VNB-induced sympathectomy. This GM1 effect was more evident in the heart and may be, at least in part, attributed to increased NGF prevention of neuronal cell death due to VNB. These results suggest an in vivo interaction between exogenous GM1 and NGF and are consistent with the view that neuronal cell repair related to in vivo administration of this ganglioside may rely on its capability to modulate the activity of endogenously occurring neuronotrophic factors.

Ganglioside treatment of streptozotocin-diabetic rats prevents defective axonal transport of 6-phosphofructokinase activity

This study measured axonal transport of 6-phosphofructokinase (PFK) and aldolase activities in the sciatic nerves of rats with short-term streptozotocin-induced diabetes. The diabetic rats showed deficits in anterograde (69% of controls; p less than 0.001) and retrograde (33% of controls; p less than 0.01) accumulations of PFK activity as well as its content per unit length of unconstricted sciatic nerve (86% of controls; p less than 0.05). There were no accumulation deficits in aldolase activity in the nerves of the diabetic rats, although the activity per unit length of unconstricted nerve was deficient (81% of controls; p less than 0.05). Treatment of diabetic rats with mixed bovine brain gangliosides (10 mg/kg of body weight/day, i.p.) did not affect the deficit in PFK activity in unconstricted nerve (84% of ganglioside-treated controls; p less than 0.01), but all the other defects in enzyme activities were prevented completely. The diabetic rats also showed a reduction of 7% (p less than 0.01) in sciatic nerve dry weight per unit length, which was prevented by ganglioside treatment. In contrast, the reduced motor nerve conduction velocity, accumulation of polyol pathway metabolites, and depletion of myo-inositol, characteristic of untreated short-term diabetes, were unaffected by ganglioside treatment.

Arachidonate activates muscle electrogenic sodium pump and brain microsome Na+,K+-ATPase under suboptimal conditions

Arachidonate 5 x 10(-5) mol.l-1 increased the rate of hyperpolarization induced in Na+-loaded mouse diaphragm fibers by 5 mmol.l-1 K+. When applied to Na+-loaded muscles without potassium, arachidonate 1 x 10(-6) and 5 x 10(-5) mol.l-1 induced a ouabain-sensitive hyperpolarization of the muscle fibers. The activity of rat brain microsomal Na+,K+-ATPase was stimulated by 1 x 10(-7)-5 x 10(-6) mol.l-1 arachidonate in reaction media with reduced amounts of ATP or K+ and after short-lasting sonication of the samples. It was concluded that, under particular conditions, arachidonate might serve as a Na+,K+-ATPase activator or inhibitor regulating its ion transport and electrogenicity.

Ganglioside treatment: reduction of CNS injury and facilitation of functional recovery

Increased attention has focused on the use of brain gangliosides as a treatment for brain injury. This review traces the progression of in vitro and in vivo research which led to studies which have demonstrated that ganglioside treatment can facilitate recovery after CNS damage in animal models (for example, lesions, transections, hypoxia, ischemia). Hypotheses regarding the ability of gangliosides to stimulate neuronal plasticity, modulate trophic factors and reduce injury processes are presented.

Acute effects of GM1 ganglioside: reduction in both behavioral asymmetry and loss of Na+, K+-ATPase after nigrostriatal transection

GM1 ganglioside injections (i.p.) reduce amphetamine-induced asymmetric rotation in rats 48 h after a partial unilateral transection of the nigrostriatal pathway. We found that this reduction was maximal when rats received their first GM1 injection within 2 h after surgery. Rats injected 4-12 h after surgery, or rats only pretreated with GM1, showed no significant effect on rotation. Striatal membrane Na+,K+-ATPase in rats injected with GM1 0-2 h after hemitransection showed only a 10% loss in activity (versus the untransected hemisphere) as compared to control losses of 38%. The maintenance of membrane Na+,K+-ATPase activity in GM1-treated rats may be one mechanism by which a balance between hemispheres in striatal dopaminergic transmission is preserved, resulting in reduced asymmetric rotation. The observation that there is a critical postsurgical period when GM1 administration results in optimal functional recovery supports our hypothesis that gangliosides are exerting an acute effect on damaged CNS tissue. This acute effect is further evidenced by the reduced loss of membrane Na+,K+-ATPase following injury.

Impaired axonal transport of acetylcholinesterase in the sciatic nerve of alloxan-diabetic rats: effect of ganglioside treatment

The anterograde and retrograde axonal flow of acetylcholinesterase were studied in the sciatic nerve of alloxan-diabetic rats after five weeks of experimental diabetes. A slight reduction of the anterograde axonal flow of the enzyme was found in alloxan-diabetic compared to control rats. Sedimentation analysis revealed a major reduction of anterograde axonal flow of the light globular forms of the enzyme (G1 + G2), which are probably conveyed by slow transport. There was also a minor reduction of the anterograde flow of the globular form G4, while no modification of the axonal flow of the heavy asymmetric form A12 was found. Both G4 and A12 molecular forms are conveyed by fast axonal transport. In contrast, no abnormality of the retrograde axonal flow of acetylcholinesterase was observed. Ganglioside treatment antagonized the decline of the anterograde axonal flow of the enzyme in alloxan-diabetic rats. These results are consistent with the view that experimental diabetic neuropathy is associated with axonal transport defects, and suggest a protective effect of ganglioside treatment against neuronal damage(s) related to the diabetic syndrome.

In vivo treatment with GM1 prevents the rapid decay of ATPase activities and mitochondrial damage in hippocampal slices

Slices from rat CA3 hippocampal area show a 30% decrement in ATPase activity after 35 min of 'in vitro' incubation. Such a drop is accompanied by an alteration of mitochondrial ultrastructure. However, if rats are treated daily with GM1 ganglioside (10 mg/kg during 3 days) both phenomena are fully prevented. These results would suggest a protective effect of gangliosides onto membrane structures under stress conditions.

GM1 ganglioside counteracts selective neurotoxin-induced lesion of developing serotonin neurons in rat spinal cord

The effect of exogenous monosialoganglioside GM1 on neurotoxin-induced lesioning of bulbo-spinal serotonergic neurons of newborn rats was studied by means of biochemical and immunocytochemical techniques. 5,7-dihydroxytryptamine (5,7-HT, a selective serotonin neurotoxin) treatment of newborn rats caused a pronounced reduction of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels in the thoracic and lumbar spinal cord, while an increase of 5-HT and 5-HIAA was found in the pons medulla. These biochemical alterations were regionally correlated with similar changes in 5-HT nerve terminal density analyzed by image analysis. GM1 administration (30 mg/kg for 4 consecutive days) antagonized the reduction of 5-HT and 5-HIAA levels induced by 5,7-HT treatment in the lumbar spinal cord of 2-month-old rats, as well as the decrease of 5-HT nerve terminal density in both thoracic and lumbar spinal cord of 1- and 2-month-old rats. A minor counteracting effect of GM1 was found in the pons medulla where the neurotoxin induced an increase of 5-HT and 5-HIAA levels. These data support the hypothesis that GM1 may have a preventing action on retrograde degenerative processes following chemical lesion and/or a growth-stimulating effect on injured 5-HT neurons.

Quantitative analysis of myelin and axolemma particle distribution in C57BL/Ks diabetic mice and the effects of ganglioside treatment

By freeze-fracture technique we estimated myelin and axolemma intramembranous particle density in C57BL/Ks mice. A decrease in myelin particle content compared to controls is present in both 180 and 280 day old genetic diabetic mice. In addition, the axolemma of myelinated axons is affected in interparanodal regions while no modification was detected at nodal level. Such alterations of myelin membrane structure may also be responsible for the lower motor nerve conduction velocity (MNCV) observed in these diabetic mice; however this hypothesis cannot be taken into consideration for the reduction in MNCV at the early stage of the neuropathy (prior to 180 days of life). Therefore the structural changes of both myelin sheath and interparanodal axolemma as visualized by freeze-fracture are most likely related to late complications of the disease instead of being responsible for the changes in excitability. The low myelin and axolemma particle density of diabetic mice was found normal after 30 days' treatment with gangliosides. Such findings are in agreement with previous results on a significant effect of ganglioside treatment on MNCV and axonal area alterations in 180 and 280 day old genetic diabetic mice.

Correlation of sinus slowing and hyperpolarization caused by adenosine in sinus node

The effect of adenosine on sinus node cells was examined in a preparation that precluded pacemaker shift. It was found that adenosine produced a dose-dependent slowing in rate. In examining the effects on the action potential parameters (n = 10), adenosine caused a significant increase in the maximum diastolic potential (control = -62 +/- 2 mV, adenosine, 1 X 10(-4) M, = -67 +/- 3 mV) and a significant increase in the rate of rise of the action potential (control = 3.3 +/- 0.6 V/s, adenosine, 1 X 10(-4) M, = 7.2 +/- 2 V/s). There was only a slight shortening of the action potential duration and a small increase in the action potential overshoot. Adenosine caused a significant decrease in the rate of diastolic depolarization (control = 100 +/- 19 mV/s, adenosine, 1 X 10(-4) M, = 42 +/- 5 mV/s). Acetylcholine caused similar effects. The effects of adenosine were not affected by atropine or propranolol but were antagonized by aminophylline, an adenosine competitive antagonist. In another set of experiments (n = 12) we sought to understand further the mechanism of sinus slowing caused by adenosine and compare with the effects of acetylcholine. The increase in cycle length due to different doses of adenosine and acetylcholine was measured. The preparation was then arrested with D-600 or NiCl2. The cells were then exposed to the same concentrations of adenosine and acetylcholine and the amount of hyperpolarization from the resting potential (means = -40 +/- 4 mV) was measured. The change in cycle length and amount of hyperpolarization were linearly correlated (r = 0.86).(ABSTRACT TRUNCATED AT 250 WORDS)