Relationship between intrathecal baclofen and the central nervous system

The GABA(B) receptor agonists display a number of pharmacological effects including central muscle relaxation, decreased self-administration of cocaine and narcotic drugs, antinociception, cognitive impairment as well as enhancement of synaptic plasticity. The main relationships between intrathecal or intracerebral baclofen and the Central Nervous System (CNS) are reviewed with particular attention to actions on pain, epilepsy and basal ganglia regulation. Since baclofen may be involved in synaptic plasticity and the development of neuronal pathways, the main issues of this field are reviewed with particular attention to the effects of baclofen on the developing brain. The role of baclofen in the regulation of movement has not been clearly understood, but recent findings support its important involvement in globus pallidus and subthalamic nucleus. The neuroprotective action of baclofen in cerebral ischemia is a matter of debate. The effects of baclofen in cognition and attention are another important issue because patients with chronic intrathecal baclofen (ITB) administration often present with impairment of cognitive functions. Drug craving and its improvement after baclofen administration is also reviewed. Finally, the clinically interesting results on the regulation of food intake and blood pressure are highlighted. The preliminary experience on the effects in cortical neuron viability at different concentrations of ITB is reported.

Protection of intrinsic nerves of guinea-pig detrusor strips against anoxia/glucopenia and reperfusion injury by taurine

There is ample evidence that ischaemia is associated with partial denervation of the detrusor muscle and that this is responsible for much of its abnormal contractile behaviour, resulting in bladder dysfunction (instability). In guinea-pig nerves are very susceptible to the ischaemic damage as compared to the muscle cells. The purpose of this study was to assess the neuroprotection afforded by taurine on guinea-pig detrusor under ischaemic-like conditions. Guinea-pig detrusor strips were subjected for 60 min to ischaemic-like conditions, followed by 150 min reperfusion. Intrinsic nerves underwent every 30 min electrical field stimulation (EFS) by 5-s trains of square voltage pulses of 0.05 ms duration (15 Hz, 50 V). Detrusor strips were perfused with 0.1, 1, 3 or 10 mM taurine during the ischaemia-like exposure and the first 30 min of reperfusion. Taurine (1 and 3 mM) significantly improved the response of the strips to EFS both at the end of ischaemia and reperfusion. On the contrary, neither 0.1 nor 10 mM taurine had significant effects. It is concluded that taurine can partially counteract the ischaemia-reperfusion injury in the guinea-pig urinary bladder.

3,5-di-t-butyl-4-hydroxyanisole (DTBHA) activation of rat skeletal muscle sarcoplasmic reticulum Ca(2+)-ATPase

3,5-Di-t-butyl-4-hydroxyanisole (DTBHA) increased in a concentration-dependent manner (calculated pEC(50) = 4.55 +/- 0.18 M) the oxalate-stimulated Ca(2+)-pumping rate of rat skeletal muscle sarcoplasmic reticulum (SR) vesicles. Kinetic analysis of this effect suggested that the activation of SR Ca(2+)-ATPase operated by (DTBHA) was of both mixed and non-competitive type with respect to ATP in the range of concentrations 0.1-0.5 mM and above 1 mM, respectively; furthermore, it was independent of the free Ca(2+) concentrations. This indicated that the enzyme activation took place through the acceleration of the enzyme-substrate complex breakdown. Moreover, it appeared that its target site was cyclopiazonic acid sensitive. The uncommon ability of (DTBHA) to upregulate SR Ca(2+) uptake is of interest in view of its possible use for treating pathological conditions characterised by cell Ca(2+) overload as well as genetic disorders where SR Ca(2+) homeostasis is altered.

Neuroprotection afforded by some hindered phenols and alpha-tocopherol in guinea-pig detrusor strips subjected to anoxia-glucopenia and reperfusion-like conditions

2-t-butyl-4-methoxyphenol (BHA), 3,5-di-t-butyl-hydroxyanisole (DTBHA), 2,6-diisopropylphenol (propofol), alpha-tocopherol (alpha-TOC) and two newly synthesised analogues of BHA, namely 1-O-(4-hydroxy-3-t-butyl)phenyl-2,3,4,6-tetra-O-acetyl-beta-D-glucopyranose (beta-TAG) and 1-O-(4-hydroxy-3-t-butyl)phenyl-beta-D-glucopyranose (beta-GLU), were tested for their capability to protect the intrinsic nerves of guinea-pig urinary bladder from damage due to anoxia-glucopenia and re-exposure to glucose and O2. Guinea-pig detrusor strips were mounted for tension recording in small organ baths, superfused with warmed Krebs solution and the nerves stimulated electrically either under control or ischaemia-like (anoxia-glucopenia) and reperfusion-like conditions (normal medium re-superfusion). The Ca2+ antagonist activity of the compounds was assessed by their effect on the contraction of detrusor strips induced by 60 mM K+ Krebs solution in the presence of either 0.5 mM or 5 mM Ca2+. The antioxidant activity was illustrated by the ability of the compounds to scavenge peroxyl radicals generated by linoleic acid oxidation. All the compounds, except beta-GLU and alpha-TOC, inhibited in a concentration-dependent manner K+-induced contractions of detrusor muscles, the inhibition being inversely related to the Ca2+ concentration of the perfusion solution; moreover, they exhibited a marked antiperoxidant activity with pIC50 values decreasing in the order: DTBHA > alpha-TOC > BHA > beta-TAG > propofol > beta-GLU. alpha-TOC, BHA, DTBHA and beta-TAG improved significantly the response of the strips to electrical field stimulation either during the anoxia-glucopenia phase or thereafter when recovering during reperfusion, as compared to untreated tissues. The neuroprotection afforded by the phenol derivatives as well as by alpha-TOC was positively correlated to their antioxidant activity, but not to their Ca2+ antagonist activity.

Pulsed electromagnetic fields affect the intracellular calcium concentrations in human astrocytoma cells

Experiments assessed whether long term exposure to 50 Hz pulsed electromagnetic fields with a peak magnetic field of 3 mT can alter the dynamics of intracellular calcium in human astrocytoma U-373 MG cells. Pretreatment of cells with 1.2 microM substance P significantly increased the [Ca(2+)](i). The same effect was also observed when [Ca(2+)](i) was evaluated in the presence of 20 mM caffeine. After exposure to electromagnetic fields the basal [Ca(2+)](i) levels increased significantly from 143 +/- 46 nM to 278 +/- 125 nM. The increase was also evident after caffeine addition, but in cells treated with substance P and substance P + caffeine we observed a [Ca(2+)](i) decrease after exposure. When we substituted calcium-free medium for normal medium immediately before the [Ca(2+)](i) measurements, the [Ca(2+)](i) was similar to that measured in the presence of Ca(2+). In this case, after EMFs exposure of cells treated with substance P, the [Ca(2+)](i), measured without and with addition of caffeine, declined from 824 +/- 425 to 38 +/- 13 nM and from 1369 +/- 700 to 11 +/- 4 nM, respectively, indicating that electromagnetic fields act either on intracellular Ca(2+) stores or on the plasma membrane. Moreover the electromagnetic fields that affected [Ca(2+)](i) did not cause cell proliferation or cell death and the proliferation indexes remained unchanged after exposure.

Vasoactive intestinal peptide protects guinea-pig detrusor nerves from anoxia/glucopenia injury

Vasoactive intestinal peptide (VIP) was tested for its capability to protect the intrinsic nerves of guinea-pig urinary bladder from damage due to anoxia/glucopenia and reperfusion. Guinea-pig detrusor strips were mounted for tension recording in small organ baths and the nerves were subjected to electric field stimulation. VIP (0.3 microM) improved significantly the response of strips to electrical field stimulation either during anoxia/glucopenia or thereafter during reperfusion, as compared to untreated tissues. The antioxidant activity of VIP assessed as its capability to scavenge peroxyl radicals during linoleic acid oxidation corresponded to 6.42+/-0.13 pIC(50) M, i.e. close to the concentration proved to protect strips against the anoxic--glucopenic and reperfusion damage.

Mechanical response to electrical field stimulation of rat, guinea-pig, monkey and human detrusor muscle: a comparative study

The aim of the present investigation was to compare mechanical responses to electrical field stimulation (EFS), as well as cholinergic and non-adrenergic, noncholinergic (NANC) neurotransmission in guinea-pig, rat, monkey and human detrusor muscle strips. Responses to EFS (0.05, 0.5 and 1 ms pulse duration, 50 V, 1-15 Hz) of guinea-pig, rat, monkey and human detrusor muscle strips were recorded isometrically before and after blockade of muscarinic receptors and/or P2-purinoreceptors, as well as after desensitisation of P2-purinoceptors or blockade of the nerve impulse propagation. Single pulses of 0.05 ms duration elicited responses, in either guinea-pig or rat detrusor strips, which were abolished by tetrodotoxin (TTX), thus suggesting their neurogenic nature. In monkey and human detrusor strips, however, the same single pulses were not sufficient to generate contractile responses. The response of either rat or guinea-pig strips to single pulses of 0.5 ms and 1 ms duration was mainly myogenic in nature. While in rat and guinea-pig strips the neurogenic response was only partly reduced in the presence of atropine, in monkey and human strips it was abolished. In the presence of atropine, while suramin only partially reduced the EFS response either in rat or guinea-pig detrusor strips, a complete alpha,beta-methyleneATP-sensitive response was evident in guinea-pig detrusor strips. This suggests the involvement of other transmitter(s) beyond ATP in the NANC response of rat detrusor strips.

The effect of pulsed electromagnetic fields on the physiologic behaviour of a human astrocytoma cell line

We evaluated the effects of 50 Hz pulsed electromagnetic fields (EMFs) with a peak magnetic field of 3 mT on human astrocytoma cells. Our results clearly demonstrate that, after the cells were exposed to EMFs for 24 h, the basal [Ca(2+)](i) levels increased significantly from 124+/-51 nM to 200+/-79 nM. Pretreatment of the cells with 1.2 microM substance P increased the [Ca(2+)](i) to 555+/-278 nM, while EMF exposure caused a significant drop in [Ca(2+)](i) to 327+/-146 nM. The overall effect of EMFs probably depends on the prevailing Ca(2+) conditions of the cells. After exposure, the proliferative responses of both normal and substance P-pretreated cells increased slightly from 1.03 to 1.07 and 1.04 to 1.06, respectively. U-373 MG cells spontaneously released about 10 pg/ml of interleukin-6 which was significantly increased after the addition of substance P. Moreover, immediately after EMF exposure and 24 h thereafter, the interleukin-6 levels were more elevated (about 40%) than in controls. On the whole, our data suggest that, by changing the properties of cell membranes, EMFs can influence Ca(2+) transport processes and hence Ca(2+) homeostasis. The increased levels of interleukin-6 after 24 h of EMF exposure may confirm the complex connection between Ca(2+) levels, substance P and the cytokine network.

On the mechanisms of the antispasmodic action of some hindered phenols in rat aorta rings

The antispasmodic effects of 3-t-butyl-4-hydroxyanisole (BHA) and some structurally related compounds were investigated in endothelium-intact rat aorta rings. Nordihydroguaieretic acid (NDGA), BHA, 3,5-di-t-butyl-4-hydroxyanisole (DTBHA), 2,6-di-isopropyl phenol (propofol) and 2,2'-dihydroxy-3,3'-di-t-butyl-5, 5'-dimethoxydiphenyl (DIBHA) did not cause relaxation when added at the plateau of phenylephrine-evoked contraction, nor did they affect the concentration-relaxation curve for acetylcholine in precontracted rings. In rings depolarised with physiological salt solution (PSS) containing 40 mM K(+), NDGA, BHA, DTBHA, 2, 5-di-t-butyl-1,4-benzohydroquinone (BHQ), propofol and nifedipine, but not DIBHA, inhibited the contraction induced by cumulative addition of Ca(2+) (0.05-10 mM) in a concentration-dependent manner; this inhibition was inversely related to the Ca(2+) concentration. In 40 mM K(+) PSS, 25 nM nifedipine blocked the 1 mM Ca(2+)-induced contraction, whereas 50 microM DTBHA, NDGA, BHA, BHQ and propofol significantly antagonised it by 84.4%, 73.0%, 52.8%, 45.6% and 35.7%, respectively. In the presence of 1 microM methyl-1,4-dihydro-2, 6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine-5-carboxylate (Bay K 8644), the response to Ca(2+) did not differ from control values with nifedipine and BHQ, was partially restored with DTBHA and NDGA, and was not affected with BHA and propofol. Nifedipine markedly inhibited (85.2%) the Ba(2+)-induced contraction and this effect was totally reversed by Bay K 8644. BHA and DTBHA showed antispasmodic activity (45.3% and 43.1%, respectively) which was partly reversed by Bay K 8644. In contrast, Bay K 8644 did not affect the inhibition exerted by BHQ, NDGA and propofol (69.5%, 53. 3% and 46.1%, respectively). Nifedipine, BHA, DTBHA, propofol and NDGA inhibited the contractile response to 1 mM Ca(2+) of aorta rings depolarised with 40 or 80 mM K(+) PSS to a similar extent. Cromakalim inhibited the Ca(2+)-evoked contraction only in 30 mM K(+) PSS and BHQ only in 80 mM K(+) PSS. DIBHA had no effect on this model. Cromakalim, but not BHA, stimulated 86Rb(+) efflux from ring preparations. In 80 mM K(+) PSS containing 1 microM nifedipine, only papaverine affected the phenylephrine-induced contraction. Moreover, when the rings were preincubated with 1 mM Ni(2+), the response to phenylephrine in the presence of BHQ was significantly reduced. In conclusion, we propose that BHA may non-specifically inhibit Ca(2+) influx at the plasmalemma level rather than affect the function of K(+) channels, Ca(2+) release from intracellular stores or endothelium-dependent relaxation.

Cytochrome P450-dependent N-dealkylation of L-deprenyl in C57BL mouse liver microsomes: effects of in vivo pretreatment with ethanol, phenobarbital, beta-naphthoflavone and L-deprenyl

The monoamine oxidase inhibitor L-deprenyl [(-)-deprenyl, selegiline] is an effective therapeutic agent for improving early symptoms of idiopathic Parkinson's disease. It appears to exert this action independently of its inhibition of monoamine oxidase B (MAO-B) and some of its metabolites are thought to contribute. Cytochrome P450 (CYP) activities are known to give rise to L-deprenyl metabolites that may affect the dopaminergic system. In order to clarify the interactions of L-deprenyl with these enzymes, C57BL mice were treated with L-deprenyl, ethanol, phenobarbital or beta-naphthoflavone to induce different CYP isozymes. After preincubation of L-deprenyl with liver microsomes from control or treated mice, the metabolites were analysed by a GLC method. L-deprenyl (10 mg/kg i.p. for 3 days) caused a significant decrease in total CYP levels (0.315+/-0.019, L-deprenyl; 0.786+/-0.124, control, nmol/mg protein) and CYP2E1-associated p-nitrophenol hydroxylase activity (0.92+/-0.04 vs. 1.17+/-0.06 nmol/min/mg). Both phenobarbital and ethanol increased the N-depropynylation activity towards L-deprenyl that leads to the formation of methamphetamine (4. 11+/-0.64, phenobarbital; 4.77+/-1.15, ethanol; 1.77+/-0.34, control, nmol/min/mg). Ethanol alone increased the N-demethylation rate of L-deprenyl, that results in formation of nordeprenyl (3.99+/-0.68, ethanol; 1.41+/-0.31, control, nmol/min/mg). Moreover, the N-dealkylation pathways of deprenyl are inhibited by 4-methylpyrazole and disulfiram, two CYP2E1 inhibitors. None of the other treatments modified L-deprenyl metabolism. These findings indicate that mainly CYP2E1 and to a lesser extent CYP2B isozymes are involved in L-deprenyl metabolism. They also suggest that, by reducing CYP content, L-deprenyl treatment may impair the metabolic disposition of other drugs given in combination regimens.

The effect of anoxia and glucose-free solutions on the contractile response of guinea-pig detrusor strips to intrinsic nerve stimulation and the application of excitatory agonists

PURPOSE

To study the effects of anoxia and substrate depletion, both separately and combined, on the contractile responses of guinea-pig detrusor smooth muscle strips to activation of intrinsic nerves, application of agonists and depolarization with high potassium solution.

MATERIALS AND METHODS

Bladders were opened and the urothelium removed. Strips of detrusor were dissected and mounted for tension recording in small organ baths superfused with warmed solutions of known composition.

RESULTS

Anoxia caused a small initial reduction of the contractile responses which then remained constant for several hours. Glucose-free solutions resulted in a slow progressive decline in the responses to field stimulation, carbachol and high potassium solution, with substantial responses still present after five hours. The response to ATP, however, was unaffected. Removal of oxygen and glucose, mimicking ischaemia, caused abolition of all responses within an hour. After reintroduction of normal conditions responses reached their maximal extent of recovery within an hour. Recovery was almost complete for responses to ATP and carbachol, but less so for high K+ solutions. Very little recovery to stimulation of intrinsic nerves was seen.

CONCLUSIONS

The results demonstrate that phasic contractions can be fuelled almost fully by oxidative phosphorylation or by anaerobic glycolysis, but that in conditions mimicking ischaemia the intrinsic nerves are more susceptible to ischaemic damage than the detrusor smooth muscle.