Lack of effect of baclofen on substance P and somatostatin release from the spinal cord in vitro

Summary High concentrations of K⁺ increase the release of substance P (SP) and somatostatin (SRIF) from superfused slices of rat spinal cord. This increase is Ca-dependent. Baclofen (100–500 M) does not significantly alter the K⁺-evoked release of SP or SRIF. Stereoisomers of baclofen and GABA, similarly, are without effect. The spinal analgesic action of baclofen does not appear to be due to alterations in the release of SP or SRIF.     

Inhibitory effects of GABA,L-glutamic acid and nicotine on the potassium-evoked release of subsaance P in substantia nigra slices of the rat

Rat substantia nigra slices were superfused with a physiological medium containing a diluted substance P (SP) antiserum, bacitracin and serum albumin to measure SP released in superfusates. As shown by measuring the degradation of a SP-labelled derivative incubated with cerebellar slices, this medium prevented the enzymatic inactivation of SP. Potassium (K⁺, 50 mM) and veratridine (5 × 10^?5M) stimulated SP release and these effects were respectively prevented in absence of calcium and in presence of tetrodotoxin (5 × 10^?7 M). GABA (5 × 10^?5 M) nicotine (10^?6 M) and L-glutamic acid (5 × 10^?5 M) reduced the K⁺ (50 mM)-evoked release of SP. In contrast, glycine (5 × 10^?5 M), oxotremorine (5 × 10^?5 M), D-glutamic acid (5 × 10^?5 M) and serotonin (5 × 10^?5 M) were without effect. Pempidine (10^? M) prevented the inhibitory effect of nicotine (10^? M) on the K⁺-evoked release of SP. Glutamic acid diethyl ester (10^?4 M) completely abolished the L-glutamic acid-induced inhibition of the K⁺-evoked release of SP. Picrotoxin (5 × 10^?5 M) did not influence the L-glutamic acid inhibitory effect excluding the intervention of GABAergic mechanisms.     

Presynaptic serotonin receptors regulate the release of 3H-serotonin in hypothalamic slices of the rabbit

Summary Hypothalamic slices of the rabbit brain were incubated with 10^–7 M of ³H-serotonin (³H-5HT). After the incubation and an initial washout period, a nearly constant basal efflux of tritium was detected. This basal efflux was not significantly altered by Ca²⁺-free solution or by the 5HT-antagonist metitepin (10^–5 M), but was augmented by chlorimipramine (10^–5 M) and by unlabelled 5HT (10^–6 M); the acceleration caused by unlabelled 5HT was absent in presence of chlorimipramine (10^–5 M). Both electrical stimulation (4 Hz, 50 mA, 2 min) and high K⁺ (50 mM) induced an overflow of ³H. This overflow was nearly abolished in Ca²⁺-free solution. In presence of chlorimipramine (10^–5 M) both the tritium overflow evoked by electrical stimulation and that evoked by high K⁺ were augmented by metitepin (10^–5 M) and decreased in a concentration dependent manner by unlabelled serotonin (10^–8–10^–6 M); the latter effect was antagonized by metitepin (10^–6 M and 10^–5 M). These experiments suggest that in rabbit hypothalamic slices, the release of ³H-5HT is controlled by a negative feedback mechanism acting via presynaptic serotonin receptors.     

Noradrenaline release from slices of the thalamus of normal and morphine-dependent rats

Summary The effect of morphine on potassium-induced stimulation of (³H)-noradrenaline release from slices of the rat thalamus was investigated. The in vitro addition of morphine (10^–6 M) significantly depressed potassium-induced tritium overflow by 42% and this was prevented by the prior addition of naloxone (3×10^–6 M) to the medium. The stimulation-evoked overflow of tritium from slices of the thalamus of morphine-dependent rats was not significantly different from normal controls. Addition of naloxone (10^–5 M) 10 min before exposure of the tissues to 20 mM K⁺ significantly enhanced noradrenaline release from dependent slices. The results suggest that the basic release mechanism may have adapted to the continuous presynaptic inhibition of release by morphine.     

Substance P enhances the release of endogenous serotonin from rat ventral spinal cord

The effect of the tachykinin neuropeptides, substance P (SP), neurokinin A (NKA) and the neurokinin B (NKB) receptor agonist, senktide, on the potassium-evoked release of endogenous serotonin (5-hydroxytryptamine, 5-HT) was investigated in superfused tissue slices of rat ventral spinal cord, where 5-HT is known to coexist with SP. Endogenous 5-HT was assayed by HPLC with electrochemical detection. The evoked release of 5-HT was significantly enhanced by 10(-4) M SP (190% increase) and 10(-5) M SP (74% increase) but not by 10(-6) M SP, NKA (10(-5) and 10(-4) M) and senktide (10(-5) and 10(-4) M) had no significant effect on the 5-HT release. The results suggest that, in the rat ventral spinal cord, where most of the 5-HT and SP is stored in the same nerve endings. SP but not NKA nor NKB potentiates the evoked release of 5-HT in a dose-dependent manner.     

Investigation of possible interactions between substance P and transmitter mechanisms in the substantia nigra and corpus striatum of the rat

The effect of substance P (SP) on the uptake and release of radiolabelled dopamine (³H-DA), 5-hydroxytryptamine (³H-5-HT) and γ-aminobutyric acid (³H-GABA) was studied in slices of rat substantia nigra and corpus striatum. SP, 10^?9 to 10^?5m , failed to modify the uptakes of these compounds during incubations (10–90 min) with slices of either brain region. SP, 10^?6m , had no apparent effect on the spontaneous output of any of these compounds in either substantia nigra or corpus striatum. In the corpus striatum, SP seemed to potentiate the potassium-stimulated outflow of ³H-DA and ³H-5-HT, but not ³H-GABA, while the releases from substantia nigra were unaffected. Morphine (10^?3m ), but not met-enkephalin (5 × 10^?6m ), weakly antagonized K⁺-evoked release of ³H-DA in the corpus striatum. These results are discussed with reference to the possible interaction of SP with transmitter mechanisms at presynaptic sites in the central nervous system.     

Regional differences in the electrically stimulated release of endogenous and radioactive adenosine and purine derivatives from rat brain slices

Summary The release of both radioactive and endogenous purines was investigated in rat brain cortical, hippocampal and striatal slices at rest and following stimulation with electrical fields.Purities were labelled by incubating the slices with ³H-adenine. The purine efflux at rest and that evoked by electrical stimulation (10 Hz, 5 min) was analyzed by HPLC with ultraviolet absorbance detection. Both radio-active and endogenous purines in the effluent consisted mainly of hypoxanthine, xanthine, inosine and adenosine. No qualitative differences in the composition of the released purines were found in the three areas investigated. Electrical stimulation evoked a net increase in both radioactive and endogenous purine release. However the increase in ³H-adenosine following electrical stimulation was twice as large as that of endogenous adenosine. The electrically evoked release of both radioactive and endogenous purines was greatest in hippocampal slices and progressively smaller in cortical and striatal slices. In the three areas the addition of 0.5 M tetrodotoxin to the superfusing Krebs solution brought about a similar (83–100%) reduction in evoked ³H-purine and endogenous purine release. Superfusion of the slices with calcium-free Krebs solution containing 0.5 mM EGTA reduced evoked release of ³H-purines by 58–60% and that of endogenous purine components by 54–89%.The results demonstrate similar characteristics for both radioactive and endogenous purine release but indicate that the most recently synthetized adenosine is the most readily available for release. The features of the electrically evoked purine release support a neuronal origin of adenosine and derivatives and are consistent with the hypothesis of discrete regional differences in adenosine neuromodulation. Send offprint requests to F. Pedata at the above address     

Agonist-Induced Substance P Receptor Down-Regulation in Rat Central Nervous System

Rat brain slices were incubated with substance P (SP), and the SP receptors on the membranes from those slices were characterized by a ³H-SP binding technique. The number of substance P receptors measured in the extensively washed membrane preparations pretreated with 3 × 10^–5 M SP was reduced by 30% compared with that in nontreated membranes. This reduction was dependent on the incubation time and temperature. The metabolic inhibitors sodium azide and 2,4-dinitrophenol protected SP receptors from the reduction. The characteristics of ³H-SP incorporation into rat brain slices were similar to those of SP receptor down-regulation, that is, the ³H-SP incorporation was time, temperature, and energy dependent. Thus these results indicate that the processes of ligand incorporation and receptor down-regulation are closely associated phenomena. These observations may be important in elucidating the phenomenon of SP-induced desensitization.     

Effect of neuroactive peptides on labeled 5-hydroxytryptamine release from rat spinal slices in vitro

Effects of neuroactive peptides on the release of labeled 5-hydroxytryptamine (5-HT) from preloaded rat spinal cord slices were investigated. The 5-HT release was significantly stimulated by somatostatin (10-50 microM) and substance P (10-50 microM), but not by neurotensin (50 microM), beta-endorphin (30 microM) and methionine-enkephalin (met-enk) (100 microM). Somatostatin-stimulated 5-HT release was markedly inhibited by gamma-aminobutyric acid (GABA) (30 microM), but not by baclofen (30 microM) and met-enk (100 microM). Substance P-stimulated 5-HT release was strongly inhibited by GABA (30 microM) and baclofen (30 microM), but not by met-enk (100 microM). High concentrations (20 mM) of potassium also stimulated 5-HT release. The high potassium-stimulated 5-HT release was not affected by GABA (30 microM) and met-enk (100 microM). These results suggested further evidence on the important role of somatostatin and substance P as modulators of serotonergic neurones.     

Effects of guanidine on synaptic transmission in the spinal cord of the frog

Summary The effects of guanidine on motoneurons of the isolated frog spinal cord were studied by adding the drug to the solution bathing the cord during intracellular recording. Guanidine (5·10^–4 M) did not alter the membrane potential of motoneurons.The main effect was a marked increase of the amplitudes and frequencies of small spontaneously occurring inhibitory postsynaptic potentials. The hyperpolarizing component of postsynaptic potentials evoked by stimulation of dorsal roots was also enhanced by guanidine. Higher concentrations of guanidine (5·10^–3 M) resulted in a very large and irreversible increase of the small spontaneously occurring inhibitory potentials, which now appeared in a regular, rhythmic pattern.The effects of guanidine could easily be blocked by increasing the magnesium ions (15 mM) in the bath solution.These results indicate that guanidine facilitates the release of an inhibitory transmitter in afferent terminals of the frog spinal cord either by a direct action on these terminals or indirectly by an action on nerve endings impinging on inhibitory interneurons.This work was supported by the Deutsche Forschungsgemeinschaft     

Interactions of dopamine and the release of [3H]-taurine and [3H]-glycine from the isolated retina of the rat

1 The dose-related, calcium-dependent, potassium-stimulated release of preloaded [³H]-dopamine from the superfused rat retina has been demonstrated.

2 A high-affinity uptake system for dopamine exists in rat retina in vitro; K_m value was calculated as 1.89 μM, V_max value as 1.4 nmol g^-1 tissue h^-1.

3 Dopamine (0.8 and 4 mM) inhibited the spontaneous release of [³H]-glycine from retina, and in the case of 0.8 mM dopamine this inhibitory effect was antagonized by 10 μM (+)-butaclamol but not by 10 μM (-)-butaclamol.

4 The potassium-evoked (25 mM) release of [³H]-glycine from rat retina was similarly inhibited by dopamine (0.4-4 mM) in a dose-related manner when added to the superfusate with the potassium. The effect of 0.8 mM dopamine was antagonized by 10 μM (+)-butaclamol but not by 10 μM (-)-butaclamol.

5 Dopamine (4 mM) significantly reduced the spontaneous release of [³H]-taurine from rat retina.

6 The potassium-stimulated (25 mM) release of [³H]-taurine occurred after the cessation of the depolarizing stimulus. This delayed release of [³H]-taurine was unaffected if dopamine was applied to the superfusate at the same time as the potassium, but it was significantly reduced if dopamine (0.8 and 4 mM) was applied after the depolarizing stimulus had been removed and during the actual amino acid release phase.

7 The inhibition of K⁺-stimulated (25 mM) delayed release of [³H]-taurine by applying dopamine (0.8 mM) after the depolarizing stimulus was blocked by 10 μM (+)-butaclamol but not by 10 μM (-)-butaclamol.

8 The results are discussed with respect to the possible neurotransmitter role for dopamine within the rat retina, and its possible interaction with glycine and taurine.

     

Evidence for the release of endogenous substance P from intestinal nerves

Summary The desensitization of receptors for substance P in the longitudinal muscle of the guinea-pig ileum has been studied. Receptors for substance P in the muscle became desensitized in the presence of relatively large concentrations of synthetic substance P; a desensitizing concentration of substance P of 7.5×10^–9 M shifted the concentration-response curve for substance P about 20-fold to the right, while a desensitizing concentration of 7.5×10^–8 M shifted the curve about 300-fold to the right. This desensitization appeared specific; concentration-response curves for carbachol, DMPP, 5-HT and bradykinin were not significantly affected by substance P, 7.5×10^–8 M. Furthermore, substance P in concentrations up to 7.5×10^–8 M did not modify transmission from either cholinergic nerves or enteric inhibitory nerves when these were stimulated electrically. However, hyoscine-resistant contractions produced by stimulation of nerves in the ileum at 10 Hz were abolished by exposure to concentrations of substance P of 7.5×10^–9 M or greater, suggesting that these nerves release a substance similar to or identical with substance P. DMPP evoked small hyoscine-resistant contractions of the ileum. These contractions were also antagonised by desensitization of receptors for substance P. Immunohistochemical studies showed substance P-like immunoreactivity in nerve terminals of both the myenteric and submucous plexuses.     

Effect of extracellular dopamine on the release of dopamine in the rabbit caudate nucleus: Evidence for a dopaminergic feedback inhibition

Summary Slices of the head of the rabbit caudate nucleus were preincubated with 10^–7 M ³H-dopamine and then superfused, and the effect of unlabeled dopamine on the outflow of tritium was investigated. In most experiments, nomifensine was added throughout superfusion in order to block uptake of the unlabeled amine. Nomifensine was a potent inhibitor of the uptake of ³H-dopamine into rabbit caudate synaptosomes, with an IC₅₀ of 5·10^–8 M at a ³H-dopamine concentration of 4·10^–8 M.In the absence of nomifensine, unlabeled dopamine (10^–7 M and higher concentrations) accelerated the basal outflow of tritium from preincubated slices. 10^–5 M nomifensine strongly counteracted the acceleration. In the presence of nomifensine, unlabeled dopamine (10^–7 to 10^–6 M) caused a concentrationdependent decrease of the overflow of tritium evoked by electrical stimulation at 0.1 Hz. Chlorpromazine and haloperidol (in the presence of nomifensine) increased the stimulation evoked overflow and antagonized the inhibitory effect of dopamine.It is concluded that extracellular dopamine shares with other dopaminergic agonists the ability to inhibit action potential-evoked release of intraneuronal dopamine. The inhibition is mediated by specific receptors. The results support the hypothesis that previously released dopamine, by an action on these receptors, can inhibit further release of dopamine.     

Differential effects of wortmannin on the release of substance P and amino acids from the isolated spinal cord of the neonatal rat

1. Effects of wortmannin, an inhibitor of myosin light chain kinase, on the release of substance P and amino acids, GABA and glutamate, were investigated in the isolated spinal cord preparation of the neonatal rat.
2. Wortmannin at 0.5–10 μM depressed the release of substance P evoked by high-K⁺ (90 mM) medium from the spinal cord (IC₅₀=1.1 μM). Wortmannin also depressed the high-K⁺ (70 mM)-evoked release of substance P from cultured dorsal root ganglion neurons of neonatal rats. In contrast, the high-K⁺ (90 mM)-evoked release of GABA and glutamate from the spinal cord was not affected by wortmannin (0.1–10 μM).
3. Upon stimulation of a dorsal root, a monosynaptic reflex and a subsequent slow ventral root depolarization were evoked in the ipsilateral ventral root of the same segment in the isolated spinal cord preparation. The magnitude of the slow ventral root depolarization was depressed gradually to about 70% of the control during the course of 30 min under wortmannin (1 μM). In contrast, the monosynaptic reflex was unaffected by wortmannin.
4. Immunofluorescent staining revealed that immunoreactivities of substance P and myosin II were colocalized at presynaptic terminals in the dorsal horn of the neonatal rat spinal cord.
5. The present results suggest that myosin phosphorylation by myosin light chain kinase may play a crucial role in the release of substance P, but not in the release of GABA and glutamate in the neonatal rat spinal cord. This may reflect a difference in the exocytic mechanisms of substance P-containing large dense core vesicles and amino acid-containing small clear vesicles.

     

NMDA receptor activation modulates evoked release of substance P from rat spinal cord

The possible modulation exerted by glutamate on substance P (SP) release from the rat spinal cord has been investigated. The N-methyl-D-aspartate (NMDA) receptor agonist, NMDA (1 μM), increased SP basal outflow by 46.5±10.9% (n=3, P<0.01) without changing the evoked release of the peptide. Conversely, NMDA antagonists but not 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) inhibited both electrically-evoked and capsaicin-induced release of SP. In particular, D-2-amino-5-phosphonopentanoate (D-AP5; 50 μM) inhibited electrically-evoked and capsaicin-induced release of SP by 93±2.4% and 93.2±3.8% (n=12, P<0.01), respectively. Functional pharmacological evidence is provided for glutamate exerting a positive feedback on SP release evoked by C fibre stimulation via NMDA receptor activation.     

In vitro acetylcholine release from rat caudate nucleus as a new model for testing drugs with dopamine-receptor activity

Summary The effects of a number of dopamine-receptor agonists on depolarization-induced (26 mM K⁺) release of ³H-acetylcholine from slices of rat caudate nucleus were examined with a superfusion method. Apomorphine (10^–6 M) and N,N-dipropyliso-ADTN (10^–7 M) inhibited acetylcholine-release in vitro by about 50% and these inhibitory effects were antagonized by haloperidol. For N,N-dipropyl-iso-ADTN an EC₅₀ of approximately 3×10^–9 M was estimated from its dose-response curve. However, dopamine (10^–6 M) itself and bromocriptine (10^–6 M) inhibited acetylcholine-release less. Presumably: the weak effect of exogenous dopamine is due to its (partial) uptake in dopaminergic nerve terminals and to the fact that released endogenous dopamine already partially activates the receptors involved in the inhibition of acetylcholine-release.Pretreatment of young rats with 6-hydroxydopamine (+ desipramine) increased the inhibitory effects of dopamine-receptor agonists, including dopamine itself, on acetylcholine-release from caudate slices, indicating dopamine-receptor supersensitivity. This was corroborated by the finding that apomorphine-induced stereotyped behavior was significantly higher in rats lesioned with 6-hydroxydopamine than in controls.It is suggested that K⁺-induced release of radiolabelled acetylcholine from caudate nucleus slices provides a functional model to study the characteristics of post-synaptic dopamine-receptors in vitro. The concentrations of dopamine-receptor agonists needed to inhibit acetylcholine-release appear to be in the nanomolar range, in agreement with their affinities as determined in dopamine-receptor binding studies. In contrast, these concentrations are much lower than those required for stimulation of dopamine-sensitive adenylate cyclase activity.     

Ein Beitrag zum Wirkungsmechanismus von Dipyridamol: Hemmung der Adenosinaufnahme in Erythrocyten durch Dipyridamol

Summary 10^–9–10^–6 M Dipyridamole, which is used for coronary dilation' lowers the permeability of erythrocytes of guinea pigs to adenosine and inosine. For inhibition of the adenosine deaminase, however, concentrations of 10^–4 M are necessary. There is a difference of 10³–10⁵ between the concentration of dipyridamole which inhibits the adenosine deaminase and the concentration which decreases the permeability of erythrocytes to adenosine or inosine.Therefore the inhibition of uptake into the cells should be more important for the pharmacological effects than the inhibition of the adenosine deaminase.The unchanged deamination of adenosine by a concentration of 10^–6 M Di-pyridamole, which inhibits the uptake of adenosine into the cells completely, indicates, that adenosine is deaminated on the outer surface of the cell membrane.

Wir bedanken uns bei der Deutschen Forschungsgemeinschaft für die Über-lassung der Isotopenmeßeinrichtung. Unser besonderer Dank gilt Herrn Prof. Dr. Rummel, der durch seine Bereitschaft die Ergebnisse zu diskutieren, wesentlich zur Arbeit beigetragen hat.     

Serotonin type-2 receptor mediated regulation of substance P release in the ventral spinal cord and the effects of chronic antidepressant treatment

Summary Regulation of the release of substance P (SP) by the coexisting neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) in the ventral spinal cord and the effects of chronic antidepressant treatment mediated changes in serotonin metabolism on the regulation, were examined.The K⁺ (40 mmol/l) evoked release of (SP) from slices of the ventral spinal cord of the rat was potentiated by (5-HT) applied to 100 mol/l concentration. This effect was blocked by the serotoninergic antagonists methysergide (10 mol/l), methiotepin (10 mol/l) and fully blocked by ketanserin (10 mol/l). Thus the 5-HT receptor which regulates the release of SP appears to belong to the type-2 5-HT receptors. Chronic treatment with the selective serotonin uptake inhibitor zimelidine (14 days, 2×10 mol/kg/day, p.o.) lowered the tissue levels of the 5-HT metabolite: 5-hydroxyindol acetic acid (5-HIAA) and elevated the tissue levels of SP in both the ventral and dorsal spinal cord as compared to that in the vehicle treated group (14 days, 2×5 ml saline/kg/day, p.o.). The decrease in the 5-HIAA levels after chronic zimelidine treatment was quantitatively similar in the dorsal (33%,p<0.01) and ventral (31%,p<0.05) spinal cord. The increase in SP levels after chronic zimelidine treatment was more pronounced in the ventral cord (80%,p<0.01) where the majority of the SP containing nerve endings also contain 5-HT, than in the dorsal spinal cord (22% increase in SP,p<0.05), where only a minor fraction of the SP-containing nerve endings shows a 5-HT/SP coexistence. Chronic treatment with imipramine (14 days, 2×10 mol/kg/day, p.o.) gave qualitatively similar results to those obtained by zimelidine treatment, but increases in SP levels, and decreases in 5-HT and 5-HIAA levels in ventral and dorsal spinal cord, were less pronounced. The K⁺ (40 mmol/l) evoked release of SP was studied in a slice preparation of the ventral spinal cord, from rats chronically treated with imipramine, zimelidine and saline. In the zimelidine treated group the amount of SP released (pmol/g tissue) and the fractional SP release upon K⁺ (40 mmol/l) stimulation was increased by 53% (p<0.01) and 42% (p<0.01) respectively, when compared to the control group. No significant changes in the amount of SP released or fractional SP release were observed when tissue preparations from rats treated with imipramine were used. Thus, it seems that treatment with specific serotoninergic or monoaminergic antidepressant drugs does not only change the tissue levels of the monoamine and its metabolite but also affects the coexisting peptidergic transmitter; SP in the ventral spinal cord. This change is also reflected in the size of the releaseable pool of SP.     

Effects of Ethanol and Acetate on Adenosine Production in Rat Hippocampal Slices

Abstract: Since adenosine has been shown to mediate some actions of ethanol we have examined the effect of ethanol (20 and 80 mM) or its metabolite acetate (5 and 20 mM) on the formation and release of adenosine by rat hippocampal slices. The ATP pool of the slices was radioactively labelled by preincubation with [³H]-adenine. The efflux of radioactivity under basal conditions and following ATP breakdown induced by combined hypoxia/hypoglycaemia was examined. Ethanol or acetate did not increase the total efflux of [³H]-purines, but changed the composition to a larger proportion of [³H]-adenosine. The release of endogenous adenosine was also increased. This type of effect exactly mirrors that previously reported for purine nucleoside transport inhibitors. The present results thus show that ethanol (20 mM) can increase adenosine release from a brain slice by a mechanism that probably involves transport inhibition.     

The serotonin receptor agonist 5-methoxy-N,N-dimethyltryptamine facilitates noradrenaline release from rat spinal cord slices and inhibits monoamine oxidase activity

1. The influences of the purported serotonergic agonist 5-methoxy-N,N-dimethyltryptamine (MeODMT) on noradrenaline release and metabolism were investigated in a rat spinal cord release model and a monoamine oxidase (MAO) assay.2. MeODMT inhibited the basal outflow of tritium from rat spinal cord slices preincubated with [³H]noradrenaline and enhanced the electrically-evoked overflow.3. Effects on basal outflow were not observed, when monoamine oxidase (MAO) was inhibited by pargyline. Effects on the evoked overflow were not observed in the presence of metitepine or phentolamine.4. Preferential inhibition by MeODMT of MAO A-type enzyme activity was found in a direct assay.5. The results provide evidence for two different effects by which MeODMT reinforces noradrenergic neurotransmission in the rat spinal cord: facilitation of stimulation-evoked noradrenaline release and inhibition of noradrenaline metabolism by MAO inhibition.