Refined carbohydrate increases blood pressure and catecholamine excretion in SHR and WKY

In spontaneously hypertensive (SHR) and normotensive (WKY) rats fed different diets, blood pressure (BP) increased significantly in both strains when the carbohydrate (CHO) source was from refined rather than from natural ingredients. This BP increase was observed whether sucrose, glucose, or starch was the principal CHO. Urinary excretion of norepinephrine, dopamine, and, to some extent, epinephrine also increased, while myocardial concentrations were unaffected. Despite a comparable elevation of catecholamine excretion in both SHR and WKY rats fed high amounts of refined CHO, the BP increases were greater in the former. The strain differences were explained by the known dissimilar response of their blood vessels to catecholamines. The results suggest that BP elevation after high CHO ingestion is mediated via increased catecholamine production and/or release, thus implying a neurogenic mechanism.

Differences in the metabolism of MPTP in the rodent and primate parallel differences in sensitivity to its neurotoxic effects

Primates and rodents show marked differences in sensitivity to the neurotoxic effects of MPTP. We and others have previously shown that the toxic effects of MPTP on nigrostriatal cells are dependent on the oxidative metabolism of MPTP to the quaternary species MPP+. We have therefore compared the distribution and metabolism of MPTP in the monkey and several rodent species. Three major differences have been identified: 1) the primate, but not the rodents, showed a persistently high concentration of MPTP metabolites in the caudate nucleus compared to other brain regions; 2) the rodent brains cleared MPTP and its metabolites much more rapidly than did the monkey, and; 3) the predominant metabolite retained by the monkey brain was MPP+, while MPP+ cannot be detected in rodent brains for more than a few hours after injection. The persistence of MPP+ in the primate brain may explain the heightened toxicity of MPTP in this species.

Primate model of parkinsonism: selective lesion of nigrostriatal neurons by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine produces an extrapyramidal syndrome in rhesus monkeys

Systemic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to rhesus monkeys (1.0-2.5 mg/kg i.v.) produces irreversible damage to nigrostriatal neurons. Dopaminergic neurons in the dorsolateral part of striatum were the most vulnerable. The major clinical signs of an extrapyramidal syndrome, but not resting tremor, appeared only in MPTP-treated monkeys suffering from more than 80% reduction in striatal dopamine. No chronic changes in the mesolimbic dopaminergic system were observed. Immunocytochemical staining of the mid-brain with a tyrosine hydroxylase antiserum indicated that MPTP produced a significant decrease of dopaminergic cell bodies in the A9, but not in the A10 ventrotegmental area. Despite greater than 80% decrease in A9 nigral cell bodies, the dopamine content decreased only by 50%. Sprouting of the surviving nigral A9 neurons was observed histologically and neurochemically in the area above substantia nigra. The present behavioral, neurochemical and histological results indicate that MPTP produces an ideal primate model for studying parkinsonism. Selective lesion of more than 80% of the nigrostrial neurons by MPTP is sufficient to produce the major clinical signs of the extrapyramidal syndrome in idiopathic parkinsonism.

Brain uptake of flurazepam and of N1-desalkyl flurazepam after administration of flurazepam to the cat

A gas chromatographic-mass spectrometric procedure was employed to identify flurazepam and several of its metabolites in the plasma, cerebrospinal fluid (CSF), and brain of cats after an iv injection of flurazepam. Following tissue redistribution, flurazepam was lost from plasma with a mean half-time of 1.4 hr; although usually not detectable in plasma by 24 hr, significant quantities were found in the brain at this time, particularly in the corpus callosum. N1-Hydroxyethyl flurazepam appeared rapidly in plasma following iv flurazepam, peaked at about 40 min, and then declined with a mean half-time of 2.1 hr. N1-Desalkyl flurazepam accumulated in plasma in the first 6 hr after flurazepam was injected, and then declined slowly with a mean half-time of about 50 hr. At 24 hr, corpus callosum concentrations of the N1-desalkyl flurazepam exceeded those of flurazepam by 16- to 63-fold and produced brain/plasma ratios of 6 to 62 in three cats. CSF concentrations of flurazepam and N1-desalkyl flurazepam did not reflect brain concentrations but only the estimated plasma fractions of the unbound drugs. The results suggest that long term central effects of iv flurazepam are mediated to a large extent by the N1-desalkyl flurazepam, in species in which that metabolite accumulates.

Intraneuronal generation of a pyridinium metabolite may cause drug-induced parkinsonism

The compound 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces an irreversible neurological syndrome in man and monkey which is similar to idiopathic Parkinson's disease in its clinical, pathological, neurochemical and pharmacological response properties. MPTP is selectively neurotoxic to the dopaminergic regions of the brain, destroying neurones in the substantia nigra (A8 and A9 cells, nigrostriatal system) but not the ventral tegmental area (A10 cells, mesolimbic system). Selective dopamine depletion and nigral cell loss after MPTP treatment has also been reported recently in the mouse. The mechanism by which a peripherally administered, low-molecular weight compound exerts permanent but selective toxic effects on dopamine systems in the brain may be relevant to parkinsonian syndromes induced by other toxins and to the disease process in idiopathic Parkinson's disease. We report here that MPTP is oxidized in the brain to a pyridinium species (a compound with potent herbicidal activity) and, in the monkey, is trapped intraneuronally. Furthermore, we demonstrate that this enzymatic oxidation is blocked in vivo in the mouse by a monoamine oxidase inhibitor, a condition which also blocks the neurotoxicity, indicating that the oxidative metabolism of MPTP is required for its neurotoxic effect.

Catecholamine synapses and contents in the paraventricular hypothalamic nucleus and nucleus tractus solitarius of DOCA-salt hypertensive rats

Central catecholamine (CA) neurons in the nucleus tractus solitarius (NTS) and paraventricular hypothalamic nucleus (PVN) were studied in Wistar rats that had been unilaterally nephrectomized. The experimental animals were then treated with deoxycorticosterone acetate (DOCA) and salt water. The control animals were treated with the vehicle and tap water. Blood pressure of animals 4 weeks after DOCA/salt treatment was significantly elevated when compared to control rats. Morphologically, CA terminals showed no noticeable changes in the DOCA/salt hypertensive rats. Furthermore, the density of CA terminals either in the NTS or in the PVN of the DOCA/salt hypertensive rats was not statistically different from that of normotensive controls, suggesting that salt does not cause lesions or destruction of CA terminals. However, an extensive electron-microscopic morphometric analysis indicated that there was an enhancement of CA synaptogenesis (expressed by increased synaptic frequency among all CA boutons labeled with 5-hydroxydopamine) in the PVN, but not in the NTS of DOCA/salt hypertensive rats. In addition, the high-performance liquid chromatography revealed decreased CA contents in the PVN, but not in the NTS, of DOCA/salt hypertensive animals. Since synapses are primary sites for neurotransmitter release, the above results collectively suggest that more CA synapses formed in the PVN may reflect a net CA release from CA terminals resulting in the decreased CA content in the axonal terminals. Such an increased CA release and enhanced CA synaptogenesis may consequently enhance CA function in the PVN of hypertensive rats 4 weeks after DOCA/salt treatment, and relate to the development and/or maintenance of hypertension in the DOCA/salt rats.

Neurochemical and behavioral effects of systemic and intranigral administration of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the rat

At doses of 5-10 mg kg-1, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (NMPTP) produces in rats acute immobility, retropulsion, straub tail, piloerection, exophthalmos, salivation and clonic movements of the forepaws. It does not produce analgesia as measured by the tail test, nor does it produce permanent motor impairment after chronic or intranigral administration. The acute retropulsion and immobilizing effects can be blocked by methysergide. Administered acutely, NMPTP doubles levels of serotonin in the raphe nucleus and substantia nigra. At the same time, levels of dopamine increase in the caudate nucleus and decrease in the substantia nigra. The NMPTP-induced decrease in dopamine content of the substantia nigra persists in chronically treated rats, but there is no significant decrease in striatal dopamine. After chronic administration of NMPTP, striatal levels of dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were decreased by about 50%. Intranigral administrations of NMPTP (10 micrograms daily for 5 days) failed to produce a 6-hydroxydopamine-like lesion in the nigrostriatal system. These results indicate that NMPTP in the rat does not cause selective destruction of dopaminergic neurons, but it does produce acute tryptamine-like effects.

The neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the monkey and man

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) selectively destroys dopaminergic neurons in the pars compacta of the substantia nigra (A8 and A9 cells). MPTP or its metabolite enters nerve cells at the level of their terminals in the caudate nucleus and putamen leading to a disturbance in axoplasmic flow and retrograde degeneration. The species-dependent neurotoxicity of MPTP (primate vs. rodent) suggests that a biochemical property of the cell related to neuromelanin may be important in the mechanism of cell injury.

A primate model of parkinsonism: selective destruction of dopaminergic neurons in the pars compacta of the substantia nigra by N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

A syndrome similar to idiopathic parkinsonism developed after intravenous self-administration of an illicit drug preparation in which N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (NMPTP) might have been responsible for the toxicity. In the present study we show that intravenous administration of NMPTP to the rhesus monkey produces a disorder like parkinsonism (akinesia, rigidity, postural tremor, flexed posture, eyelid closure, drooling) that is reversed by the administration of L-dopa. NMPTP treatment decreases the release of dopamine and dopamine accumulates in swollen, distorted axons in the nigrostriatal pathway just above the substantia nigra, followed by severe nerve cell loss in the pars compacta of the substantia nigra and a marked reduction in the dopamine content of the striatum. The pathological and biochemical changes produced by NMPTP are similar to the well-established changes in patients with parkinsonism. Thus, the NMPTP-treated monkey provides a model that can be used to examine mechanisms and explore therapies of parkinsonism.

Effects of phencyclidine on rat prolactin, dopamine receptor and locomotor activity

Plasma prolactin (PRL) was decreased in naive rats sacrificed 30 min after phencyclidine (PCP) administration (10 mg/kg, s.c.). There was, however, no decrease in plasma PRL 30 min after s.c. injection of PCP (10 mg/kg) on the 29th day following 28 days of chronic PCP administration. These data suggest the development of tolerance to the PRL-suppressive effect of PCP as result of long-term administration of the drug. The Bmax of [3H]-spiperone binding to rat striatal membranes was decreased 24 hrs after 28 days of PCP treatment without change in affinity (Kd). No indication of the development of tolerance in these rats was found with regard to the locomotor-stimulating effect of PCP. The plasma PRL-suppressive effect of the PCP analog PCMP was found to be stereospecific; (-) PCMP was much less potent than (+)-PCMP.

6-Fluorocatecholamines as false adrenergic neurotransmitters

In the present study 6-fluoronorepinephrine (6F-NE) is shown to be formed from 6-fluorodopamine (6F-DA) in vivo. The beta-hydroxylated fluorocompound is taken up by and stored in the adrenergic nerve terminals and can be released during sympathetic nerve stimulation. In the heart, the turnover rate of the exogenously administered 6F-NE was about the same as that of tritium-labeled norepinephrine. In the central nervous system, 6F-DA can be taken up by the nigrostriatal neurons. After depolarization of the dopaminergic neurons by potassium, 6F-DA is released along with the endogenous dopamine. Systemic administration of 6F-NE to the pithed rats produces dose-dependent increases in blood pressure but does not increase the heart rate. The vasopressor potency of 6F-NE is about the same as that of l-norepinephrine, about 2-fold greater than that of dl-norepinephrine. Combined treatment with yohimbine and prazosin antagonizes completely the vasopressor effect of 6F-NE. The duration of the pressor response to 6F-NE was twice that of dl- or l-norepinephrine. The present study indicates that 6-fluorocatecholamines fulfill the criteria for adrenergic false transmitters and may be useful in positron emission tomographic scanning for mapping specifically the adrenergic nervous system in the brain or in the peripheral sympathetic nerves.

Direct observation of 6-fluorodopamine in guinea pig nerve microsacs by 19F NMR

19F nuclear magnetic resonance (NMR) has been used to examine the disposition of ring-fluorinated dopamine and norepinephrine in microsacs prepared from striata of guinea pig brains. Following incubation with a 10(-4)M initial concentration of 6-fluorodopamine (6F-DA), intact micmicrosacs at 4 degrees C gave a 19F NMR spectrum in which the 6F-DA present was sufficiently mobile to be visible. Intra-vesicular 6F-DA in striatal nerve terminals thus appears to exist in an environment resembling that in chromaffin vesicles but different from that prevailing inside the amine storage vesicles of platelets. Our data also suggest that the study of fluorinated compounds by 19F NMR can be used to expand our understanding of processes related to amine uptake, metabolism, and storage in nerves.

Age related increase in catecholamine-containing paraganglia in male Fischer-344 rats

For identification of paraganglia (PG), samples of para-aortic tissue, tissues containing the coeliac-mesenteric ganglion complex, and the hypogastric ganglia were removed from 3- and 33-month-old male Fischer-344 rats and were processed by the formaldehyde-induced fluorescence method for visualization of catecholamines. Small PG containing 5-30 cells per section were found consistently in young animals. In each of six old rats, large PG containing 500-4000 brightly fluorescent cells per section were detected. Cell counting revealed a 13.5 x increase in number of PG cells between 3- and 33-month-old rats. Microspectrofluorimetric quantitation in old rats showed equal amounts of catecholamines in PG cells and in adrenal medullary cells. Most PG were located in samples from the para-aortic area.

Cerebrovascular integrity in protein-deprived rats

Protein-deprivation does not increase the permeability of the blood-brain barrier in rats aged 3.5--12 months. PA, the product of cerebrovascular permeability (P) to 14C-sucrose and of cerebral capillary surface area (A), is very low in mature rats that have been maintained either on an 8% or 25% casein diet, and equals about 8 X 10(-6) sec-1 in both groups. There is a tendency for the calculated distribution volume of 14C-sucrose within the brain to decline in protein-deprived rats. Conscious, partially immobilized, protein-deprived rats have the same mean blood pressure, heart rate, arterial plasma pH and adreno-sympathetic response to stress (as measured by plasma norepinephrine and epinephrine concentrations) as do normally fed animals.

Differential behavioral responses of spontaneously hypertensive (SHR) and normotensive (WKY) rats to d-amphetamine

A comparison was made in the behavioral responses of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats to d-amphetamine. Animals were tested at a young age (6 weeks) to minimize the effects of elevated blood pressure on drug responsiveness. SHR rats were more active than WKY rats after injections of 1.0, 2.0, and 4.0 mg/kg d-amphetamine. A significant strain difference in stereotypy was also noted; rearing occurred in SHR rats while lateral or vertical head movements (head waving) occurred in WKY rats. The lack of significant strain differences in the behavioral responses of rats to apomorphine, a direct acting dopamine agonist, suggested that the differential behavioral responses to d-amphetamine were not a result of differences between strains in receptor sensitivity. Pretreatment of rats with reserpine eliminated the strain differences in behavioral responses to d-amphetamine. Pretreatment of rats with alpha-methyl-p-tyrosine prior to administration of d-amphetamine elminated the strain differences in stereotyped behavior; however, WKY rats remained less active than SHR rats. Pretreatment of SHR rats with parachlorophenylalanine had no effect on the behavioral responses to d-amphetamine. In contrast, pretreatment of WKY rats with parachlorophenylalanine resulted in an increase in rearing and a decrease in head waving following an injection of d-amphetamine. These findings suggest that the differences in responses to d-amphetamine of SHR and WKY rats are due in part to variations in the activities of central catecholaminergic and serotonergic neurons.

The role of peripheral catecholamines in oxotremorine tremor in the rat and its antagonism by beta adrenoceptor blocking agents

Oxotremorine, 0.25 mg/kg, produces marked tremor in the rat, which is abolished by scopolamine, 0.5 mg/kg, and is substantially reduced in intensity and duration both by adrenalmedullectomy and by chemical sympathectomy with 6-hydroxydopamine. Oxotremorine increases plasma norepinephrine from 0.62 +/- 0.07 to 3.01 +/- 0.47 ng/ml and plasma epinephrine, from 0.82 +/- 0.14 to 3.42 +/- 0.48 ng/ml, in conscious unrestrained rats. l-Propranolol (0.5-2.5 mg/kg) reduces tremor, and at 2.5 mg/kg is more effective than either chemical sympathectomy or adrenal demedullation. d-Propranolol and sotalol are also active at 4 and 10 times the dose of l-propranolol, respectively. l-Propranolol does not prevent the rise in catecholamines induced by oxotremorine. It is suggested that stimulation of central muscarinic receptors causes tremor by a combination of two effects. There is an increase in cholinergic influence to motor efferents accompanied by an activation of the sympathoadrenal system to release catecholamines which augment tremor by stimulation of beta2 adrenoceptors.

Hyperresponsivitiy of spontaneously hypertensive rat to indirect measurement of blood pressure

A chronic, indwelling, tail arterial cannula was implated in conscious undisturbed rats for measurement of blood pressure and heart rate and for obtaining blood samples. As an index of sympathetic activity, plasma levels of catecholamines in arterial blood of conscious animals were assayed by a radioenzymatic, paper-chromatographic procedure. Blood pressures of unrestrained spontaneously hypertensive (SHR) rats in their home cages (161 +/- 3/141 +/- 4 mmHg) were not different from those of pentobarbitol-anesthetized, hypertensive animals but were about 25 mmHg lower than awake animals during the restraint required for the tail-cuff procedure. Basal levels of plasma catecholamines in awake, undisturbed or in pentobarbital-anesthetized animals were similar in age-matched SHR and normotensive Wistar-Kyoto (WKY) rats. SHR rats were shown to have greater increase in plasma catecholamines than WKY rats during forced immobilization or restraint for indirect measurement of blood pressure.

Entry of [3H]norepinephrine, [125I]albumin and Evans blue from blood into brain following unilateral osmotic opening of the blood-brain barrier

The blood-brain barrier in adult rats was opened unilaterally by infusing 1.58 M L (+)-arabinose in 0.9% NaCl solution into the internal carotid artery, via a catheter in the external carotid. The common carotid remained patent during the procedure. Osmotic barrier opening allowed entry into the brain of three intravascularly administered tracers--a visual tracer Evans blue (pulsely injected) and radioactive tracers [3H]norepinephrine (continuously infused) and [125I]albumin (pulsely injected). In osmotically perfused brain tissue, uptake of both 3H and 125I from blood was increased 2-5-fold above control, with maximal increases observed in the caudate nucleus, hippocampus and thalamus. In control brain regions, Evans blue and albumin remained intravascular, whereas norepinephrine was taken up, possibly by sympathetic nerve endings in cerebral vessels, as a function of blood plasma concentration and duration of exposure. The barrier closed within 4 h after intracarotid arabinose infusion, and barrier opening was not associated with edema as measured two days after infusion.

Centrally mediated release by cocaine of endogenous epinephrine and norepinephrine from the sympathoadrenal medullary system of unanesthetized rats

A radioenzymatic-paper chromatographic method for a simultaneous assay of catecholamines was used to study the effect of cocaine on the release of endogenous catecholamines from the sympathoadrenal medullary system into the blood of unanesthetized rats. Twenty-four hours after arterial cannulation, the "basal" levels of norepinephrine (NE) and epinephrine (EPI) in blood obtained through the catheter from conscious, undisturbed rats were 0.48 +/- 0.06 and 0.36 +/- 0.06 ng/ml, respectively. Administration, via the arterial catheter, of cocaine (0.4-10 mg/kg) produced dose-related increases in NE (0.59 +/- 0.03 to 1.58 +/- 0.34 ng/ml) and EPI (1.15 +/- 0.16 to 6.67 +/- 0.46 ng/ml). Inhibition of catechol O-methyltransferase by tropolone (40 mg/kg) enhanced by 5- to 10-fold the maximal response to cocaine without altering significantly the basal plasma levels of EPI or NE. Bilateral splanchnic denervation reduced the cocaine-tropolone-induced release of EPI and NE by 75 and 50%, respectively. Desipramine (10 mg/kg) failed to alter significantly plasma levels of NE or EPI, even after tropolone. Thus, the increment in plasma levels of NE and EPI in conscious rats given cocaine is mainly the result of a centrally mediated adrenal medullary discharge of catecholamines, rather than inhibition of catecholamine uptake.

Plasma catecholamine concentrations in unanesthetized rats during sleep, wakefulness, immobilization and after decapitation

A relatively unstressful technique for obtaining blood samples from rats has been employed to determine the amounts of catecholamines in blood during physiological sleep, undistrubed wakefulness, gentle handling and physical immobilization. These circulating plasma levels of catecholamines [0.46 ng of norepinephrine (NE) and 0.18 ng of epinephrine (EPI) per ml*were found to be markedly lower than previously reported for rats, which were generally handled or restrained prior to blood sampling. Compared with animals in natural sleep, awake rats had increases in plasma levels of EPI but larger increases of NE. Gentle handling, produced an additional increase in EPI only, whereas physical immobilization, produced massive elevations of circulating levels of both EPI and NE. Decapitation was found to be associated with a 10-fold increase in circulating NE and an 80-fold increase in circulating levels of EPI, whereas dopamine remained at undetectable levels. The high levels of plasma catecholamines in rats compared with other animals and humans, and changes produced in pharmacological and physiological experiments, probably reflect environmentally induced changes in sympathoadrenomedullary activity rather than differences in basal sympathetic neuronal activity.

Blockade by reserpine of methylphenidate-induced release of brain dopamine

The cerebroventricular systems of cats were perfused by introducing artificial cerebrospinal fluid into a lateral ventricle and collecting the perfusate at the aqueduct. 3-H-tyrosine was continuously added to the perfusing cerebrospinal fluid and the perfusate was analyzed for 3-H-catecholamines. Intraventricular or intravenous administration of methylphenidate increased the efflux of 3-H-dopamine. In cats pretreated with reserpine, this response to methylphenidate was reduced while the efflux of 3-H-dopamine caused by delta-amphetamine was slightly increased. These results provide direct biochemical evidence in support of the hypothesis that the central stimulant action of amphetamine and methylphenidate result from their abilities to preferentially release dopamine from "newly synthesized" and "stored" pools, respectively.

D-amphetamine-induced release of "newly synthesized" and "stored" dopamine from the caudate nucleus in vivo

The lateral and third ventricles of anesthetized cats were perfused continuously with artificial cerebrospinal fluid (CSF) containing 3H-tyrosine and the perfusate was analyzed for 3H-catecholamines. The addition of d-amphetamine sulfate to the perfusing CSF for 2 hours, beginning 2 hours after the start of the 3H-tyrosine perfusion, caused an immediate increase in the efflux of 3H-dopamine. The efflux of this amine declined subsequently despite the continued presence of amphetamine in the CSF. The addition of alpha-methyltyrosine to the CSF concurrently with the d-amphetamine did not markedly alter the immediate increase but accelerated the subsequent decline in the efflux of 3H-dopamine. This suggests that ampetamine initially releases dopamine from a "strong pool," but continuous release is dependent upon ongoing amine synthesis. The addition of d-amphetamine to the 3H-tyrosine containing CSF at the start of perfusion immediately increased the efflux of 3H-dopamine. This response was completely blocked by the presence of alpha-methyltyrosine in the CSF. Pretreatment of cats with reserpine effectively depleted the caudate nucleus of endogenous and 3H-dopamine, but did not alter the ability of d-amphetamine to increase the efflux of 3H-dopamine. Indeed, the amount of 3H-dopamine released during each collection period by either intraventricular or intravenous administration of d-amphetamine was higher than the content of the labeled amine remaining in the whole caudate nucleus. These results suggest that damphetamine can release both "stored" and "newly synthesized" 3H-dopamine from the caudate nucleus, but that the maintenance of the amphetamine-induced release of dopamine is dependent upon the newly synthetized pool.

In vitro synthesis of noradrenaline in ganglia and salivary glands after in vivo preganglionic stimulation

The extent of synthesis of [14C]noradrenaline from [14C]tyrosine and from [14C]dopamine was assessed in slices of superior cervical ganglia, representing cell bodies, and in submaxillary salivary glands, representing terminals of noradrenergic neurons of the cat. Immediately and 6 h after preganglionic stimulation for 3 h the rate of synthesis of noradrenaline from tyrosine and dopamine was not altered in ganglia. In salivary glands, however, synthesis of noradrenaline from both tyrosine and dopamine was increased at both times. These results suggest that acute periods of increased neural activity results in the acceleration of noradrenaline synthesis in the terminals but not in the cell bodies of noradrenergic neurons.

Modulation of noradrenaline incorporation by nerve activities in the rat submaxillary gland

1. Rats were anaesthetized with chloralose and prepared for electrical stimulation of the cervical sympathetic trunk. The effect of such stimulation was studied on the incorporation of intravenously infused [(3)H]noradrenaline, [(3)H]adrenaline or [(3)H]dopamine by the submaxillary gland.2. A train of 200 stimuli every min for 30 min at 20/sec increased the total incorporation of [(3)H]noradrenaline by 92% over the unstimulated side of the gland, at 50/sec by about 200% and at 3.3/sec by about 30%. The incorporation of [(3)H]adrenaline and of [(3)H]dopamine was also increased by sympathetic stimulation.3. The increases in unaltered [(3)H]noradrenaline and its metabolites were proportional to the increase in total radioactivity.4. Mean venous outflow from the gland was decreased by 15-30% by the sympathetic stimulation.5. After elimination of extraneuronal binding of noradrenaline by ligation of the common excretory ducts, nerve stimulation still increased incorporation.6. Inhibition of normetanephrine production by pyrogallol did not antagonize the nerve impulse-mediated increase of [(3)H]noradrenaline incorporation. alpha-Methyltyrosine was also without effect.7. Desmethylimipramine and bretylium completely abolished the nerve impulse-mediated increase of [(3)H]noradrenaline incorporation in concentrations which did not affect the control uptake or abolish adrenergic transmission.8. Reserpine, guanethidine and phenoxybenzamine antagonized both the control and nerve impulse-mediated incorporations of [(3)H]noradrenaline.9. The results indicate that nerve impulses modulate the incorporation of transmitter amine at the neuronal membrane. Possible mechanisms for this modulation are discussed.