Endogenous Norepinephrine Levels Research Articles

Blockade of MK-801 induced ipsiversive turning in 6-OHDA lesioned rats by α1-adrenoceptor antagonists

Previously the ipsiversive turning response elicited by MK-801 in rats with unilateral 6-hydroxydopamine lesions of the substantia nigra has been shown to be reduced by the α 1-receptor antagonist, prazosin. In these experiments the effects of additional α 1-adrenoceptor antagonists were examined to verify the involvement of α 1-adrenoceptors in the elucidation of the ipsiversive turning response elicited by MK-801. Both aceperone and azapetine did significantly reduce the ipsiversive turning evoked by MK-801. In contrast, neither agent produced a statistically significant reduction in the contraversive turning evoked by the direct acting dopamine agonist, apomorphine. In addition, aceperone also produced a weak but dose-related inhibition of amphetamine-induced ipsiversive rotation, whereas azapetine partially reduced amphetamine-induced turning in a non-dose related manner. These data suggest α 1-adrenoceptors may be partially involved in the ipsiversive turning response caused by MK-801 and to a lesser extent by amphetamine. This theory was further supported by the finding that reduction of endogenous norepinephrine levels, via administration of the dopamine-β-hydroxylase inhibitor FLA-63, markedly reduced the turning evoked by MK-801 and to a lesser degree that produced by amphetamine.

Effects of Chronic Ethanol Feeding on Sympathetic Innervated Organs: Temporal Sequence of Biochemical, Functional, and Trophic Changes

In noradrenergic nerves as well as in effector organs of the sympathetic nervous system, chronic ethanol feeding induced biochemical, functional, and trophic changes. The time sequence of modifications in the activities of tyrosine hydroxylase, phenylethanolamine-N-methyl transferase, monoamine oxidase, endogenous norepinephrine levels, as well as the neuronal uptake mechanism and secretory responses to norepinephrine in the submaxillary gland of the rat, confirms that the effects of chronic ethanol administration are related to an increase in sympathetic tone.

Abnormalities in norepinephrine turnover rate in the central nervous system of the genetically epilepsy-prone rat

Norepinephrine turnover rates were estimated in the hypothalamus-thalamus, midbrain, pons-medulla and telencephalon of genetically epilepsy-prone rats (GEPR). In each of these 4 brain areas the endogenous norepinephrine levels were significantly lower in the GEPR than in control animals. In the hypothalamus-thalamus, midbrain and telencephalon the calculated norepinephrine turnover rates were also significantly lower in GEPRs than in control. These studies confirm and extend earlier observations relating seizures in the GEPR to decrements in central nervous system noradrenergic function.

Norepinephrine levels in developing pigeon brain: Effect of monocular deprivation on the Wulst Noradrenergic System

The endogenous level of norepinephrine (NE) was measured in discrete brain areas of the pigeon during post-hatching development. The pontine tegmentum showed the highest NE content, which remained constant during the post-hatching period. On the contrary, the NE content in the Wulst and cerebellum gradually decreased from hatching to 6 days. After this period, the Wulst NE level did not change significantly. In fact, there was no significant difference between NE values at 6 days and those at 6 months of age. In contrast, the difference between the cerebellar NE level at 6 days and that at the adult stage was highly significant. The NE content in the Wulst could be related to noradrenergic afferents originating in the ipsilateral locus coeruleus and substantia grisea centralis, since an electrolytic lesion of the pontine tegmentum caused a 60% reduction in the NE level in the ipsilateral Wulst. In line with the hypothesis that NE plays an important role in cortical plasticity, effects of early monocular deprivation on the Wulst NE content were also observed. After monocular deprivation during the first 6 months of life, the NE level increased by 40% in the Wulst ipsilateral to the deprived eye in comparison to the other side, where the NE level was normal. Monocular deprivation performed in adult animals did not affect the NE content in the Wulst. These results indicate that noradrenergic systems in the Wulst are affected by early, but not late visual deprivation.

Post-ganglionic chemical sympathectomy of the cat nictitating membrane following systemic epinephrine: Degeneration of nerve terminals followed by regeneration

The present study was designed to provide further evidence that high doses of systemically administered epinephrine can result in a post-ganglionic chemical sympathectomy and to look for evidence of regeneration of nerve terminals. Three days following the systemic administration of a high dose of epinephrine a prolapse of the cat nictitating membrane was observed. Examination of the inferior smooth muscle associated with the membrane revealed ultrastructural evidence of nerve terminal destruction which was associated with a marked depletion of endogenous norepinephrine as measured with a catecholamine radioenzyme assay. Three weeks following treatment, appearance of nerve terminals and endogenous norepinephrine levels in the contralateral nictitating membrane were indistinguishable from untreated controls. High doses of epinephrine appear to result in nerve terminal degeneration, followed by regeneration, similar to that reported following 6-hydroxydopamine.

Interaction of Cyclazocine and the Sympathetic Nervous System

□ Cyclazocine, a benzomorphan derivative narcotic agonistantagonist, reduced the uptake of tritiated norepinephrine and reduced the recovery of [3H]3,4-dihydroxymandelic acid, but did not significantly alter the recovery of [3H]normetanephrine in the rat heart in vivo. Cyclazocine also reduced endogenous levels of norepinephrine in the rat heart. Comparatively, desipramine reduced the uptake of [3H] norepinephrine, the recovery of [3H]3,4-dihydroxymandelic acid, and the recovery of [3H]normetanephrine in the rat heart in vivo. Further, cyclazocine added to the perfusion medium or administered systemically reduced the uptake of radiolabeled norepinephrine by the isolated rat heart. The cyclazocine-induced decrease in the accumulation of [3H]norepinephrine in the rat heart in vivo and in vitro presumably is due to an alteration of sympathetic function through the inhibition of neuronal uptake. It is further suggested that cyclazocine has other actions on the sympathetic nervous system, such as promoting neurotransmitter release.

Determination of norepinephrine and its metabolites released from rat vas deferens using high-performance liquid chromatography with electrochemical detection

We designed a rapid, simple and sensitive method for the determination of norepinephrine (NE) and its metabolites by reversed-phase high-performance liquid chromatography (HPLC) with electrochemical detection. NE, 3,4-dihydroxymandelic acid (DOMA), and 3,4-dihydroxyphenylglycol (DOPEG) were adsorbed on alumina and eluted with 0.2 N HCl. From the remaining solution, normetanephrine and 3-methoxy-4-hydroxyphenylglycol (MOPEG) were extracted with ethyl acetate in the presence of both borate buffer and K 2HPO 4. Vanillylmandelic acid was extracted with ethyl acetate after acidification of the solution with concentrated HCl. The combined ethyl acetate phase was evaporated and the residue was dissolved in 0.1 N HCl. A 50 μl aliquot of each eluate or solution was injected onto the HPLC. Detection limits ranged from 300 pg to 1 ng per initial sampla. We used this method to determine substances in the medium following incubation of the rat vas deferens. Approximately 110 and 80 ng/g/10 min of DOPEG and MOPEG, respectively, were present under normal conditions. The electrical stimulation of tissues from the rat vas deferens led to increases in the levels of NE, DOPEG, DOMA and MOPEG. Normetanephrine and vanillylmandelic acid were not detected in the medium. This is probably the first documentation of the endogenous levels of NE and all its metabolites in medium containing tissue of the sympathetic nervous system.

Behavioural and biochemical alterations following haloperidol treatment and withdrawal: The animal model of tardive dyskinesia reexamined

1. 1. Behavioural and biochemical studies were carried out in rats given a single daily dose (1 mg kg , i.p.) of haloperidol for 30 days and subsequently withdrawn for 7 days. 2. 2. Long-term administration of haloperidol resulted in supersensitivity of dopamine receptors. This was manifested by enhanced Stereotypic biting, rearing, locomotor and floor activity of haloperidol withdrawn rats when challenged to a low dose of apomorphine (0.5 mg kg , s.c.) on the 8th day. 3. 3. Chronic haloperidol treatment significantly decreased dopamine synthesis and release as evidenced by low activity of tyrosine hydroxylase and low level of homovanillic acid in striatum. Dopamine levels did not change in the frontal cortex, striatum and midbrain. 4. 4. Haloperidol treatment significantly increased striatal γ-aminobutyric acid content and glutamic acid decarboxylase activity by 17% and 16% respectively. 5. 5. The decreased tyrosine hydroxylase activity and homovanillic acid level in corpus striatum might, in part, be due to an inhibitory effect of GABAergic neurons on dopaminergic system. 6. 6. Rats withdrawn from chronic haloperidol treatment showed significant increases in GABA level and glutamic acid decarboxylase activity. This probably resulted in further inhibition of dopamine release as evidenced by marked accumulation of dopamine in the corpus striatum and midbrain. 7. 7. No significant alterations in the endogenous levels of norepinephrine, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid were observed in haloperidol-treated and subsequently withdrawn rats. 8. 8. These data suggest that chronic haloperidol treatment and subsequent withdrawal results in the development of behavioural dopamine supersensitivity as well as biochemical alterations in dopaminergic and GABAergic system. 9. 9. The changes in these two neuronal systems seem to be interrelated.

The relationship between posture and plasma catecholamines in the pregnant woman.

The response of endogenous norepinephrine levels (NE) to changes in body posture, lateral to supine, was investigated in a prospective study of 46 primigravid patients during the last half of pregnancy. Blood samples were obtained in the lateral and supine positions. The mean supine NE levels were not significantly higher in those patients destined to develop pregnancy-induced hypertension (PIH) than in those who remained normotensive. The mean percent relative change of NE in the patients destined to develop PIH and in those who remained normotensive was not significantly different.

Effects of the noradrenaline neurotoxin DSP4 on the postnatal development of central noradrenaline neurons in the rat

The effect of the noradrenaline neurotoxin DSP4 on the postnatal development of central noradrenergic neurons in the rat has been investigated using neurochemical techniques. The results demonstrated a preferential effect of DSP4 on the locus coeruleus noradrenergic neuron system without any notable effects on the dopamine and adrenaline neurons and only a minor neurotoxic effect on the serotonin neurons. The effect of DSP4 on the serotonin neurons could be completely prevented by pretreatment with the uptake blocker zimelidine, without affecting the action of DSP4 on noradrenergic neurons. Neonatal DSP4 treatment systemically led to permanent depletions of noradrenaline in the cerebral cortex and spinal cord and marked increases of noradrenaline in the cerebellum and ponsmedulla. These effects of DSP4 were dose-dependent and could be blocked by pretreatment with the noradrenaline uptake blocker desipramine. The alterations in endogenous noradrenaline levels were quantitatively similar to changes observed in [ 3H]noradrenaline uptake in slices in vitro. There were no significant changes of these noradrenergic parameters when analysing the whole CNS after neonatal DSP4 treatment, in spite of marked regional changes in both directions. Administration of DSP4 to rats of different ages produced acutely marked depletions of noradrenaline in all regions including the pons-medulla and the cerebellum at all developmental stages. Marked and permanent depletions of noradrenaline were found in the distant noradrenergic nerve terminal projections after treatment at all ages, whereas increases in noradrenaline levels in the pons-medulla and cerebellum were only observed in rats treated with DSP4 up to the age of 3–5 days, whereas a DSP4 administration in older rats led to substantial and permanent depletions of noradrenaline in both these regions. The results indicate that the alteration of the postnatal development of noradrenergic neurons after treatment of rats up to the age of 3–5 days is mainly related to a ‘pruning effect’ of DSP4, in which prevention of the development of distant nerve terminal projections causes an increased outgrowth of nerves in collateral systems spared by the neurotoxin. The results indicate that DSP4 may be a useful denervation tool for studying various aspects of noradrenergic neurotransmission of developing locus coeruleus neurons.

Plasma catecholamine concentrations in normotensive rats of different strains and in spontaneously hypertensive rats under basal conditions and during cold exposure

Under basal conditions, the levels of circulating norepinephrine (NE) and epinephrine (E) were higher in normotensive Wistar rats of different origins than in Sprague-Dawley rats. Since the decline of 3H-NE concentration in the plasma after i.v. injection was similar in Wistar and in Sprague-Dawley rats, the higher levels of endogenous NE in the former strain probably reflect greater NE release from sympathetic nerve terminals. In normotensive Sprague-Dawley and Wistar rats, plasma NE rose to various extents during cold exposure (4°C), depending on the basal plasma NE levels. Compared with normotensive Wistar Kyoto rats (WKY), spontaneously hypertensive rats (SHR) had similar basal plasma E and NE concentrations, similar rates of 3H-NE disappearance, but more rapid increases to higher values of plasma NE during cold exposure. It is concluded that the basal rate of peripheral catecholamine release does not seem to be the main determining factor for arterial blood pressure in the various rat strains and that the sympathetic neuronal system of SHR is more responsive to cold exposure than that of WKY rats.

Substance P modifies the 6-hydroxydopamine induced alteration of postnatal development of central noradrenaline neurons

Systemic treatment of new-born rats with the catecholamine neurotoxin 6-hydroxydopamine leads to a permanent and selective alteration of the postnatal development of the central noradrenaline neurons, in particular of the locus coeruleus system. The changes involve a pronounced and permanent degeneration of distant nerve terminal projections (e.g. in the cerebral cortex and spinal cord) and a hyperinnervation of regions close to the noradrenaline perikarya (e.g. in the cerebellum and ponsmedulla). Substance P administered intracisternally was found to counteract significantly both the 6-hydroxydopamine-induced denervation and hyperinnervation, as monitored by measuring endogenous noradrenaline levels and [ 3H]noradrenaline uptake in vitro. The counteracting effect of substance P disclosed a clear dose-response relationship and was most effective when injected on postnatal days one and two, while practically no effects were observed after injection on postnatal days three and four. Substance P treatment alone of new-born rats had no effect on the postnatal development of the regional monoamine levels. Binding studies employing radioligand technique showed substance P treatment to abolish the 6-hydroxydopamine-induced increase in β-receptor binding in the frontal cortex, suggesting the ‘spared’ noradrenaline terminals to be functionally active. Substance P was shown to increase the utilization of noradrenaline in the neonatal stage. The results indicate that the counteracting effect of substance P may be due to a prevention of degeneration, growth stimulation and/or trophic influences on central noradrenaline neurons, possibly related to an excitatory effect of substance P on noradrenaline neurons.

The regrowth of right atrial noradrenergic nerves after 6-hydroxydopamine in genetically diabetic mice; effects of insulin treatment.

1 This study examined the rate of repletion of right atrial noradrenaline levels after a single dose (100 mg/kg i.p.) of 6-hydroxydopamine (6-OH Da) in diabetic and non-diabetic mice of the C57 BL/KS db/db strain. 2 In mice which received no 6-OH Da there was no significant difference, in endogenous noradrenaline levels, between diabetic and non-diabetic animals. The depletion of noradrenaline 24 h after 6-OHDa was slightly more profound in the diabetic mice than in non-diabetic controls. Thereafter the rate of repletion of noradrenaline was more rapid in the diabetic group. 3 The normal noradrenaline content was reinstated in diabetic mice between 7 and 10 days after 6-OHDa. In the non-diabetic group levels similar to those found in untreated mie were not reinstated until 14 days after 6-OHDa. 4 Ten days after 6-OHDa right atria from diabetic mice were markedly more responsive to stimulation of the intramural noradrenergic nerves than were preparations from non-diabetic mice. 5 A group of diabetic mice was treated with insulin (10 m Units/g daily) for 6 weeks. The right atria from these animals, examined 10 days after 6-OHDa, were similar in their responses to noradrenergic nerve stimulation to the preparations from the non-diabetic mice. 6 All these groups of atria gave similar responses to exogenous noradrenaline. These findings indicate that regrowth of noradrenergic terminals after 6-OHDa was more rapid in diabetic mice than in either insulin-treated diabetic mice or non-diabetic mice.

Changes in the development of central noradrenaline neurons after neonatal axon lesions

The effects of early surgical lesions of ascending noradrenaline (NA) axons and 6-hydroxydopamine (6-OHDA) induced NA denervation of the spinal cord on the postnatal development of central NA neurons of the rat have been studied using histo- and neurochemical techniques. The lesions were performed during the first week after birth and analyzed at the age of one or two weeks or in the adult stage. Complete unilateral hemisection at the mesencephalic level in the neonatal stage produced marked reductions of the 3H-NA uptake in vitro in the cerebral cortex with concomitant significant increases (+30–50%) of the uptake on the ipsilateral side of the ponsmedulla when determined in adulthood. Partial unilateral hemisection, restricted to produce an axotomy of the dorsal NA bundle, led to almost complete NA depletions in the cerebral cortex, while significant NA elevations were found in the mesencephalon (+25–40%), pons-medulla (+15%) and cerebellum (+90%) on the ipsilateral side. In the latter region a significant NA increase (+50%) was also observed in the controlateral side. Regional analysis of the 3H-NA uptake after partial hemisection gave similar results. Intraspinal injection of 6-OHDA on the day of birth resulted consistently in marked NA depletions (−90% or more) in the spinal cord, while the effects on NA in the cerebral cortex varied, being either unaffected or markedly reduced. Animals with unaffected cerebral cortex disclosed a significant NA increase in the pons-medulla only, whereas animals with cortical NA denervation displayed significant increases in endogenous NA levels both in the pons-medulla and the cerebellum. The present results give further support for the “pruning effect” concept explaining the growth response that central NA neurons exhibit after neonatal 6-OHDA treatment systemically or when one axonal branch is damaged neonatally.

Noradrenaline and dopamine-beta-hydroxylase levels in rat salivary glands after preganglionic nerve stimulation: evidence for re-use of amine storage granules in transmitter release.

The levels of endogenous noradrenaline (NA) in rat salivary glands were reduced to about 40 per cent after 1 hour of preganglionic stimulation at 4 Hz. Following 2 to 3 hours of rest the NA values had recovered to normal and remained normal for 6 hours after the stimulation. The recovered NA could be depleted by renewed nerve stimulation. After treatment with reserpine the NA disappeared almost completely. The recovered NA is discussed to be mainly present in amine storage granules that are re-used for storage and transmitter release. The axonal down-transport of new granules to the nerve terminals appears to be too small, as based on earlier results, for being of any quantitative importance in the experimental situation. The dopamine-beta-hydroxylase (DBH) level in the glands did not significantly change after the period of stimulation. The DBH content remained mainly unchanged following either post-stimulation recovery, repeated stimulation, or reserpine treatment. First when the glands were stimulated for 4 hours, there was a small decrease of the DBH levels. The mainly unchanged levels of DBH after stimulation does not appear to be explained by "trapping" in the tissue of released DBH, or recovery of the DBH by a marked axonal down-transport of new granules, as based on earlier results. The results of the DBH estimations support the view that the granules are not consumed to any marked extent at nerve activity, but can be re-used for nerve transmission. Furthermore, the results are in agreement with lack of correlation between released NA and released DBH.

High-affinity [ 3H]desipramine binding in the peripheral and central nervous system: A specific site associated with the neuronal uptake of noradrenaline

The specific binding of [ 3H]desipramine to various brain regions and peripheral tissues of the rat was of high affinity, rapid and reversible. It was inhibited with high affinity only by tricyclic antidepressants and noradrenaline uptake blockers. There was a highly significant correlation between the potencies of a series of drugs for the inhibition of [ 3H]desipramine binding and for the inhibition of noradrenaline uptake. Substrates for the noradrenaline uptake system however inhibited the binding of [ 3H]desipramine only at very high concentrations. Postganglionic sympathetic denervation of the submaxillary gland and the heart both resulted in a pronounced decrease in [ 3H]desipramine binding sites, which paralleled the reduction in endogenous noradrenaline levels. High-affinity [ 3H]desipramine binding sites thus appear to be localised on noradrenergic nerve endings and are probably closely associated with the neuronal uptake system for noradrenaline.

Noradrenergic neurotransmission in the brain of a convulsive mutant mouse, differences between the cerebral cortex and the brain stem.

The Quaking mouse is a genetically determined model of convulsive disorders. We investigated the modulation of noradrenergic neurotransmission through alpha 2-adrenoceptors in the occipital cortex and the brain stem of this mutant. The endogenous levels of noradrenaline were similar in the cerebral cortex of the Quaking mice and their corresponding controls, while a significant increase of endogenous noradrenaline was found in the brain stem of the mutants. The rate of disappearance of noradrenaline in the cerebral cortex and the brain stem after injection of FLA 63 was identical in control and Quaking mice. The calcium-dependent electrically evoked overflow of 3H-noradrenaline from slices of occipital cortex was inhibited by clonidine and enhanced by yohimbine in Quaking as well as in normal mice. The negative feed-back mechanism mediated by presynaptic alpha 2-adrenoceptors operates to a similar extent in both strains of mice. In contrast to the occipital cortex, in the brain stem, the amount of neurotransmitter released by electrical stimulation was significantly increased in Quaking mice when compared with controls. However, in the brain stem, the negative feed-back regulation of noradrenaline release operates to a similar extent in both strains of mice. When the endogenous levels of MOPEG were determined in the brain stem, they were found to be significantly higher in the Quaking mice when compared to the controls. The results suggest that an increase in noradrenergic neurotransmission in the brain stem, rather than in the cerebral cortex, could contribute to the behavioural abnormalities exhibited by the Quaking mice.

Degeneration activity of the pineal gland after sympathetic denervation.

After removal of the superior cervical ganglia the pineal gland of the rat showed a period of transient increase in activity of serotonin-N-acetyltransferase. This degeneration activity was preceded by a decline of the levels of endogenous noradrenaline and an impairment of the 3H-metaraminol uptake. Twenty-seven hours after sympathetic denervation the levels of the endogenous neurotransmitter were almost completely depleted, while either 24 h or 21 days after denervation total uptake of the tritiated amine decreased to only about 50% of the control values. Previous chronic sympathetic decentralization elicited in the pineal gland post-junctional supersensitivity, as judged by the enhanced degeneration activity observed in decentralized glands after sympathetic denervation. The present findings confirm that, in endocrine glands and similarly to other autonomically innervated organs, acute denervation induces degeneration activity.

Noradrenaline reactivity in patients with phaeochromocytoma before and after surgical correction.

1. For comparable blood pressures, plasma noradrenaline is disproportionately higher in patients with phaeochromocytoma than in those with essential hypertension. 2. The ‘pressor-dose’ of noradrenaline or its reciprocal, the reactivity index, were abnormal in patients with phaeochromocytoma before surgery and made normal by surgical removal of the phaeochromocytoma. 3. There was a significant correlation between blood pressures and the logarithm of plasma noradrenaline concentrations. 4. The higher dose of exogenous noradrenaline required in patients with phaeochromocytoma for a given rise in blood pressure seems to be the expression of the higher levels of endogenous noradrenaline rather than true decreased reactivity.

Neurochemical and behavioural correlates of the interaction between amphetamine and Δ9-tetrahydrocannabinol in the rat

A single dose of Δ 9-tetrahydrocannabinol (THC) (10 or 100 mg/kg) was administered via stomach gavage following the single injection intraperitoneally of an acute dose of amphetamine (1 or 3 mg/kg) in the rat. The THC effects, which included a reduction in spontaneous locomotor activity, the development of prostration, and circling behaviour, were antagonized in a dose-dependent manner by pretreatment with amphetamine. Although no change in the endogenous levels of noradrenaline, dopamine and serotonin in hypothalamus, hippocampus, caudate-putamen or the rest of brain occurred with THC, it appears that THC may have increased dopamine turnover in the brain. The dose-dependent amphetamine antagonism to the behavioural effects of THC was paralleled by a dose-related increase in brain dopamine concentration. This elevation in dopamine levels may be instrumental in triggering the neuronal events responsible for the amphetamine antagonism of the actions of THC. The subtle interaction of THC with brain dopamine neural systems may be involved in the reinforcing properties of the self-administration of THC.