Comparison of the monoamine and catabolite content in the cat and rabbit carotid bodies

The monoamine and catabolite contents of a large number of rabbit (n = 95) and cat (n = 32) carotid bodies (CBs) have been measured by high performance liquid chromatography with electrochemical detection (HPLC-ED). The dopamine (DA) content as well as that of its precursors tyrosine (TYR), dihydroxyphenylalanine (DOPA) and catabolites dihydroxyphenylacetic acid (DOPAC), homovanilic acid (HVA) were approximately equal in both species. The noradrenaline (NA) content was 10 times larger in the cat than in the rabbit CBs. Twenty-nine out of the 32 cat CBs contained more NA than DA while the reverse was true in 92 out of 95 rabbit CBs. In 11 cats the right CB was sympathectomized and its DA and NA contents were compared to those of intact contralateral organs.     

Regulatory aspects of nigrostriatal dopaminergic neurons

Summary In the urethane-anesthetized rat, electrical stimulation (10 Hz, 30 s, 250 A) of the medial forebrain bundle (MFB), at 20-min intervals over an 8-h period, combined with intracerebral microdialysis in the striatum caused: an undiminished increase in the release of dopamine (DA) with each stimulation episode; a decreased efflux of 3,4-dihydroxyphenylacetic acid (DO-PAC) and 4-hydroxy-3-methoxyphenylacetic acid (HVA) after the first stimulation only; a delayed increased efflux of DOPAC with no change in HVA; and a poststimulation depression of firing of dopaminergic neurons in the substantia nigra (before, 3.1±0.7 Hz; after, 1.9±1.0 Hz; P<0.05). After the last stimulation episode, the release of DA declined to prestimulation values, while the increased efflux of DOPAC persisted for three more hours. After the infusion of tetrodotoxin (4.0×10^-7 M, 1.5 l, 1.0 l/min) into the MFB, the basal release of DA was reduced (P<0.05), while the efflux of DOPAC and HVA was increased (P<0.05). A model is proposed suggesting that: (1) during increased release of DA in the striatum, the metabolism of DA is decreased; (2) inhibition of nigrostriatal dopaminergic neurons is the usual cause of increased synthesis and metabolism of DA in the striatum; and (3) increased release of DA, and increased synthesis and metabolism of DA in the striatum are not causally linked and are noncoupled processes.     

Effect of sex and age on brain monoamines and spatial learning in rats

The concentrations of noradrenaline (NA), dopamine (DA), serotonin (5-HT), and their metabolites were measured in the prefrontal cortex, caudate-putamen, and hippocampus in young (3 months) and aged (27–31 months) Wistar rats of both sexes. Age-related changes were found in prefrontal NA and HVA/DA ratio, striatal DA and DOPAC/DA ratio, and striatal and hippocampal 5-HT and 5-HIAA/5-HT ratio. Age and sex dependent changes were found in striatal DA and DOPAC/DA ratio, and hippocampal MHPG-SO₄/NA ratio. The aged rats were tested in spatial discrimination and reversal tasks in a T maze. The effects of α₂-agonist medetomidine (3 μg/kg) on the task performance were assessed in relation to individual variation in monoamine metabolism. Medetomidine impaired spatial discrimination learning of the aged rats by interacting with the hippocampal 5-HT turnover. Medetomidine improved reversal learning through an interaction with the striatal DA turnover and reduced the number of perseverative errors after reversal, mainly due to its interaction with the prefrontal NA turnover. It is concluded that the memory enhancing effect of drugs acting through the brain monoamine systems is highly dependent on the stage of degeneration of these systems that show considerable individual variation in aged animals.     

Atrial natriuretic factor,urinary catechol compounds and electrolyte excretion in rats during normal hydration and isotonic volume expansion. Influence of dopamine receptor blockade.

To investigate the influence of acute isotonic volume expansion (VE) on the plasma concentration of atrial natriuretic factor (ANF), the excretion of catechol compounds and electrolytes and the whole kidney glomerular filtration rate (GFR), these variables were measured before and during 60 min of VE (2% of body weight per hour). Atrial natriuretic factor was measured at the end of the experiment. In a control group (n= 7) without volume expansion, plasma ANF was 58 ± 4 pg ml^-1. The excretion of sodium, dopamine (DA), 3 ,4–dihydroxyphenylacetic acid (DOPAC), noradrenaline (NA) and GFR did not change during the control study. In VE animals (n= 7) plasma ANF was 82 ± 7pg ml^-1, significantly higher than in the control group. Sodium excretion increased more than 17–fold. The excretion of the DA increased by 38% and that of DOPAC by 30%. Noradrenaline excretion remained unchanged while GFR increased by 20%. In haloperidol-pretreated animals subjected to VE (n = 7). plasma ANF was 81± 8 pg ml^-1 during VE, significantly higher than in the control animals. Although the sodium excretion increased more than ninefold in this group during VE, this increase was only 55 % of that in the VE group not given haloperidol. The DA and DOPAC excretion was increased by haloperidol, indicating a feedback effect of receptor blockade. DOPAC excretion was not increased further by VE, hut the excretion of DA increased by 15% and GFR increased by 19%. In conclusion, haloperidol reduced the natriuretic response to VE without impairing either the VE-induced release of ANF or the increase in GFR. The results indicate an important involvement of ANF and DA in the natriuretic response to VE.     

Differential effects of -trytophan and buspirone on biogenic amine contents and metabolism in Lurcher mice cerebellum

The effects of serotoninergic stimulation on monoamines were studied in the heterozygous Lurcher (Lc/+) mutant mouse, a model of human cerebellar ataxia. Wild type (+/+) and Lc/+ mice were treated for 40 days with -tryptophan or buspirone, and serotonin (5-HT), dopamine (DA), noradrenaline (NA) and their main metabolites were measured in the cerebellum. In +/+ mice, only buspirone increased concentrations of 5-HT metabolites. In the hypoplastic Lc/+ cerebellum, indoleamines were higher, and increased further after both treatments. The 5-HT turnover index was increased in +/+ mice by buspirone, while in Lc/+ mutants it increased after -tryptophan but was decreased by buspirone, indicating that in the mutants nerve terminals synthesize and accumulate 5-HT, but may not utilize it efficiently. Catecholamine contents remained unchanged in +/+ mice, but in Lc/+ mutants with higher endogenous NA, -tryptophan further increased NA and 3,4-dihydroxy-phenylacetic acid (DOPAC), and buspirone augmented NA, DA and DOPAC levels.     

Pharmacological investigation on the role of dopamine in the rat locus coeruleus

The role of dopamine (DA) in the rat locus coeruleus (LC) was investigated by determining the levels of 3,4-dihydroxyphenylacetic acid (DOPAC), DA and noradrenaline (NA) in the LC after pharmacological treatments by pargyline, haloperidol, 6-hydroxydopamine (6-OHDA) and desmethylimipramine (DMI). The DA, DOPAC and NA contents of the LC were determined by high pressure liquid chromatography. Fifteen days after 6-OHDA, the DOPAC and NA levels were reduced by 60%, but they remained constant after 6-OHDA + DMI. Pargyline provoked highly significant increases in DA and NA but reduced DOPAC to non-measurable amounts. Haloperidol caused a 54% decrease in the DOPAC levels. Pargyline and haloperidol administered to rats having received 6-OHDA + DMI 15 days before, caused similar effects on DA, DOPAC and NA levels as those in non-treated rats. It is suggested that DOPAC is mainly located in noradrenergic neurons, thus eliminating the possibility of a significant DA cell body population in the rat LC.     

Enhanced monoamine release in the median preoptic area following reduced extracellular fluid volume in rats.

The role of monoaminergic neural inputs to fluid regulatory systems in the median preoptic nucleus (MnPO) was investigated by examination of monoamine metabolism during reduction of systemic extracellular fluid volume in freely moving rats. Extracellular fluid volume was decreased iso-osmotically by subcutaneous polyethylene glycol (PEG), and extracellular noradrenaline (NA), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) were measured using intracerebral microdialysis techniques. PEG treatments significantly increased NA, DA and DOPAC release in the MnPO area. The results suggest that monoaminergic neural systems in the region of the MnPO are important in the control of extracellular fluid balance.     

Atrial natriuretic factor, urinary catechol compounds and electrolyte excretion in rats during normal hydration and isotonic volume expansion. Influence of dopamine receptor blockade

To investigate the influence of acute isotonic volume expansion (VE) on the plasma concentration of atrial natriuretic factor (ANF), the excretion of catechol compounds and electrolytes and the whole kidney glomerular filtration rate (GFR), these variables were measured before and during 60 min of VE (2% of body weight per hour). Atrial natriuretic factor was measured at the end of the experiment. In a control group (n = 7) without volume expansion, plasma ANF was 58 +/- 4 pg ml-1. The excretion of sodium, dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), noradrenaline (NA) and GFR did not change during the control study. In VE animals (n = 7) plasma ANF was 82 +/- 7 pg ml-1, significantly higher than in the control group. Sodium excretion increased more than 17-fold. The excretion of the DA increased by 38% and that of DOPAC by 30%. Noradrenaline excretion remained unchanged while GFR increased by 20%. In haloperidol-pretreated animals subjected to VE (n = 7), plasma ANF was 81 +/- 8 pg ml-1 during VE, significantly higher than in the control animals. Although the sodium excretion increased more than ninefold in this group during VE, this increase was only 55% of that in the VE group not given haloperidol. The DA and DOPAC excretion was increased by haloperidol, indicating a feedback effect of receptor blockade. DOPAC excretion was not increased further by VE, but the excretion of DA increased by 15% and GFR increased by 19%.(ABSTRACT TRUNCATED AT 250 WORDS)     

High-performance liquid chromatographic analysis of monoamines in the cestodeDiphyllobothrium dendriticum

The presence of biogene monoamines in adult and larvalDiphyllobothrium dendriticum (Cestoda) was investigated by high-performance liquid chromatography with electrochemical detection (HPLC-ED). The biogene amines serotonin (5-HT), dopamine (DA), noradrenaline (NA), and adrenaline (A) as well as many of their precursors and metabolites, comprising a total of 15 different substances, were analyzed. 5-HT, DOPA, DA, NA, and A were detected in the worm, with 5-HT, DOPA, and DA being the dominating amines. The DA metabolites DOPAC and 3-MT or the 5-HT precursor 5-hydroxytryptophan could not be detected, but two unidentified substances, believed to be catecholic, were present in the worm. A high concentration of DOPA was measured in the proglottids and especially in the eggs. This is the first report of A in a flatworm.     

Components of taurine efflux in rat brain synaptosomes.

The efflux of [³⁵S]taurine from isolated rat brain synaptosomes was studied in a superfusion system. The spontaneous efflux of taurine was slow and could be described as comprising two first-order rate components, of which the slower (t_1/2 = 77.0min) represents release from intrasynaptosomal spaces. Only a high taurine concentration (10 mmol/1) in the medium enhanced the efflux of intrasynaptosomal taurine, which indicates a rather stable intrasynaptosomal taurine compartment. Depolarizing concentrations of potassium ions stimulated taurine efflux and also induced the appearance of a new ‘intermediate’ efflux component. This component was absent when calcium ions were omitted from the medium. It is therefore suggested that the component may originate from the emptying of synaptic vesicles.     

Decay of heat acclimation during exercise in cold and exposure to cold environment

Sixteen male students exercised for 14 days (1 h/day) in the heat for heat acclimation (HA). During deacclimation (DA) one group exercised in the cold (EXG, n=8) for 60 min/day (morning) and was exposed to the cold for another hour (afternoon) for 14 days. The other group was exposed to the cold (EPG, n=8) for 1 h each in the morning and afternoon (Ta: 18.0°C, RH: 58%) over the same period. All returned to exercise in the heat for reacclimation (RA) for 10 days. Subjects were tested on days 1, 16, 21, 32, 36 and 44 on a bicycle ergometer for 60 min at 60% of VO_2max in the heat (Ta: 31.1°C, RH: 70%). Rectal temperature (T _re) and heart rate (HR) at 40 min of exercise were used to determine the decay/gain of HA, which was calculated using the formula described by Pandolf et al. (Ergonomics, 20:399–408, 1977). After HA (day 16) T _re and HR decreased significantly. During DA, EXG showed decay in T _re of 24 and 35% and HR of 29 and 35% on days 21 and 32, respectively. For EPG the corresponding decay was of 2 and 9% for T _re and 17 and 17% for HR. After 10 days of RA, EXG showed gains of 11% in T _re and 12% in HR, while EPG showed gains of 47% in T _re and 38% in HR. In conclusion, EXG had greater decay during DA and lower gains in RA compared to EPG. However, the differences between groups were significant only for T _re after 4 days of DA.     

Effect of O2 availability on neuroendocrine variables at rest and during exercise: O2 breathing increases plasma prolactin

Neuroendrocrine and substrate responses were investigated in eight male athletes during inhalation of either 100% O₂ (HE), 14% O₂ (HO) or normoxic gas (NO) before, during and after 60 min of cycle ergometry at the same absolute work rate. Concentrations of prolactin (PRL), growth hormone (GH), testosterone (T), adrenocorticotropic hormone (ACTH), cortisol (COR), adrenalin (A), noradrenalin (NA), insulin (INS), ammonia (NH₃), free fatty acids, serotonin (5-HT), total protein, branched-chain amino acids (BCAA) and free tryptophan (free TRP) were determined in venous blood and lactate concentration [LA⁻], partial pressure of oxygen (PO₂), oxygen saturation (SO₂), partial pressure of carbon dioxide and pH in capillary blood. ThePO₂ andSO₂ were augmented in HE and decreased in HO (P ≤ 0.01). In HO and NO no significant changes were found for any other parameter during 30 min of rest prior to exercise. In HE, PRL increased by about 400% during this time, while NA declined (P ≤ 0.01). Heart rate (HR) and [LA⁻] were higher during exercise in HO (P ≤ 0.01). In all trials, NH₃, NA, A, T, GH and ACTH increased during exercise (P ≤ 0.01), while BCAA and INS declined. In comparison to NO and HE, increases of NA, A, GH, COR and ACTH were higher in HO (P < 0.01). The PRL in NO and COR in NO and HE did not change significantly. In HE, after the initial increase at rest, PRL declined during exercise but remained higher than in HO. Higher values for NA, A, GH, COR and ACTH in HO were likely to have reflected an augmented relative exercise intensity. Our results showed that PRL but no other hormone increased during acute exposure to hyperoxia. This PRL release was independent of exercise stress and greater than PRL augmentation during hypoxia, which was related to a higher relative exercise intensity as indicated by [LA⁻] and HR. Responses of plasma NH₃, BCAA, free TRP and 5-HT could not explain PRL augmentation induced by the increment in bloodSO₂ during hyperoxia. Deceased     

Assay of dopamine and its metabolites in human and rat retina

Human and rat retina dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were measured after various delays in enucleation and freezing of the eyes. Human eyes were enucleated 45 min to 4 h after death, kept at 4 degrees C and frozen at -70 degrees C from 1.5 to 15 h after enucleation. In human retina, maximal DA concentration (4.85 ng/mg prot.) was obtained from eyes enucleated with a delay of 1 h and frozen with a delay of 2 h. After longer delays, DA concentrations decreased. Retinas of humans who died during the night had lower DA retina concentrations compared to those who died during daytime. Rats were decapitated and the eyes enucleated within 5 min or with a delay up to 8 h before freezing at -70 degrees C or kept at 4 degrees C for 5 min to 12 h before being frozen at -70 degrees C. Delays in enucleation of the rat eyes markedly decreased DA retinal concentrations with a minimal value reached as soon as 2 h after death. However, when the rat eyes were kept at 4 degrees C the minimal value was obtained after a longer period of time (about 7 h). Our results thus show that time of death and delays in enucleation and freezing significantly influence DA and its metabolite concentrations in retinas of rats and humans.     

损毁Parkinson病大鼠腹侧苍白球对纹状体内多巴胺的影响

应用6羟基多巴胺(6OHDA)制备Parkinson病(PD)大鼠模型,插入电极通过直流电毁损腹侧苍白球(VP),观察毁损术后PD大鼠旋转行为的变化,并应用高压液相色谱检测纹状体内多巴胺(DA)及3,4二羟甲基苯丙氨酸(DOPAC)和去甲肾上腺素(NA)的含量。结果显示:直流电毁损VP可使PD模型大鼠的旋转行为明显减少;毁损侧纹状体内DA的含量减少,DOPAC和NA的含量增加。上述结果提示VP毁损可明显改善PD大鼠的旋转行为,此效应可能与抑制VP的异常兴奋有关。     

Synthesis of Noradrenaline from 3,4-Dihydroxyphenylalanine (DOPA) and Dopamine in Adrenergic Nerves of Mouse Atrium — Effect of Reserpine,Monoamine Oxidase and Tyrosine Hydroxylase Inhibition

The in vitro synthesis of noradrenaline (NA) from 3,4-dihydroxyphenylalanine (DOPA) and dopamine (DA) in the mouse atrium has been investigated, using isotope, subcellular distribution and histochemical techniques. Incubation of atrial tissue in 5 times 10^-6 M ¹⁴C-DOPA resulted in a formation of ¹⁴C-NA and ¹⁴C-DA at a rate of about 0.13 μg/g/hr, and 0.14 μg/g/hr respectively, whereas the same medium concentration of ³H-DA gave a formation of ³H-NA of about 0.25 μg/g/hr. The synthesis of NA and DA was found to be almost exclusively associated with the presence of adrenergic nerves, since it was considerably reduced after pretreatment with 6-OH-DA. Pretreatment with reserpine decreased formation of radioactive NA and DA which could be counteracted by nialamide. The effect of reserpine may be explained by inhibition of DA uptake in the amine storage granules. The antagonistic effect of nialamide is certainly due to inhibition of DA catabolism. Tyrosine hydroxylase inhibition produced by H44/68, which depleted the endogenous NA store to about 40% of normal, increased the formation of radioactive NA both from ³H-DA and ¹⁴C-DOPA. This may in part be explained by decreased competition of the endogenous precursor DA for DA-β-hydroxylase but also in part by increased storage sites available for newly formed NA.     

Tyramine‐induced endogenous noradrenaline efflux from in situ cardiac sympathetic nerve ending in cats

With the use of dialysis technique, the effects of tyramine on in situ cardiac sympathetic nerve endings were examined in anaesthetized cats. Dialysis probes were implanted in the left ventricular myocardium, and the concentration of dialysate noradrenaline (NA) served as an indicator of NA output at the cardiac sympathetic nerve ending. Locally applied tyramine (600 μM ) increased dialysate NA levels from 17 ± 1 (pg mL^?1) to 3466 ± 209 (pg mL^?1). Pretreatment with reserpine (vesicle transport NA blocker 1 μM ) did not affect tyramine‐induced NA efflux. The tyramine‐induced NA efflux was augmented by pretreatment with pargyline (1 m M ) but suppressed by pargyline (10 m M ). Pretreatment with α‐methyl‐tyrosine suppressed NA efflux evoked by tyramine. These pretreatments did not affect the time course of NA efflux but only altered peak height of NA efflux. The efflux of NA evoked by tyramine was not associated with any reduction of dihydroxyphenylglycol (DHPG). In contrast, in the pretreatment with reserpine, the efflux of NA was associated with a reduction of DHPG. This result suggests that NA graduation between axoplasm and stored vesicle contributes to maintaining the axoplasmic NA level during carrier‐mediated outward NA transport. The tyramine‐induced NA efflux provides a close reflection of the NA content at the nerve ending. With the use of dialysis, this experimental model is suitable for studying the mechanism of sympathomimetic amine‐induced neurotransmitter efflux.     

Reduced light responsiveness of the cone pathway during prolonged darkness does not result from an increase of dopaminergic activity in the fish retina

Dopaminergic activity in the fish retina during prolonged darkness was analyzed by monitoring total dopamine (DA) content, dihydroxyphenylacetic acid (DOPAC) and endogenous release of DA. Whereas DOPAC values drop to a third within the first 90 min of darkness, the releasable pool of DA increases by a third during this period. Endogenous release of DA drops to about 25% within the first 30 min and remains at this low level during continuous darkness. These data demonstrate that the electrophysiologically observed sensitivity reduction of horizontal cells during prolonged darkness is not due to an increase of dopaminergic activity during this period.     

Dopamine uptake in platelets: Two different low-affinity,saturable mechanisms

Uptake of dopamine (DA) in human blood platelets was found to encompass two different saturable components, one chloride-dependent and one non-chloride-dependent. The chloride-dependent uptake had an apparentK _m of about 4×10^–5 M, was strongly inhibited by serotonin (5HT), and moderately inhibited by ouabain, PHMB and by substituting K⁺ for Na⁺ in the incubation medium. The antidepressants imipramine, clomipramine, desipramine and nomifensine showed approximately the same inhibitory potency against this uptake as against 5HT uptake in platelets. This chloride-dependent uptake mechanism is probably identical with the 5HT uptake mechanism in platelets. The non-chloride-dependent uptake had an apparentK _m of about 1.4×10^–4 M, and was not inhibited by metabolic inhibitors or antidepressants, and only moderately by 5HT. Its characteristics seem to be in accordance with facilitated diffusion. When platelets preloaded with DA were reincubated in fresh medium without chloride, the efflux curve indicated a distribution between one superficial and one deep compartment, containing 68% and 32% of total platelet DA, respectively. The deep compartment probably corresponds to the dense osmiophilic granules. The efflux kinetics are similar to those found for 5HT.     

Action potentials,ion channel currents and transverse tubule density in adult rabbit ventricular myocytes maintained for 6 days in cell culture

 Adult rabbit ventricular myocytes were cultured in a basic medium (Medium 199) for up to 6 days to assess preservation of morphology and ion channel currents. In culture, cells remained rod shaped and striated but their ends became progressively rounded. Cell cross-sectional area declined slightly (by 14%) over the first 24 h, in contrast, whole-cell capacitance (which reflects external surface membrane plus membrane infoldings) decreased by 42% over the same time. Using whole-cell patch-clamp, we observed that the typical ”N” shape steady-state current-voltage (I-V) relation became flattened after 24 h in culture. L-type Ca channel density was assessed as barium flux (I _Ba,L) via the channel. I _Ba,L (normalised to cell capacitance) declined by 50% after 24 h and recovered partially by days 4 and 6. The density of inward rectifier K current declined by 54% after 24 h and showed no recovery subsequently. In contrast, there was no significant decline in the density of transient outward K current after 24 h, but it declined subsequently by 65% after 6 days. We speculate that the time course of change in each ion channel density may reflect a change in pattern of ion channel expression, or differential membrane loss since the density of transverse tubules decreased by 57% after 6 days in culture. These results suggest that even by 24 h in culture, ion channel density in myocytes has changed substantially from the acutely isolated state. Received: 24 July 1995 / Received after revision: 15 November 1995 / Accepted: 15 November 1995     

Evidence that the substantia nigra is a site of action for L-DOPA

Rats with unilateral 6-hydroxydopamine lesions of the substantia nigra (SN) were challenged with L-DOPA (25 mg/kg, i.p.). One hour later, during the peak of rotational behavior, the animals were killed and the striatum and the SN were dissected and assayed for dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) content. While L-DOPA treatment elevated DA levels in the lesioned striatum by only 10%, DA levels in the lesioned SN were completely restored to normal levels. DOPAC levels showed similar changes. In order to establish whether the large DA increase in the lesioned SN contributed to L-DOPA-induced contralateral circling, animals were implanted with chronic in-dwelling cannulas in the lesioned SN. Infusion of the DOPA decarboxylase inhibitor carbidopa (5 micrograms in 1 microliter) 30 min prior to peripheral L-DOPA injection not only reduced contralateral circling but reversed the direction of turning 20 min after the L-DOPA injection. The results are discussed in terms of dopaminergic regulation of the striatonigral pathway, their clinical relevance to Parkinson's disease and the suggestion that the SN is an important site for the action of L-DOPA.