Long-term depressor effects of catecholamine neuronal grafts in the third ventricle of the brain in normotensive rats

Summary Neuronal tissue containing A-6 group noradrenalin (NA) neurons of the locus ceruleus, or A-10 group dopamine (DA) neurons of the substantia nigra, was grafted into the third ventricle at the level of the preoptic-anterior hypothalamic region, in normotensive male rats. A significant and long-lasting depressor effect was shown in rats with either graft. In rats with an NA neuron-rich graft, plasma concentrations of arginine-vasopressin (AVP), plasma renin activity (PRA), and corticosterone (CS) decreased significantly, whereas in rats with a DA neuron-rich graft, AVP and PRA concentrations also decreased significantly but CS showed no significant change. Neither NA nor adrenalin in plasma changed significantly in rats with either graft.     

Use of three specific radioimmunoassays in measuring neurohypophysial hormone content and plasma concentrations of vasopressin, oxytocin and DDAVP in rats after prolonged infusion of DDAVP

Specific radioimmunoassays (RIA) were employed for measuring plasma and neurohypophysial concentrations of oxytocin (OT) and vasopressin (AVP) after administration of 1-deamino-8-D-Arg-vasopressin (DDAVP). DDAVP concentrations were measured by a newly-developed specific RIA. Through the use of minipumps, DDAVP was infused i.p. over a period of 3 days in normally hydrated rats. Despite decreased urine production and increased urine osmolality no changes could be observed in neurohypophysial and plasma hormone concentrations.     

Use of three specific radioimmunoassays in measuring neurohypophysial hormone content and plasma concentrations of vasopressin,oxytocin and DDAVP in rats after prolonged infusion of DDAVP

Summary Specific radioimmunoassays (RIA) were employed for measuring plasma and neurohypophysial concentrations of oxytocin (OT) and vasopressin (AVP) after administration of 1-deamino-8-D-Arg-vasopressin (DDAVP). DDAVP concentrations were measured by a newly-developed specific RIA. Through the use of minipumps, DDAVP was infused i.p. over a period of 3 days in normally hydrated rats. Despite decreased urine production and increased urine osmolality no changes could be observed in neurohypophysial and plasma hormone concentrations.     

The effect of guanethidine treatment of testicular blood flow and testosterone production in rats

Testicular blood flow was measured by means of Xenon-133 clearance in control rats and rats treated with guanethidine for 3 weeks. Plasma and testis testosterone concentrations were also measured, and the effect of hCG-treatment was examined. No difference in testicular blood flow between the control group and the guanethidine-treated group was found. However, in guanethidine-treated rats, plasma and testis testosterone concentrations after hCG-treatment were significantly decreased. The results may indicate that adrenergic nerves are involved in the regulation of Leydig cell function.     

The effect of guanethidine treatment of testicular blood flow and testosterone production in rats

Summary Testicular blood flow was measured bymeans of Xenon-133 clearance in control rats and rats treated with guanethidine for 3 weeks. Plasma and testis testosterone concentrations were also measured, and the effect of hCG-treatment was examined. No difference in testicular blood flow between the control group and the guanethidinetreated group was found. However, in guanethidine-treated rats, plasma and testis testosterone concentrations after hCG-treatment were significantly decreased. The results may indicate that adrenergic nerves are involved in the regulation of Leydig cell function.     

Effects of neurochemical lesions restricted to spinal cord monoaminergic neurons on blood pressure and sympathetic activity of spontaneously hypertensive rats

Intraspinal (i.s.) injection of 6-hydroxydopamine or 5,7-dihydroxytryptamine in newborn spontaneously hypertensive rats (SHR) resulted, in the adult animal (30-week-old), in a marked decrease of spinal cord noradrenaline (NA) or 5-hydroxytryptamine (5-HT) levels, respectively. Since both neurotoxin- and vehicle-injected rats developed full hypertension and had similar plasma catecholamine concentrations, it is concluded that in SHR neither spinal cord NA nor 5-HT play a major role in development and maintenance of hypertension.     

Reduced tuberoinfundibular dopaminergic neuronal function in rats after long-term withdrawal of estrogen treatment

Summary Hypothalamic fragments from female rats treated repeatedly with estradiol valerate (EV) and bearing prolactin (PRL)-secreting tumors contained, seven months after the last EV injection, lower concentrations of dopamine (DA) than age-matched controls. Depolarizing concentrations of K⁺ (35 mM) and amphetamine (50 M) evoked in PRL-secreting tumor bearing rats an endogenous DA release significantly lower than in controls.     

Effect of prostaglandin E2 (PgE2) on the biosynthesis and metabolism of noradrenaline (NA) in the isolated and perfused rabbit heart]

In isolated perfused rabbit heart, Pg E2 at concentrations ranging from 1.10(-8) to 1.10(-4) M has shown no significant action either on the biosynthesis or on the metabolism of NA. But it inhibited NA uptake, nevertheless this action was weak.     

L-threo-3,4-dihydroxyphenylserine,a noradrenaline precursor,inhibits dopamine release and metabolism in the rat striatum in vivo

The effect of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) on dopamine (DA) release and metabolism in the striatum was studied in freely moving rats by intracerebral microdialysis techniques. The DA level as well as the levels of 3,4-dihydroxyphenylacetic acid and homovanillic acid were significantly decreased 140 min after the administration of L-threo-DOPS (50 mg/kg intraperitoneally). The results suggest that L-threo-DOPS inhibits the release and metabolism of DA in the striatum.     

L-threo-3,4-dihydroxyphenylserine, a noradrenaline precursor, inhibits dopamine release and metabolism in the rat striatum in vivo.

The effect of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) on dopamine (DA) release and metabolism in the striatum was studied in freely moving rats by intracerebral microdialysis techniques. The DA level as well as the levels of 3,4-dihydroxyphenylacetic acid and homovanillic acid were significantly decreased 140 min after the administration of L-threo-DOPS (50 mg/kg intraperitoneally). The results suggest that L-threo-DOPS inhibits the release and metabolism of DA in the striatum.     

Behavior and catecholamine levels: comparative study of gregarious insects, solitary insects, and those treated with carbon dioxide in Locusta migratoria (Insecta, Orthoptera)]

The dopamine (DA) and noradrenaline (NA) was measured in Locusta migratoria for 3 groups of individuals showing differences in their motility: gregarious are very active, solitary and animals in chronic treatment by CO2 (1 mn/day) show a very low motility. NA is present in small amounts (0,120-0,250 microng/g) in the 3 groups without significant differences. On the contrary, the quantity of DA is 5 times greater in gregarious than in the 2 other groups (1,78 and 0,31-0,39 microng/g). Thus it is suggested that DA is related to motility and must play its own role of a neurochormone, distinct from that of a metabolic intermediary between DOPA and NA. The question of a relationship between the metabolism of catecholamine and melanization is open.     

Serotonergic and cholinergic interaction in the regulation of pituitary-adrenal function in rats

It has been proposed that the central serotonergic inputs which modulate pituitary-adrenal secretion are mediated by cholinergic neurons. We have tested this hypothesis in intact rats. Male Sprague-Dawley rats were injected with cholinergic and serotonergic agents which enhanced transmitter function and with receptor blocking agents. Agents were injected, singly and in combination, into both unstressed and stressed animals. Since the response to cholinergic agents might be due to changes to vasopressin release, Brattleboro (vasopressin deficient) rats were also injected with cholinergic agents. The level of plasma corticosterone at 1-h post-injection was determined. Results indicate that the serotonin receptor blockade decreased the stimulatory, cholinergic effect of physostigmine. Cholinergic receptor blockers did not significantly reduce the corticosterone rise induced by 5-hydroxytryptophan. These results do not support the hypothesis of cholinergic mediation of serotonergic input. Nicotinic and muscarinic receptors appeared to exert opposing influences on the system. The nicotinic receptor antagonist was able to block the stimulatory effect of physostigmine. The muscarinic receptor antagonist significantly elevated plasma corticosterone levels. No differences were found in the effect of physostigmine on Brattleboro rats as compared to controls. These data are interpreted as suggesting that 1) the acetylcholine-induced stimulation of pituitary-adrenal function is mediated, in part, by serotonergic neurons; and 2) stimulation of nicotinic receptors is facilitatory whereas stimulation of muscarinic receptors is inhibitory to pituitary-adrenal function.     

The effects of beta-endorphin on arginine-8-vasopressin and oxytocin levels in rat brain areas

Measurements were made of the effects of intracerebroventricular treatment with beta-endorphin (BE; 100 ng) on the arginine-8-vasopressin (AVP) and oxytocin contents of rat hypothalamic and limbic brain areas (hippocampus, amygdala and septum). The hormone concentrations were determined by radioimmunoassay. The administration of BE resulted in a significant reduction of the AVP level in the amygdala in a naloxone-reversible manner. Naloxone (Nal) administered subcutaneously significantly increased the AVP content in the septum. The results revealed that BE and Nal had regionally specific effects on the activity of the vasopressinergic system but not on that of the oxytocinergic system in the brain.     

The effects of beta-endorphin on arginine-8-vasopressin and oxytocin levels in rat brain areas

Summary Measurements were made of the effects of intracerebroventricular treatment with beta-endorphin (BE; 100 ng) on the arginine-8-vasopressin (AVP) and oxytocin contents of rat hypothalamic and limbic brain areas (hippocampus, amygdala and septum). The hormone concentrations were determined by radioimmunoassay. The administration of BE resulted in a significant reduction of the AVP level in the amygdala in a naloxone-reversible manner. Naloxone (Nal) administered subcutaneously significantly increased the AVP content in the septum. The results revealed that BE and Nal had regionally specific effects on the activity of the vasopressinergic system but not on that of the oxytocinergic system in the brain.     

Plasma adenosine concentrations are elevated in Dahl salt-sensitive rats

We measured plasma levels of adenosine in Dahl salt-sensitive rats (DS) and Dahl salt-resistant rats (DR) to examine the potential role of adenosine in cardiovascular regulation in this type of hypertension. Plasma adenosine concentrations were significantly higher in DS than in DR. The NaCl content in the diet did not affect plasma adenosine concentration in either DS or DR. Significant positive correlation was found between adenosine concentrations and systolic blood pressure when the data for DS and DR were analyzed together. These results suggest that adenosine may play an important role in the pathophysiology of hypertension in DS.     

Dopamine in the visual cortex of the cat

The endogenous content of noradrenaline (NA) and dopamine (DA) was determined by radioenzymatic assays in three different areas of the occipital (visual) cortex, in normal cats as well as in DA-deafferented animals. The use of HPLC methodology enabled us to detect and measure in addition two metabolites of DA: 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), thus confirming the existence of a DA innervation in this cortical region.     

Respective effects on locomotor activity of injections of 5, 7-DHT in median raphe nucleus and of 6-OHDA in the mesolimbic dopaminergic group area in the rat]

This experiment was performed in order to demonstrate that the locomotor hyperactivity provoked by a radiofrequency lesion of the ventral mesencephalic tegmentum-A10 DA group area was not due to a 5-HT fiber damage. Four groups of Rats were used. First groups II and IV received a 5, 7-DHT injection in the median raphe; groups I and III received the vehicle. Locomotor activity was measured in a circular corridor 10 and 30 days; no hyperactivity was obtained. Then the same groups received a 6-OHDA injection, bilaterally in the A 10 area (groups III and IV) or the vehicle (groups I and II); the activity was measured 10 days later: significant hyperactivity was obtained with groups III and IV, without statistical differences between these two groups. In conclusion (i) 5-HT neurons are not directly involved in the VMT-hyperactivity, (ii) the DA A 10 neurons seem to be a critical anatomical target for this symptom.     

An analysis of the effects of urethane on cardiovascular responsiveness to catecholamines in terms of its interference with Ca++ mobilization from both intra and extracellular pools

Urethane (1 X 10(-2) - 1 X 10(-1) M) reduced, in a concentration-dependent manner, both intra and extracellular Ca++ dependent noradrenaline-induced contractions of perfused rabbit ear artery as well as the tonic contractions produced by perfusion with high K+ solution. However, a quantitative analysis of the data indicated that for urethane concentrations similar to those found in plasma during anesthesia urethane antagonism is confined to noradrenaline-induced contractions which depend upon the mobilization of Ca++ from intracellular storage sites. In KCl-contracted arteries, urethane enhanced the relaxant effects of isoprenaline. - Urethane reduced the amplitude of contractions of spontaneously beating guinea-pig right atrium at concentrations which have only a limited effect on frequency. In addition, it decreased in a concentration-dependent manner the amplitude of isoprenaline-activated electrically driven, and K+ depolarized guinea-pig right ventricular strips. Urethane had no effect on the chrono and inotropic actions of isoprenaline on cardiac preparations. In in vivo experiments the chronotropic response to low doses of isoprenaline was significantly higher in urethane-treated as compared to unanesthetized rats. The higher dose of isoprenaline tested produced a significant fall in systolic blood pressure in urethane-anesthetized rats. A significant correlation exists between the chronotropic response to isoprenaline and resting heart rate values in urethane-anesthetized rats. These results indicate that urethane, at concentrations similar to those found in plasma during anesthesia selectively interferes with mobilization of Ca++ from intracellular storage sites. In addition, the interference of urethane anesthesia with the isoprenaline chronotropic effect 'in vivo' cannot be explained by a direct interference of urethane with beta-adrenoceptors at cardiac level.     

Effect of large mesencephalic-diencephalic lesions on the noradrenalin,dopamine and 5-hydroxytryptamine neurons of the central nervous system

Zusammenfassung Nach Ausführung von grossen symmetrischen mesencephalisch-dicncephalischen Läsionen in Ratten konnte mit Hilfe von biochemischen und histochemischen Methoden eindeutig festgestellt werden, dass die Dopamin (DA), Noradrenalin (NA) und 5-Hydroxytryptamin (5-HT) enthaltenden Nerventerminalen im Prosencephalon zu grossen aufsteigenden DA, NA und 5-HT Neuronsystemen gehören. Die Zellkörper dieser Neuronensysteme sind im Gehirnstamm lokalisiert. Dies deutet darauf hin, dass ein einzelnes NA Neuron Gebiete innervieren kann, die weit auseinander liegen, zum Beispiel auf der einen Seite im Cerebellum, auf der anderen im Prosencephalon.     

Inhibition of hepatic Na +, K + -adenosinetriphosphatase in taurolithocholate-induced cholestasis in the rat.

Na +, K + -adenosinetriphosphatase (Na +, K + -ATPase) activity was decreased in liver plasma membranes from rats in which cholestasis had been induced by i.v. administration of sodium taurolithocholate (5 mumoles/100 g b. wt). Incubation of liver plasma membranes with taurolithocholate (10--1300 muM) caused significant and dose dependent reductions of Na +, K + -ATPase activity at taurolithocholate concentrations above 100 muM. These findings lend support to the hypothesis that cholestasis induced by monohydroxy bile acids is at least partially the result of an inhibition of hepatic Na +, K + -ATPase activity.