Yoshitsugu Osumi

Attenuation of morphine analgesia in rats with lesions of the locus coeruleus and dorsal raphe nucleus

The nociceptive reflex activity and analgesic effect of morphine were studied in rats using the hind paw stimulation test. The stimulation threshold was significantly increased in animals with bilateral destruction of the locus coeruleus (LC), and was reduced after lesion of the dorsal raphe nucleus (DR). LC lesions produced a selective lowering of noradrenaline (NA) content in the forebrain, while DR lesions resulted in a reduction in serotonin levels. Lesioning both LC and DR significantly reduced both NA and serotonin contents even when the stimulation threshold was not altered. Morphine produced a significant and dose-dependent elevation of the stimulation threshold in sham-operated animals, while morphine analgesia was almost completely inhibited by destruction of LC, DR and both the nuclei. These results imply that a depression of LC-mediated noradrenergic tone results in a decreased sensitivity to painful stimuli, whereas a reduction of raphe-derived serotonergic tone produces the opposite effect against LC. It is suggested, however, that both of these monoamines from the LC and DR are necessary for the analgesic effect of morphine.

Inhibition of gastric acid secretion and mucosal blood flow induced by intraventricularly applied neurotensin in rats

Abstract To investigate the central effect of neurotensin in gastric functions, changes in gastric acid secretion and mucosal blood flow (MBF) following administration were examined in rats anesthetized with urethane. Neurotensin in doses 1–10 μg/animal injected into the lateral ventricle decreased the basal value of both gastric acid output and MBF. This effect of neurotensin on these gastric parameters was completely blocked by pretreatment of animals with reserpine (2 mg/kg, i.p., 24 hr) or 6-OH-dopamine (250 μg/animal, intraventricularly, 10–14 days). These results indicate that exogenously applied neurotensin induces an inhibition of gastric functions by a central mechanism and suggest that an interaction exists between central catecholamines and the effect of neurotensin on gastric functions.

Central noradrenergic inhibition of gastric mucosal blood flow and acid secretion in rats.

Abstract To investigate the role of central noradrenaline (NA) in gastric functions, changes in mucosal blood flow (MBF) and acid secretion following electrical stimulation of the lateral hypothalamic area (LHA) and the effects of NA on these parameters were examined in rats anesthetized with urethane. NA 10 μg/animal injected into the lateral ventricle decreased the basal value of both the gastric MBF and acid output, while the same dose of acetycholine or dopamine was without effect. Repetitive electrical stimulation of LHA at 10 cycles/sec, 0.5 mA, 2 msec for 10 min elicited a significant, reproducible increase in both gastric MBF and acid output. NA 10 μg/animal injected into the lateral ventricle completely blocked these increases induced by the electrical stimulation. These data suggest that a central noradrenergic inhibitory mechanism is involved in regulation of the gastric MBF and acid secretion.

Neurotensin potentiates the potassium-induced release of endogenous dopamine from rat striatal slices

The effects of neurotensin on the release of endogenous dopamine (DA) from rat striatal slices were investigated. DA was extracted by the aluminium adsorption method and assayed electrochemically by high-performance liquid chromatography. Neurotensin (2-100 microM) potentiated the potassium-induced release of striatal endogenous DA in a concentration-dependent manner. This neurotensin-induced release of DA was completely abolished in calcium-free medium containing EGTA 1 mM. The presence of tetrodotoxin 2 microM did not alter the effect of neurotensin 10 microM. On the other hand, neurotensin did not affect the uptake of [3H]DA into the striatal slices. In additional experiments, we confirmed that the KCl-induced release of DA in the nucleus accumbens was also potentiated b neurotensin. These results suggest that neurotensin has a direct effect on the central DA nerve terminals and releases DA in a Ca2+-dependent manner.

Hyperdipsia induced by bilateral destruction of the locus coeruleus in rats

Bilateral lesions in the locus coeruleus (LC) of rats induced a urinary disorder and hyperdipsia. Dilatation of the urinary bladder, urinary retention and hematuria with bleeding originating from the urinary bladder, occurred immediately after the lesioning and continued for 2-5 days. Water intake increased 4 days after the lesioning. This hyperdipsia persisted for at least 4 days and then gradually returned to the control level. Food intake decreased for the first 5 days, and then returned to the control level. Lesions in the ascending dorsal bundle (DB) originating from the LC also produced hyperdipsia, but not urinary disorder. Destruction of the ascending ventral vundle (VB) originating from the noradrenaline (NA) neurons in the medulla oblongata did not affect eating, drinking or urination. The LC- or DB-lesioning caused a significant reduction of NA in the whole forebrain except the hypothalamus, whereas VB-lesioning caused reduced NA in the hypothalamus. In LC-lesioned animals, no significant changes were observed in serum osmolarity, Na+, K+, albumin and glucose in serum, or in the excretion of urine in the water-loading test.

Elevation of plasma noradrenaline levels in urethane‐anaesthetized rats by activation of central prostanoid EP3 receptors

1 We studied the effects of intracerebroventricular (i.c.v.) administration of prostaglandin E2 (PGE2) and its receptor subtype ligands on plasma levels of catecholamines in urethane‐anaesthetized rats. 2 Administration of PGE2 (0.15, 0.3 and 1.5 nmol per animal, i.c.v.) dose‐dependently elevated plasma levels of noradrenaline (NA), while the levels of adrenaline were not affected. 3 Administration of sulprostone (EP3/EP1 agonist) and misoprostol (EP3/EP2 agonist) effectively elevated plasma NA levels in a dose‐dependent manner (0.1, 0.3, and 1.0 nmol per animal). Butaprost (EP2 agonist) (0.3, 1.0 and 3.0 nmol per animal) was without effect. 17‐Phenyl‐ω‐trinor PGE2 (EP1/EP3 agonist) effectively elevated plasma NA levels only at its highest dose (1.0 nmol per animal), but this elevation was not attenuated by pretreatment with SC‐19220 (selective EP1 antagonist) (20 nmol per animal, i.c.v.). 4 The potency of these test agents in elevating plasma levels of NA was as follows; misoprostol > sulprostone > PGE2> > 17‐phenyl‐ω‐trinor PGE2 > > > butaprost. These results suggest that activation of central prostanoid EP3‐receptors induces central sympathetic outflow in rats.

Inhibition of vagally mediated gastric acid secretion by activation of central prostanoid EP3 receptors in urethane-anaesthetized rats.

1 We studied the effects of intracerebroventricular (i.c.v.) administration of prostanoid EP receptor ligands on vagally stimulated gastric acid secretion in rats anaesthetized with urethane. 2 Administration of misoprostol (EP3/EP2 receptor agonist) and sulprostone (EP3/EP1 receptor agonist) reduced vagally mediated gastric acid secretion in a dose‐dependent manner (0.1, 0.3 and 1.0 nmol per animal). Butaprost (EP2 receptor agonist) (0.3 and 3.0 nmol per animal) was without effect. 17‐Phenyl‐ω‐trinor PGE2 (EP1/EP3 receptor agonist) attenuated vagally mediated gastric acid secretion only at its highest dose (1.0 nmol per animal); this antisecretory effect was not prevented by pretreatment with SC‐19220 (selective EP1 receptor antagonist) (20 nmol per animal, i.c.v.). 3 The potency of these test agents in attenuation of vagally mediated gastric acid secretion was as follows: misoprostol ≥ sulprostone ≫ 17‐phenyl‐ω‐trinor PGE2> > > butaprost. These results suggest that activation of central prostanoid EP3 receptors induces inhibition of vagally mediated gastric acid secretion in rats.

Nitric oxide mediates central activation of sympathetic outflow induced by interleukin-1 β in rats

Abstract The excitatory mechanism of central sympathetic outflow induced by interleukin-1 β was investigated in urethane-anesthetized rats. Intracerebroventricular administration of interleukin-1 β induced a gradually developing elevation of plasma noradrenaline levels in a dose-dependent manner (50, 100 and 200 ng/animal), while the levels of adrenaline were not affected. The elevation of noradrenaline levels induced by interleukin-1 β (100 ng/animal i.c.v.) was abolished by the following treatments with: (1) a chemical sympathectomizer, 6-hydroxydopamine (15 mg/kg i.v., 3 days before); (2) a prostaglandin synthesis inhibitor, indomethacin (500 μg/animal i.c.v.); (3) a nitric oxide synthase inhibitor. l -NG-nitroarginine methyl ester (100 μg plus 10 μg/min i.c.v.); and (4) a nitric oxide scavenger, oxyhemoglobin (32.3 μg plus 3.23 μg/min i.c.v.). In contrast to these results, d -NG-nitroarginine methyl ester, an inactive isomer of l -NG-nitroarginine methyl ester, and methemoglobin, a metabolite of oxyhemoglobin, were without effect. Furthermore, prostaglandin E2 (100 ng/animal i.c.v.) rapidly and markedly elevated the plasma level of noradrenaline but not adrenaline. This prostaglandin E2-induced elevation of plasma noradrenaline levels was not attenuated by l -NG-nitroarginine methyl ester (100 μg plus 10 μg/min i.c.v.). The present results suggest that nitric oxide is involved in the interleukin-1 β-induced central activation of sympathetic outflow. Furthermore, there probably exists nitric oxide-linked prostaglandin-generating system in the brain.

Perfusion of the hypothalamic paraventricular nucleus with N-methyl-D-aspartate produces thromboxane A2 and centrally activates adrenomedullary outflow in rats.

We applied a microdialysis technique for the measurement of hypothalamic thromboxane B2, a stable metabolite of thromboxane A2, in urethane-anesthetized rats. Perfusion with N-methyl-D-aspartate (1.5 and 2.5mM) of the paraventricular nucleus by microdialysis probe concentration-dependently elevated the levels of thromboxane B2 in this region and plasma levels of catecholamines. The elevation of adrenaline was much more marked than that of noradrenaline. Pretreatment with dizocilpine maleate (0.1 mM), a non-competitive antagonist of N-methyl-D-aspartate receptors, of the paraventricular nucleus by microdialysis probe attenuated the N-methyl-D-aspartate (1.5 mM)-induced elevations of both thromboxane B2 and plasma catecholamines. Intracerebroventricular administration of furegrelate (250 microg/animal), a thromboxane A2 synthase inhibitor, also abolished the responses evoked by N-methyl-D-aspartate. These results indicate that N-methyl-D-aspartate applied into the paraventricular nucleus produces thromboxane A2 in this region and elevates plasma levels of catecholamines, especially adrenaline. Thromboxane A2 produced in this hypothalamic nucleus is probably involved in the N-methyl-D-aspartate-induced central adrenomedullary outflow.

Thromboxane A2 is involved in the nitric oxide-induced central activation of adrenomedullary outflow in rats

The central effect of 3-morpholinosydnonimine, a nitric oxide donor, on the sympatho-adrenomedullary system was investigated in urethane-anesthetized rats. Intracerebroventricular administration of 3-morpholinosydnonimine (100, 250 and 500 microg/animal) induced a marked elevation of adrenaline levels and a slight elevation of noradrenaline levels in the plasma. These 3-morpholinosydnonimine (250 microg/animal)-induced elevations of catecholamines were abolished by intracerebroventricular treatments with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl 3-oxide (750 microg/animal), a nitric oxide scavenger, and indomethacin (500 microg/animal), a cyclo-oxygenase inhibitor, but not with superoxide dismutase (250 units/animal), a superoxide anion scavenger. Furthermore, the 3-morpholinosydnonimine (250 microg/animal)-induced elevation of plasma adrenaline levels was abolished by intracerebroventricular treatments with thromboxane A2 synthase inhibitors [furegrelate (100, 250 and 1000 microg/animal) and carboxyheptyl imidazole (500 microg/animal)], and also with thromboxane A2 receptor blockers [(+)-S-145 (100, 250 and 1000microg/animal) and SQ29548 (8microg/animal)]. The elevation of noradrenaline levels was, however, not attenuated by these thromboxane A2-related test agents. The present results indicate that nitric oxide but not peroxynitrite markedly activates central adrenomedullary outflow. Thromboxane A2 in the brain is probably involved in this central activation of adrenomedullary outflow.