Impairment of working memory by neuronal degeneration with NMDA in rat hippocampal CA-1.

Rats were trained on a three-panel runway task prior to injections of N-methyl-D-aspartate (NMDA; 40nmoles/µl/side) into the dorsal hippocampus. One week after the treatment, animals did not show any change in the number of errors on the first runway trial (reference memory), with one correct white and two incorrect black panels at each choice point, whereas they showed a marked increase in the number of errors on the following (2nd-6th) trials (working memory) with all black panels. The memory deficit persisted at least for 10 days. After the experiments, histological studies showed neuronal degeneration of hippocampal CA-1 pyramidal cells in all NMDA-treated rats but not in vehicle-treated rats. Pretreatment with the NMDA receptor antagonist MK-801 (3 or 10mg/kg, i.p) before the NMDA injections protected both the neuronal degeneration and the memory deficit. These findings suggest that selective neuronal degeneration induced by excessive stimulation of NMDA receptors in hippocampal CA-1 impaired working memory, but not reference memory.

Dual activation by lisuride of central serotonin 5-HT(1A) and dopamine D(2) receptor sites: drug discrimination and receptor binding studies.

To investigate central serotonergic (5-HT) and dopaminergic (DA) actions of lisuride, the discriminative properties of lisuride (0.05mg/kg, i.p.) in rats were investigated, in addition to the radioligand binding of the compound to 5-HT and DA receptor subtypes. Lisuride was found to possess high affinities for 5-HT(1A) receptor sites (Ki=0.5nM) and D(2) receptor sites (Ki=2.0nM). The autoradiographic binding pattern of 4nM [(3)H]lisuride in rat brain showed high densities of sites displaceable by the 5-HT(1A) agonist 8-OH-DPAT in hippocampus, lateral septal nucleus and amygdala, as well as those displaceable by the D(2) antagonist sulpiride in striatum, nucleus accumbens and olfactory tubercle. In drug discrimination tests, the mixed, D(1)/D(2) agonist apomorphine, the partial D(2) receptor agonists (-)-3-PPP and terguride and the 5-HT(1A) agonist 8-OH-DPAT substituted for lisuride. The D(1) agonist SKF38393, the D(1) antagonist SCH23390, the D(2) antagonist sulpiride, the 5HT(1B) agonist m-CPP and the 5-HT(2) agonist DOI were not generalized to the lisuride cue. In antagonism tests, the D(2) antagonist haloperidol and the 5-HT antagonist methysergide both induced partial but significant antagonism to the lisuride cue, but the D(1) antagonist SCH23390 did not. These results indicate that discriminative stimulus properties of lisuride are mediated by the dual activation of 5-HT(1A) and D(2) receptor sites in brain.

Effect of water-soluble contrast medium on the lung in rats. Comparison of iotrolan, iopamidol, and diatrizoate.

Aspiration is a serious complication of oral contrast media (CM). The authors investigated the effects of iotrolan, iopamidol, and diatrizoate in rats' lungs. To quantify the lung damage induced by CM, pulmonary water and hemoglobin contents were determined. Arterial blood-gas exchange (pH, PCO2, and PO2) also was determined as an indicator of respiratory function. Iotrolan, iopamidol, or sodium/meglumine diatrizoate with a concentration of 300 mg I/mL was administered intrabronchially at a dose of 1 mL/kg. Physiologic saline was administered to the control group. Ten minutes after administration, arterial blood was collected and the lung was removed. Diatrizoate and iopamidol increased pulmonary water and hemoglobin contents and decreased blood PO2. The effect of iotrolan on these parameters was slight and no significant differences were observed between the iotrolan and saline groups. These results suggest that iotrolan is a preferable CM for gastrointestinal examination in the case of suspected aspiration.

[Tissue distribution of red blood cells treated with X-ray contrast media in rats].

Tissue distribution of red blood cells (RBC) that were treated with X-ray contrast media was investigated in rats. The contrast medium mixed with an equivolume of 51Cr-labelled RBC was administered to the internal carotid artery in a dose of 200 microliters/rat; and the radioactivity in the brain, lung and spleen were determined. The contrast medium mixed with an equivolume of blood was administered to the right atrium in a dose of 4 ml/kg, and the hemoglobin content in the lung and changes in pulmonary and circulatory functions were determined. In the ionic contrast medium (meglumine diatrizoate)-treated group, the radioactivity in the brain remained 30 to 50 times higher compared with the nonionic contrast medium (iopamidol)- and saline-treated group until 15 min after infusion. The radioactivity in the spleen increased and the radioactivity and hemoglobin content in the lung decreased time-dependently in the diatrizoate-treated group, whereas iopamidol- and saline-treated groups exhibited constantly low values during the experimental period. Changes in the airway pressure, pulmonary arterial pressure, systemic blood pressure and heart rate were similar after intra-atrial administration of diatrizoate mixed with blood and diatrizoate mixed with saline. These results suggest that the ionic contrast medium affects the RBC and causes a microcirculatory disturbance in the brain.

Role of red blood cell deformation in toxicity of contrast media in cerebral angiography.

The authors investigated the effect on the brain of red blood cells that had been modified by contrast media. Rat blood was mixed with an equivolume of contrast media, and up to 200 microL of the mixture was infused to the internal carotid artery of the rat. Evans blue was administered intravenously to assess the integrity of the blood-brain barrier (BBB). Immediately after the death of the animal, or 2.5 hours after the infusion, the brain was removed for evaluation of the degree of BBB destruction and edema. Extensive destruction of the BBB, cerebral edema, and death of the animals were induced by infusion of blood mixed with an ionic contrast medium, such as diatrizoate and iothalamate, which deformed red blood cells. Microscopic observation showed atrophy and necrosis of nerve cells and decomposition of nerve fibers in the affected area of the brain. Cerebral damage was not observed in rats injected with blood mixed with a nonionic contrast medium such as iopamidol, iopromide, or metrizamide, which had less effect on red blood cells. Cerebral damage also was observed in the rats injected with blood mixed with a hyperosmotic solution of mannitol, as well as washed red blood cells mixed with an ionic contrast medium. This study's results indicate that hyperosmotic ionic contrast media affect red blood cells and cause disturbance in cerebral circulation.

[Neurotropic effects of non-ionic contrast media].

Effects of non-ionic contrast media on the central nervous system were compared in order to clarify any differences due to the side-chain structures among iopamidol, iotrolan, iocibidol, iohexol, iopromide, iosimide and metrizamide. The study included a primary screening test based on Irwin's method, antielectric convulsive tests using mice, measurement of the blood pressure using rats and electroencephalography using rats and rabbits. The general behavior of mice in the primary screening test revealed that tolerance to iopamidol, iotrolan and iocibidol was excellent; that to iopromide and iohexol was moderate; and that to iosimide and metrizamide was poor. Iosimide and iohexol suppressed the transient increase of blood pressure upon intravenous administration in the normal rats but not in the pithed rats. Electric stimulus increased the mortality of mice pretreated with iosimide and iohexol. Abnormal EEG with epileptic seizures, slow wave and/or flattening were observed with the administration of iopromide, iosimide or metrizamide as well as ionic contrast media. From these results, it was concluded that iopromide and metrizamide were not well tolerated in general behavior and EEG; iohexol, in general behavior, electroshock and blood pressure; and iosimide, in all experiments, while iopamidol, iotrolan and iocibidol were well tolerated. Therefore, small differences in their side-chain structures among these contrast media are considered to cause different effects on the central nervous system.

A possible mechanism for the neural adverse reactions caused by metrizamide.

Causality of the metrizamide-induced neural adverse effects was explored among the effects on behavior, electroencephalogram (EEG), and brain glucose utilization in rats. Iotrolan, a new myelographic contrast agent, was used as a reference substance throughout the study. Supracortical subarachnoidal administration of metrizamide caused, within a few minutes, symptoms of sedation and anxiety, which were accompanied by appearance of slow wave or flattening in EEG not only of the cortex, but also of the regions of the hippocampus and thalamus. The rates of local cerebral glucose utilization (LCGU) in a wide range of the brain, measured by using 3H-2-deoxyglucose, were also altered significantly. Despite a limited distribution of metrizamide in the lateral region of the cortex, LCGU was suppressed significantly in the administered side of the parietal cortex, thalamus, subthalamic nucleus, medial geniculate body, and mammillary body and increased in the regions of hippocampus, caudate-putamen, and globus pallidus. It is concluded that, rather than inhibiting the hexokinase reaction in the brain cell, metrizamide appears to cause reduction of a net glucose transport into the cell and that this direct effect on the cortex is amplified and propagated, via neurotransmission, to the regions of the diencephalon and midbrain, causing secondarily various types of disturbance in the mental and motor functions. Iotrolan was proved to lack any biologic activity that may relate to the neural adverse effect observed with metrizamide.

The effect of a selective phosphodiesterase inhibitor, rolipram, on muricide in olfactory bulbectomized rats.

In order to evaluate the potential usefulness of the drug as an antidepressant, acute and chronic effects of rolipram, a selective inhibitor of Ca2+- and calmodulin-independent cyclic AMP phosphodiesterase were investigated on muricide in olfactory bulbectomized (OB) rats. Upon single administration to OB rats, rolipram at a dosage of 1 mg/kg body weight suppressed the muricide for 2 hr after its administration. As a consequence of daily administration of rolipram, however, the incidence of muricide at 24 hr after the administration was decreased, and more than 60% of the rats did not exhibit the muricide on the 12th day. After the cessation of the administration, the incidence of the muricide returned to the initial level. The suppression of the muricide was not antagonized by several kinds of neurotransmitter blockers. Administrations of phosphodiesterase inhibitors and dibutyryl cyclic AMP as well as desipramine and clomipramine also suppressed the muricide dose-dependently. Repeated administration of desipramine also gave results similar to those of rolipram: repetition of a short suppression on the muricide was followed by the appearance of a long-lasting suppression. Differently from rolipram and desipramine, dibutyryl cyclic AMP did not cause long-lasting suppression, and even the direct effect (75% suppression) observed 30 min after its administration on the first day disappeared during its repeated administration for 14 days. From these results, rolipram was considered to show an antidepressant effect through the inhibition of Ca2+- and calmodulin-independent cyclic AMP phosphodiesterase.

[Suppressive effects of lisuride on the synthesis, release and metabolism of dopamine in rat brain].

Effects of lisuride, a central dopaminergic agonist of the ergot type, on the biosynthesis, release and metabolism of dopamine at the dopaminergic nerve terminals of the rat brain were studied under several experimental conditions. 1) In the rat whose impulse flow of dopamine neurons and the activity of aromatic amino acid decarboxylase were inhibited by the pretreatment with gamma-butyrolactone and with 3-hydroxybenzylhydrazine (NDS 1015), respectively, DOPA formation in the neostriatum and limbic forebrain were decreased significantly by the s.c. administration of lisuride at the dosage known to be ineffective on the postsynaptic dopamine receptor. 2) When it was measured by the accumulation of 3-methoxytyramine in the neostriatum and limbic forebrain of pargyline (MAO inhibitor)-pretreated rats, lisuride at the low dosage caused the inhibition of not only the spontaneous release of dopamine from the nerve terminal to the synaptic cleft, but also the release induced with methamphetamine. 3) In the rat whose dopamine biosynthesis was inhibited with alpha-methyl-p-tyrosine, lisuride caused the suppression of dopamine metabolism, resulting in significant increases of dopamine histofluorescence in the nucleus caudatus, olfactory tubercle and median eminence. As to the effect on dopamine histofluorescence, apomorphine at 1 mg/kg was equipotent to lisuride at 50 micrograms/kg. It was concluded from these results that lisuride administered at low dosage interacts preferentially with the presynaptic dopamine receptor, hereby causing the suppressive effects on the tyrosine hydroxylase reaction and the dopamine release mechanism in the dopamine nerve terminals of the brain.

[General pharmacology of lisuride hydrogen maleate--actions on isolated organs, especially on smooth muscles].

Pharmacological actions of lisuride hydrogen maleate (lisuride) were studied by using isolated organs. 1) Lisuride at 2.2 microM exerted a negative chronotropic effect on guinea-pig atria, the effect being antagonized completely by 2.9 microM sulpiride. 2) alpha-Adrenolytic action of lisuride was observed in the rat vas deferens and beta-adrenolytic action in the rabbit trachea, respectively. The former (ID50 = 64 nM) was potent and equivalent to that of phentolamine, whereas the latter (ID50 = 26 microM) was only 1/30 as compared to that of propranolol. 3) Anti-5-hydroxytryptamine action (ID50 = 11 nM) was detected in the rat stomach and anti-histamine (ID50 = 15 nM) in the guinea-pig ileum, respectively. In these respective activities, lisuride was equipotent to methysergide and diphenhydramine. 4) Lisuride showed a spasmodic action, which may be categolized as an ergot alkaloid action, on the guinea-pig ileum and on rabbit renal artery. A weak positive inotropic action of lisuride was also observed in guinea-pig atria. In the rat uterus, however, no uterotonic action of lisuride was detected. It is concluded that, in addition to its known effects on the central nervous system, lisuride possesses potent peripheral anti-5-hydroxytryptamine and anti-histamine activities.

[Central dopaminergic function in stroke-prone spontaneously hypertensive rats (SHRSP): I. Alteration of locomotor activity and swimming ability].

The possible alteration of central dopaminergic (DA) function, which accompanies the development and persistence of hypertension, was studied in SHRSP by measuring the lisuride-induced locomotor activity and the swimming ability. 1) When administered at a dosage of 50 micrograms/kg, lisuride, a DA agonist, induced significant increases of the locomotor activity in one- and 2-month-old Wistar Kyoto rats (WKY), but not in the 6 month-old rat. Differing from the response of WKY, SHRSP showed only a moderate increase in the locomotor activity at the age of one month (means of systolic blood pressure: 128 mmHg) and apparently no increase at the age of 2 months (176 mmHg). In 6 month-old SHRSP (238 mmHg), hypomotility but not hypermotility was induced by the lisuride administration. 2) Though no significant difference was detected at the age of 4 months, the swimming ability of SHRSP at the age of 8 months was deteriorated significantly as compared to that of WKY, and the impaired swimming performance of SHRSP was improved by the administration of lisuride. These results indicate that some alterations in the synaptic sites of the central DA neuron occurred already at an early stage of the hypertensive development, followed under persistent hypertension by the progressive deterioration of the motor-coordination ability as detected in the swimming ability.

[Central dopaminergic function in stroke-prone spontaneously hypertensive rats (SHRSP): II. Effects of chronic treatment with lisuride on the impaired swimming ability].

Eight month-old SHRSP were treated s.c. with lisuride (50 micrograms/kg per day) for 5 weeks to examine the effect of the central dopaminergic agonist on the deterioration of swimming ability that occurred and progressed under persistent hypertension. General observations on signs and symptoms and histopathological examinations were also carried out with the same rats to evaluate the drug effect on the deterioration of hypertensive symptoms. The poor swimming performance of hypertensive SHRSP was improved significantly by the direct action of lisuride with a maximal effect at the 2nd week of the treatment, although the progress of the deterioration itself was not prevented by the chronic treatment. One week after the drug treatment, 2 out of 8 rats in the control group but none in the lisuride-treated group exhibited the abnormal behavior with aggressiveness, a typical sign of the occurrence of cerebrovascular lesions. Furthermore, macroscopic and histopathological examinations carried out 2 weeks after the drug treatment revealed that severities of the histopathological lesions such as myocardiac necrosis and arteriolosclerosis in the kidney, adrenal and testis were significantly lower in the lisuride-treated group than in the control.

Some characteristics of hydrogen- and alkylhydroperoxides metabolizing systems in cardiac tissue.

The effect of hydroperoxides on the cardiac tissue was studied by using hemoglobin-free perfused rat heart. Ethylhydroperoxide was degraded mainly through the glutathione peroxidase system of the heart at a maximal rate of about 1.2 mumol/min per g wet wt. When ethylhydroperoxide infused was not degraded completely, the hydroperoxide concentration in the effluent perfusate paralleled the formation of ferrylmyoglobin in the heart. The infusion of ethylhydroperoxide caused release of oxidized glutathione into the effluent perfusate as a result of the enhancement of the cytosolic glutathione peroxidase reaction. The leakage of oxidized glutathione reached the maximal rate of 3.5 nmol/min per g wet wt with the infusion of 175 microM ethylhydroperoxide. At hydroperoxide concentrations above 150 microM, oxidations of pyridine nucleotides and of cytochrome a + a3 occurred, probably through a stimulation of the mitochondrial glutathione peroxidase reaction, and resulted in sudden failure of the heart function. The infusion of t-butyl- and cumene-hydroperoxides, which are unable to react with myoglobin, also caused the oxidations of pyridine nucleotides and cytochrome a + a3, the inhibition of oxygen consumption and the failure of heart function. The results indicate that the cardiac toxicity of hydroperoxides is due mainly to their effect on mitochondrial metabolism.

[Effects of an ergot derivative, lisuride, on the central dopaminergic system -- studies of behavioral pharmacology].

The central dopaminergic (DA) activity of lisuride hydrogen maleate (lisuride) was investigated from the view point of behavioral pharmacology in rats and mice. Lisuride exhibited a biphasic action on locomotor activity in mice and rats; with low doses lisuride caused hypomotility, whereas higher doses produced locomotor stimulation. The hypomotility induced by lisuride (0.00625 mg/kg, s.c.) was antagonized by a low dose of sulpiride (10 mg/kg, i.p.) in rats, and the lisuride (0.05 mg/kg)-induced hyperactivity was inhibited with haloperidol (0.1 mg/kg, i.p.). The stimulatory effect of lisuride on locomotion was not affected by the combined pretreatment with reserpine and alpha-methyl-p-tyrosine. The hyperactivity of mice induced by methamphetamine was inhibited by pretreatment with lisuride. In the rat lesioned unilaterally in the nigro striatal pathway by a local injection of 6-hydroxydopamine, a low dose of lisuride induced rotational behavior contralateral to the side of the lesion, and the rotational behavior was inhibited by pretreatment with haloperidol. These results indicate that lisuride at low doses effectively stimulates pre-synaptic DA receptors and the post-synaptic DA receptor under supersensitization in the mesolymbic and nigro striatal systems.

[Effects of an ergot derivative, lisuride, on the central nervous system -- stimulatory effect on local cerebral glucose utilization in the rat].

Effects of lisuride, a central dopamine and serotonin agonist of the ergot type, on local cerebral glucose utilization were studied in conscious, anesthetized, and substantia nigra-lesioned rats using the autoradiographic 2-deoxyglucose method. In the conscious rat, lisuride produced dose-dependent (0.05-0.5 mg/kg s.c.) increases of glucose utilization in the cerebellar gray structures (lobule of culmen, vermian lobule, uvula, cerebellar hemisphere) and the lateral nucleus of the thalamus. Although some other gray structures including cerebral cortex were also slightly stimulated, no change was observe in the hippocampus, hypothalamus, amygdala, mammillary body, superior colliculus, pons, and any of the white structure. The stimulatory effect of lisuride was abolished almost completely by the pretreatment with sulpiride or haloperidol. Pentobarbital and gamma-butyrolactone produced marked reduction in the glucose utilization all over the brain, and these effects were not affected by the pretreatment of lisuride. A unilateral 6-hydroxydopamine lesion at the substantia nigra caused a reduction of glucose utilization in the ipsilateral auditory cortex that was reversed by the administration of lisuride. These results indicate that lisuride modulates the motion coordination function of the cerebellum through the cerebral cortex.

Regioselectivity and reactivity in microsomal hydroxylation of a series of N-acyl- and N-sulfonylamines in rats.

Regioselectivity and overall reactivity in the hydroxylation of a series of substituted N-benzoyl- and benzenesulfonyl aliphatic and alicyclic amines with rat liver microsomes were investigated. The hydroxylation occurred predominantly at the position gamma to the nitrogen atom. para-Alkyl-substituted benzoylamines were hydroxylated at both the benzylic positions as well as the gamma-position, whereas para-substituted benzenesulfonylamines were hydroxylated mainly at the benzylic position. The relative overall reactivity of primary, secondary, and tertiary carbon atoms was about 1:3:8, and the contribution of substituents adjoining to the reaction site was negligible. Benzylic hydroxylation proceeded stereoselectively, whereas gamma-hydroxylation gave optically inactive metabolites; the inter- and intramolecular isotope effects in the hydroxylation were 1.6 and 7.2, respectively.