Hiroyuki Nakamichi

Effect of thyrotropin-releasing hormone on cerebral blood flow in conscious rat

The effect of thyrotropin-releasing hormone (TRH) was studied on local CBF (LCBF) in normal conscious rats. LCBF was measured by the autoradiographic [14C]iodoantipyrine method 5 min after TRH (5 mg/kg, i.v.) administration. TRH significantly increased LCBF in 22 of 33 brain regions. This increase of LCBF exceeded 100% of the control values in the cerebral cortices, whereas there was no significant increase in white matter or in some gray matter structures. The increase of CBF following TRH administration was abolished by pretreatment with indomethacin (5 mg/kg, i.v.). The mechanisms underlying the increase of CBF following TRH administration are discussed in relation to prostaglandin metabolism.

Quantitative distribution of rat brain monoamine oxidase A by [14C]clorgyline autoradiography

The distribution of functionally active monoamine oxidase type A (MAO-A) was investigated by in vivo quantitative autoradiography using [14C]clorgyline in normal, conscious rat brain. [14C]clorgyline was synthesized by the methylation reaction of N-desmethylclorgyline using [14C]methyliodide. Sixty minutes after [14C]clorgyline administration (1.58 MBq/animal i.v.), the brains were removed and prepared for autoradiography by washing the brain sections with 5% trichloroacetic acid solution to remove the nonbinding free tracer. The amount of MAO-A was calculated from the regional acid-insoluble tissue radioactivity and the specific activity of the tracer. The highest amount of MAO-A (5.84 nmol/g tissue) was found in the locus coeruleus. The interpeduncular nucleus, habenular nucleus, fasciculus retroflexus, and solitary tract nucleus possessed over 1.6 nmol/g tissue of MAO-A. Among 23 regions of interest, the lowest amount of MAO-A (0.37 nmol/g tissue) was found in the globus pallidus. The findings of this study suggest that the pattern of MAO-A parallels both in neuroanatomical distribution and in density that of norepinephrine and serotonin innervation. The MAO-A concentration was, however, relatively low in the dopamine-related areas. This corresponded to the previous results obtained by histochemical analysis. In addition, among the white matter structures, a high amount of MAO-A was found specifically in the fasciculus retroflexus.

FASUDIL (HA1077), AN INTRACELLULAR CALCIUM ANTAGONIST, IMPROVES NEUROLOGICAL DEFICITS AND TISSUE POTASSIUM LOSS IN FOCAL CEREBRAL ISCHEMIA IN GERBILS

The effects of an intracellular calcium antagonist fasudil (HA 1077) on protein synthesis, ion derangement, brain edema, and the neurological signs associated with focal cerebral ischemia, were investigated via a nine-hour occlusion of the left common carotid artery (CCA) in Mongolian gerbils. Protein synthesis was evaluated by the amount of incorporation of [14C]methionine into the tissue. Intravenous infusion of fasudil hydrochloride (1 mg kg-1) just after CCA ligation was effective in reducing neurological deficits six and nine hours after CCA ligation, as well as loss of tissue potassium. However, fasudil did not ameliorate the brain edema or the accumulation of sodium in the tissue. On the other hand, fasudil improved the uptake of [14C]methionine, but not its incorporation into the tissue. The improved uptake of tracer into the tissue may indicate the facilitation of collateral blood flow by fasudil. These results suggest that fasudil may mitigate ischemic damage in the penumbral zone, possibly by ameliorating collateral blood flow and preventing calcium-related cell damage.

A convenient method for regional monoamine oxidase-A determination by [14C]clorgyline autoradiography.

The availability of clorgyline for regional monoamine oxidase-A (MAO-A) determination was examined using [14C]clorgyline in rat. [14C]Clorgyline was synthesized by the methylation reaction of N-desmethyl-clorgyline and [14C]methyliodide in dimethylformamide with high radiochemical yield. The MAO-A distribution map by autoradiography correlated with that by histochemical technique and its quantity was consistent with the calculated MAO-A amount based on previous reports. The combination of labeled clorgyline and autoradiographic technique will promise the quantitative measurement of regional MAO-A distribution.

Effects of HA1077, an intracellular calcium antagonist, on neurotransmitter metabolism in rat brainIn Vivo

The effect of HA1077, an intracellular calcium antagonist, on neurotransmitter metabolism in rat brain was investigated in vivo. After administration of HA1077, at doses of 0.1, 0.3, and 3 mg/kg, 5-hydroxyindoleacetic acid (5-HIAA) levels increased in most regions except midbrain. In the striatum, parallel increases of both serotonin (5-HT) and 5-HIAA levels were observed at 0.3 mg/kg, but only the 5-HT level increased at 0.1 mg/kg. These results suggest that HA1077 may activate the turnover or synthesis of 5-HT. After administration of HA1077 at 0.3, 1, and 3 mg/kg, the dopamine (DA) level was increased in the striatum, but 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid levels were unchanged. After HA1077 administration at 1 mg/kg, both DA and DOPAC levels increased in the hypothalamus and only DA level increased in the cerebral cortex. By contrast, DOPAC level decreased in the midbrain after HA1077 treatment at 0.1 and 0.3 mg/kg, and in the brainstem at 0.1 and 10 mg/kg. The ratio of [3H]-N-methylspiperone accumulation relative to that in the cerebellum did not change after HA1077 treatment at any of the doses employed. Thus, the effects of HA1077 on neurotransmitter metabolism are complex and vary depending on the dosage and sites of the brain. Although the dose-dependent effects of HA1077 on neurotransmitter metabolism are similar to those of calcium entry blockers, HA1077 can facilitate DA synthesis in the hypothalamus and striatum, unlike the calcium entry blockers.

Does the anabolic metabolism of l-[2-18F]fluorophenylalanine and l-[2,6-3H]phenylalanine differ in the cerebrum and the cerebellum?

The anabolism of isotopically labeled amino acids was compared between the cerebrum and the cerebellum in conscious rat at three feeding conditions. After L-[2-18F]fluorophenylalanine and L-[2,6-3H]phenylalanine injections, the incorporation rate of both radioactivity into protein fraction showed no difference between the cerebrum and the cerebellum at normal condition, but the lipid fraction in the cerebellum was higher than that in the cerebrum in any conditions. These results show the usefulness of L-[2-18F]fluorophenylalanine as a positron emission tomography tracer and different anabolic rate of the amino acids to lipid between the cerebrum and cerebellum.

l-[2-18F]fluorophenylalanine and l-[U-14C]phenylalanine: a comparative study of their transport to rat brain

The transport rates of L-[2-18F]fluorophenylalanine ([18F]Phe) and L-[U-14C]phenylalanine ([14C]Phe) across the blood-brain barrier were compared in saline, large neutral amino acids (NAA) and large basic amino acids (BAA) loaded rats. The fraction of transported tracer (FTT) was expressed as the ratio of brain radioactivity to integrated plasma radioactivity at 5 min after injection of the tracers. Cerebral FTTs of [18F]Phe and [14C]Phe in the control group were 0.042 and 0.045, respectively, and decreased to 0.016 and 0.019 in the NAA loaded group. The ratios of FTT of [18F]Phe and that of [14C]Phe were approx. 0.90, and did not differ among the three groups. These results indicate that the transport of [18F]Phe from the blood to the brain can be considered to be mediated by the NAA transport system and that its transport rate is almost the same as that of [14C]Phe.

ラット脳内Cyclic nucleotidesにおよぼすClonidineの影響―Clonidine単独投与時およびα遮断薬併用時の変化―

The following 4 Wistar rat groups were sacrificed by microwave irradiation after measuring blood pressure and heart rate: 1) saline control (1 ml/kg, i.v.), 2) clonidine alone (50 micrograms/kg, i.v.). 3) prazosin pretreated (0.1 mg/kg, i.v.), 4) yohimbine pretreated (1 mg/kg, i.v.). Cyclic nucleotides were analyzed in seven brain regions. Clonidine decreased blood pressure and heart rate 20 min after administration. These effects of clonidine were inhibited by yohimbine. Clonidine increased the levels of cyclic AMP in the medulla oblongata (including pons) and hypothalamus. Prazosin attenuated the cyclic AMP-increasing action of clonidine in the cerebellum. Yohimbine inhibited this action of clonidine in the cerebellum, striatum and hippocampus. Clonidine reduced cyclic GMP levels in the hypothalamus and striatum. Prazosin potentiated the cyclic GMP-reducing action of clonidine in the medulla oblongata. Yohimbine attenuated this action of clonidine in the medulla oblongata and hypothalamus. From these results, it is concluded that clonidine changes the levels of cyclic nucleotides in brain regions, especially in the part of the autonomic nervous center. In addition, it is indicated that alpha 1- or alpha 2-adrenoceptor plays a different role in the regulation of brain cyclic nucleotides, region by region.

Effects of guanfacine on the levels of cyclic nucleotides in anesthetized rat brain regions.

Effects of an antihypertensive drug, guanfacine, on brain regional cyclic AMP and cyclic GMP levels were studied in anesthetized rats. Cyclic nucleotides were analyzed in seven brain regions. Guanfacine decreased blood pressure and heart rate 20 min after administration. Yohimbine inhibited these hemodynamic effects of guanfacine. Guanfacine reduced cyclic AMP levels in the hypothalamus. The reducing effect of guanfacine on cyclic AMP was antagonized by yohimbine in the hypothalamus. Guanfacine lowered cyclic GMP in the cerebellum, medulla oblongata and hypothalamus. Yohimbine inhibited the effect of guanfacine on cyclic GMP in the cerebellum, medulla oblongata and hypothalamus. Prazosin showed no effect on guanfacine induced change of cyclic nucleotides in any brain region. From these results, it is concluded that guanfacine decreased cyclic AMP and cyclic GMP in the hypothalamus. In addition, it is suggested that alpha-2 adrenoceptors mainly modulate these changes of cyclic nucleotides.