Yasuko Sakurai-Yamashita

Microglia with an Endothelin ETB Receptor Aggregate in Rat Hippocampus CA1 Subfields Following Transient Forebrain Ischemia

Abstract: We examined endothelin (ET) receptors in the hippocampus CA1 subfields of stroke‐prone spontaneously hypertensive rats subjected to a 10‐min bilateral carotid occlusion and reperfusion. When delayed neuronal death had occurred in the pyramidal cell layer at 7 days after transient forebrain ischemia, the quantitative receptor autoradiographic method we used revealed a dramatic increase in number of 125I‐ET‐1 binding sites in the hippocampus CA1 subfields. The highest number of de novo binding sites appeared in the area corresponding anatomically to the pyramidal cell layer with neuronal death. These binding sites were characteristically the ETB receptor. The de novo 125I‐ET‐1 binding was mainly present on microglia aggregating with a high density in the damaged pyramidal cell layer. As ET‐1‐ and ET‐3‐like immunoreactivities were highly expressed within astrocytes in damaged neural tissue, the possibility that microglia with the ETB receptor are activated to participate in the pathophysiology of ischemia‐related neural tissue damage by astrocytic ET‐1 and ET‐3 produced in response to transient forebrain ischemia would have to be considered.

Functions of peripheral 5-hydroxytryptamine receptors, especially 5-hydroxytryptamine4 receptor, in gastrointestinal motility.

Abstract: The multiple 5-hydroxytryptamine (5-HT, serotonin) receptor subtypes are distinguished. In this article, we described mainly the 5-HT4 receptor of four subtypes of functional 5-HT receptors, 5-HT1, 5-HT2, 5-HT3, and 5-HT4, recognized in the gastrointestinal tract. In-vivo microdialysis experiments determined that activation of the 5-HT4 receptor stimulated intestinal motor activity associated with a local increase in acetylcholine (ACh) release from the intestinal cholinergic neurons in the whole body of dogs. The 5-HT4 receptor-mediated response of ACh release in the antral, corporal, and fundic strips isolated from guinea pig stomach corresponds to the presence of 5-HT4 receptor in the myenteric plexus. In-vitro receptor autoradiograms of the stomach and colon indicate that the distribution of 5-HT4 receptors in human tissues is similar to that in the guinea pig, although density of 5-HT4 receptors in the myenteric plexus of human tissues is lower than that in guinea pig tissues. The 5-HT4 receptors located in the myenteric plexus may participate in gastrointestinal motility, and thus the 5-HT4 agonists and antagonists may be available for treatment of dysfunction of gastrointestinal motility.

Δ9-Tetrahydrocannabinol facilitates striatal dopaminergic transmission

Abstract We examined the effects of Δ 9 -tetrahydrocannabinol (THC) on striatal dopaminergic neurons in rats. THC inhibited the uptake of 3 H-dopamine (DA) into striatal synaptosomes. THC facilitated the release of endogenous DA but not dihydroxyphenylacetic acid (DOPAC) from striatal slices. The concentration of DA in the dorsolateral striatum was reduced by THC. We propose that THC may stimulate nigrostriatal dopaminergic neurotransmission mainly by inhibiting uptake of DA and by facilitating release of DA.

Localization of the 5-HT4 receptor in the human and the guinea pig colon

The functions of the 5-HT4 receptor in the gastrointestinal tract are complex, depending on the species and anatomical regions, and localization of the receptor was not clear. The present study attempted to examine the localization of the 5-HT4 receptor in the colon of human for comparison with that in guinea pig colon. Human specimens of sigmoid colon and the distal colon of guinea pig were used for in vitro receptor autoradiography using [125I]SB207710, (1-n-butyl-4-piperidinyl) methyl-8-amino-7-iodo-1,4-benzodioxane-5-carboxylate, as a ligand. [125I]SB207710 binding sites were distributed over the muscle layer of human colon, in the myenteric plexus and in the muscle. In the guinea pig colon, a much higher density was detected in the myenteric plexus than in the muscle. Therefore, in the human and guinea pig colon, the 5-HT4 receptor was located both in the myenteric plexus and in the muscle, and in the guinea pig colon, the receptor was located more predominantly in the myenteric plexus of the muscle than it is in the human colon.

Involvement of glial endothelin/nitric oxide in delayed neuronal death of rat hippocampus after transient forebrain ischemia.

Abstract1. We examined time- and cell-type-dependent changes in endothelin (ET)-1-like immunoreactivity, ET receptors binding and nitric oxide (NO) synthase (NOS) activity in CA1 subfields of the hippocampus of stroke-prone spontaneously hypertensive rats subjected to a 10-min bilateral carotid occlusion and reperfusion.2. Microglia aggregated in accord with neuronal death and expressed a high density of ETB receptors and an intense NOS activity in the damaged CA1 pyramidal cell layer, 7 days after the induced transient forebrain ischemia. The increased NOS activity and ETB receptor in microglia disappeared 28 days after this transient ischemia.3. In contrast to microglia, astrocytes presented a moderate level of ET-1-like immunoreactivity, ETB receptors, and NOS activity in all areas of the damaged CA1 subfields, 7 days after the ischemia. These events were further enhanced 28 days after the ischemia.4. In light of these findings, the possibility that the microglial and the astrocytic ETB/NO system largely contributes to development of the neuronal death and to reconstitution of the damaged neuronal tissue, respectively, in the hippocampus subjected to a transient forebrain ischemia would have to be considered.

Differential localization of 5-hydroxytryptamine3 and 5-hydroxytryptamine4 receptors in the human rectum.

The functions of the 5-hydroxytryptamine3 (5-HT3) and 5-hydroxytryptamine4 (5-HT4) receptors in gastrointestinal tract are complex depending on the species and anatomical regions, and the localization of these receptors in the human rectum was unclear. We examined the localization of the 5-HT3 and 5-HT4 receptors in human rectum by in vitro receptor autoradiography using [125I](S)iodozacopride and [125I] SB207710 as a ligand, respectively. Specific [125I](S)iodozacopride binding sites were clearly evident in the myenteric plexus, whereas, low levels of [125I]SB207710 binding sites were distributed over the muscle but not to the myenteric plexus. The 5-HT3 receptor located on the myenteric plexus and the 5-HT4 receptor on the smooth muscle may participate in contractility and relaxation of human rectum, respectively.

Regional difference in correlation of 5-HT4 receptor distribution with cholinergic transmission in the guinea pig stomach.

Localization and function of 5-HT4 receptors in the stomach were examined in mucosa-free preparations of antrum, corpus and fundus from guinea pig stomach by determination of acetylcholine release and in vitro receptor autoradiography. Specific [125I]SB207710, (1-n-butyl-4-piperidinyl) methyl-8-amino-7-iodo-1,4-benzodioxane-5-carboxylate, binding sites were detected in 3 regions of the stomach. High densities of binding were observed in the myenteric plexus of antrum and corpus, but not fundus. In mucosa-free preparations treated with 5-HT1, 5-HT2 and 5-HT3 receptor antagonists, 5-HT (10(-8)-10(-6) M) potentiated the electrically stimulated (0.5 Hz, 1 ms) outflow of [3H]acetylcholine from antrum and corpus strips preloaded with [3H]choline, but not from fundus strips, and the potentiation was antagonized by SB204070, (1-n-butyl-4-piperidinyl) methyl-8-amino-7-chloro-1,4-benzodioxane-5-carboxylate. Thus, 5-HT4 receptors are located on myenteric cholinergic neurons in the antrum and corpus of guinea pig stomach and their activation evokes the release of acetylcholine.

Rat peritoneal macrophages express endothelin ETB but not endothelin ETA receptors

The properties of endothelin receptors on rat peritoneal macrophages were examined in in vitro receptor autoradiographic binding experiments and in a reverse transcription-polymerase chain reaction (RT-PCR) study. Dense and specific [(125)I]endothelin-1 binding sites were detected on the macrophages. [(125)I]Tyr13-Suc-[Glu9,Ala(11,15)]-endothelin-1(8-21) , IRL1620, a selective endothelin ET(B) receptor ligand, but not [(125)I](N-[(hexahydro-1-azepinyl)carbonyl])L-Leu(1-Me)D-Trp-D-Tyr , PD151242, a selective endothelin ET(A) receptor ligand, specifically bound to rat macrophages (Kd = 0.75 +/- 0.19 nM, Bmax = 7.77 +/- 2.50 fmol/mg). RT-PCR experiments also showed the expression of endothelin ET(B) receptor mRNA, but not endothelin ET(A) receptor mRNA, in these macrophages. These results indicate that rat peritoneal macrophages apparently express the endothelin ET(B) receptor but not the endothelin ET(A) receptor.

Involvement of 5-hydroxytryptamine4 receptor in the exacerbation of neuronal loss by psychological stress in the hippocampus of SHRSP with a transient ischemia

A transient forebrain ischemia produced a delayed neuronal death of the hippocampus pyramidal cells in stroke-prone spontaneously hypertensive rats (SHRSP). Long term exposure of rats to stress has been reported to induce deleterious effects on the brain including morphological neuronal degeneration in the hippocampus. The present study was designed to examine the effects of psychological and physical stress on the ischemia-related neuronal death and the effects of 5-hydroxytryptamine(4) (5-HT(4)) receptor antagonist. SHRSP were exposed to the psychological or physical stress for 60 min in the communication box once or repeatedly for 3 days and occluded. SB204070, a 5-HT(4) receptor antagonist was injected before the occlusion. Seven days after the occlusion, the number of the neurons damaged morphologically was examined. A transient bilateral carotid occlusion produced a neuronal death of the CA1 subfield of the hippocampus in a time-dependent manner between 3 and 10 min. A 4 min occlusion induced very little morphological damage and a 5 min one produced a significant neuronal death. Exposure of rats to the psychological stress during 60 min for 3 days before the ischemic insults damaged the pyramidal cells by 4 min ischemia much more than without stress. Physical stress daily for 3 times also increased the damaged neurons. Pretreatment of SB204070 0.1 mg/kg after the stress exposure for 3 days significantly decreased the neuronal damage exacerbated by the stress exposure; however, it did not alter the damage induced by 4 or 10 min occlusion without stress. These results suggest that the repeated exposure of animals to the stress dramatically exacerbates the neuronal death by a transient ischemia and the 5-HT(4) receptor may be involved in the stress-induced exacerbating mechanism of the neuronal damage.

Expression of endothelin receptors and nitric oxide synthase in the brain of stroke-prone spontaneously hypertensive rats with cerebral apoplexy

Endothelin (ET) receptors, ET-1-like immunoreactivity and nitric oxide synthase (NOS) were examined in the brain of stroke-prone spontaneously hypertensive rats (SHRSPs) with cerebral apoplexy. Our receptor autoradiographic method with 125I-ET-1 and unlabeled selective ligands for ET receptors revealed de novo expressions of ET(A) and ET(B) receptors in areas of neural lesions with cerebrovascular damage in SHRSPs. Immunohistochemical staining for ET-1 showed clear ET-1-like immunoreactivity in areas with highly expressed ET receptors. Histochemical studies on astrocytes and microglia suggested that these glial cells, aggregating in lesions, may carry ET receptors, ET-1-like immunoreactivity. Furthermore, NOS detected histochemically using an NADPH-diaphorase staining method was rich on glial cells in damaged areas of the brain in SHRSPs with cerebral apoplexy. Our data suggest the pathophysiological significance of glial ET(A) and ET(B) receptors, ET-1 and NOS in neural lesions of SHRSPs.