摘要:

Abstract: The effect of angiotensin II on catecholamine release from bovine adrenal medulla has been investigated. In retrogradely perfused, isolated bovine adrenal glands, angiotensin II increased basal efflux of catecholamines, but the presence of angiotensin II did not increase the release of catecholamines evoked either by bolus injections of the secretogogue carbachol or by depolarization with a perfusing solution containing a raised concentration of K+. In chromaffin cells maintained in primary tissue culture, angiotensin II increased3H release from cells preloaded with [3H]‐noradrenaline but did not enhance the release evoked by carbachol or by depolarization with K+. The increase in3H release evoked by angiotensin II from chromaffin cells in tissue culture was inhibited by its analogue antagonist Sar1,Ala8‐angiotensin II (saralasin) and was entirely dependent on the presence of Ca2+in the experimental medium. These findings suggest that, in the chromaffin cells of the bovine adrenal medulla, angiotensin II acts on specific receptors to cause a calcium‐dependent catecholamine release but triggers no additional response that acts synergistically with depolarizing or nicotinic stimuli to augment catecholamine re

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb06339.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract: The relative subcellular distributions of μ‐opioid receptors and guanine nucleotide binding regulatory proteins (G proteins) in 1‐day‐old (P1) and adult rat forebrain were compared. Light membranes (LMs) were resolved from heavy membranes (HM) by sucrose density gradient centrifugation. Marker enzyme analyses indicated that LMs contained most of the endoplasmic reticulum and Golgi complexes, whereas HMs were enriched in plasma membranes. Binding distribution and properties of μ‐opioid sites were assessed using [3H][d‐Ala2,Me‐Phe4,Gly‐ol5]enkephalin. P1 LMs possessed 43% of die total μ‐opioid binding detected compared to 16% in the adult. Although NaCl inhibited μ binding in LMs to a greater extent than in HMs, age‐dependent differences were not observed. P1 LM μ binding possessed greater sensitivity to 5′‐guanylylimidodiphosphate than their adult counterpart. Moreover, P1 LMs contained more Gocr. protein than P1 HMs or adult LMs, as demonstrated by immunoblotting with antisera against Gocrafter one‐or two‐dimensional gel electrophoresis. These results suggest that P1 LMs contain a greater proportion of newly synthesized intrac

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb06340.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract: The weaver mutant mouse has a genetically determined defect in the nigrostriatal dopaminergic system. The present study was undertaken to test the hypothesis that in the weaver mutant mouse, striatal nerve terminals undergo compensatory changes in response to this deficiency. To test this hypothesis, we studied the basal and stimulated release of dopamine from striatal slices of weaver mutant mice and matched controls. By using a superfusion system and concentrating the superfusate by passage over alumina, resting dopamine release could be determined in the weaver mutant despite the fact that striatal tissue content of dopamine in these mice is reduced by>75% compared with control mice. Fractional resting release of dopamine in weaver striatal slices was significantly elevated compared with that in controls, suggesting that the release mechanisms in the weaver may be adapting to overcome the dopamine deficit. Potassium‐evoked release (24 and 48 mMpotassium) was not significantly different between the two genotypes. In contrast, amphetamine‐evoked release (1 μM) was significantly greater in the weaver mice than in controls. In both genotypes, release evoked by amphetamine was completely inhibited by cocaine, implicating the dopamine uptake carrier in this release process. These findings suggest that fundamental differences in dopamine release mechanisms exist between weaver and control mice and support the hypothesis that compensatory mechanisms may develop in neurons in response to dopamine defi

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb06341.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract: The role of nerve growth factor (NGF) and its receptor (NGFR) in the regulation of cholinergic activity has been studied during the aging process. NGFRs were quantified in cortical membranes using a radioactive binding assay. NGF levels and choline acetyltransferase (ChAT) activity were determined in cortex, hippocampus, neostriatum, and septum. These assays were performed in both adult (6‐month‐old) and aged (36‐month‐old) rats. High‐and low‐affinity125I‐NGF binding sites were present in cortex of adult and aged rats. Furthermore, we observed a decrease in number and affinity of both NGFRs in aged rats. ChAT activity in these rats was lower (⋍30%) than in adult rats in all the brainregions examined. NGF levels were not modified in cortex and hippocampus and were decreased in neostriatum (55%) and septum (35%). In conclusion, our results suggest that, during the aging process, the cholinergic impairment is related to a decrease in NGF levels in neostriatum but not in cortex and hippocampus. The reduction in level of NGF protein in septum could be due to a decrease in number of high‐affinity125I

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb06342.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract: The characteristics of the transduction mechanism(s) activated by glutamate (Glu) via the quisqualate metabotropic receptor, as well as by depolarizing agents, to trigger formation of inositol phosphates (IPs) were investigated in 8‐day‐old rat forebrain Synaptoneurosomes. The replacement of external Na+by various compounds (Li+, Tris+,N‐methyl‐D‐glucamine+, and sucrose) induces an increase in basal accumulation of IPs and depolarizes synaptoneurosome membranes. Under these conditions, Gluand K+‐induced accumulations of IPs are inhibited, whereas the carbachol (Carb)‐elicited response of IPs parallels the basal one. Agents increasing Na+influx, such as veratridine and monensin, depolarize Synaptoneurosomes and stimulate formation of IPs. These stimulations are not additive with responses of IPs elicited by Glu or K+. These data suggest that (a) Glu activates phosphoinositide metabolism via a specific mechanism (distinct from that of cholinergic agonists), (b) depolarizing agents and Glu share at least one common intermediate step in their mechanisms of activation of the metabolism of IPs, and (c) the depolarization may correspond to this common step. ID addition, Na+seems to be required for Glu stimulation of metabolism of IPs. The depolarization associated with the action of Glu on formation of IPs results neither from an influx via tetrodotoxin‐sensitive voltage‐dependent Na+ channels nor from an entry via the classically characterized Na+/Ca2+or Na+/H+exchangers. In fact, tetrodotoxin (2 μM) has no effect on the Glu‐or K+‐elicited response of IPs. Amiloride (>50 μM) and some of its derivatives similarly inhibit not only Glu‐and K+‐but also C

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb06343.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract: In this article, we demonstrate that an increase in intracellular Ca2+concentration may represent a specific common step(s) in the mechanism(s) of action of glutamate (Glu) and depolarizing agents on formation of inositol phosphates (IPs) in 8‐day‐old rat forebrain Synaptoneurosomes. In fact, A23187, a Ca2+ionophore, induces a dose‐dependent accumulation of IPs, which is not additive with that evoked by Glu and K+but is slightly synergistic with that induced by carbachol. In addition, Glu and K+augment the intracellular Ca2+concentration in synaptoneurosome preparations as measured by the fura‐2 assay. The absence of external Ca2+decreases basal and Glu‐, and K+‐stimulated formation of IPs. Cd2+(100 μM) fully inhibits both Gluand K+‐evoked formation of IPs without affecting the carbachol‐elicited response of IPs. Zn2+inhibits Gluand K+‐stimulated accumulation of IPs (IC50∽ 0.4 mM) but with a lower affinity than Cd2+(IC50∽ 0.035 mM). The organic Ca2+channel blockers verapamil (10 μM), nifedipine (10 μM), ω‐conotoxin (2 μM), and amiloride (10 μM) as well as the inorganic blockers Co2+(100 μM) and La3+(100 μM) block neither Glunor K+‐evoked formation of IPs, a result suggesting that the opening of the L‐, T‐, N‐, or P‐type Ca2+channels does not participate in these responses. All these data suggest that an increase in intracellular Ca2+concentration resulting from an influx of Ca2+, sensitive to Cd2+but not to other classical Ca2+antagonists, may play a key rote in the transduction mechanis

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb06344.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract: Intact astrocytes cultured from newborn rat cerebral cortex rapidly converted extracellular ATP to ADP. The ATPase responsible was apparently not saturated, even at 750 μMATP. In contrast, the conversion of ADP to AMP was slow, and the reaction was limiting for the subsequent dephosphorylation process. Adenosine formation was the only fate for AMP. The reaction was catalyzed by S'‐nucleotidase with an apparent Kmof 55 μMfor AMP and appeared to be inhibited by high concentrations of ATP and ADP.Astrocytes were able to take up adenosine with an apparentKmvalue of 45 μM.Uptake was inhibited by dipyridamole but not by anti‐5′‐nucleotidase IgG. The results support the proposal that astrocytes play a role in modulating synaptic events involving ATP and

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb06345.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract: Tryptophan hydroxylase in the rat pineal gland undergoes diurnal rhythmic activity. Rat pineal glands exhibit increased tryptophan hydroxylase activity when incubated with a cyclic AMP analogue in vitro. Cyclic AMP‐dependent protein kinase phosphorylates tryptophan hydroxylase, purified from rat brain, without any modification of its enzyme activity under our experimental conditions. Actinomycin O or cydoheximide decreases the stimulating effect of the cyclic AMP analogue on pineal tryptophan hydroxylase activity. Incubation of pineal glands in the presence of [35S]mcthionine showed a cyclic AMP‐induced increase in tryptophan hydroxylase synthesis. These results explain the circadian rhythm of tryptophan hydroxylase activity in the rat pineal gland and suggest that the regulation of tryptophan hydroxylase expression by cyclic AMP occurs probably either at the translational level or via transient expression of a transcriptional regulatory ele

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb06346.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract: The interphotoreceptor matrix (IPM), lying between retinal photoreceptor and pigment epithelial (RPE) cells, contains insulin‐like growth factor I (IGF‐I) immunoreactivity that co‐elutes with authentic human IGF‐I in HPLC analyses. Cultured human RPE cells synthesize and release IGF‐I, raising the possibility that the RPE serves as a source of IPM IGF‐I in vivo. Photoreceptor rod outer segments and cultured monkey RPE cells express specific IGF‐I receptors with α‐subunits of 120 and 138 kDa, respectively. They thus appear to be of the “brain” (in photoreceptors) and “peripheral” (in RPE cells) receptor subtypes. Additionally, the IPM contains high levels of an IGF binding protein (IGF‐BP) that specifically binds IGF‐I and IGF‐II. The IPM‐BP is visualized as a single radiographic band by both ligand blot and affinity cross‐linking procedures. With enzymes specific for removing N‐and O‐linked oligosaccharides, the IPM‐BP was found to contain O‐but not N‐linked glycosylated side chains. The distinctive size and glycosylation pattern of the IPM‐BP indicate that it is not derived from the vitreous or serum but instead is synthesized locally. The presence of IGF‐I and IGF‐BP in the IPM, together with the presence of IGF‐I receptors on both photoreceptor and RPE cells, suggests the pr

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb06347.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Abstract: In the rat pineal gland, α1‐adrenergic agonists, which stimulate arachidonic add release, also potentiate vasoactive intestinal peptide.(VIP)‐or β‐adrenergic‐stimulated cyclic AMP (cAMP) and cyclic GMP (cGMP) accumulation. In this study, the possible involvement of the arachidonic acid pathway in the potentiation mechanism was examined in dispersed rat pinealocytes using two inhibitors of the arachidonic acid cascade, indomethacin and nordihydroguaiaretic acid. These two inhibitors appeared to have differential effects on the α1‐adrenergic potentiation of VIP‐or β‐adrenergic‐stimulated cAMP and cGMP responses. Whereas nordihydroguaiaretic acid was effective in suppressing both the α1‐adrenergic potentiation of VIP‐or β‐adrenergic‐stimulated cAMP and cGMP responses, indomethacin inhibited selectively the VIP‐mediated cAMP and cGMP responses. The role of arachidonic acid metabolites was further determined using several prostaglandins—A2, I2, E2, and F2α—and leukotrienes—B4, C4, and D4. Of the seven compounds tested, prostaglandins E2and F2αstimulated basal cAMP but not cGMP accumulation. The prostaglandin E2‐and F2α‐stimulated cAMP responses were additive to those stimulated by VIP or β‐adrenergic receptors. The other five compounds had no effects on basal or VIP‐or β‐adrenergic‐stimulated cAMPor cGMP accumulation. Taken together, these findings indicate that the arachidonic acid cascade is likely involved in the α1‐adrenergic potentiation of VIP‐or β‐adrenergic‐stimulated cAMP and cGMP accumulation. However, the specific arachidonic acid metabolite involved in the potentiation mechanisms of VIP‐versus β

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1991.tb06348.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY