摘要:

AbstractThe subcellular storage and release of noradrenaline (NA), dopamine‐β‐hydroxylase (DβH), and neuropeptide Y (NPY) was studied in the isolated perfused sheep spleen. Subcellular distribution studies showed a bimodal distribution for NA which was well reflected by DβH and indicated the occurrence of two types of NA storage vesicles. The most dense, presumably large dense‐cored vesicles (LDV), contain both membrane‐bound and soluble DβH the less dense presumably corresponds to small dense‐cored vesicles (SDV) and at least does not contain soluble DβH. The distribution of NPY is extended but shows a peak only at the position of LDV, indicating that LDV contain NPY. Continuous electrical stimulation of the splenic nerve at 2 Hz, 5 Hz, 10 Hz, and 20 Hz or at 20 hz with bursts induced the release of NA, NPY, and DβH. The ratio among these components was constant. The fractional release of DβH and NA was comparable at all frequencies used; that of NPY was 10–20 times lower, suggesting the occurrence of a large nonreleasable NPY pool. The present data argue against a high frequency stimulation or intermittent stimulation‐induced preferential release of NPY from adrenergic neurons and question the concept of frequency‐dependent chemical coding of sympathetic transmission in general. The simplest interpretation of our data is that NA and NPY are released at all frequencies from a single pool. The present findings might signify that only large dense‐cored vesicles are involved in the sympathetic stimulation‐evoked secretion of catecholamines from adrenergic nerve terminals of the isolated sheep sple

ISSN:0887-4476    

DOI:10.1002/syn.890190202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractAllosteric modulation by neuroactive steroids of radioligand binding sites on the GABAAreceptor complex was demonstrated by autoradiography in vitro in several regions of human brain and the effects compared to those in rat brain. Comparing human and rat, two steroids known to be active in enhancing GABA‐mediated postsynaptic inhibition, 5α‐pregnane‐3α21‐diol‐20‐one (tetrahydro‐deoxycorticosterone, THDOC) and alphaxalone (5α‐pregnane‐3α‐hdyroxy‐11,20‐dione), allosterically inhibited [35S]TBPS binding to the picrotoxin/convulsant site in both species in several regions including the hippocampus. Unlike rat, human brain binding of [3]Hlflunitrazepam to the benzodiazepine site was not enhanced by alphaxalone (at any concentration), but was unaffected in many regions and inhibited in others. Binding of [3H]muscimol to high and low affinity GABA sites were enhanced by both steroids in all tested regions of rat brain, although to varying degrees. However, several lobes of human cortex showed no modulation of muscimol binding by either steroid, and THDOC, but not alphaxolone, inhibited in some areas. Comparing regions, THDOC at high concentrations (10 μM) enhanced in human frontal lobe and primary sensory and motor cortex, with greater effect in deep layers than superficial. This steroid had no effect in other parts of parietal lobe and inhibited muscimol binding in temporal lobe, primary visual cortex, and other parts of occipital lobe. Concentration‐dependence curves for THDOC showed regional variation, e.g., in the hippocampal formation and surrounding neocortex. These regional and species differences are consistent with the existence of multiple GABAAreceptor subtypes that differ in pharmacology. This heterogeneity provides both the opportunity and the difficulty of targeting clinically useful medications such as antiepileptic drugs to the appropriate human brain regions, and the species differences in regional subtype expression suggest caution in use of animal

ISSN:0887-4476    

DOI:10.1002/syn.890190203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractFocal freezing lesions in rats cause a widespread decrease of cortical glucose utilization in the lesioned hemisphere, probably as a reflection of depressed cortical activity. The noradrenergic neurotransmitter system was implicated in these alterations when it was demonstrated that prazosin, a specific norepinephrine (NE) antagonist at β1‐adrenergic receptors, prevented their development. In normal rat brain, specific binding of [125I]HEAT [(±)2‐(3‐[125I]iodo‐4‐hydroxyphenyl)‐ethyl‐aminomethyltetralone], another selective α1‐adrenoreceptor ligand, was demonstrated in vivo at sites consistent with the α1A‐ and α1B‐adrenoreceptor subtypes. In the present study, the effect of a freezing lesion on specific binding of [125I]HEAT in rat brain in vivo was determined three days after traumatization when cortical glucose use suggested the greatest degree of functional depression. The steady‐state volumes of distribution of [125I]HEAT three days after injury were significantly increased in all the cortical areas of the lesioned hemisphere, but not in the subcortical structures. Injury did not modify the binding affinities for HEAT. However, a statistically significant increase in the number of low‐affinity binding sites for this ligand was demonstrated in all cortical areas of the lesioned hemisphere, but not in subcortical structures. The traumatization did not modify Bmax. estimates for the high‐affinity binding of HEAT. The results support the hypothesis that changes in the noradrenergic system are of functional importance in brain injury and that at least some effects of injury are mediated by α1B‐adrenergic

ISSN:0887-4476    

DOI:10.1002/syn.890190204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractIt has been shown previously that methamphetamine induces dopaminergic nerve terminal degeneration, serotonin depletion and striatal reactive astrogliosis, and that the noncompetitive N‐methyl‐D‐aspartate (NMDA) antagonist MK‐801 can block methamphetamine (MA)‐induced depletion of dopamine and serotonin and reduction in activity of their synthetic enzymes. In this study, immunohistochemistry was used to evaluate the effect of MK‐801 on methamphetamine‐induced neuropathological alterations of dopaminergic and serotonergic terminals and striatal astrocytic responses. Adult male rats were treated with methamphetamine (4 injections of 10 mg/kg at 2 hour intervals) in conjunction with MK‐801 which was administered 15 min before each methamphetamine administration at doses of 1 mg/kg or 2 mg/kg. Brains were examined three days following treatment. MK‐801 administration prevented methamphetamine‐induced depletion of 5‐hydroxytryptophan (5‐HT) terminals in the forebrain and depletion of tyrosine hydroxylase‐positive dopaminergic terminals and astrocytic response in the neostriatum in most animals. These results support the concept that excitatory amino acids acting through an NMDA receptor are involved in methamphetamine‐induced neuronal damage on dopaminergic and serotonergic terminal fields. A minor depletion of TH‐positive terminals and astrogliosis in the neostriatum was seen in three of nine MA‐MK‐801‐treated animals. This indicates that the protective effects of MK‐801 on MA‐induced dopaminergic terminal degeneration varies among animals with complete protection in most animals and partial protection in the others using the present doses and

ISSN:0887-4476    

DOI:10.1002/syn.890190205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe recent cloning and expression of an opioid μ receptor has opened up new opportunities for research in opioid pharmacology. The relatively low level of transient receptor expression in COS cells emphasizes the need for radioligands with high specific activity and low nonspecific binding with which to label receptors. In addition, recent data indicating that agonists and antagonists bind to different domains on the same receptor protein indicate the utility of having both agonist and antagonist radioligands available for the study of opioid receptor mechanisms. Previous studies characterized the binding of the. opioid antagonist 6β‐[125iodo]‐3,14‐dihydroxy‐17‐cyclopropylmethyl‐4,5α‐epoxymorphinan ([125I]IOXY) and showed that this naltrexone analog labels μ and K2receptors in rat and guinea pig brain with high affinity and low nonspecific binding. In the present study, we synthesized the agonist congener of IOXY, 6β‐iodo‐3,14‐dihydroxy‐17‐methyl‐4,5α‐epoxymorphinan. We named this novel agent IOXY‐AGO for IOXY‐agonist. Competition binding studies showed that IOXY‐AGO has high affinity for δ receptors (Ki = 0.28 nM) and lower affinity for δ (Ki = 18.7 nM) and K1(Ki = 33.9 nM), K2a(Ki = 38.4 nM) and K2b(Ki = 58.2 nM) binding sites. IOXY‐AGO was radioiodinated to a specific activity of 2,200 Ci/mmol. [125I]IOXY‐AGO binding was rapid, readily reversible, and characterized by low nonspecific binding. Equilibrium binding studies showed that it labeled a single class of binding sites (Kd = 1.46 nM, Bmax = 112 fmol/mg protein) with the characteristics of an opioid μ receptor. Receptor autoradiography experiments showed that [125I]IOXY‐AGO labeled binding sites with the anatomical distribution of μ receptors. Viewed collectively, these studies suggest that [125I]IOXY‐AGO will be a useful radioligand for charac

ISSN:0887-4476    

DOI:10.1002/syn.890190206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractIn a recent study in rat medial prefrontal cortex (mPFC), a fluorescently coupled, high‐affinity ligand for the D1receptor subtype was localized to nonpyramidal neurons, while a ligand selective for the D2subtype was found on neurons with a size distribution overlapping with both small pyramidal and large nonpyramidal cells. These observations raised the possibility that a subpopulation of cortical neurons with an intermediate size range may coexpress both the D1 and D2 receptor subtypes. In the present study, the D1and D2receptor subtypes have been simultaneously localized in layer VI of rat mPFC using 20 nM SCH 23390‐Bodipy and 20 nM N‐(p‐aminophenethyl) spiperone‐Texas red, respectively, in the presence of 100 nM mianserin (5‐HT2receptor antagonist). The localization of receptor binding fluorescence was assessed in paired images using fluoresceiN isothiocyanate (FITC) and rhodamine dichroic filters for the D1and D2subtypes, respectively. Under the conditions employed here, most cell bodies showed either Dl‐like or D2‐like receptor binding fluorescence, while a colocalization of both fluoroprobes was observed on only 25% of the labeled cells. When the size of each single‐labeled cell body was measured using the respective FITC (D1‐probe) and rhodamine (D2‐probe) epifluorescence filters, the distribution of cells showing only D1‐like receptor binding fluorescence was similar to nonpyramidal neurons (68.6 ± 1.8 μm2), while that for cells showing only D2‐like receptor binding fluorescence was similar to that of both large interneurons and small pyramidal cells (106.9 ± 2.4 μm2). Cells showing both D1‐ and D2‐like receptor binding fluorescence were found to overlap in size only with nonpyramidal cells when either fluorescent filter was used. These findings are consistent with the hypothesis that the D1and D2receptor subtypes are most often found on different populations of neurons in mPFC, although approximately 25% of all such cells appear to be nonpyramidal neurons having both D1and D2receptor binding activity. These findings suggest that the dopamine projections to rat cortex probably engage in a complex interplay with intrinsic cortical neurons and their respective neurotransmitte

ISSN:0887-4476    

DOI:10.1002/syn.890190207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractIn hippocampal area CA1, long‐term potentiation (LTP) is induced by tetanic stimulation protocols that activate N‐methyl‐D‐aspartate (NMDA) receptors. In addition, some stimulation protocols can induce LTP during NMDA receptor blockade. An initial signal in both NMDA receptor‐dependent and independent LTPs is increased intracellular Ca2+concentration in postsynaptic neurons. It therefore seems possible that subsequent steps leading to expression and maintenance of potentiation are shared whether or not LTP is induced through NMDA receptor activation. We tested this hypothesis by applying a broad spectrum protein kinase, inhibitor, previously shown to inhibit NMDA receptor‐dependent LTP. In agreement with earlier reports, we found that H‐7 inhibited NMDA receptor‐dependent LTP when applied either during tetanic stimulation, or beginning 30 min following tetanic stimulation. In contrast, NMDA receptorindependent LTP was not inhibited by H‐7 applied during or following tetanic stimulation. We also tested for mutual occlusion between NMDA receptor‐dependent and independent LTPs. Although induction of NMDA receptor‐independent LTP did not occlude later induction of NMDA receptor‐dependent LTP, induction of NMDA receptordependent LTP did occlude NMDA receptor‐independent LTP. While the kinase inhibitor experiment showed a clear difference between NMDA receptor‐dependent and independent LTPs, the occlusion experiments suggest an interaction between the signalling pathways for the two L

ISSN:0887-4476    

DOI:10.1002/syn.890190208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThis study was designed to localize the population of dopamine D1‐like receptors involved in grooming and oral movements elicited by systemic administration of the Dl‐selective agonist SKF‐38393. Receptors in specific dopamine terminal regions were inactivated by intracranial injection of the nonselective irreversible antagonist N‐ethoxycarbonyl‐2‐ethoxy‐1,2‐dihydroquinoline (EEDQ). The effect of these injections on behaviors induced by systemic administration of SKF‐38393 (10 mg/kg) was measured 48 hours later. The specific populations of D1‐like receptors inactivated by the EEDQ injections were identified as a loss of3H‐SCH‐23390 binding in a given region using quantitative autoradiography. EEDQ (1.5 μg/μl/side) injected into the nucleus accumbens (NAc) did not alter SKF‐38393‐induced behaviors. Similarly, injection of EEDQ into the medial caudate‐putamen (CPu) failed to alter these behaviors. In contrast, EEDQ (0.15‐1.5 μg/μl/side) injected into the lateral CPu decreased both SKF‐38393‐induced grooming and oral movements, with complete blockade of grooming observed at the highest dose. To determine whether this effect of EEDQ was due to inactivation of Dl‐like receptors, separate groups of animals were pretreated with SCH‐23390 (3 mg/kg, S.C.) 15 min prior to injection with EEDQ. Pretreatment with SCH‐23390 prevented the disruption of SKF‐38393‐induced behaviors, as well as the loss of3H‐SCH‐23390‐labeled binding sites observed after injection of EEDQ into the lateral CPu. EEDQ injections that produced disruption of SKF‐38393‐induced behaviors were associated with a greater loss of binding in the lateral CPu relative to other regions examined including the NAc, medial CPu, and globus pallidus. Furthermore, EEDQ injections that produced the greatest loss of3H‐SCH‐23390 binding in the latter three regions did not disrupt SKF‐38393 induced behavior. These results demonstrate that stimulation of Dl‐like receptors in the lateral CPu is necessary for behaviors induced by systemic administration of SKF‐38393. The results also demonstrate the utility of this “receptor lesion”

ISSN:0887-4476    

DOI:10.1002/syn.890190209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractIt is broadly accepted that a postsynaptic “miniature” is the most elementary chemically transmitted signal and results from the all‐or‐none release of transmitter packaged in a single presynaptic vesicle. Hitherto, it has not been possible to directly verify this renowned representation, although it is consistent with evidence of vesicle traffic and, following an intense period of release, vesicle depletion. However, vesicle traffic involving molecular components similar to those implicated in transmitter release has been attributed to other functions including membrane repair. Furthermore, as a number of investigators have recently proposed, miniature signals recorded at peripheral and central synapses may actually reflect several rather than a single discharge of transmitter. It is not clear whether such putative multiple‐discharge miniatures represent near‐synchronous exocytoses of several vesicles or a burst of openings in a pore that couples a vesicle with the outer membrane. In any case, despite the popularity of the vesicular hypothesis, the molecular mechanism involved in synchronizing fast elementary secretion has not yet been elucidated. Interdependencies among subminiature discharges composing a miniature have suggested that the underlying process is a regenerative signal restricted to a presynaptic terminal unit, confirming Fatt and Katz's first speculation on miniatures, which was not vesicular exocytosis [Fatt and Katz (1952), J. Physiol., 117:109–128]. Here we discuss the possibility that this regenerative signal might be a localized cytosolic Ca2+transient and attempt to reconcile this hypothesis with the exocytotic models proposed to explain fast transmitter release. © 1995 W

ISSN:0887-4476    

DOI:10.1002/syn.890190210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:0887-4476    

DOI:10.1002/syn.890190201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY