摘要:

Abstract:Positron emission tomography (PET) with labeled neuroleptics has made possible the study of neurotransmitter‐receptor systems in vivo. In this study we investigate the kinetics of the 3, 4‐dihydroxyphenylethylamine (dopamine) receptor‐ligand binding using PET data from a series of experiments in the baboon with the18F‐labeled drugs spiperone, haloperidol, and benperidol. Models used to describe these systems are based on first‐order kinetics which applies at high specific activity (low receptor occupancy). The parameters governing the uptake and loss of drug from the brain were found by fitting PET data from regions with little or no receptor concentration (cerebellum) and from experiments in which specific binding was blocked by pretreatment with the drug (+)‐butaclamol. Receptor constants were determined by fitting data from receptor‐containing structures. Correcting the arterial plasma activities (the model driving function) for the presence of drug metabolites was found to be important in the modeling of

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1987.tb13129.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract:The phosphorylation of microtubule‐associated protein 2 (MAP2) by four different kinases was studied in vitro to determine whether MAP2is phosphorylated in its tubulin binding region or in the microtubule projection portion. Fragments corresponding to both regions of MAP2were produced not only by chymotrypsin or trypsin digestion, but also using pepsin, a broad chain‐specificity protease, a result supporting previous notions of the two‐domain structure of MAP2. The position of these two functional domains was determined with respect to the carboxy terminal of the molecule, by labeling MAP2exclusively at the carboxy terminal and subjecting it to pepsin digestion. The results suggested that the projection region of MAP2contained the carboxy terminal of the protein. A phosphorylation map was constructed by subjecting phosphorylated MAP2to enzymatic digestion usingStaphylococcus aureusV8 protease or to chemical cleavage usingN‐chlorosuccinimide. The results indicated that all four kinases phosphorylated MAP2in a 42‐kilodalton peptide that contained the tubulin binding region but differed in the level and localization of the sites at which they phosphorylated the projectio

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1987.tb13130.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract:Elevated blood levels of prolactin increase the synthesis, turnover, and release of 3, 4‐dihydroxyphenylethylamine (dopamine) from the tuberoinfundibular dopaminergic neurons, which project to the median eminence. The present study examined whether hyperprolactinemia also increases local cerebral glucose utilization, as determined by the 2‐deoxy‐D‐[I‐14C]glucose method, in the median eminence and other brain structures. Adult male rats were given ovine prolactin (4 mg/kg) subcutaneously every 8 h for 48 h. This treatment exerted an autoregulatory feedback effect on endogenous rat prolactin secretion, as evidenced by decreased circulating levels of rat prolactin. Ovine prolactin treatment also decreased plasma glucose concentrations. However, in both partially immobilized and free‐ranging rats, glucose utilization in brain structures containing tuberoinfundibular dopaminergic cell bodies (the arcuate nucleus) and terminals (the median eminence) was not affected by ovine prolactin treatment. Hyperprolactinemia was, however, associated with decreased glucose utilization in the medial forebrain bundle and the CA subfield of the dorsal hippocampus. The lack of a significant effect of prolactin treatment on glucose utilization in the median eminence indicates (a) that the resolution of the deoxyglucose technique, as used here, is not adequate to detect the ovine prolactin‐induced increase in tuberoinfundibular dopaminergic neuronal activity, (b) that the median eminence does not utilize glucose as its primary energy substrate, or (c) that ovine prolactin treatment causes a counterbalancing decrease in the activity of other neurons projecting to the me

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1987.tb13131.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract:Metaphit {1‐[1‐ (3‐isothiocyanatophenyl)cyclohexyl]‐piperidine}, a derivative of phencyclidine that contains an isothiocyanate group on the meta position of the aromatic ring, resembles its parent compound (phencyclidine) in its ability to inhibit the binding of the stimulant drug [3H]threo‐ (±)‐methylphenidate to crude synaptosomal membranes from rat Striatal tissue (IC50= 1.4 and 6.2 μMfor phencyclidine and Metaphit, respectively). Unlike phencyclidine, however, Metaphit appears to inhibit binding of the radiolabeled stimulant in an irreversible manner, as the degree of inhibition of binding of the stimulant does not diminish when the Metaphit‐treated tissue is subjected to repeated washings before determination of the binding of [3H]threo‐ (±)‐methylphenidate. This finding suggests that Metaphit may be a useful tool in the study of the molecular basis

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1987.tb13132.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract:Previous studies have shown that phorbol esters and lithium each stimulate the secretion of adrenocorticotropic hormone (ACTH) by the anterior pituitary tumor cell line AtT20/D16‐16. Pretreatment with either lithium or phorbol ester desensitizes the cells to subsequent stimulation by phorbol ester. An early consequence of phorbol ester action in other systems is the translocation of protein kinase C from cytosol to membranes. We have assayed protein kinase C activity in cytosol and membranes of AtT20 cells after treatment with phorbol dibutyrate, lithium, or other agents that stimulate secretion of ACTH in these cells. Phorbol dibutyrate clearly induced translocation of protein kinase C, but lithium treatment did not cause translocation itself, nor did pretreatment with lithium affect the translocation induced by phorbol dibutyrate. These results are consistent with a role for translocation of protein kinase C in the stimulatory and desensitizing effects of phorbol esters but fail to implicate translocation in the actions of lithium on AtT20 cell

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1987.tb13133.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract:Peripheral nerve transection triggers a series of phenotypic alterations in Schwann cells distal to the site of injury. Mitosis is one of the earliest and best characterized of these responses, although the mechanism by which axonal damage triggers this critical event is unknown. This study examines the appearance and spatio‐temporal spread of premitotic activity in distal stumps of transected cat tibial nerves. Premitotic activity was determined by measuring incorporation of [3H]thymidine (a marker of DNA synthesis during the S‐phase of the cell cycle) into consecutive segments of desheathed tibial nerve. Incorporation of [3H]thymidine spread proximo‐distally within distal nerve stumps between 3 and 4 days posttransection with an apparent velocity of at least 199 ± 67 mm/day. This suggests that anterograde fast axonal transport may directly or indirectly be associated with the Schwann cell mitotic response to axon trans

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1987.tb13134.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract:Methylation of 2‐125I‐lysergic acid diethylamide (125I‐LSD) at theN1 position produces a new derivative,N1‐methyl‐2‐125I‐lysergic acid diethylamide (125I‐MIL), with improved selectivity and higher affinity for serotonin 5‐HT2receptors. In rat frontal cortex homogenates, specific binding of125I‐MIL represents 80–90% of total binding, and the apparent dissociation constant (KD) for serotonin 5‐HT2receptors is 0.14 nM(using 2 mg of tissue/ml).125I‐MIL also displays a high affinity for serotonin 5‐HT1Creceptors, with an apparent dissociation constant of 0.41 nMat this site.125I‐MIL exhibits at least 60‐fold higher affinity for serotonin 5‐HT2receptors than for other classes of neurotransmitter receptors, with the dopamine D2receptor as its most potent secondary binding site. Studies of the association and dissociation kinetics of125I‐MIL reveal a strong temperature dependence, with very slow association and dissociation rates at 0°C. Autoradiographic experiments confirm the improved specificity of125I‐MIL. Selective labeling of serotonin receptors was observed in all brain areas examined. In vivo binding studies in mice indicate that125I‐MIL is the best serotonin receptor label yet described, with the highest frontal cortex to cerebellum ratio of any serotonergic radioligand.125I‐MIL is a promising ligand for both in vitro and in vivo labeling of

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1987.tb13135.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract:[3H]Neurokinin B ([3H]NKB) of high specific activity (75 Ci/mmol) was synthesized for study of its binding to crude synaptosomes from the rat cerebral cortex. The specific binding of [3H]NKB (75% of total binding) was temperature dependent, saturable, and reversible. Scatchard analyses and Hill plots showed the existence of a single population of noninteracting binding sites (KD= 4.3nM;Bmax= 123 fmol/mg of protein). Competition studies indicated the following rank order of potencies among tachykinins: NKB>eledoisin (E)>kassinin>physalaemin>neurokinin A (NKA)>substance P (SP), a result suggesting that NKB might be the endogenous ligand for [3H]NKB binding sites. It is of interest that127I‐Bolton Hunter (BH) NKA (127I‐BHNKA) was much more potent than NKA in inhibiting the specific binding of [3H]NKB, which raises certain questions concerning the use of125I‐BHNKA as a Iigand for NKA binding sites in the brain. These results, as well as those obtained with different SP analogues, show a close similarity to those obtained previously with125I‐BHE binding to cortical synaptosomes. This suggested that the two ligands labeled identical binding sites. In addition, using either [3H]NKB or125I‐BHE as ligands, similar displacement curves were obtained with increasing concentrations of NKB and127I‐BHE. The similarity of the [3H]NKB and125I‐BHE binding sites was further confirmed by comparison of their localization on rat brain sections by autoradiography. The distribution of binding sites for [3H]NKB and125I‐BHE was identical throughout the brain, and the highest density of binding sites for the two ligands was found in layers IV and V of the cerebral cortex, the paraventricular nucleus of the hypothalamus (magnocellular part), and the ventral

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1987.tb13136.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract:Many characteristics of proteins that are fast axonally transported have been described, but the destinations of most within the neuron remain unknown. We have studied the destinations of some fast‐transported proteins in sensory neurons of the bullfrog sciatic nerve, specifically to determine which may be deposited in axons and which may be destined for more distal, possibly terminal, areas. Dorsal root ganglia were pulse‐labeled with [35S]methionine in vitro, following which they were separated from the sciatic nerve. After additional periods of transport, radioactive proteins from two areas of the nerve were separated by two‐dimensional polyacrylamide gel electrophoresis and used to develop x‐ray film. The first area contained the wavefront of transported radioactivity (wavefront region), whereas the second area was taken from nerve through which the wavefront had already passed (plateau region). The amount of radioactivity in certain fast‐transported protein species from each area was determined by computer analysis of digitized video images of fluorographs. Certain proteins were preferentially left behind the wavefront and, therefore, may supply axon and possibly other nerve components, whereas other proteins were found almost exclusively in the wavefront and, hence, may supply more distal, possibly termin

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1987.tb13137.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Abstract:The highest concentration of neurokinin A‐like immunoreactivity and substance P‐like immunoreactivity in the guinea pig small intestine was associated with the myenteric plexus‐containing longitudinal muscle layer. Chromatographic analysis of extracts of this tissue demonstrated the presence of neurokinin A and neuropeptide K but the probable absence of neurokinin B. A fraction of synaptic vesicles of density 1.133 ± 0.003 g/ml was prepared from the myenteric plexus‐containing tissue by density gradient centrifugation in a zonal rotor and was enriched 29 ± 12‐fold in the concentration of neurokinin A‐like immunoreactivity and 43 ± 13‐fold in the concentration of substance P‐like immunoreactivity. This fraction was separated from the fraction of vasoactive intestinal peptide‐containing vesicles (density, 1.154 ± 0.009 g/ml). Chromatographic analysis of lysates of the vesicles indicated the presence of neurokinin A but not neuropeptide K. It is postulated that β‐pre‐protachykinin is processed to substance P, neurokinin A, and neuropeptide K in the cell bodies of myenteric plexus neurons but that conversion of neuropeptide K to neurokinin A takes place during packaging into storage vesicles for axonal transport. The data are consistent with the proposal that neurokinin A and substance P are stored in the same synaptic vesicle, but the possibility of cosedimentation of different vesicles of very similar

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1987.tb13138.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY