摘要:

AbstractThis study measured melanotrope mRNA and protein expression for the dopamine D2receptor, and its long isoform, in relation to the appearance of dopamine in axons of the postnatal rat pituitary intermediate lobe. At postnatal day 2, prior to the onset of dopaminergic innervation, D2receptor (D2T) mRNA was expressed heterogeneously in a subpopulation of melanotropes which also expressed the long isoform (DL). The D2LmRNA appeared to be predominant during early postnatal development, since the D2Tprobe, which did not discriminate between the isoforms, and the D2Lprobe hybridized generally to the same cells, as demonstrated in serial sections. Immunohistochemical methods, using two different antisera for the D2Treceptor, however, indicated a low level of protein in most melanotropes. Localization of D2Lprotein corresponded well to D2Lreceptor mRNA distribution. At day 10, representing a time when dopamine is present in axons throughout the lobe, both D2Treceptor mRNA and protein were detected in a significantly larger population of melanotropes than those expressing D2LmRNA and protein. This suggests the appearance of detectable short isoform (D2S) mRNA in virtually all melanotropes and implicates dopamine as a possible signal for increasing D2Sisoform mRNA expression.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00087-9

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractCerebral microvessels from rats were prepared and characterized by their enrichment of specific markers, namely alkaline phosphatase (AP) and τ‐glutamyl transpeptidase (τ‐GT). Further, it was observed that AP and τ‐GT registered marked increase in aged rats. On the contrary, lactate dehydrogenase (LDH) activity decreased with the increasing age. Monoamine oxidase A activity in the microvessels decreased with age whereas MAO‐B moved in the reverse direction. No noticeable change was seen in acetylcholinesterase activity with increasing age of rats.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00086-0

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractThe developmental profiles of the lipid composition and theirde novosynthesis and remodelling in the optic lobe of the chicken were studied. The32P incorporation to phospholipids showed an activede novosynthesis mainly of phosphatidylinositol and of a particular fraction of phosphatidylcholine during the early stages of the embryo development, concomitantly with the beginning of synaptogenesis. Thisde novosynthesis of phospholipids strongly increased at hatching. On the other hand, phosphatidylinositol presented an active lipid exchange (acylation‐leacylation) in the early stages of embryogenesis, indicating a strong incorporation of14C‐arachidonic acid during this period, followed by a fast drop in specific activity. Two different fractions of phosphatidylcholine were isolated by high‐performance thin‐layer chromatography with a different profile of fatty acid composition, disclosing their different physicochemical behavior, metabolic activities and evolution during embryogenesis.32P incorporation into phosphatidylethanolamine remained very low during the earliest stages of embryogenesis, showing an increase when the process of synaptogenesis began, until hatching, when radioactivity reached a plateau.14C‐arachidonic acid incorporation into phosphatidylethanolamine was minimal. Furthermore, the phosphatidylethanolamine pool was progressively enriched in its ethanolamine plasmalogen throughout the development. Chromatographic analysis of lipid extracts showed the presence of cerebroside traces after 16 days of embryo incubation. At hatching, a remarkable increase in non‐hydroxylated cerebrosides was observed concurrently with the appearance of hydroxylated ones. These glycosphingolipids, as well as the sulfatides, were markedly increased in the lipid extracts of optic lobes of adult animals, indicating the progressive development and maturity of the myelin sheath.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00089-5

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractThe formation of motor neurons in the spinal cord is dependent on inductive signals from the floor plate and notochord. Motor neurons in the brain stem, on the other hand, develop in the absence of both structures. This suggests that either the germinal epithelium is specified intrinsically to form specific cranial motor nuclei or that the inductive signals for the formation of cranial motor neurons arise from some other structure. These possibilities were investigated experimentally by using the formation of trochlear motor neurons in the midbrain of duck embryos as a model system. The trochlear motor neurons, which form the nucleus of the fourth cranial nerve, developed normally after early damage to the prospective germinal epithelium, suggesting that it is unlikely to be specified intrinsically to form these cranial motor neurons. Instead, their development was found to be dependent on the cells within, or associated with, the ventromedial region of the brain stem, as the extirpation of this region results in the absence of motor neuron formation. These results show that structures other than the floor plate and notochord provide inductive signals for the cellular differentiation and patterning of the developing central nervous system. They raise the possibility that the inductive signals for motor neuron differentiation in the spinal cord and the brain stem may not be necessarily identical.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00090-9

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractLevels of nitric oxide synthase (NOS) and NADPH‐diaphorase in adrenal glands of streptozotocin‐diabetic rats of 8 and 12 weeks' duration compared with control rats were assessed with histochemical and biochemical techniques. Adrenal glands from streptozotocin‐diabetic rats of 8 weeks' duration treated with ganglioside were examined also. In the adrenal medulla of 8‐weeks‐ and 12‐weeks‐diabetic rats, NOS‐immunoreactive nerve fibres were increased and decreased, respectively; additional NOS‐immunoreactive and NADPH‐diaphorase stained cells, which appeared to be cortical cells, were located in medulla and cortex compared with controls. Increased intensity in NADPH‐diaphorase staining of the cortical cells of diabetic rats was observed also. Ganglioside treatment of the 8‐weeks‐diabetic rats prevented the diabetic‐induced increase in NOS‐immunoreactive nerve fibres. Also, it reduced most of the increase in the NOS‐immunoreactive and NADPH‐diaphorase stained cells and the intensity of NADPH‐diaphorase staining of cortical cells. With biochemical assay, a significant increase in NOS activity was found in the adrenal glands from 8‐weeks‐diabetic rats, and this increase was reduced by ganglioside treatment in four out of six diabetic rats.In summary, streptozotocin‐induced diabetes causes an initial increase in the levels of NOS and NADPH‐diaphorase in the adrenal gland of rat, which was prevented by ganglioside treatment.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00091-7

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractTo evaluate the effect of long‐term exposure to heavy metals on skeletal muscle, chronic subcutaneous injections for 7 days of two level treatments (low dose, 0.1 mg/kg and high dose, 1 mg/kg) of lead acetate were investigated. Comparative analyses ofin situ dorsiflexormuscle isometric contractile characteristics were studied in urethane‐anesthetized (2 mg/g, i.p.) control and lead‐exposed male mice. Control muscle‐twitch tension reached an average of 1.81 ± 0.06 g. Chronic lead (Pb2+) treatments did not affect muscle contractile speed, but reduced significantly the twitch tension in both high and low doses when compared to control animals. This effect was in a dose‐dependent manner; 1.21 ± 0.07 g for low dose and 0.90 ± 0.05 g for high dose. These chronic Pb2+treatments accelerated muscle fatigue after 250 stimuli (25 Hz for 10 sec) in both the low and high doses equally. However, marked elevation in tetanic (25 Hz) specific tension were observed in the high‐dose, chronically treated animals, indicating some changes in contractile apparatus function. The high dose of chronic Pb2+treatment induced ultrastructural changes, including reduced number of synaptic vesicles, disruption of mitochondria and increased number of smooth endoplasmic reticulum and myelin‐like figures in the intramuscular axons and neuromuscular junctions. Chronic Pb2+treatment caused extensive disruption of the sarcoplasmic mitochondria and increased the number of myelin‐like figures in the muscle. These results suggest that exposure to Pb2+at a low concentration can compromise thein situskeletal muscle isometric contraction.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00092-5

出版商:Wiley    

年代:1999

数据来源: WILEY

摘要:

AbstractSpontaneous output patterns of embryonic spinal cord slicesin vitrowere investigated in order to study the formation of pattern‐generating networks. Patterns of spontaneous contractions of skeletal muscle fibers were recorded in co‐cultures of embryonic rat spinal cord, dorsal root ganglia and skeletal muscle. A part of these contractions was shown to be driven by spinal circuits. These neuron‐driven activity patterns changed from random to rhythmic when the inhibitory synapses in the spinal cord were blocked by strychnine, bicuculline or both. Rhythmic patterns consisted of bursts of activity (tetanic contractions) followed by periods of relaxation. The transition from random to rhythmic patterns occurred during a period of heavily increased rate of activity. Presynaptic inhibition was not involved critically in the generation of rhythmic patterns. Such patterns were, however, modulated through muscarinic and α‐adrenergic receptors. Neither NMDA nor glutamate nor its uptake blocker dihydrokainate induced rhythmic patterns of contraction, although NMDA in the presence of low magnesium increased moderately the rate of random activity. In order to study the size of pattern‐generating networks, parts of the spinal cord slices were sectioned during rhythmic activity. Tangential cuts at the lateral or dorsal side of the slices reduced either the rate or the duration of the bursts or both. Sagittal cuts suppressed the activity almost totally. These findings suggest that the pattern generators in the slices consist of excitatory networks covering the entire slice, and that these networks reverberate following spontaneous activity of some distributed elements.

ISSN:0736-5748    

DOI:10.1016/0736-5748(95)00093-3

出版商:Wiley    

年代:1999

数据来源: WILEY

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)90011-8

出版商:Wiley    

年代:2003

数据来源: WILEY

ISSN:0736-5748    

DOI:10.1016/S0736-5748(96)90012-X

出版商:Wiley    

年代:2003

数据来源: WILEY