摘要:

AbstractWe have previously shown that myelinating Schwann cells associated with motor, but not sensory, axons in peripheral nerves of adult mice express the L2/HNK‐1 carbohydrate epitope. This carbohydrate structure carried by glycolipids and neural cell adhesion molecules has been suggested to specifically foster regrowth of motor as opposed to sensory axons after infliction of a lesion. To determine which molecular components may be the carriers of the L2 carbohydrate in motor axon‐associated myelinating Schwann cells, we have isolated the purely sensory, cutaneous branch and the mixed sensory and motor muscle branch of the femoral nerve of adult mice, isolated the myelin fraction thereof and analysed the molecules expressing the L2 carbohydrate by several immunochemical methods. L2 immunoreactivity in myelin of the muscle branch was four to five times higher than that of the cutaneous branch. The 110 kDa L2‐immunoreactive glycoprotein in myelin of the muscle branch, which is not L2‐immunoreactive in the cutaneous branch, was identified as the myelin‐associated glycoprotein by a combination of immunoprecipitation and Western blot analysis. Myelin extraction with organic solvents additionally revealed the two L2‐carrying glycolipids, which amounted to‐40 ng glycolipid/mg dry weight in myelin of the muscle branch, whereas no significant amounts of the L2 glycolipids were found in myelin of the cutaneous branch. These observations suggest an astonishing degree of differential regulation of carbohydrate‐synthesizing activities in myelinatin

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00570.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe modulatory role of dopamine (DA) on the expression of mRNA encoding the large isoform of glutamic acid decarboxylase (GAD67), the biosynthesis enzyme of gamma aminobutyric acid (GABA), was examined in GABA neurons of two structures innervated by DA neurons originating from the ventral tegmental area (VTA): the medial frontal cortex (MFC) and the nucleus accumbens (NAcc). A bilateral electrolytic lesion of VTA was performed in rats to produce a DA denervation of both the MFC and NAcc. The efficacy of VTA lesions was verified by measurement of locomotor activity and by immunohistochemical detection of tyrosine hydroxylase in the mesencephalon. GAD67 mRNA was detected byin situhybridization histochemistry using a35S‐labelled cDNA probe. Densitometric analysis of GAD67 mRNA hybridization signals revealed in VTA‐lesioned rats a significant decrease (‐24%) in GAD67 mRNA levels in the prelimbic area of the MFC and no significant effect in the anterior cingulate area or the frontoparietal cortex. Single cell analyses by computer‐assisted grain counting showed that the decrease in GAD67 mRNA levels in prelimbic MFC was due to a change in GAD67 mRNA expression in a subpopulation of GABA interneurons located in the deep cortical layers (V‐VI). By contrast, in the NAcc of VTA‐lesioned rats, GAD67 mRNA levels were significantly increased in the anterior part and in the core but were unchanged in the shell part. These results suggest that in two target structures of VTA DA neurons, GAD67 mRNA expression is, in normal conditions, under a tonic stimulatory and a tonic inhibitory DA control in the MFC and the NAcc respectively. A schematic diagram is proposed for functional interactions between these

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00571.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe glutamate receptor channels of theN‐methyl‐d‐aspartate (NMDA) subtype are composed of different subunits named NR1 and NR2A‐D. These subunits can combine in different oligomers with diverging properties and their expression is developmentally regulated. We have used rat cerebellar slice cultures to test the involvement of bioelectrical activity and synaptic transmission in the changes in NR2A‐C expression observed in developing granule cells. A correlation between the functional properties of the NMDA receptors and expression of the NR2A‐C mRNAs was obtained in single granule cells by coupling patch‐clamp recording and reverse transcription followed by polymerase chain reaction. Granule cells grown under standard culture conditions expressed mainly NR2A mRNA when examined after 15–40 daysin vitro. Consistent with this observation, their responses to NMDA were only weakly reduced by 3 μM ifenprodil, a non‐competitive antagonist which discriminates between NR2A and NR2B subunits in expression systems. In cerebellar cultures chronically exposed to tetrodotoxin to eliminate spontaneous electrical activity, granule cells maintained a predominant expression of NR2B subunits and their responses to NMDA were largely inhibited by 3 μM ifenprodil. These results provide evidence that the expression of the NR2A and B subunits is regulated through an activity‐dependent mechanism leading to the formation of NMDA receptors with different pharmacological properties. Finally, the NR2C subunit, abundantly expressedin vivoby adult granule cells, was only rarely detected in slice cultures, even when excitatory synapses were formed between granule cells and fibres originating from co‐cultured brainstem explants. These data suggest that the induction of NR2C expression observedin vivorequires an additional factor(s) that r

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00572.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractTo better understand the role of insulin‐related growth factors in neural development, we have characterized byin situhybridization in chicken embryonic retina the patterns of gene expression for insulin, insulin‐like growth factor I (IGF‐I), their respective receptors and the IGF binding protein 5 (IGFBP5) from early stages (E6) until late stages (E18)‐an analysis not performed yet in any species. In addition, we studied the effect of insulin and IGF‐I on cultured neuroepithelial cells. Insulin receptor mRNA and IGF‐I receptor mRNA were both present and showed a similar, widespread pattern throughout retina development. Insulin mRNA could be detected only by reverse transcription coupled to polymerase chain reaction. IGF‐I mRNA was concentrated in the ciliary processes and extraocular muscles early in development (embryonic day 6; E6) and in maturing retinal ganglion cells subsequently (E9–15). IGFBP5 mRNA was preferentially localized in the more differentiated central retinal zone and was maximally concentrated in the inner nuclear and ganglion cell layers at E9. These findings suggest a near constitutive expression of insulin receptor and IGF‐I receptor genes, while IGF‐I and IGFBP5 showed a highly focal spatiotemporal regulation of gene expression. Insulin and IGF‐I, already at 10−8M, increased the proportion of PM1‐positive neuroepithelial cells found in E5 retinal cultures without affecting significantly the total number of proliferating cells. Together, these data support the finding that, during early neurogenesis in chicken retina, insulin and IGF‐I have a specific paracrine/autocrine action. This action, as well as possible effects elicited subsequently, may be dictated by restricted local synthesis of the ligands and limited access to the factors contained in the vitreous humour. In the case of IGF's role, local IGFBPs expression can contri

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00573.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractWith the purpose of mapping those anatomical structures participating in the processing and analysis of form, colour and disparity information, we have measured, with positron emission tomography and [15O]butanol, regional cerebral blood flow (rCBF) as an indicator of regional cerebral metabolic activity in 13 right‐handed male volunteers during visual discrimination of colour, form and disparity information. The brain images were anatomically standardized using a computerized brain atlas and statistically significant changes were localized by cluster analysis. The changes in rCBF between specific activation and reference states were measured and the volumes of changes were determined, as were the loci and volumes of areas commonly activated by two or three different tasks. Each of the tasks activated over a dozen distinct and separate fields in the cortex–in the occipital, parietal, temporal and frontal lobes as well as the cerebellum. A number of overlapping fields were commonly activated in two tasks (four in the form and colour tasks, five in the form and disparity tasks, and eleven in the colour and disparity tasks), and two field overlaps were present in all three tasks (in the right superior frontal and left lingual gyri). These findings indicate that, in a visual discrimination task, the processing and analysis of single visual submodalities take place in a number of cortical fields in the human brain. As the same visual submodality is processed and analysed by numerous fields and the same field may participate in the processing of different submodalities, a divergence‐convergence pattern of information processing is present in the human brain. This observation supports a hypothesis based on earlier studies in primates, namely that information processing in the visual system requires the concerted activation of a relatively large number of fields of functional networks in the

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00574.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe brainstem mechanisms for the generation of paradoxical sleep are under considerable debate. Previous experiments in cats have demonstrated that injections of the cholinergic agonist carbachol into the oral pontine tegmentum elicit paradoxical sleep behaviour and its polygraphic correlates. The different results on the pontine structures that mediate this effect do not agree. We report here that limited microinjections of a carbachol solution into the ventral part of the oral pontine reticular nucleus in the cat induce, with a short latency, a dramatic, long‐lasting increase in paradoxical sleep. Moreover, neuronal tracing experiments show that this pontine site is connected with brain structures responsible for the different bioelectric events of paradoxical sleep. These two facts suggest that the ventral part of the oral pontine reticular nucleus is a nodal link in the neuronal network underlying paradoxical sleep mechanism

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00575.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe present study sought to test the hypothesis that dopamine in the prefrontal cortex exerts an inhibitory influence on subcortical dopamine systems and that depletion of prefrontal dopamine may affect behaviour via an increase in dopamine release in the basal ganglia. We used prepulse inhibition of the acoustic startle response, i.e. the inhibition of the acoustic startle response by a preceding non‐startling stimulus, as the behavioural test, because this phenomenon of sensorimotor gating is modified in opposite directions by dopamine in the prefrontal cortex and in the basal ganglia. Rats were tested for prepulse inhibition before and after injections of the neurotoxin 6‐hydroxydopamine into the medial prefrontal cortex. We attempted to differentiate the contributions of prefrontal dopamine and noradrenaline by pretreating the animals with desipramine (6‐OHDADMIrats) or bupropion (6‐OHDABUPrats), selective inhibitors of noradrenaline and dopamine reuptake respectively. 6‐Hydroxydopamine lesion reduced prefrontal dopamine by 90% and noradrenaline by 80% in 6‐OHDADMIrats, while prefrontal dopamine was reduced by 54% and noradrenaline by 95% in 6‐OHDABUPrats. The ability of an acoustic prepulse (75 dB, 10 kHz) to inhibit the response to a startle pulse (100 dB noise burst) was maintained in sham‐lesioned rats and in 6‐OHDABUPrats. However, there was a marked reduction of prepulse inhibition (by 26%) in the 6‐OHDADMIrats. Systemic administration of the dopamine antagonist haloperidol (0.05 mg/kg), which did not affect prepulse inhibition in sham‐lesioned and in 6‐OHDABUPrats, antagonized the lesion‐induced deficit in prepulse inhibition in 6‐OHDADMIrats. These results suggest that prefrontal dopamine is involved in prepulse inhibition of the acoustic startle response. The haloperidol‐induced antagonism of the deficit in prepulse inhibition observed in 6‐OHDADMIrats is compatible with the view that prefrontal dopamine depletion led to overactivity of subcortical dopamine systems involved in prepulse inhibition, i.e. in the nucleus accumbens and/or anteromedial striatum. The significance of prefrontal noradrenaline depletion, which may have partially counteracted the effects of dopamine depletion on prepulse inhibition, is also discussed. Since prepulse inhibition is impaired in schizophrenics, the present findings lend support to the theory of prefrontal dopamine hypofunction in

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00576.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIn kittens, callosal axons originating either from medial area 17 (transient axons) or near the 17/18 border (mostly permanent axons) were labelled with anterogradely transported biocytin; they were reconstructed by computer from serial sections, and their morphologies compared at different ages. During the first and second postnatal weeks both sets of axons branched profusely in the white matter of the lateral gyrus and the number of branches increased with age. The most common type of axon ending was the growth cone; others may have been collapsing growth cones, branches in the process of elimination or early synaptic boutons. Axons from medial area 17 distributed over a broad territory, including the 17/18 border where callosal axons terminate in the adult cat, but without aiming specifically at any one area. The majority of axons and their branches terminated in the white matter or at the bottom of layer VI; exceptionally they extended further into the cortex. Most of the axons originating near the 17/18 border were different from those described above, and the difference increased with age. Although they also terminated profusely in the white matter of the lateral gyrus, most of the branches terminated near the contralateral 17/18 border; they frequently entered the grey matter up to the superficial layers and branched into it. During the third week, axons from medial area 17 were rarely found to extend beyond the corpus callosum, probably because they were in the process of being eliminated. In contrast, axons originating near the 17/18 border had increased their number of branches in the grey matter. In conclusion, during the first and second postnatal weeks axons grew and differentiated according to their origin, and this anticipated whether they would be maintained or eliminated. Neurotrophic signals, possibly from the white matter or the subplate, and growth‐inhibiting signals from area 17 may be involved in this proces

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00577.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThis study examines the connections of the thalamic reticular and perireticular cell groups in developing ferrets. Small crystals of Dil (1,1′‐dioctadecyl‐3, 3, 3′, 3′‐tetramethylindocarbocyanine perchlorate) were implanted into either the dorsal thalamus or the cerebral cortex of aldehyde‐fixed prenatal and postnatal ferret brains. A small implant of Dil into the presumptive lateral geniculate nucleus during early prenatal development [between embryonic day 23 (E23) and E25] reveals many retrogradely labelled cells in the reticular nucleus. At E40, just before birth, the number of cells retrogradely labelled in the reticular nucleus has become reduced compared to earlier prenatal implants, whether from small or large implants of Dil into the lateral geniculate nucleus. By postnatal day 7, an adult‐like pattern of retrograde labelling is seen in the reticular nucleus; at this age, a small implant of Dil limited to the lateral geniculate nucleus retrogradely labels a discrete group of cells located in the caudal regions of the reticular nucleus. In the internal capsule, adjacent to the reticular nucleus, there are two distinct groups of neurons. One group, called the large‐celled perireticular zone (LPR), enters the internal capsule very early in development (from E25; Mitrofanis, J.,Eur. J. Neurosci.,6, 253–263, 1994) and is not labelled from the lateral geniculate nucleus at any developmental stage. Small implants of Dil into presumptive visual and somatosensory cortices shows that the LPR lies in a distinct region of the primordial internal capsule. Corticothalamic and thalamocortical axons turn sharply in the region of the LPR, whilst corticospinal and corticobulbar axons pass straight through the LPR on towards their more caudal targets. Later, after both sets of axons have reached their targets, the LPR is not seen in the internal capsule. The other group of cells in the internal capsule, called the small‐celled perireticular zone (SPR), forms a distinct band of cells lying midway between the reticular nucleus and the globus pallidus. These cells enter the internal capsule much later in development, at about E40. Unlike the cells in the LPR, cells in the SPR are retrogradely labelled after an implant of Dil into the lateral geniculate nucleus, and there are many which remain in the adult (Clemence, A. E. and Mitrofanis, J.,J. Comp. Neurol

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00578.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractIn this study sequence‐specific antisense oligonucleotide probes have been used to investigate the distribution of the mRNAs coding for the somatostatin receptor subtypes termed somatostatin receptor 1, somatostatin receptor 2 and somatostatin receptor 3 in the rat brain and pituitary usingin situhybridization techniques. The three receptor subtype mRNAs were found to be widely distributed in the brain with different patterns of expression, but with some overlap. Somatostatin receptor 1 mRNA was particularly concentrated in the cerebral and piriform cortex, magnocellular preoptic nucleus, hypothalamus, amygdala, hippocampus, and several nuclei of the brainstem. Somatostatin receptor 3 mRNA was very abundant in the cerebellum and pituitary (in contrast to somatostatin receptor 1), but it was also found in hippocampus, amygdala, hypothalamus and in motor nuclei of the brainstem. Somatostatin receptor 2 mRNA levels were very low relative to the other two mRNAs evaluated. Receptor 2 mRNA was observed in the anterior pituitary, and in the brain it was found in the medial habenular nucleus, claustrum, endopiriform nucleus, hippocampus, some amygdala nuclei, cerebral cortex and hypothalamus. None of the three somatostatin receptor mRNAs studied here was found in the caudate nucleus. Northern analysis revealed distinct sizes of mRNAs for each subtype, and displacement experiments showed that each probe sequence was subtype‐speci

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1994.tb00579.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY