摘要:

AbstractIn the F2 neuron of the parietal ganglion of the snailHelix aspersaeither bath or iontophoretic application of serotonin (5‐HT) induces an outward current. This current has a long latency (10–60 s) and a slow time course, a 500 ms iontophoretic application of 5‐HT evoking a response lasting 3–5 min. This slow outward current reverses at ‐80 mV, a value equal to EK. After doubling the extracellular K+concentration the reversal potential of the 5‐HT response is shifted by 19 mV, as predicted by the Nernst equation. The I‐V curves reveal that the 5‐HT‐induced slow outward current is outwardly rectifying. This 5‐HT response is blocked by intracellular Cs+and tetraethylammonium (TEA+) and by extracellular TEA+and Ba2+, but is not affected by the removal of extracellular Ca2+or the intracellular injection of ethyleneglycol‐bis‐(β‐amino‐ethylether)‐N,N,N′,N′‐tetra‐acetic acid (EGTA). These results indicate that the outwardly rectifying slow outward current induced by 5‐HT in the F2 neuron is carried by K+and is Ca2+‐independent. In the single isolated F2 neuron, 5‐HT induces a 2.5‐fold stimulation of the adenylate cyclase activity. In addition, both the intracellular injection of 3′,5′‐adenosine monophosphate (cAMP) and the application of forskolin mimic the effect of 5‐HT on the F2 neuron. The phosphodiesterase inhibitor isobutylmethylxanthine also induces a slow outward current and potentiates the 5‐HT response. The intracellular injection of a synthetic 20‐residue peptide inhibitor of the cAMP‐dependent protein kinase blocks the slow outward K+current induced by 5‐HT. These results show that in the F2 neuron, 5‐HT elicits a slow K+current via the stimulation of adenylate cyclase, an increase in intracellular cAMP and the activation of the cAMP‐dependent kinase which probably phosphorylates a population of outwardly rect

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00392.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractGAP‐43 is a gene expressed only in the nervous system. The protein product is believed to be important to neuronal growth and plasticity. Most, and likely all, neurons express high levels of GAP‐43 during periods of neurite elongation. To initiate studies of GAP‐43 gene regulation we have cloned the rat gene encoding GAP‐43. The GAP‐43 gene includes three exons. The first exon encodes only the amino terminal 10 amino acids, which corresponds to the membrane targeting domain of GAP‐43. The second exon encodes a putative calmodulin binding domain and a protein kinase C phosphorylation site. The 5′‐flanking sequence is unusual in that it lacks CAAT or TATA elements, and directs RNA transcription initiation from several sites. Some of the transcription start sites are used to a different degree in the central and peripheral

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00393.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractAndrogen modulation of neurotransmitter receptor density was investigated in the nucleus intercollicularis (ICo) of male and female Japanese quail (Coturnix coturnix japonica). ICo appears to play an important role in the neural control of testosterone (T) dependent vocal behaviour. Two receptor types were investigated in this nucleus; muscarinic cholinergic receptors, labelled using [3H]N‐methyl scopolamine (NMS) as the ligand, and α2‐adrenergic receptors, labelled using [3H]p‐amino‐clonidine (PAC) as the ligand. Changes in receptor density were assessed usingin vitroquantitative autoradiography to ensure a high degree of anatomical specificity in the identification of any steroid effects. Gonadectomy was found to reduce the density of both [3H]PAC bindings sites and [3H]NMS in specific subregions of ICo. Gonadectomized animals treated with T had levels of receptor density similar to intact birds. However, the location within ICo of the effects of T was different for each ligand. [3H]NMS binding was modulated only in a rostral subregion of the nucleus while changes in [3H]PAC receptor density were found in the medial and lateral parts of ICo at a more caudal level. These changes in receptor density parallel changes in crowing frequency that are known to occur in males and females following castration and T treatment. The receptor systems may constitute a part of the neurochemical mechanism regulating vocal b

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00394.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractGlutamine synthetase (GS) catalyses the ATP‐dependent formation of glutamine from glutamate and ammonia. To determine whether dorsal root ganglion (DRG) cells from chick embryos express the enzymein vivoorin vitro, GS was detected by immunocytochemical reaction either in vibratome sections of DRG or in dissociated DRG cell cultures. The immunocytochemical detection of GS showed thatin vivothe DRG taken from chick embryos at day 10 (E10), E14, E18 or from chickens after hatching were free of any GS‐positive ganglion cells; in contrast, in neuron‐enriched cultures of DRG cells grownin vitroat E10, virtually all the neuronal cells (98.6±1.0%) express GS at 3, 5 or 7 days of culture. In mixed DRG cell cultures, only 83.6±4.6% of the neurons displayed a GS‐immunoreactivity. In both culture conditions, neither the presence of horse serum nor the age of the culture appeared to affect the percentage of neurons which displayed a GS‐immunoreactivity. After [3H]glutamine uptake, radioautographs revealed that only 80% of the neurons were labelled in neuron‐enriched DRG cell cultures while 96% of the neurons were radioactive in mixed DRG cell cultures. Furthermore the most heavily [3H]glutamine‐labelled neurons were exclusively found in mixed DRG cell cultures. Combination of both immunocytochemical detection of GS and radioautography after [3H]glutamine uptake showed that strongly GS‐immunostained neurons corresponded to poorly radioactive ones and vice versa. When skeletal muscle extract (ME) was added to DRG cell cultures, the number of GS‐positive neurons was reduced to 77.5±2.5% in neuron‐enriched cultures or to 43.6±3.8% in mixed DRG cell cultures; in both types of culture, the intensity of the neuronal immunostaining was depressed. Furthermore, combined action of ME and non‐neuronal cells potentiates the enzyme repression exerted separately by ME or non‐neuronal cells. Since GS‐immunoreactivity is expressed in DRG cells grownin vitro, but notin vivo, it is suggested that microenvironmental factors influence the expression of GS. More specifically, the repression of GS by primary sensory neurons grownin vitromay be strongly induced by soluble factors present in skeletal muscle, and to a lesser extent in brain, and pote

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00395.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractIn this study we describe the localization of formaldehyde‐fixed cGMP‐immunoreactivity (cGMP‐IR) in rat cerebellar tissue slices incubatedin vitro.In the absence of phosphodiesterase inhibition, cGMP‐immunofluorescence was of low intensity in tissue slices prepared from immature cerebella. Addition of isobutylmethylxanthine (IBMX) to the incubation medium resulted in the appearance of cGMP‐IR in clusters of astrocytes in the internal granular layer. Addition of N‐methyl‐D‐aspartate (NMDA), kainic acid, atrial natriuretic factor (ANF), or sodium nitroprusside (SNP) gave an intense cGMP‐IR in Bergmann fibres, Bergmann cell bodies, and astrocytes in the internal granular layer. Astrocytes in the white matter showed cGMP‐IR after incubation of the slice in the presence of ANF or nitroprusside, but not after NMDA or kainic acid. In addition, after SNP stimulation of cGMP production, cGMP‐IR was found in fibres which were not positive for glial fibrillary acidic protein (GFAP). In the adult cerebellar slice, intense basal cGMP‐immunostaining was observed in Bergmann fibres, Bergmann cell bodies, and astrocytes in the granular layer. No cGMP‐IR was observed in Purkinje cells. Stimulation of the cGMP‐content in the glial structures by NMDA, ANF, or SNP, was suggested by the immunocytochemical results. However, when measured biochemically, only the effect of SNP was statistically significant, and immunocytochemistry showed that SNP clearly stimulated cGMP synthesis in neuronal cell structures. In the cerebellum of the aged rat a reduced cGMP‐IR was found compared to the adult, in the same structures which showed cGMP‐IR in the adult. Basal cGMP‐immunostaining was reduced in the presence of haemoglobin, methylene blue, by inhibiting nitric oxide synthesis with NG‐monomethyl‐L‐arginine (NGMAr), or by depletion of external Ca2+. Also the stimulatory effect of NMDA and of ANF (partly) on the cGMP‐IR was inhibited by these compounds. cGMP‐IR after stimulation of guanylate cyclase by SNP was reduced by the concomitant presence of haemoglobin or methylene blue, but not by NGMAr, or by omission of Ca2+. Our results point to an important role for cGMP in the functioning of glial tissue in the cerebellum and also suggest a role for nitric oxide as an intercellular mediator in the functio

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00396.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractPrevious work has established that functional nicotinic receptors in the chick retina are blocked by neuronal bungarotoxin (NBT), and that the binding of radio‐iodinated NBT to retinal homogenates is displaced by nicotinic ligands. In the present study, we examined the desensitizing effects of agonists on nicotinically‐mediated depolarizations recorded from chick retina. The concentrations of five agonists necessary to reduce the amplitude of these depolarizations by 50% were found to correlate closely with the concentrations of these same agonists previously found necessary to displace 50% of NBT binding. In addition, bromoacetylcholine (BAC), a selective affinity alkylating agent for the agonist binding site, irreversibly inactivated the functional responses of intact chick retina with an inhibiting concentration for 50% block (IC50) near 10‐6M, the same concentration of BAC that displaced 50% of labelled NBT binding from alkylated retinal homogenates. These data suggest that NBT acts at the receptor agonist binding site. Furthermore, this binding site has a relatively low affinity for agonists, in the micromolar range, even in the desensitized state. Multiple subtypes of nicotinic receptors are known to exist in neuronal tissue, and receptors that bind agonists in the nanomolar range have been detergent‐solubilized and purified using monoclonal antibodies. Under similar conditions, detergent‐solubilization of chick retinal homogenates interfere with the interaction between NBT and the low‐affinity neuronal nicotinic receptors. These data suggest that the conditions used to purify high‐affinity neuronal nicotinic receptors may denature the subtype(s) of neuronal receptors reco

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00397.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractIn the rat, we studied the microtubular content of central nervous system (CNS) axons (pyramidal tract, dorsal funiculus, and intracord domain of motor axons), of radicular axons (ventral and dorsal roots), and of peripheral axons (sural and lateral gastrocnemius nerves). The microtubular density had an inverse relationship with the size of the axon. Within the CNS, values ranged from over 120 microtubules/μm2for axons smaller than 0.1 μm2of the pyramidal tract and dorsal funiculus to 24 for 3‐μm motor axons (area, 7 μm2) in their spinal cord domain. Peripheral nerve and CNS axons of the same size had comparable microtubular densities. In contrast, the microtubular density of dorsal and ventral root axons was one half that of CNS or peripheral nerve axons of equal calibre. Considered along the axon, the microtubular density of motor and sensory fibres is high in the CNS domain, low in the root, and high again in the peripheral nerve domain. These observations are inconsistent with the notion that the cytoskeleton moves coherently away from the perikaryon. We conclude that the axonal microtubular content accords with the calibre of the fibre and with the anatomical region where it courses. We propose that axonal microtubules are regulated by local

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00398.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractNeuronal cells expressing neural cell adhesion molecule (N‐CAM) accumulate the largest N‐CAM component (N‐CAM 180) at cell — cell contact sites. To test whether this accumulation is induced by interactions at the surface membrane, latex beads coated with several purified adhesion molecules or extracellular matrix (ECM) components were co‐cultured with neuroblastoma cells. Beads coated with L1, N‐CAM, the L2/HNK‐1 carbohydrate epitope‐carrying molecules from adult mouse brain or laminin from Engelbreth‐Holm‐Swarm (EHS) sarcoma did not induce an accumulation of N‐CAM 180 or L1 at sites of contact suggesting that these molecules are not directly involved in N‐CAM 180 accumulation or that their mobility is required for this process. Beads coated with ECM components of the PF‐HR9 cell line induced accumulation of N‐CAM 180 at sites of contact with neuroblastoma cells. Accumulation was seen at cell bodies of undifferentiated and differentiated neuroblastoma cells, as well as on neurites and growth cones of differentiated neuroblastoma cells. Accumulation of the neural adhesion molecule L1 was also seen, but less prominently and reproducibly. These observations suggest that molecules of the ECM can directly or indirectly, e.g. via molecules linked to N‐CAM 180 on the cell surface, ind

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00399.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe present study examined the role of graft placement and behavioural task complexity in determining the functional efficacy of intrastriatal grafts of dopamine‐rich fetal ventral mesencephalon (VM) placed in the dopamine (DA) depleted striatum. The functional effects of two different striatal placements of VM grafts were evaluated using tests of drug‐induced motor asymmetry, simple sensorimolor orienting response, and a more complex sensorimotor integrative task (disengage behaviour), in which the rat has to perform the orienting response while in the act of eating. Rats with complete unilateral 6‐hydroxydopamine (6‐OHDA) lesions of the mesostriatal DA pathway, received either implants of dissociated fetal VM in the central or ventrolateral portions of the denervated striatum. Nongrafted lesioned rats served as controls. Nine weeks after grafting, the rats were tested on separate days for disengage behaviour, sensorimotor orientation, and amphetamine‐induced rotational behaviour. Consistent with previous findings, the two graft placements had differential effects on drug‐induced motor asymmetry and sensorimotor responses: the centrally placed VM grafts reversed amphetamine‐induced rotational asymmetry but had little effect on the sensorimotor deficit, whereas the ventrolaterally placed grafts reversed the sensorimotor orientation deficits without any effect on the drug‐induced rotation. In contrast, fetal VM grafts, regardless of their placement, did not ameliorate the observed deficits in disengage behaviour; that is the grafted rats that had recovered their sensorimotor response in the absence of food were unable to perform the same orienting response while eating. These results provide evidence that functional intrastriatal VM grafts which are capable of restoring sensorimotor responses or motor asymmetry fail to affect lesion‐induced deficits in a task that requires more complex sensorimotor integration. It is suggested that the degree of anatomical integration of the grafted DA neurons into the host circuitry will determine the efficacy of the grafts to influence more complex sensorimotor integrative deficits in th

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00400.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00401.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY