摘要:

AbstractThe possible role of protein kinase C activation in the inhibitory action of cholinergic transmitters on the slow Ca‐dependent afterhyperpolarizing current (IAHP) in hippocampal CA3 pyramidal neurons was investigated using hippocampal slice cultures. IAHPwas inhibited reversibly by methacholine (100–600 nM) and irreversibly by the protein kinase C activator, phorbol‐12,13‐dibutyrate (PDBu, 10 nM to 1 μM). The inhibitory action of PDBu was antagonized by prior (15–60 min) exposure to staurosporin (1 μM). In contrast, the inhibitory effect of methacholine on IAHPwas not reduced after up to 3 h of exposure to this compound. In addition, methacholine produced a reversible inward current at the holding potential, which was augmented by staurosporin. However, prior exposure to PDBu reduced the effect of methacholine on IAHPand occluded the methacholine‐induced inward current. This effect of PDBu was also observed in the presence of staurosporin, suggesting that it might be exerted through a protein kinase C‐independent pathway. Noradrenalin (2–5 μM) and 8‐bromo cyclic adenosine 3′,5′monophosphate (8‐Br‐cAMP, 1 mM) also produced a reversible block of IAHP. Their action was antagonized by staurosporin, probably via its effect on protein kinase A. Thus the present experiments suggest that the action of muscarinic agonists on IAHPcannot be explained by an effect on protein kinase C, but support a role for protein kinase A in mediatin

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00188.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractMetabotropic glutamate receptors, unlike ionotropic receptors, exert their actions on ion channels via G‐proteins coupled to second messenger systems. In the hippocampus stimulation of metabotropic receptors can lead to decreased potassium channel conductance, decreased accommodation of cell firing and inhibition of the slow calcium‐dependent afterhyperpolarizing current (IAHP). Using the single‐electrode voltage‐clamp technique in hippocampal slice cultures of the rat, the role of protein kinases in mediating these metabotropic glutamate responses was investigated. In the presence of staurosporin, protein kinase C activation by phorbol esters and protein kinase A activation by 8‐bromo‐cyclic adenosine monophosphate were blocked. Under these conditions, the inhibition of IAHBby 1‐aminc‐cyclopentyl‐trans‐dicarboxylate (ACPD), a metabotropic agonist, was unchanged, whilst the inward current elicited by ACPD was enhanced. These results demonstrate that, in the hippocampus, metabotropic glutamate responses persist during inhibition of protein kinase A and C activation. Furthermore, these responses are insensitive to pertussis toxin, confirming pr

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00189.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractImmediate éarly genes such as the proto‐oncogene c‐foscan be expressed in neurons following synaptic excitation by sensory stimulation. C‐fosimmunocytochemistry has subsequently been shown to be a very sensitive marking technique for neuronal activity. Here, antibodies against the c‐fosprotein product Fos were used to map the tonotopic organization in the auditory system of adult and developing rats. After stimulating adult rats with pure‐tone pulses, bands of Fos‐immunoreactive neurons revealed the frequency representation in seven brainstem nuclei: all three subdivisions of the cochlear nucleus, the lateral superior olive, the medial nucleus of the trapezoid body, the ventral nucleus of the trapezoid body, the rostral periolivary nucleus, the dorsal nucleus of the lateral lemniscus and the inferior colliculus. With the exception of the dorsal cochlear nucleus and the inferior colliculus, tonotopicity has not been previously demonstrated in the brainstem nuclei of the rat. During development two striking results were obtained. First, beginning at postnatal day 14 (i.e. ∼2 days after physiological hearing begins in rats), not only low but also high frequencies were able to induce strong Fos immunoreactivity, indicating that gradual recruitment of formerly unresponsive high‐frequency sites does not occur in the rat. Second, a gradual age‐related shift of the position of isofrequency bands was not seen in any of the nuclei, suggesting that changes in frequency‐place code do not occur after 2 weeks postnatally. These results indicate that the rat's auditory brainstem nuclei achieve their adult‐like tonotopic organization early on, implying a somewhat different developmental time course than is found in o

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00190.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThis study investigates in detail how mitral cell activity is distributed during the respiratory cycle in freely breathing animals and how this temporal pattern changes under odour stimulation. Results were obtained from 1408 sequences composed of a 30‐s period of spontaneous activity followed by a 10‐s period of stimulation. Spontaneously, a majority of the patterns did not show any clear relationship with respiration and were categorized as unsynchronized. Stimulations evoked a high proportion of synchronized patterns. About 40% displayed a single period of firing rate increase superimposed on no background activity or on sustained background activity, and were categorized as simple excitatory synchronized patterns. Thirty‐six per cent showed a single inhibitory trough, and were categorized as simple suppressive synchronized patterns, whereas the remaining 24% showed a succession of peaks and troughs, and were categorized as complex synchronized patterns. Under pure air delivery, the position in time of the firing peak in simple excitatory synchronized patterns was found to be generally phase‐locked on late inhalation and early exhalation. During stimulation, its position did not change in patterns which originated from spontaneous patterns having the same type whereas it was shifted towards earlier portions of the cycle in patterns originating from another type. Lastly, the possibilities of transition between spontaneous and odour‐evoked patterns seemed to follow general rules. Whereas any type of spontaneous patterns may transform into any other type under stimulation, a majority of synchronized odour response patterns originated from unsynchronized spontaneous patterns. This may reflect some potential of cells having a non‐modulated spontaneous activity to be more responsive to periph

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00191.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractProtein kinase C (PKC) is a Ca2+‐dependent enzyme involved in synaptic transmission, which can be experimentally activated by the phorbol ester, phorbol 12‐myristate‐13‐acetate (TPA). We studied the effects of TPA application on acetylcholine (ACh) release at the rat neuromuscular junction by means of the focal recording technique; possible effects of TPA at the postsynaptic site had been ruled out in preliminary studies. In extracellular solutions containing 2 mM Ca2+and at the stimulation frequency of 0.1 Hz, TPA increased endplate current (EPC) amplitude. In non‐stimulated preparations spontaneous current frequency was increased at a similar rate. The similar time course of TPA action on evoked and spontaneous currents suggests that an increased presynaptic Ca2+efficacy can be considered to be the probable mechanism of action. The interactions of PKC with ACh release were further investigated. In 0.1 mM Ca2+extracellular solutions, TPA enhanced evoked currents only at stimulation frequencies (e.g. 40 Hz) that were themselves capable of inducing facilitation. This facilitation is classically associated with presynaptic Ca2+accumulation, indicating that PKC interacts synergistically with Ca2+to facilitate ACh release. In particular, since mean quantum size and release probability remained almost unchanged during TPA facilitation, it was concluded that PKC acted by enlarging the immediately available store. Interestingly, TPA also increased the presynaptic currents that were observed to be largely brought about by Ca2+‐dependent K+currents: evidence was obtained to suggest that increases in these currents provide negative feedback against excess release activation rather than being an expression of enhanced

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00192.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe responses to activation of metabotropic glutamate receptors (mGluRs) of Purkinje cells in rat cerebellar slice cultures were investigated using intracellular recordings in single‐electrode voltage‐clamp mode combined with microfluorometric measurements of cytosolic free calcium using fura‐2. Purkinje cells were perfused with saline containing 0.5 μM tetrodotoxin and 10 μM bicuculline and voltage‐clamped at –60 mV. Bath‐applied trans‐(±)‐1‐amino‐1,3‐cyclopentanedicarboxylic acid (t‐ACPD, 50–100 μM), a selective agonist of mGluRs, induced a transient inward current that was followed by an outward current. The response induced byt‐ACPD was not affected by 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, up to 40 μM). In contrast, inward currents caused by (RS)‐α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA, 1–2 μM) were completely abolished, while inward currents caused by quisqualate (0.25 μM) were only partially depressed by CNQX (5–40μM). The inward current induced byt‐ACPD was unaffected by external Ba2+(1 mM), tetraethylammonium (10 mM) and Cs+(1 mM), and was associated with an increase in apparent input conductance of the cell membrane. The extrapolated reversal potential of inward currents induced byt‐ACPD was +18 mV while Cl−currents induced by muscimol reversed at –66 mV. Inward currents induced byt‐ACPD, but not those induced by AMPA, were associated with a rise in cytosolic Ca2+concentration and suppressed by intracellular injection of a calcium chelator. Replacement of external Na+by choline or Li+d

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00193.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractBasal laminae, thin sheets of extracellular matrix covering the basal side of all neuroepithelia, are strongly supportive for neurite outgrowthin vitroand may provide a permissive environment for growing neuritesin vivo.To gain information about the biological activity and composition ofin situ‐derived basal laminae the inner limiting membranes from embryonic day (E) 7 to E11 chick and quail retinae were isolated. The basal laminae were solubilized with high‐molar guanidine hydrochloride or urea, and the solubilized proteins reconstituted by dialysis. The matrix proteins were spotted or dried onto nitrocellulose or polylysine‐coated dishes. When explants from retina or from dorsal root ganglia were incubated on the protein spots, neurite extension was very robust, at a level as high as on authentic basal lamina. Extracts from the pigment epithelial basement membrane did not support neurite extension. Western blot analysis showed that the explant from the retinal inner limiting membrane contained predominantly basal lamina‐type proteins, such as laminin, collagen type IV and heparan sulphate proteoglycan, whereas the matrix extract from the pigment epithelium contained predominantly mesenchymal‐type proteins, like collagen type I and tenascin. JG22, a β1 integrin antibody that inhibited neurite extension on EHS tumour laminin substrate, had no effect on neurite outgrowth on retinal basal lamina matrix, indicating that embryonic basal laminae contain other or additional growth promoting substrate

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00194.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractDifferent methods of inducing recovery after brain damage and different mechanisms that might mediate the induced recovery have been proposed. One possible mechanism involves the ability of one part of the brain to take over the function of another. We show here in rats that (1) bar‐pressing behaviour to eliminate an aversive stimulus, which becomes dramatically impaired after bilateral lesion of the frontal primary motor ‐ sensory cortex, is recovered when the animals receive an electrical intracranial stimulation in the ventral tegmental nucleus of the brain contingent on an adequate response during performance in the behavioural task, (2) in recovered animals an area in the posterior primary motor – sensory cortex, the hindlimb motor ‐ sensory cortex, shows a 35% increase in the number of fos‐like immunoreactive cells compared to non‐recovered animals, and (3) a bilateral lesion of this area in recovered animals reinstates the impairment in the performance of the behavioural task. These results indicate that an area of the cerebral cortex is able to assume the role of another area after induced recovery from b

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00195.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractInsulin‐like growth factor I (IGF‐I) is a trophic factor for both neurons and glia. Its presence in the developing and adult cerebellum suggests a role for this growth factor in this area of the brain. Recently, we have described the existence of an IGF‐I‐containing pathway in afferents of Purkinje neurons arising from the inferior olive. In addition, IGF‐I receptors are present in the molecular layer of the cerebellar cortex. These observations prompted us to investigate whether the Purkinje cell is a target for IGF‐I. Addition of IGF‐I to rat cerebellar cultures produced a 7‐fold increase in the number of Purkinje cells (calbindin‐positive) together with an increase in the calbindin content of the cultures. IGF‐I also doubled the number of surviving neurons and produced a moderate, non‐significant increase in [3H]thymidine incorporation by the cultures. On the other hand, basic fibroblast growth factor (bFGF), which is also present in the cerebellum, produced a dramatic increase in both the proportion of astrocytes and in the mitotic activity of the cultures, without affecting neuron survival. We conclude that IGF‐I is a specific promoter of Purkinje cell survival and that its effects differ from those produced by bFGF in fetal cerebellar cultures. These findings reinforce our hypothesis that the Purkinje cell is a target neuron for IGF‐I action in

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00196.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractVasopressin and oxytocin mRNAs, which are normally translated in the perikarya of magnocellular neurons, have recently been demonstrated to be also present in axons and nerve terminals which are located in the posterior pituitary. The physiological significance of this observation has not yet been resolved. In order to gain further insight into the function and plasticity of the peptidergic neuron the question was addressed whether axonal localization is a unique feature of the above‐mentioned transcripts. Biochemical evidence is presented that magnocellular axons and nerve terminals also contain mRNA species encoding a member of the neurofilament protein family and the prodynorphin precursor. These data imply that axons may harbour a variety of additional protein‐encoding transcripts. Furthermore, it is shown that in the mutant (Brattleboro) rat, which lacks detectable levels of vasopressin but which still transcribes the corresponding gene, axonal vasopressin but not oxytocin mRNA contents are dramatically reduced. Most likely, vasopressin transcripts are absent from the nerve terminals as a consequence of the impaired precursor biosynthesis in the cytoplasm of the mutant

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1992.tb00197.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY