摘要:

AbstractProstaglandins (PGs) are neuroactive substances which act in the vicinity of their site of synthesis through receptors coupled to G‐proteins. Since large amounts of PGE2can be synthesized by chicken spinal cord, binding sites for PGE2were looked for in various cell fractions of spinal cord. In the 17 000gpellet incubated with 0.3 nM [3H]PGE2, 70% of ligand was specifically bound. Two types of PGE2binding site were characterized (i) high affinity, low capacity binding sites (KD11.34 nM, Bmax134.5 fmol/mg prot); (ii) low affinity, high capacity binding sites (KD22.23 μM, Bmax213.2 pmol/mg prot). The high affinity binding sites fulfil several requirements for being receptors to PGE2: (i) since theKD1is increased in the presence of the GTP analogue, Gpp(NH)p, these binding sites would be regulated by a G‐protein; (ii) a desensitization was obtained by an excess of unlabelled PGE2and reversed by Gpp(NH)p; (iii) the competition experiments between PGE2and various prostanoids pointed to PGE2receptors such as EP2or EP3. The receptor characteristics of the low‐affinity binding sites were not investigated. Hence, our results support the presence of two types of PGE2binding site in the chicken spinal cord; a high affinity site, which corresponds to a PGE2receptor responding to nanomolar concentrations and a low affinity site sensitive to micromolar concentrations o

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00001.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractHigh and low affinity binding sites for PGE2were localized at the cellular level by means of radioautography. Two types of radioautographic reactions were observed in cryostat sections incubated with 0.6 nM [3H]PGE2: (i) a diffuse reaction scattered over the neuropil; (ii) a stronger reaction over the perikarya of some motoneurons. However, not all the motoneurons were equally labelled; the density of silver grains increased 12 times from poorly labelled to highly labelled cells. After incubation with an excess of unlabelled PGE2the labelling was drastically reduced over motoneurons and the neuropil, so that the specific binding corresponded to 90 and 85% respectively of the total binding. Two facts indicated that the motoneurons possessed mainly high affinity binding sites which could be saturated by PGE2concentrations in the nanomolar range: (i) a five‐fold increase of [3H]PGE2concentration (from 0.6 to 3 nM) produced only a 1.5 times increase in the density of silver grains over the perikarya; (ii) incubation in presence of 14 nM unlabelled PGE2induced a drastic reduction of 0.6 nM [3H]PGE2binding to the motoneurons. The presence of high affinity binding sites in motoneurons suggests that PGE2could act as a modulator of spinal reflexe

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00002.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractPigmented, head restrained rats were rotated on a turntable about a tilted axis (off‐vertical axis rotation; OVAR) in darkness. Evoked eye movements in the horizontal, vertical and torsional planes were recorded simultaneously with a dual search coil in a magnetic field, horizontal response components of both eyes were recorded with a coil on either eye. OVAR resulted in a persisting horizontal, unidirectional ocular nystagmus, compensatory in direction for the rotation of head in space. Superimposed upon this nystagmus were slower cyclic responses of the eye in the vertical and torsional movement planes, that were tightly phase locked with changing head positions in space: ocular depression/elevation with right ear up/down and ocular intorsion/extorsion with nose up/down. Simultaneous recordings of horizontal response components from both eyes revealed phase and gain differences between the horizontal movement components of both eyes, that resulted in a cyclic modulation of the vergence angle. Convergence of the lines of sight during nose up and divergence during nose down, adequate compensatory responses in light for changes in the viewing distance, were actually observed in darkness. Thus the utricular maculo‐ocular reflex takes part of the visual consequences of a translational gaze shift into account. It reduces expected retinal disparities by appropriate and rapid vertical, torsional and vergence response components in the same way as canal‐ocular reflexes ‘compensate’ for direction and velocity of expected retinal image slip during head

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00003.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractIn this study we have observed an inhibition of the [3H]norepinephrine ([3H]NE) accumulation into rat phaeochromocytoma PC 12 cells by phorbol 12‐myristate 13‐acetate (PMA), whereas a biologically inactive phorbol ester was without effect. The inhibition was no longer observed when the PC 12 cells were preincubated with 10 μM reserpine, which inhibits the uptake of norepinephrine into the storage vesicles. This suggested a role of the intact vesicles in the inhibitory phenomenon. Subsequently we could show that PMA increased the efflux of [3H]NE from PC 12 cells in a dose dependent manner. It seemed likely, therefore, that the increased release of endogenous norepinephrine from PC 12 cells by the phorbol ester competed with exogenous [3H]NE for uptake by the plasma membrane NE (uptake1) carrier into the cells. Two observations were in agreement with such a model: (i) an increase in the external NE concentration decreased the effect of PMA on the [3H]NE uptake; and (ii) desensitization of the protein kinase C by long term treatment of the PC 12 cells with phorbol ester abolished the PMA effect on both [3H]NE efflux and [3H]NE up

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00004.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractDirection and orientation tuning elicited by moving bars, flashing bars and a moving noise field were compared in cells in area 17 of the cat. Fourier analysis of tuning curves (SDO‐analysis) was applied to quantify the general sensitivity (S) to visual stimulation, tuning strength to direction(D) and orientation (O), as well as the preferred direction (PD) and orientation (PO). Results from SDO‐analysis were compared with the commonly used direction index and half‐width‐at‐half‐height orientational tuning parameter and it is demonstrated that the commonly used parameters can be replaced and are superseded by the results from SDO‐analysis. The comparison of the responses elicited by the different types of stimuli showed that a linear correlation between D (or O) components was mainly found in simple cells, while in most cases no correlation was obtained for complex cells. Since several of the simple cells also showed no linear relationship, a direct mutual prediction of the S, D and O components can only be achieved for ∼50% of the cortical cells applying commonly used stimulus types. The general responsiveness (S) shows that flashing bar stimuli are at least as effective as moving bars, whereas moving noise stimulates cortical cells more weakly. A moving bar tends to increase the orientation tuning (O) in most cells and with a moving noise stimulus predominantly the directional tuning (D) of complex cells is strongly enhanced. In conclusion, Fourier analysis of tuning curves (SDO‐analysis) provides a valuable and simple tool for the quantification of direction and orientation specificity. Motion enhances the cortical response specificity which indicates the involvement of facilitation or inhibition exclusively in

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00005.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractRecent studies in adult split‐chiasm cats show that the contrast gain of the visual callosal pathway is considerably lower than the gain of the direct geniculocortical system and that high spatial and temporal frequencies are strongly attenuated in the process of callosal transfer. We recorded visual evoked potentials (VEPs) and single unit activities from visual cortical areas 17 and 18 in cats which had the optic chiasm sectioned at 3 weeks of age. Our results show that, unlike the animals sectioned as adults, the contrast gain and the spatial and temporal acuities of the callosal pathway of young split‐chiasm cats were as good as the direct retinogeniculocortical pathway. Thus, under the present experimental conditions all the spatial and temporal information processed in areas 17 and 18 of one hemicortex is transferred to the other hemicortex via the callosal connections. These animals have also been tested behaviourally for the interocular (interhemispheric) transfer of learning of patterns of high spatial frequency and low contrast. In agreement with the electrophysiological results, we find a complete interocular transfer for this behavioural task. We conclude that the functional development of the interhemispheric connections can be modified by an early section of the optic chiasm and therefore the loss in binocular convergence can be partially compensa

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00006.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractBinaural neurons in the barn owl's auditory brainstem have spatial receptive fields. It is shown here that both the frequency tuning of these neurons and their tuning to interaural time difference (ITD), the prime cue for azimuthal sound localization, improves with time after stimulus onset, a process I shall term ‘dynamic sharpening’. Thus, the receptive fields of these neurons also have a temporal dimension. Data were collected in four hierarchically ordered nuclei concerned with the computation of ITD: the nucleus ventralis lemnisci lateralis, pars anterior (VLVa), and three subnuclei in the inferior colliculus. Dynamic sharpening in the frequency tuning curves is evident from a dynamic reduction of tuning width. When stimulated with a tone, the response of all neurons varies in a cyclic manner with ITD. The ITDs at the response peaks differ by one period of the stimulus tone. The responses with noise stimulation are similar to the responses with tonal stimulation in all but the hierarchically highest nucleus, the external nucleus of the inferior colliculus. In this nucleus are found neurons that, if stimulated with noise, respond maximally only to one ITD while the responses at the other peaks are suppressed. This sidepeak suppression is a dynamic process. Dynamic sharpening of ITD tuning is also evident from a dynamic reduction of the tuning width around each of the response peaks. The proportion of neurons showing dynamic sharpening of ITD tuning is the same in all collicular subnuclei, but is lower in VLVa. Therefore, a major component of dynamic sharpening of ITD tuning occurs at the first station of the inferior colliculus. Lateral inhibition is one of the mechanisms underlying dynamic sharpening. Part of the inhibition may be mediated by GABA (Fujita and Konishi, 1988). The function of dynamic sharpening of ITD tuning may be to increase the fine representation of auditory space in single neur

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00007.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe aim of this study was to identify, at the ultrastructural level, the neuronal targets of dopamine afferents to the medial prefrontal and the anterior cingulate cortex of the adult rat. Since, in addition to pyramidal neurons, the cortical neuronal population mainly consists of GABAergic nonpyramidal intrinsic neurons, the simultaneous visualization of both dopamine‐ and GABA‐containing neurons should leave the pyramidal neurons as the only unlabelled dopamine postsynaptic target. In this context, we used a double labelling immunocytochemical procedure: a pre‐embedding PAP immunostaining to visualize monoclonal conjugated‐dopamine (DA) antibody, followed by postembedding immunogold staining with a polyclonal conjugated‐GABA antibody. In a single section sampling of 369 DA‐immunoreactive (DA‐IR) varicosities observed and the GABA‐containing elements, 75% of the DA‐IR terminals showed no indication of any contact with a GABA neuron. Twenty‐five per cent were found in nonsynaptic contiguity with a GABA‐immunoreactive neuronal element: axon, dendrite or cell body. When a DA varicosity was in nonsynaptic contiguity with a neuronal perikaryon (5% of cases), this cell was GABA positive. Ten per cent of the DA varicosities were contiguous to a GABA axon, but axoaxonic synapses in either direction were never observed. A symmetrical synapse between a DA varicosity and a GABA‐containing dendrite was observed only once. The other 13 DA‐IR terminals exhibiting a clear synaptic junction were apposed to nonGABA‐containing dendrites, spines and shafts. Triads were observed in which a DA varicosity, forming or not a symmetrical synapse, was apposed to an unlabelled dendrite already receiving a symmetrical junction from another unlabelled axon. These data confirm and extend previous results designating the pyramidal cell dendritic tree as the main synaptic target of DA cortical afferents in rat and primate cerebral cortex. However, a direct effect of dopamine on a subpopulation of intrinsic GABA

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00008.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractRecently we reported that perfusion of hippocampal slices with epidermal growth factor (EGF) lead to enhancement of potentiated responses after tetanic stimulation. In the present study we report that basic fibroblast growth factor (FGF) can also lead to an enhancement of potentiated responses. FGF is a mitogen for several cell types and exhibits neurotrophic effects on neurons of the central nervous system (CNS). Rat hippocampal slices were perfused with FGF at a concentration of 10−9M. During extra‐ and intracellular recordings in the CA1‐region, the addition of FGF to the perfusing medium produced no change in evoked responses if single pulse or paired pulse stimulation was used. Furthermore FGF had no influence on the resting membrane potential and input resistance. However, after tetanic stimulation, FGF‐treated slices showed an increase in the magnitude of potentiation compared to control slices. Taken together with the EGF data these results support the hypothesis that growth factors like FGF with neurotrophic potential on CNS‐neurons can influence synaptic efficacy. Furthermore these results show that factors which are able to modulate developmental plasticity and regenerative plasticity can also modulate synaptic p

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00009.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractCurrent advances in the neurobiology of learning and memory suggest the existence of experience‐induced plasticity in sensorial pathways conveying relevant information to higher integrative brain structures. For instance, olfactory learning is known to induce long‐lasting modifications of neural activity at the level of the first relay structure of the olfactory system, the olfactory bulb. The observed forms of plasticity depend on the action exerted during learning by ascending neuromodulatory systems, such as the noradrenergic (NA) system originating from the locus ceruleus. This study was aimed at investigating the importance of olfactory bulb plasticity in learning and retention of an olfactory task. In a daily training schedule animals had to learn to use multi‐site electrical stimulation patterns of the olfactory bulb as discriminative cues for choosing between a palatable and a nonpalatable solution. We first examined the effects of a continuous intrabulbar infusion of propranolol (a β‐NA receptor antagonist) carried out during the learning period. We found that this treatment neither impaired the retention of a previously learned task nor the learning of a new task. However, the animals presented a severe deficit in long‐term retention (>5 days) of the task learned under perfusion. Unexpectedly, this effect cannot be ascribed to a selective blockade of β‐NA receptors since infusion of the drug vehicle (saline‐ascorbate) produced exactly the same deficit while a saline solution remained without effect. A final experiment showed that the selective deficit in long‐term retention was not observed when the infusion of the saline‐ascorbate solution started on the day following completion of learning. Taken together, these results suggest that ascorbate‐sensitive neural processes occurring within the olfactory bulb during learning are of functional importance for long‐term storage o

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00010.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY