ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00013.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThis study examined the effects of ibotenic acid‐induced lesions of the hippocampus, subiculum and hippocampus ± subiculum upon the capacity of rats to learn and perform a series of allocentric spatial learning tasks in an open‐field water maze. The lesions were made by infusing small volumes of the neurotoxin at a total of 26 (hippocampus) or 20 (subiculum) sites intended to achieve complete target cell loss but minimal extratarget damage. The regional extent and axon‐sparing nature of these lesions was evaluated using both cresyl violet and Fink – Heimer stained sections. The behavioural findings indicated that both the hippocampus and subiculum lesions caused impairment to the initial postoperative acquisition of place navigation but did not prevent eventual learning to levels of performance almost as effective as those of controls. However, overtraining of the hippocampus + subiculum lesioned rats did not result in significant place learning. Qualitative observations of the paths taken to find a hidden escape platform indicated that different strategies were deployed by hippocampal and subiculum lesioned groups. Subsequent training on a delayed matching to place task revealed a deficit in all lesioned groups across a range of sample choice intervals, but the subiculum lesioned group was less impaired than the group with the hippocampal lesion. Finally, unoperated control rats given both the initial training and overtraining were later given either a hippocampal lesion or sham surgery. The hippocampal lesioned rats were impaired during a subsequent retention/relearning phase. Together, these findings suggest that total hippocampal cell loss may cause a dual deficit: a slower rate of place learning and a separate navigational impairment. The prospect of unravelling dissociable components of allocentric spatial learning is d

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00014.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractA number of noradrenaline and serotonin agonists were tested to investigate which of them replicate the depressive actions of monoamines on transmission from group II muscle afferents in the cat spinal cord. The agonists were applied ionophoretically at the two sites at which maximal monosynaptic focal field potentials are evoked from group II afferents—in the intermediate zone and the dorsal horn of the 4th and 5th lumbar segments. Their effects were estimated from changes in the amplitude of the field potentials. The compounds tested fell into three categories according to the site at which they depressed transmission from group II afferents: one category with highly selective actions in the intermediate zone, a second category with similarly selective actions in the dorsal horn, and a third category with non‐selective actions. Drugs in the first category included three noradrenaline agonists (tizanidine, B‐HT 933 and clonidine), included in the second were five serotonin agonists (8‐OH‐DPAT, 5‐methoxytryptamine, α‐methyl serotonin, DOI and 2‐methyl‐serotonin), and in the third two noradrenaline agonists (phenylephrine and isoproterenol) and two serotonin agonists (RU 24969 and 5‐carboxamidotryptamine). Field potentials evoked by group I afferents remained unaffected by all but one compound (8‐OH‐DPAT). Effects of one noradrenaline agonist and one serotonin agonist (tizanidine and 5‐methoxytryptamine) were also tested on responses of single extracellularly recorded neurons. Tizanidine depressed responses induced by stimulation of group II afferents in intermediate zone interneurons, but not in dorsal horn neurons, while 5‐methoxytryptamine depressed activation of the latter. Tizanidine had no effect on responses evoked by group I afferents, either in intermediate zone interneurons or in the dorsal spino‐cerebellar tract neurons of Clarke's column. It is hypothesized that noradrenaline and serotonin released by descending monoaminergic neurons differ in the potency with which they depress transmission from group II afferents to different functional types of neuron. The results suggest that this depression may involve different membrane receptors at different locations, primarily α2adrenoceptors in the intermediate zone/ventral horn and 5‐HT‐1Aser

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00015.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractAn identified intersegmental interneuron inLocustaandSchistocerca, with its cell body in the fourth abdominal ganglion and an axon which projects to the brain is excited by mechanosensory inputs from receptors on the head and neck. The organization of its receptive field, the types of sensory receptors which contribute to it and the patterns and strengths of the afferent connections were investigated by intracellular recording from the axon of the interneuron close to a spike‐initiating site in the prothoracic ganglion. The receptive field of the interneuron consists of a small patch of hairs on the head ipsilateral to the axon, and from hairs on two regions of the prosternum (a cuticular structure on the ventral surface of the prothoracic segment), first an ipsilateral, lateral region and second a medial but contralateral region. Hairs on the pronotum (dorsal neck) also contribute but were not investigated here. Each spike in the afferent from a hair with a filiform appearance and with a pigmented base on the prosternum consistently evokes an EPSP in the interneuron. These have a short and constant latency, indicating that the connection is probably direct. The head hairs also appear to make direct connections with the interneuron in the prothoracic ganglion, so that the spike‐initiating site here can integrate signals evoked by wind on the head and on the prosternum. Stiff tactile hairs on the prosternum do not connect with the interneuron. The EPSPs evoked by the long filiform hairs are consistently larger than those produced by the short filiform hairs and a single spike in some of the afferents from the long filiform hairs can evoke a spike in the interneuron. The effectiveness of an afferent is therefore correlated with the length of the filiform hair it innervates. The hairs with the most powerful effects are always the longest and occur in the same position on every locust. The shape of the receptive field and the different strengths of connections are apparent even in early larval instars. The axonal branches of the interneuron are restricted to the same side of the ganglion as the axon itself. Afferents from filiform hairs on the medial region of the prosternum project contralaterally, and those from the lateral region project ipsilaterally. Afferents from some of the head hairs project ipsilaterally directly to the prothoracic ganglion. The terminals of all these afferents overlap with the branches of the interneuron. By contrast, the afferents of tactile hairs which do not connect, project to different regions of neuropile. The connections ensure that the high sensitivity of the filiform hairs is maintained at the first stage in the central processing and suggest a role for this interneuron in supplying information about small changes in air currents that may be of use in controlling steering manoeuvres during fli

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00016.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe multipolar somata of dorsolateral commissural (dlc) interneurons (Roberts and Clarke, 1982) lie in a superficial dorsolateral position in the spinal cord ofXenopus laevisembryos. By applying horseradish peroxidase to one‐half of the 100 μm diameter spinal cord, these neurons have been backfilled. Their dendritic branching pattern, commissural axonal projection and distribution near the time of hatching is described. Using Lucifer yellow‐filled microelectrodes a population of sensory interneurons with dlc morphology has been identified. They have multipolar somata in a dorsolateral superficial position, obliquely projecting dendrites and a ventral commissural axon. They receive presumed monosynaptic excitation in response to electrical stimulation of sensory neurites in the skin on the same side as the soma. During fictive swimming activity in curarized embryos the die interneurons are rhythmically inhibited in time with ventral root discharge on the same side. Die interneurons can fire multiple impulses and can turn on fictive swimming when stimulated by intracellular current injection. Skin stimulation is followed by excitatory postsynaptic potentials (EPSPs) in contralateral ventral rhythmic neurons. These EPSPs are reduced by the application of NMDA receptor antagonist. We conclude that dlc interneurons are excited by primary skin afferent Rohon ‐ Beard neurons, carry sensory information across the spinal cord to excite neurons on the opposite side by release of an excitatory amino acid transmitter and participate in reflexes and in the initiation of sw

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00017.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractSleep deprivation (SD) experiments have suggested that specific endogenous substances mediate the control of sleep and waking. However, such ‘sleep substances’ have not yet been unambiguously identified. The isolation of specific molecular markers would make it possible to obtain new insights into the regulatory mechanisms underlying sleep and waking. For this purpose, we have used a molecular genetical approach based on subtractive cDNA cloning. Using these techniques, we were able to detect and isolate in rat forebrain four cDNA clones whose corresponding transcripts are expressed at a lower level after 24 h of SD, and six cDNA clones whose corresponding transcripts are expressed at a higher level. For two of the former transcripts, the level showed a significant reduction of approximately 50% after 24 h of SD and a non‐significant reduction after 12 h of SD. A significant reduction was also observed after 12 h of cold exposure. A regional analysis of their level under baseline conditions revealed variation during the 24‐h cycle. The highest levels tended to occur at the onset of darkness, the beginning of the rat's activity period. Our results are compatible with the hypothesis that the cloned transcripts are associated with the regulation of the sleep‐waking cycle. Analysis of their primary structure indicated that these mRNAs have not yet been characterized. Thein vivodistribution of these transcripts in the forebrain shows some correspondence to that of receptors of excitatory amino acids, suggesting an association between the functional role of the cloned sequences and this neurotransmissi

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00018.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractWe have studied the effects of lesion of the inferior olive on the spontaneous eye movements performed both in the light and dark in head restrained pigmented rats. The inferior olive lesion was made at least 1 month before study with 3‐acetylpyridine and eye movements were recorded through a phase detection search coil apparatus. Following lesion, the spontaneous saccades performed in the dark present a postsaccadic drift which is made up of two components characterized by their different time courses, the first one being fast and the second one slow. The latter component is due to the leakage of the neural integrator and the former is mainly the consequence of a mismatch between the phasic and the tonic component of the ocular movement. In the light only the first component is present and then the eye maintains a steady position. After the lesion the saccades in the dark present a time constant of the slow component of the postsaccadic drift which is significantly reduced to −600–900 ms from a value of 1600–4000 ms of the intact rats. This means that the integrity of the inferior olive is necessary to keep the time constant of the neural integrator within the physiological range. In the light, the amplitude of the postsaccadic drift depends on two factors. First, there is a mismatch between the phasic and the tonic components of the ocular movement, which are due to the pulse and the step of innervation of the extraocular muscles respectively. Different types of analysis have shown that the gain of the pulse to step transformation is about 0.77 at all saccadic amplitudes and eccentricities. Second, there is an increased leakiness of the neural integrator. Such a contribution increases linearly as a function of the eccentricity with a slope of 0.21. The main sequence of the saccades is not appreciably affected by the olivary lesion. Thus, the consequence of the inferior olive lesion may be interpreted as a general disruption of the integration process which, in physiological conditions, generates a proper and sustained oculomotor signal. More generally, it may be viewed as a loss of coordination between phasic and tonic motor c

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00019.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractWe have studied the effects of the ablation of the cerebellar vermal area corresponding to lobules VI – VIII and of the flocculus – paraflocculus of both sides on the spontaneous eye movements performed in the light and in the dark in head‐restrained pigmented rats. These effects have been compared with those already described for the inferior olive lesion. The cerebellar lesions were performed 1 week to 6 months in advance. Eye movements were recorded through a phase detection search coil apparatus. Following vermal topectomy, the main characteristics of the spontaneous saccades are unmodified. Following the ablation of the flocculus – paraflocculus there is no change in the saccadic main sequence. However, the spontaneous saccades in the dark present a postsaccadic drift made up of two components with different time courses, the first one being fast and the second one slow. The former is due in part to a mismatch between the phasic (the pulse) and the tonic (the step) components of the eye movements; the latter to the leakage of the neural integrator. In light only the first component is present and the eye maintains a steady position. The time constant of the neural integrator is considerably reduced to ∼600–900 ms from a value of ∼1600–4000 ms in the intact rats. The amplitude of the postsaccadic drift in the light depends on both the mismatch between the pulse and the step of innervation of the extraocular muscles and the increased leakiness of the neural integrator. The gain of the pulse to step transformation is reduced to ∼0.79 at all saccadic amplitudes and eccentricities and such a reduction is due to a decreased step amplitude, while the pulse amplitude remains unchanged. The contribution of the leakage of the neural integrator to the postsaccadic drift in the light is a function of the eccentricity with a slope of 0.23. The deficits described after flocculus–paraflocculus ablation are also very similar to those described following inferior olive lesion from a quantitative point of view. The possible mechanisms of the visually activated olivocerebellar system in the control of saccadic performance and in maintaining its calibr

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00020.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractNeurotensin (NT)‐like peptides in the CNS of the lampreyLampetra fluviatiliswere studied by radioimmunoassay (C‐terminal specific NT antiserum), reverse‐phase HPLC and immunohistochemistry. Multiple peaks of NT‐immunoreactive (‐ir) material were observed upon HPLC, of which a major peak eluted in the position of bovine NT. Immunofluorescence histochemistry showed that a monoclonal antibody recognizing the N‐terminal (1–11) fragment of NT, as well as two polyclonal NT antisera labelled a large number of cell bodies in the periventricular area of hypothalamus, including the postinfundibular commissural nucleus and the ventral and dorsal hypothalamic nuclei. Additional groups of NT‐ir cells were observed in the preoptic nucleus, the postoptic commissural nucleus, the mesencephalic tegmentum (L.fluviatilis), and in the spinal cord (L.fluviatilisandIchtyomyzon unicuspis). Dense NT‐ir fibre plexuses were present in the caudal hypothalamus, corpus striatum, ventral mesencephalon, and in the dorsal horn and lateral margin of the spinal cord. At the ultrastructural level the lateral spinal margin showed NT‐ir terminal structures, which in most cases were not associated with synaptic specializations, although occasional synaptic contacts with unlabelled elements were found. The relation between NT‐ir and monoamine‐containing cells was examined with immunofluorescence double‐staining, using antisera to tyrosine hydroxylase (TH), 5‐hydroxytryptamine (5‐HT), and histamine respectively. In the periventricular nuclei of hypothalamus numerous TH‐, 5‐HT‐, as well as histamine‐ir cells were located in close association with NT‐ir cells, but none of the aminergic markers could be detected within NT‐ir neurons. The chemical properties as well as the anatomical distribution of lamprey NT‐like peptides show several similarities with those present in mammals, suggesting that NT‐containing neuronal systems in th

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00021.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractUsing primary neuronal or astrocyte cultures from the striatum of the embryonic mouse, we have observed that the β‐adrenergic agonist isoprenaline (10−5M) induced a more pronounced accumulation of cAMP in astrocytes than in neurons. In both cell types, the α‐adrenergic selective agonist methoxamine (10−4M), which alone did not affect the production of cAMP, potentiated the isoprenaline‐evoked response. In support of these observations, when associated α2‐noradrenergic and D1‐dopaminergic responses were prevented, the mixed α1‐ and β‐adrenergic agonist noradrenaline (10−5M) induced a production of cAMP which was totally blocked by propranolol (10−6M) and partially abolished by prazosin (10−6M). Since experiments were made in the presence of 3‐isobutyl‐1‐methylxanthine (1 mM), the observed effects on cAMP accumulation were not related to a modulation of phosphodiesterase activities. In addition, both in astrocytes and in neurons, the potentiation by α1‐adrenergic agonists of the β‐adrenergic‐evoked response required external calcium. Using INDO 1 as a fluorescent probe, methoxamine (25 μM) was shown to induce in astrocytes an increase in cytosolic calcium concentration which was prolonged by isoprenaline (10−5M) only in the presence of external calcium. These results suggest that the prolonged increase in cytosolic calcium concentration linked to the activation of α1‐ and β‐adrenergic receptors is responsible for the potentiation of the β‐adrenergic‐induced production o

ISSN:0953-816X    

DOI:10.1111/j.1460-9568.1990.tb00022.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY