摘要:

AbstractA new theory designed to explain the functions of the cerebellum in the control of movement and the unique anatomy of that structure is presented. The heart of this proposed explanation is that the cerebellium generates increased numbers of outputs from particular Purkinje cells whenever the same pattern of pulses in time is presented both to its mossy fiber and its climbing fiber input systems. The postulated function of the unusual anatomy of the crebellum is to permit it instantly to recognize and respond to identical patterns presented through these two channels regardless of the phase differences between these two signal, where phase differences are defined as differences in times of arrival of patterns of inputs from these two sources. The first means putatively used involves the summation of pulses comprising a given pattern of inputs simulataneously at many different Purkinje cells by virtue of the different Purkinje cells by virtue of the different speeds of conduction of the parallel fiber axons of granule cells. The second means is teh addition of an input from the climbing fiber system that, together with the simulataneous parallel fiber inputs, leads to a discharge of particular Purkinje cells, which discharge temporarily increase the size of ESPSP's generated by the parallel fiber synapses involved in the cell's discharge. This specific syanptic potentiation, in turn, makes it possible for the cell to respond by generating closely cnsecutive additional discharges provided that the same patterns of discharge are presented both to the climbing fiber system and the mossy fiber system. This happens because later pulses in identical patterns will arrive simulataneously at previously facilitated synapses via parallel fibers and at synapses of the climbing fibers, thereby causing additional spatial summations and discharges to occur. According to this explanation the patterns that are compared in the above manner are symbols (pattern of pulses) produced by sensors of current positiona and symbols derived from memory and also representing these same postitions. When patterns from these two sources are identical, the multiple outputs of specific Purkinje cells inhibit an automatic feedback loop and therby indirectly cause the attenuation and arrest of movement. The evolution of these concepts resulted in very specific “predictions” of particular connections involving the olive, pons red nucleus, dentate, thalamus, and sensrory‐motor cortex. All of these predictions were found to be consistent with evidence in the literature. Points of difference between this theory and all prior ones are discussed as are several critical tests of its validity, and the putative evolution of cerebellar structure and function. Key points are that it is comparison of recalled sensory memories of positions with current sensory inputs, rather than “error signals,” that terminates movements once a selected trajectory of movement has been completed and that intended trajectories of movements are continuously revised and updated, about seven times per second, during successive stages inthe execution of intentional

ISSN:0887-4476    

DOI:10.1002/syn.890050102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThis report further characterizes associative long‐term synaptic modification of the ipsilateral and contralateral synapses formed by the bilateral entorhinal cortical (EC) projection to the dentate gyrus (DG). The experimental model is the anesthetized hooded rat. The quatntitative results qualify this system as a model for studying the rules of associative synaptic modification formulated in terms of individual synapses. Bilateral DG microelectrodes recorded both ipsilateral and contralateral EC‐DG responses before and after brief, high‐frequency EC conditioning stimulatin. The weak contralateral pathway receivewd high‐frequency coditioning before, during, or after similar conditioning of the strong, converging ipsilateral pathway. Statistical analyses revealed two types of significant, dissociated synaptic modifications, which depend on the relationship of the ipsilateral and contralateral afferents. First, contralateral EC‐DG responses potentiated, depressed, or showed no change when the collateral ipsilateral responses concurrently either potentiated or remained unchanged. Correlation and contingency table analysis indicated that changes in the contralateral synaptic responses are not well predicted by changes at either neighboring synapses of the converging ipsilateral pathway or at synapses of the collateral ipsilateral pathway. The contingencies of associated pre‐ and postsynaptic activation determined by the conditioning paradigm, however accurately predicted the altered synaptic responses of both ipsilateral and contralateral rately predicted the altered synaptic responses of both ipsilateral and contralateral EC‐DG pathways. The results imply that associative synaptic modification in the EC‐DG system is specific to individual synapses and requires both appropriate presynaptic and postsynaptic activation. Because this system provides suitable controls for nonspecific dissociable, the EC‐DG system can be used to study further those rules of activity‐dependent associative modification that are formulated in terms of individual synapses. The discussion briefly considers published rules modification, pointing out several rules that are not consistent with the ecperimental observations and one that agrees with

ISSN:0887-4476    

DOI:10.1002/syn.890050103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe behavioral stimulant effect of peripheral cocaine injection into rats is augmented following daily adminstration. In vivo dialysis in the nucleus accumbens of conscious rats was used to determine if the increased behavioral response following daily cocaine administration is associated with in increase in extracellular dopamine concentration. Acute injection of cocaine (15 mg/kg, ip) produced and elevation in extracellular dopamine concentration in the nucleus accumbens. Following daily pretreatment with cocaine (15 mg/kg, ip × 4 days), a subsequent acute injection of cocaine (15 mg/kg, ip) significantly elevated the extracellular dopamine levels compared to that produced by a single acute injection. Although the levels extracellular dopamine metabolites was significantly lowered by both acute cocaine and daily cocaine, no difference between these two groups of animals was measured. The increase in extrecellular dopamine following a single acute injection of cocaine was not correlated to the motor stimulant response. However, after daily pretreatment with cocaine the motor stimulant response to acute cacaine was positively correlated with the increased extracellular concentration of dopamine in the nucleus accumbens. These data demonstrate that enhanced dopamine release into the nucleus accumbens may mediate the behavioral sensitization produced by daily injections of cocaine, but that other neural systems are influential in mediating the acute motor stimulant effect of cocaine

ISSN:0887-4476    

DOI:10.1002/syn.890050104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe early development of functionally active GABA and glutamate receptors on neurons from hippocampus, septal region, and neocortex of embrryonic rats were studied using primary dissociated serum‐free cell cultures. The responses to GABA and glutamate, applied to individual neurons by pressure ejection, were tested at different development stages, starting at 1 day in vitro (DIV) until 3 weeks. In all three types of neuronal cultures, the GABAA‐receptor developed prior to the glutamate receptros, and after 9 DIV most of the neurons were sensitive to both GABA and glutamate. N‐methyl‐D‐aspartate (NMDA) and non‐NMDA receptor subtypes of the glutamate receptors could be distinguished in hippocampal cultures. The development of GABA and glutamate receptors on septal region neurons appeared to be delyed as compared to hippocampal neurons. In neucortical cultures the majority of nueorns was sensitive to GABA just after plating, whereas the sensitivity to glutamate was retarded. The differences in GABA and glutamate receptor development among these three neuronal cultures provide evidence that the apearance of tranmitter receptors on cultured neurons is predominantly determined by intrinsic mechanisms rather than by environmental coditions. The proportion of spontaneously active networks in these cultures increased with a time course very similar to the rise in glutamate‐sensitive neurons suggesting that functional active glutamate receptors may be involved in the generation of spontan

ISSN:0887-4476    

DOI:10.1002/syn.890050105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe electrophysilogical effects of luteinizing hormone‐releasing hormone (LHRH) on CA1 pyramidal cells were investigated utilizing intracellular recodings from the in vitro rat hippocampal slce preparation. Bath application of LHRH (10‐7‐10‐12M) resulted in several changes in the electrophysiological properties of CA1 neurons. LHRH induced a long‐lasting depolarization associated with increased input resitance, and decrease in the afterhyperpolarization associated with increased input resistance, ad decrease in the afterhyperpolarization (AHP) following a train of action potentials, and a reduction in accommodation of repetitive cell discharge. These effects were blocked by the synthetic LHRH antagonist [Ac‐δ‐Pro1, pCl‐D‐Phe2, D‐Trp3,6]‐LHRH. These findings provide electrophysiological evidence for the role of LHRH as a neurotransmitter/neuromodula

ISSN:0887-4476    

DOI:10.1002/syn.890050106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractWe have examined the hypothesis that phenothiazines and tricyclic antidepressans interact with the N‐methyl‐D‐aspartate (NMDA) receptor bu mimicking the action of Zn2+. Using [3H]MK801 binding to well‐washed rat brain membranes, we found a disparity between the concentrations of drug required to inhibit [3H]MK801 from its binding site. These data suggest that the Zn2+site is probably not the principle site by which tricyclic drugs inhibit NMDA receptor responses. To determine whether the effects to tricyclic drugs on the dissociation of [3H]MK801 could be explained simply by membrane stabilization, we examine dthe effect of a series of alcohols. Ethanol. isopropanol. bytanol, hexanol, and heptanol all inhibited [3H]MK801 binding. However, with the exception ot heptanol, none of the molecules altered the dissociation rate. Thus, while lipid solubility may be an important factor underlying the interactions the interactions of some drugs with the NMDA receptor, it is not sufficient to explain the effects of tricyclic antidepressants and phenothiazines in this

ISSN:0887-4476    

DOI:10.1002/syn.890050107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

ISSN:0887-4476    

DOI:10.1002/syn.890050108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

ISSN:0887-4476    

DOI:10.1002/syn.890050110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

ISSN:0887-4476    

DOI:10.1002/syn.890050101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY