A contribution of synaptic plasticity in the basal ganglia to processing of visual information

The mechanism of involvement of the basal ganglia in processing of visual information on the basis of dopamine-dependent modulation of efficacy of synaptic transmission in interconnected parallel associative and limbic loops (cortex--basal ganglia--thalamus--cortex) is proposed. Each loop consists of one of the visual or prefrontal cortical areas connected with the thalamic nucleus and corresponding loci in different nuclei of the basal ganglia. Circulation of activity in such a loop provides reentrance of information into the thalamus and neocortex. Dopamine releasing in response to a visual stimulus oppositely modulates the efficacy of "strong" and "weak" corticostriatal inputs. Subsequent reorganization of activity in the loop leads to a disinhibition (inhibition) of activity of those cortical neurons that were "strongly" ("weakly)" excited by the visual stimulus simultaneously with activation of dopaminergic cells. A selected neuronal pattern in each cortical area represents a property of the visual stimulus processed by this area. Excitation of dopaminergic cells by the visual stimulus via the superior colliculi requires parallel activation of a disinhibitory input to the superior colliculi via the thalamus and a "direct" pathway through the basal ganglia. The prefrontal cortex excited by the visual stimulus via the mediodorsal thalamic nucleus performs a top-down control over the dopaminergic cell activity, supervising simultaneous dopamine release in different striatal loci and thus promotes the interconnected selection of neuronal representations of individual properties of the visual stimulus and their binding in an integrated image.     

Analysis of structural basis of information processing in basal ganglia: spatial organization of the thalamo-striatal projections in the dog brain

Distribution of neurones labelled in a retrograde way, studied in functionally different dog's thalamic nuclei, elucidated anatomical aspects of functional heterogeneity of the basal ganglia and of integrative information processing, as well as the organization of adaptive behaviour mechanisms.     

Dopamine-glutamate interactions in the basal ganglia

Summary In an attempt to formulate a working hypothesis of basal-ganglia functions, arguments are considered suggesting that the basal ganglia are involved in a process of response selection i.e. in the facilitation of wanted and in the suppression of unwanted behaviour. The meso-accumbal dopamine-system is considered to mediate natural and drug-induced reward and sensitization. The meso-striatal dopamine-system seems to fulfill similar funcions: It may mediate reinforcement which strengthens a given behaviour when elicited subsequently, but which is not experienced as reward or hedonia.Glutamate as the transmitter of the corticofugal projections to the basal ganglia nuclei and of the subthalamic neurons is critically involved in basal ganglia funcions and dysfunctions; for example Parkinson's disease can be considered to be a secondary hyperglutamatergic disease. Additionally, glutamate is an essential factor in the plasticity response of the basal-ganglia. However, opposite to previous suggestions, the NMDA-receptor blocker MK-801 does not prevent psychostimulant- nor morphine-induced day to day increase (sensitization) of locomotion. Also the day to day increase of haloperidol-induced catalepsy was not prevented by MK-801.     

Motor functions of the basal ganglia

This session dealt with the structure and function of the basal ganglia and their role in motor control. The key issues discussed in the first four presentations concerned the pathophysiology of movement performance in parkinsonian patients and in animal models of this disease. Three papers were presented on neurochemically specified subsystems of the basal ganglia. Therapeutic aspects (stereoencephalotomy and chronic electrical stimulation of neural tissue) were discussed in the last two papers. A brief account is given on the highlights of each of these reports.     

PET imaging of the basal ganglia

The present chapter reviews PET imaging in basal ganglia disorders; Parkinson's disease is used as a model of these disorders because the neurochemical pathobiology of this disease is well known and great advances in the imaging area have been achieved. Other basal ganglia disorders including Tourette's syndrome, dystonia, Huntington's chorea and Wilson's disease are also dealt with. With PET and SPECT techniques, the whole integrative dopaminergic network of neurons can be studied, which plays an important role in differential diagnostics. Furthermore, pharmacological effects of medication can be visualized and the role of stereotaxic neurosurgery can be evaluated. Finally, functional imaging gives clues about the prognosis and rehabilitation aspects of the basal ganglia disorders.     

Sex chromosomes of basal placental mammals

Placental (eutherian) mammals are currently classified into four superordinal clades (Afrotheria, Xenarthra, Laurasiatheria and Supraprimates) of which one, the Afrotheria (a unique lineage of African origin), is generally considered to be basal. Therefore, Afrotheria provide a pivotal evolutionary link for studying fundamental differences between the sex chromosomes of human/mouse (both representatives of Supraprimates and the index species for studies of sex chromosomes) and those of the distantly related marsupials. In this study, we use female fibroblasts to investigate classical features of X chromosome inactivation including replication timing of the X chromosomes and Barr body formation. We also examine LINE-1 accumulation on the X chromosomes of representative afrotherians and look for evidence of a pseudoautosomal region (PAR). Our results demonstrate that asynchronous replication of the X chromosomes is common to Afrotheria, as with other mammals, and Barr body formation is observed across all Placentalia, suggesting that mechanisms controlling this evolved before their radiation. Finally, we provide evidence of a PAR (which marsupials lack) and demonstrate that LINE1 is accumulated on the afrotherian and xenarthran X, although this is probably not due to transposition events in a common ancestor, but rather ongoing selection to retain recently inserted LINE1 on the X.     

Morphological indicators of foot posture in mammals: a statistical and biomechanical analysis

Mammalian foot posture has previously been described through the three-tiered hierarchy of plantigrady, digitigrady and unguligrady. This broadly applicable terminology has been used to categorize both living and fossil taxa, despite the fact that these postural grades, as traditionally used, do not rely on strict mechanical, kinematic or morphologic definitions. This paper redefines these terms: hind foot posture can be more accurately categorized if these definitions are based on the primary joint of flexure in the standing position. Once postures are so defined, a number of morphological features in taxa can be correlated with the use of particular postures. Bivariate and multivariate statistical analyses of morphological measurements from a large ( n = 61) group of plantigrade and digitigrade eutherian mammals indicate that foot posture can be reliably detected from a relatively small number of morphological measurements on a few limb and tarsal bones (femur, astragalus, calcaneum and metatarsals). The features important in distinguishing postural grades fit expectations from biomechanical theory, and should prove useful for the prediction of foot posture in fossil taxa, particularly when complete specimens are not known.     

基础代谢产热的分子机制

本文综述了基础代谢的功能,发生,产热的途径以及各产热途径对基础代谢率（basal metabolic rate,BMR)的贡献,基础条件下整个机体的能量消耗用来维持两种功能：服务功能和细胞维持功能,基础代谢的产生是由体内的解偶联反应引起的,产热过程涉及到细胞内的非线粒体呼吸,质子漏和ATP周转反应,产生的热量分别占BMR的10％,20－30％和60％－70％。ATP周转反应包括Na^ -K^ 泵,Ca^2 泵,肌肉收缩,蛋白质周转,糖异生和尿素合成等,各产热反应对细胞呼吸的贡献只有组织特异性,却没有种属特异性,因而它们对BMR的贡献不仅与自身活性有关,还与体内各器官的相对重量有关。     

Histoenzymology of the developing human basal ganglia

Summary Oxidative and hydrolytic enzyme activities are present in the anlage of the human basal ganglia as early as the second month of embryonic life, and acetylcholinesterase activity appears during the sixth month of pre-natal life.Clinical Research Fellow of the Medical Research Council. Presently in the Department of Neurology, Indiana University, Medical School.     

The role of the basal ganglia in habit formation

Many organisms, especially humans, are characterized by their capacity for intentional, goal-directed actions. However, similar behaviours often proceed automatically, as habitual responses to antecedent stimuli. How are goal-directed actions transformed into habitual responses? Recent work combining modern behavioural assays and neurobiological analysis of the basal ganglia has begun to yield insights into the neural basis of habit formation.     

Action,time and the basal ganglia

The ability to control the speed of movement is compromised in neurological disorders involving the basal ganglia, a set of subcortical cerebral nuclei that receive prominent dopaminergic projections from the midbrain. For example, bradykinesia, slowness of movement, is a major symptom of Parkinson''s disease, whereas rapid tics are observed in patients with Tourette syndrome. Recent experimental work has also implicated dopamine (DA) and the basal ganglia in action timing. Here, I advance the hypothesis that the basal ganglia control the rate of change in kinaesthetic perceptual variables. In particular, the sensorimotor cortico-basal ganglia network implements a feedback circuit for the control of movement velocity. By modulating activity in this network, DA can change the gain of velocity reference signals. The lack of DA thus reduces the output of the velocity control system which specifies the rate of change in body configurations, slowing the transition from one body configuration to another.     

Functional and pathophysiological models of the basal ganglia

Because of new data, anatomical and functional models of the basal ganglia in normal and pathological conditions (e.g. Parkinson's and Huntington's diseases) have recently come under greater scrutiny. An update of these models is clearly timely, taking into consideration not only changes in neuronal discharge rates, but also changes in the patterning and synchronization of neuronal discharge, the role of extrastriatal dopamine, and expanded intrinsic and input/output connections of these nuclei.     

A dynamic model of motor basal ganglia functions

 Fast aiming movements were measured in a choice reaction paradigm in a healthy control group and in Parkinsonian patients. The patients were tested without (‘off ’) and with 3,4-dihydroxyphenylalanine (‘on’) (L-dopa) medication. The movement trajectories were used to estimate the parameters of a dynamic linear model. The model is based on the functional structure of the basal ganglia-thalamocortical circuit with direct and indirect pathways linking the putamen to the basal ganglia output nuclei (Albin et al. 1989). The output of the circuit is connected to a model for the motor neuron-musculo-skeletal system. The gain k _d for the direct pathway and the gain k _i for the indirect pathway were estimated. They were found to be significantly decreased for Parkinsonian patients in ‘off ’ compared with the control group. L-dopa therapy in Parkinsonian patients increased the gains of the direct and the indirect pathway almost to normal values which implies that the long-term dopamine level in the striatum was excitatory for the direct and for the indirect pathway. This result is restricted to movements of correct size. For movements of diminished size, which are typical for Parkinsonian patients, the model predicts that the dopamine level in the striatum is excitatory for the direct pathway but inhibitory for the indirect pathway. The simulated values for neuronal activities are in agreement with expected values according to the experimental data. The proposed model of the ‘motor’ basal ganglia thalamocortical circuit implies that information about biomechanical properties of the musculo-skeletal system is stored in the ‘motor’ basal ganglia-thalamocortical circuit, and that the basal ganglia are involved in computation of the desired movement amplitude. Received: 24 April 1996/Accepted in revised form: 25 February 1997     

Metabotropic glutamate receptors in the basal ganglia motor circuit

In recent years there have been tremendous advances in our understanding of the circuitry of the basal ganglia and our ability to predict the behavioural effects of specific cellular changes in this circuit on voluntary movement. These advances, combined with a new understanding of the rich distribution and diverse physiological roles of metabotropic glutamate receptors in the basal ganglia, indicate that these receptors might have a key role in motor control and raise the exciting possibility that they might provide therapeutic targets for the treatment of Parkinson's disease and related disorders.