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PubMed1975

Convergence-evoked nystagmus. Congenital and acquired forms.

Pendular nystagmus occurring during binocualr fixation and pursuit of near objects is true convergence-evoked nystagmus. Two forms of this nystagmus are described, one congenital and the other acquired in the course of multiple sclerosis. The congenital form was conjugate and the acquired form disjunctive. Neuropathological examination provided no morphological explanation for the congenital pattern. These two unique forms of nystagmus are induced by one of the visuomotor subsystems controlling convergence.

Adult↗

PubMed1981

Accommodative and convergence insufficiency after decompression sickness.

Twelve professional divers had visual complaints after decompression sickness. Severe accommodative and convergence insufficiency, heretofore unrecognized, was detected and studied. Two rhesus monkeys were subjected to similar hyperbaric conditions and then examined before death for study of their eyes and brains. The animals seemed to have accommodative and convergence insufficiency.

Accommodation, Ocular↗

PubMed1998

Convergence and branching patterns of round, type 2 corticopulvinar axons.

Corticopulvinar connections consist of at least two morphologically distinct subpopulations. In one subgroup (E, type 1), axons have an "elongated" terminal field and thin, spinous terminations; in the other (R, type 2), axons have a small, round arbor and large, beaded terminations. Previous work (Rockland, 1996) indicates that E-type axons from several occipitotemporal areas branch extensively within and sometimes between pulvinar subdivisions, but that R-type axons tend to have spatially delimited arbors. The present report is a further investigation of R-type axons from areas V1 and MT and was initiated to test the generality of the previous findings. There are four main results: 1) By serial section reconstruction of anterogradely labeled axons, 10 of 25 axons originating in area V1 had two or three spatially separate arbors (8 and 2 axons, respectively). Sixteen axons analyzed from area MT, however, all had single arbors, although the arbors were often formed by the convergence of widely separate branches. 2) Multiple (at least 2-5) R-type corticopulvinar axons, from V1 or from MT, can converge in a single focus. 3) R-type axons originating from both areas V1 and MT can branch to other structures; namely, the superior colliculus, the pretectal area, and/or the reticular nucleus of the thalamus. 4) Finally, corticopulvinar terminations from area V1 are predominantly R-type, whereas those from MT are more predominantly E-type. These results thus provide additional evidence of the special relationship of area V1 to the pulvinar. They also emphasize that the idea of corticopulvinocortical "feedback loops," although convenient as a shorthand nomenclature, does not adequately convey the full complexity of the system.

Animals↗

PubMed1998

Convergent prefrontal cortex and mamillary body projections to the medial pontine nuclei: a light and electron microscopic study in the rat.

To study the convergence of medial prefrontal cortex and mamillary body projections to the medial pontine nuclei, light and electron microscopic, neuroanatomical, tract-tracing experiments were performed. Injections of horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP), biotin conjugated to dextran (BD), or rhodamine conjugated to dextran (RD) were made individually or in combinations into the cerebral cortex, hypothalamus, or pons. In addition, injections of WGA-HRP into the medial prefrontal cortex and electrolytic lesions of the mamillary body were made to study the synaptology of afferent projections to the pontine nuclei. In the light microscopic studies, injections of WGA-HRP into the rostromedial pontine nuclei produced dense, retrograde labeling both in the dorsal peduncular area of the medial prefrontal cortex and in the medial mamillary nucleus, pars medialis. Injections of the anterograde tracers BD and RD into the medial prefrontal cortex and the medial mamillary nuclei, respectively, resulted in partially overlapping terminal fields in the rostromedial pontine nuclei. In the electron microscopic studies, injections of WGA-HRP into the dorsal peduncular area and electrolytic lesions of the mamillary body produced anterogradely labeled axon terminals and degenerating axon terminals that synapsed on the same dendrites or neuronal somata in the rostromedial pontine nuclei. The results demonstrate that the medial prefrontal cortex and the medial mamillary nuclei have partially overlapping projections to the rostromedial pontine nuclei and implicate precerebellar relay nuclei in the integration of limbic and/or autonomic functions mediated by convergent projections from the cerebral cortex and the hypothalamus.

Animals↗

PubMed1999

Use of quantitative convergent-beam electron diffraction in materials science.

Methods for quantitative convergent-beam electron diffraction are outlined and some results of our applications of convergent-beam electron diffraction are shown, with emphasis on quantitative analysis of crystal structures in materials science. Examples of thickness measurements and determination of lattice parameters are presented. Measurements of low-order structure factors to obtain information on bonding charge-density distributions are reviewed, with examples from TiAl intermetallics. For non-centrosymmetric crystals, a method to determine three-phase structure invariants is given. Determination of polarity is also discussed.

Alloys↗

PubMed1996

Convergent validity of the Depression-Happiness Scale with measures of depression.

In recent years, the study of subjective well-being (SWB) has attracted much research interest. One recent operational definition of SWB is the McGreal and Joseph (1993) Depression-Happiness Scale. The aim of the present research was to investigate the convergent validity of the Depression-Happiness Scale with several other well established measures of depressive symptomatology. Subjects were 194 undergraduate students attending the University of Ulster. Lower scores on the Depression-Happiness Scale, indicating a higher frequency of negative thoughts and feelings and a lower frequency of positive thoughts and feelings, were associated with higher scores on the Beck Depression Inventory, the Self-Rating Depression Scale, and the Center for Epidemiological Studies Depression Scale. These data provide further evidence for the convergent validity of the Depression-Happiness Scale.

Adolescent↗

PubMedDate not supplied

Identifiability and convergence issues for Markov chain Monte Carlo fitting of spatial models.

The marked increase in popularity of Bayesian methods in statistical practice over the last decade owes much to the simultaneous development of Markov chain Monte Carlo (MCMC) methods for the evaluation of requisite posterior distributions. However, along with this increase in computing power has come the temptation to fit models larger than the data can readily support, meaning that often the propriety of the posterior distributions for certain parameters depends on the propriety of the associated prior distributions. An important example arises in spatial modelling, wherein separate random effects for capturing unstructured heterogeneity and spatial clustering are of substantive interest, even though only their sum is well identified by the data. Increasing the informative content of the associated prior distributions offers an obvious remedy, but one that hampers parameter interpretability and may also significantly slow the convergence of the MCMC algorithm. In this paper we investigate the relationship among identifiability, Bayesian learning and MCMC convergence rates for a common class of spatial models, in order to provide guidance for prior selection and algorithm tuning. We are able to elucidate the key issues with relatively simple examples, and also illustrate the varying impacts of covariates, outliers and algorithm starting values on the resulting algorithms and posterior distributions.

Algorithms↗

PubMed2002

An efficient approach towards the convergent synthesis of "fully-carbohydrate" mannodendrimers.

Glycosylation of sugar trityl ethers with sugar 1,2-O-(1-cyano)ethylidene derivatives (the trityl-cyanoethylidene condensation) has been applied to the synthesis of highly branched (dendritic) mannooligosaccharides incorporating a Manalpha1-->3(Manalpha1-->6)Man structural motif. The convergent synthetic strategy used to assemble these oligosaccharides was based on the use of glycosyl acceptors and/or a glycosyl donor already bearing this structural motif. The former were represented by mono- and ditrityl ethers of ManalphaOMe, Manalpha1-->3ManalphaOMe, and Manalpha1-->3(Manalpha1-->6)ManalphaX, where X=OMe or SEt. The pivotal glycosyl donor was the peracetylated 1,2-O-(1-cyano)ethylidene-3,6-di-O-(alpha-D-mannopyranosyl)-beta-D-mannopyranose (1), prepared by orthogonal Helferich glycosylation of the known 1,2-O-(1-cyano)ethylidene-beta-D-mannopyranose with tetra-O-acetyl-alpha-D-mannopyranosyl bromide followed by O-acetylation. Glycosylation of acetates of methyl 6-O-trityl-alpha-D-mannopyranoside and methyl 3,6-di-O-trityl-alpha-D-mannopyranoside with one equivalent of the donor 1 gave rise to the isomeric tetrasaccharide derivatives, Manalpha1-->3(Manalpha1-->6)Manalpha1-->6ManalphaOMe and Manalpha1-->3(Manalpha1-->6)Manalpha1-->3ManalphaOMe, respectively. The latter derivative was further mannosylated at the remaining 6-O-trityl acceptor site to give the protected pentasaccharide Manalpha1-->3(Manalpha1-->6)Manalpha1-->3(Manalpha1-->6)ManalphaOMe. The isomeric pentasaccharide, Manalpha1-->3(Manalpha1-->6)Manalpha1-->6(Manalpha1-->3)ManalphaOMe, was prepared by reaction of 1 with the 6-O-trityl derivative of (Manalpha1-->3)ManalphaOMe. In a similar fashion, 6'- and 6"-O-trityl derivatives of the branched trisaccharide Manalpha1-->3(Manalpha1-->6)ManalphaOMe served as precursors for two isomeric mannohexaosides. The 3,6-di-O-trityl ether of ManalphaOMe and the 6',6"-di-O-trityl ether of Manalpha1-->3(Manalpha1-->6)ManalphaX (X=OMe or SEt) were efficiently bis-glycosylated with the donor 1 to give the corresponding protected mannoheptaoside and mannononaoside. The yields of these glycosylations with the donor 1 ranged from 50 to 66 %. Final deprotection of all the oligosaccharides was straightforward and afforded the target products in high yields. Both the acylated and deprotected products were characterized, and the intersaccharide connectivities were elucidated by extensive one- and two-dimensional NMR spectroscopy. The described blockwise convergent approach allows assembly of a variety of 3,6-branched mannooligosaccharides.

Carbohydrate Conformation↗

PubMed2004

Convergence of sensory systems in the orbitofrontal cortex in primates and brain design for emotion.

In primates, stimuli to sensory systems influence motivational and emotional behavior via neural relays to the orbitofrontal cortex. This article reviews studies on the effects of stimuli from multiple sensory modalities on the brain of humans and some other higher primates. The primate orbitofrontal cortex contains the secondary taste cortex, in which the reward value of taste is represented. It also contains the secondary and tertiary olfactory cortical areas, in which information about the identity and also about the reward value of odors is represented. A somatosensory input is revealed by neurons that respond to the viscosity of food in the mouth, to the texture (mouth feel) of fat in the mouth, and to the temperature of liquids placed into the mouth. The orbitofrontal cortex also receives information about the sight of objects from the temporal lobe cortical visual areas. Information about each of these modalities is represented separately by different neurons, but in addition, other neurons show convergence between different types of sensory input. This convergence occurs by associative learning between the visual or olfactory input and the taste. In that emotions can be defined as states elicited by reinforcers, the neurons that respond to primary reinforcers (such as taste and touch), as well as learn associations to visual and olfactory stimuli that become secondary reinforcers, provide a basis for understanding the functions of the orbitofrontal cortex in emotion. In complementary neuroimaging studies in humans, it is being found that areas of the orbitofrontal cortex are activated by pleasant touch, by painful touch, by taste, by smell, and by more abstract reinforcers such as winning or losing money. Damage to the orbitofrontal cortex in humans can impair the learning and reversal of stimulus-reinforcement associations and thus the correction of behavioral responses when these are no longer appropriate because previous reinforcement contingencies change. It is striking that humans and other catarrhines, being visual specialists like other anthropoids, interface the visual system to other sensory systems (e.g., taste and smell) in the orbitofrontal cortex.

Afferent Pathways↗

PubMed2003

Convergence in peptide folding simulation: multiple trajectories of a potential AIDS pharmacophore.

To examine the conformational properties in aqueous solution of a 15-residue peptide that is a potential pharmacophore for AIDS vaccine development, molecular dynamics simulations were performed in water starting from structures determined experimentally in three different organic solvents. Convergence characteristics of the simulation are examined in Cartesian and conformational spaces. In addition, novel analysis tools are employed including a multidimensional scaling method to represent the distance between trajectory frames. As these methods are based on a variety of physical parameters, they provide a useful cross-check on the structural convergence. Theoretical two-dimensional (2D) 1H-NMR spectra are also generated. These are superficially quite different in appearance, demonstrating that backbone similarities difficult to identify by visual inspection of 2D NMR data can be revealed using the methods described here.

AIDS Vaccines↗

PubMed2003

The convergent synthesis of poly(glycerol-succinic acid) dendritic macromolecules.

The high-yield convergent synthesis of dendrons, dendrimers, and dendritic-linear hybrid macromolecules composed of succinic acid, glycerol, and poly(ethylene glycol) (PEG) is described. This convergent synthesis relies on two orthogonal protecting groups; namely, the benzylidene acetal (bzld) for the protection of the 1,3-hydroxyls of glycerol and the tert-butyldiphenylsilyl (TBDPS) ester for protection of the carboxylic acid of succinic acid. These novel polyester dendritic macromolecules are composed entirely of building blocks known to be biocompatible or degradable in vivo to give natural metabolites. Derivatization of the dendritic periphery with a methacrylate affords a polymer that can be subsequently photo-cross-linked. The three-dimensional cross-linked gels formed by ultraviolet irradiation are optically transparent, with mechanical properties dependent on the initial cross-linkable dendritic macromolecule.

Biocompatible Materials↗

PubMed2004

Unitary giant synapses embracing a single neuron at the convergent site of time-coding pathways of an electric fish, Gymnarchus niloticus.

Phase-locking neurons in the electrosensory lateral line lobe (ELL) of a weakly electric fish, Gymnarchus niloticus, fire an action potential in response to each cycle of the sinusoidal electrosensory signal (350-500 Hz) created by the fish's own electric organ. The exact firing times of the phase-locking neurons are altered (time-shifted) by capacitance of electrolocation objects or by electric organ discharges of other individuals. The magnitude of the time shifts depends on the location of the neurons' receptive field on the skin; thus, time disparities arise between the firing of phase-locking neurons. To compute these disparities, there should be a site where these phase-locking neurons converge. In this study we morphologically identified a novel cell type, which we named the "ovoidal cell", that receives the convergent projections of phase-locking neurons in the inner cell layer (ICL) of the ELL. We labeled these neurons with biocytin and examined them by light and electron microscopy. The giant cells and the S-type primary afferents, two types of phase-locking neurons, respectively terminate on the soma via chemical synapses and on the dendrite of the ovoidal cells via mixed synapses. Each terminal of the giant cells embraces the soma of an ovoidal cell, covering as much as 84% of the somatic membrane. The giant cell terminals and ovoidal cell somata were immunoreactive to SV2, a synaptic vesicle protein, but the S-afferent terminals were not, even though they contain numerous synaptic vesicles. The dendrite of the ovoidal cells also contacts the pyramidal cells of the ICL, which are known to be sensitive to time disparities. The anatomical connections of the phase-locking neurons to the ovoidal cells strongly suggest that they are involved in computing time disparity.

Animals↗

PubMed2006

Convergence of spinal trigeminal and cochlear nucleus projections in the inferior colliculus of the guinea pig.

In addition to ascending auditory inputs, the external cortex of the inferior colliculus (ICX) receives prominent somatosensory inputs. To elucidate the extent of interaction between auditory and somatosensory representations at the level of IC, we explored the dual projections from the cochlear nucleus (CN) and the spinal trigeminal nucleus (Sp5) to the inferior colliculus (IC) in the guinea pig, using both retrograde and anterograde tracing techniques. Injections of retrograde tracers into ICX resulted in cell-labeling primarily in the contralateral DCN and pars interpolaris and caudalis of Sp5. Labeled cells in DCN were either fusiform or multipolar cells, whereas those in Sp5 varied in size and shape. Injections of anterograde tracers into either CN or Sp5 resulted in terminal labeling in ICX primarily on the contralateral side. Most projection fibers from Sp5 terminated in a laminar pattern from ventromedial to dorsolateral within the ventrolateral ICX, the ventral border of IC, and the ventromedial edge of IC (collectively termed "the ventrolateral border region of IC," ICXV). Less dense anterograde labeling was observed in lateral and rostral ICX. Injecting different tracers into both Sp5 and CN confirmed the overlapping areas of convergent projections from Sp5 and CN in IC: The most intense dual labeling was seen in the ICXV, and less intense dual labeling was also observed in the rostral part of ICX. This convergence of projection fibers from CN and Sp5 provides an anatomical substrate for multimodal integration in the IC.

Afferent Pathways↗

PubMed1989

Structure-function relationships in the rat brainstem subnucleus interpolaris: VI. Cervical convergence in cells deafferented at birth and a potential primary afferent substrate.

Possible substrates for peripheral injury-induced receptive field (RF) changes were assessed in the trigeminal (V) subnucleus interpolaris (SpVi). In adult rats with infraorbital nerve section at birth, 449 cells were studied ipsilateral to the lesion by using electrophysiological methods. Of these, 33 (7.4%) had RFs that included facial vibrissae, guard hairs, and skin, as well as ipsilateral regions normally innervated by cervical primary afferents (ear, neck, shoulder, arm, forepaw). Such non-V convergence was never seen in 373 normal SpVi cells or in 641 V ganglion cells ipsilateral to the lesion. SpVi cells with cervical RFs discharged to V ganglion shocks and their latencies (1.6 +/- 0.7 ms, mean +/- s.d.) did not differ from normal (1.4 +/- 0.5). Most (71%) projected to the thalamus. None were nociceptive-biased, and many had unusually discontinuous RFs (48%). Possible pathways by which cervical inputs might reach SpVi neurons were investigated in additional anatomical and electrophysiological experiments. Eight SpVi cells with cervical RFs were intracellularly labeled with HRP. Although all had dendrites that were polarized toward SpVi regions containing spared mandibular and/or ophthalmic primary afferents, none had dendrites which extended out of SpVi. In other neonatally nerve-damaged adults, WGA-HRP was injected bilaterally into forepaw, arm, and shoulder regions. Transganglionic transport was restricted to normal targets. However, WGA-HRP injections into SpVi retrogradely labeled a total of 46 +/- 20 (mean +/- s.d.) cells in ipsilateral C1-3 dorsal root ganglia, and 24 +/- 8 cells in C4-8 ganglia. In controls, labeled cells were seen only in C1-3 ganglia (32 +/- 9). The distribution and number of labeled cells in the somatosensory cortex did not differ in experimental and control cases. No labeled cells were visible in the dorsal column nuclei of either the normal or experimental rats. Thus, retrograde labeling studies suggest that a cervical primary afferent projection to SpVi is a potential substrate for cervical convergence expressed in neonatally deafferented SpVi cells.

Action Potentials↗

PubMed1992

Converging GABA- and glutamate-immunoreactive axons make synaptic contact with identified hypothalamic neurosecretory neurons.

To study the neurochemical identity of axons in synaptic contact with identified hypothalamic neurosecretory neurons in rats, we combined retrograde axonal transport of a marker molecule with postembedding immunogold staining for amino acid neurotransmitters. After intravenous injections of horseradish peroxidase, neurosecretory neurons with axons in the median eminence or neurohypophysis transported the peroxidase retrogradely back to the cell body of origin. Serial ultrathin sections from the paraventricular and arcuate nuclei were immunostained with glutamate or GABA antisera. Peroxidase-labeled neurons and their dendrites received synaptic contact from colloidal gold-labeled axons immunoreactive for GABA or for glutamate. Axons which were highly immunoreactive for GABA and other axons immunoreactive for glutamate but not for GABA consistently made converging synaptic contact with the same peroxidase-labeled cell. Some of the peroxidase-labeled neurons from the arcuate nucleus which were postsynaptic to both GABA and glutamate axons were themselves identified as being GABA immunoreactive. Serial ultrathin sections revealed that multiple presynaptic axons immunoreactive for glutamate or GABA made repeated contacts with single neurons. These results suggest a widespread convergence of the major inhibitory and excitatory amino acid transmitter on the neurons which control both the anterior and posterior pituitary hormones.

Animals↗

PubMed1992

The striatum and the globus pallidus send convergent synaptic inputs onto single cells in the entopeduncular nucleus of the rat: a double anterograde labelling study combined with postembedding immunocytochemistry for GABA.

The entopeduncular nucleus is one of the major output stations of the basal ganglia. In order to better understand the role of this structure in information flow through the basal ganglia, experiments have been performed in the rat to examine the chemical nature, morphology, and synaptology of the projections from the globus pallidus and striatum to the entopeduncular nucleus. In order to examine the morphology and synaptology of pallidoentopeduncular terminals and striatoentopeduncular terminals, rats were subjected to a double anterograde labelling study. The globus pallidus was injected with Phaseolus vulgaris-leucoagglutinin (PHA-L), and on the same side of the brain, the striatum was injected with biocytin. The entopeduncular nuclei of these animals were then examined for anterogradely labelled pallidal and striatal terminals. Rich plexuses of PHA-L-labelled pallidal terminals and biocytin-labelled striatal terminals were identified throughout the entopeduncular nucleus. At the electron microscopic level, the pallidal boutons were classified as two types. The majority (Type 1), were large boutons that formed symmetrical synapses with the dendrites and perikarya of neurones in the entopeduncular nucleus. Type 2 PHA-L-labelled terminals were much rarer, slightly smaller, and formed asymmetrical synapses. It is suggested that the Type 2 boutons are not derived from the globus pallidus but from the subthalamic nucleus. The biocytin-labelled terminals from the striatum had the typical morphological features of striatal terminals and formed symmetrical synapses. The distribution of the postsynaptic targets of the pallidal terminals and the striatal terminals differed in that the pallidal terminals preferentially made synaptic contact with the more proximal regions of the neurones in the entopeduncular nucleus, whereas the striatal terminals were located more distally on the dendritic trees. Examination in the electron microscope of areas where there was an overlap of the two sets of anterogradely labelled boutons revealed that terminals from the globus pallidus and the striatum made convergent synaptic contact with the perikarya and dendrites of individual neurones in the entopeduncular nucleus. In order to examine the chemical nature of the input to the entopeduncular nucleus from the globus pallidus and the striatum, ultrathin sections were immunostained by the postembedding method to reveal endogenous GABA. Three classes of GABA-containing terminals were identified; two of them formed symmetrical synapses and one rare type formed asymmetrical synapses. The combination of the GABA immunocytochemistry and anterograde labelling revealed that both the striatal and pallidal afferents that make symmetrical synapses with neurones in the entopeduncular nucleus, including those involved in convergent inputs, are GABAergic.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Maturation of neuron types in nucleus of solitary tract associated with functional convergence during development of taste circuits.

Late fetal through postnatal development in sheep is a period of increasing convergence of afferent taste fibers onto second-order neurons in the nucleus of the solitary tract (NST). To learn whether neuron morphology alters in concert with convergence and neurophysiological development in NST, three-dimensional neuron reconstructions were made of cells in a functionally defined region of gustatory NST from Golgi preparations of the brainstem. Elongate, multipolar, and ovoid neurons were studied in fetuses from 85 days of gestation through the perinatal period (term = 147 days of gestation), to postnatal stages. Somal size and form, and dendritic complexity and extent, increased markedly from 85 to about 110 days of gestation in both of the proposed NST projection neurons, elongate and multipolar. From 130 days of gestation to postnatal ages, growth of dendrites of elongate neurons plateaued or declined, whereas dendrites of multipolar neurons apparently continued to increase in size and extent. In addition, spine density decreased on elongate neurons but remained stable on multipolar neurons. Morphological variables of ovoid cells, proposed interneurons in NST, did not alter over this later period. The data suggest that multipolar, not elongate or ovoid, neurons are logical candidates to receive the increasing afferent fiber input onto NST cells during late gestation. Also, neural activity from taste afferent fibers is more likely to have a role in altering NST neuron morphology at later, rather than earlier, developmental periods.

Afferent Pathways↗

PubMed1995

The glutamate-enriched cortical and thalamic input to neurons in the subthalamic nucleus of the rat: convergence with GABA-positive terminals.

Neurons of the subthalamic nucleus play a key role in the normal physiology and the pathophysiology of the basal ganglia. In order to understand better how the activity of subthalamic neurons and hence the output of the basal ganglia are controlled, we have reexamined the topography and examined in detail the synaptology and neurochemical nature of the two major excitatory projections to the subthalamic nucleus, that from the cortex and from the parafascicular nucleus of the thalamus. The approach was to use anterograde neuronal tracing and postembedding immunocytochemistry for amino acid transmitters. In confirmation of previous findings the cortical and thalamic projections were topographically organized, although the topography was more finely organized, and the projections more extensive, than previously demonstrated. Cortical and thalamic terminals made asymmetrical synaptic contacts with the dendrites and spines of subthalamic neurons. The thalamic terminals contacted larger postsynaptic targets, and therefore presumably more proximal regions of subthalamic neurons, than did the cortical terminals. Quantitative analysis of the postembedding immunolabelled sections revealed that the cortical and thalamic terminals were significantly enriched in glutamate-immunoreactivity when compared to identified gamma-aminobutyric acid (GABA)-positive terminals, supporting physiological studies that suggest that these projections use glutamate as their neurotransmitter. In addition a small population of nonanterogradely labelled terminals that formed asymmetrical synapses and were immunopositive for GABA were identified. A larger population of terminals that formed symmetrical synapses were also immunopositive for GABA and were probably derived from the globus pallidus. The latter type of terminal was found to make convergent synaptic input with cortical or thalamic terminals on the dendrites and spines of subthalamic neurons, indicating that the "indirect pathways" by which information flows through the basal ganglia converge at the level of individual neurons in the subthalamic nucleus.

Animals↗