Activation of dorsal horn cells by ventral root stimulation in the cat

Responses of dorsal horn cells to ventral root stimulation were determined for the L7 and S1 levels of the spinal cord of 14 anesthetized cats. Forty-six dorsal horn cells were found that were excited by stimulation of the distal stump of the cut ventral root. For maximum excitation it was necessary to use a train of stimuli. For the 34 dorsal horn cells whose peripheral receptive-field properties could be characterized, 14 were wide dynamic range cells and 19 were high-threshold cells. The other cell responded exclusively to stimulation of deep tissue. None of the cells responded exclusively to innocuous stimuli, and all responded more vigorously to noxious than to innocuous stimuli. Some cells also responded to noxious heat applied to the skin of the receptive field. Locations of 10 of the activated dorsal horn cells were identified. They were distributed throughout the dorsal horn, but most were found in laminae V and VI. In four animals, both the proximal and distal stumps of the cut S1 ventral root were stimulated while searching for dorsal horn cells. Ten dorsal horn cells were found that were excited by stimulation of the distal stump of the ventral root. No cells were found that responded to proximal stump stimulation. To prevent current spread by stimulation of the ventral root, an extra ground electrode was placed distal to the stimulating electrodes. When the ground electrode was removed, distinctive signs of current spread appeared in that a cord dorsum potential could be recorded and the dorsal horn neuronal responses changed. Dorsal horn neurons could also be excited by nonelectrical stimuli such as crushing the ventral root. If the ventral root was crushed distal to the stimulating electrodes, however, the initially excited cell could no longer be activated by ventral root stimulation. Activation of dorsal horn cells by stimulation of the distal stump of a cut ventral root was abolished when the dorsal root of the same segment was sectioned. Conduction velocities of the fibers in the ventral root that excited dorsal horn cells ranged between 0.25 and 1.78 m/s with a mean of 0.91 +/- 0.47 (SD) m/s. These results show that there are unmyelinated afferent fibers in the ventral root that enter the spinal cord through the dorsal root and excite dorsal horn cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Light and electron microscopic autoradiographic study of the dorsal root projections to the cat dorsal horn

The distribution of terminals arising from dorsal root primary afferents was examined in the lumbar spinal cord of cats using light- and electron-microscopic autoradiography. Tritiated proline or leucine was injected into either the L6 or L7 dorsal root ganglion. The light-microscopic spinal cord distribution of radioactivity in the ganglia was independent of the type of amino acid used. Likewise, the length of the survival time after injection had no effect. The projections to the substantia gelatinosa and the marginal zone were consistently the densest. However, the topography of the dorsal horn distribution, relative the the segment of entry, varied significantly especially in the gelatinosa, depending upon the ganglia injected. Those to the substantia gelatinosa were largely limited to the segment of entry; those to the marginal zone and nucleus proprius extended many segments beyond the level of entry. At all levels the projection was exclusively ipsilateral to the side of injection.At the electron-microscopic level the distribution of radioactivity was determined in each of the three easily recognizable areas of the dorsal horn: the marginal zone, the substantia gelatinosa and the nucleus proprius. In each dorsal horn area the total terminal population was divided into four basic categories. Each of these areas was found to contain a characteristic distribution of these four terminal categories. The difference between areas arose, primarily, as a consequence of the dorsal to ventral decreasing frequency gradient of two types of terminal: those containing large, dense-cored vesicles and the increasing gradient of those containing flattened vesicles. The terminals with small pleomorphic vesicles and those with large round vesicles were frequently encountered in all three areas without a detectable frequency gradient.Similarly, the primary afferent terminal population, that is the subset of the total terminal population labelled after dorsal root ganglion injection, was also characteristic of the area, and each area was dominated by a different terminal type. In the marginal zone the terminals containing large dense-cored vesicles dominated. In the substantia gelatinosa the terminals with pleomorphic vesicles (which included the so-called ‘C’ type terminals) dominated. And the terminals containing large round vesicles dominated the primary afferent population in the nucleus proprius. The terminals containing flattened vesicles were never found to be specifically labeled in any of the areas examined.     

Immunoelectron microscopic localization of E-cadherin in dorsal root ganglia, dorsal root and dorsal horn of postnatal mice

Summary Sensory neurons and associated glial cells are known to express the cell-cell adhesion molecule E-cadherin. The cellular and subcellular localization of this molecule in the dorsal root ganglion, dorsal root, and spinal cord of postnatal mice was studied by the pre-embedding immunoelectron microscopic labelling technique. In the dorsal root and the superficial layer of the dorsal horn, a subset of fasciculating unmyelinated axons expressed E-cadherin at their axon-axon contacts at all ages studied, and these axons were clustered together and segregated from E-cadherin-negative axons. In contrast, pre-myelinating large-diameter axons in P2 mice as well as myelinated axons in mice from P14 to adulthood were E-cadherin-negative. Glial cells also expressed E-cadherin: In the dorsal root ganglia, all of the satellite cells expressed E-cadherin at contact sites with neurons, other satellite cells, and basal lamina, at all ages studied. In dorsal roots from P14 to adulthood, myelin-forming Schwann cells expressed E-cadherin at the outer mesaxons and the contact sites with basal lamina. Non-myelin-forming Schwann cells occasionally stained for this molecule at contact sites with the plasma membrane of E-cadherin-positive axons and at other sites. These results strongly suggest that E-cadherin plays an important role in the selective fasciculation of a particular subset of unmyelinated sensory fibres, and also in glial cell contacts.     

Catecholamine effects on frog dorsal root terminals

Dopamine, norepinephrine and epinephrine applied to the isolated superfused frog spinal cord had complex effects on the terminals of primary afferent fibers. The most cosistent finding was a slow hyperpolarization of terminals with lower concentrations (10 μM or lower), but depolarization either following or admixed with the hyperpolarization were seen. These were particularly prominent when the catecholamines were applied in high concentrations or for prolonged periods of time. A part of the response of afferent terminals appears to be indirect since the potential changes were reduced following exposure of the cord to tetrodotoxin, Mn²⁺, or mephenesin. The hyperpolarizations were augmented by imipramine, a known inhibitor of catecholamine uptake. These observations are consistent with a role of catecholamines in the processing of sensory input in the spinal cord.     

Electron microscopic identification of postsynaptic dorsal root terminals: a possible substrate of dorsal root potentials in the frog spinal cord

Summary Dorsal root fibers were labeled with cobaltous chloride iontophoresis for electron microscopic investigations. In the base of the dorsal horn, where most of the coarser collaterals of dorsal root fibers terminate, many dorsal root terminals were found in postsynaptic relation to synapsing profiles. According to their morphological characteristics, three kinds of presynaptic terminals could be discerned in these complex synapses: axon terminals with spheric vesicles, axon terminals with flattered vesicles and presynaptic dendrites. These latter terminals contained relatively few flattened vesicles accumulated adjacent to a short synaptic articulation surface, and they were rich in cytoplasmic organelles. The functional significance of these structural specializations in the mediation of dorsal root potentials and recurrent inhibition is discussed.     

Pathophysiologic concentrations of lysophosphoglycerides quantified by electron microscopic autoradiography

Lysophosphoglycerides accumulate in ischemic myocardium and appear to contribute to malignant dysrhythmia. Exposure of normoxic isolated Purkinje fibers or ventricular muscle strips to exogenous lysophosphatidyl choline (LPC) results in rapid, yet reversible, electrophysiologic derangements analogous to changes associated with ischemia in vivo. However, subcellular, local concentrations required for induction of electrophysiologic effects have not yet been elucidated unambiguously. The present study was designed to delineate the subcellular distribution and the sarcolemmal concentration of LPC by quantitative electron microscopic autoradiography after exposure of canine ventricular muscle strips to 3H-methyl LPC (200 microM) for 10 minutes. Tissue was processed for electron microscopy with a new procedure developed specifically to spatially fix choline phosphatides and render them insoluble in lipid solvents. Grain distributions were analyzed in the same group of cells that had been monitored electrophysiologically while superfused with LPC. LPC significantly decreased the resting membrane potential, action potential amplitude, duration, Vmax of phase 0, and conduction time. Grains were concentrated in the membranous organelles of cardiac myocytes. Myocyte sarcolemma exhibited the highest grain density (129 grains/100 micron2 versus a background of 0.27 grains/100 micron2). Calculations based on grain densities, emulsion sensitivity, exposure time, and specific activity indicated that the sarcolemma incorporated 5.4 X 10(6) LPC molecules/micron3 of membrane volume corresponding to approximately 1% of total sarcolemmal phospholipid. Since incorporation of only this small amount of lysophosphoglyceride into the sarcolemma was sufficient to elicit electrophysiologic disturbances, the observed accumulation of lysophosphoglycerides induced by ischemia appears to be sufficient to contribute to malignant dysrhythmia in vivo.     

Task-related responses of monkey medullary dorsal horn neurons

Medullary dorsal horn neurons with trigeminal sensory properties have been previously shown to have additional responses associated with cues relevant to the successful execution of a behavioral task. These "task-related" responses were evoked by environmental cues but were independent of the specific stimulus parameters. We have examined further the characteristics of task-related responses in medullary dorsal horn neurons of three monkeys. Single-unit activity was recorded while the monkeys were performing behavioral tasks that required them to discriminate thermal or visual stimuli for a liquid reward. Forty-five percent (34/75) of the medullary dorsal horn neurons studied exhibited task-related activity that was significantly correlated with the stereotypical behavioral events that occurred during the tasks. Similar events occurring outside of the task produced no response. In addition to the task-related activity of these medullary dorsal horn neurons, responses to mechanical and/or thermal stimuli presented within the neuron's receptive field were demonstrated in 28 of 34 cases. These sensory responses also were evoked by the same stimuli presented outside of the behavioral task. Fifteen of the neurons with task-related responses could be activated antidromically from thalamic stimulating electrodes. Task-related responses were categorized according to their relationship to the three phases of the behavioral trial: trial initiation, trial continuation, and trial termination. Although an individual task-related response was associated with a single behavioral event, most medullary dorsal horn neurons (30/34) exhibited a reproducible pattern of task-related responses that occurred during more than one phase of the trial. Trial-initiation task-related responses were subdivided depending on their correlation with specific events that occurred within that phase of the trial. One-third of the 18 excitatory trial-initiation responses were associated with the visual stimulus that cued the monkey to begin the trial; the remaining two-thirds were associated with the monkey's press of the button that actually initiated the trial. Trial-continuation task-related responses (observed while the monkey waited for a thermal stimulus that triggered a rewarded motor response) were shown to be independent of the actual temperature of the thermal stimulus. In addition these trial-continuation task-related responses were also noted during trials without a thermal stimulus, in which the trigger cue was the onset of a light (in a visual task).(ABSTRACT TRUNCATED AT 400 WORDS)     

Immunohistochemical study of delta and mu opioid receptors on synaptic glomeruli with substance P-positive central terminals in chicken dorsal horn

In an attempt to clarify the mechanism underlying the regulation of the release of substance P (SP) from the central axon terminals of the synaptic glomeruli in lamina II of the dorsal horn, we examined the expression patterns of delta and mu opioid receptors (DOR and MOR) in relation to those of enkephalin (ENK) and SP in the synaptic glomeruli. DOR, MOR, ENK and SP immunoreactivities in lamina II of the dorsal horn in the chicken were examined by confocal laser scanning and electron microscopies. DOR immunoreactivity was localized in both SP-positive central terminals and peripheral elements, while MOR immunoreactivity was only localized in the peripheral elements of the synaptic glomeruli. Both of the peripheral DOR- and MOR-immunoreactive elements were shown to be vesicle-containing dendrites by electron microscopy. Dual immunohistochemistry indicated that DOR, MOR and ENK immunoreactivities were located in distinct peripheral elements. On the basis of present results, the possible roles of DOR and MOR in the regulation of the release of SP from the central axon terminals in the synaptic glomeruli are discussed.     

Light microscopic and ultrastructural localization of immunoreactive substance P in the dorsal horn of monkey spinal cord

Light- and electron-microscopic localization of substance P in the monkey spinal cord was studied by the peroxidase anti-peroxidase technique with the particular aim of examining types of interactions made by substance P-positive boutons with other neuronal elements in the dorsal horn. By light-microscopy dense labeling for immunoreactive substance P was found in laminae I, II (outer zone) and V (lateral region), consistent with findings in other mammalian species. By electron-microscopy, substance P-positive staining was mostly in unmyelinated and in some thinly myelinated small diameter fibers. Substance P-positive terminals contained both large granular vesicles (80-120 nm diameter), which were filled with reaction product, and clear round vesicles (40-60 nm). Substance P-positive large granular vesicles were sometimes observed near presynaptic sites and in contact with dense projection there. Immunoreactive substance P boutons were small to large in size (1-4 micron), formed synapses with somata and large dendrites and were the central axons of synaptic glomeruli where they were in synaptic contact with numerous small dendrites and spines. Substance P-labeled axons frequently formed synapses with dorsal horn neurons which were also postsynaptic to other types of axons. Substance P-positive profiles participated in numerous puncta adhaerentia with unlabeled cell bodies, dendrites and axons. Only rarely, some suggestive evidence was obtained indicating that axons might synapse onto substance P-containing boutons. Biochemical analysis of monkey spinal cord tissue extracts, undertaken to characterize more precisely the immunoreactive substances, indicated that only substance P and its oxide derivative were detected with the antiserum used in the immunocytochemistry. These morphological findings show that substance P is contained within a class of axon terminals, many of which have been shown previously in the monkey to originate from the dorsal root. The results suggest that modulation of substance P primary afferents terminating in the outer dorsal laminae of the monkey spinal cord occurs in part via axonal inputs onto dorsal horn neurons postsynaptic to the primary afferent.     

A light and electron microscopic study of serotonin-immunoreactive fibers and terminals in the monkey sensory-motor cortex

Summary Immunocytochemical methods were used to study the distribution and ultrastructure of serotonin (5-hydroxytryptamine; 5-HT) immunoreactive fibers innervating the monkey sensory-motor cortex. Beaded 5-HT positive fibers were found in all cortical layers of both areas but with relatively fewer in middle cortical layers. Examination of 2 m-thick plastic sections at the light microscope level, revealed that the vast majority of the bouton-like structures on the fibers lay in the neuropil and not adjacent to neuronal somata. A few beaded immunoreactive fibers were seen around certain pyramidal and nonpyramidal cell somata, very occasionally forming modest pericellular ramifications. Serial reconstructions made from electron micrographs after resectioning the 2 m-thick sections, revealed that the dilatations of the fibers are 5-HT positive boutons but the boutons examined rarely formed morphologically identifiable synaptic contacts. Of 191 reconstructed boutons only 5 made contacts with obvious membrane specializations, all of which were of the asymmetrical type. No immunoreactive synaptic contacts were seen on pyramidal cell somata in the cortex, nor on dendrites or somata in the white matter underlying the cortex, although 5-HT positive boutons commonly lay closely adjacent to neuronal profiles in both sites. 5-HT fibers in the cortex and white matter have a similar morphological appearance and both myelinated and unmyelinated types are seen.     

Serotonergic innervation of the dorsal horn of rat spinal cord: light and electron microscopic immunocytochemical study

Summary The ultrastructure of serotonergic projections to the dorsal horn of the rat spinal cord has been investigated, using a highly specific polyclonal antiserum. The highest concentrations of immunoreactive profiles were found in lamina I and the outer part of lamina II (IIo). Intermediate concentrations were found in laminae III and IV, while the inner part of lamina II (IIi) was almost devoid of immunoreactivity. Whereas 60% of the profiles show at least one varicosity studded with synaptic vesicles, only one-fifth of the latter contributes to classical synapses, the remaining profiles being devoid of a facing postsynaptic density. The results are compared with those in the literature and our own results relative to other regions of the cord. It is concluded that the pauci-synaptic projections to the dorsal horn could correspond to a diffuse influence of serotonin, the targets for which are determined by the corresponding serotonergic receptors.     

Endomorphin-2 immunoreactivity in the cervical dorsal horn of the rat spinal cord at the electron microscopic level

Endomorphin-2 is a newly discovered endogenous opioid peptide with high affinity and selectivity for the micro-opioid receptor, and potent analgesic activity, particularly in the spinal cord. Using immunoelectron microscopy, we examined the ultrastructure of the endomorphin-2-like immunoreactive processes and their synaptic relationships in the spinal cord. Endomorphin-2-like immunopositive dense-cored vesicles were observed in many axon terminals, and, in a few cases, were observed together with immunonegative dense-cored vesicles. Immunopositive axons with or without myelination were also observed. The endomorphin-2-like immunoreactive axon terminals formed synapses with both immunopositive and immunonegative processes. Most synapses were asymmetrical, but symmetrical synapses were also found. Examples of axo-dendritic, axo-somatic and axo-axonic contacts were observed.This first demonstration of the ultrastructure and synaptic relationships of endomorphin-2-like immunoreactive axon terminals in the spinal cord dorsal horn provides morphological evidence that this peptide functions as a transmitter regulating pain processes.     

Immunocytochemical and electron microscopic study of serotonin neuronal organization in the dorsal raphe nucleus of the monkey

Serotonin neurons in the dorsal raphe nucleus were identified using an antibody to a serotonin-bovine serum albumin conjugate and the peroxidase anti-peroxidase method. Nerve cell bodies showing serotonin-like immunoreactivity ranged in size from 15 to 22 micron in diameter; their dendrites were also immunoreactive. Immunostaining was present in the cytoplasmic matrix, outer membranes of mitochondria, rough endoplasmic reticulum, multivesicular bodies and dense-cored vesicles. Heavily immunoreactive axonal varicosities contained small round vesicles (18-35 nm) and larger dense-cored vesicles (50-90 nm). Both unmyelinated (0.2-0.5 micron) and myelinated (0.8-1.1 micron) serotonin-like immunoreactive axons were found, often interspersed within bundles of similar caliber unlabeled axons. Serotonin-like immunoreactive somata and dendrites were postsynaptic to numerous unlabeled terminals that contained either (a) clear round vesicles (18-25 nm) with many small dense-cored vesicles (30-50 nm), (b) clear round vesicles (18-25 nm) with large dense-cored vesicles (90-110 nm) or (c) clear round vesicles (18-25 nm) with or without flat vesicles. In addition pairs of unlabeled terminals formed crest synapses onto serotonin-like immunoreactive dendritic spines. This variety of unlabeled terminals making contact with serotonin-like immunoreactive elements suggests that several neuronal systems with possibly different transmitters may regulate serotonin raphe neurons. We occasionally observed serotonin-like immunoreactive dendrites and terminals in apposition to other serotonin-like immunoreactive dendrites with membrane specializations at the site of contact. This might represent a possible site for the self inhibition of serotoninergic neurons reported in physiological studies of the serotonin system in the dorsal raphe nucleus.     

Presynaptic modulation by neuromedin U of sensory synaptic transmission in rat spinal dorsal horn neurones

Neuromedin U (NMU) is a brain–gut peptide first isolated from the spinal cord. Recent studies on NMU and its receptors have suggested a role of NMU in sensory transmission. Here we report on the localization of NMU in sensory neurones, and the actions of NMU in the substantia gelatinosa (SG) and the deep layer of the dorsal horn (laminae III–V) in adult rat spinal cord slices using the patch-clamp technique. An immunohistochemical study revealed that NMU peptide was present in most of the dorsal root ganglion neurones. In the spinal cord, NMU-immunoreactive neurones were located in the deep layer (laminae III–V), but not in the SG. However, NMU-positive axon terminals were observed in the SG as well as the deep layer. Bath-applied NMU (10 μ m ) increased the frequency, but not amplitude, of miniature excitatory postsynaptic currents (mEPSCs) in the SG and deep layer neurones by 146 ± 14% ( P < 0.01, n = 17) and 174 ± 21% ( P < 0.01, n = 6), respectively, without inducing any postsynaptic membrane currents recorded in tetrodotoxin. On the other hand, NMU did not affect miniature inhibitory postsynaptic currents recorded in tetrodotoxin. These findings, taken together, suggest that NMU acts on the presynaptic terminals of the primary afferent fibres working as an autocrine/paracrine neuromodulator to increase mEPSC frequency of the SG and deep layer neurones. This may account for the spinal mechanisms of the NMU-induced hyperalgesia reported previously.     

免疫介导脊髓前、后角损伤的对比

目的:探讨实验性自身免疫性灰质病作为肌萎缩侧索硬化(ALS)研究模型的可行性.方法:通过免疫组织化学方法,观察实验性自身免疫性脊髓灰质病过程中脊髓前、后角神经元损伤的特征.结果:神经丝轻链(NF-L)、细胞周期素依赖蛋白激酶5(CDK5)及其激活因子P35/P25抗体阳性的脊髓前角运动神经元数量与对照组相比均明显减少,而脊髓后角阳性的神经元数量与对照组相比差异无统计学意义.结论:在实验性自身免疫性灰质病发病过程中,存在脊髓前角运动神经元相对易感性,实验性自身免疫性灰质病模型在某种程度上可以作为ALS研究模型.     

The effects of dorsal rhizotomy and spinal cord isolation on calcitonin gene-related peptide-labeled terminals in the rat lumbar dorsal horn

In the present study, the origin of calcitonin gene-related peptide (CGRP) to the dorsal horn in the rat lumbar spinal cord is investigated. CGRP immunoreactivity is examined following multiple unilateral and bilateral dorsal rhizotomies and isolated cord preparations (spinal cords are isolated by transecting the cord in two places and cutting all dorsal roots between the transections). Seven to 11 days after surgery, unilateral multiple dorsal rhizotomies result in a drastic decrease in CGRP-stained terminals on the operated side; following bilateral dorsal rhizotomies and isolated cord preparations, one or two CGRP varicosities remain in the dorsal horn in each section. The numbers of CGRP-immunostained varicosities observed in the latter two preparations are not significantly different, suggesting that few if any axons descending from the brain contribute to the CGRP terminal population in the spinal cord dorsal horn. Based on these data, we hypothesize that dorsal root ganglion cells are the only source of CGRP to the rat lumbar dorsal horn.     

Primary afferent interactions: analysis of calcitonin gene-related peptide-immunoreactive terminals in contact with unlabeled and GABA-immunoreactive profiles in the monkey dorsal horn.

The present study analyses the relationship of calcitonin gene-related peptide (CGRP)-immunoreactive primary afferent terminals with unlabeled and GABA-immunoreactive profiles in the primate (Macaca fascicularis) dorsal horn. One-hundred CGRP-immunoreactive terminals located in the superficial dorsal horn were quantitatively analysed and all profiles in apposition or in synaptic contact with these terminals were categorized as either axon terminals or dendrites with or without vesicles. These profiles were then further classified as to whether they were GABA-immunoreactive. All of the CGRP-immunoreactive terminals demonstrated axodendritic interactions; in addition to dendrites without vesicles, approximately half of the CGRP-immunoreactive terminals had dendrites with vesicles as postsynaptic elements. Of the dendrites with vesicles, 25/53 were GABAergic but only 3/67 of the postsynaptic dendrites without vesicles were GABAergic. GABAergic vesicle-containing dendrites were the most prominent CGRP-GABAergic interaction. Axoaxonic and dendroaxonic interactions were a rare occurrence, thus the classical anatomical substrate for primary afferent depolarization involving GABA- and CGRP-immunoreactive terminals could not be substantiated. CGRP-GABAergic interactions often involved diadic and triadic arrangements. These findings are discussed in relation to previously described primary afferent synaptology, primary afferent-GABAergic interactions and spinal cord mechanisms for modulation of noxious input.     

Reevaluation of synaptic relationships of cerebellar terminals in the ventral lateral nucleus of the rhesus monkey thalamus based on serial section analysis and three-dimensional reconstruction

Terminals of cerebellar afferents (CB) to different regions of the ventral lateral nucleus (VL) of the rhesus monkey thalamus were labeled with wheat germ agglutinin-horseradish peroxidase following injections into the dentate nucleus. Synaptic relationships of 17 CB with projection neuron dendrites (PNd) and local circuit neuron dendrites (LCNd) were analyzed in serial ultrathin sections from dorsal and ventral VL regions, which are known to differ cytoarchitecturally and functionally. Three terminals were reconstructed using three-dimensional (3D) computer image analysis techniques to obtain volumetric and planar measurements. CB in the ventral VL were often flat and elongated with synaptic vesicles arranged in clusters. Each CB was engaged with one PNd and one to four LCNd. A single bouton formed 8–50 synaptic contacts, with those on PNd outnumbering the ones on LCNd 4.11. Only some CB in the ventral VL were engaged in complex synaptic arrangements such as triads and serial synapses. Most CB in the dorsal VL displayed a roundish shape and numerous uniformly distributed synaptic vesicles. They formed 5–25 synaptic contacts with a 31 ratio of contacts on PNd compared with those on LCNd. CB in the dorsal VL participated in a variety of complex synaptic arrangements. Two types of triads were found: classic with CB, PNd and LCNd, and unconventional with CB and two LCNd. CB were also involved in serial synapses with two LCNd or LCNd and another PNd, and serial sequential synapses with two LCNd and a PNd. Three glomerulus-like structures were encountered in the dorsal VL. 3D reconstruction and volumetric measurements revealed that synaptic contacts formed by CB on PNd had varying shapes and sizes (0.022–0.274 m²). Synapses formed on LCNd were larger (0.09–0.407 m²). The total area of all active zones of a single CB on LCNd was either equal to or about 40% smaller than that of synapses on PNd. The entire active zone area comprised 1–1.6% of the total CB surface area and did not seem to correlate with the volume. Synaptic contacts formed by associated LCNd on PNd in complex arrangements were usually small (0.021–0.044 m²). The results suggest that: synapses formed by CB on PNd and LCNd, and synapses formed by LCNd on PNd may differ in strength; a variety of different circuits participate in the processing of cerebellar afferent information in the primate VL; and these circuits differ in functionally different VL subdivisions.