三叉神经尾侧脊束核内P物质纤维终末的超微结构

目的　进一步探讨三叉神经尾侧脊束核内SP免疫反应阳性纤维在感觉传递中的可能作用。方法　SP采用免疫细胞化学方法和电子显微镜方法 ,观察大鼠三叉神经尾侧脊束核内SP阳性标记纤维的超微结构和突触联系。结果　SP轴突终末分布于树突间 ,这些轴突终末含有大量的透明小泡、少量大致密芯小泡和线粒体。经过秋水仙素处理后 ,可见到SP免疫反应阳性树突。多数SP轴突终末与非标记树突 ,以及个别SP轴突终末与SP树突形成轴 树突触。含SP的突触复合体较为多见 ,为会聚型。其中可见SP轴突终末与中心的非标记树突形成GrayⅡ型轴 树突触 ;另有非标记的轴突终末与中心SP树突形成 (扁平小泡形 )F型轴 树突触。结论　三叉神经尾侧脊束核接受多种纤维传入 ,SP纤维只是多种传入纤维中的一种。形态学证明 ,在痛调制活动中 ,三叉神经尾侧脊束核内有SP纤维构成的突触后抑制类型 (GrayⅡ )突触参与。     

大鼠下丘脑弓状核突触的衰老性变化

用透射电镜结合体视学方法，对３月龄、１０月龄和３０～３４月龄大鼠弓状核突触进行了定性和定量研究。结果显示：老龄组大鼠神经毯呈萎缩变性相，大树突内脂褐素增多，小到中等大小的树突出现空泡变性、多泡体和膜被多层体等，棘萎缩减少；轴突终末内突触囊泡减少而大颗粒囊泡积聚，部分突触前、后膜变薄、缩短或间断，突触小球少见；轴－体、轴－树和轴－棘突触数减少，突触密度、突触连接带面密度和突触膜总长度降低，ＧｒａｙⅠ型和即Ⅱ型突触间隙增宽。上述结果表明，老年弓状核突触在数量、形态和结构上发生了衰老性改变，这是导致下丘脑神经内分泌衰老障碍的主要原因之一。     

On the identification of the afferent axon terminals in the nucleus lateralis of the cerebellum an electron microscope study

Summary Axon terminals in the neuropil of the lateral nucleus can be divided into six classes, each with a specific constellation of characteristics that consistently occur together. Two of these classes have synaptic varicosities with elliptical synaptic vesicles, one in a dense, the other in a sparse matrix, and both make axosomatic and axodendritic synapses. The remaining four classes all have round synaptic vesicles and do not make axosomatic synapses. In the first of these four, the vesicles are tightly packed in a dense matrix, in another they are loosely dispersed, and in the third they are clustered. In the fourth, large granular vesicles predominate. Of these six classes, the most numerous belong to the axons of the Purkinje cell terminal arborization. These boutons resemble their counterparts in the cerebellar cortex, the recurrent collaterals of the Purkinje axon. They have elliptical and flat synaptic vesicles in a dark matrix. The varicosities terminate on somata and dendrites of large and small neurons and constitute the majority of their input. Purkinje axons constitute 86% of the total population of terminals on large neuronal perikarya and 50% of those on their dendrites, but only 78% on the somata of small neurons and 31% on their dendrites. The terminals of climbing fiber collaterals are recognized by their resemblance in electron micrographs to the terminals of the climbing fiber arborization in the cerebellar cortex. They bear round synaptic vesicles packed into a dense axoplasmic matrix and make Gray's type 1 axodendritic synapses with large and small neurons. These axons are restricted to the lateral and ventral aspects of the nucleus and constitute 5% of the terminals on large cell dendrites and 6% of those on small neurons. The axons tentatively identified as collaterals of mossy fibers are myelinated fibers with a light axoplasm containing round synaptic vesicles, dispersed throughout their varicosities. They make Gray's type 1 synapses and constitute a fair percentage of the total axodendritic contacts in the neuropil, 22% on large neurons and 28% on small neurons. The bases for these tentative identifications are discussed in detail, as are the various synaptic relationships undertaken by each class of axon. The remaining 4 classes of axons of the neuropil will be described in subsequent papers.Supported in part by U.S. Public Health Service grants NS 10536 and NS 03659, Training grant NS 05591 from the National Institute of Neurological Diseases and Stroke, and a William F. Milton Fund Award from Harvard University.     

Quantitative analysis of axodendritic and axosomatic collateral terminals of two feline spinocervical tract cells

Summary The initial axon collaterals of two feline spinocervical tract cells have been ultrastructurally investigated after intracellular injection with horseradish peroxidase. A total of 200 axodendritic and 43 axosomatic terminals were analysed in serial sections. The following variables were measured: the diameter and area of the bouton profiles, the areal densities of synaptic vesicles and mitochondria of the bouton profiles, the width and length of the synaptic clefts, the width of the postsynaptic densities, the width of the postsynaptic dendrites, and the width and length of axons between the boutons. Ten boutons were reconstructed for an investigation of the relation between measurements in two and three dimensions. All the measured variables showed wide ranges of variation. They were analysed statistically for significant differences between the cells and between the axodendritic and axosomatic boutons of each and both cells. Significant differences were mainly observed in the former comparison but they were also found between the axodendritic and axosomatic terminals of the individual cells.     

猫孤束核胶状质亚核的突触构筑学研究

用透射电镜对猫的孤束核胶状质亚核(SNG)的突触型式进行了观察,除看到已报导的轴—树突触、轴—体突触、树—树突触外,还发现该核内含有轴—轴突触及突触球等结构。SNG内轴—树突触最常见,而轴—体突触、轴—轴突触和树—树突触则较少。各类突触中的突触囊泡多为圆形清亮囊泡,而扁平清亮囊泡和大颗粒囊泡较少。扁平清亮囊泡多与圆形清亮囊泡共存于同一轴—轴突触终末内。轴—轴突触均为对称型突触,有时与树突或胞体相连形成轴—轴—树突触或轴—轴—体突触。突触球多为以树突和棘为中心的中心树突型突触球。此外在SNG内还观察到嵴突触,并联突触等连接形式。SNG内突触的复杂性表明传入冲动在该核中可能经过扩散、汇聚和突触前抑制等多种复杂的整合过程调节内脏活动。     

The synaptic connections of basket cell axons in the developing rat hippocampal formation

Summary Recent studies have indicated that hippocampal basket cells in both the dentate gyrus and Ammon's horn develop their somal and dendritic features during the first two postnatal weeks in rats. Their axon terminals form exclusively symmetric synapses that are found as early as 5 postnatal days in both regions. The present study used Golgi-electron microscopic material from 10 and 16 day old rats to demonstrate that the axon terminals of basket cells form synapses not only with somata, dendrites, and dendritic spines as reported for adult material but also with axon initial segments. However, the terminals forming synapses with axon initial segments and dendritic spines represent only a minor portion of the total number of basket cell terminals. Quantitative results indicate that 36–62% of the total number of these terminals form axosomatic synapses and 32–50% form axodendritic synapses depending on the analyzed cell. These data indicate that hippocampal basket cells have an axonal distribution similar to that found for cortical basket cells.     

Quantitative and ultrastructural study of ascending projections to the medial mammillary nucleus in the rat

Summary We analyzed the termination pattern of axons from the superior central nucleus and the ventral tegmental nucleus of Gudden within the medial mammillary nucleus (MM) in the rat. The neuropil of the MM consists of two classes of terminals, that is, terminals containing round synaptic vesicles and forming asymmetric synaptic contact, and terminals containing pleomorphic synaptic vesicles and forming symmetric synaptic contact. The number of axodendritic terminals with round vesicles is almost equal to that of terminals with pleomorphic vesicles. Almost all axosomatic terminals contain pleomorphic vesicles with symmetric synaptic contact. Injection of WGA-HRP into the central part of the superior central nucleus permitted ultrastructural recognition of many anterogradely labeled terminals within the median region of MM. The labeled terminals contacted mainly intermediate (1–2 m diameter) and proximal dendrites (more than 2 m diameter) as well as the neuronal somata. Serial ultrathin sections of neurons of the median region of the MM revealed that 37% of the axosomatic terminals were labeled anterogradely. The pars compacta of the superior central nucleus had reciprocal connections with the median region of MM. The axon terminals from this nucleus occupied 53% of axosomatic terminals, and contacted mainly intermediate dendrites. Following injection of WGA-HRP into the ventral tegmental nucleus, many labeled terminals were found in the medial and lateral regions of MM. They contacted mainly intermediate dendrites as well as neuronal somata. In the medial region, 78% of axosomatic terminals contacting retrogradely labeled neurons were labeled anterogradely. All labeled terminals from these nuclei contained pleomorphic vesicles, and made symmetric synaptic contact.     

皮质丘脑投射神经元的超微结构及突触联系

采用ＨＲＰ逆行追踪技术与电镜相结合的方法，对猫大脑皮质体感Ⅰ区内皮质丘脑投射神经元超微结构及突触联系进行了研究。结果证明，皮质丘脑投射神经元超微结构的特点为锥体形的胞体，胞浆丰富，含有多量的粗面内质网，游离核糖体及线粒体。ＨＲＰ标记的皮质丘脑投射神经元作为突触后成份与轴突和树突分别形成轴－树突触，轴－体突触和树－体实触。这些结果提示：皮质丘脑投射神经元接受广泛的传入联系和皮质间的联系。     

Fine structural studies of synaptogenesis in the superficial layers of the chick optic tectum

Summary Synaptogenesis in the superficial layers of the rostral pole of the optic tectum has been studied in the chick from embryonic day six (E6) to seven days post-hatching. Symmetrical membrane densities orpuncta adhaerentia are observed prior to the detection of synapses and throughout development. Immature synaptic contacts are observed by E7. These early synapses are primarily axodendritic; however, somatodendritic, dendrodendritic, axosomatic and axoglial synapses are also observed. The majority of these synapses have asymmetrical membrane densities and the presynaptic terminals contain clear, spherical, synaptic vesicles. Synaptic terminals containing pleomorphic vesicles and making symmetrical synaptic contacts are not commonly observed until the third week of embryonic development, and may represent the onset of inhibitory function within the tectum.Comparison of the number of synapses per unit area in control versus experimental tecta, after unilateral eye enucleations at E3, indicates that the presynaptic terminals of some synapses present at E8 are of retinal origin. It is suggested that the development of retinotectal synapses follows a rostrocaudal gradient in the tectum and corresponds to the intrinsic tectal pattern of cytoarchitectonic differentiation.     

Synaptic organization of the dorsal lateral geniculate nucleus in the adult hamster

Summary The synaptic organization of the sector of the dorsal lateral geniculate nucleus has been examined by electron microscopy in normal adult hamsters and in adult hamsters subjected to unilateral eye enucleation or intravitreal injection of horseradish peroxidase.Two types of neuropil are apparent. Islands of complex neuropil partially enclosed by astrocyte processes (synaptic glomeruli) are surrounded by a sea of simpler non-glomerular neuropil. The latter is dominated by small axon terminals with spherical synaptic vesicles and Gray type 1 axodendritic contacts (SR-boutons) and also contains axon terminals with flattened synaptic vesicles (F-boutons). The glomerular neuropil contains (i) exclusively postsynaptic dendrites and dendritic protrusions of presumptive projection cells; (ii) pre- and postsynaptic pleomorphic-vesiclecontaining P-boutons (interpreted as appendages of the dendrites of interneurons); (iii) large axon terminals containing spherical synaptic vesicles and large pale mitochondria (R-boutons) which were experimentally identified as retinal terminals and which are presynaptic to both projection cell dendrites and P-boutons at Gray type 1 contacts; (iv) F-boutons (minority component). F-boutons and P-boutons are presynaptic to both projection cell dendrites and P-boutons and P-boutons are the intermediate elements of various serial synapses including triplet (triadic) synapses. Medium-large terminals with spherical synatpic vesicles and dark mitochondria (RLD-boutons) which were commonly invaginated by dendritic spines of projection cells in small glomerulus-like formations were also identified. The origin of RLD-boutons is unknown but SR-boutons probably derive chiefly from ipsilateral visual cortex and possibly also from superior colliculus, and non-glomerular F-boutons probably originate in the ipsilateral thalamic reticular nucleus.No differences in synaptic organization were found between the part of the nucleus which receives uncrossed retinal input and the part which receives crossed input, nor were differences seen in the size, fine structure or relationships between the terminals of identified crossed and uncrossed retinal axons.     

Immunohistochemical distribution of the two isoforms of synaphin/complexin involved in neurotransmitter release: localization at the distinct central nervous system regions and synaptic types

The cellular and subcellular localization of the two synaphin isoforms, proteins associated with the docking/fusion complex crucial to neurotransmitter release, was studied in the rat central nervous system by using light microscopic and electron microscopic immunohistochemistry with monoclonal antibodies specific to each isoform. Synaphin 1 (complexin II) was predominantly expressed in neurons of the central nervous system regions such as cerebral cortex (the II, III and VI cortical layers), claustrum, hippocampus, entorhinal cortex, amygdaloid nuclei, substantia nigra pars compacta, superior colliculus, pontine reticulotegmental nucleus and inferior olive, whereas synaphin 2 (complexin I) was in the cerebral cortex (the IV cortical layer), thalamus, locus coeruleus, gigantocellular reticular field, cuneate nucleus and cerebellar basket and stellate cells. In some regions, including the caudate–putamen, globus pallidus, pontine reticular nucleus, cerebellar nuclei and spinal gray matter, synaphin 1 was mainly present in small or medium-sized neurons, while synaphin 2 was in large cells. Medial habenular nucleus and cerebellar granule cells showed both immunoreactivities. In the neuropil of the cerebral cortex and hippocampus, synaphin 1 expression was accentuated in the axon terminals of axospinal and axodendritic synapses, while synaphin 2 was predominant in the axon terminals of axosomatic synapses. In the axon terminals, both immunolabelings were associated with synaptic vesicles and the plasma membrane, being accentuated in the vicinity of synaptic contacts. In the cerebral cortex, both immunoreactivities were also present occasionally in dendrites and dendritic spines, associated with microtubules and the plasma membrane including the postsynaptic densities.These results suggest that the two isoforms of synaphin are involved in synaptic function at the distinct presynaptic regions in the central nervous system, and that some dendrites are another functional site for the proteins.     

An ultrastructural morphometric study of developing rat substantia gelatinosa

A morphometric analysis has been done on developing rat substantia gelatinosa of the lower cervical and upper thoracic levels of the spinal cord starting on the 15th day of gestation. The following parameters were measured: cell body diameter, cytoplasmic/nuclear areas, synaptic density, synaptic type and vesicle morphology of the presynaptic terminal in axodendritic synapses. Cell body size and cytoplasmic/nuclear areas of gelatinosal cells increase until the 15th day postnatally and then decrease somewhat to the adult values. The first synapses are seen on gestation day 17. Synaptic density increases linearly until the third day postnatally. Axodendritic synapses are most common throughout development and in the adult, while the proportion of axoaxonic synapses increases and axosomatic synapses decreases during development. Most of the terminals in axodendritic synapses contain clear-spherical vesicles but the occurrence of clear-flat vesicles and dense-cored vesicles in the terminals increases during development. It appears that these morphological parameters provide a stable index of development in the substantia gelatinosa which can be correlated with functional development of the area. Hopefully, they will provide a means to assess subtle anomalies induced by nonteratogenic drugs or other environmental changes.     

Synaptic targets of calretinin-containing axon terminals in macaque monkey prefrontal cortex

The coordinated activity of specific populations of pyramidal cells and GABA-containing, local circuit neurons in the primate prefrontal cortex (PFC) appears to be critical for working memory. Different subclasses of GABA-containing neurons can be distinguished by their content of the calcium-binding proteins parvalbumin (PV) and calretinin (CR). The postsynaptic targets of PV-containing cells have been well characterized in the primate PFC, but the postsynaptic targets of CR-containing neurons in this cortical region remain unknown. In the present study, we used immuno-electron microscopy to examine the synaptic type and postsynaptic targets of CR-immunoreactive (IR) axon terminals in the superficial and deep layers of macaque monkey PFC. Labeled axon terminals formed both symmetric and asymmetric synapses. Within the superficial layers, 93% of the synapses formed by CR-IR were symmetric, whereas in the deep layers the labeled axon terminals forming synapses were more evenly divided between symmetric (57%) and asymmetric (43%). The primary postsynaptic target of these two populations of CR-IR axon terminals also differed; unlabeled dendritic shafts were the predominant target of the symmetric synapses, whereas dendritic spines were the most common target of the asymmetric synapses. In addition, the mean cross-sectional area of the terminals forming asymmetric synapses was significantly larger than that of the terminals forming symmetric synapses. The presence of CR-IR asymmetric synapses suggested that they might arise from neurons that do not utilize GABA; indeed, dual-label fluorescent immunocytochemistry revealed that a subpopulation (23%) of CR-containing neurons in monkey PFC were not GABA-IR. These findings indicate that the synaptology of CR-containing neurons is more heterogeneous than that of PV-containing cells and suggests that the contributions of CR-containing neurons to cognitive processes mediated by the PFC may be more diverse.     

Ultrastructural study of ascending projections to the lateral mammillary nucleus of the rat

Summary We examined the synaptic organization of ascending projections from the pars ventralis of the dorsal tegmental nucleus of Gudden (TDV) and the laterodorsal tegmental nucleus to the lateral mammillary nucleus (LM). The LM neuropil consists of terminals containing pleomorphic synaptic vesicles and forming symmetric synaptic contact, and terminals containing round synaptic vesicles and forming asymmetric synaptic contact. They make up 63% and 37%, respectively, of all axodendritic terminals. All axosomatic terminals contain pleomorphic vesicles and make symmetric contact. Following injection of WGA-HRP into the TDV, many anterogradely labeled terminals and retrogradely labeled cells are found in the LM. Labeled terminals contact mainly proximal (more than 2 m diameter) and intermediate (1–2 m diameter) dendrites. Serial ultrathin sections of the LM show that 55% of axosomatic terminals are labeled anterogradely. Following injection of WGA-HRP into the laterodorsal tegmental nucleus, many anterogradely labeled terminals are found in the LM, but no retrogradely labeled cells are present. Labeled terminals contact mainly distal (less than 1 m diameter) and intermediate dendrites as well as somata. In the LM neurons, 46% of axosomatic terminals are labeled anterogradely. All labeled terminals from these nuclei contain pleomorphic vesicles and make symmetric synaptic contact. These results indicate that almost all axosomatic terminals come from the TDV and the laterodorsal tegmental nucleus, which send inhibitory inputs to the lateral mammillary nucleus.     

Electron microscopic study of GABA-immunoreactive neuronal processes in the superficial gray layer of the rat superior colliculus: their relationships with degenerating retinal nerve endings

Summary GABA-immunoreactive neuronal elements were detected in the stratum griseum superficiale or superficial gray layer of the rat superior colliculus in an electron microscopic study, using postembedding immunocytochemistry with protein A-gold as a marker. In addition to neuronal somata, two types of GABA-immunoreactive neuronal processes were observed. Numerous profiles of axon terminals (1 m in diameter) with clear round or pleomorphic synaptic vesicles and mitochondria were found to establish mostly symmetrical synaptic contacts with GABA-immunonegative dendrites of various diameters. Some axosomatic synapses could also be observed. The gold particle density in this axon terminal compartment was between seven and 13 times the background level. The stratum griseum superficiale also included GABA-immunoreactive dendrites, some of which contained clear synaptic vesicles. These dendritic profiles always formed the presynaptic component of dendrodendritic synaptic contacts. The density of the gold particles in the dendritic compartment, taken as a whole, was between three and 13 times the background level. Furthermore, the relationship between the GABA-immunoreactive neuronal elements and degenerating retinal nerve endings identified in the left stratum griseum superficiale following enucleation of the right eye was investigated after a 7-day survival period. The profiles of degenerating retinal nerve endings (0.7 m in diameter) were found to be devoid of any specific labelling. Most of the retinal boutons established axodendritic synapses of the asymmetrical type with an immunonegative dendrite, which was also contacted in some cases by a GABA-immunopositive axon terminal. Other retinal endings were presynaptic to GABA-immunopositive dendritic profiles with synaptic vesicles, some of which were found to contact in turn an unlabelled dendrite, thereby completing serial synaptic relationships. More rarely, retinal endings formed the presynaptic component of possible axoaxonic synapses with GABA-positive terminals presumed to be axonic in nature. It can be concluded that the retinal input to the superficial gray layer often converges with a GABAergic axonal input on a dendritic target, the neurotransmitter specificity of which is unknown. In other cases, retinal terminals synaptically contact GABA-immunolabelled conventional and presynaptic dendrites and probably also some axon terminals; this might provide an anatomical substrate for the control of GABA release from these GABAergic processes. These results indicate that transmitter GABA plays an important role in retinocollicular transmission.     

Synaptic plasticity in the oedematous human cerebral cortex

Synaptic plastic changes are fundamental events which occur spontaneously during development, maturity and aging processes or can be induced by injury or trauma. To examine lesion-induced synaptic plasticity, cortical biopsies were taken from the frontal, parietal, temporal and occipital cortex of living patients during neurosurgical treatment of brain trauma, brain tumours and vascular malformations, and processed for transmission electron microscopy. Enlargement of both pre- and postsynaptic endings, irregularly shaped, lobulated, stellate and bifurcated presynaptic endings and conformational changes of dendritic spines were observed. Numerous flat, curved and invaginated axodendritic and axospinous asymmetric synapses were distinguished and a smaller proportion of axodendritic and axosomatic symmetric synapses. Activated or sensitized synapses showed numerous frontline spheroid synaptic vesicles, prominent dense presynaptic dense projections and increased length of synaptic membrane complex. Perforated synapses, multiple synapses and serial synapses were also found evincing synaptic splitting and formation of new synaptic connections. The overall images suggest increased number of excitatory circuits, which were correlated with the tonico-clonic convulsion or post-traumatic seizures observed in some patients. Numerous coated vesicles were observed in pre- and postsynaptic structures. Increased number of polyribosomes were found in the dendritic shafts. The dilated spine apparatus, the coated vesicles and the increased number of polyribosomes seem to represent a system for synthesis, transport and storage of synaptic proteins for the formation of new synapses. Coexisting synaptic plasticity and synaptic degeneration were observed in the patients under study. Dendritic and astrocyte synapse-like junctions were also characterized.     

A light and electron microscopic analysis of the convergent insular cortical and amygdaloid projections to the posterior lateral hypothalamus in the rat, with special reference to cardiovascular function

The synaptic organization between and among the insular cortex (IC) axons, central amygdaloid nucleus (ACe) axons and posterolateral hypothalamus (PLH) neurons was investigated in the rat using double anterograde tracing and anterograde tracing combined with postembedding immunogold analysis. After ipsilateral injections of biotinylated dextran amine (BDA) into the IC and Phaseolus vulgaris-leucoagglutinin (PHA-L) into the ACe, the conspicuous overlapping distribution of BDA-labeled axon terminals and PHA-L-labeled axon terminals was found in the PLH region just medial to the subthalamic nucleus ipsilateral to the injection sites. At the electron microscopic level, approximately two-thirds of the IC terminals made synapses with small-sized dendrites and the rest did with dendritic spines of the PLH neurons, whereas about 79%, 16% and 5% of the ACe terminals established synapses with small- to medium-sized dendrites, somata, and dendritic spines, respectively, of the PLH neurons. In addition, the IC axon terminals contained densely packed round clear vesicles and their synapses were of asymmetrical type. On the other hand, most of the ACe terminals contained not only pleomorphic clear vesicles but also dense-cored vesicles and their synapses were of symmetrical type although some ACe terminals contained densely packed round clear vesicles and formed asymmetrical synapses. Most of the postsynaptic elements received synaptic inputs from the IC or ACe terminals, and some of single postsynaptic elements received convergent synaptic inputs from both sets of terminals. Furthermore, almost all the ACe terminals were revealed to be immunoreactive for gamma-aminobutyric acid (GABA), by using the anterograde BDA tracing technique combined with immunohistochemistry for GABA. The present data suggest that single PLH neurons are under the excitatory influence of the IC and/or inhibitory influence of the ACe in the circuitry involved in the regulation of cardiovascular functions.     

Catecholamine-containing axon terminals in the hypoglossal nucleus of the rat: an immuno-electronmicroscopic study

Summary A correlative light and electron microscopic investigation was undertaken to determine the morphology and distribution of catecholamine (CA)-containing axon terminals in the hypoglossal nucleus (XII) of the rat. This was accomplished immunocytochemically with antibody to tyrosine hydroxylase (TH). The major findings in this study were the following: 1) Immunoreactive profiles were found throughout XII and included unmyelinated axons, varicosities, axon terminals and dendrites; 2) Nonsynaptic immunoreactive profiles (preterminal axons, varicosities) were more frequently observed (55.2%) than synaptic profiles (43.5%); 3) CA-containing axon terminals ending on dendrites were more numerous (71.8%) than those synapsing on somata (25.4%) or nonlabeled axon terminals (2.7%); 4) The morphology of labeled axon terminals was variable. Axodendritic terminals typically contained numerous small, round agranular vesicles, a few large dense-core vesicles and were associated with either a symmetric or no synaptic specialization, axosomatic terminals were often associated with a presynaptic membrane thickening or a symmetric synaptic specialization and contained small, round and a few elliptical-shaped vesicles, while axoaxonic synapses formed asymmetric postsynaptic specializations; and 5) CA-positive dendritic processes were identified in XII. These findings confirm the CA innervation of XII, and suggest a complex, multifunctional role for CA in controlling oro-lingual motor behavior.