Benzodiazepine binding increases in the superficial laminae of the trigeminal subnucleus caudalis following central rhizotomy

Benzodiazepine (BZ) binding is being studied in the spinal trigeminal nucleus of the cat 3 and 11 days following unilateral retrogasserian rhizotomy using in vitro autoradiography and computer-assisted densitometry. At 3 days following rhizotomy there is an increase in number and decrease in affinity of flunitrazepam binding sites in the superficial laminae of subnucleus caudalis of the spinal trigeminal complex. By 11 days, affinity remains below control values and binding site number shows an insignificant but detectable increase. There is no change in binding site characteristics in deeper laminae at either survival time. The results are discussed in relation to the physiological hyperactivity and synaptic changes which occur following such lesions and to other conditions of deafferentation.     

Contralateral degeneration in the cat spinal trigeminal nucleus following unilateral retrogasserian trigeminal rhizotomy.

Retrogasserian trigeminal rhizotomy was used to study the central projections and patterns of degeneration in the spinal trigeminal nucleus (STN). At survival times of 3-20 days, reduced silver stains show extensive degeneration throughout the ipsilateral STN and in addition, well delineated degeneration was identified in the periobex region of the contralateral STN that varied with survival time. The results suggest that primary afferents may contribute to this contralateral projection.     

Ultrastructure of supraspinal dorsal root projections in the toad. II. The cerebellar granular layer

Summary Following section of the left dorsal roots, degenerating fibres and boutons were observed in the granular layer of the ipsilateral cerebellum. The degenerating terminals were identified as largeen passant varicosities of mossy fibres contacting the dendrites of presumptive granule cells. They contained round synaptic vesicles and neurofilaments and established Gray type I contacts. The terminals initially underwent filamentous degeneration with neurofilamentous hypertrophy, swollen mitochondria and loss of synaptic vesicles. At later survival times (6–30 days) they acquired an electron-dense appearance due to an increase and clumping of the filamentous component.After injection of horseradish peroxidase into the left cerebellum, all ipsilateral spinal ganglia showed a few (2–3%) labelled cells, indicating that a primary afferent contribution to this pathway originated from each segment of the spinal cord.     

The electron microscopic localization of methionine-enkephalin within the superficial layers (I and II) of the spinal cord

The synaptic relationships of methionine-enkephalin containing axon terminals within layers I and II of the rat spinal cord have been investigated using immunocytochemical techniques. Labelled terminals contained large numbers of spherical synaptic vesicles and formed synaptic contacts with dendritic shafts and spines and to a lesser extent with cell bodies within the superficial layers of the dorsal horn. A large number of labelled terminals were seen in apposition to profiles containing pleomorphic vesicles, particularly within layer I and outer layer II. Following rhizotomy, degenerating primary afferent axon terminals were found throughout layers I and II but only in one case was a synaptic relationship with a labelled terminal observed.Thus we were unable to find a morphological correlate of the reported effects of opiates on sensory axons and terminals.     

部分去传入猫脊髓背核突触性终末的可塑性变化——电镜定量研究

本实验用猫单侧后肢背根备用模型(切断L_1-L_5、L_7-S_2背根,保留L_6背根),应用光镜体视学计量分析背核和背核神经毡的横切面积;电镜定量研究背核神经毡内三种突触性终末的数量变化。结果显示:实验侧L_3背核及背核神经毡的横切面积未因去传入而发生皱缩;实验侧单位面积内突触性终末总数和活性带数量保持不变,其中来源于背根的巨大终末数还保留对照侧的75%,而来源于L_4以下脊髓中间神经元的小扣型终末数增加了70%;上述两类含圆形小泡的终末总数保持不变;来源于背核边缘细胞的扁平小泡终末数与列照侧无显著性差异。上述结果表明去大部分后肢背根后,在背核内引起了备用背根(L_6)的同型出芽和其它来源轴突的异型出芽,并重建了突触联系。因而从数量上完全代偿了丢失的终末。     

Evidence for a bilateral ‘glomerular’ projection from the red nucleus to the spinal nucleus of the trigeminal nerve in the cat

Following unilateral lesions in the rostral, dorsolateral portion of the red nucleus degenerating fibers were observed bilaterally in the spinal nucleus of the trigeminal nerve. Of particular note, the degeneration within the alaminar, parvocellular portion of the nucleus terminated in a striking glomerular pattern. Lesion of the caudal and medial portion of the red nucleus, or the tegmentum rostral and lateral to the red nucleus produced no such pattern of degeneration. The results demonstrate the existence of a previously unknown bilateral projection from the red nucleus to the spinal trigeminal complex in the cat.     

腰骶背根全切猫脊髓Ⅱ板层突触性终末的代偿性变化──电镜定量分析

为深入探索脊髓的可塑性变化规律，用５只单侧腰骶背根全切猫，术后存活３～４个月。发现实验侧脊髓Ⅱ板层内背根来源的复合终末数下降至正常的２４％；非背根来源的简单终末数却增加至正常的１３４％；还新发现了一类双重突触性终末，本文将之称为非典型复合终末。上述变化使突触总数仍维持在正常水平。在Ｌ＿６节段的简单终末中，形成对称性突触的简单终末，其增幅（７１％）显著地大于形成非对称性突触者（３６％）；含有致密核心小泡的简单终末，其增幅（１１９％）又明显地大于仅含清亮小泡者（３４％）。这种简单终末各亚类的增幅不同，可能与丢失大量背根来源的复合终末后进行的机能调整有关。还发现一个树突截面上同时与两个简单终末形成突触的机率增加了４４％。其中含一个对称性突触者更成倍增加，达正常的２１９％。表明新形成的简单终末，除与丢失终末存留的突触后部位恢复突触性联系外，还可能有新的突触性联系形成。     

Early forms of terminal degeneration in the spinal trigeminal nucleus following rhizotomy

Summary Pars interpolaris of the spinal trigeminal nucleus in adult cats has been studied with the electron microscope at several early and consecutive postoperative survival times following retrogasserian rhizotomy. The results show that several different forms of degenerative changes occur in the axon terminals and some of these forms may be interpreted as stages in certain sequences of terminal degeneration.Synaptic vesicle depletion and mitochondrial alterations are probably the earliest changes in some terminals, but the occurrence of completely different forms also at very early survival times suggest that other processes may be involved. Electron-dense forms of terminal degeneration of later survivals are suggested as arising from any of at least four possible types or classes of earlier alterations based upon presence or absence of vesicles and neurofilaments and on the mitochondrial changes. Electron-lucent forms probably progress to dense types with time but may account for only a proportion of the later dense forms.All types of neuroglia, or reactive glia, and a possible third glia are involved in early and rapid phagocytosis and denudation of post-synaptic sites at times earlier than previously reported.The study also confirms a previous study of a time-related degeneration pattern in the same area and offers an explanation for this pattern.     

Synaptic organization of the cat entopeduncular nucleus with special reference to the relationship between the afferents to entopedunculothalamic projection neurons: An electron microscope study by a combined degeneration and horseradish peroxidase tracing technique

The synaptic organization of the feline entopeduncular nucleus was studied electron microscopically. After horseradish peroxidase injections into the ventral anterior and ventral lateral nuclear complex of the thalamus, normal axon terminals synapsing with entopedunculothalamic projection neurons were classified into four types on the basis of the size and shape of synaptic vesicles in them, and types of the postsynaptic membrane differentiation. Type I and type II axon terminals were characterized by symmetrical synaptic contacts, and large ovoid or small ovoid synaptic vesicles, respectively. Type II axon terminals were further classified into two subtypes as to their sizes: one was small (IIa), the other large (IIb). Type III and type IV axon terminals were characterized by asymmetrical synaptic contacts, and large ovoid or small ovoid synaptic vesicles, respectively.

To determine the origin of each type of terminal, electrolytic lesions of the caudate nucleus or the subthalamic nuclear region were combined with horseradish peroxidase injections into the thalamus or the subthalamic nuclear region. After electrolytic lesions of the caudate nucleus, degeneration was seen in type I axon terminals contacting entopedunculothalamic projection neurons. Following electrolysis or horseradish peroxidase injection into the subthalamic nuclear region, type IIa and type IV axon terminals showed degenerations or horseradish peroxidase labelling. Such terminals also synapsed with entopedunculothalamic projection neurons. It was demonstrated that these projection neurons relay the striatal or subthalamic inputs directly to the thalamus. After horseradish peroxidase injection into the thalamus, many labelled type II axon terminals were observed to synapse with entopedunculothalamic projection neurons. Type III axon terminals were left unchanged throughout these experiments. In addition, the entopeduncular neuron was observed to receive convergent inputs from both the caudate nucleus and probably the subthalamic nucleus. Axoaxonal synapses were also found to be involved in the synaptic triad.

These results indicate that type I axon terminals originate from the caudate nucleus, part of type IIa and type IV axon terminals originate from the subthalamic nucleus or caudal to the subthalamic nuclear region, and part of type IIa and type IIb terminals come from intrinsic axon collaterals.     

Spinal projections to the cerebellar nuclei in the cat

Summary Projections from the spinal gray matter to the cerebellar nuclei in the cat have been studied using Nauta's silver technique. Following unilateral section of the ventrolateral cord at the cervical level, heavy degeneration is seen in the nucleus medialis on both sides. Scanty degeneration is present bilaterally in the nucleus interpositus. The degeneration is most intense on the contralateral side. Scanty degeneration is also present bilaterally in subnucleus medialis parvicellularis (SMP) (Flood and Jansen, 1961). No degeneration is seen in nucleus lateralis. Following unilateral section of the dorsolateral cord at the cervical level, scanty degeneration is present bilaterally in nucleus medialis and nucleus interpositus anterior. The degeneration is more pronounced ipsilaterally and is also seen in SMP on both sides. No degeneration is present in nucleus lateralis. Fibers from the ventral and dorsal spinocerebellar tracts (VSCT and DSCT) terminate bilaterally in nuclei medialis and interpositus, with the VSCT as the most important connection.     

猫后肢背根全切后背核突触性终末的可塑性—电镜定量研究

用超微结构定量法,观察分析了猫脊髓L_3节段背核内三种突触性终末在后肢背根(L_1～S_2)全切后的数量变化。术后动物存活4～10个月,以对侧为对照。在测得实验侧背核面积无变化的情况下,比较了两侧单位面积内终末的数目变化。结果证明,背核单位面积内终末总数保持不变。其中背根来源的巨大终末数还残存正常水平的50％;而来源于中间神经元和下行传导束的小型终扣样终末数明显增加(增加了109％);来源于背核边缘细胞的扁平小泡终末数目无显著性变化。此结果说明,当去除了背核全部后肢背根传入后,发生了相邻部位背根,如尾侧骶尾背根和非背根来源的神经纤维的侧支出芽和突触重建,以代偿损伤脱落的背根终末。此结果支持背核具有可塑性的看法,为中枢神经系统突触水平的可塑性增添了新的资料。     

Fine structure of the dorsal part of the nucleus submedius of the rat thalamus: an anatomical study with reference to possible pain pathways

The dorsal portion of the nucleus submedius of the rat thalamus receives spinal and trigeminal projections which may convey noxious inputs. The present study was undertaken to analyse the fine structure of the nucleus with particular reference to a possible trigemino-thalamo-prefrontal cortical pathway relaying in nucleus submedius. Presynaptic terminals in the dorsal portion of the nucleus submedius were classified into three broad categories usually observed in thalamic nuclei: "small round", "flat" and "large round" types. Axonal tracing using either anterograde transport of horseradish peroxidase or degeneration methods indicated that some "small round" terminals originate from the pre-frontal cortex. Some "large round" terminals were labelled from the trigeminal subnucleus caudalis. These "large round" terminals exhibited distinct morphological features when compared with trigeminal terminals in other thalamic nuclei. In particular they made synaptic contacts predominantly with dendritic protrusions and were surrounded by multilamellate astrocytic processes. Double-labelling experiments were performed by means of the combined retrograde transport of horseradish peroxidase and Wallerian degradation techniques. Terminals degrading after lesion of the trigeminal subnucleus caudalis contacted submedius neurons labelled retrogradely from the prefrontal cortex. These observations demonstrate the existence of a direct monosynaptically relayed pathway from subnucleus caudalis to prefrontal cortex which relays in the dorsal part of nucleus submedius.     

Axon hillocks and initial segments in spinal trigeminal nucleus with emphasis on synapses including axo-axo-axonic contacts

Summary As a part of a continuing study of the feline spinal trigeminal nucleus, the fine structure and synaptic arrangements on the axon hillock and axon initial segment of neurons in this region are described here. Transmission electron microscopy has been used to characterize qualitatively the axon hillock and initial segment and associated synapses in pars interpolaris. Axon hillocks and initial segments are easily identified in continuity with somata or as isolated profiles in the neuropil, and they receive synaptic contacts: these we regard as axo-axonic. The presynaptic terminals contain either mainly round or mainly flattened synaptic vesicles and have Type I (asymmetric) or Type II (symmetric) thickenings respectively at their contacts with the axon hillock or initial segment. I report here also the unusual arrangement of three separate axons in a serial synaptic complex. Some of the round vesicle Type I contacts onto the axon hillock-initial segment region also receive Type II contacts from one or more flattened vesicle terminals, thus formingan axo-axo-axonic complex. These flattened vesicle terminals lack the usual features of a presynaptic dendrite. It has been shown that in this nucleus some round vesicle terminals, especially those postsynaptic to flattened vesicle terminals, are primary afferents from the periphery. Therefore the round vesicle terminal presynaptic to the axon hillock-initial segment region, some of which are included in the axo-axo-axonic complex may also be a primary afferent directly contacting the spike generator area of the relay neuron and under presynaptic control of a flattened vesicle synapse. The latter may possibly be an intrinsic contact. This strategic situation of round vesicle terminals and the axo-axo-axonic complex at the axon hillock or initial segment has major implications relevant to the overall output of these neurons.     

Pallidosubthalamic projection in the Cat

Summary The degenerative changes within the cat's subthalamic nucleus (Sth) following lesions of the external pallidum were studied by electron microscopy.Four to five days following pallidal lesions a great number of terminals undergoing degenerative changes were encountered in the ipsilateral Sth. The contralateral Sth was free of degeneration. The degenerating terminals show predominantly the light degenerative type, less frequently the dark degenerative pattern, and occasionally exhibit signs of filamentous hyperplasia. The degenerated boutons usually insert on perikarya of the large Sth neurons, on proximal dendrites, and more rarely contact dendritic spines. They were observed neither to perform synaptic contacts with the perikarya of the small Sth neurons nor with other vesicle-containing profiles. On the basis of the ultrastructural aspect of the degenerating terminals, they were identified as F1 terminals, discriminated in a previous study (Romansky et al., 1978). The normal appearance, the synaptic relationships, and the degenerative features of the F1 terminals in the Sth closely resemble the entopeduncular terminals in the thalamus described by Rinvik and Grofová (1974a), and Grofová and Rinvik (1974).The possible contribution of the interrupted passing fibers to the observed degeneration is discussed. The present findings corroborate the relevant morphological, physiological, neurochemical, and neuropharmacological data in the literature.     

大鼠后根第一级传入纤维在脊髓胶状质内的溃变和突触联系

用切断后根方法在透射电镜下观察了大鼠后根第一级传入纤维在脊髓胶状质内的溃变和突触联系。切断脊神经后根24小时后,胶状质内出现明显的溃变终末。量最多又持续时间最长的溃变是电子致密型溃变,此外,也观察到了少数的电子透明型溃变和神经微丝型溃变;溃变终末大部分位于胶状质突触小球的中央。据统计,电子致密型溃变作为突触前成分与胶状质内的树突或树突棘形成轴—树突触者占98.8％,作为突触后成分与周围轴突形成轴—轴突触者占1.2％。     

The lateral cervical nucleus in the cat III. An electron microscopical study after transection of spinal afferents

Summary The ultrastructure of terminal degeneration within the lateral cervical nucleus (LCN) after transection of its spinal afferent fibers 2 days–2 years earlier is described. The degeneration after 2 days was of both the neurofilamentous and dense type. The highest number of degenerating terminals, about 15%, was found after 4–5 days. Then most of the degenerating boutons were of the dense type. The degenerating terminals had synaptic contact with cell bodies and dendrites of LCN-neurons. Removal of the degenerating boutons seemed to be effected by a phagocytic cell present in increased number compared to the normal LCN. In cases with long survival times an increase in the number of astroglial filaments was observed. In an animal where the spinal afferents to the LCN had been cut 2 years earlier a decrease in medium size of the neurons was observed. The amount of dendritic spines was also considerably smaller than normally.     

Ultrastructure of somatostatin-immunoreactive nerve terminals in laminae I and II of the rat trigeminal subnucleus caudalis.

The morphology and distribution of somatostatin-immunoreactive synaptic boutons was studied in the rat trigeminal subnucleus caudalis using pre-embedding electron microscopic techniques. Immunoreactive terminals were found in lamina I and throughout lamina II but were more concentrated in outer lamina II. All immunoreactive terminals contained many round or pleomorphic agranular small synaptic vesicles and some large dense-cored vesicles. Lamina I terminals were all simple dome-shaped and relatively small. They established one asymmetric or slightly asymmetric synapse over a dendritic spine or a small, medium or large dendritic shaft. The large dendrites are probably derived from Waldeyer neurons. Many lamina II immunoreactive terminals were also simple dome-shaped terminals and established asymmetric synaptic contacts with one postsynaptic structure, usually a dendritic spine or a small to medium-sized dendritic shaft. However, other lamina II immunoreactive terminals were larger and displayed more complex morphology and synaptology. Complex immunoreactive terminals had scalloped or smooth contours and made synaptic contacts with more than one postsynaptic profile. In outer lamina II they sometimes constituted the central terminals of typical glomerular synaptic complexes. We conclude that many of the immunoreactive simple terminals probably originate from intrinsic somatostatin-immunoreactive interneurons while some of the more complex ones and the central glomerular terminals are likely to originate from primary afferents. These results are consistent with our accompanying light microscopic study (Alvarez and Priestley, Neuroscience 38, 343-357, 1990) which indicates that somatostatin-immunoreactive primary afferents project preferentially to outer lamina II while the lamina I somatostatin-immunoreactive plexus is likely to originate largely from laminae I and II interneurons. In addition somatostatin-immunoreactive cell bodies were found in lamina II. The heaviest immunoreactivity in these cells was in the Golgi apparatus. Also some vesicles containing dendrites were immunostained, and these were most abundant in inner lamina II. Thus, in trigeminal subnucleus caudalis, somatostatin may be derived from primary afferent synaptic boutons, interneuron synaptic boutons and interneuron dendrites. However, each of these sites probably makes a proportionately different contribution to the total amount of somatostatin released in each lamina or sublamina.     

Leucine-enkephalin-like immunoreactive afferent fibers to pudendal motoneurons in the cat

Leucine-enkephalin-like immunoreactive (ENK-LI) afferent fibers to the feline homologue of the Onuf's nucleus (pudendal motoneurons) originate mainly from lamina X of the sacral cord. They make synaptic contacts chiefly upon dendrites of pudendal motoneurons; the synaptic terminals most often contain pleomorphic synaptic vesicles and occasionally round synaptic vesicles. Large-cored vesicles in the axon terminals within the Onuf's nucleus often showed ENK-LI.     

Jaw-muscle spindle afferent feedback to the cervical spinal cord in the rat

Putative synaptic contacts between masticatory-muscle spindle afferents and brainstem neurons which project to the cervical spinal cord were studied in rats by combining retrograde and intracellular neuronal labeling. Spinal cord projecting neurons were retrogradely labeled via injection of horseradish peroxidase unilaterally or bilaterally into cervical spinal cord segments C2 through C5. Twenty-four hours after the injection of horseradish peroxidase, one to five jaw-muscle spindle afferent axons were physiologically identified and intracellularly stained with biotinamide on each side of the brainstem. Horseradish-peroxidase-labeled neurons were found bilaterally in the supratrigeminal region, trigeminal principal sensory nucleus, parvicellular reticular nucleus including its alpha division, spinal trigeminal subnuclei oralis and interpolaris and the medullary reticular formation. Retrogradely labeled neurons were most numerous in the spinal trigeminal subnucleus oralis, parvicellular reticular formation and the ventral part of the spinal trigeminal subnucleus interpolaris. A small number of horseradish-peroxidase-labeled neurons were also present in the trigeminal mesencephalic nucleus and spinal trigeminal subnucleus caudalis. Appositions between jaw-muscle spindle afferent boutons and spinal projecting neurons were found in the supratrigeminal region, dorsomedial portions of the trigeminal principal sensory nucleus and spinal trigeminal subnuclei oralis and interpolaris, and the parvicellular reticular formation including its alpha division. Putative synaptic contacts were most frequent in the parvicellular reticular formation and the dorsomedial portion of the trigeminal subnucleus oralis. These results indicate that some orofacial proprioceptive feedback transmitted via the mesencephalic trigeminal nucleus reaches the cervical spinal cord directly and suggests that jaw-muscle spindle afferent feedback reaches the cervical spinal cord predominately via relays in the dorsomedial part of the spinal trigeminal subnucleus oralis and the parvicellular reticular formation. It is hypothesized that these pathways are primarily involved in the coordination of jaw and neck movement during mastication and biting. Materials and methods 27 January 1999 / Accepted: 9 May 1999     

Ultrastructure of degenerative changes following ricin application to feline dental pulps

Summary The ultrastructure of degenerative changes within the ipsilateral trigeminal ganglion, and partes caudalis and interpolaris of the spinal trigeminal nucleus in the cat is described following the application of the potent toxin ricin to the tooth pulps of unilateral maxillary and mandibular posterior teeth, including the cuspids. Survival times ranged from 6 to 10 days. Typical changes identified within the ipsilateral trigeminal ganglion included myelin fragmentation and compartmentalization of the axoplasm of medium-sized myelinated axons, while small myelinated and unmyelinated axons underwent a more variable response ranging from electron-lucent to electron-dense changes. The affected cell body was characterized by the presence of swollen, electron-lucent mitochondria, a reduction of cytoplasmic ribosomes and a filamentous hyperplasia. Other changes often included an eccentric nucleus and satellite cell proliferation. Degenerative changes often occurred in isolated elements surrounded by normal profiles, suggesting specificity of ricin within the trigeminal ganglion. Changes within brainstem axons showed both an electron-dense and a lucent, fragmenting type of axonal alteration. Terminal changes ranged from electron-dense to lucent and also included filamentous hyperplasia and hyperglycogenesis. The altered axonal knobs contained round synaptic vesicles that were presynaptic to dendritic profiles and postsynaptic to terminals containing flattened synaptic vesicles. The above brainstem alterations were identified specifically in the following areas: ventrolateral, medial and dorsomedial pars interpolaris; the ventrolateral and mid-dorsal to dorsomedial areas of the marginalis and outer substantia gelatinosa layers of pars caudalis; and in ventral pockets corresponding to lamina V of the medullary dorsal horn. Dense alterations within terminals containing flattened synaptic vesicles that are typically presynaptic to primary afferents in these areas were rare findings, but along with vacuolization of dendritic profiles suggest a trans-synaptic effect possibly due to the exocytosis of ricin. The results are discussed in relation to different reports of dental projections and with regards to patterns of transganglionic degeneration.