Demonstration of GM1-ganglioside in nervous system in generalized GM1-gangliosidosis using cholera toxin B subunit

Summary By using cholera toxin B subunit and its antibody, the deposition of GM₁-ganglioside in the cerebral cortex and peripheral nerves including Meissner and Auerbach's plexuses in the intestine and other visceral nerves of generalized GM₁-gangliosidosis was demonstrated. The GM₁-ganglioside was found in the swollen neurons of cerebral cortex and ganglion cells of the peripheral nerves. Electron microscopically, parts of membranous cytoplasmic bodies, and amorphous substances among them, revealed a positive reaction for the cholera toxin staining.     

Differential modulatory roles of cholera toxin and pertussis toxin in the regulation of pain responses induced by excitatory amino acids administered intrathecally in mice

The present study was designed to characterize the possible roles of spinally located cholera toxin (CTX)- and pertussis toxin (PTX)-sensitive G-proteins in excitatory amino acids induced pain response. Intrathecal (i.t.) injection of glutamate (20 microg), N-methyl-D-aspartic acid (NMDA; 60 ng), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA; 13 ng), and kainic acid (12 ng) showed pain response. Pretreatment with CTX (0.05 and 0.5 microg, i.t.) attenuated pain response induced by glutamate, NMDA, AMPA and kainic acid administered i.t. in a dose-dependent manner. On the other hand, i.t. pretreatment with PTX further increased the pain response induced by glutamate, NMDA, AMPA and kainic acid administered i.t., especially at the dose of 0.5 microg. Our results suggest that, at the spinal cord level, CTX- and PTX-sensitive G-proteins appear to play opposite roles in modulating the pain response induced by spinally administered. Furthermore, CTX- and PTX-sensitive G-proteins appear to modulate pain response induced by stimuli of both NMDA and non-NMDA glutamate receptors.     

Evidence that cholera toxin B subunit (CTb) can be avidly taken up and transported by fibers of passage

It has been reported that cholera toxin B subunit (CTb) is a sensitive neuronal tracer with unique features. However, the possible uptake of CTb by non-terminal fibers passing through the injection site has not been examined thoroughly. In the present study, small iontophoretic injections (current = + 2 μA) of CTb were made in the olivocerebellar pathway in the rat ventrolateral medulla. A large number of retrogradely labeled neurons were seen in the contralateral inferior olive. In addition, prominent anterogradely labeled climbing fibers/terminals were found in the cerebellum ipsilateral to the injection site. This study, in contrast to previous report(s), indicates that CTb can be taken up avidly by fibers of passage and transported both anterogradely and retrogradely.     

Evidence against cholera toxin B subunit as a reliable tracer for sprouting of primary afferents following peripheral nerve injury

In order to investigate whether cholera toxin B subunit (CTb) is transported by unmyelinated primary afferents following nerve injury, we transected the sciatic nerves of six rats, and injected the transected nerves (and in three cases also the intact contralateral nerves) with CTb, 2 weeks later. The relationship between CTb and two neuropeptides, vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), was then examined in neurons in the ipsilateral L4 and L5 dorsal root ganglia, using immunofluorescence staining and confocal microscopy. We also immunostained sections of spinal cord and caudal medulla for CTb, NPY and VIP. Following nerve section, VIP immunoreactivity was increased in laminae I-II of the spinal cord while NPY immunoreactivity was increased in laminae III-IV of the spinal cord and in the gracile nucleus. On the contralateral side, CTb labelling was detected in laminae I and III-V of the dorsal horn of the L4 and L5 spinal segments, as well as in the gracile nucleus. CTb labelling was seen in the same areas on the lesioned side, but with a dramatic increase in lamina II. No VIP or NPY immunoreactivity was observed in L4 and L5 dorsal root ganglia on the side of the intact nerve, but on the lesioned side VIP was detected in many small neurons and NPY in numerous large neurons. In agreement with the report by Tong et al. [J. Comp. Neurol. 404 (1999) 143], we found that while CTb labelling in the dorsal root ganglion on the side of the intact nerve was mainly in large neurons, on the lesioned side CTb was present in dorsal root ganglion neurons of all sizes. The main finding of the present study was that almost all of the VIP- (96%) and NPY- (98%) positive neurons in the dorsal root ganglia on the lesioned side were also CTb-labelled. After nerve injury VIP is upregulated in fine afferents that terminate in laminae I and II, and most of these probably have unmyelinated axons. Since the cell bodies of these neurons were labelled with CTb that had been injected into the transected sciatic nerve, this suggests that many of these fine afferents, which do not normally transport CTb, are capable of doing so after injury.     

与霍乱毒素B亚单位结合的重组人AChR片断经鼻腔治疗实验性自身免疫性重症肌无力

目的 探讨与霍乱毒素B亚单位结合的重组人AChRα亚单位片断(CTB-Hα1-205)治疗实验性自身免疫性重症肌无力(EAMG)的有效性和基本作用机制.方法 将用AChR诱导的Lewis EAMG鼠随机分为3组:CTB-Hα1-205治疗组、Hα1-205组和CTB-HGG对照组,在诱导EAMG后第14天分别按上述3组从鼻腔滴入CTB-Hα1-205、Hα1-205和CTB-HGG.对各组进行临床分数评估、测定鼠血清中抗AChR特异抗体和淋巴细胞增殖反应.结果 CTB-Hα1-205组和Hα1-205组平均临床分数均较对照组有明显减少,差异有统计学意义(均为P＜0.01),同时CTB-Hα1-205组较Hα1-205组也有明显减少(P＜0.05);与对照组比较,CTB-Hα1-205组和Ha1-205组血清中鼠抗AChR特异抗体IgG、IgG2a、IgG2b和IgG2c的产生均明显被抑制(P＜0.01),CTB-Hα1-205治疗组的IgG、IgG2b和IgG2c较Hα1-205组低,且差异有统计学意义(P＜0.05);另一方面,CTB-Hα1-205组和Hα1-205组的IgG1较对照组却有明显升高(P＜0.05),同时,CTB-Hα1-205组和Hα1-205组对AChR特异性抗原的淋巴细胞增殖反应也被明显抑制(P＜0.05).结论 CTB-Hα1-205比Hα1-205能更加有效治疗EAMG,其作用机制是抑制了自身抗体的产生、IgG亚型的转换和特异的淋巴细胞增殖反应.     

Characterization of cholera toxin B subunit-induced Ca(2+) influx in neuroblastoma cells: evidence for a voltage-independent GM1 ganglioside-associated Ca(2+) channel

The role of endogenous GM1 ganglioside in neurite outgrowth has been studied in N18 and NG108-15 neuroblastoma cells with the GM1-specific ligand cholera toxin B subunit (Ctx B), which stimulates Ca(2+) influx together with neuritogenesis. Our primary goal has been to identify the nature of the calcium channel that is modulated by GM1. An L-type voltage-operated Ca(2+) channel (VOCC) was previously proposed as the mediator of this phenomenon. This investigation, employing fura-2 fluorescent measurements and specific channel blockers and other agents, revealed that GM1 modulates a hitherto unidentified Ca(2+) channel not of the L type. It was opened by Ctx B; was permeable to Ca(2+) and Ba(2+) but not Mn(2+); and was blocked by Ni(2+), Cd(2+), and La(3+). Although most dihydropyridines inhibited Ctx B-induced Ca(2+) influx as well as neurite outgrowth at higher concentrations, they and other VOCC blockers at normally employed concentrations failed to do so, suggesting uninvolvement of VOCC. In addition, Ca(2+) influx induced by Ctx B was not mediated by cGMP-dependent or G-protein-coupled nonselective cation channels, as demonstrated by the cGMP antagonist Rp-cGMPS or the G-protein/receptor uncoupling agent suramin, respectively. Finally, Ca(2+) influx was unlikely to be due to inhibition or reversal of Na(+)-Ca(2+) exchanger via Ctx B induction of Na(+) uptake, insofar as no effect was seen on blocking Na(+) channels, inhibiting Na(+)-K(+)-ATPase, or eliminating extracellular Na(+). The results suggest that this novel channel is gated by interaction with GM1, which, when associated with the channel and bound by appropriate ligand, promotes Ca(2+) influx. This in turn induces signaling for the onset of neuritogenesis.     

Three novel neural pathways to the lacrimal glands of the cat: an investigation with cholera toxin B subunit as a retrograde tracer

The distribution of ganglion neurons innervating the lacrimal gland (LG) was investigated following injection of cholera toxin B subunit into the LG of the cat. We report the first evidence that the otic ganglion (OG), and superior vagal and glossopharyngeal ganglia are also the sources of innervation of the LG. LG-innervating neurons in the pterygopalatine ganglion and the OG could be divided into two subpopulations: small and large neurons. They may mediate the vasodilatation and secretion, respectively.     

Serotonergic and non-serotonergic projections from the raphe nuclei to the piriform cortex in the rat: a cholera toxin B subunit (CTb) and 5-HT immunohistochemical study

Retrograde axonal transport of the cholera toxin B subunit (CTb) was combined with 5-HT immunohistochemistry to determine the origin of the serotonergic innervation of the piriform cortex (PC) in the rat. After iontophoretic CTb injections in the PC, a substantial number of retrogradely labeled cells were found in the middle and medio-ventral part of the dorsal raphe nucleus (RD). A few retrogradely labeled cells were also observed in the median raphe nucleus (MnR) and the B9 serotonergic cell groups. Following CTb and 5-HT immunohistochemistry on the same sections, double-labeled cells were observed in the RD, MnR and B9 groups. In the RD, 30% of CTb stained cells were immunoreactive to 5-HT. After colchicine or nialamide (a monoamine oxidase inhibitor) pretreatment the percentage of these double-labeled cells reached 70%. These results indicate that both 5-HT and non-5-HT neurons in the RD innervate the PC and that the percentage of double-labeled cells is influenced by drug pretreatment. To determine the terminal fields of the RD efferent fibers in the PC, injections of the anterograde tracer PHA-L were also performed. Analysis of the fiber distribution in the PC further revealed some medio-lateral and antero-posterior differences.     

Enhancement of NGF- and cholera toxin-induced neurite outgrowth by butyrate in PC12 cells

It has been shown that sodium butyrate (NaBu) does not elicit neurite outgrowth of PC12, one of the most widely used cell lines as a model of neuronal differentiation. In this study, the effects of NaBu on nerve growth factor (NGF)- and cholera toxin-induced neurite outgrowth in PC12 cells were examined. NaBu dose-dependently enhanced neurite formation induced by both agents. The maximum responses obtained at 0.5 mM NaBu were nearly twice those of the inducers alone. Propionate and valerate were also effective, but acetate and caproate were ineffective. Among the butyrate analogs with a moiety of three to five carbon atoms tested, isobutyrate, isovalerate, vinylacetate and 3-chloropropionate enhanced neurite outgrowth promoted by both inducers. However, neither alpha-, beta-, and gamma-aminobutyrates nor alpha-, beta-, and gamma-hydroxybutyrates were effective. All of the effective short-chain fatty acids and their analogs increased the level of histone acetylation, while ineffective ones did not. Furthermore, Helminthosporium carbonum toxin (HC toxin), a structurally dissimilar inhibitor of histone deacetylase, mimicked the effect of butyrate. These results suggest that NaBu enhances neurite outgrowth induced by NGF and cholera toxin in PC12 cells through a mechanism involving an increase in the level of histone acetylation.     

Inhibition of neurite outgrowth of neuroblastoma neuro-2a cells by cholera toxin B-subunit and anti-GM1 antibody

The role of cell surface GM1 ganglioside in neurite outgrowth of Neuro-2a neuroblastoma cells was investigated by application of anti-GM1 antibody and the B subunit of cholera toxin (cholera B) to cultured cells stimulated to grow neurites in various ways. When the cells were simultaneously treated with stimulatory agent and cholera B, inhibition, as measured by percent of neurite-bearing cells, was observed with most stimuli: neuraminidase; GD1a ganglioside, retinoic acid, and low serum. However, with dibutyryl cyclic AMP the small reduction observed was not statistically significant. The inhibitory effect of cholera B on neurite outgrowth induced by low serum was dose-dependent, reaching a maximum at 200 ng/mL; 48 h after washout of cholera B the cells were released from inhibition and regrew neurites at nearly the previous rate in the presence of low serum. When the cells were exposed to stimulus for 6 h or more the inhibitory effect of subsequent addition of cholera B was reduced or eliminated; inhibition thus occurs during an early stage of neurite initiation. Anti-GM1 anti-body at dilutions of 1∶100–1∶400 had the same inhibitory effect as cholera B with cells stimulated by GD1a or retinoic acid, whereas anti-GM2 antibody had no effect at 1∶200 or 1∶400; inhibition by the latter antibody at 1∶100 dilution was similar to that attained with control ascites fluid. These results point to a pivotal role for cell surface GM1 in Neuro-2a differentiation induced by many (but not all) neuritogenic agents. ganglioside nomenclature follows that of Svennerholm (1963).     

Involvement of metabotropic glutamate receptors in Gi- and Gs-dependent modulation of adenylate cyclase activity induced by a novel cognition enhancer NS-105 in rat brain

The effect of a novel cognition enhancer [(+)-5-oxo-

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-prolinepiperidinamide monohydrate] (NS-105) on cAMP formation was investigated in both slices and membranes of the rat cerebral cortex. NS-105 (10⁻⁸–10⁻⁶ M) inhibited forskolin-stimulated cAMP formation in membranes, however, the compound significantly enhanced the cAMP formation in pertussis toxin-pre-treated membranes, an action that was abolished by cholera toxin. In contrast, in digitonin-permeabilized membranes, NS-105 had no influence on Mn²⁺-stimulated cAMP formation. Both of the inhibitory and facilitatory actions of NS-105 on cAMP formation were mimicked by a metabotropic glutamate receptor (mGluR) agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) and an adrenergic α₂ agonist UK-14,304, and blocked by a mGluR antagonist 2-amino-3-phosphonopropanoate but not by an α₂ antagonist yohimbine. In cortical slices, NS-105 (10⁻⁸–10⁻⁷ M) inhibited forskolin-stimulated cAMP accumulation but enhanced isoproterenol-stimulated cAMP accumulation, as did by a GABA_B agonist (−)baclofen. On the other hand, (−)baclofen, while it significantly inhibited cAMP accumulation in slices, did no longer inhibit cAMP accumulation, when treated with NS-105 (10⁻⁸–10⁻⁵ M). Similarly, (−)baclofen-induced inhibition of the cAMP accumulation was reversed by 1S,3R-ACPD and UK-14,304. NS-105 (10⁻⁶) increased [³⁵S]GTPγS binding in the intact but not digitonin-permeabilized cortical membranes, as produced by UK-14,304, although the compound (10⁻⁹–10⁻³ M) had no influence on various neurotransmitter receptor bindings, including α₂ receptors. These results suggest that NS-105 modulates adenylate cyclase activity by stimulating mGluRs which might coupled to both G_i/G_o and G_s. © 1997 Elsevier Science B.V. All rights reserved.     

Trophic effect of cholera toxin B subunit in cultured cerebellar granule neurons: Modulation of intracellular calcium by GM1 ganglioside

Survival of cerebellar granule cells (CGC) in culture was significantly improved in the presence of cholera toxin B subunit (Ctx B), a ligand which binds to GM1 with specificity and high affinity. This trophic effect was linked to elevation of intracellular calcium ([Ca²⁺]_i), and was additive to that of high K⁺. Survival was optimized when Ctx B was present for several days during the early culture period. ⁴⁵Ca²⁺ and cell survival studies indicated the mechanism to involve enhanced influx of Ca²⁺ through L-type voltage-sensitive channels, since the trophic effect was blocked by antagonists specific for that channel type. Inhibitors of N-methyl-D-aspartate receptor/channels were without effect. During the early stage of culture Ctx B, together with 25 mM K⁺, caused [Ca²⁺]_i to rise to 0.2–0.7 μM in a higher proportion of cells than 25 mM K⁺ alone. A significant change in the nature of GM1 modulation of Ca²⁺ flux occurred after 7 days in culture, at which time Ctx B ceased to elevate and instead reduced [Ca²⁺]_i below the level attained with 25 mM K⁺. GM1 thus appears to serve as intrinsic inhibitor of one or more L-type Ca²⁺ channels during the first 7 days in vitro, and then as intrinsic activator of (possibly other) L-type channels after that period. This is the first demonstration of a modulatory role for GM1 ganglioside affecting Ca²⁺ homeostasis in cultured neurons of the CNS. © 1996 Wiley-Liss, Inc.     

Monoaminergic, peptidergic, and cholinergic afferents to the cat facial nucleus as evidenced by a double immunostaining method with unconjugated cholera toxin as a retrograde tracer

Using a sensitive double immunostaining technique with unconjugated cholera-toxin B subunit as a retrograde tracer, the authors determined the nuclei of origin of monoaminergic, peptidergic, and cholinergic afferent projections to the cat facial nucleus (FN). The FN as a whole receives substantial afferent projections, with relative subnuclear differences, from the following areas: 1) the perioculomotor areas, the contralateral paralemniscal region, and the mesencephalic reticular formation dorsal to the red nucleus; 2) the ipsilateral parabrachial region and the nucleus reticularis pontis, pars ventralis; and 3) the nuclei reticularis parvicellularis, magnocellularis, ventralis, and dorsalis of the medulla. In addition, the present study demonstrated that the lateral portion of the FN receives specific projections from the contralateral medial and olivary pretectal nuclei and the ipsilateral reticular formation of the pons. It was also found that the FN receives: 1) serotoninergic inputs mainly from the nuclei raphe obscurus, pallidus, magnus, and the caudal ventrolateral bulbar reticular formation; 2) catecholaminergic afferent projections from the A7 noradrenaline cell group located in the K?lliker-Fuse, parabrachialis lateralis, and locus subcoeruleus nuclei; 3) methionin-enkephalin-like inputs originating in the pretectal complex, the nucleus paragigantocellularis lateralis and the caudal raphe nuclei; 4) substance P-like afferent projections mainly from the Edinger-Westphal complex and the caudal raphe nuclei; and 5) cholinergic afferents from an area located ventral to the nucleus of the solitary tract at the level of the obex. In the light of these anatomical data, the present report discusses the physiological significance of FN inputs relevant to tonic and phasic events occurring at the level of the facial musculature during the period of paradoxical sleep in the cat.     

胞二磷胆碱、氯脂醒、神经节苷脂对大鼠癫(癎)的影响

目的 探讨胞二磷胆碱、氯脂醒、神经节苷脂(GM1)对青霉素致(癎)大鼠行为学及脑皮层电图的影响,为临床治疗颅脑损伤和外伤后癫(癎)提供理论依据.方法 制作大鼠癫(癎)模型,观察并比较对照组、模型组、胞二磷胆碱组、氯脂醒组、GM1组大鼠的行为学及脑皮层电图表现.结果 胞二磷胆碱、氯脂醒、GM1均不能阻止青霉素诱导的大鼠癫(癎)发作.胞二磷胆碱、GM1可以延长青霉素诱导的大鼠癫(癎)(癎)波潜伏期、阵挛强直波潜伏期,减少阵挛强直总时间.结论 胞二磷胆碱、氯脂醒、GM1均不能阻止青霉素诱导的大鼠癫(癎)发作;胞二磷胆碱、GM1可以延长青霉素诱导的大鼠癫(癎)(癎)波潜伏期、阵挛强直波潜伏期,减少青霉素腹腔注射后50 min内的阵挛强直总时间.     

The nuclei of origin of monoaminergic, peptidergic, and cholinergic afferents to the cat nucleus reticularis magnocellularis: a double-labeling study with cholera toxin as a retrograde tracer

Using a sensitive double-immunostaining technique with nonconjugated cholera toxin B subunit (CT) as a retrograde tracer, we examined the cells of origin and the histochemical nature of afferents to the cat nucleus reticularis magnocellularis (Mc) of the medulla oblongata. After injections of CT confined to the Mc, we found that the major afferents to the Mc arise from: (1) the lateral part of the bed nucleus of the stria terminalis, the nucleus of the anterior commissure, the preoptic area, the central nucleus of the amygdala, the posterior hypothalamus, and the nucleus of the fields of Forel; (2) the Edinger-Westphal nucleus, the mesencephalic reticular formation, and the ventrolateral part of the periaqueductal grey; (3) the nuclei locus coeruleus alpha (LC alpha), peri-LC alpha, locus subcoeruleus, and reticularis pontis oralis and caudalis; (4) the caudal raphe nuclei; and (5) the nucleus reticularis ventralis of the medulla.(ABSTRACT TRUNCATED AT 400 WORDS)     

胞二磷胆碱、氯脂醒、神经节苷脂(GM1)对青霉素致痫大鼠脑内某些内源性物质的影响

目的 探讨胞二磷胆碱、氯脂醒、神经节苷脂（GM1）对青霉素致痫大鼠脑内某些内源性物质的影响，为其临床应用提供依据。方法 将35只成年健康SD大鼠随机分为5组：对照组、模型组、胞二磷胆碱组、氯脂醒组、GM1组。制作癫痫模型，制模后1h处死大鼠，取额顶叶脑皮质测定其中超氧化物岐化酶（SOD）、丙二醛（MDA）、谷氨酸（Glu）、γ-氨基丁酸（GABA）含量。结果 ①模型大鼠均制模成功，腹腔注射胞二磷胆碱（500mg／kg）、氯脂醒（100mg／kg）、GM1（30mg／kg）预处理均不能阻止青霉素诱导的大鼠癫痫发作。②与对照组相比，模型组大鼠脑皮质内SOD活性明显降低，MDA、Glu、Glu／GABA值含量明显升高（P〈O．05或尸〈0．01）。③与模型组相比，胞二磷胆碱组、氯脂醒组、GM1组大鼠脑皮质内SOD活性明显升高，MDA、Glu／GABA值含量明显降低（P〈0．05），GM1组Glu含量亦明显降低（P〈0．05）。结论 胞二磷胆碱、氯脂醒、GM1虽不能预防青霉素诱导的大鼠癫痫发作，但可提高其脑组织清除自由基、增强抗氧化以及调节神经递质紊乱、减轻兴奋性氨基酸的毒性等作用，从而起到保护作用。     

Inhibition of neurite outgrowth of neuroblastoma neuro-2a cells by cholera toxin B-subunit and anti-GM1 antibody

The role of cell surface GM1 ganglioside in neurite outgrowth of Neuro-2a neuroblastoma cells was investigated by application of anti-GM1 antibody and the B subunit of cholera toxin (cholera B) to cultured cells stimulated to grow neurites in various ways. When the cells were simultaneously treated with stimulatory agent and cholera B, inhibition, as measured by percent of neurite-bearing cells, was observed with most stimuli: neuraminidase; GD1a ganglioside, retinoic acid, and low serum. However, with dibutyryl cyclic AMP the small reduction observed was not statistically significant. The inhibitory effect of cholera B on neurite outgrowth induced by low serum was dose-dependent, reaching a maximum at 200 ng/mL; 48 h after washout of cholera B the cells were released from inhibition and regrew neurites at nearly the previous rate in the presence of low serum. When the cells were exposed to stimulus for 6 h or more the inhibitory effect of subsequent addition of cholera B was reduced or eliminated; inhibition thus occurs during an early stage of neurite initiation. Anti-GM1 anti-body at dilutions of 1∶100–1∶400 had the same inhibitory effect as cholera B with cells stimulated by GD1a or retinoic acid, whereas anti-GM2 antibody had no effect at 1∶200 or 1∶400; inhibition by the latter antibody at 1∶100 dilution was similar to that attained with control ascites fluid. These results point to a pivotal role for cell surface GM1 in Neuro-2a differentiation induced by many (but not all) neuritogenic agents.     

Cytoarchitecture of the extranuclear and commissural dendrites of hypoglossal nucleus neurons as revealed by conjugates of horseradish peroxidase with cholera toxin

The ipsilateral extranuclear dendrites of hypoglossal nucleus (HN) neurons of the rat, as revealed by conjugates of horseradish peroxidase (HRP) with cholera toxin (CTHRP), were distributed to four distinct regions: (i) to the reticular formation proper (“external dendrites” of Cajal); (ii) to the solitary nucleus and tract; (iii) to the medial longitudinal fasciculus; and (iv) to the nucleus raphe obscurus. The latter two distributions are described for the first time. They were best revealed by CTHRP; and less adequately by a wheat germ agglutinin HRP conjugate (WGHRP). They could not be demonstrated by free HRP. Furthermore, CTHRP best revealed the distribution of commissural dendrites of HN neurons, the tuftlike structures at the termination of some external dendrites of Cajal, and the few dorsal protoplasmic commissural dendrites coursing dorsal to the central canal and to the contralateral solitary nucleus and the area postrema. To further clarify the distribution of the commissural dendrites of the HN, cholera toxin HRP was injected into the tongue of rats after one hypoglossal nerve had been severed. We found that the retrogradely labeled commissural dendrites crossed the midline horizontally to enter the contralateral HN and the solitary nucleus and tract as well as the reticular formation and the medial longitudinal fasciculus. The method greatly expanded our knowledge of the course and terminations of the commissural dendrites of the “protoplasmic commissure” of Van Gehuchten. We conclude that the cholera toxin HRP conjugate was a sensitive probe for the demonstration of the dendritic arborization of retrogradely labeled neurons.