Ventral Route Research Articles

The distribution of tenascin coincides with pathways of neural crest cell migration

The distribution of the extracellular matrix (ECM) glycoprotein, tenascin, has been compared with that of fibronectin in neural crest migration pathways of Xenopus laevis, quail and rat embryos. In all species studied, the distribution of tenascin, examined by immunohistochemistry, was more closely correlated with pathways of migration than that of fibronectin, which is known to be important for neural crest migration. In Xenopus laevis embryos, anti-tenascin stained the dorsal fin matrix and ECM along the ventral route of migration, but not the ECM found laterally between the ectoderma and somites where neural crest cells do not migrate. In quail embryos, the appearance of tenascin in neural crest pathways was well correlated with the anterior-to-posterior wave of migration. The distribution of tenascin within somites was compared with that of the neural crest marker, HNK-1, in quail embryos. In the dorsal halves of quail somites which contained migrating neural crest cells, the predominant tenascin staining was in the anterior halves of the somites, codistributed with the migrating cells. In rat embryos, tenascin was detectable in the somites only in the anterior halves. Tenascin was not detectable in the matrix of cultured quail neural crest cells, but was in the matrix surrounding somite and notochord cells in vitro. Neural crest cells cultured on a substratum of tenascin did not spread and were rounded. We propose that tenascin is an important factor controlling neural crest morphogenesis, perhaps by modifying the interaction of neural crest cells with fibronectin.

Effect of olivocochlear bundle transection on choline acetyltransferase activity in the rat cochlear nucleus.

Using a microdissection and quantitative microassay approach, choline acetyltransferase activities were mapped in the cochlear nuclei of rats having complete transections of the olivocochlear bundle on one side in the brain stem. In rats in which the trapezoid body was not significantly damaged by the lesion, consistent reductions of choline acetyltransferase activity in subregions of the lesion-side cochlear nucleus, as compared to the control side, averaged about 20%. Nevertheless, a profound lesion-side reduction of choline acetyltransferase activity was found in a branch connection from the olivocochlear bundle to the cochlear nucleus. The results suggest that branches from the olivocochlear bundle are cholinergic, but contribute a relatively minor proportion of the cholinergic synapses in all regions of the rat cochlear nucleus. In the light of previous results with more extensive lesions, it can be proposed that synapses in all regions of the rat cochlear nucleus. In the light of previous results with more extensive lesions, it can be proposed that most cholinergic input into the rat cochlear nucleus enters by a ventral route along the trapezoid body. It is noted that this represents a quantitatively somewhat different situation from that in the cat.

Galanin-like immunoreactivity in hippocampal afferents in the rat, with special reference to cholinergic and noradrenergic inputs

The distribution of galanin-like immunoreactivity in the rat hippocampal formation (hippo campus and dentate gyrus) was studied and its origins were determined using various lesioning techniques. Special reference was made to the known cholinergic and noradrenergic hippocampal inputs from the septum-basal forebrain complex and locus coeruleus, both of which have previously been shown to co-contain galanin-like immunoreactivity at the cell body level. Galanin-immunoreactive fibers in the hippocampal formation were of at least three different morphological types: (1) Fine, slender, faintly immunoreactive fibers were seen throughout the hippocampal formation. (2) A strongly fluorescent varicose fiber population was observed mainly in the strata radiatum and oriens of the ventral CA3 region (3) A population of fine, faint puncta was seen within the granule and pyramidal cell layers throughout the hippocampal formation. Knife cut lesions of the dorsal afferent pathways resulted in almost complete disappearance of all fiber types, except for the ventral fine fibers. Lesions of the fimbria affected mainly the coarse and punctate fiber types, while lesions of the supracallosal striae depleted mainly the fine fibers. Cuts anterior and ventral to the hippocampal formation caused a decrease in ventral fine fibers. Furthermore, lesions of the dorsal bundle caused an almost complete disappearance of the fine fibers in all regions of the hippocampal formation. Neurotoxin lesions of the diagonal band/septal complex resulted in decreases in faintly immunoreactive puncta within the granule cell layer and adjacent fine fibers. It is concluded that most fine galanin-positive fibers originate in the lower brain stem, presumably the locus coeruleus, and appear to reach the hippocampal formation primarily through the supracallosal striae and the ventral route. The fimbria seems to contain a large proportion of the fibers giving rise to the coarse strongly fluorescent innervation, which appears to originate rostral to the pons. The galanin-immunoreactive fibers originating in cholinergic somata of the diagonal band, medial septal nuclei, previously shown to project to the hippocampal formation, seem to give rise to faintly labeled puncta within the granule and pyramidal cell layers, and to a small proportion of the fine fibers bordering the cell layers, as revealed by immunohistochemistry using our antibody. The immunohistochemical localization of a galanin-like peptide(s) in cholinergic and noradrenergic hippocampal afferents provides a morphological basis upon which to propose a peptidergic modulation of the action of these transmitters on hippocampal functions, e.g. memory and learning.

On the Guidance of Neural Crest Migration: Latex Beads as Probes of Surface-Substratum Interactions

The experiments reviewed in this chapter examine the translocation of various cell types and latex beads on a neural crest pathway. The cells and beads are implanted into the embryo via an injection technique that can be used to characterize the embryonic pathways or the injected cells themselves. The results demonstrate that postmigratory neural crest cells, undifferentiated neural crest cells, and retinal pigment epithelial cells will translocate to ventral sites after implantation. By contrast, somitic and fibroblastic cells fail to translocate. No correlation was found between the inherent motile ability of a cell and the ability to move along the ventral route. Therefore, the role of cell surface molecules in movement along the neural crest pathway was examined. Latex beads, which lack inherent motility, were used as probes of the neural crest pathway. Uncoated beads as well as latex beads coated with a variety of ECM molecules and polyamino acids were injected into embryos in order to explore interactions between the cell surface and the embryonic substrata that might be involved in neural crest localization. The distribution pattern of the latex beads was altered by the nature of the surface properties of the beads. Two distinct patterns of localization were observed. Those beads coated with FN, cell-binding fragment of FN, laminin, or PL remained primarily associated with the dermamyotomal cells of the implantation site. By contrast, uncoated beads or beads coated with BSA, collagen, or PT translocated to ventral sites, usually around the sympathetic ganglia or dorsal aorta. In order to analyze mechanisms that may be involved in translocation of latex beads along neural crest pathways, we examined the possible effects of (1) bead surface charge; and (2) the removal of endogenous neural crest cells. To examine the effects of electrostatic interactions in bead translocation or restriction, the initial surface charge of beads coated with various macromolecules was measured and compared with their subsequent ability to translocate along the ventral pathway. No correlation was observed between the sign of the surface charge and subsequent distribution of beads, suggesting that initial surface charge properties alone cannot account for the restriction or translocation. To dissect the role of endogenous neural crest cells in bead movement, the host neural crest was ablated using a laser microbeam. After injection of latex beads into ablated embryos, the latex beads translocated ventrally even in the absence of the neural crest. Thus, latex beads are not merely carried ventrally by adhering to migrating neural crest cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Latex beads as probes of a neural crest pathway: effects of laminin, collagen, and surface charge on bead translocation.

In the trunk region of avian embryos, neural crest cells migrate along two pathways: dorsally just under the ectoderm, and ventrally between the neural tube and the somites. Previous work from this laboratory has shown that uncoated latex beads are able to translocate along the ventral neural crest pathway after injection into young embryos; however, beads coated with fibronectin are restricted from the ventral route ( Bronner -Fraser, M.E., 1982, Dev. Biol., 91: 50-63). Here, we extend these observations to determine the effects of other macromolecules on bead distribution. The data show that laminin-coated beads, like fibronectin-coated beads, are restricted from the ventral pathway. In contrast, beads coated with type I collagen translocate ventrally after injection. Because macromolecules have characteristic charge properties, changes in surface charge caused by coating the beads may confound interpretation of the results. Electrostatic effects on bead movement were examined by coating the latex beads with polyamino acids in order to predictably alter the initial surface charge. The surface charge before injection was measured for beads coated with amino acid polymers or with various biologically important macromolecules; the subsequent translocation ability of these beads was then monitored in the embryo. Polylysine-coated beads (positively charged) were restricted from the ventral pathway as were fibronectin and laminin-coated beads, even though fibronectin and laminin beads were both negatively charged. In contrast, polytyrosine -coated beads ( neutrally charged) translocated ventrally as did negatively charged collagen-coated or uncoated beads. The results demonstrate that no correlation exists between the charge properties on the latex bead surface and their subsequent ability to translocate along the ventral pathway. Therefore, an adhesion mechanism independent of surface charge effects must explain the restriction or translocation of latex beads on a neural crest pathway.

A diffuse alpha MSH-immunoreactive projection to the hippocampus and spinal cord from individual neurons in the lateral hypothalamic area and zona incerta.

The course, distribution, and possible neurotransmitter specificity of a projection from the lateral hypothalamic area (LHA) and zona incerta to the hippocampal formation (dentate gyrus, Ammon's horn, subicular region, and entorhinal area) and spinal cord were examined anatomically in the adult rat. First, small injections of the fluorescent tracer fast blue were made into either the septal part of the dentate gyrus and Ammon's horn or the entorhinal area, and the distribution of retrogradely labeled cells was plotted. In each experiment many cells were labeled in the LHA and zona incerta, and little evidence for a topographically organized projection to different parts of the hippocampal formation was found. Second, a combined retrograde transport-immunofluorescence method was used to show that some 95% of the fast blue-labeled neurons in the LHA and zona incerta were also stained with an antiserum to the opiate peptide alpha-melanocyte-stimulating hormone (alpha MSH), but not an antiserum to adrenocorticotropin (ACTH)1-24. It was also found that small numbers of retrogradely labeled neurons were stained with antisera to somatostatin 14 and 28, dynorphin (1-17), and angiotensin II. Third, the distribution of alpha MSH-immunoreactive fibers was plotted, and they were found to form a diffusely organized plexus throughout all of the subfields of the hippocampal formation. These fibers were virtually eliminated after transections of the fimbria and the region between the entorhinal area and the caudal amygdala. Forth, the course of fibers from the LHA and zona incerta was examined with the anterogradely transported lectin Phaseolus Vulgaris Leucoagglutinin (PHAL). Such fibers reach the hippocampal formation by a dorsal route through the septal region and fimbria, and by a ventral route through the amygdala. And fifth, double retrograde transport and immunohistochemical methods were used to show that at least some alpha MSH-stained neurons in the LHA and zona incerta give rise to collaterals that innervate both the hippocampal formation and the spinal cord. Alpha MSH-stained fibers in the spinal cord also form a widely scattered plexus with no obvious circumscribed terminal fields. It is suggested that the diffusely organized projection from the LHA to the cerebral cortex and spinal cord may play a role in the general arousal associated with a variety of motivated behaviors.

Cells of origin of the ventral cholinergic septohippocampal pathway undergoing compensatory collateral sprouting following fimbria-fornix transection

The axons of the septohippocampal pathway reach the hippocampal formation via the fimbria, dorsal fornix and supracallosal striae. Complete lesions of these pathways denervate most of the hippocampal formation but a small, residual innervation occurs via a different ventral route. The cells of origin for this additional route for cholinergic innervation of the hippocampal formation have been identified in the present study with a combined technique using a fluorescent retrograde tracer and acetylcholinesterase histochemistry. These cells were localized to the diagonal band of Broca. In a subsequent experiment it was demonstrated, by destroying these cells unilaterally, that they were responsible to a large extent for the cholinergic compensatory collateral sprouting in the hippocampus that has previously been shown to develop following complete fimbria-fornix transection.

Reinnervation of the partially deafferented hippocampus by compensatory collateral sprouting from spared cholinergic and noradrenergic afferents

The cholinergic and adrenergic afferents innervating the hippocampal formation in the rat reach the target region via three distinctly separate routes, two dorsal and one ventral one. Partial deafferentation of the hippocampus obtained by destruction of the dorsal routes (through the fimbria-fornix and the supracallosal striae) resulted in removal of 90% and 60% of the cholinergic and adrenergic innervations, respectively, within one month. By 6–10 months after lesion, the remaining cholinergic and adrenergic inputs, reaching the target via the ventral route, had expanded more than two-fold, resulting in a significant recovery in the original cholinergic and adrenergic innervation patterns. Because of its slow and protracted time-course and its ability to re-establish innervation also in initially denervated areas, this compensatory collateral sprouting phenomenon may be of particular interest for the understanding of the long-term, protracted functional recovery that is seen both after experimental brain lesions as well as in patients with severe brain injuries.

Endoscopy in cattle: Techniques for ovarian examination by the paralumbar and mid-ventral routes

Using commercially available fibre light optical equipment ovarian examinations were made in cattle by endoscopy via the left paralumbar fossa. An endoscopy platform allowing variable elevation of the hind quarters of the animal is described. This unit could be adapted to other commercial cattle crushes. Preparation for endoscopy requires 48 h fasting from food and water and local infiltration of the left sublumbar fossa tissues with 3% lignocaine. Disadvantages of the method include difficulty of immobilization of the animal, periodic difficulties in observing the right ovary because of omental and perirenal fat and the build-up of adhesions which prohibit further observations and may reduce subsequent fertility. With parous cows (300–500 kg) approximately five animals per hour could be examined. A technique for endoscopy via the mid ventral route is also described. It involves basal anaesthesia without tracheal intubation and the animal is manipulated for surgery and later recovery by suspension from the hydraulic blade of a farm tractor or an electric hoist. This method is safe, quick (8–10/h), reliable, provides for more complete ovarian examination and can be performed on lactating or dry cattle of all ages. It is less traumatic for the animal than the paralumbar approach. An important feature is that many observations can be performed on the same animal. Up to 15 endoscopies 6–8 weeks apart have been performed on heifers, without evidence of adhesions.

Interrelationships Between Arteries, Veins and Lymphatics in the Head Region of the Eel,Anguilla anguillaL.

Vascular casting and dissection of fresh specimens had been used to investigate the arrangement of vessels before and after the gills in the head region of the eel. Arterial and venous morphology was found to be as reported in previous works, but the presence in the eel of a venous system that does not confom to the generalised teleost plan necessitated the use of a non-standard nomenclature. The gills are the site of the connection of the arterial system with a second vascular system and it is suggested that this system should be termed the veno-lymphatic system. The veno-lymphatic system connects dorsally to the systemic lymphatic system and so to the internal jugular vein. Ventrally the veno-lymphatic vessels from the first three gill arches are collected into a connective tissue sheath around the ventral aorta. The sheath is connected to a veno-lymphatic sinus posterior to it which also collects the veno-lymphatic of the fourth gill arch. This sinus then drains into the external jugular vein which at this point is the fusion of the left and right branches. These later separate and each branch contains a valve preventing flow towards the ventral aortic sheath. It is proposed that because of the form of this ventral route for veno-lymphatic drainage, and the ease and completeness of filling of this route compared with the dorsal route, that the ventral veno-lymphatic system is probably the primary route of drainage of veno-lymphatic outflow from the gills.

The distribution and orientation of serotonin fibers in the entorhinal and other retrohippocampal areas. An immunohistochemical study with anti-serotonin antibodies in the rats brain.

The serotonin (5-hydroxytryptamine; 5-HT) innervation of the retrohippocampal region (subiculum, pre- and parasubiculum, area 29e, medial and lateral entorhinal area) in the rat brain has been examined with antibodies against 5-HT used in combination with fluorescence histochemistry. Analysis of consecutive sections cut in the coronal, sagittal, and horizontal planes revealed a widespread distribution of 5-HT immunoreactive fibers throughout the retrohippocampal region. This innervation was with regard to the morphological characteristics of the 5-HT fibers, their density and their spatial orientation. On the basis of morphological criteria, four different types of 5-HT positive processes were distinguished: (a) fine, convoluted fibers with small (approximately 0.5-0.8 micron), round and evenly spaced varicosities: (b) fine fibers with small elongated, irregularly distributed varicosities; (c) thick, possibly myelinated fibers, and (d) a terminal plexus with large (5-10 micron), irregularly spaced varicosities. Analysis of the laminar distribution of the 5-HT fibers showed that whereas all layers contain 5-HT positive fibers, the molecular layer was the most densely innervated. The 5-HT fibers were found to be oriented both parallel and transverse to the longitudinal axis of medial and lateral entorhinal area. This grid-like arrangement was less pronounced in the presubiculum. Although the 5-HT innervation of the retrohippocampal region was found to be dominated by a widespread and apparently diffuse pattern, several areas contained dense clusters of preterminal 5-HT processes: area 29e, dorsal presubiculum (layer II), lateral entorhinal area (layer III and ventral layer II) and the transitional zone of the ventral entorhinal area. The 5-HT fibers were found to enter the retrohippocampal region primarily by three different routes; from the ventral and dorsal aspects and from the piriform and lateral neocortex (via the perirhinal area). Most of the fibers enter the region by the ventral route and these were found to ascend in all layers but predominantly in layer I. The location of the 5-HT cells giving rise to the innervation of the entorhinal area was studied by combining retrograde transport of fluorescent tracers with immunohistochemistry on the same tissue section. Both ipsi- and contralaterally located cells in the dorsal and median raphe nuclei were found to project to the entorhinal area. Most, but not all, of these retrogradely labeled cell bodies also contain 5-HT immunoreactivity.

Analysis of the neural crest ventral pathway using injected tracer cells

Cloned neural crest melanocytes and nonneural crest cells were introduced into chick embryos to study questions of neural crest migration and localization. Previously we showed that cloned quail melanocytes injected directly into the newly formed somites of 2.5-day-old chick embryos were initially contained within the somitic lumen ( Bronner and Cohen, 1979); following release from the somites, the melanocytes migrated along the ventral neural crest pathway. Here we demonstrate that the migratory pattern of melanocytes freshly isolated from the skin of 9- to 11-day-old quail embryos is identical to that of the cloned quail melanocytes grown in vitro for 8 days or more. Like cloned melanocytes, quail skin melanocytes migrated beyond the dorsal root and sympathetic chain ganglia and localized in the vicinity of the adrenal gland, aortic plexus, metanephric mesenchyme, gonads, and gut. This suggests that the choice of the ventral migratory route is not simply a consequence of prolonged stay in tissue culture. Nor is the choice of the ventral pathway a consequence of introducing cells of one species into the environment of another since melanocytes derived from chick neural crest cells migrated analogously to the quail melanocytes. The ventral pathway appears to be selective for neural crest-derived cells since somite cells and single fibroblast cells did not migrate ventrally when placed into the embryo. Quail somite cells remained associated with the somitic mesenchyme and single fibroblast cells migrated under the ectoderm. Injected quail fibroblasts when clumped, however, were found on the ventral pathway indicating that the ventral route is not specific for crest cells and their derivatives. Cloned quail melanocytes injected into older developmental levels of the neural axis did not migrate as far ventrally as those implanted in younger levels where crest cells were only beginning to migrate. This demonstrates that changes in the environment that occur as a function of developmental age limit the extent of ventral migration of injected melanocytes.

Origins of axons in the cat's acoustic striae determined by injection of horseradish peroxidase into severed tracts.

Origins and terminations of fibers of the dorsal and intermediate acoustic striae were studied by surgically severing these tracts and injecting HRP into the incision. This procedure results in filling the severed axons with HRP. Filled axons were traced to cell groups of origin and to some terminations of the acoustic striae. HRP-labeled terminals were found in the cochlear nuclei as well as in periolivary cell groups. Filling of cells with HRP RANged from being complete, resulting in Golgi-like images, to being barely detectable. Labeled cells were abundant in the dorsal and posteroventral cochlear nucleus adjacent to the injection as well as scattered throughout the periolivary cell groups of both sides, being highest in concentration around the ipsilateral lateral superior olive. On the side contralateral to the injection, labeled cells were found along the medial border of the dorsal cochlear nucleus, in the interstitial nucleus of the stria of Held, and sparsely throughout the ventral cochlear nucleus. The distribution of labeled cells was similar following HRP injections of the dorsal cochlear nucleus, except that these injections revealed additional descending projections from the inferior colliculi and from the ventral nucleus of the trapezoid body of both sides. These additional projections were interpreted as entering the CN by a ventral route. Findings of this study are in accord with physiological recordings made from fibers of the acoustic striae.

Inhibition of feline collateral vessel development following experimental thrombolic occlusion.

We compared development of feline hindlimb collateral circulation after acute occlusion of the terminal aorta by ligation, thrombus formation, and formation of a "closed" aortic loop containing thromboplastin. Collateral circulation development was assessed by aortograms, scintillation scans, neurological signs following occlusion, measurement of hindlimb muscle blood flow, and forelimb and hindlimb temperature. In cats in which aortic occlusion was the result of ligation or thromboplastin in the aortic loop, paralysis was not evident. Aortograms and scintillation scans indicated hindlimb blood flow. Both muscle temperature and blood flow data indicated that the return of blood flow was rapid. The 5th lumbar artery appears to be the origin of the collateral vessels. The mid-zone component is a dorsal and ventral vertebral route and an epaxial muscle route. The reentry components are the 6th or 7th lumbar arteries. The collateral vessels arise from preexisting collateral vessels. Of those cats in which aortic occlusion was the result of a thrombus, all exhibited paralysis. Aortograms, scintillation scans, muscle temperature, and hindlimb blood flow data indicated reduced hindlimb blood flow. The results suggest that the thrombus has an inhibitory effect on the development of collateral circulation.

The efferent connections of the ventromedial nucleus of the hypothalamus of the rat.

The efferent connections of the ventromedial nucleus of the hypothalamus (VMH) of the rat have been examined using the autoradiographic method. Following injections of small amounts (0.4-2.0 muCi) of tritium labeled amino acids, fibers from the VMH can be traced forward through the periventricular region, the medial hypothalamus and the medial forebrain bundle to the preoptic and thalamic periventricular nuclei, to the medial and lateral preoptic areas, to the bed nucleus of the stria terminalis and to the ventral part of the lateral septum. Some labeled axons continue through the bed nucleus of the stria terminalis into the stria itself, and hence to the amygdala, where they join other fibers which follow a ventral amygdalopetal route from the lateral hypothalamic area and ventral supraoptic commissure. These fibers terminate in the dorsal part of the medial amygdaloid nucleus and in the capsule of the central nucleus. A lesser number of rostrally directed fibers from the VMH crosses the midline in the ventral supraoptic commissure and contributes a sparse projection to the contralateral amygdala. Descending fibers from the VMH take three routes: (i) through the medial hypothalamus and medial forebrain bundle; (ii) through the periventricular region; and (iii) bilaterally through the ventral supraoptic commissure. These three pathways are interconnected by labeled fibers so that it is not possible to precisely identify their respective terminations. However, the periventricular fibers seem to project primarily to the posterior hypothalamic area and central gray, as far caudally as the anterior pole of the locus coeruleus, while the medial hypothalamic and medial forebrain bundle fibers apparently terminate mainly in the capsule of the mammillary complex, in the supramammillary nucleus and in the ventral tegmental area. The ventral supraoptic commissure fibers leave the hypothalamus closely applied to the medial edges of the two optic tracts. After giving off their contributions to the amygdala, they continue caudally until they cross the dorsal edge of the cerebral peduncle to enter the zona incerta. Some fibers probably terminate here, but others continue caudally to end in the dentral tegmental fields, and particularly in the peripeduncular nucleus. Within the hypothalamus, the VMH appears to project extensively to the surrounding nuclei. However, we have not been able to find evidence for a projection from the VMH to the median eminence. Isotope injections which differentially label the dorsomedial or the ventrolateral parts of the VMH have shown that most of the long connections (to the septum, amygdala, central tegmental fields and locus coeruleus) originate in the ventrolateral VMH, and there is also some evidence for a topographic organization within the projections of this subdivision of the nucleus.

Histamine synthesizing afferents to the hippocampal region.

Abstract—Histidine decarboxylase activity is found in all parts of the hippocampal formation (subiculum, CA1, CA3 and area dentata), and a major portion of the enzyme is localized in a subcellular fraction containing the nerve terminal particles. The almost complete disppearance of HD (and histamine) after deafferentation of the hippocampal formation suggests that histamine synthesis in this region resides in terminals of extrinsic fibres. The results after selective lesions indicate that these alleged histaminergic fibres enter the hippocampus, like the monaminergic fibres, through a dorsal route (comprising fimbria, fornix superior and cingulum) as well as through a ventral route (via the amygdaloid area). The former was tentatively estimated to represent about 60% of the total hippocampal supply of alleged histaminergic fibres.

5-Hydroxytryptamine and noradrenaline in the hippocampal region: effect of transection of afferent pathways on endogenous levels, high affinity uptake and some transmitter-related enzymes.

AbstractThe monoaminergic fibres enter the hippocampal formation through a dorsal and a ventral route. The dorsal route consisting of fimbria, fornix superior and cingulum, was estimated to supply about 75% of the 5‐HT fibres and 40% of the noradrenaline containing (NA) fibres. The ventral route, allegedly passing through the amygdaloid area, accounts for the rest. The cingulum bundle contributes a definite part of the 5‐HT fibres but very few of the NA fibres. No evidence was found for an intrinsic origin of monoaminergic fibres in the hippocampal region. Monoamine oxidase and catechol‐O‐methyltransferase showed no change following the lesions and are considered to be localized predominantly outside the aminergic neurones. The results on DOPA decarboxylase indicate that about 50% of the enzyme is situated outside 5‐HT and NA nerves. Glutamic acid decarboxylase did not decrease even after transection of the ventral route, substantiating the earlier conclusion that this enzyme is situated in intrinsic neurones in the hippocampal region. For choline acetyltransferase and AChE the dorsal route was confirmed to be the only quantitatively important way of access. None of the enzymes studied, nor the uptake activities, were affected by cervical sympathectomy.

Clinical and experimental observations with methiodal, an absorbable myelographic contrast agent.

The intrathecal iniectuni of methiodal in myelography is associated with spinal anesthesia, pain, and autonomic dysfunction. Experiments carried out in cats revealed that methiodal blocked conduction in the ventral and dorsal route fibers, an action which did not develop in peripheral nerves. Other experiments in cats indicated that the duration of the effects on conduction is a consequence of slow removal of the drug rather than of delayed recovery. The results of these experiments are taken to indicate that the effects of methiodal may be ascribed to an action on the spinal cord or nerve roots.