Distribution of conduction system fibers in the developing and adult rabbit heart revealed by an antineurofilament antibody.

Using an immunological approach, we demonstrated previously that a neurofilament-like protein is expressed in rabbit heart conduction tissue myocytes, and we proposed that these specialized cardiac muscle cells are of neuroectodermal origin. In the present study, we used the expression of the neurofilament-like protein as a marker for identifying conduction tissue cells and studying their distribution in the developing heart. In 11-day-old rabbit embryos, myocytes expressing the neurofilament-like protein were localized at the atrioventricular and the sinoatrial junctions and had a ring-like distribution. At embryonic day 12, reactive myocytes were found also in the subendocardial layer of the dorsal ventricular wall, in continuity with labeled myocytes at the atrioventricular junction. Examination of older embryos and of neonatal and adult hearts revealed that the expression of the neurofilament-like protein was not restricted to myocytes of conduction tissue regions, but it was also detectable in myocytes of the sinoatrial ring bundle, in scattered myocytes localized in the left sinal horn wall, and in the right atrium in proximity to atrioventricular sulcus tissue. Thus, using an intracellular marker, we show that precursors of adult atrial conduction tissue are distributed at the sinoatrial and atrioventricular junctions; at variance, ventricular conduction tissue precursors do not have a ring-like distribution but are localized in the subendocardial layer, in continuity with the atrioventricular junctional myocytes.

The fascicular structure of the lingual nerve and the chorda tympani: an anatomic study.

Damage of the lingual nerve is one of the most common problems in oral surgery, especially during removal of the third molar. After microsurgery of the lingual nerve, there is a lack of regeneration of the gustatory fibers in comparison with the sensory fibers. The histologic investigation of ten human lingual nerve preparations showed that the chorda tympani fibers distribute widely in the fascicles of the lingual nerve. Therefore, after microsurgical reconstruction of the lingual nerve in the third molar region, the chance of the gustatory fibers meeting and regenerating is very low.

Structure, afferent innervation, and transmitter content of ganglia of the guinea pig gallbladder: relationship to the enteric nervous system.

Although a well-developed plexus of nerves and ganglia is known to be present in the wall of the gallbladder, little has previously been learned about the function or organization of this innervation. The current study was undertaken in order to evaluate the hypothesis that the ganglionated plexus of the gallbladder is analogous to elements of the enteric nervous system (ENS). The ganglionated plexus of the gallbladder was found to resemble closely the submucosal plexus of the small intestine in its organization into two irregular anastomosing and interwoven networks of ganglia, in the numbers of neurons per ganglion, and in the manifestation of histochemically demonstrable acetylcholinesterase activity in virtually all ganglion cells. In common with enteric ganglia, laminin immunoreactivity was observed to be excluded from the interiors of gallbladder ganglia, which were surrounded by a periganglionic laminin-immunoreactive sheath. As in the submucosal plexus, intrinsic substance P-, vasoactive intestinal polypeptide (VIP)-, and neuropeptide Y (NPY)-immunoreactive neurons were seen in the ganglionated plexus of the gallbladder. Extrinsic nerves in the gallbladder that degenerated following chemical sympathectomy with 6-hydroxydopamine (6-OHDA), and which contained NPY, tyrosine hydroxylase (TH), and dopamine-beta-hydroxylase (DBH) immunoreactivities, formed a perivascular plexus closely associated with blood vessels. Endogenous catecholamines could also be demonstrated in these perivascular nerves by aldehyde-induced histofluorescence. In addition to perivascular nerves, paravascular nerve bundles were observed that were loosely associated with vessels, did not degenerate following administration of 6-OHDA, and contained NPY immunoreactivity. Other paravascular nerves, probably visceral sensory axons, coexpressed substance P and calcitonin-gene-related peptide (CGRP) immunoreactivities. The ganglionated plexus of the gallbladder resembled enteric ganglia in having intrinsic 5-hydroxytryptamine (5-HT)-immunoreactive cells and highly varicose nerve fibers. The 5-HT-immunoreactive gallbladder axons were, like those of the gut, resistant to 6-OHDA, and separate from fibers that expressed TH immunoreactivity. Differences between the ganglionated plexus of the gallbladder and enteric ganglia of the small intestine included in the gallbladder are 1) the presence of TH-immunoreactive cells that contain an endogenous catecholamine, but not DBH; 2) DBH-immunoreactive neurons, some of which coexpress substance P immunoreactivity, but which contain neither a catecholamine nor TH immunoreactivity; 3) an apparent absence of CGRP-immunoreactive cell bodies.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanisms of differential axial blockade in epidural and subarachnoid anesthesia.

The mechanisms of persistent differential blocks that accompany subarachnoid and epidural anesthesia are clarified here with the aid of two principles derived from in vitro study of individual myelinated axons: 1) conduction can leap two consecutive blocked nodes but not three, and 2) a fiber length with more than three consecutive nodes bathed by weak anesthetic may block by decremental conduction, the requisite concentration varying inversely with the number of nodes bathed by anesthetic. Principle 1 applies in epidural blockade, where anesthetic bathes only a few millimeters of segmental nerve extradurally in the intervertebral foramen. Here, three-node block will be rare in large, long-internode fibers but likely in small, short internode fibers, thus explaining the differential retention of motor power in the presence of block of pain, which is achieved in epidural anesthesia when relatively weak solutions are used, as in obstetrics. Principle 2 may intervene in subarachnoid blockade where, cephalad to the site of puncture, increasingly concentrated anesthetic bathes increasing lengths of fibers in the craniocaudal succession of spinal nerve roots. This will produce decremental conduction block in increasingly long internode fibers in successive roots, reflected in a corresponding craniocaudal segmental sequence of blocked physiological functions: vasoconstriction, cutaneous temperature discrimination, pinprick pain sensibility, and skeletal motor activity. The segmental spatial differential sequence migrates with time but resembles the temporal differential sequence of loss seen at the onset of peripheral nerve blocks. Several other previously disparate clinical observations follow logically from the new interpretation.

Retrograde tracing of nerve fibers to the rat middle cerebral artery with true blue: colocalization with different peptides.

The origin of nerve fibers to the rat middle cerebral artery was studied by retrograde tracing with the fluorescent tracer True Blue (TB) in combination with immunocytochemistry to known perivascular peptides. Application of TB to the middle cerebral artery labeled nerve cell bodies in the ipsilateral superior cervical ganglion, the otic ganglion, the sphenopalatine ganglion, the trigeminal ganglion, and the cervical dorsal root ganglion at level C2. A few labeled nerve cell bodies were seen in contralateral ganglia. Judging from the number and intensity of the labeling, the superior cervical ganglion and the trigeminal ganglion and dorsal root ganglion at level C2 contributed most to the innervation. A moderate number of nerve cell bodies were labeled in the sphenopalatine and otic ganglia. The TB-labeled nerve cell bodies were further examined for the presence of neuropeptides. For that purpose antibodies raised against neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP) and calcitonin gene-related peptide (CGRP) were used. A considerable portion of the TB-labeled nerve cell bodies in the superior cervical ganglion contained NPY. About half of the labeled nerve cell bodies in the sphenopalatine and otic ganglia contained VIP. In the trigeminal ganglion and in the dorsal root ganglion at level C2, one-third of the TB-labeled nerve cell bodies were CGRP-immunoreactive, while only few nerve cell bodies contained SP. The study provides direct evidence for the origin of cerebrovascular peptidergic nerve fibers and demonstrates that not only ipsilateral but also contralateral ganglia contribute to the innervation of the cerebral circulation.

Corticotropin-releasing hormone in the human hypothalamus. Free-floating immunostaining method.

We have clearly demonstrated corticotropin-releasing hormone (CRH) immunoreactive cell bodies and nerve fibers in the human hypothalamus by immunocytochemistry using free-floating sections instead of paraffin-embedded sections. Human hypothalami were obtained at autopsy, fixed and cryostat-sectioned at 40 microns. Free-floating sections were immunostained with antibody to CRH using the Vector ABC system. Most of CRH immunoreactive nerve fibers from the paraventricular nucleus pass under the fornix, while some CRH immunoreactive nerve fibers pass beyond the fornix and some through the fornix. Then the CRH immunoreactive nerve fibers run downward, medially to the supraoptic nucleus and toward the pituitary stalk. This method of immunocytochemistry is a very sensitive and suitable means for immunocytochemical studies of neuropeptides in the human brain.

Reptilian somatosensory midbrain: identification based on input from the spinal cord and dorsal column nucleus.

A midbrain somatosensory area was identified in reptiles Caiman crocodilus, by orthograde degeneration techniques after midcervical spinal cord transections or after dorsal column lesions. Terminations of these somesthetic inputs were located in a caudal lateral part of the central nucleus of the torus semicircularis and contiguous dorsal mesencephalon. Dorsal column projections were contralateral while spinal connections were mainly ipsilateral. In order to confirm the results of the anterograde degeneration experiments independently, injections of horseradish peroxidase were placed in this midbrain somatosensory recipient area. Retrogradely labeled neurons were identified in the contralateral dorsal column nucleus. These findings indicated that the pattern of degeneration seen after dorsal column lesions originated from the dorsal column nucleus itself. The results of the present experiments when compared with similar studies in other amniotes emphasize the following two points. First, dorsal column and spinal cord projections to the midbrain are features common to reptiles, birds, and mammals. Second, since these pathways and midbrain somatosensory terminations are common to amniotes, dorsal column nucleus and spinal circuits to the midbrain and their mesencephalic projection areas are phylogenetically ancient.

Immunocytochemical localization of serotonergic fibers innervating the ocular circadian system of Aplysia.

The isolated eye of the mollusc, Aplysia californica, contains a circadian pacemaker whose phase can be regulated by serotonin. The results of previous biochemical and physiological studies indicate that serotonin is used as a transmitter of circadian information in the eye. Although the effects of serotonin on various physiological processes in the Aplysia eye have been studied, very little is known about the anatomy of the serotonergic innervation. We have examined the innervation of the eye using immunocytochemical methods. Serotonin-immunoreactive processes were observed in the optic nerve, in the accessory optic nerves, in the connective tissue capsule surrounding the eye, and within the eye itself. There appeared to be two sources of serotonergic input to the eye of Aplysia. One set of immunoreactive fibers was contained in the optic nerve and entered the eye in the neuropil region before radiating outward towards the peripheral retina in the layer below the photoreceptor cell bodies. A second serotonin-immunoreactive input to the eye entered from the accessory optic nerves and these fibers formed a dense plexus of fibers in the connective tissue capsule surrounding the eye. Serotonin-immunoreactive fibers from the plexus penetrated the eye and appeared to terminate in the peripheral portion of the retina. No serotonin-immunoreactive cell bodies were observed in the eye, nerves, or connective tissue capsule. These results support the hypothesis that serotonergic fibers innervate the retina of Aplysia and that these fibers travel through two distinct anatomical pathways: the optic nerve and the accessory optic nerves.

Effects of limited postnatal ethanol exposure on the development of myelin and nerve fibers in rat optic nerve.

This study was designed to morphologically evaluate the effects of limited postnatal alcohol exposure on the development of myelin and axons in the rat optic nerve. Rat pups were artificially reared on Days 5-18 with a supplemented milk diet fed via a chronic gastrostomy tube. Experimental animals received 4% ethanol in their diet on Days 5-9, otherwise the experimental and control animals received identical diets in identical volumes. Optic nerve tissues were prepared for electron microscopy on Days 10, 16, 22, 29, and 90. The cross-sectional areas of optic nerves were smaller, there were fewer myelinated nerve fibers per unit area, and the progress of myelination was slowed on Day 10 in the ethanol-exposed animals. All of these effects were compensated for at later times. The ratio of myelin thickness to axon diameter was similar in experimental and control animals, indicating that the interaction between axon size and myelin formation was not affected by alcohol. The general distribution of axon sizes was unaffected by ethanol except at 10 days when the largest fibers were smaller. There was no evidence of alcohol-induced degeneration of axons, myelin, or glial structures. Thus, alcohol exposure during myelin development causes a delay in myelin acquisition that is later compensated for.

The effect of age on normal human optic nerve fiber number and diameter.

In one optic nerve from each of 19 persons, the authors determined the number of axons, the distribution of fiber diameter, and the total neural area. The mean fiber count was 693,316, the mean neural area was 5.17 mm2, and the mean axonal fiber diameter was 0.96 microns. No significant decline in fiber number or neural area with increasing age was found. The authors found a large variability of axonal number among their patients. This variability would have obscured any small effect of aging. Linear regression analysis of the effect of age on mean axonal diameter yielded a slight negative slope (P less than 0.01), suggesting a redistribution of fiber diameter. This could occur from axonal shrinkage, from preferential large fiber loss, or from the technical features of tissue acquisition and analysis. The authors suspect that the explanation is a selective loss of large nerve fibers.

[Somatotopic representation of climbing fiber projections from limb cutaneous afferents to the paramedian lobule of the cat cerebellum].

Climbing fiber projections to the cerebellar paramedian lobule were investigated electrophysiologically by stimulation of bilateral superficial radial nerve (SR) and superficial peroneal nerve (SP) in the cat anesthetized with pentobarbitone. In the medial zone of the paramedian lobule, short latency climbing fiber responses to stimulation of the ipsilateral SR were recorded rostrally from the top caudal part of the intermediate folia and short latency responses to stimulation of the ipsilateral SP were obtained caudally from the bottom caudal part of the folia. In the central zone, long latency responses to stimulation of the bilateral SR and SP were obtained. "Four limbs area" in which these responses were recorded was 1.0-1.2 mm in width. Short latency responses to stimulation of the ipsilateral SR were observed rostrally from this area, and short and long latency responses to stimulation of the ipsilateral SP were distributed caudally from this area. In the lateral zone, short and long latency responses to stimulation of the ipsilateral SR were recorded rostrally from the rostral part of the intermediate folia, and long latency responses to stimulation of the ipsilateral SP were observed caudally from the caudal part of the folia. In the most lateral zone, short and long latency responses to stimulation of the ipsilateral SR were obtained rostrally from the rostral part of the intermediate folia, and long latency responses to stimulation of ipsilateral SP were recorded only in the bottom caudal part of the folia caudally from the caudal part of the folia.

Somatotopy of digital nerve projections to the cuneate nucleus in the monkey.

Somatotopic arrangements of cells and fibers within the dorsal columns and the dorsal column nuclei have been mapped most precisely by electrophysiological recording methods. This study uses an anatomical approach to evaluate the precision of individual digital nerve projections to the cuneate nucleus (CN) in young macaque monkeys. Digital nerves supplying about one-half the palmar skin of a digit were surgically exposed, cut, and treated with wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) on 3 successive days. After 2 additional days, animals were killed and medullas were recovered for study of serial sections reacted to display axons labeled by transganglionic transport of label. Labeled afferent fibers from each digit were found within a circumscribed columnar zone extending through the caudal CN and rostrally throughout the pars rotunda of CN. At caudal levels, diffuse projections reach the dorsal edge of the CN; more rostrally, they shift into deeper parts of the nucleus and are heaviest along its ventral and medial edges at levels near the obex. Fibers from the thumb (digit 1) project lateral (and ventral) to those from digit 2, and projections from digit 3 are medial to those from 2. Each digital projection field is closely adjacent to that from the adjacent digit. Few fibers extend to the rostral CN. Projection fields of homologous digits are quite symmetrical on the two sides. Although there do seem to be some differences in the somatotopic arrangement of digital input in macaques compared to other nonprimate mammals studied previously, these observations (precisely organized, circumscribed fields for separate digits) define a system well designed for transmission of data encoding spatial relationships.

[The lateral root of the ulnar nerve]. / Die Radix lateralis des Nervus ulnaris.

In 158 brachial plexuses the origin of the fibers of the ulnar nerve-whether only from the medial or also from the lateral fascicle-was investigated. A lateral root was found in 56%. This lateral root may either be accompanied by fibers of the median nerve (type 1) or may run separately (type 2). Where this root crosses the medial root of the median nerve, either a small minority of fibers of the latter nerve may run behind the ulnar fibers (type a), or all median fibers are in front of them (type b). Considering the relation 56:44% between ulnar nerves with and without a lateral root both possibilities have to be considered as normal variations, none as a variety. In analogy to the term 'median loop' the term 'ulnaris loop' is suggested for specimens with a lateral root.

Topographic organization of the corticonuclear fibers from the tuber vermis and paramedian lobule in the albino rat.

The topographic organization of the corticonuclear fibers from the tuber vermis and paramedian lobule in the albino rat was investigated by autoradiographic anterograde tracing method. The medial portion of the tuber vermis projects to the dorsal part of the caudomedial subdivision of the medial cerebellar nucleus (MNcm), whereas the lateral portion of the tuber vermis projects to the dorsal part of the MNcm and the caudal part of the middle subdivision of the medial nucleus. The intermediate cortex of the paramedian lobule can be subdivided mediolaterally into three portions which project to the dorsolateral protuberance of the medial cerebellar nucleus, the rostrodorsal part of the posterior interpositus nucleus, and the caudodorsal part of the lateral anterior interpositus nucleus, respectively. The lateral cortex of the paramedian lobule can also be subdivided mediolaterally into two portions: the medial portion projects to the dorsolateral hump, and the lateral one to the lateral cerebellar nucleus. These results indicate that the cortical efferent fibers from the tuber vermis and paramedian lobule are clearly organized in the mediolateral direction in the albino rat.

Zinc-containing fiber systems in the cochlear nuclei of the rat and mouse.

Zinc-containing neurons are cells which sequester zinc in the vesicles of their axonal boutons; such zinc-containing fiber systems have been previously shown to innervate many limbic and cerebrocortical brain regions. The present study of rats and mice shows that zinc-containing axons also innervate the cochlear nuclei, forming two morphologically-distinct projection systems. One zinc-containing pathway innervates the molecular stratum of the dorsal nucleus, supplying a diffuse, even band of neuropil staining throughout the stratum. The other pathway projects sparsely to the various small cell (granule cell) regions of the nuclei where the zinc-positive elements form scattered clusters and threads of bouton-like puncta amidst the granule neuron somata. Preliminary observations indicate that the pattern is the same in the cat as in the rat and mouse.

Origins and pathways of cerebrovascular vasoactive intestinal polypeptide-positive nerves in rat.

In order to clarify the origins and pathways of vasoactive intestinal polypeptide (VIP)-containing nerve fibers in cerebral blood vessels of rat, denervation experiments and retrograde axonal tracing methods (true blue) were used. Numerous VIP-positive nerve cells were recognized in the sphenopalatine ganglion and in a mini-ganglion (internal carotid mini-ganglion) located on the internal carotid artery in the carotid canal, where the parasympathetic greater superficial petrosal nerve is joined by the sympathetic fibers from the internal carotid nerve, to form the Vidian nerve. VIP fiber bridges in the greater deep petrosal nerve and the internal carotid nerve reached the wall of the internal carotid artery. Two weeks after bilateral removal of the sphenopalatine ganglion or sectioning of the structures in the ethmoidal foramen, VIP fibers in the anterior part of the circle of Willis completely disappeared. Very few remained in the middle cerebral artery, the posterior cerebral artery, and rostral two-thirds of the basilar artery, whereas they remained in the caudal one-third of the basilar artery, the vertebral artery, and intracranial and carotid canal segments of the internal carotid artery. One week after application of true blue to the middle cerebral artery, dye accumulated in the ganglion cells in the sphenopalatine, otic and internal carotid mini-ganglion; some of the cells were positive for VIP. The results show that the VIP nerves in rat cerebral blood vessels originate: (a) in the sphenopalatine, and otic ganglion to innervate the circle of Willis and its branches from anterior and caudally and (b) from the internal carotid mini-ganglion to innervate the internal carotid artery at the level of the carotid canal and to some extent its intracranial extensions.

Immunohistochemical demonstration of vasopressin nerve fibers in the cerebral artery.

Vasopressin-immunoreactive nerve fibers were demonstrated in the cerebral pial arteries by peroxidase immunohistochemistry. In the large pial artery (proximal part of the middle cerebral artery), they ran longitudinally to the long axis of the vessel. They ran in a spiral pattern in the distal part of the middle cerebral artery. Even in small arteries, vasopressin nerve fibers were found arranged in a longitudinal fashion. The present morphological data suggest that vasopressin nerve fibers in the cerebral artery may play a role in cerebral circulation.