Sequential ultrastructural study of mucosal innervation following parietal cell vagotomy and antrectomy

Summary Rats having undergone parietal cell vagotomy (PCV) or PCV with antrectomy were sacrificed and gastric mucosal samples studies by electron microscopy. Degeneration of axons was followed by the appearance of small, neurotubule-rich axons which increased in size and number with increasing postoperative interval. The source of these regenerating fibers is unknown but may have come from the fundus.     

Stimulation of olfactory ensheathing cell motility enhances olfactory axon growth

Axons of primary olfactory neurons are intimately associated with olfactory ensheathing cells (OECs) from the olfactory epithelium until the final targeting of axons within the olfactory bulb. However, little is understood about the nature and role of interactions between OECs and axons during development of the olfactory nerve pathway. We have used high resolution time-lapse microscopy to examine the growth and interactions of olfactory axons and OECs in vitro. Transgenic mice expressing fluorescent reporters in primary olfactory axons (OMP-ZsGreen) and ensheathing cells (S100ß-DsRed) enabled us to selectively analyse these cell types in explants of olfactory epithelium. We reveal here that rather than providing only a permissive substrate for axon growth, OECs play an active role in modulating the growth of pioneer olfactory axons. We show that the interactions between OECs and axons were dependent on lamellipodial waves on the shaft of OEC processes. The motility of OECs was mediated by GDNF, which stimulated cell migration and increased the apparent motility of the axons, whereas loss of OECs via laser ablation of the cells inhibited olfactory axon outgrowth. These results demonstrate that the migration of OECs strongly regulates the motility of axons and that stimulation of OEC motility enhances axon extension and growth cone activity.     

Types of nerve terminals in fetal and neonatal rabbit myocardium

Summary With the use of electron microscopy 4 types of axonal profiles were observed in the developing myocardium of rabbits: 1) adrenergic axons which contained mainly small dense-core vesicles and which presumably can store 5-hydroxydopamine; 2) cholinergic axons which contained small clear synaptic vesicles and which were acetylcholinesterase-positive; 3) axons which contained large vesicles filled with moderately electron-dense material and which resembled purinergic axons; and 4) profiles filled with mitochondria, vesicles of various sizes, lysosome-like bodies, and microtubules and which resembled sensory terminals.Supported in part by the Kentucky Heart Association and in part by the Human Development Studies Program, University of Kentucky. Excellent technical assistance of Mrs Merle Wekstein is gratefully acknowledged.     

Types of nerve terminals in fetal and neonatal rabbit myocardium

With the use of electron microscopy 4 types of axonal profiles were observed in the developing myocardium of rabbits: 1) adrenergic axons which contained mainly small dense-core vesicles and which presumably can store 5-hydroxy-dopamine; 2) cholinergic axons which contained small clear synaptic vesicles and which were acetylcholinesterase-positive; 3) axons which contained large vesicles filled with moderately electron-dense material and which resembled purinergic axons; and 4) profiles filled with mitochondria, vesicles of various sizes, lysosome-like bodies, and microtubules and which resembled sensory terminals.     

Heterogeneous effects of sinusoidal muscular stretching on frequency grams of primary endings due to stimulation of static gamma axons]

The action of sinusoidal stretching at 1,5 Hz on primary ending frequencygrams due to repetitive stimulation of static gamma axons has been studied, in nembutalized cats, on flexor hallucis longus muscle spindles. Whenever, in static conditions, driving is elicited by the repetitive stimulation of gamma axons, the elementary components of the frequencygrams increase in amplitude during muscle stretch. This effect is not observed when the stimulation of the gamma axons gives a regular acceleration of the primary endings without "driving".     

Myelination in the hippocampus during development and following lesion

Myelin is crucial for the stabilization of axonal projections in the developing and adult mammalian brain. However, myelin components also act as a non-permissive and repellent substrate for outgrowing axons. Therefore, one major factor which accounts for the lack of axonal regeneration in the mature brain is myelin. Here we report on the appearance of mature, fully myelinated axons during hippocampal development and following entorhinal lesion with the myelin-specific marker Black Gold. Although entorhinal axons enter the hippocampal formation at embryonic day 17, light and ultrastructural analysis revealed that mature myelinated fibers in the hippocampus occur in the second postnatal week. During postnatal development, increasing numbers of myelinated fibers appear and the distribution of myelinated fibers at postnatal day 25 was similar to that found in the adult. After entorhinal cortex lesion, a specific anterograde denervation in the hippocampus takes place, accompanied by a long-lasting loss of myelin. Quantitative analysis of myelin and myelin breakdown products at different time points after lesion revealed a temporally close correlation to the degeneration and reorganization pha-ses in the hippocampus. In contrast, electroconvulsive seizures resulted in brief demyelination and a faster recovery time course. In conclusion, we could show that the appearance of mature axons in the hippocampus is temporally regulated during development. In the adult hippocampus, demyelination was found after anterograde degeneration and also following seizures, suggesting that independent types of insult lead to demyelination. Reappearing mature axons were found in the hippocampus following axonal sprouting. Therefore, our quantitative analysis of mature axons and myelination effectively reflects the readjusted axonal density and possible electrophysiological balance following lesion. Received 22 December 2003; received after revision 11 February 2004; accepted 17 February 2004     

Selective blockade of components of potassium activation in Myxicola axons

The K+ conductance in Myxicola giant axons activates in two phases which are pharmacologically separable. The fast phase of K+ activation is specifically inhibited by 4-aminopyridine and by the substitution of D2O for H2O. We suggest Myxicola giant axons, like the amphibian node of Ranvier, may possess more than one variety of K+ channel.     

Innervation by W-type retinal ganglion cells of superior colliculus neurons projecting to pulvinar nuclei in cats.

Neurons of the cat superior colliculus (SC) sending their axons to the pulvinar nuclei were identified electrophysiologically as the ones responding antidromically to electrical stimulation of the pulvinar nuclei. They were located in the superficial layers of SC and found to be innervated by axons of W-type ganglion cells of the retina.     

The effect of ether, pentobarbitone sodium and fentanyl on blood gases, acid-base balance and hematological parameters in the rat

Blood gases, acid-base balance and hematological parameters (RBC, PCV and Hb) were measured in adult rats of both sexes. The use of ether and fentanyl had a very little effect on the blood gases and acid-base balance. The induction of pentobarbitone anesthesia, however, was followed by a significant increase in PCO2 and TCO2, while the pH value decreased.     

Cholinergic and adrenergic innervation of the penis artery of the bull: Transmitter concentrations and synaptic vesicles

Summary The penile artery of the bull contained significant amounts of acetylcholine, noradrenaline and dopamine, and its axon profiles contained either numerous small granular or agranular vesicles, as well as some large granular vesicles. In the dorsal metatarsal artery, only noradrenaline and dopamine were detectable, and the axon profiles observed contained numerous small granular vesicles. In the penile artery, the axons with small agranular vesicles, probably cholinergic axons, were in close contact with axons containing small granular vesicles. It is suggested that, in the penile artery of the bull, one of the functions of the cholinergic nerves is suppression of excitatory adrenergic neurotransmission.This study has been supported by grants from the Sigrid Jusélius Foundation (to O.E.), from the Medical Research Council of the Academy of Finland (to E.K.) and from the Magnus Bergvall Memorial Fund (to N.O.S.). Excellent technical assistance by Mrs Paula Hasenson and Miss Seija Ovaskainen is gratefully acknowledged.     

Signal transduction in axon guidance

Neurons establish specific connections by extending projections to contact their targets. Projections, such as axons, navigate to the target by sensing guidance cues in their environment and responding with directed movement and shape change. The recent identification of the molecular identities of many guidance cues and guidance receptors has demonstrated that axons are guided to their targets by combinations of cues that attract and repel them. The current challenge is to elucidate how these guidance cue/receptor interactions control navigation. This review focuses on recent progress in identifying the signaling pathways downstream of these receptors and in determining why an axon is attracted or repelled by a particular guidance cue.     

Impairment of rapid axonal transport and concomitant anomaly of smooth endoplasmic reticulum in acrylamide induced neuropathy]

The axonal transport of proteins was studied by radioautography in preganglionic axons of ciliary ganglia in Leghorn chickens treated by acrylamide. The slow axonal transport of proteins was hardly affected. In contrast, the fast axonal transport was severely impaired. Indeed, radioactive proteins accumulated focally at the periphery of several preterminal axons in regions showing a local disorganization of the smooth endoplasmic reticulum which seemed to be one of the earliest changes induced by acrylamide.     

Fine structures of the basophil infiltration in regional lymph nodes of the guinea-pig after the intradermal injection of T cell mitogens

Summary Basophil-rich infiltrates in regional lymph nodes of guinea-pigs were demonstrated by electron microscopy after the intradermal injection of T cell mitogens (PHA and Con A). Basophils infiltrated the stroma of the lymph node via the postcapillary venules (PCV) and migrated to the paracortex. Prior to infiltration of the lymph nodes a cutaneous basophil hypersensitivity reaction was seen in the mitogen-injected skin. B cell mitogen (LPS) injection did not induce this response.     

Fine structures of the basophil infiltration in regional lymph nodes of the guinea-pig after the intradermal injection of T cell mitogens

Basophil-rich infiltrates in regional lymph nodes of guinea-pigs were demonstrated by electron microscopy after the intradermal injection of T cell mitogens (PHA and Con A). Basophils infiltrated the stroma of the lymph node via the postcapillary venules (PCV) and migrated to the paracortex. Prior to infiltration of the lymph nodes a cutaneous basophil hypersensitivity reaction was seen in the mitogen-injected skin. B cell mitogen (LPS) injection did not induce this response.     

Sensory projections from dorsal and ventral appendages inDrosophila grafted to the same site are different

Summary Owing to a new transplantation technique, we have been able to study the sensory projections of homologous and heterologous appendages grafted to the same abdominal site inD. melanogaster. Axons from homologous transplants exhibit similar terminal patterns, whereas those from heterologous transplants do not. It is suggested that ectopic sensory axons specifically recognized central areas and pathways occupied by axons from homologous appendages.     

Ultrastructural evidence for the innervation of human pulmonary alveoli

Summary Electron Microscopic observations of the biopsied human pulmonary alveoli showed the occurrence of unmyelinated axons in the interstitium near the type I pneumocytes. These axons very likely have sensory functions.     

Identification of actin microfilaments in the neurosecretory axons of rat neural lobe]

Incubation of rat neural lobes with heavy meromyosin (HMM) after prolonged glycerination, induced characteristic arrowhead decoration of a number of microfilaments at different levels of the neurosecretory axons. In non terminal sections of axons the labelled microfilaments showed preferential relationships with microtubules in addition to occasional contacts with the axolemma and various axonal organelles. In axonal endings, they were mainly associated to microvesicles and appeared to be anchored on the axolemma facing the perivascular space at the level of membranous densifications.     

Schwann cell mitochondria as key regulators in the development and maintenance of peripheral nerve axons

Formation of myelin sheaths by Schwann cells (SCs) enables rapid and efficient transmission of action potentials in peripheral axons, and disruption of myelination results in disorders that involve decreased sensory and motor functions. Given that construction of SC myelin requires high levels of lipid and protein synthesis, mitochondria, which are pivotal in cellular metabolism, may be potential regulators of the formation and maintenance of SC myelin. Supporting this notion, abnormal mitochondria are found in SCs of neuropathic peripheral nerves in both human patients and the relevant animal models. However, evidence for the importance of SC mitochondria in myelination has been limited, until recently. Several studies have recently used genetic approaches that allow SC-specific ablation of mitochondrial metabolic activity in living animals to show the critical roles of SC mitochondria in the development and maintenance of peripheral nerve axons. Here, we review current knowledge about the involvement of SC mitochondria in the formation and dysfunction of myelinated axons in the peripheral nervous system.     

Axon guidance at the central nervous system midline

A key feature of the central nervous system of most higher organisms is their bilateral symmetry about the midline. The specialised cells that lie at the midline have an essential role in regulating the axon guidance decisions of both neurons that project axons across the midline and those that project on one side. The midline cells produce both attractive and repellent short- and long-range signals to guide axonal growth. The axons themselves express specific receptors that can be dynamically regulated in response to midline-derived signals. In this way, axons extend toward or away from the midline and those that do cross change their behaviour to respond to longitudinal signals on the contralateral side.     

Selective blockade of components of potassium activation inMyxicola axons

Summary The K⁺ conductance inMyxicola giant axons activates in two phases which are pharmacologically separable. The fast phase of K⁺ activation is specifically inhibited by 4-aminopyridine and by the substitution of D₂O for H₂O. We suggestMyxicola giant axons, like the amphibian node of Ranvier, may possess more than one variety of K⁺ channel.