Transfer of material from efferent axons to sensory epithelium in the goldfish vestibular system

Axoplasmic incorporation of amino acids in a myelinated fiber exceeds that of its soma: a radioautographic study

The axoplasmic incorporation of amino acids was studied in the giant Mauthner axon to determine its magnitude, to estimate the half-life of the resulting material, and to establish whether or not it undergoes transport. The incorporation of labeled leucine, lysine, and proline was followed by radioautography. The tracers were injected away from the cell body, either in the floor of the IV ventricle or into the spinal cord. Radioautographic reaction on the Mauthner somata was barely discernible. However, at the site of injection, for survivals to 5.6 days, a peak of reaction was observed on the Mauthner axoplasm, with a sharp and symmetric decrement in both central and distal directions; the intensity of the peak decreased with survival (14% at 5.6 days). In intact fibers, the intensity of the reaction was 1.4% compared with that over the Nissl substance of neighboring somata; by contrast, in severed fibers whose axoplasm had been directly exposed to the tracers the reaction rose to 4.1%. At early times, the intensity of the response of the axoplasm as a function of survival of the fish did not have a lag time. In high-resolution radioautograms, most of the grains overlay the ground axoplasm. Cycloheximide depressed the reaction over the fiber open to the extracellular space by 55% whereas only by 20% over the intact fiber. Adsorption of free amino acids or their binding to tRNA were ruled out as a cause of the radioautographic response. Our results indicated that incorporation of amino acids into macromolecules of the Mauthner fiber occurred locally, and its magnitude over the whole axoplasm was estimated to be one order of magnitude larger than that occurring in the soma. The bulk of the material resulting from this incorporation did not undergo transport and survived some days. We suggest that the amino acids were incorporated by a ribosomal mechanism.

Radioautographic study of the axonal transport of proteins into the sensory nerve endings of avian mechanoreceptors

The axonal transport of proteins to the nerve endings of Herbst and Grandry sensory receptors has been investigated by electron-microscope radioautography. Soon after the injection of [3H]leucine into the trigeminal ganglia of young ducks, labeled proteins are conveyed along the suborbital sensory nerves to the sensory nerve endings at rates of at least 200-280 mm/day. Most of these rapidly transported proteins accumulate in areas containing vesicles of various kinds and along the axolemmal region. Later, the bulk of labeled proteins migrate along the axons at rates of about 15 mm/day and are distributed mainly to the mitochondria. A small portion of labeled material is transferred to the adjoining modified Schwann and specialized Grandry receptor cells. It is concluded that the transport of proteins from sensory ganglia to sensory nerve endings of mechanoreceptors is conveyed at fast and intermediate rates and is mainly used for the renewal of vesicles, axolemmal constituents and mitochondria.

Experimental studies on the olfactory marker protein. I. Presence of the olfactory marker protein in tufted and mitral cells

Partial, unilateral olfactory nerve section was performed in mice, and the behavior of the olfactory marker protein (OMP) studied, after this experimental manipulation, with the peroxidase--antiperoxidase method. The protein, which in normal mice is present only in mature olfactory sensory neurons, after unilateral lesion of the fila olfactoria was observed in mitral and tufted cells of both olfactory bulbs. Positive elements, present at 5 days postoperative, increased in number up to 30 days and some could still be detected at 60 days. The functional implications of this finding are briefly discussed.

Origin of efferent fibers of the vestibular apparatus in goldfish. A horseradish peroxidase study

After injecting a horseradish peroxidase (HRP) solution into the vestibular apparatus in goldfish (Carassius auratus), cells in the medulla oblongata exhibited retrogradely transported HRP reaction product. These labeled cells were confined to 3 nuclei, i.e. the nucleus motorius tegmenti of Bartelmez (with the most prominent labeled cell groups), the ventral vestibular nucleus (Dieter's nucleus) and the medial vestibular nucleus. We consider these labeled cells to be the origin of the efferent innervation to the vestibular apparatus in goldfish. Neurons providing efferent innervation to the sensory periphery in the nucleus motorius tegmenti have, as yet, not been described.

Inhibition by puromycin of transneuronal transport in the mouse accessory olfactory bulb

Application of [3H]proline to the vomeronasal organ (VNO) in mice results in the transport of labelled material along the vomeronasal axons to their terminals in the glomerular layer of the accessory olfactory bulb (AOB). In addition labelled material leaves the vomeronasal nerve terminals and is found over the external plexiform layer (EPL), where a previous electron microscopic autoradiographic study showed that it is preferentially accumulated in mitral cells. Grain densities over the glomerular layer and the EPL were counted in light micrographs. After subtracting background, the overall density of grains in the EPL is about 10% of that over the glomerular layer at 6 h after administration of [3H]proline to the VNO (5 mice). In a further 7 mice, puromycin (or saline) was applied directly to the AOB at hourly intervals during the 6 h after [3H]proline administration. Under these circumstances the labelling in the EPL is only 2--4% of that in the glomerular layer (9% for the 2 saline controls). These observations are evidence that a major part of the transsynaptic transfer mechanism is dependent on protein synthesis, and also favour the view that free amino acids are an important component of the material transferred.

Selective trans-synaptic migration of tetanus toxin after retrograde axonal transport in peripheral sympathetic nerves: a comparison with nerve growth factor

Adult rats were injected unilaterally into the anterior eye chamber and the submandibular gland with either [125I]tetanus toxin or [125I]nerve growth factor (NGF). Fourteen and 24 h later in electron microscopic autoradiographs of the superior cervical ganglia of the injected side the labeling was confined to a limited number (15-20%) of adrenergic ganglion cells and the silver grains were localized over axons, perikarya and dendrites providing evidence for a retrograde intraaxonal transport of the two macromolecules. Moreover, after injection of [125]tetanus toxin there was a very marked labeling of the presynaptic cholinergic nerve terminals. In contrast, after [125I]NGF these terminals were free of label. In both cases no specific labeling could be detected over glia and extracellular space. In the postganglionic axons the radioactivity seemed to be mainly associated with vesicles and smooth endoplasmic reticulum, in the perikarya and dendrites of the adrenergic neurons with secondary lysosomes, vesicles and smooth endoplasmic reticulum. The Golgi cisternae and the nuclei were free of radioactivity. The specific labeling of presynaptic terminals after injection of [125I]tetanus toxin together wirans-symaptic migration of [125I]tetanus toxin from the adrenergic ganglion cell to its innervating presynaptic terminals following retrograde intraaxonal transport.

[Kinetics of resorption in the cochlear perilymph after charging with radionuclides (author's transl)]

The perilymphatic space of the guinea pig's cochlea is filled within 1 to 3 min with an isotonic Ringer solution labelled with a radionuclide. The cochlea is neatly sealed immediately afterwards, thus causing only a minimal disturbance in the inner ear. The animal's cochlea is brought into the strict focus of a small detector as quickly as possible, the decay of activity is continuously controlled for 2 to 10 hrs. The radionuclides used are Cl36, Na22, and Tc99m. The decay of activity of the cochlea is strongly believed to accord to a simple exponential law; half lives range from about one to about three hours. Cl36 and Tc99m were used for the first time in studying cochlear kinetics.

Demonstration of a pallido-nigral projection innervating dopaminergic neurons

Afferents to the substantia nigra from the neostriatum and globus pallidus were studied in the rat by means of the autoradiographic tracing technique. 3H-leucine was injected stereotaxically into either the globus pallidus or neostriatum. Twenty-four hours later the axoplasmic transport of labelled proteins to the substantia nigra was studied by light and electron microscopic autoradiography. In animals used for electron microscopy, degeneration of dopaminergic cells in the substantia nigra was induced by intraventricular injection of 6-hydroxydopamine 72 hours before sacrifice. After neostriatal injections, light microscopic analysis revealed heavy labelling of the globus pallidus and entopeduncular nucleus, but only background labelling of the subthalamic nucleus. There was preferential labelling of the zone reticulata of the substantia nigra, with significantly less labelling of the zone compacta. After pallidal injections, light microscopic analysis showed very light labelling of those parts of the caudate-putamen in the vicinity of the injection site. There was intense labelling of the subthalamic nucleus and heavy labelling of the entopeduncular nucleus. The zona compacta of the substantia nigra was also heavily labelled. There was considerably less labelling of the zona reticulata. The electron microscopic analyses showed that after neostriatal injections, autoradiographic grains in the substantia nigra were located preferentially over boutons which terminated on normal dendritic processes. After pallidal injections, however, grains were preferentially located over boutons synapsing with degenerating dendritic processes. The degeneration produced in these dopaminergic processes by 6-hydroxydopamine was invariably of the dark type. Except for the different association with degenerating vs. non-degenerating dendrites, the subcellular distribution of autoradiographic grains in the substantia nigra was the same after injection into either the globus pallidue or caudate-putamen. Approximately 80 percent of the grains were over axons or boutons which invariably made symmetrical synaptic contacts. These observations demonstrate the existence of a pallido-nigral projection which terminates preferentially on dopaminergic cells in the pars compacta of the substantia nigra. They also confirm previous studies indicating that the strionigral projection terminates mainly in the pars reticulata. These terminations appear to be principally to non-dopaminergic cells.