Axoplasmic transport with velocities induced by pargyline

The axoplasmic transport of proteins in spinal motor neurons is altered by pargyline, a drug that causes increased release of monoamines. Two new peaks of transported protein were detected in the sciatic nerves of rats treated with pargyline (75 mg/kg/day ip for three days). These peaks moved with velocities of 595 mm/day (peak I) and 1,230 mm/day (peak II). The bulk of labeled protein was still transported at the control rate of 362 mm/day. Electrophoresis of transported polypeptides labeled with [35S] methionine showed that peak I material was qualitatively similar to material transported at the normal rate in controls, but peak Ii material contained fewer labeled polypeptides. Both peak I and peak II differed from controls in the relative intensity of labeling of various polypeptides. Fast axoplasmic transport in sensory neurons was unaffected by pargyline. Intraspinal injection of pargyline (50 microgram/day for three days) caused changes in axoplasmic transport similar to those induced by intraperitoneal pargyline. These results show that transport of certain proteins along a peripheral nerve can be accelerated by a mechanism initiated in the region of the nerve cell bodies.     

Type II cochlear ganglion cells in the chinchilla

In order to ascertain whether Type II cochlear ganglion cells project to the brain, we have studied the retrograde transport of horseradish peroxidase (HRP) from the cochlear nucleus to the spiral ganglion of the chinchilla. In this animal there exist two types of ganglion neurons, which closely correspond to those previously described in guinea pigs, cats and rats. As in the guinea pig, the majority population (Type I) consists of relatively large, myelinated neurons. The minority population (Type II, 10% of the total population) consists of small, mostly unmyelinated cells, with filamentous cytoplasm and finely grained nuclear chromatin. Type II neurons tend to be clustered toward the peripheral side of Rosenthal's canal, often in close proximity to the intraganglionic spiral bundle. By 24 h after injections of HRP into the cochlear nucleus, incubation of the cochlear ganglion in diaminobenzidine/H2O2 reveals abundant HRP label in both Type I and Type II neurons. Type II neurons, however, tend to be labelled less intensely than Type I neurons. Control experiments, consisting of spillage of HRP solution over the cochlear nucleus, were carried out to determine how much HRP might be picked up by neurons after HRP diffusion. Comparison of cochleae from injected animals and from the control animals suggests that most of the label that was found in ganglion neurons after cochlear nucleus injections represents axonally transported HRP. We conclude, at least tentatively, that Type II neurons project to the brain. The fact that less label is found in Type II neurons that in Type I neurons suggests that the former have thinner axons and/or finer terminals in the cochlear nucleus.     

Morphine-induced activation of A10 dopamine neurons in the rat

The effects of intravenous administration of morphine (MOR) on the spontaneous discharge rate of dopamine (DA) neurons in the ventral tegmental area (VTA or A10) and the substantia nigra pars compacta (SNC or A9) were compared. MOR (0.5-3.5 mg/kg) produced a marked increase in the spontaneous firing of both A10 and A9 DA neurons. Naloxone (NAL) reversed the MOR effects. Acute transection of the medial forebrain bundle (MFB) did not interfere with the observed MOR effects on either A10 or A9 DA neurons. However, following chronic lesions of the MFB (6 days), A9 DA neurons were no longer responsive to MOR whereas A10 DA cells were still activated by MOR. Neither radiofrequency lesions of the dorsal raphe nucleus (DRN) nor administration of the 5-HT2 antagonist ketanserin affected the stimulatory effect of MOR on either A10 or A9 DA cells. Thus, it is confirmed that the effects of MOR on A9 DA cells depend on striatonigral feedback pathways. In contrast, it appears that the MOR-induced activation of A10 DA cells does not depend on afferents from the forebrain or on projections from the DRN, suggesting a more direct action of MOR on A10 DA cells. Microiontophoretic application of MOR or enkephalin analogues significantly increased the spontaneous activity of both A9 and A10 DA cells. However, these effects were not reversed by either iontophoretic or intravenous NAL. On the other hand, both intravenously (0.5-1.5 mg/kg) and iontophoretically administered MOR markedly suppressed the electrical activity of non-DA cells found in the vicinity of A10 DA neurons, and this effect was completely reversed by NAL. It is proposed that the MOR-induced activation of A10 DA cells could be mediated indirectly by non-DA cells.     

A computer electron microscope plotter for mapping spatial distributions in biological tissues

We have designed a computer-based electron microscope plotting system which maps the locations of organelles in tissue specimens and analyzes their distribution. The system includes: (1) two optical incremental shaft encoders which translate stage drive rotation to electrical pulses; (2) a Display/Control unit used to convert encoder pulses to binary code for computer input; (3) two 16-bit parallel interfaces for transferring data to the computer; (4) a Hewlett-Packard 9845T microcomputer, used to control data input and to store, graph, and analyze the plots. The software for the plotter is written in enhanced BASIC.The plotter system is driven by 4 programs called Trace, Plot, Analyze, and Density. The Trace program “draws” an outline of the edges of the tissue. The Plot program maps the positions of profiles within the tissue. The Analyze program compares trace and plot data and calculates the depth and medial-lateral distance of each plotted profile from the surfaces of the tissue. The Density program sorts and counts profile types, measures surface areas, and calculates profile densities. Commercial statistical software is used to analyze the data. Our laboratory uses the system to map the spatial distribution of synapses and neurons in the central nervous system. The plotting system will also be of value in other areas of neurobiology research.     

Effect of exposure to anti-NGF on sensory neurons of adult rats and guinea pigs

Nerve growth factor (NGF) deprivation was produced in adult rats and guinea pigs by immunization against mouse NGF. Exposure of adult animals to anti-NGF had no effect on sensory ganglion neuronal number or size-frequency histograms. However, the substance P content of sensory ganglia, spinal cord and hind paw skin decreased to as great an extent as was seen in animals exposed to anti-NGF in utero. We conclude that NGF has two separate effects on sensory neurons: adult sensory neurons require NGF for normal function whereas developing neurons require NGF for both survival and transmitter expression.     

Localization of motoneurons controlling the extraocular muscles of the rat

The localization of extraocular motoneurons in the rat was investigated by injecting horseradish peroxidase and [¹²⁵I]wheat germ agglutinin¹⁷ as retrogade tracer substances into individual eye muscles. The organization of subnuclei was found to be most similar to the rabbit. The subgroups representing the medial rectus and inferior rectus muscles are located in the rostral two thirds of the ipsilateral oculomotor nucleus (nIII) with some medial rectus motoneurons scattered laterally along the edge of the medial longitudinal fasciculus. The motor pool controlling the inferior oblique muscle is located in the middle third of the ipsilateral nIII. The motoneurons of the superior rectus muscles are in the caudal two-thirds of contralateral nIII while the levator palpebrae muscle has a bilateral innervation in the oculomotor nucleus. The motoneurons of the superior oblique are located in the contralateral trochlear nucleus although a few labeled neurons were scattered laterally in amongst the fibers of the medial longitudinal fasciculus. The cell bodies of lateral rectus motoneurons regional separation between the latter and internuclear neurons was found after injecting HRP into the oculomotor nucleus.     

Synaptogenesis and myelination in dissociated cerebral microcarrier cell cultures

A new approach for cultivating dissociated cerebral neurons is described. It is based on a rapid attachment of neurons to the DEAE-cellulose cylindrical MC and their subsequent interconnection to form cell-MC conglomerates. Intensive fiber growth followed by synaptogenesis and progressive myelin formation are indicative of optimal conditions of nutrition and oxygenation.