Principal neurons projecting to the pineal gland in close association with small intensely fluorescent cells in the superior cervical ganglion of rats

Summary The localization in the superior cervical ganglia (SCG) of small, intensely fluorescent (SIF) cells and of principal nerve (PN) cells innervating the pineal gland was examined in adult male Sprague-Dawley rats. PN cells were demonstrated by means of the retrograde neuron-tracing method using the fluorescent tracer Fluoro-Gold (FG) injected into the pineal gland. SIF cells were visualized by the formaldehyde-induced fluorescence method. Twentynine percent of the FG-labeled PN cells were found closely associated with SIF cells. In the rostral half of the ganglion, 43% of the SIF cells were situated in juxtaposition to one or several labeled neurons. The possible influence of SIF cells on the regulation of pineal metabolism is discussed with respect to their role as both local endocrine cells and interneurons.     

Monoamine storage sites in the rat superior cervical ganglion following synthesis inhibition

Summary Monoamine storage sites in paraganglionic (PG-)cells of the rat superior cervical ganglion were investigated by electron and fluorescence microscopy following treatment with p-chlorophenylalanine (pCPA), disulfiram or guanethidine respectively.Dense core vesicles in PG-cells are significantly decreased (p< 0.001) in number following pCPA, and in the majority of these cells following disulfiram and guanethidine. However in a minor portion of PG-cells the latter agents cause an increase in number and in size of dense core vesicles, in parallel with structural alterations. In agreement with these electron microscopic findings fluorescence microscopic and cytophotometric evaluations reveal a general decrease in catecholamine content with few cells showing an increase.The findings provide a morphological basis for the assumption, that monoamine storage sites in PG-cells can be decreased by inhibition of monoamine synthesis, following administration of pCPA, disulfiram and guanethidine. However the two types of responses of PG-cells which occur after disulfiram and guanethidine demonstrate a functional heterogeneity of this cell system in the rat superior cervical ganglion which is discussed.Supported by Deutsche Forschungsgemeinschaft — Grant He 919/1.I like to thank Prof. Arnold, Tübingen, for the kind disposal of cytophotometric equipment.     

Changes in the intracellular calcium concentration upon activation of rat superior cervical ganglion neurons

Changes in the intracellular calcium concentration induced by activation of neurons of the isolated intact rat superior cervical ganglion were recorded. It is concluded that stimulation within the physiological range of frequencies can effectively increase the intracellular calcium concentration in these neurons. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 400–402, July–October, 2007.     

S-100 antigen in satellite cells of the adrenal medulla and the superior cervical ganglion of the rat

Summary Measurable amounts of the nervous-system specific S-100 protein were detected by microcomplement fixation assay both in the superior cervical ganglion and in the adrenal medulla of adult rats, though at a significantly higher concentration in the ganglion. By the unlabeled antibody PAP method, the antigen was localized at: he ultrastructural level in the Schwann cells and in the satellite cells of the ganglion, but not in neurons. Similarly, the protein was found in the Schwann cells of the adrenal medulla, but not in the chromaffin cells. Moreover, the S-100 immunolabeling allowed detection of a class of satellite cells closely enveloping the chromaffin cells. In the labeled cells of both organs the reaction product was diffusely distributed in the cytoplasmic matrix as well as in the nucleoplasm.The presence of the S-100 antigen in the satellite cells of the sympathetic ganglion and in satellite cells of the adrenal medulla suggests a possible homology for the two cell types, and one could hypothesize the presence in peptide hormone-secreting endocrine organs of glia-like cells exhibiting functional relationships with the secretory cells comparable to those of the glial cells with the neurons.     

Immunocytochemical and circadian biochemical analysis of neuroactive amino acids in the pineal gland of the rat: effect of superior cervical ganglionectomy

Summary Semiquantitative immunocytochemistry by immuno-gold techniques revealed differences in the spatial distribution of glutamate, glutamine, and taurine within the pineal gland, with greatest labeling over pinealocytes, glia, and endothelia, respectively. At the subcellular level, glutamate labeling tended to be highest over pinealocyte synaptic ribbons and mitochondria, and lowest over lipid inclusions. Pineal levels of glutamate, glutamine and taurine, as measured by high performance liquid chromatography, did not vary over a light: dark cycle. Superior cervical sympathetic denervation, which abolishes pineal melatonin synthesis, resulted in a nearly 50% reduction in pineal glutamate levels, but had no effect on levels of glutamine and taurine. Other amino acids (alanine, arginine, aspartate, serine) were reduced by 23%–33% following sympathectomy. These data suggest an important role for glutamate in pinealocyte function(s) possibly related to the noradrenergic innervation of the gland.     

Distribution and relative proportions of neuropeptide Y- and proenkephalin-containing noradrenergic neurones in rat superior cervical ganglion: Separate projections to submaxillary lymph nodes

The distribution and relative proportions of neuropeptide Y (NPY)- and [Met]enkephalyl-Arg-Gly-Leu (ME-RGL)-containing sympathetic neurones in the rat superior cervical ganglion (SCG) and their projections to submaxillary lymph nodes (SLN) were determined by retrograde tracing and immunocytochemistry. Three subpopulations of neurones were detected in the SCG: 64% contained NPY, 30% contained ME-RGL, and 6% were immunonegative for both. Immunoreactive neurones were also present inside the external carotid nerve of the SCG. An injection of Fluoro-Gold (FG) into the left SLN retrogradely labeled a few neurones in the ipsilateral SCG. FG-labeled neurones contained tyrosine hydroxylase (TH) and were either positive for ME-RGL or for NPY. FG-labeled neurones immunostained for ME-RGL outnumbered by 4:1 FG-labeled neurones immunopositive for NPY. It is suggested that the sympathetic/peptidergic innervation to SLN may have distinct vasoregulatory and immunomodulatory functions.     

Cholinergic innervation of the mouse superior cervical ganglion: light-and electron-microscopic immunocytochemistry for choline acetyltransferase

Summary The cholinergic innervation of the mouse superior cervical ganglion was investigated by means of immunocytochemistry using a well-characterized monoclonal antibody against choline acetyltransferase (ChAT). Immunopositive nerve fibers entered the superior cervical ganglion from the cervical sympathetic trunk. Light-microscopically, these fibers appeared to be heterogeneously distributed among the principal ganglion cells. The rostral part of the ganglion contained more ChAT-positive fibers then the middle or the caudal one. The axons branched several times before forming numerous varicosities. Most of the ChAT-stained fibers and varicosities aggregated in glomerula-like neuropil structures that were surrounded by principal ganglion cell bodies, whereas others were isolated or formed little bundles among principal neurons. None of the neurons or other cell types in the ganglion exhibited ChAT-positivity. ChAT-immunoreactive fibers disappeared from the ganglion 5 or 13 days after transection of the cervical sympathetic trunk. At the ultrastructural level, most axon terminals and synapses showed ChAT-immunoreactivity. An ultrastructural analysis indicated that immunostained synapses occurred directly on the surface of neuronal soma (1.8%) and dendritic shafts (17.6%). Synapses were often seen on soma spines (18.4%) and on dendritic spines (62.2%). All immunoreactive synapses were of the asymmetric type. The results provide immunocytochemical evidence for a heterogeneous cholinergic innervation of the ganglion and the principal neurons.     

The effect of the transplanted pineal gland on the sympathetic innervation of the rat sublingual gland

We investigated the effect of the pineal on sympathetic neurons that normally innervate the sublingual gland of the rat. When the pineal gland was transplanted into the sublingual gland, it remained as a distinct mass that was innervated by sympathetic axons. Injection of the retrograde tracer, Fast Blue, into the sublingual gland labelled sympathetic neurons in the ipsilateral superior cervical ganglion (SCG). Thirty per cent of all neurons labelled retrogradely by Fast Blue injection into transplanted pineal glands were immunoreactive for both neuropeptide Y (NPY) and calbindin. This combination is characteristic of sympathetic neurons innervating the pineal gland in its normal location, but not the sympathetic vasoconstrictor neurons normally innervating the sublingual gland. This, and our previous study in which the pineal gland was shown to similarly influence the phenotype of salivary secretomotor neurons, suggests that a range of different functional classes of sympathetic neuron are able to change their phenotype in response to signals released by the pineal gland.This work was supported by Project Grant No. 145634 from the National Health and Medical Research Council of Australia     

Alterations in the morphology of ganglion cell dendrites in the adult rat retina after optic nerve transection and grafting of peripheral nerve segments

Summary Transected ganglion cell axons from the adult retina are capable of reinnervating their central targets by growing into transplanted peripheral nerve (PN) segments. Injury of the optic nerve causes various metabolic and morphological changes in the retinal ganglion cell (RGC) perikarya and in the dendrites. The present work examined the dendritic trees of those ganglion cells surviving axotomy and of those whose severed axons re-elongated in PN grafts to reach either the superior colliculus (SC), transplanted SC, or transplanted autologous thigh muscle. The elaboration of the dendritic trees was visualized by means of the strongly fluorescent carbocyanine dye DiI, which is taken up by axons and transported to the cell bodies and from there to the dendritic branches. Alternatively, retinofugal axons regrowing through PN grafts were anterogradely filled from the eye cup with rhodamine B-isothiocyanate. The transection of the optic nerve resulted in characteristic changes in the ganglion cell dendrites, particularly in the degeneration of most of the terminal and preterminal dendritic branches. This occurred within the first 1 to 2 weeks following axotomy. The different types of ganglion cells appear to vary in their sensitivity to axotomy, as reflected by a rapid degeneration of certain cell dendrites after severance of the optic nerve. The most vulnerable cells were those with small perikarya and small dendritic fields (type II), whereas larger cells with larger dendritic fields (type I and III) were slower to respond and less dramatically affected. Regrowth of the lesioned axons in peripheral nerve grafts and reconnection of the retina with various tissues did not result in a significant immediate recovery of ganglion cell dendrites, although it did prevent some axotomized cells from further progression toward posttraumatic cell death.     

Changes in lectin binding of lumbar dorsal root ganglia neurons and peripheral axons after sciatic and spinal nerve injury in the rat

Summary The effects of chronic lesions of rat lumbar spinal or sciatic nerves on the binding of Glycine max (soybean) agglutinin to galacto-conjugates, in small-and medium-size primary sensory neurons of the L₄ and L₅ dorsal root ganglia, were examined over a 580-day period. Spinal nerve section resulted in a marked decrease in the population of stained neurons within 7 days. However, despite some retrograde morphological changes triggered by axonal injury, the proportion of stained nerve cells was normalized 180 days postoperatively. This temporary decrease in perikaryal lectin reactivity was initially associated with a marked accumulation of stained material in the nerve, proximal and distal to the site of section, with similar accumulations also being noticeable at each level of injury in sciatic nerves subjected to double ligature. This may reflect the presence of glycocompounds linked to the autolysis of nerve fibers during the phase of retrograde dying-back and Wallerian degeneration. At later stages, stained deposits could be seen scattered along central and peripheral axonal processes of the dorsal root ganglion neurons in the vicinity of the cell body. They may indicate a disturbance in the peripheral turnover of glycoproteins in chronically-transected nerves, with piling up of neuronal products. Sciatic nerve injury caused similar but less severe effects which, except for the L₄ ganglion cells, were rapidly reversible.     

Misidentification of cardiac vagal pre-ganglionic neurons after injections of retrograde tracer into the pericardial space in the rat

We evaluated whether pericardial injections of the retrograde tracers cholera toxin subunit B (CTb) or Fast Blue (FB) reliably labelled cardiac vagal pre-ganglionic neurons. Injections of CTb into the pericardial space of the rat labelled neurons in both the external and compact formations of the nucleus ambiguus. Most labelled neurons were found in the compact formation of the nucleus ambiguus, and the majority of these, and only these, expressed immunoreactivity for calcitonin gene-related peptide. This distribution of labelled neurons and their immunohistochemical properties is characteristic of oesophageal motoneurons. Examination of the oesophagus following intra-pericardial CTb applications revealed strong labelling of motor end plates within the skeletal muscle of the thoracic but not the abdominal oesophagus. When a second retrograde tracer, FB, was injected into the abdominal oesophagus, labelled somata were found adjacent to CTb-labelled neurons in the compact formation of the nucleus ambiguus. No co-localisation of tracers was found, but identical proportions of calcitonin gene-related peptide (CGRP) immunoreactivity were observed in both groups of neurons. FB injected into the pericardial space labelled intra-cardiac neurons but not brainstem neurons. We conclude that intra-pericardial, and perhaps sub-epicardial, injections of some retrograde tracers are likely to label a subset of oesophageal, as well as cardiac, vagal motor neurons in the brainstem.This work was supported in part by grant No. G 00 M 0670 from the National Heart Foundation of Australia.     

Clusters of nerve cell bodies enclosed within a common connective tissue envelope in the spinal ganglia of the lizard and rat

Summary A careful search for groups of nerve cell bodies enclosed within a common connective envelope was made in the spinal ganglia of the lizard and rat using a serial-section technique. Nerve cell bodies sharing a common connective envelope were found to be more common in the lizard (9.4%) than in the rat (5.6%). These nerve cell bodies were arranged in pairs, or, less frequently, in groups of three. At times, they appeared to be in immediate contact, with no intervening satellite cells; at other, they remained separated from one another by a satellite cell sheet. The clusters of nerve cell bodies enclosed within a common connective envelope probably result from the arrest of developmental processes in the spinal ganglion. It is possible that, as a result of the cell arrangement here described, certain neurons electrically influence other sensory neurons at the level of the ganglion.