J.D. Coulter

Noradrenergic projections to the spinal cord of the rat

Noradrenergic terminals were identified in the spinal cord of rats by immunocytochemical staining for dopamine-beta-hydroxylase. Although immunoreactive fibers and terminals were observed throughout the spinal grey matter, heavier accumulations of terminal labeling were observed in the marginal layer of the dorsal horn, in the ventral horn among motoneurons, and in the autonomic lateral cell columns of the thoracic and sacral spinal cord. Two specific retrograde transport techniques were employed to identify the origins of these noradrenergic terminations in the spinal cord. Cells of origin were observed in the locus coeruleus, the subcoeruleus, the medial and lateral parabrachial, and the Kölliker-Fuse nuclei, as well as adjacent to the superior olivary nucleus. These regions correspond to the A5-A7 cell groups of the pons. No spinally projecting noradrenergic cells were ever observed in the medulla. It was concluded that pontine noradrenergic cell groups are the sole source of noradrenergic terminals in the spinal cord.

Descending serotonergic, peptidergic and cholinergic pathways from the raphe nuclei: A multiple transmitter complex

The localization of serotonergic, various peptidergic and possibly cholinergic neurons in the medullary raphe nuclei that project to the lumbosacral spinal cord have been studied using a retrograde transport method combined with immunocytochemical and histochemical techniques. Spinally projecting neurons stained for serotonin-like, substance P-like, enkephalin-like and thyrotropin-releasing hormone-like immunoreactivity and for the histochemical marker acetylcholinesterase were all observed in each of the raphe nuclei of the medulla, as well as in the adjacent ventrolateral reticular formation. The similar distributions of the descending serotonergic and peptidergic neurons in the raphe nuclei as well as quantitative data on their relative numbers suggest that a large fraction of raphe-spinal neurons contain serotonin co-existing with one or more peptides in the same cell.

Origins of serotonergic projections to the spinal cord in rat: An immunocytochemical-retrograde transport study

The origins of the serotonergic projections to the spinal cord in the rat were determined by employing the retrograde cell marker HRP coupled with the unlabeled antibody, peroxidase-antiperoxidase immunocytochemical method of Sternberger. Large numbers of stained neurons (greater than 70%) in the medullary raphe nuclear complex were found to contain both HRP retrogradely transported from the spinal cord and positive 5-HT staining. These serotonergic cell groups, including the nucleus raphe obscurus, raphe pallidus, raphe magnus, and the ventral parts of the reticular formation, project to all spinal cord levels. In addition, some neurons contained HRP granules, but were unstained for 5-HT, suggesting that they may contain other non-serotonergic neurotransmitters. More rostrally in the midbrain reticular formation, many 5-HT neurons were found to have projections exclusively to the cervical spinal cord. These findings indicate that the descending serotonin inputs to the spinal cord originate not only from the serotonergic neurons located in the medullary raphe complex, but also from other new sources located in the central gray and reticular formation of the midbrain.

Origins and terminations of descending noradrenergic projections to the spinal cord of monkey

This report describes the distribution of noradrenergic cells in the brainstem and the pattern of terminal varicosities in the spinal cord of monkey using the immunocytochemical localization of dopamine-beta-hydroxylase (DBH). Using two separate and equally reliable techniques, retrograde transport of the antibody to DBH and a double-labeling method, the cells of origin of noradrenergic fibers in the spinal cord have been identified. The results of these studies indicate that 79% of all noradrenergic cells with axons projecting to the spinal cord are located in the nucleus subcoeruleus and nucleus locus coeruleus. Other pontine noradrenergic cell groups contribute the remainder of the fibers to the cord. No medullary cells contribute to the noradrenergic innervation of the spinal cord.

Organization of Descending Serotonergic Projections to the Spinal Cord

Publisher Summary This chapter discusses the organization of descending serotonergic projections to the spinal cord. The indolamine serotonin is believed to have important neurotransmitter and/or neuroregulatory roles in the descending pathways influencing various somatosensory, motor, and autonomic functions within the spinal cord. The autonomic preganglionic neurons of the thoracic spinal cord, as well as the motoneurons of the ventral horn, are also under the influence of descending serotonergic cell groups. Cells in these various motoneuron pools can be inhibited and/or excited by iontophoretic application of serotonin or by electrical stimulation of the descending serotonergic pathways. In recent years, the introduction of immunocytochemistry to neurobiology has provided a very sensitive method for studying the organization of descending serotonergic pathways. In contrast to the previously employed histofluorescence methods with which rapid photodecom-position of the yellow fluorescing cells and terminals was a constant problem, the peroxidase-antiperoxidase (PAP) immunochemical method results in a relatively permanent marker for 5-HT neurons and terminals.

Organization of corticospinal neurons in the cat.

The cells of origin of the corticospinal tract of the cat were identified using the retrograde horseradish peroxidase (HRP) labeling technique. Cortical neurons labeled from the spinal cord were confined to layer V and included large Betz cells, as well as many smaller neurons of this layer. Collections of 5-10 labeled neurons concentrated in areas of 300-500 micrometer diameter were observed, suggesting a columnar-type of organization of corticospinal neurons. Injections of HRP into different spinal segments were used to determine the somatotopic distribution of corticospinal neurons. Cortical neurons projecting to the cervical spinal enlargement were found in the lateral hemisphere, with more caudal spinal levels being represented successively more medial. There appeared to be little, if any, overlap in the distributions of neurons labeled from the cervical versus the lumbosacral spinal cord. Neurons projecting to the spinal enlargements were most abundant in the primary area 4, motor cortex (MI), but substantial populations of neurons were located in each of the subfields, areas 3a, 3b, 1 and 2, of the primary somatic sensory cortex (SI), plus area 2 pre-insularis of the second somatic sensory region (SII), and area 5 of the suprasylvian gyrus. This suggested, in view of the differences in inputs and response properties of neurons in these cortical regions, that the corticospinal projections from the different areas could represent multiple, independent functions in spinal cord sensory and motor control. The soma diameters of HRP-labeled corticospinal neurons varied widely, with a distinct, large-celled (Betz-type) and a small-celled population being present in the area 4 motor cortex. The largest labeled neurons of the somatic sensory cortical areas were intermediate in size. Three types of corticospinal neurons may exist, corresponding to the giant pyramidal (Betz) cells, the largest pyramidal neurons of the somatic sensory regions, and the abundant, smaller pyramidal cells which are found throughout the sensory and motor cortical fields.

Transneuronal transport of lectins

Axonal and transneuronal transport of the plant lectins wheat germ agglutinin (WGA), Pisum sativum agglutinin (PSA), Lens culinaris agglutinin (LCA), soybean agglutinin (SBA), peanut agglutinin (PNA), Concanavalin A agglutinin (Con A), and Ulex europeus agglutinin (UEA) were examined and compared using an immunocytochemical staining method. WGA, which binds to N-acetylglucosamine and sialic acid carbohydrate residues, and the 3 mannose binding lectins (Con A, PSA and LCA) were found to undergo retrograde transport to the facial nucleus after injection into the facial muscles, and anterograde transport to the optic tectum after injection in the vitreous, and to the spinal trigeminal nucleus caudalis after injection into the mystatial vibrissae. SBA showed a slight tendency to be transported retrogradely, but not in the anterograde direction, whereas UEA and PNA were not axonally transported in any of these systems. All lectins which were transported in the anterograde direction labeled neuronal somata in their respective terminal fields indicating that transneuronal transport had taken place. Axonal and transneuronal transport of the lectins appears to be dependent upon their respective carbohydrate affinities. Transneuronal transport which can be demonstrated for certain lectins indicates that mechanisms exist whereby neurons exchange large molecules which could be involved in mediating trophic and other influences on target cells.

Serotonergic projections to the caudal brain stem: a double label study using horseradish peroxidase and serotonin immunocytochemistry

Cells of origin of serotonergic and non-serotonergic projections to the caudal brain stem in the primate were examined using a double label technique. Following HRP injections into medullary raphe nuclei and the adjacent reticular formation double labeled cells were found in the dorsal raphe nucleus, the central superior nucleus and the ventrolateral tegmentum. Retrogradely labeled cells that did not stain for serotonin-like immunoreactivity were found primarily in the periaqueductal gray (PAG) and the mesencephalic and pontine reticular formation. The results are discussed in relation to the descending pathway(s) mediating the effects of PAG stimulation.

Transmitters of the raphe-spinal complex: Immunocytochemical studies

The localization of serotonergic and various peptidergic neurons in the medullary raphe nuclei that project to the lumbosacral spinal cord have been studied using a retrograde transport method combined with immunocytochemistry. Spinally projecting neurons stained for serotonin-like, substance P-like, enkephalin-like and thyrotropin-releasing hormone-like immunoreactivity were all observed in the raphe nuclei of the medulla, as well as in the adjacent ventrolateral reticular formation. The distribution of the descending serotonergic and peptidergic neurons in the raphe nuclei as well as quantitative data on their relative numbers suggest that a large fraction of raphe-spinal neurons contain serotonin co-existing with one or more peptides in the same cell.

Organization of tectospinal neurons in the cat and rat superior colliculus

Neurons in the superior colliculus which send axons to the spinal cord were identified by the retrograde axonal transport method. Injections of the retrograde axonal tracer, horseradish peroxidase, made into different levels of the cervical spinal cord indicate that the spinally projecting neurons in the superior colliculus are topographically organized. Tectospinal neurons projecting to the rostral segments of the cervical spinal cord are found over a larger extent of the contralateral superior colliculus than those terminating in the cervical enlargement. The tectospinal projection to the cervical enlargement in both rats and cats arises almost exclusively from the caudolateral quadrant of the contralateral superior colliculus, whereas the tectal projection to the rostral (upper) cervical spinal cord originates, in cats, from almost the entire extent of the colliculus and, in rats, from its greater part. No evidence for tectospinal projections to the thoracic or lumbar levels of the spinal cord was found. In the context of the hypothesis that, in these species, head and body movements which orient the animal toward stimuli in its environment may be mediated by the superior colliculus, these data are consistent with the view that direct tectospinal connections may play a role in such movements.