Experiments using two retrogradely transported fluorescent dyes (bisbenzimide-true blue, and Evans blue-granular blue) were performed in order to determine whether the same or different populations of neurons of the paraventricular nucleus of the hypothalamus (PVH) project to the pituitary gland, dorsal vagal complex, and spinal cord in the rat. The results suggest that cells projecting to the pituitary gland are concentrated in the magnocellular core of the nucleus, while the descending connections arise primarily from the surrounding parvocellular division. The occurrence of neurons double-labeled with both dyes further indicate that at lease 10-15% of the labeled cells in the parvocellular division send divergent axon collaterals to the dorsal vagal complex and to the spinal cord. Cell counts suggest that at least 1,500 cells in the PVH project to the medulla and/or spinal cord. These results, combined with a cytoarchitectonic analysis, show that the PVH consists of eight distinct subdivisions, three magnocellular and five parvocellular. The lateral hypothalamic area and zona incerta also contain a large number of cells projecting to the dorsomedial medulla and spinal cord; approximately 15% of such cells are the double-labeled following injections of separate tracers into these two regions of the same animal.

The paraventricular nucleus of the hypothalamus: Cytoarchitectonic subdivisions and organization of projections to the pituitary, dorsal vagal complex, and spinal cord as demonstrated by retrograde fluorescence double‐labeling methods

The glucose oxidase-DAB-nickel method in peroxidase histochemistry of the nervous system.

A method that allows the concurrent localization of an antigen and a retrogradely transported fluorescent dye (true blue) was used to identify, immunohistochemically, cells in the paraventricular nucleus of the hypothalamus (PVH) that project to autonomic centers in the brainstem or in the spinal cord of the adult albino rat. After placing injections of true blue in the dorsal vagal complex or in upper thoracic segments of the spinal cord, series of evenly spaced sections through the PVH were stained with antisera directed against oxytocin, vasopressin, somatostatin, methionine-enkephalin, or leucine-encephalin. The results indicate that both oxytocin- and vasopressin-stained cells in the PVH project to the spinal cord and (or) to the dorsal vagal complex, although about three times as many oxytocinstained cells were doubly labeled after injections centered in either terminal field. The oxytocin- and vasopressin-stained cells that give rise to these long descending projections were found primarily in caudal parts of the parvo cellular division of the PVH, where immunoreactive cells were shown to be significantly smaller than oxytocin- and vasopressin-stained cells in parts of the nucleus that project to the posterior pituitary. Small populations of cells in the PVH that cross-react with antisera against somatostatin, leucine-enkephalin, or methionine-enkephalin were also shown to project directly to the region of the dorsal vagal complex and to the spinal cord, and to have a unique distribution within the PVH. Collectively, the total number of doubly labeled cells that were identified in these experiments accounts for only about one-fourth of the total number of PVH neurons with long descending projections, thus suggesting that additional neuroactive substances are contained within these pathways.

Immunohistochemical identification of neurons in the paraventricular nucleus of the hypothalamus that project to the medulla or to the spinal cord in the rat

Axons in the peripheral nervous system (PNS) and central nervous system (CNS) form sprouts after injury. Elongation of regenerating axonal sprouts has been observed as the exception within the adult mammalian CNS but is the rule in the PNS of mammals as well as in the CNS of some fish and amphibians. The relative importance of intrinsic neuronal properties and axonal environment in determining the extent of axonal regrowth is unknown. Neuroglial cells, nerve growth factor and target tissues such as smooth muscle are known to influence neuronal responses to injury. Here we have examined the capacity of transected axons originating in the CNS to regrow into nerve grafts containing Schwann cells.

Axons from CNS neurons regenerate into PNS grafts.

The avidin-biotin complex in bioanalytical applications

The distribution in the spinal cord of the rat of preganglionic neurons sending fibers into the hypogastric nerve was determined with the retrograde transport of horseradish peroxidase (HRP). Labeled cells were present in the intermediate gray matter of spinal segments L1-L2. The majority (81%) of HRP-filled cells formed a continuous column along the midline in the dorsal gray commissure. This cell column was termed the dorsal commissural nucleus (DCN). The remainder of HRP-labeled cells were present bilaterally in the middle and lateral regions of the intermediate gray; the majority of the latter cells were located along the lateral border of the intermediate gray.



The present finding of a midline preganglionic autonomic cell column in the spinal cord of a mammal is contrary to previous reports, in which sympathetic preganglionic neurons have been localized primarily in the lateral intermediate gray. The DCN may be species-specific and related to the system of short adrenergic neurons present in the pelvis.

A preganglionic autonomic nucleus in the dorsal gray commissure of the lumbar spinal cord of the rat

The sequential application of the peroxidase-antiperoxidase (PAP) technique with nickel-intensified DAB and with DAB alone was used to visualize black peptide-immunoreactive endings on amber serotonin-immunoreactive cells in 1-2-micron paraffin sections of the hamster medulla. Met-enkephalin- and substance P-positive terminals were present on serotonin cells in the raphe nuclei, the ventral reticular formation, and in the nucleus interfascicularis hypoglossi. The presence of enkephalin-immunoreactive endings on medullary serotonin-immunoreactive cells correlates with the analgesia and autonomic changes that result from the application of morphine or met-enkephalin to the medulla.

Visualization of peptide-immunoreactive processes on serotonin-immunoreactive cells using two-color immunoperoxidase staining.

Preganglionic neurons in the sacral spinal cord of the rat: an HRP study

Cells of origin of hypothalamo-spinal projections in the rat

Spinal projections from the nucleus locus coeruleus and nucleus subcoeruleus in the cat and monkey as demonstrated by the retrograde transport of horseradish peroxidase

Michael B. Hancock

Papers

A preganglionic autonomic nucleus in the dorsal gray commissure of the lumbar spinal cord of the rat

Visualization of peptide-immunoreactive processes on serotonin-immunoreactive cells using two-color immunoperoxidase staining.

Preganglionic neurons in the sacral spinal cord of the rat: an HRP study

Cells of origin of hypothalamo-spinal projections in the rat

Spinal projections from the nucleus locus coeruleus and nucleus subcoeruleus in the cat and monkey as demonstrated by the retrograde transport of horseradish peroxidase