The purpose of the present investigation was to examine the topographical organization of efferent projections from the cytoarchitectonic divisions of the mPFC (the medial precentral, dorsal anterior cingulate and prelimbic cortices). We also sought to determine whether the efferents from different regions within the prelimbic division were organized topographically. Anterograde transport of Phaseolus vulgaris leucoagglutinin was used to examine the efferent projections from restricted injection sites within the mPFC. Major targets of the prelimbic area were found to include prefrontal, cingulate, and perirhinal cortical structures, the dorsomedial and ventral striatum, basal forebrain nuclei, basolateral amygdala, lateral hypothalamus, mediodorsal, midline and intralaminar thalamic nuclei, periaqueductal gray region, ventral midbrain tegmentum, laterodorsal tegmental nucleus, and raphe nuclei. Previously unreported projections of the prelimbic region were also observed, including efferents to the anterior olfactory nucleus, the piriform cortex, and the pedunculopontine tegmental-cuneiform region. A topographical organization governed the efferent projections from the prelimbic area, such that the position of terminal fields within target structures was determined by the rostrocaudal, dorsoventral, and mediolateral placement of the injection sites. Efferent projections from the medial precentral and dorsal anterior cingulate divisions (dorsomedial PFC) were organized in a similar topographical fashion and produced a pattern of anterograde labeling different from that seen with prelimbic injection sites. Target structures innervated primarily by the dorsomedial PFC included certain neocortical fields (the motor, somatosensory, and visual cortices), the dorsolateral striatum, superior colliculus, deep mesencephalic nucleus, and the pontine and medullary reticular formation. Previously unreported projections to the paraoculomotor central gray area and the mesencephalic trigeminal nucleus were observed following dorsomedial PFC injections. These results indicate that the efferent projections of the mPFC are topographically organized within and across the cytoarchitectonic divisions of the medial wall cortex. The significance of topographically organized and restricted projections of the rat mPFC is discussed in light of behavioral and physiological studies indicating functional heterogeneity of this region.

Topographical organization of the efferent projections of the medial prefrontal cortex in the rat: An anterograde tract-tracing study with Phaseolus vulgaris leucoagglutinin

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

Efferent connections of the parabrachial nucleus in the rat.

A stereotaxic atlas of the rat brain

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

The distribution of spinocerebellar tract (SCT) neurons has been studied in the entire length of the spinal cord of the cat following injections of horseradish peroxidase into the cerebellum, and whether or not the axons of the labeled neurons crossed within the spinal cord was determined in cases with injections preceded by hemisections at the cervical levels.



The SCTs were classified into the following corssed and uncrossed tracts according to the cell origin and the fiber course; The crossed SCTs originate from (1) the central cervical nucleus (the CCN-SCT), (2) lamina VIII neurons of the cervical to the lumbar cord (the lamina VIII-SCT), (3) spinal border cells (the border cell-SCT), (4) neurons in the medial lamina VII of the lumbar to the caudal spinal segments (the medial lamina VII-SCT), (5) ventral horn neurons (laminae VII and VIII) of the sacral and caudal segments (the ventral horn-SCT) and (6) dorsal horn neurons (lamina V) of the sacral and the caudal segments (the dorsal horn-SCT). The uncorssed tracts originate from (1) neurons of the medial lamina VI of C2 to T1 (the medial lamina VI-SCT of the cervical cord), (2) neurons in the central part of lamina VII of C6 to T1 (the central lamina VII-SCT of the cervical enlargement), (3) lamina V neurons of the lower cervical to the lumbar cord (the lamina V-SCT), (4) Clarke's column (the Clarke's column-SCT) and (5) neurons in the medial lamina VI of L5 and L6 (the medial lamina VI-SCT of the lumbar cord).



The present study suggests that the spinocerebellar system originates from more diverse laminae than has previously been known, and further refined studies on the topographic projections of each tract will yield more important and valuable information in this field.

Anatomical organization of the spinocerebellar system in the cat, as studied by retrograde transport of horseradish peroxidase.

Brainstem projections from the lateral hypothalamic area in the rat, as studied with autoradiography

The distribution of labeled neurons in the paraventricular nucleus of the hypothalamus (PVN) was studied following injections of horseradish peroxidase (HRP) into the spinal cord (C8 to T1) or the hypophysis in the rat. Injections were also made in the spinal cord in another group of animals, which were subjected to water deprivation for a period of 3 days, and the PVN of these animals was examined with the electron microscope. Spinal projection neurons (paraventriculospinal tract, PVST, neurons) formed two groups; the dorsal and the ventral groups. They were located within the parvocellular part of the PVN and fused into one at the caudal level. The neurons of the dorsal group were well assembled whereas those of the ventral group were intermingled with paraventriculohypophyseal tract (PVHT) neurons, which were concentrated in the magnocellular part. Electron microscopic observations revealed that HRP-labeled neurons after spinal injections did not contain neurosecretory granules and that they were not affected by water deprivation. On the other hand, neurons containing a number of neurosecretory granules displayed a significant degree of dilatation of the endoplasmic reticulum as the result of water deprivation. These neurons contained no HRP granules. The present findings suggest that the PVST neurons are distinct from the PVHT neurons and that the neuronal groups of both systems form different cell columns within the nucleus.

Identification and distribution of the spinal and hypophyseal projection neurons in the paraventricular nucleus of the rat. A light and electron microscopic study with the horseradish peroxidase method.

Cells of origin of the spinocerebellar tract in the rat, studied with the method of retrograde transport of horseradish peroxidase.

The distribution spinal neurons with long descending axons was studied in the cat by means of retrograde transport of horseradish peroxidase. Labeled neurons appeared bilaterally in the cervical and the thoracic cord following injections in the lumbosacral cord. In some cases hemisections were made rostrally and contralaterally to the injections in an attempt to determine whether or not the axons crossed. Neurons with uncrossed descending axons were located in laminae I, V, VII and VIII. Lamina I neurons were present in all the spinal segments. In lamina V labeled neurons were distributed mainly laterally in the cervical cord but medially and laterally in the thoracic cord. In the upper cervical and the thoracic cord laminae VII and VIII neurons were distributed very densely along the lateral cord, accounting for 30 and 40 of the total labeled neurons, respectively. In the cervical enlargement they were located in the middle part of lamina VII and in lamina VIII, accounting for about 25% of the total labeled neurons. Neurons with crossed descending axons were found in laminae V, VII and VIII, in the medial part of lamina VII including the intermediomedial nucleus of the thoracic levels and close to the central canal. Lamina V neurons were very small in number. The largest collections of labeled neurons were present in the medial part of laminae VII and VIII. They accounted for about 45% to 55% and 37% of the total in the cervical and the thoracic cord. These neurons may function as the long spinal reflex paths for forelimb-hindlimb synergies and the intercalated paths between the supraspinal descending tracts and the spinal motor centers.

The location of spinal neurons with long descending axons (long descending propriospinal tract neurons) in the cat: a study with the horseradish peroxidase technique.

Matsuo Matsushita

Papers

Anatomical organization of the spinocerebellar system in the cat, as studied by retrograde transport of horseradish peroxidase.

Brainstem projections from the lateral hypothalamic area in the rat, as studied with autoradiography

Identification and distribution of the spinal and hypophyseal projection neurons in the paraventricular nucleus of the rat. A light and electron microscopic study with the horseradish peroxidase method.

Cells of origin of the spinocerebellar tract in the rat, studied with the method of retrograde transport of horseradish peroxidase.

The location of spinal neurons with long descending axons (long descending propriospinal tract neurons) in the cat: a study with the horseradish peroxidase technique.