G.R. Leichnetz

Connections of the medial posterior parietal cortex (area 7m) in the monkey

The afferent and efferent cortical and subcortical connections of the medial posterior parietal cortex (area 7m) were studied in cebus (Cebus apella) and macaque (Macaca fascicularis) monkeys using the retrograde and anterograde capabilities of the horseradish peroxidase (HRP) technique. The principal intraparietal corticocortical connections of area 7m in both cebus and macaque cases were with the ipsilateral medial bank of the intraparietal sulcus (MIP) and adjacent superior parietal lobule (area 5), inferior parietal lobule (area 7a), lateral bank of the IPS (area 7ip), caudal parietal operculum (PGop), dorsal bank of the caudal superior temporal sulcus (visual area MST), and medial prestriate cortex (including visual area PO and caudalmedial lobule). Its principal frontal corticocortical connections were with the prefrontal cortex in the shoulder above the principal sulcus and the cortex in the shoulder above the superior ramus of the arcuate sulcus (SAS), the area purported to contain the smooth eye movement‐related frontal eye field (FEFsem) in the cebus monkey by other investigators. There were moderate connections with the cortex in the rostral bank of the arcuate sulcus (purported to contain the saccade‐related frontal eye field; FEFsac), supplementary eye field (SEF), and rostral dorsal premotor area (PMDr). Area 7m also had major connections with the cingulate cortex (area 23), particularly the ventral bank of the cingulate sulcus. The principal subcortical connections of area 7m were with the dorsal portion of the ventrolateral thalamic (VLc) nucleus, lateral posterior thalamic nucleus, lateral pulvinar, caudal mediodorsal thalamic nucleus and medial pulvinar, central lateral, central superior lateral, and central inferior intralaminar thalamic nuclei, dorsolateral caudate nucleus and putamen, middle region of the claustrum, nucleus of the diagonal band, zona incerta, pregeniculate nucleus, anterior and posterior pretectal nuclei, intermediate layer of the superior colliculus, nucleus of Darkschewitsch and dorsomedial parvicellular red nucleus (macaque cases only), dorsal, dorsolateral and lateral basilar pontine nuclei, nucleus reticularis tegmenti pontis, locus ceruleus, and superior central nucleus. The findings are discussed in terms of the possibility that area 7m contains a “medial parietal eye field” and belongs to a neural network of oculomotor‐related structures that plays a role in the control of eye movement. Anat Rec 263:215–236, 2001.

The projection from nucleus raphe magnus and other brainstem nuclei to the spinal cord in the rat: a study using the HRP blue-reaction

Abstract Horseradish peroxidase injections, or solid HRP placements, were made into the dorsolateral quadrant of the spinal cord in ten adult rats, processed according to the blue-reaction (benzidine dihydrochloride) protocol [6]. When the interventions involved the dorsal lateral funiculus (DLF) HRP-labelled somata were observed primarily in the ipsilateral nucleus raphe magnus (NRM), with an occasional cell in nucleus raphe obscurus (NRO) and pallidus (NRP). Other brainstem raphe nuclei consistently lacked labelled neurons. The red nucleus and paralemniscal reticular formation of the rostal pons also contained appreciable numbers of HRP back-filled perikarya. The direct NRM-spinal projection in the rat, involved in the modulation of pain transmission in the spinal cord dorsal horn, originates primarily from the expanded region of the nucleus in the rostralmost medulla.

Frontal cortical projections to the periaqueductal gray in the rat: A retrograde and orthograde horseradish peroxidase study

The retrograde and orthograde capabilities of the horseradish peroxidase (HRP) technique were used to study the projection from the frontal cortex to the periaqueductal gray (PAG) in the rat. Small pyramidal neurons in layer V of the frontal (MD-dependent) cortex were the primary source of these projections and the system terminated primarily in the lateral PAG. Since the projection is homologous to that in the monkey, the rat may serve as a model for the study of the cortical influence on PAG-mediated behaviours such as analgesia, aversion and reward.

The efferent projections of the medial prefrontal cortex in the squirrel monkey (Saimiri sciureus)

Unilateral partial ablations were made in the medial granular frontal cortex of 6 adult squirrel monkeys. Fiber degeneration was traced using the Nauta-Gygax and Fink-Heimer selective silver impregnation techniques into the cingulum, uncinate fascicle, corpus callosum, internal capsule and sublenticular (ventral extracapsular) bundle. Corticocortical projections were observed to the lateral orbital, parietal, rostral inferior temporal, and entorhinal cortices, as well as to the hippocampus proper. Subcortical projections were observed to the basal amygdaloid nucleus, lateral hypothalamus, lateral dorsal, anterior ventral, mediodorsal, pulvinar, and intralaminar nuclei of the thalamus. Preterminal and terminal fiber degeneration were notably sparse in most of the neostriatum, except the dorsolateral region of the caudate nucleus. Fiber degeneration traversed the medial crus cerebri of the midbrain, where fibers of passage ascended into the tegmentum through the medial substantia nigra. Preterminal and terminal degeneration were present in the mesencephalic reticular formation lateral and dorsal to the red nucleus and a few degenerating fibers were followed into the dorsolateral periaqueductal gray. Degeneration was observed as far caudal as the reticulotegmental nucleus of the rostral pons. On the basis of its connections, the medial prefrontal cortex resembles the remainder of the prefrontal lobe and probably also has an important role in cortical and subcortical limbic mechanisms.

Cortical projections to the periaqueductal gray in the monkey: A retrograde and orthograde horseradish peroxidase study

Stereotaxic fluid microinjections of horseradish peroxidase (HRP) into the periaqueductal gray (PAG), coupled with cortical HRP gel placements in macaque and cebus monkeys, have provided substantive retrograde and orthograde evidence that the rostral dorsal convexity and rostral medial prefrontal cortex are the principal sources of cortical-PAG projections. The prefrontal cortex projects to the dorsolateral quadrant of the PAG, precisely the area shown to receive spinothalamic inputs in mammals, including monkey. The findings are discussed in terms of a possible affective role in central analgesic mechanisms.

Efferent connections of the orbitofrontal cortex in the marmoset(Saguinus oedipus)

Unilateral partial ablations were made in the orbitofrontal cortex of 4 adult marmosets (Saguinus oedipus) and fiber degeneration was traced using the Nauta-Gygax and Fink-Heimer selective silver impregnation techniques. Corticocortical projections were found to the ipsilateral convexity and medial aspect of the frontal lobe and to the homologous orbitofrontal areas of the contralateral hemisphere. Fiber degeneration was followed through the uncinate fascicle to the temporal and insular cortices, and caudally into the rostrolateral entorhinal cortex. Other fibers joined the cingulum bundle and terminated throughout the cingulate cortex. Subcortical projections were observed to the lateral and basal amygdaloid nuclei, caudate head, ventrolateral putamen and ventral claustrum. The lateral preoptic and hypothalamic areas received a small number of fibers, as did the intralaminar and reticular thalamic nuclei. The dorsomedial nucleus of the thalamus was recipient of a large group of fibers which followed the ventral internal capsule and joined the inferior thalamic peduncle to terminate there. Preterminal debris appeared heaviest in the dorsomedial thalamic nucleus, pars magnocellularis (MDmc) in more caudal orbital lesions. A subthalamic projection to field H of Forel was observed. A small number of fibers terminated in the lateral midbrain tegmentum, but no appreciable fiber degeneration was observed more caudally than the midbrain. These results are compared in some areas to findings in the rhesus monkey. The possibility of a topical organization in the orbital cortical and thalamic projections is discussed.

Connections of the caudal cerebellar interpositus complex in a new world monkey (Cebus apella).

The afferent and efferent connections of the cerebellar interpositus complex were studied in a capuchin monkey (Cebus apella) that had received a transcannular horseradish peroxidase implant into the caudal portion of the anterior interpositus nucleus and posterior interpositus nucleus. While the heaviest anterogradely labeled ascending projections were observed to the contralateral ventral posterolateral nucleus of the thalamus, pars oralis (VPLo), efferent projections were also observed to the contralateral ventrolateral thalamic nucleus (VLc) and central lateral (CL) nucleus of the thalamic intralaminar complex, magnocellular (and to a lesser extent parvicellular) red nucleus, nucleus of Darkschewitsch, zona incerta, nucleus of the posterior commissure, lateral intermediate layer and deep layer of the superior colliculus, dorsolateral periaqueductal gray, contralateral nucleus reticularis tegmenti pontis and basilar pontine nuclei (especially dorsal and peduncular), and dorsal (DAO) and medial (MAO) accessory olivary nuclei, ipsilateral lateral (external) cuneate nucleus (LCN) and lateral reticular nucleus (LRN), and to a lesser extent the caudal medial vestibular nucleus (MVN) and caudal nucleus prepositus hypoglossi (NPH), and dorsal medullary raphe. The heaviest retrograde labeling was corticonuclear Purkinje cells in the paramedian cerebellar cortex lateral to the vermis of lobules IV-VIII. Otherwise, retrogradely labeled sources of afferents were predominantly contralateral in the dorsal, dorsomedial, paramedian, and peduncular sectors of the basilar pons, NRTP, and dorsal accessory (DAO) and medial accessory (MAO) of olivary nuclei, but were predominantly ipsilateral in the LCN, LRN, and in the medullary reticular formation along the roots of the hypoglossal (XII) cranial nerve. It appeared that the connections with the contralateral dorsal basilar pons, NRTP, DAO and MAO, and ipsilateral LCN and LRN are reciprocal.(ABSTRACT TRUNCATED AT 250 WORDS)

An intrahemispheric columnar projection between two cortical multisensory convergence areas (inferior parietal lobule and prefrontal cortex): An anterograde study in macaque using HRP gel

Horseradish peroxidase (HRP) gel and tetramethylbenzidine neurohistochemistry were used successfully in demonstrating the columnar organization of an intrahemispheric projection from the inferior parietal lobule to the prefrontal cortex in the macaque monkey. Following an HRP gel implant within the upper portion of the posterior (caudal) bank of the intraparietal sulcus, a prominent anterograde terminal projection field, consisting of alternate light and dark (300-500 microns) columns, was observed using low-power dark-field microscopy in the caudal third of the sulcus principalis cortex (area 46). At higher magnification large numbers of small retrogradely-labeled pyramidal cells were present in layers III and V of the same cortex. The regionally-specific projection, coupled with its discrete anatomical organization, lends support to the reputed functional/behavioral subsectors within the prefrontal cortex and its apparent capacity for spatial representation.

Inferior frontal eye field projections to the pursuit-related dorsolateral pontine nucleus and middle temporal area (MT) in the monkey.

Inferior frontal eye field (FEF) projections to the dorsolateral pontine nucleus (DLPN), and corticocortical connections with the superior temporal sulcal (STS) cortex, were studied in five macaque monkeys which had received horseradish peroxidase (HRP) gel implants into the inferior prearcuate cortex (including area 45 of Walker, 1940). These connections were contrasted with those from the dorsal FEF (area 8a) in another macaque monkey. Findings of heavy inferior FEF projections to the ipsilateral DLPN (light to the contralateral DLPN) and reciprocal connections with the deep caudal bank and fundus of the superior temporal sulcus (STS), presumed to be the middle temporal (MT) visual area (Maunsell & Van Essen, 1983a), appeared to go hand in hand with more pronounced projections to the stratum superficialis of the superior colliculus (SC). In contrast, the HRP gel implant in the dorsal prearcuate cortex (area 8a of Walker, 1940) resulted in only very light projections to the ipsilateral DLPN, more pronounced projections to the dorsomedial pontine nucleus (DMPN), almost no projection to the stratum superficialis (SS), and more pronounced reciprocal connections with the upper bank of the STS, presumed to be the medial superior temporal (MST) area (Maunsell & Van Essen, 1983a). Both the inferior and dorsal FEF also had extensive reciprocal connections with the ventral intraparietal area (VIP; Maunsell & Van Essen, 1983a) in the caudal bank of the intraparietal sulcus. The correlated projections of the inferior FEF to the DLPN, MT area, and SS may explain its reported role in smooth pursuit (Lynch, 1987), in addition to its well-established role in the production of voluntary purposeful saccadic eye movements (Bruce et al., 1985).

Prearcuate cortex in the Cebus monkey has cortical and subcortical connections like the macaque frontal eye field and projects to fastigial-recipient oculomotor-related brainstem nuclei.

The cortical and subcortical connections of the prearcuate cortex were studied in capuchin monkeys (Cebus apella, albifrons) using the anterograde and retrograde transport capabilities of the horseradish peroxidase technique. The findings demonstrate remarkable similarities to those of the macaque frontal eye field and strongly support their homology. The report then focuses on specific prearcuate projections to oculomotor-related brainstem nuclei that were shown in a companion experiment to entertain connections with the caudal oculomotor portion of the cerebellar fastigial nucleus. The principal corticocortical connections of the cebus prearcuate cortex were with dorsomedial prefrontal cortex, lateral intraparietal sulcal cortex, posterior medial parietal cortex, and superior temporal sulcal cortex, which were for the most part reciprocal and columnar in organization. The connections of the dorsal prearcuate region were heavier to the dorsomedial prefrontal and posterior medial parietal cortices, and those of the ventral region were heavier to the superior temporal sulcal cortex. The prearcuate cortex projects to several brainstem areas which also receive projections from the caudal fastigial nucleus, including the supraoculomotor periaqueductal gray matter, superior colliculus, medial nucleus reticularis tegmenti pontis, dorsomedial basilar pontine nucleus, dorsolateral basilar pontine nucleus, nucleus reticularis pontis caudalis, pontine raphe, and nucleus prepositus hypoglossi. The findings define a neuroanatomical framework within which convergence of prearcuate (putative frontal eye field) and caudal fastigial nucleus connections might occur, facilitating their potential interaction in saccadic and smooth pursuit eye movement.