Minor Projections Research Articles

Corticothalamic connections of the superior temporal sulcus in rhesus monkeys

The corticothalamic connections of the superior temporal sulcus (STS) were studied by means of the autoradiographic technique. The results indicate that corticothalamic connections of the STS in general reciprocate thalamocortical connections. The cortex of the upper bank of the STS-multimodal areas TPO and PGa-projects to four major thalamic targets: the pulvinar complex, the mediodorsal nucleus, the limitans-suprageniculate nucleus, as well as intralaminar nuclei. Within the pulvinar complex, the main projections of the upper bank of the STS are directed to the medial pulvinar (PM) nucleus. Rostral upper bank regions tend to project caudally and medially within the PM nucleus, caudal upper bank regions, more laterally and ventrally. The mid-portion of the upper bank tends to occupy the central sector of the PM nucleus. There are also relatively minor projections from upper bank regions to the lateral pulvinar (PL) and oral pulvinar (PO) nuclei. In contrast to the upper bank, the projections from the lower bank are directed primarily to the pulvinar complex, with only minor projections to intralaminar nuclei. The rostral portion of the lower bank projects mainly to caudal and medial regions of the PM nucleus, whereas the caudal lower bank projects predominantly to the lateral PM nucleus, and also to the PL, PO, and inferior pulvinar (PI) nuclei. The mid-portion of the lower bank projects mainly to central and lateral portions of the PM nucleus, and also to the PI and PL nuclei. The rostral depth of the STS projects mainly to the PM nucleus, with only minor connections to the PO, PI, and PL nuclei. The mid-portion of multimodal area TPO of the upper bank, areas TPO2 and TPO3, projects preferentially to the central sector of the PM nucleus. It is possible that this STS-thalamic connectivity has a role in behavior that is dependent upon more than one sensory modality.

Topography of efferent vagal innervation of the rat gastrointestinal tract

The gastrointestinal territories innervated by the gastric, celiac, and hepatic abdominal vagi were identified in rats with selective branch vagotomies by means of 1) anterograde tracing with the carbocyanine dye DiI injected into the dorsal motor nucleus and 2) measurement of cervical vagal stimulation-induced motility responses throughout the gut axis. Presence of DiI-labeled vagal terminals in the myenteric plexus and evoked motility responses were well correlated across the sampled gastrointestinal (GI) sites. In animals with only the two gastric branches intact, the entire stomach and the most proximal duodenum showed significant motility responses and were densely innervated, having DiI-labeled vagal terminals in almost every ganglion. The hepatic branch was found to primarily innervate the duodenum, with minor projections to the distal antral stomach and the intestines. The two celiac branches were found to almost exclusively innervate the jejunum, ileum, cecum and entire colon, and, together with the other vagal branches, the duodenum. Therefore, while there is some degree of specific innervation by the abdominal vagal branches of the oral-to-anal gut axis, which could be called "viscerotopic," the considerably overlapping innervation of the duodenum does not satisfy a viscerotopy criterion and needs further functional analysis.

1990 – a year of change in hydrocarbon-geological activities at the Geological Survey of Greenland

The background for the Geological Survey of Greenland's (GGU's) hydrocarbon-geological activities was briefly outlined in the Report of Activities for 1989 (Stemmerik et al., 1990a). In that report it was intimated that a shift of emphasis in hydrocarbon-geological activities was under way, not only from onshore to offshore but also from East to West Greenland (Fig. 1). 1990 saw this shift take more concrete form. Thus field work in East Greenland was limited to minor projects that focus on diagenesis and reservoir properties of siliciclastic sediments. All other projects onshore East Greenland have reached or are entering into final report stage

Brainstem connections of the rostral ventral respiratory group of the rat

The pontomedullary connections of the rostral division of the ventral respiratory group (rVRG), the largest medullary population of inspiratory bulbospinal and propriobulbar neurons, were identified in the rat by retrograde and anterograde tracing techniques. These experiments revealed that: (i) the Kölliker-Fuse nucleus, portions of the medial and lateral parabrachial nuclei, and all levels of the ipsilateral and contralateral VRG complex have dense reciprocal connections with the rVRG; (ii) the lateral paragigantocellular nucleus has reciprocal but less dense connections with rVRG; (iii) portions of the nucleus of the solitary tract have prominent projections to, but weaker inputs from rVRG; (iv) the raphe, magnocellular tegmental field and spinal trigeminal nuclei have minor projections to rVRG and receive only sparse inputs from rVRG, and; (v) the retrotrapezoid nucleus, pontine lateral tegmental field and area postrema each have only efferent projections to rVRG. These findings are consistent with previous studies of pontomedullary connections of rVRG in the cat, and further document the extensive reciprocal connections between principal respiratory groups. These connections are likely to be important for generation of the respiratory pattern, for the coordination of effector responses of the cranial and spinal respiratory motor neurons to afferent stimuli, and coordination of the central respiratory and cardiovascular control systems.

Blurring the Borders: Voices of African Liberatory Pedagogy in the United States and Canada

The 1983 report of the Commission on Excellence in Education declared that the United States was a Nation at Risk because of its mediocre educational system. Since then we have seen a spate of follow-up reports and improvement efforts commonly referred to as the educational reform movement. This effort, designed to improve the quality of education at every level, has virtually bypassed students of color (Quality Education for Minorities Project, 1990). Most noticeable among those the reform movement has overlooked are Afro-North American students* At the same time that education has placed the United States at risk, both African-American and African-Canadian youngsters have been defined as the at-risk.

Developing Graduate School Awareness for Engineering and Science: A Model

As the United States economy faces increased competition from other technology-based nations, there are indications that we will need more technically trained individuals than will be available domestically in the near future. The report, Workforce 2000 Johnson & Packer, 1987) asserts that the American economy needs greater participation of minorities and women to maintain our competitive edge in world trade and to sustain our standard of living. Another report, from the Quality Education for Minorities Project (1990), stresses that the United States will not be able to remain globally competitive if it continues to rely upon populations that traditionally have supplied its technical needs. That report also argues that if we Americans are to maintain our ability to compete in the world and sustain our standard of living, improving education and significantly increasing the participation of minority students in higher education (with special emphasis on the study of mathematics, science, and engineering) must become our most important challenge. A study by the MIT Commission on Industrial Productivity (Dertouzos et al., 1989) further underscores the issue of a shortage of technically trained individuals. The MIT report outlines key policy objectives to encourage underrepresented groups to pursue engineering and science degrees and careers and alleviate faculty shortages. While efforts to broaden the diversity of technically trained individuals with undergraduate degrees have been largely successful since the late 1960s, far less progress has been made in efforts to produce individuals with graduatelevel degrees in engineering and science. Clearly, the technological demands of the future will require more individuals at not only the bachelor's level but at the master's and doctoral levels as well.

Anatomical investigation of projections to the basis pontis from posterior parietal association cortices in rhesus monkey

The projections to the basis pontis from cytoarchitectonically defined subregions of the superior (SPL) and inferior (IPL) parietal lobules were investigated in 14 rhesus monkeys by using the anterograde tracing techniques of autoradiography and horseradish peroxidase histochemistry. The results of our study confirm and complement available information regarding the parietopontine projections. The projections are found in clusters distributed in lamellae approximately concentric to the peduncle. They are directed most heavily towards the peripeduncular and lateral nuclei of the pons. There are also lesser, but nevertheless substantial projections to other nuclei including the intrapeduncular, ventral, dorsolateral, extreme dorsolateral, and dorsal nuclei. The dorsomedial, paramedian, and NRTP nuclei receive only minor projections. The SPL projections are relatively widespread with respect to the more focussed IPL projections. The IPL projections are, in general, situated more laterally and at more rostral levels of the pontine nuclei than are those of the SPL. The sulcal cortex of the SPL (area PEa) favors the dorsolateral, extreme dorsolateral, and ventral nuclei compared to the light projections to these nuclei from the convexity of the SPL. The sulcal cortex of the IPL, area POa, differs from the gyral cortex in favoring the ventral and extreme dorsolateral nuclei. The rostral IPL differs from the caudal IPL in that the intrapeduncular nucleus receives projections only from rostral regions, while the lateral nucleus receives projections preferentially from caudal regions. The pontine projections from the medial SPL, area PGm, are unique in the parietal lobe in that they include the paramedian nucleus. Projections arising from multimodal regions located caudally in the SPL (areas PEa and PGm) and IPL (areas PG and Opt) are more strongly represented and more laterally placed within the pontine nuclei than projections arising from more rostral, unimodal, posterior parietal regions. The heavy projections to the pontine nuclei from the posterior parietal cortex, and particularly from those caudal parietal regions that have prominent associative and limbic connections, seem to suggest that the corticopontocerebellar pathways permit a cerebellar contribution not only to the coordination of movement, but also to the modulation and integration of higher function.

Direct synaptic contacts of medial septal efferents with somatostatin immunoreactive neurons in the rat hippocampus

Anterogradely labeled projections from the medial septum to hippocampal somatostatin immunoreactive (SOM-i) neurons were studied with double-label immunocytochemistry under light (LM) and electron microscopic (EM) conditions. Medial septal projections were identified after injecting the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) followed by immunohistochemical visualization of PHA-L presynaptic terminal labeling and concurrent immunocytochemical staining of SOM in hippocampal target cell bodies. This double-label procedure yielded blue-black nickel enhanced DAB stained, PHA-L-immunoreactive terminals on light brown SOM-i neurons that were investigated by correlative LM and EM observations. PHA-L-labeled terminal contacts with often basket-like appearance were localized with highest densities on soma and proximal dendrites of SOM-i neurons in stratum oriens of Ammon's horn and hilus of dentate gyrus, and some minor projections to stratum pyramidale and radiatum. Most double-labeled contacts could be identified as symmetric type synapses equally divided over soma and proximal dendrites of several forms of SOM-i neurons. These data indicate monosynaptic regulation of the hippocampal intrinsic SOM system by septal input, which probably represents a peptidergic subpopulation of the hippocampal GABAergic system.

Diagonal band projection towards the hypothalamic supraoptic nucleus: light and electron microscopic observations in the rat.

Supraoptic nucleus (SON) neurons receive a prominent gamma-amino-butyric acid (GABA) input. This study evaluated the hypothesis, partly on the basis of recent electrophysiological data, that this innervation might arise from GABAergic neurons located in the ventral diagonal band of Broca area. For retrograde transport studies, pentobarbital-anesthetized male Long-Evans rats received 0.03-0.20-microliter injections of a suspension of rhodamine tagged latex microspheres into the SON. In two cases where such injections were confined to the SON, less than 60 retrogradely labeled neurons were detected in the ipsilateral diagonal band. In three animals where injections extended into the perinuclear zone around the SON, more than 2,000 retrogradely labeled cells were counted in the ipsilateral diagonal band. For anterograde transport studies, another group of animals received either 30% horseradish peroxidase (HRP) in 0.5% poly-L-ornithine (0.05-0.10 microliter injections) or Phaseolus vulgarus (iontophoresed from a 2% solution) into the diagonal band. After survivals of 18-24 hours (HRP) or 5 days (PHAL-L) labeled axon terminals invested the perinuclear zone above the SON. The presence of just a single fiber within the nucleus indicated a minor projection to the SON itself. The HRP-injected material was processed for ultrastructural examination and revealed dense HRP-labeled axon terminals in this perinuclear zone, most often (98%) forming axodendritic appositions. A postembedding colloidal gold technique to visualize GABA-synthesizing terminals revealed that fewer than 5% of these perinuclear HRP-labeled terminals also exhibited GABA-like immunoreactivity. Within the SON, where GABAergic axon terminals are abundant, few (less than 5%) GABAergic terminals contained HRP.(ABSTRACT TRUNCATED AT 250 WORDS)

Origin, distribution, and morphology of serotonergic afferents to the cat superior colliculus: a light and electron microscope immunocytochemistry study

We have studied the serotonergic (5-HT) projection to the cat superior colliculus (SC) using serotonin antibody immunocytochemistry and retrograde transport of peroxidase-conjugated wheatgerm agglutinin (WGA-HRP). In 3 experiments, the two labels were combined in order to double label cells with both anti-5-HT and WGA-HRP. In the remaining experiments, the two labels were examined separately. Serotonin-like immunoreactive fibers were found throughout all layers of SC, but were most densely distributed within the zonal and upper superficial gray layers. Most 5-HT fibers were thin and had characteristic varicosities and terminal swellings. At the EM level, immunoreactive terminals and varicosities were found to contain small agranular vesicles and occasionally large granular vesicles (LGVs). Conventional synaptic densities were only rarely observed. Injections of WGA-HRP into SC resulted in labeling of neurons throughout the dorsal raphe nucleus and surrounding ventrolateral periaqueductal gray. Only a few cells were found in the raphe medianus and raphe pontis and none within the raphe magnus or other medullary raphe nuclei. Cells in the dorsal raphe giving rise to the SC projection varied in shape, size, and morphology and must represent more than one cell type. The morphology of these cells was indistinguishable from that of cells in the dorsal raphe which were double labeled by anti-5-HT and WGA-HRP. We conclude that the 5-HT innervation of the superior colliculus varies in density in different laminae, arises from several different cell types, and originates primarily from the dorsal raphe nucleus with minor projections from raphe medianus and raphe pontis.

Projections of the nucleus of the tractus solitarius in the pigeon (Columba livia)

With the aid of autoradiographic and histochemical (WGA-HRP) tracing techniques, the projections of the nucleus of the tractus solitarius (nTS) in the pigeon have been delineated and related to the viscerotopic organization of the nucleus. As in mammals, nTS projects to both brainstem and forebrain structures. At medullary levels, projections were seen to nTS itself, to the dorsal motor nucleus of the vagus and to the subjacent and more ventral reticular formation. There is a substantial projection to the parabrachial nuclear complex with terminations in all its subnuclei and minor projections to locus coeruleus and several mesencephalic areas, including the ventral area of Tsai, the nucleus of the ascending brachium conjunctivum, and the compact portion of the tegmental pedunculopontine nucleus. At diencephalic levels, projections to the hypothalamus (magnocellular periventricular nucleus, stratum cellulare internum and externum) and dorsal thalamus were seen. Terminal fields within the basal telencephalon included the nucleus of the pallial commissure, the bed nucleus of the stria terminalis, and the nucleus accumbens. The organization of nTS projections in pigeons is correlated with the pattern of inputs to specific nTS subnuclei. Lateral tier subnuclei receiving cardiovascular and pulmonary inputs project upon the ventrolateral reticular formation and the ventrolateral parabrachial complex. Medial tier subnuclei receiving gustatory and gastrointestinal inputs project upon dorsal and medial parabrachial nuclei. Transparabrachial projections arise from nTS subnuclei receiving little or no primary input from the viscera.

Projections from the red nucleus and surrounding areas to the brainstem and spinal cord in the cat. An HRP and autoradiographical tracing study

HRP injections at the C 2, T 1 and S 1 spinal levels and in the medullary lateral tegmental field revealed that the contralaterally projecting rubro-bulbospinal neurons are located not only in the caudal but also to a certain extent in the rostral red nucleus (RN). These RN projections are somatotopically organized. Neurons projecting to the sacral cord are located in the ventrolateral RN, those projecting to the upper part of the spinal cord lie in the dorsomedial RN and those projecting to the medullary lateral tegmentum were found in the dorsal portions of the RN. These last neurons are smaller than many of the other RN neurons. The HRP results also revealed that the RN does not project to the caudal raphe nuclei. The autoradiographical results confirmed the HRP findings. They further indicated that the contralateral RN projections to the caudal brainstem precerebellar nuclei (nucleus corporis pontobulbaris, lateral reticular nucleus, lateral cuneate nucleus) and the dorsal column nuclei are also somatotopically organized. This was also true for the RN projections to the dorsomedial and intermediate facial subnuclei and the caudal pontine and medullary lateral tegmental field. These areas receive afferents from mainly the dorsal portions of the RN. Regarding the RN projections to the spinal cord, the autoradiographical tracing results revealed somatotopically organized contralateral RN projections to laminae V, VI and VII. Moreover, a small but distinct RN projection to a dorsolaterally located group of motoneurons at the C 8-T 1 level was demonstrated. Ipsilaterally a minor projection to the cervical and upper thoracic lateral intermediate zone was observed. Finally, strong ipsilateral projections from the rostral mesencephalon to the inferior olive were seen. These projections were derived from various rostral mesencephalic areas, including the nucleus of Darkschewitsch, the nucleus accessorius medialis of Bechterew, the interstitial nucleus of Cajal and the area of the rostral interstitial nucleus of the medial longitudinal fasciculus. In the cat it was difficult to define which of the mesencephalic areas projecting to the inferior olive represented the parvocellular RN. A new subdivision of the RN is proposed based on its projections and not on the size of its cells. In this concept the first group is formed by the RN neurons projecting contralaterally to the caudal brainstem and spinal cord. The second group consists of RN neurons projecting to the inferior olive. However, it is difficult, especially in the cat, to determine the exact location of this second group of RN neurons, since they take part in a much wider mesencephalo-olivary projection system.

Entorhinal projections to the hippocampal CA1 region in the rat: An underestimated pathway

The projections of the entorhinal cortex to CA1 in relation to the entorhinal-dentate projections were studied in the rat, using the anterograde transport of Phaseolus vulgaris leucoagglutinin. It was observed that the entorhinal cortex is heterogeneous with respect to the origin of these projections. Caudomedial portions of the entorhinal cortex mainly distribute fibers to the fascia dentata, whereas only a minor projection reaches CA1. Progressively more rostral and lateral parts of the entorhinal cortex project more strongly to CA1, at the expense of the number of fibers that terminate in the fascia dentata. The rostrolateral part of the entorhinal cortex, adjacent to the olfactory cortex and the amygdaloid complex, projects only to CA1.

Haitian Creole Syntax

In this paper we examine several aspects of Haitian Creole syntax in light of the recent proposal that a determiner can be the head of a minor maximal projection. We argue that an incorporation of this proposal into the analysis of several aspects of Haitian Creole syntax, including clause structure, question formation, and relative-clause formation, can resolve several puzzling problems. In addition, the paper adds to the theory of minor heads in that it shows that such heads must be considered to inherit major category features from their complements.

British language diversity surveys (1977–87): A critical examination

Abstract. The last ten years of surveys of users of languages in addition to English in Britain are examined here through a review of the work of three bodies, which have operated mainly in London schools: The Inner London Education Authority Language Census, The Survey of Linguistic Diversity in London Schools, and The Linguistic Minorities Project. Various flaws and problems in the methodology of these surveys are discussed. Methodological problems in the nature of language diversity surveys as social surveys, as linguistic research, and as ideological activities, are summarised. The conclusion is made that under‐reporting has occurred in all cases. Some suggestions for future practice are indicated.

Thalamic projections to fields A, AI, P, and VP in the cat auditory cortex.

Thalamocortical projections to four tonotopic fields (A, AI, P, and VP) of the cat auditory cortex were studied by using combined microelectrode mapping and retrograde axonal transport techniques. Horseradish peroxidase (HRP) or HRP combined with either tritiated bovine serum albumin or nuclear yellow was injected into identified best-frequency sites of one or two different fields in the same brain. Arrays of labeled neurons were related to thalamic nuclei defined on the basis of their cytoarchitecture and physiology. In some cases, patterns of labeling were directly compared with thalamic best-frequency maps obtained in the same brain. We compared only patterns of labeling resulting from injections into similar parts of the frequency representation in different fields to insure that observed differences in patterns of labeling did not simply reflect differences in the frequency representation at the injection sites. The thalamic projection to the four fields is divided among seven nuclei, three tonotopic nuclei (ventral nucleus, V; lateral part of the posterior group of thalamic nuclei, Po; and dorsal cap nucleus, d) and four nontonotopic nuclei (caudodorsal nucleus, cd; ventrolateral nucleus, vl; and small, Ms; and medium-large, Mg, cell regions of the medial division). Projections to each field differ, and each field receives inputs from tonotopic and nontonotopic nuclei. Field A receives its major inputs from Po and Mg, and a minor input from V. Field AI receives its major inputs from V, Po, and Mg, although Po and Mg have heavier projections to field A. Field P receives its major inputs from V, d, and vl; and minor inputs from cd, Ms, Mg, and Po. Field VP receives major inputs from V, vl, and cd; and minor inputs from d, Ms, and Mg. There are segregated territories in V and Po in which most neurons projects to one cortical field (major projection), and a smaller proportion projects to one or more other fields (minor projections). Field VP receives a major projection from the caudal pole of V. Field P receives a major projection from the caudal half of V, and from a thin band along the dorsal border of rostral V. Field AI receives a major projection from most of the rostral one-half of V, and smaller areas in Po and the caudal half of V exclusive of its caudal pole. Field A receives a major projection from most of Po.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatosensory projection to the mesencephalon: An anatomical study in the monkey

The terminal areas and cells of origin of the somatosensory projection to the mesencephalon in the monkey were investigated by the intraaxonal transport method. Following injection of wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) into the spinal enlargements, the lateral cervical nucleus (LCN), the dorsal column nuclei (DCN), or the spinal trigeminal nucleus, anterograde labeling was observed in several regions of the mid-brain. (1) Injection of tracer into the spinal enlargements resulted in dense terminal labeling in the parabrachial nucleus (PBN) and the periaqueductal gray matter (PAG); moderate termination was observed in the intercollicular nucleus (Inc), the intermediate and deep gray layers of the superior colliculus (SGI, SGP), the posterior pretectal nucleus (PTP), and the nucleus of Darkschewitsch (D); and scattered terminal fibers were seen in the cuneiform nucleus (CNF) and the pars compacta of the anterior pretectal nucleus (PTAc). The projections from the cervical enlargement to PAG, Inc, and the superior colliculus terminated more rostrally than those from the lumbar segments, indicating a somatotopic organization. (2) Terminal labeling after injection of tracer into LCN was found mainly in Inc, SGI, and SGP, but sparse labeling was also observed in the nucleus of the brachium of the inferior colliculus (BIN), PAG, PBN, PTP, and D. (3) The projection from DCN terminated densely in the external and pericentral nuclei of the inferior colliculus (ICX, ICP), Inc, SGI, SGP, PTP, PTAc, the nucleus ruber, and D, and weak terminal labeling was seen in BIN, PAG, and PBN. Comparisons of the anterograde labeling following injections involving both the gracile nucleus and the cuneate nucleus with that after injection restricted to the gracile nucleus alone suggested a somatotopic termination pattern in Inc, the superior colliculus, and the pretectal nuclei. (4) The patterns of projection from the laminar and alaminar parts of the spinal trigeminal nucleus differed: injection of tracer into the caudal part of the alaminar spinal trigeminal nucleus (nucleus interpolaris) resulted in dense anterograde labeling in SGI and SGP, moderate termination in Inc, and minor projections to PBN, PAG, and PTP, whereas after tracer injection into the laminar trigeminal nucleus (nucleus caudalis) terminal labeling was present only in PBN and PAG. Following injection of tracer into the midbrain terminal areas retrogradely labeled neurons were found in the spinal cord, LCN, DCN, and the spinal trigeminal nucleus, with the majority of labeled cells situated on the side contralateral to the injection site.(ABSTRACT TRUNCATED AT 400 WORDS)

Phaseolus vulgaris leuco-agglutinin tracing of intrahypothalamic connections of the lateral, ventromedial, dorsomedial and paraventricular hypothalamic nuclei in the rat

Intrahypothalamic connections of the lateral (LHA), ventromedial (VMH), dorsomedial (DMH) and paraventricular (PVN) hypothalamic nuclei were studied with anterograde transport of iontophoretically injected Phaseolus vulgaris Ieuco-agglutinin and the immunocytochemical detection of labeled structures. The LHA was found to give rise to a minor projection in the VMH, whereas the VMH in reverse maintains few connections with the ventromedial part of the tuberal LHA. Tracer deposits in both the LHA and VMH resulted in anterograde terminal labeling in the DMH. The DMH, in turn, donates a small number of projections to the LHA and VMH. The main projection of the DMH is aimed at the parvocellular paraventricular nucleus. Direct outflow pathways from the VMH to the PVN were not found, but lectin injections in the LHA on the other hand gave rise to terminal labeling in both the parvocellular and magnocellular divisions of the PVN. The PVN in turn was found to give only minor reciprocal projections to the LHA, DMH and VMH. These findings indicate that the main stream of connections in the hypothalamus runs from the LHA and VMH to the DMH, and from the DMH to the PVN. The identified circuitry patterns were discussed with respect to the role of the hypothalamus in the control of homeostasis and metabolic regulation, and more specifically in relation to the modulation of the hormone release from the pancreas and adrenal glands.

The projection to the mesencephalon from the sensory trigeminal nuclei. An anatomical study in the cat

The terminal areas and the cells of origin of the projection from the sensory trigeminal nuclei to the mesencephalon were investigated, using the method of anterograde and retrograde transport of horsedish peroxidase or wheat germ agglutinin-horseradish peroxidase conjugate. Injection of tracer into the nucleus interpolaris or nucleus oralis (in the latter cases with involvement of the nucleus principalis) resulted in dense anterograde labeling in the deep and intermediate gray layers of the contralateral superior colliculus, extending throughout the rostrocaudal extent of the colliculus with the exception of its caudalmost part, which was not labeled. Minor projections to the intercollicular nucleus, posterior pretectal nucleus and nucleus of Darkschewitsch were found. Injection of tracer into the nucleus caudalis yielded a completely different result; terminal labeling in the midbrain was now present only in the periaqueductal gray matter, in its rostral and middle parts. The retrograde labeling observed after injection of tracer into the midbrain terminal areas showed that the cells of origin were located mainly in the alaminar spinal trigeminal nucleus, and the highest density of labeled neurons was found in the rostral part (subnucleus y) of the nucleus oralis.The retrograde labeling in the nucleus principalis was very sparse and almost exclusively involved peripherally located neurons. In the caudalis the overwhelming majority of the retrogradely labeled neurons were situated in its marginal layer. The functional implications of the above observations are discussed in relation to the findings in previous studies of the projections from the dorsal column nuclei and spinal cord to the midbrain. The combined results suggest that the trigeminal projections to the superior colliculus may be involved in the mechanisms of orientational behavior. The observation that the projection to the periaqueductal gray matter originates in the marginal layer suggests that it transmits information related to noxious stimuli.

Cuspate ore-wall rock interfaces, piercement structures and the localization of some sulfide ores in deformed sulfide deposits

Studies on three deformed massive sulfide deposits (Trojan nickel deposit, Zimbabwe; Matchless copper deposit, Namibia (South-West Africa); Broken Hill silver-lead-zinc deposit, Australia) show that the interfaces between massive sulfide rock and silicate wall rock are characterized by irregularities and projections of sulfide rock into the wall rock. The structures range from simple cusps, in which ore layering remains parallel to the ore-wall rock interface and to wall-rock layering, to veins which occupy brittle fractures in the wall rocks. In size, the features range from minor projections less than 1 m across to major piercement structures which may exceed 50 m in length. The structures can usually be related to specific phases of rock deformation. In most cases, the contained sulfide rock is a tectonic breccia with a foliation parallel to margins of the structure.The cusp and related structures reflect competency contrast during rock deformation. Simple cusps develop in a similar manner to certain types of mullions. However, where the competent wall rock is relatively brittle, ductile sulfides take advantage of brittle fractures and other zones of weakness to penetrate into the wall rock and develop discordant vein structures. The mechanism by which the sulfides move is plastic flow, although there is some evidence for the activity of a fluid phase.The process has economic significance in the generation of locally thickened parts of ore-bodies.