Subcortical projections to the centromedian and parafascicular thalamic nuclei in the cat.

The primary objective of this study is to identify the totality of input to the centromedian and parafascicular (CM-Pf) thalamic nuclear complex. The subcortical projections upon the CM-Pf complex were studied in the cat with three different retrograde tracers. The tracers used were unconjugated horseradish peroxidase (HRP), horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP), and rhodamine-labeled fluorescent latex microspheres (RFM). Numerous subcortical structures or substructures contained labeled neurons with all three tracing techniques. These labeled structures included the central nucleus of the amygdala; the entopeduncular nucleus; the globus pallidus; the reticular and ventral lateral geniculate nuclei of the thalamus; parts of the hypothalamus including the dorsal, lateral, and posterior hypothalamic areas and the ventromedial and parvicellular nuclei; the zona incerta and fields of Forel; parts of the substantia nigra including the pars reticularis and pars lateralis, and the retrorubral area; the pretectum; the intermediate and deep layers of the superior colliculus; the periaqueductal gray; the dorsal nucleus of the raphe; portions of the reticular formation, including the mesencephalic, pontis oralis, pontis caudalis, gigantocellularis, ventralis, and lateralis reticular nuclei; the nucleus cuneiformis; the marginal nucleus of the brachium conjunctivum; the locus coeruleus; portions of the trigeminal complex, including the principal sensory and spinal nuclei; portions of the vestibular complex, including the lateral division of the superior nucleus and the medial nucleus; deep cerebellar nuclei, including the medial and lateral cerebellar nuclei; and lamina VII of the cervical spinal cord. Moreover, the WGA-HRP and rhodamine methods (known to be more sensitive than the HRP method) revealed several afferent sources not shown by HRP: the anterior hypothalamic area, ventral tegmental area, lateral division of the superior vestibular nucleus, nucleus interpositus, and the nucleus praepositus hypoglossi. Also, the rhodamine method revealed labeled neurons in laminae V and VI of the cervical spinal cord.

Thalamocortical connections of the rostral intralaminar nuclei: an autoradiographic analysis in the cat.

In this study the pattern of projections from the rostral intralaminar thalamic nuclei to the cerebral cortex was examined in the cat by autoradiography. Injections of tritiated proline and leucine were placed into the central lateral, paracentral, central medial, and para-stria medullaris nuclei. After injections into the central lateral nucleus, label is present on the lateral side within the presylvian sulcus, in most of the suprasylvian gyrus, including the adjacent lateral and suprasylvian sulci, and in the posterior corner of the ectosylvian gyrus. On the medial side, label is present in the orbitofrontal (Of), precentral agranular (Prag), anterior limbic (La), retrosplenial (Rs), and postsubicular (Ps) areas, as defined by Rose and Woolsey ('48a). The cingulate gyrus also contains label throughout (part of which was defined as the "cingular area," Cg, by Rose and Woolsey, '48a). Label is also found on both banks of the splenial and cruciate sulci. In addition, label is present within the lateral gyrus, on both its lateral and medial sides. The paracentral projections are similar to the central lateral input. On the lateral side, label is found within the presylvian sulcus, suprasylvian gyrus and adjacent lateral and suprasylvian sulci, and posterior ectosylvian gyrus. Medially, label is present in the Of, Prag, La, Cg, Rs, and Ps areas, and within the cruciate and splenial sulci, and in portions of the lateral gyrus. Following injections of the central medial nucleus, label is present in the presylvian sulcus; but in contrast to the central lateral and paracentral projections, the suprasylvian gyrus is labeled only in its posterior part. The central medial nucleus also projects to the posterior lateral gyrus, both laterally and medially. Also, the central medial nucleus projects heavily to rostral cortical zones, which include the Of, Prag and La areas, cruciate sulcus, and the rostral cingulate gyrus. The para-stria medullaris nucleus projects only to the presylvian sulcus and orbitofrontal cortex laterally, but, medially, has an extensive input similar to the central lateral and paracentral projections in that label is present in the Of, Prag, La, Cg, Rs, and Ps areas, in the cruciate and splenial sulci, and in the posterior lateral gyrus. The laminar distribution of label is as follows: the central lateral, paracentral and para-stria medullaris nuclei project primarily to layers I and III, whereas the central medial nucleus projects to layers I and VI. In addition, the central lateral projection has a patchy appearance in the retrosplenial and postsubicular cortices.

A Golgi and ultrastructural analysis of the centromedian nucleus of the cat.

The morphology of neurons in the centromedian nucleus (CM) was studied in rapid Golgi preparations of the adult cat. The ultrastructure of the nucleus, particularly its synaptic organization, was also studied with electron microscopy. The CM contains three types of neurons referred to as principal neurons, Golgi type II neurons, and bushy neurons. Principal neurons are the most numerous, have long dendrites, which branch infrequently, and are divided into two subgroups: principal-A neurons with dendrites that arborize radially, whereas principal-B neurons display horizontal orientations. Both subgroups show a frontal orientation in their dendritic organization and give rise to myelinated axons. Golgi type II neurons with their characteristic sinuous dendrites and unmyelinated axons are thought to be interneurons. The occurrence of bushy neurons in the cat's CM is a new finding. These bushy neurons resemble those of thalamic specific relay nuclei and give rise to myelinated axons. In addition to these three cell types, neurons with intermediate features between these three neuronal types are also described. The ultrastructure of CM neurons resembles, in general, typical central nervous system neurons. Presynaptic profiles are classified into four main categories. SR (small round) boutons are small in size, contain clear, round vesicles, and form asymmetrical synaptic contacts with predominantly small-diameter dendrites. LR (large round) boutons are relatively large and contain both clear and dense-cored vesicles. They interdigitate and form multiple, moderately asymmetrical synapses with their postsynaptic targets. Pale profiles are identified by their relatively electron-light appearance. They contain round vesicles and are thought to be dendritic in origin. The last category of presynaptic profiles is pleomorphic boutons. They contain vesicles of different shapes and are further subdivided into two subtypes: pleomorphic-I ends on soma and dendritic trunks, whereas pleomorphic-II contacts small-diameter dendrites. Both subtypes form symmetrical synapses. The glomeruli of specific thalamic relay nuclei generally contain dendrites, LR boutons, and pale profiles. In addition to these, pleomorphic-II boutons also participate in the formation of the glomerulus of the cat's CM.

Efferent connections of the centromedian and parafascicular thalamic nuclei: an autoradiographic investigation in the cat.

The efferent projections of the centromedian and parafascicular (CM-Pf) thalamic nuclear complex were analyzed by the autoradiographic method. Our findings show that the CM-Pf complex projects in a topographic manner to specific regions of the rostral cortex. These fibers distribute primarily to cortical layers I and III; however, the projection to layer I is more extensive. Following an injection into the rostral portion of the CM-Pf complex, label is found within the lateral rostral cortex, particularly within the presylvian, anterior ectosylvian, and anterior lateral sulci, and within the rostral medial cortex where label is present within the cruciate and anterior splenial sulci and anterior cingulate gyrus. An injection into the caudal dorsal portion of the CM-Pf complex results in label within the more ventral portions of the rostral lateral cortex where it is present within the anterior sylvian gyrus, presylvian regions, and gyrus proreus; and within the rostral medial cortex, where it is present within the rostral cingulate gyrus, and within the cruciate sulcus, and an extensive region ventral to the cruciate sulcus which includes the anterior limbic area. Injections into the caudal ventral portion of the CM-Pf complex result in virtually no cortical label, although a few labeled fibers are found in the subcortical white matter. The subcortical projection from the CM-Pf complex terminates within the caudate nucleus, putamen, globus pallidus, subthalamic nucleus, zona incerta, fields of Forel, hypothalamus, thalamic reticular nucleus, and rostral intralaminar nuclei. Prominent silver grain aggregates are also present within the ventral lateral, ventral anterior, ventral medial, and lateral posterior nuclei, and ventrobasal complex. The aggregates in the thalamus appear to be fibers of passage, but whether these are also terminals cannot be determined with the techniques used in the present study.

Efferent connections of the caudate nucleus, including cortical projections of the striatum and other basal ganglia: an autoradiographic and horseradish peroxidase investigation in the cat.

Tritiated tracer was injected into the head of the caudate nucleus in cats. Following such injections, labeling is present within extensive regions of both the globus pallidus and entopeduncular nucleus, where it presents a mottled or meshlike appearance. These projections are topographically organized in that there is simple correspondence between the mediolateral, dorsoventral, and rostrocaudal origin of the caudate projection and its input to the globus pallidus and entopeduncular nucleus. Transported tracer is also present within the substantia nigra, where it is most abundant within the pars reticularis. However, distinct labeling also overlies cells of the pars compacta, and lesser amounts of labeling are present within the pars lateralis and within the retrorubral area. Following injections of horseradish peroxidase into the caudate nucleus, and subsequent tissue processing by the tetramethylbenzidine (TMB) method of Mesulam ('78), labeled anterograde fibers are present in abundance within the globus pallidus, entopeduncular nucleus, and all subdivisions of the substantia nigra, thus confirming the autoradiographic findings. Also, it is especially obvious in this HRP material that, contrary to previous degeneration studies, both the rostromedial and caudolateral parts of the pars lateralis of the substantia nigra contain numerous anterogradely labeled fibers. Retrogradely labeled neurons are also present within the substantia nigra of these same tissue sections, where they are most abundant within the pars compacta, but lesser numbers of labeled neurons are also present within the pars reticularis, pars lateralis, retrorubral area, and ventral tegmental area on the ipsilateral side, and all of these same subdivisions of the substantia nigra on the contralateral side. Also, within the subthalamic nucleus in these experiments, there are anterogradely labeled fibers, as well as retrogradely labeled neurons, which are interpreted to represent a reciprocal connection between the subthalamic nucleus and the striatum. In a separate series of experiments, horseradish peroxidase was injected into the motor cortex-specifically into the anterior sigmoidal gyrus. Following such injections, labeled neurons representing afferents to the motor cortex are found in all subcortical nuclei commonly known as the "basal ganglia," including the caudate nucleus, putamen, globus pallidus, entopeduncular nucleus, substantia innominata, nucleus of the diagonal band of Broca, medial septal nucleus, claustrum, and basolateral amygdaloid nucleus.

Single thalamic neurons which project to both the rostral cortex and caudate nucleus studied with the fluorescent double labeling method.

After injections of fast blue into the rostral cortex and Evans blue into the caudate nucleus in cats, doubly labeled neurons were present in the ventral anterior, ventral lateral, rhomboid, and mediodorsal thalamic nuclei. Doubly labeled cells were also found in most members of the intralaminar group, including the central medial, paracentral, central lateral, and parafascicular nuclei. Although the centromedian nucleus contained large numbers of cells labeled with Evans blue which project to the caudate nucleus, and a few fast-blue labeled cells which projected to the cortex, doubly labeled neurons were absent from this posterior intralaminar nucleus in this study.

Cortical neurons with collateral projections to both the caudate nucleus and the centromedian-parafascicular thalamic complex: a fluorescent retrograde double labeling study in the cat.

The retrograde fluorescent technique was used to label cortical neurons which project to both the caudate nucleus and also to the centromedian-parafascicular (CM-Pf) thalamic nuclear complex. After experimentation with many other pairs of fluorescent tracers, Evans Blue (EB) and Fast Blue (FB) were chosen as the best combination for studying the systems involved. Following injections of EB into the caudate nucleus and FB into the CM-Pf complex, doubly labeled medium-sized pyramidal neurons were present within layer V and VI of specific cortical regions. These cells were found on the inferior bank of the cruciate sulcus, in the anterior limbic area, in the cingulate and anterior sylvian gyri and within the buried cortex of the presylvian sulcus. The doubly labeled cells were relatively few in number compared to the more numerous singly labeled FB (corticothalamic) cells found in layers V and VI, and the very numerous singly labeled EB (corticostriatal) neurons, located in layers II, III, V, and VI.

Cells of origin of corticothalamic projections upon the centromedian and parafascicular nuclei in the cat.

The horseradish peroxidase method was used to study the cortical projections upon the centromedian and parafascicular (CM-Pf) thalamic complex in the cat. Following HRP injections into the CM-Pf complex, labeled corticothalamic neurons are found predominantly in cortical layer V, and rarely in layer VI. They are medium in size, pyramidal in shape, and usually occur singly, though occasionally in small clusters. These retrogradely labeled neurons have an extremely widespread distribution, being scattered throughout approximately the rostral four-fifths of the cat's neocortex. They are found in all neocortical gyri, except the posterior lateral and posterior suprasylvian gyri, but are more numerous in the rostral neocortical regions, especially within the depths of the cruciate and presylvian sulci. The pattern of distribution of these corticothalamic neurons, as revealed herein, bears a remarkable resemblance to the organization of the corticostriatal projection, as shown in another study. The similarity between the corticothalamic and corticostriatal projections is discussed. Also discussed are the present results regarding the corticothalamic projection with regard to other studies using neurophysiological and neuroanatomical methods.

Laminar origin of cortical neurons which project upon the caudate nucleus: a horseradish peroxidase investigation in the cat.

The horseradish peroxidase method was used to study the cortical projections upon the caudate nucleus in the cat. The cells of origin of the corticostriatal projection arise from both the supragranular (II and III) and infragranular (V and VI) cortical layers, in contrast to all other known corticofugal pathways to subcortical structures, which appear to arise only from the infragranular layers. This finding has been verified in the present study by several novel surgical procedures, which include direct injections into the caudate nucleus, after the overlying tissues have been removed. The present study also shows that there is a truly widespread distribution of the cells contributing to the corticostriatal projection. Some portion of every neocortical gyrus contains labeled cells, though their relative numbers vary greatly. Also, simple topographical relationships are maintained, but there is much overlap. In addition, present findings show that the corticostriatal projection is strikingly bilateral and originates from regions which are homotopic to the ipsilateral projection.

Ascending pathways from the monkey superior colliculus: an autoradiographic analysis.

The autoradiographic tracing method has been used to analyze the distribution of ascending tectofugal pathways in the rhesus monkey. Our findings show that axons which arise from deep collicular neurons terminate within several dorsal thalamic nuclei which in turn project upon the frontal eye fields (area 8) and the inferior parietal lobule (area 7). Both of these cortical areas are functionally quite similar to the deep colliculus, and we suggest that ascending channels from the deep tectum must account, at least in part, for these functional similarities. The present autoradiographs reveal projections to several nuclear zones previously not identified as deep collicular targets in the monkey. Such targets include the visceral cell columns of the oculomotor complex, the rostral interstitial nucleus of the medial longitudinal fasciculus, and the magnocellular division of the ventral anterior nucleus. Deep tectal input also has been shown to terminate quite extensively within the paralamellar region of the mediodorsal nucleus and in the parafascicular nucleus; very little input to the central lateral and centromedian nuclei was observed. Radioisotope injections restricted to the superficial layers reveal dense projections to the parabigeminal nucleus, the pretectum, the inferior and lateral pulvinar nuclei, and to the ventral and dorsal lateral geniculate nuclei. Transported protein within the dorsal lateral geniculate nucleus occupied the "S" layers and the interlaminar zones.

An autoradiographic study of the rubroolivary tract in the rhesus monkey.

Autoradiographic tracing methods were employed to study the course and distribution of the rubroolivary tract following unilateral injections of tritiated leucine into the rostral red nucleus of seven rhesus monkeys. A topographic organization of projections to the ipsilateral principal nucleus of the inferior olivary complex was demonstrated. Lateral and medial portions of the rostral red nucleus projected to medial parts of the dorsal and ventral laminae of the principal inferior olive respectively; neurons in intermediate lateralities emitted fibers which terminated in lateral parts of the principal olive. Injections involving the oral end of the rostral red nucleus elicited label overlying the medial accessory olive in addition to the principal nucleus. Projections to the medial accessory olive may have arisen from the rostral end of the red nucleus and/or the immediately adjacent tegmentum. There were no projections to the dorsal accessory olive. Fibers of rubral origin also were distributed ipsilaterally to several reticular nuclei including the pedunculopontine, pontis oralis, caudalis, and gigantocellularis.

Cells of origin of subcortical afferents to the caudate nucleus: a horseradish peroxidase study in the cat.

The horseradish peroxidase tracing method was used to investigate the sources of subcortical input to the caudate nucleus in the cat. Of considerable interest was the finding, not previously described, that labeled neurons were present outside of the intralaminar complex, in the ventral anterior and mediodorsal thalamic nuclei. Another new finding was that retrogradely labeled cells were present within the basolateral amygdaloid nucleus, following the caudate injections. In addition, neurons containing enzyme granules were found within all of the intralaminar thalamic nuclei, most prominently in the central lateral and centromedian nuclei. Also, HRP-positive cells were strikingly apparent within the ipsilateral pars compacta of the substantia nigra, and a few labeled cells were found in the ipsilateral pars reticularis, and the contralateral pars compacta of the substantia nigra. Cells containing peroxidase granules were also found in the ventral tegmental area and the retrorubral area. The most caudal projection to the caudate nucleus in the cat was demonstrated by labeled neurons found bilaterally in the dorsal nucleus of the mesencephalic raphe.

Respiratory influence on the total and regional cerebral blood flow responses to intracranial hypertension.

The effect of respiration on the cerebrovascular response to elevated intracranial pressure (ICP) was studied in anesthetized dogs. Total and regional cerebral blood flows were measured using labelled microspheres. In spontaneously breathing dogs total and regional cerebral blood flows increased when cerebral perfusion pressure was reduced to 20 mm Hg. The increase in regional flows was greater in the infratentorial areas than in the supratentorial areas. The increase in cerebral flow in spontaneously breathing dogs was associated with the development of hypoxemia and respiratory acidosis secondary to depression of ventilation. Elevation in ICP while regulating PO2, PCO2, and pH by controlled ventilation resulted in decrease in the total and regional cerebral blood flows. The decrease in regional flows was greater in the supratentorial areas. Induction of respiratory acidosis during elevated ICP in the controlled ventilated dogs with a 5% CO2 in air gas mixture, reversed the decrease in cerebral flows. The results suggest that the increase in cerebral blood flow during elevated ICP in spontaneously breathing dogs is secondary to the development of hypoxemia and respiratory acidosis since cerebral vessels retain responsiveness to increased PaCO2 when the vessels are dilated due to elevated ICP. The results also indicate that the regional cerebrovascular response to elevated ICP is non-uniform.

Retinofugal pathways in two marsupials.

Autoradiographic and anterograde degeneration tracing methods were used to study and compare the organization of retinofugal pathways in two marsupial opossums, Didelphis virginiana and Marmosa mitis. Seven identical retinal targets were demonstrated for each opossum. These include: (1) the suprachiasmatic nucleus of the hypothalamus, (2) the dorsal and (3) ventral lateral geniculate nuclei, (4) the lateral posterior nucleus, (5) the pretectal complex, (6) the superior colliculus and (7) the accessory optic nuclei. While the pattern of retinal input to six of the seven targets was quite similar in the two species, the organization of the retinogeniculate pathways exhibited striking differences. In particular, our autoradiographs reveal no separation of ocular inputs within the lateral geniculate nucleus of Didelphis, i.e. the ipsilateral input is overlapped completely by the more extensive contralateral projection. In contrast, there is considerable separation, as well as overlap, of the occular inputs within the lateral geniculate nucleus of Marmosa. Our autoradiographs reveal several distinct bands of label within each geniculate nucleus, and upon superimposing the nuclei, ipsilateral and contralateral to the placement it is apparent that two of the bands overlap, while five do not (three ipsi, two contra).

An autoradiographic analysis of the tecto-olivary projection in primates.

Autoradiographic tracing methods were used to demonstrate a well-defined projection from the superior colliculus to the inferior olivary complex in the monkey. This projection originates within the deep layers of the superior colliculus, descends within the contralateral tecto-spinal tract, and terminates within the caudal 1/3 of the medial accessory nucleus. The terminal field is restricted to a densely packed, darkly stained group of cells located in the most dorsal segment of subnucleus b. In one animal, another group of olivary afferents was identified. These fibers also descend within the contralateral tecto-spinal tract, and terminate within the dorsal cap of Kooy. While it was not possible to determine the origin of this projection, our data suggest that it arises within a region adjacent to the rostral pole of the superior colliculus. The present study further indicates that in the monkey relatively few axons which course within the classical tecto-spinal tract pass caudal to the medulla.

Functional localization and cortical architecture in the nine-banded armadilli (Dasypus novemcinctus mexicanus).

A functional map of the armadillo neocortex was produced by cortical stimulation and recording evoked potentials following somatic, auditory and visual stimuli. The results obtained were then correlated with the cortical architecture as revealed by Nissl, Golgi and myelin-stained sections. Cortex rostral to the supraorbital sulcus has a wide layer IV and is mostly silent, except for a motor eye field and a part of the tongue sensory region in its caudal part. Two types of motor-sensory cortex are present caudal to the supraorbital sulcus. Postsupraorbital I is mostly motor and has prominent pyramidal layers. Layer V is particularly well developed and in rostral sections its superficial zone is broken up into clusters similar to the solid "barrels" seen in layer IV of other species. Postsupraorbital II has less prominent pyramidal layers and layers II and III are organized into clusters. This region corresponds to the sensory area for the limbs and trunk and the partially overlapping (surface recordings) sensory and motor areas for head, snout and tongue. Digits and limbs are rostral to the trunk representation in both the sensory and motor "homunculi." Even though surface recording was employed, potentials evoked by visual stimuli could only be recorded from a small caudal area with a very thin layer IV. Although striate and peristriate areas appear similar in Nissl stained preparations, they can be readily differentiated in Weil stained sections. The stellate character of neurons in layer IV of the visual cortex is particularly apparent in Golgi material. Auditory evoked surface potentials were recorded from a broad oval region in the caudal lateral cortex which has a wide layer IV and aggregates of neurons in layers II and III. A Weil stain demonstrates inner and outer bands of Baillarger in this same region. The presumptive insular cortex is electrically silent to sensory stimulation and presents as a narrow band just dorsal to the rhinal fissure with indefinite cell lamination and little myelin.

Olfactory bulb projections in the bullfrog Rana catesbeiana.

The projections of the accessory and main olfactory bulbs of the bullfrog are described as part of a long term analysis of the morphological differences in amphibian and reptilian telancephalons. Unilateral aspiration of the accessory olfactory bulb results in an ipsilateral projection to the pars lateralis of the amygdala via the accessory olfactory tract. Degenerating fibers from the accessory olfactory bulb are tracable into the cell-free zone between the dorsal striatum and the lateral pallium, and projections to these neural populations may also exist. Unilateral lesions of the main olfactory bulb reveal two major secondary pathways: an ipsilateral medial olfactory tract that projects to the rostral ventromedial portion of the medial pallium, the postolfactory eminence and the rostal, lateral and medial septal nuclei; and an ipsilateral lateral olfactory tract that projects to the dorsal striatum, the lateral pallium and the ventral half of the dorsal pallium. Two crossed secondary olfactory pathways to the contralateral telencephalon decussate via the habenular commissure after entering the ipsilateral stria medullaris. A crossed lateral pathway terminates in the dorsal striatum, the caudal, lateral pallium and the ventral portion of the dorsal pallium. A crossed medial pathway terminates in the internal granule layer of the main olfactory bulb.