Dorsomedial Cortex Research Articles

Projections from the medial cortex in the brain of lizards: Correlation of anterograde and retrograde transport of horseradish peroxidase with timm staining

Efferent projections of the medial cortex of the lizards Podarcis hispanica and Gallotia stehlinii were studied by examining the transport of horseradish peroxidase; results were correlated with those from Timm-stained sections. Two efferent systems were found. The first reaches the distal part of the outer plexiform layer in the medial, dorsomedial, and dorsal cortices, i.e., zones that are negative to Timm staining, and possibly originates from horizontal fusiform neurons. The second reaches the Timm-positive zones in the cortex and septum and is topographically arranged: the vertical portion of the intermediate and caudal medial cortex and the entire rostral medial cortex project to the inner two-thirds of the outer plexiform layer of the dorsomedial cortex and of the medial subfield of the dorsal cortex; to the paraventricular zone of the inner plexiform layer of the medial cortex; and bilaterally to the dorsal part of the dorsal precommissural septum. The dorsal part of the intermediate and caudal medial cortex and the ventralmost folded part of its caudal edge project rostrally to the juxtasomatic zone of the outer plexiform layer and the entire inner plexiform layer of the intermediate and lateral subfields of the dorsal cortex and to the ventral part of the dorsal septum. In its intense Timm reaction and its ultrastructural properties, as reported in earlier studies, the Timm-positive fiber system of the lizard brain shows a close resemblance to the mossy fiber system of the mammalian hippocampus.

Immunocytochemical localization of somatostatin in the cerebral cortex of lizards

The distribution of somatostatin-like immunoreactivity in the cerebral cortex of two lizards has been studied. Results are similar in both species. Somatostatin-positive neurons show variable morphology; they are bipolar, multipolar or pyramidal cells. Their distribution within the cerebral cortex is not homogeneous; they tend to be found in the innermost cortical layer, the deep plexiform layer, where they constitute a constant population in the region of the dorsomedial cortex. All immunoreactive processes observed in the cerebral cortex belong to somatostatin cortical neurons since no immunoreactive fiber is found to reach or leave the telencephalic cortex. Most of the dendrites are smooth or sparsely spinous. Axons are abundant in the deep plexiform layer; in the dorsomedial cortex a prominent terminal field appears in the outermost region of the superficial plexiform layer, which may arise from the neuronal somatostatin immunoreactive population found deeper in the same cortex.

Neuroimmunomodulation: potentiation of delayed hypersensitivity and antibody production by chronic electrical stimulation of the rat brain.

This study deals with the structural and functional correlates of the immunoneuroendocrine interconnections, and explores the effects of localized brain stimulation on immune response. Bilateral symmetrical electrodes were placed in the dorsomedial nucleus, ventromedial nucleus and posterior area of the hypothalamus, and in the sensorimotor cerebral cortex of the rat brain. Electrical stimulations were applied for 39 consecutive days, 10 days before and 29 days after single immunization. In sham-stimulated rats, electrodes were lowered into the hypothalamic areas and sensorimotor cortex without passing any current. Animals with electrodes were divided post mortem into groups according to the histological location of the electrode tips. Intact rats served as additional controls. All animals were immunized with bovine serum albumin in complete Freund's adjuvant and tested for immune reactions 7, 14, 21, and 28 days after immunization. The most significant finding was the potentiated delayed skin hypersensitivity and, to a lesser extent, antibody production to bovine serum albumin in rats with stimulated dorsomedial hypothalamus and sensorimotor cortex. On days 21 and 28, skin reactions increased in rats with stimulated posterior hypothalamus. These immune effects could not be obtained when the stimulation was applied to the hypothalamic ventromedial nucleus. Several pathways of the immunoneuroendocrine interplay are suggested.

Quantitative autoradiography of muscarinic and benzodiazepine receptors in the forebrain of the turtle, Pseudemys scripta.

The distribution of muscarinic and benzodiazepine receptors was investigated in the turtle forebrain by the technique of in vitro receptor autoradiography. Muscarinic binding sites were labeled with 1 nM 3H-quinuclidinyl benzilate (3H-QNB), and benzodiazepine sites were demonstrated with the aid of 1 nM 3H-flunitrazepam (3H-FLU). Autoradiograms generated on 3H-Ultrofilm apposed to tissue slices revealed regionally specific distributions of muscarinic and benzodiazepine binding sites that are comparable with those for mammalian brain. Dense benzodiazepine binding was found in the anterior olfactory nucleus, the lateral and dorsal cortices, and the dorsal ventricular ridge (DVR), a structure with no clear mammalian homologue. Muscarinic binding sites were most dense in the striatum, accumbens, DVR, lateral geniculate, and the anterior olfactory nucleus. Cortical binding sites were studied in greater detail by quantitative analysis of autoradiograms generated by using emulsion-coated coverslips. Laminar gradients of binding were observed that were specific for each radioligand; 3H-QNB sites were most dense in the inner molecular layer in all cortical regions, whereas 3H-FLU binding was generally most concentrated in the outer molecular layer and was least dense through all layers in the dorsomedial cortex. Because pyramidal cells are arranged in register in turtle cortex, the laminar patterns of receptor binding may reflect different receptor density gradients along pyramidal cell dendrites.

Frontal eye field as defined by intracortical microstimulation in squirrel monkeys, owl monkeys, and macaque monkeys II. cortical connections

Physiological (intracortical microstimulation) and anatomical (transport of horseradish peroxidase conjugated to wheat germ agglutinin as shown by tetramethyl benzidine) approaches were combined in the same animals to reveal the locations, extents, and cortical connections of the frontal eye fields (FEF) in squirrel, owl, and macaque monkeys. In some of the same owl and macaque monkeys, intracortical microstimulation was also used to evoke eye movements from dorsomedial frontal cortex (the supplementary motor area). In addition, in all of the owl and squirrel monkeys, intracortical microstimulation was also used to evoke body movements from the premotor and motor cortex situated between the central dimple and the FEF. These microstimulation data were directly compared to the distribution of anterogradely and retrogradely transported label resulting from injections of tracer into the FEF in each monkey. Since the injection sites were limited to the physiologically defined FEF, the demonstrated connections were solely those of the FEF. To aid in the interpretation of areal patterns of connections, the relatively smooth cortex of owl and squirrel monkeys was unfolded, flattened, and cut parallel to the flattened surface. Cortex of macaque monkeys, which has numerous deep sulci, was cut coronally. Reciprocal connections with the ipsilateral frontal lobe were similar in all three species: dorsomedial cortex (supplementary motor area), cortex just rostral (periprincipal prefrontal cortex) to the FEF, and cortex just caudal (premotor cortex) to the FEF. In squirrel and owl monkeys, extensive reciprocal connections were made with cortex throughout the caudal half of the lateral fissure and, to a much lesser extent, cortex around the superior temporal sulcus. In macaque monkeys, only sparse connections were present with cortex of the lateral fissure, but extensive and dense connections were made with cortex throughout the caudal one-third to one-half of the superior temporal sulcus. In addition, very dense reciprocal connections were made with the cortex of the lateral, or inferior, bank of the intraparietal sulcus. Contralateral reciprocal connections in all three species were virtually limited to regions that correspond in location to the FEF and the supplementary motor area. The results of this study reveal connections between the physiologically defined frontal eye field and cortical regions known to participate in higher order visual processing, short-term memory, multimodal, visuomotor, and skeletomotor functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Electron microscopy of the dorsomedial cortex in the lizard Psammodromus algirus.

The cellular populations and the plexiform layers of the dorsomedial cortex of Psammodromus algirus are described at the ultrastructural level. Solitary globous cells are located in the outermost layer of the cortex, the superficial plexiform layer. Double pyramidal cells of the cellular layer show uniform ultrastructural characteristics. Displaced double pyramidal cells, vertical fusiform cells, and globous cells are found in the deep plexiform layer. Two types of dendritic spines are described. Large spines may contain membranous sacs and mitchondira and are located at the upper third of the superifical plexiform layer; small spines do not contain organelles and are located throughout the entire cortex. Two types of axon terminals are widely distributed in both plexiform layers: terminals with only clear vesicles and terminals with both dense-core and clear vesicles. Terminals with large dense-core vesicles may be related to peptidergic synapses and are more frequent at the upper levels of the superficial plexiform layer. The neuroglia described in the dorsomedial cortex of Psammodromus are protoplasmatic astrocytes and oligodendrocytes.

Connections of the pigeon dorsomedial forebrain studied with WGA‐HRP and 3H‐proline

The afferent-efferent connections of the pigeon dorsomedial forebrain, which is composed of the "hippocampus" (Hp) and "parahippocampus" (APH), presumed homologues of the mammalian hippocampal complex, were studied. Afferent projections were identified by wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) and efferent projections were identified by 3H-proline and WGA-HRP. In addition to identified intrinsic connections within Hp and APH, both Hp and APH were found to be in receipt of ipsilateral forebrain afferents from each other, the hyperstriatum accessorium, nucleus of the diagonal band, nucleus taeniae, and area corticoidea dorsolateralis. Only Hp received input from the contralateral Hp while only APH received input from the ipsilateral hyperstriatum dorsale and archistriatum, pars ventralis. Both Hp and APH received ipsilateral diencephalic afferents from the nucleus mamillaris lateralis, stratum cellulare internum, nucleus lateralis hypothalami, and nucleus paramedianus internus thalami. Only APH received bilateral input from the nucleus superficialis parvicellularis (this nucleus may send a small projection to Hp) and nucleus dorsolateralis anterior thalami, pars medialis, and an ipsilateral projection from the nucleus subrotundus. Brainstem afferents to Hp and APH included ipsilateral projections from the area ventralis (Tsai) nucleus reticularis pontis oralis, nucleus raphes, nucleus subceruleus dorsalis, and nucleus centralis superior of Bechterew, and bilateral projections from the nucleus linearis caudalis and locus ceruleus, of which the nucleus subceruleus dorsalis, nucleus centralis superior of Bechterew, and locus ceruleus projected to APH only. Forebrain efferents from both Hp and APH were found to project ipsilaterally to the septum, the area of the fasciculus diagonalis Brocae, nucleus taeniae, and area corticoidea dorsolateralis. Only Hp appeared to send efferents to the contralateral septum and Hp, while only APH sent efferents to the hyperstriatum dorsale and the archistriatum. A hypothalamic projection from Hp and APH was found to partially terminate near the nucleus mamillaris lateralis. At the level of pathway connections, the results demonstrate a striking similarity between the avian dorsomedial forebrain and the dorsomedial cortex of reptiles and the mammalian hippocampus.

Unit activity related to spontaneous saccades in frontal dorsomedial cortex of monkey.

Single unit activity was studied in the dorsomedial edge of the frontal lobe, above the superior arcuate sulcus in three trained monkeys (Macaca nemestrina). Gaze and head movements were recorded with two magnetic search coils. Discharges preceding spontaneous eye movements in a preferred direction were consistently observed in light and in dark, in a limited cortical territory at the anterior border of the supplementary motor area. Microstimulation at these sites elicited saccades in the unit preferred direction. Five presaccadic units were studied head fixed and head free and showed the same saccade-related activity under both conditions. Preliminary data suggest that the area studied may be a supplementary eye field distinct from the arcuate frontal eye field.

Apical dendritic spines and axonic terminals in the bipyramidal neurons of the dorsomedial cortex of lizards (Lacerta).

Gold-toned bipyramidal neurons of the dorsomedial cortex of Lacerta have been studied using light and electron microscopy. The spines have been classified as stubby, mushroom-shaped or thin. Thin and mushroom-shaped spines are only found on proximal and intermediate dendritic segments, whereas stubby spines are found on distal dendritic segments. A Timm's method modification for electron microscopy (sulphide-osmium procedure) has been used. Timm-positive axonal endings usually synapse on thin and mushroom-shaped spines, whereas Timm-negative axonal endings usually synapse on stubby spines. Timm-positive afferents and their post-synaptic spines on bipyramidal neurons of Lacerta's dorsomedial cortex are compared with the corresponding elements on pyramidal neurons of the CA3 region of the hippocampus of mammals, on the basis of several histochemical and morphological studies. The possibility that these two neuronal types may be homologous is discussed.

Light microscopy of the medial wall of the cerebral cortex of the lizard Psammodromus algirus.

The telencephalic medial wall of the lizard Psammodromus algirus was studied using Golgi and conventional light microscopic techniques. The area is formed by two different cytological fields-medial cortex and dorsomedial cortex. These two cortices possess three layers dorsoventrally: a superficial plexiform layer, a cellular layer, and a deep plexiform layer. The alveus, a deep fiber system, runs adjacent to the ependyma. Four classes of neurons are found in the cellular layer of the medial cortex on the basis of soma shape, dendritic pattern, and position in the layer: horizontal, double pyramidal, and candelabra cells. Solitary cells are present in the superficial and deep plexiform layers of the medial cortex. Those of the superficial plexiform layer are stellate cells. Horizontal and vertical cells are found in the deep plexiform layer. Double pyramidal cells are the most frequently impregnated in the cellular layer of the dorsomedial cortex. In addition, candelabra cells are present at the lateral end of the layer. Two cell types are found in the deep plexiform layer of the dorsomedial cortex: solitary pyramidal cells and, among the fibers of the alveus, horizontal cells. Ependymal tanycytes line the ventricular surface, and protoplasmic astrocytes are found in the plexiform layers of both medial and dorsomedial cortices.

Thick caliber projections from brainstem to cerebral cortex in the snakes Thamnophis sirtalis and natrix sipedon

Unilateral transections of the midbrain in snakes produce degeneration in a thick caliber system of fibers that effects widespread projections to the telencephalon. The anatomy of this diffuse projection system was investigated using Fink-Heimer, horseradish peroxidase, Golgi and electron microscopic preparations. The projection originates, at least in part, from a population of neurons located in the dorsolateral mesencephalic tegmentum. They have fusiform somata and dendrites with isodendritic branching patterns. The axons are of thick caliber and ascend through the forebrain bundles into the caudal, basal telencephalon. Some of the axons cross the midline around the anterior commissure. The major bundle of fibers splits into three fascicles at this level. One fascicle continues into the striatum, the second continues into the anterior dorsal ventricular ridge and the third continues into the septum and cerebral cortex. Fibers in the cortical fascicle are aligned primarily concentric with the ventricle. Some of the thick caliber fibers slant obliquely into the dorsomedial cortex and run concentric with the ventricle in layer 1. Other fibers bear thin caliber collaterals that ascend into layers 2 and 3 of the medial cortex, layers 2 and 1 of the dorsomedial cortex and layers 3 and 2 of the dorsal cortex. Varicosities are present on both the thick, parent fibers and on their thin collaterals. Electron microscopic observations suggest that the varicosities are presynaptic elements. These form synapses with clear, round vesicles and asymmetric active zones, principally on dendritic spines. This study demonstrates the existence in snakes of a thick caliber system of projections that parallels the widespread projections of monoaminergic systems to the cortex.

Direct and indirect pathways from the amygdala to the frontal lobe in rhesus monkeys.

To elucidate the anatomical relationships between the frontal association cortex and the limbic system in primates, projections from the amygdala to frontal cortex were studied in the rhesus monkey using retrograde and anterograde tracing methods. Following injections of horseradish peroxidase (HRP) into the orbital prefrontal cortex, the gyrus rectus, the superior frontal gyrus, and the anterior cingulate gyrus of the frontal lobe, labeled neurons were found in the basolateral, basomedial, or basal accessory nuclei of the amygdala. None of these nuclei contained labeled neurons following HRP injections into the principal sulcus or the lateral inferior convexity of the frontal lobe. This selective distribution of amygdala connections was confirmed by injection tritiated amino acids into the amygdala. Silver grains were present only over the orbital cortex and gyrus rectus on the ventral surface of the frontal lobe and over the superior prefrontal gyrus and anterior cingulate gyrus on the medial wall of the hemisphere, while the dorsolateral prefrontal cortex was free of radioactivity. The isotope injection of the amygdala also revealed a projection to the magnocellular moiety of the mediodorsal nucleus (MDmc) which is known to innervate the same ventromedial regions of the frontal lobe that receive direct connections from the amygdala. Although MDmc and amygdala project to the same cortical regions, their terminal fields are different. The direct amygdala input terminates in layer 1 in orbital cortex and gyrus rectus and layer 2 in the dorsomedial cortex and cingulate gyrus, while the thalamic input is primarily to layer 3 and, in some areas, also the superficial half of layer 1. These findings indicate that the frontal lobe of rhesus monkeys can be subdivided into two separable cortical regions: 1) A ventromedial region including the anterior cingulate gyrus which receives both direct (amygdalo-cortical) and indirect (amygdalo-thalamo-cortical) input from the amygdala; and 2) a dorsolateral frontal region which is essentially devoid of either direct or indirect amygdalofugal axons. On the basis of its selective relationship with the amygdala, the ventromedial region may be considered the "limbic" portion of the frontal association cortex.

Intrinsic organization of snake lateral cortex.

Lateral cortex is the most laterally placed of the four cortical areas in snakes. Earlier studies suggest that it is composed of several subdivisions but provide no information on their organization. This paper first investigates the structure of lateral cortex in boa constrictors (Constrictor constrictor), garter snakes (Thamnophis sirtalis), and banded water snakes (Natrix sipedon) using Nissl and Golgi preparations; and secondly examines the relation of main olfactory bulb projections to the subdivisions of lateral cortex using Fink-Heimer and electron microscopic preparations. Lateral cortex is divided on cytoarchitectonic grounds into two major parts called rostral and caudal lateral cortex. Each part is further divided into dorsal and ventral subdivisions so that lateral cortex has a total of four subdivisions: dorsal rostral lateral cortex (drL), ventral rostral lateral cortex (vrL), dorsal caudal lateral cortex (dcL) and ventral caudal lateral cortex (vcL). Systematic analyses of Golgi preparations indicate that the rostral and caudal parts each contain distinct populations of neurons. Rostral lateral cortex contains bowl cells whose dendrites arborize widely in the outer cortical layer (layer 1). The axons of some bowl cells can be traced medially into dorsal cortex, dorsomedial cortex and medial cortex. Caudal lateral cortex contains pyramidal cells whose somata occur in layers 2 and 3 and whose dendrites extend radially up to the pial surface. In addition, three populations of neurons occur in both rostral and caudal lateral cortex. Stellate cells occur in all three layers and have dendrites which arborize in all directions. Double pyramidal cells occur primarily in layer 2 and have dendrites which form two conical fields whose long axes are oriented radially. Horizontal cells occur in layer 3 and have dendrites oriented concentric with the ependyma. Fink-Heimer preparations of snakes which underwent lesions of the main olfactory bulb show that the primary olfactory projections to cortex are bilateral and restricted precisely to rostral lateral cortex. Electron microscopic degeneration experiments indicate that the olfactory bulb fibers end as terminals which have clear, spherical vesicles and asymmetric active zones. The majority are presynaptic to dendritic spines in outer layer 1. These studies establish that lateral cortex in snakes is heterogeneous and contains two major parts, each containing two subdivisions. The rostral and caudal parts have characteristic neuronal populations. Primary olfactory input is restricted to rostral lateral cortex and seems to terminate heavily on the distal dendrites of bowl cells. Axons of some of these cells leave lateral cortex, so that the rostral lateral cortex forms a direct route by which olfactory information reaches other cortical areas. The functional role of caudal lateral cortex is not clear.

Functional recovery after serial ablation of prefrontal cortex in the rat

In two experiments, adult rats with 1-stage or 2-stage ablation of discrete subfields of the prefrontal cortex were compared on spatial delayed alternation, one way active avoidance, food hoarding, ingestive behavior, and postoperative body weight. Single stage removal of the ventrolateral (sulcal or orbital) cortex produced aphagia and adipsia for several days postoperatively and a chronic reduction in body weight. Serial removal of this same cortex produced a milder effect on postoperative food and water intake, and there was no chronic reduction of body weight. Ablation of dorsomedial cortex either in one or two stages did not significantly reduce food or water intake or body weight. In contrast, single stage removal of dorsomedial cortex produced dramatic impairment on spatial delayed alternation, active avoidance, and food hoarding; whereas ventrolateral lesions either in one or two stages did not significantly affect performance on these tasks. Animals with dorsomedial lesions produced in two stages were not significantly impaired on delayed alternation or active avoidance, but on food hoarding they were just as impaired as the animals with comparable lesions induced in a single stage. It is apparent that removal of either dorsomedial or ventrolateral prefrontal cortex in two stages causes an amelioration of the deficit that is obtained with single stage destruction of these areas on some tasks, but sparing of function is not an invariant consequence of serial destruction of rat prefrontal cortex.

Lntracortical Connections in the Snakes Natrix sipedon and Thamnophis sirtalis

The association and commissural connections between the four cortical areas in water (Natrix sipedon) and garter (Thamnophis sirtalis) snakes were studied by placing lesions on the cortical surface and studying the resulting degeneration in Fink-Heimer preparations. Lateral cortex projects to the outer one third of layer 1 of ipsilateral medial cortex. Dorsal cortex projects to the middle third of layer 1 of ipsilateral medial cortex. Dorsomedial cortex projects bilaterally to the inner third of layer 1 and to layer 3 of medial cortex. It also projects to layer 1 of contralateral dorsomedial cortex. Medial cortex projects ipsilaterally to each of the other cortical areas. With the apparent exception of the projection of medial cortex to lateral cortex, each projection is organized such that each rostrocaudal segment of a cortical area projects to all segments of the target area lying at the same or more caudal levels.

The projection of the auditory cortex upon the diencephalon and brain stem in the cat

Summary The site of termination in the diencephalon and brain stem of fibers arising in the auditory cortex of the cat has been studied with the method of Nauta and Gygax. Such corticofugal fibers end in the corpus striatum, the reticular nucleus of the ventral thalamus, the medial geniculate and the posterior group of the dorsal thalamus, in the interstitial nucleus of the brachium of the inferior colliculus, the parabrachial region and adjoining midbrain tegmentum, the inferior colliculus (of both sides) and the pontine nuclei. All fields of the auditory cortex contribute to this projection, but there are different patterns of connections to the subdivisions of the medial geniculate body and to the posterior group of the thalamus. A I, A II and EP send fibers to the ventral and deep dorsal nuclei of the medial geniculate body, but in varying proportions to each of these nuclei, A I sending the greatest number and EP the fewest number of fibers to the ventral nucleus. The insulo-temporal region is related to the dorsal and deep dorsal nuclei. This cortico-geniculate projection is well organized and probably reciprocates the geniculo-cortical projection. There appears to be a correlation between the field of origin in the auditory cortex and the site of termination of corticothalamic fibers in the medial geniculate body and in the posterior group respectively: those fields (A I and A II) which send a considerable number of fibers to the ventral nucleus of the medial geniculate body are related predominantly to the lateral division of the posterior group, whereas the insulo-temporal region and EP, which send most of their fibers to the dorsal division of the medial geniculate nucleus, project to more medial parts of the posterior group. The 3 parts of the inferior colliculus—the dorsomedial cortex, the lateral nucleus and the central nucleus—all receive fibers from the auditory cortex. In the ventral nucleus of the medial geniculate body and in the central nucleus of the inferior colliculus the degenerating corticofugal fibers have a parallel arrangement between the cell columns present in these nuclei, are of smaller diameter than the afferent fibers to these nuclei from lower levels of the auditory pathway, and enter the nuclei at the end of the column opposite to that of the ascending afferent fiber; these observations have suggested certain principles of the columnar organization in subcortical sensory relay nuclei.