Anterior Medial Nuclei Research Articles

Thalamic connections with limbic cortex. II. Corticothalamic projections

The corticothalamic projections from the cat limbic cortex have been investigated with anterograde and retrograde axonal transport techniques. Five limbic cortical areas-the anterior limbic area, the cingular area, the granular and dysgranular retrosplenial areas, and the presubiculum-were identified on the basis of their cytoarchitecture. Emphasis was placed on determining the laminar distribution of the cells of origin of the efferent projections, the projection pathways, and the sites of termination within the thalamus. Projections to the thalamus originate in layers V and VI of limbic cortex. In the cingular region the cells of origin are predominantly in layer V and to a lesser extent in layer VI, while the majority of cells projecting from the more caudal retrosplenial areas and presubiculum are in layer VI. There are two fiber pathways from each cortical area to the thalamus. One system of fibers passes through the internal capsule and lateral thalamic peduncle, and a second system travels in the cingulate fasciculus before piercing the corpus callosum to join the postcommissural fornix. The lateral dorsal nucleus and the anterior nuclear group, including the anterior dorsal, anterior ventral, and anterior medial nuclei, are the major thalamic recipients of projections from limbic cortex. Corticothalamic projections also terminate sparsely in the midline and intralaminar nuclear complex, including the central lateral, central dorsal, paracentral, central medial, rhomboid, and reuniens nuclei. Projections from the anterior limbic area project predominantly to the anterior medial, central lateral, and paracentral nuclei. the anterior ventral nucleus, anterior medial nucleus, and lateral dorsal nucleus are the major thalamic recipients of projections from the cingular area, the granular and dysgranular retrosplenial areas, and the presubiculum. It appears that the anterior dorsal nucleus receives afferents only from the dysgranular retrosplenial area. Bilateral cortico-thalamic projections were found in the anterior medial, dorsal medial, central lateral, central medial, paracentral, and reuniens nuclei.

Thalamic connections with limbic cortex. I. Thalamocortical projections

The thalamocortical projections to limbic cortex in the cat have been studied with retrograde and anterograde axonal transport techniques. Five limbic cortical areas were identified on the basis of cytoarchitecture. The five areas are the anterior limbic area, the cingular area, the dorsal and ventral retrosplenial areas, and the presubiculum. Each of these cortical areas received small injections of horseradish peroxidase, and the afferent thalamic nuclei were identified by retrograde labelling of cells. The cortical projection of each of the anterior thalamic nuclei and the lateral dorsal nucleus was determined autoradiographically. Each of the anterior thalamic nuclei and the lateral dorsal nucleus projects to limbic cortex by two pathways. One group of fibers leaves the rostral thalamus by the fornix, pierces the corpus callosum, joins the cingulate fasciculus to reach limbic cortex. The other group travels through the lateral thalamic peduncle and internal capsule. The anterior ventral nucleus projects primarily to the dorsal retrosplenial area, particularly to layer I, the deep portion of layer II, and superficial portion of layer III. Sparse projections also exist to the ventral retrosplenial area, the cingular area, and the presubiculum. Very sparse projections to the anterior limbic area are seen. The anterior dorsal nucleus projects primarily to the ventral retrosplenial area, particularly layers I, the deep portion of layer II, and superficial layer III. sparse projections exist to the dorsal retrosplenial area and presubiculum, but apparently no projections exist to the cingular or anterior limbic area. The anterior medial nucleus projects primarily to layers I and superficial III of the ventral retrosplenial area. sparse projections exist to each of the other limbic cortical areas. The lateral dorsal nucleus projects extensively onto limbic cortex. Prominent projections occur to layer I, the external granular layer and lamina dessicans of the presubiculum, layers I and III-IV of the dorsal retrosplenial area, and layers I, III, and IV of the cingular area. Sparse projections occur to the ventral retrosplenial area and the anterior limbic areas. Thalamocortical projections also originate in the midline and intralaminar nuclei including the central medial, reuniens, rhomboid, paracentral, central lateral, and central dorsal nuclei. These data indicate that the anterior thalamic nuclei project upon limbic cortex in a complex manner. Further, the projections to limbic cortex from the anterior nuclei overlap with projections from the lateral dorsal nucleus. This overlap of thalamic projections onto limbic cortex suggests a convergence of information from nonprimary sensory systems with information from the classical limbic system.

Anatomical and behavioral effects of colchicine administration to rats late in utero.

Offspring from pregnant rats injected with 4mg/kg body weight colchicine on Embryonic Days 18, 19, and 20 were found to have isocortical and hippocampal structures greatly reduced in mass when examined at birth. Cells with pyknotic nuclei were found in Layers 5, 4, and 3 of the cerebral isocortex, the habenula, and anterior medial nuclei of the thalamus. Brains taken at Postnatal Days 22 and 132 were reduced in overall size, and had a 20-30% reduction of cells at the vertex of the neocortex with up to 50% reduction in the thickness of the corpus callosum. A decrease in activity, an increase in fearfulness and/or decreased tendency to explore, reduced error scores on the Hebb-Williams maze, poor performance on the Maier elevated maze, and a lessened sensitivity to sound-induced seizures were correlated with these anatomical changes.

Transfer of the hippocampal output by the anterior thalamic nuclei

This study was performed in the cat with the aim of clarifying the transfer properties of the thalamic nuclei anterior ventralis and anterior medialis with respect to volleys of impulses elicited by delivering trains of electrical stimuli of different frequency and intensity to the contralateral hippocampus. The results show that the responses of the nucleus anterior ventralis are only intensity-dependent whereas those of the nucleus anterior medialis depend on both stimulus intensity and frequency. The nucleus anterior ventralis performs an operation of input-output transfer within one of the loops of the Papez circuit. The nucleus anterior medialis is under the influence of both the hippocampus and a thalamoneocortical feedback activated by the output of the nucleus itself. This nucleus, therefore, operates as a gate controlling the integration of archicortical and neocortical activities.

Some golgi observations in the nucleus anterior ventralis and anterior medialis thalami of the cat.

The characteristic dendritic arborization of different cell types, the axon arborization of Golgi type II neurons, and the terminal parts of the specific and non-specific afferents in the nucleus anterior ventralis and medialis were observed, using the Golgi-Kopsch perfusion method. The cell types and their special characteristics, such as the dendritic tree, dendritic processes and axon-arborization patterns are similar to those described in the other specific nuclei of the thalamus. The significance of Golgi type II/a cells and their synaptic relations are discussed from the point of view of inhibitory mechanisms postulated in the thalamic relay nuclei. The synaptic articulations of specific (Vicq d'Azyr) and non-specific afferents with the different cell types have been studied.

On the functional significance of the circuit of papez

Summary This study was performed with the aim of clarifying the functional properties of the circuit of Papez as a feedback loop regulating hippocampal activity. The circulation in the loop of volleys of impulses elicited by delivering to the hippocampus trains of low-frequency electrical stimuli was studied in the cat by recording unit activity at mammillary, thalamic, cingulate and hippocampal levels. The results show the properties of two feedback loops, one related to the nucleus anterior ventralis and the other to the nucleus anterior medialis. The output of the nucleus anterior ventralis is dependent on the hippocampal output, whereas the output of the nucleus anterior medialis is affected by both hippocampal and extralimbic thalamo-neocortical influences. The intermodulation of septal and feedback volleys at the level of the hippocampal region appears, in physiological conditions, to underlie the regulation of hippocampal bioelectrical activity in general and of theta rhythm in particular. A revelant effect of the output of the anterior thalamic nuclei consists in the depression of unit activity of the gyrus cinguli and area retrosplenialis.

Effects of systemic and intracerebral administration of two opposite acting ACTH-related peptides on extinction of conditioned avoidance behavior.

The effects of the decapeptide ACTH-(1–10) and [D-phe⁷]-ACTH-(1–10) were tested on the rate of extinction of a pole-jumping avoidance response in rats. ACTH-(1–10) in doses of 20, 50, and 100 <i>µ</i>g inhibited extinction of the avoidance response 4 h following subcutaneous administration. [D-phe⁷]-ACTH-(1–10) in doses of 20, 50, and 100 <i>µ</i>g facilitated extinction 4 h after injection. Intracerebral implantation of approximately 10 <i>µ</i>g of these ACTH-analogues in the freely moving rat had similar effects on extinction of avoidance response when implanted into the region of the rostral mesencephalon and the caudal diencephalon, at the posterior thalamic level, or in the cerebrospinal fluid. Ineffective sites were the nucleus ventralis thalami, the nucleus anterior medialis thalami, the nucleus reuniens, the globus pallidus, the nucleus accumbens, the fornix, and the hippocampus. The results support the hypothesis that the site of action of ACTH and of ACTH-analogues on extinction of an avoidance response is localized in the central nervous system.

Nuclear configuration of the diencephalon of Tamandua tetradactyla and Myrmecophaga jubata.

AbstractThe nuclear configuration of the diencephalon of Tamandua tetradactyla (lesser anteater) is figured, described and compared with that of Myrmecophaga jubata (greater anteater) and other mammals, particularly the cat. Their nuclear organization represents, in general, all the elements (or their homologues) found in the mammalian diencephalon.There is an unusually large nucleus centralis lateralis which penetrates into the nucleus medialis dorsalis from above. The size of the latter group, in the presence of a poorly developed orbitofrontal cortex, suggests that it is primarily dependent upon the marked development of the corpus striatum. The nuclei of the tractus habenulopeduncularis are displaced ventrally, apparently by the medial enlargement of the nucleus centralis lateralis. The nuclei parataeniales bear strong resemblance to those in the armadillo.There is no nucleus ventralis pars anterior in either Tamandua or Myrmecophaga. The nucleus ventralis medialis is much larger than that in carnivores. The presence of the nucleus submedius and its intimate relation to the nucleus anterior medialis of the anterior nuclear complex, accounts fairly well for questionable homologues in such forms as Tarsius.The existence of both the large‐celled nucleus of the optic tract and the nucleus limitans indicates the gradual incorporation, at least in part, of the former into the latter. Hypothalamic nuclei, except for the supraoptic and paraventricular groups, are rather poorly differentiated.

Limbic nuclei of thalamus and connections of limbic cortex.

I. Organization of the Projections of the Anterior Group of Nuclei and of the Midline Nuclei of the Thalamus to the Anterior Cingulate Gyrus and Hippocampal Rudiment in the Monkey Introduction The views expressed in the literature on the cortical projection fields of the anterior nuclei, midline nuclei, and lateral dorsal nucleus of the thalamus are vague and often contradictory. LeGros Clark and Boggon5were apparently the first to point out that the anterior thalamic nuclei in the cat project to the whole length of cingulate gyrus. Walker26suggested that the anterior medial nucleus in the monkey projects to the inferior surface of the frontal lobe. Later he was inclined to the view that the anterior group of nuclei projects mainly to the posterior part of the cingulate gyrus and that the anterior part of the gyrus (area 24-LA in terminology used by us) receives few if any fibers from the thalamus.27Bailey and co-workers,1using the neuronographic method of strychnine-evoked potentials also came to the conclusion that the anterior cingulate gyrus is athalamic. However, Mettler

Chromatolysis and vacuolation of specific diencephalic nuclei induced by actue pyrexia.

To determine the effects of high body temperature upon cells of the central nervous system, chicks were exposed to radiant heat. An increase in body temperature 3°C above normal resulted in chromatolysis and vacuolation in the cells of the nucleus rotundum, the nucleus entopeduncularis inferior and nucleus anterior medialis of the hypothalamus. A decrease in body temperature 15°C below normal had no effect upon these cells. It is suggested that the nuclei affected by the induced acute pyrexia may be involved in sensing and responding to the specific thermal overload.