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PubMed1977

Effects of vagal volleys on units of intralaminar and juxtalaminar thalamic nuclei in monkeys.

As part of an attempt to clarify the nature of inputs to the limbic cortex, the thalamic intralaminar and juxtalaminar nuclei were explored for unit responses to vagal volleys in awake, sitting squirrel monkeys. Vagal shocks elicited responses of a large percentage of units in the anterior medial, paracentral, lateral dorsal, and lateral, and medial dorsal nuclei, as well as in part of the ventral lateral nucleus adjacent to the paracentral. Responsive units showed either initial excitation or initial inhibition. As in the preceding study on the cingulate and supracingulate cortex, there were two main types of initially excited units: type 1 responded with a discharge of 1-3 spikes at relatively short and constant latencies, while type 2 units were characterized by a burst of 3-14 spikes at longer and more variable latencies. Although the findings were compatible with the hypothesis that the anterior and paracentral nuclei transmit vagal impulses to the cingulate and supracingulate cortex, an analysis of latencies suggested that a more rapidly conducting pathway(s) accounts for latencies as short as 12 msec of some cingulate units. Twenty-eight percent of 367 units in the medial dorsal nucleus responded to vagal volleys. This finding gives substantial support to the traditional view that the medial dorsal nucleus transmits interoceptive information to limbic and neocortical areas of the orbitofrontal region.

Afferent Pathways↗

PubMed1977

The cortical projections of the mediodorsal nucleus and adjacent thalamic nuclei in the rat.

The mediodorsal nucleus of the rat thalamus has been divided into medial, central and lateral segments on the basis of its structure and axonal connections, and these segments have been shown by experiments using the autoradiographic method of demonstrating axonal connections to project to seven distinct cortical areas covering most of the frontal pole of the hemisphere. The position and cytoarchitectonic characteristics of these areas are described. The medial segment of the nucleus projects to the prelimbic area (32) on the medial surface of the hemisphere, and to the dorsal agranular insular area, dorsal to the rhinal sulcus on the lateral surface. The lateral segment projects to the anterior cingulate area (area 24) and the medial precentral area on the dorsomedial shoulder of the hemisphere, while the central segment projects to the ventral agranular insular area in the dorsal bank of the rhinal sulcus, and to a lateral part of the orbital cortex further rostrally. (The term "orbital" is used to refer to the cortex on the ventral surface of the frontal pole of the hemisphere.) A ventral part of this orbital cortex also receives fibers from the mediodorsal nucleus, possibly its lateral segment, but the medial part of the orbital cortex, and the ventrolateral orbital area in the fundus of the rhinal sulcus receive projections from the paratenial nucleus and the submedial nucleus, respectively. All of these thalamocortical projections end in layer III, and in the outer part of layer I. The basal nucleus of the ventromedial complex (the thalamic taste relay) has been shown to have a similar laminar projection (layer I and layers III/IV) to the granular insular area immediately dorsal to, but not overlapping, the mediodorsal projection field. However, the principal nucleus of the ventromedial complex appears to project to layer I, and possibly layer VI, of the entire frontal pole of the hemisphere. The anteromedial nucleus does not appear to project to layer III of the projection field of the mediodorsal nucleus, although it may project to layers I and VI, especially in the anterior cingulate and medial precentral areas. A thalamoamygdaloid projection from the medial segment of the mediodorsal nucleus to the basolateral nucleus of the amygdala has also been demonstrated, which reciprocates an amygdalothalamic projection from the basolateral nucleus to the medial segment. The habenular nuclei also appear to project to the central nucleus of the amygdala. These results are discussed in relation to the delineation and subdivision of the prefrontal cortex in the rat, and to amygdalothalamic and amygdalocortical projections which are described in a subsequent paper (Krettek and Price, '77).

Amygdala↗

PubMed1978

Afferent and efferent subcortical projections of behaviorally defined sectors of prefrontal granular cortex.

Although the functional significance of the midprincipalis region is well known, the afferent and efferent connections of this zone, in comparison to the anterior and posterior portions of the cortex lining the principal sulcus, are poorly understood. In 3 animals the retrograde tracer HRP and the anterograde tracers, tritiated proline, lysine and leucine, were injected into the sulcal cortex lining the principal sulcus. The cortex forming the banks of the principal sulcus was divided into anterior, middle and posterior sectors with one animal used for each zone. As expected from previous studies, the heaviest afferents to the cortex forming the principal sulcus were from the parvocellular portions of the medical dorsal nucleus. The medial pulvinar nucleus and the nucleus limitans projected to only the anterior and posterior portions of the cortex lining the principal sulcus. Projections were seen to all 3 sectors from the anterior, midline, intralaminar and lateral thalamic nuclei. Although cells were seen in the hypothalamus following injections in all 3 sectors of the cortex lining the principal sulcus, the heaviest hypothalamic projections were noted after injections into the mid-sector of the cortex. These HRP-positive cells were in the dorsal and lateral hypothalamic area, dorsal medial nucleus and in the lateral mammillary nucleus. These findings link the midprincipalis region with the prefrontolimbic circuit, and suggest that the midprincipalis region, n. medialis dorsalis, the mammillary bodies and perhaps the cingulate gyrus constitute part of an anatomical circuit concerned with memory processes.

Afferent Pathways↗

PubMed1978

Limbic lobe involvement in presenile dementia.

Limbic lobe involvement in presenile dementia was studied from a neuropathological and neuropsychiatric viewpoint. The material consisted of seven cases of Alzheimer's disease, four cases of Pick's disease, and four cases of Jacob-Creutzfeldt's disease. These three groups showed different patterns of distribution of the degeneration characteristic for each group, in particular for the first two. Among the groups, these patterns differed with regard to involvement both of nonlimbic and limbic areas. Thus the Alzheimer group had a mainly temporoparieto-occipital and posterior cingulate gyrus involvement. The Pick group in many respects showed an inverse distribution with frontotemporal and anterior cingulate gyrus accentuation of the damage. Basal temporal limbic areas were involved in both groups. The Jacob-Creutzfeldt group had a less schematic lesion pattern, without involvement of limbic areas. From a neuropsychiatric aspect, these differences were reflected in symptoms that could be referred both to areas spared and those more pronouncedly destroyed by the degenerative process. Thus the Alzheimer group long retained emotional qualities that were lost early in the Pick group. The possible relationship between neurotransmitters and regional accentuation of the degeneration is discussed.

Aged↗

PubMed1977

An autoradiographic study of the organization of the efferent connections of the hippocampal formation in the rat.

The efferent connections of the hippocampal formation of the rat have been re-examined autoradiographically following the injection of small quantities of 3H-amino acids (usually 3H-proline) into different parts of Ammon's horn and the adjoining structures. The findings indicate quite clearly that each component of the hippocampal formation has a distinctive pattern of efferent connections and that each component of the fornix system arises from a specific subdivision of the hippocampus or the adjoining cortical fields. Thus, the precommissural fornix has been found to originate solely in fields CA1-3 of the hippocampus proper and from the subiculum; the projection to the anterior nuclear complex of the thalamus arises more posteriorly in the pre- and/or parasubiculum and the postsubicular area; the projection to the mammillary complex which comprises a major part of the descending columns of the fornix has its origin in the dorsal subiculum and the pre- and/or parasubiculum; and finally, the medial cortico-hypothalamic tract arises from the ventral subiculum. The lateral septal nuclei (and the adjoining parts of the posterior septal complex) constitute the only subcortical projection field of the pyramidal cells in fields CA1-3 of Ammon's horn. There is a rostral extension of the pre-commissural fornix to the bed nucleus of the stria terminalis, the nucleus accumbens, the medial and posterior parts of the anterior olfactory nucleus, the taenia tecta, and the infralimbic area, which appears to arise from the temporal part of field CA1 or the adjacent part of the ventral subiculum. The projection of Ammon's horn upon the lateral septal complex shows a high degree of topographic organization (such that different parts of fields CA1 and CA3 project in an ordered manner to different zones within the lateral septal nucleus). The septal projection of "CA2" and field CA3 is bilateral, while that of field CA1 is strictly unilateral. In addition to its subcortical projections, the hippocampus has been found to give rise to a surprisingly extensive series of intracortical association connections. For example, all parts of fields CA1, CA2 and CA3 project to the subiculum, and at least some parts of these fields send fibers to the pre- and parasubiculum, and to the entorhinal perirhinal, retrosplenial and cingulate areas. From the region of the pre- and parasubiculum there is a projection to the entorhinal cortex and the parasubiculum of both sides. That part of the postsubiculum (= dorsal part of the presubiculum) which we have examined has been found to project to the cingulate and retrosplenial areas ipsilaterally, and to the entorhinal cortex and parasubiculum bilaterally.

Animals↗

PubMed1977

Ascending projections of the locus coeruleus in the rat. II. Autoradiographic study.

The ascending projections of the locus coeruleus were studied using an autoradiographic method. The major projection of locus coeruleus neurons ascends in a dorsal pathway traversing the midbrain tegmentum in a position ventrolateral to the periaqueductal gray. At the caudal diencephalon the locus coeruleus axons descend to enter the medial forebrain bundle at a caudal tuberal hypothalamic level. They are jointed in the medial forebrain bundle by a much smaller locus coeruleus projection which takes a ventral course through the midbrain tegmentum and enters the medial forebrain bundle via the mammillary peduncle and ventral tegmental area. Terminal projections are evident in the midbrain to the periaqueductal gray, tegmentum and raphe nuclei. There are widespread projections to the dorsal thalamus. The heaviest of these are to the intralaminar nuclei, the anteroventral and anteromedial nuclei, the dorsal lateral geniculate and the paraventricular nucleus. In the hypothalamus the largest projections are to the lateral hypothalamic area, periventricular nucleus, supraoptic nucleus and paraventricular nucleus. As the locus coeruleus projection ascends in the medial forebrain bundle, fibers leave it to traverse the lateral hypothalamus and zona incerta and enter the internal capsule, the ventral amygdaloid bundle and ansa peduncularis. These appear to terminate in the amygdaloid complex and, via the external capsule, in the lateral and dorsal neocortex. At the level of the septum 4 projections are evident. One group of fibers enters the stria medullaris to terminate in the paraventricular nucleus and habenular nuclei. A second group joins the stria terminalis to terminate in the anygdaloid complex. The third group turns into the diagonal band and medial septum; some fibers terminate in the septal nuclei and others continue into the fornix to termimate in hippocampus. A large component continues around the corpus callosum into the cingulum to terminate in the cingulate and adjacent neocortex, the subiculum and hippocampus. The remaining fibers continue rostrally in the medial forebrain bundle to terminate in olfactory forebrain and frontal neocortex. Commissural projections arise at 4 locations. The first decussation occurs in the dorsal tegmentum just below the central gray rostral to the locus coeruleus. The crossing fibers enter the contralateral dorsal bundle. A second group of fibers leaves the ipsilateral dorsal pathway, crosses in the posterior commissure and enters the contralateral dorsal pathway at the level. The third commissural projection arises more rostrally and crosses in the dorsal supraoptic commissure to enter the contralateral medial forebrain bundle. The fourth commissural projection is through the anterior commissure. The termination of the contralateral projection appears similar to that of the ipsilateral projection.

Afferent Pathways↗