Showing papers on "Rhinal sulcus published in 1997"

Insular cortex and neighboring fields in the cat: a redefinition based on cortical microarchitecture and connections with the thalamus.

Abstract: The insular areas of the cerebral cortex in carnivores remain vaguely defined and fragmentarily characterized. We have examined the cortical microarchitecture and thalamic connections of the insular region in cats, as a part of a broader study aimed to clarify their subdivisions, functional affiliations, and eventual similarities with other mammals. We report that cortical areas, which resemble the insular fields of other mammals, are located in the cat's orbital gyrus and anterior rhinal sulcus. Our data suggest four such areas: (a) a “ventral agranular insular area” in the lower bank of the anterior rhinal sulcus, architectonically transitional between iso- and allocortex and sparsely connected to the thalamus, mainly with midline nuclei; (b) a “dorsal agranular insular area” in the upper bank of the anterior rhinal sulcus, linked to the mediodorsal, ventromedial, parafascicular and midline nuclei; (c) a “dysgranular insular area” in the anteroventral half of the orbital gyrus, characterized by its connections with gustatory and viscerosensory portions of the ventroposterior complex and with the ventrolateral nucleus; and (d) a “granular insular area”, dorsocaudal in the orbital gyrus, which is chiefly bound to spinothalamic-recipient thalamic nuclei such as the posterior medial and the ventroposterior inferior. Three further fields are situated caudally to the insular areas. The anterior sylvian gyrus and dorsal lip of the pseudosylvian sulcus, which we designate “anterior sylvian area”, is connected to the ventromedial, suprageniculate, and lateralis medialis nuclei. The fundus and ventral bank of the pseudosylvian sulcus, or “parainsular area”, is associated with caudal portions of the medial geniculate complex. The rostral part of the ventral bank of the anterior ectosylvian sulcus, referred to as “ventral anterior ectosylvian area”, is heavily interconnected with the lateral posterior-pulvinar complex and the ventromedial nucleus. Present results reveal that these areas interact with a wide array of sensory, motor, and limbic thalamic nuclei. In addition, these data provide a consistent basis for comparisons with cortical fields in other mammals. J. Comp. Neurol. 384:456–482, 1997. © 1997 Wiley-Liss, Inc.

Organization of the entorhinal projection to the rat dentate gyrus revealed by Dil anterograde labeling

Abstract: It has been suggested that the entorhino-hippocampal circuit is involved in memory formation. To investigate the way that associative memory is elaborated in the circuit, the entorhino-dentate projection was studied with the fluorescent lipophilic tracer Dil. We investigated the projection originating in the dorsal part of the entorhinal cortex by injecting Dil along the rhinal sulcus. Anterograde fluorescent labeling allowed us to examine sections of the sample with a confocal microscope or in wholemount preparations with a fluorescence microscope. Quantitative analysis of the distribution of the Dil-labeled perforant path by confocal microscopy was performed in the septal one third level of the hippocampus. The analysis confirmed that the topographical map along the mediolateral dimension of the entorthinal cortex was transferred to the proximodistal level (from the inner one third to the edge of the molecular layer) of the granule cell dendrites in a gradually shifting manner. The fiber profile observed after lateral entorhinal injection was thick in the suprapyramidal blade and thin in the infrapyramidal blade. The fiber profile observed after medial entorhinal injection was thin in the suprapyramidal blade and thick in the infrapyramidal blade. Fluorescence microscopic observation of wholemount preparations showed that projections from the Dil injection site were distributed wider than half the dentate gyrus in the longitudinal direction. In transverse sections, the range of the labeled fiber distribution was confirmed to be more than two thirds of the dentate gyrus in the same direction regardless of the mediolateral level of the injection site. It has been suggested that the dorsoventral axis of the entorhinal cortex is represented in the septotemporal levels of the dentate gyrus, but that the topographical correspondence might be weak and vague. Although our investigation was limited to the projection from the dorsal entorhinal cortex to the dorsal part of the dentate gyrus, we conclude that the widely distributed projection covers the dentate gyrus in a nontopographic manner.

Sulcal pattern of the anterior parahippocampal gyrus in the human adult

Abstract: Summary The sulcal pattern of the human entorhinal region, located in the anterior portion of the parahippocampal gyrus, was investigated in 184 brain hemispheres of both sexes between the ages of 19 and 85 years. A new classification of the sulcal pattern is introduced with reference to the extension of the collateral and rhinal sulci. Both sulci were found in all the investigated hemispheres. The collateral sulcus is a continuation of the rhinal sulcus in 41.9%. The rhinal sulcus represents the anterolateral border of the entorhinal region. By defining four branches of the rhinal sulcus all the possible ramifications occurring in the investigated hemispheres could be described. In 19.0% of the cases, a well developed entorhinal sulcus emerges in the central portions of the entorhinal region. An incipient entorhinal sulcus is evident in 29.6% and the sulcus is absent in 51.4% of the investigated cases. The intrarhinal nick, resulting from the impression of the free edge of the cerebellar tent, is seen as a dip in 35.1% and as a notch in 34.5%. It is absent in 30.4% of the cases. A comparison between the right and left hemispheres, as well as between the female and male sexes, revealed only minor differences of the sulcal pattern.

Collateral projections of single neurons in the posterior thalamic region to both the temporal cortex and the amygdala: a fluorescent retrograde double‐labeling study in the rat

Abstract: It has been reported that the acoustic thalamus of the rat sends projection fibers to both the temporal cortical areas and the lateral amygdaloid nucleus to mediate conditioned emotional responses to an acoustic stimulus. In the present study, fluorescent retrograde double labeling with Fast Blue and Diamidino Yellow has been used in the rat to examine whether single neurons in the posterior thalamic region send axon collaterals to both the temporal cortical areas and lateral amygdaloid nucleus. One of the tracers was injected into the lateral amygdaloid nucleus and the other into the temporal cortical areas close to the rhinal sulcus. Neurons double-labeled with both tracers were found mainly in the posterior intralaminar nucleus and suprageniculate nucleus, and to a lesser extent in the subparafascicular nucleus and medial division of the medial geniculate nucleus. No double-labeled neurons were seen in either the dorsal or ventral division of the medial geniculate nucleus. When one of the tracers was injected into the lateral amygdaloid nucleus and the other into either the dorsal portion of the temporal cortex, the dorsal portion of the entorhinal cortex, or the posterior agranular insular cortex, no double-labeled neurons were found in the posterior thalamic region. The present results indicate that a substantial number of single neurons in the acoustic thalamus project to both the limbic cortical areas and lateral amygdaloid nucleus by way of axon collaterals. These neurons may be implicated in affective and autonomic components of responses to multi-sensory stimuli, including acoustic ones.

Lesions of the Posterior Insular Cortex Impair Water Maze Performance in the Rat

Abstract: Performance of rats in the Morris water maze was measured after small excitotoxic lesions were produced bilaterally in two areas in the insular cortex, 0.3 and 2.3 mm posterior to bregma in the upper bank of the rhinal sulcus. The rats were trained and tested in two successive days to find an underwater platform. Compared to intact animals groups with lesions at AP-0.3 and AP-2.3 were impaired as measured by latency. These animals also did not prefer the correct quadrant while searching for the platform. There were no differences between the groups in percentage of time spent in periphery and speed of swimming. The results do not support the hypothesis that the destruction of an autonomic center at AP-0.3 will impair performance while the destruction of a more posterior part of the insular cortex will not, and are interpreted as further evidence for multifactor sensitivity of the water maze task.

Pigmentarchitectonic subfields of the entorhinal region as revealed in tangential sections.

Abstract: The entorhinal region is an important center of the limbic system involved in many dementing disorders The boundaries of the entorhinal region of the left and right hemispheres were investigated in tangential sections (5 individuals, age range 21 to 29 years) This method preserves the rostral portion of the entorhinal region which is usually lost in coronal sectioning The sections were stained with the pigment-Nissl-method The superficial cellular layer of the centromedial part of the entorhinal region consists of large heavily pigmented neurons forming islands clearly separated from each other The anterior and posterior parts of the entorhinal region display an opposite pattern consisting of small islands and stripes with ill-defined boundaries The islands contain small and sparsely pigmented neurons surrounded by large and well pigmented cells Close to the adjacent proisocortex, the small cell containing islands confluent while the large and well pigmented neurons disappear Hence, the medial side of the entorhinal region extends up to the uncus and the lateral side into the main branch of the rhinal sulcus The entorhinal region covers the frontal portion of the parahippocampal gyrus up to the periamygdaloid cortex and the posterior part ends acute-angled within the medial portion of the parahippocampal gyrus