Distribution of heavy metals in the hippocampal region of the guinea pig. A light microscope study with Timm's sulfide silver method

Intravesicular localization of zinc in rat telencephalic boutons. A histochemical study

A transition metal (presumably zinc) has been localized inside the synaptic vesicles of rat telencephalic boutons which make asymmetric synaptic contacts (Gray type I). A modification of Timm's sulphide-silver method for electron microscopy was applied to different areas of the rat forebrain: olfactory bulb, septum, caudate-putamen, amygdaloid complex, neocortex, entorhinal cortex and different parts of the hippocampal formation, viz. subiculum, stratum radiatum and oriens of both regio superior (CA1) and regio inferior hippocampi (CA3), the mossy fibre zone and the hilus fascia dentata and stratum moleculare in the gyrus dentatus. It was observed that the Timm staining in all these areas was located in synaptic boutons. Labelled boutons displayed a population of round clear vesicles and few dense core vesicles and made asymmetric synaptic contacts on dendritic spines. Silver granules in these boutons were confined to only a minor fraction of the round clear vesicles (approximately 10%). Labelled boutons occasionally showed silver granules in the synaptic clefts. The possible involvement of vesicular zinc in synaptic transmission is discussed.

The distribution of cholecystokinin-like immunoreactivity in the hippocampal formation of the guinea pig: localization in the mossy fibers

Immunocytochemical techniques were used to localize cholecystokinin octapeptide (CCK-8)-like immunoreactivity in the hippocampal formation of the guinea pig. As in the rat, CCK immunoreactive perikarya are most dense in and around the stratum pyramidale, within the superficial cell layer of the subiculum, and within the polymorph zone of the hilus. Immunoreactive axons are observed within and loosely surrounding the stratum pyramidale, within the stratum lacunosum moleculare, and diffusely distributed across the subiculum. In contrast to the rat, the mossy fiber system also exhibited significant CCK immunoreactivity. The latter system has previously been demonstrated to contain enkephalin-like immunoreactivity in the guinea pig. The present results suggest, therefore, that the enkephalin-like and CCK-like substances either coexist within the mossy fiber boutons or are present within separate subpopulations of the mossy fibers.

The distribution of Timm's stain in the nonsulphide-perfused human hippocampal formation

A detailed description is given of the distribution of Timm's staining in the human hippocampal formation. In sections cut transverse to the long axis of the hippocampal formation the same pattern of staining is seen throughout almost all of the structure, i.e., through all the main body except the most caudal region and, following the medial bend made by the long axis, through most of the pes hippocampi. The staining typically filled almost the whole of the hilus of the dentate gyrus and the whole depth of the adjacent stratum pyramidale and stratum lucidum of subfield CA3. Rostrally, staining was traced into the tip of the uncus. Caudally, staining was traced to the inferior surface of the splenium at the apex of the caudal taper of the hippocampus. No staining was found in the gyrus fasciolaris, indusium griseum, or anterior hippocampal rudiment. Except in the medial part of the pes hippocampi, the Timm's staining did not reach the proximal border of the subfield CA1. In some sections of the main body of the hippocampus a narrow, infragranular stain-free zone was observed in the hilus. In the dentate gyrus of three older subjects, but not in those of three younger subjects, supragranular staining was found. It is argued that the Timm's staining described in this study is specific to the hippocampal mossy fibres. The distribution of the staining is discussed in relation to the boundaries of subfields CA3 and CA2 as delineated by other authors.

Tracing of two-neuron pathways in the olfactory system by the aid of transneuronal degeneration: projections to the amygdaloid body and hippocampal formation

Following an olfactory bulb lesion in guinea pig (2 to 3 days), neuronal degeneration occurs in several olfactory-bulb-related areas, primarily in the piriform cortex. The degenerating neurons, which are argyrophilic, are also found in the posterolateral cortical amygdaloid nucleus and the ventrolateral entorhinal cortex. It is suggested that the neurons degenerate because of a transneuronal effect due to a sudden loss of afferent input from the olfactory bulb, although a retrograde effect acting in concert with transneuronal factors cannot be excluded. Terminal degeneration can be identified in several areas outside the olfactory bulb projection area, and is interpreted as degeneration in the axons of the degenerating cortical neurons. Such terminal degeneration, which is best seen 3 to 4 days postoperatively, has been identified in part of the basolateral amygdaloid complex, in the basomedial amygdaloid nucleus, and in the temporal parts of the fascia dentata of the hippocampal formation. Terminal degeneration has also been observed in the deep layers of the anterior olfactory nucleus, the olfactory tubercle, the nucleus of the lateral olfactory tract, and the anterior amygdaloid area. All these projections, apparently, represent the second link in two-neuron pathways, where mitral or tufted cells in the olfactory bulb make up the first neuron. This interpretation was confirmed in control experiments in which areas of argyrophilic neurons coincided with the location of retrogradely labeled neurons following injection of fluorescent substances into several of the above-mentioned areas of terminal degeneration.

Hippocampal mossy fibers in the regio superior of the European hedgehog

The hippocampal mossy fiber zone of the European hedgehog has been studied at the light and electron microscopic levels. In contrast to the organization of this zone in other mammals, the mossy fiber zone of the hedgehog is not confined to the region of Ammon's horn that is characterized by large pyramidal cells (i.e. regio inferior) but extends into the region that contains small pyramidal cells (i.e. regio superior). The terminals, throughout the relatively extensive mossy fiber zone of the hedgehog, have the large multivesicular, multicontact morphology that characterizes the mossy fiber terminals observed in other species and can be demonstrated to be the axon terminals of granule cells located in the fascia dentata. In view of the primitive organization of the forebrain of the European hedgehog, which is believed to be representative of that of the first mammals, the boundaries of the mossy fiber zone of these animals suggest that the mossy fibers extended over a larger part of Ammon's horn during the first phases of mammalian evolution and became restricted to the regio inferior during the early stages of mammalian evolution.

Lack of correlation between trace metal staining and trace metal content of the rat hippocampus following colchicine microinjection

Following the intrahippocampal injection of colchicine, the trace metal staining with Timm's method is shown to change in the hippocampus. The histochemical examinations were supplemented with atomic absorption spectrophotometric measurement of the trace metals (Zn, Fe, Cu). It was found that intrahippocampal colchicine treatment induces the temporary disappearance of the trace metal staining of the pyramidal cells of the regio superior, while there is a considerable reduction in the staining in the granular cells of the area dentata and in their mossy fibre terminals. Simultaneously, in contrast with the histochemical results, quantitative studies on the trace metal levels showed that colchicine does not lead to evacuation of the trace metals from the hippocampal formation. The combined atomic absorption and trace metal staining investigations prove that there is no correlation between the trace metal staining and the quantitative amounts of the trace metals.

A quantitative approach to cytoarchitectonics. VII. The areal pattern of the cortex of the Guinea pig

The cerebral cortex of the guinea pig has been examined by means of a quantitative cytoarchitectonic method (Schleicher et al. 1978; Zilles et al. 1978a). In this method, a computer-controlled automatic image analyzer determines the grey level index of microscopic fields measuring 50 X 50 mu m in Nissl-stained sections by a systematic scanning procedure. Computer plots of serially sectioned histological slides from three hemispheres were produced by printing selected ranges of grey level indices. The delineation of cortical areas was worked out in these plots based on quantitative criteria. Cortical maps of the areal pattern were reconstructed graphically. The resulting cortical map of the guinea pig differs from that of Rose (1912), but it corresponds to the results of Friede (1960) and is in agreement with neurophysiological studies. In general, the areal pattern of the guinea pig is similar to that of the rat (Zilles et al. 1980), but there are also some differences. These differences are discussed with respect to functional considerations.

Genetic variation in the histoarchitecture of the hippocampal region of mice

Timm's sulphide-silver method and the histochemical procedures for the demonstration of AChE, MAO and SDH were applied to the brains of three strains of adult mice of either sex: C57/BL/6J, DBA/2J and NMRI. Differences between strains were found 1) in the sulphide-silver pattern of the molecular layer of area dentata, probably reflecting differences in entorhinal, ipsilateral and/or commissural connections, 2) in the distribution of the mossy fibers, 3) in the AChE-staining of a suprapyramidal zone of regio inferior, probably reflecting differences in septal connections, 4) in the AChE-staining of the induseum griseum. The staining patterns for MAO and SDH did not vary, at least not qualitatively, between the strains investigated. Variation in adult age and sex did not influence the results. Since the differences observed seemed to reflect a pattern of genetic differentiation, five more inbred mice (A/J, AKR/A, BALB/c/A, C3H/Tif, St/6Fi) were included to strengthen the hypothesis that different genetic systems are operating at separate septo-temporal levels in the same areas during the development of the hippocampal formation.

Ipsilateral projection from the subiculum to the retrosplenial cortex in the guinea pig

A projection from the subiculum to the retrosplenial cortex (area 29a and b) was studied by autoradiographic tracing of anterogradely transported proteins following injections of radioactive amino acids into ventral and dorsal parts of the subiculum. Only the dorsal parts of the subiculum projected to the retrosplenial cortex. The projection was exclusively ipsilateral, and topographically arranged along both the longitudinal septotemporal axis and the transverse plane of the subiculum. The termination in the retrosplenial cortex was confined to the relatively cell-free superficial layer (lamina 1) and the underlying cell-rich layers (laminae 3-4). Between these two terminations a narrow zone (lamina 2) was only weakly labeled. The projection constitutes an output route for hippocampal activity in addition to the fimbria-fornix system and the subicular projections to the parahippocampal areas.

Generation of theta rhythm in medial entorhinal cortex of freely moving rats

A regular slow wave theta rhythm can be recorded in the medial entorhinal cortex (MEC) of freely moving rats during voluntary behaviors and paradoxical sleep. Electrode penetrations normal to the cortical layers proceeding from the deeper to the more superficial layers reveal a continuous theta rhythm in layers IV-III (deep MEC theta rhythm) with an amplitude maximum in layer III, a null between the outer one-third of layer III and the inner one-half of layer I, and a continuous phase-reversed theta rhythm in layers II-I (superficial MEC theta rhythm) with an amplitude maximum there. Deep MEC theta rhythm is similar in phase and wave shape to CA1 theta rhythm; superficial MEC theta rhythm is similar in phase to DG theta rhythm. Laminar profiles throughout MEC show that the theta rhythm is generated there; it is not volume conducted from hippocampus.

Projections from the subiculum to the deep layers of the ipsilateral presubicular and entorhinal cortices in the guinea pig

Projections from the subiculum to retrohippocampal areas were studied by reduced silver impregnation of anterograde degeneration and by autoradiographic tracing of transported proteins following injections of radioactive amino acids. The subiculum was found to project to the presubiculum and to the medial and lateral parts of the entorhinal area. The projections are exclusively ipsilateral, and arranged in a dorso-ventral topographical order with the terminations confined to the deep cortical layers. The projections form part of multisynaptic chains within the hippocampal region and must also be implicated in output routes for hippocampal activity additional to the fimbria-fornix system.

The morphology of the hippocampus and dentate gyrus in normal and reeler mice

The morphology of the hippocampus and dentate gyrus in normal and reeler mice has been studied in Nissl, myelin, Golgi, Timm's sulfide silver and gold chloride-sublimate preparations. It is evident from both cell-and fiber-stained sections that despite the obvious defect in the positioning of the hippocampal pyramidal and dentate granule cells in the reeler mouse within the radial dimension, the hippocampal formation as a whole shows a normal and consistent progression of cytoarchitectonic fields along its transverse axis, and a normal and consistent progression of changes in the structure of the hippocampus and dentate gyrus along their longitudinal axes. Thus, at least in these structures, the reeler gene seems to exert its effect only in the radial dimension. Cell counts in the area dentata indicate that the number of dentate granule cells in the reeler mouse is reduced compared to that found in normal or heterozygous animals. Although it has been known for some time that the number of granule cells in the reeler cerebellar cortex is markedly reduced, this appears to be the first evidence for a reduction in cell number in a forebrain structure. All the major cell types normally found in the hippocampus and the dentate gyrus are recognizable in Golgi-stained preparations from the brains of reeler mutants. However, in both regions there are a number of abnormalities in the appearance of the cells which seem to be related to the cellular ectopia. Thus, whereas most of the pyramidal and granule cells which attain a normal position in the mutant usually have normal, or near-normal dendritic arbors, the dendrites of nearly all ectopic cells are severely distorted, both in their orientation and general configuration. In preparations stained by the Timm's sulfide silver technique it is evident that the general lamination pattern seen in normal mice is retained in the reeler hippocampus and dentate gyrus despite the gross malpositioning of many of the relevant neurons. However, although the overall laminar arrangement is preserved, there are some fairly consistent abnormalities; for example, the normal trilaminar staining pattern seen in the stratum moleculare of the dentate gyrus is replaced in the reeler by a bilaminar pattern. In gold chloride-sublimate impregnated preparations there is no obvious alignment of the astrocytes in the stratum moleculare of the dentate gyrus in either normal or reeler mice. Moreover, the distribution of the astrocytes within this zone is fairly normal in the reeler mouse, although, in general, these cells appear to be more consistently stellate in form than in normal animals.

Multi-element analysis of the rat hippocampus by proton induced X-ray emission spectroscopy (phosphorus, sulphur, chlorine, potassium, calcium, iron, zinc, copper, lead, bromine, and rubidium)

A technique for multi-element analysis of brain tissue by proton induced X-ray emission spectroscopy (PIXE) is described and data from analysis of fixed and unfixed samples from rat hippocampus, neocortex, amygdala, and spinal cord is presented and commented on. The atoms present in the tissue are bombarded with protons which causes the ejection of electrons from the inner shells. When the "holes" are refilled with electrons from outer shells, X-ray quanta characteristic for each element are emitted. Using a high resolution energy dispersive detector a complete X-ray spectrum of the specimen can be recorded in a single measurement. Detection limits less than or approximately 5 p.p.m. of dry matter are obtained for most elements with atomic number greater than 14 (silicon). Around 13 elements were found in concentrations above the detection limits. The grand means for non-fixed hippocampi were e.g. for Zn - 120 p.p.m.; Rb - 20 p.p.m.; Fe - 150 p.p.m.; Pb - 3 p.p.m; Ni - 5 p.p.m.

Organization of the mossy fiber system of the rat studied in extended hippocampi. II. Experimental analysis of fiber distribution with silver impregnation methods

The mossy fibers, a major intrinsic hippocampal pathway connecting the dentate granule cells with the pyramidal cells in CA4 and CA3, have been reexamined in rats using mainly Fink-Heimer silver impregnation methods for demonstration of degenerating axons. By extending isolated hippocampi and cutting sections normal to the long axis, simple two-dimensional reconstructions of both the lesions and the resultant degeneration could be made. In the hilus, the zone with the greatest concentration of degenerating boutons was found between the lesioned granule cells and the CA3 pyramidal cells abuting on the hilus; outside this zone the concentration declines rather rapidly. Degenerating boutons were also observed in low concentration up to 200-300 microgram septal and temporal to the lesion. The mossy fibers in CA3 nearest the hilus have an intrapyramidal course and display a lamellar organization with fibers from the granule cells of the medial blade lying deep to those from the dentate crest. These in turn lie deep to those from the graule cells of the lateral blade. A mediolateral difference in the projection of the graule cells on the CA3 pyramidal cells was discovered: fibers from the medial granule cells descend about 600 micrometer in the temporal direction, whereas fibers from the lateral granule cells descend about 1,200 micrometer. This causes a divergence of the fibers from one single level, especially of the part of the fibers, being farthest away from the hilus. The degree of descent of the fibers from each mediolateral position of the granule cells was constant at all septotemporal levels examined.

Sulfide silver architectonics of rat, cat, and guinea pig spinal cord. A light microscopic study with Timm's method for demonstration of heavy metals

The distribution of heavy metals in the spinal cord of the cat, rat, and guinea pig has been studied histochemically with Timm's sulfide silver method. There was considerable variation in the degree of staining of the neuropil. The dorsal horn showed a laminar staining pattern corresponding to the cytoarchitectonic lamination. Lamina I in the cat and guinea pig was light. Lamina II in all three species was heavily stained. In the rat and guinea pig it could be subdivided in a ventral and a dorsal layer, and moreover in the rat a darkly staining borderzone abutting on lamina III was present. Lamina III, characterized by heterogeneous staining, also appeared dark, although less obvious in the guinea pig. In the ventral horn the coarser stained particles in lamina IX contrasted with the surrounding lamina. Cell staining varied between different cell groups, and within single cell populations. In the cat thoracic cord the cells in nucleus intermedio-lateralis (IL) and nucleus intercalatus (IC) stained very weakly. In Clarke's column and in the motoneuron area cells, uniform in Nissl preparations, could be seen different after Timm staining. The results are discussed in relation to other histochemical patterns, cytoarchitectonics, and terminal fields of afferents. Considerable correlation of the Timm pattern to these data was found.

Crossed pathways from the entorhinal area to the fascia dentata. I. Normal in rabbits

The entorhinal area projects to the Ammon's horn and the fascia dentata by way of the medial and lateral perforant paths that originate in the medial and lateral part of that area, respectively. The two tracts terminate at different laminar levels in the molecular layers of the ipsilateral hippocampal regio inferior and fascia dentata. Using the Fink-Heimer technique, each of the perforant paths in the normal rabbit is now shown to innervate the antero-dorsal extremes of the Ammon's horn and fascia dentata in both hemispheres. The crossed and uncrossed components of each path innervate homotopic zones on each side. This bilateral innervation contrasts with the situation in the rat where only very weak crossed components exist. Degeneration particles in the fascia dentata contralateral to a lesion of the perforant paths diminish in number along the course of the fibers as they proceed away from the midline, but are traceable for several millimeters. Crossed fibers are shown to pass from one hemisphere into the other directly through the fused molecular layers of the fasciae dentatae. The bilateral innervation in the rabbit indicates that even though the axons of the perforant paths are highly specific with respect to the class of neuron and the dendritic segments upon which they form synapses, they apparently do no possess a mechanism by which they can distinguish between the receptive fields in the two hemispheres. It is concluded that during ontogeny the perforant path fibers from both sides most likely compete for available synaptic sites in the rostral part of their terminal fields and that their relative amounts in the two hemispheres is governed by spatial and temporal factors.

The topographical and laminar organization of the presubiculum's projection to the ipsi- and contralateral entorhinal cortex in the guinea pig

This is a detailed report of a previously described projection from the presubiculum to the entorhinal area (Shipley, '74). The terminal degeneration in the entorhinal area is specifically confined to the outer three layers of this cortex. The projection is topogtaphically organized and confined to dorsal and medial parts of the entorhinal area. A similarly organized projection courses via the dorsal psalterium (dorsal hippocampal commissure) to the contralateral entorhinal area. Thus each presubiculum has an organized terminal pathway to the entorhinal cortices of both hemispheres.