Entorhinal cortex of the monkey: V. Projections to the dentate gyrus, hippocampus, and subicular complex.

The topographic and laminar organization of entorhinal projections to the dentate gyrus, hippocampus, and subicular complex was investigated in the Macaca fascicularis monkey. Injections of 3H-amino acids were placed at various positions within the entorhinal cortex and the distribution of anterogradely labeled fibers and terminals within the other fields of the hippocampal formation was determined. Injections of the retrograde tracers Fast blue, Diamidino yellow, and wheat germ agglutinin-horseradish peroxidase (WGA-HRP) were also placed into the dentate gyrus, hippocampus, and subicular complex, and the distribution of retrogradely labeled cells in the entorhinal cortex was plotted using a computer-aided digitizing system. The entorhinal cortex gave rise to projections that terminated in the subiculum, in the CA1, CA2, and CA3 fields of the hippocampus, and in the dentate gyrus. Projections to the dentate gyrus, and fields CA3 and CA2 of the hippocampus, originated preferentially in layers II and VI of the entorhinal cortex whereas projections to CA1 and to the subiculum originated mainly in layers III and V. Anterograde tracing experiments demonstrated that all regions of the entorhinal cortex project to the outer two-thirds of the molecular layer of the dentate gyrus and to much of the radial extent of the stratum lacunosum-moleculare of CA3 and CA2. While the terminal distributions of entorhinal projections to the dentate gyrus, CA3, and CA2 were not as clearly laminated as in the rat, projections from rostral levels of the entorhinal cortex preferentially innervated the outer portion of the molecular layer and stratum lacunosum-moleculare, whereas more caudal levels of the entorhinal cortex projected relatively more heavily to the deeper portions of the entorhinal terminal zones. The entorhinal projection to the CA1 field of the hippocampus and to the subiculum followed a transverse rather than radial gradient of distribution. Rostral levels of the entorhinal cortex terminated most heavily at the border of CA1 and the subiculum. More caudal levels of the entorhinal cortex projected to progressively more distal portions of the subiculum (towards the presubiculum) and more proximal portions of CA1 (towards CA2). Lateral portions of the entorhinal cortex projected to caudal levels of the recipient fields and more medial parts of the entorhinal cortex projected to progressively more rostral portions of the fields.     

Neurons co-localizing calretinin immunoreactivity and reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity in the hippocampus and dentate gyrus of the rat

Co-localization of calretinin immunoreactivity and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity was studied in the rat hippocampus and dentate gyrus. Neurons co-expressing both markers (CR/NADPH-d) were observed throughout the hippocampus and dentate gyrus. However, they were more abundant in the stratum pyramidale and radiatum of CA3, stratum pyramidale of CA1, and in the juxtagranular zone of the hilus. The NADPH-d activity appeared in 37% of the calretinin immunoreactive neurons in CA3, 42% in CA1, and 36% in the dentate gyrus, whereas calretinin immunoreactivity occurred in 41% of the NADPH-d positive neurons in the hippocampus, and 16% in the dentate gyrus. The morphology and location of the double marked cells could not be used as a characteristic of the co-localizing neurons. The heavily stained NADPH-d neurons occurring mainly in CA1 do not show calretinin immunoreactivity. NADPH-d fiber swellings could be observed in close apposition to calretinin immunoreactive neurons and dendrites, suggesting synaptic contacts. It has been reported that calretinin immunoreactivity and NADPH-d activity co-localize infrequently in other areas such as the neocortex, striatum, hypothalamus and tegmental nucleus. The relatively high proportion of double marked cells found in the hippocampus and dentate gyrus could be indicative of the importance of the CR/NADPH-d interneurons in the circuitries of these areas.     

Chronological alterations of neurofilament 150 immunoreactivity in the gerbil hippocampus and dentate gyrus after transient forebrain ischemia

In this study, we observed the chronological alterations of neurofilament 150 (NF-150) immunoreactivity in the gerbil hippocampus and dentate gyrus after 5 min transient forebrain ischemia. NF-150 immunoreactivity in the sham-operated group was mainly detected in mossy fibers and in the hilar region of the dentate gyrus. NF-150 immunoreactivity and protein contents of NF-150 and RT 97 (polyphosphorylation epitopes of neurofilament) were significantly decreased at 15 min after ischemic insult. Between 30 min and 12 h after ischemic insult, NF-150 immunoreactivity and protein content were significantly increased as compared with the sham-operated group. Thereafter, NF-150 immunoreactivity and protein content started to decrease. At 12 h after ischemic insult, unlike dentate gyrus, NF-150 immunoreactivity increased in pyramidal cells of the CA1 region. Thereafter, NF-150 immunoreactivity in the CA1 region started to decrease, and 4 days after ischemic insult, NF-150 immunoreactivity nearly was similar to that of the sham-operated group. These biphasic patterns of NF-150 immunoreactivity in the hippocampus and dentate gyrus are reverse correlated with that of the intracellular calcium influx. For calcium detection in the CA1 region, we also conducted alizarin red staining. Alizarin red positive neurons were detected in some neurons at 15-30 min after ischemic insult. At 12 h after ischemia, alizarin red positive neurons were decreased. Thereafter, alizarin red positive neurons started to decrease, but alizarin positive neurons were significantly increased in dying neurons 4 days after ischemia. These results suggest that ischemia-related changes of NF-150 expression may be caused by the calcium following transient forebrain ischemia.     

The entorhinal cortex of the mouse: organization of the projection to the hippocampal formation

The origin and the terminations of the projections from the entorhinal cortex to the hippocampal formation of the mouse (C57BL/6J strain) have been studied using anterogradely and retrogradely transported tracers. The entorhinal cortex is principally divided into two areas, the lateral entorhinal area (LEA) and the medial entorhinal area (MEA). LEA is the origin of the lateral perforant path that terminates in the outer one-third of the molecular layer of the dentate gyrus, and MEA is the origin of the medial perforant path that ends in the middle one-third of the molecular layer of the dentate gyrus. This projection is mostly to the ispsilateral dentate gyrus; only a few labeled axons and terminals are found in the contralateral dentate gyrus. The projection to the dentate gyrus originates predominantly from neurons in layer II of the entorhinal cortex. The entorhinal cortex also projects to CA3 and CA1 and to subiculum; in both CA3 and CA1, the terminals are present in stratum lacunosum-moleculare, whereas in the subiculum the terminals are in the outer part of the molecular layer. The projection from the entorhinal cortex to CA3, CA1, and subiculum is bilateral, and it originates predominantly from neurons in layer III, but a small number of neurons in the deeper layers of the entorhinal cortex contributes to this projection. The projection of entorhinal cortex to the hippocampus is topographically organized, neurons in the lateral part of both LEA and MEA project to the dorsal part (i.e., septal pole) of the hippocampus, whereas the projection to the ventral (i.e., temporal pole) hippocampus originates from neurons in medial parts of the entorhinal cortex.     

Immunohistochemical analysis of ubiquilin‐1 in the human hippocampus: Association with neurofibrillary tangle pathology

This post mortem immunohistochemical study examined the localization and distribution of ubiquilin‐1 (UBL), a shuttle protein which interacts with ubiquitin and the proteasome, in the hippocampus from Alzheimer's disease (AD) dementia cases, and age‐matched cases without dementia. In Braak stages 0–I–II cases, UBL immunoreactivity was detected in a dense fiber network in the neuropil, and in the cell cytoplasm and nucleoplasm of neurons in Cornu Ammonis (CA) fields and dentate gyrus granular neurons. In Braak stages III‐IV and V‐VI cases, UBL immunoreactivity was reduced in the neuropil and in the cytoplasm of the majority of CA1 neurons; some CA1 pyramidal neurons and the majority of CA2/3 pyramidal, CA4 multipolar, and dentate granular neurons had markedly increased UBL immunoreactivity in the nucleoplasm. Dual immunofluorescence analysis of UBL and antibody clone AT8 revealed co‐localization most frequently in CA1 pyramidal neurons in Braak stage III‐IV and V‐VI cases. Further processing using the pan‐amyloid marker X‐34 revealed prominent UBL/X‐34 dual labeling of extracellular NFT confined to the CA1/subiculum in Braak stage V‐VI cases. Our results demonstrate that in AD hippocampus, early NFT changes are associated with neuronal up‐regulation of UBL in nucleoplasm, or its translocation from the cytoplasm to the nucleus. The perseverance of UBL changes in CA2/3, CA4 and dentate gyrus, generally considered as more resistant to NFT pathology, but not in the CA1, may mark a compensatory, potentially protective response to increased tau phosphorylation in hippocampal neurons; the failure of such a response may contribute to neuronal degeneration in end‐stage AD.     

Differential alteration of NMDA receptor subunits in the gerbil dentate gyrus and subiculum following seizure

In the present study, a chronological and comparative analysis of the immunoreactivities of N-methyl-D-aspartate (NMDA) receptor subunits in hippocampus of both seizure resistant (SR) and seizure sensitive (SS) gerbils was made in order to clarify the temporal and spatial alterations of NMDA receptor subunit expressions in the hippocampus complex. The changes in NMDA receptor immunoreactivity in the hippocampi of SS gerbils were restricted to both the dentate gyrus and the subiculum. At 30 min postictal, a decline in NMDA receptor subunit 1 (NR1) immunoreactivity in the suprablade of dentate gyrus was observed. This is in contrast to the enhancement of its immunodensity in the infrablade. At 3 h postictal the NR1 immunoreactivity in the infrablade also declined significantly. At 12 h postictal, its immunoreactivity in the hilar neurons was reduced. The NMDA receptor subunit 2A/B (NR2A/B) immunoreactivity did not alter until 12 h following seizure-onset, when it was slightly decreased in the granule cells and hilar neurons. In the subiculum, NR1 immunoreactivity was significantly decreased, and was almost undetectable in this region until 12 h postictal; in contrast the NR2A/B immunoreactivity in this region increased significantly in this time point. These results suggest that the altering NMDA receptor expression in both the dentate gyrus and subiculum may affect tissue excitability and have an important role in regulating seizure activity in SS gerbils.     

Immunohistochemical distribution of protein kinase C isozymes is differentially altered in ischemic gerbil hippocampus

We used monoclonal antibodies to examine the immunohistochemical distribution of the three major Ca(2+)-dependent protein kinase C (PKC) isozymes (I, II, and III) in ischemic gerbil hippocampus. Groups of four animals were sacrificed at 15 min, 4 h, 1 day, 2 days, 3 days, and 7 days after a 10-min episode of global forebrain ischemia. In control animals, PKC-I immunoreactivity was greater in CA1 neurons than in CA3-4. Terminal-like staining was not evident. PKC-II immunoreactivity was observed in all CA fields and in the outer molecular layer of the dentate gyrus. PKC-III staining was present in the CA fields, the inner molecular layer of the dentate gyrus and the subiculum. Dentate granule cells and mossy fibers were not stained with any of the PKC antibodies. Fifteen minutes and 4 h after ischemia, PCK-I, -II and -III immunoreactivity were all increased in CA1 neurons and PKC-III immunoreactivity alone was visualized in granule cells and mossy fibers. Staining patterns returned to baseline one day after ischemia. PKC-II and -III terminal-like staining were preserved in the stratum lacunosum-moleculare for 3 days and 2 days after ischemia respectively and then disappeared. The altered patterns of PKC staining in the hippocampus may reflect activation and/or down-regulation of PKC isozymes. Ca(2+)-dependent PKC isozymes may, therefore, potentially play a role in the pathogenesis of delayed ischemic neuronal death.     

Induction of Calcitonin Gene-Related Peptide-like Immunoreactivity in Hippocampal Neurons Following Ischemia: A Putative Regional Modulator of the CNS Injury/Immune Response

Calcitonin gene-related peptide (CGRP) is a potent vasodilator and immune cell modulator. In two studies within the hippocampal formation (HF), CGRP-like immunoreactivity (CGRP-LI) was increased in the inner molecular layer of the dentate gyrus after adrenalectomy and in mossy cells after colchicine-induced destruction of granule neurons. Given the increase in CGRP-LI following damage to the granule cell region of the HF, we investigated another trauma model, ischemia, that targeted different areas of the HF, CA1 region, and subiculum to ascertain the regional expression of this peptide after insult. Following ischemia, light microscopic evaluation showed CGRP-LI in basket cell-like neuronal perikarya within the dorsal subiculum and CA1 region of the hippocampus and in varicose fibers within the CA2 region of the hippocampus. Control rats rarely expressed CGRP-LI within neurons in these regions. In ischemic brains, double-labeled immunocytochemistry with antibodies to various neural markers demonstrated co-localization of CGRP-LI primarily within surviving subicular and CA1 cells resembling interneurons containing parvalbumin-LI or calbindin-LI. Electron microscopic analysis of the CA1 region from ischemic brains showed that CGRP-LI was contained in terminals with numerous small synaptic vesicles that formed symmetric synapses with perikarya and large dendrites of pyramidal cells, some of which were degenerating. Collectively, the data from this study and our previous study indicate that damage induces CGRP-LI expression in interneurons and nonprincipal cells in the area of damage, and we hypothesize that CGRP expression in surviving neurons within damage-related regions of the hippocampus is likely to be an important, and possibly a protective, component of the response of the nervous system to injury.     

Neuronal inputs to hippocampal formation in Alzheimer's disease and in parkinsonism-dementia complex on Guam

Summary This study concerns the expression of synaptophysin in the hippocampal formation of normal controls, of patients with Alzheimer's disease (AD) and of patients with parkinsonism-dementia complex on Guam (P-D complex). A monoclonal antibody was used to visualize synaptophysin, an integral component of presynaptic vesicle membranes. In the normal controls, a strong synaptophysin immunoreactivity was seen in the stratum pyramidale, stratum radiatum and stratum lacunosum-moleculare of the hippocampus proper, in the subiculum and in the molecular layer of the dentate gyrus. In the dentate gyrus molecular layer, the reaction product was distributed in a laminar fashion. By contrast, in AD and in P-D complex a significant decrease in immunoreactivity was observed in all hippocampal strata, and especially of the hippocampal subfield CA1 and the subiculum. In both diseases, synaptophysin expression was also diminished in the molecular layer of the dentate gyrus of all patients examined, with the inner portion exhibiting almost normal and the outer portion a strikingly reduced synaptophysin immunoreactivity.     

Expression and changes of Ca2+-ATPase in neurons and astrocytes in the gerbil hippocampus after transient forebrain ischemia

Ca2+-ATPase is one of the most powerful modulators of intracellular calcium levels. In this study, we focused on chronological changes in the immunoreactivity and protein levels of Ca2+-ATPase in the hippocampus after 5 min of transient forebrain ischemia. Ca2+-ATPase immunoreactivity was significantly altered in the hippocampal CA1 region and in the dentate gyrus, but not in the CA2/3 region after ischemic insult. In the sham-operated group, Ca2+-ATPase immunoreactivity was detected in the hippocampus. Ca2+-ATPase immunoreactivity in the CA1 region and in the dentate gyrus, and its protein levels peaked 3 h after ischemic insult. At this time, CA1 pyramidal cells and dentate polymorphic cells showed strong Ca2+-ATPase immunoreactivity. Thereafter, Ca2+-ATPase immunoreactivity reduced in the CA1 region and in the dentate gyrus. One day after ischemic insult, Ca2+-ATPase immunoreactivity was observed in some CA1 non-pyramidal cells, and 4 days after ischemic insult, Ca2+-ATPase immunoreactivity was detected in astrocytes throughout the CA1 region, but Ca2+-ATPase immunoreactivity in the dentate gyrus had nearly disappeared. Our results suggest that Ca2+-ATPase changes may be associated with a response to ischemic damage in hippocampal CA1 pyramidal cells, and that increased Ca2+-ATPase immunoreactivity in the reactive astrocytes may be associated with the maintenance of intracellular calcium levels.     

Species differences in the projections from the entorhinal cortex to the hippocampus

Both differences and similarities exist between mammalian species in the projections from entorhinal cortex to the hippocampal formation. In most species, layer II cells of the entorhinal cortex project to the dentate gyrus, and they terminate in the outer two-thirds of the molecular layer of the dentate gyrus. The axons from layer III cells project bilaterally to areas CA(1) and CA(3) of the hippocampus, terminating in the stratum lacunosum moleculare. We have analyzed these projections in mice, and in general, the entorhinal cortex-to-hippocampus projections are similar to those in rats. Axons from layer II neurons terminate in the outer and middle thirds of the molecular layer of the dentate gyrus, and axons from layer III neurons terminate bilaterally in the stratum lacunosum moleculare of areas CA(1) and CA(3), and in the molecular layer of the subiculum. However, in contrast to rat, mouse entorhinal cortex neurons do not appreciably project to the contralateral dentate gyrus. Most species, including mice, show a similar topographical organization of the entorhinal-hippocampal projections, with neurons in the lateral part of both the lateral and medial entorhinal cortex projecting to the dorsal part or septal pole of the hippocampus, whereas the projection to the ventral hippocampus originates primarily from neurons in medial parts of the entorhinal cortex.     

Impaired activation of CA3 pyramidal neurons in the epileptic hippocampus

We employed in vitro and ex vivo imaging tools to characterize the function of limbic neuron networks in pilocarpine-treated and age-matched, nonepileptic control (NEC) rats. Pilocarpinetreated animals represent an established model of mesial temporal lobe epilepsy. Intrinsic optical signal (IOS) analysis of hippocampal-entorhinal cortex (EC) slices obtained from epileptic rats 3 wk after pilocarpine-induced status epilepticus (SE) revealed hyperexcitability in many limbic areas, but not in CA3 and medial EC layer III. By visualizing immunopositivity for FosB/ΔFosBrelated proteins—which accumulate in the nuclei of neurons activated by seizures—we found that: (1) 24 h after SE, FosB/ΔFosB immunoreactivity was absent in medial EC layer III, but abundant in dentate gyrus, hippocampus proper (including CA3) and subiculum; (2) FosB/ΔFosB levels progressively diminished 3 and 7 d after SE, whereas remaining elevated (p<0.01) in subiculum; (3) FosB/ΔFosB levels sharply increased 2 wk after SE (and remained elevated up to 3 wk) in dentate gyrus and in most of the other areas but not in CA3. A conspicuous neuronal damage was noticed in medial EC layer III, whereas hippocampus was more preserved. IOS analysis of the stimulus-induced responses in slices 3 wk after SE demonstrated that IOSs in CA3 were lower (p<0.05) than in NEC slices following dentate gyrus stimulation, but not when stimuli were delivered in CA3. These findings indicate that CA3 networks are hypoactive in comparision with other epileptic limbic areas. We propose that this feature may affect the ability of hippocampal outputs to control epileptiform synchronization in EC.     

No evidence for loss of hippocampal neurons in non-Alzheimer dementia patients

OBJECTIVE: To use stereological methods for estimating the total number of neurons in hippocampi of non-Alzheimer demented patients. MATERIAL AND METHODS: Hippocampi from six women with severely impaired memory but without Alzheimer pathology were compared with six mentally intact age-matched female controls. The total number of neurons was estimated in the granule cell layer of the dentate gyrus, the hilus of the dentate gyrus, the pyramidal cell layer of CA3 and CA2, the pyramidal cell layer of CA1 and the cellular layer of subiculum using the optical fractionator. RESULTS: The total neuron number was the same in the dementia cases, 22.4 x 106, compared with 22.7 x 106 in the controls (P = 0.85). No region-specific group differences or side difference were found. Two cases without clinical signs of dementia but with abundant plaques and tangles in hippocampus and neocortex had total neuron numbers within normal limits. CONCLUSION: Our results indicate that severely impaired memory can occur in the presence of intact numbers of hippocampal neurons in non-Alzheimer dementia and that nerve cell loss in the hippocampus might be characteristic for Alzheimer's disease, and perhaps other forms of primary cortical dementia.     

NADPH-Diaphorase in the central nervous system of the larval lamprey (Lampetra planeri)

The anatomy of the hippocampus, including the organization of its intrinsic neural circuits and afferents, is organized along a rostrocaudal axis. Dopamine D2 receptors are expressed in specific regions of the hippocampal complex (hippocampal subfields, entorhinal cortex, perirhinal cortex) and show differential expression along this axis. The dentate gyrus and CA3/CA4 subfields show higher numbers of D2 receptors in the rostral than in the caudal levels. In contrast, the subiculum shows the reverse gradient. We report here that Alzheimer's disease (AD) is associated with reduced expression of the dopamine D2 receptor, but the effects differ with respect to the rostrocaudal axis and area within the hippocampal complex. The number of D2 receptors is significantly reduced in the molecular layer of the dentate gyrus, CA3 subfield, and subiculum. For the dentate gyrus and subiculum, there were greater losses at more rostral levels. The CA3/CA4 subfields showed the greatest losses caudally. The entorhinal cortex, which shows only modest expression of D2 receptors in controls, does not exhibit reduced numbers in AD. The external laminae of the rostral perirhinal cortex showed more significant losses than more caudally in this cortical field. The regions showing loss of D2 receptors do not typically contain neuritic plaques, neurofibrillary tangles, or significant neuron loss. Thus other mechanisms must account for the unique gradient of D2 receptor loss in the hippocampus. The regions of reduced expression of dopamine D2 receptors do correlate well with the terminal zone of the dentate association pathway, the afferents from the anlygdala and perirhinal cortex, and the sources of those afferents within the amygdala and perirhinal cortex. The specific patterns of reduced D2 receptor expression in AD are likely to contribute significantly to the disrupted information flow into and out of the hippocampus and, thus, of functions subserved by this system. © 1994 Wiley-Liss, Inc.     

Distribution,morphological features,and synaptic connections of parvalbumin- and calbindin D28k-immunoreactive neurons in the human hippocampal formation

Calcium binding proteins calbindin D_28k (CaBP) and parvalbumin (PV) are known to form distinct subpopulations of gamma-aminobutyric acid (GABA)ergic neurons in the rodent hippocampal formation. Light and electron microscopic morphology and connections of these protein-containing neurons are only partly known in the primate hippocampus. In this study, CaBP and PV were localized in neurons of the human hippocampal formation including the subicular complex (prosubiculum, subiculum, and presubiculum) in order to explore to what extent these subpopulations of hippocampal neurons differ in phylogenetically distant species. CaBP immunoreactivity was present in virtually all granule cells of the dentate gyrus and in a proportion of pyramidal neurons in the CA1 and CA2 regions. A distinct population of CaBP-positive local circuit neurons was found in all layers of the dentate gyrus and Ammon's horn. Most frequently they were located in the molecular layer of the dentate gyrus and the pyramidal layer of Ammon's horn. In the subicular complex pyramidal neurons were not immunoreactive for CaBP. In the prosubiculum and subiculum immunoreactive nonpyramidal neurons were equally distributed in all layers, whereas in the presubiculum they occurred mainly in the superficial layers. Electron microscopy showed typical somatic and dendritic features of the granule, pyramidal, and local circuit neurons. CaBP-positive mossy fiber terminals in the hilus of the dentate gyrus and terminals of presumed pyramidal neurons of Ammon's horn formed asymmetric synapses with dendrites and spines. CaBP-positive terminals of nonprincipal neurons formed symmetric synapses with dendrites and dendritic spines, but never with somata or axon initial segments. PV was exclusively present in local circuit neurons in both the hippocampal formation and subicular complex. Most of the PV-positive cell bodies were located among or close to the principal cell layers. However, large numbers of immunoreactive neurons were also found in the molecular layer of the dentate gyrus and in strata oriens of Ammon's horn. PV-positive cells were equally distributed in all layers of the subicular complex. Electron microscopy showed the characteristic somatic and dendritic features of local circuit neurons. PV-positive axon terminals formed exclusively symmetric synapses with somata, axon initial segments and dendritic shafts, and in a few cases with dendritic spines. The CaBP- and PV-containing neurons formed similar subpopulations in rodents, monkeys, and humans, although the human hippocampus displayed the largest variability of these immunoreactive neurons in their morphology and location. Calcium binding protein-containing neurons frequently occurred in the molecular layer of the human dentate gyrus and in the stratum lacunosum-moleculare of Ammon's horn. The corresponding areas of the rat or monkey hippocampus were devoid of such neurons. In both rodents and primates similar populations of principal neurons contained CaBP. In addition, CaBP and PV were localized in distinct and nonoverlapping populations of nonprincipal cells. Their target selectivity did not change during phylogeny (e.g., PV-positive cells mainly innervate the perisomatic region and CaBP-positive cells the distal dendritic region of principal cells). © 1993 Wiley-Liss,Inc.     

Glutamate-, glutaminase-, and taurine-immunoreactive neurons develop neurofibrillary tangles in Alzheimer's disease.

Although formation of neurofibrillary tangles is a major pathological feature of Alzheimer's disease (AD), the neurotransmitter content of neurofibrillary tangle-bearing neurons has not been well characterized. We studied the hippocampus of 6 patients with pathologically verified AD and 6 control subjects using a monoclonal antibody to glutamyl-glutamate and polyclonal antisera against glutaminase and taurine. In normal hippocampus, glutamate and glutaminase stained pyramidal neurons in the cornu ammonis (CA) fields and the subiculum, as well as the dentate granule cells. Fiber staining was better seen with glutamate antisera, which in AD specimens showed reduced numbers of glutamate-immunoreactive fibers in the molecular layer of the dentate gyrus. In AD specimens, glutamate- and glutaminase-immunoreactive pyramidal neurons in the hippocampal CA fields were decreased in number and remaining neurons showed irregular shortened and disorganized dendritic fields. Taurine immunoreactivity was localized to a subset of hippocampal pyramidal neurons, which showed similar degenerative changes in AD specimens. Glutamate-, glutaminase-, and taurine-stained neurons were found to contain neurofibrillary tangles using either double immunofluorescence with tau antisera, double immunoperoxidase stains, or silver and thioflavine S counterstains. These studies show that two distinct neurochemically defined populations of pyramidal neurons in allocortex frequently show degenerative changes and develop neurofibrillary tangles in AD.     

Mossy Cells of the Rat Dentate Gyrus are lmmunoreactive for Calcitonin Gene-related Peptide (CGRP)

The neuropeptide calcitonin gene-related peptide (CGRP) was localized in the hippocampus and dentate gyrus of the rat by immunocytochemistry at the light and electron microscopic levels. Without colchicine treatment only faint neuropil labelling was found in the inner molecular layer of the dentate gyrus. Following colchicine treatment, a large number of neurons with numerous complex spines along the proximal dendrites were visualized in the hilus of the dentate gyrus, particularly in the ventral areas, and, in addition, staining of the inner molecular layer became stronger. Several CA3c pyramidal cells located adjacent to the hilar region in the ventral hippocampus also appeared to be faintly positive, although in most cases only their axon initial segments were labelled. Outside this region, the subicular end of the CA1 subfield contained occasional CGRP-positive non-pyramidal cells. The hilar CGRP-positive neurons were negative for parvalbumin, calretinin, cholecystokinin and somatostatin, whereas most of them were immunoreactive for GluR2/3 (the AMPA-type glutamate receptor known to be expressed largely by principal cells). Correlated electron microscopy showed that the spines along the proximal dendritic shafts indeed correspond to thorny excrescences engulfed by large complex mossy terminals forming asymmetrical synapses. Pre-embedding immunogold staining demonstrated that CGRP immunoreactivity in the inner molecular layer was confined to axon terminals that form asymmetrical synapses, and the labelling was associated with large dense-core vesicles. The present data provide direct evidence that CGRP is present in mossy cells of the dentate gyrus and to a lesser degree in CA3c pyramidal cells of the ventral hippocampus. These CGRP-containing principal cells terminate largely in the inner molecular layer of the dentate gyrus, and may release the neuropeptide in conjunction with their 'classical' neurotransmitter, glutamate.     

Distribution of m1 muscarinic acetylcholine receptors in the hippocampus of patients with Alzheimer's disease and dementia with Lewy bodies-an immunohistochemical study.

Of the five subtypes (m1-m5) of muscarinic acetylcholine receptors (mAChR), the m1 subtype is the most abundant in the human cerebral cortex and hippocampus. Impairment of the muscarinic cholinergic system in the brain may cause cognitive dysfunction in patients with Alzheimer's disease (AD), and choline esterase inhibitors (ChE-I) are used to improve cognitive dysfunction. Severe impairment of the cholinergic system has also been reported in the brains of subjects with dementia with Lewy bodies (DLB). There have been a few reports about the distribution of mAChR subtypes in the human brain. In the present study, we investigated the distribution of m1 mAChR in the human hippocampus using an antibody against the m1 subtype.In the control brains, m1 immunoreactivity was observed in the apical dendrites and cell bodies of granular neurons of the dentate gyrus and pyramidal neurons of CA1-3 and the subiculum. The dendrites and the cell bodies of the pyramidal neurons in layers III and V of the parahippocampal cortex and other temporal cortices were also positive for m1 immunoreactivity. This m1 immunoreactivity was markedly reduced in AD and DLB brains.     

The organization of the descending ventral pallidal projections in the monkey

We studied the distribution and light- and electron-microscopic morphology of neurons in the hippocampal formation containing nitric oxide synthase (NOS), and thus likely to release nitric oxide, a freely diffusible neuromediator implicated in long-term potentiation. Only a small fraction of hippocampal neurons contained NOS or its marker, NADPH diaphorase. Most of the positive neurons were in the pyramidal layer of the subiculum, stratum radiatum of Ammon's horn, and subgranular zone of the dentate gyrus. Positive neurons were also conspicuous in the molecular layer of the dentate gyrus and in the pyramidal layer of CA3, sparse in the pyramidal layer of CA2 and CA1, and almost absent from presubiculum and parasubiculum. Numerous positive fibers were seen, especially in stratum radiatum and stratum lacunosum-moleculare of Ammon's horn. Double staining experiments demonstrated that nearly all NADPH diaphorase-positive neurons in the hippocampus also contained γ-aminobutyric acid. On the basis of their morphology, distribution, and inhibitory neurotransmitter content, most NOS-positive cells in the hippocampus are probably local circuit neurons. These data suggest that nitric oxide in CA1 may function as a paracrine agent, rather than a spatially precise messenger, in long-term potentiation. © 1993 Wiley-Liss, Inc.     

Localization of enkephalin-like immunoreactivity to identified axonal and neuronal populations of the rat hippocampus

The distribution of enkephalin-like immunoreactivity in the hippocampal formation of the rat was analyzed. Two specific projection systems are described. The first emerges from the hilus of the dentate gyrus and appears to terminate with notably large boutons on the proximal apical and, to a lesser extent, basal dendrites of hippocampal regio inferior pyramidal cells. This projection corresponds in source, position, and character to the hippocampal mossy fiber system. The second axonal population enters the temporal hippocampal formation from the medial wall of the subicular complex and follows the hippocampal fissure to occupy stratum lacunosum-moleculare of the hippocampus proper and the distal third of the dentate gyrus molecular layer; this pattern corresponds to the distribution of afferent input from the lateral entorhinal cortex and/or perirhinal area. Lesions of the hilus or retrohippocampal area caused a selective depletion of immunoreactivity in the mossy fiber fields and molecular layers of the dentate gyrus, respectively. Enkephalin-like immunoreactivity was found within the somata of three types of hippocampal neurons: (1) granule cells of the dentate gyrus, (2) occasional pyramidal shaped cells of field CA1 stratum pyramidale, and (3) varied scattered interneurons. Of this last group, two types of interneurons were consistently seen. The first occupy the border between stratum radiatum and stratum lacunosum-moleculare and extend processes at right angles to the long axis of the pyramidal cell dendrites, whereas the second lie within stratum radiatum of field CA1 and extend processes in alignment with the long axis of the pyramidal cell dendrites. Cells containing enkephalin-like immunoreacactivity were also observed in the subiculum and retrohippocampal region, most notably including layers II and III of the lateral entorhinal cortex-perirhinal area—the probable source of extrinsic immunoreactive input to the hippocampal formation. Intraventricular colchicine treatment intensified the immunoreactive staining of some hippocampal neurons but did not reveal any cell types not seen to be labeled in untreated rats.