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PubMed1994

Posterior piriform and perirhinal cortex relay seizures evoked from the area tempestas: role of excitatory and inhibitory amino acid receptors.

The functional relationship between the area tempestas (AT), an epileptogenic site within the deep prepiriform cortex, and the regions in the posterior piriform cortex which are innervated by AT, were studied in the rat. The GABAA receptor agonist, muscimol (390 pmol) was microinjected unilaterally into the posterior piriform cortex and adjacent regions in the same hemisphere from which seizures were evoked by focal application of bicuculline into AT. Pretreatment with muscimol into either the ventral posterior piriform cortex or perirhinal cortex, protected against the bilateral clonic seizures evoked from the ipsilateral AT. No seizure protection was obtained when muscimol was placed into adjacent areas of amygdala, entorhinal cortex, neocortex and ventral hippocampus. Seizure protection was also obtained when kynurenic acid, but not 2-amino-7-phosphonoheptanoic acid, was microinjected into the ventral posterior piriform cortex, suggesting that glutamate transmission mediated via non-N-methyl-D-aspartate (non-NMDA) receptors is required for the relay of seizure discharge through this region. Our data indicate that a specific region of the temporal cortex, the posterior piriform and perirhinal area, functions as a critical link in the propagation of limbic seizures evoked from AT.

2-Amino-5-phosphonovalerate↗

PubMed1994

Multiple anterograde tracing, combining Phaseolus vulgaris leucoagglutinin with rhodamine- and biotin-conjugated dextran amine.

The simultaneous use of different neuroanatomical anterograde tracers provides a potentially powerful method to study the convergence of afferent systems in a particular brain area. However, a simple routine procedure to apply multiple anterograde tracers in conjunction with their simultaneous visualization is still missing. We report an easy and straightforward application of three sensitive anterograde tracers: Phaseolus vulgaris leucoagglutinin (PHA-L), rhodamine-conjugated dextran amine (RDA) and biotin-conjugated dextran amine (BDA). These tracers can be visualized simultaneously and permanently through a triple-staining procedure with nickel-enhanced diaminobenzidine (DAB-Ni), DAB and 1-naphthol/Azur B as chromogens. Our test model comprised the projections from the nucleus reuniens thalami and entorhinal cortex. Both projection systems show a high degree of overlap in their terminal fields in the hippocampus. Two tracers were injected in the left and right entorhinal cortex, respectively; a third tracer was injected in the nucleus reuniens. This combination of injections provided a good opportunity to compare the three tracers in one and the same animal. PHA-L, RDA and BDA, injected in either of the injection sites, turned out to be equally sensitive and revealed the morphology of the involved projection systems in great detail. The triple-staining protocol yielded an excellent, simultaneous detectability of the three tracers with a remarkably low background level. Thus, the combination of the anterograde tracers PHA-L, RDA and BDA, in conjunction with the triple-staining procedure, offers a very attractive approach for neuroanatomical research.

Animals↗

PubMedDate not supplied

Glycogen synthase kinase 3 alpha and 3 beta do not colocalize with neurofibrillary tangles.

Glycogen synthase kinase (GSK) 3 alpha and 3 beta are two proline-directed serine/ threonine kinases that have been shown in vitro to hyperphosphorylate tau, and therefore, may contribute to neurofibillary tangle (NFT) formation in Alzheimer's disease (AD). We report here that, in the human hippocampal formation of both control and AD individuals, GSK 3 alpha and 3 beta are immunohistochemically localized to neurons within the presubiculum > CA1, CA3, and CA4 subfields of the hippocampus, layers III > II > IV, V, VI of entorhinal cortex, and occasional neurons in layers III, V, and VI of temporal neocortex. By contrast, NFTs occur primarily in CA1. subiculum, layers II and IV of entorhinal cortex, and layers II, III, and V of temporal neocortex. The presubiculum and other subfields are frequently spared. Thus, localization of GSK 3 alpha and GSK 3 beta does not correspond to the expected pattern of neuronal vulnerability to NFT formation in AD. Interpreted within the limitations of immunohistochemical detection, these results argue against a major role of GSK 3 alpha or GSK 3 beta in NFT formation in AD.

Aged↗

PubMed1995

Region-specific effects of chronic lithium administration on neuropeptide Y and somatostatin mRNA expression in the rat brain.

The aim of this study was to examine the effects of 4-week lithium (Li+) food supplementation on neuropeptide mRNA expression in the rat brain. In situ hybridisation was used to determine the effects on the expression of neuropeptide Y (NPY) and somatostatin (SS) mRNA. Increases in NPY mRNA levels were seen in the hippocampus, layers II-III of the entorhinal cortex, nucleus accumbens shell and in the medial caudate-putamen. Increases in SS mRNA expression were seen in the layers IV-VI of the entorhinal cortex and in the lateral caudate putamen. Thus, Li+ appears to affect discrete populations of NPY and SS mRNA expressing neurons, with possible relevance to beneficial effects of Li+ in affective disorders.

Animals↗

PubMed2004

Common pathway in the medial temporal lobe for storage and recovery of words as revealed by event-related functional MRI.

Lesion studies have provided compelling evidence that episodic memory is dependent on the integrity of the medial temporal lobe (MTL). This role of the MTL in episodic memory has been supported by several neuroimaging studies during both episodic encoding and retrieval. After two meta-analyses of positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies, we investigated a possible dissociation within the MTL memory system in relation to encoding and retrieval processes. Based on previous reports that specifically related the function of the MTL in episodic memory to successful encoding and actual recovery of information, we applied event-related fMRI to compare successful encoding of words (ES) directly with successful recognition of those same words (RS). Our results did not indicate a clear dissociation between encoding and retrieval activations in the MTL. Instead, a region in the left MTL, covering the parahippocampal cortex and hippocampal formation, which was activated during ES almost completely overlapped with the area that was activated during RS. An additional region in the left anterior MTL, including the entorhinal cortex, was found to be activated exclusively during ES. Research has indicated that a large percentage of cells in this region are particularly sensitive to the relative novelty of stimuli. Our results, therefore, suggest that the parahippocampal/hippocampal region is involved in the formation and subsequent reactivation of memory traces, whereas the activity observed in the entorhinal cortex may reflect elementary memory processes related to novelty detection.

Adult↗

PubMed2001

Chronic psychosocial stress differentially affects apoptosis in hippocampal subregions and cortex of the adult tree shrew.

We studied the effect of chronic psychosocial stress on cell death and volume changes in the tree shrew hippocampus. In situ end labelling (ISEL) identified low frequent but convincing apoptosis in many hippocampal subregions. Also in entorhinal cortex, apoptosis was found, generally at higher frequencies. After 28 days of chronic stress, apoptosis was significantly reduced in the CA1 stratum radiatum, whereas an increase was observed in the hilus (P < 0.04). With all subregions taken together, the hippocampus showed a decrease, whereas in the cortex, an increase in apoptosis was found after stress (P < 0.04). In a parallel and similar chronic stress study, post mortem morphometry of the same brain regions was performed, revealing mild decreases (7.6%) in entire hippocampal volume. We conclude that (i) low frequent apoptosis occurs throughout the adult tree shrew brain, and (ii) 28 days of chronic stress differentially affects its occurrence in distinct hippocampal subregions and entorhinal cortex. As previous stereological investigations failed to detect any loss in the principal neuronal layers, psychosocial stress, therefore, must affect other (structural) parameters like dendritic tree, interneurons, neurogenesis, or glia.

Animals↗

PubMed1998

Functional anatomy of limbic epilepsy: a proposal for central synchronization of a diffusely hyperexcitable network.

The limbic/mesial temporal lobe epilepsy syndrome has been defined as a focal epilepsy, with the implication that there is a well defined focus of onset, traditionally centered around the hippocampus. The pathology of the hippocampus in this syndrome has been well described and a number of physiological abnormalities have been defined in this structure in animal models and humans with epilepsy. However, anatomical and physiological abnormalities have also been described in other limbic sites in this form of epilepsy. Previous studies have shown broadly synchronized or multifocal seizure onset within the limbic system of the animal models and human patients. We hypothesized that the epileptogenic circuit for the initiation of seizures was distributed throughout the limbic system with a possible central synchronizing process. In vitro studies showed that multiple limbic sites in epileptic animals (hippocampus, entorhinal cortex, piriform cortex and amygdala) have epileptiform changes with prolonged depolarizations and multiple superimposed action potentials. In vivo studies revealed that thalamic stimulation yields short latency excitatory responses in the entorhinal cortex and hippocampus. In addition, in epileptic animals, thalamic stimulation caused epileptiform responses in the hippocampus. Based on the findings of this study and on previous anatomy and physiology reports, we hypothesize that the process of seizure initiation involves broad circuit interactions involving multiple independent limbic structures, and that the midline thalamus may act as a physiological synchronizer. We offer a new proposal for the functional anatomy of limbic epilepsy that takes widespread hyperexcitability in the limbic system and the potential for thalamic synchronization into consideration.

Animals↗

PubMed2002

Neuropathological changes in a mouse model of progressive myoclonus epilepsy: cystatin B deficiency and Unverricht-Lundborg disease.

Progressive myoclonus epilepsy of the Unverricht-Lundborg type (EPM1) is a recessively inherited neurodegenerative disease caused by loss-of-function mutations in the gene encoding cystatin B, a cysteine protease inhibitor. Mice with disruptions in this gene display myoclonic seizures, progressive ataxia, and cerebellar pathology closely paralleling EPMI in humans. To provide further insight into our understanding of EPM1, we report pathological findings in brains from cystatin B-deficient mice. In addition to confirming the loss of cerebellar granular cell neurons by apoptosis, we identified additional neuronal apoptosis in young mutant mice (3-4 months old) within the hippocampal formation and entorhinal cortex. In older mutant mice (16-18 months old), there was also gliosis most marked in the presubiculum and parasubiculum of the hippocampal formation, as well as the entorhinal cortex, neocortex, and striatum. Furthermore, widespread white matter gliosis was also noted, which may be a secondary phenomenon. Within the cerebral cortex, cellular atrophy was a prominent finding in the superficial neurons of the prosubiculum. Finally, we show that mutant mice in either a "seizure-prone" or "seizure-resistant" genetic background display similar neuropathological changes. These findings indicate that neuronal atrophy is an important consequence of cystatin-B deficiency independent of seizure events, suggesting a physiological role for this protein in the maintenance of normal neuronal structure.

Animals↗

PubMed1991

Innervation of Entorhinal Principal Cells by Neurons of the Nucleus Reuniens Thalami. Anterograde PHA-L Tracing Combined with Retrograde Fluorescent Tracing and Intracellular Injection with Lucifer Yellow in the Rat.

The innervation of dendrites of identified entorhinal principal cells by fibres originating in the nucleus reuniens thalami was studied in the rat. The lectin Phaseolus vulgaris-leucoagglutinin (PHA-L, anterograde tracer) was injected into the nucleus reuniens and the fluorescent dye Fast Blue (retrograde tracer) into the hippocampus. After survival, perfusion-fixation and the preparation of brain slices, entorhinal neurons retrogradely labelled with Fast Blue were intracellularly injected with the dye Lucifer yellow to introduce a specific marker into their dendrites. The transported PHA-L and the injected Lucifer yellow were visualized through dual peroxidase immunohistochemistry. Varicosities on PHA-L labelled reuniens fibres abut ascending and descending Lucifer yellow-filled secondary dendrites of multipolar and pyramidal principal entorhinal neurons that possess either spiny or sparsely spiny dendrites, but they do not appose the perikarya of these cells. In the electron microscope, PHA-L labelled boutons in the entorhinal cortex were observed forming asymmetrical synaptic contacts with dendritic spines (50%) or shafts (50%). The results indicate that direct thalamic input occurs on dendrites of neurons in the entorhinal cortex which project to the hippocampus.

Journal Article↗

PubMed1989

Neuropeptide Y-containing neurons in the human infant hippocampus.

Using immunohistochemistry, high concentrations and widespread distribution of neuropeptide Y-immunoreactive (NPY-IR) neurons were found and examined in each region of the hippocampal formation from birth to 42 years. NPY interneurons are particularly numerous in the stratum oriens of the CA1 subfield, in the deep layers of the subicular complex and entorhinal cortex. They are multipolar round, ovoid or triangular or bipolar and fusiform. There is a dense network of NPY-IR nerve fibers in the subicular complex and the entorhinal cortex. In addition, numerous NPY-IR nerve cell bodies and fibers are observed in the angular bundle and the adjacent white matter and this contrasts with the absence of NPY immunoreactivity in the fiber tracts of the alveus. These NPY-IR neurons which correspond to the interstitial neurons of the white matter, have the morphology and the size of the interneurons detected in the cortex. During the postnatal brain growth spurt which corresponds to the phase of rapid myelination, there is no decline in total number of NPY-IR neurons but there is a decrease in density. They have been spread apart by the growth of the rest of the tissue. So in humans, the total number of NPY nerve cell bodies in the hippocampal system, firmly established at birth, is not modified during consequent brain growth which continues until ages 3-4 years and stays stable at least until age 42 years.

Adult↗

PubMed1995

Limbic effects of repeated electroconvulsive stimulation on neuropeptide Y and somatostatin mRNA expression in the rat brain.

The aim of this study was to determine the effect of repeated electroconvulsive stimulation (ECS) on the expression of neuropeptide Y (NPY) and somatostatin (SS) mRNA in the rat brain. For that purpose, quantitative in situ hybridization histochemistry and RNA blot analysis were used. In the hippocampal formation the prevalence of NPY mRNA positive neurons increased in the hilus of the dentate gyrus and the CA3 while a decrease was seen in layers II-III of the entorhinal cortex. In contrast, SS mRNA was increased in the granule cells of the dentate gyrus and in most neurons of the outer parts of the layer III in the entorhinal cortex with cell bodies of perforant pathway projections to the hippocampal CA1 region. Both NPY and SS mRNA expressing neurons were increased in numerical density in the prefrontal cortex with similar amounts of mRNA in individual NPY positive neurons after the stimulations while SS mRNA levels decreased in hybridization positive neurons. In the striatum the only observed significant effect was an increased prevalence of NPY mRNA positive neurons in the caudal nucleus accumbens. Our results provide an outline of a complex functional anatomy of ECS in the rat brain. This type of investigations contributes to map the neuronal systems involved in the action of ECT used in the treatment of affective and schizophrenic disorders.

Animals↗

PubMed1990

Castration enhances expression of glial fibrillary acidic protein and sulfated glycoprotein-2 in the intact and lesion-altered hippocampus of the adult male rat.

This study concerns effects of the testes on two macromolecules in the rat hippocampus that were previously not known to be responsive to this endocrine axis. Castration for 3 weeks elevated the expression of glial fibrillary acidic protein (GFAP) and sulfated glycoprotein-2 (SGP-2) in male rat hippocampus, as shown by Northern blots and immunocytochemistry. SGP-2 mRNA was colocalized with GFAP, implying increased prevalence in astrocytes after castration. During hippocampal responses to deafferentation by entorhinal cortex lesions that damage the perforant path and induce synaptic reorganization, both mRNA and protein for SGP-2 and GFAP increase. Moreover, prior castration had an additive effect with entorhinal cortex lesions in the increase in GFAP and SGP-2 mRNA. These data suggest that testicular hormones regulate hippocampal astrocyte activity in intact adult rats as well as during synaptic reorganization in response to deafferenting lesions.

Animals↗

PubMed1976

Efferent connections of the basolateral amygdaloid part to the archi-, paleo-, and neocortex in dogs.

Small electrolytic lesions were placed in the basal and lateral amygdaloid nuclei of the dog and the distribution of degenerating fibers was studied with Nauta and Fink-Heimer modifications of the impregnation methods. Degenerating axons were followed into the hippocampal region and entorhinal cortex as well as insular and temporal cortices. The present results suggest that: (i) The hippocampal region receives projections from the basal parvocellular and basal magnocellular nuclei; (ii) the entorhinal cortex from the lateral and basal parvocellular nuclei; (iii) the insular cortex, cortex of the anterior ectosylvian and sylvian gyri, and to a smaller degree the claustrum, from the lateral and basal magnocellular nuclei; (iv) the temporal cortex of the posterior suprasylvian gyrus from all nuclei of the basolateral part of the amygdala. It is concluded that the basolateral part of the amygdala in the dog has a complex and highly developed connections with the archi-, paleo- and neocortex.

Amygdala↗

PubMed1984

Regulation of axonal ingrowth into area dentata as studied by sequential, double intraocular brain tissue transplantation.

The anterior eye chamber was used as a model environment to study, in isolation, the interaction of embryonic area dentata transplants with transplants of one of three important sources of in situ innervation: entorhinal cortex, locus coeruleus or septal nuclei. None of these brain regions significantly affected the morphogenesis or in oculo growth of area dentata transplants. All three brain regions innervated the area dentata transplant. Entorhinal cortical transplants sent nerve fibers into a limited, and apparently specific, region of area dentata that was adjacent to the entorhinal transplant. This light innervation contrasts to the predominant innervation of area dentata by entorhinal cortex in situ. The fluorescent, noradrenergic neurons of locus coeruleus provided the area dentata transplant with an abundance of fine varicose nerve fibers. Given about 100 noradrenergic neurons in the locus coeruleus transplant and 4 to 6 months joint survival, the area dentata transplant was noradrenergically hyperinnervated. The cholinergic neurons of the septal nuclei transplant had a prolific ingrowth of acetylcholinesterase (AChE)-positive nerve fibers to the area dentata transplant. There appeared to be a mutual exclusion between the extrinsic AChE-positive fibers and the intrinsic Timm's-positive granule cell mossy fibers in the area dentata transplant. We conclude that isolated replicas of the coeruleo-, septo-, and entorhinal cortico-dentate pathways can be made through sequential intraocular double grafting. The nature of the in oculo connectivity between these replicates offers clues as to the mechanisms that might account for the regulation of nerve growth.

Animals↗

PubMed1981

Conditioned emotional response after dorsohippocampal, ventrohippocampal or entorhinal cortical lesions in rats.

Acquisition and extinction of the conditioned emotional response (CER) was studied in 24 male hooded rats which, prior to training, received small electrolytical lesions in the dorsal hippocampus, the ventral hippocampus, the entorhinal cortex, or were given sham operations. The rate of the on-going bar-pressing behavior for food pellets was highest in rats with lesions in the ventral hippocampus and the lowest after lesions in the entorhinal cortex. CER acquisition was markedly retarded and suppression was the weakest only in rats with dorsal hippocampal lesions. When compared with the level of suppression established toward the end of training, the greatest resistance to extinction of the CER was observed after entorhinal cortical lesions. The results of the experiment indicate functional heterogenity of the hippocampal formation.

Animals↗

PubMed1977

Histochemical evidence of altered development of cholinergic fibers in the rat dentate gyrus following lesions. I. Time course after complete unilateral entorhinal lesion at various ages.

The entorhinal cortex of rats was removed at various times during development, and the reaction of the cholinergic septohippocampal input to the dentate gyrus was examined by use of acetylcholinesterase histochemistry. When the ipsilateral entorhinal cortex is completely removed, the outer 70-75% of the molecular layer of the dentate gyrus is almost completely denervated. After such a lesion at 5 to 33 days of age, the acetylcholinesterase staining initially intensified throughout the denervated area, indicating that the septohippocampal fibers branched or elongated. This reaction could be detected within one day after a lesion at 11 days of age and within three or five days after lesions at earlier or later times. Whereas the initial response of the septohippocampal fibers was independent of the age at which the lesion was made, their final localization depended on the developmental state of the animal. After lesions at the age of 5 or 11 days, the reactive septohippocampal fibers became restricted to the outer one-sixth to one-third of the molecular layer within two days after appearance of their initial reaction. A similar concentration of reactive fibers was demonstrable after lesions at 16, 18 or 21 days of age, but some reaction persisted in the middle third of the molecular layer. Finally, after lesions at 26 or 33 days of age the proliferating cholinergic fibers ultimately were uniformly distributed throughout the outer 60% of the molecular layer. These results suggest that septohippocampal fibers initially extend or sprout throughout the denervated area to replace the lost perforant path fibers. However, the reactive fiber population becomes restricted to the outer edge of the molecular layer if the entorhinal lesion is made before the period of cholinergic synaptogenesis and concentrates in this same zone if it is made while cholinergic synapses are forming. We suggest that either the proliferative reaction continues in the outer part of the molecular layer and subsides in other parts of the denervated area or septohippocampal fibers move outward through the molecular layer to assume a more superficial location. After entorhinal lesions at 16 days of age or later the pale-staining zone (containing fibers that originate in hippocampus regio inferior) immediately deep to the denervated area widened. If the lesion was made earlier, this zone never developed at most septotemporal levels of the dentate gyrus. These results are probably related to the extension of regio inferior fibers into the denervated area.

Acetylcholinesterase↗

PubMedDate not supplied

Prenatal ethanol exposure decreases hippocampal 3H-vinylidene kainic acid binding in 45-day-old rats.

The effect of prenatal ethanol exposure on the kainate-sensitive subtype of glutamate receptor binding sites was studied using in vitro 3H-vinylidene kainic acid (VKA) autoradiography. Pregnant Sprague-Dawley rats were fed a liquid diet containing either 3.35% or 6.7% ethanol throughout gestation. Pair-fed dams received isocalorically matched liquid diets and a lab chow ad lib group served as control for paired feeding. At 45 days of age, the offspring were sacrificed and their brains analyzed for specific 3H-VKA binding. Compared to pair-fed controls, specific 3H-VKA binding was reduced by 13% to 32% in dorsal and ventral hippocampal CA3 stratum lucidum, entorhinal cortex and cerebellum of 45-day-old rats whose mothers consumed either 3.35% or 6.7% ethanol diets. The binding site reductions were statistically significant only in the ventral hippocampal formation and entorhinal cortex of the 3.35% ethanol diet group rats. Saturation of binding studies in the ventral hippocampal formation of 3.35% ethanol rats indicated that the decrease in specific 3H-VKA binding was due to a decrease in the total number of binding sites. Given the excitatory effect of kainic acid on the spontaneous firing rate of hippocampal CA3 pyramidal neurons, the reduction of kainate-sensitive glutamate binding in this region is consistent with the electrophysiological observation of decreased spontaneous activity of CA3 pyramidal neurons in fetal alcohol rats.

Alcoholism↗

PubMed2005

The temporal context model in spatial navigation and relational learning: toward a common explanation of medial temporal lobe function across domains.

The medial temporal lobe (MTL) has been studied extensively at all levels of analysis, yet its function remains unclear. Theory regarding the cognitive function of the MTL has centered along 3 themes. Different authors have emphasized the role of the MTL in episodic recall, spatial navigation, or relational memory. Starting with the temporal context model (M. W. Howard & M. J. Kahana, 2002a), a distributed memory model that has been applied to benchmark data from episodic recall tasks, the authors propose that the entorhinal cortex supports a gradually changing representation of temporal context and the hippocampus proper enables retrieval of these contextual states. Simulation studies show this hypothesis explains the firing of place cells in the entorhinal cortex and the behavioral effects of hippocampal lesion in relational memory tasks. These results constitute a first step toward a unified computational theory of MTL function that integrates neurophysiological, neuropsychological, and cognitive findings.

Humans↗