SEARCH · PubMed Health

Results for “Hippocampus”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources

PubMed1979

Functional reinnervation of rat hippocampus by locus coeruleus implants.

Transplants of the embryonic locus coeruleus (LC) region were implanted into the circuity of the hippocampal formation in adult rats in which the normal adrenergic afferents to the hippocampus had been removed. The growth of new adrenergic axons from the implant in the denervated hippocampus was followed for 1-14 months after surgery by means of fluorescence histochemistry, and the function of the implant-hippocampal connections was tested electrophysiologically after 2-3 months survival. In the successful cases the entire hippocampal formation was reinnervated from the LC implant within 3-6 months after operation, and the newly formed innervation still persisted unchanged by 14 months. The reinnervation was equally effective irrespective of the route by which the axons entered the hippocampus, i.e. along the lesioned fornix-fimbria or along a retrosplenial route. The pattern formed by the ingrowing LC axons mimicked to a large extent that of the normal LC afferents. Little growth was seen into denervated terminal fields of the commissural, septal or entorhinal afferents, pointing to a preference of the ingrowing LC fibers for the areas normally innervated by adrenergic afferents. In the electrophysiological experiments, stimulation of the LC implants caused (in 20 out of 29 cells monitored) an inhibition of the spontaneous activity of neurons in the host hippocampus. This inhibition had a relatively long latency and a long duration, similar to that observed after stimulation of the innate LC in the intact rat. As in the normal rat, the inhibitory responses were blocked by systemic or local application of the beta-adrenergic receptor blockers propranolol or sotalol. It is concluded that the adult rat brain is capable of carrying out all steps involved in correct functional reinnervation of a denervated region. Moreover, the implant-hippocampal preparation should be a highly suitable model system for functional studies of a central noradrenergic connection.

Adrenergic Fibers↗

PubMed1979

Accumulation of apomorphine in caudate nucleus and hippocampus of the rabbit.

Apomorphine concentration was assayed in the caudate nucleus, hippocampus and cerebellum of rabbits injected with various doses of the drug 30 min earlier. Apomorphine accumulation was dose-dependent but uneven in the structures tested: the accumulation in the caudate nucleus being approx. 5 times higher than in cerebellum. Pretreatment with haloperidol significantly depressed the accumulation of apomorphine in the caudate nucleus and hippocampus, but not in the cerebellum. The amount of apomorphine displaceable by haloperidol was approx. 10 times higher in the caudate nucleus than in the hippocampus. The results suggest the existence of small number of apomorphine binding sites in the hippocampus.

Animals↗

PubMed1979

A comparison of the glucocorticoid receptor in cytosol from rat liver and hippocampus.

The [3H]corticosterone- and [3H]dexamethasone-binding proteins in cytosol from liver and hippocampus of the rat were compared by isoelectric focusing analysis in slabs of polyacrylamide gel. A single peak of radioactivity with a pI of 6.1--6.2 was obtained during analysis of cytosol from both liver and hippocampus using either corticosterone or dexamethasone as radiolabelled ligand, provided the tissue was carefully perfused with buffer prior to preparation of cytosol. Rat serum or insufficiently perfused tissue contained a corticosterone-binding component with pI of 5.2--5.5 representing corticosteroid-binding globulin. Limited trypsin digestion resulted in fragmentation of the dexamethasone- and corticosterone-binding protein in cytosol from liver and hippocampus. Incubation of radiolabelled cytosol with 0.5 microgram of trypsin/A280--310nm of cytosol gave a sharp radioactive peak with a pI of 5.9--6.1 when analyzed by isoelectric focusing; when 5.0 microgram of trypsin/A280--310nm of cytosol was used, a double peak with pI values of 5.9--6.1 and 6.3--6.5, respectively, was seen. The same trypsin-induced peaks were seen with both [3H]dexamethasone and [3H]corticosterone as ligands. The substrate specificity and the sensitivity of this glucocorticoid binder for limited trypsin digestion is in good agreement with what was previously found for the glucocorticoid receptor in rat liver cytosol. It is concluded that cytosol from liver and hippocampus contains an identical or very similar receptor for glucocorticoid hormones.

Animals↗

PubMed1977

Age-dependent changes in the oxygen consumption of the cerebral cortex, hypothalamus, hippocampus, and amygdaloid in rats.

The oxygen consumption of the cerebral cortex, hypothalamus, hippocampus, and amygdala, of both sexes, ranging in age from 21-805 days for male rats and from 21-780 days for the estrus and diestrus female rats, was measured. The oxidative activity of the hypothalamus, hippocampus, and amygdala decreased rapidly from Day 21 until the 4th mo. and stabilized till the 27th mo. in the hippocampus and amygdala and gradually decreased from the 12th mo. to the 27th mo. in the hypothalamus. The cerebral cortex showed a different pattern which kept a constant level from day 21 to 12 mo. of age. There was no statistically significant change in any of the regions at the time of vaginal opening. Low oxidative activity of the hypothalamus and amygdala in old age was still observed in castrated/hypophysectomized male rats compared with young ones. Therefore, the decreased oxygen consumption in old age seems to be due primarily to changes in the brain tissue itself and not due secondarily to changes in the gonadotropin and sex hormone levels. Female rats had higher oxygen consumption values than males in the cerebral cortex, the hypothalamus, and the hippocampus. In the amygdala the males had a higher consumption. Estrus female rats showed significantly higher oxygen consumption than diestrus females only in the hypothalamus.

Aging↗

PubMed1979

Functional relationships between the hippocampus and the cerebellum: an electrophysiological study of the cat.

1. Functional interrelationships between the hippocampus and the cerebellum have been investigated in the anaesthetized cat. Plots of the stimulating and recording sites as well as the latency range of the responses indicated the extent of ascending and descending lines of operation between these two structures. 2. Stimulation of the fastigial nucleus evoked the discharge of single hippocampal units on both sides of the brain. Early responses had a mean latency of 12 msec and late responses had a mean latency of 21 msec. Increasing the intensity of the stimulus had little effect on the patterns of discharge. 3. There was no topographical organization within the hippocampus. On the other hand, the activity evoked by a cutaneous stimulus was shown to be greatly depressed by a preceding cerebellar stimulus, particularly at intervals 30--40 msec between the two stimuli. 4. Cerebellar responses evoked by stimulating the hippocampus were found mainly in lobule VI of the posterior lobe. Early and late responses were frequently recorded in the same trace, ipsilateral stimulation yielding the shortest latencies. Increasing the intensity of the stimulus increased the likelihood of there being a response and increased the number of spikes in each discharge. Hippocampal stimulation also had a profound influence on resting cerebellar discharges. 5. Symmetrical points in the two hippocampi were chosen for conditioning and testing sequences. The conditioning stimulus had a long-lasting inhibitory effect on the test response followed by a slow recovery. 6. The location and extent of hippocampal influences on the cerebellum were determined by plotting the presence or absence of a response at each stimulated site. The results indicated the existence of bilateral descending projections containing fast and slow components in conformity with the known conduction properties of mossy fibre and climbing fibre inputs. 7. The physiological significance of interrelationship between the hippocampus and the cerebellum is discussed. It seems that there are many similarities as well as fundamental differences in the cerebellar control of movement under normal circumstances and in conditions of stress.

Animals↗

PubMed1976

Effect of electrical stimulation of the hippocampus upon corticosteroid levels in the freely-behaving, non-stressed rat.

The influence of the hippocampus upon pituitary release of adrenocorticotropic hormone (ACTH) was studied in male Sprague-Dawley rats which had concentric bipolar stainless stell electrodes chemically implanted in the dorsal and ventral hippocampus. Blood samples were withdrawn at half-hour intervals from a cannula in the right atrium. Plasma corticosterone levels reflected ACTH release. 30 min of 25 or 250-cps electrical stimulation of the hippocampus in the freely-behaving, non-stressed rat resulted in significant increases in basal plasma corticosterone levels evident at the end of stimulation. In afternoon experiments, after stimulation at either hippocampal site with 25 cps only, the increase was followed by a delayed inhibitroy phase and temporary inhibition of the circadian rise in corticosterone levels. The inhibitory effect was more pronounced with ventral than with dorsal hippocampal stimulation. The basis for these differential effects is discussed in terms of the anatomical organization of the hippocampus.

Adrenal Cortex↗

PubMed1992

Electrical stimulation-evoked release of endogenous taurine from slices of the hippocampus, cerebral cortex and cerebellum of the rat.

Release of endogenous taurine by electrical stimulation of slices of the hippocampus, cerebral cortex, cerebellum and medulla oblongata of the rat was studied and compared with that of alanine and/or gamma-aminobutyric acid (GABA). Electrical stimulation caused a calcium-dependent release of taurine from slices of the hippocampus, cerebral cortex and cerebellum but not from slices of the medulla oblongata. The stimulus-evoked release of taurine in the hippocampus was rapid in onset and declined to baseline fast, which was essentially similar to the time course pattern of the stimulus-evoked release of GABA. In addition, there were distinct regional differences in the relative amounts of taurine released. Electrical stimulation did not release alanine from any regions examined. These results support the hypothesis that taurine plays a neurotransmitter role in the hippocampus, cerebral cortex and cerebellum of the rat.

Alanine↗

PubMed1992

[Guiding effect of embryonic fimbria graft on cholinergic fiber growth in hippocampus of adult rats].

In view of the fact that in embryonic and neonatal central nervous system (CNS), the pathway of developing fiber tracts is capable of guiding the axonal growth, it would be interesting to know whether a similar effect exists on the axonal growth in adult CNS. Embryonic fimbria was grafted into the hippocampus of the adult rat. Two weeks later, the grafts were examined for cholinergic fibers with AChE histochemical method. It was found that a lot of cholinergic fibers appeared in the embryonic graft, but none of them in the adult fimbria graft as control. If the fimbria-fornix was transected at the time of grafting, no cholinergic fibers could subsequently be detected in both the embryonic graft and the host hippocampus. If a suspension of embryonic fimbria was used as a graft, only a few of long cholinergic fibers could be found in the grafted area. However, if tissue fragments of embryonic fimbria adhered to a strip of nitrocellulose filter were grafted as previously, numerous cholinergic fibers from the host hippocampus were found to be attracted around the strip and grow along the surface of the filter. The results seem to indicate that grafted embryonic fimbria or its tissue fragments are able to guide cholinergic fiber growth in adult hippocampus. It is possible that embryonic fimbria and other pathways of developing CNS fiber tracts provide a natural substrate for guiding axonal growth in adult CNS.

Acetylcholine↗

PubMed1977

Stimulation of the hippocampus and its effect on electrographic manifestations of the brain in unrestrained rats.

The dorsal hippocampus was electrically stimulated in unanaesthetized, unrestrained rats with a cobalt-gelatin rod in their cortex. The significance of the hippocampus in the elicitation of both physiological spontaneous rhythmic activity (episodic activity of 8--9/sec frequency bound, in rats, to a state of quiet wakefulness, and "sleep spindles") and pathological rhythmic activity of the self-sustained after-discharge (SSAD) type was determined from the aspect of the EEG and behavioural characteristics. 1. Single electrical pulses (0.1 msec, 1--10 V, 0.3/sec) elicited an evoked potential bilaterally in the somatosensory cortex. Elicitation of rhythmic after-activity (of the type of episodes or sleep spindles) was observed only in some cases in which an adequately strong stimulus was used. 2. Repeated series of rhythmic electrical stimuli following each other at short intervals (2--3 min) led to the formation of SSAD in about one third of the cases and at all stimulation frequencies (3-15/sec), although low frequencies (3--4/sec) were the least effective. The character of the SSAD and simultaneous behavioural phenomena differed fundamentally from those evoked by electrical stimulation of the thalamus (Chocholová et al. 1977). The development of paroxysmal after-activity was signalled by responses of a more or less distinct "recruiting" character during stimulation. On the basis of a comparison of electrographic and behavioural manifestations after electrical stimulation of the thalamus and hippocampus, the possibility of both thalamic and extrathalamic projection from the hippocampus to the cortical region is considered.

Animals↗

PubMedDate not supplied

[Effect of pheprazet and its alkylated analogs on the neuronal populations of the dorsal and ventral portions of the hippocampus].

The action of pheprazet, a derivative of amphethamine, and of the pheprazet alkylated analogues on the excitability of the neuron populations in the dorsal and ventral parts of the hippocampus was studied in non-anesthetized rabbits with electrodes and chemotrodes indwelt in the hippocampus and other brain structures. Most active drugs are shown to be pheprazet and (formula: see text). The former affects the beta- and the latter the alpha-adrenoreceptors of the hippocampus. Pheprazet pre-eminently increases while the drug (see formula: see text) reduces the excitability of the neuron populations in the dorsal and ventral parts of the hippocampus. The opposite effects of these drugs are considered by authors from the standpoint of interaction between different mediator systems.

Amphetamines↗

PubMedDate not supplied

[Role of the hippocampus in conditioned reflex activity].

The role of the hippocampus in animals' conditioned activity was studied in experiments on rats and cats with ablated hippocampus. It was shown that in rats the ablation leads to a statistically significant slowing down in learning of the avoidance reaction. The effect becomes stronger in stress situation. The process of learning and optimization of choice reaction in the maze with alimentary reinforcement if sharply impaired in rats with bilateral ablation of hippocampus. The bilateral ablation of the hippocampus in cats in experiments with choice of the side of the alimentary reinforcement prolonged the latencies and sharply increased the number of erroneous reactions. The obtained data are analyzed in terms of fronto-pallido-hippocampal system, which selects, compares and integrates sensory information at the stage of the afferent synthesis.

Animals↗

PubMedDate not supplied

Interaction of morphine and 5-hydroxytryptamine in the raphe-hippocampus system.

In order to describe the interaction of morphine and 5-hydroxytryptamine (5-HT) in the raphe-hippocampus system we tested the influence on the antinocifensive effect of topic administrations of morphine and serotonergic substances into the dorsal hippocampus and the median raphe nucleus in rats. 5-HT administered into the dorsal hippocampus increased the morphine analgesia. Lysergic acid diethylamide injected into the raphe nucleus antagonized the morphine effect. Morphine given into the raphe nucleus was highly effective, while its injection into the striatum was ineffective. The effect of the intrahippocampal morphine was antagonized by methysergide. The results indicate the important role of the serotonergic raphe-hippocampus system in the mechanism of the morphine analgesia.

Animals↗

PubMed1979

Two types of epileptic cortical after-discharges evoked by the stimulation of the hippocampus and thalamic nuclei in rats.

Rhythmic cortical phenomena were evoked by stimulation of hippocampus and/or thalamus in rats. Electrical stimulation of thalamic nuclei (nc. ventralis dorsomedialis VDM and nc. lateralis anterior--LA) by single pulses elicited rhythmic after-discharge ("spindle") as a late component of the cortical response, whereas identical stimulation of hippocampus did not trigger such an activity. Rhythmic stimulation of thalamic nuclei elicited cortical incremental responses more often than stimulation of hippocampus. Epileptic self-sustained after-discharges (AD) occurred after the endo of rhythmic stimulation in 66% of hippocampal stimulations, in 35% of VDM stimulations and in 30% of LA stimulations. AD evoked by stimulation of the hippocampus (long duration discharges of slow serrated waves) differed characteristically from AD following stimulation of the VMD (short duration spike and wave complexes). Stimulation of the LA in half of the cases led to the "hippocampal" pattern of serrated wave after-discharges, in the remaining cases spike-and-wave complexes or a combined AD pattern was recorded.

Animals↗

PubMed1978

A Golgi study of cell types in the hilar region of the hippocampus in the rat.

The morphology of neurons in the "hilar region" of the hippocampus (fields CA3c and CA4 of Lorente de Nó, '34) was analyzed with several variants of the Golgi technique. Hippocampi were dissected from the brains of 28-day-old rats, fixed and impregnated by immersion, and sectioned perpendicular to the long axis. Based on the resident cell types, aspects of the neuropil, and published data related to afferent termination, the area under study was divided into four zones. At least 21 cell types were observed throughout these zones, several of which had not previously been described. Many cells in this area exhibited an impressive number and variety of dendritic and axonal appendages, including spines on the proximal portion of some axons. The close apposition of fibers to these axonal spines suggested the possibility of axo-axonal interactions. The influence of dentate granule cells, through their mossy fibers, on the synaptic economy of the "hilar region" was found to be more extensive than previously reported. Mossy fibers appeared to terminate on the dendrites of several types of non-pyramidal cells, which bear no thorny excrescences, by means of thin filiform extensions which emanate from the mossy fiber expansions and by means of thin mossy fiber collaterals which are devoid of typical expansions. Consideration is given to a long-standing debate as to whether the deep "hilar region" (CA4 of Lorente de Nó, '34, hilus of the fascia dentata of Blackstad, '56) is related more to the hippocampus or to the fascia dentata and it is concluded that the deep hilar region is an area of mergence of the polymorphic zones of these two cortical structures. The results of the present study do not support the proposition that the deep hilar region is an extension of the pyramidal layer of the hippocampus as suggested by Lorente de Nó ('34), and thus CA4 is a misnomer. Rather, the cells in this area are most closely related to the fascia dentata and should thus be considered to lie in the polymorphic zone of "area dentata" as proposed initially by Blackstad ('56).

Animals↗

PubMed1979

Proliferative and migratory activity of glial cells in the partially deafferented hippocampus.

The proliferative response of the glial cell population of the adult rat hippocampus deafferented by unilateral lesion of the entorhinal cortex was studied using 3H-thymidine autoradiography. Two experimental paradigms were used, involving: (1) intraventricular 3H-thymidine injection at a number of post-lesion intervals with sacrifice six hours later and (2) intraventricular injection at 30 hours post-lesion with sacrifice at 6, 96, or 192 hours later. The first increase in the number of labeled glial cells was obtained at 20 hours post-lesion and was confined to areas of degenerating axons. By 30 hours a large and uniformly dense proliferative response was observed throughout the ipsilateral, and medial aspects of the contralateral, hippocampus encompassing both deafferented and intact regions. Cell division continued through 50 and 65 hours post-lesion particularly in directly deafferented regions, but diminished to control levels by 80 hours. Although oligodendroglia and astrocyte-like cells were sometimes found to have incorporated the label the most common proliferative element within the hippocampus corresponded to previous light microscopic descriptions of "microglial" cells. The experiments using thymidine injection given at the peak proliferative period followed by survival periods of varying lengths indicated that a progressive redistribution of labeled nuclei occurred resulting in an accumulation of labeled cells in the zones of deafferentation. Multiple division of cells within these areas as well as the migration of nuclei from non-deafferented regions was found to contribute to this effect. The possible involvement of glial proliferation with other morphological effects of deafferentation, including the sprouting response of intact afferents, is discussed.

Animals↗

PubMed1992

Fast (beta) rhythms in the hippocampus: a review.

Spontaneous or evoked brain activity in the hippocampus showed a 20-70 Hz beta rhythm under some conditions, typically during behavioral activation and accompanied by a theta rhythm. Beta rhythms are generated locally, perhaps by a recurrent feedback loop involving pyramidal cells and inhibitory interneurons. Modulation of the local circuit and rhythm by cholinergic inputs has also been demonstrated. Under some behavioral states, neural impulses modulated at the beta frequency may transmit preferentially through the trisynaptic circuit in the hippocampus. It is suggested that the beta rhythm may serve to establish transient physiological connections, reflected in coherence at the beta frequency, among neurons in the hippocampus and related structures. Thus, the beta rhythm may play an essential role in hippocampal function.

Animals↗

PubMed1977

Regional properties of dorsal and ventral hippocampus in suppression of intralaminar thalamic unit responses.

In chloralose-anaesthetized, Flaxedil-paralysed cats, the suppression of extra-lemniscal thalamic units by dorsal and ventral hippocampus was investigated. Unitary responses to test somatic stimuli, recorded in centrolateral and neighbouring thalamic nuclei, were interacted with conditioning electric stimulation in different regions around the hippocampal arch, including parahippocampal gyrus (entorhinal and retrosplenial areas). Stimulation of dorsal (dhc) and ventral (VHC) hippocampus suppressed roughly equal proportions of responses. However, within each of DHC and VHC, effectiveness depended on the region stimulated. In DHC, fields CA1 and CA3, subiculum (SUB), and retrosplenial area, but not field CA4 or dentate gyrus, usually suppressed extralemniscal units at currents below 1.0 mA. In VHC, the most effective regions were entorhinal cortex, CA3, and CA4 with dentate gryus (FD), while stimulation of CA1 or subiculum was almost ineffective, at currents below 1.0 mA. In VHC, the regions were ranked for effectiveness: Entorhinal cortex=CA3 is greater than FD is greater than SUB is greater than CA1. No topographic relationship was found between hippocampal region and thalamic loci for unit suppression. Lemniscal-type unit responses in ventrobasal thalamus were unaffected by stimulation of the hippocampus or parahippocampal gryus. Interruption of the fornix-fimbria system prevented suppression elicited from CA1 of DHC, or from CA3 but not FD of VHC. It had no effect on suppression elicited from retrosplenial or entorhinal cortex. Hippocampal regional variation of effectiveness in suppressing extralemniscal pathways may contribute to the differential behavioural involvements reported for different hippocampal structures.

Animals↗

PubMed1977

Some enzyme histochemical characteristics of the human hippocampus.

The histochemical distribution of acetylcholinesterase (AChE) and alpha-glycerophosphate dehydrogenase (alpha-GPDH) was studied in the area dentata and hippocampus proper of the human brain. Although differences did exist, there were many features in common with the distribution of these two enzymes in the rat and guinea pig. The laminar chemoarchitectonic picture was not as distinct in the human brain as in the rat and guinea pig. Most of the AChE reaction products were confined to the neuropil, with the strongest staining intensity in supra- and infrapyramidal zones. The layer of mossy fibres (stratum lucidum), was characteristically pale. On the other hand, AChE-positive cell bodies were observed in the hilus of the area dentata and a few scattered cells in the hippocampus proper. The AChE reaction products were sparse in the pyramidal cells, conforming similar observations in the rat and guinea pig. Based on our previous description of the AChE-positive cell bodies and fibres in the human septum and a considerable body of experimental material obtained in the rat, it is suggested that most of the AChE in the dentate area and the hippocampus proper is confined to terminals of cholinergic septal efferents in both man and other species. alpha-GPDH was particularly reactive in the cell layers, hilus fasciae dentatae and the layer of mossy fibers. These observations are similar to those described for the rat and guinea pig. They indicate, furthermore, a particular metabolic property common to the archicortex of man and other species.

Acetylcholinesterase↗