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C Leranth

Publications and source records attributed to C Leranth.

At least 91 records · Page 5Linked to original sources
PubMed1992

Identification of neuronal connections by means of electron microscopic immunocytochemistry.

For many years neuroanatomical research has focused on the tracing of connections between populations of neurons in the central nervous system. With the development of immunocytochemical procedures employing antibodies against transmitters, transmitter-synthesizing enzymes and various neuropeptides, it has become possible to study the chemical characteristics of nerve cells. By combining tracer techniques and immunocytochemical approaches the transmitter identity of a projection can be determined. Moreover, electron microscopic double-labeling procedures allow the identification of the target cells of immunocytochemically characterized presynaptic terminals. This way, by the immunocytochemical identification of transmitters or neuropeptides in defined projection neurons, a more functional interpretation of neuroanatomical data has become possible. In the present report, these combinations of techniques are demonstrated by describing recent studies of cholinergic septohippocampal projection neurons.

Animals↗
PubMed1991

Synaptology and origin of somatostatin fibers in the rat lateral septal area: convergent somatostatinergic and hippocampal inputs of somatospiny neurons.

This study deals with the synaptology, morphologically identified postsynaptic targets, and origin of somatostatin (SOM) fibers in the rat lateral septal area (LSA) with special reference to those forming pericellular baskets. Septal vibratome sections were immunostained for SOM-14 in 3 experimental groups: control animals, rats subjected to a chronic transection of the ascending afferents to the septum, and animals with acute fimbria-fornix lesion. Light microscopy revealed that the SOM-immunoreactive fibers form pericellular baskets predominantly in the intermediate and ventral parts of the caudal half of the LSA. Electron microscopic analysis showed that the somatospiny neurons are postsynaptic targets of these pericellular baskets. Eight days after a unilateral cut placed at the ventral border of the septum, virtually all SOM-immunoreactive axon terminals disappeared from the ipsilateral intermediate and ventral LSA, and they were substantially reduced in the dorsal LSA. However, in these rats SOM-positive neurons could be observed in the LSA on the lesioned, but not on the contralateral side. Furthermore, on the lesion side of the anterior periventricular hypothalamus an increase was detected both in the number and the intensity of immunostaining of SOM-positive neurons. Thirty-six h following a unilateral transection of the fimbria-fornix, the SOM-immunoreactive axon terminals in the LSA remained intact; only immunonegative degenerated hippocamposeptal boutons were detected forming synaptic contacts with somatospiny neurons. Axosomatic synapses of SOM-positive boutons regularly appeared at the neck of somatic spines which were postsynaptic to degenerated hippocamposeptal fibers. The results indicate that the septal SOM fibers are of multiple origin. Those forming pericellular baskets in the LSA originate in ventral extraseptal, probably periventricular hypothalamic areas. SOM fibers scattered in the dorsal LSA are most likely processes of local SOM neurons. The accumulation of immunoreactive SOM in some cells of the undercut septum is a sign of axonal lesion, indicating that these neurons project outside the septum. The SOM innervation of somatospiny neurons which also receive hippocampal input and have been reported to contain gamma-aminobutyric acid (GABA) may be a morphological substrate of the SOM-related disinhibition in the LSA.

Afferent Pathways↗
PubMed1991

Neuropeptide Y (NPY)-immunoreactive neurons in the primate fascia dentata; occasional coexistence with calcium-binding proteins: a light and electron microscopic study.

Neuropeptide Y (NPY)-containing neurons are known to be highly vulnerable following sustained electrical stimulation in rats and in humans suffering from temporal lobe epilepsy. This has been related to a strong excitatory input. In contrast, there is evidence that neurons containing calcium-binding proteins exhibit a high resistance under experimental seizure and hypoxia conditions. The aim of this study was to determine the coexistence of NPY and calcium-binding proteins in inhibitory neurons of the primate fascia dentata and their synaptic connections. Vibratome sections of hippocampi of African green monkeys (Cercopithecus aethiops) were immunostained with antibodies against NPY, PARV, and CB. A quantitative coexistence study was performed for NPY and PARV on consecutive semithin sections. In contrast to the rodent hippocampus, NPY-immunoreactive neurons were found exclusively in the hilus of fascia dentata with horizontally oriented dendrites which did not extend into the granular and molecular layer. Conversely, PARV-immunoreactive neurons were also present in the granular and inner molecular layer and extended their dendrites far out in the molecular layer and the hilus. Axon terminals immunoreactive for NPY were mostly concentrated in the middle and outer molecular layer and the hilar region and were rare in the granular layer. PARV-immunoreactive boutons were basically restricted to the granular layer where they formed typical baskets. The antibody against calbindin stained almost exclusively granule cells. Coexistence of NPY- and PARV-immunoreactivity was found only in hilar neurons and was rare (9 out of 152 cells analyzed). These results suggest that most NPY-immunoreactive neurons do not contain calcium-binding proteins. NPY-containing neurons exhibited ultrastructural characteristics as described for inhibitory neurons. Their dendrites were only sparsely contacted by mostly asymmetric synaptic terminals, including a very small number of mossy fiber axon terminals. In turn, numerous NPY-immunoreactive axon terminals formed symmetric synapses with spines and dendritic shafts of unlabeled neurons in the middle and outer molecular layer, whereas no contact with granule cell bodies was evident. Thus, we conclude that the vulnerability of NPY-containing inhibitory neurons may be due more to the lack of calcium-binding proteins than to a strong excitatory innervation. As their axons may contribute to the inhibitory control of the major excitatory input from the entorhinal cortex, their loss following overstimulation may play a role in perpetuating hippocampal seizure activity.

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PubMed1991

Calcium-binding proteins are concentrated in the CA2 field of the monkey hippocampus: a possible key to this region's resistance to epileptic damage.

Previous immunocytochemical studies have shown a heterogeneous distribution of parvalbumin (PA) and calbindin (CB) in the rat hippocampal formation. The results of the present study showed a heterogeneous distribution of PA and CB in primate Ammon's horn. The density and intensity of immunoreactivity for both of these calcium-binding proteins was greatest in CA2 as compared to CA1 and CA3. CB-immunoreactivity was localized to the cell bodies, dendrites, and axon initial segments of pyramidal cells whereas PA-immunostaining was found in the axon terminals, dendrites and cell bodies of interneurons that have features similar to GABAergic inhibitory neurons. Based on previous studies that have shown a protective role of calcium-binding proteins in neurons exposed to hyperstimulation, these results suggest that the resistance of CA2 pyramidal cells in temporal lobe epilepsy is due to the high concentration of CB and PA in this region of Ammon's horn.

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PubMed1991

Convergent vasopressinergic and hippocampal input onto somatospiny neurons of the rat lateral septal area.

Electron microscopic immunocytochemistry, was combined with acute anterograde axon degeneration, following transection of the fimbria-fornix, to describe the innervation of somatospiny neurons by vasopressin-immunoreactive and degenerated hippocamposeptal axon terminals in the rat lateral septal area. Vasopressin-immunopositive boutons characterized by symmetric synaptic membrane specializations, and the degenerated hippocamposeptal axon terminals which form asymmetric synaptic contacts, frequently terminate on the same dendritic and somatic profiles, and particularly on the somata of somatospiny neurons. Although hippocamposeptal fibers predominantly form axospinous synapses in the lateral septal area, they terminate mainly on the dendritic shafts and soma of the vasopressin-receptive neurons. Of 720 vasopressin-immunoreactive terminals in the mediolateral part of the lateral septal area, 80% form synaptic contacts with dendritic shafts; 50% on small (distal) dendritic profiles and 30% on large (proximal) dendrites. Synaptic contacts between vasopressin-immunoreactive terminals and dendritic spines were not observed. The remaining 20% of immunoreactive boutons formed axosomatic synaptic contacts with a total of 58 neurons; 31% of these neurons exhibited somatic spines in the plane of the section analysed. Previous studies have demonstrated that in the lateral septal area vasopressin modulates the action of the excitatory amino acid-containing hypocamposeptal fibers, and also plays a role in the maintenance of long term potentiation evoked by fimbria-fornix stimulation. The convergent vasopressinergic and hippocampal input onto the same somatospiny neurons of the lateral septal area suggests that these neurons are targets of these physiological actions.

Animals↗
PubMed1991

Estrogen induces ultrastructural changes in progesterone receptor-containing GABA neurons of the primate hypothalamus.

Estrogen affects gonadotrophin levels and sex behavior in monkeys. This action could be via inhibitory GABA-ergic neurons in the hypothalamus. We tested for direct estrogen actions on such neurons. Seven days after ovariectomy (OVX) or OVX + estrogen treatment (10 mg estradiol valerate in 1 ml sesame oil s.c. on the day of OVX), light- and electron-microscopic double immunostaining procedures were used for simultaneous visualization of immunoreactivity for progesterone receptors (PR) and glutamic acid decarboxylase (GAD), and to detect ultrastructural changes in PR-containing neurons in the arcuate and ventromedial hypothalamic nuclei of colchicine- and noncolchicine-treated African green monkeys (Cercopithecus aethiops). Immunoreactivity for PR was found only in cell nuclei, and estrogen treatment enhanced the intensity of the immunostaining: in estrogen-treated monkeys in the arcuate nucleus 62%, while in the ventromedial nucleus 42% of the neurons contained PR-immunoreactive nuclei. All of the PR-containing neurons were immunopositive for GAD in colchicine-pretreated monkeys. OVX induced whorl body formation, while estrogen treatment of OVX animals resulted in a large number of nematosomes. While all of the whorl bodies and the majority of nematosomes were observed in PR-immunopositive GAD neurons, nematosomes were also found in non-PR-containing GAD-immunoreactive cells.

Animals↗
PubMed1990

Catecholaminergic, GABAergic, and hippocamposeptal innervation of GABAergic "somatospiny" neurons in the rat lateral septal area.

This study deals with the neurochemical characterization of the rat lateral septal area (LSA) somatospiny neurons and their innervation by hippocamposeptal, catecholaminergic, and GABAergic fibers. Electron microscopic single and double immunostaining methods were used to label catecholaminergic fibers and GABAergic cells and boutons. Axon terminals originating in the hippocampus were labeled by acute anterograde axon degeneration induced by fimbria-fornix transection 36 hours before sacrifice. Three types of experiments were performed. The convergent catecholaminergic and hippocamposeptal innervation of LSA somatospiny neurons was studied by combining immunostaining for tyrosine hydroxylase (TH) with fimbria-fornix transection. GABAergic neurons and their hippocamposeptal afferents were identified and characterized in colchicine pretreated animals immunostained for glutamic acid decarboxylase (GAD) combined with fimbria-fornix transection. The third experiment aimed at simultaneously visualizing the relationships between catecholaminergic boutons, hippocamposeptal excitatory amino acid containing axon terminals and GABAergic profiles by double immunostaining for TH (the PAP technique) and GAD (the immunogold method) combined with fimbria-fornix transection. The results are summarized as follows: 1) The same LSA somatospiny neurons receive synaptic inputs from the hippocampus and TH immunoreactive fibers which form pericellular baskets around these cells. 2) LSA somatospiny neurons are GABAergic and are postsynaptic targets of GABAergic boutons with unknown origin and hippocamposeptal axon terminals. 3) The double immunostaining experiment, finally, provided direct evidence that the same GABAergic somatospiny neurons are postsynaptic targets of both catecholaminergic and hippocamposeptal afferents. The synaptic interconnections described in this study provide anatomical basis for a better understanding of the action of catecholamines, excitatory amino acids, and GABA on the activity of LSA neurons.

Animals↗
PubMed1990

Synaptic connections of neuropeptide Y (NPY) immunoreactive neurons in the hilar area of the rat hippocampus.

Synaptic connections and fine structural characteristics of neuropeptide Y-immunoreactive (NPY-i) neurons in the fascia dentata were studied using an antiserum against NPY. Normal and colchicine pretreated rats were examined to study the synaptic connections of NPY-i neurons in the normal fascia dentata. The perforant pathway and fimbria fornix were transected to label afferent fibers to NPY-positive cells. Horseradish peroxidase conjugated with wheat germ agglutinin (HRP-WGA) was injected into the contralateral hippocampus to study commissural projections of hippocampal NPY-i neurons, and to search for NPY-i synaptic contacts on immunonegative commissural cells. Since earlier reports have shown that at least half of the NPY-i neurons also contain somatostatin (SS), the distribution of NPY-i neurons in the hilar area was determined and compared with that of SS-i neurons. Four types of dentate NPY-i neurons were distinguished: Type 1: large multipolar cells in the deep hilus (9%). Type 2: medium-sized multipolar and fusiform hilar neurons with dendrites occasionally reaching the outer molecular layer (64%). Type 3: pyramidal shaped cells in the granule cell layer with long apical dendrites reaching the outer molecular layer (20%). Type 4: small multipolar NPY-i cells located in the molecular layer (7%). Our results indicate two overlapping but not identical cell populations of NPY-i and SS-i neurons. Light and electron microscopic analysis of the normal fascia dentata demonstrated that the majority of NPY-i terminals are located in the outer molecular layer of the dentate gyrus, where they establish symmetric synaptic contacts on dendritic shafts and occasionally on spines of granule cells. A moderate number of NPY-i synapses were also found on dendrites in the inner molecular layer and on the cell body of granule cells. Numerous symmetric NPY-i synapses were found on dendrites and somata of neurons in the hilar area. Some NPY-i dendrites in the hilar area received mossy axon collateral input. After transection of the perforant pathway degenerated axon terminals could be found in synaptic contact with NPY-i dendrites in the outer molecular layer. Commissurotomy revealed direct commissural input to NPY-i dendrites in the inner molecular layer and in the hilus. After injection of HRP-WGA into the contralateral hippocampus 2% of hilar NPY-i neurons were retrogradely labeled and symmetric NPY-i synapses were found on the cell bodies and dendrites of unstained HRP-WGA labeled neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Most somatostatin-immunoreactive neurons in the rat fascia dentata do not contain the calcium-binding protein parvalbumin.

A selective loss of somatostatin (SS)-containing neurons in the hilar region has been reported in patients suffering from temporal lobe epilepsy. Conversely, neurons containing calcium-binding proteins such as parvalbumin (PARV) are known to be very resistant under experimental seizure conditions. In this study, we analyzed the coexistence of SS and PARV in neurons of the rat fascia dentata by using serial semi-thin cryostat sections for pre-embedding immunocytochemistry. Our results show that only 5.7% of the SS-immunoreactive hilar neurons contain PARV. The data suggest that SS-containing hilar neurons are less protected against seizure-induced calcium overload than other neurons containing calcium-binding proteins.

Animals↗
PubMed1990

Afferent and efferent synaptic connections of somatostatin-immunoreactive neurons in the rat fascia dentata.

The aim of this study was to determine whether somatostatin (SS)-immunoreactive neurons of the rat fascia dentata are involved in specific excitatory circuitries that may result in their selective damage in models of epilepsy. Synaptic connections of SS-immunoreactive neurons were determined at the electron microscopic level by using normal and colchicine pretreated rats. Vibratome sections prepared from both fascia dentata of control animals and from rats that had received an ipsilateral lesion of the entorhinal cortex 30-36 hours before sacrifice were immunostained for SS by using a monoclonal antibody (SS8). Correlated light and electron microscopic analysis demonstrated that many SS-immunoreactive neurons in the hilus send dendritic processes into the outer molecular layer of the fascia dentata, and dendrites of the same neurons occupy broad areas in the dentate hilar area. The majority of SS-immunoreactive axon terminals form symmetric synapses with the granule cell dendrites in the outer molecular layer and also innervate deep hilar neurons. Via their dendrites in the outer molecular layer, the SS-immunoreactive neurons receive synaptic inputs from perforant pathway axons which were identified by their anterograde degeneration following entorhinal lesions. The axons from the entorhinal cortex are the first segment of the main hippocampal excitatory loop. The hilar dendrites of the same SS-immunoreactive cells establish synapses with the mossy axon collaterals which represent the second member in this excitatory neuronal chain. These observations suggest that SS-immunoreactive neurons in the dentate hilar area may be driven directly by their perforant path synapses and via the granule cells which are known to receive a dense innervation from the entorhinal cortex. These observations demonstrate that SS-immunoreactive neurons in the hilar region are integrated in the main excitatory impulse flow of the hippocampal formation.

Animals↗
PubMed1990

Somatospiny neurons in the rat lateral septal area are synaptic targets of hippocamposeptal fibers: a combined EM/Golgi and degeneration study.

The mediolateral part of the lateral septal area (LSA) is a common target of hippocamposeptal afferents, neuropeptide containing, catecholaminergic, cholinergic, and GABAergic pericellular baskets of different origins. This specific innervation pattern as well as electrophysiological data concerning this area suggest a convergent input from different sources to particular LSA neuron populations. Light and electron microscopy combined with Golgi impregnation and acute anterograde degeneration techniques following transection of the fimbria-fornix were employed to determine whether LSA neurons with hippocampal input have any characteristic and distinctive morphological signs. About 20% of all Golgi impregnated LSA neurons were found to have somatic spines. All of these somatospiny neurons are synaptic targets of hippocamposeptal fibers. The degenerated hippocamposeptal boutons establish asymmetric synaptic contacts on their soma, somatic and dendritic spines, and on dendritic shafts. Somatospiny neurons located in the most medial and dorsal parts of the LSA seem to project toward the medial septum while all of the others appear to send descending fibers to ventral areas. Somatospiny neuron axons occasionally give out recurrent collaterals. Quantitative analysis on the spatial distribution of the somatospiny neurons revealed that practically all of them are encountered in the mediolateral division of the LSA. This area includes the lateral part of the intermediolateral septal nucleus and adjacent lateral portions of the dorsolateral and the ventrolateral septal nuclei.

Afferent Pathways↗
PubMed1990

Estrogen effects on the synaptology and neural membranes of the rat hypothalamic arcuate nucleus.

The concept of estrogen-induced "sexual differentiation of the brain" has been a useful focus for investigation. However, it has become clear that the action of estrogen on the rat brain is lifelong, including effects on neurogenesis in the fetus, synaptogenesis in the newborn, and synaptic remodeling in the adult. Estrogen imparts sex differences in the rat's brain by shaping synaptology, postsynaptic membranes, and glia within the arcuate nucleus. These effects of estrogen on the arcuate nucleus also could underlie sexual maturation in both sexes and the development of senescent constant estrus in females.

Animals↗
PubMed1990

Ultrastructural characterization of prolactin-like immunoreactivity in rat medial basal hypothalamus.

Prolactin-like immunoreactivity has been reported in the medial basal hypothalamus at the light microscopic level, in hypophysectomized rats. Here, with preembedding immunocytochemistry at the electron microscopic level, we have observed prolactin-immunoreactive neurons and synapses in the hypothalamus. Reaction product was discovered in medial basal hypothalamic neurons, which had typical large nucleoli and received axosomatic synapses. In the cytoplasm, reaction product was distinctly granular. Immunoreactive neurons were usually surrounded by nonreactive cells. Reaction product was also seen in dendrites, some of which had spines. Some axons in the hypothalamus contained reaction product, usually surrounded by nonreactive axons, and immunopositive synapses were detected both in the hypothalamus and in the midbrain. In a small number of cases immunoreactive axons could be seen synapsing on immunoreactive dendrites.

Animals↗
PubMed1989

Organization of the septal region in the rat brain: cholinergic-GABAergic interconnections and the termination of hippocampo-septal fibers.

This study deals with two characteristic cell types in the rat septal complex i.e., cholinergic and GABAergic neurons, and their synaptic connections. Cholinergic elements were labeled with a monoclonal antibody against choline acetyltransferase (ChAT), the acetylcholine synthesizing enzyme. Antiserum against glutamate decarboxylase (GAD), the GABA synthesizing enzyme, was employed to identify GABAergic perikarya and terminals, by using either the peroxidase-antiperoxidase (PAP) technique or a biotinylated second antiserum and avidinated gold or ferritin. With these contrasting immunolabels we have studied the cholinergic-GABAergic interconnections in double-labeled sections of intact septal regions and the GABAergic innervation of medial septal area cholinergic neurons in sections taken from animals 1 week following lateral septal area lesion. In other electron microscopic experiments we have studied cholinergic and GABAergic neurons in the septal complex for synaptic contacts with hippocamposeptal fibers, which were identified by anterograde degeneration following fimbria-fornix transection. Our results are summarized as follows: (1) GAD-positive terminals form synaptic contacts on ChAT-immunoreactive dendrites in the medial septum/diagonal band complex (MSDB), (2) surgical lesion of the lateral septal area resulted in a dramatic decrease of the number of GABAergic boutons on MSDB cholinergic neurons, (3) cholinergic terminals establish synaptic contacts with GAD immunoreactive cell bodies and proximal dendrites in the MSDB as well as in the lateral septum (LS), (4) degenerated terminals of hippocampo-septal fibers were mainly observed in the LS, where they formed asymmetric synaptic contacts on dendrites of GABAergic neurons and on nonimmunoreactive spines. We did not observe degenerated boutons in contact with ChAT-positive dendrites or cell bodies in the MSDB. From these results and from data in the literature we conclude that excitatory hippocampo-septal fibers activate GABAergic cells, and as yet unidentified spiny neurons in the LS, which may control the discharge of medial septal cholinergic neurons known to project back to the hippocampal formation.

Animals↗
PubMed1989

Dopamine synaptic complex with pyramidal neurons in primate cerebral cortex.

Dopamine (DA)-containing projections to the cerebral cortex are considered to play an important role in cognitive processes. Using a recently developed monoclonal antiserum directed against DA and an antibody directed against tyrosine hydroxylase in combination with Golgi impregnation and electron microscopy, we have observed that DA and tyrosine hydroxylase afferents establish symmetric membrane specializations with the soma, dendritic shafts, and spines of identified pyramidal cells in the prefrontal, cingulate, and motor cortex of primates. The axospinous contacts invariably formed part of a synaptic complex in which the dendritic spine of a pyramidal neuron was the target of both a DA-positive symmetric and an unlabeled asymmetric bouton. This arrangement allows direct DA modulation of the overall excitability of cortical projection neurons by altering local spine responses to excitatory inputs.

Animals↗
PubMed1989

Yolk sac failure in embryopathy due to hyperglycemia: horseradish peroxidase uptake in the assessment of yolk sac function.

We described previously the morphologic alterations of the visceral endodermal yolk sac cells of rat conceptuses cultured under hyperglycemic conditions which occurred concomitantly with major embryonic malformations. To determine whether the transport function of the yolk sac was impaired simultaneously as a result of these hyperglycemic conditions, horseradish peroxidase was used as a tracer protein to assess the transport function of the visceral endodermal yolk sac cells of conceptuses cultured in both control and hyperglycemic media. Cellular uptake of peroxidase, which was added to the culture medium for 3 or 24 hours, was observed in controls. This differed from the marked diminution in peroxidase uptake seen in conceptuses cultured in hyperglycemic medium. These results demonstrate that during hyperglycemia-induced embryopathy, there is concomitant yolk sac failure evidenced by morphologic alterations and impaired endocytosis. These findings therefore strengthen our hypothesis that diabetes-related malformations, as demonstrated experimentally in rat conceptuses, are associated with impairment in the structure and functions of the visceral yolk sac cells during a critical period of organogenesis.

Animals↗
PubMed1988

Cryopreservation, culture, and transplantation of human fetal mesencephalic tissue into monkeys.

Studies in animals suggest that fetal neural grafts might restore lost neurological function in Parkinson's disease. In monkeys, such grafts survive for many months and reverse signs of parkinsonism, without attendant graft rejection. The successful and reliable application of a similar transplantation procedure to human patients, however, will require neural tissue obtained from human fetal cadavers, with demonstrated cellular identity, viability, and biological safety. In this report, human fetal neural tissue was successfully grafted into the brains of monkeys. Neural tissue was collected from human fetal cadavers after 9 to 12 weeks of gestation and cryopreserved in liquid nitrogen. Viability after up to 2 months of storage was demonstrated by cell culture and by transplantation into monkeys. Cryopreservation and storage of human fetal neural tissue would allow formation of a tissue bank. The stored cells could then be specifically tested to assure their cellular identity, viability, and bacteriological and virological safety before clinical use. The capacity to collect and maintain viable human fetal neural tissue would also facilitate research efforts to understand the development and function of the human brain and provide opportunities to study neurological diseases.

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