Biomedical subjects

E Sermasi

Publications and source records attributed to E Sermasi.

10 recordsLinked to original sources

PubMed2000

Trk B signalling controls LTP but not LTD expression in the developing rat visual cortex.

Neurotrophins have been suggested to act as liaison molecules between activity-dependent synaptic plasticity and the establishment of patterns of synaptic connectivity during postnatal developmental in different brain areas, including the visual cortex. In particular, recent studies have shown that Trk B ligands are involved in the formation of the ocular dominance columns during postnatal development. Here, we examined the contribution of endogenous Trk B activation to the regulation of different forms of synaptic plasticity including long-term potentiation (LTP), long-term depression (LTD) and LTP after LTD in the developing visual cortex. Rat cortical slices were incubated with a soluble form of Trk B receptor (TrkB IgG) preventing Trk B activation by endogenous ligands. LTP expression was also studied at P23 (postnatal), when the expression of brain-derived neurotrophic factor (BDNF) reaches a peak and the LTP expression is normally downregulated. The present results demonstrate that Trk B activation is required for the long-term maintenance, > 30 min, of both LTP and LTP after LTD at P17. At P23, a higher concentration of TrkB IgG was necessary to impair LTP. In contrast, neither amplitude nor duration of LTD were affected by Trk B ligands blockade. Taken together, these results indicate that endogenous Trk B ligands are necessary for the expression of LTP but not LTD at a critical time during postnatal cortical development.

Animals↗

PubMed1999

Synaptic plasticity of feedback connections in rat visual cortex.

The issue we want to address in the present paper is to establish whether electrical stimulation of latero medial (LM) area, a secondary visual area in the rat, is able to induce Long Term Potentiation (LTP) and Long Term Depression (LTD) in primary visual cortex (V1). To this aim rat slices containing area V1 and LM were prepared at P23 and P40 and field potentials in layers 2/3 of area V1 were recorded stimulating LM. We showed that it was never possible to induce LTP in area V1, unless bicuculline, a gamma-aminobutyric acid (GABA) receptors blocker, was applied to the slice. In contrast, LTD was normally inducible. Thus, cortical gabaergic circuitry in area V1 controls LTP but not LTD elicited by stimulation of feedback connections from LM.

Aging↗

PubMed1999

Long term depression is expressed during postnatal development in rat visual cortex: a role for visual experience.

Long term forms of synaptic plasticity and in particular LTD/LTP are both present in the mammalian visual cortex. However, while LTP is not inducible in adulthood LTD can be elicited in the mature brain, but its developmental pattern is unknown. Aim of this work was to investigate whether LTD is expressed during postnatal development and if it is modulated by visual experience. To investigate these points we have used rat primary visual cortex slices taken at different stages of functional maturation process, i.e., postnatal day 17 (P17), P23 and P30-35. LTD was assessed by measuring the amplitude of extracellular field potentials recorded in cortical layers 2/3 and elicited by low frequency stimulation to the white matter. LTD was expressed at all ages investigated without significant differences between age groups. These data indicate that LTD developmental expression is not temporally related with the period of functional maturation of rat visual cortex. Dark rearing from birth to P23 resulted in a reduction of LTD amplitude while light deprivation from P17 to P30 did not affect LTD expression in comparison to age matched control values. We suggest that light imprinting is essential for a normal LTD expression during postnatal development.

Animals↗

PubMed1999

A new form of synaptic plasticity is transiently expressed in the developing rat visual cortex: a modulatory role for visual experience and brain-derived neurotrophic factor.

Synaptic plasticity has been implicated in the mechanisms contributing to the shaping of the cortical circuits responsible for the transmission of the visual input in the rat primary visual cortex. However, the degree of plasticity of the thalamocortical synapse may change during development, perhaps reflecting the degree of stabilization of the circuitry subserving it. We have chosen the ability of this synapse to be first depressed and then potentiated as a specific indicator of its plasticity. In this study we have investigated how this parameter changes during development and the factors controlling it. Extracellular field potentials in cortical layers 2/3 were evoked by stimulation of the white matter in rat primary visual cortex slices prepared at different postnatal ages. Low-frequency stimulation (900 pulses at 1 Hz) of the white matter was used to induce long-term depression of field potential amplitude, whereas long-term potentiation was evoked by high-frequency stimulation consisting of three trains at 100 Hz. We provide evidence that while it is possible to potentiate previously depressed synapses soon after eye opening (postnatal day 17) this synaptic characteristic decreases rapidly thereafter. The decrease in this form of cortical synaptic plasticity closely matches the stabilization of the cortical circuitry towards an adult pattern of connectivity and function. Depressed cortical synapses cannot be potentiated in normal rats at postnatal 23, but they can be potentiated in rats reared in the dark from postnatal days 17 to 29. Moreover, application of brain-derived neurotrophic factor, known to be expressed in an activity-dependent manner, was able to restore the ability of synapses to be potentiated after long-term depression, thus indicating its important modulatory role in brain development.

Animals↗

PubMed1998

Localisation of arginine vasopressin V1a receptors on sympatho-adrenal preganglionic neurones.

Vasopressin-containing nerve terminals are present in the spinal cord of several species. This study was designed to determine whether sympatho-adrenal preganglionic neurones (SPN) express vasopressin receptors (VPRs). SPN in the spinal cord were revealed by retrograde labelling of Fluorogold following its unilateral injection into the adrenal medulla of 12-20 day postnatal rats. VPRs were simultaneously visualised in the Fluorogold-labelled slices of spinal cord using a recently developed biotinylated vasopressin receptor antagonist [1-phenylacetyl,2-O-methyl-D-tyrosine,6-arginine,8-arginine,9-lysinam ide(Nepsilon-biotinamidocaproamide)]vasopressin, PhAcAL(Btn)VP. The VPR:PhAcAL(Btn)VP complexes were visualised either with Texas Red-conjugated avidin or with a Vectastain avidin:alkaline phosphatase detection kit. These dual-labelling experiments revealed VPRs to be present in the spinal grey matter and to be particularly dense in the intermediate grey matter and adjacent regions of the ventral horn. Many SPN were associated with receptor-specific labelling of PhAcAL(Btn)VP, thereby demonstrating that VPRs are expressed by these neurones. These VPRs were pharmacologically defined as the V1a subtype. It is concluded that sympatho-adrenal preganglionic neurones express VPRs and that these are of the V1a subtype. The distribution of VPRs is not, however, restricted to these SPN in the spinal cord.

Adrenal Glands↗

PubMed1995

Intramedullary blood vessels of the spinal cord express V1a vasopressin receptors: visualization by a biotinylated ligand.

The neurohypophysial peptide hormone [Arg8]vasopressin (AVP) has well documented pressor effects in the periphery. These are mediated by vasopressin receptors (VPRs) of the V1a subtype, expressed by vascular smooth muscle cells, which induce vascular contraction when activated. AVP also has effects on the vasculature of the brain, where it has been reported to induce both vasodilation and vasoconstriction. The responsiveness of blood vessels of the spinal cord, however, has received little attention. To determine the morphology and distribution of blood vessels within the spinal cord, vessels were vizualised using a mouse anti-rat smooth muscle alpha actin IgG as primary antibody and fluorescein isothiocyanate-conjugated anti-mouse IgG secondary antibodies. A complementary vizualisation strategy which detected the endogenous peroxidase activity of red blood cells within vessels was also utilised. The characteristics of the structures observed using both visualisation strategies were typical of blood vessels. VPRs were localized using recently characterized high affinity biotinylated analogue of AVP (PhAcAL(Btn)VP), which is selective for the V1a subtype of VPR. PhAcAL(Btn)VP:VPR complexes were subsequently visualized by avidin-Texas red. The pharmacological characteristics of these sites were established using selective analogues of vasopressin and oxytocin. This confirmed that V1a receptors were indeed being visualized. The structures observed following visualization of VPRs had the same morphology as the vasculature revealed by the anti smooth muscle alpha-actin antibody. It can therefore be concluded that the blood vessels of the spinal cord express VPRs and are potentially responsive to AVP. Furthermore, VPRs were detected on capillaries of the microvasculature. As these capillaries are devoid of smooth muscle, VPRs must be expressed by endothelial cells as well as by smooth muscle cells. This distribution of VPRs would enable AVP to regulate local blood flow. The source of the AVP could be the general circulation, or perhaps more likely, to be local release from vasopressinergic hypothalamic neurones which are known to innervate specific regions of the spinal cord.

Animals↗

PubMed1994

Oxytocin acts at V1 receptors to excite sympathetic preganglionic neurones in neonate rat spinal cord in vitro.

Intracellular recordings were made from sympathetic preganglionic neurones (SPNs) in transverse slices of thoraco-lumbar spinal cord of young rats (12-20 days old). A small group of SPNs generally having higher membrane potentials (-70 mV) compared to a remaining group (-66 mV) showed spontaneous oscillations of their membrane potential. Oxytocin superfused in concentrations of 0.1-30 microM had four effects on SPNs, inducing slow depolarisation, EPSPs, IPSPs and brief rhythmic oscillations. The slow depolarisation was unaffected by TTX whereas this abolished the other changes. The oxytocin-induced depolarisation was associated with a slow inward current and was not reversed at membrane potentials negative to EK, it increased at more positive potentials and was still present in low Ca2+ and high Mg2+ solutions. These features of the oxytocin induced current are similar to those of the TTX resistant voltage dependent Na+ current described in brainstem autonomic neurones. Vasopressin superfused at concentrations of 0.1 microM to 30 microM had similar effects on SPNs to those of oxytocin. A comparison of the effects of oxytocin and vasopressin on the same neurones revealed that oxytocin was almost 10 times less potent than vasopressin. The effects of oxytocin were not mimicked by a selective oxytocin agonist but were mimicked by a selective vasopressin V1a agonist and blocked by a selective V1a antagonist. Therefore it is concluded that the effects of oxytocin on SPNs are mediated by the vasopressin V1a receptor. It is suggested that oxytocin and vasopressin terminals in the lateral horn are part of a descending system controlling oscillating networks of SPNs in the spinal cord.

Animals↗

PubMed1993

Excitatory and indirect inhibitory actions of 5-hydroxytryptamine on sympathetic preganglionic neurones in the neonate rat spinal cord in vitro.

The action of 5-hydroxytryptamine (5-HT) on sympathetic preganglionic neurones (SPN) was studied by intracellular recordings in thin slices of neonatal rat spinal cord in vitro. Superfusion of 5-HT (1-270 microM) to SPN caused a concentration dependent slow depolarization or inward current and an increase in synaptic activity consisting of both EPSPs and IPSPs. The slow depolarization was still present after superfusion with TTX. Similar effects were seen during superfusion with 5-carboxamidotryptamine (5-CT) or alpha-methyl-5-hydroxytryptamine (alpha-me-5-HT). A comparison with the potency of 5-HT was made for 5-CT or alpha-me-5-HT on the same neurone by determining the magnitude of the slow depolarization to different concentrations of agonist. This showed that the apparent potency of the agonists was 5-CT > 5-HT > alpha-me-5-HT even in the presence of fluoxetine, a 5-HT uptake inhibitor. The 5-HT-induced slow depolarization was partially blocked by ketanserin but full recovery was not observed. The results suggest that the excitatory action of 5-HT on SPN is mediated via an atypical 5-HT2 receptor or a 5-HT1C-like receptor. The 5-HT-induced IPSPs were reversibly blocked by superfusion with strychnine, suggesting they were mediated by glycine.

Action Potentials↗

PubMed1991

Vasopressin generates a persistent voltage-dependent sodium current in a mammalian motoneuron.

During the period of life that precedes weaning, the facial nucleus of the newborn rat is rich in 3H-vasopressin binding sites, and exogenous arginine vasopressin (AVP) can excite facial motoneurons by interacting with V1 (vasopressor-type) receptors. We have investigated the mode of action of this peptide by carrying out single-electrode voltage-clamp recordings in coronal brainstem slices from the neonate. Facial motoneurons were identified by antidromic invasion following electrical stimulation of the genu of the facial nerve. When the membrane potential was held at or near its resting level, vasopressin generated an inward current whose magnitude was concentration related; the lowest peptide concentration still effective in eliciting this effect was 10 nM. The vasopressin-induced current, IAVP, was resistant to tetrodotoxin (TTX) and was insensitive to a reduction in extracellular calcium concentration. It was sustained, was inward at all potentials tested (-120 to -25 mV), and increased in magnitude during depolarization. IAVP was not generated by the blockade of a potassium current, because it did not reverse at hyperpolarized potentials, was not affected by a two-fold increase in the transmembrane potassium gradient, and was not modified by the potassium channel blockers tetraethylammonium bromide (TEA), 4-aminopyridin (4-AP), barium, cesium, quinine, glibenclamide, and apamin. Also, IAVP was not affected by changes in the transmembrane chloride gradient. In contrast, it could be reduced by partially substituting extracellular sodium with equimolar N-methyl-D-glucamine or Tris. Our results suggest that vasopressin increases the excitability of facial motoneurons by generating a persistent sodium-dependent membrane current that is voltage gated and TTX resistant.

Animals↗

PubMed1986

Purification, characterization, and in vitro differentiation of cytotrophoblasts from human term placentae.

Highly purified functional cytotrophoblasts have been prepared from human term placentae by adding a Percoll gradient centrifugation step to a standard trypsin-DNase dispersion method. The isolated mononuclear trophoblasts averaged 10 microns in diameter, with occasional cells measuring up to 20-30 microns. Viability was greater than 90%. Transmission electron microscopy revealed that the cells had fine structural features typical of trophoblasts. In contrast to syncytial trophoblasts of intact term placentae, these cells did not stain for hCG, human placental lactogen, pregnancy-specific beta 1-glycoprotein or low mol wt cytokeratins by immunoperoxidase methods. Endothelial cells, fibroblasts, or macrophages did not contaminate the purified cytotrophoblasts, as evidenced by the lack of immunoperoxidase staining with antibodies against vimentin or alpha 1-antichymotrypsin. The cells produced progesterone (1 ng/10(6) cells . 4 h), and progesterone synthesis was stimulated up to 8-fold in the presence of 25-hydroxycholesterol (20 micrograms/ml). They also produced estrogens (1360 pg/10(6) cells . 4 h) when supplied with androstenedione (1 ng/ml) as a precursor. When placed in culture, the cytotrophoblasts consistently formed aggregates, which subsequently transformed into syncytia within 24-48 h after plating. Time lapse cinematography revealed that this process occurred by cell fusion. The presumptive syncytial groups were proven to be true syncytia by microinjection of fluorescently labeled alpha-actinin, which diffused completely throughout the syncytial cytoplasm within 30 min. Immunoperoxidase staining of cultured trophoblasts between 3.5 and 72 h after plating revealed a progressive increase in cytoplasmic pregnancy-specific beta 1-glycoprotein, hCG, and human placental lactogen concomitant with increasing numbers of aggregates and syncytia. At all time points examined, occasional single cells positive for these markers were identified. RIA of the spent culture media for hCG revealed a significant increase in secreted hCG, paralleling the increase in hCG-positive cells and syncytia identified by immunoperoxidase methods. We conclude that human cytotrophoblasts differentiate in culture and fuse to form functional syncytiotrophoblasts.

Actinin↗