Biomedical subjects

E Margotti

Publications and source records attributed to E Margotti.

4 recordsLinked to original sources

PubMed2000

Blocking the NGF-TrkA interaction rescues the developmental loss of LTP in the rat visual cortex: role of the cholinergic system.

Although nerve growth factor (NGF) is a crucial factor in the activity-dependent development and plasticity of visual cortex, its role in synaptic efficacy changes is largely undefined. We demonstrate that the maintenance phase of long-term potentiation (LTP) is blocked by local application of exogenous NGF in rat visual cortex at an early stage of postnatal development. Long-term depression (LTD) and bidirectional plasticity are unaffected. At later postnatal ages, blockade of either endogenous NGF by immunoadhesin (TrkA-IgG) or TrkA receptors by monoclonal antibody rescues LTP. Muscarinic receptor activation/inhibition suggests that LTP dependence on NGF is mediated by the cholinergic system. These results indicate that NGF regulates synaptic strength in well-characterized cortical circuitries.

Animals↗

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

Functional blockade of tyrosine kinase A in the rat basal forebrain by a novel antagonistic anti-receptor monoclonal antibody.

We have exploited a new monoclonal antibody against the tyrosine kinase A (TrkA) nerve growth factor (NGF) receptor to block the NGF-TrkA interaction in the rat basal forebrain. The monoclonal antibody MNAC13 is a potent antagonist that prevents the binding of NGF to TrkA in a variety of systems. This antibody was used to study the maintenance of the cholinergic phenotype in the rat basal forebrain in vivo, by the implant of antibody-secreting cells. Basal forebrain cholinergic neurons (BFCNs) are greatly affected by the antibody treatment, both in terms of cell number and of cell soma size. When antibody-secreting cells are implanted at postnatal day 2 (P2), the effects observed at P8 are as severe as those obtained with anti-NGF antibodies and, interestingly, are observed also if anti-TrkA cells are implanted at P8, when anti-NGF antibodies, delivered by the same route, are no longer effective (). The effects induced by anti-TrkA, as those induced by anti-NGF, are reversible, but the time required for recovery and the critical period in the sensitivity of BFCNs to the functional inactivation of TrkA is twice as long than that observed when NGF is intercepted. These results demonstrate that BFCNs are more sensitive to the block of TrkA activation than they are to the block of NGF. The cloning of MNAC13 variable regions and their assembly into a functional polypeptide of reduced size (single chain Fv fragment) will allow its use in gene transfer applications.

3T3 Cells↗

PubMed1999

6-thioguanine resistance in a human colon carcinoma cell line with unaltered levels of hypoxanthine guanine phosphoribosyltransferase activity.

Cell populations resistant to high doses (30 microM) of 6-thioguanine (6-TG, 6-TG(r) cells) were selected from a human colon carcinoma cell line, LoVo. This cell line, which lacks hMSH2, a component of the human mismatch binding heterodimer hMutSalpha, is resistant to low doses of 6-TG. The level of activity of hypoxanthine-guanine phosphoribosyltransferase, the enzyme responsible for the phosphoribosylation of the thiopurine, was comparable to that expressed in the parental cells. No significant difference was found in the levels of enzyme activities involved in the conversion of 6-TG or its derivatives into non-toxic compounds. In contrast, a significant difference was found in the uptake kinetics of 6-TG in the 2 cell types. Net uptake of 6-TG ceased after 100-sec incubation in the 6-TG(r) cells, while it appeared to continue throughout the 10-min incubation in the wild-type cells. As a consequence, after 10-min incubation, the total amount of 6-TG taken up by the parental LoVo cells was approximately 3 times higher than that present in the 6-TG(r) cells.

Antimetabolites, Antineoplastic↗