Search PubMed⌕ Search

Biomedical subjects

P Parra

Publications and source records attributed to P Parra.

24 records · Page 2Linked to original sources
PubMed1985

The distribution of somatostatin-immunoreactive neurons in the visual cortex of adult rabbits and during postnatal development.

In the adult rabbit, the somatostatin-immunoreactive neurons are seen in all visual cortical layers, with the majority of them being found in layers II-III, V and VI. During postnatal development, we can see labeled cells in layer VI at birth and in layers V and VI on the 3rd day. The labeled cells are seen in layers II-III beginning on the 5th day, and on the 10th day, these labeled neurons reach distribution typical in the adult rabbit. The number of somatostatin-immunoreactive cells increase from birth to the 10th day, and decrease about 15%, from the 10th day to adulthood.

Age Factors↗
PubMedDate not supplied

[Long-term depression of excitatory synapses in the cortex and hippocampus].

The efficacy of excitatory synapses terminating on cortical and hippocampal pyramidal cells may be persistently depressed as well as potentiated. Homo-synaptic long-term depression (LTD) seems to be triggered by an entry of calcium into a post-synaptic cell less than that needed to initiate long-term potentiation (LTP). Theoretical work predicted, and experimental studies confirmed, that moderate elevations of calcium initiate LTD via a cascade of biochemical interactions involving calcium-dependent phosphatases. Genetically modified animals confirmed the prediction of a sliding threshold that defines the limit between LTD and LTP. While mechanisms for the initiation of LTD are quite well established, it remains unclear whether pre- or post-synaptic mechanisms, or both, are involved in its maintenance. A role for LTD in processes of learning and forgetting in the adult animal remains to be firmly established. It seems probable, however, that a persistent reduction in synaptic weight is a basic process used in the establishment and refinement of neuronal circuits during development.

Animals↗
PubMedDate not supplied

Primary esophageal lymphoepithelioma.

Lymphoepitheliomas are extremely rare outside the nasopharynx. Extranasopharyngeal lymphoepithellomas may be located in the stomach or digestive tract, and only one single case of esophageal location has been found in our review. In many cases the tumor is related to Epstein-Barr virus infection. We report a case of undifferentiated carcinoma of the distal third of the esophagus in a 79 year-old man. Pathological examination of the esophagus revealed an undifferentiated carcinoma with lymphold stroma (lymphoepithelioma). In situ hybridization of the neoplastic cells was negative for Epstein-Barr virus. To our knowledge, the present case is the first documented esophageal lymphoepithelioma in Western countries.

Aged↗