Differential expression of AMPA-type glutamate receptor subunits during development of the chick optic tectum

Glutamate receptors have been often associated with developmental processes. We used immunohistochemical techniques to evaluate the expression of the AMPA-type glutamate receptor (GluR) subunits in the chick optic tectum (TeO). Chick embryos from the 5th through the 20th embryonic day (E5-E20) and one-day-old (P1) chicks were used. The three types of immunoreactivity evaluated (GluR1, GluR2/3, and GluR4) had different temporal and spatial expression patterns in the several layers of the TeO. The GluR1 subunit first appeared as moderate staining on E7 and then increased on E9. The mature GluR1 pattern included intense staining only in layer 5 of the TeO. The GluR2/3 subunits presented low expression on E5, which became intense on E7. The staining for GluR2/3 changed to very intense on E14 in tectal layer 13. Staining of layer 13 neurons is the most prominent feature of GluR immunoreactivity in the adult TeO. The GluR4 subunit generally presented the lowest expression starting on E7, which was similar to the adult pattern. Some instances of transient expression of GluR subunits were observed in specific cell populations from E9 through E20. These results demonstrate a differential expression of the GluR subunits in the embryonic TeO, adding information about their possible functions in the developmental processes of the visual system

Avaliaçäo morfométrica de fibras nervosas do nervo ulnar após reparaçäo cirúrgica com auto-enxerto e prótese tubular em cäes / Morphometric evaluation of nerve fibers after surgical repair by allograft and tubular prothesis of the ulnar nerve in dogs

O objetivo da investigaçäo foi o de comparar os resultados observados por meio de avaliaçäo morfométrica de fibras nervosas regeneradas, em cäes, após 26 semanas da reparaçäo cirúrgica de falhas do nervo ulnar, através de auto-enxertos e próteses tubulares de silicone. Para cada procedimento foram utilizados quatro animais. Dos nervos regenerados e dos enxertos foram retirados segmentos para avaliaçäo em nível de microscopia eletrônica. De cada corte foram amostrados seis campos distintos com 1,750µm elevado ao quadrado cada, que foram fotografados com aumentos de 1.880 vezes. Através de sistema computadorizado de morfometria (SigmaScan - Jandel Co., USA), obtiveram-se os seguintes parâmetros: diâmetros das fibras mielínicas; diâmetros dos axônios mielínicos; espessuras das bainhas de mielina e diâmetro dos axônios amielínicos. Os nervos regenerados no interior das próteses tubulares apresentaram diâmetros das fibras mielínicas com média de 5,12ñ1,67µm; média dos diâmetros dos axônios mielínicos de 4,08ñ1,52µm; média das espessuras das bainhas de mielina de 0,52ñ0,18µm; média dos diâmetros dos axônios amielínicos de 0,98ñ0,37µm. Os enxertos apresentaram os seguintes valores: média dos diâmetros das fibras mielínicas de 6,04ñ2,27µm; média dos diâmetros dos axônios mielínicos de 4,59ñ1,95µm; média das espessuras das bainhas de mielina de 0,72ñ0,23µm; média dos diâmetros dos axônios amielínios de 0,96ñ0,40µm. Estes resultados permitiram concluir que os procedimentos cirúrgicos utilizados, quando analisadas as fibras regeneradas no interior das próteses tubulares e dos auto-enxertos, näo apresentaram diferenças morfométricas significantes, decorridas 26 semanas de observaçäo pós-operatória

Distribution of AMPA-type glutamate receptor subunits in the chick visual system

Several glutamate receptor (GluR) subunits have been characterized during the past few years. In the present study, subunit-specific antisera were used to determine the distribution of the AMPA-type glutamate receptor subunits GluRl-4 in retinorecipient areas of the chick brain. Six white leghorn chicks (Gallus gallus, 7-15 days old, unknown sex) were deeply anesthetized and perfused with 4 per cent buffered paraformaldehyde and brain sections were stained using immunoperoxidase techniques. The AMPA-type glutamate receptor subunits GluRl, GluR2/3 and GluR4 were present in several retinorecipient areas, with varying degrees of colocalization. For example, perikarya in layers 2, 3, and 5 of the optic tectum contained GluRl, whereas GluR2/3 subunits appeared mainly in neurons of layer 13. The GluR4 subunit was only detected in a few cells of the tectal layer 13. GluRl and GluR2/3 were observed in neurons of the nucleus geniculatus lateralis ventralis, whereas GluR4 was only present in its neuropil. Somata in the accessory optic nucleus appeared to contain GluR2/3 and GluR4, whereas GluR1 was the dominant subunit in the neuropil of this nucleus. These results suggest that different subpopulations of visual neurons might express different combinations of AMPA-type GluR subunits, which in turn might generate different synaptic responses to glutamate derived from retinal gangliom cell axons.