Constitutive expression of p21H-ras(Val12) in pyramidal neurons results in reorganization of mouse neocortical afferents.
The effect of constitutive expression of p21H-ras(Val12) in pyramidal neurons upon the establishment of afferent input has been investigated in the primary somatosensory cortex of transgenic mice. In these animals, relevant transgene expression is confined to cortical pyramidal neurons and starts postnatally at a period when neuronal morphogenesis has been largely completed. We have shown recently that overexpression of p21H-ras(Val12) in these cells results in considerable enlargement of their size and consequently in expansion of the cortex. In the present study we demonstrate that the density of terminals representing intra- or interhemispheric afferents within cortical layers II/III, however, is only slightly decreased. The density of thalamocortical boutons within layer IV is even higher and the number of afferent contacts to transgenic pyramidal neurons is significantly increased compared to the wild-type. The number of catecholaminergic and cholinergic terminals is augmented proportionally to cortical size or even overproportionally, respectively. Along intercortical and striatal fibers arising from p21H-ras(Val12)-expressing pyramidal neurons, frequency of varicosities is significantly increased, but remains unchanged on cortical cholinergic and catecholaminergic axons originating from "nontransgenic" neurons. Additionally, a higher number of multiple synaptic bodies are found in transgenic mice, suggesting subtle effects on synaptic plasticity. It is concluded that the enlargement of pyramidal neurons due to transgenic expression of p21H-ras(Val12) is paralleled by significant changes in the quantity and pattern of afferent connections. Moreover, expression of p21H-ras(Val12) in pyramidal cells induces an enhanced establishment of efferent boutons.
Department of Neuroanatomy, Paul Flechsig Institute for Brain Research, University of Leipzig, D-04109 Leipzig, Germany. dralpar@gmx.net
Alán
A
Alpár
Ulrich
U
Gärtner
Gudrun
G
Seeger
Wolfgang
W
Härtig
Kurt
K
Brauer
Thomas
T
Arendt
D000344:Afferent Pathways / Q000378:metabolism*; D000818:Animals; D001710:Biotin / Q000031:analogs & derivatives* / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002452:Cell Count / Q000379:methods; D002795:Choline O-Acetyltransferase / Q000378:metabolism; D003911:Dextrans / Q000378:metabolism; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D026901:Membrane Transport Proteins; D051379:Mice; D008822:Mice, Transgenic; D008854:Microscopy, Electron / Q000379:methods; D019579:Neocortex / Q000166:cytology*; D015689:Oncogene Protein p21(ras) / Q000235:genetics / Q000378:metabolism*; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure; D017966:Pyramidal Cells / Q000378:metabolism*; D016622:Silver Staining / Q000379:methods; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins
D002352:Carrier Proteins; D003911:Dextrans; D026901:Membrane Transport Proteins; C493477:Slc17a6 protein, mouse; D050598:Vesicular Glutamate Transport Protein 1; D050599:Vesicular Glutamate Transport Protein 2; D033921:Vesicular Transport Proteins; C076397:biotinylated dextran amine; D001710:Biotin; D014446:Tyrosine 3-Monooxygenase; D002795:Choline O-Acetyltransferase; D015689:Oncogene Protein p21(ras)