The expression of the five
somatostatin receptor subtypes, sst1-5 was compared on tissue containing glial tumours (
glioblastomas or
oligodendrogliomas),
medulloblastomas, and on normal human cortex. By semiquantitative reverse transcription coupled to polymerase chain reaction, the receptor expression profiles were high in cortex and in tissue containing
oligodendrogliomas. It was moderate in
medulloblastomas. Tissue containing
glioblastomas displayed lower expression of
somatostatin receptor subtypes, sst1 and sst3 being mostly expressed. By 125I-Tyr0DTrp8
somatostatin-14 or 125I-Leu8DTrp22 Tyr25
somatostatin-28 autoradiography combined with
synaptophysin immunohistochemistry, it was possible to differentiate between isolated tumoral cell component infiltrating the cerebral parenchyma (cortex or white matter) and tumoral tissue (without residual parenchyma) in
glioblastomas or
oligodendrogliomas. Glial tumoral tissue per se presented few
somatostatin receptors. By contrast,
medulloblastoma tumoral cells exhibited numerous
octreotide sensitive
somatostatin receptors. sst2 immunocytochemistry demonstrated immunostaining of neuronal cells and neuropile; sst2 and sst3 immunostaining was identified on
glioblastoma proliferating vessels endothelial cells and on
medulloblastomas tumoral cells. Faint sst2 immunostaining among glial tumoral cells was due to microglia, while
glioma cells did not significantly
stain. In summary,
medulloblastoma tumoral cells express sst2/sst3 receptors at a high level while
glioma cells do not. In
gliomas, sst expression is restricted to endothelial cells on proliferating vessels (displaying both sst2 and sst3 receptors), including parenchyma and reactive microglia (only sst2). The differential expression of sst2/sst3 receptors on
gliomas and
medulloblastomas has implications for the
therapy of these tumours.