Glutamate-mediated spreading depression is currently thought to be a k
ey event in the pathogenesis of potential neuronal degeneration in the
ischemic 'penumbra'. Glutamate receptor stimulation causes induction
of transcription factors that belong to the class of immediate early g
enes (IEGs), thought to be involved in coupling neuronal excitation to
target gene expression. Focal cerebral ischemia elicits a homogeneous
expression of several IEGs, prominently in cortex. In the ischemic co
re, discrepancies are observed between mRNA and protein levels, due to
a severe, persistent protein synthesis deficit, preventing the transl
ation of IEG encoded mRNAs. Outside the ischemic core, widespread IEG
expression occurs in the entire ipsilateral cortex at mRNA as well as
at protein level. This homogeneous expression of transcription factors
can be pinpointed to at least two different pathogenetic mechanisms b
y means of appropriate pharmacological antagonists. Prolonged IEG indu
ction in the 'penumbra', an area in which neurons are metabolically co
mpromised but not yet energy-depleted, cannot be suppressed by the adm
inistration of Iv-methyl-D-aspartate (NMDA) receptor antagonists. In c
ontrast, short-lasting IEG induction in undamaged neurons remote from
the ischemic territory, though also caused by ischemia-elicited spread
ing depression, can be blocked by NMDA receptor antagonists. In both a
reas, IEG expression identifies neurons destined to survive but is lik
ely to be mediated by different signal transduction pathways, at the r
eceptor, second messenger and/or the DNA level.