COLOCALIZATION OF SOMATOSTATIN MESSENGER-RNA AND PARVALBUMIN IN THE DORSAL RAT HIPPOCAMPUS AFTER CEREBRAL-ISCHEMIA

Following transient global ischemia most of the neurons containing som atostatin in the fascia dentata of the dorsal hippocampal formation di e, while somatostatinergic neurons in the CA1 region survive. These ne urons react to ischemia with a transiently reduced expression of somat ostatin mRNA and peptide. We have tested the hypothesis that this sele ctive vulnerability is solely related to those somatostatinergic neuro ns which do not express the calcium-binding protein parvalbumin. Posti schemic changes were studied in rat dorsal hippocampus at 2 and 16 day s after 10 min of global cerebral ischemia using a four-vessel occlusi on model. We performed a double-staining visualizing the mRNA coding f or somatostatin by non-radioactive in situ hybridization and parvalbum in protein by immunocytochemistry. Only 5% of the somatostatinergic ce lls in the fascia dentata contained parvalbumin. The number of somatos tatinergic cells was permanently reduced following ischemia. Among sur viving neurons we found cells with and without parvalbumin expression. Thus, expression of parvalbumin is not predictive for survival of som atostatinergic cells in the fascia dentata. In contrast, in CA1, 37% o f the somatostatinergic cells contained parvalbumin. These cells were unaffected by the transient ischemic period. The somatostatinergic cel ls lacking parvalbumin showed transiently reduced mRNA levels at day 2 , but recovered to control values at the 16th postischemic day. Thus, expression of the calcium-buffering protein parvalbumin coincides with resistance of somatostatinergic neurons in CA1 to transient effects o f ischemia. We conclude that the calcium-buffering capacity of parvalb umin may partially contribute to the protection of somatostatinergic n eurons from ischemia in the dorsal hippocampus. However, the survival of somatostatinergic cells without parvalbumin indicates the importanc e of other factors as well. (C) 1995 Wiley-Liss, Inc.