FOREBRAIN ISCHEMIA IN THE GERBIL INCREASES LAMBDA-OPIATE BINDING IN HIPPOCAMPAL MOSSY FIBERS

Transient forebrain ischemia was produced in gerbils by short-term occ lusion of the common carotid arteries under halothane anesthesia. Hist ological analysis of brains 7 days post-ischemia demonstrated characte ristic destruction of CA1 pyramidal cells. Lambda Opiate binding (meas ured with [H-3]naloxone in the presence of 300 nM diprenorphine) at 7 days post-ischemia was significantly increased in the stratum lucidum of the hippocampus (the mossy fiber layer), but not in any other regio n measured, including other hippocampal regions, cortex, amygdala, cau date putamen, thalamus, and hypothalamus. The increase in mossy fiber lambda binding was slow to develop (no increase detected up to 48 h po st-ischemia), and long-lasting (binding remained elevated at 32 days p ost-ischemia). While MK-801 significantly inhibited CA1 pyramidal cell destruction when administered 20 min prior to ischemia, the increase in mossy fiber A binding was still evident. None of seven different op ioid agonists and antagonists examined had an effect on either the pyr amdal cell damage or increased mossy fiber lambda binding seen 7 days after ischemia.