BDNF AND TRKB MESSENGER-RNA EXPRESSION IN THE RAT HIPPOCAMPUS FOLLOWING ENTORHINAL CORTEX LESIONS

QUANTITATIVE in situ hybridization was used to determine whether the prevalence or topographical distribution of brain-derived neurotrophic factor (BDNF) or tyrosine receptor kinase (trk) B mRNA is altered in the hippocampal formation following lesions of excitatory afferents from the entorhinal cortex which provides an external source of innervation for the hippocampal formation. BDNF mRNA levels were not altered in the hippocampal formation up to 10 days following entorhinal cortex lesions (ECLs). The levels of mRNA coding for all known forms of trkB receptors also remained unchanged. The prevalence of the synaptic plasticity marker SNAP-25 mRNA was increased in the CA2 and CA3 pyramidal cell layers and the dentate gyrus by 6 days following ECLs and remained elevated at 10 days following ECLs. Our findings indicate that hippocampal neuron sprouting which occurs in response to ECLs is not the result of changes in the expression of the BDNF or trkB mRNA.