Distinct Changes in Peptide YY Binding to, and mRNA Levels of, Y1 and Y2 Receptors in the Rat Hippocampus Associated with Kindling Epileptogenesis

: Electrical kindling of the rat dorsal hippocampus induced significant changes in the binding of 125I‐peptide YY to Y1 and Y2 subtypes of neuropeptide Y receptors and in their mRNA levels in the area dentata as assessed by quantitative receptor autoradiography and in situ hybridization histochemistry. Binding to Y1 receptor sites decreased by 50% (p < 0.05) in the molecular layer of the stimulated dentate gyrus, 2 days after preconvulsive stage 2 and 1 week or 1 month after generalized stage 5 seizures compared with sham‐stimulated rats. Binding to Y2 receptor sites increased bilaterally by 36–87% (p < 0.05) in the hilus at stage 2 and 1 week or 1 month after stage 5. No significant changes were observed after one afterdischarge or in the other hippocampal subfields or in the cortex. Y1 receptor mRNA signal decreased bilaterally by 50–64% (p < 0.01) in the granule cell layer, 6 h but not 24 h after stages 2 and 5. The Y2 receptor mRNA signal was enhanced by 283% (p < 0.01) in the stimulated granule cell layer 24 h after stage 2. At 6 and 24 h after stage 5, mRNA levels were increased both ipsilaterally (283 and 360%, respectively; p < 0.01) and contralaterally (190 and 260%, respectively; p < 0.05). No significant changes in level of either mRNA was found following one afterdischarge. These modifications, and the enhanced neuropeptide Y release previously shown in the hippocampus, suggest that kindling is associated with lasting changes in neuropeptide Y‐mediated neurotransmission.