Changes of NMDA receptor binding in spontaneously epileptic rat and parent strains.

We measured the binding of [3H]3-[(+/-)2-carboxypiperazin-4-yl] propyl-1-phosphonic acid ([3H]CPP), a competitive ligand for N-methyl-D-aspartate (NMDA) receptors, in double mutant spontaneously epileptic rats (SER: zi/zi, tm/tm) and their parent strains, zitter rats and tremor rats, and WTC rats (control rats from tremor rats derived from Kyoto:Wistar rats) before and after the onset of seizures in tremor rats and SER. Significantly lower [3H]CPP binding receptor density (Bmax) was found in the cortex of SER and zitter rats at 12-15 weeks of age than in that of WTC rats and tremor rats, and at 4 weeks of age the Bmax in zitter rats was lower than that in the other strains. The reduction of Bmax in SER at 12-15 weeks of age may reflect a down regulation of NMDA receptors due to repetitive tonic seizures in SER.