Abstracts

RATIONALE: To determine the nature of the NPY receptors that mediate presynaptic inhibition of glutamate release in the dentate gyrus of epileptic patients METHODS: Hippocampus was resected en bloc from 5 adult patients with mesial temporal sclerosis. Tissue was sectioned in ice-cold saline containing 1 mM kynurenic acid at 350 m, then kept at room temperature in standard, bicarbonate-buffered ACSF (2 Mg, 2 Ca) until recording, performed at 33 - 35 C. Whole-cell recordings were made blind or using infrared videomicroscopy, with a K+-gluconate solution containing ATP, GTP and biocytin. Tungsten electrodes placed in nearby tissue were used to elicit synaptic potentials. Drugs were applied in ACSF via the bath. RESULTS: Recordings were made from 20 dentate granule cells, identified by their negative resting membrane potential, their position in the slice and subsequent biocytin histology. Neurons were held in voltage clamp at rest. Synaptic currents (largely excitatory) were elicited by stimulation in or near the molecular layer or the nearby hilus. In 14 of these neurons, application of Neuropeptide Y (500 nM - 1 M) resulted in the suppression of the EPSC, as we have previously reported. To determine the pharmacology of the presynaptic receptor, in 8 neurons which had a robust response to NPY which reversed substantially upon washout, we applied the selective Y2 receptor antagonist, BIIE 0246 (300 nM) prior to the application of NPY. Pretreatment with the antagonist resulted in a reduction of the NPY effect in all 8 cells. NPY alone inhibited the EPSC by 54.09%  7.59% while in the presence of BIIE0246, the effect was reduced to 31.6  9.67% (P< 0.015), which reversed upon washout. CONCLUSIONS: Consistent with previous results, it appears that NPY activates presynaptic Y2 receptors in the human epileptic dentate gyrus. The antagonism was not complete, suggesting that either the antagonist did not reach blocking concentrations in the tissue or that other presynaptic NPY receptors are also involved in the actions of NPY in the dentate gyrus. Supported by MRC (Canada). Thanks to Boehringer Ingleheim for the gift of BIIE 0246