bibp-3226 and Epilepsy

Neuropeptide Y (NPY) potently inhibits excitatory synaptic transmission in the hippocampus, acting predominantly via a presynaptic Y(2) receptor. Recent reports that the Y(5) receptor may mediate the anticonvulsant actions of NPY in vivo prompted us to test the hypothesis that Y(5) receptors inhibit synaptic excitation in the hippocampal slice and, furthermore, that they are effective in an in vitro model of anticonvulsant action. Two putative Y(5) receptor-preferring agonists inhibited excitatory postsynaptic currents (EPSCs) evoked by stimulation of stratum radiatum in pyramidal cells. We recorded initially from area CA1 pyramidal cells, but subsequently switched to cells from the subiculum, where a much greater frequency of response was observed to Y(5) agonist application. Both D-Trp(32)NPY (1 microM) and [ahx(8-20)]Pro(34)NPY (3 microM), a centrally truncated, Y(1)/Y(5) agonist we synthesized, inhibited stimulus-evoked EPSCs in subicular pyramidal cells by 44.0 +/- 5.7% and 51.3 +/- 3.5% (mean +/- SE), in 37 and 58% of cells, respectively. By contrast, the less selective centrally truncated agonist, [ahx(8-20)] NPY (1 microM), was more potent (66.4 +/- 4.1% inhibition) and more widely effective, suppressing the EPSC in 86% of subicular neurons. The site of action of all NPY agonists tested was most probably presynaptic, because agonist application caused no changes in postsynaptic membrane properties. The selective Y(1) antagonist, BIBP3226 (1 microM), did not reduce the effect of either more selective agonist, indicating that they activated presynaptic Y(5) receptors. Y(5) receptor-mediated synaptic inhibition was more frequently observed in slices from younger animals, whereas the nonselective agonist appeared equally effective at all ages tested. Because of the similarity with the previously reported actions of Y(2) receptors, we tested the ability of Y(5) receptor agonists to suppress stimulus train-induced bursting (STIB), an in vitro model of ictaform activity, in both area CA3 and the subiculum. Neither [ahx(8-20)]Pro(34)NPY nor D-Trp(32)NPY were significantly effective in suppressing or shortening STIB-induced afterdischarge, with <20% of slices responding to these agonists in recordings from CA3 and none in subiculum. By contrast, 1 microM each of [ahx(8-20)]NPY, the Y(2) agonist, [ahx(5-24)]NPY, and particularly NPY itself suppressed the afterdischarge in area CA3 and the subiculum, as reported earlier. We conclude that Y(5) receptors appea

Topics: Action Potentials; Animals; Anti-Anxiety Agents; Arginine; Binding, Competitive; Epilepsy; Excitatory Postsynaptic Potentials; Hippocampus; In Vitro Techniques; Male; Neuropeptide Y; Patch-Clamp Techniques; Peptides, Cyclic; Rats; Rats, Sprague-Dawley; Receptors, Neuropeptide Y; Synapses

Repeated electroconvulsive stimulations and other seizure modalities produce an increase in neuropeptide Y synthesis and local release in the rat hippocampus, and perhaps as a consequence, a change in the concentration of neuropeptide Y binding sites in the same region. The aim of the present study was to determine possible changes in the expression of neuropeptide Y receptor subtypes affected by repeated stimulations in the hippocampus. Rats were exposed to 14 daily stimulations, and the brains were removed 24h after the last stimulation. For in vitro receptor autoradiography and in situ hybridisation histochemistry, the brains were frozen, sectioned, and levels of neuropeptide Y binding sites and messenger RNA expressions were determined quantitatively on sections from the same animals. In order to determine the contribution of different neuropeptide Y receptor subtypes, serial sections were incubated with either 125I-labelled peptide YY alone or the same radio-labelled peptide mixed with an excess of a number of displacing compounds with affinity for either neuropeptide Y receptor subtype Y1, Y2, or both. Binding studies revealed that the majority of peptide YY binding sites was represented by Y2, and that electroconvulsive stimulations reduced the binding capacity or the concentration of this receptor. A prominent reduction of Y1-preferring binding sites was determined in the dentate gyrus, and to a lesser extent in the CA1 and CA3 regions. Similarly, the treatment produced a significant reduction of Y2-preferring binding sites in the CA1 and CA3 region, but not in the granular cell layer of the dentate gyrus. Using semi-quantitative in situ hybridization, Y1 receptor messenger RNA level in the granular cell layer of the dentate increased by the stimulations. In the same region, Y2 receptor messenger RNA was expressed in low to undetectable amounts, but after the repeated stimulations, this transcript was found in moderate to high levels. These data suggest that the neuropeptide Yergic system in the dentate gyrus and the pyramidal cell layer are affected by the treatment, and that this includes both Y1 and Y2 receptor subtypes. Because levels of messenger RNA and binding are distinctly regulated, the turnover of both Y1 and Y2 molecules is strongly increased under electroconvulsive stimulations, suggesting that the intrahippocampal neuropeptide Yergic neurotransmission is also increased under the stimulations.

Topics: Animals; Anti-Anxiety Agents; Arginine; Autoradiography; Down-Regulation; Electric Stimulation Therapy; Epilepsy; Gene Expression; Hippocampus; In Situ Hybridization; Iodine Radioisotopes; Male; Neuropeptide Y; Radioligand Assay; Rats; Rats, Wistar; Receptors, Neuropeptide Y; RNA, Messenger; Seizures