peptide-yy and Epilepsy

125I-[Leu31,Pro34]peptide YY (PYY) and 125I-PYY3-36, initially described as selective neuropeptide Y Y1 and Y2 receptor ligands, respectively, were recently shown to label also Y4 and Y5 receptors. We used receptor autoradiography to assess whether these ligands can be reliably used to investigate the various neuropeptide Y receptors in rat forebrain. In most of the brain regions examined (in coronal sections at the level of dorsal hippocampus), specific 125I-[Leu31,Pro34]PYY binding was completely inhibited by 1 microM BIBP-3226, a selective Y1 receptor ligand, but unaffected by 10 nM rat pancreatic polypeptide, selectively inhibiting Y4 receptors, suggesting that Y4 receptors are present in negligible numbers compared with Y1 receptors in the areas examined. Significant numbers of BIBP-3226-insensitive 125I-[Leu31,Pro34]PYY binding sites were measured in the CA3 subfield of the hippocampus only, possibly representing Y5 receptors. 125I-PYY3-36 binding was unchanged by 1 microM BIBP-3226, whereas a population of 125I-PYY3-36 binding sites was sensitive to 100 nM [Leu31,Pro34]neuropeptide Y, likely representing Y5 receptors. The possibility of distinguishing between Y2 and Y5 receptors using 125I-PYY3-36 as radioligand was validated by their different regional distribution and their distinct changes 24 h after kainate seizures, i.e., binding to Y5 receptors was selectively decreased in the outer cortex, whereas binding to Y2 receptors was enhanced in the hippocampus. Thus, the use of selective unlabeled compounds is required for distinguishing the various receptor subtypes labeled by 125I-[Leu31,Pro34]PYY and 125I-PYY3-36 in rat brain tissue.

Topics: Animals; Autoradiography; Brain Chemistry; Epilepsy; Excitatory Amino Acid Agonists; Gastrointestinal Hormones; Iodine Radioisotopes; Kainic Acid; Male; Peptide Fragments; Peptide YY; Prosencephalon; Protein Binding; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, Neuropeptide Y

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.

Topics: Animals; Autoradiography; Epilepsy; Hippocampus; Histocytochemistry; In Situ Hybridization; Kindling, Neurologic; Male; Peptide YY; Rats; Rats, Sprague-Dawley; Receptors, Gastrointestinal Hormone; RNA, Messenger

Kainic acid-induced limbic seizures cause lasting increases in neuropeptide Y (NPY) expression in hippocampal granule cells/mossy fibers. The expression of NPY-Y1 receptors in these neurons were investigated, using in situ hybridization for Y1 mRNA and receptor autoradiography with the Y1-specific ligand [125I][Pro34]PYY. Six hours after kainic acid-induced seizures, Y1 receptor mRNA levels decreased by 80% in granule cells and concomitantly increased (by 75%) in CA2 pyramidal neurons. Subsequently, persistent decreases in Y1 mRNA were seen, both in the stratum granulosum and in CA2. Changes in mRNA concentrations were accompanied by a transient, although non-significant, increase in [125I][Pro34]PYY binding in the molecular layer of the dentate gyrus after 4-6 h which was succeeded by a lasting decrease in binding which indicates a persistent down-regulation of Y1 receptors in hippocampal areas in kainic acid-induced epilepsy.

Topics: Animals; Autoradiography; Dentate Gyrus; Epilepsy; Hippocampus; Iodine Radioisotopes; Kainic Acid; Male; Neurons; Peptide YY; Peptides; Pyramidal Cells; Rats; Rats, Sprague-Dawley; Receptors, Neuropeptide Y; RNA, Messenger; Time Factors; Transcription, Genetic

Repetitive electroconvulsive stimulations (ECSs) increase neuropeptide Y (NPY) synthesis in hippocampal neurons, but whether NPY release and the density of NPY receptors are affected is unknown. In rats exposed to 14 daily ECSs, the concentration of NPY specific binding sites in hippocampal membranes was reduced by about 75% compared with sham, but was unchanged in membranes isolated from the cerebral cortex and the thalamus. In accordance with this, in vitro autoradiography revealed a similar reduction in binding in the dentate gyrus and the CA1 and CA3 regions, but not in the parietal cortex, the entorhinal cortex or the thalamus. These results show significant changes in NPY receptor binding after repeated ECSs, suggesting that NPYergic neurotransmission, most likely within the hippocampus, is strongly affected by ECSs.

Topics: Animals; Autoradiography; Binding Sites; Cell Membrane; Electroshock; Epilepsy; Hippocampus; Male; Neuronal Plasticity; Neuropeptide Y; Peptide YY; Rats; Rats, Wistar; Receptors, Neuropeptide Y