Neuropeptide Y release from cultured hippocampal neurons: stimulation by glutamate acting at N-methyl- d-aspartate and AMPA receptors

Abstract

l-Glutamate, N-methyl- d-aspartate, dl- α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and kainate increased the release of neuropeptide Y-like immunoreactivity from primary cultures of rat hippocampal neurons incubated in Mg 2+(1.2 mM)-containing medium. The neuropeptide Y-like immunoreactivity released by 100 μM glutamate was mainly accounted for by neuropeptide Y (1–36), but consisted in part (about 20%) of peptide YY. The effect of 100 μM glutamate on neuropeptide Y-like immunoreactivity release was largely (about 70%) prevented by the N-methyl- d-aspartate receptor antagonist dizocilpine maleate (10 μM), while the remainder (about 30%) was sensitive to the AMPA/kainate receptor antagonist 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2-3-dione (10 μM). The AMPA(100 μM)-evoked release of neuropeptide Y-like immunoreactivity was strongly antagonized by 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2-3-dione and by 1-aminophenyl-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine, but it was in part (15–20%) sensitive to dizocilpine. The releases of neuropeptide Y-like immunoreactivity elicited by glutamate, N-methyl- d-aspartate, AMPA and kainate were all strongly Ca 2+-dependent. Tetrodotoxin (1 μM) abrogated the N-methyl- d-aspartate-evoked release and partly inhibited the release caused by glutamate, but did not modify significantly AMPA- or kainate-evoked release. Removal of Mg 2+ from the medium caused increase of neuropeptide Y-like immunoreactivity release, an effect prevented by dizocilpine maleate or 7-Cl-kynurenate. Cyclothiazide (10 μM), a drug known to prevent AMPA receptor desensitization, enhanced the neuropeptide Y-like immunoreactivity release elicited by 100 μM AMPA, but not that caused by 100 μM kainate. However, when used at a lower concentration (50 μM), kainate elicited a response that was potentiated significantly by cyclothiazide. It is concluded that glutamate can stimulate Ca 2+-dependent release of neuropeptide Y from hippocampal neurons mainly through N-methyl- d-aspartate receptors and, less so, by activating cyclothiazide-sensitive receptors of the AMPA-preferring type.