Spermine-induced toxicity in cerebellar granule neurons is independent of its actions at NMDA receptors

The neurotoxic actions of polyamines such as spermine have been linked to t heir modulation of NMDA receptors, resulting in an excitotoxic cell death. Here, we demonstrate that chronic exposure to the polyamine spermine and ac ute exposure to the combination of spermine and glutamate result in signifi cant toxicity to primary cultures of cerebellar granule neurons (CGNs). How ever, in both cases this cell death (a) lacks the characteristic cell swell ing associated with the necrotic cell death induced by glutamate and (b) is characterized by the widespread formation of apoptotic nuclei. Whereas diz ocilpine (MK-801) blocks the synergistic cell death resulting from acute ex posure to spermine plus glutamate, neither MK-801 nor the calcium chelator EGTA appreciably attenuates CGN death resulting from chronic exposure to sp ermine. Consistent with previous reports, glutamate, both acute and chronic , causes CGN death that is characterized by cell swelling, sensitivity to M K801 and EGTA, and only small numbers of apoptotic nuclei. Spermine-induced toxicity is not blocked by either the protein synthesis inhibitor cyclohex imide or the pan-caspase inhibitor tert-butoxycarbonyl-Asp-(O-methyl) fluor omethyl ketone. However, the antioxidant butylated hydroxyanisole is an eff ective blocker of spermine-induced CGN death, suggesting a free-radical com ponent to this cell death. The intact spermine molecule, rather than a cata bolic by-product, is required for cell death because the amine oxidase inhi bitors N-1,N-2-bis(2,3-butadienyl)-1,4-butanediamine and aminoguanidine fai l to block this toxicity. Thus, in CGNs, spermine-induced toxicity does not occur by its modulation of NMDA receptors, although, under some circumstan ces, NMDA receptor activation can modulate spermine-induced toxicity.