EFFECTS OF SIGMA LIGANDS ON MOUSE CEREBELLAR CYCLIC GUANOSINE-MONOPHOSPHATE (CGMP) LEVELS INVIVO - FURTHER EVIDENCE FOR A FUNCTIONAL MODULATION OF N-METHYL-D-ASPARTATE (NMDA) RECEPTOR COMPLEX-MEDIATED EVENTS BY SIGMA LIGANDS

In the present investigation, the effects of sigma ligands [WY-47384 {8-fluoro-2,3,4,5-tetrahydro-2[3-(3-pyridinyl)propyl)1H-pyrido(4, 3b)indole}, (+)-pentazocine, (+)-SFK 10,047 (N-allylnormetazocine), mafoprazine, opipramol, dextromethorphan, dextrorphan, (+)-3-PPP [3-(3-hydroxyphenyl) -N-propylpiperidine], (-)-butaclamol, DTG [1,3-di(2-tolyl)guanidine], rimcazole, ifenprodil and BMY-14802 {alpha-(fluorophenyl) -4-(5-fluoropyrimidinyl)-l-piperazine butanol}] on harmaline-, pentylenetetrazol (PTZ)-, methamphetamine (MA) and D-serine-induced increases in mouse cerebellar levels of cGMP were determined. Ifenprodil, BMY-14802, dextromethorphan, dextrorphan, (+)-SKF 10,047, opipramol and mafoprazine reversed harmaline-, PTZ-, MA- and D-serine-induced increases in levels of cGMP. Rimcazole reversed only the harmaline-induced response. WY-47384 reversed harmaline-, MA-, D-serine-, but not PTZ- or quisqualate-induced increases in levels of CGMP. (+)-Pentazocine attenuated harmaline- and D-serine-, but not PTZ- and MA-induced cGMP responses. Haloperidol did not affect harmaline- and D-serine-induced cGMP responses. (+)-3-PPP and (-)-butaclamol did not affect any of the responses studied. Furthermore, (+)-3-PPP-induced increases in levels of cGMP were reversed by the competitive N-methyl-D-aspartate (NMDA) antagonist, CPP }3-(2-carboxypiperazin -4-yl)propyl-1-phosphonic acid, the non-competitive NMDA antagonist, (+)-MK-801 (dizocilipine maleate), the NMDA-associated glycine receptor antagonist, HA-966 (3-amino-1-hydroxypyrrolidin-2-one), the partial glycine agonist, DCS (D-Cycloserine) as well as by the sigma ligands, ifenprodil, WY-47384, (+)-pentazocine, (+)-SKF 10,047, dextromethorphan and dextrorphan but not by rimcazole. These data further support functional modulation by sigma ligands of events mediated by the NMDA receptor complex established in earlier investigations.