Autospectral and coherence analyses were used to determine the role of and interactions between PVN nitric oxide, GABA, and the NMDA-glutamate receptor in regulation of sympathetic nerve discharge (SND) frequency components in anesthetized rats. The following observations were made. 1) PVN microinjection of bicuculline (BIC) (GABAA receptor antagonist), but not single PVN injections of NMDA (excitatory amino acid) or L-NMMA (nitric oxide synthase inhibitor), altered SND frequency components. 2) Combined PVN microinjections of L-NMMA and NMDA changed the SND bursting pattern; however, the observed pattern change was different than that produced by PVN BIC and was not observed after sinoaortic denervation. 3) PVN microinjection of kynurenic acid prevented and reversed BIC-induced changes in the SND bursting pattern. 4) Vascular resistance (renal and splenic) was significantly increased after PVN BIC microinjection despite the lack of change in the level of renal and splenic SND. These data demonstrate that the PVN contains the neural substrate for altering SND frequency components and suggest complex interactions between specific PVN neurotransmitters and between PVN neurotransmitters and the arterial baroreceptor reflex in SND regulation.