Serotonergic hallucinogens differentially modify gamma and high frequency oscillations in the rat nucleus accumbens

The nucleus accumbens (NAc) is a site critical for the actions of many drugs of abuse. Psychoactive compounds, such as N-methyl-d-aspartate receptor (NMDAR) antagonists, modify gamma (40-90) and high frequency oscillations (HFO, 130-180 Hz) in local field potentials (LFPs) recorded in the NAc. Lysergic acid diethylamide (LSD) and 2,5-dimethoxy-4-iodoamphetamine (DOI) are serotonergic hallucinogens and activation of 5HT(2A) receptors likely underlies their hallucinogenic effects. Whether these compounds can also modulate LFP oscillations in the NAc is unclear. This study aims to examine the effect of serotonergic hallucinogens on gamma and HFO recorded in the NAc and to test whether 5HT(2A) receptors mediate the effects observed. LFPs were recorded from the NAc of freely moving rats. Drugs were administered intraperitoneally. LSD (0.03-0.3 mg/kg) and DOI (0.5-2.0 mg/kg) increased the power and reduced the frequency of HFO. In contrast, the hallucinogens produced a robust reduction in the power of low (40-60 Hz), but not high gamma oscillations (70-90 Hz). MDL 11939 (1.0 mg/kg), a 5HT(2A) receptor antagonist, fully reversed the changes induced by DOI on HFO but only partially for the low gamma band. Equivalent increases in HFO power were observed after TCB-2 (5HT(2A) receptor agonist, 0.1-1.5 mg/kg), but not CP 809101 (5H(2C) receptor agonist, 0.1-3 mg/kg). Notably, hallucinogen-induced increases in HFO power were smaller than those produced by ketamine (25 mg/kg). Serotonergic hallucinogen-induced changes in HFO and gamma are mediated, at least in part, by stimulation of 5HT(2A) receptors. Comparison of the oscillatory changes produced by serotonergic hallucinogens and NMDAR antagonists are also discussed.