M100907, a serotonin 5-HT2A receptor antagonist and putative antipsychotic, blocks dizocilpine-induced prepulse inhibition deficits in Sprague-Dawley and Wistar rats.

In a recent study using Wistar rats, the serotonergic 5-HT2 receptor antagonists ketanserin and risperidone reduced the disruptive effects of the noncompetitive N-methyl-D-aspartate (NMDA) antagonist dizocilpine on prepulse inhibition (PPI), suggesting that there is an interaction between serotonin and glutamate in the modulation of PPI. In contrast, studies using the noncompetitive NMDA antagonist phencyclidine (PCP) in Sprague-Dawley rats found no effect with 5-HT2 antagonists. To test the hypothesis that strain differences might explain the discrepancy in these findings, risperidone was tested for its ability to reduce the PPI-disruptive effects of dizocilpine in Wistar and Sprague-Dawley rats. Furthermore, to determine which serotonergic receptor subtype may mediate this effect, the 5-HT2A receptor antagonist M100907 (formerly MDL 100,907) and the 5-HT2C receptor antagonist SDZ SER 082 were tested against dizocilpine. Recent studies have found that the PPI-disruptive effects of PCP are reduced by the alpha 1 adrenergic receptor antagonist prazosin. Furthermore, the alpha 1 receptor agonist cirazoline disrupts PPI. As risperidone and M100907 have affinity at the alpha 1 receptor, a final study examined whether M100907 would block the effects of cirazoline on PPI. Risperidone partially, but nonsignificantly, reduced the effects of dizocilpine in Wistar rats, although this effect was smaller than previously reported. Consistent with previous studies, risperidone did not alter the effects of dizocilpine in Sprague-Dawley rats. Most importantly, M100907 pretreatment fully blocked the effect of dizocilpine in both strains; whereas SDZ SER 082 had no effect. M100907 had no influence on PPI by itself and did not reduce the effects of cirazoline on PPI. These studies confirm the suggestion that serotonin and glutamate interact in modulating PPI and indicate that the 5-HT2A receptor subtype mediates this interaction. Furthermore, this interaction occurs in at least two rat strains.