Anxiogenic treatments do not increase fear-potentiated startle in mice
Received 23 April 2004; received in revised form 9 August 2004; accepted 20 October 2004.
Background
In rodents, the fear-potentiated startle paradigm (FPS; exaggerated startle as a measure of the conditioned fear response to cues associated with footshock) has demonstrated predictive validity for anxiolytic drugs. The predictive validity of the model for anxiogenic drugs, however, remains unclear. Therefore, we evaluated the bi-directionality of the FPS model for anxiety-modulating compounds in mice.
Methods
The clinical anxiogenics FG-7142 (1–20 mg/kg), yohimbine (.1–10 mg/kg), and m-Chlorophenylpiperazine (mCPP; .3–3 mg/kg), and the putative anxiogenics atipamezole (.3–3 mg/kg) and corticotropin-releasing factor (h/r-CRF; .03–1 μg) were tested in DBA/1J mice trained for FPS.
Results
Contrary to predictions, FG-7142 (10 and 20 mg/kg) and yohimbine (10 mg/kg) reduced FPS in mice without affecting baseline startle. Atipamezole (3 mg/kg), mCPP (3 mg/kg), and h/r-CRF (.3, 1 μg) did not affect FPS, but increased startle independently from the presence of the cue. FG-7142 and h/r-CRF had similar effects in 129SvEv mice.
Conclusions
Murine FPS is not bi-directionally predictive for anxiety-modulating compounds, although murine baseline startle may have some utility as a bi-directional model of anxiety. These data corroborate the recent hypothesis that systems mediating FPS are independent from systems mediating increased startle from unconditioned and putatively anxiogenic stimuli.
aDepartments of Psychiatry and Neurosciences, University of California, San Diego, La Jolla, California
Address reprint requests to Dr. M.A. Geyer, Department of Psychiatry-0804, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0804
ABSTRACT