Intraventricular insulin suppresses the acoustic startle response in rats

We and others have previously reported that the hormone insulin alters brai n noradrenergic function at the synaptic and molecular levels. In the: pres ent study, we examined the in vivo effect of insulin (administered chronica lly via osmotic minipumps at a dose of 5 mU/day into the third cerebral ven tricle) on thr acoustic startle response. Rats receiving chronic intraventr icular insulin had a significantly reduced startle response relative to veh icle-treated controls (i.e., 47 +/- 21% of baseline control startle respons e). Because our previous findings suggest that on an acute basis, insulin m ay enhance endogenous noradrenergic activity by inhibiting norepinephrine r euptake, we speculate here that the chronic effect of insulin is similar to that of the noradrenergic reuptake blocker, desipramine, which has been re ported to decrease baseline startle performance. (C) 2000 Elsevier Science Inc. All rights reserved.