The effects of midazolam on the acquisition and expression of fructose- and maltodextrin-based flavour preferences.

The effects of the benzodiazepine agonist midazolam on the acquisition and expression of flavour preferences were investigated. Rats (Experiment 1) were given one-bottle training with one flavoured solution (CS+) mixed with either fructose or maltodextrin and another solution (CS-) presented alone. Animals receiving 1 mg/kg midazolam during training consumed more CS- than did animals receiving vehicle injections although there was no drug effect on CS+ consumption. In two-bottle tests the CS+ was preferred to the CS- with the preference being larger in fructose trained animals. Midazolam (0.3-3 mg/kg) increased total intake but not CS+ preference. Training under midazolam reduced the CS+ preference when fructose, but not maltodextrin, was the reinforcer. In Experiment 2 training consumption was restricted to 10 ml/session. This removed the difference in CS+ preference between reinforcer types but otherwise the results were as in Experiment 1. The midazolam induced attenuation of fructose-based preferences might reflect an increase in CS- palatability during training which would reduce the difference between the reinforced and non-reinforced solutions. As maltodextrin supports preferences due to post-ingestive effects manipulation of palatability should be ineffective. Midazolam does not influence the expression of conditioned flavour preferences despite prior evidence that benzodiazepine agonists enhance palatability.